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SPPU Mechanical Engineering (Semester 8)
Mechanical System Design
December 2013
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

Answer any one question from Q1 and Q2
1 (a) A cylindrical pressure vessel with 1500 mm inside diameter & 15 mm thick is subjected to an internal pressure of 1.5 N/mm2. A nozzle of 300 mm inside Diameter & 12mm thickness is to be provided in the shell. Welds joint efficiency for shell as well as nozzle is 85% while corrosion allowance is 2 mm. The nozzle project 20 mm on outside & 30 mm on inside of shell. If the allowable tensile stress for the shell & nozzle material is 120 N/mm2. Determine, whether the reinforcement is adequate, if not find the dimensions of reinforcing pad if plate thickness is 15 mm.
13 M
1 (b) What is Pre-stressing of thick cylinder, Explain Autofrettage.
3 M

2 (a) What are different types of supports used in Horizontal & Vertical pressure vessel, explain any one with sketch in each type.
5 M
2 (b) Differentiate class I, II & III requirement of pressure vessel as per IS 2825 standard.
3 M
2 (c) A high pressure vessel consist of steel tube with inner & outer diameter 20mm & 40mm respectively. It is a jacketed by an outer tube having outer diameter 60 mm. The tubes are assembles by shrinking processes in such a way that maximum principal stress induced in any tube is limited to 100 N/mm2. Assume modulus of elasticity is 207 KN/mm2
Calculate.
i) Shrinkage pressure
ii) Original Dimensions of tube
8 M

Answer any one question from Q3 and Q4
3 (a) Explain whipping stress in connecting rod.
3 M
3 (b) Explain with sketch construction of Piston.
3 M
3 (c) Following data is given for the Cap & Bolt of big end of connecting rod of Diesel engine,
Engine speed - 1800 RPM
Length of connecting rod - 350 mm
Mass of reciprocating parts - 2.5 kg
Length of crank pin - 76 mm
Diameter of crank pin: 58mm
Thickness of bearing Bush - 3 mm
Permissible tensile stress for bolts - 60 N/mm2
Permissible bending stress for Cap - 80 N/mm2
Determine,
i) Nominal diameter of bolt
ii) Thickness of Cap for big end
12 M

4 (a) Explain dry and wet liner with neat sketch. Discuss the stresses developed in the cylinder wall.
5 M
4 (b) Following data is given for piston of four stroke diesel engine,
Cylinder bore-250 mm
Maximum gas pressure - 4 N/mm2
Bearing pressure at small end of connecting rod-15 N/mm2
Length of piston pin in bush of small end?0.45D
Ratio of inner to outer diameter of piston pin 0.6
Mean diameter of piston boss - 1.4 x Outer diameter of piston pin
Allowable bending stress of piston pin-84 N/mm2
Calculate,
i) Outer diameter of piston Pin
ii) Inner diameter of piston Pin
iii) Mean diameter of piston boss and
iv) Check design for bending stress
10 M
4 (c) What are types of piston rings, state their function.
3 M

Answer any one question from Q5 and Q6
5 (a) A tensile bar of cross section area 85mm & length of 200 mm is subjected to constant load of 5000 N. Design a bar for minimum cost of following materials. Assume factor of safety.
 Material Material Density Kg/m3 Material Cost per unit weight Rs/N Yield Strength N/mm2 Steel 7500 16 130 Alluminum Alloy 3000 32 50 Magnesium Alloy 2100 32 20
16 M

6 (a) Differentiate between optimum design problem with normal specifications and redundant specifications.
4 M
6 (b) A cantilever beam of length 250 mm and rectangular cross-section is to function as a Spring subjected to load of ± 100 N . The width to depth ratio of beam is 5:1 if factor of safety is 1.5. Design the beam for optimum material cost, Specify the material, cross-section and cost for selected design. The following are the material available.
 Material Material Density Kg/m3 Material Cost per unit weight Rs/N Endurance limit N/mm M11 8400 100 17 M12 8020 100 37.5 M13 7830 60 32
12 M

Answer any one question from Q7 and Q8
7 (a) It is observed from a sample of 1000 bearings bushes that the internal diameters are normally distributed with mean of 50.015 mm and standard deviation of 0.008mm. Dimension of this diameter specified on drawing is 50.01 ± 0.1mm. Calculate the approximate number of rejected bushes from that sample.
Refer Table No:03 for the Areas under normal distribution curve from Z = 0 to Z.
Table No : 3, Areas below Normal Distribution Curve for 0 to Z.
12 M
7 (b) Justify that the Display and Control elements of a car are designed based on the ergonomic considerations.
4 M

8 (a) Transmission shafts are manufactured on a machining center. The designer has specified the dimension of OD as 40+0.04mm. The natural tolerance is normally distributed with mean of 40mm but only 34% out of the manufactured shafts are found to be acceptable. So what is the standard deviation of this manufacturing process?
Refer Table No:03 above for the Areas under normal distribution curve from Z = 0 to Z.
10 M
8 (b) Explain the design considerations for Design of Forgings.
6 M

Answer any one question from Q9 and Q10
9 (a) Justify the statement: 'All the structure formulae of the form N=P1 (S1).P2(S2) ..... Pn (Sn) can not be converted into structure diagrams and hence are not feasible'.
4 M
9 (b) Decide the number of teeth of all gears from a 9 speed gearbox with speeds starting from 100 RPM and based on R5, to transmit 10KW power from a motor running at I 440rpm. (Assume that the minimum number of teeth in all stages is 20 and that the design is based on symmetric structure diagram only).
10 M
9 (c) Draw the deviation diagram of designed gearbox.
4 M

10 (a) Justify the statement: 'The difference between numbers of teeth of successive gears in a change gear box must be greater than 4'.
6 M
10 (b) Draw Structure Diagrams for following structure formulae, find out optimum formula out of them and draw the gearing diagram for the optimum formula:
2(1 )3(2), 2(3)3(1), 3(1 )2(3), 3(2)2(1).
12 M

Answer any one question from Q11 and Q12
11 (a) Explain the advantages of Troughed Conveyor over Flat Belt conveyor.
4 M
11 (b) Compare different belt materials and discuss the types of belts.
6 M
11 (c) A horizontal belt conveyor is to be used for transporting 450 tons of iron ore with mass density 1750kg/m3 . If surcharge factor is 0.06. Determine belt width.
6 M

12 Following data relate to a horizontal belt conveyor used for conveying coal in a thermal power station:
Capacity of conveyor: 1000 ton/hr
Density of coal: 700 Kg/m3
Belt speed: 1.4 m/s
Surcharge factor: 0.1
Number of plies: 4
Material Factor K 1:2
Belt tension and contact factor K2:100
Material conveying length: 355m
Center distance between snub pulleys: 350m
Ratio of tail pulley to drive pulley dia. :1.0
Ratio of snub pulley to drive pulley dia. : 0.5
Mass of each carrying run idler: 25 kg
Mass of each return run idler: 20 kg
Pitch of carrying run idlers: 1m
Pitch of return run idlers: 2.5m
Friction factor for idlers: 0.02
Snub Factor for snub pulleys: 0.03
Snub factor for Drive and tail pulleys: 0.06
Material velocity component along belt drive: 1 m/s
Angle of lap on drive pulley: 200°
Coefficient of friction between belt and pulley: 0.4
Drive efficiency: 93%
Mass of belt / mm width / mm length =.015kg/mm/m
Motor speed 1440 RPM
Determine following parameters of the conveyor:
Standard belt with rounded off to nearest hundred mm.
Reduction ratio of the gear reducer
Power required to drive the conveyor.
16 M

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