SKF life modification factor aSKF
As mentioned, this factor represents the relationship between the fatigue load limit ratio (Pu/P), the lubrication condition (viscosity ratio κ) and the contamination level in the bearing (ηc). Values for the factor aSKF can be obtained from four diagrams, depending on bearing type, as a function of ηc(Pu/P) for SKF standard and SKF Explorer bearings and different values of the viscosity ratio κ:
The diagrams are drawn for typical values and safety factors of the type normally associated with fatigue load limits for other mechanical components. Considering the simplifications inherent of the SKF rating life equations, even if the operating conditions are accurately identified, it is not meaningful to use values of aSKF in excess of 50.
Calculation of the life modification factor
The Bearing life calculation can be used to facilitate the calculation of aSKF. Furthermore, SKF has also developed sophisticated computer programmes incorporating the SKF rating life equation directly at the rolling contact stress level thus permitting other factors influencing bearing life, such as misalignment, shaft deflection and housing deformation to be taken into account, see the section SKF calculation tools.