An electric charge may develop in a bearing within a split second leading to discharge via the bearing balls and raceways. This phenomenon can result in serious bearing damage. Equipment transporting plastic foil or paper are particularly at risk due to the potential for static electrical build up and discharge. Electric motor bearings and generators (wind power stations...) may also suffer similar electrical discharge damage failures.
Electrical current passage through the bearing may result in elec- trical arcing damage to balls and raceways which can appear as craters or grooves, often with a “bar-code” like symmetry. Craters may be formed due to localised melting of the surfaces of the bearing raceways and balls. Fragments of molten metal may well be removed and re-deposited in other areas of the raceways where they are rolled over into the raceway substrate. Tell-tale electrical erosion grooves are formed as a result of the simultaneous stressing of the rolling elements and raceways in the load area where the current flow is most apparent. It is normal to have to replace a damaged bearing once electrical erosion damage has taken place, no form of repair is possible.
In an attempt to prevent electrical erosion damage the operator or equipment designer can either change machinery construction elements or select and use an electrically conductive lubricant, particularly when only low voltage currents occur. Such lubricants are able to conduct the electrical current through the bearing so that point-to-point flashovers are eradicated. It should be noted that specially developed electrically conduc- tive greases have a very low electrical resistance in the region 105 ohms ∙ cm.