Tribology of Coatings for Use in Oil-Less Swashplate Compressors

Increasing efficiency through the use of tighter tolerances and more extreme conditions is becoming more prevalent in current compressor design. In an effort to enable oil-less operation, greater protection is sought through the application of hard protective coatings. Unlubricated unidirectional experiments were performed with a pin-on-disk tribometer to simulate swashplate compressors. Experiments included 52100 crowned steel pins and coated aluminum A390-T6 disks. WC/C, WC/C + DLC and TiAlN + WC/C were applied while some aluminum disks also contained a CrN underlayer to increase load bearing capacity. In step-loading testing the best performance was attained with one type of the CrN + WC/C multi-layered coatings, exhibiting friction coefficients as low as 0.05 with scuffing loads ten times larger than uncoated experiments. Based on the research presented in this work, hard coatings have the potential to replace oil in future compressors.