Electrically Insulated Rolling Bearing

Protection against bearing damage caused by the passage of electric current.

Electrically insulated rolling bearings feature electrical insulation that is built into the bearing, providing reliable protection against current passage and electrical corrosion. Typical applications are electric motors, generators and other electrical machines. In this article, Nine Star explains the causes of passage of electrical current through rolling bearings, damage symptoms and countermeasures, properties and production processes of electrically insulated bearings.

A difference in electrical potential between the outer and inner ring of a rolling bearing can lead to a damaging electric current that permanently damages the bearing’s raceways and impairs its running characteristics. A current flow results in electrical discharge in the contact zone between the rolling elements and the inner or outer ring. This, in turn, causes local melting of the surfaces. The result: pitting, material transfer and local microstructural damage through thermal stress. At least a very thin layer of the eroded surface is re-hardened, making it extremely hard and prone to cracking. This process is called electrical corrosion and often affects bearings in electromechanical applications, such as generators and electric motors, but also machines that are powered by electric motors, such as pumps and gearboxes. In addition, the electric discharge renders the lubricant useless. The base oil and additives contained in the lubricant oxide, resulting in the characteristic black color of the lubricant. Premature aging permanently impairs the lubricant’s ability to form a separating layer between the metal surfaces. The bearing’s damaged functional surfaces and the loss of lubrication action result in a rapid loss of the bearing’s functionality.