Edited by Leslie Gordon
Magnetic separators from Eriez, Erie, Pa., use ceramic or AlNiCo magnets and an electric circuit to generate magnetic fields that remove tramp iron from lines processing powdery bulk materials such as plastics, abrasives, or glass cullet.
The company also makes drum separators that use its proprietary Erium 3000 rare-earth (RE) permanent magnets. In these magnets, the lines of flux concentrate in each internal pole, creating a high–gradient magnetic field. According to the company, Erium 3000 generates magnetic fields up to 25 times stronger than conventional ceramic or AlNiCo units — with no increase in size. The magnets grip contaminants so tightly that wipe-off caused by product flow is almost eliminated.
The RE magnets remove exceedingly fine iron particles, which are difficult to attract and hold because of their small mass. They also separate out weakly magnetic particles such as rust or iron oxide, which are not strongly attracted to conventional ferrite magnets, as well as stainless-steel particles rendered paramagnetic through work hardening.
Separators with RE magnets work like this: As the material to be cleaned goes into the rotating drum, the magnetic field attracts and holds ferrous particles to the drum shell. Cleaned, nonmagnetic materials fall freely into a chute, while ferrous particles stick to the drum until its rotation carries them past the magnetic field, where they fall into another chute to be dumped or sold as scrap.
All RE magnets are not created equal, according to Eriez. It conducted studies of RE compounds and magnetic circuits, which showed that some were only slightly better than ferrite-ceramic magnetic circuits, while others were much stronger. The research led to the development of Erium 3000.
REs’ magnetic strength falls in the medium-intensity range — 4,000 to 10,000 gauss. Previously, it took high-intensity electromagnets to generate fields this strong. But high-intensity electromagnets are bulky, expensive, and costly to operate. RE magnets economically fill the gap between high-intensity electromagnets and low-intensity conventional magnets.