ABSTRACT
After the invention of the wheel, it was learned that less effort was required to move an object
on rollers than to slide it over the same surface. Even after lubrication was discovered to
reduce the work required in sliding, rolling motion still required less work when it could be
used. For example, archeological evidence shows that the Egyptians, ca. 2400 BC, employed
lubrication, most likely water, to reduce the manpower required to drag sledges carrying huge
stones and statues. The Assyrians, ca. 1100 BC, however, employed rollers under the sledges to
achieve a similar result with less manpower. It was therefore inevitable that bearings using
rolling motion would be developed for use in complex machinery and mechanisms. Figure 1.1
depicts, in a simplistic manner, the evolution of rolling bearings. Dowson [1] provides a
comprehensive presentation of the history of bearings and lubrication in general; his coverage
on ball and roller bearings is extensive. Although the concept of rolling motion was known
and used for thousands of years, and simple forms of rolling bearings were in use ca. 50 AD
during the Roman civilization, the general use of rolling bearings did not occur until the
Industrial Revolution. Reti [2], however, shows that Leonardo da Vinci (1452-1519 AD), in his
Codex Madrid, conceived of various forms of pivot bearings that had rolling elements and
even a ball bearing with a device to space the balls. In fact, Leonardo, who among his prolific
accomplishments studied friction, stated:
Thus did Leonardo conceive of the basic construction of the modern rolling bearing; his
ball bearing design is shown in Figure 1.2. The universal acceptance of rolling bearings by
design engineers was initially impeded by the inability of manufacturers to supply rolling
bearings that could compete in endurance with hydrodynamic sliding bearings. This situation,
however, has been favorably altered during the 20th century, and particularly since 1960, by
the development of superior rolling bearing steels and the constant improvement in manu-
facturing, providing extremely accurate geometry and rolling bearing assemblies with long
lives. Initially, this development was triggered by the bearing requirements for high-speed
aircraft gas turbines; however, competition between ball and roller bearing manufacturers for
worldwide markets increased substantially during the 1970s, and this has served to provide
consumers with low-cost, standard design bearings of outstanding endurance. The term
rolling bearings includes all forms of bearings that utilize the rolling action of balls or rollers
to permit minimum friction, from the constrained motion of one body relative to another.
Most rolling bearings are employed to permit the rotation of a shaft relative to some fixed
structure. Some rolling bearings, however, permit translation, that is, relative linear motion,
of a fixture in the direction provided by a stationary shaft, and a few rolling bearing designs
permit a combination of relative linear and rotary motions between two bodies.
