Cutting fluid
Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping.
There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other gases.
Cutting fluids are made from petroleum distillates, animal fats, plant oils, water and air, or other raw ingredients.
Ambient air cooling is sometimes adequate for light cuts and low duty cycles typical of maintenance, repair and operations (MRO) or hobbyist work.
Production work requires heavy cutting over long time periods and typically produces more heat than air cooling can remove.
Every conceivable method of applying cutting fluid (e.g., flooding, spraying, dripping, misting, brushing) can be used, with the best choice depending on the application and the equipment available.
For many metal cutting applications the ideal has long been high-pressure, high-volume pumping to force a stream of liquid (usually an oil-water emulsion) directly into the tool-chip interface, with walls around the machine to contain the splatter and a sump to catch, filter, and recirculate the fluid.
It is often not a practical option for maintenance, repair and overhaul or hobbyist metal cutting, where smaller, simpler machine tools are used.
It has been complemented since the 2000s by new permutations of liquid, aerosol, and gas delivery, such as minimum quantity lubrication and through-the-tool-tip cryogenic cooling (detailed below).
Many of these are also high-pressure coolant systems, in which the operating pressure can be hundreds to several thousand psi (1 to 30 MPa)—pressures comparable to those used in hydraulic circuits.
These properties include: rust inhibition, tolerance of a wide range of water hardness (maintaining pH stability around 9 to 10), ability to work with many metals, resist thermal breakdown, and environmental safety.
The official technique to measure oil concentration in cutting fluid samples is manual titration:[4] 100ml of the fluid under test is titrated with a 0.5M HCl solution to an endpoint of pH 4 and the volume of titrant used to reach the endpoint is used to calculate the oil concentration.
A hand-held refractometer is the industrial standard used to determine the mix ratio of water-soluble coolants[5] that estimates oil concentration from the sample refractive index measured in the Brix scale.
Others include: Cutting fluid may also take the form of a paste or gel when used for some applications, in particular hand operations such as drilling and tapping.
Some cutting fluids are used in aerosol (mist) form (air with tiny droplets of liquid scattered throughout).
The main problems with mists have been that they are rather bad for the workers, who have to breathe the surrounding mist-tainted air, and that they sometimes don't even work very well.
MQL's aerosol is delivered in such a precisely targeted way (with respect to both location and timing) that the net effect seems almost like dry machining from the operators' perspective.
In this application pressurized liquid CO2 is allowed to expand and this is accompanied by a drop in temperature, enough to cause a change of phase into a solid.
Safer cutting fluid formulations provide a resistance to tramp oils, allowing improved filtration separation without removing the base additive package.
Room ventilation, splash guards on machines, and personal protective equipment (PPE) (such as safety glasses, respirator masks, and gloves) can mitigate hazards related to cutting fluids.
[14] Additionally, Skimmers may be used to remove tramp oil from the surface of cutting fluid, which prevents the growth of micro-organisms.
Modern cutting fluid disposal involves techniques such as ultrafiltration using polymeric or ceramic membranes which concentrates the suspended and emulsified oil phase.
Over the decades they have been improved, to the point that many metalworking operations now use engineered solutions for the overall cycle of collecting, separating, and recycling both chips and coolant.
