Eddy current separator (eddy current separator)

An eddy current separator (ECS) ejects non-ferrous metals — aluminium, copper, brass, zinc — from a conveyor stream by inducing repulsive eddy currents in conductive fragments. It is the single most important machine for monetising e-waste and shredded WEEE plastics, since non-ferrous metal recovery often accounts for 35-55% of plant revenue.

The mechanism is electromagnetic induction. A high-speed rotor (typically 3,000-3,600 RPM) fitted with alternating-pole rare-earth magnets (neodymium-iron-boron, Nd2Fe14B) spins inside a non-magnetic drum at the discharge end of a conveyor. As conductive fragments cross the rapidly alternating field, circulating eddy currents are induced inside them, which interact with the rotor's field to generate a repulsive Lorentz force. The fragments launch forward off the belt while non-conductive material (plastic, glass, rubber) and ferrous residue drop vertically. A splitter divides the two streams.

Performance depends on three variables. Particle size — ECS works best on fragments 5-50 mm; below 5 mm, surface-to-mass ratio collapses the launch distance, and fines must be routed to fine-ECS units or wet density separation. Conductivity-to-density ratio (σ/ρ) — aluminium (3.5) ejects strongly, copper (6.5) ejects further, lead (0.4) barely moves. Belt speed and depth — single-layer feed on a 1.5-2.5 m/s belt is mandatory for clean separation.

Two rotor designs exist. Concentric rotors are cheaper, simpler, suited to coarse aluminium (UBC, cast). Eccentric rotors shift the magnet pack to the discharge side, keeping ferrous contaminants from being heated, sticking or burning out the bearings — essential for mixed e-waste with residual steel. Pre-treatment with a magnetic drum separator upstream is mandatory; tramp iron destroys ECS belts and overheats bearings within hours. Capital cost runs Rs 25-65 lakh for a 600-1,500 mm unit; operating cost is modest (4-12 kWh per tonne) but belt life (12-30 months) and rotor magnet integrity are the recurring expenses.