Defoamants, also called antifoam additives, are found in many oils. Most oils need to keep foam levels to a minimum, and it is very easy for foam to form in lube systems due to their design and flow throughout the equipment.
When foam enters the oil, it can affect its ability to provide adequate surface lubrication. This can lead to wear occurring at the surface level, damaging the equipment.
Many oils require defoamants to provide various functions and in differing ratios depending on their application. In automatic transmission fluids (ATFs), defoamants are usually needed in concentrations of 50-400ppm to prevent excessive foaming and air entrainment3. On the other hand, for manual transmission fluids and axle lubricants, defoamants are required in slightly lower concentrations, between 50 and 300 ppm.
However, OEMs must verify these concentrations. If the concentration of defoamants is too high, this can actually increase foaming. Additionally, defoamants must be properly balanced with the other additive packages to ensure they do not negatively counteract another additive.
There are two main types of defoamants: silicone defoamers and silicone-free defoamers. Silicone defoamers are considered the most efficient defoamants, especially at low concentrations of around 1%. These defoamants are typically pre-dissolved in aromatic solvents to provide a stable dispersion.
However, there are two significant disadvantages associated with silicone defoamers. Due to their insolubility, they can easily transition out of the oil and have a powerful affinity to polar metal surfaces.
On the other hand, silicone-free defoamers are another alternative, especially for applications that require silicone-free lubricants. Such applications include metal-working fluids and hydraulics, which are used close to silicone-free ones, and even those involved in applying paints or lacquers to these pieces.
Some silicone-free defoamers include poly(ethylene glycol)s (PEG), polyethers, polymethacrylates, and organic copolymers. Tributylphosphate is also another option for defoamers4.
