Spinning a Profit

Redesigned waste centrifuge filters more with less breakdown

Very few process operations don’t perform some kind of recycling of materials from their waste stream—not to do so would be exactly like pouring money down the drain. Metals that come from such processes as grinding lines and plating operations, particularly in operations that run 24/7, are purchased for eventual recycling back into usable materials. There are a broad range of techniques to separate out particulate matter from a waste stream loop, starting with filters, evaporators and sludge tanks, but operating cost of these simple systems escalates because they are labor-intensive and have a limited effectiveness.

James Beatty, who founded Midwest Engineered Products Corp, Indianapolis, IN, in 1981, had observed, while making the rounds selling filtration products, that more efficient centrifuge separators were often found in company boneyards or resting, unused, in a plant corner. The problems were many-fold—the units were mechanically complicated, requiring one motor to rotate the bowl (or rotor) at high speeds, and a second gear motor to perform the bowl scraping. Pneumatic clutches, chains and sprockets (or pinion gears) connected the motors to their loads. The speeds and torques were brutal on the rotor bearings, which led to lengthy down-times because the rotors would take four hours or more to pull. And on manual units, once the bowl was full, the solids would have to be removed manually—additional down time.

Son Jeff Beatty, president of Midwest, worked with electrical designer John Emmert to develop the CentraSep, an automatic centrifuge that has demonstrated capability of removing particles from 1/2-in. down to sub-micron sizes at the rate of 25-135 gpm from coolants and lubricants—as much as four times the quantity of previous centrifuge designs. And it does this with a single AC motor and drive.

The CentraSep’s bowl and blade assembly (two scraper blades and two stilling vanes) are synchronized through a positive locking clutch so that both rotate at the same speed. This smoothes the flow of fluid and maximizes the forces that separate out the particulates. Additionally, the synchronized rotation eliminates blade oscillation, further improving separation efficiency and minimizing bearing wear. When the process is complete, the feed pump turns off and the clutch disconnects the blades from the main rotor spindle, locking the blades to a fixed position. Rotation of the bowl scrapes the walls of the dry particulate, which then falls into a collection drum.

Performing these tasks required a motor and drive with high breakaway torque and precise control. After trying several different controls and drives, the choice was an ACS 600, 10 hp drive built by ABB Automation Inc, New Berlin, WI, that works with a 10 hp vector-duty motor.. The unit features ABB’s open-loop Direct Torque Control, which can calculate the torque and flux of a motor 40,000 times per second. This becomes critical in a waste centrifuge, where loads vary from fill to fill. When the load is sensed as too heavy, the AC motor is put into stall mode, rather than breaking the shaft or blade assembly, as occurred with gear motors. Midwest also built a PLC onto the control panel to adjust speed for different types of process fluids, further adding flexibility. The motor links to the main spindle by a toothed belt, simplifying servicing.

Says Jeff Beatty, “This centrifuge is at 8,000 hours and counting in a zinc-removal application, one of the toughest possible. And it’s removing aluminum fines in a wire-drawing application where the oil is as viscous as 4,000 SSU.” Of the ACS 600, Beatty adds, “Without this drive technology, a single-motor centrifuge would not be a reality.” —RM