Eddy current vs. magnetic separation: what each actually removes
Both machines sit in the sorting stage of a recycling line, and both are often described as "metal separators". They separate completely different things. Confusing them is one of the most expensive mistakes in line design, because the machine you leave out is the one holding your non-ferrous revenue.
Magnetic separation removes ferrous only
Overband magnets, drum magnets and pulley magnets attract iron and steel. They do nothing for aluminium, copper, brass, zinc or stainless steel — the last of which is a common surprise, since stainless is largely non-magnetic.
The job of the magnet is to take ferrous out early, before it reaches equipment that would be damaged or blinded by it. In a shredder line, that usually means a magnet directly after the shredder.
Eddy current separation removes non-ferrous
An eddy current separator uses a fast-rotating magnetic rotor to induce currents in conductive particles, which generates a repulsive force. Aluminium, copper, brass and zinc are thrown on a different trajectory from plastic, glass, rubber and stone.
Rotor speed is the critical variable. High-frequency designs running at 3,000–4,500 rpm hold separation down to roughly 3 mm particles; older low-frequency units lose the fine fraction to the waste stream, which is exactly where a lot of the value sits.
Order matters: magnet first, eddy current second
Eddy current separation works best on a ferrous-free stream. Large ferrous pieces in the feed disturb the belt, can damage the belt surface and reduce separation accuracy on the material you actually care about. Run the magnet first.
Screening between the two stages is equally important. An eddy current separator performs very differently on a 5–60 mm band than on a mixed stream containing both fines and oversize.
Where recovery actually gets lost
The usual losses are not in the machines but in the flow: mixed particle sizes reaching the separator, insufficient belt speed adjustment for the material, and a splitter plate set once and never revisited. Separation efficiency above 99% for aluminium is achievable on prepared feed — and much lower on unprepared feed.
This is why a material test before purchase is worth more than any specification comparison. Send the actual material, get the actual result.
What to take away
- Magnets remove ferrous; eddy current separators remove non-ferrous. Stainless typically behaves as non-magnetic.
- Always run magnetic separation upstream of eddy current separation.
- Screen before sorting — eddy current performance collapses on badly graded feed.
- Ask for a test on your own material instead of comparing datasheet efficiency figures.
Written by the Miracle Machinery engineering team. Figures quoted are from published equipment specifications; project-specific results are confirmed by material test.