2008 Volume 3 Issue 5 Pages 274-279
From the viewpoint of natural environmental requirement, the applications of biodegradable lubricants are growing. Most of vegetable oils are biodegradable and have good lubricating performance even at high contact pressure conditions in spite of their lower pressure-viscosity coefficient. In vegetable oils, however, the optimum suppression of oxidative degradation is required to improve the longevity of vegetable oils. Therefore, it is required to clarify the actual lubrication mechanism in vegetable oils with appropriate antioxidant additives. In this study, the tribological properties of four kinds of vegetable oils of different composition were evaluated in four-ball tests at different sliding speed conditions. As an antioxidant additive, α-tocopherol was used. The types of fatty acids in triglycerides appeared to control the lubricating performance through adsorbed film and friction polymer formation, depending on the operating conditions. Therefore, the paraffinic oils containing fatty acid were tested. It was shown that the influences of fatty acid types on lubricating performance were different depending on sliding speeds. These differences are discussed from the viewpoints of the role of friction polymer and oxidation of oils evaluated by FTIR analyses. Finally, effective application of various vegetable oils is discussed on the basis of relationship between tribological behaviors and operating conditions.
