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Suspended Electromagnet Purifies Reclaimed Sand, Captures Tramp Metal

April 8, 2011
There is nothing new about sand molding, but The Quality Castings Company has found a way to make the process more environmentally friendly.
Molten metal at The Quality Castings Company is fired up to 2,600°F, before pouring into sand molds to form products ranging from electric motors and pipe fittings to compressor parts and transmission housings.
An Eriez SE Model 7525 electromagnet is suspended 14 in. above a 48-in.-wide conveyor belt during the shakeout process. The magnet captures tramp metal embedded in the passing sand.
Tramp metal recovered with the help of the Eriez suspended electromagnet is conveyed into a collection bin, waiting to be remelted.

The self-cleaning Eriez SE Model 7525 suspended electromagnet helps capture tramp metal as the sand molds proceed through the shakeout stage after casting. Then, the captured sand is reclaimed for moldmaking, while the separated tramp metal is collected, remelted, and poured as new castings, according to Bill Sampson, engineering manager at The Quality Castings Co., Orrville, OH, a foundry that produces high-volume and short-run orders of gray and ductile iron products.

The process is familiar to most foundries. During molding, a cavity is created in the molding sand by pressing a pattern into the mixture. Once the pattern is withdrawn and the mold is set, molten iron is poured into the resulting impression. The hot iron is allowed to cool and solidify, and then conveyed over a highenergy vibrating, perforated shakeout deck that screens the sand from the castings.

“We produce castings in thousands of different shapes, sizes, and configurations for products ranging from electric motors, pipe fittings, compressor parts, transmission housings … the list goes on,“ Sampson said. “These castings weigh anywhere from five pounds to 600 lb., and vary in size from as small as your fist up to automotive engine size.”

The Eriez magnetic separator was incorporated in Quality Castings’ existing, 90-tons-per-hour green sand system. “It is a four-screen, AFS-55 sand with typically 8% live clay and 3.3% moisture,” he continued. “We use Lake Michigan sand. We inject a custom-mix clay and additives to 4,500-lb sand batches in a B&P 100-B batch muller to produce molding sand with a high bonding strength, which makes for an excellent mold, especially since we are pouring molten metal at 2,600°F,” Sampson detailed.

After the castings are poured cooled, the shakeout separates the molding sand from the finished castings. Sand from the shakeout stage is dropped onto a 48-in. wide X 12-in. high conveyor at a feed rate of 120 tons/hour, according to Sampson. At this point the sand is still very hot, typically 400-500°F. The goal is to reprocess all the sand for future mold production, thus reducing the company’s need to source more sand. As Sampson explained, the hot sand that leaves the shakeout contains pieces of iron “ranging from bullet-size to as big as a fist.”

He continued: “During the pouring process, some molten metal lands on top of the sand mold and spreads out like a puddle of water, and solidifies into tramp metal. These small pieces of metal are still in the sand after the shakeout, along with some slivers of iron that break off and accumulate within the sand.”

The Quality Castings Co. simplified the removal of tramp metals after it installed the Eriez self-cleaning Model SE 7525. The magnet is positioned 14 in. above the 48-wide conveyor belt and easily captures tramp metal embedded in the passing sand at a maximum burden depth between 6 and 8 inches, according to Sampson.

Eriez develops advanced technology for magnetic, vibratory, and inspection processes, including magnetic separation, metal detection, x-ray, materials feeding, screening, conveying and controlling equipment used in numerous industries.

The Eriez SE unit installed at The Quality Castings Co. measures 54 X 54 X 25 in. and comes with an exclusive external oil expansion tank; space wound coils with nondeteriorating, fiberglass spacers; a manganese bottom plate; high-dielectric transformer oil coolant; and a NEMA 4 junction box. The unit has a five-year warranty on electrical coils.

The external oil expansion tank is a particularly effective feature on the Eriez SE because it helps to prevent coil burnout. The expansion tank, where the coils are always fully immersed in cooling oil, effectively controls heat and moisture, which are always the greatest threats to electromagnets’ effectiveness.

Eriez’ self-cleaning design consists of several components that provide the magnetic force necessary to collect the pieces of tramp metal found in the sand. The coil, core, backbar, and steel enclosure provide an effective and efficient magnetic circuit for this particular collection process.

“Once the tramp metal is pulled out of the sand, another conveyor takes this perfectly good metal to the melt department where it is re-melted into molten metal for another turnaround,” said Sampson.

Removing tramp metal from the sand also helps to protect any downstream equipment, according to Sampson. “Immediately removing the metal helps to protect our other conveying equipment,” he observed. “The sand moves into a vertical bucket elevator with a rubber belt. If we still have tramp metal at that stage, the metal could slit the rubber belt, and cause damage and downtime.”

The Eriez SE was installed while The Quality Castings Co. was implementing a major renovation of its shakeout department. The project aimed to allow the department to handle 120 tons per hour of sand and 110 molds per hour, with castings that weigh up to 800 lb. New equipment installed included an inclined mold dump conveyor, a Carrier variable-frequency Delta Phase shakeout, a sorting conveyor, a secondary shakeout, and a return sand conveyor. A Clansman manipulator now sorts and removes the cleaned castings. And, the department’s ventilation was enhanced with the installation of a new 52,000- scfm ETA baghouse dust collector.

Originally, a smaller suspended electromagnet was being used, but it was too small to handle the larger 48 12-in. (W D) conveyor installed during the update, according to Sampson.

“The entire renovation project was very ambitious. We tore out old equipment and installed new equipment in two weeks,” he said. “Our goal was to increase capacity and increase efficiency. We did some shopping and purchased the Eriez SE because it could handle the larger conveyor system,” he explained. Since installing the Eriez SE, we have found it to be very reliable and trouble-free.”