In the past 30 years, the global permanent magnet material industry has developed vigorously, and the magnetic properties have continued to set new records, and the variety and grade of materials have been increasing. With the expansion of the market, its manufacturers are also increasing, and many customers are inevitably caught in such confusion, how to judge the advantages and disadvantages of products?
The most comprehensive judgment method:
Magnet performance
First of all, the guarantee of magnet performance comes from the control of the raw material production process.
1. According to the requirements of enterprises to manufacture high-grade or mid-range or low-grade sintered NdFeB, raw materials are purchased in accordance with the raw material composition specified in national standards.
2. Magnetic field orientation, China is the only country in the world that adopts two-step pressing molding, vertical molding with small pressure during orientation, and finally quasi-isostatic pressing molding, which is one of the characteristics of China's sintered NdFeB industry.
3. Moreover, the monitoring of the quality of the production process is very important, which can be controlled by SC sheet thickness measurement and JM powder particle size distribution. The products depend on the control of the production process, but the customer will be very confused, how to judge the performance of the product I purchased? The Institute of Metrology has successively developed a variety of models of permanent magnet material technology magnetic parameter measuring instruments. Pulsed magnetic field magnetometer (PFM) is a test instrument for testing ultra-high coercivity permanent magnets, mainly to adapt to the high coercivity permanent magnets required by the electric vehicle field and large permanent magnet motors.
Customers can select the NdFeB grade they need according to the magnet parameters Br (residual magnetism), Hcb (coercivity), Hcj (internal coercivity), (BH)max (maximum magnetic energy product), and these four parameters are to determine whether the product is produced in accordance with the customer's requirements.
The size of the magnet
Secondly, the guarantee of magnet size depends on the processing strength of the factory The shape of NdFeB permanent magnets for practical applications is diverse, such as disc, cylindrical, cylindrical (with inner hole); squares, squares, square columns; Tile, fan, trapezoidal, polygonal and various irregular shapes, etc. Each shape of permanent magnet has different sizes, and it is difficult to mold it in one go.
The general production process is: Mr. produces large (large size) blanks, after sintering and tempering treatment, and then through mechanical processing (including cutting, punching) and grinding, surface coating treatment, and then magnet performance, surface quality and dimensional accuracy testing, and then magnetizing, packaging and shipping.
1. Machining is divided into three categories:
(1) Cutting processing: cutting cylindrical and square cylindrical magnets into round sheets and square sheets;
(2) Shape processing: processing round and square magnets into sector-shaped, tile-shaped magnets or magnets with grooves or other complex shapes;
(3) Drilling processing: processing round rods and square rod-shaped magnets into cylindrical or square cylindrical magnets. Its processing methods are: grinding and slicing processing, EDM processing and laser processing.
2. The surface of sintered NdFeB permanent magnet elements is generally required to be smooth and achieve a certain accuracy, and the surface of the magnet delivered by the blank needs to be surface grinded. The commonly used grinding methods of square NdFeB permanent magnet alloy include plane grinding, double-end face grinding, internal cylindrical grinding, external cylindrical grinding, etc. Cylindrical commonly used coreless mill, double-end face mill, etc. Tile, sector and VCM magnets are used with multi-station grinding machines.
Whether a qualified magnet not only needs to meet the performance standard, but also the control of dimensional tolerances directly affects its application. The guarantee of size directly depends on the processing strength of the factory, processing equipment with the economy and market demand is also constantly updated, more efficient equipment and the trend of industrial automation, not only to meet the growing demand of customers for product accuracy, but also to save labor and costs, making it more competitive in the market.
Magnet plating
Thirdly, the quality of the magnet coating directly determines the application life of the product Experiments have shown that 1cm3 sintered NdFeB permanent magnets stay in air at 150 °C for 51 days, and will all be oxidized and corroded. In weak acid solutions it is more susceptible to corrosion. In order to make the NdFeB permanent magnet durable, it is required to have a service life of 20-30 years, and it must withstand surface corrosion resistance treatment to resist the corrosion of the magnet by the corrosive medium. At present, the sintered NdFeB permanent magnet manufacturing industry generally adopts electroplating metal, electroplating + electroless plating metal, electrophoretic coating and phosphating treatment, etc., and plates an additional isolation on the surface of the magnet to isolate the magnet surface from the corrosive medium to prevent the medium from attacking the magnet.
1, generally zinc plating, nickel plating + copper + nickel, nickel plating + copper + electroless nickel plating three processes are the mainstay, other metal plating requirements, generally after nickel plating and then apply other metal electroplating.
2, in some special cases will also use phosphating: (1) when the NdFeB magnet product is too long due to the turnover and storage time and the subsequent surface treatment method is not clear, the use of phosphating is simple and easy; (2) When the magnet needs epoxy adhesive bonding, painting, etc., the adhesion of epoxy organic matter such as glue and paint requires the matrix to have good wettability performance. The phosphating process improves the aggressiveness of the magnet surface.
And how can customers judge whether the plating meets the requirements? The purpose of salt spray experiment is to do a rapid anti-corrosion test on the surface of the sintered NdFeB magnet treated by anti-corrosion coating, at the end of the experiment, the sample is taken out of the test chamber, dry, with eyes or magnifying glass to observe whether there are spots on the surface of the sample, the size of the spot area of the box color changes. In summary, customers can only correctly judge the qualification of products if they understand their production process and understand the requirements of the products.
To sum up, it is the grasp of performance, the control of dimensional tolerances, the inspection of coatings and the evaluation of appearance. In terms of performance.
