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This information reprinted courtesy of the Rolling Bearing Institute
and SKF, Inc. It is representative of the type of information
you'll find on the Rolling
Bearings Troubleshooter's Guide on CD-ROM as
featured in the Product
Showcase. |
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Since everything in industry turns on bearings, it is necessary for those
persons responsible for keeping equipment running to fully understand bearings.
There are two types of bearings; namely, sliding bearings and rolling bearings.
The majority of bearings used are rolling bearings and the subject of this
article will concentrate only on rolling bearings. |
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Rolling bearings were developed in order to eliminate sliding friction.
Sliding friction is the resistance that takes place when one object slides
against another, as shown in Figure 1. In some applications, sliding
friction is almost eliminated with smooth machined or cast metal bearing
elements that slide against equally smooth surfaces separated by a thin
film of lubricant. |
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Figure 1
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Figure 2
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A better way to eliminate sliding friction in many applications is the
introduction of rolling elements. Placing rolling elements namely balls
or rollers, between the moving surfaces, as illustrated in Figure 2,
replaces sliding friction with rolling motion. This principle is the basis
of all anti-friction bearings. |
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Practically all rolling bearings consist of four basic parts; namely: inner
ring, outer ring, rolling elements, and cage or separator, as shown in
Figure 3. Three of these parts the inner ring, outer ring, and rolling
elements - support the bearing load. The fourth part - the cage or separator
- provides positive separation of adjacent rolling elements. |
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Figure 3
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Depending on the internal design, rolling bearings may be classified as
radial bearings or thrust bearings. A radial bearing is designed
primarily for carrying a radial load. Radial load is a pressing force at
right angles to the shaft (Figure 4). Thrust load is a pushing force
against the bearing parallel to the shaft
(Figure 5). |
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There are two basic bearing families, namely
ball and roller.
Each family includes a variety of bearing designs, depending on the following
requirements: |
1) Available space
2) Loads
a) Magnitude of load
b) Direction of load
(1) Radial load
(2) Axial load
(3) Combined load
3) Misalignment
4) Speed
5) Precision
6) Quiet running
7) Stiffness
8) Axial displacement
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Since most types of radial bearings can carry some thrust, there is no
sharp distinction between them; however, bearings having a contact angle
a = 45 or smaller (a < 45 degrees) are considered radial bearings and
their ratings are given as radial load. Some of these bearings are shown
in Figure 6 and are identified as shown below: |
A. Ball bearing
B. Cylindrical roller bearing
C. Angular contact ball
bearing
D. Tapered roller bearing
E. Spherical roller bearing
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Bearings with a contact angle a greater than 450 (a > 45 degrees) are considered
thrust bearings and are rated axially. Some of these bearings are shown
in Figure 7 and are identified as shown below: |
A. Spherical roller thrust
bearing
B. Ball thrust bearing
C. Ball thrust bearing
D. Cylindrical roller thrust
bearing
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