Slip in Roller Bearings under Hydrodynamic Contact Friction

Abstract—

The study considered the known hydrodynamic friction model based on the generalized Eyring equation and taking into account the phenomenon of oil film self-heating. The concept of effective friction coefficient is introduced the use of which makes it possible to perform bearing dynamic simulation taking into account the dependence of friction coefficients on cyclically changing contact forces without increasing the calculation time. The effective friction coefficients of the contacts with the inner and outer rings are calculated for the range of specified slip values. As a result, dependences of the effective friction coefficients on slippage of both the cage and the rolling elements are obtained. These dependences have the same form as conventional friction curves: as slip increases, the effective friction coefficient first increases and reaches a certain maximum value, and then decreases, which is caused by self-heating of the oil film and a decrease in its viscosity. A decrease in the friction coefficient during bearing operation, in turn, leads to even greater slippage. A process with such a “positive feedback,” if not interrupted, leads to an increase in heating of the oil, a decrease in the thickness of the oil film and, as a result, to its rupture, the occurrence of boundary friction, intense wear, and seizure. The amount of cage slip that achieves the maximum effective friction coefficient on the inner ring is critical. In the example considered in the paper, the critical slip of the cage is 11%. The slip allowed during operation of the bearing must be determined taking into account the margin in relation to its critical value.