In this article, we learn what is belt drive and the types of belt drive.
What is Belt Drive?
The belt drive is used to transmit power from one shaft to another shaft by using pulleys that rotate at the same speed or at different speeds.
A belt drive consists of the following three elements:
- Driving pulley or head pulley
- Driven pulley or tail pulley
- Endless belt
The power is transmitted from the driving pulley to the driven pulley because of the frictional grip between the belt and pulley surface.
Speed Ratio of Belt Drive
Speed ratio or velocity ratio is defined as the ratio between the speed of the driver and the driven shaft.
Generally, the speed ratio is given by
Speed ratio = Speed of driving pulley/Speed of driven pulley
Let, d and D = Diameters of driving (small) and driven (big) pulley in mm,
n and N = Speed of driving (small) and driven (big) pulley in r.p.m.,
t = Thickness of belt in mm
Speed ratio = n/N = D/d
If the thickness of the belt is considered then, Speed ratio = n/N = D+t/d+t
Types of Belt Drive
1. Open belt-drive
It is used when both, the driving and driven shaft are arranged in parallel and rotating in the same direction
Normally, the tight side of the belt should be the lower one, especially when the distance between the two shafts Is large.
2. Crossed belt drive-Drive
It is used when both the driving and driven shaft are arranged in parallel, but rotating In opposite directions.
This arrangement provides increased frictional contact between the belt and pulley.
It is prone to excessive wear at a point where the belt crosses and rubs against each other.
It is used for low-speed applications.
3. Open belt with idler pulley drive
It consists of an open belt-drive with an idler pulley.
The idler pulley causes an increase in frictional contact between the belt and the driving pulley.
It is used to obtain high-velocity ratio and high belt tension.
The position of the Idler pulley can be changed to increase the belt tension.
4. Compound belt-drive
It is used when power is transmitted from one shaft to another through a number of intermediate pulleys.
It provides a high reduction ratio.
Advantages of Belt Drive
Belt-drive can be used for long center distances.
As belts are flexible, they possess the capacity to absorb shocks and vibrations.
For belt-drive, lubrication is not required.
Belt-drive is not affected by dust and dirt.
Belt-drive does not require precise alignment of the shaft and pulley.
Belt-drive is relatively cheap and easy to maintain.
Disadvantages of Belt Drive
Some of the belts have low power transmitting capacity.
Belt-drive cannot be used at extremely high speeds.
As compared to gear drives, belt drives have a shorter life.
As compared to gear drives, belt drives occupy more space.
The belt-drive is not a positive drive.