Equipment Focus: Lifting Magnets 2017

Dec 5, 2017, 22:36 PM
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November/December 2017

To get the longest life span from your lifting magnet attachments, minimize heat, moisture, and misuse, manufacturers say. That means using them for lifting and lifting only

By Ken McEntee

Equipment-Focus-Lifting-Magnets-ArtBattering ram. Railcar mover. Scrap compactor. In some scrapyards, a lifting magnet attachment is one tool that does it all. But subjecting magnet attachments to that kind of misuse, manufacturers say, can drastically shorten their life as a tool for lifting ferrous scrap.

If you use and maintain it properly, a lifting magnet can provide five to 10 years of productive use—and some have been known to last for more than 20 years. Conversely, “we’ve seen magnets destroyed in eight to 10 months,” says Bob Bedard, manager of the National Association Supply Cooperative (New Philadelphia, Ohio). “I have seen the abuse these magnets take,” he says, admitting that he was once one of the culprits when he worked in a scrapyard earlier in his career.

“We had a big 72-inch, 8,000-pound magnet that we used to tamp down scrap into railcars to get more material loaded into them,” he says. “We used it as a battering ram to take apart iron items. We would use it to move the railcars around the yard. All of these things are just terrible for a magnet, but at the time I had no concept [of] what was inside them or how much they cost. I just saw giant circular things hanging in the air from a crane.” That lack of understanding “is still common among operators today,” he says. “It was after I left the scrapyard and started to sell magnets that I gained a better understanding and appreciation for them.”

How They Work—and Fail

Electric lifting magnets are among the simplest pieces of equipment in a scrapyard, especially when compared with the material handlers to which you attach them. “It’s the same idea as the electromagnets we made in science class with a steel bolt, a dry cell battery, and some wire,” Bedard observes, “except these are bigger, and they can pick up cars and refrigerators instead of paper clips.”

Scrapyards should be using lifting magnets primarily “to pick up steel and move it from one place to another, or to clean the ground where you previously had a pile of steel,” explains the president of a Toronto-based equipment manufacturer. The thicker the steel that you’re moving—such as structural steel in 2-foot pieces, beams, and channels—the better it is to use a magnet rather than a grapple, he says.

Inside a magnet’s rugged case is an electrical conductor layered with a thin insulator to prevent electrical shorts and wound into a coil. The aluminum conductor can be in the form of a strap or wire; both are popular in the industry, Bedard says. Feeding 230 volts of direct current through the coil creates a magnetic field that can lift hundreds or thousands of pounds of ferrous metal, depending on the magnet’s size. Typically, a generator attached to the material handler powers the magnet attachment. The machine’s operator directs power to the magnet to pick up a pile of steel and cuts the power to release the load.

The biggest enemies of a lifting magnet are traumatic impact, excessive heat, and moisture, manufacturers agree. Training is essential to reduce operator behaviors that can rapidly reduce the life of your magnet, they say. “As a repair facility, a crane operator is our best friend,” says a magnet repair expert. “If they used the magnets as they are supposed to use them, our business would probably drop off the map.”

Lifting magnets “are abused on a daily basis,” says an eastern Ohio magnet manufacturer’s sales director. “A crane operator knows that he has this big yellow thing that weighs 2,500 to 7,000 pounds at the end of his stick and that it’s a convenient tool to use as a battering ram or to nudge a railcar.”

How bad is this problem? “I’ve seen magnets that, instead of being round, there is an entire flat spot on [them] from banging [them] against things,” Bedard says. “This not only damages the case, causing welds to break, but it also destroys the integrity of the aluminum coil and the insulation that protects against shorting and grounding.”

In addition to operator abuse, overheating and moisture can cause a magnet to fail. Overheating can occur when a magnet is powered on beyond its intended duty cycle. Most scrapyard lifting magnets run at a duty cycle of 50 to 75 percent, with most newer products rated at 75 percent. A 75-percent duty cycle means that during a 10-minute period, the magnet should be powered up no more than 75 percent of the time—or 7½ minutes. Different manufacturers vary the way they calculate duty-cycle ratings, although 10 minutes is usually the basic time interval measured. Some ratings consider that certain operations allow a magnet to cool completely following an eight-hour workday, while other operations work around the clock, giving the magnet no extended cooling-off period.

 “What happens when you put 230 volts of DC current through the conductor material is that it generates a lot of heat,” the eastern Ohio sales director explains. “It needs time to dissipate the heat. When a magnet is powered up for too long, the insulation between the aluminum windings is heated beyond the temperature it is designed to protect, and it breaks down, causing the magnet to fail.”

Over time, the insulation will naturally wear out, leaving charred remains and allowing the conductor material to short, points out the sales manager for a northern Ohio manufacturer. But running the magnet beyond its duty cycle can considerably shorten the process—sometimes causing immediate failure.

The heat the magnet generates also makes it a sponge for moisture. Once inside the coil cavity, moisture can cause shorts in the conductor material, reducing the magnet’s lifting ability and increasing the risk of failure.

“The magnet looks like a well-sealed case, so it’s hard for people to imagine that a small crack or fissure can allow moisture to get in. But as that coil cavity cools down, it creates a vacuum and sucks the moisture in,” says Chuck Kinsey, assistant manager at NASCO-OP. “If you leave the magnet resting on the ground overnight, it can suck up that moisture. It’s recommended that a magnet rest on a pallet or a scrap pile or [that you] suspend it off the ground when it’s not in use to avoid wicking moisture into the coil cavity.”

Preventing Problems Has Payoffs

Inspections, preventive maintenance, and operator training are three easy ways to maintain performance and increase the life span of a lifting magnet. Inspect the magnet’s case—including the bottom plate—at least monthly, but ideally daily, for cracks and damaged welds, these sources advise. The seal at the terminal box, where the electrical cables enter at the top of the magnet, is another area where moisture can seep in. Manufacturers fill the area with a rubbery potting compound to prevent moisture from entering, but over time the seal can be compromised. The first 5 feet of cable coming out of the magnet are particularly vulnerable to being severed while moving scrap, says the international sales manager of a Pennsylvania-based magnet manufacturer, thus the inspection should examine that as well.

Other items to inspect regularly include the magnet chain, as well as the lugs and pins that connect the chain to the magnet. “You should never weld on a chain,” Bedard cautions. “If you have a link worn beyond acceptable limits, replace the chain.”

Along with routine visual inspections, regular electrical tests are a good idea, the northern Ohio sales manager says. “We recommend taking two basic electrical readings every month—coil resistance and ground resistance,” he says. “Those are good barometers [that will show] if the magnet is starting to deteriorate and if it is accumulating moisture internally.”

“A magnet failure will usually happen in varying degrees,” the eastern Ohio sales director says. “It may stop working one day, but if you track it over a period of months, you usually can start to see its electrical readings deteriorate. Sometimes you can save money by fixing problems when they’re small instead of waiting for a catastrophic failure that can cause extended downtime. If you see a small fracture, it’s easy to send a maintenance guy over to weld it.”

Many companies operate their magnet until it quits, this sales director says, but “the younger generation [of managers] is becoming more proactive,” he says. “They understand the importance of taking readings and tracking them to be alerted to potential problems coming up.”

Scrap processors need to be just as proactive in operator training, the Pennsylvania rep says. “Proper use can save money. Just explaining to operators not to use a magnet as a sledgehammer, or not to drag it across the concrete ground, does a lot to preserve the bottom plate.”

Replacing a Magnet

The most important variables to consider when replacing or buying a lifting magnet are the lifting capacity of the handler you’re going to attach it to, what types of scrap you process, and how much scrap you process, manufacturers say.

Generally, scrapyard magnets range in size from 30 to 92 inches in diameter, but the most common are between 56 and 72 inches. One manufacturer based in Quebec offers smaller 12- and 24-volt magnets that range from 6 to 40 inches in diameter, the company’s magnet division manager notes.

“Most of today’s material handlers … are designed to handle a 57- or a 67-inch magnet, so those are the most popular,” NASCO-OP’s Kinsey says. “But there are a lot of smaller, mom-and-pop operations that are using 40-inch magnets.”

A 40-inch magnet weighs about 1,800 pounds and can lift about 1,100 pounds, depending on the density of the pile it is pulling from. It costs about $8,000. A 72-inch magnet weighs about 8,000 to 8,300 pounds and will lift about 4,700 pounds. It costs about $40,000.

“The first question I ask anybody who is buying a magnet is what kind of [base] machine they have,” the Toronto president says. “That narrows the choice down quite a bit. Most machines already have a generator attached. So that is going to determine in large measure what kind of magnet will fit on it.”

 As Kinsey explains, “you can’t hang a 72-inch magnet on a machine that can only lift a 48-inch magnet or has the power source for a 48-inch magnet. But you also want to think about how you’re going to use the magnet. If you’re a mom-and-pop operation on 1 acre, you might have a material handler that can handle a 72-inch magnet, but if you’re only getting peddler traffic across your scale, it doesn’t make sense to buy a magnet that is too large for your operation.”

Surprisingly, as material handlers have evolved, the magnets they hold have gotten smaller. “In the past, scrapyards used to use a lot of cable cranes, which hold larger magnets but are slow to operate,” the eastern Ohio sales director says. “The hydraulic equipment [today is] more nimble and faster to operate. The downside is that [these machines] don’t have the capacity that the cable crane did. Generally, you will see that most mobile cranes are going to handle on average a 58- to 65-inch magnet. Small feeder yards will probably have smaller cranes, and large corporate operations that export huge quantities of scrap and load barges are probably going to have larger magnets than that.”

The Pennsylvania rep agrees that, on average, lifting magnets used in scrapyards are getting a little smaller. “Seven or eight years ago, people were going bigger in excavators, and more people were buying 67- and 72-inch magnets,” he says. “Today, we’re seeing more 48- and 58-inch magnets being sold. Everybody was upsizing at one time, and now they are downsizing, probably for all the right reasons.”

Nearly all lifting magnets used in scrapyards are round. “Round magnets generate the most uniform field and the deepest and strongest field as opposed to rectangular [magnets],” the northern Ohio sales manager says. Rectangular magnets—which are heavier and more typically found at steel mills—are also available, however. One scrap processor purchased a rectangular magnet after complaining about having too much scrap left in the corners of his railcars, the Pennsylvania rep reports. “The trick is to be able to use the magnet to sweep the bottom and the corners without pulling the railcar off the track,” he says.

While a magnet is among the less expensive pieces of equipment in a scrapyard, an idled magnet can cost a processor a lot of money, the eastern Ohio sales director notes. “That $500,000 to $1 million excavator is probably the single biggest investment that a scrapyard is going to make, [and] at the end of the crane is a magnet or a grapple that might cost $20,000. But without it, your million-dollar machine is sitting idle. In the big picture, your magnet is a relatively inexpensive piece of equipment to maintain. But the cost of not maintaining it is huge.”

Ken McEntee is the Strongsville, Ohio–based editor and publisher of The Paper Stock Report and other business periodicals.

Choosing A Controller

Magnet operators have the choice of mechanical or solid-state technology for magnet controllers, and each technology has its proponents. “Scrapyards love the traditional mechanical controllers,” says the sales manager for a northern Ohio manufacturer. “They are simple and easy to fix. If a lead goes bad, a maintenance guy can usually make a quick repair. With the solid-state controllers, there is nothing to fix. You usually have to replace it, which creates a lot of downtime. And in the scrap business, it’s all about reducing downtime.”

But solid-state controllers also have advantages, an eastern Ohio manufacturer's sales director says. A solid-state controller “performs the same function as the contact controller, but it also offers more protection to the system,” he says. “It will detect electrical shorts and shut down the power if necessary. It powers on and off faster, which makes the operation more efficient and increases the magnet’s lifting power. But it also is more susceptible to heat, which is one of the things that can wear down a magnet. So there is a tradeoff between the two options.”

Most magnet manufacturers offer both options, and the controllers can usually be switched out. “They can be interchangeable,” the eastern Ohio sales director says. “If you don’t like the solid-state controller, you can replace it with the contactor controller; however, this change will require an additional converter box to utilize the contactor controller.”

To get the longest life span from your lifting magnet attachments, minimize heat, moisture, and misuse, manufacturers say. That means using them for lifting and lifting only

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