Transiently Stable Emulsions for Metalworking Fluids

Modern high speed machining would not be possible without the use of metalworking fluids (MWFs). MWFs perform a number of useful functions like cooling and lubrication. They also assist with metal chip evacuation and short-term corrosion protection. It is estimated that 90 million U.S. gallons of water-soluble MWF concentrate are manufactured annually in the U.S. alone to meet the above needs. MWFs become process effluents when the accumulation of contaminants such as extraneous oil, particulate debris from machining operations, and bacteria negatively impact functionality. One to two billion U.S. gallons of oily wastewater result annually from the use of MWFs. Reducing this environmental footprint has become an important objective for both manufacturers and end-users of MWFs. Oil-containing MWFs are conventionally formulated to be highly stable emulsions. These emulsions are difficult to maintain, recycle, and treat (Byers, 1994). Preliminary work indicated that transiently stable emulsions can provide comparable lubrication, while also potentially being easier to maintain and recycle. They also offer fewer problems for waste treatment than their stable counterparts. This report focuses on a rational approach to designing such transiently stable emulsions by elucidating the important factors affecting lubrication, cooling, and phase separation.