The Effects of Additives on Friction and Wear Characteristics of Lubricants for Alternative Refrigerant.

Abstract

The effects of the addition of TCP and stearic acid to synthetic lubricating oils, polyolesters (POE), polypropylene glycols (PPG), polyvinylethers (PVE) for alternative refrigerants were studied using two different friction testers together with hydrogenated coal-tar oil (TN), and paraffinic and naphthenic mineral oils. The effectiveness of the additives was significantly affected by the polarity of the base oils. For the oils without polarity such as TN oil, paraffinic oil and naphthenic oil the additives improved their friction and wear characteristics compared with the oils with polarity such as POE, PPG and PVE which hindered the additives from the adsorption to the rubbing surfaces according to their reactivity. Particularly POE with highest adsorption ability was not improved in friction and wear performance by containing TCP. In contrast, the wear and friction performance of PVE which formed a solidified film more easily than POE was considerably improved by containing the additives. Although solidified films formed could prevent the rubbing surfaces from the direct contact, they were broken at a high contact pressure. The addition of the additives to an oil forming a boundary film of a solidified film considerably improved the friction and wear performance, while the movability of the additives in the oil became poor resulting in suppressing to some extent the formation and recovery of the adsorption film.