Tribology of Hard Protective Coatings Under Realistic Operating Conditions for Use in Oilless Piston-Type and Swash-Plate Compressors
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abstract
In current compressor designs, increasing efficiency through the use of tighter tolerances and extreme application conditions is becoming more prevalent. Moreover, in an effort to enable reduced oil usage and the ambitious goal of oil-less compressor operation, greater surface protection is sought through the application of hard protective tribological coatings. Unlubricated laboratory experiments were performed to simulate two common types of compressors: piston-type and swash-plate compressors. Bare materials investigated (52100 steel against cast iron and against Al390-T6) exhibited high friction, high wear, and abrupt scuffing failures. Using WC/C and WC/C + DLC coatings applied on 52100 steel wrist pins and tested against uncoated cast iron disks (piston-type compressor) as well as uncoated 52100 crowned pins tested against coated Al390-T6 disks (swash-plate compressor), the authors achieved significant improvements in the tribological performance. Specifically, under the operating conditions investigated-including high temperatures, different refrigerant environments, and different loading conditions-minimal wear, low friction coefficient values of the order of 0.05, and no abrupt scuffing failures were observed. Based on this research, hard protective tribological coatings have the potential to replace oil in future compressors. Society of Tribologists and Lubrication Engineers.
