Belt and Chain drives are used to transmit energy from one shaft to another when both shafts are separated by a distance greater than that required for gears. They are also used to change the speed of the pulley, change the running direction of a pulley and carry materials as conveyors from one point to another.
Belts are made of rubber and materials whose length and nature change with temperature. So the rotation of the shafts cannot be guaranteed to remain in the same fixed ratio. In the belt and chain drives, friction is greatly needed as it is the sustaining factor. If friction is lacking, it is possible for the belt particularly to slip over its drum or pulley. Examples of belt drives are:
- Sewing machine
- Corn and Rice grinders
- Record players
- Turn tables
- Radio and Air-conditioners
TYPES OF BELTS AND PULLEYS
There are various types of belt and pulleys. They are:
- Crossed Belt
- Open Belt
- Chain Belt
A crossed belt changes the direction of the pulleys.
An open belt connecting two pulleys makes them run in the same direction.
V-belts run on V-pulleys, both the pulley and the belts are V-shaped. V-belts are most often made of a combination of rubber,cord and canvas. A common use of the V-belt and V-pulley is the fan belt of an automobile, for heavy loads, several V-belts are often used side by side.
RELATIONSHIP BETWEEN BELTS AND PULLEYS
A pulley is the wheel on which a belt runs. Cone pulleys also called step pulleys have several steps and are used in pairs to get different speeds. The pulley from which power is taken is called the driving pulley or driver. The pulley to which power is carried is called the driven pulley. Flat pulleys are larger in diameter at the center of the rim than at the edges, because the belt always runs to the highest point on the pulley. This highest part or top of the rim is called the crown of the pulley.
When the driving pulley is enlarged, or the driven pulley is decreased in size, the speed of the machine is increased. The increase in speed also means less power, just as an automobile has more power in a low gear than in a high gear.
MATERIALS USED FOR MAKING BELT
Belts are made with of the following materials:
- Special composition material
Leather belts are made from hides of bulls.cows. Rubber belts are used in moist or damp places. They cannot function where there is dust or oil. However, canvas belts are used where leather or rubber belts would be ruined. Chain belts are used for high speeds, heavy loads and close connection.