MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous...

MAHARASHTRA STATE BOARD OF TECHNICAL EDUCATION (Autonomous)

(ISO/IEC - 27001 - 2005 Certified)

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SUMMER – 14 EXAMINATIONS Subject Code: 12308 Model Answer Page No: ____/ N Important Instructions to examiners: 1) The answers should be examined by key words and not as word-to-word as given in the model answer scheme. 2) The model answer and the answer written by candidate may vary but the examiner may try to assess the understanding level of the candidate. 3) The language errors such as grammatical, spelling errors should not be given more importance. (Not applicable for subject English and Communication Skills) 4) While assessing figures, examiner may give credit for principal components indicated in the figure. The figures drawn by candidate and model answer may vary. The examiner may give credit for any equivalent figure drawn. 5) Credits may be given step wise for numerical problems. In some cases, the assumed constant values may vary and there may be some difference in the candidate’s answers and model answer. 6) In case of some questions credit may be given by judgment on part of examiner of relevant answer based on candidate’s understanding. 7) For programming language papers, credit may be given to any other program based on equivalent concept.



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Q. NO.

MODEL ANSWER

MARKS T O T A L

1.a) Attempt any three: 4*3 12

1) Parameters Reciprocating Power Hacksaw

Cold saw

Cost of machine Low capital

investment Greater capital

investment. Sawing time More time Less time

Labor skill Unskilled or semi-

skilled. Semi - skilled

Job (simple/complex shapes)

Simple but versatile Limited complex shapes (portable types)

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2) Web stiffeners are fabricated structural elements, required when a beam or plated structure is subjected to a twisting force (torsion) or a sideways thrust. The need for web stiffeners or gussets increases as the depth of the beam increases as shown in the figures below:

The smaller sizes of universal beam sections will resist a twisting force within its web which has relatively little depth, presenting a short lever arm The larger sizes of universal beam sections are unable to resist a twisting force within its web as effectively as the smaller sizes. This is because of the much greater depth presenting a very much longer lever arm. In addition, the thickness of the web of universal beam sections does not increase proportionally with the depth of the beam

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3) Pre-forming of ends is an operation prior to rolling of plates and sheet metals in order to remove flats at the two meeting edges after rolling. The need is to obtain a true cylinder without flats where the opposite edges touch.

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4) Hand riveting: The two methods in hand riveting are; direct riveting where there is access to both ends of the rivet and blind riveting where the closing head is inaccessible. Direct method:

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In case of countersunk head rivets, manufactured head should be made to rest on a flat anvil and the shank should be struck upon right along the axis. To make the joint even, first every second or third rivet, beginning with the extreme ones and then the rest of them should be headed. Blind method:

This method is used where access to the closing head is difficult. By this method, the manufactured head are struck upon. The shanks are inserted from above and dolly bar is held under the shank. The manufactured head is struck through a drift so that the dolly bar shapes the closing head. This method provides a somewhat lower quality of joints than the direct method. Tubular and explosive rivets are also set by the blind method.

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5) The following figures show the basic types of abrasive cut-off machines:

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a) Inserting the rivet

b) Heading the point



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1.b) Attempt any one: 6*1 06

1)

It is the simplest of all the presses, operated by hand. The frame is a rigid ‘C’ shaped casting, with the front open to facilitate feeding of the job below the ram from the side. The two heavy cast iron balls are mounted at the two ends of the arm. The arm is bolted to the screw. Turning the handle causes the screw to rotate within a nut, provided at the top end of the frame. Attached to the lower end of the screw is a ram, which moves up and down in slides provided at the extension of the frame, only when the screw is rotated. The punch and die constitutes the press tools. The punch (i.e. upper member) is fixed to the lower end of the ram. The die (i.e. lower member) is fixed on a plate on the table, known as bolster. Both are of high speed steel (HSS).

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2) A typical composite material is a system of materials composing of two or more materials (mixed and bonded) on a macroscopic scale. Generally, a composite material is composed of reinforcements (fibres, particles, flakes

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and/or fillers, additives) embedded in a matrix (polymer/resins, metals or ceramics). The matrix holds the reinforcement to form the desired shape while the reinforcement improves the overall mech. properties of the matrix. When composites are selected over traditional materials such as metal alloys or woods, it is usually because of one or more of the following advantages: 1. Cost: o Prototypes o Mass production o Part consolidation o Maintenance o Long term durability o Production time o Maturity of technology

2. Weight: o Light weight o Weight distribution 3. Strength and stiffness: o High strength to weight ratio o Directional strength and/or stiffness 4. Dimension: o Large parts o Special geometry 5. Surface properties: o Corrosion resistance o Weather resistance o Tailored surface finish 6. Thermal properties: o Low thermal conductivity o Low coefficient of thermal expansion 7. Electric property: o High dielectric strength o Non-magnetic o Radar transparency

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2 Attempt any two: 8*2 16

1) Single cutting support: This simple device may either be a ‘spade support’ or a single ‘roller guide’ which can be adjusted vertically for ‘standoff’. The figure below shows a single cutting support used in conjunction with a ‘straight edge’.

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2) i)

1. Hot bending is used for tubing over 100mm in diameter. In hot bending

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with filler, the tube is annealed, layed out and one end is stopped with a wooden or metal plug. To prevent its crushing, bulging or cracking, the tube is filled with dry sand sifted through a sieve with 2mm meshes. 2. To facilitate the filling and compacting of sand, use is made of hammer or vibratory type devices. Where such devices are not available, the tube is filled with sand through a funnel and the sand is compacted by hammering the tube on the outside from the bottom upwards while turning it around, until the striking produces a dull sound. With the tube filled, the second end is stopped with a wooden plug having outlets for gases generated in heating as shown in the figure below. 3. The minimum permissible bend radius is determined for every tube, depending on its diameter and material; this radius must equal no less than three diameters. The length of the section to be heated is determined by the angle of the bend and the tube diameter. If a tube is to be bent, say, at 90° or 60°or 45°, the length of its section that needs to be heated should be equivalent to its six or four or three diameters, respectively. The length of the heated section is found from the formula, L = αd/15 where, L is the length, mm; α is the bend angle; d is the tube outside diameter, mm and 15 is the constant ratio ( 90:6 = 60:4 = 45:3 = 15) The boundaries of a bend are marked with chalk using templates prepared in advance. In the course of bending, the work is checked by direct measurement or by comparison with a wire template. 4. Tubes are heated red hot with blow lamps, in furnaces or with gas burners. When handling hot tubing, the operator must put on mittens. After bending as shown in the figure above the plugs are extracted or burnt out and the sand is removed. Poor compacting of sand and inadequate or non-uniform heating before the operation may cause the formation of folds or even rupture of the tube.

OR ii)

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1. As in previous method 2. As in previous method 3. As in previous method 4. For bending in a screw clamp, the heated pipe is inserted in between the recessed jaws of the clamp as shown in the figure below and secured by rotating its handle. With welded tubing, the weld must be on the outside of the bend, because otherwise the tube may crack at the seam. A length of pipe is put on the end of the work so that its end comes just short of the bend, and it is forced with both hands in the required direction.

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3) When a bending force is gradually applied to a work piece under free bending conditions, the first stage of bending is elastic in character. This is because the tensile and compressive stresses that are developed on opposite faces of the material are not sufficiently high to exceed the yield strength of the material. The movement or strain which takes place as a result of this initial bending force is elastic only, and upon removal of the force the work piece returns to its original shape. As the bending force is continued and gradually increased, the stress produced in the outermost fibres of the material eventually exceeds the yield strength. Once the yield strength of the material has been exceeded, the movement or strain which occurs is plastic. This permanent strain occurs only in the outermost regions furthest from the neutral plane. Between the outermost fibres and the neutral plane there is a zone where the strain produced is elastic. On release of the bending force, that portion adjacent to the neutral plane loses its elastic stress, whilst the outer portions, which have suffered plastic deformation, remain as a permanent set. Thus the elastic recovery of shape in this zone on removal of the bending force is known as ‘springback’.

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3 Attempt any four: 4*4 16

1) Resins are divided into two major groups known as thermoset and thermoplastic. Thermoplastic resins become soft when heated and may be shaped or moulded while in a heated semi-fluid state and become rigid when cooled. Thermoset resins, on the other hand, are usually liquids or low melting point solids in their initial form. When used to produce finished goods, these thermosetting resins are “cured” by the use of a catalyst, heat or a combination of the two. Once cured, solid thermoset resins cannot be converted back to their original liquid form. Unlike

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thermoplastic resins, cured thermosets will not melt and flow but will soften when heated (and lose hardness) and once formed they cannot be reshaped. The most common thermosetting resins used in the composite industries are unsaturated polyesters, epoxies, vinyl esters, phenolics and polyurethane. Additives for FRP: i. Catalysts and promoters

ii. Inhibitors iii. Release agents iv. Pigments v. UV absorver

vi. Fire retardent

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2) Parameters Bolting Riveting

Cost Low cost High cost

Reliability Less High

Labor skills Unskilled to semi - skilled Semi – skilled to skilled

Joint strength Low (fluctuating loads) High (fluctuating loads)

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3) Load indicating bolts:

As shown in the diagram above, the bolt tightening is checked with the gap present by the use of a feeler gauge. Tightening is stopped when the gap is as per the manufacturer’s specification. Load indicating washer:

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The ‘Coronet’ load indicator is an especially hardened washer with protrusions on one face. They bear against the underside of the bolt head leaving a gap. As the bolt is tightened, the protrusions are flattened and the gap is reduced. At a specified average gap, measured by a feeler gauge, the induced shank tension should not be less than the minimum required by standards.

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4) Rivets are produced from materials having a good compressive strength, ductility, fatigue limit, shear strength, yield strength, corrosion resistance, etc. Materials normally used are steel, copper, brass, aluminum alloys; for vital joints, rivets are made from stainless steel and alloy steel. (As a rule, rivets should be of the same material as the parts to be joined; otherwise corrosion may arise or the joint may break because of the differences in temperature deformations.)

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5)

A certain amount of cone rolling may be carried out on both hand and power operated rolls. To enable this to be done provision must be made to adjust the curving roll to a suitable angle in the horizontal plane to the pinch rolls, or in the pyramid rolls to the other two. Cones may then be formed by adjusting the front roller by the use of a cone rolling attachment or on the pyramid type by sloping the top roll. Some machines have an additional attachment for rolling angle and bar sections. This attachment is an extension of the rolls, but positioned outside the bearing housing as shown in figure above.

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6) For Huge Smith Vertical plate bending machine: • For bending cylinders from large to small diameters used in the production of pressure vessels, boilers, nuclear plant and legs/piles for oil platforms and modules • Sizes from 300 – 5000 Tonnes or more for plate widths up to 4.5

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meters and thicknesses to 200mm cold • The vertical machine requires minimum crane attendance and occupies minimum floor space • Complete cylinders can be formed in a floor to floor time of 20 mins or less depending on diameter • Plate edge pre-setting is easily carried out using the direct acting hydraulic force of the machine • Adjustable bending centres provide the most suitable conditions for bending all sizes and thicknesses of plates • Crane attendance is not required once the plate is entered into the machine • RE-rounding and correction of weld seam can easily be carried out • Machine can be used to form cones and for plate straightening and also can be used for heavy duty flanging work including closed boxes A vertical angle ring bender is shown below for pictorial representation purpose only;

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4.a) Attempt any three: 4*3 12

1) Metal sawing is one of the important cutting operations chiefly concerned with cutting bar stock to a convenient length or size for machining. In metal sawing, the individual teeth of the saw “track” through the work, each tooth deepening the cut made by the preceding tooth in the direction of feed. Either the saw or the work may be fed and by controlling the direction of feed, either straight or curved cut can be produced. The width of the cut is approximately equal to the width of the saw itself.

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2) The basic principle of stiffening can be illustrated by supporting a tumbler of water on a piece of note paper bridging two other tumblers as shown in the figures below;



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c) Principle --- The corrugated shape provides a greater distance between the neutral axis and the areas of compression (top of paper) and tension (bottom of paper) thus enabling the thin note paper to support the applied load. From the figures it is clear that a sheet metal panel will not support a very great load due to the thinness of the material. A metal plate of the same surface area will support a fairly substantial load because of its extra thickness. But, although the metal plate is much more rigid than the sheet metal panel, this rigidity is obtained at the expense of considerable additional weight. Strength/weight ratio is an important factor in the fabrication industry and by stiffening the sheet metal in an appropriate manner, it is possible to produce a multiplicity of light fabrications which are very rigid and strong.

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3) The figures below shows methods of stiffening large panels;



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A large sheet metal panel may be stiffened with all four edges made rigid by folding. ‘Top hat section’ is used to stiffen the centre section of the panel and is usually secured in position by spot welding. Another method of stiffening large sheet metal panels is to attach them to a rigid frame-work. The welded frame is fabricated from lengths of ‘P-section’ which has a very high Strength/weight ratio for a sheet metal section. All four edges of the panel are folded at 90⁰ to a suitable width. The panel is then placed in position over the frame and the edges ‘paned-down’ over the flange on the ‘P-section’. The centre of the panel is stiffened by means of a diagonal top-hat section.

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4) High strength friction grip bolts (HSFG): HSFG Bolts are of high tensile strength and used in conjunction with high strength nuts and hardened steel washers in structural steel works. The bolts are tightened to a specified minimum shank tension so that transverse loads are transferred across the joint by friction between the plates rather than by shear across the bolt shank. These bolts have high yield strength. They should conform to IS: 3757-1985. They are tightened by torque wrenches and require hardened washers to induce initial tensions, which causes friction between the plate surfaces. Due to friction, there is no slip in the joint and therefore the joints with HSFG bolts are called friction type or non-slip type joints. These bolts are made by a special cold working process which includes two operations: heading and thread rolling. Close tolerances ensure accuracy and heat treatment is carried out afterwards. The surfaces in contact must be free from paint, oil, dirt, loose rust and scale. Clearance --- The diameter of the bolt hole is usually 1.6mm larger than the nominal diameter bolt shank.

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4.b) Attempt any one: 6*1 06

1) Classification of composites: Based on matrix material 1)Metal Matrix Composites (MMC): Metal Matrix Composites are composed of a metallic matrix (aluminum, magnesium, iron, cobalt, copper) and a dispersed ceramic (oxides, carbides) or metallic (lead, tungsten, molybdenum) phase. Applications: Carbide drills, tank armors, automotive disc brakes, etc. 2) Ceramic Matrix Composites (CMC): Ceramic Matrix Composites are composed of a ceramic matrix and embedded fibers of other ceramic material (dispersed phase). Applications: Heat shield systems for space vehicles, components for high-temperature gas turbines, burners, flame holders, and hot gas ducts, brake disks, components for slide bearings, etc. 3) Polymer Matrix Composites (PMC): Polymer Matrix Composites are composed of a matrix from thermoset (Unsaturated Polyester (UP), Epoxy (EP)) or thermoplastic (Polycarbonate (PC), Polyvinylchloride, Nylon, Polystyrene) and embedded glass, carbon, steel or Kevlar fibers (dispersed phase).

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http://en.wikipedia.org/wiki/Drill

http://en.wikipedia.org/wiki/Automobile

http://en.wikipedia.org/wiki/Disc_brake

http://en.wikipedia.org/wiki/Heat_shield

http://en.wikipedia.org/wiki/Space_vehicle

http://en.wikipedia.org/wiki/Gas_turbine

http://en.wikipedia.org/wiki/Gas_burner

http://en.wikipedia.org/wiki/Flame_holder

http://en.wikipedia.org/wiki/Disc_brake

http://en.wikipedia.org/wiki/Slide_bearing



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Applications: Boat decking, transport, civil engineering works, general engineering works, aerospace, sport utilities, domestic consumer products, etc.

OR Based on reinforcing material structure 1)Particulate Composites Particulate Composites consist of a matrix reinforced by a dispersed phase in form of particles.

1. Composites with random orientation of particles.

2. Composites with preferred orientation of particles. Dispersed

phase of these materials consists of two-dimensional flat platelets (flakes), laid parallel to each other.

Applications: Toys, electrical products, computer housings, cell phone casings, office furniture, helmets, automotive applications, brakes, cermets, concrete, reinforced rubber in auto tires, etc. 2)Fibrous Composites

1. Short-fiber reinforced composites. Short-fiber reinforced composites consist of a matrix reinforced by a dispersed phase in form of discontinuous fibers (length < 100*diameter).

1. Composites with random orientation of fibers.

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2. Composites with preferred orientation of fibers.

2. Long-fiber reinforced composites. Long-fiber reinforced

composites consist of a matrix reinforced by a dispersed phase in form of continuous fibers.

1. Unidirectional orientation of fibers. 2. Bidirectional orientation of fibers (woven).

Applications: Railings, fences, landscaping timbers, cladding and siding, park benches, molding and trim, window and door frames and indoor furniture, etc. 3)Laminate Composites When a fiber reinforced composite consists of several layers with different fiber orientations, it is called multilayer (angle-ply) composite. Applications: Bushes, spherical plain bearings, wear pads, rollers, wear rings, wear strips, pipe, bar, plate, customized products, etc.

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2) Parameters Advantages over power press

Disadvantages over power press

Fly press

Simple in construction and operation

Simple piercing, blanking and similar operations. Fitting, assembling, punching and embossing thin sheets below 1mm thickness only.

It is very versatile. Tool changing is rapid and simple. With the correct tooling one can punch coin, tube end form, bend, slot, form, dimple,

Mass production for a particular tooling arrangement is possible but time consuming due to human intervention.

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clinch fasteners, edge fold, rubber form, etc.

Etc. Etc.

5 Attempt any two: 8*2 16

1)

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2) Datas: Plate details (rolled to cylinder); T = 12.7mm Dist. of neutral line in from compression or inner side of bend, x= 0.5T i.e. = 0.5*12.7 i.e. = 6.35mm Outer diameter of cylinder, D = 330mm Inner radius of bend, r = (D – 2T)/2 = (330 – 25.4)/2 = 304.6/2 = 152.3mm θ = Subtended angle of bend = 360 – angle of bend = 360 – 5 = 355 Length of blank, L = 0.0175 * (r+x) * θ i.e. = 0.0175 * (152.3+0.5T) * 355 = 0.0175 * (152.3+6.35) * 355 = 0.0175 * (158.65) * 355 =

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3) Flame lighting: The procedure used for lighting a welding torch is adopted when lighting a cutting torch, but with some difference. The fuel gas regulator is set to the correct working pressure in the normal way and the oxygen regulator is set to the correct working pressure with the cutting oxygen valve on the torch in the open position. --- The fuel gas is lit and the flame adjusted, until it ceases to smoke. --- The heating oxygen valve is then opened and adjusted (similar to a

neutral flame setting) until there is a series of nicely defined white inner cones in the flame (in the case of the multi-port type nozzle) or a short white conical ring, if the nozzle is of the annular port type.

--- The cutting oxygen valve is then opened at this stage and the flame readjusted to a neutral condition. The oxygen cutting valve is then closed and the torch is ready for use.

Flame adjustment: When oxy-propane is used for cutting, the correctly adjusted pre-heating flame will be indicated by a small non-luminous central cone with a pale blue envelope. In the case of oxy-natural gas the flame is adjusted until the luminous inner cone has a clear definite shape, usually up to 8-10mm in length).

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Extinguish the flame: The correct procedure to extinguish the flame is as follows; --- Turn off the cutting oxygen. --- Close the fuel gas control valve. --- Close the heating oxygen control valve.

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6 Attempt any four: 4*4 16

1) •Cutting teeth and the blade should be positioned to cut on the draw stroke. •Blade should be so tightened that the tension is adequate to hold the blade firmly during the cutting operation. •Blade pins should be checked regularly to ensure that they are not being sheared. •The work piece should be tightened securely. •Ends of long pieces, projecting from the power hacksaws must be supported using a roller stand. •Cut-off sections must be cooled before handling to avoid burns and cuts from burred pieces. •Cutting fluid must be directed towards the cutting area and cutting saw teeth.

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•Before starting the power hacksaw, blade must be moved away from the work. •Cutting fluid and reservoir must be kept clean. Regular testing for the ratio of water and oil and correcting of fluid ensures that the evaporation of liquid does not change the efficiency of the cutting fluid.

2) The figures below show the use of angle stiffeners for duct work:

Welded angle frames are widely used as a means of stiffening and supporting rectangular ducts for high velocity systems. They also serve as a joining media when assembling sections together by bolting as shown in the figures above.

The large sizes of square or rectangular ducting tend to drum as the air pressure passing through them varies. To overcome this drumming it is

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necessary to provide adequate stiffening to the walls of the duct. This may be achieved by use of swaging, but often a ‘diamond-break’ is used as shown in the figure above.

3) Just as production of Washer component is a Punching and Blanking operation, so also the same concept is extended to below two operations.

Blanking: It is the operation of cutting of flat sheet to the desired shape. The metal punched out is the required product and the plate with the hole left on the die goes as waste. The die governs the size of the blank produced and clearance is left on the punch.

+ Piercing: It is the operation of production of a hole in a sheet metal by the punch and die. The material punched out to form the hole constitutes the waste. The punch governs the size of the hole (punch point diameter is less than or equal to material thickness) and clearance is provided on die.

+ Punching: It is similar to the piercing operation. But, difference between punching and piercing is that, in the case of punching, a cylindrical hole is produced, whereas in the case of piercing, the hole produced may be of any other shape. The punch governs the size of the hole and clearance is allowed on the die

Blanking and piercing operation is a follow/progressive die or a compound die operation wherein the end product required is necessarily formed by both operations carried out in successive stages or together respectively. Piercing and punching operation is also a follow/progressive die or a compound die operation wherein the end product required is necessarily formed by both operations carried out in successive stages or together respectively.

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4) Pop rivet: There are many other kinds of rivet used for joining sheet metal but the pop rivet is one of the most popular. It is fitted into the drilled hole and formed either by using lazy tongs or a plier type tool. Applications are in assembly of light fabrications, vehicle panels, ductwork and containers, used for all open blind riveting locations for normal materials with no structural or access problems. The rivet is a hollow tube of relatively soft material with a formed head on one side. The rivet is pre-assembled on a headed mandrel made from a stronger material than the rivet, the plain end of the mandrel projecting a relatively high distance through the head

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of the hollow rivet. The rivet shank is inserted through the hole in the parts to be joined such that it projects a set distance out of the far end of the hole. The mandrel is pulled through the rivet using a special tool causing the projecting end to be upset. The mandrel is engineered to snap at a set tension resulting in the correct formed head on the far side and the joint being under compression.

OR

The ability to set blind rivets without the need for access at the back of the work makes their use mandatory in many instances. They are ideal for limited access installations. Minimum back-up clearance is needed. However, their many additional advantages make blind rivets the logical choice in numerous applications where the blind-setting feature is not of primary importance.

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5) Pinch type rolling machine:



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Roll-up type in which the machines have adjustment in a vertical direction on the top or bottom pinch roll and in an upward direction on the back roller. This type will roll any size of curvature above the size of the top roll. Roll-down type in which the machines have adjustment in a vertical direction on top or bottom pinch roll and in a downward direction on the back roller. This type will not roll more curvature than will pass beneath the pedestal frame of the machine. Pyramid type rolling machine:

Pyramid-type rolls, as the name suggests have three rolls arranged in pyramid fashion as shown. Most plate rolling machines are provided with longitudinal grooves along the lower rolls to assist in gripping the plate. These grooves are useful for initial alignment of the plate.

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