Ball Bearings

A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the moving parts of the bearing.

The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit the loads through the balls. Usually one of the races is held fixed. As one of the bearing races rotates it causes the balls to rotate as well. Because the balls are rolling they have a much lower coefficient of friction than if two flat surfaces were rotating on each other.

It tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller contact area between the balls and races. However, they can tolerate some misalignment of the inner and outer races.

Compared to other rolling-element bearings, this type of bearing is the least expensive, primarily because of the low cost of producing the balls used in the bearing.

Designs:

There are several common designs, each offering various trade-offs. They can be made from many different materials, including: stainless steel, chrome steel, and ceramic. A hybrid ball bearing is a bearing with ceramic balls and races of metal.

The basic parts of a ball bearing:

Inner Race - This is the part that is mounted on the rotating shaft and tends to rotate the shaft.

Outer Race - This is the part that is mounted to the housing and is stationary. This also serves as a means for transferring the loads from the bearing to the housing.

Rolling Element 'Balls' - These are the elements that carry the load distributing it throughout the raceways. They tend to rotate about the inner race, but not at the speed the inner race rotates. It is something like the relation between the earth and the moon.

Cage - This is an important element in the bearing. This acts as a barrier between the balls preventing them from bumping into each other.

Apart from this the ball bearings are available with certain special constructional features like shielded bearings and sealed bearings.

Shielded:

The main difference between them is that in the case of a shielded bearing, it shields the rolling elements from the external dirt and the shield is normally made up of plastic or special rubber.

Sealed:

The sealed ball bearing is one which is completely sealed with lubricant inside. It prevents the flow of other lubricants into the rolling element area and also prevents the lubricant inside i.e. grease from getting out of the rolling element area.

Load Carrying Capability:

Ball bearing has a good capability to run at high speeds but average in carrying loads. They are able to carry only medium loads and hence find use in almost all the household items such as ceiling fans, Mixes, Grinders, etc.

These are capable of carrying good amount of radial loads but axial loads can be carried only to an extent. Hence, these bearings are not used in applications that require heavy axial load to be carried.

Notations:

1. The ball bearings are normally indicated with '6' as the starting series. Eg. 6006, 6204, etc. Hence a bearing with the starting number as '6' denotes a ball bearing.

2. A shielded ball bearing is normally denoted by '2RSR' as suffix to the bearing number. Example: 6006.2RSR

3. A sealed bearing is normally denoted by 'Z' as suffix if it is sealed on a single side and by 'ZZ' as suffix if it is sealed on both sides.

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