Belts and belt drives

Mechanical Engineering

Belts and belt drives:

A belt drive is used to transmit motion from one shaft to another shaft.  Belt drives are considered as flexible machine elements which can absorb shocks and vibrations. The main applications of belt drive are

Conveyor – Used for long distance transportation of mineral ores and coal.

Power transmission – Used to transmit power from one shaft to another.

Types of belts:

Flat belt – It is rectangular in cross section. It is used for high power transmission for a long distance. These are mainly made of rubber, leather and canvas. Heavy load on belt can result in slippage on pulley face. It can be used for maximum belt speed of 70 m/s.    

Vee belt – It is trapezoidal (V shape) in cross section. The belt runs in a mating groove (V shape) in the pulley. It is done to overcome the problem of slippage and misalignment. It is used to transmit power for a smaller distance. It is mainly made of rubber. Multiple belts can be used for large power transmission. The maximum belt speed for V-belt is 30 m/s. 

Round belt – It is circular in cross section. It is made to run in a groove having an angle of 60°. It transmits low power at a smaller distance. It is used in sewing machines.

Timing (toothed) belt – It enables positive displacement. The belt has teeth on inner side which fits into mating pulley. It is one of the most efficient belts. It can be used for a maximum belt speed of 50 m/s.

Material for Belts: The material used for belt should be elastic, flexible and durable. The most commonly used materials are Leather, Rubber, Fabric or Cotton, Balata etc

Slip of a belt: When the pulley moves forward without taking the belt with it is known as slip of a belt. Slip reduces velocity ratio of a belt drive and its power transmission capacity. It occurs due to insufficient friction between belt and pulley.

Creep of a belt: The length of belt increases as it moves from slack side to tight side. It means that a shorter length approaches driven pulley and a longer length leaves it. This results in movement of driven pulley at a slower speed than the belt. In the same manner when the belt moves from tight side to slack side, its length decreases. It means a longer length approaches driver pulley and a shorter length leaves it. This results in movement of driver pulley at a fast speed than the belt. This phenomenon is known as elastic creep.