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 acC 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.
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.
Depending on the operating temperature, Isotect A has a high resistance ranging from several Ohm up to 10Gohm. To allow for the capacitive resistance of bearings used with a frequency converter, Schaeffler has selected not only the appropriate material for the insulating layer, but also the most suitable layer thickness, which both play a key role in ensuring optimum protection.
As capacitance is derived from the surface area of the protective layer and its thickness, the coating is applied to either the inner or outer ring external surfaces, depending on the application. If operating conditions require even higher protection, Schaeffler offers rolling element bearings assembled with ceramic rolling elements across most of its bearing range.