DescriptionIn this work, requirements for sealing surface of shafts used in industrial gears were identified and the best solution for improving surface properties was considered. There had been problems regarding the wear of the sealing surface of shafts. Scratches formed into the sealing surface and wear of the radial shaft seal had led to oil leaks of the gear boxes in the worst case. In order to improve wear resistance of the sealing surface of the shaft, different surface treatment and coating techniques were considered. As a novel and promising technique, EHLA or Extreme High-Speed Laser Cladding was considered as one potential option for solving the wear issues. Therefore, the method and preparation of wear-resistant coatings were experimentally investigated in Tampere University facilities. For the EHLA trials, simplified shafts were manufactured, and metal powders were ordered for preparing the coatings. 42CrMo4, C45 and S355 steel grades were used as substrate materials, whereas AISI 420, Rockit 401 and Stellite 6 metal powders were used for preparing coatings. Several narrow coatings were prepared using different process parameters in order to find optimal parameters for each material. Coatings were analyzed by measuring hardness profiles and investigating the microstructure of each sample which were metallographically prepared. Optical microscopy, hardness testing, SEM and EDS were used for studying the coatings. Additionally, the machinability of the coatings was studied by preparing a few wider samples to be machined according to requirements of the sealing surface. Coatings prepared by using Stellite 6 material turned out to be most suitable for the application, being hard, dense and flawless when coated on C45 substrate by optimized process parameters. Microhardnesses of those samples were around 600 HV. In the case of Stellite coatings prepared on 42CrMo4-substrate, there were some cracks formed into HAZ due to high carbon equivalent of the steel grade and rapid cooling. However, Stellite 6 coated on C45 substrate performed well and was
selected for block-on-ring wear test, where the adhesive wear resistance of Stellite coatings were tested and compared to surface hardened C45 samples. There were no clear differences between hardened C45 samples and Stellite coatings observed based on the wear tests. In lubricated conditions, the seal block used in the test was damaged slightly more when pressed against Stellite 6 coating than against hardened steel. EHLA-technique was successfully tested, and high-quality coatings were prepared on steel rods. Based on the experimental trials and literature survey, EHLA-technique proved several advantages over competitive coating techniques, and therefore, it is a potential way for preparing wear resistant coatings on critical surfaces of shafts used in industrial gearboxes.
|6 Jul 2023
|Degree of Recognition