Effect of Particulate Contamination in Grease-Lubricated Hybrid Rolling Bearings

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Abstract
The presence of hard contaminants in lubricated rolling bearings is a major cause of premature failure, for example by fatigue or by abrasive wear of rolling elements, races or cages. However, the introduction of much harder ceramic (usually silicon nitride) balls or rollers running against steel races, in the hybrid bearing concept, is likely to change the interactions of hard particulate contaminants with the bearing components. The performance of all-steel and hybrid rolling bearings was investigated in the presence of two well-defined particulate contaminants. Experiments were carried out with grease-lubricated thrust bearings, contaminated with titania (anatase) and silica (quartz) particles. A significant beneficial effect was observed in the hybrid bearings in the presence of fine (<5 μm) anatase particles, as lower cage wear and running temperature were recorded. This improvement was associated with the formation of thin and relatively soft titania films on the silicon nitride ball surfaces. In the all-steel bearings, silica particles caused severe wear of the balls and cage, whereas in the hybrid bearing no wear could be detected on the balls, and cage wear was significantly lower than for the all-steel bearing. The wear losses of the steel race-ways were similar in both cases.