Page 317 - Analysis and Design of Machine Elements

11.1.3 Types of Rolling Contact Bearings and Their Selection Rolling Contact Bearings 295
11.1.3.1 Classification of Rolling Contact Bearings
Rolling contact bearings can be classified either by the shape of rolling elements or by
the load a bearing carries. According to the shape of rolling elements, rolling contact
bearings include ball bearings and roller bearings, both of which have many variants
within the divisions. Ball bearings are generally nonseparable, that is, the balls, retainer
and rings are installed as an assembly [4]. They operate with less friction than roller
bearings and are suitable for higher speeds. Roller bearings are distinguished by the
design of rollers and raceways. They are usually separable, that is, the rollers and retainer
may be not permanently assembled with one of rings [4]. Roller bearings have rolling
contact along a line rather than at a point like ball bearings and therefore are suitable
for heavier loads.
As described before, according to the loads they carry, rolling contact bearings can be
classified as radial bearings, thrust bearings and angular contact bearings.

11.1.3.2 Types of Rolling Contact Bearings

Single-Row, Deep-Groove Ball Bearings, 60000
Single-row, deep-groove ball bearings (Figure 11.3a) are the most widely used rolling
contact bearings because they can support both radial loads and moderate axial loads
in either direction. Further, these bearings operate smoothly over a wide speed range

and are relatively inexpensive.
When a deep-groove ball bearing carries a load, the load passes across the side of
groove, through the ball, to the opposite side of outer ring and finally to the housing
[1]. The contact between a ball and raceway is theoretically a point, but actually a small
circular area due to deformation leading to high local contact stresses. Compared with
roller bearings, deep grove ball bearings operate at higher speeds yet carry less load.
Cylindrical Roller Bearings, N0000
Cylindrical roller bearings (Figure 11.3b) are designed for heavy duty applications.
The contact between a roller and races is theoretically a line, but practically a small
rectangular area because of deformation, resulting in lower contact stresses compared
to those for the equivalent-sized ball bearings. Even heavier radial load support can
be achieved with double-row roller bearings.
In contrast with ball bearings, the axial load carrying capacity of a cylindrical
roller bearing is usually poor. In a cylindrical roller bearing, rollers are located axially
by flanges on the inner, outer or both raceways. The inner ring and outer ring are
usually made axially separable. Therefore, a roller bearing can readily accommodate
small axial displacements of a shaft relative to the housing due to differential thermal
expansion.
Needle Bearings (NAs), NA0000
Needle bearings can be regarded as a special case of cylindrical roller bearings in
which rollers have a far smaller diameter. They are often used without an inner ring,
running directly on hardened shafts. Needle bearings are very useful in limited radial
space and at low operating speeds. As with other roller bearings, axial load carrying
capacity and misalignment capabilities of needle bearings are poor.