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.

Keywords

electrohydrodynamic (EHD)polyolester film thickness hydrofluoroether refrigerant

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