Ready Eddy

Are you getting the highest nonferrous recovery from your eddy-current system? This advice from top manufacturers can ensure that you do.

By Robert L. Reid

Robert L. Reid is managing editor of Scrap.

By the time eddy-current separators caught the attention of U.S. scrap processors in the late 1980s, the technology was about 100 years old. Still, finding a practical, economical application for this long-overlooked technology was as revolutionary as the process itself.
   The eddy-current separation process is based on a series of permanent magnets embedded in a high-speed rotating drum. The drum turns within a freewheeling head pulley that moves a conveyor belt. Recyclers feed material—such as auto-shredder residue—onto the conveyor. Since the outward-facing surface of the magnets are arranged in a series of north and south polarities, their rotation creates an alternating electrical field that repels highly conductive nonferrous metal such as aluminum. The metal literally jumps off the conveyor and over a divider, or “splitter,” that directs the metal into one bin and nonmetallics into another bin.
   This process of using magnets to sort metals that aren’t magnetic may seem magical or mysterious, but eddy-current manufacturers and distributors note that it’s just down-to-earth science—rare-earth science, to be specific. 
   Most eddy-current systems use rare-earth elements such as neodymium that are pressed into magnets along with iron and other ingredients. These rare-earth elements come in various grades, with the purity of the grade and amount of rare earth in each magnet affecting both performance and price. Low-grade magnets, for instance, are often used to separate easily repelled UBCs while higher-grade magnets are needed to send difficult-to-repel materials—such as a balled-up aluminum radiator core and small castings—flying over the splitter, explains Thomas Wendt Sr., chairman of Wendt Corp. (Tonawanda, N.Y.), a manufacturer of eddy-current separators, shredders, and other scrap processing machinery.
   In addition to the specific makeup of the magnets themselves—“Everybody’s got a secret formula” for their magnets, Wendt notes—all manufacturers size and shape their magnets differently, employ varying numbers of magnets per eddy-current machine (anywhere from eight to more than 20), attach the magnets to the rotors differently, and sometimes even vary the construction from eddy current to eddy current within their own firm. Wendt Corp., for instance, makes “completely different” rotors for its three eddy-current units.
   In general, most eddy currents use a similar “concentric” design for their rotors, which means that the rotor and conveyor pulley spin on the same axis. One manufacturer, however—Steinert Elektromagnetbau GmbH (Köln, Germany)—developed an “eccentric” version, which features a rotor that spins “distinctively off-center” from the conveyor pulley, explains Don Wolfram, vice president of engineering at Resource Recycling L.L.C. (St. Petersburg, Fla.) and chief North American sales representative for Steinert.

Who’s in Charge?
Eddy-current separators—especially those used in auto and appliance shredding systems—are sometimes considered just a nonferrous add-on to the recycler’s “real” business of recovering iron and steel, manufacturers note. In fact, the nonferrous metal culled from a shredder’s residue can easily become a bigger revenue stream than the recovered ferrous scrap.
   “The way the economy is today, it’s almost imperative that a shredder not lose any material,” says Ben Davis, manager of magnetics at Huron Valley Steel Corp., a Belleville, Mich.-based nonferrous processor that also makes eddy-current equipment in Anniston, Ala. The problem, he asserts, is that processors “need instruction on how to use their eddy-current machine, how to feed it properly, how to keep it clean—it all goes hand-in-hand with a good nonferrous recovery operation.”
   For Thomas Wendt, deciding who is responsible for the eddy-current system and where to locate it are the first steps toward maximizing performance. Though the eddy current often complements a shredder, it’s a mistake to put the two machines under the same operator or supervisor, Wendt says. That’s because there’s a risk that the people running the shredder will see that equipment as their primary job while “off to the side there’s this little eddy-current system, like a stepchild,” he warns.
   The reality, Wendt stresses, is that “you’re running two different businesses”—a ferrous business that focuses on producing as many tons as possible and a nonferrous business that focuses on all the metal you can recover. As he notes, “the key to an eddy current is to get all the metal you can.”

The In-Line/Off-Line Question
Many eddy-current users run their system off-line from their shredder while others have their eddy currents in-line, or directly connected to the shredder’s downstream system. There are pros and cons to both approaches.
   On the plus side, an in-line eddy current saves processors from handling their residue twice. With an off-line system, for instance, residue must be moved from the shredder area and loaded into the eddy system.
On the downside, an in-line eddy current is generally tied to the shredder’s production schedule, processing residue while the shredder is running and sitting idle when the shredder is stopped.
   Wendt and other manufacturers recommend “decoupling” the shredding and eddy-current systems. “Move the eddy current away from the shredder, out of harm’s way, and have separate people responsible,” he suggests. In his view, separate supervision will help guarantee that the eddy current gets the maintenance and cleaning it needs, that “somebody will notice when the splitter is dirty or the belt is cut, and more importantly that someone is watching to make sure the machine is set correctly,” Wendt says.
   Dedicating a team to running the eddy current also makes it easier to set up a bonus system based on criteria such as the machine’s uptime or the amount of metal recovered, which can ensure that you’re not throwing away metal, says Jim Schwartz, vice president of Texas Shredder Inc. (San Antonio, Texas), a shredder manufacturer that also distributes eddy currents from Huron Valley, Steinert, and other smaller manufacturers. “It does cost money to move the material off-line from point A to point B,” he says, “but it costs more money to throw away metal.”
   Running off-line also allows the eddy-current operator to control both the amount and type of material being fed into the separator. Material that comes directly from the shredder is subject to surges that can overload an eddy current, notes Steinert’s Don Wolfram. Running off-line helps even out the flow of material and can provide better separation, he says.
It can also be a good idea to have a second infeed system for the eddy current that’s completely separate from the shredder. That way, processors can diversify their operations and recover nonferrous metal from sources other than their own shredder residue, says Huron Valley’s Davis.
   One processor, General Iron Industries Inc. (Chicago), feeds its two eddy-current systems off-line from the shredder, which gives it better control of the type of material being separated, explains Adam Labkon, operations manager.
   On any given day, he notes, the material that General Iron shreds might contain more fines and dirt or have more fluffy debris than at other times, or the infeed might be wetter or drier. By running the eddy currents off-line and building up a stockpile of material, “we can mix the material with the front-end loader, making a consistent product so we’ll know what to expect,” Labkon says. A metering drum also helps General Iron keep a consistent flow of material through its eddy current, he adds.

Now Presenting ...
After deciding where to operate the eddy current and who will run it, the next way to maximize the system’s perfor-mance is to focus on the “presentation” of the infeed material, explains Wolfram. By presentation, he means considering issues such as the size of individual pieces of material, how uniform those sizes are, and what kind of screens, trommels, shaker tables, or other equipment are used when feeding the material onto the eddy-current belt.
   First, be sure to remove as much tramp ferrous as possible from the residue before feeding it to the eddy current, manufacturers note. Otherwise, the separator’s powerful magnets will grab the ferrous and hang on, possibly damaging the rotor’s shell and requiring expensive repairs. So run the residue under magnets before sending it through the eddy-current system.
   Sizing the material properly is also important because “if you have a 6-inch piece of material next to a 1-inch piece, their trajectories are very different—the 6-inch piece will go much farther,” Wolfram says. Thus, the smaller material might not repel far enough and end up in the waste bin, notes Al Gedgaudas, recycling equipment manager for eddy-current maker Eriez Manufacturing Co. (Erie, Pa.). Or, if the processor moves the splitter closer to catch the smaller pieces, then long pieces of debris such as rubber gaskets or plastic trim might “raft” over the divider into the clean metal bin, he says, explaining that “if you get your size ratio closer together, you raise recovery and the grade or purity of the metallics is cleaner.”
   Some processors divide their residue into two or three size “fractions” to maximize recovery. General Iron, for instance, discards anything under 3/8 inch, combines all material 3/8 inch to 11/4 inches to run through one eddy current, then runs everything larger than 11/4 inches through a second separator. As Labkon notes, “If you don’t size the material, it’s hard to separate small metal from big garbage.”
   Unfortunately, says Huron Valley’s Davis, “a lot of people aren’t using any screens—they’re just using magnets to get the ferrous out, but then the rest of the material goes across the eddy current straight from the shredder.” As a result, the separator must handle “a lot of dirt and fines that take up volume, making it more difficult for the machine to do its job,” he says. 

Shake It Up
Shaker or vibratory tables are another key tool for making a good presentation to an eddy current. These devices spread the material across the full width of the eddy-current belt, which makes it much easier for the separator to do its separating. The “burden” of material on the belt should ideally be one layer deep, with space between each piece, says Gedgaudas. A higher burden—two or three layers deep—makes it easy for good metal to end up being carried into the waste bin or for debris to ride along with metal into the recovery bin.
   When the material drops from the slow-speed vibratory feeder belt—operating at, say, 100 feet a minute—onto the much faster eddy current belt—moving at 400 feet a minute—“this tends to help disperse the material into the single layer that’s needed for good separation,” says Steinert’s Wolfram.
   Just make sure the vibratory feeder’s lip isn’t too high above the eddy-current belt—2 or 3 inches is best—otherwise the material will bounce, says Gedgaudas. “It may look settled as it goes across the head pulley, but it might actually be dribbling just a fraction, which lowers recovery,” he explains.
   Most eddy-current systems are installed with a vibratory feeder, either sold separately or as a package with the system itself, notes Tim Conway, vice president of engineering for B.E.S.T. Inc. (Brunswick, Ohio), a manufacturer of feeding equipment. Often, scrap processors want to improve the capacity of that feeder, especially if there’s a change in the bulk density of the material being separated, he says. Depending on the product, adjustments to the feeder’s speed, amplitude or strokes, and inclination can increase the feed rate, Conway explains. For instance, installing a larger drive mechanism will help the unit increase strokes and feed material faster.

Keeping Eddy Clean and Healthy
Cleanliness and good maintenance are also critical for getting the most out of an eddy-current system. This means making sure the separator’s conveyor belt has no cuts or holes, cleaning the belt and splitter periodically, and taking care of the bearings and rotor.
   “It’s very important to keep the rotor balanced and the bearings lubricated,” explains Thomas Wendt, noting that some rotors turn at 2,600 rpms or more. “You’ll know a rotor is out of balance if it starts to vibrate on you.”
It’s also important to keep the separator’s electrical systems sealed to keep out dirt and dust, says Howard Smith, plant manager for OmniSource Corp.’s Athens, Ga., operation. In fact, he recommends keeping the whole area around the eddy current as clean as possible to maximize performance. To that end, it can be prudent to install the system indoors or at least put some sort of roof over it to keep out the rain, snow, and dust.
   Be sure to check the belt periodically, manufacturers stress. Some recommend a visual inspection twice a shift, while others suggest locking out the unit and inspecting the belt by hand.
   It’s important to clean the belt and splitter periodically, say Wendt and Gedgaudas. Many shredders now use some water, Wendt notes, so the material coming through the eddy current can easily be damp and somewhat oily. The result can be a thick, puttylike buildup on the belt “that takes your nonferrous material further and further away from the rare earth magnets, decreasing their efficiency,” he says. According to Gedgaudas, 1/16 inch of buildup on the belt can lower the repelling force 7 percent or more.
   Likewise, the splitter’s efficiency can drop if long, stringy—and often sticky—material builds up along its metal edge, so take time to clean these parts. Make sure you do it, however, with a scraper that’s made out of plastic or nonferrous metal, Gedgaudas says. A steel device in close proximity to the eddy rotor can get pulled by the separator’s powerful magnets and could even create a pinch hazard for the cleaner’s hands or fingers.

Running and Rerunning
During the actual operation of the eddy-current system, a few simple adjustments or added steps can boost nonferrous recovery. Capturing smaller material requires a higher frequency from the magnet assembly, which is basically a function of how fast the rotor spins, explains Steinert’s Wolfram. Simply turning a knob one way or the other on the control panels enables the system to handle different sizes of material, he says. Likewise, something as easy as speeding up the separator’s conveyor belt can help spread out material even if you don’t use a vibratory feeder.
   At General Iron, adding a second splitter to its larger-fraction eddy current helps the company separate a large sheet-aluminum product from other recovered metal, while a powerful fan placed along the conveyor blows light, fluffy debris off the belt and into a bin. After running that debris slowly through the system again, General Iron is able to collect an upgraded aluminum clip product, Labkon says.
   It’s also wise to test your fluff every three months or so to “make sure you’re not losing metals,” OmniSource’s Smith advises. In addition, he knows that his sorting line—which many eddy-current operators use to recover stainless steel or other material that isn’t caught by the separator—will alert him to a possible problem if too much recoverable nonferrous starts showing up in the eddy-current’s waste stream.
   Texas Shredder’s Jim Schwartz even advises processors to run their fines through the separator rather than discarding the material. “Anyone who’s not running the fines is throwing away metal,” he states, noting that European eddy-current operators do a much better job recovering metal from fines and make money doing it. Schwartz also recommends running the eddy current’s waste stream through the system a second time since it could still contain recoverable metal.

What’s Ahead for Eddy?
Over the past decade, eddy currents have grown larger, more powerful, and more automated—all trends that are expected to continue, manufacturers note. While most eddy currents are generalists in that they can handle a wide variety of materials, some systems are designed specifically to handle fines or UBCs.
   Steinert’s Wolfram predicts that wider units—up to 80 inches wide—will become more standard in processing systems. “Some manufacturers,” he continues, “are even branching out into equipment that could be added onto an eddy-current system to capture stainless steel, which today’s separators generally don’t recover.”
   Eriez’s Gedgaudas says high-frequency eddy-current systems—some with as many as 22 magnets—are becoming more popular because they excel at capturing smaller metals.
   Still, no one sees big changes ahead for the basic eddy-current technology, especially not with the scrap industry’s long-running downturn hampering capital equipment sales. As a result, it seems likely that today’s eddy-current separators will just keep rolling along well into tomorrow.  •