The use of defoamer in metalworking fluids (MWF) is essential for the lubrication and cooling of metals during a machining process. Defoamer is added to the MWF to reduce or eliminate foam formation. The selection of the right defoamer for a given MWF is important, as the wrong one can cause poor performance, resulting in a decrease in machining speeds and finish quality.
Different types of foam are created during the operation of a machining process. Common foam types include air-entrained foam, mechanical foam, and hydraulic foam. A common way to reduce foam is to add defoamer to the MWF. There are several types of defoamers that can be used in metalworking fluids.
Air-entrained foam is a result of air bubbles becoming admixed to the MWF. To reduce this type of foam, a defoamer that breaks the surface tension of air bubbles, such as silicone-free silicone oil, is recommended.
Mechanical foam is caused by the churning of the MWF by the rotating machining tool. This type of foam is more resistant than air-entrained foam, and a silicone-containing defoamer is best suited to deflate it.
Hydraulic foam is caused when MWF is forced through high pressure machining tools. It usually requires a defoamer with a higher efficiency than those used for air-entrained and mechanical foam. A silicone-containing defoamer, such as decamethylcyclopentasiloxane, is recommended.
In addition to the type of foam, the MWF should also be taken into consideration when selecting a defoamer. Water-soluble defoamers may perform well in aqueous MWF, but can be toxic and not recommended for use in MWF that contains a synthetic fluid. Synthetic fluid-soluble defoamers should be used instead.
The selection of the right defoamer for a given MWF should be based upon the foam type, the MWF, and the desired end-use application. The type of defoamer selected must be compatible with the MWF and should offer low toxicity, low foam production, and the maximum defoaming action.
Organic defoamers, such as organic silicones, fatty acid esters, and vegetable-oil derivatives, are generally safe and effective in reducing normal foam formation. Inorganic defoamers are also effective at reducing foam; they tend to have higher toxicity, but also have better performance in reducing foam.
A good defoamers can greatly improve the performance of a metalworking fluid. The correct choice of defoamer to be added to a MWF should be based upon the foam type, MWF, and application. Organics and inorganics each have their advantages and disadvantages, and the choice should be based on the desired end use application.
