The quality of sintered NdFeB Magnet can be judged from three aspects: magnet performance, magnet size and magnet coating.
Super NdFeb magnet, sintered NdFeb
The 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 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), hydrogen crushing (HD) and air flow grinding (JM).
Small capacity vacuum induction furnace (10kg, 25kg, 50kg) is replaced by large capacity (100kg, 200kg, 600kg, 800kg) vacuum induction furnace
The rapid casting technology of SC (StripCasting) has gradually replaced large ingot
Hydrogen Crushing (HD) technology and Air flow Mill (JM) replace jaw crusher, disc mill, ball mill (wet milling)
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. It is very important to monitor the quality of the production process, which can be controlled by means of SC thickness measurement and JM powder particle size distribution.
The magnet size
Secondly, the guarantee of magnet size depends on the processing strength of the factory.
The shape of ndFeb permanent magnet in practical application is varied:
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:
Production of bulk (large size) billet → sintering and tempering → machining (including cutting and punching) → grinding → surface coating (coating) → testing (magnet performance, surface quality and dimensional accuracy) → magnetizing → packaging → leaving the factory.
1. Mechanical processing is divided into three categories:
Cutting: Cut cylindrical and square cylindrical magnets into round and square sheets;
Shape processing: The processing of round and square magnets into sectors, tiles, grooves or other complex shapes;
(3) Punch processing: Round bar and square Bar magnets are processed into cylindrical or square barrel magnets. The machining methods include: grinding chip machining, edM cutting and laser machining.
2. The surface of sintered Ndfeb permanent magnet generally requires smooth and certain precision. The surface of the magnet delivered by blank shall be ground.
The common grinding methods of ndfeb permanent magnetic alloy are:
Square: plane grinding, double end grinding, inside grinding, outside grinding, etc
Cylinder: Commonly used non-core grinding, double end face grinding, etc
Tile, sector and VCM magnets: multi-station grinding machines
A qualified magnet 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 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.
At present, sintered NdFeb permanent magnet system is widely used in the manufacturing industry
Electroplating + chemical plating
Electrophoretic coating and phosphating treatment
1. Phosphating is also used in some special circumstances :(1) it is easy to use when ndfeb magnets are kept for a long time due to turnover, and the subsequent surface treatment method is not clear; (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.
2. 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 moisture and heat is poor.