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Why electric current insulating bearings?
To ensure smooth, trouble-free operation, it is necessary to prevent the bearing from electric current passage. The contact areas between housing, outer ring, rolling elements, inner ring and shaft can act as electric contacts. The resulting arcs – characterized by very high temperatures like that produced by melting and welding processes – will damage rolling elements as well as raceways of bearing rings.
The passage of electric current through rolling bearings can lead to damage in a relatively short period of time. Small craters caused by electric current passage which have been tolerated occasionally in the past are no longer acceptable. As a consequence, some bearing leaders of world developed their electric current insulating bearings products, which have special coated outer rings with a ceramic electrically-insulated coating for a breakdown voltage up to 1,000 V or even higher.
The technical process that overlaying the ceramic electrically-insulated coating is called plasma spray, which fuses the ceramic powder by heat from the plasma arc and sprays the melting or soften ceramic particles onto the surface of bearing rings. Today, current insulating bearings have been substantially applied on some crucial industrial products like traction motor, wind turbine generators etc., and exhibit very good function effect. Recent reports, however, has shown that after years of application in the field, although the service life of the current insulating bearings is remarkably extended as compared to non-insulation coating bearings, still some random passage of electric current happens and lead to damage of bearings, even there is ceramic coating on the bearing rings.
Beijing United Coatings Technologies Co. (UCT) is committed to explore the nature of ceramic coating’s failure. By combining the plasma spray specialists with bearing manufacturers, UCT did some in-depth research on the issue and came with the conclusion that three causes may result in such a failure:
1. The nature of porosity remained in the structure of plasma sprayed coating.
2. The copper in the ceramic coating which introduced during thermal plasma spraying process from the copper electrode in the plasma torch.
3. Ceramic coating thickness matters
With the above understanding in mind, UCT improved its plasma spraying process by modifying the plasma spraying equipment and parameters recipes, marketed its new line of current insulating bearings SAT series.
