Department of Mechanical Engineering 15-3-11
Sub: Design of machine members-II Assignment-2
1. (a) Derive an expression for the length of cross belt drive for flat belts.
(b) Determine the percentage increase in power capacity made possible in changing over from a flat belt to a V- belt drive. The diameter of flat pulley is the same as the pitch diameter of the grooved pulley. The pulley rotates at the same speed as the grooved pulley. The coefficient of friction for the flat belt and V- belt is the same and is equal to 0.35. The V- belt pulley groove angle is 600. The belts are of the same material, and have the same cross-sectional area. In each case, the angle of lap is 1600.
2. a) What is meant by creep of a belt and what is its effect?
(b) A belt, 100×10mm is transmitting power at 15m/s. The angle of contact on the driver (smaller) pulley is 1560. If the permissible stress for the belt material is 2N/mm2; determine the power that can be transmitted at this speed. Take the density of leather as 1000kg/m3, and coefficient of friction as 0.25. Calculate the maximum power that can be transmitted by this belt, and the speed at which this can be transmitted.
3. (a) Classify the wire ropes, based on the direction of twist.
(b) A rope drive is to transmit 250kW from a pulley of 1.2m diameter, running at a speed of 300 rpm. The angle of lap may be taken as _ radians. The groove half angle is 22.50. The ropes to be used are 50mm in diameter. The mass of the rope is 1.3 kg per meter length and each rope has a maximum pull of 2.2kN, the coefficient of friction between rope and pulley is 0.3. Determine the number of ropes required. If the overhung of the pulley is 0.5m, suggest suitable size for the pulley shaft if it is made of steel with a shear stress of 40MPa.
4. a) Derive Lewis equation for beam strength of gear.
b)A motor shaft rotating at 1440rpm has to transmit 15kWpower to a low speed shaft rotating at 500rpm. A 200 pressure angle involute tooth gear pinion is used. The pinion has 25 teeth. Both gear and pinion are made of cast iron having allowable strength of 55N/mm2. Design a suitable gear drive. Check wear load, dynamic load, static load.
5. a) What are the causes of gear tooth failure?
b) A helical cast steel gear with 400 helix angle has to transmit 80kW at 1800 rpm. If the gear has 24 teeth, determine the necessary module, pitch diameter and face width for 200 full depth. The static stress for cast steel may be taken as 56MPa. The width of face may be taken as 3 times the normal pitch. What would be the end thrust on the gear? The tooth factor for 20degree full depth involute gear may be taken as 0.154-0.912/ no. of teeth.
6. A screw press is to exert a force of 60kN with an applied torsional moment of 550Nm. The unsupported length of the screw is 0.45 and a thrust bearing of hardened steel on CI is provided at the power end. The screw is to be made of steel having an ultimate strength of 530MN/mm2 and a yield stress of 265MN/mm2. The design stresses are to be 87.5MN/mm2 in tension and compression 52.5MN/mm2 in shear and 14MN/mm2 in thread bearing. The nut is of CI and the permissible shear is 21MN/mm2. Determine the dimension of the screw and nut.
7. A vertical square threaded screw of a 75mm nominal diameter and 10mm pitch, supports a vertical load of 50kn. It passes through the boss of a spur gear of 72 teeth, which acts as a nut. For raising or lowering the load, the spur gear is turned by means of a pinion having 24 teeth. The mechanical efficiency of the gear is 90%. The axial thrust on the screw is taken-up by a collar bearing having a mean diameter of 110mm. The coefficient of friction for the screw and nut is 0.15, and that for collar bearing is 0.12. Determine,
(a) the torque applied to the pinion shaft,
(b) the maximum (principal) shear stress induced in the screw, and
(c) height of the nut, if the permissible bearing pressure is 12MPa.
8. a) Sketch the different thread profiles.
b) A screw jack carries a load of 20kN. Assuming the coefficient of friction between the screw and nut as 0.15, design the screw and nut. Neglect collar friction and column action. The permissible compressive and shear stresses in the screw should not exceed 40MPa and 25MPa respectively. The shear stress in the nut should not exceed 20MPa.The bearing pressure in the nut is 12MPa. Also determine the effort required at the handle of 250mm length, in order to raise and lower the load. What will be the efficiency of the screw jack?
9. (a) What type of material is suitable for slide ways? Give some important properties.
(b) Write a design procedure for the slide ways.
10 a) A bed is subjected to torsional loading is constructed as a closed box type structure while a bed subjected to bending is constructed as an I section. Why? Give mathematical proof to support your conclusion.
b) Write notes on stiffness and rigidity of machine tools.
Sub: Design of machine members-II Assignment-2
1. (a) Derive an expression for the length of cross belt drive for flat belts.
(b) Determine the percentage increase in power capacity made possible in changing over from a flat belt to a V- belt drive. The diameter of flat pulley is the same as the pitch diameter of the grooved pulley. The pulley rotates at the same speed as the grooved pulley. The coefficient of friction for the flat belt and V- belt is the same and is equal to 0.35. The V- belt pulley groove angle is 600. The belts are of the same material, and have the same cross-sectional area. In each case, the angle of lap is 1600.
2. a) What is meant by creep of a belt and what is its effect?
(b) A belt, 100×10mm is transmitting power at 15m/s. The angle of contact on the driver (smaller) pulley is 1560. If the permissible stress for the belt material is 2N/mm2; determine the power that can be transmitted at this speed. Take the density of leather as 1000kg/m3, and coefficient of friction as 0.25. Calculate the maximum power that can be transmitted by this belt, and the speed at which this can be transmitted.
3. (a) Classify the wire ropes, based on the direction of twist.
(b) A rope drive is to transmit 250kW from a pulley of 1.2m diameter, running at a speed of 300 rpm. The angle of lap may be taken as _ radians. The groove half angle is 22.50. The ropes to be used are 50mm in diameter. The mass of the rope is 1.3 kg per meter length and each rope has a maximum pull of 2.2kN, the coefficient of friction between rope and pulley is 0.3. Determine the number of ropes required. If the overhung of the pulley is 0.5m, suggest suitable size for the pulley shaft if it is made of steel with a shear stress of 40MPa.
4. a) Derive Lewis equation for beam strength of gear.
b)A motor shaft rotating at 1440rpm has to transmit 15kWpower to a low speed shaft rotating at 500rpm. A 200 pressure angle involute tooth gear pinion is used. The pinion has 25 teeth. Both gear and pinion are made of cast iron having allowable strength of 55N/mm2. Design a suitable gear drive. Check wear load, dynamic load, static load.
5. a) What are the causes of gear tooth failure?
b) A helical cast steel gear with 400 helix angle has to transmit 80kW at 1800 rpm. If the gear has 24 teeth, determine the necessary module, pitch diameter and face width for 200 full depth. The static stress for cast steel may be taken as 56MPa. The width of face may be taken as 3 times the normal pitch. What would be the end thrust on the gear? The tooth factor for 20degree full depth involute gear may be taken as 0.154-0.912/ no. of teeth.
6. A screw press is to exert a force of 60kN with an applied torsional moment of 550Nm. The unsupported length of the screw is 0.45 and a thrust bearing of hardened steel on CI is provided at the power end. The screw is to be made of steel having an ultimate strength of 530MN/mm2 and a yield stress of 265MN/mm2. The design stresses are to be 87.5MN/mm2 in tension and compression 52.5MN/mm2 in shear and 14MN/mm2 in thread bearing. The nut is of CI and the permissible shear is 21MN/mm2. Determine the dimension of the screw and nut.
7. A vertical square threaded screw of a 75mm nominal diameter and 10mm pitch, supports a vertical load of 50kn. It passes through the boss of a spur gear of 72 teeth, which acts as a nut. For raising or lowering the load, the spur gear is turned by means of a pinion having 24 teeth. The mechanical efficiency of the gear is 90%. The axial thrust on the screw is taken-up by a collar bearing having a mean diameter of 110mm. The coefficient of friction for the screw and nut is 0.15, and that for collar bearing is 0.12. Determine,
(a) the torque applied to the pinion shaft,
(b) the maximum (principal) shear stress induced in the screw, and
(c) height of the nut, if the permissible bearing pressure is 12MPa.
8. a) Sketch the different thread profiles.
b) A screw jack carries a load of 20kN. Assuming the coefficient of friction between the screw and nut as 0.15, design the screw and nut. Neglect collar friction and column action. The permissible compressive and shear stresses in the screw should not exceed 40MPa and 25MPa respectively. The shear stress in the nut should not exceed 20MPa.The bearing pressure in the nut is 12MPa. Also determine the effort required at the handle of 250mm length, in order to raise and lower the load. What will be the efficiency of the screw jack?
9. (a) What type of material is suitable for slide ways? Give some important properties.
(b) Write a design procedure for the slide ways.
10 a) A bed is subjected to torsional loading is constructed as a closed box type structure while a bed subjected to bending is constructed as an I section. Why? Give mathematical proof to support your conclusion.
b) Write notes on stiffness and rigidity of machine tools.
Prepared by
K.Srinivas
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