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LOAD RATING AND BEARING LIFE
As
stated previously, most small bearings are used in applications
where rotational accuracy and low torque are primary requirement and
loads are light. Therefore the operating lifetime of the bearing is
relatively long, and, if properly operated, failure is rare.
Nevertheless, all bearings have a finite life under use and will
eventually fail to perform satisfactorily due to an increase in
noise and vibration, loss of running accuracy, deterioration of
lubricant, or fatigue flaking of the rolling surfaces. Such failure
modes are considered “normal” and can be predicted using
standardized
techniques.
In
addition to normal deterioration, bearings may fail due to heat
seizure, fracture, scoring of the rings and other conditions caused
by improper use, selection or maintenance of the bearing. Such
failures are not normal and can only be avoided by careful handling
and correct operation of the bearing in a given
application.
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| BASIC BEARING
FATIGUE LIFE |
The basic fatigue life of a rotating
deep-groove ball bearing is given as:
| |
 |
|
.gif) |
3 |
.
|
106 |
revolutions |
|
| |
where: |
L10 |
= |
rated fatigue life with a
statistical reliability of 90% |
| |
P |
= |
bearing equivalent
load |
| |
C |
= |
basic radial dynamic load rating (see
individual bearing selection
charts) |
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| TEMPERATURE CORRECTION
FACTOR |
If rolling bearings are used at high
temperature, the hardness of the bearing steel decreases.
Consequently the basic radial dynamic load rating C must be
corrected:
Ct = ft • C
Bearing
temperature oC |
<
150 |
175 |
200 |
250 |
Temperature factor
ft |
1.00 |
0.95 |
0.9 |
0.75 |
Note: The temperature
correction factor assumes that a lubricant is used that is suitable
for given temperature. |
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