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ROLLING BEARING FAILURE
- 0.001 amp no effect on life
- 0.01 amp ca. 20% reduction in life expectancy; failure has normal fatigue characteristics
- 0.01-0.1 amp life expectancy reduced by 20-80% over this range; failure has still normal fatigue characteristics
- 0.5 amp life expectancy reduced by more than 80%;'washboard' damage occurs
From a practical point of view, the impressed voltage should not exceed 0.3 V on ball bearings, 0.5 V on rolling bearings.
Electric discharge damage does not, however, always result in 'washboarding'. Figure 10b shows pitting damage caused by high voltage discharge. This is similar to corrosion pitting, figure 7b, but is distinguished by the absence of oxide and the rounded pits that show evidence of melting.
10. Electrical Damage
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Passage of an electrical current through a rolling bearing causes surface damage and hence decreased fatigue life. With currents above 0.5 amp a characteristic ripple or 'washboard' pattern is formed on the contacting surfaces (figure 10a), but even with currents as low as 0.01 amp there is still some deterioration, which although not visible results in a decrease of life as shown
below.
Note that the 'washboarding' in figure 10a is very severe, and milder forms of washboarding occur, some of which can only be detected by rotating the race while viewing in good lighting. The wavelength of the washboard pattern is highly variable, and shows no obvious correlation with features such as roller spacing, electrical frequency etc.
| Click on photograph to enlarge | |
 | Electrical 'washboard' damage on outer race of ball bearing |
 | Electrical pitting damage on ball from ball |
 | Note corresponding pattern on race and on ball, suggesting single large discharge. |
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| Main Characteristics | Effect of electric currents on the life of rolling bearings |
Other Types of Damage