What is belt drive? Types and advantages and disadvantages of belt drives

What is belt drive?

A belt is a loop of flexible material used to mechanically link two or more rotating shafts, usually parallel. Belts can be used as a source of motion, for efficient energy transfer, or for relative motion tracking. The belt wraps over the pulleys and there can be twisting between the pulleys and the shafts need not be parallel.

In a two-pulley system, the belt can drive the pulleys normally in one direction (same if on parallel shafts), or the belt can be crossed, so that the direction of the driven shaft is reversed. opposite direction to driver if on parallel axis).

As a source of motion, a conveyor is an application where the conveyor is adjusted to carry a continuous load between two points. Belt drives can also be used to change the rotational speed, up or down, using pulleys of different sizes.

The transmitted power depends on the following factors:

- Velocity of the belt.
Tension force that the belt exerts on the pulleys.
- Contact arc between belt and small pulley.
- Conditions of belt use.

Types of belt drives today

There are 7 different types of belt drives that can be found and they are:

1 - Open the belt drive

Open belt drives are used with shafts arranged in parallel and rotating in the same direction. In that case, the driver pulls the belt from one side and transfers it to the other. Thus, the tension in the lower belt will be higher than the upper belt. The belt below is known as the tight side belt while the upper belt is known as the loose side belt.

When the axes are too far apart, the bottom side of the belt should be the tight side and the top side should be the slack side. This is so that, when the top surface becomes translucent, it expands due to its own weight and thus increases the arc of contact.

2 - Closed or cross belt drive

Cross or torsion belt drives are used with axes rotating in parallel and in opposite directions. In this case, the driver pulls the belt from one side and transfers it to the other.

As a result, the tension on the underside of the belt will be higher than on the top of the belt. The belt is called the high tension side, while the low tension belt is called the slack side.

This type of belt drive uses a belt when two parallel shafts must rotate in opposite directions. At the belt's intersection, it rubs against itself and wears out. To avoid excessive wear, the shafts must be kept at maximum distance from each other and operated at very low speeds.

3 - Conical and loose pulley

This type of belt drive is used when the drive shaft or the machine shaft is started or stopped whenever desired without interfering with the drive shaft. A pulley that is locked to the machine shaft is called a fast pulley and runs at the same speed as the machine shaft.

A loose pulley runs freely on the machine shaft and is not capable of transmitting any force. When the drive shaft is required to stop, the belt is pushed onto the loose pulley by a slider with belt forks.

4 - Stepper cone pulley drive

A step or cone pulley actuator is used to vary the speed of the driven shaft, while the main shaft or drive shaft moves at a constant speed. This is done by shifting the belt from one section to another.

The stepped cone pulley is an integrated casting consisting of three or different numbers of different sizes of adjacent pulleys, as shown in the figure. A set of driving conical pulleys is placed backwards on the drive shaft. An endless belt will be wound around a pair of pulleys.

By shifting the belt from one pair of pulleys to another, the speed of the drive shaft can be changed. Diameter of the driving and operating pulleys so that the same belt will operate when passed through different pairs of pulleys.

5 - Jockey pulley drive

In an open-belt drive arrangement, if the center distance is small or if the driving pulley is too small, the contact arc of the belt with the driving pulley will be very small, which reduces the belt tension, or if the belt requires stress which cannot be achieved by other methods, a slow pulley, known as a carriage pulley, is placed on the slack side of the belt. This increases the contact arc and hence the stress resulting in increased force transfer.

6 - Right angle belt drive

Used with shafts arranged at right angles and rotated in a certain direction. In order for the belt not to leave the pulley, the width of the face of the pulley shall be 1.4b or more, where b is the width of the belt. If a pulley arrangement is not possible or when reverse speed is desired, a quarter-turn belt drive with a guide pulley can be used.

7 - Compound belt drive

Composite belt drives are used when transferring force from one shaft to another through multiple shafts.
 

Factors to consider before using a belt drive:

- The shaft must be properly lined to ensure uniform tension in the belt section.
- The pulleys must not be too close together so that the contact arc on the small pulley is as large as possible.
- The pulley should not be far enough to place a heavy load on the belt shaft, increasing the frictional load on the bearings.
- A long belt rotates from side to side, causing the belt to come out of the pulley, causing warping points in the belt.
- The tightening side of the belt should be at the bottom so that any sag that occurs on the loose side will increase the contact arc on the pulley.
- To obtain good results with flat belts, the maximum distance between the shafts should not exceed 10 m and the minimum should not be less than 3.5 times the diameter of the larger pulleys.
 

Belt drive classification

Belt drives are generally classified into the following three groups:

- Light drives: They are used as agricultural machines and small machine tools to transmit small forces with belt speeds of about 10 m/s.
- Medium Drives: They are used to transmit medium force at belt speeds of more than 10 m/s but up to 22 m/s like machine tools.
- Heavy duty drives: They are used in compressors and generators to transmit large forces with belt speeds above 22 m/s.
 

Advantages of belt drive

The advantages of belt drives include:

- Cost effective and simple to use.
- The new belt drive efficiency can be up to 95-98%.
- Belt drive requires low maintenance costs.
- Belt drive does not require parallel shafts.
- They come with overload and jam protection
- Speed ​​Differences can be obtained by using step or bevel pulleys.
- Belt drive is the most economical option when the transmission distance is large between the shafts.
- Reduce noise and vibration, shock absorption of load fluctuations, increase machine life
Clutch action can be activated by releasing belt tension
 

Disadvantages of belt drive

However, belt technology also comes with certain disadvantages of belt drive. That is:

- Belt drive is not suitable for small distances.
- Loss of performance due to high degree of slip and creep.
- A constant speed ratio cannot be achieved between the drive and the drive pulley.
- It makes high noise.
- Has low mechanical efficiency.
 

Applications of the belt drive:

Belt drives are used in many places such as:

- A belt drive is used to transmit the force.
- Drive the rotor on a rotor spinning machine.
- Belt Drives are used in Conveyors.
- Drive to extension rollers and other rolling elements on a single distribution plotter.
- Drive to open roller, friction drum and take off roller on friction spinning machine.
- Main drive on structural tractors.
- Belt drive is used in factory industry.
- Drive to the roller of the high-speed plotter.

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