In general, there are two different types of bearings. The principal differences are:
– sliding friction
– rolling friction
Plain bearings, sliding friction occurs when two surfaces, generally separated by a third medium (e.g. air and/or lubricant), move relative to each other. The maximum forces transmitted by plain bearings determined basically by the permissible specific pressure in the contacting area between the component elements. The specific pressure is determined by the strength of material selected.
Rolling element bearings, however, work with the principle of rolling friction. The applied load is transmitted by rolling elements, rotating around and between two bearing rings, guided by ring raceway grooves. The rolling elements are positioned within the bearing by separators, also termed retainers or cages. As described for plain bearings, rolling bearings also require lubricant of the metallic parts.
This along with good surface finish ensures smooth running surfaces and reduces friction from the transmitted forces, resulting in minimizing power loss.
In practice no pure rolling motion occurs within rolling bearings. The basic rolling motion of the rolling elements will include elements of sliding friction. The amount of sliding friction within the bearing is dependent upon the kinematic properties of the respective bearing itself. An excessive amount of sliding friction may cause serious damage on the bearing components, high friction and thus may cause premature failure.