Most rolling bearings consist of bearing
rings (an inner ring and an outer ring), rolling elements and a rolling element retainer (cage). The
retainer separates the rolling elements at regular
intervals, holds them in place within the inner and
outer raceways, and allows them to rotate freely.
Rolling bearings fall into two main classifications: ball bearings and roller bearings. Balls
geometrically contact the raceway surfaces of the
inner and outer rings at “points,” while the contact
surface of rollers is a “line” contact. Rollers come
in four basic geometric styles: cylindrical, needle,
tapered and spherical. Rolling bearings can further be classified according to the direction in
which the load is applied: radial, thrust, or a combination of both.
While the rolling elements and the bearing
rings take any load applied to the bearings (at the
contact point between the rolling elements and
raceway surfaces), the retainer takes no direct
load. It only serves to hold the rolling elements at
equal distances from each other, forcing the rolling elements to enter the load zones and prevent
them from falling out.