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Cutting Fluid

Thursday 28th March 2013

Cutting Fluid

Cutting Fluid Points to consider:

  1. Conventional Cutting Fluid ‘milky’ emulsions. High oil content (60-80%) products that can be relatively cheap in price and may contain biocide for bacterial protection. The opaque appearance is due to the comparatively large size of the emulsion droplets that prevent the transmission of light.
  2. Semi-synthetic Cutting Fluid translucent emulsions Generally these products contain between 5 to 60% oil and are translucent in appearance due to the smaller droplet size. These products may have a relatively long sump life because of the presence of additives that limit bacterial growth.
  3. Fully synthetic Cutting Fluid solutions This type of solution is completely watermiscible giving a true solution which is clear in appearance. As the name suggests this product is completely free of oil and is often to be found in grinding operations. Wit h the addition of performance additives, these products can be used for a wide spectrum of operations. A wide variety of factors influence the specific fluid selection. For tough materials (e.g. inconel, titanium, etc.), or for tough machining operations such as deep hole drilling, a fluid with some form of extreme pressure additive is necessary


Cutting Fluid - Steel

Low tensile steels can be readily machined unlike the higher tensile steels which are more difficult to machine.

The higher tensile steels, such as stainless, tool and alloy steels require the use of some form of extreme pressure additive.

Staining is not a problem when machining steels.

Cutting Fluid - Cast Iron

Cast iron is easily machinable due to the presence of graphite, except for white cast iron which is strong and hard and difficult to machine.

Fluids with a low oil content must be used. For normal cast irons to minimise ‘drag out’ of oil by the fine swarf particles. Staining is not a problem when machining cast iron.

Cutting Fluid - Aluminium

Aluminium is a soft ‘draggy’ material, which can make it difficult to achieve a good surface finish. Lubricity additives, normally in the form of a fatty material, are necessary.

Additives containing chlorine or sulphur must be avoided as these will result in staining. Staining can be reduced by the incorporation of a passivator.

Cutting Fluid - Copper and Copper Alloys

These are generally soft, ‘draggy’ metals which are difficult to machine. Fluids should therefore contain some form of extreme pressure additive together with a

passivator. Insoluble copper soaps can be formed during the process, which will turn the fluid green and could exacerbate the tendency to staining.

Cutting Fluid - Titanium

Titanium can tend to work harden, and is usually cut at low speeds. Often used in aerospace work along with aluminium alloys and therefore an aluminium coolant is often

used a rationalisation product. Chlorine and sulphure extreme pressure agents should generally be avoided due to the potential for stress crack corrosion.

Cutting Fluid - Magnesium

Magnesium exhibits excellent machining properties, and a good surface finish can be readily obtained. Care must be taken as magnesium swarf can react exothermically (generating heat) with water.

The use of sulphurised additives must be avoided otherwise staining can occur.

Cutting Fluid - Nickel

Nickel and its alloys are prone to work-hardening so low cutting speeds are essential. Extreme pressure additives are necessary to ensure adequate machining performance. The use of sulphurised additives must be avoided otherwise staining can occur