Bearing Classifications

 
The second way bearings can be classified is by the type of friction they create. Bearings are either sliding contact or rolling contact. Rolling contact bearings are sometimes called anti-friction bearings. In a sliding contact bearing, the surface of the shaft slides over the surface of the bushing. To prevent friction, both surfaces are separated by a thin film of lubricating oil. Generally, the bushing is made from bronze or white metal. Examples of sliding contact bearings are plain, journal, and sleeve bearings. Rolling contact bearings reduce friction a great deal. As such, they are used in automobile axles & gearboxes, machine tool spindles, and small electric motors.
 
Rolling contact bearings are by far the most commonly used. Therefore, many types exist. The most prevalent rolling contact bearings are deep groove ball bearings, cylindrical roller bearings, angular contact bearings, taper roller bearings, and thrust ball bearings. In deep groove ball bearings, the radius of the ball is slightly less than the radius of the curvature of the groove, creating points of contact. Because of this, the friction level is much lower and can be used in high-speed applications. Cylindrical roller bearings are used in applications where high load-carrying capacity is required. In these bearings, rolling elements are cylindrical in shape rather than spherical. This helps decrease friction, but also means the bearing cannot withstand a thrust load.
 
Angular contact bearings are designed with points of contact for a ball at both the inner and outer race. This allows them to withstand radial and axial loads simultaneously. The load carrying capacity of these bearings is similar to that of deep groove ball bearings. In a taper roller bearing, the rolling element is a spherical roller. They are arranged such that axes of individual rolling elements intersect at a common point to enhance rolling motion. The final type of bearing, thrust ball bearings, feature two rows of balls in the inner and outer races. Due to the large number of balls, thrust ball bearings can take a high thrust load. Despite this, it can take thrust in only one direction.