May/June 2002
Electrolifting magnets pick up where grapples and other lifting tools leave off, providing just the right touch for a variety of scrap-handling tasks.
By Beth Rogers
Electrolifting magnets are a fixture in scrap operations.
“I don’t think there’s a scrap yard in the world that can survive without a magnet of some kind,” asserts Frank Giglia Jr. of Allied Scrap Processors Inc. (Lakeland, Fla.).
Such magnets, which act like giant sticky tape as they pick up material, are typically used in scrap plants for loading and unloading vehicles and railcars, feeding scrap into processing equipment, moving material where it needs to be, housekeeping, and more.
Compared with other scrap-handling equipment, the technology behind electrolifting magnets is fairly simple. “Magnets are pretty much the same as they were in the early 1900s,” says Loren Hecker of the magnet division of Magnetech Industrial Services Inc. (Hammond, Ind.).
Of course, there have been some refinements in the past century. In the past, for instance, all magnets used to have cast cases whereas today they’re also offered with fabricated cases. Tar was previously the encapsulating compound inside magnets, but now manufacturers use a more user-friendly material. Also, magnets used to be insulated with asbestos while today they incorporate composite insulation materials like Nomex.
The main influence on magnet technology, however, have been changes in the cranes and material handlers that operate the magnets, says Mike Kozminski of Walker Magnetics (Worcester, Mass.). Hydraulic handlers, for example, made magnets more susceptible to side impact because of their ability to rotate. Before, when magnets were used mostly on nonrotating cable cranes, they were only susceptible to front and bottom impact. Also, because hydraulic handlers tend to be more efficient and have higher duty cycles than cable cranes, magnets’ own duty cycles have had to become higher, which has in turn created the need for cooler-running magnets.
Magnet manufacturers have met such challenges by developing magnets that are more durable, more efficient, and more productive than ever before.
Magnet Matters
In general, there are three kinds of electromagnets, each with a different shape and magnetic configuration:
• round, with an outer pole and center pole;
• bipolar, with two poles running the length of the magnet; and
• rectangular or tripolar, with a center pole and two outer poles.
Round magnets prevail in the scrap industry because “the circular magnet is probably the most-efficient design,” says Dick Ptak of Ohio Magnetics Inc. (Maple Heights, Ohio). “You get the most lifting power for the weight.” While round magnets are great for handling mixed and shredded material, they’re not as efficient at lifting billets or bundles of rebar. Those lifting tasks are better handled by a bipolar magnet, while tripolar units are best at picking up sheet and plate.
Electrolifting magnets also have different magnetic fields. The stronger, or “deeper,” the magnetic field, the better suited the magnet is for handling loose, nondense material like turnings and punchings. How much a magnet can pick up is largely a function of the type of scrap being handled. For instance, a 3,700-pound magnet could lift 10 times its weight of solid steel but might only be able to lift 850 pounds of turnings because the void spaces in the turnings significantly reduce the magnet’s lifting capacity, Ptak says.
Making the Right Match. When selecting an electrolifting magnet, it’s essential to match the magnet to the crane or material handler being used, notes Kozminski. Too big a magnet could topple the crane, while too small a magnet could limit the crane’s operating potential.
To avoid overloading a crane, operators need to look at the weight of the magnet as well as its maximum lifting capacity on the heaviest or densest material it could handle. The weight of a magnet is determined by a number of factors including the magnet’s size (usually expressed in terms of inches in diameter), the type of coil used, the steel section, and the case. “A lighter weight means that you can put a bigger magnet on a crane and give the customer a more efficient magnet assembly,” says Ptak.
What Size? The prevalent magnet sizes in the scrap industry range from 47 to 68 inches, with 55-to-58-inch units being the most popular. Such magnets fit the cranes and material handlers most commonly used in the scrap industry—generally those in the 60,000-to-80,000-pound range, Kozminski says.
Copper or Aluminum Coil? Electromagnets can have either a copper or aluminum inner coil, which conducts the magnet’s electrical current. Scrap operations almost always use aluminum-coil magnets because such units reportedly deliver a larger diameter without the weight and cost of copper. Steel mills, in contrast, tend to use copper-coil magnets because they can pick up hot materials without distorting the coil. Notably, 80 percent of the cost of a magnet is linked to the amount of conductor used, according to Ptak.
On the Case. Most magnets had cast cases until welding technology improved after World War II, which led to the advancement of fabricated cases. Today, most magnet manufacturers offer both cast and fabricated cases, though some make only fabricated models. “The advantage of an all-welded fabricated magnet is that it lends itself readily to custom applications or modifications,” says Kozminski. “With a casting, I’m limited to the casting sizes that are available. A casting is made from a pattern, and there’s a significant investment in that pattern.”
According to Kozminski, fabricated and cast magnets cost about the same and are equally durable. “A casting looks more rugged,” he says. “It looks strong, it looks beefy, it looks traditional. But if you ask a scrap processor how he breaks up cast material, he basically just drops something heavy on it. Whereas if he has something that’s been fabricated or made out of rolled steel plate, he has to run it through a shear or use a torch to cut it up. The argument could be made that a fabricated magnet could stand up better to the beating and abuse of scrap operations. However, we’ve found that in a typical scrap application, there really is no difference.”
Joe Schatz of Winkle Magnetics (Canfield, Ohio), however, notes that some of his customers prefer fabricated magnets for repair reasons. “When you bust a casting,” he says, “you’ve got to replace it, whereas with a fabricated unit you can replace pieces and parts. Castings can be welded and patched, it’s just not as economical to do.”
The Duty-Cycle Issue
When an electrolifting magnet is turned on, the power on the coil creates a magnetic field. The discharge cycle, which allows material to be released from the magnet, involves dissipating the magnet’s energy in resistors and then reversing the current to eliminate the residual magnetism. This is all done in a matter of seconds or fractions of a second in what is known as the “duty cycle.”
Initially, magnets were designed with a 50-percent duty cycle, which meant that a magnet should be on the same amount of time it’s off in any given lifting cycle. If it was operated for one minute, for example, it should be on 30 seconds and off 30 seconds to avoid overheating. Today’s magnets, however, can offer higher duty cycles such as 75 and even 100 percent. In general, the higher the duty cycle, the heavier and more expensive the magnet, notes Ptak.
When turned on, the coils generate 10,000 to 40,000 watts and, in the process, build up tremendous heat internally. Beating this heat is always a challenge—and a goal—because a magnet’s lifting capacity decreases as the unit gets hot. As Ptak explains, a magnet with a 50-percent duty cycle might start the day picking up 2,000 pounds each time, but by the end of the day—as the magnet builds up heat—it might only be able to lift 1,500 pounds. A magnet with a 75-percent duty cycle might decrease from 2,000 pounds in the morning to 1,800 pounds by the end of the day. One problem with beating this heat is that manufacturers are limited by the available insulation technology, which currently can withstand 180 degrees C, Kozminski says.
The duty-cycle issue is a tad touchy for scrap operators because many don’t abide strictly by their magnets’ rated duty cycles.
In theory, a magnet is supposed to be turned on only after it has been lowered onto the material it is lifting. In reality, says Hecker, operators turn their magnet back on immediately after dropping a load to save time. The problem is that the magnet is on, generating heat but not doing any work.
To help address such operating habits, some manufacturers have developed 100-percent duty-cycle magnets that allow operators to keep the magnet on continuously. These magnets come with a trade-off, however—they require more coil, which makes them heavier, taller, and ultimately less efficient for the cranes or handlers running them.
While a magnet should be operated in accordance with its duty cycle, it seldom is. Even with 75-percent duty-cycle magnets, users are too pressed for time to allow magnets to cool sufficiently. “In the real world,” Hecker says, “a magnet is never going to dissipate heat as fast as it’s going to build. Scrap processors have customer demands. In order to meet those demands, they have to work the magnet hard. A magnet’s job is abusive by nature. It’s not a toy. It’s going to be thrown around, it’s going to be bumped, it’s going to get dinged. That’s the nature of the business.”
That helps explain why well-maintained magnets can last 20 to 25 years while those in the scrap industry generally last only 10 to 15 years, Ptak says.
What can scrap recyclers do? The key, Hecker suggests, is to train operators in the proper use of a lifting magnet. “Try not to turn the magnet on when it’s not performing any work,” he says. “Try not to throw the magnet around and intentionally bang it into something just because the magnet looks like a big, strong piece of steel. An electrolifting magnet is an electrical device and should be treated with the respect it deserves.”
Problems and Repairs
The two main causes of deterioration in electrolifting magnets are overheating (usually due to the operator exceeding the magnet’s duty cycle) and moisture.
Overheating degrades a magnet’s insulation, ultimately causing shorted or grounded conditions in the wiring. For every 5 degrees C that a magnet exceeds its 180-degree insulation rating, the magnet’s life is cut in half, Ptak says. Unfortunately, no manufacturer has figured out a way to vent the heat buildup inside a magnet without admitting moisture.
As for moisture, it usually gets in through cracks in a magnet’s case, though a hot magnet left on the ground also “sucks up water like soda pop through a straw,” says Hecker.
Unfortunately, “magnets have always been looked at as the lowest animal on the maintenance food chain,” he asserts. Fortunately, there are a number of safety and preventive maintenance “peripherals” available to help owners protect their employees as well as their magnets. One of these is a battery backup to make sure the magnet doesn’t experience a power interruption. Most manufacturers feel that such backups aren’t necessary in scrap operations since material isn’t usually lifted over equipment or people.
Magnet owners can also install volt and amp meters in the crane cab so the operator can monitor the magnet’s electrical readings. Regrettably, Hecker says, few buy such meters though they cost less than $500. “I ask everyone, ‘Would you drive your car without a fuel gauge and a temperature gauge?’” he states. One manufacturer also sells alarms that let the operator know when he has left the magnet on too long.
At some point—whether or not it is operated or maintained properly—every magnet needs to be repaired or retired. Magnets that need repairs are machined open, and their coil is usually rewound or replaced, with fresh insulation added. Also, the outer or center pole shoes are often worn or missing and need to be replaced.
Rebuilding a magnet costs about half to two-thirds the price of a new magnet, notes Kozminski. Rebuilding work is expensive because manufacturers can’t diagnose and repair a magnet without opening the case. Most manufacturers rebuild both their own magnets and those made by others. One magnet maker gives its customers digital photos of the inside of their magnets as well as a failure report so they can see what went wrong.
The Processor Perspective
What factors are most important to scrap processors when they’re in the market for a magnet?
Frank Giglia Jr. of Allied Scrap Processors says that he mainly looks at a magnet’s size and what it will pick up in relation to the size of his crane. Because he generally handles light, fluffy scrap, he always buys extra-deep-field magnets “because they pick up the most for the size of the magnet.” If he were picking up denser scrap, in contrast, he’d get a magnet with a regular field, he notes.
“If I can buy a 54-inch magnet with an extra-deep-field, I’d buy that over a 58-inch magnet with a regular field because the former has less weight and size,” Giglia explains. “The smaller the magnet, the more I can do with it, the more places I can put it.”
Ed Arnold Jr. of Edward Arnold Scrap Processors Inc. (Corfu, N.Y.) uses six round magnets from 48 to 60 inches to handle plate and structural, No. 1 heavy melt, and bales. Arnold prefers deep-field magnets because he believes that they last longer than standard or extra-deep-field magnets.
Both Giglia and Arnold prefer fabricated magnets—Giglia because he finds them lighter and less expensive and Arnold because he finds them easier to repair. Giglia always buys 100-percent duty-cycle magnets because his operators refuse to heed the manufacturer’s recommendation to only turn on a magnet when it’s placed on a load. Arnold looks for at least a 75-percent duty cycle, noting that much of the time he uses the magnets for sorting material, which means he has to hold onto the material longer.
When it comes to repairs, neither Giglia nor Arnold send their magnets back to the manufacturer. Giglia used to have a local electronic shop that could rewind his magnets, but no more. Now, the cost of shipping magnets back to the manufacturer leads him to treat them as disposable. “By the time I ship a 3-ton magnet and have it rewound, I don’t feel like I’m getting my money’s worth,” Giglia says. As Arnold adds, “When you send a magnet in for repair, you’re down five or six weeks, but you can get a new one and immediately put it into service.”
Both Giglia and Arnold admit that scrap operators frequently abuse their magnets, though proper maintenance can minimize some of this mistreatment. Magnet casings, for instance, need to be built up when they start to wear out.
Arnold learned that lesson the hard way when one of his magnets wore down past the welds, took on water, and shorted out. Consequently, he recommends inspecting magnets at least annually to make sure they don’t have any cracks that could lead to failure. The bolts on a magnet’s junction box should also be periodically tightened to prevent water from entering, says Ptak, who notes that operators would be wise to periodically test their magnets’ electrical system.
Magnet Makers
Dings Co. Magnetic Group, 414/672-7830, www.dingsco.com
Gensco Equipment Inc., 800/268-6797 or 416/465-7521, www.genscoequip.com
Magnetech Industrial Services Inc., 219/937-0100 or 574/234-8131, www.magnetechindustrial.com
Ohio Magnetics Inc., 800/486-6446 or 216/662-8484
SGM Magnetics Corp., 440/333-1300
Steinert Elektromagnetbau GmbH/Resource Recycling L.L.C., 727/573-2482, www.steinert.de
Walker Magnetics, 800/962-4638 or 614/481-0007, www.walkermagnet.com
Winkle Industries/Winkle Magnetics, 330/533-2233, www.winkleindustries.com •
Beth Rogers is a writer based in Bethesda, Md.
Electrolifting magnets pick up where grapples and other lifting tools leave off, providing just the right touch for a variety of scrap-handling tasks.