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
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.