Micropitting Performance of Oil Additives in Lubricated Rolling Contacts

Abstract

In the present study, an existing theoretical micropitting model, based on the competitive interaction between surface fatigue and mild polishing wear, is employed to predict the effects of different base oil/additive solutions and the relative humidity of the environment on micropitting damage. These effects, though expected to be tribochemical in nature, manifest themselves mechanically; for example, by possibly affecting the fatigue strength of the surface and increasing or reducing the boundary friction and/or the mild wear rate, which altogether may cause an appreciable influence on the degree of micropitting. The present model takes into account only the last two issues (i.e., the change in boundary friction and wear) due to the presence of additives; nevertheless, it is able to predict their performance under micropitting conditions in most cases, showing good agreement with the corresponding experimental data. The results of the present work establish the basis of a blueprint for selecting oil additives for bearing applications.

KEY WORDS:

• Micropitting
• Surface Distress
• Boundary Friction
• Mild Wear
• Additives
• Tribolayers
• Rolling Bearings

ACKNOWLEDGEMENTS

The authors express their gratitude to Alexander de Vries, Director SKF Group Product Development, for his kind permission to publish this work. The authors also thank Hui Cen and Berry Peek for carrying out the tests and sharing the results and express special gratitude to Dr. Andriy Rychahivskyy for scanning the samples.