Coolant Stewards

Author Kimberly R. Pontius
September 01, 2000 - 12:00pm

Responsibility for a fluid extends beyond the time it’s in your plant.

While it’s certainly not news to managers at large manufacturing facilities, some small-shop managers and owners still believe that once a metalworking fluid and its byproducts are hauled off by a disposal service, their responsibility ends. The fact is that all manufacturers—big and small—have virtually a “cradle-to-grave” responsibility for any hazardous material used in their facility.

Waste disposal is not just an environmental issue, either. It can also be a business-survival issue. Tier 1 automotive suppliers are already under pressure from the Big Three to achieve ISO 14000 certification (the environmental equivalent of ISO 9000). Environmental stewardship may soon become an integral part of any business’ plan that wants to retain its automotive-related contracts.

The cost of ensuring the safe disposal of a metalworking fluid is constantly rising. This is partly because more and more hazardous-material handlers are requiring that an independent chemical analysis be performed on a waste product before they will accept it. For a small shop with a dozen or so barrels of spent coolant sitting around, such an analysis can be an expensive addition to the cost of the actual waste disposal.

A national waste-treatment company recently charged me $195 to analyze a few barrels of spent oil and grinder sludge that had been sitting around for a while. This was on top of the $200-per-barrel disposal charge.

Clearly, disposal costs and the auto industry’s push toward ISO 14000 make waste disposal an integral part of cutting fluid selection.

Fluid Overview

Water is an excellent coolant, but it does not provide enough lubricity for most applications and can lead to rust. And oil, a great lubricant, does not dissipate heat as effectively as water.

Moreover, oils—especially fatty oils—are prone to bacterial growth. Germs in the shop environment can contaminate cutting oils and create problems that may affect individuals in the form of skin and respiratory infections. Biocides and antiseptics can be added to machine sumps to reduce the amount of bacteria and extend fluid life, but these “cures” can also turn an otherwise environmentally friendly sump into something that proves hazardous to the environment and shop workers.

That was the case with a coolant recycling company that I once “fired.” The company’s representative indiscriminately poured way too much of an extremely hazardous biocide into one of our sumps. The skin, eye, nose and throat irritation experienced by our workers cleared up immediately following a cleaning and refilling of the sump with fresh coolant. But it made me wonder how many times this product had been introduced into the waste-disposal system.

Coolants are often blended to provide optimal results for specific processes and materials. Cutting oils can be active or inactive, based on how they react with metal surfaces at high temperatures. Mineral oils and sulfured-fatty/ mineral-oil blends are considered inactive cutting oils. And since they are not prone to chemical reactions at high heat, they are excellent choices for high-temperature applications.

The active cutting oils include sulfured mineral oils, sulfo-chlorinated mineral oils, and sulfo- or sulfo-chlorinated fatty oil blends. These cutting fluids are often employed in operations where high cutting temperatures are not prevalent. Screw machining, gear hobbing and broaching are common applications for active cutting oils.

But these oils can be very expensive to deal with, both internally and when the time comes to dispose of them. My company realized this several years ago because of an incident that occurred in our shop.

The aluminum fines and sulfured cutting oil on the floor reacted to a cleaner that contained sodium hydroxide. The facility had to be evacuated because the cloud of gas this reaction created contained sulfuric acid. The lesson we learned was that in today’s shop, even seemingly benign compounds must be evaluated carefully for potential consequences when they are exposed to any other compound in the shop.

Soluble, or emulsifiable, oils combine with water to provide lubrication and prevent rusting. Emulsifiers break up the oil and keep it dispersed in water for long periods of time. The formulation can play a key role in an application’s success. Lean emulsification ratios are used for light machining, where more cooling is desired, and higher concentrations of oil are used when lubrication and rust prevention are desired.

Semisynthetics are mixtures of water-soluble oils and chemicals such as synthetic hydrocarbons and esters. Oil content is low (less than 20 percent), and the percentage of emulsifiers is high. Tool life and surface finish depend on extreme-pressure chemicals such as sulfur, chlorine and phosphorus.

Full-synthetic cutting fluids blend a number of chemical agents. They contain no mineral oil and generally work best in ferrous applications involving high material-removal rates, high speeds and feeds, and the desire for extended tool life under these rigorous conditions.

Like semisynthetics, full-synthetic fluids can contain any number of different chemical formulations that go far beyond the knowledge of most manufacturing professionals. This can make it difficult to choose a fluid that meets a company’s production needs and is environmentally acceptable.

Drink This

The manufacturers of cutting fluids are often quick to tout the merits of their product, particularly when it comes to environmental issues. One of my favorite claims salespeople make about their “green” fluid is that it’s “safe enough to drink.” What I want to know is if they are willing to drink a cocktail made from their product after my machines are done with it.

It’s true that certain biodegradable cutting fluids obtained from renewable resources, such as vegetable oils, have the potential to produce environmentally harmless and inert byproducts. But the problem usually does not lie in the virgin product.

A cutting fluid can be altered, sometimes dramatically, by the rigors of the manufacturing process. Students in the most basic chemistry classes are taught that heat can significantly alter the chemical composition of compounds. One of the primary functions of a coolant is to extract heat. The fluid’s success at doing this is also the reason that what we start with is not always what we finish with.

Approximately 60 percent of the heat in a typical machining process is generated in the shear zone. So coolants that possess heat-friendly chemical characteristics, such as a high specific heat, vapor point or thermal conductivity, can avoid the chemical reactions that turn them into liquids that are anything but environmentally friendly.

The effects of heat aren’t the only reason that coolants can turn ugly, though. Machine lubricants, dissolved metals, carbide dust and cobalt leaching from the cutting tools are among the process contaminants that can be introduced into a previously “safe” coolant.

Besides the stench most of us have experienced after firing up a machine after a long holiday weekend, there is also the occasional case of dermatitis among operators. This is often indicative of an anaerobic bacteria bloom, of which much has been written. What often goes unmentioned, though, are the various chemical changes that are occurring in the cutting fluid.

Corral Your Coolant

It’s wise to establish a coolant-management program to track how your fluids perform over time. Testing should be done twice weekly.

To help you keep tabs on changes to a cutting fluid, it’s wise to establish a coolant-management program. My company instituted such a program, basing it on the recommendations of Gregory Mac, vice president of engineering at Superior Filtration Inc., Wixom, Mich.

The first step is to form a team made up of people who have a stake in how well the coolant performs in the shop. You might want to draw from production personnel, process engineers, plant engineers and quality-control lab personnel.

Next, group members should receive extensive training about coolant usage, disposal, and the features and operation of various coolant delivery and control equipment. Once the training is complete, the team must adopt a practical set of testing methods for each coolant sump and spell out an action plan for times when the coolant exceeds specifications.

Each sump must be tested and analyzed to establish a baseline for improvement and set reachable goals. At my company, we established these parameters as part of our baseline for each sump:


Sump life   1 year
Suspended < 300 ppm by volume
Concentration setpoint ±0.5 percent
Tramp oil < 2 percent
pH 8.6 to 9.2


While the frequency of testing will vary according to usage, a good starting point is twice a week. If you don’t run equipment during weekends, one of those dates should be Monday morning.

A good baseline will also establish the current level of coolant use and additives applied during the life of each sump. The types of filters used, sump-change frequency and pump pressure should be determined, monitored and modified as testing dictates.

Our company found that squeezing a few extra pennies out of a coolant by running it beyond the recommended service life ended up costing us more money in scrap, maintenance materials and tools.

Meeting our goals required us to install filtration systems and tramp-oil-removal equipment. We also found it helpful to add low-power circulation pumps to keep the sumps from building anaerobic bacteria while the machines were idle, especially during weekends. This not only increased sump life, but it also had a positive impact on morale by eliminating the dreaded Monday morning startup odors.

Be Selective

If the time ever comes that you decide your current coolant is either too hazardous or expensive, consider replacing it. Someone within your organization should undergo advanced training to bring a good working knowledge of typical coolant chemical composition and the potential effects that machining has on those compositions.

Carefully research the information on the vendor’s Material Safety Data Sheet. Think about how the new coolant will impact your current waste-disposal practices.

Remember, the tanker that just left your facility is headed somewhere with the problem you helped create. Proper waste disposal is your financial, legal and moral responsibility for as long as the waste is hazardous—and that could be forever.


All companies pushed to handle waste properly

During a recent trip to California’s beautiful Monterey Bay, a tour guide told the group I was with that everything that goes down the drain or into the ditch ends up in the bay. For me, an operations manager at a Midwestern manufacturing facility, the term “waste stream” suddenly took on a new meaning.

Manufacturers, like everyone else, have an obligation to protect the environment. That goes for companies large and small.

Recently, there’s been a big push at the local level to see that smaller shops comply with waste-disposal regulations. Why? Because many publicly owned water-treatment centers have difficulty separating organic from inorganic compounds. And communities that don’t comply with stringent federal and state regulations can be heavily penalized.

As a result, what goes down a company’s drain is likely to be monitored to determine if it contains hazardous materials. If it does, the penalty could be significant and, especially for a small company, may threaten its survival.

K. Pontius

About the Author
Kim Pontius is the manufacturing operations manager at TD&M Production Machining, New Haven, Ind.

Related Glossary Terms

  • broaching


    Operation in which a cutter progressively enlarges a slot or hole or shapes a workpiece exterior. Low teeth start the cut, intermediate teeth remove the majority of the material and high teeth finish the task. Broaching can be a one-step operation, as opposed to milling and slotting, which require repeated passes. Typically, however, broaching also involves multiple passes.

  • centers


    Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.

  • coolant


    Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

  • cutting fluid

    cutting fluid

    Liquid used to improve workpiece machinability, enhance tool life, flush out chips and machining debris, and cool the workpiece and tool. Three basic types are: straight oils; soluble oils, which emulsify in water; and synthetic fluids, which are water-based chemical solutions having no oil. See coolant; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

  • lubricity


    Measure of the relative efficiency with which a cutting fluid or lubricant reduces friction between surfaces.

  • material safety data sheet ( MSDS)

    material safety data sheet ( MSDS)

    Form containing safety, regulatory, physical and other pertinent information regarding a chemical.

  • metalworking


    Any manufacturing process in which metal is processed or machined such that the workpiece is given a new shape. Broadly defined, the term includes processes such as design and layout, heat-treating, material handling and inspection.

  • tramp oil

    tramp oil

    Oil that is present in a metalworking fluid mix that is not from the product concentrate. The usual sources are machine tool lubrication system leaks.


Kimberly R. Pontius is a regular contributor to CUTTING TOOL ENGINEERING and an executive directorat Ivy Tech State College, Region 3, Fort Wayne, Indiana.