Formulation of emulsifiable cutting fluids and extreme pressure behaviour

Extreme pressure tests following the ASTM D 2783 standard were carried out to evaluate the performance of several oil-in-water (O/W) emulsions used as lubricating and cooling fluids in machining operations. The effect of concentration of three different emulsifiers (anionic, non-ionic, and cationic surfactants) on the extreme pressure properties of the O/W emulsions was studied in more detail. The base oil was a mixture of a synthetic poly-α-olefin and a trimethylol propane trioleate ester, to which emulsifiers were added at concentrations below, equal, and above their critical micelle concentrations (CMC). Contact angles were determined to obtain a relationship between wetting and lubricating properties. Results show that O/W emulsions have a lubricating performance similar to base oils under non-severe conditions. Furthermore, the ability of oil droplets to wet the metal surface plays a key role in their tribological behaviour and the lubricating performance depends to a great extent upon the type and concentration of emulsifier.