In the recycling business, separating non-ferrous metals by hand can be tedious work and much can be missed by human error. Eddy current systems can help attain purity in recovered product.
The use of eddy current separators in recycling started in the 1990s, while eddy current devices have actually been around for over 100 years. Thomas Edison, with his partner H.S. Makim, had the first patent issued on an eddy current devise in 1889.
In 1969, Eriez Magnetics patented its first eddy current separator, according to company literature. Al Gedgaudas, Eriez manager of recycling equipment, said the use of eddy current for recycling took off in the 1990s in the United States and sometime before that in Europe.
An eddy current actually repels the non-ferrous metals and throws them from the rest of the scrap from which it is being separated. A thin layer of scrap pieces on a conveyor is run over an eddy current rotor. The spinning of the eddy current rotor creates a field of energy around non-ferrous items and these items are repelled from the rest of the scrap.
Mr. Gedgaudas described the repulsion as the same as when a person has two magnets and as the magnets are brought together they actually push away from each other. The energy field around the non-ferrous material gives the material a charge the same as the magnet which pushes them away from each other.
Todd Guagliardo of Dings Company, referring to aluminum can separation, said, "the repulsion throws the aluminum out of the stream. It looks like it just flies."
At the end of the eddy current is a splitter that sends the non-ferrous material into one bin as it is thrown. The other material falls into another bin. How far the non-ferrous material falls from the eddy current depends on two things- the surface area of the material and the density of the material.
Don Morgan of O.S. Walker Company, said, "a small piece of aluminum may be thrown as far as a large piece of stainless steel. Both the conductivity and density of the particle, as well as its shape and size influence the separation."
Mr. Morgan explained how three different shapes of aluminum cans can go different distances. "There are really three configurations to the aluminum can that most aluminum recyclers handle. The first is the whole aluminum can, uncrushed. The second is a flattened aluminum can and the third is the 'hockey puck' where a can is pushed down vertically. A whole aluminum can has a low density but a large surface area; the flattened has less surface area, but the same density and the hockey puck has a much smaller surface area, but a much higher density," he said.
"Because of the large surface area and low density, the whole aluminum can will travel farther. The flattened can will not travel as far because there is less surface area to create the energy force. A hockey puck, with less surface area and a higher density will travel the least distance away from the eddy current," he said.
Similarly, copper and other non-ferrous metals have a higher density than aluminum and will react much like the "hockey puck" in the previous situation.
Particle size can matter, since the eddy current depends on surface area. Mr. Morgan said pieces of scrap that are a half-inch in size or larger work best.
The material used in most eddy current systems is called rare earth magnetics. Ceramic is another common material that can create an eddy current field.
Mr. Gedgaudas said, "rare earth is the 'catch phrase' in the eddy current industry. Everyone wants the rare earth. Rare earth has a stronger field than ceramics do.
Mr. Gaudliardo said, "Ceramics are made to pick up large size objects. It has a large depth of field, but it is not as strong as rare earth. Rare earth on the other hand does not have as high a depth of field."
Most producers of eddy current separators say ceramics are good for aluminum can separation. Mr. Gedgaudas added, "a well-designed ferrite magnet, though, will work better than a poorly designed rare earth magnet."
Most eddy current systems are part of a larger conveyor system and vibrators that remove ferrous material and spread out remaining material into a thin layer.
Marshall Gralnick, owner of Global Equipment Marketing, stressed that it is important to remove ferrous materials before they reach the eddy current.
"Too much ferrous material can cause a melt down in the eddy current rotor and that is the expensive part of the system," he said.
Mr. Gedgaudas added that the eddy current head will hold on to ferrous material and that if a piece falls into the eddy current rotor it needs to be removed before it has a chance to melt into the magnet.
The importance of a thin layer of material was another point that Mr. Gralnick and Mr. Gedgaudas made.
Mr. Gralnick said, "If you have a thick layer of material, it is not going to work very well. You need to have a very thin layer. The material on top might not get separated if the volume going over the eddy current is too large."
Eddy current separators can be used for a wide range of recycling separation. The separators can be used in electronics, plastics, auto and white goods shredding, foundry sand, material recovery facilities, wood waste, glass cullet, medical waste, and so on.
In plastics recycling, an eddy current will help pull out any non-ferrous material, such as aluminum caps and rings from a PET bottle. Auto and white goods fluff run over the eddy current will pull out non-ferrous material. Shredded computer items can be run over for aluminum, gold, and silver (if the precious metal isn't held down in other components). Wood waste can contain stainless steel and aluminum conduits. Wood can also contain ferrous metal that needs to be removed with a magnet. Material recovery facilities can use these for the different materials they receive and recycle.
Mr. Morgan said, "We see a lot of material recovery facilities that had opened and used hand-sorting for the materials. Many are now getting separators. They are great in those situations and it gives them automation for some of the steps.
" Mr. Gralnick said he has seen an increase in the number of electronic recycling facilities looking into purchasing eddy current systems.
There is a wide range of sizes and prices of these systems. Average prices range from $30,000 to $100,000 for complete systems with conveyors, splitters, vibrators and so on. Some manufacturers offer complete systems while others provide certain parts directly to recyclers or to other equipment manufacturers who then offer turnkey separation systems to recyclers.