Friction and Wear of Rolling Bearings

ROLLING-ELEMENT BEARINGS, also called rolling bearings and antifriction bearings, have rolling elements (either balls or rollers) placed between two raceways that conform more or less closely to the shape of the rolling elements. Most rolling bearings have a cage (also called a separator or retainer) that spaces and guide the rolling elements. Relative motion is permitted by the rotation of these elements. The term "antifriction" bearing is used because these bearings tend to have very low friction characteristics compared to plain bearing fluid film bearings or simple sliding bearings (Usually 1 to 2 orders of magnitude less). From the basic contact equation of Hertz (Ref 3 ) to the work of STRIBECK on load ratings, of WEIBULL and PALMGREN on the , fundamental work on computing stresses for basic bearing geometries and considerable fatigue testing lead to the first bearing ratings and life theories and various fatigue and material “constants.” Following the work of GRUBIN in 1949 (Ref 4 ), DOWNSON & HIGGINSON in 1966 (Ref 5 ), and DOWSON & TOYODA in 1978 (Ref 6 ), to name just a few, the important role of lubricant in the contacts of bearings was then developed. It was recognized that the type of lubricant and the thickness of the lubricant film impacted bearing fatigue life and even influenced modes of failure. As knowledge in all these areas grew, the requirements for a bearing are better understood to develop longer life and produce acceptable life in a variety of adverse environments, such as low speed, high speed, elevated temperatures, misalignment, and contamination. Fatigue failure (contact fatigue) is a key endurance criterion of the surfaces in rolling contact, and rolling element fatigue has been recognized since the early 1900s by rolling bearing manufacturers. Because of the concentration of load in in a small volume of the material with the geometry of rolling bearings . Internal stress raisers, such as nonmetallic inclusions or carbides, are the beginning sites for incipient cracking. Special materials are thus required to give sufficiently long fatigue life for rolling element bearings, as described further in this article.