Impedance Measurement and Demonstrator Tests of Developed Thermally Sprayed and Sealed Coating Systems for Bearing Applications

Abstract

To avoid early stage failure of rolling bearings as components of train drives of electrical engines, the bearings must be protected. As state of the art, alumina coatings are applied by atmospheric plasma spraying and subsequently an organic sealer is used to enhance the service life of these bearings under harsh conditions. This includes high applied frequencies and high ambient air humidity. For further improvement, mullite coatings and a newly developed an epoxy‐ and silicon‐based sealer applied by different sealing techniques are investigated to further enhance the electrical insulation of the bearing coatings. Impedance measurements under dry and wet conditions are conducted to analyze the capacitive behavior of the coatings. X‐ray diffraction measurements are used to correlate the influence of the present crystallographic phases of the ceramic coating on the capacitive behavior. In a following step, selected coating systems are applied onto bearings and tested in demonstrator tests. For higher currents of roughly IBearing ≥ 0.6 A, all newly developed coatings exhibit a decreased number of electrical breakdowns compared to the reference. Consequently, choosing this coating system as electrical protection coating for bearings in electrical engines can reduce the damage occurring from electrical current breakdowns.