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SPPU Mechanical Engineering (Semester 8)
Mechanical System Design
May 2017
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

Solve any one question from Q.1(a,b) &Q.2(a,b)
1(a) What are the various laws for stepped regulation of speeds in multi-speed gear boxes? State the advantages and limitations any one of them.
4 M
1(b) Define Design Tolerance and Natural Tolerance and explain the difference between them?
6 M

2(a) Explain the following terms with reference to machine tool gear box. How these parameters are decided while designing machine too drives
i) Range ratio
ii) Number of transmission group or stages.
4 M
2(b) A particular type of rolling contact bearing has a normally distributed time to failure with a mean of 10000 hours and standard deviation of 750h. If there are 100 such bearings fitted at a time, how many May be expected to fail within the first 11000h?
 z 0 1 2 3 4 5 6 7 8 9 1.1 0.3643 0.3665 0.3686 0.3708 0.3729 0.3749 0.377 0.379 0.381 0.383 1.2 0.3849 0.3869 0.3888 0.3907 0.3925 0.3944 0.3962 0.398 0.3997 0.4015 1.3 0.4032 0.4049 0.4066 0.4082 0.4099 0.4115 0.4131 0.4131 0.4162 0.4177 1.4 0.4192 0.4207 0.4222 0.4236 0.4251 0.4265 0.4279 0.4279 0.4306 0.4319
6 M

Solve any one question from Q.3(a,b) & Q.4(a,b)
3(a) Explain on the basis of applications selection between
i) chain conveyor
ii) screw conveyor
iii) belt conveyor
4 M
3(b) A three idler thorughed belt horiziontal conveyor is to be used for transporting 400 ton/ hours of iron core having weight density of 1.67*10-8 KN/m3. If the belt speed is 7.2 kmph and surcharge factor is 0.1 calculate the width of belt is mm.
6 M

4(a) Explain the advantages and limitaitions of throughed conveyors over flat belt conveyor.
4 M
4(b) Mr.X is required to transmit the coal from coal storage to boiler house by conveyor. So suggest him suitable type of conveyor and explain the different resistive forces consider to estimate the power requirement for the conveyors.
6 M

Solve any one question from Q.5(a,b) & Q.6(a,b)
5(a)(i) What are the objectives of providing openings in pressure vessel.
4 M
5(a)(ii) What is pre stressing of thick cylinder? Explain Auto frettage.
4 M
5(b)(i) Derive Birnie'equation. Explain under what conditions it is used.
5 M
5(b)(ii) A hydraulic cylinder with closed ends is subjected to an internal pressure of 15MPa. The inner and outer diameter of the cylinder is 200mm and 240mm respectively. The cylinder material is cast iron FG300. Determine the factor of safety used in design. If the cylinder pressure is further increased by 50%. What will be the factor of safety.
5 M

6(a)(i) What are types of end closure for cylindrical vessel? State the design procedure of hemispherical head.
4 M
6(a)(ii) Explain the various categories of the welded joints used in unfired pressure vessel.
4 M
6(b) A hydraulic control for a straight line motion as shown in fig. Utilizes a spherical pressure tank A connected to a working cylinder B. The pump maintains a pressure of 3 MPa in the tank.
If the diameter of pressure tank is 800mm, determine its thickness for 100% efficiency of the joint. Assume the allowable tensile stress as 50MPa. ii) Determine the diameter of a cast iron cylinder and its thickness to produce an operatinf force F = 25KN. Assume
1) an allowance of 10% of operating force F for friction in cylinder and packing and
2) a pressure drom of 0.2 MPa between the tank and cylinder. Take safe stress for cast iron as 30MPa.
iii) Determine the power output of the cylinder if the stroke of the piston is 450mm and time required for the working stroke is 5 seconds.
iv) Find the power of the motor if the working cycle repeats after every 30 seconds and the efficiency of the hydraulic control is 80% and that of 60%.
!mage
10 M

Solve any one question from Q.7(a,b) &Q.8(a,b)
7(a)(i) What is the function of the cup on the piston head?
3 M
7(a)(ii) Why are more number of thin piston rings preferred over small number of thick rings?
3 M
7(b) The following data is given for the piston of a four stroke diesel engine: Cylineder bore 0.25m, maximum pressure = 4MN/m2, Bearing pressure at small end of connecting rod = 15 MN/m2, Length of piston pin in bush of small end = 0.45D, inner diameter of piston pin is 0.6 times outer diameter of piston pin and mean diameter of piston boss is 1.4 times outer diameter of piston pin, Allowable bending stress for piston pin = 84 Mpa. Calculate:
i) outer and inner diameter of the piston pin
ii) mean diameter of the piston boss
iii) check the design for bending stress
10 M

8(a)(i) Why are connecting rod made of I sections?
3 M
8(a)(ii) Why do inlet and exhaust valves have conical heads and seats?
3 M
8(b) The following data is given for the cap and bolts of the big end of the connecting rod:
Engine speed = 1500rpm
Length of connecting rod = 0.320m
Length of stroke = 1.40m
Mass of reciprocating parts = 1.75Kg
Length of crank pin = 54mm
Diameter of crank pin = 38mm
Permissible tensile stress fot bolts = 120MN/m2
Calculate the nominal diameter of bolts and thickness of cap for the big end.
10 M

Solve any one question from Q.9(a,b) Q.10(a,b)
9(a) What is design for manufacture? Explain the general principles to be followed while designing the parts of manufacture.
6 M
9(b) A shaft is required to transmit 10KW at 1000 rpm and torsional stiffness of the shaft is 90N.m/ degree. Design the shaft using maximum shear stress theory of minimum weight. Material properties are given below. Also find out diameter and length of shaft for the same. Assume factor of safety is 1.5 and combined shock and fatigue load factor = 1.5.
 Material Density Kg/m3 Tensile  strength MN/m2 Modulus  or Rigidity MN/m2 M1 7800 450 82000 M2 2800 150 27000 M3 1800 100 17000
10 M

10(a) What is design for safety? Explain the general principles to be followed while designing the product for safety?
6 M
10(b) A tensile rod of diameter 'd' having length 0.6m is subjected to a tensile force 5KN. Calculate the rod diameter with the objective of minimizing the weight of material. Assume factor of safety 2. Use following table.
 Material Density Kg/m3 Syt in N/m2 Modulus of Right MN/m2 Material cost Rs./Kg Steel 7800 400*106 82000 14 Aluminium Alloy 2800 150*106 27000 70 Titanium Alloy 4500 800*106 41000 1100
10 M

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