How are rare earth ndfeb strong magnets made?
Sintered ndfeb permanent magnet is produced by powder metallurgy. There are 16 processes in total, and several monitoring and analysis are included in different stages. Strictly speaking, these 16 links are indispensable. The production of sintered Nd-Fe-B is a systematic project, which is closely linked. Each link should lay a good foundation for the next link. Once one process link fails to meet the requirements, the permanent magnet produced may fail to meet the target performance requirements and become a waste product, or the yield is not high.
The following figure shows the production process of sintered NdFeB strong magnet
The raw materials
Good raw materials are the basis of producing high quality magnetic materials. Raw materials generally according to the magnetic material production plant to produce high-grade, mid-grade or low-grade sintered ndfeb magnet requirements, in accordance with the corresponding national standards to choose and buy. Before smelting, raw materials should be cut off and surface treated.
The composition design of sintered ndfeb is very important, it involves the product quality and magnetic property index can meet customer requirements, because many of the material's intrinsic magnetic properties, such as magnetic polarization strength, Curie temperature are determined by the composition of the material. The basic principle of ingredient design is to ensure that the temperament is sufficiently high, while considering the cost of materials. (the cost of raw materials accounts for about 65-90% of the total cost of sintered ndfeb materials. On the premise of meeting the requirements of magnetic properties of users, it is necessary to use cheap grouping elements as far as possible, with less use of rare earth metals and other precious metals)
Smelting ingot casting
Smelting cast ingot/sheetSmelting is the first process that sintered ndfeb strong magnets enter into the production process. The melting furnace produces alloy swash strip. This process requires a furnace temperature of about 1300 degrees and lasts for four hours to complete.After this process, the raw materials are processed into alloy pieces by hot melting and cooling, and then the next process is carried out.
The purpose of powder making is to break large alloy ingots into powder bodies of a certain size. In order to obtain a well-oriented magnet, powder particles are required to be small in size (3-4 cm) and concentrated in size distribution. Powder particles are spherical or nearly spherical.
Orienting and Pressing
Magnetic field orientation of powder is one of the key technologies in producing high performance sintered ndfeb. After loading the broken magnetic powder into the mold, apply external magnetic field for orientation, and then press the powder. At present, there are three widely used pressing methods: membrane pressing, mold pressing and cooling isostatic pressing and isostatic pressing of rubber mold. Under the same content of neodymium, the isostatic pressing of rubber mold can obtain more magnetic energy product.
Sintering and tempering
The relative density of sintered Nd-Fe-B powder compacts is relatively large, the contact between particles is mechanical contact, and the bonding strength is low. In order to further improve the density, improve the contact property between particles, improve the strength, and make the magnets have the microstructure characteristics of high permanent magnetic properties, it is necessary to heat the compacts to a temperature below the basic phase melting point of the powder, and conduct heat treatment for a period of time The process is called sintering.
After the sintered magnet is quenched at high temperature, the grain boundary phase distribution is not uniform and the grain boundary is not clear. Therefore, it is necessary to temper at a certain temperature to optimize the structure and obtain the best magnetic properties. Tempering refers to cooling the sintered magnetic powder blank to a certain temperature and then heating it up again. The tempering temperature needs to be tested or determined by thermal difference analysis.
Machining and surface treatment
The shapes of sintered ndfeb magnets are various, such as discs, cylinders, rings, squares, tiles, fan shapes and various irregular shapes. Due to the different shapes and sizes of the permanent magnet components, it is difficult for other magnets to be formed at one time except for the large-size regular permanent magnet components in the production process. Therefore, in general, in the process of powder metallurgy, Mr. Output large blank, after sintering and tempering treatment, and then through mechanical processing (including cutting, drilling, etc.) and grinding, surface coating treatment, to produce the shape and size of the customer's needs. There are three types of machining, including
1. Cutting cylindrical and square cylindrical magnets into circular and square components is called cutting processing
2. The processing of round or square magnets into fans, tiles, or magnets with grooves or other complex shapes is called contour processing