Mechanical Engineering Design
rolling-contact bearing, antifriction bearing,
are all used to
describe that class of bearing in which the main load is transferred through elements in
rolling contact rather than in sliding contact. In a rolling bearing the starting friction is
about twice the running friction, but still it is negligible in comparison with the starting
friction of a sleeve bearing. Load, speed, and the operating viscosity of the lubricant do
affect the frictional characteristics of a rolling bearing. It is probably a mistake to describe
a rolling bearing as “antifriction,” but the term is used generally throughout the industry.
From the mechanical designer’s standpoint, the study of antifriction bearings
differs in several respects when compared with the study of other topics because the
bearings they specify have already been designed. The specialist in antifriction-bearing
design is confronted with the problem of designing a group of elements that compose
a rolling bearing: these elements must be designed to ﬁt into a space whose dimen-
sions are speciﬁed; they must be designed to receive a load having certain character-
istics; and ﬁnally, these elements must be designed to have a satisfactory life when
operated under the speciﬁed conditions. Bearing specialists must therefore consider
such matters as fatigue loading, friction, heat, corrosion resistance, kinematic prob-
lems, material properties, lubrication, machining tolerances, assembly, use, and cost.
From a consideration of all these factors, bearing specialists arrive at a compromise
that, in their judgment, is a good solution to the problem as stated.
We begin with an overview of bearing types; then we note that bearing life cannot
be described in deterministic form. We introduce the invariant, the statistical distribution
of life, which is strongly Weibullian.
There are some useful deterministic equations
addressing load versus life at constant reliability, and we introduce the catalog rating at
The reliability-life relationship involves Weibullian statistics. The load-life-reliability
relationship, combines statistical and deterministic relationships giving the designer a way
to move from the desired load and life to the catalog rating in