Conveyor belts can be equipped with Metal Detector.

A Metal Detector is a device that gives a signal (open or close a contact) when the magnetic field change because of some metals.

This means that in the area around it shouldn't be any metal, including the frame of the conveyor belt itself.

It can be mounted on flat, inclined conveyors with rubber or plastic bands.

When metal is detected, you should configure the electrical circuit in the way not only the conveyor on which the device is mounted stops, but all the machinery working before it should stop as well.

And for safety reasons, after the metal has been manually removed, the operator must push the reset button and re-start everything single machine.

As far as automatic metals removing, there are two way to get results.

First is the overband conveyor with a magnetic plate that will pick up carbon steel.

Second is the electrostatic separator that will make to jump all conductive metals (aluminum included).

Unfortunately this last one has little effect on small particles (because rejection is proportional to the mass) therefore small particles can be left into plastic flakes.