tailieunhanh - Text Book of Machine Design P18

CONTENTS CONTENTS .lat Belt Drives C H A P T E R n 677 18 .lat Belt Drives Introduction. Selection of a Belt Drive. Types of Belt Drives. Types of Belts. Material used for Belts. Working Stresses in Belts. Density of Belt Materials. Belt Speed. Coefficient of Fr iction Between Belt and Pulley 10. Standard Belt Thicknesses and Widths. 11. Belt Joints. 12. Types of Flat Belt Drives. 13. Velocity Ratio of a Belt Drive. 14. Slip of the Belt. 15. Creep of Belt. 16. Length of an Open Belt Drive. 17. Length of a Cross Belt Drive. 18. Power transmitted by a Belt. 19. Ratio of. | CONTENTS C H A P T E R 18 Flat Belt Drives 1. Introduction. 2. Selection of a Belt Drive. 3. Types of Belt Drives. 4. Types of Belts. 5. Material used for Belts. 6. Working Stresses in Belts. 7. Density of Belt Materials. 8. Belt Speed. 9. Coefficient of Friction Between Belt and Pulley 10. Standard Belt Thicknesses and Widths. 11. Belt Joints. 12. Types of Flat Belt Drives. 13. Velocity Ratio of a Belt Drive. 14. Slip of the Belt. 15. Creep of Belt. 16. Length of an Open Belt Drive. 17. Length of a Cross Belt Drive. 18. Power transmitted by a Belt. 19. Ratio of Driving Tensions for Flat Belt Drive. 20. Centrifugal Tension. 21. Maximum Tension in the Belt. 22. Condition for Transmission of Maximum Power 23. Initial Tension in the Belt. Introduction The belts or ropes are used to transmit power from one shaft to another by means of pulleys which rotate at the same speed or at different speeds. The amount of power transmitted depends upon the following factors 1. The velocity of the belt. 2. The tension under which the belt is placed on the pulleys. 3. The arc of contact between the belt and the smaller pulley. 4. The conditions under which the belt is used. It may be noted that a The shafts should be properly in line to insure uniform tension across the belt section. b The pulleys should not be too close together in order that the arc of contact on the smaller pulley may be as large as possible. Rope drives are discussed in Chapter 20. 677 CONTENTS 678 A Textbook of Machine Design c The pulleys should not be so far apart as to cause the belt to weigh heavily on the shafts thus increasing the friction load on the bearings. d A long belt tends to swing from side to side causing the belt to run out of the pulleys which in turn develops crooked spots in the belt. e The tight side of the belt should be at the bottom so that whatever sag is present on the loose side will increase the arc of contact at the pulleys. f In order to obtain good results with flat belts the