Foil tramp oil: People & Companies

If you want to prevent or solve a host of problems at your shop, there’s no way around it: The tramp has got to go.

That is, the hydrocarbon-based substances known as tramp oils that find their way from a machine into its coolant. Tramp oil serves as food for anaerobic bacteria, which multiply and quickly break down coolant, reducing its life. A large bacterial colony in coolant also produces a rotten egg smell. The problem can worsen until biofilm spreads throughout the machine, requiring an expensive remediation process in which harsh chemicals are run through the machine for an extended period.

In addition, tramp oil at the point of cut generates heat, which shortens tool life. Machining also can turn the oil into a mist that contributes to poor air quality at shops.

The good news is that tramp oil and all the trouble it causes can be banished from a shop by devices called oil skimmers. Operating in machine sumps, skimmers make use of an oleophilic element, one to which oil adheres. As the element moves through the cutting fluid in the sump, the element picks up nonemulsified floating oil. Wiper blades or pinch rollers remove the collected oil from the surface of the oleophilic element so the oil can be transferred to a container for disposal or reclamation.

Skimmer Types

The most common skimmer elements are disks, belts and tubes. The disks are made of steel, aluminum or polyvinyl chloride and can be smooth or grooved. Rotated by an electric motor, the disks recover large amounts of floating oil. Belt oil skimmers use metal or polymer belts to attract tramp oil when inserted into a sump while tube skimmers employ an oleophilic polymer tube to do the job.

The TubeTastic! easily can be mounted on the side of virtually any machining center coolant sump. Image courtesy of Abanaki

When deciding which skimmer is right for a particular situation, shops need to consider how a skimmer will reach the coolant.

“The coolant sumps in different machines will have different locations and access points,” said Simon Bennett, vice president of Chagrin Falls, Ohio-based Abanaki Corp., a supplier of industrial oil skimmers.

Some sumps have overhead access, and some have side access. The first type of skimmer to be used in the machine tool industry and traditionally the most common, disk skimmers require overhead access to a sump, as well as a relatively large slot for the disk, he said.

“The most common size is a 12″ (304.8 mm) dia. disk,” Bennett said. “You can get bigger, but you rarely see smaller.”

As for belt skimmers, he describes them as moderate-to-low-cost solutions that also require overhead access to a coolant sump. But belt skimmers call for a much smaller opening in the sump than disk skimmers.

Although belt skimmers need a bigger opening than tube skimmers, “it’s not a very large hole,” said Bill Burkey, president of Zebra Skimmers Corp., a maker of industrial oil skimmers in Solon, Ohio. “For a 2″ (50.8 mm) belt skimmer, you might want a 3″ (76.2 mm) opening in the sump. Whereas the disk skimmer (needs) a pretty large slot, and it’s a pretty big unit to fit onto the sump.”

He recommends belt skimmers to deal with heavy tramp oil loads. A 25.4 mm (1″) belt skimmer can remove a gallon an hour, he said, while a 50.8 mm belt skimmer can remove up to 2 gallons an hour.

Belt skimmers are also a good choice for deeper sumps because shops can get belts with different lengths to go down as far as necessary, said Ron Wendt, product manager at Erie, Pennsylvania-based Eriez Manufacturing Co., which sells belt skimmers.

In situations in which a sump is very difficult to access, he believes that tube skimmers are a wise option because they can go in through the side of the tank. Featuring a magnetic base add-on, for example, Zebra Skimmers’ Sidewinder tube skimmer can be mounted to the side of a sump so the tube can drop in through the side. Typically, however, Burkey said shops mount tube skimmers on top of the sump where there’s an opening.

With its magnetic base add-on, the Sidewinder tube skimmer can be mounted to the side of a sump. Image courtesy of Zebra Skimmers

Less expensive than belt skimmers, tube skimmers “are made to get into those hard-to-remediate places,” he said. “So long as the tube isn’t brushing against a surface that would wipe off the skimmed oil, it can go almost anywhere and fit through a very small opening.”

Burkey said tube skimmers like the Sidewinder are well suited for newer machines, which normally have a lower tramp oil load because no way oil or hydraulic oil enters the sump.

“In those situations, it will get up to a quart an hour of tramp oil removal, which is a lot when it’s run 24/7,” he said. “But if there’s a very high tramp oil load, it’s much better going with a belt skimmer.”

In addition to applications with large amounts of tramp oil, tube skimmers are unsuitable for high-temperature situations. While tube skimmers should function well when temperatures are under the boiling point, Burkey points out that the tubes are made of polymers, so they melt from too much heat, as do polymer belts on belt skimmers.

“What you want for higher-temperature, more caustic situations is a stainless steel belt,” he said.

When a belt or tube skimmer is chosen, a shop needs to provide the vendor with the depth of the sump so the oleophilic element can be sized to always be in the fluid.

“If it’s up in the air, it won’t do you any good,” Wendt said, though he added that it’s better not to have the element extend all the way to the bottom of the tank because of the chips and sludge there.