JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008

DESIGN OF MACHINE MEMBERS-II

( Common to Mechanical Engineering and Production Engineering)

SET-I

1. (a) Indicate the influence of operating temperature on rolling bearing materials

(b) A journal bearing with a diameter of 200 mm and length 150 mm carries a load of 20 kN, when the journal speed is 150 rpm. The diametral clearance ratio is 0.0015. If possible, the bearing is to operate at 35oC ambient temperature without external cooling with a maximum oil temperature of 90oC. If external cooling is required, it is to be as little as possible to minimize the required oil flow rate and heat exchanger size.

i. Will the bearing operate without external cooling?

ii. If the bearing operates with external cooling, determine the operating oil temperature.

iii. If the bearing operates with external cooling, determine the amount of oil in kg/min required to carry away the excess heat generated over heat dissipated, when the oil temperature rises from 85oC to 90oC, when passing through the bearing.

2. (a) What is equivalent static load.

(b) The radial reaction on a bearing is 9000 N. It also carries a thrust of 5000N. The speed of the shaft is 1000 rpm. The outer ring stationary. Expected average life of bearing is about 25,000 hours. The load on the bearing is smooth, the service is 8 hours/day. Select,

i. Suitable roller bearing

ii. What is the rated 90% life of selected bearing?

iii. Compute the probability of the selected bearing surviving 25,000 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. What are the stresses to which an over hanging shaft is subjected to? How would you proceed to design such a crank shaft.

5. (a) What are the factors to be considered for design of springs subjects to fatigue

loading?

(b) A helical torsion spring of mean diameter 60 mm is made of a round wire of 6mm diameter. If a torque of 6 N-m is applied on the spring, find the bending stress induced and the angular deflection of the spring in degrees. The spring index is 10 and modulus of elasticity for the spring material is 200 kN/mm2.

The number of effective turns may be taken as 5.

6. (a) Design a cast iron pulley of 630mm diameter to transmit 10kW at a speed of 500 r.p.m. The center plane of the pulley overhangs the nearer bearing by 300mm. The belt ends are parallel and horizontal and the belt tension ratio is 2:1.

(b) Design a belt pulley to transmit 10kW at 180 r.p.m. The velocity of the belt is not to exceed 500 meter / minute and the maximum tension is not to exceed 15 N/mm width. The tension on the slack side is one half that on the tight side. Calculate all the dimensions of the pulley. Sketch neatly the sectional elevation and end view showing all leading dimensions.

7. Design the full depth 20o teeth of a pair of cast iron spur gears to transmit intermittently 7.5 kW at 625 rev/min of the pinion. The velocity ratio should be about 3.5. The pinion is to have not less than 22 teeth. Find the module, face width and diameters of the gears. Strength alone considered. Check for dynamic load.

8. (a) Discuss the important points to be taken into account while selecting a proper material for various elements of machine tools.

(b) Discuss the various types of power threads. Discuss their relative advantages and disadvantages.