The following is an article that appeared in the September issue of the Shop Talk Magazine.
The good, the bad, and the ugly
Publish Date - 09/01/2005
Source: Shop Talk Magazine
By Tim Erdman
Today’s soupy world of coolants and their method of filtration are about microns and microbes. Like a bacteria-infested swimming pool that’s been treated, some misconceptions are clearing up as well.
With coolants and filtration systems, there’s good news and bad news.
First, the bad. In the general scheme of things, metalworking fluids have typically gotten short shrift. Metalworking fluids, aka coolants, “cool” the grinding wheel and other tools so they last longer. But while they also lubricate the tool’s edge for a faster and cleaner cut, shop owners and operators unfortunately tend to think of coolants as fluids that simply blow chips away from the workpiece. The sad fact is that as machine tools themselves keep getting more and more accurate with faster cycle times and unattended operation, the lack of attention to coolants and the filtration process itself can still mean less than optimal machining.
The apathy is usually accompanied by rising maintenance and disposal costs. “Filtration (in the past) has been one of the most misunderstood and neglected aspects of the machining process,” remarks Irv Kaage, president of Transor Filter Systems in Elk Grove, Ill. “Shop owners who do not look at all the variables that might influence the machine’s performance are like the car buff that buys a new Ferrari, has tires from a ’57 Chevy installed, and then complains he can’t drive over 80 mph. The Ferrari has the capability. But the tires create a limitation.”
And now for the good news: Kaage thinks the pendulum is swinging the other way. He sees companies looking more closely at their machining operations for higher production levels and less maintenance. And they’re putting more thought into their coolant systems.
Factors worth considering
Such thinking can start with a proper selection of coolant. Today’s coolants are a sophisticated soup of chemicals. They “all try to do the same thing: blend the best properties of oil into the best properties of water,” states a website for Zebra Skimmers of Chagrin Falls, Ohio. Concerns tend to vary, which means the selection can depend on which of your requirements can be the more pressing issue. Are you concerned about rust inhibition, for example? Or is it equally (or more) important that the coolant tolerate a wide range of water hardness? Must it work with lots of different metals, or just a few?
Do you (should you) prioritize for environmental safety?
Then there’s the level of filtration. Transor’s filtration systems, for example, are said to trap any particles larger than one micron. This kind of filtering could have great appeal, especially if low-to-zero maintenance is high on your list of considerations. Tools like grinding wheels tend to stay cleaner when there are fewer particles in the oil.
Kaage claims his own company’s concept in filtering has provided an attractive alternative to other types of filtration systems: cartridge, diatomaceous earth, paper roll, and centrifuge. Transor Filter’s Edge Filter “provides one micron filtration capability and is virtually maintenance free,” says Kaage. “Maintenance-free” can be music to one’s ears; replacing a filter, after all, can be messy. Sludge has to be removed from time to time. If the oil is sufficiently contaminated, it may have to be replaced as well. And coolant disposal can be a costly proposition (just ask any California shop owner).
Kaage’s system requires no foreign filter media such as diatomaceous earth. Filter elements clean automatically and are not replaced. The debris is placed into a cloth bag for ready disposal or reclamation. Filter element’s life can reach as high as 70,000 operating hours. The parts themselves come off the machine cleaner.
“Machining with a coolant filtered to this level provides for much faster cycle times, extended wheel life, and increased machine uptime,” says Kaage.
Kaage also puts a priority on maintaining a consistent oil temperature. “Temperature control is very important as it relates to grinding speed,” he explains. A rule of thumb is that if the oil temperature exceeds 105° C, one percent of grinding efficiency is lost for each additional degree. If the oil temperature is, say, 125° C, you could be losing 20 percent efficiency in your machining process.
An ecosystem in your sump?
Ignore your filtration system, and it’s like ignoring your teeth by not flossing. Things can get downright ugly…and smelly!
The enemy of all metalworking fluids, according to Zebra Skimmers, is the microbe. It’s a little like drinking beer with eating cheese, or allowing bread to spoil with penicillin. “Given the right conditions and a little bit of time,” says Zebra Skimmers’ President Steve Davidian, “your pristine pump can go from having only a few hundred microbes in every milliliter (about 10 drops) to over a million.” Biology simply cannot be overstated, he says.
In the 1970s, an environmentally sensitive government mandated numerous changes to coolants. These included the abandonment of carcinogenic compounds in favor of more organic materials. Today’s coolants consist of approximately 25 ingredients. “Fundamentally, all metalworking fluids can be traced to biological degradation,” says Davidian, who explains the coolant sump in terms of an aquarium or a pond. Because of its biological nature, the sump tends to consume oxygen. This can lead to conditions that favor the spawning of anaerobic bacteria, the kind that smell and can eat oil and kill fish, according to Davidian. “Since many metalworking fluid components are oil-based, the bacteria eat them as well, and in so doing help diminish the fluid’s ability to do its job,” he continued.
A machine shop that has many individual sumps might find that most are working perfectly. But if only one is sufficiently “infected,” it can cause the operator to get sick and also ruin the metalworking fluid. When more than one sump has a high level of biological activity, each machine might have a different ecology, says Davidian. “No one knows exactly how many different species of fungi or single-celled plants and bacteria (single-celled “animals”) reside in coolant, but the smallest number I have seen is 30,” claims Davidian. “The largest is 3,000. Believe it or not, there is no way for us to know the true number, because there is as yet no way to definitively determine how many microscopic species there truly are.”
Davidian illustrates the problem with a simple test that can be done in the home. Take a saucer of milk and add to it a teaspoon of cooking oil on top. Let it sit for a few days and watch what happens.
“You should see a funny textured layer forming under the oil. Eventually all the oil will be consumed and nothing but a ‘biomass’ remains.” For a better dose of reality, try placing some coolant in a tray at work, then add a teaspoon of machine oil and wait a few days or weeks. The same results will occur, according to Davidian. “The layer will be more like a slimy dark film. It represents a bacterial colony.
“We are learning that it is not the individual bacteria or fungi that float around in the coolant that cause the problems. It’s the colony they form when enough of them get together.” Such congregations of biomasses form slime, the stuff from the movie Ghostbusters and an indicator of the biology going on. Operators, Davidian says, tend to assume that the dark stuff floating on their coolant is pure oil, even though it appears slimy and acts more like mucous than oil. A skimmer doesn’t attract it, it smells, and it doesn’t flow.
In worst-case scenarios, the slime clumps up and forms rugged islands, according to Davidian. “If it doesn’t act exactly like oil, then it’s not oil,” he insists.
So put on your sniffer and be honest: Just how is your shop smelling these days?
“The best strategy is start fighting the bacteria right from the beginning,” says the company’s website, www.coolantmaintenance.com, “using everything we know about chemistry and mechanics. Chemistry will tell us to monitor the pH and concentration, while mechanics will keep us aerating and skimming using disk skimmers, belt skimmers, coalescers, etc. Once we accept the fact that a stalemate is the best we can hope for, our lives become that much easier.”
Note: Shop Talk publishes a regular Coolant Column, called “Coolant Ed-Ucation,” by Ed Thaves of S.C. Chemical, which tackles the many issues surrounding coolant and coolant maintenance. You may read previously published columns at www.shoptalkmag.com. Watch for Ed’s next column appearing in the November issue of Shop Talk magazine.