Abstract
The theory of failure of rolling contact bearings is based on fluctuating high level loading and material fatigue. This theory is unimodal, considering only the solid components of the bearing, and ignoring the liquid phase, which is the lubricant. Bearing life is rather dispersed, reaching a ratio of 20 between the extreme values. Since this theory was established, several exceptional phenomena were detected that could not be explained by it, such as: 1) Pitting damage beyond the contact path; 2) Detrimental effect of a minute quantity of water in the lubricant on bearing life. 25 ppm of water in the lubricant brought about shorter bearing life by over than 30%. The bimodal failure theory considers both solid and liquid bearing components. The damaging process of the lubricant evolves from its cavitation. During this process vapor filled cavities are formed in low pressure zones. When these cavities reach high pressure zones they implode exothermally. These implosions cause local high pressure pulses reaching 30,000 at accompanied by a temperature rise of about 2000 degrees K [1]. This paper includes cavitation erosion test results on stainless steel samples by vibratory and water tunnel test rigs. Various methods of lubricant dehydration are presented and evaluated. The main conclusion from this analysis is the use of water-free lubricants, for long life of RC bearings and more uniform service life thereof.
Highlights
In spite of this, when identical RC bearings are tested under identical conditions they fail after a wide range of test durations
Water is absorbed in lubrication oils and has a detrimental effect on RC bearing life
Cavitation erosion of stainless steel specimens can be performed in laboratory tests
Summary
RCB, are high precision machine elements, made of high quality materials, see Appendix A, and machined by high precision ma-. Cantley [3] reported life tests he performed on full scale RC bearings lubricated with SAE-20 oil, containing a minute quantity of water of 25, 100 and 400 ppm These small quantities of water were chosen to represent extreme conditions of relative humidity. He found that when tested with these mixtures of oil and water, bearing life was reduced by 32% - 48%. Let us examine the possibility that the typical bearing curve can be represented by the Weibull equation In this case T = 6.73 Relative life units, and the equation will be Equation (1): F= 100 1− exp− (t T ). In any case this equation reasonably represents the actual bearing life dispersion
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