Sintered ndfeb Permanent magnets, as promoting the advancement of modern technology and society is one of the important material, widely used in the following areas: computer hard drives, nuclear magnetic resonance imaging (fmri) permanent magnet motor, electric cars, wind power generation, industry, consumer electronics (CD, DVD, mobile phones, audio, duplicator, scanners, cameras, camera, fridge, TV, air conditioning, etc.) and the magnetic force, magnetic levitation, magnetic mechanical transmission industry.
Since 1985, it has been industrialized in Japan, China, Europe and The United States simultaneously. In the past 30 years, the global permanent magnet material industry has been developing rapidly, with continuous record breaking magnetic properties and increasing material varieties and brands. With the expansion of the market, its manufacturers are also increasing, and many customers are inevitably trapped in such confusion, how to judge the pros and cons of the product?
The most comprehensive judgment method: 1. 2. Magnet size; Three, magnet coating.
First of all, the guarantee of magnet performance comes from the control of the raw material production process
1. According to the requirements of manufacturing high-grade, intermediate or low-grade sintered Ndfeb, choose and purchase raw materials according to the raw material composition stipulated by national standards.
2. The performance and quality of the magnet are directly determined by the advanced production technology. The most advanced technologies are scale ingot (SC) technology, hydrogen crushing (HD) technology and air flow grinding (JM) technology. Small capacity vacuum induction furnace (10kg, 25kg, 50kg) has been replaced by large capacity (100kg, 200kg, 600kg, 800kg) vacuum induction furnace. StripCasting fast casting technology has gradually replaced large ingot (ingot with cooling thickness greater than 20-40mm), hydrogen crushing (HD) technology and air flow grinding (JM) have replaced jaw crusher, disc mill and ball mill (wet powder) to ensure the uniformity of powder and facilitate liquid phase sintering and grain refinement.
3. In terms of magnetic field orientation, China is the only country in the world that adopts two-step pressing molding. In the orientation, it adopts small pressure vertical molding and finally adopts quasi-isostatic pressing molding, which is one of the most important characteristics of China's sintered Ndfeb industry.
4. Moreover, it is very important to monitor the quality of the production process, which can be controlled by measuring the thickness of SC slices and the size distribution of JM powder particles. The quality of the product depends on the control of the production process, but the customer must be very confused, how to judge the performance of the product I bought? The Chinese Academy of Metrology has developed various types of magnetic parameters measuring instruments for permanent magnet materials. Pulsed magnetic field magnetometer (PFM) is a test instrument for testing ultra-high coerced permanent magnets, which are mainly used in the field of electric vehicles and large permanent magnet motors.
The customer can select the NdFeb brand he needs according to the magnet parameters Br (remanence), Hcb(coercivity), Hcj(intrinsic coercivity) and (BH) Max (maximum magnetic energy product). At the same time, these four parameters are the standards to determine whether the product is produced according to the customer's requirements.
Secondly, the guarantee of magnet size depends on the processing strength of the factory
The actual shape of ndFeb permanent magnet is various, such as disc, cylinder, cylinder (with inner hole). Square piece, square piece, square column; Tile, sector, trapezoid, polygon and various irregular shapes, etc. Permanent magnets of each shape come in different sizes, making it difficult to be molded once in the production process. The general production process is as follows: the bulk (large size) blank is produced, sintered and tempered, and then machined (including cutting, punching) and ground, surface coating (coating) treatment, and then the performance, surface quality and dimensional accuracy of the magnet is tested, and then magnetization, packaging and delivery.
1. Mechanical processing is divided into three categories:
(1) Cutting: Cut cylindrical and square cylindrical magnets into circular and square sheets;
(2) Shape processing: Round or square magnets are processed into fan shaped, tile shaped, fluted or other complex shapes;
(3) Punch processing: Round bar and square Bar magnets are processed into cylindrical or square barrel magnets. Its processing methods are: grinding chip processing, edM cutting processing and laser processing.
2. The surface of sintered Ndfeb permanent magnetic element is generally required to be smooth and reach a certain precision. The surface of the magnet delivered by blank shall be ground. The common grinding methods of square NdFeb permanent magnetic alloy include plane grinding, double end grinding, inner round grinding, outer round grinding and so on. Cylinder is commonly used without core grinding, double end face grinding and so on. Tile, sector and VCM magnets are multi-station grinders.
Whether a magnet is qualified or not not only needs to meet the standard of performance, but also the control of dimensional tolerance directly affects its application. The guarantee of size directly depends on the processing strength of the factory, processing equipment is constantly updated with the economic and market demand, more efficient equipment and the trend of industrial automation, not only to meet customers' increasing demand for product precision, but also save labor and cost, making it more competitive in the market.
Thirdly, the quality of the electromagnet coating directly determines the service life of the product
The experiment shows that the 1cm3 sintered NdFeb permanent magnet will be completely corroded by oxidation after being kept in the air at 150℃ for 51 days. It's more susceptible to corrosion in a weak acid solution. In order to make the NdFeb permanent magnet durable, it is required to have a 20-30 year service life. It must be subjected to surface corrosion treatment, so as to resist the corrosion of corrosive media on the magnet. At present, the manufacturing industry of sintered NdFeb permanent magnet system generally adopts the methods of electroplating metal, electroplating + chemical gold plating, electrophoresis coating and phosphating treatment, etc., to coat the surface of the magnet with an additional layer of isolating material, separating the surface of the magnet from the corrosive medium, so as to prevent the medium from harming the magnet.
1, generally to galvanized, nickel + copper + nickel, nickel + copper + electroless nickel plating three processes, other metal plating requirements, generally in nickel plating and then applied to other metal plating.
2. Phosphating will also be used in some special circumstances :(1) it is easy to use phosphating when the NdFeB Magnet product has been kept for a long time due to turnover and is not clear about the subsequent surface treatment; (2) When the magnet needs to be bonded with epoxy glue and paint, the bonding force of epoxy organic matter, such as glue and paint, requires the matrix to have good wetting performance. The phosphating process can improve the wetting ability of the magnet surface.
3. Electrophoretic coating has become one of the widely used anti-corrosion surface treatment technologies. It not only has good adhesion with the surface of the porous magnet, but also has corrosion resistance such as salt spray, acid and alkali resistance and excellent corrosion resistance. However, compared with spray coating, its resistance to heat and humidity is poor.
Customers may choose coatings according to their product work requirements. With the expansion of the field of motor application, customers on ndFeb corrosion resistance has higher requirements. So there's the PCT experiment, where you could specifically test for corrosion resistance of sintered NdFeb permanent magnets up to moisture and heat.
And how does the customer determine whether the coating meets the requirements? The purpose of the salt spray test is to do a rapid anticorrosion test on the sintered NdFe-B magnet whose surface has been treated with anticorrosive coating. At the end of the test, the sample is taken out of the test box and dried, and the color change of the box with eyes or magnifying glass to observe whether the sample has spots on the surface and the area of spots.
To sum up, only when customers understand the production process and the requirements of the product, can they correctly judge the conformity of the product. In a nutshell, it is to grasp the performance, dimensional tolerance control, coating detection and appearance evaluation.
In terms of performance, its Br (remanence), Hcb(coercivity), Hcj(intrinsic coercivity), (BH) Max (maximum magnetic energy product) and demagnetization curve can be detected by the performance. Dimension tolerance, the accuracy can be measured by vernier caliper; On the coating, the color and brightness of the coating can be observed by naked eye, and the coating can be detected by binding force, salt spray test and other methods. The overall appearance, mainly with the naked eye or magnifying glass, or optical microscope (for products with a linear degree less than 0.2mm), the magnet surface is clean, there are no visible particles and foreign bodies, no spots, no edges and corners, and the appearance is qualified.