Eddy Current Separators by Mark Henricks

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Eddy current separators have made manual removal of nonferrous materials from recycling waste streams a thing of the past. As they’ve become standard equipment for recyclers, the machines have become more powerful with larger magnetics and capacity. The result is increased efficiency and improved operating margins for recyclers handling incinerated, industrial and household waste.

Eddy current separators apply to a wide range of materials, including electronics, plastics, auto and white goods shredding, foundry sand, and wood and medical waste. Specific applications work to remove aluminum from plastic bottles, gold and silver from computers, and stainless steel and ferrous metal from wood waste, depending on the grade of the material.

Manufacturers offer separators as discrete units or as part of a system that includes conveyors, splitters and vibrators. Prices range from $30,000 to $140,000 for the whole package.

The recycling industry likes eddy current separators because they’re versatile machines that offer a more economical method to capturing nonferrous metal from different types of waste. Compared to other metal separation processes, eddy current separators are simple, stand-alone units that cost less. Many consider the end product to have better quality than possible with other separation techniques thanks to a higher degree of separation and efficiency. For example, the purity of nonferrous auto scrap has increased to 85 and 95 percent due to improvements in eddy current separator technology.

“There’s a continuous requirement for cleaner materials,” says Richard Bergan, sales manager of eddy current separators at Magnetic Products, Inc., in Highland, Michigan. “Eddy current separators are not just recovering aluminum and tin cans now, they help to purify products also.”

Manufacturers continue to tweak eddy current separators so volume and efficiency continues to increase. For recyclers, Bergan says, it’s a matter of “how big a burden can I put on this machine and how fine a product will I get and still be efficient.”

Saving energy is another way separators have become more efficient. Machines from Magnetic Products, for example, work on a soft-start power supply that builds to maximum speed gradually. “You don’t need as much draw that way,” Bergan says.

The drive toward more efficiency is apparently showing results. “You see a lot more metal retrieved from the waste stream now,” says Ben Davis, general manager at Huron Valley Steel Corp., in Belleville, Michigan.

With only minor variations, most eddy current separators are made with high-speed magnetic rotors that can spin up to 3,000 RPM within a nonmetallic drum that spins at a slower speed. The speed variance creates an electrical charge that captures and expels nonferrous metallic elements thinly laid out on a conveyor belt equipped with two to four pulleys. A splitter at the end of the separator propels the nonferrous metal into a collecting bin in the last fundamental step of separation.

Because the metal particles come in various sizes, the short circuit current flows irregularly around the objects as they move along the conveyor belt. That jumpy current is what gives the separator the name of eddy current.

Choosing the separator that works best for a specific recycling operation depends on a number of variables. Some manufacturers suggest owning units of different sizes to handle the variety of nonferrous elements to be separated. Factors to consider before purchasing include particle size and shape, conductivity, density, moisture content, stickiness, size distribution, and fibrous and metallic content. A combination of these factors will determine the optimum rotor for efficiently handling of these materials as well as determine the optimum machine settings for belt and rotor speed, feed method and splitter operation.

“Magnetic separation is an art, not a science,” says Don Morgan, the product manager for eddy current separators at Walker Magnetics Group in Worcester, Massachusetts, “which means your selection of equipment for the appropriate application is important.”

The rotor’s magnetic blocks are made with rare earth magnets or standard ferrite ceramic. Most recyclers prefer the rare earth magnet because they’re considered to have a stronger magnetic field than ceramics. Ceramic magnets do offer a somewhat higher depth of field that some say is better for handling larger size objects, but most vendors consider the advantage marginal. “Rare earth is much more mainstream,” says Davis at Huron Valley Steel. “The only reason someone would choose ceramic is because of price.”

Rotor widths can range from 20 to 80 inches, which in turn determines the volume of material moving over the conveyor belts. Capacity can range widely, from 4 tons an hour to as much as 60 tons an hour. A 7-inch long, 36-inch wide rotor works best for low-volume loads while a 13-inch long, 48-inch wide rotor can handle heavy-duty loads like shredded cars.

Separators made by Eriez Manufacturing Co. in Erie, Pennsylvania, exemplify the variety of features that adapt an eddy current separator to each scrap load. Splitters, which are an option on some units, are positioned higher and closer to the drum for smaller particles while a rear splitter captures materials with weaker magnetic content. Separators today can capture particles as small as 3/32 inches or 2 mm.

Not only do today’s separators do more, but they last longer too. Dings Magnetic Group in Milwaukee, Wisconsin, makes eddy current separators with a triple shell design it says increases strength and durability while producing a deeper field that lets recyclers process more tons per hour with better recovery rates.

In general, today’s eddy current separators can recover up to 95 percent of recyclable materials from metallic-contaminated waste. From such a simple, straightforward technology, that’s a percentage that looks good in an increasingly refined marketplace.