Flat Belt Pulleys | CONTENTS c H A P T E R 19 Flat Belt Pulleys 1. Introduction. 2. Types of Pulleys for Flat Belts. 3. Cast Iron Pulleys. 4. Steel Pulleys. 5. Wooden Pulleys. 6. Paper Pulleys. 7. Fast and Loose Pulleys. 8. Design of Cast Iron Pulleys. Introduction The pulleys are used to transmit power from one shaft to another by means of flat belts V-belts or ropes. Since the velocity ratio is the inverse ratio of the diameters of driving and driven pulleys therefore the pulley diameters should be carefully selected in order to have a desired velocity ratio. The pulleys must be in perfect alignment in order to allow the belt to travel in a line normal to the pulley faces. The pulleys may be made of cast iron cast steel or pressed steel wood and paper. The cast materials should have good friction and wear characteristics. The pulleys made of pressed steel are lighter than cast pulleys but in many cases they have lower friction and may produce excessive wear. 715 CONTENTS 716 A Textbook of Machine Design Types of Pulleys for Flat Belts Following are the various types of pulleys for flat belts 1. Cast iron pulleys 2. Steel pulleys 3. Wooden pulleys 4. Paper pulleys and 5. Fast and loose pulleys. We shall now discuss the above mentioned pulleys in the following pages. Cast Iron Pulleys The pulleys are generally made of cast iron because of their low cost. The rim is held in place by web from the central boss or by arms or spokes. The arms may be straight or curved as shown in Fig. a and b and the cross-section is usually elliptical. a Fig. . Solid cast iron pulleys. When a cast pulley contracts in the mould the arms are in a state of stress and very liable to break. The curved arms tend to yield rather than to break. The arms are near the hub. The cast iron pulleys are generally made with rounded rims. This slight convexity is known as crowing. The crowning tends to keep the belt in centre on a pulley rim while in motion. The crowning may by 9 mm for 300 mm .
