Eddy Current Market Matures

One of the most popular types of equipment used in the scrap processing industry today is the eddy current separator. Eddy current systems are often used in processing operations where nonferrous metals need to be removed from the material stream, including material recovery facilities and heavy-duty shredding plants.

Eddy current separators have been on the market for more than a decade, and during that time they have gone through a maturing process. The main benefit for the processor is that eddys have become more affordable due to competition in the marketplace. Also, through the years, there have been some improvements such as employing eccentric rotation of the magnets, increasing the magnetic field strength and overall product downsizing. As a result, many manufacturers are now on their second and even third model generations. Future improvements could involve the use of electromagnets that emit pulses instead of rotating, rare earth magnets, and methods to adequately remove stainless steel. Be that as it may, it pays to examine more closely this vital piece of equipment as operators look to recover all they can from the scrap stream.

The term "eddy" is usually used to describe an air or water current that runs contrary to the main current. Thus, eddy current separators use a magnetic current to propel nonferrous metal in a direction contrary to the main material flow. A charge is imparted to the highly conductive nonferrous metals from a magnetic field created by rare earth magnets. When that charge is reversed (by virtue of the magnetic drum spinning under the conveyor belt and alternating the positive and negative poles), the nonferrous metal is repelled, making it jump. The strength of the magnetic field, the speed of the belt, the rotation speed of the magnetic drum, the number of poles, and the weight of the piece of metal all play a role in determining how far the material will jump. Once the optimum jumping spot or "split" is determined, a divider can be placed to segregate the nonferrous from the ferrous metal or from other material.

When talking about eddy current separators, the gauss rating is usually discussed. The gauss rating of an eddy refers to the strength of its magnetic field at a given point. Although some manufacturers will say that the gauss rating is not the most important feature of an eddy, it must be strong enough to jump the nonferrous material that is coming down the stream. The static gauss rating of a rare earth magnet is highest at its surface and decreases about 450 gauss for every one sixteenth of an inch directly perpendicular from the surface. Therefore, a magnet with a 3,600 gauss rating will have a gauss reading of zero at one-half inch from its surface.

The addition of an eddy current separator to many processing operations is particularly favorable now mainly due to the strong market for nonferrous material. Since processors are able to get more money for commodities such as aluminum, they are able to recover the money spent on purchasing an eddy current more quickly.

"Let’s say that an operation is processing 18 tons of material an hour, and 2 percent of that material stream is aluminum," says Tom Wendt, president of Wendt Corp., Tonawanda, N.Y. "That means that there are 720 pounds of aluminum going through every hour. If aluminum is selling for 50 cents a pound, then that operation is losing $360 an hour if it is not recovering 100 percent of that material. And an eddy will get you very close to that 100 percent."

Manufacturers say that payback for most operations can be achieved in as short a period as three months, but usually no longer than one year. "I would really take a look at that figure," says Wendt. "Personally, I would buy an eddy if it would take less than two years to recover my money – at three years, I don’t think I would add one."

Phil Lombardo, president of Steinart Inc., Norwalk, Conn., agrees. "The payback from an eddy current purchase should be about one year," he says. "Some of our customers, however, are reporting paybacks as fast as three months, and an eddy should last 20 years or more with regular maintenance and routine belt changeovers."

"Clearly, a processor can achieve a faster recovery rate today of the money that he spent on buying an eddy current separator due to the favorable market," says Scott Brenner, the sales coordinator at Lindemann Recycling Equipment, Charlotte, N.C. "Competition among manufacturers of equipment has also brought prices down, and the payback in a MRF is even more dramatic because the eddy replaces personnel on the line."

Dennis Pederson, president of Count Recycling Systems, Des Moines, Iowa, says that when eddys first came out they cost as much as $200,000. "Today, you can get one for less than half that," he says.

One area that eddys are being used a lot is in the heavy-duty auto and appliance shredding business. Shredder efficiency includes separating the shredded material to get the most ferrous and nonferrous as possible out of the stream. Auto shredders usually have several levels of sorting to separate the material being shredded. A typical shredder uses a cascade/zig zag box (commonly referred to as a Z-box) whereby the shredded material is moved past magnets to separate the ferrous from the nonferrous material, then the material is passed through either a wet or dry system to remove the fluff. Eddy current separators are being used as a final separation method to catch any remaining nonferrous material still in the fluff.

According to Phil Bienstock, formerly of Wendt Corp., eddy current separators can enable an auto shredder to pull out 99 percent of the available nonferrous from the stream, whereas with an air (cyclonic) or wet system alone, the shredder will be less efficient.

"With the air system, the cyclonic action can be increased, but more nonferrous – as much as 4 percent – would go out with the fluff," says Bienstock. "And with the wet system, about 2 percent of nonferrous material goes out with the fluff. Those extra percentages, although small, are costing processors money. With an eddy current separator, a large processor can recover the money spent to purchase the machine in as little as 90 days, and begin capturing more profits."

Even processors that do not currently use eddy current separators acknowledge the advantages of this type of equipment.

Phil Mervis, operations manager of Mervis Industries, Kokomo, Ind., now uses only an air separation system for end processing. "Eddy current separators are so good these days, it makes sense to buy one," he says.

"We use the standard Z-box to separate the material after processing; however, we are in the process of installing a new eddy current separator on one of our shredders," says Drew Luntz, president of the Luntz Corp., Canton, Ohio.

The basic technology used in eddy current separators is based on simple magnetic principles that are as old as the Earth, and that were first explained by English physicist Michael Farady in the 18th century. And those principles are still valid today. So, improvements of eddys to date have revolved around ancillary features of the equipment. Those include placing the rotation of the magnets off-center (called eccentric rotation) to achieve a cleaner separation and release of ferrous material, and increasing the strength of the magnetic field or the number of poles to increase separation efficiency.

The eccentric design, which is used by Steinart, has been on the market for the last six years. The main advantage of this design is that ferrous particles are carried out of the magnetic field and released so that they do not stick to the drum. According to Lombardo, this minimizes damage to the drum, and allows for a "highly defined jumping point for nonferrous materials."

Another upgrade has been the increase of rare earth magnets in the rotating drum to achieve a further and more defined split. The increase of gauss strength also makes more nonferrous jump, too. Recently, Wendt Corp. introduced its SuperEddy which it touts as being twice as powerful as before. "The increase in gauss increases the jump length and the addition of more material jumping, allowing the processor to employ two splits instead of one," says Wendt. "Before the first split is the waste, between the two splits is a mixture of different grades of nonferrous plus some fluff, and the last split can be positioned to achieve 100 percent of a specific grade of nonferrous metal."

The increase in gauss also allows the processor to run the conveyor faster, thus achieving a higher throughput capacity, says Wendt.

Steinart has also made an adjustment to its line of eddys by adding more poles. "The number of poles is important because you achieve a greater number of alternating fields per rotation so more nonferrous metal is repelled," says Lombardo. "The more poles the better separation."

Overall, equipment manufacturers agree that processors should consider two issues before buying a system. First, investigate the historical performance of the system, and particularly its down-time record. And second, go with a system that will give acceptable separation quality. For example, eddys for MRFs may not need the extra power or width that a scrap metal processor would need because the main nonferrous item being separated at a MRF is aluminum cans.

According to Pederson, whose company installs turnkey separating systems for MRFs, "The eddy current separator that we install is a smaller scale eddy between 20 inches and 30 inches wide, whereas ones used in scrap operations are 48 inches or wider. That’s because eddy current systems for MRFs are primarily designed to remove only beverage containers from the post-consumer stream. With system ratings close to 100 percent, an MRF can’t be competitive without it."

When eddy current separators first entered the market, some companies tried to apply electromagnetic technology to the equipment. However, the efforts were flawed because too much heat was generated by the electromagnetic current, and the eddys were burdened with large cooling systems, according to several industry experts. Since then, the market has been dominated by rare earth eddys.

Reportedly, though, two companies appear to be on the verge of reintroducing new electromagnet eddys due to recent advances. Those companies are Osborn Engineering, Tulsa, Okla., and Rustec Inc., Camden, N.J.

Officials from both companies did not want to discuss their research and development efforts, but some basic information is available.

Rustec is working with Lockheed Martin Energy Systems, Oak Ridge, Tenn., as part of a U. S. government-led coalition designed to promote technology exchanges with former communist countries. Apparently, Rustec is field testing an electromagnetic pulse separation system based on ex-Soviet technology. Rustec is working with the Association of Centers for Engineering and Automation in St. Petersburg, Russia, to advance the technology in scrap processing.

James MacFarlane, vice president of Rustec, would not talk about his company’s new process either, saying that he is under a confidentially agreement. "The technology is still being developed," he says, "but when it is completed it will be very interesting. All I can say is that it will have an international flavor, and that we are only months away from making an announcement."

Marlin Bills, president of Osborn, says that his company’s advancements were all accomplished in-house and that he, too, is close to unveiling a prototype system. He would not elaborate further on his company’s developments.

Osborn received a patent for its technology last May, and it is unknown if Rustec’s process is patented.

Speculatively, using an electromagnet instead of a rare earth magnet could offer several advantages. One, the frequency of the magnetic field could be changed and adjusted depending on the amount of electrical current supplied. The frequency could then be set to the optimal level to allow for the maximum separation of material, and the electromagnetic waveform could be adjusted to minimize heat generation and to increase magnet and separation efficiency as well.

Theoretically, an electromagnetic-based system could be comprised of a three-to-four stage setup with an electromagnet behind each screen and set to a different frequency and waveform to separate the material being screened in the most efficient way possible. This is because each type of nonferrous metal has a different level of conductivity and will react differently to each frequency level and waveform.

Another possible advantage is reduced weight. The electromagnetic system should weigh considerably less than the rare earth stone which can weigh more than 1,000 pounds. In addition, the electromagnet is stationary and does not have to rotate, thus saving on wear-and-tear and maintenance.