Proper fluid management, filtration keep sumps cleaner

For shops that haven’t invested in the right equipment, cleaning the sump on a machine tool is a dirty, tiring job. Depending on the machine configuration, several pieces of sheet metal must first be removed. Hoses and electrical connections come next, followed by the often-herculean effort needed to position a sludge-filled tank far enough from the machine that access with shovel, suction hose and plenty of shop rags becomes feasible.

Once clean, the now-weary machinist must haul a seemingly endless series of 5-gal. buckets of fresh cutting fluid back to the machine and dump them into the sump. Chips and puddles are everywhere, and an hour or more of production time has been lost.

The Smelly Truth

Sound familiar? If so, you’re not alone. According to those interviewed for this article, 70 percent or more of all shops clean their sumps in a similar manner. Because the job is such a hassle, most wait far longer than they should, creating a host of problems.

This filter basket offers a good indication of the oily gunk hiding in most machine sumps,
which creates a prime breeding ground for microorganisms. Image courtesy of CECOR.

Dermatitis and dry skin are common with neglected cutting fluid. So, too, is the “morning stink” caused by microorganisms munching overnight on their favorite food: tramp oil. And from a productivity perspective, the worst—but often least obvious—problem is the gradual degradation of cutting tool performance and part quality that comes with dirty or tired cutting fluids.

One simple measure even the most cash-strapped shop can take is to install of a tramp-oil skimmer on each machine tool. Tramp oil is comprised of lubricant that collects on way surfaces or escapes through small leaks in bearing and gearbox seals before traveling through a machine and into the chip pan and sump. Much of this oil then floats to the surface of the cutting fluid in the sump, ready for capture.

Wayne Products, Broomall, Pa., developed the Mini-Skimmer and Maxi-Skimmer oil skimmers to remove tramp oil. General manager Don Ware said these low-cost devices mount directly on the sump. A small hole is cut in the sump’s sheet metal, allowing a skimmer’s pulley-driven belt to extend into the cutting fluid. As the vertically situated belt slowly turns, it drags tramp oil up and out of the sump, where a blade scrapes it into a receptacle. The company also offers models that fit in the bung hole of a 55-gal. drum and tube-style skimmers for enclosed sumps and tight areas.

CECOR’s Sump Shark has a discharge filter for cleaning fluids
before disposal or recycling. Image courtesy of CECOR.

“There are many benefits to removing tramp oil,” Ware said. “Not only does it increase tool life, it also improves the possibility of coolant recycling and saves a lot of money. And from the operator’s point of view, it’s better for his skin, lungs and general well-being.”

Checking the Boxes

Most oil skimmers sell for a few hundred dollars. Ron Wendt, product manager at Eriez Manufacturing Co., Erie, Pa., agreed that tramp-oil removal is a necessary part of cutting fluid maintenance, and said a number of other regular activities must also be performed.

“In most situations, you should check the cutting fluid concentration daily,” he said. “If you don’t keep it at the level recommended by the manufacturer, and, especially if you let it run lean, you’ll always be fighting an uphill battle.” Wendt added that the pH level should be monitored regularly with a test strip or electronic meter.

The concentration of cutting fluids is checked with a hand-held device called a refractometer. The user places a few drops of cutting fluid on the glass, closes the lid and holds the refractometer up to a light source while peering through the opposite end; the concentration level will be clearly displayed as a percentage of the mixture of water and cutting fluid, which most fluid manufacturers suggest should be from 8 to 12 percent. Wendt recommends digital refractometers, as they are more accurate and easier to read than analog models and offer automatic calibration and temperature compensation.

Some shops plumb the production area with vacuum lines to clean machine sumps and pressurized clean-fluid lines
for refilling them. Image courtesy of Sanborn Technologies.

Wendt also recommends wiping down a machine’s sheet metal enclosure and safety glass daily and frequently emptying the chip pan and—you guessed it—cleaning the sump.

“No matter what you do, small fines accumulate in the bottom of the tank,” he said. “Even with a skimmer, there’s always some tramp oil present, which grabs onto these fines and creates the black sludge most of us have seen in machine sumps. Anaerobic bacteria love this stuff, and there’s no way to kill it by adding chemicals or bactericides. About all you can do is clean the sump at regular intervals, depending on the number of shifts, the materials you’re cutting and the type of coolant. Once a quarter is a good starting point.”

Fortunately, there are much easier—and faster—ways to clean a sump than using a shop vac and big bundles of rags. Eriez sells an array of fluid filtration and recycling systems, including portable devices, that make cleaning a sump about as easy as running your pickup truck through a car wash.

Shark Attack

CECOR, Verona, Wis., also offers portable filtration devices. Owner Jeff Urso estimated that many shops don’t clean their machine sumps at all.

“I visited a shop once that bought a $2 million machining center 2 years earlier and had never changed the cutting fluid,” he said. “People often don’t see the importance of it or recognize the toll improperly maintained fluid takes on tool life and the operator.”

Central recycling systems are increasingly popular as machine shops recognize the importance
of clean cutting fluids. Image courtesy of Sanborn Technologies.

Other often-overlooked negatives of the pail-and-shovel approach are slippery floors, the risk that comes with lifting heavy objects and future health problems. These may lead to litigation and higher insurance premiums. Add to those the negative environmental impact and expense incurred from hauling and disposing of used cutting fluids and you have to ask: How can shops not implement a routine maintenance and recycling program?