Bearing

 2010-05-15

A bearing is a sliding or rolling component used to reduce friction in a machine. There are at least three common kinds of bearings: sliding bearings, often called "bushings"; rolling-element bearings, such as ball and roller bearings; and fluid bearings, in which the load is carried on a gas or liquid.

The first bearings were wood, but ceramic or glass can be used, and steel is quite common. The path that a bearing travels is called a "race". Bearings need to be as hard as the race that they are rolling against, or either the bearing or race will wear out prematurely. Different types exist for both linear and rotary motion.

Linear bearings

An early type of linear bearing was an arrangement of tree trunks laid down under sleds. This technology is known to date at least as far back as the construction of the Pyramids of Giza. Modern linear bearings use a similar principle, sometimes with balls in place of rollers.

Rotary bearings

Rotary bearings are required for many applications, from heavy-duty use in vehicle axles and machine shafts, to precision clock parts. The simplest rotary bearing is the sleeve bearing, which is just a cylinder inserted between the wheel and its axle. This was followed by the roller bearing, in which the sleeve was replaced by a number of cylindrical rollers. Each roller behaves as an individual wheel. The first practical caged-roller bearing was invented by horologist John Harrison in his H3 chronometer of 1760.



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