Elastohydrodynamic properties and boundary lubrication performance of polyolester in a hydrofluoroether refrigerant environment

Abstract

The electrohydrodynamic (EHD) properties of polyolester (POE) in refrigerant environments were determined with a ball-on-sapphire disc-type EHD tester. The film thickness and the traction were both lower for hydrofluoroether HFE-245mc than for hydrofluorocarbon (HFC) at an identical gas pressure. This is because of the higher refrigerant concentration (RC) for HFE-245mc than for HFC, which resulted in a lower atmospheric viscosity and a lower viscosity-pressure coefficient of the refrigerant/POE mixture for HFE-245mc. The boundary lubrication performance was studied with a block-on-ring type tribometer. The coefficient of friction in HFE-245mc was lower than that in HFC, and HFE-245mc was superior to HFC in terms of antiwear performance. X-ray photoelectron spectroscopy (XPS) of the surface film showed the presence of FeF2 and iron oxide whose concentration was much higher, and the boundary film thickness was much thicker for HFE-245mc than for HFC. Thus, it was inferred that HFE-245mc adsorbed on to the rubbing surface was decomposed to form an effective antiwear film having a low shear resistance which resulted in reduction in the friction and wear.