Lubricant Replenishment in Rolling Bearing Contacts

Abstract

It is generally assumed that starved lubricated contacts in rolling element bearings are replenished by side flow. The rolling elements partly push the lubricant to the side of the contacts after which the re-flow will provide fresh lubricant for the next rolling element. This re-flow is driven by surface tension and restricted by the viscosity. Hence, thick oils or greases may yield problems here, which is generally observed in practice. This paper quantifies this re-flow by means of a numerical model using a so-called thin layer/film assumptions. The results here show that this form of replenishment may happen to some extent in single contacts but for sure not in rolling element bearings. There are two reasons for this: the time between successive overrollings is too short and secondly, the centrifugal effects on the inner ring will drive the flow in a vertical direction rather than transversely. This applies to cylindrical roller bearings (CRB)-type of surfaces. This may be different for tapered or spherical bearings, which should be the topic of future research.

KEY WORDS:

• Film Geometry
• Film Thickness
• Starvation
• Surface Tension
• Lubricant Rheology
• Cylindrical Roller Bearing (CRB)

ACKNOWLEDGEMENTS

The authors would like to thank Prof. E. Ioannides, Technical Director of SKF Group Technology Development, for his kind permission to publish this paper.

Review led by Jane Wang