Tribological performance of PTFE- and PEEK-based coatings under oil-less compressor conditions

Due to favorable tribological performance, PTFE- and PEEK-based polymeric coatings have received interest in air-conditioning and refrigeration compressor applications, as a potential solution to supplement and potentially replace conventional oil lubricants. The literature in this area is somewhat scarce, especially on the tribological performance of PTFE- and PEEK-based polymeric coatings under aggressive conditions simulating compressor operation. In this work, several PTFE-, PEEK-, resin- and fluorocarbon-based polymeric coatings, coated on gray cast iron were tribologically evaluated using a specialized tribometer under compressor specific conditions, that included oscillatory motion (simulating piston-type compressors) and unidirectional motion (simulating swash plate compressor operation). The coatings showed good to excellent tribological performance, and in general PTFE-based coatings exhibited better friction and wear behavior than the rest of the coatings, including PEEK-based coatings. Long-term durability experiments also showed the superiority and suitability of PTFE/Pyrrolidone coating for potential use in oil-less compressors (where oil-less conditions refer to operation in the absence of any liquid lubricant).