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Equipment Spotlight

Eddy current separators

Ordinary electromagnets suffice to separate iron and steel from all kinds of shredded recyclable materials. But when it comes to removing other valuable metals such as aluminum and copper, recyclers have to turn to eddy current separators. These machines employ a somewhat lesser known but very well tested magnetic phenomenon to separate non-ferrous metals from other materials.

Dings Co.
Eriez Magnetics
Huron Valley Steel Corp.
Magnetic Products, Inc.
Osborn Engineering, Inc.
SGM Magnetics Corp.
Steinert US LLC
Van Dyk Baler Corp.
Walker Magnetics
Zmag America, Ltd.

Eddy current separators (ECS) use powerful rotating permanent magnets to induce a magnetic field in conductive non-ferrous metal items passing by on a conveyor belt. The field that is created is opposite to the magnetic rotor, causing the items to be repulsed so they can be separated from the other material using a splitter. Sometimes the separation occurs quite dramatically. “When you’re doing beverage containers, sorting aluminum from tin cans, there’s so much aluminum that they literally fly across the room,” said Keith Rhodes, president of Magnetic Products, Inc. in Highland, Michigan.

Even much smaller particles can be effectively removed using well-designed magnetic rotors and well-placed separators. Today eddy current separators are widely used to separate non-ferrous metals from auto shredder output, solid waste incinerator ash, crushed glass CRT tubes and other electronics waste and foundry sand as well as sorting steel and aluminum beverage cans.

Magnetic Products, Inc.

Rhodes, whose company makes three eddy current separators in widths from 20 inches to 40 inches and of 4 to 8 tons per hour, said that the technology of eddy current separators differ significantly from manufacturer to manufacturer. Magnetic Products, for instance, emphasizes building rotors with a large amount of high-grade neodymium iron boron in order to increase the strength of the effect. “The customer is trying to separate out as much metal as he can,” Rhodes reasoned. “That’s directly related to the strength of the rotor.”

Another feature Rhodes emphasizes is the control system. Magnetic Products’ eddy current separators employ a soft start approach that allows operators to bring the spinning magnet rotor up to its operating speed of approximately 2,500 rpm before engaging the conveyor bringing material past the rotor and separator. This, Rhodes said, avoids having material passing over the separator before the eddy current effect has reached full potential. That reduces the amount of unwanted contamination of non-ferrous metals in the separated stream of material.

Another important consideration involves how robustly the machine is constructed. The rapidly spinning rotors weigh hundreds of pounds, so bearings and shafting must be up to the powerful forces brought to bear. “The general construction of the unit becomes a very critical design element of the system,” Rhodes said.

Finally, Rhodes said his customers are looking for well-designed splitters, where the non-ferrous items reacting to the eddy current are actually separated from the other materials. “The real essence of an ECS is your ability to separate the non-ferrous materials from the conductive ferrous materials,” Rhodes said. And aluminum cans are not the biggest challenge here. “When you get into wire and other materials where you’re trying to influence copper and stainless steel that is machined down to small levels, that splitter becomes important,” he said.

SGM Magnetics Corp.

At Huron Valley Steel Corp. in Belleville, Michigan, General Manager Ben Davis said powerful magnets are also a key feature of his company’s eddy current separators. “We can go through 4 inches depth of burden,” he said. “The more power you have the more separation you can get.” However, the company also employs smaller, less powerful magnets for removing fines.

Most eddy current machines are low maintenance when properly cared for, Davis said. Spending a few minutes to wipe down the rotor accomplishes most necessary maintenance. “It takes very little effort to take care of,” he said. “Consequently that’s not always done.”

Steinert US LLC in Clearwater, Florida, uses a twist on the basic eddy current separator design with its eccentric pole rotor system. The company said this approach allows it to concentrate the eddy current effect at the most optimal spot for separation to occur. Sales Manager Dennis Ciccotelli also emphasized the flexibility of Steinert’s designs.

“Most of our eddy current separator lines are totally adjustable,” he said. “What we seem to see as a rule in the scrap industry is that each operation is slightly different, either in the feed stock or rate of feed or environment it has to be operated under.” Steinert therefore set out to make a machine adjustable enough to handle a variety of situations. “You can adjust the speed of the belt, the speed of the rotor, the position of the rotor and the position of the splitter,” said Ciccotelli. “Those major factors give you an almost infinite variety of settings for different materials.”

Durability is also a major factor in waste-to-energy applications. These facilities may run 24 hours a day, 7 days a week, something which Steinert’s eddy current separators are up to, Ciccotelli said. “You can maintain these machines in constant operation. The only requirements are a minimal amount of housekeeping and periodic lubrication.”

One big change in today’s market compared to a year ago is that payback periods for eddy current separator purchases have lengthened. “We were having payback periods in like 20 to 26 weeks,” Ciccotelli said. “Today, it’ll be two or three years in some cases.”