Foam in metalworking fluids is much more than annoying; it also costs manufacturers big chunks of money. For starters, cutting tools wear faster than they should when the coolant looks like an overpriced latte. This not only increases the number of drills, inserts and end mills a shop must buy each year, but—adding insult to injury—operators must stop the machine more often than they otherwise would to replace worn or broken tools.

Part quality also suffers. When tools don’t cut as effectively, the result is poor surface finishes, dimensional variability and even scrap parts. Then there’s the big kahuna of routine machine maintenance: stopping for an hour or two (at least) to empty and clean the sump, replace the foamy fluid, then pay someone to haul it away.

MSC Industrial reached out to an expert in this area—Eric Hefner, technical services manager at Master Fluid Solutions in Perrysburg, Ohio—for immediate, actionable foam control solutions that don’t require costly equipment overhauls. He offers some quick troubleshooting steps, such as adjusting concentration, monitoring water quality and using the proper additives, along with a few long-term practices that can help keep foam from rearing its ugly head.

Understanding Coolant Foam: Causes and Costly Consequences

Ironically, one of the reasons behind this irritating, costly foaming problem is a technology that many shops are using to increase both productivity and tool life significantly: high-pressure coolant.

With HPC quickly becoming the norm, and for good reason, such foaming issues are occurring more frequently. In addition, these systems tend to get a bit more powerful with each passing year, while the volume of machine tool sumps continues to shrink. At the same time, cutting tool manufacturers are continually introducing products that require higher surface speeds to operate as designed.

“This means shops must introduce coolant to the cutting zone in the most effective manner possible, so as to penetrate the vapor barrier that forms at these high temperatures,” says Hefner. “High-pressure coolant delivery does this quite well, while also doing a great job at clearing the chips.”

He’s quick to point out that HPC is only one of several “mechanical” causes for foaming, however. Others include:

• Air entrainment:

  Under high pressure, coolant can collect air as it’s blasted through small nozzles or jets, especially if the fluid hits the part at an angle that causes turbulence.

• Low fluid level:

  When the tank is too low, return fluid splashes more violently, often pulling air into the mix and creating foam.

• Short dwell time:

  This refers to the amount of time the fluid spends in the sump before being recirculated. If it doesn’t sit long enough, the entrained air doesn’t have time to rise and escape, so the fluid stays aerated and foamy.

• Misdirected nozzles:

  If coolant nozzles spray onto surfaces or into tanks in a turbulent or vertical fashion, they may agitate the fluid or create splashing that pulls air in.

• Waterfalls:

  In coolant systems, “waterfalls” refer to fluid returning to the tank from a height or in a cascading manner. Just like a natural waterfall, this introduces air and turbulence, contributing to foaming.

• Air leaks:

  If the pump intake or fluid lines have leaks, they may suck in air (especially if the system runs under vacuum or negative pressure), leading to foam.

• Deadheaded pipes:

  A “deadhead” condition happens when a pump runs but the discharge is blocked. This can cause cavitation and air bubbles that lead to foam buildup.

Some foaming is chemical in nature, though. Sump contamination, overly high concentration and using the wrong product for the application can all cause foaming. “Foam is not a good lubricant,” Hefner says. “It can lead to broken tools, surface finish problems, scrap parts and downtime due to cleaning. The good news is, it’s easily solvable.”

The Three-Step Foam Diagnosis: Identifying Your Problem Type

Hefner says that he or one of his colleagues at Master Fluid can typically identify the root cause by doing a “shake test” on-site. This consists of filling a clean bottle halfway with the fluid in question, shaking it for about 15 to 20 seconds, then setting it down and timing how long it takes the foam to dissolve. “If it dissipates quickly, the problem is likely due to a mechanical issue, but if it persists and creates a stable foam—like that seen on a pint of Guinness beer, perhaps—it’s most likely chemical in nature and requires further testing.”

Chemical Solutions: Antifoam Additives and Application Methods

Master Fluid Solutions and other cutting fluid suppliers offer various additives to enhance product performance or to solve some of the problems that can arise during use (or misuse). For example, as explained on the Master Fluids Solutions website, TRIM® TC257 is a nonsilicone antifoam or defoamer and is used as a tank-side additive to control foam in water-miscible coolants, washing compounds, floor soaps and so on.

While there, check out some of the other additives. TRIM TC 155 is a nonferrous corrosion inhibitor for use in water-soluble and straight oil systems that is said to be “particularly effective in preventing staining and white rust on die cast alloys containing copper.” And TRIM TC 175 is a chlorinated EP (extreme pressure) lubrication/emulsifier additive package that may be added to water-soluble coolant systems to replace or increase chlorine EP additives in the system.

“Additives are one option, but root cause analysis is cheapest in the long run,” says Hefner. “By identifying and eliminating the problem’s source, it will allow all the machines in the shop to run mostly foam-free. In addition, maintaining the correct concentration and making daily adds will also go a long way in controlling foam.”

System Optimization: Equipment Adjustments for Foam Reduction

Operators can also make the following machine adjustments to help minimize foaming:

• Reduce nozzle pressure where high pressure isn’t critical.

• Disable or reduce the use of rinse nozzles (e.g., on filters or tools) that contribute to turbulence.

• Limit the number or flow rate of washdown or curtain nozzles to reduce agitation.

• Increase the time between coolant cycles to allow more air to escape.

• If possible, expand the sump volume to increase dwell time and improve air separation.

Monitoring and Maintenance: Keeping Foam Problems from Returning

Regular machine maintenance—adjusting nozzles, fixing piping issues and maintaining pumps, for example—are all important steps when trying to prevent foam. But there’s also the need to eliminate contamination. Tramp oil skimmers are one of the best ways to achieve this, but there are also good housekeeping practices, like not using the machine as a spittoon and not pouring cold coffee or warm soda into the machine. And as Hefner points out, check coolant concentration daily. “Concentration control is one of the easiest ways to help maintain a fluid so it performs the way it was intended.”

When to Replace vs. Treat: Making the Right Economic Decision

As indicated earlier, sometimes shops have to throw in the towel. “If there is gross contamination that cannot be fixed through normal means, then the fluid most likely will need to be replaced,” Hefner says. “Most shops will try to wait until the absolute last minute, though, which can lead to further downtime and scrap. The lesson is to manage your coolant, perform the maintenance steps listed here, and when in doubt, ask your supplier for advice.”

Read more: 19 Hacks to Avoid Metalworking Fluid Foul-ups and Freakouts