Cutting oil facilitates the cutting or shaping of metal by machining, grinding and honing. Its purposes is to lubricate, reduce heat, reduce wear and galling between the tool and workpiece, and assist in chip removal from an active cutting surface. The choice of cutting oil depends on the machine, type of metal being machined, cutting speed, and other parameters.
Low Speed, High Speed
In metal removal applications, a metal blank is shaped by removing metal. The most important function of a cutting oil depends partly on workpiece processing speed. In low-speed applications, the primary function of cutting oil is to lubricate the working interface between the tool and the workpiece. In high-speed applications, a cutting oil functions mainly as a coolant.
In general, thinner cutting oils with low viscosity cool the working interface better than more viscous cutting oils. Thinner oils are more prone to splashing about the workpiece and running off, carrying problematic heat away from the working interface. Coolant misting can be problematic in such situations.
In contrast, thicker cutting oils are fed to the work area slowly and dwell there longer. Their ability to cool the workpiece is inferior to the water. They lubricate the workpiece at lower speeds, reducing process heat through the minimization of friction rather than the heat transfer mechanisms prevalent in dilutable metalworking fluid.
Since a high-viscosity cutting oil dwell longer on the workpiece, its temperature can elevate and the oil, rather than misting as high speed-fluids do, may instead smoke from the heat of friction and hot metal chips.
Types of Cutting Oil
There are three types of lubricants used in metal removal: straight (mineral) oils, soluble (emulsifiable) oils, and synthetic fluids.
Straight, or mineral, oils are based on refined petroleum products. They contain no water and are formulated for medium to heavy duty applications in which lubrication, more than cooling, is required. These oils are most often used on older machine tools or at slower speeds.
Synthetic oils are made from detergent-like compounds, synthesized hydrocarbons, organic esters, polyglycols, phosphate esters and other synthetic bases. They are formulated to lubricate, cool, reduce oxidation, eliminate smoke, reduce misting, and provide rust protection. In use since the 1950s, synthetics are typically the cleanest and clearest, providing a transparent formulation that is often dyed green.
Soluble (emulsifiable) oils are mineral oil-based concentrates that are mixed with water. Commonly called soluble oils, they don't actually dissolve in water but the concentrates contain emulsifiers that form a milky emulsion when mixed. They usually contain additives to enhance lubrication, inhibit rust and corrosion, and a biocide to prevent objectionable odor.
Still Wondering.... ...which cutting oil is best for your application?
Call Acculube, and an experienced fluid specialist will help you to choose the natural, semi-synthetic or synthetic cutting oil best suited to your parts, machinery, facility, and budget.
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