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Bearing rating life theory and formula


For modern high-quality bearings, the nominal or basic rating life may be very different from the actual service life in a particular application. In a specific application, the service life is affected by various factors, including lubrication, pollution, misalignment, correct installation and environmental factors.

Therefore ISO 281: 1990 / Amd 2: 2000 contains a revised life equation to supplement the calculation of the basic rating life. This life calculation method uses a correction factor to account for bearing lubrication, pollution, and material fatigue limits. ISO 281: 1990 / Amd 2: 2000 also allows bearing manufacturers to recommend appropriate methods to calculate available bearing life correction factors based on operating conditions. SKF correction factor a, SKF uses the concept of fatigue load limit Pu, similar to the algorithm used for other machine components. The values of the fatigue load limit are listed in the product list. In addition, the SKF life correction factor aSKF also uses the lubrication condition (viscosity ratio) and a coefficient ηc indicating the degree of contamination to reflect the operating conditions in use.

The equation of SKF rated life is consistent with ISO 281: 1990 / Amd 2: 2000 Lnm = a1 aSKF L10 = a1 aSKF (C / P) p If the speed is constant, the life can be applied to the equation and expressed in working hours Lnmh = a1 aSKF 106 / (60n) L10, where Lnm = SKF rated life (reliability is 100-n1)%, million revolutions Lnmh = SKF rated life (reliability is 100-n1)%, operating hours L10 = basic rated life (Reliability is 90%), million revolutions a1 = life reliability factor, aSKF = SKF life correction factor = basic rated dynamic load, KNP = equivalent dynamic load, KN
n = rotational speed, r / minp = exponent of life calculation equation 3 for ball bearings 10/3 for roller bearings

1) The coefficient n represents the probability of failure, for example: the difference is between the required reliability and 100%.

In some cases, instead of millions of revolutions or hours, it is preferable to use other units to express bearing life. For example, the bearing life of axle bearings used in road and rail vehicles is usually expressed in kilometers traveled.