Adjustment Factors for Rating Life

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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.