Question Paper: Machine Design - 2 Question Paper - December 2016 - Mechanical Engineering (Semester 7) - Mumbai University (MU)

Machine Design - 2 - December 2016

MU Mechanical Engineering (Semester 7)

Total marks: --
Total time: --
(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 question 4 Q1(a,b,c,d,e,f)

1(a) Discuss the applications of the following types of the gears
i) Spur gears
ii) Helical gears
iii) Bevel gears and
iv) Worm and worm gears
5 marks

1(b) Explain the following terms as applied to rolling contact bearing:
i) Rated life
ii) Basic static load rating
iii) Basic dynamic load rating
5 marks

1(c) What is pressure angle and its significance in the design of cam and roller follower mechanisms. 5 marks

1(d) Enumerate the qualities of the friction material used in clutches . 5 marks

1(e) What do you mean by experience or service factor? How is it decided in different applications. 5 marks

1(f) What are the desirable properties of good bearing materials used in sliding contact bearings. 5 marks

2(a) Design a spur gear derive to transmit 25H.P. at 850 r.p.m. Speed reduction is 2.5. Materials for pinion and wheel are C15 steel and CI grade 30 respectively. Take pressure angle of 20° . Design bending stress for pinion materials is 85 N/mm2 and surface endurance limit for pinion materials is 620N/mm2. 5 marks

2(b) Design a pair of helical geaars to transmit a power of 36,800 Watts at 30 rps of the pinion. Gear ratio is 4. Helical angle is 15°. Teeth is 20° full depth. Material used is C50. 5 marks

3(a) A CI bevel gear pair, having pitch circle diameters of 80 mm and 100 mm is used for transmitting 3kW power at a pinion speed of 1200 r.p.m. The tooth is 14 &frac1,2° composite. If the static strength of pinion and gear is 56MPa, determine:
i) the module
ii) the face width; and iii) the surface hardness Assume velocity factor accounts for dynamic load.
5 marks

3(b) Why dissimilar materials for worm and worm wheel? In worm gear derive, the worm gear always governs the design. Justify. 5 marks

4(a) A single row deep- groove ball bearing No.6403 is used to support the lay shaft of a four speed automobile gear box. It is subjected to the following loads:

Gear Axial Load (N) Radial Load (N) Time Engaged
I 3250 4000 1%
II 500 2750 3%
III 50 2700 21%
IV 0 0 75%
The lay shaft is connected to the engine shaft and rotates at 1750 r.p.m. If the bearing is expected to be in use for 4000 hours, determine the reliability of bearing. 5 marks

4(b) The following data is given 360° hydrodynamic bearing:
Jounnal diameter: 110mm
Bearing lebgth:
Journal speed: 1400 r.p.m
Minimum oil-flim thickness: 15microns
Visosity of lubricant: 30cP
Specific gravity of lubriciant:
Specific heat of lubricant: 2kJ/kg °C Calculate:
i) The load carrying capacity of bearing;
ii) the coefficient of friction;
iii) the power lost in friction;
iv) the side leakage; and
v) the temperature rise.
5 marks

5(a) V-belt drive is used to transmit 38 kW power at 1440 r.p.m. from a three phase induction motor to a centrifugal pump, required to be operated 360 r.p.m. The motor pulley pitch diameter is 225 mm and the groove angle is 38°. The central distance between the pulleys is 1m. The coefficient of friction for the belt pulley combination is 0.2 and the density of the belt material is 0.97 gm/cc. If the allowable tension in the belt is 800N, determine:
i) the number of belts required; and ii) the pitch length of the blelt. Assume suitable cross-section for the belt based on the power to be transmitted.
5 marks

5(b) A chain drive is to be transmit 5kW power from an electric motor running at 1000 r.p.m. to a machine at 500 r.p.m. The service conditions involve light shock.
i) Select a standard roller chain.
ii) Determine the pitch circle diameter of driving and driven sprockets.
iii) Determine the length of the chain.
iv) Specify the correct center distance between the axes of sprockets.
5 marks

6(a) A plate cam operates a radial, translator roller follower having following particulars: Rise of 24 mm in an angle of 80° of cam rotation by cycloidal motion, dwell for 20° return in 70° by SHM and remaining dwell to complete cycle. Speed of rotation 500 rpm,maximum pressure angle 20°, mass of follower is 1.3kg, minimum spring force 20% of maximum interia force and external resistance 500 N during rise and 50 N during return.
i) Determine base circle diameter and draw can profile to scale.
5 marks

6(a)(ii) Design spring for the follower using static approach. 5 marks

6(a)(iii) Determine width of the follower. 5 marks

6(b) An engine developing 30kW at 1250 r.p.m is fitted with a cone clutch built into the flywheel. The cone has a face angel of 12.5° is filled with a mean diameter of 350 mm. The coefficient of friction is 0.2 and normal pressure on the clutch face is not to exceed 80kN/m2. Determine the required face width and the force necessary to engage the clutch. Assume uniform wear criterion. 5 marks

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