Film-forming properties and traction of non-functionalized polyalkylmethacrylate solutions under transition from elastohydrodynamic lubrication to thin-film lubrication

Oil film thickness of the oils containing non-functionalized polyalkylmethacrylate (PAMA) was determined under pure rolling condition between 0.001 and 1 m/s and a temperature of 40 degrees C with a glass disc-on-steel roller tester. The measurements for PAMA solutions with short-chain alkyl group (C1mix) showed a pronounced enhancement of film thickness in the low speeds, while those for long chain (C16mix) fell on the theoretical line. Adsorption test indicated that the increase in film thickness for C1mix was due to the absorbed layer formed by polymer molecule. Then, traction behaviour was studied by varying the rolling speed under a slide/roll ratio of 50 per cent with a sapphire disc-on-steel roller tester. In traction-speed curves, the measurements of all the polymer solutions fell on the base oil line in the high speeds. In the region below 0.1 m/s, as the speed was decreased, the traction for high-molecular-weight (HMw) C1mix and C16mix solutions deviated downward from the base oil line. The traction-film parameter curves suggested that the traction for C1mix and HMw-C1mix solutions was influenced by the mutual interaction of polymer molecules in the partial EHL region including thin-film lubrication, where the concentration of the polymer is high compared to bulk solution.