Reduce Foam: How to Prevent Foam in Oil
Most metal cutting fluids, in addition to cooling and lubricating, are also used to keep machines clean, As a result, foam in oil is an issue. The basic cause is entrained air within the fluid caused by mechanical or chemical processes. This is an undesirable fluid property, and there are two types -- stable and unstable. Unstable foam is often caused by high levels of agitation in the fluid system and does not cause much of a problem in machining operations; its large bubbles break quickly and dissipate. Stable foam, however, forms a dense lingering blanket of smaller bubbles on the cutting fluid surface that causes machining problems and obscures sight of the workpiece. It occurs mostly because of chemical issues.
So, how can we prevent foam in oils and coolants?
The first step is to determine the cause, and it could be mechanical, chemical - or both.
To find out, place some fluid from the sump in a clear container. Shake it well for 10 seconds to create foam in the container, then observe the behavior of the foam. If there is little or no foam and/or it dissipates quickly, the problem is mechanical. If there is a lot of foam that just sits there and not reduce, the problem is a likely chemical.
Aside from the obvious problem of obscuring an operator's view of the workpiece, foam works its way through the system, creating problems along the way with the sump and filter media. Suspended swarf and dirt are suspended in the foam and deplete fluid ingredients. They circulate and recirculate through the system and mar surface finishes; they also create product loss.
How can I reduce foam that's from mechanical causes?
If you suspect your foam is caused by mechanical (or physical) means, first check the level of the sump to make sure there is adequate fluid to keep the pump intake filled with fluid. Too little fluid causes pump cavitation and entrains air in the system lines. If this is the case, charge the sump to proper operating levels.
Next, check the entire fluid system and all its components. Look for areas in which air might be leaking into the system. Make sure connections and seals are tight. Replace any worn or cracked parts as required and repair or tighten any faulty connections.
Review your system's design, checking for areas in which excess agitation or something other than the smooth, uninterrupted flow of fluid is present. Anywhere fluid flow changes direction might be an area requiring attention. Additionally, the fluid in the sump should have a sufficient retention time to settle before it is recirculated.
Also, check the pressure from nozzles and other areas that may lead to excessive turbulence and agitation. If you absolutely need high pressures, look for a fluid designed to operate under those conditions.
How can we reduce foam that comes from a chemical cause?
If your foam problem is chemically derived, the first thing to do is check the hardness of the water. In some products, soft water (a hardness level less than 5 grains per gallon) will cause foam in oil. If this is the case, the water must be treated or the fluid substituted.
Assuming your water checks out, the next thing to do is check the concentration of your cutting fluid using a refractometer or titration kit. Foaming may be caused by a mixture too rich in concentrate. Generally, if the concentration of your cutting fluid is above 10 percent, it may be too high. Check the manufacturer's recommendation for the fluid and adjust accordingly.
If foaming persists after making these adjustments, there may be contamination. Tramp oils, cleaners and other products could be finding their way into the system. Determine where and how contaminants are entering your fluid system and take corrective measures.
Acculube technicians work with machine shops to identify the products best suited to the work, and the work environment. Some cutting oils foam more than others; some are specifically engineered for low-foaming. Our fluid technicians have seen it all, and are eager to help in finding the fluids that will help you reduce foam in oil and coolant - and prevent other problems as well.
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