The effect of powder modified additive in the production process of NdFeb blank.
In order to produce high-performance sintered NdFeb permanent magnet material, we have to control the size of airflow grinding magnetic powder particles, so that the size of magnetic powder particles in 2.5~5μm accounted for more than 95%. Xinfeng Magnet found that the process can be greatly improved by adding special powder modification additives to the airflow milling process.
Powder modified additives should have a composite function, namely:(1) anti-oxidation function; (2) Improve the powder fluidity function; (3) Prevent powder combustion, namely inflaming retarding function. The amount of additive is about 0.035%~0.05% (mass fraction) of the magnetic powder, which is usually added at the same time with the magnetic powder at the airflow mill feeding place.
Additive is a multi-component organic compound, with lipophilic groups, namely hydrocarbon chains, containing small polar groups, such as lipid groups, so that the hydrocarbon chain has an appropriate chain length. Magnetic powder particles repeatedly collide and touch with additives in the airflow grinding process, so that the surface of each particle is coated with a layer of additive film with a thickness of about 5~8nm. It plays the following roles:(1) Prevent powder particles from contacting with air, play the role of anti-oxidation; (2) Weaken the magnetostatic effect between powder particles, reduce the agglomeration between powder particles, play the role of dispersant; (3) Increase the fluidity and mobility of powder particles and play the role of lubricant; (4) It is beneficial to the orientation of powder particles in the magnetic field, which can improve the orientation; The BR can be increased by 0.02-0.04 T, and the magnetic energy product (BH) m can be increased correspondingly. It should be noted that the volatile temperature of this additive is 350℃. Sintering temperature needs to be held at 400-420℃ for a period of time, so that additives can be discharged from the magnet, so as not to carburize.
The necessary conditions for producing high quality sintered NdFeb permanent magnet.
In order to obtain a good orientation of magnets, Xinfeng magnet came to the conclusion after years of experimentation and integrated feedback on market customer usage that it is necessary to make sintered NdFeb magnetic powder to meet the following requirements so that the high-quality products can be created, and only the medicinal materials are good, the medicine will be better. (1) The powder particle size is small (3~4μm), and the size distribution is narrow, that is, the requirements of 3~4μm particles accounted for 95%, do not have less than 1μm or more than 7μm particles, to ensure that all the particles are single crystal. (2) The particles of powder are spherical or approximately spherical. (3) The crystal defects of powder particles should be as little as possible. (4) When crushing, it is better to break along the crystal stage, and strive to achieve the surface of each particle has Rich Nd phase, which lays the foundation for the liquid phase sintering behind and prevents the occurrence of class ⅱ grain boundary. (5) The impurities and gases adsorbed on the surface of powder particles should be as little as possible, especially the oxygen content should be less. Therefore, the powder preparation process should be carried out in high purity inert gas protection or vacuum conditions, in order to prevent magnetic powder contact with oxygen or humid air. The above five conditions are necessary for manufacturing high quality sintered NdFeb permanent magnets, lack of each is not desirable, looks like simple, actually each can do perfect is not simple, Xinfeng magnets is willing to work together with people from all walks of life to make more perfect products, and strive to provide customers with more quality services.
Xinfeng Magnet’s new breakthrough in improving the coercivity of sintered NdFeb magnet.
Coercivity is one of the important technical parameters of permanent magnet. Increasing the coercivity can increase the large magnetic energy product of the magnet, improve the demagnetization resistance of the permanent magnet in use, and improve its stability. At present, in the preparation of pure ternary sintered NdFeb permanent magnets, the technical magnetic properties and the theoretical values, and the remanence BR has already reached 96.27% of its theoretical value, and large magnetic energy product BH has reached 91.5% of its theoretical value. However, coercive force has reached only 12% of its theoretical value. It is big potential to improve its coercive force, there is still a great increase in space. Xinfeng magnet has been working hard for this.
First, the coercivity of the magnet can be effectively improved by replacing Nd with partial Dy and Tb. However, in rare earth metal resources, Dy and Tb are relatively low in content and expensive, and Dy and Tb can only be added in trace amounts. Second, the addition of some metal elements such as AL, Nb, Ga, Ti, Zr, Mo, etc., when these elements enter into the crystal, the microstructure and process performance are obviously improved, and increase the coercivity of the magnet. Third, the coercivity of the magnet can be effectively improved by adding elements and using low temperature sintering or double alloy method to reduce the average crystal size.
Next, Xinfeng magnet will continue to work hard to improve the large magnetic energy product of sintered NdFeb, and constantly provide better products for customers.
Post time: Jul-12-2018