Rolling bearings in electric machines can be damaged by current passing through them. Under the worst conditions, craters and fluting in the raceways cause premature bearing failure. A conventional solution minimizes risk by providing an effective insulation between the bearing shield and housing or between the shaft and bearing. A simpler and more economic solution consists of providing a current-insulated rolling bearing at one of the two bearing locations. Deep-groove ball bearings and cylindrical roller bearings have an oxide ceramic layer applied by plasma coating on the outer ring's outside diameter. Its faces have proved suitable under field conditions. The hard layers feature high electrical and wear resistance. Load-carrying capacity and service life of the bearings are identical to those of standardized bearings. They have the same dimensions, so retrofitting is possible.

In one application, the bearings on a special electric machine require current protection. Hybrid bearings with steel rings and ceramic balls provided an alternative to coated deep-groove ball bearings. The ceramic balls provide the current insulation.

Hybrid bearings offer several other benefits as well. For example, designers can increase speed, and reduce friction and temperature, especially with sealed hybrid bearings. Their longer grease life leads to a longer service life.

This information provided by FAG Bearings Corp., Danbury, Conn.