Bearings are used to reduce friction when there is relative motion between two parts like shaft and housing. There are two major groups of bearings, sliding contact bearings and rolling contact bearings.
Sliding contact bearings are also called as journal bearings or bush bearings. Rolling contact bearings are also called as antifriction bearings or simply ball bearings.
Bearing is a mechanical element that permits relative motion between two parts such as shaft and the housing, with minimum friction.
The idea of using a rolling element to reduce friction dates back to ancient Egypt. The Egyptians used logs to roll large stone pieces closer to the construction sites of pyramids. The first known discovery of a ball bearing type device was found in the roman empire about 40 AD. This was a simple rotating table with the ball underneath, presumably to allow the people eating at the table to simply rotate the table to get at other foods. Leonardo da Vinci was first to develop an early model of ball bearing in the 16th century. In 1791, British inventor Philip Vaughn obtained the first patent of today's ball bearing.

#### The functions of the bearings are as follows:

1. The bearing ensures free rotation of the shaft or the axle with minimum friction.
2. The bearing supports the shaft or the axle and holds it in the correct position.
3. The bearing takes up the forces that act on the shaft or the axle and transmits them to the frame or the foundation.
Bearings are classified in different ways. Depending upon the type of load, bearings are classified into two categories.

### Bearing classification based on the type of load

2. Thrust bearings
A radial bearing supports the load, which is perpendicular to the axis of the shaft.
A thrust bearing supports the load which is parallel to the axis of the shaft.

### Bearing classification based on the type of lubrication

The type of lubrication means the extent to which the contacting surfaces are separated in a shaft bearing combination. This classification contains
• Thin-film lubrication
• Thick film lubrication
• Boundary lubrication
The most important criterion to classify the bearings is the type of friction between the shaft and the bearing surface.

### Bearing classification based on the type of friction

Depending upon the type of friction, bearings are classified into two main groups
1. Sliding contact bearing.
2. Rolling contact bearing.

### Sliding Contact Bearing

Sliding contact bearings are also called plain bearings, journal bearings, or sleeve bearings. In this case, the surface of the shaft slides over the surface of the bush resulting in friction and wear. In order to reduce the friction, these two surfaces are separated by a film of lubricating oil. The bush is made of special bearing material like white metal or bronze.

#### Sliding contact bearings are used in the following applications:

• Centrifugal pumps
• Large size electric motors
• Crankshaft bearings in petrol and diesel engines
• Concrete mixer, marine installations, and rope conveyor.

### Rolling Contact Bearing

Rolling contact bearings are also called anti-friction bearings or simply ball bearings. Rolling elements such as balls or rollers are introduced between the surfaces that are in relative motion. In this type of bearing, sliding friction is replaced by rolling friction.

#### Rolling contact bearings are used in the following applications:

• Automobile front and rear axles
• Gearboxes
• Machine tool spindles
• Small size electric motors
• Rope sheaves, crane hook and hoisting drum.
Types of Bearings, Their Classification and Applications Reviewed by Admin on 23:41 Rating: 5