A kind of preparation method of bulk neodymium iron boron

Abstract

The invention relates to a preparation method for chunk neodymium iron boron. The preparation method is characterized by comprising the steps of designing multiple convex points which are distributed in a central symmetry manner on an upper pressing surface of a pressing blank during designing the pressing blank of a chunk magnet; designing concave points, corresponding to the convex points designed on the upper pressing surface of the pressing blank, on a surface, corresponding to the upper pressing surface of the pressing blank, of a die when the die is designed; installing the die, and completing powder weighing, pressing, packaging and isostatic pressing to obtain the pressing blank which can be put into a sintering furnace; and enabling the surface, having the convex points, of the pressing blank to be in contact with a sintering basin, forming an interval between the magnet and the sintering basin, and completing sintering. The preparation method has the advantages as follows: by increasing the convex points on the surface of the chunk magnet, the friction force between the magnet and the sintering basin is reduced in the sintering process, and the magnet deformation is lowered; and meanwhile, smooth degasification of the magnet in the sintering process is realized, so that carbon and hydrogen contents in the magnet are reduced, thereby improving the brittleness and magnetic property of the magnet.

Description

technical field [0001] The invention relates to a bulk NdFeB preparation method capable of reducing the deformation of sintered NdFeB large-scale magnets and improving the consistency of magnetic properties of the large-scale magnets, belonging to the technical field of preparation methods for sintered NdFeB magnets. Background technique [0002] Sintered NdFeB magnets are the most powerful permanent magnets in contemporary times. They not only have the advantages of high magnetic energy product and high cost performance, but also can be easily processed into various sizes. In the 21st century, the rare earth permanent magnet material industry has become one of the most strategic emerging industries with special resources in China. It has attracted market attention in the three fields of energy conservation and environmental protection, wind power generation, and new energy vehicles. develop. The domestic rare earth permanent magnet material industry represented by sintered...

AI Technical Summary

Problems solved by technology

On the side where the magnet is in contact with the graphite basin, due to the close contact with each other, the volatilization of the rare earth components of NdFeB is aggravated, resulting in the loss of rare earth components on the surface of the magnet, thus affecting the consistency of the magnetic properties of the magnet;

[0012] 5. Since the lubricants and antioxidants added in the NdFeB powder making process need to be released during the sintering process, if the space is limited during the gas discharge process, especially when the basin surface is pasted, the gas release channel will be blocked. Blockage, resulting in a lot of residual gas near this part. After sintering, the surface of the magnet attached to the basin shows a high content of carbon and hydrogen, which in turn leads to differences in magnetic properties and material brittleness, resulting in poor performance consistency of various parts of the large sintered magnet.

[0014] 1. The way to solve defects such as corner strain, missing corners and corner cracks in the magnet sintering process is to increase the density of the compact. At present, the density of the formed compact is 3.8-4.0g / cm³, in order to reduce the magnetization orientation caused by the forming. In order to reduce the deformation of the compact, it is necessary to increase the density of the compact to above 4.5 g / cm³ in the forming stage to reduce the deformation of the compact. It is extremely difficult to achieve 4.5 g / cm³, especially for large magnets;

[0015] 2. To reduce the trapezoidal deformation of the magnet, a round rod can be placed at the bottom of the compact to assist the compact to shrink, but this method is time-consuming and laborious, and the production efficiency is low, so it is difficult to implement in mass production;

The internal stress of the green compact before sintering is produced during the pressing process of the green compact. The reduction or elimination of the internal stress needs to be achieved through the improvement of the forming press. However, there are some technical bottlenecks in the improvement of the forming press at present, and it is temporarily difficult to achieve; sintering The shrinkage of the compact during the process will release the internal stress. If the compact is not restricted by external force and allowed to shrink freely, it will cause the problem of bending deformation of the magnet after sintering. However, if you want to apply an external force to the compact during the sintering process, There is currently no suitable solution to achieve it;

[0017] 4. The loss of rare earth on the surface of the magnet attached to the basin causes the problem of poor performance consistency. The current solution is to place an iron plate or molybdenum plate at the bottom of the sintered basin to reduce the loss of rare earth on the surface of the magnet attached to the basin. However, due to the repeated use of the iron plate and molybdenum plate, The iron plate and molybdenum plate will adhere to many impurities, which will also affect the performance of the magnet on the surface of the basin;

[0018] 5. In order to completely remove the hydrogen and various additives in the compact during sintering, it can be improved by prolonging the sintering degassing time, or the compact can be sintered overhead so that all six sides of it can participate in degassing, but currently there is no There is no suitable sintering pot structure to realize the overhead of the green compact. Even if the overhead is achieved, new magnet deformation problems will be caused by too few or inappropriate support points

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