Impact of oxidation on grease life in rolling bearings

In this paper the lubrication mechanism of lithium grease lubricated ball bearings in the bleed phase is described. Oxidation plays an important role and therefore grease life “in air” and grease life “in nitrogen” is studied in real bearings. It is shown that grease life is strongly dominated by oxidation but that this is by far not deterministic. Oxidation starts up at a certain time, the induction time, which is the point at which the anti-oxidants have been consumed. This induction time is a function of the bearing operational conditions and the oxygen concentration. Oxidation leads to loss of base oil and loss of lubricity, partly repaired by replenishment and oil release from the grease reservoirs (bleed).