Foaming of watermiscible metal cutting fluids in machine tools – why is this such a problematic phenomenon?

The foam created in the process of machining parts negatively affects many issues. First of all:

• Deteriorates the effectiveness of lubrication (resulting in a deterioration of the quality of the machined surface and a significant reduction in tool life)
• It lifts chips and abrasion. These can be sucked into pumps and, in the worst case, clog them.
• Interferes with the proper functioning of filtration systems.

In addition, it is worth remembering that a large amount of foam usually overflows outside the coolant tanks, which creates problems with keeping the plant clean. This has a bad effect on employees safety.

In turn, impurities suspended in the emulsion destructively affect the components of metalworking coolant, which contributes to liquid degradation and other troublesome scenarios.

Where does the foam come from?

Foaming of coolant in a CNC machine tool is an abnormality that occurs due to aeration and the retention of air in the fluid.

Water-based machining coolants contain surface-active additives and have good cleaning properties. For this reason, under certain conditions, they may have a tendency to form foam during machining. Foaming occurs when air bubbles that enter the coolant during operation or in circulation do not burst and begin to accumulate.

This can be caused by external processes (mechanical factors) or internal processes (chemical factors) as described below:

• Internal factors: concentration, hardness of water and coolant solution used, chemical contamination (for example with detergent), consumption of anti-fouling additives in the coolant, e.g. due to the use of too fine filtration (filters with an accuracy of less than 5 microns), the influence of a clogged filter, the intense influence of other factors that cause foaming.
• External (or mechanical) factors: low level of coolant in the tank, lack of tightness in the supply pipelines, presence of cascading fluid flows (“waterfalls”) in the system, too high coolant pressure, coolant outlet or pump clogged with dirt.

Is it possible to dermine what factor caused the foaming?

You can easily determine what is actually the cause of foam formation in a system with coolant: whether it is an internal or external factor.

To do this, you need to pour into a transparent container a sample of liquid taken from the tank with a volume of about 100 ml. Then you need to shake it vigorously for about 10 seconds for foam to form. After that, it is worth observing the falling time and the height of the foam. If the latter is low and the bubbles fall quickly, it means that the problem is related to the system. So the reason for foaming is external. The situation is different if the foam is high, but falls slowly, longer than 30 seconds. Then it is considered that the problem is internal.

What to do with this knowledge?

Once you have determined what caused the foaming, you can take certain steps.
For external (mechanical) causes:

• Make sure the fluid level in the tank is at the right level. The coolant level must not be below the level of the coolant outlet, and the pump must not suck in air.
• Check that the coolant piping is unobstructed, that there are no sharp angles that can cause additional turbulence, that there are no cascading flows (“waterfalls”) in the system that cause additional aeration.
• Take a look at the pumps for air leaks.
• Make sure about the size of the tank. Is it large enough for the coolant to vent under high pressure conditions?

For internal (chemical) causes:

• Check the concentration of the coolant. If the concentration is high – more than 11-12% then lower it to the recommended ranges to restore the optimal balance.
• Determine the hardness of the coolant (it should be above 5 dH). If the hardness of the starting water and coolant solution is below 5 dH, most fluids will be prone to foaming. A special additive can be used to increase the hardness. Also, you can use a coolant that is designed for soft water or demineralized water.
• If the coolant is contaminated with detergent, it may be necessary to replace it with cleaning and flushing of the system.
• If your machines have a foaming problem, you can use a special anti-foaming additive, such as Antifoam 46 from the FUCHS range. It is dosed at a concentration of about 0.005%.

Choose fluids that meets specific requirements

There are machining coolants on the market that are not prone at all or have a very low tendency to foam, and their use solves the problem of foaming, and there are many other advantages to using these products. Here are some examples:
Modern machines, where small tanks (100-300 l) are installed and where high pressures occur, require coolants with a low tendency to foam. Such products in the FUCHS range are selected items from the ECOCOOL line:

• ECOCOOL VHCM-1 CP
• ECOCOOL S-FC VW
• ECOCOOL MG 22 B

If microfiltration is used in the system, it is recommended to use coolants that do not require anti-foaming additives. These include

• ECOCOOL S-FC VW
• ECOCOOL MG 22 B

As you can see, the solutions provided by FUCHS fit perfectly into the needs of owners of modern processing machines.