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Bearing rating life theory and formula

For modern high-quality bearings, the nominal or basic rating life may differ significantly from the actual service life in a particular application. In a particular application, the service life is affected by a variety of factors, including lubrication, degree of contamination, degree of misalignment, correct installation, and environmental factors.

Therefore ISO 281: 1990 / Amd 2: 2000 includes a modified life equation to supplement the calculation of the basic rating life. This life calculation method uses a correction factor that takes into account 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 parts. The values for the fatigue load limits are listed in the product list. In addition, the SKF life correction coefficient aSKF also uses the lubrication condition (viscosity ratio) and a coefficient c indicating the degree of pollution to reflect the operating conditions in use.

The equation of the rated life is in accordance with ISO 281: 1990 / Amd 2: 2000. Lnm = a1 aSKF L10 = a1 aSKF (C / P) p If the speed is constant, the life can use the equation to express Lnmh = a1 aSKF in working hours. 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 dynamic load rating, KNP = equivalent dynamic load, KN

n = rotation speed, r / minp = exponent of the life calculation equation 3 for ball bearings 10/3 for roller bearing coefficients n represents the possibility of failure, ie the difference is between reliability and 100%.

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


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