The effect of lubricant additives on the coefficient of friction in the flat-die test

The effectiveness of various lubricants and their additives in reducing the coefficient of friction in the flat-die test was examined. The load, relative velocity, the additives, the base oils and the viscosity of the lubricants were the independent variables. Nine lubricants – six with and three without additives – were studied.The 10% high molecular weight polymer ester (HMW) additive in the high viscosity base oil (HVBO) caused the largest reduction of the coefficient of friction. The 10% HMW additive in the liquid ester as well as the 10% Phosphor I additive in the HVBO also decreased the friction at higher relative velocities. The least successful combination was the 5% HMW additive in the medium viscosity base oil. In general, the majority of the additives created significant improvements over the base oils. The more effective additives were those that increased the lubricant's viscosity.