DEPARTMENT OF MECHANICAL ENGINEERINGME6503 – DESIGN OF MACHINE ELEMENTS

ICT –I Question Bank (Unit 4 & 5)

PART-A 1. What is the effect of increase in wire diameter on the allowable stress value? (N/D2010)2. What type of stress produced in disc flywheel? (N/D2010)3. For a journal bearing, the maximum operating temperature is 80oC. Why? (N/D2010)4. Why is piston head of a connecting rod kept smaller than crank pin? (N/D2010)5. What is Soomerfield number? State its importance in the design of journal bearing. (A/M 2015)6. What is the effect of change in spring index on Wahl’s factor and on the stress induced in helical compression springs? (A/M

2015)7. What is meant by semi-elliptical leaf spring? (M/J 2014)8. Define surge in a spring. (M/J 2014)9. List the theories of hydrodynamic lubrication. (N/D2011)10. Under what force the big end bolts and caps are designed? (N/D2011)

PART-B (5 x 16 = 80 Marks)11. The connecting rod of a petrol engine is to be designed for the following data.

Piston diameter 80 mmStroke 120 mmWeight of the reciprocating parts 15NLength of connecting rod 240 mmMax speed 2800 rpm.Explosion pressure corresponding to 10° of crank angle is 3 MPa.Factor of safety 6If the connecting rod is to be made of 40Cr1 Steel, find the dimensions of the I-section connecting rod. (Nov/Dec 2010)

12. i) Derive the stress equation for a helical spring. (Nov/Dec 2007)ii) Design a helical compression spring for a maximum load of 1000 N for a deflection of 25 mm using the value of spring index as 5. The maximum permissible shear stress for spring wire is 420 MPa and modulus of rigidity is 84 kN/mm2.

13. The turning moment diagram of a multi-cylinder engine is drawn with a scale of (l mm = 1°) on the abscissa and (1 mm = 250 N-m) on the ordinate. The intercepted areas between the torque developed by the engine and the mean resisting torque developed by the engine and the moan resisting torque of the machine, taken in order from one end are - 350, +800, -600, +900, -550, +450 and -650 mm 2 . The engine is running, at a mean speed of 750 rpm and the coefficient of speed fluctuations is limited to 0.02. A rimmed flywheel made of gray cast iron FG 200 (ρ= 7100 kg/m3) is provided. The spokes, hub and shaft are assumed to contribute 10% of the required moment of inertia. The rim has rectangular cross section and the ratio of width to thickness is 1.5. Determine the dimensions of the rim. (May/June 2013)

14. A punching press pierces 30 holes per minute in a plate using 12 kN-m of energy per hole during each revolution. Each piercing takes 35% of the time needed to make one revolution. The punch receives power through a gear reduction unit which in turn is fed by a motor driven belt pulley 750 mm diameter and turning at 240 rpm. Find the power of the electric motor if overall efficiency of the transmission unit is 80%. Design a cast iron flywheel to be used with the punching machine for a coefficient of fluctuation of speed is 0.05, if the space considerations limits the maximum diameter to 1.3 m. Allowable shear stress in the shaft material = 48 MPa Allowable tensile stress for cast iron = 5 MPa Density of cast iron = 7200 Kg/m3 . (Apr/ May 2008)

15. A helical compression spring is used to absorb the shock. The initial compression of the spring is 30 mm and it is further compressed by 50 mm while absorbing the shock. The spring is to absorb 250 J of energy during the process. The spring index can be taken as 6. The spring is made of patented arid cold drawn steel wire with ultimate strength of 1500 N/mm 2 and modulus of rigidity of 81370 N/mm2. The permissible shear stress for the spring wire should be taken as 30% of the ultimate tensile strength. Design the spring and calculate: (i) Wire diameter (ii) Mean coil diameter (iii) Number of active turns (iv) Free length; and (v) Pitch of the turns.

16. A Belleville spring is made of silicon steel. The spring is compresses completely flat when it is subjected to axial force of 4500 N. The corresponding maximum stress is 1375 x 106 N/m2. Assume d0 /d1= 1.75 and h/t = 1.5. Calculate: (i) Thickness of washer (ii) Free height of washer minus thickness (h) (iii) Outer diameter of washer and (iv)Inner diameter of washer. (Apr/May 2010)

17. Load on a hydrodynamic full journal bearing is 30kN. The diameter and speed of the shaft are 150mm and 1200 mm respectively. Diametral clearance 0.2 mm. Sommerfield number is 0.631, L/D ratio 1:1. Calculate temperature rise of oil, quantity of the oil, heat generated and type of oil required. (Apr/May 2015)

18. Enumerate the detail steps involved in the selection of bearing from the manufacturers catalogue. (Apr/May 2015)19. Design a leaf spring for a truck to the following specifications: Assume FOS = 2

Maximum load on the spring = 100kNNumber of spring = 4Material = Chromium vanadium steel (σu= 1380 Mpa, E = 206 x 103 Mpa)Width of the central band = 150mmSpan of the spring = 1000mmPermissible deflection = 100mmAssume 2 full length leaves and 6 graduated leaves. (Apr/May 2015)

20. Design a helical compression spring for a load range of 4kN and deflection being 80mm. Spring index is 6. Modulus of

rigidity is 81GPa. Permissible shear stress is 350Mpa. (Apr/May 2015)