The third process of the neodymium magnet production process: airflow mill

The air-milling technology of NdFeB magnets has been popularized and promoted for many years in the milling process of magnetic materials. With the maturity of NdFeB belts and hydrogen crushing processes, new energy-saving and more efficient airflow mills Gradually developed and utilized.

The jet mill used in the neodymium iron boron magnet is a circulating tube type jet mill, which is composed of a jet mill and a cyclone separator, a dust collector and an induced draft fan. After the compressed air is filtered and dried, it is sprayed into the crushing chamber at high speed through the Laval nozzle. At the intersection of the multiple high-pressure air streams, the material is repeatedly collided, rubbed, sheared and crushed, and the crushed material rises under the action of the fan. The airflow moves to the classification zone, and the coarse and fine materials are separated under the strong centrifugal force generated by the high-speed rotating classification turbine. The fine particles meeting the particle size requirements are collected by the classification wheel into the cyclone separator and the dust collector, and the coarse particles are lowered to the crushing zone to continue to be crushed. . In combination with the characteristics that the rare earth magnetic material is easy to oxidize and the granularity is fine, the whole process uses nitrogen as the power flow, and the return gas is compressed by the compressor to form a closed loop by the pipeline.

At present, most NdFeB producers use enamel strips and hydrogen crushing technology. The ruthenium strips after hydrogen pulverization become very loose, and are directly subjected to jet milling after being crushed by hydrogen. Not only the discharge speed is increased, but also the NdFeB magnetic powder can be ground finer, which can reach 2.8-3.5 micrometers, so that the magnet crystal grains can reach 10 micrometers or less, and the grain size can be increased to increase the coercive force of the magnet. Improve the corrosion resistance of the magnet. At present, many companies in the first line have been able to develop more efficient high-power airflow grinding equipment suitable for crushing hydrogen. The hourly powder may reach 150-200 kg or even higher. This kind of jet mill uses high-power frequency conversion. Screw compressors, precise automatic nitrogen supplementation technology, make equipment operation more reliable and stable, and save production costs as much as possible.

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