Magnetic elimination and surface treatment of NdFeB magnets after magnetization

NdFeB magnet is a kind of rare earth permanent magnet with small volume and high magnetic energy product, which is easy to be oxidized and magnetized in the production process. Due to the need to demagnetize and repair during demagnetization, the current demagnetization, hot bath demagnetization and other methods are commonly used. Current demagnetization, equipment investment is large, in demagnetization, magnets often need to be oriented arrangement, workload, low efficiency, and remanence. The existence of residual magnetism will lead to repair failure, which is shown in the following aspects: first, the magnetic products will absorb the small metal particles in the plating solution during the electroplating process, resulting in poor appearance; second, the magnetic products overlap each other in the electroplating process, which is difficult to open, resulting in uneven coating thickness, poor adhesion and even blistering; high temperature demagnetization is easy to oxidize, which needs to be protected in vacuum or inert gas The whole demagnetization process takes a long time and costs a lot. If the demagnetization method is used on the coated magnet, it will cause the coating discoloration, poor adhesion between the coating and the substrate and other defects, and it is difficult to repair. The demagnetization treatment needs to be carried out, which increases the cost and pollutes the environment. There are many ways of hot bath demagnetization because of different media, and oil bath demagnetization is one of them. Oil bath demagnetization is widely used because of its convenient material and simple process. After demagnetization in oil bath, it is difficult to deal with the oil collapse on the surface of the magnet, which brings great difficulty to the repair.
1422126715 - Magnetic elimination and surface treatment of NdFeB magnets after magnetization
In order to solve the problem that it is difficult to repair the surface of NdFeB magnet after demagnetization in oil bath, this paper provides a treatment method of NdFeB magnet after demagnetization. This method can be used to remove the surface of NdFeB magnet after demagnetization in oil bath and realize the repair. It includes the following steps:

  • (1) The demagnetized magnet after oil bath is quickly transferred into the container containing edible oil and cooled to below 220 ° C (that is, after repeated cooling treatment of edible oil and multi-stage cooling method, the temperature required by us can be quickly reached; the edible oil used can be salad oil, various kinds of edible blend oil and other oil products with low impurity content. The volume of salad oil in the container is based on the fact that the magnet is not exposed, so it can be put more, but not less; for the convenience of operation, when demagnetizing, we can use stainless steel wire mesh to make a mesh bag, and then put the magnet into the mesh bag).
  • (2) The magnet cooled in step (1) is transferred into a container containing diesel oil for cooling treatment to below 60 ° C (the method of multi-stage cooling can also be adopted, i.e. after several times of diesel oil cooling treatment);
  • (3) Remove the oil from the treated magnet in a high-temperature degreasing tank at 55-75 ° C for 40-80 minutes, and turn it every 15-20 minutes; then repeat this step at least once (the high-temperature degreasing method should be more than 2 levels, the temperature of the degreasing tank should be controlled at 60 ° C ± 5 ° C, and turn it gently every 20 minutes for each degreasing I · h). If the magnet degreasing temperature is 60 ° C, the treatment time is 60 minutes, and it is better to turn every 20 minutes. The temperature of the magnet when it is taken out of the diesel oil should be controlled below 60 ° C. We can adopt the multi-stage cooling method in step (2) to quickly reach the required temperature).
  • (4) Remove the magnet from the last high-temperature degreasing tank and rinse with water.
  • (5) Clean the washed magnet with ultrasonic wave (if the magnet after ultrasonic wave cleaning needs to be re plated, it can be activated, cleaned and then plated. If it does not need to be re plated, it can be directly cleaned and dried).

The water film on the surface of NdFeB magnet treated by this method is uniform and can pass through No. 30 The test of mixed solution for surface wetting tension test above 0 can effectively remove the oil film of magnet, greatly improve the hydrophilicity of magnet, and better realize the repair, which solves the problem of difficult repair caused by oil collapse on the surface of magnet after demagnetization in oil bath.

Source: China Permanent Magnet Manufacturer www.ymagnet.com

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