270 Lubricant Additives: Chemistry and Applications
used, although it is possible to adjust almost any activity/lubricity ratio while using the combination
of appropriate sulfurized products.
9.5.1.4 Copper Corrosion
Depending on the process and on the metals machined, corrosion control toward yellow metals can
be a requirement. If inactivity (no staining) toward yellow metals is required, it is important to use
either absolute inactive sulfurized products or medium-active sulfur carriers in combination with
yellow metal deactivators. Active sulfurized products can be inhibited short term but will, in the
long term, turn active again.
9.5.1.5 Substitutes for Chlorinated Paraffi ns
The driving forces for the replacement of chlorinated paraffi ns are mainly ecological and toxico-
logical reasons. Users and waste oil disposal facilities have additional concerns over the corrosivity
of the chlorinated paraffi n decomposition products, primarily hydrochloric acid.
Chlorinated paraffi ns work because of their ability to form a highly persistent lubricating fi lm
even at low temperatures or moderate pressure. At high-temperature/high-pressure conditions, they
decompose, and the formed hydrogen chloride forms metal chloride with the metals involved in the
process [39].
Chlorinated paraffi ns can be substituted with sulfurized products. Depending on the main
function of the chlorinated compound in the particular process used, lubricity, or activity, suitable
sulfurized products are available, which can function as alternatives. The lubricity performance
is mainly covered by highly polar, inactive sulfur compounds (see Section 9.4.1.1.6), whereas the
activity will be covered by reactive sulfurized olefi ns or mixed sulfurized olefi ns/triglycerides.
9.5.1.6 Substitute for Heavy Metals
Heavy metals, particularly antimony, molybdenum, and zinc compounds are used as EP and AW
additives in severe metalworking processes. Sulfur carriers have proven to be suitable substitutes,
particularly when used with synergistic compounds such as polymer esters, phosphates, phosphites,
dialkyldithiophosphates, and sulfonates.
9.5.1.7 Carbon Residue Reducing in Rolling Oils
Sulfur carriers are used in cold rolling of steel to prevent carbon residues build up on the surface of
the metal sheets during the annealing process. Carbon residues are generated by oxidation/polym-
erization of additives used in rolling oils. Therefore, typical rolling oils contain sulfur-based anti-
snakey edge and carbon-reducing additives [40]. Clean burning of the lubricant is important to
obtain a clean metal surface that can be evenly coated in subsequent process steps.
Typical products used for this application are sulfurized olefi ns with low to medium activity or
inactive sulfurized triglycerides.
9.5.1.8 Water Miscible Metalworking Products
Sulfurized products are used in water-miscible metalworking systems to provide EP performance
and, depending on the type of sulfur carrier, lubricity. By far the biggest applications are soluble
oils or emulsions. Standard sulfurized products are not water-soluble. Surfactants must be used to
keep the sulfur carrier in the emulsion. Compared to applications in non-water-based systems, the
water-based systems require hydrolytically stable products that can react at relative low temperature.
Therefore, active sulfurized olefi ns, preferably pentasulfi des, are widely used for this application.
Sulfurized esters and triglycerides are also used, especially if additional lubricity is required. Spe-
cialty sulfur carriers are reaction products of sulfurized fatty acids and sulfurized olefi ns. These
sulfur carriers have good emulsifying properties with relatively high hydrolytic stability and activity.