Post on 19-Oct-2015
A
PROJECT REPORT
ON
DESIGN, FABRICATION AND TESTING OF A PRESSURE TRANSDUCER FOR THE CONDITION MONITORING OF THE OIL
LUBRICATION SYSTEM FOR GENERATOR SET
SUBMITED TO THE UNIVERSITY OF PUNE,
IN THE PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE AWARD OF THE DEGREE
OF
BACHELOR OF ENGINEERING
(MECHANICAL ENGINEERING)
SUBMITTEED BY:
SUMEET GHODKE B8310830
KEDAR LELE B8310865
RAVISH NAGARKAR B8310874
DEPARTMENT OF MECHANICAL ENGINEERING
PROGRESSIVE EDUCATION SOCIETYS
MODERN COLLEGE OF ENGINEERING, SHIVAJINAGAR,
PUNE-05.
2011-2012
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-05
CERTIFICATE
This is to certify that this project report entitled Design, fabrication and testing of
a pressure transducer for the condition monitoring of the oil lubrication system
for generator set submitted by
Sumeet Ghodke, University Seat No: B-8310830
Kedar Lele, University Seat No: B-8310852
Ravish Nagarkar, University Seat No: B-8310864
is a partial fulfilment of BE Mechanical Engineering project work, under the
University of Pune, year 2011-2012.
Date: 16/06/2012 Place: Pune
Internal Guide Head of Department
Prof. M. M. Nadkarni Prof. Dr. A. D. Desai
Prof. Dr. Mrs. K. R. Joshi EXAMINER
Principal
PESs MCOE, Pune-5
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
Page 2 of 112
ACKNOWLEDGEMENT
It is with great pleasure that we present the report on our project work at the end of
the final year. We take this opportunity to share a few words of gratitude to all those
who have supported us in making it possible. Our heartfelt gratitude to our project
guide Prof. Mr. M. M. Nadkarni for his able and expert guidance. We would also like
to thank Mr. V. S. Deshpande (M.D. Sam Integrations Pvt. Ltd.) for trusting us with
this project and providing unconditional support and guidance.
We are very thankful to Dr. Mr. Gajanan Ekbote (Chairman), Dr. Mrs. K. R. Joshi
(Principal) and Prof. Mr. A. D. Desai (Vice Principal) for their moral support and
encouragement. We are also indebted to our college including the staff members,
technical assistants of various laboratories and other non-teaching staff for providing
us with all the resources.
Place: Pune
Date: 16/06/2012
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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LIST OF FIGURES
Figure 1: Tank Unit for gensets ............................................................................................ 13
Figure 2: S-series Fuel Indicator ........................................................................................... 13
Figure 3: Fuel Indicator ....................................................................................................... 13
Figure 4: Drain Pump .......................................................................................................... 13
Figure 5: Fire Safety Equipments ......................................................................................... 13
Figure 6: Fuel Filling Neck .................................................................................................... 13
Figure 7: Oil lubrication system ........................................................................................... 16
Figure 8: Pressure gauge mounting on gen-set .................................................................... 17
Figure 9: Assembly of RICO pressure transducer ................................................................. 23
Figure 10: C-shaped bourdon tube ...................................................................................... 25
Figure 11: Helical bourdon tube .......................................................................................... 26
Figure 12: Spiral bourdon tube ............................................................................................ 26
Figure 13: Flat diaphragm ................................................................................................... 27
Figure 14: Schematic diaphragm pressure gauge ................................................................. 27
Figure 15: Convoluted diaphragm ....................................................................................... 28
Figure 16: Capsule ............................................................................................................... 28
Figure 17: Set of bellow pressure gauge .............................................................................. 29
Figure 18: Single acting cylinder .......................................................................................... 29
Figure 19: U-tube manometer ............................................................................................. 30
Figure 20: Circumferential Stress......................................................................................... 33
Figure 21: Longitudinal Stress ............................................................................................. 33
Figure 22: Von-mises stress in cylinder ................................................................................ 38
Figure 23: Maximum principal stress on cylinder ................................................................. 38
Figure 24: Maximum shear stress on cylinder ...................................................................... 39
Figure 25: Total deformation on cylinder ............................................................................ 39
Figure 26: Sequence of operation for cylinder manufacturing ............................................. 41
Figure 27: Cylinder .............................................................................................................. 41
Figure 28: Sequence of operation for spring manufacturing ................................................ 46
Figure 29: Spring ................................................................................................................. 46
Figure 30: Piston with two grooves ..................................................................................... 48
Figure 31: Piston with one groove ....................................................................................... 49
Figure 32: Piston with two split ring and one O-ring ............................................................ 50
Figure 33: Teflon piston head and brass rod (Detachable) ................................................... 51
Figure 34: Threaded teflon piston head and brass rod (detachable) .................................... 52
Figure 35: Sequence of operation of Piston ......................................................................... 53
Figure 36: Threaded joint used ............................................................................................ 54
Figure 37: Von-mises stress on head hex ............................................................................. 55
Figure 38: Maximum principal stress on head hex ............................................................... 55
Figure 39: Maximum shear stress on head hex .................................................................... 56
Figure 40: Total deformation on head hex ........................................................................... 56
Figure 41: Von-mises stress on end hex ............................................................................... 58
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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Figure 42: Maximum principal stress on end hex ................................................................. 58
Figure 43: Maximum shear stress on end hex ...................................................................... 59
Figure 44: Total deformation on end hex ............................................................................ 59
Figure 45: Sequence of operation for hex nut manufacturing .............................................. 60
Figure 46: Basic O-Ring........................................................................................................ 61
Figure 47: Basic Gland ......................................................................................................... 61
Figure 48: Gland and O-Ring Seal ........................................................................................ 61
Figure 49: O-Ring Installed .................................................................................................. 62
Figure 50: O-Ring under pressure ........................................................................................ 62
Figure 51: O-Ring Extruding ................................................................................................. 63
Figure 52: O-Ring Under Extrusion Failure ........................................................................... 63
Figure 53: Abrasion ............................................................................................................. 63
Figure 54: Compression Set ................................................................................................. 64
Figure 55: Chemical degradation ......................................................................................... 65
Figure 56: Explosive Decompression ................................................................................... 65
Figure 57: Extrusion ............................................................................................................ 66
Figure 58: Installation Damage ............................................................................................ 66
Figure 59: Outgassing/Extaction .......................................................................................... 67
Figure 60: Overcompression ............................................................................................... 67
Figure 61: Plasma Degradation ............................................................................................ 68
Figure 62: Spiral Failure ....................................................................................................... 69
Figure 63: Thermal Degradation .......................................................................................... 69
Figure 64: O-Ring ................................................................................................................ 76
Figure 65: Friction due to O-ring compression ..................................................................... 78
Figure 66: Friction due to fluid pressure .............................................................................. 78
Figure 67: Variation in Pressure Force (Fp), Friction Force (Fc) with Cylinder ID ................... 79
Figure 68: Protective cover for pressure transducer ............................................................ 81
Figure 69: Principal of linear potentiometer ........................................................................ 82
Figure 70: Principal of LVDT ................................................................................................ 84
Figure 71: Bonded resistance strain gauge .......................................................................... 85
Figure 72: Variable area capacitors ..................................................................................... 87
Figure 73: Test rig suggested ............................................................................................... 89
Figure 74: Pressure Vs Displacement Graph for 8mm ID cylinder ......................................... 94
Figure 75: Pressure Vs Displacement Graph for 10mm ID cylinder ....................................... 97
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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LIST OF TABLES
Table 1: SAM Customers ..................................................................................................... 12
Table 2: Oil for different temperature ranges ...................................................................... 14
Table 3: Design selection chart ............................................................................................ 31
Table 4: Cylinder Thickness for 8mm ID Cylinder ................................................................. 35
Table 5: Selected thickness for 8 mm ID cylinder ................................................................. 36
Table 6: Cylinder Thickness for 10mm ID Cylinder ............................................................... 36
Table 7: Selected thickness for 10 mm ID cylinder ............................................................... 36
Table 8: Stresses on cylinder by ANSYS ................................................................................ 40
Table 9: Spring calculations ................................................................................................. 44
Table 10: Spring Manufactured ........................................................................................... 45
Table 11: Stresses on head hex by ANSYS ............................................................................ 57
Table 12: Stresses on end hex by ANSYS .............................................................................. 60
Table 13: Abressive Failure contributing factors and Suggested solutions ............................ 64
Table 14: Compression set failure Contributing factors and Suggested solutions ................. 64
Table 15: Chemical degradation failure Contributing factors and Suggested solutions ......... 65
Table 16: Explosive decompression failure Contributing factors and Suggested solutions .... 65
Table 17: Extrusion Failure contributing factors and Suggested solutions ............................ 66
Table 18: Installation Damage contributing factors and Suggested solutions ....................... 67
Table 19: Outgassing/ Extraction failure Contributing factors and Suggested solutions ....... 67
Table 20: Overcompression Failure contributing factors and Suggested solutions ............... 68
Table 21: Plasma Degradation contributing factors and Suggested solutions ....................... 68
Table 22: Spiral Failure contributing factors and Suggested solutions .................................. 69
Table 23: Thermal degradation failure contributing factors and Suggested solutions........... 70
Table 24: Stick slip- Possible causes and troubleshooting tips .............................................. 70
Table 25: O-Ring Compression ............................................................................................ 72
Table 26: Recommended Maximum Compression for O-Ring .............................................. 73
Table 27: Comparison of dynamic seal type......................................................................... 74
Table 28: Comparison of commonly used materials for O-Rings .......................................... 75
Table 29: Important parameters for friction determination ................................................. 77
Table 30: Determined values for friction determination ...................................................... 79
Table 31: Values from graph ............................................................................................... 79
Table 32: Total available force for piston movement ........................................................... 80
Table 33: Observation Table for 8mm ID cylinder in reverse direction ................................. 92
Table 34: Observation Table for 8mm ID cylinder in reverse direction ................................. 93
Table 35: Observation Table for 10mm ID cylinder in forward direction .............................. 96
Table 36: Observation Table for 10mm ID cylinder in reverse direction ............................... 97
Table 37: FMECA Chart for Manufactured Pressure Transducer ........................................ 102
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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TABLE OF CONTENT
CERTIFICATE ....................................................................................................................................... 1
ACKNOWLEDGEMENT ........................................................................................................................ 2
LIST OF FIGURES ................................................................................................................................. 3
LIST OF TABLES ................................................................................................................................... 5
TABLE OF CONTENT ............................................................................................................................ 6
SYMBOLS USED .................................................................................................................................. 8
1. ABSTRACT ................................................................................................................................ 10
2. COMPANY PROFILE .................................................................................................................. 11
3. OBJECTIVE OF THE PROJECT ..................................................................................................... 14
4. NEW PRODUCT DEVELOPMENT AND ITS NEED ........................................................................ 15
5. INTRODUCTION: THE SYSTEM .................................................................................................. 16
6. STEPS OF PROJECT WORK ........................................................................................................ 18
7. BACKGROUND: ........................................................................................................................ 19
HOW OIL CONDITION MONITORING OCCURS? ................................................................................. 19
8. MARKET SURVEY ..................................................................................................................... 22
9. PRESSURE MEASUREMENT MECHANISMS IN BRIEF ................................................................. 25
10. MAJOR COMPONENTS OF THE SINGLE ACTING CYLINDER FOR TRANSDUCER ...................... 32
11. CYLINDER ............................................................................................................................. 33
12. SPRING ................................................................................................................................ 42
12. PISTON ................................................................................................................................ 47
13. JOINT USED.......................................................................................................................... 54
14. O RING ............................................................................................................................... 61
15. PREDICTING SEAL FRICTION ................................................................................................. 77
16. PROTECTIVE COVER ............................................................................................................. 81
17. MEASUREMENT OF LINEAR DISPLACEMENT ........................................................................ 82
18. TESTING OF THE PRESSURE TRANSDUCER ........................................................................... 88
19. COSTING .............................................................................................................................. 98
20. MAINTENANCE OF THE PRESSURE TRANSDUCER ................................................................. 99
21. FAILURE MODE, EFFECT AND CRITICALITY ANALYSIS ......................................................... 100
22. SWOT ANALYSIS ................................................................................................................ 104
23. FUTURE SCOPE .................................................................................................................. 106
24. CONCLUSIONS ................................................................................................................... 108
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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25. REFERENCES ...................................................................................................................... 109
ANNEXTURE-I: MATLAB PROGRAM FOR GRAPH GENERATION .................................................. 110
ANNEXTURE-II: SHENDE SALES CORPORATION CATALOGUE FOR O RINGS ............................. 111
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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SYMBOLS USED
T -torque
Di -cylinder inner diameter
t -cylinder thickness
t -hoop stress
l -longitudinal stress
r -radial stress
-poisons ratio
-allowable shear stress
p -pressure inside the cylinder
Syt -tensile yield strength
Sper -permissible tensile stress
Ss -permissible shear stress
G -modulus of rigidity
c -spring index
D -mean coil diameter of spring
d -wire diameter
Kw -wahls factor
N -number of spring turns
Nt -total number of spring turns
Lw -working length of spring
Lc -clearance allowance for spring
Li -initial compression of spring
Lf -free length of spring
Ps -pitch of spring
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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F -load acting on spring
S -stretch value for O-Ring
Gd -O-Ring groove diameter
Srec -recommended stretch value for O-Ring
ID -inner diameter for O-Ring
Bd -bore diameter
CS -cross section diameter of O-Ring
C -compression of O-Ring
GW -groove width
F -total friction force
FC -friction force due to seal squeeze
FH -friction force due to pressure
fC -friction factor for seal squeeze
fH -friction factor for pressure
Lh -piston circumference
Ar -seal projected area
RPN -risk priority number
S -severity
O -occurrence
D -detection
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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1. ABSTRACT
Condition monitoring service gives an ongoing program of sampling, analysis and
reporting of the system under observation. It provides the information you need to
pin-point and solve equipment problems as well as implement a more effective
maintenance system. In condition monitoring of oil lubrication system, there are
various parameters to be analysed, pressure being the most important one. This
pressure when continuously monitored, gives an idea about the health of the
lubrication system. This confirms the importance of pressure gauges in condition
monitoring of oil lubrication system.
The main intention of the project is to design a pressure transducer to give the
pressure readings for the condition monitoring of a lubrication system of a generator
set. This objective is persuaded with design theory, ANSYS, manufacturing processes
with a great fruit of success.
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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2. COMPANY PROFILE
A. History:
Having started the business under the banner of Ideas Toolings, SAM holds over 17
years of experience in this industry. Later in the year 2004, it merged as SAM
Integrations Private Limited and have established as one of the premier manufacturers
and exporters of a comprehensive range of Electro Mechanical Products.
B. Directors:
Chairman: Mr. V. S. Deshpande
M. Des., IIT, Bombay.
Having more than 27 years of hands on experience
Managing Director: Mr. N. B. Tembe
B. Tech., Specialisation in production.
Having more than 32 years of hands on experience.
C. Basic Information of company:
Business Type:
Manufacturer
Exporter
Ownership & Capital:
Year of Establishment- 2004
Ownership Type- Private Limited Company
Certification & Membership:
Certification Name- ISO 9001:2008
Start Date- 26-APR-11
Expiry Date: 11-JUN-14
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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D. Customers:
E. Team & Staff:
Total Number of Employees-51 to 100 People
F. Application Areas:
The Electro Mechanical Products designed in the unit are evaluated for maximum
durability, ability to withstand wear & tear and accurate performance. These features
make SAMs products compatible to withstand most severe applications and
environments. The product range offers solutions to the following areas:
Generator
Compressor
Escalators
Automotives
Diesel Engines
Other Industrial Applications
R.T.S. Inc., MI 49015, USA Fike Safety Technology Ltd, United Kingdom
Kirloskar Brothers Limited Shirwal Kirloskar Engines India Ltd.
Jakson Enterprises Silvassa Ashok Leyland Limited
Mahindra & Mahindra Ltd. Powerica Ltd Silvassa, Banglore, Taloja
Cummins India Ltd Greaves Cotton Limited
Premier Engineering Works Sterling Generators Pvt. Ltd.
Nasan Medicals Jeevan Diesels & Electricals Ltd.
Standard Meter Mfg. Co. Mahalasa Acoustic Pvt. Ltd.
Shamraj Engineering Power Engineering (I) Pvt. Ltd.
Philip Harris UK Maya Engineering
Core Objects Sunbeam Generators Pvt. Ltd.
Table 1: SAM Customers
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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G. PRODUCT RANGE AT SAM
Tank Units for Gensets
Figure 1: Tank Unit for gensets
S-Series Fuel Indicator
Figure 2: S-series Fuel Indicator
Fuel Indicator
Figure 3: Fuel Indicator
Drain Pump
Figure 4: Drain Pump
Fire Safety Equipments
Figure 5: Fire Safety Equipments
Fuel Filling Neck
Figure 6: Fuel Filling Neck
(Reference# 1)
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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3. OBJECTIVE OF THE PROJECT
The pressure transducers used in generator sets for condition monitoring of
lubrication system in the current industrial scenario consist of a diaphragm
mechanism which gives minimum deflection with respect to the pressure, to measure
this deflection to calibrate the pressure; we need some arm effect to get good range of
output. This arm effect does add some rounding-off errors, which leads to unreliable
output from the transducer, where transducer is a device which convert the parameter
to be measured into a proportional electrical quantity which can be directly read using
an indicator.So to overcome this error in readings it is required to look for some more
appropriate mechanism which will lead to less errors or at least avoid some
complications in the current designs followed by the industry.
A. Technical specification to be attained:
Pressure range: 0-5 bar
Output deflection required: 15mm for 5 bar
Accuracy expected: +/- 5%
Temperature: 70C max
Engine oil viscosity: Use an oil having viscosity best suited to the atmospheric
conditions. Use of an all season SAE 10W/30 having low viscosity change
with change in temperature is suggested.
Temperature (C) Viscosity
68F (20C) or higher SAE 30 or SAE10W/30
41F (5C) to 68F (20C) SAE 20 or SAE10W/20
Below 41F SAE 20
Table 2: Oil for different temperature ranges
(NOTE: Do not use an engine lubricating oil with a SAE rating number above 30 in
the engine.)
So the prime objective of the project is to design such a pressure transducer which
satisfies the technical specifications, minimizes the errors found in current industrial
design and redesign the product.
(Reference# 1)
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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4. NEW PRODUCT DEVELOPMENT AND ITS NEED
New product development is a vital part of any business. It doesn't matter whether the
product is for consumers or other businesses, whether it is a tangible object or a
service. The constant change in markets and technology require that companies take
steps to meet new challenges. Developing new products and improving existing
products is an important step in meeting this challenge. New product development can
be just what it sounds like the creation of a completely new product that fills a
previously unaddressed niche in the economy. Product development also includes re-
examining an existing product to maximize its market potential through adding
features, a design change or maybe just tweaking the marketing.
Fortunately, product innovation is not a completely hit or miss proposition. There are
steps a company can take to improve the likelihood of a successful development
process. There is no one "best" method for developing products, and what works for
one segment of a particular industry may not work for another industry, or maybe not
even for another segment of that industry. The mix of elements will be different for
every product development project, but companies can look to a basic framework to
help keep all the different elements on track.
The goal of the product development process is to end up with the best possible
product. One that is well suited for the intended audience and contains features that is
needed and desired. No matter how great the new product may seem, if the market
rejects it, it's a failure. Taking the product development process seriously can go a
long way toward making the end result a success.
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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5. INTRODUCTION: THE SYSTEM
In the system, the oil is forced under pressure through the oil line by a pump. In the
oil line it passes through the filter and then to the manifold. The manifold supplies the
oil to the main lubrication system and various components requiring oil. One oil line
is passed to the pressure gauge which measures the pressure in the oil line produced
by the pump.
Looking at the schematic, many factors come into play when setting oil pressure.
Each of the manifold outputs is designed for certain volume, and the individual
calculated circuit resistances come into play to determine overall resistance to oil
flow. This is much like having four or five hoses connected to one hose bib on the
side of the house if one bursts, all will lose pressure. If one is plugged up, the pressure
increases for the rest. This system is much the same. So if an output is clogged, like
the governor line for instance, pressure will rise. If your transmission has worn out
main bearings allowing much of the oil to slide back into the crankcase prematurely,
pressure will be lower. The bottom line here is that any rather sudden rise or fall in oil
pressure should be taken as a signal that your engines oiling system needs attention.
This way pressure gauge plays an important role oil lubrication system.
(Reference# 17)
Figure 7: Oil lubrication system
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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PRESSURE GAUGE MOUNTING ON GEN-SET
Figure 8: Pressure gauge mounting on gen-set
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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6. STEPS OF PROJECT WORK
Market survey
Analyzing available market products
Brain storming for all possible concepts of pressure transducers
Studying for best workable concept
Drawing the basic structure of the pressure transducer
Optimizing the design with dimensions, material, joining processes, surface
finish, etc.
Manufacturing the prototype of the product
Testing the product and reviewing design
Working on the steps of aesthetics, durability, safety, recyclability, ease of use,
etc.
Finalizing the design with optimum parameters
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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7. BACKGROUND: How oil condition monitoring occurs?
An oil condition monitoring service gives you an ongoing program of sampling,
analysis and reporting. It provides the information you need to pinpoint and solve
equipment problems as well as implement a more effective maintenance system.
Lubricating oils contain all the requisite additives to protect the equipment from wear,
corrosion and excess friction. The additives in the oil are multi-functional, therefore,
it is important they do not deplete (and is one of the reasons oil types should not be
mixed). This is particularly important in long term usage.
A. Types of oil condition monitoring:
1. On-line testing
2. Off-line testing
Visual darkening of oil
A burnt smell to the oil
An increase in viscosity
Visual haziness
Foaming
It is important that oil condition monitoring is completed on a regular basis to ensure
that the oil quality is stable. Regular monitoring soon builds a history of the fluid
condition allowing informed decisions to be taken.
Continued operation with degraded oil will lead to accelerated wear of moving parts
and filtration problems resulting in an accumulation of sludge in the tank and pipe-
work.
B. Conventional analysis makes use of oil sampling techniques
which suffer from some serious drawbacks:
1. It takes to process the sample; machinery can be damaged from poor lubricant
quality.
2. Secondly, one can never be sure that the oil sampled is representative of the entire
lubricating system. Various sampling techniques are used in an attempt to acquire
the best sample, but there are still possibilities that the sample collected is not the
most representative of the system.
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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3. When a sample is taken, it is difficult to ensure no outside contamination from the
sampling procedure, container or laboratory has been introduced.
4. Finally, off-line oil sampling and analysis can be costly.
Real time monitoring is a vital tool, which can allow lubricants to be used to their
fullest potential while minimizing machinery downtime, resulting in increased savings
and productivity. Real time sensors provide the ability to conduct continuous
monitoring. This is beneficial on many levels, especially in responding to suddenly
occurring faults and condition trending.
C. On-line oil condition monitoring
Oil is forced under pressure through the oil line by a pump. Filtered oil is then forced
through oil lines to the manifold. The manifold supplies the oil to the main lubrication
system and various components requiring oil. One oil line from manifold is passed to
the pressure gauge which measures the pressure in the oil line produced by the pump.
An oil pressure gauge gives an excellent indication of the health of various systems in
the engine. The key is to establish baseline readings when the engine is healthy, and
then be aware of any changes over the time.
D. Cause of low pressure:
The contaminant in oil line and mostly in the filter block the flow of oil in the
system which tends to reduce the pressure at which the is to be supplied to the
engine and other parts.
Low oil level
Damaged oil pan or pick-up tube
High Oil Temperature- Generally not a big factor, but if you're pulling a trailer or
running flat out in really hot weather, your oil can run well over 250F., and oil
pressure will be lower.
Worn Oil Pump - This could be anything from a slight reduction all the way to
catastrophic failure (which is rare unless the pump has ingested bits of metal from
some other failure).
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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E. Cause of high pressure:
High oil pressure is not generally a concern, but if pressure suddenly increases, there
may be a problem with the pressure relief valve. Switching to higher viscosity oil will
also show higher readings.
(Reference# 17)
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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8. MARKET SURVEY
The project started with a search for all available and possible mechanisms for the
particular objective of condition monitoring of lubrication system ie. pressure gauge.
Starting with internet, we found many makers of such pressure transducers with
different principles been utilized some of which are also used for automobiles
application.
A. COMPETITOR MANUFACTURER
Pricol
RICO
Saudamini
VDO
B. RICO COMPONENT ANALYSIS
ADVANTAGES
Robust construction
Small in size
Ease of mounting
DRAWBACKS
Hystersis due to torsional spring
Not precisely and accurate
Assembly not easy to repair
Less life due to use of diaphragm
(Reference# 14, 18)
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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Figure 9: Assembly of RICO pressure transducer
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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C. DIFFERENT MECHANISMS FOR PRESSURE
MEASUREMENT
Mechanical
1. Bourdon tube
a. C-shaped bourdon tube
b. Helical bourdon tube
c. Spiral bourdon tube
2. Diaphragm
a. Flat diaphragm
b. Convoluted diaphragm
c. Capsule
3. Set of bellow
4. Single acting cylinder
5. Manometer
Electrical
1. Capacitive type.
2. Strain gauge.
3. Piezo-electric type.
As the requirement is for the mechanical type pressure transducer, hence electrical
types of pressure measuring elements are neglected.
(Reference# 2, 4, 6, 8)
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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9. PRESSURE MEASUREMENT MECHANISMS IN BRIEF
A. Bourdon tube:
i. C-shaped bourdon tube:
Eugene Bourdon invented this type of gauge in 1851. He stated that round tubing
which has been flattened and bent into a circular arc will tend to return to its original
shape when a pressure is applied inside it. The operation is similar to that of the paper
coiled-tube blowers used at parties. In its simplest form it consists of a length of thin-
walled metal tubing which has been flattened, to approximately an elliptical cross
section and then rolled into a C shape, having an arc span of about 270.
Figure 10: C-shaped bourdon tube
The external pressure is guided into the tube and causes it to flex, resulting in a
change in curvature of the tube. These curvature changes are linked to the dial
indicator for a number readout.
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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ii. Helical bourdon tube:
Figure 11: Helical bourdon tube
Helical bourdon tube pressure gauge sensing element is formed in the helical spring
shape. The distance of the bourdon tube from the center tube is very much more than
the C-Type. The sensitivity of this type is more due to its angular length.
When input pressure is applied, pointer will rotate along with its axis and pointer end
showing reading on a scale which is marked in pressure units. It converts pressure to
displacement; in this type of bourdon tube no additional gain mechanism is required.
iii. Spiral bourdon tube:
Figure 12: Spiral bourdon tube
The radius of the tube from the centre is continuously vary in figure it increasing. The
inner end of the tube is treated as reference and outer free end gives the displacement
according to applied pressure. If a pointer is attached to the outer free end of the tube,
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then it directly gives the pressure measurement on a scale which is marked in pressure
units. In some designs the free end of the Bourdon is wound round several times with
the socket-pressure connection at the centre. Figure 13 shows the general idea of such
an element. The amount of movement varies directly with the angle subtended by the
total arc. By increasing the number of turns in the spiral or helix, a greater movement
of the tip is obtained.
B. Diaphragm :
i. Flat diaphragm:
Figure 13: Flat diaphragm
The flat diaphragm pressure gauge uses the elastic deformation of a diaphragm (i.e.
membrane) instead of a liquid level to measure the difference between an unknown
pressure and a reference pressure.
A typical Diaphragm pressure gage contains a capsule divided by a diaphragm, as
shown in the schematic below. One side of the diaphragm is open to the external
targeted pressure, PExt, and the other side is connected to a known pressure, PRef. The
pressure difference, PExt - PRef, mechanically deflects the diaphragm.
Figure 14: Schematic diaphragm pressure gauge
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ii. Convoluted diaphragm:
Figure 15: Convoluted diaphragm
The working principle is just the same as the flat diaphragm only the construction is
different.
iii. Capsule:
A capsule is formed by joining the peripheries of two diaphragms through soldering
or welding.
Figure 16: Capsule
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C. The set of bellow:
Figure 17: Set of bellow pressure gauge
Bellow type pressure gauges use a spring loaded elastic material bellow to measure
the pressure and the indication is with linkages.
D. Single acting cylinder:
Piston cylinder type is utilized in this kind of pressure gauge assembly, where on one
side of piston there is the application of pressure and on the other side a counter
weight is applied which also measures the deflection, hence giving pressure reading.
Figure 18: Single acting cylinder
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E. Manometer:
Manometers are working on the principle of hydrostatic balancing. The force acting
due to one liquid column on the same level or reference balances the force acting due
to another liquid column. The simplest manometer consists of a tube made of glass or
other transparent material bent into the shape of a U and with both ends left open. A
few spoonfuls of water poured into the tube is all that is required to make a
manometer. The liquid-filled manometer is one of the most useful and inherently
accurate instruments for measuring any variable that is a function of pressure.
Because of its simplicity and accuracy the manometer is widely used.
Figure 19: U-tube manometer
(Reference# 2, 4, 6, 8)
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F. DESIGN SELECTION
Parameter
Bo
urd
on
tu
be
Dia
ph
ragm
Set
of
bel
low
Sin
gle
acti
ng
cylin
der
Man
om
eter
Ease of manufacturing
Ease of assembly
Ease of calibration
Design strength
Output accuracy
Product reliability
Long product durability
Low product cost
Table 3: Design selection chart
INFERENCE
Single acting cylinder assembly has the most no. of checks, which indicates that it has
the most no. of desired properties with this mechanism. For this particular application
of condition monitoring of lubrication system the output is required for the change in
pressure not for accurate readings, hence the single acting cylinder mechanism is best
suited for the application of pressure measurement.
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10. MAJOR COMPONENTS OF THE SINGLE ACTING CYLINDER FOR TRANSDUCER
1. Cylinder Design
2. Helical Compression Spring Design
3. Piston Design
4. Joint Used
5. O Ring Selection
6. Protective Cover
7. Electronic System and Pointer Arrangement
These are the major components of the single acting cylinder assembly for the
pressure transducer. Designing for strength, manufacturing, assembly, aesthetics and
environmental impact completes the primary design of pressure transducer.
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11. CYLINDER
A. DESIGN OF CYLINDER
i. INTRODUCTION
Depending upon whether the cylinder wall thickness is appreciable or not, in relation
to the inner diameter of the cylinder, the cylinder are classified into two categories:
1. Thin cylinder (Di/t>20)
2. Thick cylinder (Di/t
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The magnitude of the radial stress is equal to the internal pressure at the inner surface
of the cylinder and zero at the outer surface of the cylinder.
As the cylinder is subjected to three principal stresses, different theories of failure are
used in the design of the cylinder subjected to internal pressure. The selection of the
theory depends upon two parameters:
i. Cylinder material (whether brittle or ductile)
ii. Condition of cylinder ends (open or closed)
iii. Different theories of failures used in the design of the cylinders subjected to
internal pressure are
1. Maximum principal stress theory (Lames theory)
Used when the cylinder is made of brittle material like cast iron.
2. Maximum principal strain theory
Cylinder with closed end (Clavarinos theory)
Cylinder with open end (Birnies theory)
3. Maximum shear stress theory
Used when the cylinder is made of ductile material like MS, brass etc.
4. Distortion energy theory
As the cylinder for the particular application is to be made with ductile material,
the theories used are
A. Maximum principal strain theory (Clavarinos theory)
B. Maximum principal strain theory (Birnies theory)
C. Maximum shear stress theory
D. Distortion energy theory
iv. Formulae Used:
A. Maximum principal strain theory (Clavarinos theory)
t=
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B. Maximum principal strain theory (Birnies theory)
t=
C. Maximum shear stress theory
t=
D. Distortion energy theory
t=
(Reference# 3, 9, 10, 12, 13)
The following table contains specifications for three categories namely plastics,
metals, and glass-fibers. Specifications have been calculated for the given set of
values:
v. SET-1
1. Pressure=P = 5 bar = 0.5 N/mm2
2. Dia. Of Piston=Di= 8 mm
3. Factor of safety= 4
The cylinder is provided with a threading at both ends hence forming a critical
thickness at that section.
Thread used:
M121.25
material syt per.
stress
(sper)
per. shear
stress
(ss)
thickness by
clavarinos theory
thickness by
birnies theory
thickness by
maximum
shear stress
theory
thickness by
distortion
energy
theory
(MPa) (MPa) (MPa) (mm) (mm) (mm) (mm)
Steel 480 120 60 0.014218550 0.016722480 0.016771562 0.014512351
Brass 200 50 25 0.034300754 0.040323599 0.040610178 0.035097611
Table 4: Cylinder Thickness for 8mm ID Cylinder
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The thickness allowance for the threads t=0.77mm
Total thickness required= t+safe value of thickness from chart
Material Total thickness required (mm) Approximated thickness (mm)
Steel 0.77+0.01677=0.78677 2
Brass 0.77+0.04061=0.81061 2
Table 5: Selected thickness for 8 mm ID cylinder
(with considering the manufacturing limitation the thickness is assumed as 2mm)
vi. SET-2 1. Pressure=P = 5 bar = 0.5 N/mm2
2. Dia. Of Piston=Di= 10 mm
3. Factor of safety= 4
Table 6: Cylinder Thickness for 10mm ID Cylinder
The cylinder is provided with a threading at both ends hence forming a critical
thickness at that section.
Thread used:
M141.5
The thickness allowance for the threads t=1.08mm
Total thickness required= t+safe value of thickness from chart
Material Total thickness required (mm) Approximated thickness (mm)
Steel 1.08+0.02096=1.10096 2
Brass 1.08+0.05076=1.13076 2
Table 7: Selected thickness for 10 mm ID cylinder
(with considering the manufacturing limitation the thickness is assumed as 2mm)
material syt per.
stress
(sper)
per. shear
stress
(ss)
thickness by
clavarinos
theory
thickness by
birnies
theory
thickness by
maximum
shear stress
theory
thickness by
distortion
energy
theory
(MPa) (MPa) (MPa) (mm) (mm) (mm) (mm)
Steel 480 120 60 0.017773187 0.020903101 0.020964452 0.018140443
Brass 200 50 25 0.042875942 0.050404499 0.050762722 0.043872014
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vii. INFERENCE
1. With the consideration of material availability, ease of manufacturing and the
critical thickness required for brass and M.S., they are selected for the prototype
design purpose.
2. Not knowing the critical diameter for least friction between O-ring and cylinder
the two diameters 8mm and 10mm are selected for analysis.
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B. ANSYS REPORT FOR CYLINDER
STRUCTURAL ANALYSIS (Mat- Brass)
i. VON-MISES STRESS
Figure 22: Von-mises stress in cylinder
ii. MAXIMUM PRINCIPLE STRESS
Figure 23: Maximum principal stress on cylinder
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iii. MAXIMUM SHEAR SHTRESS
Figure 24: Maximum shear stress on cylinder
iv. TOTAL DEFORMATION
Figure 25: Total deformation on cylinder
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v. INFERENCE
Type Equivalent (von-
Mises) Stress
Maximum
Principal Stress
Maximum
Shear Stress
Total
Deformation
Minimum 1.1252e-003 MPa -1.1213 MPa 5.6626e-004
MPa 0. mm
Maximum 1.6202 MPa 0.28252 MPa 0.88713 MPa 3.0369e-005 mm
Table 8: Stresses on cylinder by ANSYS
With reference to allowable stress on brass (50 MPa), the maximum stress developed
in cylinder (1.6202 MPa) from ANSYS, the cylinder is safe.
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C. MANUFACTURING OF THE CYLINDER
Machines used: Lathe m/c, grinding m/c
Operations performed: Turning, drilling, boring, threading, chamfering, grinding
Sequence of operation:
Figure 26: Sequence of operation for cylinder manufacturing
Figure 27: Cylinder
RAW MATERIAL CUTTING
.
FACING
TURNING
DRILLING
FINISH
REAMING
THREADING
START
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12. SPRING
i. DESIGN OF SPRING
i. INTRODUCTION
The design of a new spring involves the following considerations:
ii. Space into which the spring must fit and operate.
iii. Values of working forces and deflections.
iv. Accuracy and reliability needed.
v. Tolerances and permissible variations in specifications.
vi. Environmental conditions such as temperature, presence of a corrosive
atmosphere.
vii. Cost and qualities needed.
The designers use these factors to select a material and specify suitable values for the
wire size, the number of turns, the coil diameter and the free length, type of ends and
the spring rate needed to satisfy working force deflection requirements. The primary
design constraints are that the wire size should be commercially available and that the
stress at the solid length be no longer greater than the torsional yield strength. Further
functioning of the spring should be stable.
Springs are fundamental mechanical components which form the basis of many
mechanical systems. A spring can be defined to be an elastic member that exerts a
resisting force when its shape is changed. Most springs are assumed linear and obey
the Hooke's Law.
ii. SPRING MATERIAL
The most extensively used spring material is high-carbon hard drawn spring steel. It is
often called Patented and cold-drawn steel wire. This material has been used for
most spring manufacturing due to its good response to spring requirements and hence
it is selected for the particular spring design.
iii. SPRING CHARACTRISTICS
End style- Square and ground end
Right handed spring
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Spring material- Unalloyed, oil hardened and tempered spring steel valve spring
wire (VW)
Expected deflection- 22.5mm for 7.5 bar pressure
iv. FORMULAE AND DATA USED FOR DESIGN
1. Modulus of rigidity (G) = 83170 N/
2. Spring Index (C) =
3. Wahls Factor ( ) =
4. Number of Turns (N) =
5. Total number of turns ( ) = N + 2
6. Working Length ( =
7. Solid Length ( = * d
8. Clearance Allowance ( ) = 15% of working length
9. Total Length ( +
10. Pitch (Ps) =
11. Shear Stress () =
(Reference# 9, 10, 11, 12, 15)
v. SPRING HYSTERSIS Hysteresis is the loss of mechanical energy under cyclic loading and unloading of a
spring. It results from frictional losses in the spring support system due to tendency of
the ends to rotate as the spring is compressed. Hysteresis for compression springs is
low and the contribution due to internal friction in the spring material itself is
generally negligible.
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vi. INFERENCE
The highlighted spring designs are selected for the manufacturing purpose on the
basis of its ease of manufacturing and dimensional limitations.
Table 9: Spring calculations
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vi. MANUFACTURING OF THE SPRING
The spring is not manufactured in the firm, so it was order from the Bhalchand
Spring Pvt. Ltd.
The material available were stainless steel, M.S. and spring steel. The spring is the
recommended one by the manufacturer and design data book, hence we preferred the
spring steel for the application.
Dimensions of the springs manufactured:
Parameter Spring 1 Spring 2
Mean spring diameter 5.8 mm 8 mm
Inner diameter 5 mm 7 mm
Outer diameter 6.6 mm 9 mm
Pitch 3 mm 4.5 mm
Total no. of turns 15 10
Wire diameter 0.8 mm 1 mm
Free length 42 mm 40.5 mm
Material Spring steel Spring steel
Type of end Square and ground end Square and ground end
Spring hand Right handed Right handed
Table 10: Spring Manufactured
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SEQUENCE OF PROCESS
Figure 28: Sequence of operation for spring manufacturing
Figure 29: Spring
RAW MATERIAL CUTTING
Stainless Steel / Spring Steel
SIZING
COLD WINDING
GRINDING
FINISH
START
STRESS RELIVING IN A FURNACE
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12. PISTON
A. PISTON DESIGN
i. INTRODUCTION
The function of piston is to take pressure of oil on one side and on the other side the
spring force. As the stresses acting on the piston are very small compared to the piston
strength hence the piston is not designed on strength basis. The more important
aspects are mass of piston, no. of groves, piston end design, pointer attachment at the
end of the piston rod, buckling reaction of spring on the piston rod.
Factors considered in piston design:
Mass of the piston: The mass of the piston primarily depend upon the material of
the piston. M.S., brass, aluminum, delrin and Teflon are the materials which were
available for manufacturing. As the application is in the oil the M.S. is prone to
rust hence it is eliminated. Brass has been used for hydraulic cylinders hence it
was of prime focus, but the density of brass is quiet high. Aluminum was quiet
likely material for the application but the availability has been the problem.
Delrin and Teflon were rejected based on its buckling tendency ie strength basis
as the rod is likely to experience a buckling from the spring buckling as it is
supposed to act as a guide for the spring. Hence brass is selected for the
manufacturing.
No. of groves: While testing on single grooved piston, it was observed that there
was quite a lot of play at the end of piston, so double grooved piston is preferred.
Pointer attachment: There have been many possibilities for pointer attachments
but the threaded joint is chosen for its ease of handling for primary testing
purpose.
Piston rod diameter: The piston rod is supposed to be as thin as possible but the
manufacturing problems constraints the size of the piston rod to 4mm. Hence
4mm rod is preferred.
Groove width: Groove width for O-ring attachment is kept a bit more than the
O-ring diameter so as to allow play for O-ring between the grooves, so as to
avoid crushing stresses.
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ii. DIFFERENT PISTON DESIGNS TRIED
a) PISTON WITH TWO GROOVES
Figure 30: Piston with two grooves
Characteristics
No leakage observed
Robust construction
Two O-rings helps in avoiding oscillation of piston
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b) PISTON WITH ONE GROOVE
Figure 31: Piston with one groove
Characteristics
Leakage was observed after 3.2 bar pressure
Robust construction
One O-ring doesnt make it fully leakage proof
One support allows piston to oscillate
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c) PISTON WITH TWO SPLIT RING AND ONE O-RING
Figure 32: Piston with two split ring and one O-ring
Characteristics
Leakage was observed after 2.6 bar pressure
Robust construction
O-ring gives positive sealing
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d) TEFLON PISTON HEAD AND BRASS ROD (DETACHABLE)
Figure 33: Teflon piston head and brass rod (Detachable)
Characteristics
Leakage was observed after 1.2 bar pressure
Kinematic constraints are utilised for improving manufacturing
No positive sealing
With lack of precise manufacturing process the piston was prone to leakage
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e) THREADED TEFLON PISTON HEAD AND BRASS ROD
Figure 34: Threaded teflon piston head and brass rod (detachable)
Characteristics
Leakage was observed after 3.2 bar pressure
Threads reduce contact area, O-ring gives positive sealing
Kinematic constraints are utilised for improving manufacturing
With lack of precise manufacturing process the piston was prone to leakage
iii. INFERENCE
Piston with two grooves was the best design which avoided leakage. It also has simple
construction and does not need precise machining; hence piston with two groove
design is selected.
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B. MANUFACTURING OF PISTON
The piston is manufactured on a lathe machine, so the primary drawback that came to
the product was the accuracy of the dimensions. The piston is manufactured with
brass as it was available at SAM. The threading at the end of piston for pointer
attachment is made of M3 as it was the least tap available.
SEQUENCE OF OPERATION
Figure 35: Sequence of operation of Piston
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13. JOINT USED
A. INTRODUCTION
Currently the market trend is to make the product such that it wont be possible to
open the assembly and repair or get the mechanism behind the joints. As the product
is in the design phase we assumed the threaded joints to be most appropriate for the
primary design.
While thinking about the product to be manufactured we assumed plastic welding to
be the most appropriate joining process, as the whole component is to be
manufactured from plastic for the mass production.
Figure 36: Threaded joint used
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B. ANSYS REPORT FOR HEAD HEX
i. VON MISES STRESS
Figure 37: Von-mises stress on head hex
ii. MAXIMUM PRINCIPAL STRESS
Figure 38: Maximum principal stress on head hex
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iii. MAXIMUM SHEAR STRESS
Figure 39: Maximum shear stress on head hex
iv. TOTAL DEFORMATION
Figure 40: Total deformation on head hex
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v. INFERENCE
Type Equivalent (von-
Mises) Stress
Maximum
Principal Stress
Maximum
Shear Stress
Total
Deformation
Minimum 6.5967e-007 MPa -1.2119 MPa 3.5209e-007
MPa 0. mm
Maximum 2.8344 MPa 4.7225 MPa 1.4901 MPa 4.9975e-005 mm
Table 11: Stresses on head hex by ANSYS
With reference to allowable stress on brass (50 MPa), the maximum stress developed
in cylinder (4.7225 MPa) from ANSYS, the cylinder is safe.
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C. ANSYS REPORT FOR END HEX
i. VON MISES STRESS
Figure 41: Von-mises stress on end hex
ii. MAXIMUM PRINCIPAL STRESS
Figure 42: Maximum principal stress on end hex
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iii. MAXIMUM SHEAR STRESS
Figure 43: Maximum shear stress on end hex
iv. TOTAL DEFORMATION
Figure 44: Total deformation on end hex
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v. INFERENCE
Type Equivalent (von-
Mises) Stress
Maximum
Principal Stress
Maximum
Shear Stress
Total
Deformation
Minimum 1.1977e-005 MPa -1.4534 MPa 6.8174e-006
MPa 0. mm
Maximum 2.345 MPa 1.8894 MPa 1.3525 MPa 4.727e-005 mm
Table 12: Stresses on end hex by ANSYS
With reference to allowable stress on brass (50 MPa), the maximum stress developed
in cylinder (2.345 MPa) from ANSYS, the cylinder is safe.
D. SEQUENCE OF OPERATION
Figure 45: Sequence of operation for hex nut manufacturing
START
RAW MATERIAL CUTTING
Brass
DRILLING
BORING
TAPING
FINISH
THREADING
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14. O RING
A. INTRODUCTION
An O-ring seal is used to prevent the loss of a fluid or gas. The seal assembly consists
of an elastomer O-ring and a gland. An O-ring is a circular cross-section ring moulded
from rubber.
Figure 46: Basic O-Ring
Figure 47: Basic Gland
Figure 48: Gland and O-Ring Seal
i. Advantages of O-Rings seals:
a) They seal over a wide range of pressure, temperature and tolerance.
b) Ease of service, no smearing or retightening.
c) No critical torque on tightening, therefore unlikely to cause structural damage.
d) O-rings normally require very little room and are light in weight.
e) Where differing amounts of compression effects the seal function, an O-ring is
not affected because metal to metal contact is generally allowed for.
f) They are cost-effective.
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ii. O-RING INSTALLATION
The rubber seal should be considered as essentially an incompressible, viscous fluid
having a very high surface tension. Whether by mechanical pressure from the
surrounding structure or by pressure transmitted through hydraulic fluid, this
extremely viscous fluid is forced to flow within the gland to produce zero clearance
or block to the flow of the less viscous fluid being sealed.
The rubber absorbs the stack-up of tolerances of the unit and its internal memory
maintains the sealed condition. Figure illustrates the O-ring as installed, before the
application of pressure. Note that the O-ring is mechanically squeezed out of round
between the outer and inner members to close the fluid passage.
Figure 49: O-Ring Installed
iii. VARIOUS STAGES O-RING UNDER APPLICATION OF
MECHANICAL PRESSURE
STAGE I- PRESSURE APPLIED
The seal material under mechanical pressure extrudes into the micro-fine grooves of
the gland. Figure illustrates the application of fluid pressure on the O-ring. Note that
the O-ring has been forced to flow up to, but not into, the narrow gap between the
mating surfaces and in so doing, has gained greater area and force of sealing contact.
Figure 50: O-Ring under pressure
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STAGE II PRESSURE LIMIT REACHED
Figure shows the O-ring at its pressure limit with a small portion of the seal material
entering the narrow gap between inner and outer members of the gland.
Figure 51: O-Ring Extruding
STAGE III EXTRUSION FAILURE
Figure illustrates the result of further increasing pressure and the resulting extrusion
failure. The surface tension of the elastomer is no longer sufficient to resist flow and
the material extrudes (flows) into the open passage or clearance gap.
Figure 52: O-Ring Under Extrusion Failure
iv. COMMON MODES OF FAILURE
a) ABRASION
Figure 53: Abrasion
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Description:
The seal or parts of the seal exhibit a flat surface parallel to the direction or motion.
Loose particles and scrapes may be found on the seal surface.
Contributing Factors Suggested Solutions
a. Rough sealing surfaces.
b. Excessive temperature.
c. Process environment containing
abrasive particles.
d. Dynamic motion.
e. Poor elastomer surface finish.
a. Use recommended gland surface
finishes.
b. Consider internally lubed elastomers.
c. Eliminate abrasive components.
Table 13: Abressive Failure contributing factors and Suggested solutions
b) COMPRESSION SET
Figure 54: Compression Set
Description: The seal exhibits a flat-sided cross-section, the flat sides correspoding to
the mating seal surfaces.
Contributing Factors Suggested Solutions
a. Excessive compression.
b. Excessive temperature.
c. Incompletely cured elastomer.
d. Elastomer with high compression set.
e. Excessive volume swell in chemical.
a. Low compression set elastomer.
b. Proper gland design for the specific
elastomer.
c. Confirm material compatibility.
Table 14: Compression set failure Contributing factors and Suggested solutions
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c) CHEMICAL DEGRADATION
Figure 55: Chemical degradation
Description:
The seal may exhibit many signs of degradation including blisters, cracks, voids or
discoloration. In some cases, the degradation is observable only by measurement of
physical properties.
Contributing Factors Suggested Solutions
Incompatibility with the chemical and/or
thermal environment.
Selection of more chemically resistant
elastomer.
Table 15: Chemical degradation failure Contributing factors and Suggested solutions
d) EXPLOSIVE DECOMPRESSION
Figure 56: Explosive Decompression
Description:
The seal exhibits blisters, pits or pocks on its surface. Absorption of gas at high
pressure and the subsequent rapid decrease in pressure. The absorbed gas blisters and
ruptures the elastomer surface as the pressure is rapidly removed.
Contributing Factors Suggested Solutions
a. Rapid pressure changes.
b. Low-modulus/hardness elastomer.
a. Higher-modulus/hardness elastomer.
b. Slower decompression.
Table 16: Explosive decompression failure Contributing factors and Suggested solutions
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e) EXTRUSION
Figure 57: Extrusion
Description: The seal develops ragged edges (generally on the low-pressure side)
which appear tattered.
Contributing Factors Suggested Solutions
a. Excessive clearances.
b. Excessive pressure.
c. Low-modulus/hardness elastomer.
d. Excessive gland fill.
e. Irregular clearance gaps.
f. Sharp gland edges.
g. Improper sizing.
a. Decrease clearances.
b. Higher-modulus/hard-ness elastomer.
c. Proper gland design.
d. Use of polymer backup rings.
Table 17: Extrusion Failure contributing factors and Suggested solutions
f) INSTALLATION DAMAGE
Figure 58: Installation Damage
Description:
The seal or parts of the seal may exhibit small cuts, nicks or gashes.
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Contributing Factors Suggested Solutions
a. Sharp edges on glands or
components.
b. Improper sizing of elastomer.
c. Low-modulus/hardness elastomer.
d. Elastomer surface contamination.
a. Remove all sharp edges.
b. Proper gland design.
c. Proper elastomer sizing.
d. Higher-modulus/hardness elastomer.
Table 18: Installation Damage contributing factors and Suggested solutions
g) OUTGASSING / EXTRACTION
Figure 59: Outgassing/Extaction
Description:
This failure is often very difficult to detect from examination of the seal. The seal may
exhibit a decrease in cross-sectional size.
Contributing Factors Suggested Solutions
a. Improper or improperly cured
elastomer.
b. High vacuum levels.
c. Low hardness/plasticized elastomer.
a. Avoid plasticized elastomers.
b. Ensure all seals are properly post-
cured to minimize outgassing.
Table 19: Outgassing/ Extraction failure Contributing factors and Suggested solutions
h) OVERCOMPRESSION
Figure 60: Overcompression
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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Description:
The seal exhibits parallel flat surfaces (corresponding to the contact areas) and may
develop circumferential splits within the flattened surfaces.
Contributing Factors Suggested Solutions
Improper designfailure to account for
thermal or chemical volume changes, or
excessive compression.
Gland design should take into account
material responses to chemical and
thermal environments.
Table 20: Overcompression Failure contributing factors and Suggested solutions
i) PLASMA DEGRADATION
Figure 61: Plasma Degradation
Description:
The seal often exhibits discoloration, as well as powdered residue on the surface and
possible erosion of elastomer in the exposed areas.
Contributing Factors Suggested Solutions
a. Chemical reactivity of the plasma.
b. Ion bombardment (sputtering).
c. Electron bombardment (heating).
d. Improper gland design.
e. Incompatible seal material.
a. Plasma-compatible elastomer and
compound.
b. Minimize exposed area.
c. Examine gland design.
Table 21: Plasma Degradation contributing factors and Suggested solutions
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j) SPIRAL FAILURE
Figure 62: Spiral Failure
Description:
The seal exhibits cuts or marks which spiral around its circumference.
Contributing Factors Suggested Solutions
a. Difficult or tight installation (static).
b. Slow reciprocating speed.
c. Low-modulus/hardness elastomer.
d. Irregular O-ring surface finish
(including excessive parting line).
e. Excessive gland width.
f. Irregular or rough gland surface
finish.
g. Inadequate lubrication.
a. Correct installation procedures.
b. Higher-modulus elastomer.
c. Internally-lubed elastomers.
d. Proper gland design.
e. Possible use of polymer backup
rings.
Table 22: Spiral Failure contributing factors and Suggested solutions
k) THERMAL DEGRADATION
Figure 63: Thermal Degradation
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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Description:
The seal may exhibit radial cracks located on the highest temperature surfaces. In
addition, certain elastomers may exhibit signs of softeninga shiny surface as a
result of excessive temperatures.
Contributing Factors Suggested Solutions
a. Elastomer thermal properties.
b. Excessive temperature excursions or
cycling.
a. Selection of an elastomer with
improved thermal stability.
b. Evaluation of the possibility of
cooling sealing surfaces.
Table 23: Thermal degradation failure contributing factors and Suggested solutions
v. STICK SLIP
Stick-slip is characterized by distinct stop-start movement of the cylinder, and may be
so rapid that it resembles severe vibration, high pitched noise or chatter. Seals are
often thought to be the source of the stick-slip, but other components or hardware can
create this issue.
Possible Causes Troubleshooting Tips
Surface finish out of
specification
Verify surface is neither too smooth or too rough
Poor fluid lubricity Change fluid or use oil treatments or friction reducers
Binding wear rings Check gland dimensions, check for thermal or chemical swell
Side loading Review cylinder alignment, incorporate adequate bearing
area
Seal friction Use material with lower coefficient of friction
Cycle speed Slow movement increases likelihood of stick-slip
Temperature High temperature softens seals, expands wear rings, and can
cause thermal expansion differences within hardware
Valve pulsation Ensure valves are properly sized and adjusted
External hardware Review system for harmonic resonance
Table 24: Stick slip- Possible causes and troubleshooting tips
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vi. O-RING FAILURE ANALYSIS
Prevention of seal failures through proper design, material selection and maintenance
certainly minimizes the risk of failure. Attention to the condition of replaced seals, as
well as the equipment performance over time, will result in improved process
reliability, reduced operating costs and a safer work environment.
O-ring seals often fail prematurely in applications because of improper design or
compound selection. This section is designed to provide the user with examples of
common failure modes. By correctly identifying the failure mode, changes in the
design or seal material can lead to improved seal performance.
From the end-users point of view, a seal can fail in three (3) general ways:
Leaking
Contamination
Change in Appearance
vii. ENVIRONMENTAL ANALYSIS
One major factor in possible seal failure is the extreme and harsh environment in
which seals are expected to perform. The sealing environment can consist of virtually
anything from inert gases at room temperatures to aggressive chemicals at very high
temperatures. The sealing environment may result in chemical degradation or
swelling of the sealing components. Elevated temperatures may cause seal
degradation, swelling or outgassing. And the pressure or more often, the vacuum
environments can cause outgassing and weight loss.
Contributing factors to seal failure in the sealing environment include:
Chemical the type of chemical(s) in service
Thermal the operating ranges of the seal (also any thermal cycling)
Pressure/Vacuum the range of pressures or vacuum levels in the process
viii. SEAL DESIGN ANALYSIS
Analysis of the seal application is crucial to the understanding of possible failure.
Most seal design is performed by component suppliers and equipment manufacturers.
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The seal design and application can provide information about the cause of failure:
Static Seals axial and radial, confined or unconfined
Dynamic Seals axial (open-close) or radial (reciprocating or rotary)
Sealing Gland Dimensionsshape (square, trapezoidal, etc.), compression, gland fill,
stretch
Installation Procedures stretch
ix. DESIGN GUIDELINES FOR RADIAL SEALS
In radial seals, the gland is defined by the Bore Diameter on the outside radius, the
Groove Diameter on the inside radius and the Groove Width in the axial direction (see
schematic).
a) INNER DIAMETER
In order for the O-Ring to fit snugly in the groove, it is desirable to circumferentially
stretch the O-Ring slightly. The recommended amount of stretch S is between 1% to
5% , with 2% as the preferred stretch value.
The O-Ring inner diameter ID can be found from the recommended Srec and the
Groove Diameter Gd,
By stretching the O-Ring, we ensure that the O-Ring will stay in the groove and will
not fall out or otherwise twist in some unpredictable manner during assembly.
b) CROSS SECTION DIAMETER
The O-Ring is compressed in the radial direction when seated in the gland. Hence,
one can think of the O-Ring cross-section as being pinched between the Bore
Table 25: O-Ring Compression
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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Diameter Bd and the Groove Diameter Gd . In order for the ORing to be compressed
when in the gland, its cross-section diameter CS must be greater than the total
effective depth of the groove,
The difference between CS and the effective gland depth represents the compression
C of the O-Ring (a dimensionless quantity),
C is required to be greater than zero in order for the O-Ring to be compressed. The
recommended upper limit of C depends on the type of seal. In static seals, where the
O-Ring is not in axial motion in the bore, the recommended maximum compression is
approximately 40%. In dynamic seals, such as a piston moving inside a cylinder, the
recommended maximum compression is somewhat less at 30%.
Table 26: Recommended Maximum Compression for O-Ring
Typically, compression is a design input assigned by the design engineer. In this case,
CS is found by inverting the above compression equation,
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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To account for manufacturing tolerances, a range of cross-section diameters (CSmin
to CSmax) can be provided by the following two equations,
c) GROOVE WIDTH
When the O-Ring is compressed radially, it will expand axially (since most
elastomeric materials are effectively incompressible). The Groove Width GW should
therefore be about 1.5 times the O-Ring cross-section diameter to accomodate this
axial expansion,
x. Comparison of dynamic seal types:
Type
Periodic
adjustment
required
Moving
friction
Tolerance
required
Space
sequired Availability Cost
O-ring No Medium Close Small Easy Low
T-seal No Medium Fairly
close Small Difficult High
U-packing No Low Close Small Difficult High
V-packing Yes Medium Fairly
close Large Difficult High
Cup type
packing No Medium Close Medium Difficult High
Table 27: Comparison of dynamic seal type
The comparison chart gives clear indication that O-rings and U-packing are the most
suitable ones for the application but with availability and cost giving advantage to O-
rings, hence O-rings are selected.
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xi. Comparison of commonly used materials for O-rings:
(P=Poor, F=Fair, G=Good, E=Exelent)
Elastomer type
Ab
rasi
ve
resi
stan
ce
Aci
d r
esis
tan
ce
Ch
emic
al
resi
stan
ce
Cold
res
ista
nce
Dyn
am
ic p
rop
erty
Ele
ctri
cal
pro
per
ty
Fla
me
resi
stan
ce
Hea
t re
sist
an
ce
Imp
erm
iab
ilit
y
Oil
res
ista
nce
Tea
r re
sist
an
ce
Ten
sile
str
ength
Wea
ther
res
ista
nce
Butadiene E FG FG G F G P F F P GE E F
Butyl FG G E G F G P G E P G G GE
Chlorinated polyethylene G F FG PF G G GE G G FG FG G E
Flurocarbon G E E PF GE F E E G E F GE E
Flurosilicon P FG E GE P E G E P G P F E
Isoprene E FG FG G F G P F F P GE E F
Natural rubber E FG FG G E G P F F P GE E F
Neoprene G FG FG FG F F G G G FG FG G E
Nitrile G G FG G GE F P G G E FG GE F
Polysulfide P P P G F F P P E E P F E
Silicon P FG GE E P E F E P FG P P E
Table 28: Comparison of commonly used materials for O-Rings
Taking into consideration the different properties required for the particular
application, cost and availability, silicon and nitrile are selected. While testing on both
the material O-rings, it was observed that nitrile gives more resistance for the piston
movement inside the cylinder compared to the one with silicon O-ring. Hence Silicon
O-ring is selected for the application.
(Reference# 5, 16)
P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-5
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Selection of dimensions of O-ring:
Selection criteria:
The O-ring diameter should be least possible so as to touch the least area and give
least friction.
The mean diameter of the O-ring should be less than the grove outer diameter.
The excessive O-ring diameter should be 10% of the O-ring diameter.
The grove provided should be wider than the O-ring diameter, so as to provide
some play for O-ring and avoid excessive friction by compression of the O-ring.
After following all these parameters the O-ring dimensions are selected by trial
and error method.
With experience the art of O-ring selection can be easily grasped.
The finalization of the O-ring is done by prior testing with some selected number of
O-ring dimensions for finding out the pressure required for first displacement of the
piston. This gives the idea about the friction offered by the O-ring while it is in
compression. The care should be taken that, the O-ring should always be taken of
lower size than the inner grove diameter so as to avoid loose fit, which gives leakage
after some working hours.
The O-rings are brought from Shende Sales.
Figure 64: O-Ring
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15. PREDICTING SEAL FRICTION
Friction and Wear
O-rings load a sealing surface due to their own resilience compounded with any
system pressure. When the surface to be sealed moves relative to the O-ring, frictional
forces are set up, producing two effects: one leads to wear and the other reduces the
useful load which a cylinder can transmit.
In d