How to Judge the Quality of Sintered NdFeB Magnets?
Sintered NdFeB permanent magnets, as one of the important materials to promote modern technology and social progress, are widely used in the following fields: computer hard disk, magnetic resonance imaging, electric vehicle, wind power generation, industrial permanent magnet motor, consumer electronics (CD, DVD, cell phone, stereo, duplicator, scanner, camera, the refrigerator, TV sets, air conditioners, etc.) and magnetic machinery, magnetic levitation technology, magnetic drive and other industries. 
How to judge the product? The most comprehensive method of judgment: A, magnet performance; B, magnet size; C, magnet coating. First of all, the protection of magnet performance comes from the control of raw material production process. 1, according to the requirements of manufacturing high-grade or medium grade or low grade sintered NdFeB, enterprises should choose raw materials according to the national standards. 2, the production process directly determines the performance and quality of the magnet. At present, the most advanced technologies are scale ingot (SC) technology, HD technology and JM technology. The small capacity vacuum induction smelting furnace has been replaced by large capacity (100kg, 200kg, 600kg, 800kg) vacuum induction furnace. 3. On the orientation of the magnetic field, the orientation is formed by the vertical compression molding with the small pressure, and the quasi-isostatic pressing is used at the end. This is one of the most important features of the NdFeB industry. 4. Monitoring the quality of the production process is very important. It can be controlled by means of SC thickness measurement and JM particle size distribution. The customer can select the NdFeB brand according to the magnetite parameters Br (remanence), Hcb (coercive force), Hcj (intrinsic coercive force) and (BH) max (maximum magnetic energy product). At the same time, these four parameters are the criteria to determine whether the product is produced according to the customer's requirements. Secondly, the protection of magnet size depends on the processing strength of the factory. The shape of the NdFeB permanent magnet is varied, such as circular, cylindrical (with inner hole), square, square column, tile, fan, trapezoid, polygon, and various irregular shapes, etc. The permanent magnets of each shape have different sizes. 2, the surface of sintered NdFeB permanent magnet generally requires smooth and certain accuracy. The surface of the magnet for rough delivery needs surface grinding. The common grinding methods of square NdFeB permanent magnet alloys are planar grinding, double face grinding, internal grinding and cylindrical grinding. The cylinder is often used for noncore grinding and double end grinding. Tile, fan and VCM magnets are the multi-station grinder. Thirdly, the quality of the magnet coating directly determines the life of the product. 
In order to make NdFeB permanent magnet durable, it requires 20-30 years of service life, and it must withstand surface corrosion resistance, in order to resist corrosion of corrosion medium to magnets. At present, the manufacturing industry of sintered NdFeB permanent magnets generally adopts electroplating metal, electroplating + electroless metal, electrophoretic coating and phosphating treatment. A layer of additional isolation is deposited on the surface of the magnet to separate the surface of the magnet from the corrosive medium, so as to prevent the invasion of the magnet.
