How is sintered neodymium iron boron permanent magnet produced?
Sintered neodymium iron boron permanent magnets are produced using powder metallurgy method, which generally involves more than ten process steps from material preparation to finished product delivery, including several testing and analysis at different stages.https://chinese.alibaba.com/product-detail/HC004B-Single-Pole-Parylene-Coating-Round-60830071185.html
The entire production process is a systematic engineering, interconnected. Generally, we refer to the process of producing magnet blanks as the preceding production stage, and the process of processing the blanks into the final product as the succeeding processing stage. Magnetic material manufacturers are mainly divided into two categories: those that have both front-end production and back-end processing, and those that focus on back-end processing.
There is a saying in the 01 material preparation that goes, "Good medicinal herbs make good medicine." This sentence is very applicable to the production of sintered neodymium iron boron magnets. Good raw materials are the foundation for producing high-quality magnets. When manufacturers choose raw materials, they generally select them according to the performance requirements of the magnets and the corresponding national standards. Before smelting, the raw materials are cut and surface treated.
02 Smelting is the first process of sintering neodymium iron boron permanent magnets into the production process. The raw materials are melted and cooled in the melting furnace to form alloy ribbon strips. This process requires a furnace temperature of around 1300 degrees Celsius and lasts for more than four hours to complete.
03 Hydrogen breakthrough+04
The two process steps of gas flow milling, hydrogen cracking and gas flow milling, are collectively referred to as powder production, which is the process of crushing the alloy strip produced by melting and producing magnetic powder. In order to obtain well oriented magnets, it is required that the powder particle size is small (3-4 μ m) and the size distribution is concentrated, with the powder particles being spherical or approximately spherical.
05 Pressing: Load the crushed magnetic powder into the mold, apply an external magnetic field for orientation, and press the powder after orientation. Powder magnetic field orientation is one of the key process technologies for producing high-performance sintered neodymium iron boron. In terms of molding technology, there are currently three commonly used methods in the industry: compression molding, compression molding with cold isostatic pressing, and rubber mold isostatic pressing. Under the same neodymium content, rubber mold isostatic pressing can obtain a larger magnetic energy product.
After the 06 heat treatment, the relative density of the pressed magnet is relatively high. In order to make the magnet have high permanent magnetic properties, it is necessary to heat the pressed magnet to a temperature below the melting point of the basic phase of the powder and perform heat treatment for a period of time. This process is also known as sintering. After high-temperature quenching, it is necessary to perform tempering treatment at a certain temperature to optimize the microstructure 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.)
Due to the characteristics and technical limitations of the magnetic field orientation forming process, it is difficult for sintered magnets to achieve the shape and dimensional accuracy required for practical applications in one go. Many finished magnets have small volumes and complex shapes, and can only be processed from rough magnets of certain shapes. Sintered neodymium iron boron material is hard and brittle, and general mechanical processing can only be carried out by cutting, drilling, grinding, and rolling.
Japanese and European and American companies mostly choose near final forming technology due to considerations of raw material and labor costs, with subsequent mechanical processing as a supplement; Chinese enterprises produce a wide range of sintered neodymium iron boron products, mainly using a comprehensive production process of combining raw magnets with processing, fully drawing on the technological advantages of ceramic and crystal processing, and maximizing the mechanical processing level of rare earth permanent magnets. With the increasing pressure of raw material and labor costs, near final forming and automatic forming technologies are rapidly developing in China.
The diffusion of rare earth elements dysprosium and terbium at grain boundaries can significantly improve the coercivity and temperature stability of materials. For sintered neodymium iron boron materials with high requirements for coercivity and operating temperature, dysprosium and terbium are often added. However, the high prices of these two elements can significantly increase the production cost of magnets. Currently, grain boundary diffusion technology is widely used in the industry to reduce the amount of heavy rare earth elements added.
09 surface treatment sintered neodymium iron boron is a highly chemically active powder material with small pores and voids inside, which are easily corroded and oxidized in air. Over time, it will cause a decline or even loss of magnetic properties. Therefore, strict surface anti-corrosion treatment must be carried out before use. At present, neodymium iron boron anti-corrosion treatment generally adopts methods such as electroplating, chemical plating, electrophoresis, phosphating treatment, etc. Among them, electroplating is widely used as a mature metal surface treatment method.
Magnetization is a crucial step in obtaining magnetism in sintered neodymium iron boron permanent magnets. A magnetizer is a tool used to magnetize magnetic materials or devices, applying a magnetic field to the magnetized neodymium iron boron magnet. If the magnetized magnetic field does not reach the technical saturation magnetic field, the residual magnetism Br and coercive force Hcj of the permanent magnet will not reach the expected values. In addition to ordinary unipolar magnetization, sintered neodymium iron boron can also be magnetized with multipole magnetization according to actual needs, that is, after magnetization, multiple N and S poles can be presented on one plane. Packaging and shipping is the last step before the magnet leaves the factory. Magnet manufacturers can package according to the requirements of the purchaser. If the purchaser has special packaging requirements, they can inform the supplier in advance. Sintered neodymium iron boron permanent magnets have strong magnetism, so domestic transportation generally uses land transportation. For exports to the open sea, air transportation can be used after special magnetic packaging and professional organization testing and identification.
11 Quality Inspection
The quality monitoring during the production process of sintered neodymium iron boron permanent magnets and the quality inspection of the final product should include the items listed in the table below, but not every item needs to be tested. Purchasing personnel can negotiate with the manufacturer on the required testing items according to actual needs.