Automatic magnetic projection for one-step separation of mixed plastics using ring magnets.

Magnetic projection, a novel separation method proposed recently, can separate multiple mixed materials in an efficient and low-cost way. Although promising, existing magnetic projection method cannot achieve the automatic feeding of mixed materials, which limits its applications. To address this challenge, ring magnets were used to replace conventional square magnets in this research. Specifically, a mixture of particles with different densities were fed through the hole of ring magnets and then projected to the corresponding area. Moreover, to increase the magnetic field strength, magnets were superimposed. To predict the projection process, magnetic field analysis was conducted. And from the results, an interesting trap area was found, where the separated materials may be constrained, leading to the failure of projection. The simulation of the projection process revealed that with the increase of the number of magnets (1-3 magnets), the magnetic field strength increased. However, the projection distance will not keep increasing with the increase of the magnetic field strength, which also was verified by experiments (Err within 10%). Based on this principle, an automatic feeding device with ring track and pendulum was designed and manufactured. In the separation experiment, six different plastics, that were PP, ABS, PC, PLA, PET and PVC, were used to verify the separation effect. The experimental results showed that the proposed method can automatically separate a plastic mixture with a recovery rate of over 95%. This study presents a break-through in magnetic projection, laying the foundation for the practical application of magnetic projection.