Sintered Ndfeb permanent magnets, as one of the important substances to promote the progress of contemporary technology and society, are widely used in the following fields: Computer HARD disk, nuclear MAGNETIC resonance imaging, electric vehicles, wind power generation, industrial permanent magnet motor, consumer electronics (CD, DVD, mobile phone, audio, photocopier, scanner, camera, camera, refrigerator, television, air conditioner, etc.) and magnetic machinery, magnetic levitation technology, magnetic transmission and other industries.

Since its industrialization began in Japan, China, Europe and the United States at the same time in 1985, the global permanent magnet material industry has been booming in the past 30 years, and the magnetic properties have continuously set new records, and the types and brands of materials have been increasing. With the expansion of the market, its manufacturers are also increasing, and many customers are inevitably in such confusion, how to judge the merits of the product?

The most comprehensive judgment method: one, magnet performance; Two, magnet size; Three, magnet coating.

First of all, the guarantee of magnet performance comes from the control of raw material production process

1, according to the enterprise manufacturing high-grade or middle or low grade sintered Ndfeb requirements, according to the national standard of raw material composition to buy raw materials.

2, the advanced production process directly determines the performance and quality of the magnet. The most advanced technologies are scale ingot (SC) technology, hydrogen crushing (HD) technology and airflow milling (JM) technology. Small capacity vacuum induction smelting furnace (10kg, 25kg, 50kg) has been replaced by large capacity (100kg, 200kg, 600kg, 800kg) vacuum induction furnace. SC(StripCasting) rapid casting technology has gradually replaced large ingot (ingot with cooling thickness greater than 20-40mm), hydrogen crushing (HD) technology and air flow milling (JM) have replaced jaw crusher, disk mill and ball mill (wet powder), ensuring the uniformity of powder, and conducive to liquid phase sintering and grain refinement.

3, On magnetic field orientation, our country is the only country in the use of two steps of pressing formation, in orientation of small pressure vertical molding, quasi isostatic pressing forming, this is one of the most important characteristics of the NdFeb industry in our country sintering.

4. In addition, it is very important to monitor the quality of the production process, which can be controlled through the measurement of SC thickness and the size distribution of JM powder particles. Quality products depend on the control of the production process, but customers will be very confused, how to judge the performance of the products I buy? China National Institute of Metrology has developed a variety of permanent magnetic materials technology magnetic parameters measuring instruments. Pulsed field magnetometer (PFM) is a kind of testing instrument for ultra-high coercivity permanent magnets, which is mainly used to meet the needs of electric vehicles and large permanent magnet motors.

Customers can choose their required NdFeb grade according to the magnet parameters Br(remanent magnetism), Hcb(coercivity), Hcj(intrinsic coercivity), (BH) Max (maximum magnetic energy product). At the same time, these four parameters are to determine whether the product is produced according to customer requirements.

Secondly, the guarantee of magnet size depends on the processing strength of the factory

The actual application of Ndfeb permanent magnet shape is diverse, such as disc, cylinder, cylinder (with inner hole); Square, square, square column; Tile, fan, trapezoidal, polygonal and various irregular shapes. Each shape of permanent magnet has a different size, the production process is difficult to do a shape. The general production process is: you produce large (large) blanks, after sintering and tempering, and then through mechanical processing (including cutting and drilling) and grinding, surface coating (coating) treatment, and then the magnet performance, surface quality and dimensional accuracy testing, and then magnetization, packaging and delivery.

1. Mechanical processing is divided into three categories:

(1) Cutting processing: cutting cylindrical and square cylindrical magnets into round sheets and square sheets;

(2) Shape processing: round and square magnets are processed into sectors, tiles, grooves or other complex shapes of magnets;

(3) Drilling processing: the round rod, square rod magnet processing into cylindrical or square cylinder magnet. Its processing methods include: grinding slice processing, electric discharge cutting and laser processing.

2. The surface of sintered Ndfeb permanent magnet elements is generally required to be smooth and reach a certain accuracy, and the surface of the magnet delivered by rough materials needs to be surface grinding. Common grinding methods of block Ndfeb permanent magnet alloy are plane grinding, double end grinding, inner grinding, outer grinding and so on. Cylinder commonly used core-free grinding, double end grinding, etc. Shingle, sector and VCM magnets use multi-station grinders.

A qualified magnet, not only needs to meet the performance standards, size tolerance control also directly affects its application. The size of the guarantee directly depends on the factory's processing strength, processing equipment with the economic and market demand is also constantly updated, more efficient equipment and industrial automation trend, not only to meet the customer's increasing demand for product precision, but also to save manpower and cost, so that it has more market competitiveness.

Again, the quality of the magnet coating directly determines the application life of the product

The experiment shows that 1cm3 sintered Ndfeb permanent magnet stays in the air of 150℃ for 51 days, will be all oxidation corrosion away. It's more likely to corrode in a weak acid solution. In order to make the NdFeb permanent magnet durable, it is required to have a 20-30 years of service life, it must undergo surface corrosion resistance treatment, in order to resist the corrosion of the magnet corrosion medium. At present, sintered Ndfeb permanent magnet system manufacturing industry generally uses electroplating metal, electroplating + chemical gold plating, electrophoretic coating and phosphating treatment and other methods, on the surface of the magnet plated with an additional layer of isolation, the surface of the magnet and corrosive medium separated, in order to prevent the damage of the medium to the magnet.

1, generally galvanized, nickel plating + copper + nickel, nickel plating + copper + electroless nickel plating three kinds of process, other metal plating requirements, are generally in nickel plating after other metal plating.

2, in some special cases will also use phosphating :(1) in ndfeb magnet products because of turnover, preservation time is too long and not clear follow-up surface treatment method, the use of phosphating is simple and easy; (2) When the magnet needs epoxy adhesive and paint, the adhesive force of epoxy organic matter such as glue and paint needs the matrix to have good penetration performance. Phosphating process can improve the penetration ability of magnet surface.

3, electrophoretic coating has become one of the widely used anti-corrosion surface treatment technology. Because it not only with porous magnet surface binding force is very good, and has salt spray resistance, acid resistance, alkali resistance and other corrosion, corrosion resistance is excellent. But compared with spray coating, its moisture - heat resistance is poor.

Customers can choose coating according to their product working requirements. With the expansion of the motor application field, customers have higher requirements for the corrosion resistance of Ndfeb. The HAST test (also known as PCT test) is designed to test the corrosion resistance of sintered Ndfeb permanent magnets in humid and high temperature environments.

And how do customers judge whether the coating meets the requirements? The purpose of the salt spray experiment is to do a rapid anti-corrosion experiment on the surface of the sintered Ndfeb magnet treated by anti-corrosion coating. At the end of the experiment, the sample is removed from the test box and dried, and the sample surface is observed with eyes or magnifying glass without spots, spot area of the size of the box color change.

To sum up, only by understanding the production process and the requirements of the product, can the customer correctly judge the quality of the product. In short, they are performance control, dimensional tolerance control, coating inspection 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 performance; Dimensional tolerances can be measured by vernier calipers for accuracy; On the coating, the color and brightness of the coating can be observed by the naked eye and the detection method of the binding force and salt spray test; Overall appearance, mainly with the naked eye or magnifying glass, or optical microscope (for line less than 0.2mm products), the surface of the magnet is smooth, no particles and foreign bodies visible to the naked eye, no spots, no edge off Angle, is qualified appearance.