Then & Now - Eddy Current Separation

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July 7, 2008

THEN

In 1851 when French physicist Léon Foucault discovered the magnetic repelling phenomenon that is used in eddy current separators, he likely did not envision the wide variety of applications in which the force could be used.

As described by Wikipedia, the name for the eddy current derives from the whirlpool (or eddy) phenomenon of the electrical charge involved. "It is caused when a moving (or changing) magnetic field intersects a conductor or vice-versa. The relative motion causes a circulating flow of electrons, or current, within the conductor. These circulating eddies of current create electromagnets with magnetic fields that oppose the change of the magnetic field. The . . . greater the relative velocity of motion, the greater the currents developed, and the greater the opposing field."

The eddy current force has subsequently been used in a variety of applications, including to apply the brakes to roller coasters or to detect the presence of the proper coins in vending machines.

Metals recyclers with mixed materials, and the magnetic companies that serve them, began applying eddy current principals to metals separation in the 1960s.

An initial recycling application was using eddy current automation to separate aluminum cans from steel cans and other containers in the same stream. While standard belt or drum magnets could pull steel cans away, the positive sort provided by an eddy current separator could help recyclers obtain a clean, desirable aluminum used beverage container (UBC) product.

Publicity photos and news release summaries from the early 1990s from companies such as Eriez Magnetics, Erie, Pa., show eddy currents for this application.

But manufacturers and recyclers were already putting eddy currents to use in more complicated sorting situations. By 1991, Huron Valley Steel in Belleville, Mich., was well underway with its efforts to use eddy current separation as one of several techniques to identify and separate nonferrous metals from the post-auto-shredder materials stream.

NOW

Much of the action for technological innovation and greater volume eddy current separation in the past two decades has been in the post-shredder downstream arena.

In addition to North American companies such as Eriez, Huron Valley and Walker Magnetics, several European-based magnetic equipment companies have enjoyed a healthy sales climate as they have introduced increasingly larger, wider, technologically advanced and heavier-duty machines to North American shredder operators.

Germany’s Steinert has introduced its NES 250, an eddy current separator with a working width of 98 inches. The 2.5-meter wide NES 250 eddy current separator offers an alternative to splitting material flows to two different eddy current separators with 1.25- or 1.5-meter working widths. Steinert estimates the machine can achieve a high throughput of nearly 130 cubic meters per hour.

In addition to offering increasingly large eddy currents, the same companies are also offering supplemental technologies involving induction sorting, X-ray alloy identification or the separation of increasingly smaller fragments to provide recyclers with a higher yield in terms of volume and purity.

For example, the Wendt Finder 2400 (German technology marketed in the U.S. by Wendt Corp., Tonawanda, N.Y.) is touted as being "designed to pick up where eddy currents leave off, recovering more stainless steel, copper windings, insulated and bare copper wire."

Northern Italy’s SGM (with U.S. offices in Sarasota, Fla.), in addition to offering eddy currents and induction sorters, has sold several DSRP units to shredder operators. The DSRPs are powerful traditional iron-attracting magnets that allow shredder operators to get the fines and other small pieces of steel scrap that may have otherwise slipped through.

Eriez Magnetics, Erie, Pa., has found success with its ProSort and FinesSort machines, which shredder operators use separately or in tandem to harvest a variety of metal pieces in sizes that are small individually—but that quickly add up to tons of saleable scrap material.