You can get rid of foam in a coolant tank temporarily by adding defoamers, but some defoamers helps to emulsify leak oil, which is food for bacteria. Therefore, you should always try to find what causes the foam.
The first thing you should do if you have foam in the tank is to try to determine whether the problem has a chemical or mechanical cause. Take a sample and shake vigorously for 10 seconds. If the foam settles quickly it is something mechanical or physical in the system that is causing the problem, otherwise there is something with the chemistry of the fluid that is causing the foam.
If the chemistry is the problem - look at this
Water quality
If the water that you use for production is too soft for the metalworking fluid, there will be a lot of foam when a system is newly filled. Over time, the hardness of the water increases as water evaporates and foam problems are reduced. Check with your process fluid supplier if the suggested fluid is tested and adapted for the water that you use in production.
Concentration
A high concentration (usually over 10%) can lead to foam.
Leak oil and other chemical pollutants
There are many chemicals in a workshop which could cause foam, for example alkaline machine cleaners, anti-rust agents and fluids from previous processes. A high level of leak oil can also cause foam. All liquids that may come into contact with the current fluid should be compatible. Maybe you can clean the machine with coolant instead of using a surfactant?
Bacteria
Some bacteria may contain or produce surface active components that cause foaming. Many sumps are constructed in such a way that they are difficult to clean, and this can lead to bacteria. Test the fluid regularly with dip-slides to see if it contains bacteria.
If the mechanics are the problem - look for this
Temperature
A high temperature may lead to foam in some synthetic fluids. Is it possible to cool the fluid or make the sump bigger?
Air
A leaky pump or a low level of liquid can lead to the pump sucking in air. Make sure the pump is sealed and that the lowest level of filling is not set too low.
Circulation in the tank
The tank volume should be at least 10-15 x flow per minute in the machine, depending on the process. Check if that is accurate for your system and you can also check if the flow has changed since the machine was new. As with all rules, there are exceptions and some processes (eg grinding) may need a larger volume.
Particles and swarf
Small particles can help to bind the foam and make it more stable. It is therefore important that the tank is large enough so the particles have time to settle and foam to die down. If too much of the volume of the tank consists of swarf, there is less remaining volume of liquid. This can lead to a higher temperature, which may promote foaming.
High pressure and agitation
Sharp bends in the return lines, "waterfalls", high flows and high discharge pressure may cause unnecessary movement of the liquid. This can usually be improved with relatively simple redesigning of the system. If process changes require a higher pressure, the fluid might have to be replaced with one that is compatible with the new requirements.
Foam is especially common in smaller sumps, where all changes happens faster. We write more about how to best manage small sumps in this e-book:
(JÖ)
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