Belt and Chain Drive – JSS2 Basic Technology Lesson Note (Third Term)

Belt and chain drives are mechanical systems that transmit power from one rotating shaft to another.

• Belt drive: uses a looped strip of flexible material to link rotating shafts.
• Chain drive: uses pin-connected links that engage toothed wheels called sprockets.

Behavioural objectives

By the end of the lesson, students should be able to:

1. define a belt drive and a chain drive;
2. state the types of belt drive and explain each one;
3. describe the open belt, crossed belt and V-belt arrangements;
4. state the types of chain drive and explain each one;
5. state the differences between a belt drive and a chain drive.

What is a belt drive?

A belt drive is a looped strip of flexible material used to link two or more rotating shafts mechanically.

• Smooth transmission: a belt drive passes power smoothly between shafts that are far apart.
• Uses: it is used as a source of motion, to transmit power efficiently or to track relative movement.
• Sheave: a sheave is the grooved or flat wheel (pulley) that carries the belt.
• Speed reduction: the smaller sheave goes on the high-speed shaft, such as the shaft of an electric motor.
• Driven machine: the larger sheave is put on the driven machine.

What are the types of belt drive?

There are many types of belt drive, and four common ones are the flat belt, synchronous belt, cog belt and vee-belt.

• Other types: round belts, multi-groove belts, ribbed belts, film belts, metal belts, endless round belts and specialty belts.

1. Flat belt: the simplest type, often made from leather or rubber-coated fabric.
   • The sheave surface is also flat and smooth.
   • The driving force is limited by the pure friction between the belt and the sheave.
2. Synchronous belt, or timing belt: rides on sheaves with pockets that have mating grooves, where the teeth on the belt seat.
   • It is a positive drive, so it does not slip.
   • It is limited only by the tensile strength of the belt and the shear strength of the teeth.
3. Cog belt: applied to standard V-grooved sheaves.
   • The cogs give the belt greater flexibility.
   • It has higher efficiency than standard belts.
4. Vee-belt: the V-shape makes the belt wedge tightly into the groove.
   • This increases friction.
   • It allows high torques to be transmitted before slipping occurs.

What are the belt and pulley arrangements?

There are three common belt and pulley arrangements: the open belt, the crossed belt and the V-belt.

1. Open belt: an open belt connecting two pulleys makes them run in the same direction.
2. Crossed belt: the belt crosses itself and makes the pulleys run in opposite directions.
3. V-belt: V-belts run on V-pulleys. A common use is the fan belt of an automobile.

What is a chain drive?

A chain drive is a way of transmitting mechanical power from one place to another using a chain.

• Chain: a power transmission element made as a series of pin-connected links.
• Flexibility: the design lets the chain bend while it carries large tensile forces.
• Sprockets: between rotating shafts, the chain engages mating toothed wheels called sprockets.
• Everyday example: a bicycle uses a chain and two sprockets to drive the rear wheel.

What are the types of chain drive?

There are four types of chain drive: roller chain, conveyor chain, inverted tooth chain and leaf chain.

1. Roller chain drive: the most common type of chain.
   • The roller on each pin gives very low friction between the chain and the sprockets.
   • It is classified by its pitch, the distance between corresponding parts of adjacent links.
   • Pitch is usually measured between the centres of adjacent pins.
   • Standard roller chain carries a size designation from 40 to 240.
2. Conveyor chain: the rollers stand out from the links and can roll along supporting surfaces.
   • It can transport materials, because the rollers support weight.
   • It can also support the weight of the chain when power is transmitted over long distances.
3. Inverted tooth (or silent) chain: sprocket teeth mesh with shaped links instead of rollers.
   • Joints between links use rolling contact rather than sliding contact.
   • The link profiles are more like involute gear teeth.
   • The overall effect is to reduce noise.
4. Leaf (or lifting) chain: designed for lifting rather than power transmission.
   • It does not mesh with sprockets, so it has no rollers.
   • It can be narrower than a roller chain of equivalent strength.
   • An example of its use is in a forklift truck.

What is the difference between a belt drive and a chain drive?

A belt drive passes power by friction or belt teeth on a flexible belt, while a chain drive passes power through links that mesh with sprockets.

Evaluation

1. What is a belt drive?
2. State the types of belt drive.
3. Explain each type of belt drive.
4. What is a chain drive?
5. State the types of chain drive and explain each one.

Assignment

Answer both parts:

1. State the difference between an open belt and a crossed belt.
2. Name the type of chain used in a forklift truck and say why it has no rollers.