New line helps plastic recycler to minimise contamination

A UK plastic recycler has installed a solution to separate ferrous and non-ferrous metal from plastic flake. The Metal Separation Module from machinery provider Bunting features vibratory feeders, a drum magnet and an eddy current separator (ESC).

The successful recycling of plastic waste is often hindered by the presence of contamination including ferrous and non-ferrous metals. In this project, the plastic recycler approached Bunting to address the issue of metal contamination in <20mm plastic flake.

First step: material testing

Initially, the recycler undertook extensive material tests at Bunting’s Customer Experience Centre in Redditch, UK. These tests identified the best model of ECS for the project and confirmed operating parameters including the throughput per metre width.

The Metal Separation Module acquired for the project includes a high-strength rare earth drum magnet followed by an eccentric-rotor ECS. 

Controlled flow

In operation, a vibratory feeder presents a controlled and regulated flow of plastic flake feeds onto the drum magnet which has a stationary, permanent rare earth magnet element mounted inside a rotating stainless-steel shell. Plastic flake flows onto the rotating shell, with ferrous metal and magnetic materials being held to the surface and then deposited below the material flow. The high-strength element enables the separation of both large and small magnetic particles.

Magnetic forces

The plastic flake then flows onto the belt of the ECS and is conveyed onto the head-pulley separation zone. The separator utilises magnetic forces to physically repel non-ferrous metals and enables separation from non-conductive materials. The ECS is a dual pulley conveyor system in which the non-metallic rotor cover houses an independently rotating high-speed magnetic rotor. 

Separation occurs when a non-ferrous metal particle such as aluminium, copper or zinc is conveyed into the magnetic zone. The non-ferrous metal particle is exposed to rapidly changing magnetic polarity. This induces ‘eddy currents’ into the particle generating an electrical current (Fleming’s left-hand rule) that subsequently creates its own magnetic field. The two magnetic fields oppose each other (i.e. North vs North pole), causing the repulsion of the non-ferrous metal particle and change in trajectory. The measured positioning of a splitter enables the separation of non-ferrous metals from other non-metallic material due to the altered and unaltered material trajectories.

The material tests had determined that the eccentric-rotor design gave the best non-ferrous metal separation. In the eccentric-rotor ECS, the smaller-diameter rotor is mounted off-centre inside a non-metallic shell.

To meet the capacity demands of the recycler for two tonnes per hour, the feed widths of both the drum and the ECS are set at 1 250mm. All the equipment is mounted on a common frame with a single control panel.

Addressing plastic waste

‘The tests at our centre allowed us to demonstrate the separation capabilities and operational parameters,’ says Bradley Greenwood, Bunting’s sales manager, Europe. ‘This is another exciting project where our separation equipment is helping address the issue of plastic waste.’

Bunting designs and manufactures magnetic separators, ESCs, metal detectors and electrostatic separators. Its European manufacturing facilities are in Redditch, just outside Birmingham, and Berkhamsted, both in the United Kingdom.