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# SKF rating life

ISO 281:2007 uses a modified life factor to supplement the basic rating life. The SKF life modification factor aSKF applies the same concept of a fatigue load limit Pu as used in ISO 281:2007. Values of Pu are listed in the product tables. Like ISO 281:2007, the SKF life modification factor aSKF takes the lubrication conditions (viscosity ratio κ) and a factor ηc for the contamination level into consideration to reflect the operating conditions using

Perform calculation

If the speed is constant, the life can be expressed in operating hours, using the equation

where
 Lnm = SKF rating life (at 100 – n1) % reliability) [millions of revolutions] Lnmh = SKF rating life (at 100 – n1) % reliability) [operating hours] L10 = basic rating life (at 90% reliability) [millions of revolutions] a1 = life adjustment factor for reliability (table 1, values in accordance with ISO 281:2007) aSKF = SKF life modification factor, (diagram 1, diagram 2, diagram 3 and diagram 4) C = basic dynamic load rating [kN] P = equivalent dynamic bearing load [kN] n = rotational speed [r/min] p = exponent of the life equation = 3 for ball bearings  = 10/3 for roller bearings
Table 2 provides commonly used conversion factors for bearing life in units other than million revolutions.
1. 1)The factor n represents the failure probability, i.e. the difference between the requisite reliability and 100%.