Additive influence on wear and friction performance of environmentally adapted lubricants

In this paper, the influence of concentration level and chemical composition of three different additive types on friction and wear coefficient are presented for a synthetic ester base fluid and a mineral base oil. One extreme-pressure (EP), two antiwear (AW) and two yellow metal passivator (Cu-passivators) additives were used. Factorial experimental design was used as the basis for a systematic evaluation of wear rates under mixed and boundary lubrication conditions. A total of 33 different lubricant blends were tested in a Plint and Partner High Frequency Friction Machine. For the synthetic ester, the extreme-pressure (EP) additive, containing phosphorus and nitrogen, was found to be much more effective in reducing wear than either of the two antiwear (AW) additives tested. In fact, the AW and Cu-passivator additives made little or no contribution to the wear protection in most of the cases studied. A synergy effect between the three additive combinations was observed only for the reference mineral oil blend. A significant difference between the antiwear performance of the test lubricants was found. This study suggests that the traditional “AW” and “EP” labels associated with commonly used additives are poor aids when designing of ester based lubricants.