Evaluation of hybrid sol-gel alumina coating for electrical resistance applications

In an electric motor, bearing plays a vital role in the performance and reliability which fails frequently due to electrical pitting. To avoid this issue, the bearing can be coated with insulation material. In this present investigation, hybrid sol-gel coating was carried out on bearing steel by dip-coating method. The hybrid sol-gel was prepared using aluminium isopropoxide and calcined alumina powder. The ratio of Sol-Gel to calcined alumina and thickness of the coating was optimized to attain a crack-free surface coating. The crack behaviour was studied. The characterization of Hybrid Sol-Gel was carried out using Fourier-transform infrared spectroscopy and the surface morphology was observed using an optical microscope. The electrical resistance of the coating was measured using an insulation resistance tester. The crack-free surface coating of 40 microns was achieved at a low sol-gel to calcined alumina ratio. The electrical resistance of the coating is found suitable for bearing application. The thermodynamically stable hybrid sol-gel i.e., alpha alumina - alumina coating surface is proposed for electrical insulation coating.