Problem
Centrally located in Fulton, IL, Drives Inc. manufactures power transmission chains, conveyor components and helical augers for movement of granulated solids. Heat-treating at 1600°F, quenching and tempering at 750°F are sequential processes in producing small parts of requisite hardness and toughness. One wash system is required to remove cutting oil from the parts before heat treatment and a second separate wash is necessary to remove quench oil prior to tempering. Wash water is conserved by recycling and must be kept oil-free.

The question in the original plant design was, "What kind of oil removal equipment would provide substantial recovery and assure washwater free from interfering oil content?"

Solution
Following a review of several methods, a skimming process based on the affinity of oil for plastic was selected for both systems. Each skimmer is comprised of a plastic tube, which floats in an oil film on the water and then moves through a closed loop. The oil preferentially collects on the tube; then it is removed in an overhead pulley and scraper mechanism.

In practice, a skimmer collection tank is placed beneath the pulley mechanism. The tank is dimensioned for a reasonable retention time with minimum turbulence from the in-flow.
The separation of water and oil occurs naturally in the tank, forming the characteristic oil film. Clean water is removed from below the surface and oil is taken away continuously by the skimmer.

The skimmer mechanism is enclosed in a cast-aluminum housing approximately 27-1/2" long, 5-1/2" wide and 12" high. A 1/2-hp motor with gear drive adds about 9" to the width. The assembled unit weighs about 125 lb. Operating position is achieved by a column and boom support, which raises the unit some 6' above the water surface. The 3/4"-diameter tube is made of a specially compounded polyurethane plastic. Only the outside of the tube contacts oil. The tube is looped through two 9-1/2"-diameter pulley wheels in the housing, with at least two scrapers located between them. The first pulley serves to align the tube into a horizontal run for the scraper and to separate the top of the loop by about 30". This pulley is unusual in that it is powered by a motor drive, so as to turn at a peripheral velocity to match the movement of the tube. Movement of the tube is imparted by the second, or drive wheel. This wheel is driven by the motor and is designed to have a firm, non-slip grip on the oily tube.

The grip is attained by 24 ceramic, flat lugs, alternated in position around the wheel and scored with radial ridges. The ceramic is made with a hard alumina component, which resists abrasion from metallic inclusions, grinding compounds and dirt. In order that they will securely grasp the tube, the lugs are installed in a tapered configuration. Multiple scrapers remove the oil within the casing near the intake pulley. The scrapers conform to the tube curvature and the oil falls into a retention basin, from which it flows into a reservoir.

At Drives, the washwater collection tank for the shop oil removal uses two skimmers. The residual oil is stored and periodically sold.

The water is removed from the bottom of the tank and returned for recycle. The quench oil, on the other hand, is collected by one Model 6V skimmer and returned to the quench oil tank. This oil is clear and light colored. Estimates are made that more than 75% of the quench oil is saved by this recovery.

The post-quench washwater is returned to its circuit by a double decanting, which not only skims but also separates trace oil in a second tank. The water in both systems is renewed about every 6 months in a scheduled preventive maintenance program.

Results
The skimming equipment has logged a relatively maintenance-free history.
Periodic updating has been easy since improved components are made to fit the previous design. Water quality is high, and the wash process is satisfactory.

Model 6V Oil Skimmer is manufactured by
Oil Skimmers, Inc., P.O. Box 33092, Cleveland, OH 44133
Phone: 1-800-200-4603 Fax: 440-582-2759

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