The term “neat” describes a cutting oil that is not mixed with water. Cutting oils mixed with water, better known as “water extendible” fluids, are designed to provide better cooling during the machining process, especially high-speed processes. In an emulsion, water provides cooling and oil provides lubrication. While neat oils have traditionally been used in low-temperature applications such as slow-speed machining, they are becoming used more and more in higher speed applications, edging out water extendible fluids, for a variety of reasons:
• More difficult alloys are being used in many machining processes and machining processes are becoming more complex, both requiring better lubrication
• Water-extendible fluids require a unique waste disposal process since the water is typically contaminated with metals
• Use of tri-purpose fluids for machining, hydraulic/waylube and stock feed minimize inventory requirements
Other advantages to using neat oils in the machining process are higher tool speeds and stock feeds, longer drain intervals, consumption reduction and overall fluid-related cost reductions.
Traditional base fluids for industrial neat oils are napthenic and paraffinic petroleum fluids. Group II paraffinic is being increasingly used due to widespread availability. GII paraffinic brings benefits such as high temperature viscosity and oxidation stability as well as lower volatility, but it also has lower additive solvency which is a concern.
A growing alternative to petroleum-based fluids are vegetable-based fluids and synthetic esters including canola, soybean, rapeseed, sunflower, palm and others. These fluids are not new, but are increasing in use due to airborne mist being safer than petroleum-based oils, availability, environmental impact and pricing coming more into line with traditional fluids.
Chlorine has long been the go-to additive for machining lubricants because it is polar (clings to metal) and has an active temperature range that is suitable for typical machining processes. However, chlorinated parrafins are being increasingly regulated by the EPA as they fall under similar classifications to chlorinated solvents. Short chain CP’s have already been discontinued. Active sulfur has limited applications due to potential staining of various metal alloys. The current trend is toward phosphorous, inactive sulfur and blends of the two to meet regulatory criteria as well as needs for higher speeds, feeds and temperatures at the tooling surface.
As environmental concerns and their associated costs become a more prominent factor in the use of water extendible fluids, we expect to see the use of neat oils, especially bio versions, increase. As we learn more about the use of these fluids and their associated additives their viability and desirability will increase.