Abstract
Organo-chlorine compounds have widely been used as an effective extreme pressure (EP) additive in metal working fluids because of their excellent performance in various metal working operations. However, environmental and safety issues demand to replace these chlorinated oils by chlorine-free oils. One of the major replacements would be organo-sulfur compounds combined with overbased sulfonates. It has been well known that, this combination shows the higher performance than that of organo-sulfur compounds alone. Regarding such high performance, in this study, we showed that calcium carbonate greatly contributed to the synergistic lubrication effect. We further found that the combination lubricant provided much low friction compared with organo-sulfur compounds alone.
