Cutting fluid

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Cutting fluid or coolant is liquid used to cool and lubricate the cutting edges of machine tools and the pieces they are shaping. It is pumped over the cutting site of machines such as lathes, milling machines, shapers and saws.

Metal cutting operations involve generation of heat due to friction between the tool and the pieces and due to energy lost deforming the material. This heat needs to be carried away otherwise it creates "white spots". Water is a great conductor of heat but is not stable at high temperatures, so stability is often achieved by making an emulsion or microemulsion of water with oil.

There are three types of coolants: mineral, semi-synthetic and synthetic. Mineral coolants are cheap and have a short life. Semi-synthetic coolants use special chemicals to solubalize the oil into water. Synthetic coolants do not contain oil and hence are much more stable but more expensive.

Bacterial growth can be a problem in cutting fluids that contain water. When tramp oil forms a layer on the top of the liquid, anaerobic bacterials proliferate due to warm temperatures. This leads to a bad smell and renders the fluid unusable.

The properties that are sought after in a good cutting fluid are the ability to:

  • keep the workpiece at a stable temperature (critical when working to close tolerances).
  • maximize the life of the cutting tip by lubricating the working edge and reducing tip welding.
  • prevent the growth of bacteria or fungi.

Cutting fluid may also take the form of a paste when used for some applications, in particular hand operations such as drilling and tapping.

In many areas, disposal of cutting fluid is subject to environmental regulations intended to prevent pollution. Modern cutting fluid disposal may involve techniques such as ultrafiltration using polymeric or ceramic membranes which concentrates the suspended and emulsified oil phase.

[edit] Other lubricants

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