Preparation And Properties Of Al₂O₃-based Composite Ceramic Insulating Coating For Motor Bearings

Insulation bearing is mainly used the electric equipment in railway,wind energy,mining and other fields,especially in high frequency and high voltage motor.It solves the failure problem for the key component due to the electrical erosion.The Al₂O₃-based composite ceramic insulating coating is used for insulating bearings,which has more characteristics such as the high temperature corrosion resistance,high mechanical strength,good insulation performance.It has a great important influence on the service life and work stability of bearings or motors.The thesis based on the Al₂O₃-based composite ceramic insulating coating,combines spraying material optimization experiment and the process parameters optimization test.The main researches are as follows:The experiment used the plasma spraying technique,and selected these materials which include two types of high purity Al₂O₃ powder?namely imported Al₂O₃ powder,domestic Al₂O₃ powder?and two types of different proportion of Al₂O₃-TiO2powder?namely AT3 powder,AT13 powder?as the coating spraying raw material.The ceramic insulation coating was prepared on GCr15 steel substrate surface of the sample using the recommended plasma spraying parameters,of which the properties including insulation,adhesion and mechanical properties were studied.In order to determine the optimum scheme of coating spraying material,the primary screening test and in-depth optimization test were carried out for the Al₂O₃ based ceramic insulation coating.In the primary screening test,the optimum spraying raw materials of coatings were made of Al₂O₃ powder and AT3 powder by taking into account the performance test results and economic cost factors.The in-depth optimization test,the spraying process parameters were optimized by setting different parameters of arc current,and the insulation resistance,porosity,bonding strength and microhardness of the coatings were tested under different parameters?CPSP?.The microstructure and phase composition of coatings were analyzed with the aid of scanning electron microscope?SEM?and X-ray diffraction?XRD?and finally a better insulation coating solution to determine the material of Al₂O₃-based ceramic coating.The research results show that the Al₂O₃ coating not only has a good insulation performance and moderate bonding performance and its price is low compared with the AT3 coating.Al₂O₃ powder is more suitable for the ceramic insulation coating by comprehensive analysis.The three-factored,four-leveled orthogonal experiment was carried out to optimize the Al₂O₃ ceramic insulation coating process parameters.The factors for study included arc current,feeding rate and the main gas flow,and the five coating`s performance indexes such as volume resistivity,dielectric strength,porosity,bonding strength and micro-hardness were optimized as the targets.Using sensitivity analysis method based on orthogonal test and objective comprehensive evaluation method based on entropy weight method,the range analysis and sensitivity analysis of the performance indexes of the coating were carried out.The results show that the most sensitive factors influencing the performances of Al₂O₃ ceramic insulation coating is the arc current and the least sensitive factor is the feeding rate,and the main gas flow rate is in the middle.Its maximum sensitivity is up to 47.91.Based on studies of different process parameters towards the coating performance,a finally spraying process parameter scheme is as follows: the arc current is 510 A,the main gas flow feeding rate is 60 L/min,the feeding rate is 35 g/min.