Machine Design 2 Question Paper - Dec 18 - Mechanical Engineering (Semester 7)

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Machine Design 2 - Dec 18

Mechanical Engineering (Semester 7)

Total marks: 80
Total time: 3 Hours INSTRUCTIONS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Draw neat diagrams wherever necessary.

1 Attempt any four

1.a. Prove theoretically , in gear design tangential force transmitted is directly proportional to beam strength

(5 marks) 00

1.b. Enumerate the factors that influence most the formation and maintenance of the thick oil film in hydrodynamic bearings

(5 marks) 00

1.c. State the characteristics of the chain drive and discuss the polygon effect.

(5 marks) 00

1.d. How much reduction in loading of a roller bearing will cause the expected life to be fifty percent more?

(5 marks) 00

1.e. Justify the significance of pressure angle in gear tooth design

(5 marks) 00

2.a. A rotary disc cam and central translator follower has following motion :-

Forward stroke = 25 mm in 100$^\circ$ rotation of cam with SHM, dwell to complete the cycle.

Return stroke = 25 mm with SHM in 90$^\circ$ of cam rotation remaining dwell to complete.

Mass of follower is 1Kg and cam shaft rotates at 850 rpm and maximum pressure angle is 25$^\circ$ during forward stroke . The external force is 200 N during forward stroke and 50 N during return stroke. Determine

Base circle radius
Design the cam
Design the spring
Calculate maximum cam shaft torque

(20 marks) 00

3 A V-belt drive is to transmit 15 KW to a compressor. The motor speed is 1200 rpm and compressor pulley rums at 550 rpm. The coefficient of friction between the belt and pulley is 0.25. The compressor operates for 12 hrs/day. Design the drive for above application. Design should include the following:

Section of V belt material
Exact centre distance
Belt size
Number of belts
Life of belt

(20 marks) 00

4 Design a helical gear pair for the first stage of gear box having following specifications:

Power = 20KW
Input speed = 1440 rpm
Output speed = 90rpm

(Design should include, module selection, checking for dynamic Load and contact stresses and construction type and constructional details of gear)

(20 marks) 00

5 A worm and worm wheel pair is to be design for a following specifications, Power = 15 KW , Worm speed = 960 RPM, velocity ratio = 28

i Find the number of start and number of teeth on the gear

ii Select suitable material and find the axial module of the worm based on wear criteria.

iii Check design for bending and dynamic load

iv Check the design for thermal conditions

(20 marks) 00

6.a. Select suitable deep grove ball bearing for following specifications:

Shaft diameter = 40 mm , Radial load = 850 N , Axial load = 700 N , Speed = 760 rpm , Expected life = 5000 hrs , Reliability = 92%

(10 marks) 00

6.b. Design a chain based on bearing failure and check for tensile failure for the following specification :

Rated power : 22 KW

Input speed : 1200 rpm

Output speed : 250 rpm

Nature of load and duty : mild shock and 8-10 hrs

(Design should include, Number of teeths on sprockets, centre distance , pitch , number of link and chain length)

(10 marks) 00

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