The life of a bearing depends on several physical and application related factors. Even under ideal operating conditions all bearings will eventually fail due to fatigue failure, which results from repeated contact stresses. Unfortunately, it is not possible to predict the statistical life of a group of identical bearings – typically expressed in hours or millions of revolutions, the L10 life calculation is based on the criteria that 90% of the group will achieve the predicted life without and initial signs of fatigue failure.
The following is a basic engineering outline to determine the L10 Life Rating.
- Basic Dynamic Load Rating (Cr) -Value of load that a bearing can carry 1,000,000 revolutions with 90% reliability. For radial bearings, the rating is based on the amount of radial load that a bearing can tolerate for 500 hours at 33’/3 rpm. For stainless steel bearings, the basic dynamic load ratings are approximately 75% of the load ratings for 52100 chrome steel bearings.
- Basic Static Load Rating (Cor) – Static radial load which corresponds to a calculated contact stress at the center of the most heavily loaded rolling element/raceway contact. For stainless steel bearings, the basic static load ratings are approximately 75% of the load ratings for 52100 chrome steel bearings.
- Equivalent Dynamic Load (P) – Load that is placed on the bearing during application. It is based on the combination of simultaneous radial and axial forces exerted on the bearing.
- Basic Rated Life – Amount of hours a bearing can operate given rotating speed and loading conditions.
- L10 Life Rating – Amount of operating hours in which 90% of identical bearings subjected to identical operating conditions will attain (or surpass) before bearing failure.
L10 = Basic Life (hours)
n = Speed of Rotation (rotations per minute)
Cr = Dynamic Load Rating (N or Ibf)
P = Equivalent Load (N or Ibf)
K = Bearing Coefficient (Ball Bearings = 3, Roller Bearings = 10/3)