A bearing is machine part, which support a moving element and confines its motion. The supporting member is usually designated as bearing and the supporting member may be journal. Since there is a relative motion between the bearing and the moving element, a certain amount of power must be absorbed in overcoming friction, and if the surface actually touches, there will be a rapid wear.
Bearings are classified as follows:
Depending upon the nature of contact between the working surfaces: 1)Sliding contact bearings and
2)Rolling contact bearings.
1)SLIDING BEARINGS: Hydro dynamically lubricated bearings Bearings with boundary lubrication Bearings with Extreme boundary lubrication.Bearings with Hydro static lubrication.
2)Rolling element bearings: Ball bearings ,Roller bearings ,Needle roller bearings.