Eddy current sorting is a sorting technique that utilizes different conductivity of materials. Its sorting principle is based on two important physical phenomena: an alternating magnetic field that changes over time is always accompanied by an alternating electric field (electromagnetic induction law); A current carrying conductor generates a magnetic field (Biot Savart's law). The principle of eddy current separation is shown in Figure 1.

Figure 1 Principle of Eddy Current Separation

The magnetic cylinder embedded with permanent magnets rotates at high speed, generating an alternating magnetic field. When a metal with conductive properties passes through the magnetic field, eddy current will be generated inside the metal. The eddy current itself generates an alternating magnetic field, which is opposite to the direction of the magnetic field generated by the magnetic cylinder, producing a repulsive force (Lorentz force) on the metal, separating it from the material flow and achieving the purpose of sorting.

The linear motor type eddy current sorting machine is a linear motor when the cage induction motor is cut along the axial direction and unfolded into a plane shape. A linear motor generates a linear force under the action of electromagnetism and current. The aluminum sheet placed on the plane of the linear motor moves in the direction of electromagnetic field force. When using a vibrating feeder or belt conveyor to feed in the direction perpendicular to the linear motor, the aluminum sheets in the material undergo biased movement, causing them to separate. The inclined eddy current sorting machine in the permanent magnet eddy current sorting machine is a permanent magnet arranged alternately in N and S stages embedded at a certain angle on the inclined plate. During the sliding process of the aluminum sheet fed into the material from the upper part of the inclined plate, the magnetic force generated by eddy current changes the direction of movement, allowing it to separate. In addition, permanent magnet eddy current sorting machines also have eddy current sorting machines that install a rotating permanent magnet system on the outer side of the cylinder or a rotating disk embedded in the permanent magnet on the feeding belt. The structure of the cylindrical eddy current separator is basically the same as that of the cylindrical magnetic separator. When the rotation direction of the electromagnetic or permanent magnetic system inside the rotating cylinder is consistent with the rotation direction of the cylinder, the aluminum sheets in the material sent to the surface of the cylinder fly away from the cylinder under the action of magnetic force, thus separating them from the waste. Sometimes the magnetic poles can also use alternating magnetic fields.