The diameters of standard pulleys are: 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1400 and 1600 mm. pulley may be straight faced or crowned. The crown serves to keep the belt centered. The height of the crown is usually 0.5% of the pulley width, but not less than 4 mm. The pulley diameter Dp depends on the number of plies of belt and may be also be determined from the formula:
Dp > K.i (mm)
K = a factor depending on the number of plies (125 to 150)
i = no of plies
The compound value should be rounded off to the nearest standard size. While selecting the pulley diameter it should be ascertained that the diameter selected is larger than the minimum diameter of pulley for the particular belt selected.
The drive pulley may be lagged by rubber coating whenever necessary, to increase the coefficient of friction. The lagging thickness shall vary between 6 to 12 mm. The hardness of rubber lagging of the pulley shall be less than that of the cover rubber of the running belt.
Pulleys are manufactured in a wide range of sizes, consisting of a continuous rim and two end discs fitted with hubs. In most of the conveyor pulleys intermediate stiffening discs are welded inside the rim. Other pulleys are self cleaning wing types which are used as the tail, take-up, or snub pulley where material tends to build up on the pulley face. Magnetic types of pulleys are used to remove tramp iron from the material being conveyed.
Typical welded steel pulley-Drum conveyor pulley
Spun end curve crown pulley
Spiral drum conveyor pulley
Welded steel pulley with diamond grooved lagging
Welded steel pulley with grooved Lagging
Spiral Wing Conveyor pulley
Power calculation for the drive unit:
The horse power required at the drive of a belt conveyor is derived from the following formula:
H.P = Te . V
Te is the effective tension in the belt in N
V = velocity of the belt in m/s
The required effective tension Te on the driving pulley of a belt conveyor is obtained by adding up all the resistances.