Rolling bearings in electric motors, generators or associated equipment are at risk from the passage of electric current, which can damage the surfaces of rolling elements and raceways in the bearing and degrade the grease rapidly.

The risk of damage, so called electric erosion, increases greatly if a frequency converter controls the electrical machinery, which is becoming increasingly common. An additional risk for high frequency bearing currents occurs in the application due to the inherent stray capacitances within the electrical machinery.

To protect the bearings against electric current passage, SKF has developed INSOCOAT® bearings - electrically insulated rolling bearings (fig. 1). An INSOCOAT bearing is a very economical solution compared with other insulation methods to protect the bearing. By integrating the electrical insulation function into the bearing, SKF has been able to increase reliability and machine uptime by virtually eliminating electric erosion problems.

INSOCOAT bearings have a nominal 100 μm thick layer of aluminium oxide on the exterior surfaces of the outer or inner ring, that can withstand voltages up to 1 000 V DC. The SKF plasma spray coating technique provides an extremely coherent coating of uniform thickness, which is further treated to make it insensitive to moisture and humidity.

SKF INSOCOAT bearings are robust and should be handled in the same way as normal non-insulated bearings.