New bearing surface coating and ceramic rolling elements

A new surface coating for rolling element bearings has been developed by Schaeffler that insulates the bearings from damage caused by the passage of electrical current in large AC or DC motors.

Schaeffler’s Isotect® A coating is an insulating layer for rolling element bearings that can be applied to the outer or inner ring external surfaces. Alternatively, depending on the application, the bearings can be assembled with ceramic rolling elements.

In the past, bearings used in large AC or DC motors with only a few pairs of poles were prone to damage from the passage of electrical current. Today, due to the increasing use of frequency converters, this potential danger is growing. Around 3 per cent of all electrical machines manufactured worldwide are controlled by a frequency converter. This figure is expected to rise to 10 per cent over the next couple of years.

Isotect® A acts like a resistor and capacitor connected in parallel. With DC voltage and low frequency AC voltage, the choice depends on the ohmic resistance of the bearing. With higher frequency AC voltage, which is often found in frequency converters, it depends on the capacitive reactance of the bearing. To ensure good insulation, the ohmic resistance should be high and the capacitance should be as low as possible.