bearings have evolved into an engineered product

Conventional bearings provide support to rotating machinery by allowing relative movement in a plane of rotation.
They allow rotation and provide support in either radial or axial planes of rotation. The most common types of bearings are rolling element bearings, and oil film or journal bearings.

A bearing is a device to allow constrained relative motion between two parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle.

Rolling element bearings consist of a stationary outer race and a rotating inner race; in between them are the rolling elements – most common are spherical balls, but cylinders or tapered pins are also used. During rotation, these 3 items are in contact with each other and the weight being supported is transferred through the rolling elements between the inner and outer races.

Oil film bearings have no rolling elements, but make use of pressurized oil to provide a film of support, and prevent galling between the shaft and the bearing journal. The oil is circulated so that fresh, cool oil is constantly entering the space between the stationary and rotating pieces. The shaft rotation shears the oil in this gap, causing it to heat up. The oil then exits the journal for cooling, filtering, and recirculation.



Over the hundreds of years since they first appeared, bearings have evolved into an engineered product. The world's largest rolling element bearing company, SKF, manufactures millions of bearings annually, both standardized designs as well as custom engineered designs for very specialized applications.

The resources devoted to traditional bearings have revealed a great deal of knowledge about them including models of life expectancy for a given application, established rules of thumb for sizing, selection, and behaviour under various types of loading.