Influence of Voltage on Friction Coefficient Displayed by Oil Additives

ABSTRACTThe present work investigates the influence of direct current (D. C.) voltage, applied on the sliding surfaces lubricated by different oil additives dispersed in paraffin oil, on the friction coefficient. The additives are graphite, molybdenum disulfide (MoS2), detergent additive (calcium sulphonate), zinc dialkyldithiophosphates (ZDDP), metalloid fusion lubricant as an anti-wear additive of nanospheres less than 0.1 µm in diameter and heteropolar organic base additive (CMOC). The concentration of the additives in the lubricant was 5.0 wt. %. Experiments were performed with and without voltage applied to the sliding surfaces using cross pin wear tester. The values of voltage used were 0, 3, 6 and 9 volts. Based on the experimental results, it was found that friction coefficient displayed by the sliding surfaces lubricated by oil free and oil dispersed by the tested additives increased with increasing applied voltage. The response of the additives to the applied voltage depended on the polarity of their molecules. Besides, friction coefficient displayed by the sliding surfaces lubricated by oil dispersed by MoS2 and graphite additives showed relatively higher friction than that observed for oil free of additives and oil dispersed by ZDDP. The effect of voltage was more pronounced in the presence of graphite, where the friction decreased with voltage increasing. Friction coefficient displayed by the sliding surfaces lubricated by oil dispersed by detergent additive (calcium sulphonate) and the nanospheres particles (< 0.1 µm) of the metalloid fusion additive displayed the minimum friction values (0.035). The effect of voltage was highly pronounced.