Personal and Public Transport

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ES/S6 - HSC 41092 P0022157

Engineering StudiesHSC CourseStage 6

Personal and public transport

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AcknowledgmentsThis publication is copyright Learning Materials Production, Open Training and Education Network –Distance Education, NSW Department of Education and Training, however it may contain material fromother sources which is not owned by Learning Materials Production. Learning Materials Production wouldlike to acknowledge the following people and organisations whose material has been used.

Board of Studies, NSW

All reasonable efforts have been made to obtain copyright permissions. All claims will be settled ingood faith.

Materials development: David Jackson, John Shirm, Ian Webster

Coordination: Jeff Appleby

Edit: John Cook, Jeff Appleby, Josephine Wilms, Stephen Russell

Illustration: Tom Brown, David Evans

DTP: Nick Loutkovsky, Carolina Barbieri

© Learning Materials Production, Open Training and Education Network – Distance Education,NSW Department of Education and Training, 2000. 51 Wentworth Rd. Strathfield NSW 2135.

Revised 2002

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Module contents

Subject overview ................................................................................iii

Module overview................................................................................vii

Module components ................................................................ viii

Module outcomes...................................................................... ix

Indicative time............................................................................x

Resource requirements..............................................................xi

Icons ..............................................................................................xiii

Glossary............................................................................................. xv

Directive terms................................................................................xxiii

Part 1: Transport systems –development .................................................................. 1–49

Part 2: Transport systems –mechanics/hydraulics .................................................. 1–45

Part 3: Transport systems –materials ......................................................................... 1–81

Part 4: Transport systems –electricity/electronics .................................................... 1–91

Part 5: Transport systems –communication .............................................................. 1–55

Part 6: Transport systems –engineering report......................................................... 1–39

Bibliography.......................................................................................41

Module evaluation ............................................................................45

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Subject overview

Engineering Studies Preliminary Course

Household appliances is the introductory module whichintroduces several basic engineering techniques.Common appliances found in the home are used tocomplete material investigation and mechanicalanalysis. Appliances are analysed to identify materialsand their applications. Relationships between thematerials used and the effect those materials have ondesign are investigated. Electrical principles,researching methods and techniques to communicatetechnical information are introduced. The first studentengineering report is completed by investigating thematerials used in a household appliance.

Landscape products investigates engineering principlesby focusing on common products such as lawnmowersand clothes hoists. The historical development of thesetypes of product demonstrates the effect materialsdevelopment and technological advancements have onthe design of products. Engineering techniques of forceanalysis are described. Orthogonal drawing methods areexplained. An engineering report is completed thatanalyses a landscape product.

Braking systems uses braking components and systemsto describe engineering principles. The historicalchanges in materials and design are investigated. Therelationship between internal structure of iron and steeland the resulting engineering properties of thosematerials is detailed. Hydraulic principles are describedand examples provided in braking systems. Orthogonaldrawing techniques are further developed. Anengineering report is completed that requires an analysisof a braking system component.

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Bio engineering is the first of the focus modules. Thismodule looks at both engineering principles and alsothe scope of the bio engineering profession. Careerdescriptions are researched and current issues in thisfield are discussed. Engineers as managers and ethicalissues confronted by the bio engineer are considered.An engineering report is completed that investigates acurrent bio engineered product and describes the relatedissues that the bio engineer would need to considerbefore, during and after this product development.

Irrigation systems is the elective topic for the last of thepreliminary modules. The historical development ofirrigation systems is described and the impact of thesesystems on society discussed. Hydraulic analysis ofirrigation systems is explained. The effect on irrigationproduct range that has occurred with the introduction ofpolymers is detailed. An engineering report on anirrigation system is completed.

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HSC Engineering Studies modules

Civil structures is the first of the HSC course modules.Engineering principles as they relate to civil structuressuch as bridges and buildings are described. The historicalinfluences of engineering, the impact of engineeringinnovation, and environmental implications are discussedwith reference to bridges. Mechanical analysis of bridgesis used to introduce concepts of truss analysis andstress/strain. Material properties and application areexplained with reference to a variety of civil structures.Technical communication skills described in this moduleinclude assembly drawing. The engineering report asks thestudent to compare two engineering solutions to solve thesame engineering situation.

Personal and public transport uses bicycles, motorvehicles and trains as examples to explain engineeringconcepts. The historical development of cars is used todemonstrate the developing material list available for theengineer. The impact on society of these developments isdiscussed. The mechanical analysis of mechanismsinvolves the effect of friction. Energy and powerrelationships are explained. Methods of testing materials,and methods of modifying material properties areexamined. A series of industrial manufacturing processesare described. Electrical concepts such as powerdistribution and AC motors are detailed in this module.Students are introduced to the use of freehand technicalsketches.

Lifting devices investigates the social impact that thesedevices from complex cranes to simple car jacks have hadon our society. The mechanical concepts are explained,including the hydraulic concepts often used in liftingapparatus. The industrial processes used to form metalsand the processes used to control physical properties areexplained. Electrical requirements for many devices aredetailed. The technical rules for sectioned orthogonaldrawings are demonstrated. The engineering report isbased on a comparison of two lifting devices.

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Aeronautical engineering is the first focus engineeringmodule in the HSC course. The scope of the aeronauticalengineering profession is investigated. Careeropportunities are considered, as well as ethical issuesrelated to the profession. Technologies unique to thisengineering field are described. The mechanical analysistopics include aeronautical flight principles and fluidmechanics. Materials, and material processes concentrateon those most associated with the aeronautical engineer.The corrosion process is explained and preventativetechniques listed. Communicating technical informationusing both freehand and computer aided drawing arerequired. The engineering report is based on theaeronautical profession, current projects and issues.

Telecommunications engineering is the final focus modulein the HSC course. This field of engineering, its historyand impact on society are discussed. Ethical issues andcurrent technologies are described. The materials sectionconcentrates on specialised testing, copper and its alloys,semiconductors and fibre optics. Electronic systems suchas analogue and digital are explained and an overview of avariety of other technologies in this field are described.Analysis, related to telecommunication products, is used toreinforce mechanical concepts. Communicating technicalinformation using both freehand and computer aideddrawing is required. The engineering report is based onthe telecommunication profession, current projects andissues.

Figure 0.1 Modules

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Module overview

Part 1 investigates the historical developments of some types of transportsystems. You will learn about environmental issues and the effect thatinnovations in transport systems have had on society and an individuals.

In part 2 considers mechanical concepts to build your knowledge andhelp your understanding of how transport vehicles are able to work,given that friction, and a source of energy or power are required.

Part 3 examines the many types of materials that are used in transportsystems. You will learn about testing procedures, material propertymodification and manufacturing techniques in relation to specific ferrousand non-ferrous materials.

Part 4 explains generation and transmission systems, electric motors andelectric systems in various types of transport. You will also learn somebasic concepts relating to electric/electronic control technologies used inthe transport industry.

In Part 5 you will learn more about the use of AS1100 in developing yourtechnical drawing skills so important in communicating technicalinformation.

In Part 6 you will further develop your research skills and report writingskills as well as learning about alternative technologies being developedfor use in transport systems. You will prepare an engineering report analternative energy source for powering a small transport system toeliminate or minimize the amount of pollution being generated by thecurrent fuel-burning vehicles.

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Module components

Each module contains three components, the preliminary pages, theteaching/learning section and additional resources.

• The preliminary pages include:

– module contents

– subject overview

– module overview

– icons

– glossary

– directive terms.

Figure 0.2 Preliminary pages

Figure 0.3 Teaching/learning section

• The teaching/learning parts mayinclude:

– part contents

– introduction

– teaching/learning text and tasks

– exercises

– check list.

• The additional information mayinclude:

– module appendix

– bibliography

– module evaluation.

Additional resources

Figure 0.4 Additional materials

Support materials such as audiotapes, video cassettes and computer diskswill sometimes accompany a module.

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Module outcomes

At the end of this module, you should be working towards being able to:

• differentiate between properties of materials and justify the selectionof materials, components and processes in engineering (H1.2)

• determine suitable properties, uses and applications of materials inengineering (H2.1)

• demonstrate proficiency in the use of mathematical, scientific andgraphical methods to analyse and solve problems of engineeringpractice (H3.1)

• use appropriate written, oral and presentation skills in the preparationof detailed engineering reports (H3.2)

• develop and use specialised techniques in the application of graphicsas a communication tool (H3.3)

• apply knowledge of history and technological change to engineering-based problems (H4.2)

• appreciate social, environmental and cultural implications oftechnological change in engineering and apply them to the analysisof specific problems (H4.3)

• work individually and in teams to solve specific engineeringproblems and in the preparation of engineering reports (H5.1)

• demonstrate skills in research, and problem solving related toengineering (H6.1)

• demonstrate skills in analysis, synthesis and experimentation relatedto engineering (H6.2)

Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.

Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

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Indicative time

The Preliminary course is 120 hours (indicative time) and the HSCcourse is 120 hours (indicative time).

The following table shows the approximate amount of time you shouldspend on this module.

Preliminary modules Percentage of time Approximatenumber of hours

Household appliances 20% 24 hr

Landscape products 20% 24 hr

Braking systems 20% 24 hr

Bio-engineering 20% 24 hr

Elective: Irrigation systems 20% 24 hr

HSC modules Percentage of time Approximatenumber of hours

Civil structures 20% 24 hr

Personal and public transport 20% 24 hr

Lifting devices 20% 24 hr

Aeronautical engineering 20% 24 hr

Telecommunications engineering 20% 24 hr

There are six parts in Personal and public transport. Each part willrequire about four to five hours of work. You should aim to complete themodule within 20 to 25 hours.

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Resource requirements

During this module you will need to access a range of resourcesincluding:

• bicycle brakes

• paper clip

• car suspension spring (attached to a car)

• file

• old hacksaw blade

• old lawnmower blade

• 2 high density polyethylene bags, such as a freezer or shopping bag

• low density polyethylene little plastic food wrap

• rubber band

• technical drawing equipment

– drawing board, tee square, set squares (30∞–60∞, 45∞),

protractor, pencils (0.5 mm mechanical pencil with B lead),eraser, pair of compasses, pair of dividers

• calculator

• rule.

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Icons

As you work through this module you will see symbols known as icons.

The purpose of these icons is to gain your attention and to indicateparticular types of tasks you need to complete in this module.

The list below shows the icons and outlines the types of tasks for Stage 6Engineering studies.

ComputerThis icon indicates tasks such as researching using anelectronic database or calculating using a spreadsheet.

DangerThis icon indicates tasks which may present a danger andto proceed with care.

DiscussThis icon indicates tasks such as discussing a point ordebating an issue.

ExamineThis icon indicates tasks such as reading an article orwatching a video.

Hands onThis icon indicates tasks such as collecting data orconducting experiments.

RespondThis icon indicates the need to write a response or drawan object.

ThinkThis icon indicates tasks such as reflecting on yourexperience or picturing yourself in a situation.

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ResearchThis icon indicates you will need to do someinvestigative work.

ReturnThis icon indicates exercises for you to return to yourteacher when you have completed the part. (OTEN OLPstudents will need to refer to their Learner's Guide forinstructions on which exercises to return).

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Glossary

As you work through the module you will encounter a range of terms thathave specific meanings. The first time a term occurs in the text it willappear in bold.

The list below explains the terms you will encounter in this module.

ABS a very tough polymer – short for acrylonitrilebutadiene styrene

active safety features features in a vehicle that reduce the likelihoodof an accident

allotrophy change in the physical properties withoutchanging the composition of the substance

angle of inclination angle of the slope of a plane

angle of repose equal to the angle of inclination when body ison the point of sliding

angle of static friction angle between the resultant reaction and thenormal reaction

annealing heating and soaking a material above itsrecrystallisation temperature followed byslow cooling to promote grain growth andreduce stresses

BMX an abbreviation of bicycle motocross

bogie One of a pair of units that supports thecarriages of a train; the wheels and the drivingmechanism are attached to the bogies

bowden cables flexible cables made from thin strands of steelwound together and housed inside a protectivesheath

brake power power available to do useful work

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cadence the peddling rate of a rider – usuallymeasured in rotations per minute

carbon fibre a composite material of fibres of carbon castin a polymer matrix

carburising this is the creation of a carbon-rich 'skin' onthe surface of a low carbon steel component

casting the pouring of molten or fluid material into amould where it is allowed to set

catenary When related to the electrical railway system;the wires that support conductors that carrycurrent to supply power to the trains

cementite an interstitial compound of iron and 6.67%carbon

chrome molybdenum a steel alloy processing high strength andcorrosion resistance – often shortened to cro-moly

coefficient of friction ratio of the limiting friction to the normalreaction

cold working the plastic deformation of a metal below itsrecrystallisation temperature

counterbore the widening of the top of a drilled hole toform a larger cylindrical shape to enable ascrew, bolt or other components to fit into thecounterbored hole

countersink the widening of the top of a drilled hole toform a conical or tapered surface to enable ascrew to fit flush with or below the surface ofa component

cro-moly alloys alloys of iron, carbon, chromium andmolybdenum that have excellent strength toweight ratios

cross-links the covalent bonding between the longpolymer chains at various 'sites' along thechains

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derailleur gear system a gearing system for bicycles consisting of achain passing over front and rear sprockets ofvarying sizes. The chain is derailed fromsprocket to sprocket to vary the overall gearratio

die casting a casting process where the molten metal isforced into a permanent metal mould

drop down handle bars handle bars for bicycles that curl downwardsforcing the rider into a crouch position – mostoften seen on road racing bicycles

efficiency ratio of output to input usually expressed as apercentage

elastomer an amorphous polymer that stretches greatlyunder a tensile load but then returns to itsoriginal shape

energy capacity of a body to do work

fatigue failure the type of failure caused when a lower thanmaximum stress is repeated many times

ferrite an interstitial solid solution body centredcubic iron with a very small amount ofdissolved carbon

ferrous metal an alloy that has iron as its principal element

fillers fairly inert materials added to a polymer toeither fill in space or to provide specialproperties

generic general; not specific

greenhouse gas carbon dioxide and other gases produced bypollution on the earth’s surface which act asglass does in a greenhouse to increasetemperatures

gyro headset a component of the braking system thatallows the handlebars of a bicycle to berotated 3600 without the brake cablesrestricting the rotation

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hot worked the application of heat to metal above itsrecrystallisation temperature resulting inplastic deformation

hybrid-electric vehicles powered by both a conventionalpetrol engine and an electric motor

indicated power power generated by motor not consideringfrictional losses

joule unit of work equal to a newton metre (1J = 1Nm)

kevlar the trade name of a tough, high performancearamid fibre often used as part of a compositematerial similar to glass reinforced polymeror blended with other fibres in fabric

kinetic moving

kinetic energy capacity of a body to do work by virtue of itsmotion

knurl a raised area on the surface of a cylindricallyshaped component that provides a grippingarea to hold when turning the component. Itmay be a straight knurl or a diamond knurl

limiting friction frictional force when body is on the point ofsliding

logogram a symbol or sign used to represent a word,group of words, idea, instruction or acompany name. The third angle projectionlogogram is used as a symbol to replace thewritten words

magnesium a metal 35% lighter than aluminium

malleable CI a cast iron that has been heat-treated to allowmuch of the carbon to precipitate into freerosettes

nitriding the creation of nitrides in the surface ofspecial alloy steels to provide a hard surface

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normalising heating and soaking of a material above itsrecrystallisation temperature then cooling instill air. This produces a refined grainstructure

ordinaries the type of bicycle popular in the 1870s,remarkable for having a very large frontwheel and a small rear wheel (penny farthing)

pantograph A roof-mounted mechanism that is designedto contact the current-carrying conductorsabove

parameterise To define or specify the parameters orvariables in a system

passive safety features features in a vehicle that protect the usersduring an accident

pearlite a combination of ferrite and cementite wherethe phases appear as alternating layers in thestructure

personal transport any mode of transport that allows the user ahigh degree of say in how, where and when itwill be used

pneumatic tyre a rubber tyre that is filled with air

polymer a material composed of long molecular chainsthat have a basic repeating pattern or structure

potential energy capacity of a body to do work by virtue of itsposition or composition

power time rate of doing work

precipitation hardening in some alloys, the precipitation of a phase atroom temperature leads to the distortion of themetal's structure and therefore an increase inhardness

proving tests tests in which a product is subjected to typicalloads, for example seat belt in an autoaccident

public transport any of the modes of transport that are sharedbetween many users

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quench hardened rapid cooling from an elevated temperaturecan be performed with some alloys resultingin the material becoming very hard andbrittle, tool steel is an example of this

rail trails bicycle paths and footpaths built alongsiderailway corridors

random breath testing the testing of the blood alcohol level of arandom selection of drivers using a devicethat the drivers blow into or speak into –usually abbreviated to RBT

recovery application of low heat to allow some stressrelief in cold worked metals

regenerative brakingsystem

a braking system possible on electric poweredvehicles where the electric motor switches tobecome an electric generator whenever thebrakes are applied

rover safety the first bicycle with a modern style frameand a rear wheel driven by a chain andsprocket

safety bicycles bicycles designed to improve the safety forthe rider compared to riding a penny farthing

sand casting a casting process which uses a 'single use'sand mould

selective hardening a process used to harden the surface whileretaining a tough core in a component

spherical having the shape of a sphere

spotface the formation of a flat surface on a curved orrough surface to enable a bolt or nut to fitflush with that surface

stainless steel an alloy of iron, carbon, chromium andnickel, notable for its resistance to corrosion

static stationary, not moving

strain energy capacity of a body to do work by virtue of itsstored energy in a spring

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supercapacitors very high capacity capacitors capable ofstoring a large electric charge for a short time

symbol a mark, character, letter or a combination ofeach which is used to indicate an object, ideaor process

tempering heating of quench hardened steels to relievesome of the stresses and reduce brittleness

thermosoftening a polymer that, once set, can be reformedunder heat

thermosetting a polymer that once set under heat andpressure will not soften under future heating

TIG welded articles welded by the Tungsten Inert Gasmethod

torque twisting moment; a force that acts to createtwisting or turning effect

transport system all of the elements associated with gettinggoods and people from one place to another

triathlon a race consisting of a run, a swim and abicycle leg

turbine a wheel with a set of ‘blades’ that is driven ormade to turn by water, air, steam or gas

ultraviolet radiation electromagnetic radiation invisible to thehuman eye. Extremely powerful, producingsunburn and allowing vitamin D production inthe skin

watt unit of power equal to a joule per second (1W= 1J/s)

white cast iron a cast iron in which all of the carbon isincluded in the cementite phase

work product of force and displacement, consumesenergy

work hardening cold working of materials leading to astressed internal structure and an increase inthe hardness of the material

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Directive terms

The list below explains key words you will encounter in assessment tasksand examination questions.

account account for: state reasons for, report on;give an account of: narrate a series of events ortransactions

analyse identify components and the relationship betweenthem, draw out and relate implications

apply use, utilise, employ in a particular situation

appreciate make a judgement about the value of

assess make a judgement of value, quality, outcomes,results or size

calculate ascertain/determine from given facts, figures orinformation

clarify make clear or plain

classify arrange or include in classes/categories

compare show how things are similar or different

construct make, build, put together items or arguments

contrast show how things are different or opposite

critically(analyse/evaluate)

add a degree or level of accuracy depth, knowledgeand understanding, logic, questioning, reflectionand quality to (analysis/evaluation)

deduce draw conclusions

define state meaning and identify essential qualities

demonstrate show by example

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describe provide characteristics and features

discuss identify issues and provide points for and/or against

distinguish recognise or note/indicate as being distinct ordifferent from; to note differences between

evaluate make a judgement based on criteria; determine thevalue of

examine inquire into

explain relate cause and effect; make the relationshipsbetween things evident; provide why and/or how

extract choose relevant and/or appropriate details

extrapolate infer from what is known

identify recognise and name

interpret draw meaning from

investigate plan, inquire into and draw conclusions about

justify support an argument or conclusion

outline sketch in general terms; indicate the mainfeatures of

predict suggest what may happen based on availableinformation

propose put forward (for example a point of view, idea,argument, suggestion) for consideration or action

recall present remembered ideas, facts or experiences

recommend provide reasons in favour

recount retell a series of events

summarise express, concisely, the relevant details

synthesise putting together various elements to make a whole

Extract from The New Higher School Certificate Assessment Support Document,© Board of Studies, NSW, 1999.



Part 1: Transport systems –developments

Part 1: Transport systems – developments 1

Part 1 contents

Introduction..........................................................................................2

What will you learn?................................................................... 2

Transport systems..............................................................................3

Personal transport ..................................................................... 3

Public transport ......................................................................... 5

Bicycles .................................................................................... 6

Social and environmental implications........................................18

Exercises ...........................................................................................33

Exercise cover sheet........................................................................47

Progress check.................................................................................49

2 Personal and public transport

Introduction

In this part of the module you will look at the elements that make up atransport system and the positive and negative influence different formsof transport have had on our society.

The historical development of bicycles, a common form of personaltransport, will be investigated to see how changes in design reflected thematerials development of the time.

Other forms of transport you may have the opportunity to study includemotor cars, trucks, boats, buses, trains, trams and motor cycles.

What will you learn?

You will learn about:

• historical developments in transport systems

• effects of engineering innovation in transport on people’s lives

• construction and processing materials over time

• environmental effects of transport

• environmental implications from the use of materials in transport.

You will learn to:

• investigate the history of technological change related to transportand its impact on society

• identify design features in the engineering of transport systems overtime

• critically examine the impact of developments in transport systemson the environment and society.


Refer to <http//ww.boardofstudies.nsw.edu.au> for original and current documents.


Transport systems

A transport system includes all of the elements associated with gettingpeople and goods from one place to another. Some transport systems aresmall in scale such as a system designed to move people around a zoo oran amusement park. Other transport systems enable you to travel all theway round the world.

For a transport system to be effective, the designers of the system need toknow how the different elements relate to each other. Developing asuccessful transport system is a very complex task because:

• many people are involved in the designing and controlling of smallparts of the overall system making coordination difficult

• many of the users of the system have conflicting priorities. For somelow cost is a priority, for others it is the convenience of being able touse their own personal transport while some may prefer theenvironmental benefits offered by the increased use of publictransport

• transport systems require a lot of supporting infrastructure such asroads, bicycle paths, train stations and so on. The cities and townswith the best transport systems are usually those that have had a longterm plan that made allowances for the construction of past, presentand future infrastructure in a coordinated manner.

Mention has been made of personal transport and public transportsystems – so what are the differences?

Personal transport

Personal transport is any mode of transport that allows the user a highdegree of say in how, where and when it will be used. Bicycles,motorbikes, motor cars and trucks are common examples of personaltransport. The rich and famous may also include aeroplanes as personaltransport.


Advantages of personal transport:

• available on demand

• greater convenience

• greater prestige

• greater levels of personal comfort and security

• may be used for sport, fitness, and pleasure.

Figure 1.1 Motor cars are a common form of personal transport

Disadvantages of personal transport:

• owner responsible for running costs

• some costs apply whether you use the vehicle or not for exampleregistration, maintenance, insurance and the like

• may involve a high start up cost depending on the vehicle

• for most vehicles the driver requires special training and licensing

• strict laws apply to the use of most vehicles

• greater chance of accident causing death or injury

• greater impact on air pollution due to under-utilisation of privatevehicles. The average occupancy rate for cars on Sydney roads isless than one and a half people per car.


Public transport

Public transport is transport that is shared between many users. Trains,buses, ferries, trams and planes are examples of public transport. Thecommuter pays a fare to use public transport with the route taken and thetimetable pre-determined. Public transport is often subsidised by thegovernment because many forms of public transport do not run at aprofit. As a society we accept this because of all the other benefits thatpublic transport systems provide.

Advantages of public transport:

• you only pay when you use it

• cost of fares reduced due to government subsidies

• no special training or licence required

• can be used by those that may not be able to operate personaltransport for example the young, the old, the disabled

• less chance of an accident

• the driver is responsible for adhering to speed limits

• less air pollution generated due to reduced traffic on roads

• parking and garaging not a problem.

Disadvantages of public transport:

• little control over the route taken or the timetable

• not available in all areas

• waiting time and time spent travelling to and from drop off pointsmay be considerable

• taxpayers’ money used to subsidise running costs

• very high initial capital costs to be paid for by the community

• comfort and feeling of personal security may not be as high as whenusing personal transport.

If you were asked to develop a ‘transport system’ for your area what sortof things would you consider?

• who would have priority on the road - cars, buses, bicycles, trucks?

• could you keep everyone happy?

• would your plan favour public transport?

• would it be a user pays system or would you expect others tosubsidise the costs of the system?


Some other issues you may not have thought of include:

• who is going to use the system?

• where do they want to go and when?

• are there likely to be peak periods or can demand on the transportsystem be evened out?

• what are the public transport options?

• can you link the varying forms of transport – that is can a travellerswap easily from their own car to public transport or from one formof public transport to another?

• what will be the transport needs in the near and long term future?

• will environmentally friendly options be more costly?

• what will be the long term cost if the environment is not lookedafter?

Bicycles

The bicycle is an inexpensive, highly efficient, environmentally friendlyform of transport. They take up less than one-tenth of the space requiredby a car, cause very little damage to the road surface and in congestedconditions they are quicker than other modes of transport. They areenjoyable to ride and may be used for sport and recreation. There arenearly 2 million bicycles in NSW with about 160 000 students riding toschool, college or university each day.

The following information investigates the historical development of thebicycle.

A few questions to consider are:

• why aren’t you riding around on the same sort of bicycles that yourolder relatives used in the past?

• what is different about the bicycles you ride now compared to thoseridden thirty, fifty, maybe even a hundred years ago?

• what brought about the changes?

• you need to ask yourself was the change due to the development of anew and improved material, a different manufacturing method or aninnovative approach to an old problem?


Historical development of bicycles

With bicycles as with many other machines with a long history, the useof timber preceded the use of iron and steels. Light metals followedbefore the introduction of composite materials just as ‘found’ materialspreceded man made materials. You will notice that as you move fromone era to another the strength of the material increases. This meansdesigners could do things they couldn’t do before or they could constructcomponents with less material thus saving weight. In many cases whatwas lacking in early bicycle designs was not imagination and ingenuitybut simply the right materials for the job.

1791 – just the beginning

Bicycles had their origins just over 200 years ago starting in 1791 withthe appearance of a wooden two-wheeled ‘toy’ developed by the Countde Sivrac. It is difficult to say that this was the first bicycle but it didhave two wheels and you could sit on it and push yourself along but itwas never really a serious form of personal transport. For starters youcouldn’t steer it, there were no brakes and sitting on its wooden framewas very uncomfortable. After a brief burst of interest the novelty of theCount’s toy quickly wore off.

Figure 1.2 The Count de Sivrac’s two wheeled toy

1817 – steering is added

The Count de Sivrac’s idea was revived by a German baron, Karl vonDrais when in 1817 he developed the ‘draisienne walking machine’.The main improvement was that the draisienne now had a steerable frontwheel. The draisienne and variations to the basic design were also knowas the Hobby Horse and the Dandy Horse, the latter in reference to therich young men or ‘dandies’ with whom the draisienne was most popular.


Figure 1.3 The Draisienne made by the Baron von Drais

The frame of the draisienne was still principally timber with wroughtiron forks. The wheels were now rimmed with wrought iron to improvetheir strength and abrasion resistance. For added comfort the machinehad a padded section on the frame to sit on and an armrest.

The draisienne also proved to be a passing fad with the cobbled roads ofthe time proving too uncomfortable to ride on.

1840 – pedal power

The first person to give the bicycle pedal power was a Scotsman namedKirkpatrick Macmillan. In 1840 he added treadles to the rear wheel ofhis hobbyhorse. They were operated by rods connected to foot stirrups.To propel the bicycle the foot stirrups where pushed backwards andforwards. Macmillan’s machine was no more comfortable than earlierdraisiennes and the reciprocating pedalling motion was tiring, inefficientand hindered steering. Not surprisingly Macmillan’s ideas did not catchon.

Figure 1.4 The first pedal powered bicycle


1861 – the first true bicycle?

About twenty years after Macmillan another attempt was made to givethe bicycle pedal power. In 1861 cranks were fitted to the front wheel byErnest and Pierre Michaux in much the same manner as is found on amodern tricycle used by a small child. The Michaux brothers called theirmachine a ‘velocipede’. The velocipede had a wrought iron frame withsome cast iron fittings and timber wheels with metal rims. Despite a seatmounted on a metal frame designed to flex when going over bumps thenickname for this velocipede was ‘the boneshaker’.

Figure 1.5 The velocipede

With increased speed comes the need to slow down safely so a ropeoperated rear brake was fitted.

The velocipede was an immediate success and heralded the start of thebicycle industry. The bicycle now had the potential to become a seriousform of personal transport. By 1869 improvements to the original designincluded increasing the size of the front wheel a little and fitting solidrubber tyres to give a better ride than previous iron rimmed wheels. Animportant innovation of this time was the development of ball-bearinghubs to reduce rolling friction.

1870 – now to go faster

It didn’t take long for bicycle manufacturers to realise that the velocipedewould go faster if it had an even larger front wheel. One rotation of thepedals would push the bicycle further. By 1870 the front wheel hadgrown to a maximum determined by the leg length of the riders. The rearwheel got smaller so that the overall length of the bicycle remainedmanageable. These bicycles were called ‘ordinaries’ because comparedto a number of other variations that were around during the same periodthey were the ordinary type of bicycle for the time. The nickname‘penny farthing’ was based on the wheel size of the ordinaries. A pennywas about the size of a fifty-cent piece and a farthing was about the sizeof a five-cent piece.


Figure 1.6 The ordinary or penny-farthing bicycle

Riding an ordinary required skill and bravery. The rider sat nearly twometres above the ground and almost directly above the centre of gravity.The ordinary was very difficult to climb on board as the rider tried to getgoing and stopping meant a large drop to the ground. The ordinary hadmodern style scissor brakes but using them often sent the rider flyingover the handlebars, as did hitting a rock or a pothole.

However, the larger front wheel of the penny-farthing had anothersignificant benefit. Combined with thin wrought iron spokes and a solidrubber tyre it absorbed a lot more shock than the old ‘boneshaker’.

With ongoing development such as the introduction of hollow wroughtiron forks in 1872 the ordinary remained top of the bicycle tree for justover a decade. Many designs tried to improve the rideability of theordinary but in doing so the design often became too complex.This increased the price and reduced the reliability of the bicycle.The new designs were called ‘safety bicycles’. The American Star,looked like a penny-farthing being ridden backwards. With the smallwheel at the front the rider was less likely to be thrown forwards.

Most safety designs at this time simply couldn’t match the ordinary forspeed. For many young men of the late 1800’s going fast was moreimportant than being safe. Considering the modern fatality rates ofyoung male road users it appears little has changed in the past onehundred and twenty years.

1884 – the birth of the ‘modern’ bicycle

The end for the high-wheel bicycles was in sight in 1884 when JohnStarley produced the Rover Safety. The rover safety is considered thefirst ‘modern’ bicycle because it had many of the features still seen onbicycles today. Both wheels were the same size, it had a steerable frontwheel, but most importantly the rear wheel was driven by pedals linked


to the rear wheel by a chain and sprocket. By having a large frontsprocket and a small rear sprocket a velocity ratio similar to that of thehigh-wheeled bicycles was achieved. In other words it could go as fastas a penny-farthing, was easier to start and dismount and was much saferto ride. The chain and sprocket system was made possible by theemerging steel technology that enabled small parts of high strength to bemanufactured.

The lower centre of gravity of the safety meant that the brakes could nowbe applied more effectively. In many races between penny-farthings andthe rover safety it was the greater control and the ability to slow downwhen required, more than outright top speed, that won the day for therover.

Early riders of the rover safety complained about the harsh ridecompared to the high-wheel bicycles – remember that large front wheelwas very good at absorbing shock. The solution for this came in 1888when a Scottish doctor, John Dunlop ‘re-invented’ the pneumatic tyre.A W Thompson had actually developed the idea in 1843 but his idea wasnever applied.

The original rover safety bicycle had a curved frame that quickly evolvedinto the traditional double diamond shape that is still the standard frameshape today.

Figure 1.7 A Humber safety bicycle from 1890

With the bicycle becoming a serious form of transport with wide appealacross the community greater effort was made to make it even safer,more comfortable and more efficient. This lead to improvements such asthe introduction of Bowden cables to operate the brakes, increased use ofhollow steel tube throughout the frame and other improvements such asadjustable padded sprung seats, mud guards, lights for night time riding,rubber pedals and bicycles in a range of sizes.

By 1895 a simple derailleur gear system was patented. This allowedthe rider to peddle at the same cadence or peddling speed irrespective ofthe road or trail conditions or the speed of the bicycle.


1900 to 1950 – a period of decline

The increased development of the motor car and the aeroplane throughthe 1900s saw a steady decline in support for the bicycle. Manycompanies originally set up to design and manufacture bicycles went onto become major players in the development of other more profitableforms of transport. Henry Ford and the Wright Brothers are just threewell-known identities that started their manufacturing careers buildingbicycles.

With less money being spent on research and development the first halfof the 1900s produced only a gradual refinement of the standard bicycledesign. Sport was the one area that continued to provide an avenue forthe modification and improvement of the bicycle design. Materials andspecial features that proved themselves in the sporting arena becamestandard features in the following years. Sport continues to be theproving ground for many new materials and designs.

Even so the bicycles of 1950 looked very similar to those of fifty yearsearlier. New materials such as light aluminium alloys were available atthis time but the cost restricted their use to only serious racing bikes.Drop down handle bars, another legacy from racing, was onedevelopment that did find its way into common bicycle design.The handle bars placed the rider into a crouch position reducing windresistance and making more efficient use of both the arm and legmuscles. The modern bicycle in figure 1.8 still retains most of thefeatures and appearance of a bicycle produced in the 1950s.

Figure 1.8 A modern road bicycle

1970 – BMX bicycles

The 1970s saw the introduction of small, squat BMX bicycles with theirbeefed up frames and tyres. Originally designed to imitate moto-crossmotor cycles they have evolved into a number of variations that are used


for tricks riding and freestyle competitions. Due to the nature of the dirttracks, ramps and bowls in which they are ridden BMX bikes have a verylow gear ratio with many having no gear system at all.

Figure 1.9 A freestyle BMX bicycle

The bicycle in figure 1.9 features:

• a chrome molybdenum frame

• a gyro headset braking system that allows the handlebars to berotated 360° without having to worry about the brake cablesrestricting the rotation

• front and rear foot pegs for trick riding

• ABS spokes and rims

• slick tyres to reduce rolling resistance.

Frames for BMX bicycles are most commonly either the traditionaldouble diamond design but using very low angles as can be seen inFigure 1.9 or a solid box frame made from an aluminium alloy as seen inFigure 1.10.


Figure 1.10 A BMX bicycle with a box aluminium frame

Their low gear ratio, small low frames and an ‘off the seat’ riding stylemake them unsuitable for fast, long distance journeys. BMX bikes andtheir variations are usually considered kids bicycles restricting theirpopularity amongst older riders.

1980 – mountain bikes

The BMX boom in the late 1970s also produced an important offshoot –the mountain bike. The mountain bike was developed in California as abicycle that could be ridden by adults along dirt trails. To eliminate theshortcomings of the BMX, fat tyres and straight handlebars wereoriginally fitted to traditional road bicycles. In many cases even todaythat is still the only difference between some so-called mountain bikesand their road-touring relatives.

Figure 1.11 A mountain bike suitable for a young teenager


As components failed under the increased stress the early mountain bikeswere modified by making the components thicker and heavier. The earlymountain bikes weighed in at about 20 kilograms. The weight of amodern mountain bike has been trimmed to about 12 kilograms byfinding lighter and stronger materials. As with the earlier BMX bikessome versions of mountain bikes have borrowed their look andcomponents from motorbikes.

The small mountain bike in figure 1.11 has:

• dual front shock absorbers

• a rear centre sprung frame

• knobbly tyres for better grip on dirt tracks

• a TIG welded, high tensile steel frame.

Top line mountain bikes may use a frame made from a carbon fibre tubewith aluminium alloy stays. The tubes are joined using cast aluminiumlugs and an aircraft adhesive. The wheels incorporate aluminium alloyrims, stainless steel spokes and kevlar reinforced tyres. Hydraulic shockabsorbers and disc brakes are also available.

Figure 1.12 Hydraulic filled front shock absorbers

Along with designing their bicycles to absorb shock, mountain bikemanufacturers have spent a lot of attention on the gearing system of theirbicycles. Derailleur gears are standard now with the number of gearratios available ranging from between five and thirty. This has givenriders the ability to negotiate extremely varied terrain such as steep hillsusing very low gears through to high-speed travel using the high gearratios when conditions are more favourable.

With shock absorbing suspension, fat tyres, well padded seats and anupright riding position the standard mountain bike has proved a popular,comfortable and versatile touring bicycle with riders of all ages. It isestimated that 80 % of all bicycles now sold in Australia are mountainbikes.


A measure of the spectacular rise in popularity of mountain bikes is thatmountain bike races were introduced into the 1996 Atlanta Olympicsonly fifteen years after the first mass produced mountain bikes wereoffered for sale.

Turn to the exercise section and complete exercise 1.1.

2000 – the latest designs

A feature of the bicycle industry at the moment is the wide range ofdesigns and the variety of materials used. A quick glance at a bicycleshop will illustrate the way bicycles are being used for more specificpurposes nowadays. The bicycle an athlete would use in a triathlon onthe road is different from the touring bicycle a road racer will use andvery different to the bicycles the everyday rider will purchase. One teamin the 1999 Tour de France used a specially prepared road bicycle for thehill climbing stages that weighed just 6.5 kilograms. This was almost adisposable bicycle, being unsuitable for the other stages of the race.A standard road bicycle would weigh about 9 to 10 kilograms.

Figure 1.13 The front wheel and forks of a modern road bicycle


Bicycles may range in price from a couple of hundred dollars to manythousands. Aluminium alloys, chrome-molybdenum alloys, lightweightmagnesium and composite materials such as carbon fibre are all framematerials once considered too exotic and certainly too expensive for theaverage bicycle. The bicycle in figure 1.13 features tear drop forks andfront tube for improved strength and reduced wind-resistance.

The increased strength of the materials used has also allowed traditionalladies’ framed bicycles to be more functional than they have been in thepast. This frame style is popular amongst older riders of both gendersbecause it is easier to mount and dismount.

Figure 1.14 Ladies framed mountain bike

The range of accessories and the variations available in all componentsallows the modern bicycle owner to adapt their bicycle to suit theircycling needs and preferences as well as their budget.

Figure 1.15 Disc brakes for a bicycle


The future for bicycles

The future for the bicycle lies in how well it can continue to contribute tothe areas of sport, recreation and transport.

New forms of sport will provide the incentive to experiment with newmaterials and new designs just as triathlons and mountain bike races haveover the past twenty years.

Do you think lightweight one-piece carbon fibre frames, as used in tracktime trials now, will become the common frame design for all bicycles?Will we see bicycles with automatic gearing systems? Will new uses befound for the bicycles currently available?

It is difficult to image in that riding a bicycle will cease to be apleasurable past time for people of all ages. With renewed communityemphasis on the environment and a healthier lifestyle the influence of thebicycle in an integrated transport system may well increase.

Social and environmental implications

Mobility of the populationYoung people tend to have this idea that everyone in the ‘olden days’rode around like cowboys on horses. In fact in urban areas of Britain,Europe, America and Australia until the latter parts of the 19th and theearly parts of the 20th century the main mode of everyday transport wasto walk. Longer journeys were possible in developed countries bycatching a train or sailing ship but this was not an everyday event andwas out of the price range for many people. This obviously limited themobility of the population and their opportunity to meet others and shareideas. Most people lived, were educated, worked and socialised in afairly local area.

With the introduction of an efficient affordable bicycle at the start of the20th century the world of many people was suddenly expanded and aperiod of unprecedented social change took place especially amongst theunder-privileged. Even though the automobile has become increasinglymore affordable over the past one hundred years the bicycle hasremained a significant means of transport for many people in manycountries and communities.

Find out which countries have the highest rate of bicycle usage.


Outline why some countries encourage the use of the bicycle over otherforms of transport.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

General population can’t afford cars.

Government lacks funds to construct modern highway and road network.

Population densities very high.

Roads already gridlocked.

Terrain flat and distances to be covered fairly short.

Environment impact low

The past century has seen a number of other changes to the modes oftransport use. The declining use of ships in moving people longdistances such as from country to country and the subsequent rise in thepopularity of air travel is an example of one mode of transportsuperseding another.

The obvious reasons for this shift from sea to air travel were thereduction in the price of air travel in real terms and the greatly reducedtravelling times. People today still use sailing ships of all types butmainly in a recreational sense. That is for some it is a pleasurable way totravel. It is interesting to note that modern cargo ships are our largesttransport vehicles and they still play a major role in moving a wholerange of goods over long distances since the time of the journey is less ofa factor in these situations.


Figure 1.16 Sailing for pleasure

© T. Brown

The chance for inter-state and even international travel is now a realpossibility for a wider cross-section of the community.

Ask an older relative or friend about their holidays when they were achild. Where did they go and how did they get there? How often didthey leave their local area? Did they regularly travel interstate oroverseas? You may not have travelled far afield just yet but if youwanted to it would be easier for you to travel than it was for your parents.

The ease with which people can travel internationally raises seriousquarantine issues. Being an island nation with a large coastline can be ahindrance in Australia’s efforts to keep out undesirable animals, plants,diseases, drugs and criminals.

Safety issues

In travelling from one spot to another there is always some dangerinvolved. The level of danger varies with the mode of transport used.In general terms public transport is statistically a safer option than mostmodes of personal transport yet most people feel safer in their ownvehicle. You will now examine some of the safety issues associated withsome common modes of transport.

Bicycles

Being a popular form of transport and recreation for young children,bicycles pose a special safety problem. Young riders have limitedexperience in handling their machine and lack awareness of the dangersinvolved especially those posed by other road users. A recent initiative


has seen the law changed to allow riders younger than twelve years ofage the right to ride on the footpath away from the traffic.

Riding in the city involves competing for space with a lot of cars. Ridingon country roads may mean less traffic but the speed of passing cars andtrucks will be higher. Country roads are also more likely to have gravelshoulders forcing the rider to choose between a bumpy ride away fromthe traffic or a smoother ride on the bitumen closer to the centre of theroad. Some people are fortunate to live in an area with a well-developedbicycle path network allowing them to ride in safety.

The safety features of a bicycle are limited but the compulsory wearingof crash helmets provides some protection for the cyclist.

Figure 1.17 Bicycle helmets come a range of styles and colours

In Sydney there has been a move to develop a network of bicycle pathsalong the current railway corridors. These ‘rail trails’ will provide goodseparation of cyclists from other traffic along paths with few steep hillsto negotiate.

Motor cars

In the middle to late 1800s when steam powered vehicles were firstappearing on European and American roads there was significantobjection to this new machine. Many thought the increased speedswould be dangerous to the health of the drivers and the noise producedwas likely to scare horses and pedestrians. In England the Red Flag Actrestricted the speed of a motorised vehicle to 6 kilometres per hour. Thislaw remained in force for thirty-one years even after petrol supersededsteam power.

Has the motor car become too dangerous to use?


Look at the following graph of the national road toll. You will noticethere was a steady increase in the road toll up until 1970. That year 3 798people were killed on Australian roads. At this time there wereapproximately 8 fatalities per 10 000 vehicles on the road.

Fatalities

‘64

‘66

‘68

‘70

‘72

‘74

‘76

‘78

‘80

‘82

‘84

‘86

‘88

‘90

‘92

‘94

‘96

‘98

38003500320029002600230020001700

Figure 1.18 Australian road fatalities 1964 to 1999

Source: Australian Transport Society Bureau <www.atsb.gov.au>

You will notice there was an even larger reduction in the road tollfollowing the introduction of random breath testing (RBT), firstly inVictoria in 1978 and then in NSW in 1982. By 1999 the national roadtoll had reduced to 1 759 fatalities at a rate of 1.5 fatalities per 10 000motor vehicles.

All manufacturers will highlight the active safety features and passivesafety features of their products.

Active safety features are those that help prevent an accident in the firstplace. Constant four-wheel drive, ABS braking systems, the general cardynamics of handling and braking are all examples of active safety features.Passive safety features are those that help protect the occupants of a vehiclein the event of a crash. Seat belts, air bags, shock absorbing panels,collapsible steering columns and pedals designed to break away, side impactintrusion bars are examples of passive safety features.


Motor cycles

Motor cycles have the potential to be one of the great forms of personaltransport. They are inexpensive, they take up little space on the road andhave very good fuel economy.

Why don’t more people ride motor cycles?


In some countries they do, however there are many factors to consider.You are not protected from the weather. It requires more physical effortto ride a motor cycle than to drive a car. Carrying a passenger greatlychanges the dynamics of the motor cycle. It is difficult to communicatewith your passenger or to carry large sized objects. Of greatest concernare the safety issues as motor cycles do not possess many passive safetyfeatures to protect the rider in the event of a crash.

Some motor cycle manufacturers and potential customers appear to beobsessed with high performance. The current record for the top speed ofa road registered production bike is 311 kilometres per hour, about threetimes the legal limit on most Australian highways. There have beensome concessions granted recently with all manufacturers agreeing tolimit the top speed of their bikes to a mere 250 kilometres per hourstarting from 2001.

Figure 1.19 A road ready 250cc motor cycle

Motor cycles are popular with young adults but because of their highperformance, licensing laws restrict inexperienced riders to motor cycleswith an engine size of 250 cc or less.

Trains

Trains play a particular role in reducing the national road toll. If youhave ever had the opportunity to watch a long freight train hauling wheat,coal or maybe just containers you will appreciate how many large truckswould be required to haul the same amount of cargo. Trains get a largenumber of trucks off the road. Of course the disadvantage of trains isthat they can only go where the tracks have been laid and in most casestrucks will still be necessary at either end of the train journey.


Aeroplanes

When you take into account the number of people travelling and thedistances involved, flying is one of the safest ways to travel.

Why is flying rated a more stressful mode of travelling than thestatistically more dangerous option of travelling by car?

It is not an everyday experience for most people. There is still thefeeling that it is unnatural for us to fly.

When a passenger flight crashes it often leads to large numbers of deaths,which receives wide media coverage across the world. It concerns usthat if we crash it wouldn’t be a sudden thing – we would possibly have acouple of minutes to pass before the inevitable crash.

Figure 1.20 Aeroplanes are a fast and safe way to travel long distances

© Tom Brown

Our major airline, QANTAS, prides itself on its safety record. Tomaintain its excellent safety record a significant proportion of its budgetgoes towards preventative maintenance.

Air pollution

All forms of transport create some air pollution if you take into accountthe total life cycle of the vehicle. Some like the bicycle produce little tono pollution in use but some is created during the manufacturing stage.Other forms of transport create air pollution due to factors such as, theinefficiencies in the motor, the way they are used and the types of fuelsinvolved.


Motor cars

Carbon dioxide produced by a car’s engine is a major contributor tosmog levels and global warming. Each litre of petrol a car uses releasesabout 2.5 kilograms of greenhouse gases into the atmosphere. Theweight and size of vehicle, a large engine, automatic transmission and airconditioning are all features that incur a fuel consumption penalty.Adding to the problem is the dramatic increase in pollutants produced inthe stop – start traffic experienced during peak times on our city roads.

New freeways are promoted for their environmental benefits by reducingstop-start travelling along with a saving in travelling times. A commonproblem however is that new freeways encourage more people onto theroads which increases the amount of pollution produced. The amount oftraffic on the Sydney Harbour Bridge is now at the same level it wasbefore the Harbour Tunnel was opened in 1992. Instead of buildingmore roads it may be argued that greater emphasis should be placed onpublic transport options to get more cars off the roads. The catch is thatif more people used public transport there would be less traffic on theroads, which would encourage more people to use their cars to takeadvantage of the reduced traffic levels. This is known as the publictransport conundrum.

Some ways to encourage the increased use of public transport that havebeen suggested include:

• make petrol very expensive through increased government taxationand use the money raised to subsidise public transport

• link the registration fee of vehicles to the amount of pollutants theyproduce

• increase the number of bus only lanes or transit lanes on all roads.

• reduce the amount of parking available in city areas

• charge a toll to use all major roads in the city

• restrict the days owners can use their cars.

You will notice that most of the alternatives involve the governmenttaking unpopular action with the aim of improving the environment.

Will governments risk not being re-elected in the name of improving thequality of the air and how much are we as a society willing to contributefinancially and in the form of inconvenience?

Electric trains and light rail

Electric vehicles of all sorts are seen by some as a solution to many ofour air pollution worries. It is not true to say that electric vehicles such


as trains and light rail trams don’t create any air pollution, the pollutionhas already been created back at the power stations. Solar poweredvehicles are an exception. However, solar power is still not yetconsidered a serious form of power for transport applications.

Figure 1.21 A modern suburban electric train

Trains are very good at moving large numbers of people quickly.Sydney Olympic station has been designed to move 50 000 people perhour with trains leaving the station every three minutes. Approximately12 500 cars each hour would be needed to move the same number ofpeople.

A major factor in the high energy efficiency of electric trains and lightrail systems is the smooth, predominantly straight and level nature of thetracks they operate on. This reduces the energy required to overcomefriction and means large volumes of freight can be moved using smallamounts of energy.

An important advantage of electric trains and in fact all electric vehiclesis the possibility to include a regenerative braking system in thevehicle. All vehicles lose energy when the brakes are applied as kineticenergy is converted to other forms of energy, usually heat. When thebrakes are applied on a train fitted with a regenerative braking system theelectric motor switches to become an electric generator. The electricityproduced can be used to power other systems on the train such as thelighting or air-conditioning, it may be stored in batteries or capacitors forlater use or it may be fed back into the overhead wires to be used byother trains on the same line.


A variation to the full-scale train system is the use of light rail trams.Trams have had a long history of usage in cities such as Melbourne.Light rail systems are best suited to city areas of high population densitywhere it would be impractical or too costly to build the infrastructureneeded for a full-scale rail line. The tracks required can be set into theroadway allowing light rail trams to use the existing road network.Likewise cars, bicycles and pedestrians can use the tramways when notin use by the trams.

Features of the current breed of light rail include:

• they can carry about 200 passengers – approximately two and a halftimes the capacity of a typical bus

• they have a very low floor height making them accessible for parentswith prams and small children, shoppers with trolleys, the elderlyand less mobile

• they can negotiated the tight turns and steep gradients often found onexisting roadways.

A new light rail network was opened in 1997 in the inner-city suburbs ofSydney as part of an urban renewal plan for the area. With segregatedtracks and priority at traffic signals there are no hold-ups in traffic jamsmaking the light rail trams fast and reliable. In the less-populated areasof western Sydney buses running on dedicated bus-only lanes are seen asa cheaper, more flexible public transport option.

Figure 1.22 Bus only transitway, incorporating a cycleway, linking the Sydneysuburbs of Parramatta and Liverpool

© Road and Traffic Authority, 1999, p6



Hybrid-electric motor cars

Purely electric motor cars have not been the commercial success manyhad predicated, or at least hoped, they would be. The designs till nowhave suffered from a range of weaknesses such as:

• lack of performance

• small range between charging

• batteries taking up too much space and weighing too much

• extremely high cost compared to conventional petrol vehicles.

A recent break-through has been the development of new low cost, highcapacity lead-acid batteries. Currently, vehicles using the nickel-hydridebatteries weigh about 500 kilograms and could cost as much as $30 000.The latest generation of lead acid batteries weigh 100 kilograms and can beinstalled for about $3 000. Even so the time of the purely electric vehiclestill appears to be some way in the distance.

Many motor car manufacturers are currently developing hybrid-electriccars. Hybrid-electric cars make use of both an electric motor and a smallconventional engine. The conventional engine is employed only in timesof high-energy drain on the electric motor such as during fast acceleration.At other times it either switches off completely or is used to charge thebatteries of the car. Supercapacitors are used to temporarily store unusedelectricity and electricity created through regenerative braking. Thesupercapacitors can deliver the stored charge back to the electric enginewhen needed. A family sized car using current hybrid-electric technologywill use 50% less fuel and so produce 50% less pollutants than itsconventional counterpart with the same level of performance.


Noise pollution

Like air pollution all forms of transport produce some level of noiseranging from the very minor levels associated with a bicycle to thepotentially health damaging levels produced by a large jet aeroplane.

What measures have been taken to reduce the effects of noise pollution?

Alternatives that can reduce the impact of noise pollution include:

• choosing quieter alternatives where possible such as using electricvehicles instead of petrol driven ones


• reducing the noise at the source through the use of mufflers andsound absorbing materials close to the engine or building soundbarriers along major roads

• isolating the transport system such as restricting the building ofhouses close to airports

• restrict the hours of use to a time that is less intrusive for thoseaffected.

In 1995 the federal government took the dramatic step of paying to soundinsulate the homes and schools closest to Sydney airport after a thirdrunway was built in preference to building a second Sydney airport. Thisfixed some of the problems but for the sound insulation to be effective alldoors and windows in the buildings have to be kept closed – a situationthat is less than ideal for the people inside. This remedy also doesnothing for the residents and students once they are outside in the open.


Should rural commuters be forced to use less polluting forms of transportif cleaner alternatives are more expensive?

Should parking meters, like those in cities, be introduced across the stateto raise revenue for transport alternatives?

Questions relating to equity of access to varing modes of transport aredifficult to answer.

Equity issuesIn 1989 the Sydney to Broken Hill and Sydney to Griffith train serviceswere scrapped and replaced by a bus service. The service was re-instatedin 1996 amongst much fanfare but unfortunately in April 2000 theservices were again halted; this time because the engines and carriagesused were considered to be in need of urgent repair and funds were notavailable to replace them. This situation has been repeated a number oftimes across NSW. Reduction of services in the country is in response toeconomic rationalisation or the ‘user pays’ system. That is, it is toocostly to maintain the services and too few people use the system.Despite its many advantages, rail transport is considered to be tooinflexible and costly whereas buses and trucks are more versatile andcheaper.

To the people in the country the reduction in rail services is verysymbolic. The cancelling of services is often seen as a case of the citybased governments turning their backs on rural Australia. This leaves thepeople in the country with a feeling that they have been isolated and


abandoned. To the people in the city there is a feeling that they are beingused as a cash cow to prop up the transport systems in the country.

Other issuesIssues additional to the social and environment issues include:

• the resumption of homes and land for the construction of supportingtransport infra-structure

• the building of new freeways, bridges, tunnels and so on throughsensitive bushland

• the environmentally responsible disposal of motor car bodies andcomponents such as tyres and batteries.

Given the size of Australia and the distribution of the population it isdifficult, in the short term at least, to imagine Australian’s abandoningtheir cars to take up other forms of personal and public transport. Anyshift in transportation behaviour will be a gradual process requiringgovernment support or incentives. The long-term future is less certain.Many people a century ago would have laughed at the prospect of airtravel let alone think that it would one day be a common mode oftransport for those travelling long distances. Remember it was less than70 years after the Wright Brothers that Neil Armstrong walked on themoon. Who is to say that space travel won’t be a common journeysometime during this century?



Time line of personal and public transport1791 Count de Sivrac manufactured a

two-wheeled toy.

1817 Karl von Drais developed thesteerable ‘Draisienne’.

1840 Kirkpatrick Macmillan developeda two wheel pedal poweredvehicle.

1861 Ernest and Pierre Michauxdeveloped the ‘velocipede’.

1865 The ‘Red Flag Act’ restricted theuse and speed of steam poweredvehicles to 6 km/h.

1868 Roller bearing used on thevelocipede.

1870 High wheel bicycles became theordinary style for the period.

1872 First hollow tube frame was usedon a bicycle.

1879 Joseph Lucas startedmanufacturing cycle lamps.

1884 John Starley produced the ‘RoverSafety’ – the first modern bicycle.

1886 Karl Benz lodged the patent forhis petrol powered Motorwagen’.

1890 Bowden cables were used tooperate the brakes on both carsand bicycles.

1890 J B Dunlop introduced thepneumatic tyre for bicycles.

1895 Derailleur gear system forbicycles was patented.

1896 The British ‘Red Flag Act’ isrepealed and the speed limitraised to 20 km/h.

1899 The first car to exceed 100 km/hwas an electric car driven byCamille Jenatzy.

1901 Sturmey and Archer gearsdeveloped.

1903 Britain introduces a licensingsystem for motor car drivers.

1903 Wilbur and Orville Wright makefirst successful powered flight atKitty Hawk, North Carolina, USA.

1904 Louis Rigolly exceeds 160 km/hin a motor car.

1905 H. Piper filed for a patent on ahybrid electric, petrol engine.

1906 Charles Rolls and FrederickRoyce started Rolls-Royce Ltd.

1909 Henry Ford sold his first ModelT Ford for $850.

1909 The first car offering a four wheelbraking system was constructed.

1914 Production line introduced cuttingconstruction time for the ModelT Ford from several days totwelve hours.

1919 The first set of traffic lights wereinstalled in Detroit, USA.

1922 QANTAS maked first commercialflight.

1925 A Model T Ford could be boughtfor $260.

1934 Citroen pioneer front wheel driveand automatic transmission.

1934 Adolf Hitler commissions DrFerdinand Porsche to develop a‘peoples car’ – the VolkswagenBeetle.

1935 First commercial flight overseasfrom Australia. (Darwin toSingapore).

1938 Disc brakes fitted to anIndianapolis race car.

1947 First regular commercial flightfrom Australia to the UK.

1948 General Motors – Holden producetheir first ‘Australian’ designedand manufactured car.

1955 Citroen fits disc brake to its DS19model passenger car.

1959 The first Morris Mini constructed.

1960 Aluminium alloys used in framesof bicycles.

1969 Apollo 11 landed on the moon.

1970 Wearing of seat belts was madecompulsory in all motor cars inVictoria.

1970s BMX bikes first appeared.

1972 Australia became the first countryto make the wearing of seatbeltscompulsory nation-wide.

1973 Middle East oil embargoincreased the price of petroldramatically. Bicycles, alternativefuel vehicles and fuel efficientmotors gain wider support.

1982 NSW followed Victoria’s lead inintroducing Random BreathTesting (RBT).

1996 Mountain bike races held at theOlympics for the first time.

1997 Light rail network in inner-citySydney opened.

2000 Model T Ford named Car of theCentury.

Figure 1.23 Timeline of major transport events


Can you add at least three more important events to this timeline? Thinkabout the development of trains, trams or solar cars.



Exercises

Exercise 1.1

Describe how performance, comfort and/or safety was improved in thefollowing five bicycles compared to earlier designs. List the materialsused in the construction of the frame and the wheels.

a

Figure 1.24 The Draisienne developed by Baron von Drais – 1817

Improvements

___________________________________________________________

___________________________________________________________

___________________________________________________________

Materials used

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________


b

Figure 1.25 The velocipede developed by Ernest and Pierre Michaux – 1861\

Improvements

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Materials used

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________


c

Figure 1.26 The ordinary or penny-farthing bicycle – 1870

Improvements

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

Materials used

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________


d

Figure 1.27 The Humber safety bicycle – 1890

Improvements

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Materials used

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________


e

Figure 1.28 A mountain bike – 2000

© Avanti, 2000, p8

Improvements

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

Materials used

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________


Exercise 1.2

Despite improvements in engine efficiency, safety features and comfortlevels a modern family car today is comparatively cheaper to purchasebrand new than a family car purchased in 1970. Talk to an older personabout the equipment levels and safety features in a car from the early1970s.

a List four standard features found in a modern family car that werenot commonly available in the early 1970s. Divide the list into twocomfort features and two safety features.

i Comfort features

• ________________________________________________

________________________________________________

• ________________________________________________

________________________________________________

ii Safety features

• ________________________________________________

________________________________________________

• ________________________________________________

________________________________________________

b Explain how four of the safety features listed have improve driverand passenger safety.

i ___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________


ii ___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

iii ___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

iv ___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________


Exercise 1.3

A light rail tram network is operating in inner city Sydney.

a Explain why this is an appropriate transport option for this locationbut may not be a satisfactory solution to the transport needs of otherurban and rural locations.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b List four advantages light rail systems have over other forms ofpublic transport.

i ___________________________________________________

___________________________________________________

ii ___________________________________________________

___________________________________________________

iii ___________________________________________________

___________________________________________________

iv ___________________________________________________


Exercise 1.4

Select the alternative a, b, c or d that best completes the statement.Circle the letter

1 In materials development through time:

a found materials preceded manufactured materials

b heavy metals preceded light-weight metals

c light-weight metals preceded man made composites

d all of the above.

2 The velocipede was an improvement over earlier bicycle designsbecause:

a it was steerable

b it could be pedalled efficiently

c it was the first bicycle with pedals

d it was more comfortable.

3 The velocipede was superseded because:

a it had poor brakes

b it was too heavy

c it was too slow

d it was too uncomfortable.

4 Mountain bikes are the most popular form of bicycle currently soldin Australia because:

a they are comfortable and versatile

b they can be ridden on dirt tracks

c they are inexpensive but strong

d they can go fast.

5 Carbon fibre is increasingly being used for bicycle frames because:

a it is very flexible

b it is inexpensive

c it has a high strength to weight ratio

d it can be tinted a range of colours.


6 The major cause of accidents involving bicycles is:

a the lack of helmets worn by the riders

b the inexperience of the typical bicycle rider

c motor car drivers not wanting to share the road

d the lack of bike paths for the riders to use.

7 The road fatality rate in Australia has declined since 1982 because:

a cars are safer now and the community is more aware of unsafedriving practices

b there are less cars on the roads now

c more people are using public transport

d modern cars contain more passive safety features.

8 Motor cycle riders have a high fatality rate because:

a motor cycles have few passive safety features

b motor cycles only have two wheels

c car drivers don’t like them on the road because they can go sofast

d motor cycles have few active safety features.

9 Motor cars contribute a lot of pollution to the air because:

a their motors are less efficient than other forms of transport

b they burn leaded fuel

c they have low occupancy rates

d there are so many of them on the road.

10 Electric powered vehicles have been expensive because:

a electricity is expensive to produce

b there hasn’t been much demand for them

c the batteries used to store the electricity were very expensive

d the lightweight materials used in the body of the vehicle werevery expensive.


Exercise 1.5

a All modes of transport create some pollution. Describe the types andrelative levels of pollution generated by the modes of transportlisted.

i Bicycle

___________________________________________________

___________________________________________________

___________________________________________________

ii Motor car powered by a traditional petrol engine

___________________________________________________

___________________________________________________

___________________________________________________

iii Motor car powered by a hybrid petrol/electric engine

___________________________________________________

___________________________________________________

___________________________________________________

iv Electric train

___________________________________________________

___________________________________________________

___________________________________________________

v Jet aeroplane

___________________________________________________

___________________________________________________

___________________________________________________


Exercise 1.6

a Explain why alternative modes of transport are increasingly beingused to move both people and goods instead of the rail network inrural NSW.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b List three advantages and three disadvantages of replacing rural trainservices with alternate forms of transport.

i advantages

• _________________________________________________

• _________________________________________________

• _________________________________________________

ii disadvantages

• _________________________________________________

• _________________________________________________

• __________________________________________________


Exercise 1.7

a Date the following events and sequence them on the time line below.The first one has been completed for you.

• General Motors – Holden produce their first Australian designedand manufactured car

• Wearing of seatbelts made compulsory Australia wide

• The production line method of constructing motor carspioneered by Henry Ford

• Wright Brothers make successful flight at Kitty Hawk

• QANTAS makes its first commercial flight

• Karl Benz patents his Motorwagen design

• Random Breath Testing (RBT) is introduced in NSW

• The introduction of the Rover safety bicycle greatly improvescycling safety and efficiency

• Mountain bikes first mass-produced

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

Figure 1.30

1884The introduction of the Rover safety bicycle greatly improvescycling safety and efficiency


b State three of the events from part a, then explain how each impactedon modes of transport or transport systems in the years following.

i ___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

ii ___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

iii ___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________

___________________________________________________


Exercise cover sheet

Exercises 1.1 to 1.7 Name: _______________________________

Check!

Have you have completed the following exercises?

❐ Exercise 1. 1

❐ Exercise 1.2

❐ Exercise 1.3

❐ Exercise 1.4

❐ Exercise 1.5

❐ Exercise 1.6

❐ Exercise 1.7

Locate and complete any outstanding exercises then attach yourresponses to this sheet.

If you study Stage 6 Engineering Studies through a Distance EducationCentre/School (DEC) you will need to return the exercise sheet and yourresponses as you complete each part of the module.

If you study Stage 6 Engineering Studies through the OTEN OpenLearning Program (OLP) refer to the Learner’s Guide to determine whichexercises you need to return to your teacher along with the Mark RecordSlip.


Progress check

In this part you explored transport systems and their social and environmentalimplications. You have also investigated the historical development of thebicycle with particular emphasis on the materials used.

Take a few moments to reflect on your learning then tick the box whichbest represents your level of achievement.

❏✓ Agree – well done

❏✓ Disagree – revise your work

❏✓ Uncertain – contact your teacher

Ag

ree

Dis

agre

e

Un

cert

ain

I have learnt about

• historical developments in transport systems

• effects of engineering innovation in transport onpeople’s lives

• construction and processing materials over time

• environmental effects of transport

• environmental implications from the use of materials intransport.

I have learnt to

• investigate the history of technological change relatedto transport and its impact on society

• identify design features in the engineering of transportsystems over time

• critically examine the impact of developments intransport systems on the environment and society.



In the next part you will investigate the concepts of friction, work, energyand power by their application to transport problems.


Part 2: Transport systems –mechanics/hydraulics

Part 2: Transport systems – mechanics/hydraulics 1

Part 2 contents

Introduction..........................................................................................2


Friction ................................................................................................3

Normal force ............................................................................. 4

Friction force ............................................................................. 5

Work, energy and power.................................................................17

Work........................................................................................17

Energy.....................................................................................19

Power......................................................................................26

Exercises ...........................................................................................33


Progress check.................................................................................45


Introduction

In this part you will investigate mathematical and graphical methods tosolve engineering problems involving friction relating to transport. Theconcepts of power and energy relating to transport will also be studied ingreater depth.



• engineering mechanics and hydraulics

– static friction, concept of friction and its use in engineering,coefficient of friction, normal force, friction force, angle ofstatic friction, angle of repose, energy, power, potential energy,kinetic energy, work, power.

You will learn to:

• apply mathematical and/or graphical methods to solve engineeringproblems related to transport

• analyse problems involving static friction

• differentiate between the concepts of energy and power and applyappropriate calculations.




Friction

When developing personal or public transport systems engineersendeavour to maximise efficiency and safety.

Friction is often considered to be the enemy of efficiency as it can causewear on moving parts and provides resistance to the movement of avehicle.

With society becoming more and more conscious of environmentalissues, engineers have addressed these by developing different ways ofproducing power to move the transport. Manual power, as used forbicycles, is good for the environment. Internal combustion engines, asused in motor vehicles such as cars, buses, and motor cycles, havecontinued to cause concern with vehicle emission, depletion of the ozonelayer and the greenhouse effect. Electric motors are still beinginvestigated for use with motor vehicles. Electricity has become thepreferred power source on trains, replacing the steam and diesel-electrictrains in the public transport system.

Friction allows you to walk. If there was no friction, or resistancebetween the ground and your feet, then there would be no reaction as youpush forward and your feet would simply slide out from underneath you.You have perhaps experienced this when walking on a slippery surface(ice, slime on rocks in water, muddy hillsides).

Bicycles, cars and trains would not be able to move, stop or to turncorners if it were not for friction. Most forms of transport will beequipped with a braking system that will allow it to slow down or stop byconverting kinetic energy (motion) into heat energy.

Friction is present in all machines. It will always cause wear in theindividual parts of a machine and to overcome friction, energy is wasted.Friction can be reduced to a minimum by lubrication (oiling, greasing,use of graphite) of the surfaces that are rubbing together.

You will recall that you have already studied friction in Braking systems.


Normal force (N)The normal force is a reaction force. It always acts normal (at 90∞ or

perpendicular) to the supporting surface. It balances all the forces thathave perpendicular components to the contacting surface.

The normal force will often be equal to, but opposite in direction to theweight force.

FR

P

mg

N

N = mg

Figure 2. 1 Normal force equal to the weight

Care should be taken when there are forces that are inclined to thehorizontal.

FR

P

mg

N

N = mg + P sin

Figure 2. 2 Normal force equal to weight + component of inclined force

Care should also be taken when the supporting surface is itself inclined.The weight force has two components; one parallel (tending to createmotion down the plane) and one perpendicular to the surface.


mg sin

N

N = mg cos

mg

cos mg

Figure 2. 3 Normal force equal to perpendicular weight component

Friction force (FR)

Frictional force is a reaction force that is exerted between the contactingsurfaces which tends to prevent movement. It acts along the surface asshown in figure 2.1 and 2.2.

Consider a body with an applied force on it.

When the applied force is small, the body will not move, and the reactionforce, the friction force, will be equal to the applied force. As the appliedforce is increased, so the friction force will increase to balance it. Thisfriction force is preventing motion. It is called the static-friction force.

At a certain maximum value of applied force, the body will be on thepoint of sliding. At this point, the frictional force is called the limitingfriction.

Once the body starts to move, the frictional force will be slightly lessthan the limiting friction. This condition is known as kinetic friction andis due to less interpenetration of the roughness of the contacting surfacesas they move over one another.

Fl

Fric

tiona

l for

ce (

N)

Fs

Fk

Equilibrium(static)

Motion(kinetic)

Applied force (N)

Figure 2. 4 Relationship between friction force and applied force


Coefficient of friction (mmmm)

Experimental evidence shows that the limiting friction is proportional tothe normal component, N. The ratio of the limiting friction to thenormal reaction is given by

m =

FN

R

where m is called the co-efficient of friction and gives an indication of

the ‘stickyness’ of two surfaces.

Typical values for m range from 0.2 to 0.6

Worked example 1

An electric locomotive has a mass of 260 tonnes evenly distributed overits driving wheels. Calculate the greatest pulling force that thelocomotive can exert before the wheels begin to slip.

Solution

The greatest pulling force will equal the limiting frictional force.

The mass of the train must be converted to a weight.

This is done by using the formula W = mg. Note also that 1 tonne isequivalent to 1000 kg (or 103 kg in engineering notation)

The gravitational acceleration (g) is taken as 10 m/s2

The normal force will equal the weight force

N = mg

= 260 10 103¥ ¥

= 2600 kN

FR = mN

= 0 25 2600. ¥

= 650 kN

\ The greatest pulling force will equal the limiting friction of 650 kN.

Laws of friction1 Friction always acts along the contacting surface between the two

bodies.


2 The friction force always acts in a direction and sense so as tooppose any impending motion.

3 If the bodies are in equilibrium, then the frictional force will be equalto the force tending to produce the motion.

4 The magnitude of the ratio of limiting friction to the normal force isa constant. This constant (known as the coefficient of friction) isdetermined by the nature of the contacting surfaces.

5 The limiting friction is independent of the area of contact.

Angle of static friction (ffffs)

There will be two reaction forces. The normal force which balances theweight force and the limiting friction force which balances the appliedforce.

Fl

P

mg

NRfs

Figure 2. 5 Horizontal plane – angle of static friction

A single force (called the resultant reaction) can replace these tworeaction forces. The angle between the resultant reaction and the normalreaction is called the angle of static friction (fs).

How many forces are now acting on the body?What is the significance of this?

Consider the some body placed on an inclined slope.

The angle of the slope is called the angle of inclination (q).


mg sin

N

mg

R

Fl

Figure 2. 6 Inclined plane – angle of static friction

The weight force can be converted into two components:

• one component is parallel to the plane. This component, equal to mgsin q, will be the force that attempts to move the body down the

plane. Because the motion would be down the plane, then thefriction force must act up the plane so as to oppose any motion.

• one component is perpendicular to the plane. This component, equalto mg cos q, will be balanced by the normal reaction.

That is, the weight force will create two reactions, the normal reactionand a limiting friction reaction.

These two components can be combined to form a resultant reaction in asimilar way as was done with the horizontal plane. The angle of staticfriction will again be the angle between the resultant reaction and thenormal reaction.

Angle of repose

It is useful to know if an object will slide on an inclined surface.The roughness between the surfaces can prevent movement up to a point,but if the slope is too steep, then the object may move despite the staticfriction acting between the two contacting surfaces. This may beincorporated into design situations.

When the angle of inclination (q) is equal to the angle of static friction

(fs), the body will be on the point of sliding and the friction will be

limiting. This angle is called the angle of repose.

At the point of limiting friction, q = fs = angle of repose

Because the normal force is always perpendicular to the surface and thelimiting friction is always along the contacting surface, then when they


are combined together to form the resultant reaction, they will alwaysform a right-angled triangle. The resultant will equal the hypotenuse (theside opposite to the right angle).

NR

Fl

Figure 2. 7 Resultant reaction and angle of static friction

Using the trigonometry ratio, tan f =

oppositeadjacent

=

lim iting frictionnormalreaction

=FN

1

= ms (coefficient of friction)

Worked example 2

A suitcase is placed on an inclined plane. The angle of inclination of theplane is increased until the suitcase is on the point of sliding. At the instantthe suitcase starts to move, the plane is inclined at 30∞ to the horizontal.

Determine the coefficient of static friction between the contactingsurfaces.

At point of limiting friction; fS = q

mS =

EN

1

= tan fS

= tan 30∞

= 0.58

Determine the coefficient of friction between a flat bottomed object and areasonably smooth flat surface


Place the object onto the flat surface (a wide board would do here).

Gradually lift the end of the board until the object is just on the point ofsliding down the slope.

Measure the angle of the slope at this point. This can be done with theaid of a protractor, or you can measure the height of the end that has beenlifted up and compare it with the length of the board.

Calculate the angle with your calculator.

Hint: sin q =oppsite

hypotenuse

=height

lengthof board

As q = fs, now take tan f to determine the coefficient of friction.

Verify this result by applying a force to the object. This can be donewhen the surface is horizontal. Measure the applied force by using aspring balance. Weigh the object using the spring balance.

Coefficient of friction (m) is the ratio of the limiting friction (= applied

force) to the normal reaction (N), (= weight).

m =

EN

R

How does this compare with determining the angle of repose?

What happens if the board is lowered slightly when the object has startedsliding?

How can you explain this?

Worked example 3

A 20 kg wooden crate is sitting on the floor. A force is applied at 30∞ as

shown. Determine the force (P) if the crate is on the point of sliding.

The coefficient of friction between the floor and the crate is 0.55.

P

30∞

Figure 2. 8 Wooden crate on floor


Draw a free body diagram of the forces acting.

P30∞ Fl

mg

N

Figure 2. 9 Free body diagram showing all forces acting

As the forces are in equilibrium, use the equilibrium equations SH = 0

and SV = 0.

When drawing the free body diagram, change the inclined force into itshorizontal and vertical components. Also convert the mass into weight.

P sin 30∞Fl

mg

N

P cos 30∞

= 20 10= 200 N

Figure 2.10 Free body diagram showing components

Analytical solution

Fl = mS N

= 0.55 N

Summing the forces horizontally

+ Æ SH = 0

P cos 30∞ - Fl = 0

P cos 30∞ = 0.55 N (1)

This equation has two unknowns and can’t be solved by itself.

Summing the forces vertically

+ ≠ SV = 0

N – P sin 30∞ - 200 = 0

N = P sin 30∞ + 200 (2)


Substitute (2) into (1)

P cos 30∞ = 0.55 (P sin 30∞ + 200)

P ( cos 30∞ - 0.55 sin 30∞) = 0.55 ¥ 200

P =

1100 866 0 55 0 5( . . . )- ¥

=

1100 591.

= 186 N

Graphical solution

The graphical solution is a much simpler method that requires fewmathematical skills.

The free body diagram should still be used. It is important that thecorrect direction for the limiting friction is established. That is, it mustoppose any impending motion.

P30∞ Fl

mg

N R

Figure 2.11 Free body diagram – resultant reaction

It is also necessary to find the angle of friction. You should recall thatthis is the angle between the normal reaction and the resultant reaction.

This can be constructed by using the ratio of Fl / N is equal to m (0.55) in

this example.

The angle of friction can be constructed by drawing N at right angles tothe surface and making it 100 mm long. From the end of this line, drawFl in the direction established in the free body diagram.

Because m = 0.55, then Fl will be constructed 55 mm long. This will now

establish the angle of friction. fS.

There are now three forces acting on the body. These are:

• the weight of the crate, (magnitude and direction known),

• the force P (direction only known, magnitude unknown) and


• the resultant reaction (direction only known, magnitude unknown).

From these forces, the known force is drawn to a suitable scale first.The known force in this example is the weight force of 200 N. Select asuitable scale (a scale of 10 mm = 25 N in this case). This ensures thediagram is large enough to establish an accurate solution. A vertical line80 mm long is drawn. An arrowhead is placed on this line to indicatethat the weight force is acting down.

The force polygon is now completed by drawing the other two forces inthe directions of those forces, then scaling off the magnitude of the forcethat is required.

From the end of the weight vector, the angle of friction is constructed bymeasuring up 100 mm (representing N), then from the end of the 100 mmline, another line 55 mm long (representing Fl) is drawn. This gives theratio of 55/100 (= 0.55). Note this only establishes a direction equal tothe angle of friction. It does not give the actual values of the normalreaction or the limiting frictional force, but shows the line of action of theresultant reaction.

From the top end of the weight vector, the direction of P (30∞ in this

example) is drawn until it intersects with the line of action of theresultant reaction.

The value of P is now scaled off from the force diagram. This determinesthe magnitude of the required force P.


30∞

mg

= 2

00 N

100

mm

55 mm

P is scaled off diagram = 74 mm = 185 N

R

P

= 0.55

ratio = 55100

determines

Scale 10 mm = 25 N

Figure 2.12 Force diagram drawn to scale

Worked example 4

When unloading suitcases from the luggage compartment of an interstatetourist coach, the driver pulls the suitcase at an angle of 30° to thehorizontal. The suitcase slides along the floor and the coefficient offriction between them is 0.3.

Determine:

• the effort the driver must exert so as to move the 30 kg suitcase

• the best angle he should pull at so as to minimize his effort.

P mg = 30 10 = 300 N

Figure 2. 13 Suitcase being pulled


A graphical solution is the easiest way to solve this problem.

The known force is drawn to a suitable scale. The magnitude of theweight force is calculated by multiplying the mass (30 kg) of the suitcaseby gravity. Using a value of g = 10 m/s2, the weight of the suitcase isequal to 300 N. A suitable scale could be 10 mm = 30 N, so the weightforce would be drawn 100 mm long.

The angle of the resultant reaction is constructed. The coefficient offriction is 0.3. This is converted to a ratio of 3/10. The angle of frictionis constructed by measuring up 100 mm (in the direction of N), then 30mm (in the direction of Fl). This is shown as point X in the followingdiagram. Point X is joined to the lower end of the weight force to givethe direction of the resultant reaction.

The direction of the pull is given as 30∞. This is drawn from the top of

the weight force until it intersects with the line of action of the resultantreaction. The length of this line is scaled off the diagram to determinethe size of the pull required at 30∞.

To determine the best angle to pull the suitcase from the luggagecompartment, the force diagram is again used. The weight force and theangle of friction are the same as in the first part of the problem.

The smallest force must be the shortest distance from the line of action ofthe resultant reaction and the top of the weight force. This will beperpendicular to the line of action of the resultant reaction.

The magnitude of this force is again scaled off the diagram. It is alsonecessary to measure the angle of this force. This is done by using aprotractor.


100

30

x

300

N30∞

15∞P1

P2

R2

R1

Scaled from diagram

Scale 10 mm = 30 N

15∞

P1 = 90 N

P2 = 84 N

30∞

Figure 2. 14 Force diagram

Turn to the exercise section and complete exercises 2.1 and 2.2.


Work, energy and power

In the transport system, work is continually used to provide motion tocars, bicycles, trains and other vehicles used for private and publictransport. It is also required to provide a resistance to stop a vehicle.

Energy, the capacity to do work, is constantly converted from one formto another. You recall how this was applied when you studied brakingsystems. Work and power are required to overcome friction in thecomponent parts of any machine.

The concepts of work, energy and power are closely related. The studyof these helps the engineer select the correct size motor to perform acertain task, or predict what performance could be expected from a givenmotor.

Work (W)

Work done on a body is defined as the product of two vectors; the force(F) and the displacement (s) created by the application of the force.The displacement must be measured in the same direction as the force.

W = F x s

It may be convenient to use

W = F x s cos f

where f is the angle between the line of action of the force and the

direction of the displacement.

F

displacement (s)

Figure 2. 15 Force not applied in the same direction as displacement


The unit of work has been given the name of Joule (J), named in honourof James Joule (1818–89), who conducted experiments to determine thework required to produce a unit of heat.

Total work

When more than one force is acting on a body to produce motion, thetotal work done can be found by finding the work done by the individualforces and adding these together, or by finding the work done by theresultant force.

A special case occurs when a body is moving with constant velocity.Constant velocity implies there is no acceleration. This also impliesthere is no resultant force which in turn implies there is no work done.

Similarly, if the object doesn’t move, then s = 0 also implies there is nowork done.

Work done by a force

The work done on a body can also be determined graphically from aforce-displacement graph.

Work (Joule)

For

ce, F

(N

)

Displacement, s (m)

Figure 2. 16 Work done by a constant force

The shaded area represents the amount of work done over a givendisplacement.

Worked example 5

A cyclist exerts a constant force of 250 N over a distance of 12 metres.Determine graphically the amount of work done over this distance.A graph may be constructed to plot force against displacement.

For

ce, F

(N

)

Displacement, s (m)

250

120


Figure 2. 17 Force-displacement graph for a constant force

Shaded area = 250 (N) ¥ 12 (m)

= 3000 Nm

= 3000 J

\ Work done = 3 kJ

EnergyEnergy is the capacity to do work. There are many forms of energy suchas heat, electrical, chemical, radiation and nuclear energy.

In studying the mechanics of private and public transport you willexamine two forms of mechanical energy; kinetic energy and potentialenergy.

The unit for energy is the same as for work – the joule (J). Because thejoule is a small quantity, it is more common to use multiples of the joule,in particular the kilojoule (kJ) and the megajoule (MJ).

Kinetic energy (KE)

The energy that a body possesses due to its motion is called its kineticenergy.

Kinetic energy may be calculated mathematically by the formula:

KE = 12

mv2

where m is the mass of the body measured in kilograms (kg), and v is thevelocity of the body measured in metres per second (m/s).

Potential energy (PE)

The energy that a body possesses by virtue of its position is called itspotential energy.

The potential energy is equal to the work done in lifting a body’s weight(mg) through a vertical height (h).

Potential energy can be divided into two forms:


1 gravitational potential energy due to height

2 elastic or strain potential energy due to elastic deformation (springs).

Gravitational potential energy is found by the formula

PE = mgh

where h is the vertical height and is independent of the path taken toachieve that height.

In a hydro-electric scheme to produce energy, water is stored in a reservoiror dam high above the power station. The water has gravitational potentialenergy due to its height. This potential energy changes to kinetic energy asit flows down through the pipes. At the power station, the water turns theturbines to create electrical energy, which can then be used to drive electrictrains, or produce light or heat energy.

Dam

Pipe

Power stationTurbine

Mountain

Figure 2. 18 Schematic diagram of hydro-electric power station

Energy can’t be created or destroyed but it can be transformed from oneform to another form of energy. This is known as the principle ofconservation of energy.

Strain energy (SE)

Strain energy is a form of potential energy. It is recoverable and isequal to the amount of work done in stretching or compressing a spring.When the load is removed, providing that no permanent deformation hasoccurred, the energy is recovered.

A retractable ball point pen has a refill cartridge and a spring inside it.When the pen is ready to use, the spring is compressed.


The spring now has some strain energy, which when released, will returnthe refill back to its writing position.

For

ce (

N)

Extension, e (m)

Elastic limit

W=SE

Figure 2. 19 Force – extension diagram up to the elastic limit.

The work done in producing deformation is found by the area under thegraph.

This is known as the strain energy and equals the area of the triangle.

S E = W = 12

F e

You will recall from your work with force – extension diagrams that theslope of the line up to the elastic limit is known as the stiffness.

When working with springs, the slope of the line up to the elastic limit isknown as the spring constant (k). The spring constant of a coiled springis determined by the force required to stretch (or compress) a spring by aunit length. It is measured in N/m.

F = k e

Substitute this into the strain energy formula

S E = 12

F e

= 12

k e2

Strain energy can be used to advantage by loading up a spring.When released, the spring does useful work.

A mousetrap is a good example of this principle. The spring is deformedand secured in position. When the trigger is activated by the mouse, thespring is released and traps the mouse.

By using the strain energy formula, the amount of stored energy can becalculated. This energy may be converted to another form of energy togenerate motion, heat or noise.


Conservation of mechanical energy

If a body is in motion under the action of external forces, the total energyin the system is constant.

For a free falling body, for example, the sum of the kinetic energy andthe potential energy is a constant.

This can also be written as:

Loss in potential energy = gain in kinetic energy

or conversely

Gain in potential energy = loss in kinetic energy

Worked example 6

A bicycle and rider, of total mass 90 kg, coasts at 7 m/s and continues tocoast up a raised section in the road 0.2 metres high.

AB

C

Figure 2. 20 Bicycle and rider with raised section in the road

i Determine the velocity of the bicycle at point B, if frictional lossesare negligible, and the rider still does not pedal.

Using the conservation of energy principle:

Total energy at point A = Total energy at point B

KEA + PEA = KEB + PEB

12

mv2 + mgh =12

mv2 + mgh

12

¥ 90 ¥ 72 + 0 =12

¥ 90 v2 + 90 ¥ 10 ¥ 0.2

2205 – 180 = 45 v2

v = 6.7 m/s

ii The rider applies the brake at B and comes to rest on the raisedsection at point C. Determine the energy dissipated in the brakingprocess.

The bicycle has lost kinetic energy in coming to rest. This loss ofenergy is equivalent to the work done in bringing the bicycle from


the initial velocity, u = 6.7 m/s to a final velocity, v = 0 (that is, atrest).

Work done = Change in Energy

= Change in KE (as there is no changeof height)

=12

mv2 – 12

mu2

= 0 – 12

¥ 90 ¥ 6.72

= -2025 J

Negative sign indicates that the force doing the work acts in the oppositedirection to the displacement.

Energy dissipated = 2.025 kJ

Worked example 7

A cyclist pedals his bicycle up a 5∞ slope with a constant velocity as

shown. The resistance to motion due to friction is 300 N. The combinedmass of the cyclist and the bicycle is 90 kg.

5∞

300 N

mg

Figure 2. 21 Cyclist on a slope

i Determine the work done by the cyclist when the bicycle hastravelled 40 metres up the slope.


5∞

300 N

mg sin 5∞

5∞

mg = 90 10 = 900 N

mg

cos

5∞

P

Figure 2. 22 Free body diagram – moving up the slope

SF = ma (a = 0 if constant velocity)

The cyclist travels at constant speed, therefore the forces parallel to theplane are balanced.

P needs to overcome the component of the weight force parallel to theslope, that is, mg sin 5°, and the friction.

P – mg sin 5∞ - 300 = 0

P = 300 + (90 ¥ 10 ¥ sin 5∞)

= 378.4 N

Work Done = Force ¥ displacement

= 378.4 ¥ 40

= 15136 J

= 15.1 kJ

ii Determine the driving force required at the wheels if the cyclist nowturns around and travels down the slope with a constant velocity.The total resistance due to friction to motion is still 300 N.


5∞

FD

mg sin 5∞

5∞

mg

mg

cos

5∞

300 N

Figure 2. 23 Free body diagram – moving down the slope

S F = ma (a = 0 if constantvelocity)

FD + mg sin 5∞ - 300 = 0

FD = 300 – 78.4

= 221.6 N

For another set of conditions, the bicycle starts from rest at the bottom ofthe slope. When it has travelled 20 metres up the slope, it has a velocityof 3 m/s. Determine the increase in the energy associated with thismotion.

At the bottom of the slope

Potential Energy, PE = 0 (as height = 0)

Kinetic Energy, KE = 0 (as bicycle is at rest, v = 0)

At 20 m up the slope

Potential Energy = mgh

= 90 ¥ 10 ¥ 20 sin 5∞

= 1568 J

Kinetic Energy =12

mv2

=12

¥ 90 (3)2


= 405 J

Total Energy increase = 1568 + 405

= 1973 J

= 1.97 kJ

Turn to the exercise section and complete exercises 2.3 to 2.5.

Power (P)

Most transport will be driven by some sort of motor. This may be in theform of an internal combustion engine, an electrical motor or the humanbody as in the case of the bicycle.

Power (P) is the time rate of doing work.

P =

Wt

=

Est

= Fv (since velocity = displacement/time)

P = Fv is a particularly useful derived formula. The formula sheetsupplied with the HSC examination paper uses P = W/t, but not P = Fv.

Maximum power is the power required at maximum velocity. It is themaximum power that determines the size of the motor that is required.

The average power determines the amount of fuel or electricity used in agiven period of time.

The unit of power is also given a special name of watt (W). The wattwas named after the Scottish engineer, James Watt (1736–1819). Hedeveloped the steam engine and was the first to introduce a unit todescribe the rate of doing work. The unit he described was thehorsepower which is equivalent to 745.7 watts.

The watt is equal to a joule per second.

1 W = 1 J/s


Worked example 8

The Tangara motor carriage as used on suburban services in Sydney has amass of 50 tonnes. The Electric Multiple Unit (EMU) exerts a constantforce of 80 newtons/tonne on a carriage.

Calculate the power exerted by the locomotive if the train is travelling ata speed of 72 km/h.

Before the formula P = Fv can be used, the velocity of 72 km/h must beconverted to m/s. To convert km/h to m/s, multiply by 1000 (thisconverts km to m), then divide by 3600 (this converts hours to seconds).

72 km/h =

72 10003600

¥m s/

= 20 m/s

P = Fv

= 80 ¥ 50 ¥ 20

= 80000 W

= 80 kW

Worked example 9

A 1 tonne car uses power at the rate of 15 kW when traveling at 20 m/son a level road. The driver turns off the engine when he reaches anincline of 10∞. How far up the hill will the car run before it stops?

Assume the frictional resistances remain constant.

P = FR v

Resistance force, FR =

Pv

=

1500020

= 750 N

Weight component down incline, F = mg sin 10∞

= 1000 ¥ 10 ¥ 0.1736

= 1736 N

Total force opposing motion = 1736 + 750

= 2486 N

KE at bottom of incline =12

mv2


=12

¥ 1000 ¥ (20)2

= 200 000 J

KE of car = work done against friction

= F ¥ s

200 000 = 2486 ¥ s

= 80.5 metres

Efficiency (hhhh)

In most practical cases, some of the power is lost in overcomingresistance forces. Friction and heat are the two main factors preventing amachine from making all the theoretical power available.

Indicated power (ip)

This is the power that is generated at the cylinders of the combustionengine. Frictional losses of power due to frictional forces are notconsidered. Indicated power is the power stated when advertising thepower of a car.

Brake power (bp)

There are many frictional losses along the drive train of any vehicle.Brake power is the power that is available to do useful work at thedriving wheels.

The efficiency (h) of an engine is found by dividing the power output by

the power input.

h =

outputinput

=

brake powerindicated power

Note that the ratio of output/input can refer to work or to power.

The indicated power will always be greater than the brake power, so themechanical efficiency will always be less than one.

Due to the action of friction in most machines, the work output is lessthan the work input. In a perfect (frictionless) machine, the input and


output of work will be equal. This is called 100% efficient. In practice,this is never obtainable.

The ratio is always less than one, and is normally expressed as apercentage.

Worked example 10

A car with a mass of 0.9 tonne is travelling at a constant velocity of 80km/h down an incline of 1 in 30.

Calculate the power delivered by the engine if the value of m is 0.4.

What power would be required of the engine if the car was travelling upthe same incline at 80 km/h.

Because the inclination has been given as a ratio, you need to convert thisto an angle. The inclination is sometimes known as rise (vertical height)over run (horizontal length).

30 (Run)1 (Rise)

Figure 2. 24 Inclination of slope

tan q =

130

q = tan-1 0.0333

= 1.9∞

mg = 900 10 = 9000 N

N

Fl

Figure 2. 25 Free body diagram showing forces acting

Weight component down the plane (helps drive car down plane)

mg sin 1.9∞ = 900 ¥ 10 ¥ sin 1.9∞

= 298 N

Weight component at 90∞ to the plane = mg cos 1.9∞


N = 9000 ¥ cos 1.9∞

= 8995 N

Limiting friction, Fl = mN

= 0.4 ¥ 8995

= 3598 N

FD + 298 – 3598 = 0

FD = 3300 N

Convert the velocity 80 km/h Æ m/s

80 km/h = 80 x 10003600

= 22.2 m/s

Power to drive down the slope = FD v

= 3300 ¥ 22.2

= 73260 W

= 73.3 kW

Friction now has to be overcome (to drive it up the plane)

FD - 298 – 3598 = 0

FD = 3896 N

Power to drive up the slope = FD v

= 3896 ¥ 22.2

= 86491 W

= 86.5 kW


Worked example 11

A moving footpath is transporting people at a constant velocity of 2 m/sup a 1 in 20 slope. The footpath rises 4 metres over its effective length of80 metres.

Calculate the number of people that can be conveyed in an hour if theaverage mass of the people is 74 kg. the power rating of the driving motoris 3 kW, and the efficiency of the equipment is 70%.

Work to move one person = mgh

= 74 ¥ 10 ¥ 4

= 2960 J

To move n people = 2960 ¥ n J

h =

Power outputPower input

70100

=output3000

Power output = 0.7 ¥ 3000 W

= 2100 W

E = 1 hr or 3600 sec

P =

Wt

Total work available for one hour 2100 =

2960 n3600

¥

n =

2100 36002960

¥

= 2554 people

Turn to the exercises section and complete exercises 2.6 to 2.8.

You have now used some common mathematical techniques to analyse avariety of practical situations involving the concepts of friction, work,energy and power.

Graphical methods of solving frictional and work problems have alsobeen described. You can now use these techniques not only to solveproblems associated with transport, but also in other fields ofengineering.


Exercise

Exercise 2.1

a Explain why rubber is a very suitable material from which to makecar tyres. (Note the co-efficient of static friction or rubber onconcrete 0.6 – 0.90.)

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Explain why many drive belts, like the fan belt on a car, are madefrom moulded rubber and fibre.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

c Explain why some grips on a recreation bicycle pedal are made fromrubber, whereas pedals on performance and cross country bicyclesoften use alloy pedals with clips.

_______________________________________________________

_______________________________________________________

_______________________________________________________


Exercise 2.2

A 25 kg suitcase is pushed into the luggage compartment of aninterstate tourist coach. The driver pushes with a downward force of70 N at an angle of 30∞ to the horizontal.

Apply a graphical method to determine:

• the coefficient of static friction if the suitcase is on the point ofsliding

• the maximum force that can be applied, by either braking oraccelerating, in order that the suitcase will not slide on the floor.


Exercise 2.3

An electric car of mass 0.8 tonnes is travelling at 60 km/h and entersa 40 km/h speed zone outside a school. Calculate the total work doneby the brakes, frictional forces and air resistance to reduce the car’sspeed to the new speed limit.


Exercise 2.4

The car now travels at the speed limit of 40 km/h. Name the type ofenergy possessed by the car if it is travelling along a flat section ofroad. Calculate the numerical value of this energy.


Exercise 2.5

A railway carriage is moved from rest up a 3° slope by a diesel-electric powered locomotive exerting a force of 20 kN. The carriagehas a mass of 30 tonnes.

Apply the mathematical method using the work / energy principle tosolve how far up the slope the carriage will have moved when itsvelocity is 15 km/h. Neglect frictional forces acting.


Exercise 2.6

A bus and its passengers have a combined mass of 5 tonnes. The busis obeying the speed limit and is travelling at a constant velocity of 50km/h on an inner city level stretch of road.

Apply a mathematical method to calculate the total value of frictionalforces acting if the bus is using 14 kilowatts of power.

Calculate how much extra power with a gradient in the road of 10°the engine must develop to maintain the velocity of 50 km/h up thehill? Assume the losses due to friction remain constant.


Exercise 2.7

An electric car is coasting down a slope of 20° at 60 km/h. The carand driver have a combined mass of 850 kg.

a Differentiate between the concepts of energy and power anddetermine, with appropriate calculations, what power the enginewould need to supply to enable the car to climb the same hill at 60km/h.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Explain what would happen if the power of the motor of the car wasdoubled.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

c Discuss the changes in energy during the decline of the slope.Explain why the speed of the car would remain constant whiledescending the slope.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________


Exercise 2.8

Select the alternative a, b, c or d that best completes the statement.Circle the letter.

1 Friction is:

a the property created between contacting surfaces when theroughness of one surface interpenetrates with another surface

b a reaction force which acts along the contacting surface inthe same direction as the net force supplying motion

c a reaction force which is equal to the net force supplyingmotion

d a resistance force that only acts when a body is in motionand it opposes that motion.

2 The coefficient of friction is:

a the product of the limiting friction and the normal force

b the ratio of the limiting friction to the normal force

c the ratio of the normal force to the limiting friction

d a numerical value that is always equal to or greater than 1.

3 The normal force is:

a always equal to the body’s weight (mg)

b the resultant force that creates motion to a body

c a reaction force acting perpendicular to the contactingsurface

d the product of the limiting friction and the coefficient offriction (m).

4 The friction force is:

a the force that overcomes friction and supplies motion to abody

b the force exerted between contacting surfaces of two bodieswhich tends to prevent movement between them

c the force that will stop a body from turning over and allowsit to slide

d a set force that is constant between two different materials.


5 The angle of static friction is found when the normal force andthe limiting friction force are replaced by a single resultantreaction. It is:

a the angle between the resultant reaction and the contactingsurface

b the angle between the resultant reaction and the normalreaction

c equal to the tangent of the coefficient of static friction

d only used on an inclined plane.

6 The angle of repose is:

a when a body is resting in equilibrium on an inclined plane

b when an inclined force is not big enough to create motion

c equal to the angle of inclination of a plane when it is equal tothe angle of static friction at the point of limiting friction

d the angle of the resultant reaction force to the horizontal.

7 Work is:

a done on a body when an external force is applied to thebody, but does not move it

b the product of force acting and displacement

c found by the area under a stress-strain diagram

d always done when a force acts on a body.

8 Potential energy is:

a always equal to the kinetic energy due to the principle ofconservation of energy

b the capacity of a body to do work by virtue of its position

c measured as the work done in lifting a body through avertical height in a given amount of time

d measured as the work done in moving a body’s weight (mg)through a distance to a new position.


9 Kinetic energy is:

a always equal to the potential energy due to the principle ofconservation of energy

b the capacity of a body to do work by virtue of its motion

c found from the product of the mass of the body and theheight of the body

d measured as the work done by a body before being broughtto rest by an externally applied force.

10 Power is:

a the rate at which work is done

b the product of work and time and is measured in watts

c a measure of the efficiency of a motor

d also known as torque.




Check!


❐ Exercise 2.1

❐ Exercise 2.2

❐ Exercise 2.3

❐ Exercise 2.4

❐ Exercise 2.5

❐ Exercise 2.6

❐ Exercise 2.7

❐ Exercise 2.8





Progress check

In this part you applied the concepts of friction, work, energy and power,to analyse engineering problems related to transport.





Ag

ree

Dis

agre

e

Un

cert

ain

I have learnt about:

• engineering mechanics and hydraulics

– static friction, concept of friction and its use inengineering, coefficient of friction, normal force,friction force, angle of static friction, angle ofrepose, energy, power, potential energy, kineticenergy, work, power.

I have learnt to:

• apply mathematical and/or graphical methods to solveengineering problems related to transport

• analyse problems involving static friction

• differentiate between the concepts of energy andpower and apply appropriate calculations.



In the next part you will examine materials used in the manufacture oftransport components and the processes used to produce desirableproperties in these materials relating to their applications.


Part 3: Transport systems –materials

Part 3 Transport systems – materials 1

Part 3 contents

Introduction..........................................................................................2


Testing of materials............................................................................3

Non-destructive tests ................................................................. 3

Destructive tests........................................................................ 5

Ferrous metals..................................................................................12

Plain carbon irons and steels.....................................................12

Alloy steels ..............................................................................14

Forming processes...................................................................21

Non-ferrous metals...........................................................................36

Aluminum and some of its alloys................................................37

Brasses ...................................................................................40

Bronzes ...................................................................................42

Strengthening and heat treatment..............................................43

Polymers............................................................................................46

Thermosoftening polymers........................................................48

Elastomers...............................................................................52

Thermosetting polymers............................................................54

Polymer forming processes.......................................................57

Engineering textiles ..................................................................62

Laminated and tempered glass..................................................63

Exercises ...........................................................................................67


Progress check.................................................................................81


Introduction

Engineers are interested in the development, properties and availabilityof materials and how this has affected the design of various forms ofpersonal and public transport. In this part you examine specific materialsand investigate structure/property relationships and testing procedures asthey relate to transportation systems.

What you will learn?


• specialised testing of engineering materials and/or systems

• heat treatment of ferrous metals

• structure/property relationships in the material forming processes

• non-ferrous alloys

• ceramics and glasses

• polymers.

You will learn to:

• explain the properties, uses, testing and appropriateness of materialsused in transportation

• identify appropriate heat treatment processes

• justify appropriate choices for ferrous and non-ferrous materials andprocesses used in transportation parts and systems

• experiment with metals to reinforce the concepts of heat treatment

• explain the method and applications of various ferrous metal forming processes

• justify appropriate choices for ceramics and glasses used intransportation parts and systems

• justify appropriate choices of polymers and their manufacturingprocesses used in transportation parts and systems.




Testing of materials

Testing of materials provides critical data to the design engineer andensures that products are manufactured to the required specifications.

There is an ever increasing array of tests that can be performed.They can be categorised as either non-destructive or destructive tests.

Non-destructive tests

Mechanical tests that don't damage the item being tested are known asnon-destructive tests. These tests are vital in determining the specificproperties of manufactured items or in determining the effect of formingprocesses on a material's properties.

Radiographic examination

X-rays, gamma rays and ultrasonic testing were all dealt with in detail inCivil structures. When you consider devices associated with bothpersonal and public transport there are many components that could betested by one of these types of testing.

Describe how a x-ray test would be carried out.

___________________________________________________________

___________________________________________________________

___________________________________________________________

Did you answer?

Radiation is used to penetrate the item tested and then register on either a photographicfilm or a fluorescent screen. Any internal void allows the rays to pass through moreeasily, resulting in a dark area on the film.


These types of tests are used to investigate internal features ofcomponents. This allows the engineer to check that there are no points ofweakness inside a casted, forged or welded joint.

Explain why is it important to thoroughly check components used forhigh-speed trains.

___________________________________________________________

___________________________________________________________

___________________________________________________________

Did you answer?

The consequences of failure in a structural component of a high-speed traincould be catastrophic, hence the importance of thorough and regular checks.

Modelling

As you read in the previous module, engineers use both scale and full sizemodels to test design concepts. For example full size crash tests areconducted on both trains and motor vehicles to determine theeffectiveness of design changes. With the continuing development ofcomputer simulations much of the data gained from actual tests is used tovalidate the computer predictions.

In the case of trains, cars and bicycles, aerodynamics have becomeincreasingly important for a number of reasons. When a transportvehicle slips easily through the air it uses much less fuel, can travel at afaster speed and generates much less wind noise.

Over the past 30 years engineers in Europe and Japan have slowlydeveloped high-speed rail networks and there are now trains that cantravel at well over 500 kph and commuter services that average close to400 kph. Much of this development has occurred through sophisticatedcomputer simulation programs, scale-model tests in wind and watertunnels and analysis of wind-flow around full-sized models on tracks.Specialised wind tunnels that use moving ground planes to simulateconditions underneath vehicles have been used to show that most winddrag is caused by the wheels, bogies and other equipment under the train.Future generations of trains will have much smoother under-framecontours.


Discuss how current designs of racing bicycles and rider equipment allowfor less air resistance than historical cycles, such as the ordinary, and howcurrent designs of passenger vehicles are much more aerodynamic thancars that were built in the early 1900s.

Bicycles

__________________________________________________________

__________________________________________________________

__________________________________________________________

Cars

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

For bicycles did you mention tube shapes, shaped helmets, skin-tight clothing,rider position for bicycles? In car design did you mention smoother, curvedbody designs, closer to the road, air scoops and spoilers?

Destructive testsThese are mechanical tests that test specimens to destruction. Oftenstandard specimens are used so that the results of the tests can be directlycompared. This allows an easy comparison of the mechanical propertiesof materials.

Tensile tests

When considering the strength properties of materials in transportcomponents, it is important to look again at the tensile test.

List some of the mechanical properties that are indicated on a stress/straincurve derived from the load/extension graph created during a tensile test.

___________________________________________________________

___________________________________________________________

___________________________________________________________


Did you answer:

Str

ess

Strain0

Ultimate tensile stress

Yield stress

Elastic limit

Figure 3.1 Low carbon steel stress/strain graph

Some critical properties, from this type of graph, that are considered bythe engineer include elasticity, yield strength and ultimate tensilestrength.

Define each of the following terms:

elasticity

__________________________________________________________

__________________________________________________________

yield strength

__________________________________________________________

__________________________________________________________

ultimate tensile strength

__________________________________________________________

__________________________________________________________

Did you answer?

Elasticity – the ability of the material to return to its original condition

Yield strength – the point at which plastic deformation commences

UTS – the maximum stress that can be applied to a material.


Notched-bar impact tests

These tests attempt to measure the toughness and impact strength ofmaterials. They are often used to assess the affect of a variety of heattreatment procedures on a common material.

The tests use a notched standardised specimen. The notch establishes astress point where a failure may start.

A swinging pendulum is used to simulate an impact loading. Thependulum always starts from a known height with known potentialenergy. The height that the pendulum attains after impacting with thespecimen, when compared to its starting height, gives an indication of theenergy used to fracture the specimen.

There are two tests commonly used:

• Izod test

• Charpy test.

Scale

Start angle

End angleSpecimen

Hammer

Anvil

Figure 3.2 Impact testing machine

Izod test

A standard specimen, 10mm square in cross-section, is mountedvertically with the notch facing the approaching pendulum as shown infigure 3.3.


Striker

Swings on an arc

Standard notch (sameside as striker)

10 mm square specimen

SIDE VIEW

Figure 3.3 Izod notched-bar impact test

Charpy test

The standard square-sectioned specimen is mounted as a beam betweentwo supports 40 mm apart. The notch is on the opposite side to theapproaching pendulum as shown in figure 3.4.

Striker

Standard notch

Standard 10 mmsquare specimen

TOP VIEW

FRONT VIEW

Specimen Striker

Figure 3.4 Charpy notched-bar impact test


Fatigue tests

Most pieces of machines, including trains, cars and bikes, are subjectedto many different loads leading to fluctuating or changing stresses.Things may break when a stress is repeated enough times, even thoughthe maximum applied stress is a lot less than the known breaking strengthof the material. This is called fatigue failure.

A good example of fatigue can be seen in the performance of bicycleframes made from steel, aluminium and titanium. Steel and titaniumhave clear minimum fatigue limits and even if the frame bends it doesn'talter the life expectancy of the frame. On the other hand, the yieldstrength and UTS of aluminium are quite close together which meanseach small bending stress takes the frame closer to fatigue failure. Themost visible engineering response to this problem is seen in the largertubing often seen in aluminium bicycle frames. This stiffens the framepreventing flex and therefore fatigue.

The ability of a material to resist fatigue is tested in a number of differentways.

Testing of a specimen

A number of tests have been developed that allow a standard sizedspecimen to be assessed for fatigue. One test, the Wohler system, has thespecimen mounted in a revolving chuck, like a metalwork lathe. The freeend is loaded with a known load on a bearing. As the specimen revolves,the known load causes a fluctuating bending stress in the material. Whilethis test can't exactly copy service conditions, the results provide a pointof comparison between materials.

Chuck

Standard specimen

Load

Ball race

Figure 3.5 The Wohler cantilever fatigue test

Testing of components

Tests have been developed that allow the actual loading conditions to besimulated. An example of this would be the testing of the suspension


assemblies in cars. Machines are designed that clamp onto the wheelsand, under test conditions, provide loading similar to the car travellinghundreds of thousands of kilometres, in a much shorter time-frame.Fatigue failure will eventually occur and design decisions can be made asto whether component parts need to be redesigned.

List parts of a motor vehicle that are subjected to cyclic loads andtherefore would possibly fail due to fatigue.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

Did you suggest things like suspension springs, steering pins, wheels, axles,connecting rods and brake slide pins. Even door handles, window winders, seatsprings, windscreen wipers and hinges are all loaded in a way that could causefatigue failure.

Other tests

As part of the production of bicycles, cars and trains other tests would becarried out on various component parts. Some of these tests have beendescribed in detail in previous modules.

Hardness and wear resistance of components like bearings, wear plates,brake discs and train wheels would be tested by the Rockwell, Vickers orBrinell tests. Bending stresses of components like chassis rails andbicycle frame tubes could be assessed by a transverse beam test.Compression tests are used to test the compressive stresses of items likethe balls and rollers used in bearings

Special proving tests have been designed for assessing the effects ofimpacts involving bicycles, cars and trains. Bicycle helmets were madecompulsory in New South Wales after extensive testing and developmentthat proved the value of helmets to riders involved in collisions.

Part of the development of each new car is collision testing. Cars arecrash tested, at various speeds, and the data recorded is used to improvethe safety of vehicles. Seat belts, air bags and side intrusion bars have allbeen introduced and refined through the use of crash testing.


High-speed trains have been carefully designed with end crumple zones.Much of this design work was done using computer simulation but fullsize crash tests are also used to validate the computer-generated data.



Ferrous metals

The following section details the most significant, versatile andinfluential metals used by engineers.

Define the term ferrous metal.

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

The element iron is the predominant material in ferrous metals.

Plain carbon irons and steels

In a number of preliminary modules, you examined the structure,properties and applications of plain carbon ferrous metals. The followingtable below reviews this work and suggests some applications specific tobicycles, motor vehicles and trains.


Applications of plain carbon irons and steels

Composition %C Microstructure Properties Applications

Dead Mild

0.05-0.1 Pearlite

soft, ductile, can beseverely cold worked,malleable.

chains, automobilebody panels

Mild

0.1-0.3Pearlite

doesn't hardenappreciably whenquenched, weldable,can be cold worked

brackets, bolts, nuts,screws, car wheels,

Medium Carbon

0.3-0.6

Pearlitecan be hot or coldformed, suitable forforging and heattreatment

crankshafts, brakecables, railway track,axles

High Carbon

0.6-0.9

Pearlitesuitable when highstrength and hardnessare needed.

heat treatable

suspension springs,wire cables, wearplates

Carbon Tool

0.9-1.5

Pearlite excellent wearresistance in plain orhardened condition

balls and rollers forbearings

White Cast Iron Fe3C

Pearlite

very hard and brittle,white colour onfractured surface

intermediate step inproduction ofmalleable iron

Grey Cast Iron

Graphiteflakes

Pearlite

grey on fracture, weakin tension, strong incompression, brittle,castable

engine blocks

Malleable CastIron

Pearlite

Graphite

excellent castingproperties, improvedstrength and ductility

auto disc brake rotors,brake drums


By referring to the previous modules and other sources, you may be ableto add other relevant applications to the table.

Figure 3.6 provides a good graphical representation of thestructure/property relationships in plain carbon steels.

Pearlite

0 0.2 0.4 0.6 0.8 1.0 1.2

Ferrite

UTS

HB

%Elongation

Cementite

% P

earli

te

100

50

Carbon (%)

Figure 3.6 Structure/property relationships in steels

© Schlenker, B. 1974, Introduction to materials, p 214, John Wiley and SonsAustralia.

Alloy steels

Engineers are continually designing steels with the most appropriateproperties for any service situation.

One method to achieve this control over properties is to alloy the steelwith additional materials.

Stainless Steel

When more than 12% of chromium is present, the alloy steel is protecteddue to the film of chromium oxide that forms on the surface and hasincreased strength and hardness.

Stainless steels are used extensively for body panels in trains, internalfittings and structures in carriages, bicycle gear cables, derailleur cages,woven protective sheathing on flexible brake lines and motor vehicletrim.


If 12–25 % chromium is added to low carbon steel, the alloy can't behardened, except by cold working. It is suitable for cold workingapplications such as woven protective sheathing on flexible brake lines.

When 12-18% chromium is added to medium carbon steel, the alloy canbe quench hardened. The disc rotors used on disc brakes on top-of-therange bicycles and rust-free springs are made from this material.

Alloys containing 18% chromium and 8 % nickel are commonlyavailable and are suitable for constructional work.

Chrome-molybdenum alloys

These alloys typically contain around 0.3% carbon and small quantitiesof around 1.1% chromium and 0.25% molybdenum. The combination ofthese elements produces an alloy that posseses good deep hardeningproperties, ductility and weldability.

Cro-moly alloys are used widely for high-quality steel bicycle frames asthey create a frame that is inexpensive, strong, stiff, easy to repair andhas a resilient and lively feel.


Heat treatment of ferrous metals

Heat treatment is the controlled heating and cooling of a material toobtain required properties. Details on the recrystallisation of metals canbe found under Forming Processes section later in this module.

Steel is basically an interstitial solid solution. This means that the carbonfits into spaces within the lattice structure of the iron. Heat treatment ofsteel can cause dramatic effects on the properties of the metal. This isonly possible because of the change in allotropy that occurs in iron ataround 910∞C.

At room temperature, iron exists in a body-centred cubic structure whileabove 910∞C it exists as a face-centred cubic structure. The face-centred

cubic iron can dissolve up to 2% carbon within its lattice structure (at1100∞C) while at room temperature body-centred cubic iron can only

dissolve 0.008% carbon.

When iron-carbon alloys are cooled, causing them to change from FCCto BCC, sufficient time must be allowed for the majority of the dissolvedcarbon to move out of the spaces or interstices and form the interstitial


solid solution ferrite and the compound cementite. Ferrite is iron with0.008% carbon and is a soft, ductile material. Cementite is iron with6.67% carbon and is quite hard and brittle. Variations in cooling ratesprevent this movement of the carbon and provide dramatic differences inproperties.

The different grades of steel can be heat treated in a number of wayswhich result in a very wide range of properties.

Annealing

Annealing of all ferrous alloys can be done using one of two basicprocesses.

a Full annealing

Full annealing involves the heating of the alloy to over 900∞C, then

soaking it until the iron changes back from a BCC structure to a FCCstructure. Slow cooling, to a low temperature, then takes place eitherin a furnace or in good heat insulating material.

The purpose of full annealing is to allow the grain structure to returnto equilibrium condition. This will achieve large unstressed grains,induce softness and improve magnetic and electrical properties.

b Process annealing

This is suitable for softening cold-worked low carbon steels andrecognises that these alloys are made mainly from ferrite. As ferriterecrystallises at around 500∞C, annealing between 500–600∞ will

produce total recrystallisation of the ferrite while leaving the smallamount of pearlite in its stressed state.

Process annealing is much faster than full annealing and is theindustrial process normally selected for softening this grade of steel.

Normalising

Normalising is similar to full annealing except the steel is heated to aslightly higher temperature and then is cooled in still air. This slightlyfaster cooling rate produces a finer equiaxed, equilibrium structure thandoes full annealing. These smaller grains provide increased yieldstrength, UTS, notched-bar toughness values and greater hardness whilegiving a slight reduction in ductility.

Castings and forgings are often normalised to relieve some of the stressesinduced due to uneven cooling rates. There are many castings andforgings in transport devices that would be heat treated in this way.


Hardening

As described in previous modules, the hardening of steel depends on thedifferent solubilities of carbon in FCC and BCC iron. Figure 3.6 showsthe relative difference in hardness between steels that have been annealedand those that have been quenched.

Hardness as quenched

Hardness as annealed

% Carbon

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

100

200

300

400

500

600

700

800

Brin

ell h

ardn

ess

% in

crea

se in

har

dnes

s

Figure 3.7 Hardness of annealed and quenched steel

© Schlenker, B. 1974, Introduction to materials, p230, John Wiley and Sons,Australia.

Explain why increasing carbon content results in increasing strength inannealed steels with reference to the structure and the properties ofphases present in steels.

__________________________________________________________

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Did you answer?

To quench harden an alloy it must be heated and soaked till all the carbon isagain dissolved into the FCC lattice. The item is then quenched in salt water oroil. As there is insufficient time for the dissolved carbon to be relocated as theiron tries to change back to BCC, the carbon trapped in the lattice of the irondistorts the structure and produces a highly stressed state. This stressedstructure is known as martensite.

As indicated in figure 3.7, quench hardening a 0.6% carbon steelincreases the hardness 3 to 4 times that of annealed steel.


Tempering

While martensite is a very hard structure, it is also extremely brittle. Mosthardened steel components require tempering before they can be used.

When martensite is heated, some of the trapped carbon diffuses out of thestructure in the form of iron carbide particles. This movement relievessome of the stress and reduces the brittleness and hardness of thestructure.

Tempering temperatures and times are important as the higher thetemperature and the longer the time the greater the reduction in hardness.When tempering martensite the aim is generally to retain hardness whileincreasing toughness. When hardness is important, as in the case of abicycle chainwheel, a tempering temperature of around 240∞C would be

used. When more elasticity and toughness are required, as in the case ofa vehicle suspension spring, a temperature around 300∞C is more

appropriate.

Surface hardening of steels

Often there is a need to create a component with a hard skin but a toughcentre. This will provide wear resistance while allowing for shockloadings. Carburising, nitriding or selective hardening can all be usedto achieve surface hardening.

a Carburising

Pins and linkages used in the suspension and steering assemblies ofmotor vehicles must be both tough and resistant to wear. Thesecomponents are machined from very low carbon steel and thenheated to around 950∞C in a special carbon-rich atmosphere for

between 3–6 hours. Carbon enters the surface layer of the steelchanging this 'skin' to medium-high carbon steel.

When the item is quench hardened, martensite forms in the skinwhile the low carbon steel is unaffected and remains soft and tough.

b Nitriding

Automotive crankshafts, camshafts and some high strength ball racesrequire a very high core-strength combined with high surfacehardness. They are often made from low carbon steels containingsmall proportions of aluminium, chromium and molybdenum.

Once all machining is completed, these components are heated to500∞C in a nitrogen-rich atmosphere for 40–100 hours. Very hard

nitrides of the trace metals form in the 'skin' and as the componentdoesn't need to be quenched the finished part is free from distortionand has a good surface finish.


c Selective hardening

When higher core strength is needed it may be more appropriate touse a medium or high carbon steel than a low carbon steel. Splineson axles and drive shafts and the teeth of gears may have their 'skins'hardened by rapidly heating the surface of the part to over 900∞C,

then quenching. Martensite would form on the surface and the corewould be unaffected. A gas powered flame or electrical inductioncoil is used as the heating source. Water jets that quench the surfacefollow the heat source.

Investigate the effects of heat treatment on various ferrous alloys.

You will need:

• bicycle brakes

• a paper clip

• a car suspension spring (still attached to the car is O.K.)

• a file

• an old hacksaw blade

• old lawn mower blades that have been replaced on your mower

Carry out the following:

1 Squeeze the brake handle, observe how the stress induced in themetal by the cold working gives the spring elasticity.The springs on the bicycle that stop the brake blocks from rubbingon your rims are cold drawn from low carbon steel.

2 Bend the paper clip, note how easy it is to bend out of shape. This isbecause it hasn’t been as severely deformed.

3 Look up under the front of a car near one of the front wheels. Thereis a big coil spring providing suspension for the car. Stand up andcarefully push down, on a strong point of the car body, to squash thespring, see how the car bounces back up. (If it keeps bouncing upand down you should think about getting the shock absorbersreplaced!). This spring is made from medium carbon steel that hasbeen hot coiled then hardened and tempered. Its internal structure isalso stressed to provide elasticity. This stress is achieved throughheat treatment not through the forming process.

4 Take a file and try to file a groove into the hacksaw blade. First tryfiling on the teeth edge then try filing on the smooth back edge, notewhich is easier. The blade has been only hardened on the teeth edgeand not on the back. This should explain why it was easier to file onthe non-hardened smooth back edge.


5 Take the file again and try to file the lawn mower blades, see if theythe same hardness all over.They should be as they have been hardened and tempered!

1 Suggest reasons why the teeth edge has been hardened and the backedge has not.

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2 Outline why is it necessary to both harden and temper lawn mowerblades.

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3 List other parts that need to have a hard, wear resistant surface andare possibly heat-treated. Think specially of components onbicycles, cars and trains.

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Did you answer?

1 If you mentioned that the teeth need to be really hard because they arecutting metal then you are on the right track. Did you also realise thathardness and brittleness go together so that a fully hardened blade wouldprobably break too easily? Not hardening and tempering the back of theblade makes the whole blade tougher. It really becomes a type of compositestructure.

2 The blades need to be hard to resist bending and deformation in use and toextend the life. They also need to tough and not brittle. Tempering willreduce brittleness so they won’t shatter if hit by a small stone or twig andwill increase toughness so they are more durable and longer lasting.

3 You could mention many, many different components including:

• the gear teeth on a bicycle

• the chain links on a bicycle gear chain


• brake dics on a car

• engine cylinders and pistons in cars

• wheel bearings

• contacting components in the gear box

• wheels on trains

• brake components on trains.


Forming processes

Forming processes are the techniques used to shape the material.

The following information describes several techniques and highlightsthe advantages and disadvantages of each forming method.

Casting

Casting of liquid metal into a mould cavity is a convenient method ofmanufacturing components.

Casting processes have a number of common features:

• a mould cavity is made either from a reusable pattern or as apermanent metal mould

• there must be a method for removing the solidified casting from themould

• the metal to be cast is melted and delivered to the cavity by gravityor by pressure.


Casting Method Advantages Disadvantages Applications

Sand casting

(Sand mould)

intricate shapescan be produced,slow cooling rate,simple equipmentso economical

labour intensive,separate mouldrequired for eachpour, correct mouldpacking is essential

engine block,rolling stockbogies

shell casting

(Sand mould)

good qualitysurface finish,dimensionalaccuracy, relativelyfree of defects, lesslabour intensivethan sand casting

high initial cost of themetal patternstherefore onlysuitable for long runs

someautomotivecrankshafts,exhaustmanifolds,

Die casting

(Metal mould)

improveddimensionalaccuracy, excellentsurface finish, highoutput rates,uniform internalstructure

confined mainly tozinc and aluminiumalloys, metal 'dies'are costly so onlysuitable for largeruns

bicyclecomponents,carburettors,handles, gearboxes

Investment casting

(Plaster/sand mould)

ability to accuratelyproduce intricateshapes notpossible withforging ormachining

limited to theproduction of smallcomponents, heavylabour intensityincreases costs

levers, cams,turbine blades,any smallaccuratecomponent

Sand casting

A pattern of the item to be cast is made in timber or metal. Speciallyprepared sand, mixed with clay or other binders, is packed in a boxaround the pattern. The box is divided into a number of parts, usuallytwo, so that the pattern can be removed. When the mould parts arereassembled, a cavity of the shape of the required item remains.

Molten metal is poured into the mould through a 'runner' and air isallowed out through a 'riser'. Once solid, the casting is liberated from themould by breaking the sand mould apart. The sand can be reused.


Drag

Pattern

Drag rammed with sand

Cope

Drag turned over and copeplaced on top with riser andsprue pins

Pattern placed on bottomof drag

Riser Sprue

Cope rammed with sand

Patterns and pins areremoved and runnerand gates are formed

Runner Gate

Moulten metal poured in

Figure 3.8 Sand casting

Shell casting

This process is similar to sand casting except the sand is bound togetherby an artificial polymer bonding material. Each half of the shell is madeon a metal pattern plate that is heated and then covered with theresin/sand mix. A skin of sand forms on the surface due to the melting ofthe resin binders. Excess sand mixture is tipped off, the half-mould skinis cured in an oven and then stripped off the pattern plate. The twomould halves are joined together with glue or fasteners. This completedmould is placed in a box and supported with either extra sand or smallmetal balls. The molten metal is poured in and the solidified casting isreleased by breaking the shell away from the outside.


Pattern and dump box invertedSand with resin is put inthe dump box

Hotpattern

Sand withresin

Dumpbox

Pattern and dump boxrotated again

Shell removed using ejector pins

Shell Ejector pins

Flask

Shells

Molten metal

Clamp

Metal shot

The shells are clampedtogether and moltenmetal is poured in

Figure 3.9 Shell casting

Die casting

This process involves the molten metal being forced into a permanent metalmould. The mould is designed in such a way that the casting can be easilyremoved once the mould is opened. Mould production is expensive thereforethis process is only suitable when a large number of castings are required.Mass production labour costs are much less than for other casting processes.


Moltenmetal

Movingplatten

Fixedplatten

Injectionpiston

Finished casting

Castingcavity

Die Ejectorpins

Fixedblock

Casting solidified withmould ready to open

Figure 3.10 Cold chamber die casting

Investment casting

This is thought to be an ancient process that started with prehistoric man whoshaped items from beeswax. This was then coated with clay and the whole lotwas then thrown in the fire. In the fire, the clay hardened and the wax wasmelted out leaving a cavity into which molten metal could be poured.

Wax patternsmounted ontoa wax runner

Bottom plate

Flask is filledwith investmentmould slurry

After mould material hasset and dried the patternsare melted out of mould

Molten metal poured intomould by vacuum, gravityor centrifugal force

Mould materialis broken awayfrom castings

Casting is trimmedand polished

Figure 3.11 Investment casting

Today, permanent moulds are used for casting the intricate wax patterns.These wax patterns are attached to a central runner and the whole 'trunkand branches' is placed in a cylindrical metal 'flask'. This flask is filledwith a mixture of very fine sand and plaster of Paris. Once the plasterhas dried, the mould is inverted and passed through an oven so the waxmelts out leaving a series of mould cavities. Molten metal can then be


either poured into the mould or, if wall thicknesses are thin, forced inunder pressure.

Hot and cold working

Many forming methods involve the plastic deformation of metal so that apermanent change in shape occurs. If the metal is heated above itsrecrystallisation temperature, it is hot worked and the distorted grainsare able to regrow as equiaxed grains. If this deformation occurs belowthe metal's recrystallisation temperature the internal structure remainsdistorted and it is called cold working.

Hot working

A metal is hot worked when it is heated to a temperature that is above itsrecrystallisation temperature.

When a metal is hot worked, it is more malleable at the highertemperature so it is easier to deform. As recrystallisation takes place atthe same time as forming, the final product has regular, small equiaxedgrains replacing the course as-cast grains in the original metal ingot.This new structure is stronger, tougher and more ductile than the as-caststructure.

Some common hot working processes used in bicycles, cars and trainsinclude:

• rolling – of plate, sheet and profile sections

• forging – of shapes with superior properties to those of castings

• extrusion – of both solid and hollow sections

• piercing – of solid metal to form tubes.

The disadvantages of hot working include poor surface finish due to theoxides and scaling and poor dimensional accuracy due to the necessityfor simple tools. Other procedures such as acid-pickling and machiningare normally carried out on hot worked components.

Cold working

Cold working takes place at a temperature below the recrystallisationtemperature.

Cold working has some distinct advantages if good surface finish andincreased strength and hardness are required. The following table lists


some of the advantages and disadvantages of cold working whencompared to hot working.

Advantages of cold working Disadvantages of cold working

no need for heatingi

improved dimensional control

better surface finish

increased strength properties

directional properties are produced

reduced metal loss and tool wearbecause of scaling

only method of hardening mild steeland most non-ferrous metals

more rigid and powerful equipmentneeded

larger forces needed

work hardening occurs

undesirable directional properties maybe produced

metal must be free of oxides andscales before working

Some common cold working procedures used in bicycles, cars and trainsinclude:

• drawing of rod, wire and tube

• rolling of plate, sheet and strip and threads

• cold-heading or upsetting

• extrusion of a variety of profiles.

Recrystallisation

After a metal has been cold worked, its crystal lattice structure is greatlydistorted and the material is in a stressed state. If the metal is heatedabove its recrystallisation temperature, nucleii form at the areas ofgreatest stress, the grain boundaries. From each nucleus, a newdistortion-free lattice structure develops and in time new small equiaxedgrains form out of and replace the distorted grains. Each metal has aunique recrystallisation temperature. Aluminium recrystallises at 150∞C,

iron at 450∞C and molybdenum at 900∞C, just to name a few.

If the recrystallisation temperature is maintained for a longer time, thesmall eqiaxed grains will be replaced by larger equiaxed grains. This isknown as grain growth and is generally avoided as it causes a reductionin the strength properties of the metal.


Recrystallised metal is not as strong or hard as the original cold workedstructure but recrystallising improves electrical conductivity andductility. A recrystallising process, such as annealing, may be carried outat an intermediate stage or at the conclusion of a cold working procedure.Alternately, hot working may be used which produces a final structure offine equiaxed grains similar to an item that has been cold worked andthen annealed.

Define both hot and cold working.

1 Hot working

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2 Cold working

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Did you answer?

Did you mention plastic deformation of the material and talk about whether theworking was done above or below the recrystallisation temperature? They'rethe principles that should be mentioned!

Drawing

Generally done cold, drawing is used in the production of wire, rod andtubing. Wire is done in large spools while rod and tube is cut to lengthand then drawn. The internal diameter of tube is controlled through theuse of a mandrel.

The original equiaxed structure is pulled through very hard steel dies thatreduce in diameter and consequently reduce the cross-section andincrease stresses in the drawn material.

Only ductile materials, such as low carbon steel, are suitable for drawing.Wire used in brake and gear cables is drawn as is the wire from whichbolts and screws are formed. Metal tubes used in bicycle frames are colddrawn to increase the strength properties of the tubes while allowingthem to be as light as possible.


Drawing direction

Die

Hardened insert

Figure 3.12 Wire drawing

Drawingdirection

Fixedmandrel

Floatingmandrel

Drawingdirection

Figure 3.13 Tube drawing

Rolling

In rolling, the cross-sectional shape is altered by passing the metalthrough a series of rollers of a certain shape and set distance apart. Pairsof rollers rotate in opposite directions and drive the metal between.

Recrystallised fine-grained structure

Recrystallisationtaking place

Rolling direction

Figure 3.14 Hot rolling


Cold worked structure

Original cast structure

Rolling direction

Figure 3.15 Cold rolling

Some hot rolled sections like round, square and rectangular may be thestock from which other components are manufactured while railwaytrack is an example of a finished hot rolled section.

Cold rolling is commonly used to increase the strength and resilience ofsheet materials for items such as body panels on train rolling stock andcars.

Forging

Forging occurs when localised compressive forces deform metal. Theadvantage of forging, both hot and cold, is that the forming processcauses the grain of the metal to 'flow' and follow the shape of thecomponent. This makes the component stronger than similar cast andmachined components.

Figure 3.16 Grainflow or 'fibre' in a forged component

Hot forging or drop forging is similar to the methods used by the oldblacksmith except large hydraulic 'hammers' are used. Special two-partdies, normally with several impressions, are used to allow forming in


stages. As dimensional accuracy is not very high, some form ofmachining is always needed.

Components such as axles and bottom brackets on bicycles, connectingrods and drive yokes in cars and couplings in trains are all drop forged.

Cold forging also uses large machinery but doesn't always requirefollow-up machining as the surface finish is relatively good. Ends arefitted to the flexible cables used in bicycle brakes by the process ofswaging which is a type of cold forging.

Upsetting or heading is a very common type of forging done both hot andcold. It involves the gripping of rod in a 'vice' so that excess material, atone end, is squashed by a closed die. Automotive engine valves andaxles are hot upset and then machined while bolt and screw heads areupset cold.

ForceForce Grainflow or fibre in

the upset bolt headPunch

Figure 3.17 Upsetting

Extrusion

Any component with a continuous, parallel profile can be extruded.Some metals can be extruded cold but the addition of heat willconsiderably increase the plasticity of the metal.

The direct extrusion process involves an amount of metal being placed ina chamber. A ram then pushes the metal through a simple profile die atthe end of the chamber. Most low strength, non-ferrous metals are easilyextruded while special lubricants and high strength dies are necessary forthe extrusion of steel. The extrusion of hollow profiles requires the useof mandrels or bridge dies to allow the hollows to be formed.


Billet pushedthrough die

DieRam

Extruded solid shape

DieRam

PlugMandrel

Extruded pipe

Figure 3.18 Direct extrusion of solid and tube

Piercing

Tube can be made from rod by the Mannesmann process. It is a hotworking process where the rod is rotated between two rollers whichrotate in the same direction. This action produces an elliptical section inthe rod drawing metal away from the centre. A rotating mandrel piercesinto the centre forming the bore of the tube. The tubes produced will besized and straightened on other rollers and can undergo further hot andcold forming processes.

Rotating skew rolls

Seamless pipe

Billet

Rotating mandrel

Figure 3.19 The Mannesmann process


Seamless tubes used in bicycle frames start their life via this process andare then drawn cold to give dimensional accuracy and increased strengthproperties. Tubes used in light weight frames are butted at the ends.This involves controlled upsetting of the tube to thicken and thereforestrengthen it at the ends as the joints are the regions of greatest stress.

After looking at these forming processes it is possible to consider variouscomponent parts of a bicycle.

Complete the following table by suggesting a likely material andforming process for each of the parts.

For this activity, it would be good if you had a bicycle to closelyinspect. If this isn't possible, one of the pictures found earlier in thismodule will do!

Component Material Forming process

Wheel hub Aluminium alloy Cold forged then CNC machined andspoke holes drilled

Spokes Stainless steel Cold drawn, thread rolled and endupset and bent

Rims Aluminium alloy Hot extruded profile then cold rolledand the joint tungsten inert gas welded

Chainwheel Aluminium alloy(anodised)

Cold forged then anodised to increasewear resistance

Frame tubes Steel alloy oraluminium alloy

Pierced, cold drawn then butted

Brake cable(inner)

Stainless steel Cold drawn then twisted into a flexiblecable

Brake cable(outer)

Medium carbonsteel

Cold drawn then spiral wound

Brake calipers Aluminium alloy Die cast

Brake disc Stainless steel Cold stamped then machined

Pedal crank Aluminium alloy Hot forged then machined

Seat frame Mild steel oraluminium alloy

Cold drawn then bent to shape

Bottombracket axle

Medium carbonsteel

Drop forged and machined


Seat post

Brake levers

Gear frame

Bolts andscrews

Handle bars

Did you answer?

Seat post Steel alloy oraluminium alloy

Pierced and cold drawn

Brake levers Aluminiumalloy

Die cast

Gear frame Steel alloy oraluminium alloy

pierced, cold drawn than bent to shapeand butted

Bolts andscrews

Mild steel Wire is drawn to make bolts and screwsthen heads are upset cold

Handle bars Steel alloy oraluminium alloy

Pierced, cold drawn then bent to shape

Note that those components may be made of different materials and by differentforming processes depending on the style and quality of the bicycle. Forexample, the brake levers may be made of cast or moulded polymer.

Turn to the exercises section and complete exercise 3.4.

Powder forming

Powder forming, also known as powder metallurgy, has three clear stepsin the manufacture of components.

1 Powder manufacture

Brittle powders can be mechanically disintegrated while ductilemetals are atomised by blasting a stream of molten metal with a jetof air. Chemical and electrolytic methods can also be used. Once


produced, these powders are blended in the correct proportions readyfor the next stage.

2 Pressing

Hardened steel or carbide dies are filled with the powder that is thenpressed. Pressing contols the porosity of the powder, mechanically'keys' some of the particles together and can cold weld some of theparticles together. The pressed component is rigid but has littlestrength.

3 Sintering

After pressing, the component is heated in a furnace to a temperaturebelow the metal's melting point. With powder mixtures, thetemperature may be set so that the lowest melting point metal meltsand flows through the structure 'cementing' the component together.In cemented carbides the ceramic particles are cemented with cobaltor nickel.

Powder forming is suitable for producing a number of different types ofcomponents including:

• solid bronze bearings, with voids to trap lubricants, and solid metalfilters are common uses of this technology. These bearings are usedto support many spindles found in cars such as in the alternator,starter motor and windscreen wiper motor.

• complex shapes such as gears, cogs and levers that would otherwiserequire a lot of careful machining. The gears in the gear box of a carare manufactured by this process.

• very hard materials that would be too difficult to machine

• composites between materials that don't normally mix. The brushesused in electrical devices such as the starter motor in a car are oftenmade from a blend of copper and graphite.


Non-ferrous metals

Non-ferrous metals are routinely used by design engineers. The choiceof what metal to use is necessarily based on the properties of the metal,and the cost of the metal.

The table below briefly lists some common non-ferrous metals and alloysthat are used in bicycles. The table also includes each material'sproperties and suggests some specific applications.

Metal Properties Uses

Aluminium corrosion resistant, soft,can be cold worked

swaged ends on cables

Aluminium 6061-T6

Al - 98% with Fe, Si,Mg, Ti, Cu, Mn, Cr, Zn

combines relatively highstrength, workability, andcorrosion resistance

used extensively for tubein bicycle frames, bicyclewheel hubs and rims

Aluminium 7075-T6

Al - 90%, Zn - 6%, Mg,Cu, Cr, Ti, Si, Zr, Fe

a very stiff and highstrength alloy used forstructural parts, resistsstress-corrosion cracks

forged bicycle driveparts such as cranksand chain wheels.Anodised for hardness

Titanium light and strong, resilientand shock absorbing,non-corrosive

used for tube in highquality bicycle frames,

light weight fittings ontop quality bicycles

Scandium twice as strong assimilar size aluminiumand around the sameweight

used for tube in veryhigh quality bicycleframes

Brass

70% Cu /30% Zn

corrosion resistant, soft,can be cold worked

spoke eyelets inaluminium alloy rims,

swaged ends on cables

Chromium hard element with awear resistant, clearoxide

plating for bothincreasing wearresistance andaesthetics


Some properties of non-ferrous metals and alloys are:

• good formability

• low density

• corrosion resistance

• high thermal and electrical conductivity

• stiffness and strength usually lower than ferrous metals

• poor weldability.

Non ferrous metals are also used in cars and trains. To reduce mass inhigh-speed trains, aluminium alloys are used for carriage bodies, bogiesand even seat frames. Using aluminium sheets, instead of copper wires,in transformers has reduced the overall mass of these by 33%.

Have a good look all over a motor vehicle, and list the parts that appear tobe made from or coated with a non-ferrous metal. You can normally tellfrom the colour. Many non-ferrous metals are silvery or many differentshades of yellow in colour.

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Did you answer?

Did you find things like the rear-view mirror frame, door handles, rocker cover,head, master cylinder, carburettor, fuel injectors, alternator body, water pump,gearbox housing and sump?

Aluminium and some of its alloys

Pure aluminium

Aluminium's high affinity for oxygen proved to be a disadvantage whentrying to extract the metal from it's ore, bauxite. Aluminium has a higheraffinity for oxygen than has carbon so aluminium can't be burnt out ofbauxite and can only be separated from oxygen economically byelectrolytic means.


In 1825, an expensive reducing agent was used to produce the firstsamples of aluminium. In the Court of Napoleon III only the mostfavoured guests were privileged to use forks and spoons made fromaluminium while the others had to 'make do' with mere gold plate andsilver cutlery.

Aluminium's great affinity for oxygen is advantageous in that a dense,impervious film of oxide forms on the surface and protects the metalfrom further oxidation. This natural corrosion resistance can be furtherimproved by anodising, a treatment that artificially thickens the naturaloxide film, and the slight porosity of the oxide allows it to be colouredwith organic or inorganic dyes. Since aluminium oxide is extremelyhard, this oxide layer also increases wear resistance.

As aluminium has over 50% of the specific conductivity of copper,weight for weight it is a better conductor of electricity than copper and iswidely used, normally twisted around a steel core, as a current carrier inthe electric grid system.

Pure aluminium is relatively soft and weak in its annealed condition andis generally used in the alloyed condition for most engineeringapplications.

Aluminium alloys

The addition of alloying elements is made to improve mechanicalproperties such as tensile strength, hardness, rigidity and machinabilityand sometimes to improve casting properties. Aluminium alloys may beused in both the cast and wrought conditions and some may have theirproperties further modified through precipitation hardening.

Some elements added to aluminium and their effects include:

• copper, which is used in a majority of alloys that are destined forprecipitation hardening

• magnesium, which allows precipitation hardening to occur whileretaining high electrical conductivity and good corrosion resistance

• silicon, which allows precipitation hardening to occur whileretaining high electrical conductivity and good corrosion resistance

• iron, which assists in precipitation hardening

• titanium and manganese, which refine the grain structure

• zinc and chromium, which help to produce excellent tensile strength.


Aluminium – silicon alloys

Various alloys within this system are used in the cast and wroughtcondition. Those alloys containing aluminium and between 9% and 13%silicon are near to the eutectic composition. They therefore have a lowmelting point and are suitable as die-casting alloys. These alloys haveexcellent foundry characteristics and resistance to corrosion.

Common casting uses include general-purpose sand castings and pressureor gravity die-castings in the form of intricate fittings, engine sumps andgearboxes.

Wrought alloys have good forgability and a low coefficient of thermalexpansion. Uses include forged automotive pistons, sheet panelling andwelding wire.

Aluminium – copper alloys

Alloys that contain between 2.5% and 5% copper will respond totreatment by precipitation hardening. This phenomenon was firstobserved in 1906 and the alloy was first produced commercially asduralumin around 1910. The first significant use of duralumin wasduring WWI as structural members of Zeppelin airships.

Consider an alloy containing 4% copper. Above 500∞C the

microstructure will be all single-phase alpha solid solution. Underequilibrium cooling, a precipitate of CuAl2 will occur. A few largeparticles of hard and brittle CuAl2 intermetalic compound will appear inthe alpha grains. The resulting structure will lack strength and will bebrittle.

If the alloy is reheated to 500∞C, the alloy once again contains all single-

phase alpha. On quenching the alloy, the copper is retained in solutionand in this condition the alloy is stronger, harder and more ductile thanthe equilibrium structure. If the alloy is allowed to remain at roomtemperature, it will be found that the strength and hardness graduallyincrease - to a maximum after six days. This change is due tosubmicroscopic particles of CuAl2 moving out of solid solution andcausing slight distortion of the alpha lattice structure.

This process of natural ageing is often replaced by artificial ageing. Thealloy is reheated to 120∞C causing precipitation of the fine copper-rich

phase to occur within a few hours. Care must be taken not to allow over-ageing to occur which will allow the alloy to return to near equilibriumconditions of alpha with visible CuAl2 precipitate. This will reduce themechanical properties of the alloy.


These alloys are used in both the cast and wrought condition for generalpurposes, goose necks and seat posts on bicycles and framing andcladding in the aircraft industry.

Aluminium – Silicon-magnesium alloys

Magnesium and silicon combine to form magnesium silicide (Mg2Si)which in turn forms a simple eutectic system with aluminium.Precipitation of Mg2Si after artificial aging, allows these alloys to reachtheir full strength.

Wrought alloys in this system are characterised by excellent corrosionresistance and more workability than other heat-treatable alloys.Applications include canoes, furniture, vacuum cleaner tubing, bridgerailings and architectural applications.

Casting alloys exhibit good castability, strength, pressure-tightness andcorrosion resistance. In the heat-treated condition their mechanicalproperties are similar to those of the aluminium-copper alloys. Usesinclude aircraft applications, machine-tool parts and general-purposecastings.

Aluminium – zinc alloys

Commercial wrought and forging alloys, such as the 7000 series, containaround 6% zinc and smaller amounts of magnesium, copper, manganeseand chromium. Subsequent heat treatment produces a high strength alloywith high corrosion resistance that is used for aircraft structural parts,bicycle cranks and chain-wheels and other applications that require ahigh strength to weight ratio.

The alloys may also be cast and have very good machinability. Theymay be used for aircraft fittings, turret housings and radio equipment.

Brasses

These are alloys of copper and up to 45% zinc plus other elements suchas tin, lead, manganese, aluminium and iron.

Alloys containing up to 37% zinc have a single-phase structure existingentirely of a. This a phase is typically tough and ductile making these

brasses suitable for severe cold working by pressing, drawing andextrusion. This is also true of other a phases such as ferrite in the iron-

carbon system.


Under equilibrium cooling a brasses form large equiaxed grains creating

a soft and malleable structure. If they are cooled at a slightly faster rate,a cored structure is produced with the centre of each grain richer in thehigher melting point copper and the outer portion richer in zinc. Theseskeleton-like cores will reduce the malleability of the material.

The microstructures in figure 3.20 show brass containing 70% copper &30 % zinc, commonly known as cartridge brass, cooled underequilibrium and faster that equilibrium conditions.

cored

Equilibrium Cooling Cored Structure

Figure 3.20 Cartridge brass microstructures

In alloys with more than 37% zinc, a hard and brittle b phase is also

present. In fact a brass containing 60% zinc contains all b until it cools

to around 750∞C when the a starts to precipitate out within the grains of

b. Brass containing 60% copper and 40% zinc is commonly known as

Muntz metal and its structure is shown in figure 3.21.

b

precipitatea

Figure 3.21 Muntz metal under equilibrium cooling

The following table briefly lists some common brasses, includes eachmaterial's properties and suggests some specific applications.


Metal Properties Applications

Cartridge Brass

70/30 copper/zinc

corrosion resistant, soft,can be severely coldworked

cold rolled sheet, wire,tube, electrical contactsin motor vehicles.

Muntz Metal

60/40 copper/zinc

corrosion resistant, highstrength, excellent hotworking properties.

extruded as tubes androds, hot rolled plate,screwed electricalterminals in cars

High Tensile Brass

58% Cu, 28% Zn withsmall amounts of Mn,Al F Pb & S

high strength combinedwith excellent wearresistance

pressings, forgings andstampings, switchgear,clutch discs in motorvehicles

Brazing Alloys

50/50 Cu/Zn

hard and brittle,essentially b brasses

used as a filler rod whenapplying low temperativejoining methods

Bronzes

Bronzes are any copper alloy, except for the copper zinc series.

Tin bronzes

Bronzes containing copper and around 10% tin were probably the firstalloys to be used by man. In Britain, bronze articles almost fourthousand years old have been found. One of the significant factors in theEarly Roman conquests was probably the bronze sword. They realisedthat 10% tin gave a hard bronze while less tin produced a softer alloy.

Alloys up to 7% tin are all a phase which is a tough and ductile solid

solution that can be successfully cold worked. The hard and brittled phase is normally present in all alloys containing more than 7% tin and

alloys above this composition are hot worked or cast.

Wrought alloys contain up to 7% tin and are supplied as rolled sheet anddrawn rod. Coinage bronze containing copper with 4% tin and 1% zinc,is soft and ductile and, as implied by the name, is used for "copper"coins.

Casting alloys contain up to 18% tin and are used for bearings with thehard d phase resisting wear and the a phase matrix providing toughness


and shock resistance. These alloys typically have high strength,toughness, a low coefficient of friction and resist corrosion. Uses includelock washers, cotter pins, bushes, clutch discs and springs.

The inclusion of up to 1% of phosphorous will further improve strengthproperties and lead will improve machinability and wear resistance.Leaded alloys are used for automotive crankshaft bearings.

Aluminium bronzes

These bronzes are single-phase cold worked structures up to 5%aluminium and hot worked alloys contain around 10% aluminium.

The 10% alloy can be heat treated in a similar way to steel producing amartensitic structure when quenched from 900∞C.

The main uses of aluminium bronzes depend on features such as:

• the ability to retain strength at elevated temperatures

• good corrosion resistance at ordinary temperatures

• high resistance to oxidation at elevated temperatures

• good wearing properties

• pleasing colour making some of these alloys useful for decorativework.

The table outlines the details of two common aluminium bronzes.

% Other Properties Applications

80 Al – 10%

Fe – 5%

Ni – 5%

suitable for casting orforging, good strength andhardness, can be hardenedand tempered

shafts, spindles andcastings that requirestrength and corrosionresistance, valve seatsand spark plug bodies

95.5 Fe – 2.5%

Ni – 1%

Mn – 1%

can be cast or cold worked,good strength, resistscorrosion, fatigue and wear

widely used for die andsand casting, valves,gears


Strengthening and heat treatmentList processes that are used to change the properties of non-ferrous alloys.

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Did you answer?

Did you come up with cold working, annealing, quench hardening, tempering,precipitation hardening and artificial aging?

Many non-ferrous metals can only have their strength altered by coldworking. As the cold working process distorts the lattice structure of themetal, tensile strength, yield strength and hardness increase whileductility and conductivity decrease. The degree of changes to propertiesis relative to the amount of deformation.

For example, if a piece of annealed 70/30 is compared with another piecethat is cold rolled to half the thickness the following results are observed.The cold rolled piece has twice the tensile strength and eight times thehardness of the annealed piece. The annealed piece is nine times asductile and fifteen percent more conductive than the cold rolled piece.

Normalised Cold worked

Refined grains

Flattenedelongatedgrains of

Figure 3.22 Normal and cold worked structures

Temper designations

Properties resulting from cold working are well understood andmanufacturers carefully control the amount of deformation to producejust the right properties in the product. Terms such as half-hard, extra-hard, and extra spring have traditionally been used to describe theproperties of cold worked copper-based items and to also indicate thepercentage reduction. Half-hard is caused by a reduction of around 20%while extra spring is caused by around a 70% reduction.


Classifications of aluminium and its alloys are achieved through the useof a notation rather than a name. The 6061 alloy used in some bicycleframes has a temper notation of T6.

Recovery

In a highly stressed material, the combined effects of internal stresses andintergranular corrosion may cause ‘season cracks’ to appear along thegrain boundaries. In some cold worked materials it is therefore desirableto slightly relieve some of the stresses.

Low temperature annealing, well below the recrystallisation temperature,will not change the distorted structure or desirable properties but slightlyrelieves some of the stresses at the grain boundaries.

Annealing

Annealing involves heating and soaking the metal above itsrecrystallisation temperature then cooling it back to room temperature.With most non-ferrous materials the rate of cooling isn't important soonce annealing is completed the metal can be cooled rapidly.

The more heavily a material is cold worked the more nucleii will form onrecrystallisation. This will initially lead to a large number of smallerequiaxed grains. When lightly cold worked material is recrystallised theinitial structure is fewer larger grains

While ever the metal soaks above the recrystallisation temperature, thegrain structure continues to grow into larger equiaxed grains. This graingrowth produces a softer material because the large grains are easier todeform and there are less grain boundaries to restrict the movement ofthe grains.

Nucleationcommences at

grain boundaries

Grain growthoccurs

Recrystallisedstructure

Grain growth

Figure 3.23 Structures showing recrystallisation and grain growth


Precipitation hardening

Some non-ferrous alloys, when cooled under equilibrium conditions,become hard and brittle due to the complete precipitation of a metalcompound. If these alloys are reheated back into a single-phase structurethen quenched, the compound is not allowed to precipitate.

In time, a week at room temperature or a couple of hours under low heat,submicroscopic particles of the compound move into the lattice structureof the single-phase structure. This has the effect of slightly distorting thelattice structure and increasing the hardness and strength of the material.

One common alloy that is treated in this way is duralumin. It is an alloyof aluminium and 4% copper that has been used on bicycles for seatposts, pedal cranks and goose necks.

Hardening and tempering

Just like steels, some non-ferrous alloys can be hardened and tempered.The advantage of these materials over steel is they have much greatercorrosion resistance.

A common example is an aluminium bronze containing copper with 10%aluminium. It is quenched from around 1 000∞C to produce a martensitic

structure. Reheating and soaking at around 550∞C improves the

toughness of the aluminium bronze while reducing its brittleness.



Polymers

Define the term polymer. Check the glossaries from the preliminarymodules for a definition.

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Did you answer?

A definition that indicated many repeating parts or long molecular chains with abasic repeating structural pattern would have been on the right track.

As you have learned previously, polymers can be both naturallyoccurring, like cellulose and rubber, and man-made, like nylon andBakelite. Polymers are of two basic types, thermosoftening that remeltwhen heated and thermosetting that don't. There are also otherstructural factors that can greatly influence the properties of polymers.

Look over your car and bicycle then identify any parts that are made froma polymer.

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Did you answer?

Did you find items like the dashboard, console, seat belts, carpet, mirrorhousings, bumper panels, light covers, cable covers, reflectors, body trim coverstrips, hub caps, tyres, tubes, handle grips and brake blocks?

By the end of this module you will have a good idea of the types ofpolymers used for these parts and will know how they have been made.


Thermosoftening polymers

Most thermosoftening polymers are based on covalently bondedhydrocarbon chains with carbon and hydrogen as the basic buildingblocks. Any hydrocarbon that has a multiple covalent bond in itsstructure can be polymerised. A good example is ethene or ethylene thatcan be polymerised to form polythene or as more commonly knownpolyethylene.

C

H

H

C

H

H

C

H

H

C

H

H

+ C

H

H

C

H

H

C

H

H

C

H

H

Bond broken

Figure 3.24 Polymerisation of ethylene

This type of simple polymerisation is known as addition polymerisationand involves the linking of monomers with the inclusion of all parts ofthe structure and without leaving any waste. Heat, pressure and asuitable catalyst are required to break the multiple bonds and then reformthem to create a very long molecule that is covalently bonded along itslength. Copolymerisation occurs when different monomers are addedtogether to provide a combination of properties. Acrylonitrile butadienestyrene or ABS is an example of a copolymer.

Break the double bonds in the vinyl chloride monomers in figure 3.24 tocreate polyvinyl chloride or PVC.

C

H

Cl

C

H

H

C

H

Cl

C

H

H

+

Figure 3.25 Polymerisation of vinyl chloride

Did you answer?

C

H

Cl

C

H

H

C

H

Cl

C

H

H


There shouldn't be any double bonds in your polymer as all these willhave been broken in the forming of the polymer. You should have acontinuous string of carbon atoms with chlorine and hydrogen atomsattached to them in the ratio of one chlorine atom for every threehydrogen atoms.

Generally you can consider a thermosoftening polymer to have astructure that looks like a plate of cooked spaghetti. The long chains arerandomly arranged in an amorphous pattern and any crystalline regionsare purely by chance not by design.

Tangled polymer chains

Figure 3.26 Structure of a simple linear polymer

Properties of thermosoftening polymers

Linear thermosoftening chains all have the same basic structure. Thereare strong covalent bonds along the chains but no primary bond at allbetween the chains. Because of the uneven distribution of electronsinvolved in some of the covalent bonds, often one part of the linear chainhas a positive charge while other parts are negatively charged. If thesetwo regions are close there will be an attraction that can influence theproperties of the polymer. This attraction is a type of secondary bondknown as a Van der Waal’s force. This attraction can occur both withinand between chains.

Low softening temperature

Only the weak secondary bonds need to be broken to allow the polymerto 'flow'. This occurs around 100∞C for most thermopolymers.

Nylon is an exception to the rule! Oxygen atoms on one chain areattracted to hydrogen atoms on adjacent chains through a stronger type ofsecondary bond. This elevates the softening temperature of nylon toaround 240∞C and also increases its strength properties. Unfortunately it

also gives nylon a greater attraction for water and special dryers must beused when moulding nylon to ensure steam bubbles don't form inside themouldings.


Transparent verses opaque

As in glasses, any polymer that is amorphous can be transparent whilecrystalline polymers will be opaque.

Some polymers are made up of simple, uniform groups that form simpleparallel chains. These polymers often have areas where the chains areclosely aligned and consequently light will not pass through. High-density polyethylene is an example of this type of structure.

Other polymers have a mixture of large and small groups that don't allowalignment and therefore the light can easily pass through the structure.Perspex, used in tail light lenses, is an example of this type of polymer.

Get hold of:

• a freezer bag (you know the noisy, grey ones that hang in rolls infruit shops). This is high density polyethylene.

• a clear bag (like a Glad snaplock) or some clear non-adhesive bookcovering ‘plastic’ or some ‘plastic’ food wrap. This is probably lowdensity polyethylene.

Suggest, in terms of their structure, why one type of 'plastic' is clear butthe other is, at best, translucent.

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Did you answer?

Did you talk about the freezer bag being crystalline while the other wasamorphous?

Take the clear non-adhesive ‘plastic’ and stretch it till it is just about tobreak.

Hopefully your ‘plastic’ went white or grey at this point.

Explain what has happened to the structure to cause this colour change.

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Did you answer?

Did you mention that the polymer had become crystalline at this point andtherefore it had also become opaque?

Strength

It is much harder to break primary bonds than secondary bonds so anymaterial will be stronger when its primary bonds are stressed. Ifthermosoftening polymers have simple linear chains they will be strongeralong the chains than across them. A good example of this is a ‘plastic’supermarket bag.

Get hold of a 'plastic' supermarket bag (you know the ones that thebottoms fall out of when you fill them with bottles of soft drink). This ishigh density polyethylene.

When this bag was manufactured the polymer chains would have beenaligned from top to bottom so that really only secondary bonds are actingacross the bag.

Would you expect it to be stronger when you pulled between the handlesand the base or when you pulled from side to side?

Prove your answer! Take hold of the bag and see in which direction itstretches more easily. Were you right?

It is quite significantly stronger from top to bottom because you aretrying to break strong covalent bonds.

Strength and rigidity can also be caused in some polymers because of thelarge groups that are attached to the long chains. These large groups actlike branches and when they catch on other branches on adjacent chainsthe chains are prevented from sliding over each other. Of course thelarge groups also prevent crystallisation so these types of materials aretypically clear and rigid. Polycarbonate, used as an unbreakable glasssubstitute in windows, is an example of this type of polymer.

Branches do not link between chains

Figure 3.27 A linear polymer with branched chains


Elastomers

Some thermosoftening polymers still have a multiple bond in theirstructure after polymerisation. Rubbers, both natural and synthetic, areexamples of this type of polymer.

Due to the sliding of the chains, natural rubber items will becomedistorted under a tensile load. This can be minimised through the processof vulcanising. This involves the controlled breaking of some of the'spare' multiple bonds in the polymer and the formation of covalent bondsbetween adjacent chains. Sulfur is introduced as the vulcanising agent orlink between the chains and the process also requires both heat andpressure.

These strong and permanent covalent bonds between chains means that itwill no longer completely soften under heating but the strength propertiesof the rubber are improved. The greater the number of cross-linksbetween chains the more rigid the rubber becomes. Ordinary vulcanisedrubber contains about 4% sulfur and about 10% of the spare doublebonds are involved. Ebonite contains 45% sulfur and all the doublebonds are broken.

Unfortunately, double bonds not involved in the vulcanisation processcan be broken and cross-linked by oxygen or ozone. This form ofoxidation is known as perishing and embrittles the rubber.

or CH2 C

CH3

CH CH2 nC

H

HC C

H

C

H

HCH

HH

S

S

S

SS

S

Sulfur cross-link

Figure 3.28 The vulcanisation of natural rubber

Fillers such as carbon black and silica are often added to vulcanisedrubber as they increase the materials resistance to both abrasion andtearing.


Neoprene or polychloroprene is a synthetic rubber commonly used incontact with oils and solvents. Used in the flexible hoses in the hydraulicbrake systems and fuel systems of cars, this polymer is crosslinked withthe oxides of zinc or magnesium.

Butyl rubber is another common synthetic. As it doesn't have any sparedouble bonds, it is often copolymerised with just the right amount ofisoprene to provide cross-linking sites. After vulcanisation there are nosites left for oxidation to occur so the life of the rubber is prolonged.This rubber holds air and gases very well and is used extensively in themanufacture of bicycle tubes and tyres.

Properties of elastomers

A lightly vulcanised elastomer will display the following properties:

• electrical insulator as all electrons are involved in bonding

• relatively good abrasion resistance

• extend to many times its original length, under a tensile load, thenreturn to its original shape after the load is removed – this propertyknown as resilience.

Str

ess

Strain

Figure 3.29 Stress/strain curve of an elastomer

Note how the curve in figure 3.29 is a different shape to the stress/straincurves for metals. It doesn't start with a straight-line section and istherefore seen to be an inelastic material. The early part of the curveshows much extension with little applied load. At this time the longtangled chains are being straightened out and only secondary bonds arebeing broken.

Towards the end, the graph rises sharply indicating that a greater load isneeded but produces little extra extension. This is because all the chainsare now straight and the strong primary bonds are resisting further


change. Ultimately these primary bonds will be broken and theelastomer will fail.

Get hold of a 'rubber' band (a wide one would be best)

Stretch the rubber band with your hands and confirm the stress/straincurve shown in figure 3.29.

The band is easy to stretch at the start but gets harder the more youstretch it. Eventually it becomes white and, if you are strong enough, itbreaks.

Thermosetting polymers

Some polymers form a network structure that has primary bonds in allthree dimensions. This form of polymerisation often occurs through acondensation reaction where molecules combine and a by-product is leftover. Phenol-formaldehyde, or bakelite, is one example of this type ofpolymer.

+ + + H2OCH2O C6H5OH C6H5OH C13H10(OH)2Formaldehyde Phenol Phenol Phenol formaldehyde Water

Figure 3.30 Condensation polymerisation

The strong covalent bonds, in all three dimensions, means that thesepolymers are typically rigid, hard, opaque and will not soften under heat.

The polymers can take the form of powder or liquid resins and catalyststhat are mixed together in the correct proportions. Some are just mixedand formed, like polyester resin used when fibre glassing and epoxy resin(araldite), while others, like Bakelite, require heat and pressure forpolymerisation to occur.

Fillers such as chopped fabric and glass fibre improve the impactstrength while mica improves electrical resistance and graphite reducesthe coefficient of friction.

Thermosetting polymers, like polyurethane, can also be foamed and usedas the light weight core in foam sandwich fibre reinforced polymers.Foamed polymers, like foamed polystyrene, also absorb impact and canbe used in items such as bicycle helmets.


Additions to polymers

Polymers are nearly always mixed with additives to enhance theproperties of the composite body. Some of these additives are:

• pigments that provide colouring

• plasticisers that lubricate between the polymer chains to increaseflexibility

• stabilisers, such as carbon black, that prevent damage from uv rays

• fillers that simply reduce the amount of polymer needed but alsoalter the properties. these include glass fibres for strength and woodflour to increase rigidity.


Some polymers used in bicycles and cars

Thermosoftening

Polymer Properties Applications

Polyethylene

Polythene

low melting temperature, tough,flexible, insulator, low density hasbranched chains reducingcrystallinity, high density is linear

coating on outer of bikegear and brake cables

Polycarbonate high impact strength, transparent,UV stable, dimensional stability

unbreakable window'glass', bike helmets,bike light bodies

Polypropylene very tough, rigid, electricalinsulator, inert, bends as a hingewithout cracking

seat belting, carpet, one-piece accelerator pedal,battery outer casing

PVC

Polyvinylchloride

excellent electrical insulator,hard, rigid and tough or withplasticisers added it is soft, toughand flexible, backed with textileas a fabric

covering on electricalwiring, covering on bikeseats and someupholstery trim in cars,handle grips


Polyamide(nylon)

excellent chemical resistance,high strength, heat resistant,dimensional stability, wearresistant

gears insideinstruments, bushes,low-friction washers,fabric belts in tyres

Acrylic

perspex

transparent, excellent opticalproperties, weather resistant

car weather shields,bicycle and car reflectorsand light lenses,instruments

ABS fatigue resistant, hard, rigid,tough, impact strength, goodsurface finish, metallic in feel,can be chrome plated

Helmet outers, chromeplated body trim

Elastomers


Vulcanisedrubber

low cost, good all-roundproperties, flexible, tough

car tyres, enginemounts, bike brakeblocks

Neoprene good heat resistance andresistance to oils, flexible, tough

radiator hoses, flexiblefuel and brake fluid lines

Butyl rubber good resistance to ozone, holdsair and gases well

inner tubes, bicycletyres, singles

Thermosetting


Silicones inert, resists oxidation, excellentelectrical insulator, can beformed into rubbers

insulators, seals in air,water and hydraulicsystems

Polyurethanefoam

excellent insulators, trap air in theway of sponge, inert

upholstery foam, noiseinsulation


Polymer forming processes

The following processes are used in the manufacture of parts forbicycles, cars and trains.

Injection moulding

Extrusion – film and solid

Blow moulding

Calendering

Rotational moulding

Casting

Compression moulding

Transfer moulding

Injection moulding

Polymer granules are placed in a hopper that feeds into a heatingchamber. The polymer is forced through the chamber by a 'screw' whereit is melted. The molten polymer is injected into a cool permanent metalmould. Once the polymer sets, the mould opens and the finished item isremoved. Mould design must allow items to be removed from themould.

This is the most widely used type of polymer forming process and is usedon all types of polymers.

Movable mould

Moulded partRotating screwor hydraulic ram

Heater

Polymer pelletsloaded into hopper

Spreader

Nozzle

Figure 3.31 Injection moulding

Polymer components such as pedals, lights, handle grips and reflectorson bicycles and consoles, body trims, rear light assemblies and gloveboxes on cars are all made by injection moulding.


ExtrusionEach form of extrusion starts with the melting of polymer granules as forinjection moulding.

A continuous profile is made when molten polymer is pushed through aspecially shaped die. As this polymer solidifies it may be cut to length orrolled up.

Thermosoftening polymers and elastomers are commonly extruded intoitems such as seals around car doors. Bicycle tubes are extruded, joinedto form a ring and then the valve is fitted.

Polymer can also be extruded around another material as in the case ofPVC insulation extruded onto the outside of copper wire that is used inthe electrical systems of trains and cars.

Rotating screw feed

Heating coils

Hopper feed forplastic granules

Die

Extruded product

Figure 3.32 Continuous extrusion

Polymers can also be extruded as films as shown in figure 3.33.


Film wound onto rolls

Cooling air

Air to inflate film

Blown film

Extruded plastic

Rollers to guide film

Figure 3.33 Film extrusion

Though not used much in transport components, this process is used tomake thin films or bags in many different thermopolymers.

Blow moulding

This process can be used to make bottles and narrow necked containers.

Polymer is softened by heat then it is extruded, with the assistance ofgravity, as a tube. The metal mould closes around the viscous polymertube sealing the lower end and leaving a hole at the top. Air is blowninto the top pushing the hot polymer against the walls of the mould.


Compressed airMouldBlow pin

Hot extruded plastic Closing mould sealspolymer tube

Plastic blown totake the shapeof the mould

Compressed air

Figure 3.34 Blow moulding

Thermosoftening polymers are moulded using this process and blowmoulding is used to form items such as the drink bottle on a bicycle andfluid reservoirs for cooling, cleaning, brake and clutch systems in cars.


Calendering

This process was once used for the production of films but is now moreoften used to form composite materials. For example viscous PVC isspread onto the surface of a fabric and then rolled. Patterned rollers canbe used to produce a textured surface on the polymer.

Vinyl coated fabrics used in some upholstery in cars and on the seats ofbicycles is made using this process.

Coating knife

Coating liquid

Fabric backing Knife over roll coating

or

Figure 3.35 Calendering


Rotational moulding

Rotational moulding is used to mould hollow stress-free items. Apermanent metal mould is made of the outer shape of the product. Ameasured quantity of polymer granules is loaded into the mould which isthen closed. The mould is moved into a heating chamber and rotatedconstantly through 360∞. The polymer granules melt when they come

into contact with the heated mould and a 'skin' forms on the inside of themould.

Powdered plasticpoured into mould

Heated to 170–270∞Cand rotated

Cooled while stillrotating and then

removed from mould

Figure 3.36 Rotational moulding

Casting

All types of polymers can be cast once in a viscous state. Acrylic,polycarbonate and polyurethane foams are cast into large sheets.Polyester resins are blended with glass fibres and cast into moulds eitherby hand or by spraying techniques. Many of the internal panels in trainsare made from glass reinforced polymers that have been cast in this way.

Carbon fibre reinforced bicycle frames are also made through thisprocess of casting. Careful placement of the carbon fibres provides muchgreater control of the flexibility and response of the bicycle frame. Avariety of frame tubes can be made and then glued together or aninflatable internal mould may be used and a one-piece frame cast.

Compression moulding

This process is commonly used for forming elastomers and thermosettingpolymers. Polymer powders are mixed with fillers and then placeddirectly into a heated mould. The closing mould compresses the polymerand this combination of heat and pressure polymerises and forms theitem.


Car tyres are manufactured in a type of compression mould.

A variation of this process is transfer moulding which is also used forthermosetting polymers. The polymer is combined and melted in anotherchamber then transferred into the mould where it is subjected to pressureand further heating to promote curing.

Mouldplunger

Heatedmould

Mouldingmaterial

Force

Ejector pin or Split mould

Moulded pot

Figure 3.37 Compression moulding


Engineering textiles

Many of the man-made polymer fibres have properties that are notalways typical of textiles. However, a very common application of apolymer in a textile form is ‘shade cloth’, used to restrict ultra violet raysand provide shade.

Polypropylene, polyethylene, polyester and nylon are all woven intofabrics that are used in filtration systems. Different applications andenvironments will require careful assessment of each material by thetextile engineer.

A social problem, such as vandalism on trains has provided textileengineers with a number of difficulties. Train seats were once covered


with a vinyl fabric on foam padding. Unfortunately this fabric was easilytorn so the challenge was to develop a comfortable, non-rip and easilycleaned fabric for train seats. Seats in current trains are covered with atough woven polymer fabric that is extremely hard to tear, is comfortableand fairly easy to clean.

Laminated and tempered glass

In most cars today, the windscreen is made from laminated glass and theother windows are made from tempered or toughened glass.

1 Have a good look at the windows in your car. You should find somedetails about the window stamped in one corner. Jot those detailsdown.

_______________________________________________________

_______________________________________________________

_______________________________________________________

2 Explain how glass is toughened or tempered with the aid of a sketch.

_______________________________________________________

_______________________________________________________

_______________________________________________________

Did you answer?

1 Did you find the name of the manufacturer, probably Pilkington if it's anAustralian made car, and details of the manufacturing and heat treatmentprocesses? Did you find the words 'safety glass' on the windscreen? Thisindicates that the windscreen is laminated.

2 The dampening process involves heating the glass to its annealing range andrapidly cooling the outside surfaces by air blasting. As the glass mass cools,it contracts to develop compressive stresses in the skin and tensile stresses inthe interior.


1 Heat the glass to the annealing range 2 Air blast the outside surfaces

3 Slowly cool to room temperature

Compressive stresses in skin

Tensile forces in the interior

Figure 3.38 Tempering glass

Sketch and label the failure patterns for untreated, laminated andtoughened glasses.

Did you answer?

Untreated glass Toughened glassLaminated glass

Figure 3.39 Feature patterns of glass


The laminated windscreen on your car has been carefully manufacturedusing the following procedure:

• annealed glass is cut to the correct size and shape using a template.

• pairs of windscreen glass are heated in a lehr or furnace and drapedinto a metal mould to form the correct shape

• the shaped glass is cooled slowly to an annealed condition

• the pairs are split and thoroughly cleaned

• a layer of polyvinyl butyl is laid between the layers of the glass (thetint at the top of a screen is in this polymer layer before laminating)

• the laminated screen is then run between rollers to remove most ofthe trapped air

• time in an autoclave with heat and pressure will remove the rest ofthe air and leave the screen clear

• each screen is tested to check for optical clarity.

It is only in recent years that all windscreens have been made fromlaminated glass as they were once mainly made from toughened glass.

Suggest why it is safer to make windscreens from laminated glass ratherthan toughened glass.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

It is all to do with the failure pattern for each type of glass. While toughenedscreens are much stronger than laminated screens, when a toughened screendoes break the driver can't see at all. This is very dangerous when a truck flicksa stone up while you are travelling at 110 km/ph on a country road.

Of course all the other glass in the car is toughened making it verystrong. If it does break, the stresses in the glass cause the whole panel toshatter into small pieces with relatively smooth edges. This means itwon’t cut you and, as these are side and rear windows, your view of theroad ahead will not be obscured.


Exercises

Exercise 3.1

a With the aid of a sketch, describe the Izod notched bar impact test.

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Complete the following table by suggesting an important serviceproperty and the most suitable test that could be used to assess thisproperty.

Component Service property Test

A cast train wheel

A bicycle frame

Suspension springs

Bicycle helmets

A brake cable


c Discuss situations where modeling or proving tests may be used inthe development of bicycles, cars or trains.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

Exercise 3.2

a Sketch and clearly label the microstructures of the two carbon steelsidentified and the cast iron.

Low Carbon Steel Grey Cast Iron Carbon Tool Steel

b Complete the following table by suggesting a plain carbon steelsuitable for the application and the forming process used tomanufacture the component.

Component Steel type Forming process

Gear and brakecables

Common bolts

Railway track

Auto disk brake

Auto suspensionsprings


c Name one steel alloy and explain how its properties differ from thoseof mild steel.

_______________________________________________________

d State the changes in strength properties that occur as carbon contentis increased in plain carbon steels.

_______________________________________________________

_______________________________________________________

Exercise 3.3

a Explain how the structure of medium and high carbon steels allowthem to be quench hardened.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Suggest why normalising would be carried out on a ferrous casting.

_______________________________________________________

_______________________________________________________

_______________________________________________________

c Complete the following table by suggesting the properties achievedand typical applications, in transportation components, for each ofthe forms of surface hardening listed.

Hardening process Properties Applications

Carburising

Nitriding

Selective Hardening


d Explain the purpose of tempering hardened structures.

_______________________________________________________

_______________________________________________________

Exercise 3.4

a Describe the process of die-casting.

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Sketch and label the grain structure that results from hot rolling.

c Explain the grainflow that occurs in an upset bolt head with the aidof a sketch.


d Explain the processes involved in making a butted bicycle frametube from a piece of solid alloy steel rod.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

e Complete the following list by suggesting a suitable manufacturingprocess for each of the aluminium alloy components:

i bike wheel rim___________________________________________________

___________________________________________________

___________________________________________________

ii bike pedal crank___________________________________________________

___________________________________________________

___________________________________________________

iii bike wheel hub___________________________________________________

___________________________________________________

___________________________________________________

iv auto engine sump___________________________________________________

___________________________________________________

___________________________________________________

Exercise 3.5

a State four reasons why powder forming may be used.

i ___________________________________________________

ii ___________________________________________________

iii ___________________________________________________

iv ___________________________________________________


b List three stages of the 'powder forming' process.

_______________________________________________________

_______________________________________________________

_______________________________________________________

c Complete the table below by suggesting at least one (but more ifpossible) non-ferrous metal that can hardened by the process given.

Process Non-ferrous metal

Cold working

Precipitation hardening

Quench hardening

d Discuss the structural changes that cause precipitation hardening.

_______________________________________________________

_______________________________________________________

Exercise 3.6

a Compare and contrast addition and condensation polymerisation,with the aid of sketches.

addition condensation

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________


b List some of the typical properties of thermosoftening polymers.

_______________________________________________________

_______________________________________________________

_______________________________________________________

c i Sketch the structures of a linear thermosoftening polymer and abranched thermosetting polymer.

Linear Branched

ii Give a specific example of each type and then list typicalproperties.

Linear thermosofteningpolymer

Branched thermosettingpolymer

Example: ______________________ ______________________

Properties: ______________________ ______________________

d List three typical fillers used in polymers and suggest the use ofeach.

_______________________________________________________

_______________________________________________________

_______________________________________________________


Exercise 3.7

a Explain the process of vulcanising in rubber, with the aid of a sketch.

_______________________________________________________

_______________________________________________________

b Complete the following table by suggesting a service propertyrequired, a suitable polymer and probable forming process for eachof the applications listed.

Application Service property Polymer Formingprocess

Reflector lens

Bicycle tube

Drink bottle


c With the aid of a sketch describe blow moulding,

_______________________________________________________

_______________________________________________________

b Explain why normally flexible polymers turn white and reduce inflexbility under a severe tensile load.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________


Exercise 3.8

Select the alternative a, b, c or d that best completes the statement oranswers the question. Circle the letter.

1 Testing by modelling would be used when designing a high speedtrain to assess:

a movement of air over the train

b movement of air under the train

c movement of air over and under the train

d position of emergency exists.

2 Both the Izod and Charpy tests use a:

a notched specimen, pendulum and ruler

b notched specimen, pendulum and energy indicator

c parallel specimen, pendulum and ruler

d hammer, wire specimen and energy indicator.

3 By definition, a ferrous metal is one that:

a rusts when exposed to still air

b contains any amount of iron

c becomes hard when quenched

d has iron as its major element.

4 Phases found in the structures of all plain carbon steels at roomtemperature are:

a ferrite and cementite

b cementite and austenite

c pearlite and ferrite

d pearlite and graphite.


5 As carbon content increases in plain carbon steels, up to 0.8%C, thesteel becomes:

a stronger and more ductile

b softer and more ductile

c stronger and tougher

d weaker and softer.

6 Hot working is the:

a plastic deformation of a material above its recrystallisationtemperature

b working of a material when it is heated above 250∞C

c plastic deformation of a material when it is hot

d controlled working of any material with the aid of any heatingsource.

7 Cold working processes include:

a rolling, upsetting and casting

b piercing, rolling and upsetting

c forging, casting and drawing

d upsetting, rolling and drawing.

8 The following can all be used to increase the hardness of variousnon-ferrous alloys:

a precipitation hardening, quenching and cold working

b annealing, quenching and normalising

c precipitation hardening, recovery and tempering

d quenching, cold working and annealing.

9 Compression and transfer moulding are both used for forming:

a non-ferrous alloys

b thermosetting polymers

c ceramics

d thermosoftening polymers.


10 Which of the following groups of processes use a permanent metalmould?

a Die casting, injection moulding and shell moulding

b Blow moulding, investment casting and extrusion

c Blow moulding, die casting and rotational moulding

d Film extrusion, shell moulding and injection moulding.

11 The best sheet polymer to use as 'unbreakable' window panels wouldbe:

a acrylic

b polypropylene

c nylon

d polycarbonate.



Exercises 3.1 to 3.8 Name: ___________________________________

Check!


❐ Exercise 3.1

❐ Exercise 3.2

❐ Exercise 3.3

❐ Exercise 3.4

❐ Exercise 3.5

❐ Exercise 3.6

❐ Exercise 3.7

❐ Exercise 3.8





Progress check

In this part you investigated materials used to make transport component parts –their, how they can be modified and the processes used in manufacturing.

Take a few moments to reflect on your learning then tick the box which bestrepresents your level of achievement.




Ag

ree

Dis

agre

e

Un

cert

ain


• specialised testing of engineering materials and/or systems• heat treatment of ferrous metals• structure/property relationships in material forming processes• non-ferrous alloys• ceramics and glasses• polymers.

I have learnt to:

• explain the properties, uses, testing and appropriateness ofmaterials used in transportation

• identify appropriate heat treatment processes• justify appropriate choices for ferrous and non-ferrous materials

and processes used in transportation parts and systems• experiment with metals to reinforce the concepts of heat

treatment• explain the method and applications of various ferrous metal

forming processes• justify appropriate choices for ceramics and glasses used in

transportation parts and systems• justify appropriate choices of polymers and their manufacturing

processes used in transportation parts and systems.



In the next part you will examine the generation and transmission ofelectricity, and electric motors and systems in various types of transport.


Part 4: Transport systems –electricity/electronics

Part 4: Transport systems – engineering/electronics 1

Part 4 contents

Introduction..........................................................................................2What will you learn?................................................................... 2

Electricity for power and information...............................................3AC and DC electricity................................................................. 5

Electrical power......................................................................... 7

Generating electricity .........................................................................9Coal fired power stations............................................................ 9

Hydro-electricity .......................................................................13

Solar energy ............................................................................14

Wind power..............................................................................17

Other sources of energy............................................................19

Transmission and distribution of electricity ..................................22The grid system........................................................................22

Single-phase versus three-phase ..............................................22

Generating voltages and losses.................................................28

Electrical transmission ..............................................................28

The distribution system.............................................................38

Principles of electrical motors.........................................................42Motors .....................................................................................42

Introduction to digital systems........................................................57Analogue signals......................................................................57

Digital signals...........................................................................59

Boolean logic ...........................................................................59

Combination logic circuits..........................................................60

Electricity systems in transport.......................................................64Parameterising electrical systems in transport ............................66

Exercises ...........................................................................................81

Progress check.................................................................................89



Introduction

Electricity is the fundamental to our lifestyles yet we generally take it forgranted. Most forms of transport that we use today are reliant anelectricity in some form. Electricity is used in transport systems forproviding motive power and for communicating information.

In this part you will investigate how electricity is produced and how it isused in the myriad of ways that make it an invaluable source of energyfor transportation systems. You will also examine howelectricity/electronics can be used for communicating information incontrol systems.



• power generation/distribution

– electrical energy and power

• AC/DC circuits

• electric motors used in transport systems

– principles

– applications

• control technology.

You will learn to:

• identify the electrical systems used in the transport industry

• investigate the principles and application of electric motors used inthe transport indusrty

• analyse the basic principles of control technology as applied to thetransport industry

• explain elementary digital logic.




Electricity for power and information

We take advantage of electricity in many different ways. At home weuse electricity to cook our food, to give us light, and to wash our clothes.At work we use electricity to run our computers, irrigation pumps andphotocopiers. For fun, electricity runs our video player, television andmobile phone. However, none of these examples use electricity in itspure form. Pure electricity is simply a flow of electrons along aconductor. There are not many practical uses for that! In each case theelectricity is converted into another form of energy or into information.

Almost all applications of electricity can be classified into one of twocategories: using electricity for power (or energy), or using electricity torepresent information.

What is meant by ‘power’?

In ‘power’ applications of electricity, we are primarily interested in theamount of energy or power being delivered. For example, a 50 Watt lightmight be powered by 240 Volts at 50 Hz (mains voltage) or by 12 Volts asDC (as in a car). The power, and hence light, is the same in each case,although the height and frequency of the electrical waveform powering thelamp is quite different.

Identify three electrical appliances in your home that are specified in terms otheir power rating. What are the devices, and what are their power ratings?

Figure 4.1 A toaster – an appliance that uses electricity for power to generate heat


What is meant by ‘information’?

Using electricity to represent information is less obvious than usingelectricity for power. In the information context, we are interested incertain properties of the electrical signal such as its frequency, amplitude,or duty cycle (ratio of on-time to off-time). For example, radio waves usedifferent amplitudes and frequencies to transmit information (such asspoken words or music). We refer to different radio stations in terms oftheir transmission frequencies, but not in terms of their powers.

Computer modems use electricity to communicate with other computers.Here we are interested in data rates and signaling protocols rather thanthe power being transmitted or received.

Identify three electrical appliances in your home that are used to processinformation. What are the devices, and what sort of information do theyprocess?

Figure 4.2 An unusual view of a common appliance – a PC that uses electricity toprocess information

You will learn more about the use of electricity to process information inthe module on Telecommunications engineering.



AC and DC electricity

In Household appliances you learned the difference between AC andDC.

AC and DC stand for ‘alternating current’ and ‘direct current’respectively. The terms describe a fundamental property of an electricalsignal.

In an AC circuit the electrons that constitute the current oscillate backand forth in the circuit: that is, the direction of the current alternates.

The rate at which the current alternates is called the ‘frequency’. Themains electricity we obtain from our domestic supply has a frequency of50 Hertz (Hz) which means that the direction of current alternates 50times per second (or if you like, the electrons change direction 50 timesper second). Figure 4.3 shows the instantaneous amplitude of the currentas it varies with time. Note that the shape is sinusoidal.

Currentamplitude

max

0

–

T = 1f

time

T = periodf = frequency

max

Figure 4.3 AC current waveform

If the waveform is equally positive and negative, how can it do any work?

A simple analogy is that of sandpaper being rubbed over a block ofwood. The sandpaper can go back and forth over the same area but stilldo real work.

Alternating current is also very useful in communications applications.We can take advantage of different frequencies to allow multiple users tooccupy the same medium without interfering with each other. Forexample, two radio stations with broadcast frequencies of 102.4 MHzand 104.2 MHz can both broadcast in the same space using the sametechniques without interfering with one another.


In a DC circuit, the current always flows in the same direction. This canbe thought of as a special case of AC where the frequency is 0 Hz asshown in figure 4.4.

Currentamplitude

DC

0 time

Figure 4.4 DC current waveform

The most common source of DC is from a battery. (There is no suchthing as an AC battery.) Solar cells also generate DC power.

DC is used in some power applications. The most common is in motorvehicles where the electrical systems run at 12 Volts DC (cars) or 24Volts (trucks). DC is also used where we want to control the speed ofelectric motors (such as in electric trains).

DC is rarely used in communications because of the potentialinterference that multiple users of the same channel would experience.

It is possible to convert AC into DC by using a rectifier (or converter)circuit. DC may be used to generate AC signals using an inverter circuit.

Finally, the terms AC and DC refer to current (alternating and direct).What about voltage?

Of course, the voltage waveform is the same shape as the currentwaveform (although its amplitude is usually different). That is, in an ACcircuit the voltage polarity (direction) changes at the same frequency asthe current direction.

Why aren't AC circuits called ‘alternating voltage’ or AV?

The reference to current instead of voltage is essentially an historicalartifact. In the pioneering days of electrical engineering, engineersfocussed on current instead of voltage. Hence the terms AC and DC.Nowadays, even though we tend to refer to voltage more often thancurrent, the older terms are still retained.


Electrical power

The terms ‘power’ and ‘energy’ are often used interchangeably, thoughfrom their definitions it is clear that they are technically different (referback to Household appliances if you need to refresh your memory). It isimportant to be clear in your mind as to exactly what you mean when youuse either term.

Uses of electrical power

Electrical power has many applications in contemporary society,including:

• heating: in the home for cooking, hot water, ironing; in industry forfurnaces and process industries

• motors: in the home for washing machines, refrigerators, vacuumcleaners, video cassette players; in industry for fans, rolling mills,conveyor systems, pumps

• lighting: in the home for room and outdoor lighting, decorativelights; in industry for factory illumination, advertising, safetywarnings and security

• radiation devices: in the home for microwave ovens; and in thecommunity for radio and television transmissions (here the power isimportant to reach as many people as possible).

Other uses of electricity include:

• cooling systems (these are usually based in motors)

• electric arc welding (essentially another form of heating)

• lifting devices (again, based on motors).

Can you think of another application in your home that uses electricity asa source of energy or power?

Impact of electrical power on society

Modern societies have so embraced electrical services that we often takethem for granted. Indeed, many of us only think about our electricalsupply when it fails!

Electricity is now considered to be an essential supply, and an emergencysituation arises when the electrical supply fails. In times of crises, repairof the electrical supply is one of the key priorities for emergency serviceteams.


Dependence on a reliable supply of electricity hasn't always been thecase. Older generations in our communities can still recollect livingwithout electricity.

Can you find someone in your own community who had to live withoutelectricity. How did they manage? Could they keep their food cool?What did they do for entertainment?

In developing countries, where the supply of electricity is not reliable oris non-existent, foreign aid is often used to establish a dependableelectrical infrastructure. Together with clean water and acommunications infrastructure, electrical supply is seen as one of thefoundations of a modern community.

This module focuses on the use of electrical systems in personal andpublic transport systems. In particular, the module looks at sources ofenergy (both mainstream and alternate), the generation, transmission anddistribution of electricity, principles of rotating electrical machines(motors and generators), and introduces the concept of control systemsand digital logic. These are evaluated in the context of transport systems,using bicycles, motor cycles, cars and railway locomotives as examples.


Generating electricity

In this section we look at various sources of energy, where they arefound, how they are harnessed, and the salient operational characteristicsof plants designed to generate electricity from the energy sources.

Coal fired power stations

History of coal fired power generation

In 1904 the first substantial power station began operations at Pyrmont inSydney. Prior to that, electrical generation had been undertaken by localcouncils, primarily for the purposes of electric lighting. The first electricstreet lighting in Australia was established in Tamworth in northern NewSouth Wales in November 1888.

The Electricity Commission of New South Wales was formed in 1950 inresponse to the increasing demand for electricity in the years followingWorld War II, at a time characterised by chronic power shortages. TheCommission's initial task was to increase generating capacity as quicklyas possible while planning for future electricity requirements.

One of the key strategies employed was to locate coal-fired powerstations next to their fuel source. By the 1960's, a number of new powerstations had been constructed next to coal deposits. These includedstations at Tallawarra in the Illawarra region (opened 1951, closed 1989),Wangi Wangi on Lake Macquarie in the Hunter region (opened 1953,closed 1986), and Wallerawang in the Central West of NSW (opened1957, still operating).

As demand for electrical energy increased further, small power stationswere closed or upgraded, and new, larger power stations built inlocations close to coal supplies. For example, the Tallawarra powerstation had a total generating capacity of 320 MW. The newer stationssuch as Eraring and Bayswater have four units each of 660 MW.

Try to find out where the closest power station to your home is located.


The major power generating stations

Responsibility for the primary power generation in New South Wales isshared between Pacific Power, Delta Electricity and MacquarieElectricity. Between them, these three organisations operate the state’sseven main power stations and produce over 90 percent of the state'selectricity.

Other energy providers in the state are developing alternative energysources such as wind and solar generation in response to consumerdemand for ‘green’ energy, but these supplies represent only a fraction ofthe total power generated. We will look at these alternate energy sourceslater.

New South Wales' major power stations are:

Station Name Location Adjacent to Power output

Bayswater Upper HunterValley

Lake Liddell 2640 MW

Liddell Upper HunterValley

Lake Liddell 2000 MW

Vales Point Lake Macquarie Lake Macquarie 1320 MW

Munmorah Central Coast Lake Munmorah 1320 MW

Wallerawang Central West Lake Wallace,Lake Lyell

1000 MW

Mount Piper Central West Thompsons CreekDam

1320 MW

Eraring Lake Macquarie Lake Macquarie 2640 MW

Table 1 Major power generating stations in New South Wales

Figure 4.5 shows an aerial view of Bayswater power station in the UpperHunter Valley near Muswellbrook. The water supply for the coolingsystem can be seen at the left bottom of the image. The coal receival areais visible on the left, while the four steam condensing towers areprominent.


Figure 4.5 Bayswater Power Station near Muswellbrook

How a modern coal fired power station works

The coal used in a typical modern power station is sourced from localmines and transported to a station stockpile by conveyor belts. Here, thecoal is sampled, weighed and stored for later recovery by reclaimers andbulldozers for use in the power station. Coal is stored at the station incase the supply of coal from the mines is disrupted for some time, duringwhich the power station must be able to continue producing electricity.

Before being used in the furnace, coal is crushed into a fine powder.This increases the efficiency of the combustion process. The coalpowder is blown into the furnace using a stream of pre-heated air.

The heat generated by the burning coal is used to boil fresh water in aboiler to produce high-pressure steam. This is done by circulatingpurified fresh water through the inner 'walls' of tubing lining the boilerfurnace chamber. Pure fresh water is used so that the salts found inseawater and unpurified water do not clog or corrode the boiler plant.

In a boiler supplying a modern 660 MW turbo-generator, over twomillion litres of water are converted to steam each hour. The steam isheated to around 540 degrees Celsius. Maximum coal consumption isabout 250 tonnes an hour.

The exhaust gases from the boiler furnace are passed through a series offilters to recover the ash that results from burning coal. This ash iscollected and then used in other applications. (A common application isas landfill where excellent drainage properties are required.)


The steam that is produced by the boiler is injected at very high pressureonto the blades of a turbine. The turbine shaft is directly coupled to thedrive shaft of the electrical generator.

After being used to drive the high-pressure turbine, the steam is used todrive a medium pressure turbine. This turbine has a larger diameter thanthe first (high-pressure) turbine. Finally the steam exhausted from themedium-pressure turbine is uses to drive a low-pressure (larger diameter)turbine. By using a succession of increasingly larger diameter turbines,maximum energy can be extracted from the steam as its temperature andpressure decrease.

Figure 4.6 shows a portion of a high pressure steam turbine from Eraringpower station. This turbine blade has been damaged (see circularmarking on right-most blade) and has been brought to the engineering labfor examination and testing.

Figure 4.6 A portion of high pressure steam turbine

On leaving the low-pressure turbine, the steam is cooled back into liquidform in a condenser, and then re-used in the boiler. This is done in largecooling towers that visually dominate coal-fired power stations. Thesetowers exude large volumes of steam that are often mistaken for smokepollution. The cooling towers at Bayswater power station can be seenclearly in figure 4.5.


The steam turbine shaft is directly coupled to the shaft of the electricalgenerator.

The generator shaft rotates at 3000 revolutions per minute. This equatesto 50 revolutions per second, which gives us the mains power frequencyof 50 Hertz.

Hydro-electricity

‘Hydro’ is a Greek word that means water.

Energy or power from water has been used for thousands of years.However, for most of this time, the energy was not converted toelectricity, but used directly to mill flour, drive winches and so forth.

Hydro-electricity is obtained from the conversion of the kinetic energy inflowing water into electrical energy.

History of hydro-electricity in Australia

The first hydro-electric generating plant in Australia, Duck Reach PowerStation, was constructed in 1895 on the South Esk River near LauncestonTasmania, comprising three 100 kW generators.

The first relatively large use of hydro-electric generation in mainlandAustralia was built on the Nymboida River by the then Clarence RiverCounty Council in 1923. That plant was rated at 4.8 MW and is still inoperation.

In 1927 two 5 MW units were installed at Burrinjuck Dam by the NSWPublic Works Department.

In 1949 agreement was reached between the Commonwealth, NSW andVictorian Governments to form the Snowy Mountains Hydro-electricAuthority. The Authority subsequently built seven power stations,together with many dams and tunnels. It is still considered to be one ofthe greatest engineering feats in Australia, if not the world.

How a hydro-electric power station works

Hydro-electric power generation harnesses the potential energy stored inelevated bodies of water. Water stored in a dam is released through hugepipes into a power station located below the dam wall. The water isdirected through the base of a vertical turbo-generator where it passes


through the turbine blades, which are attached to the shaft and generator.The shaft spins at a controlled speed to maintain the required 3000 rpm(or 50 Hz).

The principle of electricity generation is essentially the same in bothhydro and thermal (steam) power stations. However, in coal-fired powerstations high-pressure steam is used to drive the horizontal turbine, in ahydro-electric station water is used to drive vertically oriented turbines.

The amount of power that can be generated by a hydro station dependson the height from which the water falls (called the ‘head’) and theamount of water available (the ‘flow’). The greater the head and theflow, the more electricity can be produced.

Where hydro power is generated

Electricity generated by the energy of falling water provides about 10%of the electricity produced in New South Wales each year. The largestamount is generated in the seven hydro-electricity power stations of theSnowy Mountains Scheme with a total generating capacity of 3756 MW.

The 5.5 MW Glenbawn Dam hydro station has been operating sinceFebruary, 1995. The Glenbawn station was constructed in an existing8.23 m diameter diversion tunnel and utilises energy from water which isused for irrigation and flushing. In the past, this water had beenchannelled down the Hunter River and its energy wasted.

A number of other hydro stations are located throughout Australia. InNSW these include Hume Weir, Burrinjuck Dam, Kangaroo Valley,Bendeela, Keepit Dam, Warragamba Dam, Brown Mountain andWyangala Dam. Operation of these hydro stations is generallydependent on the level of water in their associated storage dams and theneed for water downstream for irrigation or other purposes.

Why do you think Australia generates relatively small amounts of hydroelectricity compared with the output of its coal-fired power stations?

Solar energy

Solar energy is the term used to describe the conversion of sunlight intoelectrical energy using photovoltaic cells. Solar photovoltaic cellsdirectly convert sunlight to electricity. This differs from solar thermal(hot water) technology, which converts sunlight to heat directly, but notto electrical power.


History of solar power in Australia

The adoption of solar energy in Australia is a relatively recenttechnology when compared with, for example, coal-fired and hydropower stations.

Solar energy was first used in the 1950s to power space capsules andtelecommunications satellites. It is a good example of space technologyfinding subsequent application in broader markets.

How solar power works

Solar power is based on the use of photovoltaic cells. Individualphotovoltaic cells are manufactured on thin wafers of silicon. Each cellproduces only around 2.2 Volts, with the silicon wafers themselves beingvery fragile. Consequently, photovoltaic cells are not very convenientfor practical use.

A solar panel is the generic name given to a number of photovoltaic cellsconnected together and packaged together in a more robust form (such aswithin an aluminium frame with a protective glass cover). This type ofpackaging allows panels to be produced with more practical (higher)output voltages and to withstand reasonable handling without damage.

The physics underlying the production of electrical energy fromphotovoltaic cells is much less readily understood than the basicoperation of coal-fired and hydro power systems. A properunderstanding of the technology requires an appreciation of quantumphysics and semiconductor physics.

Where solar power is generated

Significant quantities of solar power are generated at a number of sitesthroughout New South Wales:

• Singleton solar farm Stage 1 – it consists of 3456 modules across anarea of 1.25ha. The modules are supported by steel framing facingtrue north and angled at 30 degrees to the horizontal. Each module –consisting of 36 polycrystalline solar cells - is rated at 60 Watts.This gives a peak output of more than 200 kW. The system isconnected to the electricity grid at 11kV.

• Singleton solar farm Stage 2 – consists of a further 3312 Canonamorphous solar modules producing a peak power of 200 kW. Theindividual modules are rated at 60 Watts and are mounted on a steelbase with a polymer coating instead of glass.


• the Olympic Village – each house in the suburb has rooftop solarpanels capable of generating 1600 kW hours per year.

• Queanbeyan – the solar farm consists of 720 solar panels arranged innine separate modules. Each solar panel has a 77 Watt capacity, witha total system capacity of 50 kW.

• Homebush Business Park – using 140 silicon solar modules (eachmodule consisting of 36 monocrystaline solar cells) and producing asystem output of about 11 kW.

• at the National Innovation Centre in Redfern, to produce systemoutput of about 10 kW.

• at Foreshore Park in Newcastle – the system installed on the roof ofthe carriage shed comprises 80 silicon solar modules and is rated at6.5 kW. (Interestingly, the railway carriage shed once housed thelocomotives that brought coal to the Newcastle Power station thatwas very close by.)

Figure 4.7 Solar panel installation on the roof of the old carriage shed atNewcastle Foreshore Park

Why do you think that the solar panels at the Singleton solar farm (andelsewhere) are oriented towards true north and inclined at 30 degrees tothe horizontal?

There are many other applications where solar cells are used to generatesmaller amounts of power for specific needs. For example, many marinenavigation markers are powered by solar cells mounted on the markers.Many new street light designs are incorporating solar power generation.Remote telecommunications equipment is often powered by solar energy.

Solar installations are popular on boats and caravans, where the power isused to complement other sources of power or to keep batteries charged.

Photovoltaics are also used to power many consumer products, such ascalculators, torches, battery chargers and watches. These types ofapplications have significantly reduced the dependence on batteries forsmall quantities of electrical power.


Australia has the highest per capita use of photovoltaics in the world.Total installed capacity is around 13MW and is growing by about 2MWper annum.

Figure 4.8 Calculator that uses solar power to complement a battery

Can you find an example of electricity being generated by solar powernear to your home? How much power do you think is being generated bythe system? Assume that photovoltaic cells generate approximately 100Watts per square metre of solar panelling.

Wind power

History of wind power in Australia

Perhaps the most quintessential image of rural Australia is that of awindmill drawing water from a bore. Of course this application does notconvert the wind power to electrical energy, but uses the mechanicalenergy to drive the pump directly.

The first commercial wind farm in Australia was designed and built byWestern Power Corporation in 1993 at Esperence Western Australia.Nine turbines generate up to 2MW providing about 12 per cent of thetown's base load electricity requirements.

Generally, applications of wind power being used to generate electricalpower in Australia are in their infancy. Other forms of power generationhave been more attractive in most situations, particularly given that manyparts of Australia do not experience consistently strong winds to ensurean adequate supply of electricity. However, interest in wind poweredgeneration is strong, and many commercial developments are under way.


How wind power works

The principle of wind powered generation is relatively simple: windflowing across the blades of a wind turbine cause the turbine shaft torotate. This shaft is connected to a generator, often through a system ofgearing to increase the rotational speed of the generator's shaft. (Highershaft speeds means that the generators can be physically smaller toproduce the amount of electricity.)

The amount of energy generated is dependent on wind speed and thediameter of the blades.

The power output is in fact proportional to the cube of the speed of thewind. That is, every time the wind speed doubles, the energy that can beextracted increases by a factor of eight. This has a down side: if a windturbine is designed to produce, say, 1000 Watts at a wind speed of 30kph, it will only produce 10 Watts at a wind speed of 15 kph. This rapidchange in power output limits the actual power that can be generatedfrom a turbine designed to withstand a given maximum wind speed.

Increasing the blade diameter increases the swept area (that is, the crosssection of the wind that is passed through the turbine). However,increasing the blade diameter also imposes significant demands on themechanical strength of the blades due to the large forces that result fromthe high tip speeds and torques produced.

Where wind power is generated

The first grid-connected commercial wind farm is located at Crookwellin NSW, and consists of 8 turbines each capable of generating 600 kW,giving a total of 4.8 MW.

The largest site of wind powered generation in NSW is at Blayney incentral NSW. The wind farm consists of 15 wind turbine generators eachof 660 kW capacity, giving a total maximum capacity of 10 MW.

Kooragang Island near Newcastle hosts one of the most accessible windturbines, being located immediately beside a busy road. The turbinenacelle (hub) measures 8 m x 3 m, weighs 28 tonnes and is mounted ontop of a 50 m tubular steel tower. The turbine's blades are reinforcedpolyester. Each blade is 22 m long, giving a total swept area of 1502 m2

(more than 1/4 of a football field). From blade tip to ground level, theturbine is 72 m. The peak power output from the plant is 600 kW.

Numerous smaller plants can be found in many areas. Most of theseturbines tend to have a capacity of no more than 5 kW and are usedprimarily for remote domestic applications, often in conjunction withother sources of power such as solar and diesel generation.


Figure 4.9 Kooragang wind turbine near Newcastle, the apparent height of thestructure is no illusion

Other sources of energy

There are many other sources of energy that can be used for electricalpower generation. These include:

• internal combustion engines

• biomass

• tidalwave energy

• geothermic.

Internal combustion engines

These applications include diesel, petrol and natural gas powered enginesthat are used to drive local generators. Such systems are generally usedeither in remote locations where connection to the grid is uneconomic, orfor back-up power supplies in critical applications (such as hospitals) foruse when the main grid supply fails. Plant sizes can be quite varied, froma couple of kW in small portable petrol generators, to hundreds of kW forsubstantial installations.


A significant advantage of these systems is that they can be started in arelatively short time, and run only as, and when, required.

Another application for generators driven by engines is of course foundin cars, trucks, buses and other vehicles. The power to drive lights,ignition systems, electric windows and sound systems is provided by agenerator (technically an alternator – see later material on electricalmachines) driven by a belt off the engine. Figure 4.10 shows thealternator in a car driven by a belt of the crankshaft.

Figure 4.10 A mobile generator – in this case, the alternator of a car

Biomass

This source of energy is derived from the decomposition or combustionof biodegradable materials.

During decomposition, combustible gases such as methane are given offand used to power gas turbine engines which in turn drive generators.Such plants are commonly known as ‘landfill gas’ systems, and are builtaround old large tip sites. Examples can be found at Lucas Heights and atBare Creek in Sydney. These plants total around 22 MW in generatingcapacity, and can be run continuously while ever the supply of gasremains.

In combustion, materials such as fuelwood, forestry residues, bagasse(the waste from sugar cane) and municipal solid waste can be combustedin furnaces and boilers to produce heat and hence steam to feed steamturbine generators.


Tidal

Tidal generators use the changing height of ocean water with tidalvariations to create small dams which can then be used in a similar wayto hydro power generating systems. Since the power obtainable is relatedto the height of the water, tidal plants tend to be viable only wheresignificant tidal heights can be found, such as in the north-west ofWestern Australia.

Wave energy

This mode of energy extraction is similar to tidal, but uses the morefrequent but less intense action of waves to drive turbines. Unless thegenerating plant can be made to float, the principle is only applicable inareas that have minimal tidal influence.

Geothermic

This source of energy is derived from deep underground where thetemperatures of the bedrock are hundreds of degrees Celsius. Thistemperature is sufficient to generate steam, and hence generate electricitythrough the normal means.

The energy is accessed by pumping water into the bedrock, where it boilsin contact with the heated rock. The resulting steam is then drawn offand used to power turbines. In some situations, the water occursnaturally, and steam can be drawn off directly.

In each of the alternate energy forms described above, we only harness avery small fraction of the total energy available from that source.



Transmission and distribution ofelectricity

The previous section looked at how electrical energy is generated on alarge scale. In this section we will look at how that energy is transmittedand distributed to consumers, and identify some of the key issues incontrolling and maintaining that infrastructure.

The grid system

Having generated the electricity in large power stations, it is necessary totransport the power to the people and industries that need it. The systemof electrical power lines that connect the power stations to the populationcentres is known as the ‘electrical grid system’ or simply, ‘the grid’.

The grid system carries energy from the power stations through anetwork of ‘transmission lines’ to major distribution points. From here,the energy is carried via a ‘distribution network’ to consumers.

The transmission grid can be thought of as the main arteries of the energydistribution system. The distribution network can similarly be thought ofas the capillaries, being made up of many smaller lines reaching into allparts of the state.

We will look more closely at the generation, transmission anddistribution networks in this section.

Single-phase versus three-phase

Figure 4.11 shows the variation of voltage with time of a single-phasedomestic supply.


Currentamplitude

max

0

T = 1f

time

T = 20 msf = 50 Hz

– max

Figure 4.11 Single-phase voltage supply showing variation of voltage with time

From earlier work we noted that the power in an electrical circuit wasproportional to the square of the voltage, that is:

P = V ¥ VR

= V2

R

Consequently, the power from a single-phase supply also varies withtime. Figure 4.12 shows the variation of power versus time for a single-phase supply. Note that at some instants, the power is at a maximum,and at other times (10 ms after the maximum power is attained) thepower is zero. Note also that the average power is only 50 per cent of themaximum instantaneous value.

Power

0

T = 1f

time

T = 10 msf = 100 Hz

maxP

averP

Figure 4.12 Single-phase supply showing variations of power with time


Problems with single-phase power

The pulsating power is not usually a problem for typical appliancesfound in domestic situations such as washing machines and refrigerators.However, for larger appliances and installations (of the order of severalkW and upwards), the power pulses can impose excessive torques onmechanical components, leading to vibration, or at worst mechanicalfailure.

Ideally, we would like the power in the system to be constant.

Three-phase system

One way in which constant power can be achieved is by designing asystem with three separate circuits that are displaced in time relative toone another, such that the sum of the powers from the three circuits isconstant. Such a system is known as a ‘three-phase’ system. You willremember the term ‘three-phase’ from Household appliances when youlearned about the induction motor. Figure 4.13 shows the variation ofvoltage with time for a three-phase system.

Voltage

0 time

maxV

max–V

“A” phase “B” phase “C” phase

Figure 4.13 Single-phase and three-phase electrical circuits

The three-phase-to-phase voltages are all sinusoidal, with the samemaximum amplitude, and displaced in time (phase) by 120o from eachother.

The power in a three-phase system is the vector sum of the powerobtained between each of the three-phases. It can be shown (using vectorarithmetic) that the sum of the power from the three phases is constant,that is, it does not vary with time!


Because of its constant power property, the three-phase system causesmuch less stress to the mechanical components of generators and motorsconnected to the system. Virtually all generators use three-phase for thisreason.

Figure 4.14 shows the powers obtained from the three-phase-to-phasevoltages, together with the total power.

Power

0 time

averP

PAB PBC PCA

Figure 4.14 Power in each of three-phases together with the total (constant) power

Advantages of three-phase power

The three-phase system has a number of other advantages over single-phase systems:

• a single-phase circuit can be obtained from a three-phase supply byconnecting the electrical load between one phase of the three-phasesupply and the neutral (or common) point of the three-phases. Thisenables electricity distributors to supply some homes with single-phase supplies, and others with three-phase supply, from the samedistribution network.

• by connecting an electrical load between any two phases of thethree-phase supply, higher voltages can be obtained (415 Voltsbetween phases, as compared with 240 Volts from a single-phase toneutral). Since power is proportional to the square of the voltage,higher powers can be obtained from the phase-to-phase connectionthan from the phase-to neutral (single-phase) connection. See figure4.15. This is why large hot water systems and heaters sometimesrequire a three-phase supply.


“A” phase

“B” phase

“C” phase

Neutral

Phase to phaseconnection

415 V 240 VPhase to neutral

connection

Figure 4.15 Connections and voltages for phase to phase and phase to neutralcircuits

• it is possible to transmit three-phase power over long distances byusing only the three separate phase conductors (that is, without theneed to run a fourth neutral conductor: under certain conditions, anew neutral connection can be made at the destination of the powerlink). By comparison, three separate single-phase systems wouldrequire six wires.

• it can be shown that the three-phase system is more efficient in termsof resistive losses than three separate single-phase systems for thesame net power transmission.

Almost all transmission and distribution of electrical power is done viathree-phase systems. That is why the most common arrangement ofwires seen on a power pole is to have three conductors. Sometimes, andmost often nearer to consumers than to generators, a fourth conductor(the neutral wire) will be seen.

Occasionally, just two conductors will be seen on power poles. This isusually a single-phase circuit. In some circumstances (usually only inremote areas), the earth itself is used in place of one of the conductors.This results in a single wire, earth return (SWER) system!

Figure 4.16 shows a power pole carrying a three-phase supply (at 11 kV)on the upper crossarm, and a three-phase plus neutral (at 415/240 V) onthe lower crossarm. The wires exiting to the left and right of the pictureare providing single-phase supplies to three adjacent houses. The angledbar mounted lower down the pole is a streetlight.


Figure 4.16 Power pole carrying a three-phase system at 11 kV and three-phase plus neutral at 415/240 V

Electrical supply voltages are highly dangerous. Do not touch, or evenget close to, the electrical wires supplying your home, or any otherbuilding.

What sort of electrical supply feeds your home? Is it single-phase (twowires) or three-phase (four wires)? You should be able to tell by lookingwhere the wires are connected to the house.

If you have three-phase connected, ask somebody which appliances inyour home run on three-phase supply.

If you have a single-phase supply, try to locate where the nearest three-phase supply is to your home. You should be able to follow the wiresback towards their source.



Generating voltages and losses

The main coal-fired stations in New South Wales typically generatepower at around 20 kV. For example, Liddell generates at 22 kV, whileEraring and Bayswater both generate at 23 kV. Power is generated usingthe three-phase system to maintain constant power and hence torque inthe generator.

The choice of generating voltage used in generating plants represents atrade-off between the insulation needed to withstand higher operatingvoltages and the resistive losses associated with high currents.

Higher voltages require a greater level of insulation to prevent shortcircuits. Insulation increases the initial cost of the equipment. Hence itwould appear that low voltages would be preferable for generation.

Recall that power is the product of voltage and current; that is P = V x I.For a constant generator power, lower voltage results in increasedcurrent.

All conductors, such as commonly used copper, have a resistance.Consequently, when a current flows through such a conductor, some heatis generated (so-called ‘resistive losses’). In a generator, the heat that isproduced is difficult to dissipate because the generator is a rotatingmachine, and cooling pipes need to be able to rotate with the machine.

We can calculate the amount of power lost through P = V x I = (I x R) x I = I2R.Note that the power lost is proportional to the square of the current.This indicates that resistive losses can be minimised by reducing the current.

Thus, on the one hand, we want to reduce voltage to reduce insulatingcosts, but on the other hand we want to reduce the current to minimiseresistive losses. There is no simple answer. The generating voltages of22–23 kV represent an engineering compromise between these twofactors. We will see later that the optimal compromise for this sameproblem in transmission lines results in much higher voltages than areused for generation.

Electrical transmission

The transmission system represents the main arterial route fortransmitting large quantities of electrical energy. The transmissionsystem connects the generating sites with regions of significant demand(cities, large towns, large industries and mines). The transmissionnetwork in New South Wales is administered centrally by TransGrid.


The transmission network is highly visible (some would say too visible),and perhaps looks deceptively simple. It represents, however, one of thebackbones of our technological society. The key components of thesystem are:

• transmission towers

• insulators

• conductors

• transformers

• switchyards

• protection systems

• metering systems.

Transmission towers

The transmission towers are probably the most prominent part of thetransmission system. Towers on the principal links are often constructedof fabricated steel, while structures on lesser links may be based onconcrete or wooden poles.

Figure 4.17 shows a steel transmission tower. The tower is carryingthree-phase power at 330 kV. The multiple conductors are used toreduce resistive losses. This particular tower is unusual in that it is theend of the line: the conductors are terminated on this tower and go nofurther.


Figure 4.17 Steel tower carrying transmission lines

The spacing of the towers is very dependent on the nature of the land thelines cross. On flat land, the spacings between towers are quite even, andof the order of hundreds of metres apart. In rough country (over moutainranges) towers can be very close together or far apart, depending on thelocation of towers required to maintain a minimum clearance above theground.

Insulators

The insulators are necessary to isolate the current carrying conductorsfrom each other and from the ground. These insulators may besuspended from transmission towers, or may be found on ground basedplant such as transformers and protection equipment. Figure 4.18 shows atypical disc insulator.

As a general rule, the number of insulating discs is indicative of thevoltage at which the system was designed to operate. That is, a systemdesigned to operate at 500 kV will have more insulating discs than asystem designed to operate at 220 kV.

The insulators themselves are typically made from glazed porcelaindiscs, with galvanised steel fittings on either side. Steel is, of course,conductive, and hence the insulating properties are achieved from theporcelain components only.


Insulators are generally maintenance free. However, under someconditions the surface of the insulating discs can become contaminatedwith conductive particles. While this occasionally results in a completefailure of the insulator, it is not uncommon to hear a crackling noise orsee a faint glow at night from the insulators as small amounts of currenttrickle over the surface of the dirty insulator, especially in wet or dampconditions.

Figure 4.18 Close up of high voltage disc insulators

Conductors

The electrical conductors carry the current throughout the system.Historically, these conductors have been made from copper. Over the lastfew decades, however, aluminium has replaced copper in many situationsdue to the decreased cost and weight of aluminium over copper.

Electrical conductors are subject to a phenomenon known as ‘skineffect’. This phenomenon results in a non-uniform current density acrossthe section of a conductor. In particular, more current flows closer to thesurface of the conductor (the ‘skin’) than it does down the middle. Thusin conductors with large cross sections, the central core of the conductoris essentially wasted as negligible current flows there.

Electrical conductors used in transmission lines (and distributionnetworks) are thus made up of multiple thin strands twisted together.This gives more surface area (‘skin’) for a given diameter of conductor,and the resulting conductor has effectively a lower resistance (there ismore conducting material where it is needed) as see in figure 4.19.


At very high voltages, the phenomenon is even more pronounced. Thatis why on high voltage transmission towers you will often see four smalldiameter conductors in close proximity to each other on each phase of thesystem. These four conductors give more surface area than one largerconductor, again enhancing transmission efficiency.

Multicore conductor. Theouter conductors havemore “skin” area than asingle solid conductor ofthe same cross sectionalarea. The centreconductor is steel fornecessary tensilestrength.

Single solid conductorshowing higher currentdensity on thecircumference, withnegligible current in thecentre.

Multiple multicoreconductor. High voltagetransmission lines usespacers to separatemultiple conductors.Again, steel cores givetensile strength.

Figure 4.19 Typical current densities in solid, multicore, and multiple multicore conductors


Transformers

It was noted above that for a given power, generator voltages represent acompromise between the level of insulation needed to withstand highervoltages, and the resistive losses associated with current carryingconductors.

While the best compromise for generators is of the order of 20 kV, this isnot necessarily the case for transmission lines. The compromise fortransmission lines results in optimal transmission voltages of 200 kV to500kV, with a consequential reduction in transmission currents.

What factors do you think contribute towards higher voltages and reducedcurrents for transmission than are used for generation?

(Hint: think about the distances involved.)

There is thus a need to be able to increase the voltage and decrease thecurrent (while keeping total power constant) where the generator isconnected to the transmission line. A device that achieves this is called a‘transformer’.


Transformers work by converting the electrical energy into magneticenergy through a wire coil wrapped around an iron core (somewhatsimilar to an electromagnet). The iron core has a second coil of wirewrapped around it, with the second coil having a different number ofturns to the first coil. The second coil is connected to the output of thetransformer. The magnetic energy produced by the first coil is absorbedby the second coil, which results in a current flowing in that coil. Figure4. 20 illustrates the principle involved.

Magnetic flux

Magnetic flux

Vp

Primarywinding Secondary

winding

Vs

s

Figure 4.20 Principle of operation of a power transformer

The ratio of the number of turns (of wire) on each coil determines theratio of the voltages produced in each coil (circuit). We can usetransformers to step up (increase) voltages and also to stepdown(decrease) voltages, with corresponding decreases and increases in theassociated currents respectively.

The power at the input (the ‘primary winding’) is virtually the same asthe power at the output (the ‘secondary winding’). There is some loss ofenergy in the transformer, but this is usually negligible in comparisonwith the amount of power passing through the transformer.

Transformers can be found at both ends of a transmission line: at thegenerating end to increase the voltage from around 20 kV to 330 or 500kV, and at the end of the transmission line to decrease the voltage fordistribution to consumers. (They are also used extensively in thedistribution network to further reduce voltages before they are connectedto your home.)

What would be the consequences of operating an electrical power systemwithout transformers?


Transformers tend to be large uninteresting looking boxes, invariablypainted grey. They have two sets of insulating posts to accommodate theprimary and secondary windings. The transformers are usually filledwith oil to help keep the internal conductors cool (remember thoseresistive losses?) and to help insulate the windings. Larger transformersalso have radiators and fans attached to cool the oil.

Figure 4.21 shows a large power transformer. (This one is actually atEraring power station.) The radiators and cooling fans can be clearlyseen. The ceramic post insulator seen protruding from the top of thetransformer is close to two metres in length – this gives some idea of thesize of the transformer.

Figure 4.21 Typical high voltage transformer showing cooling radiators and fans

Why do you think transformers need oil cooling, where as transmissionlines, which carry the same amount of power, do not?

(Hint: think about how to dissipate heat caused by resistive losses insidethe windings of the coils.)


Switchyards

A diagram of the transmission system of New South Wales shows thatsome transmission lines are duplicated, that is, some areas can be fed viamultiple paths.

This situation is beneficial from the point of view of redundancy. If oneof the duplicated lines fails, the load may be diverted through theremaining functional lines. In order to be able to perform thesediversions, some form of switching must be used.

Transmission switchyards need to be carefully laid out so that the highvoltages they withstand do not short circuit between conductors, or toearth. All of the switches need to be rated to withstand the very highvoltages and currents. The yards also need to be safe both for operationaland maintenance personnel.

Switching can be very dangerous.

The switches require a more sophisticated technology than that found indomestic 240 Volt 10 Amp applications. High voltage switchgear usescontacts immersed in inert gases or oil to quickly extinguish theinevitable electric arcs resulting from opening a high current circuit.

Figure 4.22 shows a typical high voltage switchyard. (This one is atWaratah in Newcastle.) The switchyard is fed from a 330 kV supply thatenters from the top left. The yard enables switching of supply frommultiple incoming feeders (transmission lines) to multiple outgoingfeeders. All of the live conductors are supported on large insulators.

Figure 4.22 High voltage switchyard


Protection systems

Power systems represent both a substantial monetary investment, and anessential service. We want to protect them, and users of the system, fromdamage that might be caused by internal or external faults.

In thinking here about protection, we focus on electrical protectionmechanisms as opposed to mechanical protection. For example, adomestic fan heater has mechanical protection to stop users fromtouching live electrical parts. It also usually has electrical protection inthe form of:

• an earth connection to prevent the external casing from becomingelectrically live caused by a breakdown in the insulation

• an earth leakage protection circuit (either in the heater itself or in thedomestic switchboard) to switch the power off if current flows in theearth lead (which indicates a fault in the insulation)

• a fuse or circuit breaker (either in the heater itself or in the domesticswitchboard) to prevent fire in the case of over currents caused by ashort circuit.

Electrical protection in a grid network is similar, though more elaborate,than that found in domestic installations. The most common forms ofprotection are:

• over current

Electrical conductors in the network are designed to withstandcurrents up to a fixed maximum, beyond which they may fail due tooverheating caused by resistive losses. If the current in a conductorexceeds a preset threshold, the overcurrent circuit breaker protectionis triggered, isolating that link. The overcurrent circuit breaker issimilar in principle to the circuit breakers found in domesticinstallations, but of course is much larger and more sophisticated tohandle the higher currents and voltages.

• over voltage

Insulation in the network is designed to withstand a certainmaximum voltage, beyond which the insulation may fail causing ashort circuit. If the voltage at some point in the network exceeds apreset threshold, the over voltage protection trips a circuit breaker,again isolating that link.

• under voltage

Recall that power is the product of voltage and current. If the systemvoltage is allowed to fall too low, then the current in any constantpower devices connected to the system will increase. Highercurrents increase resistive losses (remember P I R= 2 ) and can cause


those devices to overheat. Hence there is a need to protect the systemfrom operating under specified voltages.

• lightning

A direct lightning strike onto power lines or associated infrastructurecan cause excessive voltages and currents in the system. Lightningdoes strike in the same place twice, especially when attracted bylarge steel towers dominating the landscape.

The transmission system has lightning conductors located above thevarious apparatus to prevent direct strikes from hitting the mainconductors. On transmission towers and lines, one or two thinconductors are positioned above the main conductors attached to thehighest points of the towers for this purpose. In switchyards, tallsteel towers (sometimes with lightning-attracting aerials) arepositioned between and around the main equipment.

Figure 4.22 showed a high voltage switchyard. The steel towers andaerials seen rising above the main conductors and switches are forlightning protection. These aerials are connected directly to earthand protect the yard from direct lightning strikes.

• earth leakage

If there is a fault on the transmission line causing some or all of thecurrent to flow to earth (for example, through a fallen tree touchingpower lines and the ground), that same current must also flow fromthe earth back into the transmission system at some other point tocomplete the circuit. The earth leakage protection monitorsconductors connecting the transmission system to earth, and if acurrent in the earth link is detected (indicating a fault elsewhere onthe system), the circuit breakers are tripped preventing furtherpossible damage to life or property. The same principle is used inearth leakage relays in domestic and industrial systems.

• thermal overload

If transformers or other equipment in a system get too hot, it isusually indicative of a fault developing in that equipment. Thethermal overload protection is designed to generate alarms, or isolateequipment, if excessive temperatures are detected.

• moisture penetration

While pure water is an insulator, contaminated water is invariably aconductor. If moisture penetrates into transformers, circuit breakersor other enclosed apparatus, the insulation in that equipment canbreak down, causing a short circuit.


Metering systems

It is important to monitor key variables in the system (such as power,current and frequency) so that the system can be kept within designedoperating limits. The monitoring equipment has to be able to carry fullload current at transmission voltages without compromising the integrityof the insulation.

Metering is an equally important task. The role of the transmissionsystem is to deliver power to the distribution network, for on-selling toconsumers. Invariably, the transmission and distribution networks aremanaged by different organisations, and hence there is a need to meterpower so that appropriate billing can be arranged.

The distribution system

The transmission system is used to carry bulk electrical energy from thegenerating sites to the main population centres. From here, the electricityis distributed to consumers via the distribution network.

The distribution network in New South Wales is administered by anumber of energy retailers:

• Energy Australia

• NorthPower

• Integral Energy

• Great Southern Energy

• Advance Energy

• Australian Inland Energy.

Who supplies electricity to your home? What area does that suppliercover?

In general, the distribution network contains many of the principalcomponents already described in the transmission network. For example,transformers, switchyards, protection equipment and metering andmonitoring equipment all perform the same roles in a distributionnetwork as in a transmission network.

The key differences between distribution and transmission networks are:

• no generation

The distribution system has traditionally not included any sources ofpower, instead simply distributing the power obtained from thetransmission system.


(Deregulation of the power industry in New South Wales has inrecent times encouraged the state’s electrical energy retailers, whoare invariably also responsible for the distribution network, todiversify into alternate or ‘green’ energy production, and toencourage cogeneration by their consumers.)

• many more lines

The distribution network is numerically more dense than thetransmission network. There are many more power poles,switchyards, transformers and so on in the distribution network.This is simply because there are many more consumers to beserviced, with these consumers being spread over a more diversearea.

• lower operating voltages

By the time the power reaches the individual distribution lines, thetotal power in each line is relatively small, given that there are somany lines going to different areas. Consequently, the need toincrease voltage to reduce resistive losses is less significant. Thedistribution network thus uses system voltages of 132 kV down to11kV, and then 415/240 V close to the consumer. The lowervoltages also provide a safer working environment where there arehigher populations, and offer savings in terms of lesser insulationrequirements.

Figure 4.23 shows a typical distribution transformer found in manyurban areas.

Three-phase 11 kV is carried on three conductors on the uppermostcrossarm. The next highest crossarm is carrying a set of fuses thatprotect the 11 kV supply from faults in the transformer below. Theshort crossarm below the fuses carries 11 kV insulator posts to holdthe 11 kV conductors securely in place as they pass between the415/240 V conductors on the way to the transformer.

The fourth crossarm from the top carries the 415/240 V supply fromthe transformer for distribution to households in the area. Note thatthis supply has four conductors – one for each phase, and one for theneutral wire. The transformer itself is oil filled and has cooling finson its outer casing.


Figure 4.23 Typical 11 kv to 415/240 V distribution transformer

Why might distribution networks use poles instead of towers forsupporting the network? (Hint: the higher the system voltage, the greaterseparation must be maintained between the conductors of each of thethree phases, and between each phase and the ground.)

• more ring feeds

We observed previously that some areas of the state enjoy duplicateor ‘ring’ feed by transmission lines feeding those regions. Thesering feeds offer the possibility of continuity of supply when one ofthe feeders is out of service.

The distribution network has many such ring feeds, particularly inurban areas, that permit continuity of supply when feeders are takenout of service by fault or for routine maintenance.

• higher proportion underground, particularly in urban areas:

There is increasing pressure on power authorities to put theirnetworks underground (instead of leaving them on overheadstructures), particularly in urban areas. This pressure is both byconsumers seeking more reliable power supplies, and byenvironmental groups seeking a more aesthetically pleasinglandscape. However, the capital cost (that is, initial cost) ofunderground cabling is many times that of overhead construction,with these costs rising with increasing system voltages and currents.


Distribution authorities have more of their network underground thanhave transmission authorities. Figure 4.24 shows a cablehead, whereoverhead power lines are connected to an underground cable. Theseconversions are common at the boundary between an older residentialsubdivision (with overhead conductors) and a newer subdivision (withunderground supplies).

Figure 4.24 Cablehead where overhead power lines are converted tounderground cable


Principles of electrical motors

Approximately 99%of all power generated is done so via rotatingelectrical machines. Similarly, approximately 75% of all electricalpower is consumed in rotating machines. Electrical machines areimportant!

Motors (and generators) have evolved for around 100 years. Manyclever minds have been applied to the task of inventing, refining andapplying all manner of machines to many different and specificapplications. Consequently, we cannot expect to understand all of thetypes of motors that exist.

Our aim is to understand the principles of operation of the most commontypes of motors, and to appreciate why particular types of motors areemployed in specific applications.

How many electric motors do you think there are in your house?

Motors

In Household appliances you learned about magnetic induction and howan induction motor works. You will now look at some other kinds ofmotors.

Synchronous motors

Consider the arrangement of magnets shown in figure 4.25. If we wereto slide the stator magnets in an arc around the rotor magnet, we couldinduce the rotor magnet to rotate.


Resultanttorque

Rotor magnetFixed stator magnet Fixed stator magnet

Figure 4.25 Configuration of permanent bar magnets to induce torque

This is the principle of the synchronous motor.

In practice, it is not quite that easy: in order to rotate the stator magnets,we would need a motor. But we are trying to make a motor …

Single-phase synchronous motor

In figure 4.26, the permanent magnets have all been replaced withelectromagnets. Each is a wire coil around an iron core. Remember thatwhen a current flows through a coil, a magnetic field is set up, similar tothat produced by a permanent magnet. The iron core simply strengthensthe magnetic field produced.

Torque

Figure 4.26 An electrical machine to generate torque

If we supply DC current to the stator coils, the magnetic field producedby the stator electromagnets will always be in the same direction. Atorque is induced on the rotor coil that tries to align the rotor and statormagnetic fields. That is, the rotor will tend to spin until its north andsouth poles align with the south and north of the stator.

If, on the other hand, we were to supply an alternating current to thestator coils, the magnetic poles would change their polarity every half-cycle of the electrical supply. That is, for the positive half cycle of theAC waveform the stator magnets would be, say, N – S, and for thenegative half cycle of the supply, the magnets would reverse to S – N.See figure 4.27. Note that the cross and dot in a circle on either side ofthe magnet represent several windings of a coil with an iron core.


Power supplyPower supply

Figure 4.27 Stator fed by alternating current to give oscillating magnetic field

Suppose we were to place a rotor in this oscillating field. The rotormight be a permanent magnet, or an electromagnet fed by a direct current(both of which give a constant magnetic field).

Initially the north pole of the rotor will be attracted to the south pole ofthe stator, and hence the rotor will rotate to align the magnetic fieldsaccordingly. Then, when the stator field changes polarity, the rotor willrotate another half-revolution in order to align its north pole with thestator's new south pole. Every time the stator changes polarity, the rotoragain spins another half-revolution. We thus have achieved our goal ofcontinuous rotation of the rotor!

Clearly the rate at which the rotor spins is related to the rate at which thestator field changes its polarity. The faster the stator field changes, thefaster the rotor will spin. That is, the rotor and stator speeds are alwayssynchronised. Hence the term ‘synchronous motor’.

If the stator is fed from a fixed frequency supply, such as the 50 Hzmains supply, the rotor will run at a single speed of 3000 revolutions perminute.

Why does the rotor run at 3 000 rpm when the stator is fed with 50 Hzalternating current?

This simple arrangement of a synchronous machine has two potentialproblems:

• if the rotor's magnetic field is aligned at q = 0o or q = 180o to the

stator's magnetic field, the motor has no torque (remember that thetorque is proportional to sin q), and hence the motor cannot start

itself

• the torque produced by the machine is uneven. This variation arisesfrom two sources:

i the alternating current supplying the stator windings is(sinusoidally) time varying: the torque produced is directlyproportional to the magnitude of this current


ii as the rotor spins, the angle q between the stator and rotor

magnetic fields varies, and torque is also proportional to sin q.

Both of these problems can be resolved by adding additional statorwindings as explained below.

Three-phase synchronous motor

Figure 4.28 shows a machine with three pairs of stator windings. Thiscontrasts with the single pair of stator windings shown in the machine offigure 4.26. The pairs of windings are labelled ‘A’, ‘B’ and ‘C’, witheach pair displaced around the circumference of the machine by 120o

from each other (equally spaced).

Coil A Coil A'

Coil B' Coil C

Coil BCoil C'

Figure 4.28 Synchronous motor with three pairs of stator windings

If we now supply the three stator winding pairs with three-phasealternating current (one phase to each pair of windings), the resultingstator magnetic field can be shown (using vector arithmetic) to be ofconstant magnitude, and rotates around the stator at a constant angularvelocity. This is known as a ‘rotating magnetic field’. You have learnedabout this technique already. It is used in the induction motor.

This situation contrasts with the single-phase stator where the magnitudeof the magnetic field varies sinusoidally with time, and only ever liesdiametrically across the machine between the winding cores. Figure 4.29illustrates the rotation of the magnetic field around the three-phase stator.


A A'

B' C

BC'

A A'

B' C

BC'

A A'

B' C

BC'

A A'

B' C

BC'

A A'

B' C

BC'

A A'

B' C

BC'

Figure 4.29 Constant amplitude rotating magnetic field in a three-phase stator winding

The rotating magnetic field achieves the same outcome as if we manuallymoved the permanent magnets of figure 4.25 in an arc around the rotor.

The rotating magnetic field means that there is always a torque imposedon the rotor, regardless of the position of the rotor with respect to thestator windings.

The constant amplitude field ensures that the torque produced is constantinstead of time varying.

The angle q now needs to be more clearly defined. In particular we use qto describe the angle between the stator and rotor magnetic fields (andnot to describe the angle of the rotor with respect to a fixed point on thestator). The torque produced is proportional to the sine of this angle.


This means that the rotor can spin at a synchronous speed (determined bythe frequency of the alternating current supply) with a constant angle qbetween the rotor and stator magnetic fields. Figure 4.30 shows thedefinition of q for a synchronous motor with three-phase stator.

Angle betweenmagnetic fields

Figure 4.30 Definition of q in a rotating magnetic field

Characteristics of synchronous motors

Single-phase synchronous motors are rarely, if ever, used because of theproblems outlined earlier. All practical synchronous machines use three-phase stator windings for the reasons given above.

The rotor winding is fed by a direct current to maintain theelectromagnetic rotor field. Feeding a current to a rotating electromagnetrequires the use of slip rings.

Slip rings allow the rotor to rotate while still maintaining an electricalconnection between the rotor winding and the direct current sourcesupplying it. Figure 4.31 shows a set of slip rings on a synchronousmachine.


Figure 4.31 Slip rings in a synchronous machine

Synchronous motors can only run at the speed of rotation of the stator'smagnetic field.

The torque generated by a synchronous motor is self-regulating in thefollowing sense. If there is negligible load on the rotor it is free tovirtually line up exactly with the stator field (q = 0o).

However, if we attach a significant load torque to the motor (such as apump or fan) the rotor will tend to lag behind the stator field. The torqueproduced by the machine is of course proportional to sin q, and thus qincreases until the motor torque is exactly equal to the load torque.

If the load torque exceeds the maximum motor torque (when q = 90o),

the rotor will lose synchronism with the rotating stator field and stall.This situation is known as ‘pole slipping’.

In practice a synchronous motor with load attached is difficult to start.This is because the rotor needs to accelerate from standstill tosynchronous speed in a very short period of time. This is virtuallyimpossible with any significant inertia on the rotor.

In order to overcome starting problems, special additional windings canbe added to the rotor. These additional windings only contributesignificant torque to the motor while it accelerates. Once at synchronousspeed, these windings do not contribute any torque.

Synchronous motors have limited practical application because of theirlow starting torque and fixed speed.


Direct current (DC) motor

Figure 4.32 shows a machine that is very similar to that shown in figure4.26, but now with many coils distributed around the rotor. Note thatthese additional coils and their spacings are not associated with anyconcepts of three-phase systems. In this instance, we would like as manyadditional coils as we can afford.

Mark

N

S

Mark

N

S

Mark

N

S

Figure 4.32 Direct current motor

A ‘mark’ on the rotor is used in the figure to indicate the rotor positionwith respect to the stator.

The stator is supplied with a direct current. This creates a constantmagnetic field between the stator's north and south magnetic poles. Thelines of flux are not shown for clarity.

The rotor, too, is supplied with direct current.

In the uppermost diagram of figure 4.32, all of the coils on the left hand sideof the rotor have current flowing into the page, while the coils on the righthand side have current flowing out of the page, as indicated in the figure.


These currents produce a constant electromagnetic field in the iron rotorwhose north and south poles are as shown. The location of the boundarybetween coils with opposing current directions is fixed in theconstruction of the machine.

The rotor experiences a torque that seeks to spin it clockwise. It is seenthat the angle between the stator and rotor magnetic fields is 90o,corresponding to the position of maximum torque.

In the middle diagram, the rotor has moved slightly in a clockwisedirection. The direction of currents in the rotor windings, however, is thesame relative to the stator position as in the previous diagram. This hasbeen achieved by switching of current direction in the top and bottomcoils. The magnetic north and south poles have moved anti-clockwisearound the rotor by an angle corresponding to the rotor coil spacing.

The rotor again experiences maximum torque from its interaction withthe stator's magnetic field.

In the lowermost diagram, the rotor has moved further again in aclockwise direction; another coil has had its current direction reversed,and the rotor's magnetic field is again in the same place with respect tothe stator field.

It is evident that if we continue to switch the direction of current in onecoil at a time, we can establish a magnetic field that is rotating withrespect to the rotor, but that is stationary with respect to the stator. (Theangle between the rotor and stator fields is 90o giving maximum torquefrom the machine.)

We have thus enabled the rotor to experience torque whilst rotatingcontinually with respect to the stator. This is the principle of the directcurrent, or dc, motor!

The switching of the direction of the currents in the rotor coils isachieved by means of a cylindrical switch known as a ‘commutator’.This switch is made up of carbon brushes that make contact withindividual segments of a copper cylinder mounted on the rotor. Seefigure 4.33.


Figure 4.33 A commutator on a medium sized DC machine. The commutatorsegments and carbon brushes are evident, as is a slight build-upof carbon on commutator segments.

The commutator is in some ways similar to the slip rings found in asynchronous machine. They both use carbon brushes acting on coppersurfaces attached to the spinning rotor in order to feed current to the rotorcoils. However, the slip rings are continuous around 360o of the rotorcircumference, whereas each commutator segment spans only severaldegrees of the rotor circumference.

The commutator is the weak link in a DC machine. Being anelectromechanical device it requires regular maintenance to ensureproper operation.

If the commutator gets dirty (from build-up of carbon deposits) excessiveheat can be generated by current flowing across a high resistance joint(remember the problems associated with switching high voltages andcurrents).

The carbon brushes themselves must be replaced when they wear. If not,the brushes will become too short to make proper contact with thecommutator segments which results in arcing between brushes andcommutator. Again, this results in excessive heat build-up which canmelt the commutator.

Characteristics of DC motors

Unlike synchronous machines, DC motors do not have a fixed speed. ADC motor can be made to run at any speed (up to a point) by simplyincreasing the stator and/or rotor currents to increase torque (remember


that the torque produced is proportional to the product of the stator androtor currents).

In contrast, alternating current motor speeds are limited by the frequencyof the power supply. This is the principal advantage of DC machines.

The rotor and stator currents can be controlled separately, giving what iscalled a ‘separately excited’ machine, or concurrently giving a ‘series’ or‘shunt’ machine. This enables motor characteristics to be tailored to suitparticular applications. We will look more closely at these conceptslater.

In some DC motors, particularly smaller motors such as those found inmodel cars, the stator is made up of permanent magnets instead of theelectromagnets shown in figure 4.32. This enhances the simplicity androbustness of these motors.

Smaller motors also tend to have fewer rotor coils (and hence fewercommutator segments). For example, small DC motors used in modelcars and trains can have as few as four coils. The number of coils isclearly evident when the number of commutator segments is examined.Again, this is done to reduce complexity and cost of such motors.

Figure 4.34 shows a small DC motor used in a model train.

Figure 4.34 A small permanent magnet DC motor in a model train

DC motors can produce very high starting torques. This characteristicmakes them very suitable for applications where substantial loads have tobe started from rest.

The main disadvantages of DC machines are the high initial cost, thehigh maintenance required on the commutator, and the need to have adirect current supply.


The complexity of the DC motor's commutator adds considerably to theconstruction cost of DC motors, and especially to those motors withmany rotor coils and commutator segments. The subsequentmaintenance required also costs time, and requires the removal fromservice of the motor during the maintenance period.

The direct current supply is problematic given that most of our electricalpower is alternating current produced by synchronous generators. Directcurrents must be obtained through rectification of the alternating current,adding further cost to a DC motor installation. If variable speed isrequired, the DC supply must be made to be variable.

DC machines are losing their significance in modern applications asmore advanced power electronic circuits are devised to enable othermotor types (primarily induction motors) to be run at variable speeds.Many older industrial plants still use DC machines, but their years ofservice are likely to be numbered.

Applications of DC motors

DC motors are used in many applications where variable speed, highstarting torques or high power to size ratios are required. Theseapplications include:

• trains – the motors must be able to start a fully laden train from rest,run at variable speed, and be small enough to fit within the bogies ofthe train

• conveyor systems – here the primary need is high starting torque forstarting under load, though variable speeds can be useful where therate of product delivery needs to be varied

• steel rolling mills – as metal plate is rolled thinner it travels faster(the excess material has to go somewhere!). Variable speed drivesare required to accommodate varying plate thicknesses during therolling process

• model trains, cars and so forth – high power to size ratios andvariable speeds are provided

• electric windows, aerials, windscreen wipers and so forth in cars,trucks and buses – here the primary advantage is that the DC poweris readily available, though the high power to size is also attractive.



Universal motors

We have looked at the principle of operation of a DC motor. In thismachine, a constant magnetic stator field is created using anelectromagnet fed by direct current or by a permanent magnet. The rotorhas direct current fed to it through a commutator.

One might be tempted to ask what would happen if a DC motor wasprovided with alternating current instead of direct current?

The answer is that the motor will still work!

Think again about the DC motor diagram in figure 4.32. Let us assume thatthe rotor and stator are connected to the same alternating current supply.

During the positive half cycle of the supply waveform, the current directionis positive, and the currents in the motor are as shown in figure 4.32.

During the negative half cycle, the direction of the alternating current isreversed. Since the stator and rotor share the same supply, the currents inboth the stator and rotor reverse. This means that all of the north polesbecome south poles, and the south poles become north poles. The motor,however, still experiences torque in the same direction as it did duringthe positive half cycle.

That is, the motor runs in the same direction during both positive andnegative half cycles of the alternating current supply!

While the direction of rotation is constant, the torque produced by themotor is not. Because the magnitude of the AC supply variessinusoidally with time, the torque produced also varies sinusoidally withtime. By comparison, the same machine fed with direct current willproduce constant torque.

Motors that are designed to run on either AC or DC are called ‘universalmotors’.

Characteristics of universal motors

While universal motors can work on either DC or AC supplies, in practicetheir design and construction is optimised for use on AC supplies. Thereason is simple: all of our mains electricity is alternating current. That is,universal motors are designed for use at 240 Volts 50 Hz.

Universal motors can be run at variable speed by controlling themagnitude of the voltage supplied to the motor. As it turns out, it isrelatively simple to build electronics to vary the magnitude of the voltageobtained from the mains; at least it is easier than having to convert the


AC mains into DC, and then vary the voltage of the DC supply. Unlikeother AC motors, the range of speeds of a universal motor is not limited.

Universal motors offer high torque for their size. For relatively smallmotors sizes (no bigger than hand-sized), universal motors produce moretorque than any other AC motor design.

Universal motors, like DC motors, have brushes in them to make contactwith the rotor coils. Like DC machines, the brushes need to bemaintained to ensure proper operation.

The high torque, variable speed and ability to run on AC make thesemotors ideal for domestic applications.

It was noted that a DC motor could also be used as a DC generator.However, the same is not true for universal motors.

Applications of universal motors

Universal motors are used in many appliances found in and around thehome. Almost all hand power tools such as drills, sanders and powersaws use universal motors. Inside the home, universal motors can befound in vacuum cleaners, food blenders and hair dryers. Almost everydomestic appliance with a small motor has a universal motor in it. Figure4. 35 shows a universal motor in an orbital sander.

Figure 4.35 A universal motor in an orbital sander



The induction motor

All of the machines described so far have required some means ofconnecting the rotor to an external power supply (except for the case ofthe permanent magnet synchronous machine). These connections are byway of slip rings in a synchronous machine, and by commutator in DCand universal machines.

Slip rings and commutators are expensive to build, and require on-goingmaintenance during the life of the machine. A motor that has no physicalconnection to the rotor is the induction motor, which you learnt about inHousehold appliances.

Table 2 shows a concise summary of the types of motors we haveconsidered.

Machine type Stator current Rotor current Shaft torquedirection

Comments

Synchronousmotor

AC supplied DC supplied (orpermanentmagnet)

Torqueproduced

Runs at fixed(synchronous)speed only.

DC motor DC supplied (orpermanentmagnet)

DC supplied Torqueproduced

Variable speed.

Universalmotor

AC supplied AC supplied Torqueproduced

Variable speed.

Inductionmotor

AC supplied Induced Torqueproduced

No connectionto rotor.

Table 2 Summary of electrical motors


Introduction to digital systems

The focus on the previous sections has been on applications of electricalpower. In this section we are concerned with information, and therepresentation of information using electrical signals.

We introduce the key concepts of analogue and digital signals, and ofusing binary signalling to represent both logical information (true/false)and arithmetic information (counting and numbers).

The concepts all find significant application in modern transport systems;either on board vehicles or in information and control infrastructure.

Analogue signals

An analogue signal is one that is both continuous in amplitude and intime. A good example of an analogue signal is the ambient temperature.

If we were to measure the temperature at midday, we might observe thatit is, say, 28oC. If we had a more accurate thermometer, we find that thetemperature is actually 28.3oC. A visiting scientist with some veryexpensive equipment might be adamant the temperature is 28.37oC.

The actual temperature need not correspond to an integer number ofdegrees Celsius. In fact, the temperature could be measured arbitrarilyaccurately (to any number of decimal points), assuming we have suitableequipment available.

Furthermore, when the temperature changes, it does so in infinitesimalincrements. That is, the temperature does not jump suddenly from 28oCto 27oC, but instead varies gradually.

Temperature, then, is continuous in amplitude.

The temperature is also continuous in time. We might measure thetemperature once per day, or once per hour, or even every minute. Inbetween our observations, however, there is still a temperature.


Since the temperature is continuous in amplitude and time, we say that itis an ‘analogue’ signal.

Other examples of analogue signals include your own body weight, the speedof a car (although it may be zero for long periods) and the height of a tree.

Can you think of any other analogue signals – that is, variables that arecontinuous in amplitude and time?

Quantisation

In measuring temperature, we usually approximate the temperature to thenearest integer number of degrees. That is, we might say the temperatureis 28oC even though it is in fact 28.3oC, which is generally close enoughfor most of us. We do not bother talking in fractions of a degree.

Most measuring devices have an upper and lower bound on the range they canmeasure. A thermometer, for example, might read from -10o C up to 50oC.

It is important to note that the variable itself being measured is notbounded. The temperature may in fact rise to 200oC. However, ourquantising thermometer will only report 50oC. When the variable exceedsthe measurement range of the instrument, we say that the measurementhas ‘saturated’.

Sampling

The term sampling refers to the frequency at which we take ourmeasurements.

If we measure the temperature every hour, we are said to be sampling ata frequency of 24 times per day. We might get very keen and sample 10times per second. Then our sampling rate would be 10 Hz.

The rate at which we take the measurements generally depends on howquickly we expect the variable to change.

If we are measuring the ambient temperature, observations every hourare usually sufficient to capture the expected variations. If, on the otherhand we measured the temperature once every three months we could notexpect to be able to capture the inevitable daily variations.

It is important to note that sampling does not imply quantisation. Whenwe refer to sampling, we refer to the process of making measurements atregular time intervals. Each of the those measurements, however, can bearbitrarily accurate, and need not be quantised.


Digital signals

A digital signal is one that has been quantised and sampled. That is, theoriginal (usually analogue) signal has been sampled at regular intervals,with each measurement yielding a value from a finite set of possiblevalues.

A digital signal can thus be simply represented by a regular stream ofsymbols.

A digital signal can, but need not, be restricted to two possiblequantisation levels.

A signal that is represented by only two possible levels is called a ‘binarysignal’. Binary signals are used widely as the basis for binary computingmachines, upon which much of modern technology is based. However,common (if technically incorrect) usage of the term ‘digital’ has becomesynonymous with binary systems.

Boolean logic

The term ‘logic’ is used to describe a set of formal relationships betweeninput and output variables.

Input variables are factors that determine whether a particular outcomewill occur, or be true. The output variable describes the particularoutcome that we are interested in.

As a simple example, consider a switch controlling a lamp. The input inthis case is the switch position – it determines whether the lamp will beon or off. The output variable is the illumination of the lamp. The rulesdescribing the relationship are simple: if the switch is in the on position,then the lamp is illuminated.

(Here we have ignored all the other things that might go wrong, such asthe lamp being blown or the power being off. Technically we shouldinclude all of these factors as additional inputs.)

Boolean logic is named after George Boole, an Irish mathematician ofthe 1800’s who undertook pioneering work in the study of logic.

Consider the following scenario. You ask your parents if you can borrowthe family car to drive to Perth. The answer given is ‘No!’ From yourperspective, your parents’ logic seems to be hard to follow.


The main difficulty here is in the number of possible values that eachinput variable can take. In making their decision, your parents will havetaken into account variables such as:

• How long will it take?

• How much school will you miss?

• How much will the petrol cost?

If the possible answers to each question were a simple ‘yes’ or ‘no’, youmight be able to understand the reasoning behind your parents’ decision.But when the variables can take on many possible values, the logicbehind the decision is harder to understand.

Boolean logic is a set of rules specifically relating to logical variablesthat can only take on two possible values. These values might be True –False, Yes – No, or 1-0.

Suppose a particular Boolean expression has two inputs A and B. We canthen consider all possible combinations of A and B (there are four ofthem), and evaluate the expression for each possible combination.

The ability to consider all possible combinations is one of the keyattractions of Boolean, or binary, logic.

If there are M input variables in a Boolean expression, there are 2M

possible combinations to consider. As long as M is fairly small – saythree or four – then we can reasonably consider all possibilities.

Combinational logic circuits

A logic gate is an electrical circuit that is specifically designed toimplement a particular Boolean logic function.

There are literally thousands of different types of gates manufactured.We will restrict ourselves to just three of these: AND, OR and NOT.(Even then, we will look at generic properties only.)

It can be shown that these three types of gates are sufficient to build anylogic circuit that you can design. To do so, we use combinations of AND,OR and NOT gates to implement the various functions. Thesecombinations of gates to implement logic functions gives rise to the term‘combinational logic’. These hardware devices are the fundamentalbuilding blocks of all digital electronic equipment, including PC’s,mobile phones and MP3 players.


Common logic gates

The three logical operators we have considered are AND, OR and NOT.The operators can be represented symbolically as shown in figures 4.36to 4.38.

(It should be noted that the symbols shown in figures 4.36 to 4.38 arecurrently the most frequently used in engineering practice. However, newsymbols are finding their way into some texts, and readers should beaware of these developments.)

Figure 4.36 shows a digital logic circuit with a single AND gate, togetherwith switches A and B to control the inputs, and a lamp Z that isilluminated when the output of the gate is true.

(0 Volts)

(+5 Volts)

+Vcc

[A]

(+5 Volts)

+Vcc

Lamp

ZAND gate

[B]

(0 Volts)

Lamp Z comes on when switch A is on AND switch B is on.

Figure 4.36 Logic circuit with AND gate

The AND gate is represented by the elongated ‘D’ shape. By conventionits inputs are on the left hand side, and its output is on the right hand side.

Let us look more closely at the input. The switch on each gate inputallows one of two possible voltages to be connected to that input of theAND gate. These voltages are +5 Volts to represent a True, and 0 Voltsto represent.

The symbols +Vcc and the three lines used to represent Ground or 0Volts are the conventional electrical symbols for these same voltages.

We can use the switches to represent whether or not the input statement(variable) is true.


In drawing logic ciruits, we do not bother to show the return connectionsthat allows the current to flow back to the source. We assume that suchconnections must always be present for the circuit to work, but do notbother to draw them so that the diagram does not get too cluttered.

Figure 4.37 shows a circuit containing an OR gate. The circuit isarranged with switches and a lamp in the same way as figure 4.36.

Lamp Z comes on when switch A is on OR switch B is on.

+Vcc

[A]+Vcc

Lamp

ZOR gate

[B]

Figure 4.37 Logic circuit with OR gate.

The OR gate is represented by the shape shown. Its left hand side curvesinwards, and the right hand side has a pronounced point.

Figure 4.38 shows a NOT gate. In this case, there is only one inputswitch.

Lamp Z comes on when switch A is not on.

+Vcc

[A]

Lamp

Z

Figure 4.38 Logic circuit with NOT gate

We look to see how these gates can be used to implement logic functions.


Simple logic circuits

Let us revisit a previous example. How can we design a circuit toimplement the logical expression:

‘The bus can depart if the doors are closed and the passengers areseated.’

Figure 4.39 shows a logic circuit to implement this function.

+Vcc

[A]

The bus can depart

Z

Doors are closed

AND gate

+Vcc

[B]Passengers are seated

Figure 4.39 Logic circuit to implement bus departure problem

The statement ‘Doors are closed’ is associated with +Vcc (or +5V ortrue). If the statement is false, the switch should be moved to the lower(0V position).

In practice, we would use a switch physically connected to the door toimplement this part. Then if the doors were open, input A to the ANDgate would be automatically connected to 0V. When the doors closedinput A would be automatically connected to +Vcc.

Input B (‘Passengers are seated’) works the same way. (It is not clearhow we might easily ensure all passengers were seated, but we willassume that such a circuit exists!)

The output lamp Z will be illuminated when the bus is safe to depart.

Let us look now at another problem:

‘The driver should stop the car if the traffic light is red or if there is apedestrian on the crossing or if the wheels fall off.’

This seems straightforward at first, but then we realise that we have threeinputs to manage, while the OR gate in Figure 4.37 had only two inputs.


Figure 4.40 shows a logic circuit that implements the driver stoppingproblem.

+Vcc

[A]

+Vcc

Drivershouldstop

Z

(A or B)

[B]

Traffic lightis red

(A or B) or CPedestrian oncrossing

+Vcc

Wheels fallen off [C]C

Figure 4.40 Logic circuit to implement the driver stopping problem

We can see from figure 4.40 that we have used two two-input OR gatesto solve the problem. We have used the fact that (A OR B) OR C is thesame as A OR B OR C. It can be shown using the laws of Booleanalgebra that such an equality holds.

Not only are AND, OR and NOT gates sufficient to build any logiccircuit, but two-input AND and OR gates, together with one-input NOTgates, is sufficient!

The heart of any microprocessor (the ‘brain’ inside a computer) is adevice called an ‘arithmetic logic unit’. This device, as the namesuggests, is designed to carry out all of the arithmetic and logicalprocesses required by the computer's software. Arithmetic logic units (orALU's) are no more conceptually difficult than the design we have justcompleted. Yes, there are more gates in them, but it is really onlyrepetition of the same concepts.

You might like to try exercises 4.7 and 4.8 in the exercise section. Notethese are optional exercises.


Electrical systems in transport

This section now looks at applications of electrical systems in personaland public transport. This review is necessarily brief: almost everyconceivable means of transport has some degree of electricalinfrastructure.

Perhaps the most simple means of transport is walking.

On the other hand, the most sophisticated means of public transport is themodern aircraft. The term ‘fly by wire’ has been coined to describe aflight control system that relies completely on electronics to function.That is, there is no mechanical connection between the pilot and theprinciple control surfaces (flaps, rudder, etc), but instead electronicsignals are sent from the cockpit to servo mechanisms and motors invarious parts of the aircraft.

Electronics are also used for navigation, communications, and indeed forthe autopilot. Of course, there is also a need to generate significantquantities of electrical power on board the aircraft to supply all of thesesystems. Power generators are duplicated and paralleled to give back-upsystems in case of failures.

In between these extremes are many, many applications of electricalsystems. They are used in cars, trucks, buses, and boats. They are usedfor motive power (that is, propulsion), lighting, heating, entertainment,signalling and communications.

We will not attempt to investigate or describe all of these systems. Instead,we will look at electrical systems in a small sample of transport vehicles.

In each case, we will try to understand these systems in terms of theelectrical concepts we have learned, and to categorise them according tosome simple parameters. This approach will not only foster anappreciation of current technologies, but also enable us to understandnew technologies as they are developed.


Parameterising electrical systems intransport

There are many ways to parameterise electrical systems in transport.For this exercise, we will use the following:

• Is the system used for power/energy, or is it used forinformation/communication?

If power/energy:

• What is the source of energy used to provide the electrical power?

• Does the circuit use AC or DC voltages and currents?

• Is the power being consumed as it is generated, or is the powerassociated with some form of storage?

• What form of energy is the electrical power converted to?

• What quantities of power or energy are being used?

If information/communication:

• What is the source of the information?

• Is the signal analogue or digital?

• Is the main function of the system arithmetic or logical?

• Is the information represented in text or graphical form?

Electrical systems in bicycles

Bicycles are one of the most simple (and indeed efficient) modes oftransport. Most commonly we find only a couple of electrical systems onboard. These are :

• lighting

• speedometer/odometer.

Lighting• Is the system used for power/energy, or is it used for

information/communication?

If we consider a bicycle in isolation, we would argue that lighting is apower application. That is, we are interested in the ability of the lightingsystem to illuminate the road ahead: the more lighting power we have,the better the system.


If we considered a bicycle amongst other traffic in a built-up area withstreet-lighting, we could equally well argue that the lighting system isused as a means of signalling the bicycle's presence to other road users:that is, the lights are a source of information.

For the purposes of this exercise, we will classify the lighting system as apower application.


Historically, bicycle lighting systems were powered by small generatorsdriven directly off the revolving tyre. In this case, the source of powerwas the rider's legs!

More recently, bicycle lighting has been powered by rechargeablebatteries. Figure 4.41 shows a typical battery powered headlamp for abicycle. In this case, the batteries are re-charged using mains poweredchargers.

Figure 4.41 Battery powered bicycle lamp.


The generator supplies AC power. The frequency of that power isproportional to the speed of the rotor, and hence to the speed of thebicycle.

The batteries supply DC power.


In the generator case, the power is consumed as it is generated.

In the case of batteries, the power is being consumed from chemicalenergy stored in the battery.



In each case, the energy is converted to light, and heat. The heatcomponent is undesirable and wasted. Ideally, there would be no heatgenerated.


The lamps in bicycle headlights are of the order of 5 Watts at 6 Volts.This gives a current of 0.8 Amps. The batteries used in the lamps areusually AA-sized rechargeables. These batteries have a storage capacityof around 0.6 to 1 Amp hour.

Speedometer/Odometer• Is the system used for power/energy, or is it used for


A bicycle speedometer/odometer unit is shown in figure 4.42. Thesedevices are used to calculate and display distance travelled, and averageand maximum speeds. The part on the upper left is known as the ‘senderunit’ and is mounted on a spoke. The component on the right is mountedon the frame of the bicycle and detects the sender unit as it passes oneach rotation of the wheel. Electrical pulses are carried by wire to theprocessor unit that is shown on the lower left.

Figure 4.42 Bicycle speedometer/odometer unit


The information is generated by the receiver unit in response to rotationof the bicycle wheel.



The information is considered to be digital, since either a pulse is sent, orit is not. There is no continuous range of signal.


The function of the speedometer/odometer is to calculate distances andspeeds from the pulses received, which are correlated with the unit's owninternal clock. In this sense, the device is performing arithmeticfunctions.


The information provided to the user is in text format, as seen on thescreen of the unit in figure 4.42.

Electrical systems in motorcycles

Figure 4.43 shows a typical road registered motorcycle. Motorcyclescontain many electrical systems not found in bicycles. The types ofelectrical systems found on a typical motorcycle include:

• an alternator to generate electrical power (typical power outputs areof the order 200 to 300 Watts at 12 Volts)

• a battery to store energy for starting and for use when alternatoroutput is too low (for example, while idling with lights on)

• a rectifier to convert the AC current from the alternator into DCcurrent for storage in the battery

• a voltage regulator to limit the voltage supplied to the battery:batteries are designed to have a fixed voltage

• a spark ignition system to supply high voltage pulses to thesparkplugs to ignite the fuel-air mixture in the cylinders

• a starter motor to start the engine

• lights for illumination of the road ahead, for signalling to othertraffic, and for instrumentation (such as warning lights to indicatelow oil pressure)

• a horn to signal your presence to other road users and pedestrians.


Figure 4.43 A road going motorcycle

Brake light system

The brake light system illuminates the rear brake lamp(s) when either thefront brake (lever) or the rear brake (pedal) is activated. The ‘either’function here is identical to the OR logical function seen previously; inthis case, the ‘either’ is implemented by using two switches in parallel(one on the lever, one on the pedal) so that either switch closes the circuitbetween the battery and the brake lamp.


This form of lighting is used to signal the rider's intention (to stop) toother road users behind the motorcycle. Therefore it is used forinformation/communication.


The information source is the switches on both lever and pedal that closethe circuit to the stop lamp.


The stop lamp is either on or off. There is no proportional illumination ofthe lamp to indicate rate of stopping. Hence the signal is digital.


The main function is logical.



The information (that the bike is slowing or stopping) is presented ingraphical form by illumination of the lamp (there are no words to read).

Starter motor• Is the system used for power/energy, or is it used for


The starter motor system is used for power to turn the engine oversufficiently quickly to start it.


The energy for the starter motor comes from the battery. The battery is inturn charged by the alternator that is driven off the engine. The originalenergy source is thus the petrol used to fuel the engine.


The starter motor is a DC motor, chosen for its high starting torque, andfor its ability to run directly off the battery without the need foradditional electronics. The variable speed capability of the DC machineis not used.

The high maintenance usually associated with a DC motor is generallynot a problem with starter motors since they are used relativelyinfrequently, compared to say, an alternator (that runs when the engine isrunning).


The starter motor must use stored energy from the battery, since thealternator is not being driven by the engine before it is started.


The electrical power in the motor is converted to mechanical energy tospin the engine. Some heat is generated in resistive losses inside the DCmotor.


The starter motor is rated at around 700 Watts. (Note that the maximumoutput of the alternator is only around 250–300 Watts.) Given that thebattery voltage is 12 Volts, the current drawn by the starter motor is700/12 = 58 Amps. The battery in a large motorcycle is rated at around15 to 20 Amp hours. Given that we should not discharge a lead acidbattery more than 50 per cent of its (theoretical) capacity, it is clear thatwe should not run the starter motor for too long.


Antilock braking system

Antilock or antiskid braking systems are used to prevent either wheel onthe motorcycle from locking during severe braking. It is important toprevent wheel lockup because the rotating wheels are the principal sourceof gyroscopic stability for the two-wheeled machine. The bike becomesmuch less stable if one wheel is locked. (The bike is almost impossible tocontrol if both wheels lock.) Locking of the front wheel also severelydegrades steering capability.

The antilock system works by monitoring wheel rotation speed using asensor in close proximity to a toothed wheel (usually cast into the wheelitself). The wheel speed sensing technique is not dissimilar to that seen inthe bicycle speedometer/odometer, though in this case there are manymore trigger pulses per revolution of the wheel.

Figure 4.44 shows the toothed rotor on the front wheel of a motorcycle.The wires running from the sensor can just be made out to the right(behind) of the fork tube in line with the rotor teeth.

Figure 4.44 Toothed rotor on antilock braking system of a motorcycle

When the system detects that the wheel has stopped rotating under brakingconditions (determined by activation of the brake light circuit), pressure inthe hydraulic linkage between lever/pedal and the brake caliper is releasedmomentarily to allow the wheel to resume rotating, thus avoiding wheellockup. The hydraulic pressure is released by an electrically operated servo(effectively, an electromagnet that activates a piston in the hydraulic line).



The system is clearly reacting to information provided by the rotorsensor, but its action is one of applying a force to relieve the pressure inthe hydraulic braking line.


The electrical power to energise the pressure relief servo and to run thespeed sensor is provided by the motorcycle's electrical system, whichultimately gets its energy from the fuel fed to the engine.


The motorcycle's electrical system is direct current.


Sufficient current is probably provided by the alternator while the engineis running to power the antilock braking system. However, the battery isan integral part of the electrical system, and can continue to provideelectrical power even if the engine stalls.


The electrical energy is converted into a linear force in the servo.This force acts on hydraulic valves to relieve pressure.


There is some electronics involved in sensing wheel speed.This electronics would draw a few Watts. The servo would consume tensof Watts while it is activated.

Electrical systems in rail transport

We have seen that a motorcycle is significantly more complicated than abicycle in terms of its electrical systems. Rail transport, and in particularthe locomotives and power units in passenger trains are morecomplicated again.

Furthermore, just as we observed that motorcycles are dependent on amuch larger traffic infrastructure that itself has many electricalcomponents, so too does a rail system.

Instead of examining individual components of locomotives or theinfrastructure and classifying them as power or information as we havepreviously for bicycles and motorcycles, in this section we look tounderstand a little about how electric passenger vehicle and dieselelectric locomotives operate.


Electric passenger trains

Figure 4.45 shows a V Set driver motor unit on an electrically poweredpassenger train. These trains are operated by Cityrail on the interurbannetwork between Newcastle, Lithgow and Wollongong. The V sets wereprogressively introduced between 1970 and 1989, and have a maximumspeed of 120 kph.

We will consider the motive power aspects of these trains in terms of theparameters set out above.

Figure 4.45 V Set driver motor carriage operated by CityRail


The trains are used to provide power. (They do of course include manysubsystems used for information/communication, but our focus here is onthe motive power.)


The trains are powered by the overhead electrical supply. This supply isin turn obtained from the mains grid. The rail authority operates its owndistribution network along the rail corridors.

Power is fed from the overhead conductors by a catenary system, withthe return current path being provided by the steel rails on which the trainruns. Figure 4.46 shows a closer view of the pantograph used to makecontact with the overhead wiring. This pantograph is spring loaded so asto be able to maintain vertical pressure on the overhead wire to ensurecontinuity of supply.


Figure 4.46 Pantograph used to connect electric trains to overhead catenary


The New South Wales electric train network was established in the1920s, and was initially restricted to the Sydney suburban areas. Sincethen, the network has expanded to include rail corridors to Newcastle,Lithgow and Wollongong.

The system operates on a voltage of 1500 Volts DC. At the time thenetwork was established, this voltage was considered ideal for the DCmotors that propelled trains with high starting torque and variable speed.More recent developments in motor control technology have made ACdrives more cost efficient, but the substantial investment in the existingnetwork prevents consideration of a change of system voltage.


Power is obtained from the grid network, and hence is consumed as it isproduced. During evening peak hour, when hydro plants are used tosupplement coal-fired power stations, some energy is being obtainedfrom hydro storage.

It is interesting to note that electric trains can regenerate electricity.DC motors can also be used as DC generators.


Trains motoring up the various grades in the network (such as over theBlue Mountains) use considerable energy to lift the train mass to higherelevations. (The typical mass of the unit shown in Figure 4.46 is around60 tonnes. A complete train of four power cars plus four unpoweredtrailers has a mass of around 400 tonnes.)

However, when the trains descend the same grades, the motors are usedas generators, converting the mechanical energy from the train intoelectrical energy for use by other trains on the network. In essence, trainscoming down the Blue Mountains are powering trains climbing the samesection. This technique is called regenerative braking, and is much moreenergy efficient than dissipating the mechanical energy of the train intoheat as is the case with conventional braking systems.


The electrical power consumed by the train motors is converted to kineticenergy in the moving mass of the train.


Each powered unit has four 150 kW motors, operating at 1500 Volts.Each motor thus draws 100 Amps on full load. A train of four power carsthus draws 2400 kW, and 1600 Amps, on full load.

Diesel electric locomotives

Figure 4.47 shows a New South Wales 81 Class diesel electriclocomotive. This form of locomotive uses a diesel engine to drive anelectrical generator to power electric motors geared to the wheels. Theselocomotives are typical of the principal form of motive power employedon railways all over the world.

The 81 Class, introduced into NSW from 1982, were built by ClydeEngineering at Clyde's Kelso plant near Bathurst in Central West NewSouth Wales.

They are used for a variety of purposes, including intercapital freight and(until recently) passenger services, as well as for export coal and grainhaulage. Early on, most of their time was on the southern line or theHunter Valley, though this has now expanded.


Figure 4.47 New South Wales 81 Class diesel electric locomotive


The principal purpose of the locomotives is to provide motive power.


The source of the power is a turbo-charged 16 cylinder 169 litre fourstroke diesel engine. (This is somewhat larger than a typical 8 cylinderfive litre petrol engine used in large cars!) The diesel engine drives mainand auxiliary alternators, and an auxiliary generator that convertsmechanical thrust into electrical power.

The engine idles at a speed of 300 rpm, and has a maximum speed of just900 rpm. It consumes fuel at the rate of approximately 500 litres per 100kms.


The main alternator provides power for the six traction motors (one oneach axle). Since the traction motors are DC, the alternator output has tobe rectified (converted from AC to DC) before feeding the tractionmotors.

An auxiliary alternator provides AC power for the large fans needed tocool the traction motors and main alternator (remember the resistivelosses), the engine cooling radiators, and the dynamic brake.An auxiliary generator is used to provide DC power for other locomotivesystems such as lighting, heating and instrumentation.

Figure 4.48 shows the driver's seat of an 81 class locomotive.The extensive instrumentation to monitor the locomotive's varioussubsystems can be seen set out before the driver.


Figure 4.48 Driver's view in an 81 class diesel electric locomotive


The power generated for traction, cooling and auxiliary systems isconsumed instantaneously.

Some degree of regeneration is possible and is used for ‘dynamicbraking’. In this mode, the DC traction motors are used as generators.The electrical power so produced is dumped (wasted) in a large heatingelement situated on the roof of the locomotive. This provides brakingforce, but does not provide much usable power (the regenerated powercan drive the main alternator, but the diesel fuel cannot be reconstituted!)


The main traction alternator supplies high voltage AC to a power rectifierassembly which then delivers high voltage DC to the traction motors forlocomotive pulling power. The companion alternating current generatorfurnishes power to the static exciter, various transductors, the threeradiator cooling fans, and the inertial separator blower motor. Theauxiliary generator charges the storage battery and supplies low voltagedirect current for the control and lighting circuits.


The diesel engine produces 2640 kW on full load.

The main alternator has a nominal voltage of 600 Volts and can produceup to 7000 Amps for distribution to the six traction motors. The auxiliaryalternator produces around 200 Volts AC, while the auxiliary generatorproduces 10 kW at 72 Volts DC.


Each traction motor consumes over 400 kW of power, with currents ofthe order of 1000 Amps and voltages up to 600 Volts. (The voltage andcurrent are not linearly related in a DC motor under load.).

Figure 4.49 shows a traction motor on the axle of an 81 class locomotive.The four cables feeding the motor represent one pair each for the statorand rotor windings of the DC motor. Six such motors are used, with onebeing hung from each of the locomotive's axles.

Battery capacity is of the order of 420 Amp hours at 72 Volts DC. This isused primarily for starting the diesel engine.

Figure 4.49 Traction motor on the axle of an 81 class diesel electric locomotive

One of the main instruments used by the driver of an 81 class locomotiveto control the speed and load on the motors is the main alternatorammeter. This instrument shows the current being produced by the mainalternator and being fed to the traction motors, and is an indicator of theefficiency at which the locomotive is being operated. The ammeter is thelargest dial on the right of the four dials in figure 4.48.

Turn to the exercise section and complete exercises 4.9 to 4.12.


Exercises

Exercise 4.1

Describe the two main uses for electricity. Give three examples ofdevices that correspond to each usage.

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Exercise 4.2

Complete the following table:

Type ofGenerator

Example ofType

Source ofEnergy

Amount of PowerGenerated byGiven Example

Coal-fired powerstation

Bayswater Coal 2640MW

Wind turbine

Solar power

Hydroelectric

Diesel electriclocomotive

Motorcyclealternator

Bicycle lightingbattery

Exercise 4.3

Explain why three-phase systems are preferred over single-phasesystems in most high power applications.

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Exercise 4.4

a Explain why transmission towers use strings of porcelain discs tosupport electrical conductors.

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b Explain why transmission lines use several small diameterconductors instead of one large diameter conductor for each phase.

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Exercise 4.5

Why are DC motors relatively expensive to manufacture and maintain,particularly in comparison with induction machines.

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Exercise 4.6

a What is a ‘universal motor’.

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b Where are they used?

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c Why are they used?

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Exercise 4.7 – optional extension exercise

Design a combinational logic circuit to implement the followingstatement.

‘The TV will turn on if the door is shut and the lights turned off’.

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Exercise 4.8 – optional extension exercise

Design a logic circuit to implement the following statement:

'A student will pass the subject if her examination mark is greater than50 per cent, or if she completes all of the assessment tasks and submitsthem on time.'

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Exercise 4.9

Evaluate the following three sub-systems found in a modern car accordingto the parameters described in the section on electrical systems in transport.

a windscreen wiper motor

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b tail lights

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c car radio

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Exercise 4.10

A V Class interurban train has a mass of 400 tonnes, and is capable oftravelling at 120 kph.

a How much kinetic energy does the train have a maximum speed?

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b If the train's sixteen DC traction motors are capable of delivering150 kW each, how long does it take for the train to accelerate fromrest to its top speed at its maximum rate of acceleration?

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c What happens to the kinetic energy calculated in part (a) when thetrain slows to a halt at a station?

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Exercise 4.11

The New South Wales railway system has around ten 85 Class andthirty eight 86 Class electric locomotives currently in storage. Bothclasses of locomotive are rated at 2880 kW each, and designed to do thework of diesel electric locomotives in the electrified rail corridorsbetween Newcastle, Lithgow and Wollongong.

The forty eight locomotives are currently set aside in favour of dieselelectric locomotives for use on electrified lines because under the currentpricing structures for diesel and electricity, it is cheaper to run the dieselelectric locomotives than it is to run the electric locomotives.

Give reasons why this policy should be questioned.

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Progress check

In this part you investigated applications of electricity/electronics inengineering.





Ag

ree

Dis

agre

e

Un

cert

ain


• power generation/distribution

– electrical energy and power

• AC/DC circuits

• electric motors used in transport systems

– principles [and] applications

• control technology

– digital technology.

I have learnt to:

• identify the electrical systems used in the transportindustry

• investigate the principles and application of electricmotors used in the transport indusrty

• analyse the basic principles of control technology asapplied to the transport industry

• explain elementary digital logic.



In the next part you will develop your freehand sketching.




Check!


❐ Exercise 4.1

❐ Exercise 4.2

❐ Exercise 4.3

❐ Exercise 4.4

❐ Exercise 4.5

❐ Exercise 4.6

❐ Exercise 4.7 (optional)

❐ Exercise 4.8 (optional)

❐ Exercise 4.9

❐ Exercise 4.10

❐ Exercise 4.11




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Part 5: Transport systems –communications

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Part 5: Transport systems – communications 1

Part 5 contents

Introduction..........................................................................................2

What will you learn?...................................................................2

Orthogonal projection.........................................................................3

Preparing drawing sheet.............................................................5

Technical drawing, the universal language ....................................7

Symbols, AS 1100 101 – 1992....................................................8

Additional AS 1100 standards...................................................21

Exercises............................................................................................37

Progress check .................................................................................53



Introduction

In this part you will consolidate the communications content covered inprevious modules from both the Preliminary Course and the HSCCourse. You will further develop your freehand sketching, completingsome pictorial drawings and designing solutions to orthogonal drawingproblems.

Some of the drawings will require you to use CAD. However, the optionwill be there to complete these drawings using instruments.

You will learn to produce orthogonal drawings involving the use ofAS 1100 standards, and be introduced to some new AS 1100 standards.You will learn how to represent compression springs, knurls, and how toindicate a flat surface on a cylindrical object.

You will further your knowledge of AS 1100 standard dimensioningtechniques, including the standards from AS 1100.101 – 1992 wheresymbols replace the written word for such features as countersink,counterbore, spotface, and spherical surfaces.

You will complete activities in this part to give you more experience inorthogonal drawing.

What will you learn?You will learn about:

• freehand sketching, designs, pictorial, orthogonal

• Australian standard AS 1100

• computer graphics, Computer Assisted Drawing applications solving problems.

You will learn to:

• produce orthogonal drawings applying appropriate AS 1100

• produce quality graphics

• apply dimensing to AS 1100 standards.

Extract from Stage 6 Engineering Studies Syllabus © Board of Studies, NSW, 1999.


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Orthogonal projection

In the Preliminary Course you covered many AS 1100 drawingstandards. You were introduced to standard dimensioning methods,detail drawings and various methods of sectioning. You also were shownhow to prepare a sheet by drawing a border and title block. All of thesewill be used in this section of work.

In Module 1 of the HSC course you were shown some specialisedtechniques used in orthogonal drawing as applied to Civil structures.You learnt the method of representing webs when they are sectioned.You also learnt more about fastenings, standard and special sized nuts,and bolts, and their representation, using AS 1100 standards. Some ofthese techniques will be used again in this part.

References and research

The following notes and exercises were researched from a number ofreference areas.

Past Engineering Science examination papers were referred to formany of the drawings through the Board of Studies web site,<http://www.boardofstudies.nsw.edu.au>.

Research was also conducted at Standards Australia, both at theirinformation centre, referencing the relevant publications and throughtheir web site. The address of Standards Australia is:

1 The Crescent

Homebush NSW 2140

Sales: phone 1300 65 46 46, web site <[email protected]>

Internet site <www.standards.com.au>

The publication used were:

• AS 1100.101-1992 Technical Drawing, Part 101 General principles

• AS 1100.201-1992 Technical Drawing, Part 201 Mechanicalengineering drawing.


The cost of these publication is high, currently $114.00 and $69.50respectively. However, your local library, school library or distanceeducation centre may have a reference copy.

Alternatively, an abridged version is available, SAA/SNZ HB1: 1994Technical drawing for students, the current student price is $17.60. Thisis not a replacement for AS 1100, but contains information that StandardsAustralia considers sufficient for technical drawing students, bothsecondary and tertiary.

AS 1100 standards also contain three other parts but these are notconsidered to be included in the content of the syllabus. They are:

• AS 1100.301–1985 Technical Drawing, Part 301 Architecturaldrawing, plus 1 supplement – 1986

• AS 1100.401–1984 Technical Drawing, Part 401 Engineering surveydrawing, plus 4 supplements – 1984

• AS 1100.501–1985 Technical Drawing, Part 501 Structuralengineering drawing, plus 1 supplement – 1986.

Textbooks with current AS 1100 standards are not always available.Some of the standards used have been superseded by the 1992publication. When using textbooks you must be aware that the standardsmay have changed. If unsure, refer to the notes in these modules ofwork, they are current.

Some of the textbooks that contain drawing relevant to your course are:

• Boundy, A .W. and Hass, I. L. 1992, Technical Drawing, An AustralianCourse in Graphics, McGaw Hill, Sydney.

• Mullins, R. K. and Cooper, D. A. 1977, Programmed Technical Drawing,Book 1, Book 2 and Book 3, Hutchinson, London.

• Park, A. Dodds, K. and Bland, S. 1989, Technical Drawing, LongmanCheshire, Melbourne.

• Rochford, J. 2000, Engineering Studies – A Student’s Workbook,KJS Publications, Gosford.

Other publications, such as those used in Distance Education Centres andSchools, are good reference materials.

Engineering Science – 2 Unit Course

Technical Drawing, Lobes 1, 2 and 3 are excellent

TAFE – Introduction to CAD – Using AutoCAD.

Many schools have developed their own resources and programs forteaching technical drawing and you may be able to access some of these.

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Preparing a drawing sheet

Borders, title blocks and materials lists

In the preliminary module on Landscape Products you were introduced toborders, title blocks and materials lists. You will need to refer to thissection of work when you commence the drawing exercises. However,the title block will be modified to suit the HSC course and to cover therequirements of AS 1100 standards.

From now on all of your drawing sheets must have a border and titleblock. The exercises you have to complete will be presented to you onsheets with a border and title block.

For your engineering report, all drawings completed by you must also bepresented with a border and title block, and, if necessary, a materials list.A convenient way to do this is to draw the border and title block using aCAD or Draw Program, and saving the drawing to disk. Whenever youneed to complete a drawing exercise you can print off a copy of theprepared sheet using the computer, then use the sheet for your drawing.

Exercise 5.1 will require you to prepare a sheet with a title block andborder, using a CAD program, or alternatively, using technical drawinginstruments. Copies of this prepared sheet can then be used each timeyou have to complete a drawing.

AS 1100.101 – 1992. Title block requirements

The title block featured in the communication section of Landscapeproducts will now be developed.

The new title block will include a logogram, that is, a symbol thatindicate the angle of projection used to complete the orthogonal drawing.The preferred method is third angle projection, so you will learn to drawthe third angle projection logogram.

The title block also needs to include the size of the drawing sheet onwhich the original drawing was completed. This is required asmeasurements are sometimes scaled from the drawing. If the drawinghas been reduced by photocopying, or printed to a reduced scale, themethod of scaling from the drawing will produce an incorrect dimension.If the size of the original drawing sheet is given, this problem can beavoided.

Another addition to the title block is the date that the drawing iscompleted. This is important in industry as often the drawings aremodified and the date can be used to indicate which drawing is current.


These changes require the original sizes to be modified. The left handcolumn needs to be enlarged to 25 mm, the right hand column to 20mm,and the space for the Drawing Title reduced to 80 mm. All other sizesremain the same.

The following figure shows the new sizes and modifications to be used inyour HSC course.

DATEDRAWN

THIRDANGLE LOGO

DRAWING TITLE

STUDENT NAME SCALE USED

DRAWINGNUMBER

SHEETSIZE (A4)

25 50 30 20

1010

SAMPLE HSC TITLE BLOCK

DISTED STUDENT SCALE 1:1

WE 5.112 - 2 - 01

A4

Figure 5.1 Title block (not to scale)

Third angle projection logogram

There are no standard sizes given in the AS 1100 standards book for thethird angle projection logogram. The sizes given in the drawing belowwill produce a logogram similar in proportion to the ones drawn in thestandards book, and will give a logogram that will fit into the 10 mm x25 mm space on the left hand side of the title block.

6 7 9 3

10

Ø 4

Ø 8

SCALE 2:1

Figure 5.2 Sizes for the third angle projection logogram


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Technical drawing, the universal language

Technical drawing is used to convey specific design, manufacturing andtechnical information quickly, accurately and without ambiguity so thatthe receiver understands fully the information supplied and items can bemanufactured to fulfil their function.

With the growth of electronic technology, and since 1989, the use of theWorld Wide Web, technical drawings can be transmitted almostinstantaneously throughout the world. The drawings need to be read,interpreted and understood internationally.

Technical drawings have been standardized, world wide, through theInternational Organisation for Standardisation, (ISO). StandardsAustralia is a member of, and active participant in this organization.

Technical drawing is the only international and universal language, thatis understood and used throughout the world. Symbols have been usedextensively to replace written notes and words on drawings. Symbols areindependent of language and therefore can be more easily understood.

New symbols were introduced in the revised standard AS 1100.101 –1992 to replace notes and abbreviations for; countersink, counterbore,spotface, depth of a hole, spherical diameter and spherical radius.

You need to know and be able to interpret these symbols.


Symbols, AS 1100.101 – 1992

Shape of holes

The shape of a hole can be square or round. The shape is indicated bythe symbol preceding the size of the hole.

A square hole of size 15 mm is indicated as shown in the followingdiagram. Note that when no depth is given, the hole passes right throughthe component. This is a very important standard which must beinterpreted correctly for the correct manufacture of a product.

2 x 15

TOP VIEW

FRONT VIEW

SYMBOL

SIZE h

Figure 5.3 Indicating a square, through hole

The standard sizes, which must be used for the symbols, are given withreference to ‘h’, where ‘h’ is the size of the dimensioning that is beingused on the drawing.

A round hole of diameter 15 mm is indicated as shown in the followingdiagram. Note that again no depth is indicated, so the hole passes rightthrough the component.

4 x 15

TOP VIEW

FRONT VIEW

SYMBOL

SIZE h

1.4

h

60∞

Figure 5.4 Indicating a round, through hole

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Depth of holes

The depth of a hole is indicated by the depth symbol, followed by therequired depth of the hole. As indicated in the Preliminary module onBraking systems, the depth of a round hole is always measured as thedistance of the full diameter of the hole, and does not include the distanceto the pointed end.

A round hole of diameter 10 mm and depth 25 mm is indicated as shownin the following diagram.

SYMBOL

SIZE h

h

0.6 h drill

10

TOP VIEW

FRONT VIEW

25

DE

PT

H

Figure 5.5 Indicating a round hole of depth 25 mm

Countersink

The countersinking of a hole is used to widen the top of a drilled hole toprovide a tapered seat that allows a countersunk screw to fit flush with,or just below the surface of a component. A tapered, countersink drill isused to countersink the drilled hole.

The countersink is indicated by the countersink symbol, followed by thediameter of the top of the countersink, and the required angle of thetapered hole. The countersink details are given in conjunction with thesize of the original hole and are written after the given size of the originalhole as indicated in figure 5.6.

Previous standards used the abbreviation ‘C’sink’. You may still see thisused in older textbooks and drawings. You should be able to appreciatewhy the ISO and Australian Standards prefer to use symbols for thisuniversal language.


A round hole of diameter 8 mm, passing through the component,countersunk diameter 16 mm at an angle of 90∞ is shown in the following

diagram.

SYMBOL

countersinkdrill

SIZE h

90∞

8

TOP VIEW

FRONT VIEW

16 x 90∞

Figure 5.6 Indicating a countersink on a round hole

Counterbore

The counterboring of a hole is used to widen the top of a drilled hole toprovide a cylindrical seat that allows a socket head screw to fit flushwith, or just below the surface of a component. A specialized,cylindrical, counterbore drill is used to counterbore the drilled hole.

The counterbore is indicated by the counterbore symbol, followed by thediameter of the counterbore. The depth is then given, using the depthsymbol followed by the required depth.

Again, the counterbore details are given in conjunction with the size ofthe original hole and are written after the given size of the original holeas indicated in the diagram below.

Previous standards used the abbreviation ‘C’bore’. Again, you may stillsee this used in older textbooks and drawings.

A round hole of diameter 8 mm, passing through the component,counterbored diameter 16 mm to a depth of 6 mm is shown in thefollowing diagram.

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SYMBOL

counterboredrill

8

TOP VIEW

FRONT VIEW

16

SIZE h

2 h 6

Figure 5.7 Indicating a counterbore on a round hole

Turn to the exercise section and complete exercise 5.2

Spotface

Spotfacing is used to provide a flat surface on a rough or curved area toallow a nut or bolt to fit flush with the surface of a component. Aspecialised spotfacing drill is used to form the flat surface around the topof the previously drilled hole.

The spotface is indicated by the spotface symbol, followed by thediameter of the spotface. The spotfacing operation produces a flat surfaceso depth is not required. Note that the spotface symbol is the same as thecounterbore symbol, but that in the spotfacing operation no depth isindicated.

Previous standards used the abbreviation ‘S’face’. Again, you may stillsee this used in older textbooks and drawings.

A round hole, diameter 12 mm, passing through the component, spotfacediameter 25 mm is shown in the following diagram.


SYMBOL

spotfacetool

TOP VIEW

SIZE h

2 h

(no depth)

FRONT VIEW

25

12

Figure 5.8 Indicating a spotface on a round hole

Spherical radius and spherical diameter

Spherical radius is indicated using the letters SR before the given size.Spherical diameter is indicated using the letters S followed by thediameter symbol, then the given size.

Previous standards used the abbreviation ‘Spher’. Again, you may stillsee this used in older textbooks and drawings.

A spherical radius of 20 mm and a spherical diameter of 40 mm areshown in figure 5.9.

SR 20

SYMBOL SR

S 40

SSYMBOL

Figure 5.9 Indicating a spherical radius and a spherical diameter

Dimensioning chamfers

Chamfers must be dimensioned so that the size and the angle of thechamfer are fully described. Various methods are shown in the standardsbook, you only need to be shown two methods, a normal size chamferand a small chamfer.

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The method of dimensioning a small chamfer is used only when thedrawing of the chamfer is too small for the conventional method to beused. The example shown below is for a 0.5 mm chamfer, drawn to ascale of 1:1, that is full size.

You must be careful when a ‘small chamfer’ is drawn using an enlargingscale. If the 0.5 mm chamfer was drawn to a scale of 10:1, that is tentimes full size, the chamfer would no longer be considered as a ‘smallchamfer’, and thus would be dimensioned using the conventionalmethod.

10 x 45∞ 0.5 x 45∞

LARGE CHAMFER SMALL CHAMFER

Figure 5.10 Dimensioning chamfers

Worked example 5.1

Worked example 5.1 is the first of five worked examples. It shows adrawing that incorporates the work that has been covered in the notes. Inthis example, the use of a border, the modified title block and the thirdangle projection logogram are shown.

The worked examples will also be used to revise some of the AS 1100standards and drawing methods that you used in previouscommunication’s exercises. In this example, a detail drawing of a locknut is presented. The drawing sheet was prepared using a CAD program.

Lock nut

A lock nut is used to ensure that the assembled parts remain tightlysecured and not become loose due to vibration. When assembled thelock nut and adjusting sleeve are screwed tightly together – they aresecured by friction acting between the two surfaces.

Revised work in this example

You will notice that the drawing of the lock nut uses much of the workcovered in previous modules. Some of the work you should recallincludes:


• detail drawing giving shape, size and material for the lock nut

• half-sectional front view used for symmetrical components

• sizes used for, and the method of drawing, the top view of an internalthread

• hatching the internal thread, and not hatching the drilled hole

• dimensioning technique for the thickness, diameter and the thread.

You should also recall that the detail drawing given is only one of apossible three accepted solutions. A part-section could have been used toshow the threaded hole as visible outline, but this would not have givensufficient space to indicate the knurl. Alternatively, a single half-sectioned front view, with the dimensions of the thread and diametershown on this view could have been used, but as you needed to revise thetop view method of drawing an internal thread, the two view method wasused.

New work in this example

The new work shown on the drawing of the lock nut, introduced duringthis section of the course, includes:

• the modified title block including date drawn, sheet size and the thirdangle projection logogram

• the straight knurl.

Turn to the exercise section and complete exercise 5.3 and 5.4

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Part 5: Public and personal transport – communications 17

Worked example 5.2

Worked example 5.2 is the second of five worked examples. In thisexample, a detail drawing of an acorn nut is presented. The drawingsheet, with the border and the modified title block had previously beenprepared using a CAD program.

Acorn nut

An acorn nut is used on bicycle brake assemblies in place of a standardhexagonal nut for both aesthetic and safety reasons. The spherical endgives a neat appearance and a safe rounded end to the nut.


The detail drawing of the acorn nut uses work covered in the PreliminaryCourse and in the notes for the HSC Course. The work you should recallincludes:

• detail drawing, a half-sectional front view and an internal thread

• the shape and depth of the drilled hole

• the depth of the thread – the end is shown by a thick dark line

• the use of the modified title block


The new work shown on the drawing of the acorn nut, that wasintroduced during this section of the course, includes:

• dimensioning technique for the depth of the thread and of the drilledhole

• dimensioning technique for the spherical radius

• dimensioning technique for the distance across the flats

• dimensioning technique for the chamfer.

The fillet curves

Where the chamfered surface meets the flat surfaces of the hexagonalshaped portion of the nut, curved edges are formed. These are shown inthe external drawing of the nut, below the centreline. They are oftenreferred to as fillet curves.

The construction of fillet curves is not in the content of the syllabus,however they will often need to be represented in an orthogonal drawing.


The top of the curve is level with the top of the chamfer, and occurs atthe centre of the flat surface. The bottom of the curve occurs at thebottom of the chamfer. Locate these top and bottom points then draw thefillet curves with a convenient size radius using your radius curves. Theconstruction is shown on the drawing of the acorn nut.

Turn to the exercise section and complete exercise 5.5 and 5.6.

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Additional AS 1100 standards

Compression spring

Compression springs are commonly used components in personal andpublic transport vehicles. They are used in cars, bicycles, trams, trainsand monorails. The standard representation has changed dramaticallyover the years, and is now simplified to a line drawing. The lines usedare thin dark lines, drawn at a convenient angle. The angle is notspecified in AS 1100. The angle suggested for small springs is 75∞, and

for longer springs, is 60∞ – you do not want to take up too much time

completing the drawing. The drawing must appear to be a spring, andmust be able to be interpreted as such.

SMALL SPRING LARGE SPRING

75∞ TOHORIZONTAL

60∞ TOHORIZONTAL

Figure 5.11 Indicating compression springs

Knurls

A knurl is a raised area on the surface of a cylindrical shaped component,usually on a fastener, that provides a gripping area to hold when turningthe component. A knurl is usually formed on a lathe using a knurlingtool. Alternatively, it may be formed during injection moulding on apolymer component.

The two types that are covered by AS 1100 are a straight knurl and adiamond knurl.

The straight knurl is drawn in a convenient position, using five thin darkparallel lines on the knurled area. The diamond knurl is drawn in aconvenient position, using crossed thin dark 30∞ lines on the knurled area.

DIAMOND KNURLSTRAIGHT KNURL

Figure 5.12 Indicating a straight and a diamond knurl


A flat surface on a cylindrical component

Flat surfaces are frequently formed on cylindrical components. Whendrawing a view in orthogonal projection it is often difficult todifferentiate between the flat and the cylindrical surface.

To indicate that part of the cylindrical component is a flat surface, thindark diagonal lines are drawn on the view of the flat surface.

FRONT VIEWLEFT SIDE VIEW

FLAT SURFACE

Figure 5.13 Indicating a flat surface

Breaks

When drawing cylindrical shaped bars it is often more convenient toshow only a portion of the length of the bar. Similarly, rectangular barsand cylindrical tubes are often shortened in drawings. The AS 1100standard break for rectangular shaped components is different for a longbreak, used in large drawings, and for a short break, used in smallerdrawings. However, the standard does not define the difference betweena long and short break; you have to use your judgement.

AS 1100 indicates a standard for these ‘breaks’.

PIPECYLINDER SECTIONEDPIPE

SMALLRECTANGULAR

LARGERECTANGULAR

Figure 5.14 Indicating breaks for cylinders, pipes and rectangular bars

Assembly drawing

An assembly drawing is a drawing involving two or more componentswhich are part of an assembly or sub-assembly. It is important tounderstand how the parts fit together, and how the assembled partsfunction when fitted together.

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You will be shown two assembly drawings as worked examples. Foreach drawing the specific function of the components will be explained.You must gain experience in understanding assembled components in thevarious areas of study. A good start is to look at a bicycle and see howvarious assemblies and sub-assemblies work.

Differentiation of adjacent parts

Assembly drawings usually involve a number of sectioned components.Where two or more sectioned components touch, you must indicate thatthe components are different.

Differentiating the touching parts can be done using one of the followingmethods:

• by changing the direction or angle of the hatching

• by changing the spacing of the hatching.

Standard washers

The AS 1100 standards do not include details and sizes for drawingstandard washers, and as such you should always be given the size of anywasher that you would be expected to draw.

However, you will encounter standard washers in some textbooks andeven in past examination questions. For these reasons you will need toknow how to represent a standard washer.

The washer is drawn as a rectangular shape, diameter equal to 2D andthickness equal to D divided by 20, plus 1 mm, where ‘D’ is the nominalsize of the threaded component.

The following diagram shows a standard washer to fit an M20 bolt.

2 D

D20

+ 1 mmM20 WASHER

Figure 5.15 Drawing a standard washer


Worked example 5.3

Worked example 5.3 is the third of five worked examples. In thisexample, an assembly drawing of an equalization mechanism ispresented.

Equalization mechanism

Equalization mechanisms were used on handbrake assemblies on cars,trucks and buses prior to the use of disc brakes on all wheels. Theyequalized the force applied to the brakes when the handbrake lever wasoperated.


The assembly drawing of the equalization mechanism uses work coveredin the Preliminary Course and in the notes for the HSC Course. Thework you should recall includes:

• the standard representation of an external thread

• the auxiliary view method of drawing a special size hexagonal nut,given the distance across the flats.


The new work shown on the drawing of the equalization mechanism, thatwas introduced during this section of the course, includes:

• representation of a compression spring, using thin dark lines

• representation of a flat surface on a cylindrical shaped component,using thin dark diagonal lines

• a standard size washer

• a break on the end of the cable

• assembly of the components.

The assembly of the components

The components are drawn in the exploded isometric drawing in such aposition as to indicate the way they are to be assembled. The washer fitsonto the threaded cable end, hard up against the square portion. Thespring then fits hard up against the washer, the balance shaft fits againstthe spring and the adjusting nut is screwed onto the threaded cable end,hard up against the flat portion of the balance shaft.

The position of the adjusting nut is given; “the threaded cable end is toprotrude 11 mm through the adjusting nut”. If you were to draw thisassembly, you would commence by lightly drawing the threaded cableend, then positioning the adjusting nut and the washer, and finallydrawing the balance shaft then the compression spring.

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Threads and fasteners

The representation of threads has also changed dramatically in the pastthirty years. The current AS 1100 standards were covered in thePreliminary course. You should revise the methods before proceedingwith the exercises.

Similarly, the drawing of standard machine nuts and bolts was covered inthe Civil Structures, and should be revised.

The auxiliary view method was used to determine the sizes whendrawing the non standard, special hexagonal nuts and bolts, in which thedistance across the flats was given. The auxiliary view method ofdetermining sizes for drawings has a wider application. You will now beshown two applications that are relevant to this course.

Auxiliary view constructions

The shape and size of a flat surface

You have been shown how to indicate a flat surface on a cylindricalsurface, using thin dark diagonal lines. Sometimes, when only a singleorthogonal view of a component is drawn, a method has to be used todetermine the shape and position of the flat surface. The auxiliary viewmethod is used.

The drawing below shows how an auxiliary end view is constructed todetermine the shape and position of the flat surface on the bicycle axle.

FRONT VIEWAUXILIARY VIEW

CURVE OFINTERSECTION

P1

P3

P2

12

3 4

5

FLATSURFACE

Figure 5.16 Using an auxiliary view to determine flat surface


Method

The following steps are used to determine the shape and position of theflat surface:

• the outline for the front view of the axle is commenced, and thethread and cylindrical break completed

• an auxiliary end view is drawn showing the position of the flatsurface cutting the circle at points P1 and P2

• project points P1 and P2, where the flat surface cuts the circle in theauxiliary view, to the position in the front view

• as the flat surface cuts the fillet, the right side of the flat surface willbe curved. The ‘top point’ on this curve is numbered P3 in theauxiliary view

• to find point P3 in the front view:

– rotate point P3 onto the vertical centreline in the auxiliary view(1, 2)

– project from this rotated position (3)

– project to the fillet in the front view (4)

– draw a vertical line from this position on the fillet to locate the‘top point’ of the curved surface on the centreline of the frontview (5)

– using radius curves draw a curve through the three locatedpoints.

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The shape and size of a hole drilled through acylindrical shape

When a circular hole is drilled through a cylindrical bar or shaft, a line ofintersection is formed between the hole and the cylindrical surface.When a single orthogonal view of the component is drawn, a method hasto be used to determine the shape and position of this line of intersection.The auxiliary view method is again used.

The drawing below shows how an auxiliary end view is constructed todetermine the shape and position of the line of intersection on the bicyclebrake special bolt.

FRONT VIEWAUXILIARY VIEW

LINE OF INTERSECTION

P1 P3

P2

P1 P3

P2

Figure 5.17 Using an auxiliary view to determine the line of intersection

Method

The following steps are used to determine the shape and position of theline of intersection:

• the outline for the front view of the special bolt is commenced, andthe head, shank, thread and cylindrical break completed

• draw the position of the drilled hole in the front view, using hiddenoutline technique

• an auxiliary end view is drawn showing the end view of the head andthe position of the drilled hole

• points P1, P2 and P3 are numbered on the auxiliary view

• project point P2, where the drilled hole cuts the circle in the auxiliaryview, to the centreline position of the drilled hole in the front view

• locate points P1 and P3 in the front view

• using radius curves draw a curve through the three located points P1,P2 and P3 in the front view

• repeat this method to locate the line of intersection at the top of thehole.


Worked example 5.4

Worked example 5.4 is the fourth of five worked examples. In thisexample, a front view of a hub skewer is presented.

Hub screw

Hub skewers are used on quick-release mechanisms for bicycle wheels.They allow the wheel to be released and removed quickly from the forkof the frames.


The work you should recall includes:

• the standard representation and dimensioning of an external thread

• the standard representation and dimensioning of a chamfer

• the standard representation of a break in a shaft.


The new work shown on the drawing of the hub skewer, that wasintroduced during this section of the course, includes:

• the plotting of the shape and size of a hole drilled through acylindrical shape using an auxiliary view method.

Turn to the exercise section and complete exercise 5.7 and 5.8.

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Worked example 5.5

Worked example 5.5 is the last of the five worked examples. In thisexample, a front view of a pedal crank axle is presented.

Pedal crank axle

Pedal crank axles are used to secure the pedals to the pedal cranks of abicycle.


The work you should recall includes:

• the standard representation of an external thread

• the standard representation a chamfer

• the standard representation of a break in a shaft

• the standard representation of a flat surface

• how to draw a fillet

• the standard representation of a part-section

• the use of an auxiliary view to plot the size of a hexagonal shape.


The new work that is shown on the drawing of the pedal crank axles, thatwas introduced during this section of the course, includes:

• the plotting of the shape and size of the flat surface on a cylindricalshape using an auxiliary view method

• the hatching of the external thread when sectioned.

Plotting of the shape and size of the flat surface

Commence the drawing of the front view, and mark in the position of theflat surface. The steps used to draw the size and shape of the flat surfaceare listed below:

• lightly draw an auxiliary end view of the axle, commencing with thecircle of diameter 20 mm; note that you are using a scale of 2:1, sothe size is doubled to 40 mm.

• using the scale of 2:1, measure 20 mm on either side of the centerlineand draw vertical lines to cut the circle

• project across to the front view of the flat surface where thesevertical lines cut the circle


• outline the flat surface

• draw the circle of diameter 18 mm to represent the chamfer

• repeat the construction to determine where the flat surface cuts thechamfer.

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Exercises

Exercise 5.1

Use a CAD program or a draw program to prepare a drawing sheetshowing a border and modified HSC title block. The sizes must conformto those given in this part.

Save the drawing sheet to disk and use a copy when you are presentingany drawings for your engineering reports.

Include in the title block, your name, the word ‘scale’ and the sheet size‘A4’.

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Part 5: Public and personal transport - communications 53

Progress check

In this part you developed your freehand sketching skills, completingpictorial drawings and designing solutions to orthogonal drawingproblems applying AS 1100.





Ag

ree

Dis

agre

e

Un

cert

ain


• freehand sketching, designs, pictorial, orthogonal

• Australian standard AS 1100

• computer graphics, Computer Assisted Drawingapplications solving problems.

I have learnt to:

• produce orthogonal drawings applying appropriateAS 1100

• produce quality graphics

• apply dimensing to AS 1100 standards.



In the next part you complete an engineering report based on the analysisof a transport system.

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Part 5: Public and personal transport - communications 55


Exercises 5.1 to 5.8 Name: _________________________________

Check!


❐ Exercise 5.1

❐ Exercise 5.2

❐ Exercise 5.3

❐ Exercise 5.4

❐ Exercise 5.5

❐ Exercise 5.6

❐ Exercise 5.7

❐ Exercise 5.8


If you study Stage 6 Engineering Studies through a Distance EducationCentre/School(DEC) you will need to return the exercise sheet and yourresponses as you complete each part of the module.


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Part 6: Transport systems –engineering report

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Part 6: Transport systems – engineering1

Part 6 contents

Introduction..........................................................................................2

What you will learn?................................................................... 2

An engineering report .......................................................................3

Structure of an engineering report............................................... 3

Sample engineering report ......................................................... 5

Exercises ...........................................................................................35


Progress check.................................................................................39

Bibliography.......................................................................................41

Module evaluation ............................................................................45


Introduction

This part contains four sections.

The first section describes the components of an engineering report, andexplains what you will be asked to research for this part of the module.

The second section analyses a transport system (petrol engine vehicles)being used to transport workers to and from a work place.

The third section provides background information before youcommence your report on an alternative electric vehicle system.

The fourth section is the student exercise and requires you to analyse anelectric vehicle and determine several design specifications.



• research methods including the internet, CD-ROM and libraries

• [working] collaboratively when appropriate

• engineering report writing.

You will learn to:

• work with others and appreciate the value of collaborative working

• complete an engineering report based on the analysis and synthesisof an aspect of personal and public transport.


Refer to <http://www.boardofstudies.nsw.edu.au> original and current documents.

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An engineering report

An engineering report requires analysis of a situation, product orcomponent. The report is a formal document and needs to be constructedin a logical and sequenced format.

The required components of the report are described in the followingtext.

This module’s student engineering report exercise is structureddifferently from previous engineering report exercise. You havepreviously been presented with a situation and then asked to analyse thealternatives. A sample report has been provided that analyses a similarengineering situation.

In this exercise you are to analyse a proposed electric alternative vehicle.You will be given guidelines to structure your report, but you will needto make decisions on the most appropriate design features of the electricvehicle based on calculations and interpretation of data.

The structure of this engineering report

The student engineering report should be written under the followingheadings:

• title page

• abstract

• introduction

• analysis

• result summary

• conclusions and recommendations

• acknowledgments

• bibliography

• appendices.


Title page

The title page gives the title of the report, identifies its writer or writersand the date when the report was completed. You might add a drawingof the object on the title page.

Abstract

The abstract is a concise summary of the report. The purpose of theabstract is to allow a reader to decide if the report contains informationabout which they are researching.

The abstract should be no more than two or three paragraphs of text, andshorter if possible. It should cover the scope of the report (what it isabout), and the approach or approaches used to complete the analysis(how the information was assembled).

Introduction and the purpose of the report

Outlines the subject, purpose and scope of the report. It may containbackground information regarding the topic. A brief description of eachsection of the report should be made.

Analysis

This is the body of the report and should show evidence of research andexperimentation. Information about materials and the mechanics ofproducts should be collected or calculated for all engineering reports.This section must contain information required to satisfy the aim andpurpose of the report. Tables and graphs are common features.

Result summary

This section presents the results concisely. The results will be used tojustify your conclusions and recommendations.

Conclusions and or recommendations

This section requires the writer to draw conclusions based on datacollected. If the purpose of the report was to ‘select the best solution…..’,then the selection is now stated and the reason for the selection isexplained.

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Acknowledgments

The acknowledgment section provides the opportunity to credit otherpeople’s work that has contributed to the report.

Bibliography

You must demonstrate that the report is well researched. Standards forbibliography entries must follow the strict guidelines. All references mustbe included.

Appendices

This section contains information that has been separated from the mainbody of the report because it is not essential that every reader look at thisinformation. It is information that enhances the other data. Exampleswould be the comparison engineering drawings.

During the engineering course this section will always contain a technicaldrawing.

Sample engineering report

The following section contains a sample engineering report whichaddresses each of the sections and indicates breadth and depth ofinformation required.

The engineering report analyses a transport system (petrol enginevehicles) to convey workers to and from a workplace.

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Title: Transport investigation

Author/s: Johnny Diesel

Date: January 2000

Abstract

Analysis of pollution, and energy cost, of a transport system that usespetrol internal combustion engines.

Introduction

An isolated company town is analysing the effect of transporting its workforce from home to the work place using internal combustion enginevehicles. The main mode of transport operating between the town and theindustrial centre is by private vehicle; this report is an analysis of thattransport system. The purpose of this engineering report is to provide datafrom which a comparison can be made between the pollution and cost ofthe present vehicle and a proposed electric vehicle.

The long term objective of the town community is to develop a transportsystem based on an underlying philosophy of being ‘clean and green’.

This report will provide details of energy costs and pollution created by thetransport system that relies on personal vehicles that are petrol enginepowered. Several tables of data that describe the pollution caused by thistype of system are shown. A summary of the data is made and severalconclusions are presented.

The research for this project has been based on establishing the majorpollutants in the environment that are created by transport vehicleemissions. The source of this data has been Internet web-sites such as theNew South Wales Government’s Environmental Protection Authority(NSWEPA) and the Commonwealth Scientific and Industrial ResearchOrganisation (CSIRO). The web sites for these institutions are<www.epa.nsw.gov.au> and <www.csiro.au>.

The data provided in the NSWEPA web site is based on research carriedout on transport emissions in the Sydney Region in 1992. This data alongwith other data from research into transport in London has been used as thebasis for this report.

Analysis

This analysis of transport between the Industrial Centre and the town isbased on the following criteria:

• the round trip distance is 20kms, comprising 10kms in the morningand 10kms eight hours later at the end of a working shift

• each shift sees a total turnover of workers of 100 between the townand industrial area

• each vehicle transports 1 worker

• the cost of petrol is $1 per litre

• each vehicle has a fuel consumption rate of 1 litre per 10 km.

An illustrated overview of the transport system analysed in this report isshown in the appendix – figure 6.1.

Pollutants

The atmosphere is never completely free from impurities. It alwayscontains materials from sources such as dust, fire smoke and sea saltparticles. Pollutants exist as primary or secondary pollutants.

Primary pollutants:

• oxides of sulphur, nitrogen and carbon related compounds

• organic compounds such as hydrocarbons (fuel vapour and solvents)

• acid gases including sulphuric acid and hydrochloric acid

• particulate matter such as smoke and dust

• metal oxides and related compounds including those of lead,cadmium, copper and iron

• fluorides

• toxic and non-toxic odours

• radioactive substances.

Secondary pollutants include:

• ozone, nitrogen dioxide, and other components of photochemicalsmog.

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Pollutants that are the product of motor vehicles or engine emissionsinclude lead, oxides of nitrogen and carbon monoxide.

Oxides of nitrogen, Nitric oxide (NO) and nitrogen dioxide (NO2) aremainly produced from fuel combustion in motor vehicles. Oxides ofnitrogen remain in the atmosphere for several days before they are oxidisedto nitric acid and to particulate nitrates and nitrides, which settle and arewashed out by rain. In the presence of sunlight they undergo complexchemical reactions with hydrocarbons and oxygen to producephotochemical smog. NO2 is a respiratory irritant which may contribute tobronchitis in infants, children and older people.

Sector Kilograms per day

Motor vehicle 269 000

Power generation 229 150

Basic metal processing 32 850

Non-metallicmineral processing 25 520

Petroleum refining 16 920

Coal mining 21 850

Rail transport 11 120

Commercial shipping 9 640

Chemical manufacturing 8 230

Carbon monoxide (CO) is an odourless, colourless gas which has as itsnatural source, the oxidation in the atmosphere of methane. Motor vehicleengines are by far the greatest source of this gas.

Ninety percent of the lead in urban air comes from motor vehicle exhausts.Lead is an extremely toxic chemical, which can cause damage to humanhealth when ingested or inhaled. Research has indicated that there are highblood lead levels in children 0–4 years when they are surrounded by highlead levels in the atmosphere. Lead is known to cause neurologicalmalfunction and learning disabilities, and to retard mental development inchildren. Studies have shown that 10 micrograms per decilitre increase inblood-lead concentrations is associated with a decrease of between 2 and 8intelligence points (IQ) in young children.

Volatile organic compounds (VOC) is a name given to hydrocarbons, aswell as alcohols, aldehydes and others. They occur in air mainly due toautomotive fuels and industrial solvents. Chemical reactions betweensunlight, VOCs and oxides of nitrogen form ozone which is a gas that isharmful to humans, animals and plants. Ironically, ozone in thestratosphere is essential to life as we know it, protecting the earth fromharmful ultraviolet light.

Acid rain: Pure rain water is slightly acidic with a pH of from 6 to 5. Itcan become more acidic due to fuel combustion and industrial processeswhich release compounds containing oxides of sulphur or nitrogen. Thesecompounds can reach the ground in wet or dry form, both of which areharmful to soil, lakes, plants, buildings and people.

Acidic pollutants can travel thousands of kilometres in the air before theyare deposited. This means that a country or an area may have a cleanenvironment but suffer the effects of pollution from other areas.

The problem of acid rain is being attacked in two ways. Firstly, authoritiesthroughout the world such as Governments are setting standards thatreduce pollution emissions from car exhausts. Since 1986, new cars inAustralia have had to have catalytic converters installed in their exhaustsystems. Secondly, neutralising agents such as lime are being added tolakes and soil to reduce acidity.

Table 2 shows the tighter design rules (ADR 37/00 and ADR 37/01) for carexhaust that will be applied to passenger vehicles. ADR 37/00 will applyfrom 1997 for new models and ADR 3701 from 1999 for all existingpassenger vehicles. (The terms used in Table 2 are: HC – hydrocarbons,CO – carbon monoxide, NOx – nitrogen oxides all in grams per kilometreand EVAP HC refers to evaporated hydrocarbons from a measured test).

HC (g/km) CO (g/km) NOx (g/km) EVAP HC (g/test)

ADR 37/00 1997 0.93 9.3 1.93 2.0

ADR 37/01 1999 0.25 2.1 0.61 2.0

Table 2 Design rules

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Table 3 gives a summary of the major pollutants in the air, their majorsources and effects on health.

Pollutant Sources Health effects

Carbonmonoxide

Car exhausts, burningfossil fuels.

Carbon monoxide is absorbedby the blood more readily thanoxygen, thus reducing theamount of oxygen beingcarried through the body. Itcan produce tiredness andheadaches.

Sulphurdioxide

Coal and oil burningpower stations, mineralore processing andchemical manufacture.

Attacks the throat and lungs.

Nitrogendioxide

Burning of fossil fuels. Affects the throat and lungs.

Ozone Formed from nitrogenoxides and hydrocarbonsin sunny conditionswhich are released bymotor vehicles andindustry.

Ozone attacks the tissue of thethroat and lungs and irritatesthe eyes.

Lead Exhaust gases frommotor vehicles whichuse leaded petrol,smelters.

Particles containing lead in theair can enter the lungs. Thelead can then be absorbed intothe bloodstream. Over aperiod lead can affect thenervous system and the body’sability to produce blood.

Particles Motor vehicles, burningof plant materials,bushfires.

May cause brea th ingdifficulties and worsenrespiratory diseases. Someparticles contain cancer-producing materials.

Table 3 Major air pollutants

Table 4, from the NSW Environmental Protection Authority based onresearch undertaken in 1992 in the Sydney Region gives the annualemission of pollutants from various sources in cities and major centresacross Australia is extensive. All values are in tonnes.

Source category VOCS NOx CO SO2

M o b i l e s o u r c e s(transport)

83 820 83 480 729 760 2 780

Domestic/commercialactivity

70 020 4 810 58 210 4 310

Industrial/commercialactivity

16 820 13 440 13 510 12 700

Annual Total (tonnes) 170 660 101 730 801 410 19 790

Table 4 Annual emission of pollutants from various sources in cities andmajor centres

CO2 CO VOC NOx SOx

Car 237 18.5 2.2 2.0 0.11

Large Bus 1035 17.5 4.7 14.6 1.22

Average Bus 670 18.8 2.8 8.7 0.91

Minibus 944 17.5 4.7 14.7 1.22

Taxi 330 2.0 0.4 1.6 0.43

Motorcycle 119 9.2 1.1 1.0 0.06

Table 5 Emission rates for passenger vehicles (in grams per vehicle per-kilometre)

The figures given above are from a research project carried out onLondon's transport system by Wood in 1995 (1996). A copy of the articleis also available at <www.gda.50.dial.pipex.com/fuels.htm>.

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Calculations

Pollution:

Emission per vehicle equals 260 grams/kilometre travelled.

Each vehicle travels

20 kilometres/day, which is

100 kilometres/week or

5 200 kilometres/year.

The annual pollution therefore is:

5 200 x 0.260 = 1 352 kilograms/vehicle

With 100 cars, the annual pollution is:

135 tonnes

Fuel Costs:

Each car travels 5 200 kilometres/year

At a fuel economy rate of 1 litre per 10 kilometres, and with 1 litre of fuelcosting $1

The annual cost of fuel is:

100 cars = 520 000 kilometres

520 000/10 = 52 000 litres

at $1/litre = $52 000 per year.

Summary

From the data in the table it is evident that pollutants caused by vehicleemissions are all harmful to the health of humans and to the environment inwhich they live. The current transport vehicles are producing an excessiveamount of pollutants as can be seen from the total emissions given at thebottom of the calculations section above. In gross figures based on theseestimates, transport between the town and the industrial centre isgenerating approximately 135 tonnes of pollution at an annual cost toworkers of $52 000 in fuel costs.

It would appear from these estimates and the community philosophy ofattempting to become ‘clean and green’, that there are alternative transportsystems that are more appropriate.

Conclusions and recommendations

The data indicates the current transport system using the internalcombustion engine vehicle is producing a high level of pollution. It isrecommended that an alternative transport vehicle be developed. Thisdesign should take advantage of alternative power sources such aselectricity. A vehicle such as this should reduce localised pollution and beless expensive to run.

Glossary

acid rain acidic rainfall caused by the release into theatmosphere of sulphur dioxide and oxides ofnitrogen

aldehydes any group of organic chemical compoundsprepared by oxidation of primary alcohols

catalytic converter device fitted to the exhaust system of a motorvehicle in order to reduce toxic emissions fromthe engine

hydrocarbon the basic molecules of fossil fuels, made up ofhydrogen and carbon atoms

neurological malfunction damage to the brain

ozone O3 – a form of oxygen with an extra atom causedby ultraviolet radiation or electrical discharge.Forms a thin layer that protects the earth fromultraviolet rays

particulate matter small particles that may not be visible, but are‘suspended’ in a medium and may settle overtime

pH a measure of acidity from 1 to 7

stratosphere that part of the atmosphere 10 – 40 km above theearth’s surface

vehicle emission toxic gases emitted form the exhaust of cars

volatile organic compounds a name given to hydrocarbons, as well as alcoholsand aldehydes that occur mainly due toautomotive fuels and industrial solvents

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Appendices

90 80 70 60 70 80 90 100

100

90

80

70

70

80

90

80 7090 70 80

Residential area

Industrial area

0 0.5 1

KilometresTrain trackRoadway

Figure 6.1 Transport system

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Part 6: Transport systems – engineering 17

Preparation for your report

Alternative power vehicles

The community has decided to research a pollution-free strategy to movepeople to and from their work place. Due to costs, the currentinfrastructure (the road) will need to be the used with ‘greener’ vehicles.To power these vehicles a suitable source of pollution free energy willneed to be identified. Often the term ‘pollution free’ is synonymous with‘alternative’, ‘sustainable’ or ‘green’ energy.

Energy and power

The terms ‘energy’ and ‘power’ are often used interchangeably. Weshould be aware that power is the rate at which work can be done and ismeasured in Watts. Energy is the total amount of work done and ismeasured in Joules. Energy is the product of power and time. Alternately,power is the rate of delivery of energy.

Example: a person who runs 10 kms uses the same energy as a personwho walks 10 kms. The difference is the time, not the energy.

In most cases we understand what is meant when we use both energy andpower in general conversation. However, we must be sure we knowexactly what we are referring to when it comes to calculations!

‘Pollution free’ power

The term ‘alternative energy’ indicates that the source of energy is otherthan the most commonly used. In New South Wales the majority ofpower is generated in coal-fired power stations. The other sources ofpower – hydro systems in the Snowy Mountains, wind power fromKooragang Island near Newcastle, solar power from farms such as thatnear Singleton and land fill gas derived plants such as at Lucas Heights –are all alternatives to coal-fired plants.

If you have access to the internet you may like to visit the followingsites for further information on alternate sources of energy:

<http://www.eneergy.com.au/ >(accessed 01/08/03).

‘Sustainable’ energy generally refers to the impact of a given technologyon the environment. While we have vast reserves of coal in New SouthWales – quite enough to provide power for many years to come – theeffects of burning that coal may not be sustainable. The combustionprocess generates substantial quantities of carbon dioxide that can have


harmful effects on the atmosphere. In that sense, coal fired powerstations might be considered not ‘sustainable’.

‘Green’ energy is another term for the same technologies, and often usedby the popular media to describe alternative or sustainable energysources.

List examples of four types of sustainable energy as used in Australia.State where the plant is, how much power is generated, and how thepower is used.

1 _______________________________________________________

2 _______________________________________________________

3 _______________________________________________________

4 _______________________________________________________

Did you answer?

1 Solar energy – Newcastle foreshore, 80 silicone solar cells. 6 500 watts.

2 Wind turbine – Kooragang Island, Vestas V44 turbine, 3 blades, 22 metres, 66 kW.

3 Hydro power – Glenbawn Dam, 2 turbines, 1 generator, 5.5 MW.

4 Bio-mass – Bare Creek Sydney, methane gas from landfill, 4 MW.

Sources: <www.energy.com.au/environment/pureenergy.asap>

A prototype electric vehicle

The company has agreed to purchase one prototype electric vehicle toallow us to experiment. This vehicle has a single 12 Volt electric motorrated at 18 kW already fitted to a suitable transmission. The vehicle alsohas a total payload capacity of 1200 kgs. The payload is the amount ofweight the vehicle can carry in addition to the weight of the vehicle itself.This payload is to include a driver, passengers and the energy source.

Let us assume that the driver and passengers have an average weight of70 kgs. This means, for example, that the vehicle could carry a total of:

1200 kg divided by 70 kg/passenger = 17.1 passengers

(We'd better call that 17 passengers, since finding 0.1 passengers to makeup the difference could be difficult!)

However, this number of passengers does not make allowance for anenergy source to power the vehicle! There will be less passengers oncewe include the energy source into the total weight calculation.

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Which is the best source of power for the electric vehicle?

There are many sources of alternative or sustainable energy. Tidal, wind,solar and hydro generation are all used or under development inAustralia. Each has its own benefits in particular situations. Of thesetypes of sustainable energy, solar power is probably the best suited tomounting on a vehicle.

There are already many solar powered vehicles in development and in usetoday. The Australian Electric Vehicle Association has its own web site at:

<http://www.aeva.asn.au/>(accessed 01.08.03).

Explain why you think solar power is the most appropriate for use in anelectric vehicle.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

Solar panels have no moving parts, therefore are low maintenance and sunlightis available most days. However, tidal/hydro need to be near water and windrequires appropriate geographical position.

Consider fitting our electric vehicle with direct solar power: that is, withsolar panels connected to the motor via a speed controller.

Power from solar energy

The key component in a solar powered system is the photovoltaic cell.Photovoltaic cells convert solar energy (from the sun) directly intoelectricity. Strictly speaking, the term 'photovoltaic cells' refers to thethin semiconductor wafers that do the actual energy conversion. The cellsare blue/black in colour.

In practice, these structures are very brittle and need to be mounted insomething more solid for use in normal applications. Consequently, thecells are mounted in aluminum frames (for lightness) and covered inglass for protection. The photovoltaic cell mounted in its frame is oftencalled a ‘solar panel’ or ‘solar cell’.


You will probably have seen solar panels in use. They are found attachedto cars and boats, street lighting, on roofs of houses and other buildings,or even at solar energy farms, usually aligned to face the strongestsunlight.

a Identify a particular application of solar electrical generation near you.

_______________________________________________________

b Describe how the photovoltaic cells are mounted.

_______________________________________________________

c Indicate what the electricity generated is used for.

_______________________________________________________

There is also quite a deal of research being conducted into thedevelopment of photovoltaic cells, and particularly into making themmore efficient. Typical photovoltaic cells have maximum efficiencies ofonly about 20 percent – that is, only 20 percent of the solar energy thatilluminates the cell is available as electrical energy. The efficiency isdependent on factors such as:

• operating temperature (the cooler the better)

• intensity of solar illuminance

• cleanliness of the solar panel.

State the maximum efficiency obtained from photovoltaic cells.

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

The maximum efficiency of solar cells is about 20%.

The most efficient cells in the world are made in Australia! Much groundbreaking work has been undertaken by researchers at the University of NewSouth Wales where they have developed solar cells that are 24.7% efficient.

How much solar power is required?

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Getting back to our electric vehicle: can you calculate how many solarcells are needed to power our motor? Table 1 shows various parametersrelating to a range of commercial solar panels available in Australia.

Model Current Power Length Width WeightNumber (Amps) (Watts) mm mm kg

SX85 4.97 85 1456 502 9.50

SX80 4.75 80 1456 502 9.50

SX75 4.54 75 1456 502 9.50

SX65 3.77 65 1110 502 7.20

SX60 3.56 60 1110 502 7.20

SX55 3.33 55 1110 502 7.20

SX50 2.97 50 939 502 5.70

SX40 2.37 40 767 502 4.90

SX30 1.78 30 594 502 3.50

SX20 1.19 20 424 502 2.50

SX10 0.59 10 421 269 1.50

SX5 0.27 5 250 269 0.80

Table 1 Solar panel characteristics

Determine the approximate power developed per square metre of solarpanel using the data in Table 1 model number SX80.

__________________________________________________________

__________________________________________________________

Did you answer?

Using SX80 with a power of 80W and area = 1.456 m x 0.502 m = 0.73 m2

Power per square metre of panel

=

800 73.


= 110 Watts/m2

Recall that the motor we want to supply is rated at 18 kW. We can nowcalculate how many square metres of solar panels are required to supplythe necessary power to drive our motor.

Determine how many solar panels are required to supply 18kW using theSX80 panel and the information derived in the previous exercise.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Don't be surprised if the number you obtain seems unrealistic!

Assume that the electric vehicle made available to us is the size ofa small mini-bus.

Sketch the electric vehicle with the required area of solar cellsattached. Remember that the panels should be oriented towards thesun for maximum efficiency.

Did you answer?

The SX80 model provides 110/m2

Total area required =

18000

110

= 164 m2

if each panel has an area of 0.73 m2

then the number of panels =

164

0 73.

= 225 panels

Note: panels could not be inclined to the direction of sunlight.

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16.4 m

5 m

Figure 6.2

Outline why you think this vehicle is not a feasible proposition.

__________________________________________________________

Did you answer?

The panel area is too large.

How many passengers?

Let’s continue with the concept of the solar powered vehicle for amoment longer. Now that you have figured out how many solar panelsyou will need, you can calculate the total weight of the solar panels, andtherefore how much weight carrying capacity is left for the passengers.(Remember the total payload of driver plus passengers plus energysource is 1200 kgs.)

a State the total weight of the solar panels that you have decided willneed to be used.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

b Indicate the number of passengers the vehicle can carry withoutexceeding the 1200 kg capacity.

_______________________________________________________

_______________________________________________________

Did you answer?

a SX80

No of panels = 0.73 = 225

Weight per panel = 9.5 kg

Total weight = 2138 kg


b Nil

2138 kg is greater than the capacity of 1200 kg

Again, don't be alarmed if the outcome seems unworkable. We now havea couple of reasons to explore other approaches!

Concentrating the energy into a smaller space

You probably discovered that the total weight of solar panels requiredexceeds the payload of the vehicle! And that is even without carrying anypassengers! There is also the problem of powering the vehicle on cloudydays, or even at night! There must be a better way!

Mounting the solar panels directly onto the vehicle means that the panelshave to generate the electrical power at the same instant and same ratethat it is consumed. If there was a way in which we could generateenergy, store that energy until it is needed, and then use it later, we mightbe able to make the system work! Furthermore, we might not have togenerate the energy at the rate we use it, because we could save upenergy over a long period, then use it up in a shorter period. That mightlead to weight or space savings on our vehicle!

You have probably already thought of a way to store electrical energy:batteries.

Storing electrical energy in batteries

Strictly speaking, batteries do not store electrical energy. Instead, theenergy is converted from electrical energy into chemical energy as thebattery is being charged. The chemical energy is stored in various formsin different types of batteries – lead/acid, lithium, nickel/cadmium and soon. The energy is converted back from chemical to electrical energywhen the battery is discharged.

There is also much work being done to develop new battery technologiesfor electric vehicles.

If you have access to the Internet visit the following site for furtherinformation on the many applications of batteries:

<http://www.batteryallsorts.com.au> (accessed 01.08.03).

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State the aspects of battery construction and performance are beinginvestigated for use in electric vehicles.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

• reliability

• life cycle – maintenance free

• increased battery energy

• efficient battery plates

• faster battery recharging.

Lead acid batteries

Of all the technologies currently available, lead/acid batteries are themost economical due to the mass production techniques used in theirmanufacture. (This will almost certainly change as new batterytechnologies are proven and adopted.) Let us focus on these types for ourelectric vehicle.

There are several types of lead/acid batteries available to us: automotive,marine, deep cycle, industrial. All of these use the same basicconstruction and chemical process to store energy. The differences inthem reflect the different applications in which they are used.

A car battery, for example, is required to provide large amounts of powerfor relatively short durations (that is, when the starter motor is being usedto start the car). On the other hand, a car battery can be significantlydegraded if it is allowed to run flat. This is not normally a problemthough, as most cars have good charging systems to put the energy backinto the battery as soon as the engine is running.

A deep cycle battery has a slightly different internal construction (thickerlead plates) which allows it to give up more of its stored energy withoutbeing damaged. The downside is that these types of batteries cannotproduce the same amount of short term power as a comparable carbattery. Deep cycle batteries are designed for use where the battery has tosupply power for extended periods between charging.


Explain why you think a car battery or a deep cycle battery would be bestfor our electric vehicle application.

__________________________________________________________

__________________________________________________________

Did you answer?

A deep cycle battery would be best because of the constant power over longerperiods and no high peak starting requirements.

Measuring battery capacities

Batteries come in many different sizes.

What sized battery do we need for your electric vehicle? How manybatteries will you need?

Before you can answer these questions, you need to understand howbattery sizes are measured.

Obviously all batteries have physical dimensions – length, width, heightand weight. Batteries are also measured in terms of their electricalstorage capacity. Because car batteries and deep cycle batteries are usedin different applications, their electrical storage capacities are stated indifferent ways.

Car batteries are measured in terms of the ‘cranking current’ (CA) or‘cold cranking current’ (CCA). This is a measure of how much currentthey can deliver for a short period of time. The distinction between CAand CCA is the temperature at which the test is done. Batteries performbetter at lower temperatures, and the CCA is invariably higher than theCA figure.

Deep cycle batteries are measured in terms of their ‘ampere hour’capacities. This is a measure of the product of current and time. Forexample, a capacity of 100 ampere hours means that the battery can(theoretically) deliver 100 amperes for 1 hour, or 10 amperes for 10hours, or 1 ampere for 100 hours. There are of course limits, it is unlikelythat a 100 ampere hour battery will be able to deliver 1000 amperes for0.1 hours.

The most common figure used to determine the capacity of deep cyclebatteries is the ampere hours delivered over a 20 hour period. This isoften referred to as the C20HR rating. Other figures sometimes quotedare the C5HR or C2HR ratings – these are the battery ampere hourcapacities delivered over a five hour or two hour period respectively.

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Indicate the measure of battery capacity most appropriate for determiningits suitability for our electric vehicle application.

__________________________________________________________

__________________________________________________________

Did you answer?

Amp hours – this tells us how long the battery will provide power current whileranking current only indicates the maximum power.

If you know how long you want the vehicle to run for between re-chargings, you can work out what battery capacity you need. In yourcalculations you will assume that the electric motor is running at fullpower all of the time.

Will this assumption give you the minimum or maximum ampere hoursthat will be drawn from the battery.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

If we assume the vehicle is running at maximum power, this information willgive us the maximum amp hours. Note: more ‘time’ will be available if thebattery is not used at full power.

Calculating the number and size of batteries required

The motor power is 18 kW. The motor voltage is 12 V.

Indicate the corresponding motor current.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________


Did you answer?

Current =

Power

Voltage

=18000

12

= 1 500 amps

How many hours do you expect the vehicle to run for between charges?Note there is no right or wrong answer here - it is simply your ownopinion of how long the vehicle should be able to run without having tostop to charge the batteries.

Using the motor current calculated above, together with the number ofhours you expect the vehicle to run between charges, calculate the amperehour rating of the battery (or batteries) you will require for the vehicle(allow an outward journey of 45 mins and a return journey of 45 mins).__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

Total running time = 45 min + 45 min = 90 min

= 1.5 hr

Amp hour rating = Battery current x hours in use

= 1 500 x 1.5 hours = 2 250 amp hours

Often it is impractical to use a single battery for large loads. In suchcases it is more convenient to use a number of smaller batteries.

Determine how many batteries you will require, and what type they are usingthe data from the following web page.

Also note the weight of each battery. Don't forget – you need 12 V batteries.

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CODE VOLTAGE AmpsC5Hr

AmpsC2Hr

LENGTH WIDTH WEIGHT

SSB6/1 6 80 70 215 202 15.9

SSB6/2 6 100 83 304 173 24

SSB12/1 12 30 26 213 195 22

SSB12/2 12 115 100 237 210 26

SSB12/3 12 150 130 237 230 28

SSB24/1 24 160 120 450 230 43

SSB224/2 24 200 187 435 250 44

Figure 6.3 Web page

Remember that the total payload for the vehicle is 1200 kgs.

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

Did you answer?

Choosing a SSB12/3 gives the greatest amps

Hours/kilograms Need 2 250 amp hours

\ =

2250

130a amp hours battery/ /

= 17.3 batteries

= 18 batteries


State how many passengers can the vehicle carry given the total batteryweight calculated above. Don't forget about the driver!

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

Did you answer?

18 batteries

Each weighs 28 kg

\ total = 18 x 28 = 504 kg

Maximum payload – battery weight

= 1 200 – 504

= 696 kg

Passangers = 696 = 10 passangers (9 + driver) 70

Sometimes you don't always make the best judgements first time. Inthese cases you have to go back to some assumptions you made, changethem, and recalculate the answer. (This is often the case where there isno singular correct solution, and many possible options have to beexplored.)

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Recalculating battery requirements

Suppose you are told that the vehicle must carry at least five people(driver plus four passengers). Using the available remaining payloadcapacity for the batteries, calculate the maximum range in hours ofrunning you can obtain using the same, or different, batteries to thoseused previously.

__________________________________________________________

__________________________________________________________

__________________________________________________________

__________________________________________________________

If the motor is not at full power all of the time, will the maximum rangeactually be greater or less than the figure you have just calculated?

__________________________________________________________

Did you answer?

Greater.

Recharging the batteries

Obviously we will have to recharge the vehicle batteries at some stage.How much will it cost?

We have already calculated the required energy storage capacity of thebattery in ampere hours. Because we know that the battery operates at 12volts, we can work out the total energy required to recharge the batteries.

1 How many Watt hours are required to recharge the batteries? Hint:remember Watts are the product of volts and amperes.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________


2 How many Joules are required to recharge the batteries? Hint:remember that Joules are equivalent to Watt seconds, and that thereare 3600 seconds in an hour.

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

Did you answer?

1 Battery capacity = 18 x 130 = 2 340 amp hours

Battery voltage =12 V Total energy to recharge

=2 340 x 12

= 28 080 amp volt hours

=28 080 watt hours

=28 kW hours

2 Energy required =28 080 watt hours

= 28 080 watt hours x 60 minutes/hour

= 1 684 800 watt minutes x 60 seconds/minutes

= 1.01 x 108 watt seconds

= 1.01 x 108 Joules

= 101 MJ

In physics, Joules is often the measurement for energy. Sometimes, inapplications involving electrical energy, you use Watt hours, or kiloWatthours (abbreviated as kWhrs).

Arial Arial bold


1 Find a copy of your household electricity bill. Does it measureenergy consumption in Joules or kWhrs? How much are you chargedper unit of energy?

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

2 If you had to charge the batteries in the electric vehicle from yourdomestic supply, how much would it cost for one full charge?

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

_______________________________________________________

Did you answer?

1 kWhrs

Total charge = 10.15 cents/kWhr

2 Energy = 28 080 watt hours

= 28 kWhr

Cost/kWhr = 10.15 cents

Cost of recharge = $2.85 cents

You have read the engineering report analysing the transport systembased on private vehicles using petrol engines. You have also workedthrough the notes on the use of solar energy and electric vehicles. It isnow time to begin your report.

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Exercises

Exercise 6.1

A company has decided to sponsor a solar electric transport system usingan electric powered minibus with batteries charged by solar energy.

During the trial period, the vehicle is expected to run the 20 km roundtrip four times per day, at an average speed of 40 kph. Two runs will bemade before 8:00 am and two runs after 4:00 pm.

The minibus is based on a 12 volt 18 kW motor and has an availablepayload of 2 400 kg (twice that available in the previous work).In yourreport you should identify:

• number and type of batteries required on board the bus to meet theexpected running times

• number of passengers that can be carried on each trip (assume an averageweight of 75 kgs per passenger, and don’t forget to include a driver)

• number, size and power rating of the solar panels required to chargethe batteries during the day or during the night.

• total amount of electrical energy used in one year to power theelectric vehicle

• an estimate of the amount of pollution avoided through not usingpetrol powered vehicles and how many journeys those vehicleswould have made.

Your report should include:

• calculations used to design the vehicle’s energy system, the dataused for those calculations and the source of that data

• sketches of the electrically powered bus showing relative spaceavailable for driver, passengers and batteries (you will need to notethe dimensions of the batteries used)

• the usual headings employed in an engineering report, including anintroduction, conclusion, abstract and references.


Present your report following the structure of the sample engineeringreport.

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Exercises 6.1 Name: _________________________________

Check!

Have you have completed the following exercise?

❒ Exercise 6. 1

• title

• abstract

• introduction

• analysis

• result summary

• conclusions

• acknowledgments

• bibliography

• appendices.




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Progress check

In this part, you have gained more practice in writing and researching foran engineering report. You have also learned about how to analyse atransport system.





Ag

ree

Dis

agre

e

Un

cert

ain


• research methods including the internet, CD-ROM andlibraries

• [working] collaboratively when appropriate

• engineering report writing.

I have learnt to:

• work with others and appreciate the value ofcollaborative working

• complete an engineering report based on the analysisand synthesis of an aspect of personal and publictransport using appropriate software and computerassisted drawing.



Congratulations! You have completed Personal and public transport.

41

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44

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45

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Learning Materials ProductionTraining and Education Network – Distance Education

NSW Department of Education and Training

Personal and Public Transport

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Transcript of Personal and Public Transport