Controlling Foam with Advanced Defoamer Technology
Ernest C. Galgoci, IFL Technology Director
Foam is ubiquitous in our daily lives through the use of soaps, shampoos, cleaners, and other household items. The foam that we see provides us with the feeling that those products are working properly. However, in most industrial processes foam is undesired, as it detracts from the effectiveness of the process. This is the case for aqueous metalworking fluids, where foam minimization is required to maintain effective lubrication and heat removal and to prevent overflow of sumps and pump cavitation. For these reasons, a defoamer(s) is a critical component of a fluid’s formulation. Although the criteria for choosing a defoamer will vary depending on the specific fluid and requirements, the defoamer must generally exhibit strong initial and persistent defoaming and be compatible (no significant separation) with the fluid. Additionally, it is desired that the defoamer should maintain defoaming despite filtration of the fluid and not cause defects (e.g. craters) on parts that are subsequently painted.
Causes and Breaking of Foam On the surface of a liquid, foam can form as entrained gas bubbles reach the surface and are stabilized by surface active chemicals such as surfactants. For metalworking fluids, the use environment is conducive to forcing large volumes of air into the fluid. Due to their formulation requirements, aqueous metalworking fluids contain surfactants that can stabilise foam. Although formulation strategies can help reduce foam, a defoamer is inevitably needed. Defoamers exist as droplets in the fluid and break foam by disrupting the interfacial forces imparted by the stabilizing surfactants. Defoamers based on siloxanes are the most effective, since they meet the requirement of having a very low surface tension.
Münzing’s FOAM BAN® 3D siloxane
defoamers have a decades-long track record as the state-of-the-art technology for metalworking fluids. Unlike silicones (e.g. polydimethylsiloxane) which are
linear polymers, the 3D technology is based on siloxane polymers that are linked together (“crosslinked”) to form a 3-dimensional structure. The 3D structure along with other formulation components impart stability to the defoamer droplets, and this leads to excellent compatibility in metalworking fluid concentrates and superior initial and persistent foam control.
spread layer, which has a low surface energy, can be particularly difficult to clean, and even a monolayer left on the surface will cause retraction of the applied paint. On the other hand, defoamers based on the 3D siloxane technology have good washability due to optimized formulations and the 3D siloxane particles’ crosslinked nature, which inhibits spreading on the metal substrate surface. Multiple studies by Münzing presented at the last several International Colloquium Tribology and STLE Conferences and many years of field experience have demonstrated the excellent washability and paintability of the 3D siloxane technology.
Filterability of 3D Siloxane Technology
For metalworking fluids, filtration is important during use of the fluid to ensure its cleanliness. However, filtration can affect the defoaming performance of the fluid. To better understand the potential impacts, Münzing has investigated how different defoamer types perform during filtration with various filter materials. The 3D-based defoamers showed better persistence during filtration than alternative technologies based on organo-modified siloxanes, silicones, or mineral oils. An interesting finding of the study was that polar filter material (nylon) had much less of an effect on defoaming performance compared to non-polar material (polypropylene).
Looking to the Future
Washability and Paintability of 3D Siloxane Technology As mentioned previously, it is important that the defoamer does not cause paint defects. Silicone-based defoamers cause defects such as craters in painting operations due to residual silicone adsorbed on the substrate surface. Silicone oil droplets, which have relatively low viscosities, can readily spread on a metal surface. This
As the demands placed on metalworking fluids evolve, improvements in defoamer technology will be necessary to meet stricter requirements. Münzing is committed to the continual development of innovative products that deliver a superior level of initial and persistent defoaming, concentrate compatibility, filterability, washability/paintability, and other needs that may arise.
LINK
www.munzing.com
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LUBE MAGAZINE NO.139 JUNE 2017
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