Adjustment Factors
for Rating Life
IntroductionSelection GuideEngineeering DataBrochure
If a bearing design
and operation deviates significantly from normal, it may be necessary
to use additional factors to estimate the fatigue life Ln.
Ln = a1 * a2 * a3
* L10hrs
a1 = reliability factor
a2 = material & processing factor
a3 = application factor
Reliability
Factor a1
Reliability is the
percentage of a group of apparently identical ball bearings that is
expected to attain or exceed a specified life. For an individual bearing
it is the probability that the bearing will attain or exceed a specified
life. Typical bearing lives are calculated for 90% reliability. The
life adjustment factors for other reliability numbers are shown below.
|
Reliability
%
|
Ln
|
Reliability
Factor a1
|
|
90
|
L10
|
1.00
|
|
95
|
L5
|
.62
|
|
96
|
L4
|
.53
|
|
97
|
L3
|
.44
|
|
98
|
L2
|
.33
|
|
99
|
L1
|
.21
|
Material
Factor a2
For standard bearings
the material factor a2 is equal to 1.00. Factor a2 is determined by
material processing, forming methods, heat treatment, and other manufacturing
methods. Some commonly used material factors are listed below:
| Material,
Condition |
a2 max |
| 52100, Air
melt |
1.00 |
| 52100, Vacuum
degassed |
1.50 |
| 52100, Air
melt & TDC Plate |
2.00 |
| 52100, Vacuum
melt, (CEVM) |
3.00 |
| 440C, Air melt |
1.00 |
| 440C, Vacuum
melt (CEVM) |
2.00 |
| M50, Vacuum
melt (CEVM) |
5.00 |
| M50, Vacuum
re-melt (VIM-VAR) |
8.00 |
Application Factor
a3
The application
factor a3 is equal to 1.0 for most applications. Unusual or extreme
conditions in certain applications such as low speed, shock loading,
vibration, and extreme temperature may lower the application factor
to 0.50. Contact your RBC Sales Engineer for help in determining this
factor for your special application.
|
