Lubrication of Nonmetallic Materials

Abstract

With the increased use of ceramic components in passenger cars, there is a need for a lubricant which can be used in ceramic/metal contacts. A recent study by the author showed that molybdenum dithiocarbamate (MoDTC) performed better than zinc dithiophosphate (ZDP) in ceramic/metal contact. Oils containing MoDTC provided lower wear volumes and friction coefficients for a Si3N4/cast iron pair than for a 52100/cast iron pair, while oils containing ZDP showed increased wear volumes for the Si3N4/cast iron pair than the 52100 steel/cast iron pair. In this study, the effect of calcium over-based sulfonate detergent and ashless succinimide dispersant on the antiwear and antifriction performance of MoDTC and ZDP was investigated in Si3N4/cast iron and cast iron/cast iron contacts. The addition of calcium overbased sulfonate or ashless succinimide to MoDTC or ZDP resulted in higher wear volumes for the cast iron/cast iron pair compared to cast iron/cast iron tested with MoDTC and ZDP alone. The addition of calcium overbased sulfonate and ashless succinimide to MoDTC or ZDP showed lower wear volumes than those of the cast iron/cast iron pair tested with MoDTC or ZDP containing calcium overbased sulfonate or ashless succinimide. For cast iron/Si3N4 pairs, the addition of calcium overbased sulfonate and/or ashless succinimide to ZDP increased wear volumes compared to those tested with ZDP alone. However, the addition of calcium overbased sulfonate to MoDTC did not increase the wear volumes, and the addition of calcium overbased sulfonate and ashless succinimide to MoDTC in cast iron/Si3N4 pairs increased wear volumes slightly. A time delay to reach steady-state friction coefficients was observed for cast iron tested against Si3N4 with oils containing MoDTC, calcium overbased sulfonate and ashless succinimide. The wear volumes seem to depend on the time to reach steady-state friction coefficients in cast iron/Si3N4 pairs. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in London, United Kingdom, September 8–12, 1997