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

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

SKF rating life in hours

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%.
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