Steel ball bearings can conduct electricity whereas full ceramic bearings, hybrid ceramic bearings and plastic bearings are non-conductive. In a steel bearing, current passes from inner ring to outer ring via the balls. This often occurs in electric motors and generators and applications where there is a build-up of static electricity.
With standard bearing lubricants that do not readily conduct electricity, voltage can temporarily build up inside the bearing leading to frequent arcing through the bearing lubricant, usually where oil film is at minimum thickness. These discharges generate a great deal of heat and cause welding between the surfaces which can be seen as pitting or fluting on the balls and bearing raceways. This will also degrade the lubricant. The result is excess noise and early bearing failure.
Electrical damage to bearings can be avoided by preventing the current from passing through the bearing. This can be done by diverting the current, typically by grounding the shaft, or by using non-conductive bearings such as hybrid bearings (steel bearings with ceramic balls).
Another possibility is to make sure that the current can pass continuously through the bearing by using a conductive grease. This prevents arcing and subsequent bearing damage.
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