Two Keller Model #455 tramp oil separators keep sumps of 20 CNC machines clean

Well before “Lean Manufacturing” had become the standard term for efficient manufacturing, Stevens Manufacturing Co. (Milford CT), a supplier of precision parts to the aerospace aftermarket, was implementing the principles of lean manufacturing with its on-going process improvement programs. In fact, Steve Fogler Jr., shop manager, credits Stevens’ success in maintaining its competitive position during difficult times to its emphasis on continually upgrading the processes.

One aspect of the operation to which Steve has devoted continuing attention is maintenance of the coolant. Stevens runs 20 CNC machines, none older than 10 years, cutting everything from plastics to steel to titanium in relatively short production runs. Their customers, such as Boeing, Sikorsky, and the U. S. government, set extremely tight dimensional and surface finish specifications. Tramp oil and other contaminants in coolant greatly increase the difficulty in meeting the tight specifications. High levels of tramp oil in coolant cause accelerated tool wear, degradation of parts finish, and the requirement to adjust machine settings frequently to achieve the dimensional specifications. In addition, tramp oil in the coolant generates smoke in the shop, plus odor and the potential for operator dermatitis as a consequence of bacteria attack on the oil. Also, when cutting relatively low density materials such as plastics and titanium, the chips which remain suspended in the coolant are picked up by the coolant pump and sprayed onto the working part, compromising the surface finish. In order to maintain product quality and achieve production targets, Stevens was dumping coolant and recharging with new coolant every three months. The cost was substantial––not only the cost of new coolant and disposing of about 100 gallons of spent coolant for each of 20 machines every three months, but also the roughly four hours of labor per machine to drain and clean the sump, and replenish the coolant. In addition, each machine is down during coolant changeover.

Steve Fogler recognized that the coolant problem had to be solved in order to improve shop efficiency and reduce costs. It was clear that belt or disc skimmers, a conventional method for removing tramp oil from sumps, would not address the Stevens requirements, because a skimmer does not create circulation in a sump and therefore is ineffective on larger sumps, and a skimmer does not reduce the quantity of solids suspended in the coolant. To improve the situation significantly, Stevens required a coolant purifier which would separate tramp oil efficiently, recirculate the coolant at high rate even when the machine tool is idle, and filter to remove suspended chips.

In 1998, Stevens purchased a coolant purifier supplied by Keller Products, Inc. (Lexington MA), which met all these requirements. With the new purifier, coolant life was immediately extended from 3 months to one year. After recently adding several new machining centers, Stevens purchased a second Keller coolant purifier, the Model #455 Separator. Steve Fogler says, “The money saved on hauling waste coolant and buying new coolant by greatly extending the coolant life is only a small part of the savings. The biggest saving is in the labor and downtime to dump, clean, and recharge the sumps of 20 machines every three months.”

A Keller coolant purifier operates by pulling oily coolant from the surface of the sump via a compact inlet device and then through a high capacity bag filter to remove suspended solids. The coolant/tramp oil mixture, free of solids, is pumped through the patented Keller oil separator elements, which are immersed in a plastic tank. The permanent oil separator elements, constructed from stacks of plastic discs with fine flow passages, efficiently split oil from coolant at high flow velocity, creating the opportunity to design high flow rate separators in compact packages. The cleaned coolant is continuously returned to the sump, and the tramp oil collected in the separator tank is drained to a waste oil container periodically, usually once per day. A sump typically can be cleaned in a few hours, and then the pump/separator can be easily moved to another sump and set up to run in about five minutes. The Keller separator, which requires only a 1/4-inch compressed air line for operation, can be run while the machine tool is operating or when shut down.

Despite the fact that the Model #455 is the largest separator in the Keller line, capable of treating individual sumps up to 1000 gallons, it requires only 20” x 30” of floor space and is easily portable. With a coolant recirculation rate of 180 gallons per hour, a Model #455 can clean a 100 gallon sump in less than two hours. Steve Fogler says, “I can easily cover the whole shop with the two Keller units. I run for about one or two hours every other week on each sump, and the coolant looks like swimming pool water.” The resulting operating benefits are: improved machine efficiency, extended tool life, better parts finish, and greatly reduced machine downtime. Another advantage to operating with clean coolant, obvious to any visitor, is the overall cleanliness of the Stevens shop and the absence of smoke in the air which can be caused by tramp oil in the coolant.

Steve Fogler says, “To stay competitive, I have to stay lean, and to me lean means minimizing time spent on non-value-added projects. Lean isn’t about not spending money, and it is not always about exotic new machines or programs. Sometimes lean is just making sure your existing assets are operating at maximum efficiency. Our coolant maintenance system is an important element in our on-going program to maximize operating efficiency.”

#555-09 Large Floating Inlet Device works perfectly even in the presence of floating aluminum chips.	#555-05 Compact Floating Inlet Device, in a typical installation, sweeps tramp oil from the sump surface.