JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008
DESIGN OF MACHINE MEMBERS-II
( Common to Mechanical Engineering and Production Engineering)
1. (a) What do you understand by boundary lubrication in journal bearings?
(b) The following data refer to a journal bearing
Diameter of the journal = 100 mm
Length of the journal = 175 mm
Load = 28 kN
Speed = 250 rpm
C/D = 0.001
Determine the coefficient of friction and heat generated.
2. (a) What is meant by square bearing?
(b) Select a suitable spherical roller bearing from SKF series 222C to support a radial load of 4 kN and an axial load of 2 kN. Minimum life required is 10,000 hours at 1000 rpm. For the selected bearing find.
i. The expected life under the given loads
ii. The equivalent load that can be supported with a probability of survival of 95% with 10,000 hours
3. Design a mild steel connecting rod with an I -section for a single cylinder spark ignition engine from the following data:
Diameter of the piston = 0.104m
Weight of the reciprocating parts =18.2 N
Length of the connecting rod from the center = 0.314m
Stroke length = 0.14 mt
Speed of the engine =1500 rpm
Maximum explosion pressure = 2.28 Mpa.
Assume that maximum thrust takes place at T.D. C during the explosion stroke.
4. The maximum connecting rod force on a steam engine running at 90 rpm is 70kN. Determine the necessary size of the over hanging crank pin. Determine the diameter of the crankshaft journal if the stroke is 0.90 m and distance between centerline of bearing and pin is 0.36 m.
5. (a) Classify various types of springs with sketches and give their applications.
(b) A helical spring is made from a wire of 6 mm diameter and has outside diameter of 75 mm. If the permissible shear stress is 350 Mpa and modulus of rigidity 84kN/mm2, find the axial load which the spring can carry and the deflection per active turn.
6. An open belt connects two flat pulleys. The pulley diameters are 300 mm and 450mm and the corresponding angles of lap are 160o and 210o. The smaller pulley runs at 200 r.p.m. The coefficient of friction between the belt and pulley is 0.25. It is found that the belt is on the point of slipping when 3 kW is transmitted. To increase the power transmitted two alternatives are suggested, namely
(a) increasing the initial tension by 10%, and
(b) increasing the coefficient of friction by 10% by the application of a suitable dressing to the belt. Which of these two methods would be more effective? Find the percentage increase in power possible in each case and also design the system.
7. It is desired to determine the proportions of a spur gear drive to transmit 8kW from a shaft rotating at 1200rpm to a low speed shaft, with a reduction of 3:1. Assume that the teeth are 20o full depth involute, with 24 teeth on pinion. The pinion is to be of 40C8 Steel and gear of 30C8 steel. Assume that the starting torque is 130 percent of rated torque.
8. (a) Enumerate the differences between differential screw, ball screw and compound
(b) Explain step by step procedure to design a lathe machine bed.