Tribological evaluation of hybrid ceramic and surfacetreated rolling bearings lubricated with oils heavily diluted by refrigerants
Heat pumps are increasingly recognized as a key technology not only for building and district heating but also for industrial decarbonization and significantly enhancing the overall efficiency of data centers. High-temperature heat pumps and advanced chiller systems operate under increasingly severe conditions including high pressure differentials, large speed variations, elevated temperatures, and significant oil dilution by refrigerants. These factors lead to mixed and boundary lubrication regimes in the rolling bearings used in refrigerant compressors. This study evaluates hybrid ceramic bearings and surface-treated steel bearings as alternatives to standard steel bearings. Component-level tests and functional bearing tests under oil dilution rates as high as 50% demonstrated that the tested Tribological Black Oxide (TBO) coating significantly improves running-in performance, reduces friction and vibration, while maintaining surface integrity. The post analysis of the tested bearings revealed that both TBO-coated and hybrid ceramic bearings exhibited strong resistance to the refrigerant dilution, whereas steel suffered from micropitting and adhesive wear. TBO-coated bearings clearly outperformed standard steel bearings. These findings suggest TBO as a cost-effective solution and hybrid ceramic bearings as a more robust option for demanding refrigerant compressor environments. Complementary investigations addressing lubrication modelling and fatigue life prediction are also cited at the end of this publication.