Belt Drives: Types, Advantages, Disadvantages

A belt is a looped strip of flexible material used to mechanically link two or more rotating shafts. A belt drive offers smooth power transmission between shafts at a considerable distance. Belt drives are used as the source of motion to transfer power efficiently or to track relative movement.

Types of Belt Drives:

In a two-pulley system, depending on the direction in which the belt drives the pulley, belt drives are divided into two types: open belt drive and crossed belt drive. The two types of belt drives are briefly discussed below.

Open belt drives:

An open belt drive rotates the driven pulley in the same direction as the driving pulley. In the motion of a belt drive, power transmission results in one side of the pulley being more tightened than the other side. In horizontal drives, the tightened side is always kept on the lower side of the two pulleys because the sag of the upper side slightly increases the angle of folding of the belt on the two pulleys.

Crossed belt drives:

A crossed belt drive rotates the driven pulley in the opposite direction of the driving pulley. A higher wrap value enables more power to be transmitted than an open belt drive. However, bending and wear of the belt are important concerns.

Advantages of belt drives:

• Belt drives are economical and straightforward.
• They don’t need parallel shafts.
• Belts drives are provided with overload and jam protection.
• Noise and vibration are damped out. Machinery life is increased because load fluctuations are shock-absorbed.
• They are lubrication-free. They require less maintenance cost.
• Belt drives are highly efficient (up to 98%, usually 95%).
• They are very economical when the distance between shafts is considerable. 

Disadvantages of belt drives:

• The angular velocity ratio in Belt drives is not necessarily constant or equal to the pulley diameter ratio because of slipping and stretching.
• Heat buildup occurs. Speed is usually limited to 35 meters per second. Power transmission is limited to 370 kilowatts. Operating temperatures are generally restricted to –35 to 85°C.
• Some adjustment of center distance or use of an idler pulley is necessary for the belt drive compensation to account for wear and stretch.