# JNTU Previous Papers- BE-II-Design Of Machine Members-II-Set-IV-Aug/Sep-2008

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

DESIGN OF MACHINE MEMBERS-II

( Common to Mechanical Engineering and Production Engineering)

SET-IV

1. (a) Explain factors to be considered when selecting bearings?

(b) Design a full journal bearing for the following specifications.

Journal diameter = 120 mm

Speed of the journal = 500 rpm

Minimum oil film thickness = 0.025 mm

2. (a) A roller bearing is selected to withstand a radial load of 40 kN and life of 1200 hrs at 600 rpm. What load rating would you look for in searching from manufacturers catalogue if it specifies loud at speed 500 rpm and life 3000 hrs

(b) Select a suitable rolling bearing for a 55 mm diameter shaft. The bearing should be capable of withstanding 3 kN radial and 1.5 kN axial load at 750rpm. The bearing is to have a desired rated life of 2000 hrs at a reliability of 94% . There is a light shock load and inner ring rotates

3. (a) Why I-section is selected for high-speed I.C engines?

(b) A double acting steam engine has the following specifications

Cylinder bore =500 mm

Piston stroke=750 mm

Maximum pressure on piston=175 N/sq.cm

Connecting rod length= 1400 mm

Select the suitable material and design the connecting rod.

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) Derive an expression for maximum shear stress induced in the helical spring of circular wire.

(b) Find the maximum shear stress induced in a helical spring of the following specifications, if it has to absorb 1000 N-m of energy. Mean diameter of spring is 100 mm; Diameter of steel wire, used for making the spring is 20mm; Number of coils is 30; Modulus of rigidity of steel is 85 kN/mm2.

6. Design a flat belt drive to transmit 110kW at a belt speed of 25m / s between two pulleys of diameters 250mm and 400mm having a pulley center distance of 1 metre. The allowable belt stress is 8.5 kg/m2. Given that the coefficient of friction between the belt and pulleys is 0.3, determine the minimum required belt width. What would be the necessary installation force between the pulley bearings and what will be the force between the pulley bearings when the full power is transmitted?

7. (a) State and explain the necessity of Barth’s equation in design of spur gear

(b) Design a pair of 20o full depth spur gears to transmit 15kW at 1400 rpm to another shaft rotating at 720 rpm. Design the gear drive and check for dynamic load.

8. A power elevating screw of 64 mm diameter has a single start square thread of 6mm pitch and is engaged with a non-rotating bronze nut on which rests a load of 200 kN. The screw is supported by a thrust collar bearing. The pitch diameter of the screw is 60 mm, the coefficient of static friction between the screw and the nut is

0.18 and the same value may be assumed between the collar and the bronze thrust washer. Determine the length of nut, number of threads, and size of collar integral with screw, diameter of bronze thrust washer and efficiency of screw. Assume the following allowable stresses:

Shear stress in steel = 45 N/mm2

Shear stress in bronze = 25 N/mm2

Bearing pressure on bronze washer = 15 N/mm2