Lower Boundary Friction of Plane Slide Bearing Developing with Combination of Phosphate and Fatty Acid at Ultimately Low Sliding Velocity

摘要

Reduction in friction of slide guide-ways of machine tools is considerably important to guarantee machining precision. Therefore, there are many studies of lubricating oils for machine tools focusing on additives developing low friction at lower sliding velocity. For this purpose, alkyl acid phosphate and fatty acid could be typical additives. Especially, it is reported that oleyl acid phosphate (OLAP) indicates extremely low friction at ultimately low sliding velocity. This study investigated effect of a combination of phosphate and fatty acid on lowering ability of boundary friction of a plane slide bearing at ultimately low velocity condition. A thrust collar-type friction tester is employed for realizing lower normal contacting condition. Sliding velocity ranges from 0.1 nm/s to 100 mm/s. Initial surface roughness (R_(zJIS) 3.0 - 3.5μm), applied pressure (0.3MPa) and viscosity of base oil (ISO VG68) are conformed to practical slide guide-ways of common machine tools. Friction coefficient is estimated after enough running-in duration. From obtained results, it is found that the friction coefficient with lubricant containing OLAP and oleic acid is lower than that containing only OLAP. Additionally, it is found that the lowering ability of friction coefficient depends on the type of fatty acid. It is indicated that the chain length and structure of fatty acids are important factors to determine this lowering ability. In this study, mechanism of developing lowering ability with fatty acids is discussed.