Factors and Methods Affecting the Performance of NdFeB Magnetic Materials
Since the advent of NdFeB permanent magnet materials, it has attracted much attention due to its superior magnetic properties. promote. We generally use remanence, coercive force and maximum energy product to measure the performance of magnetic materials.
If the magnet is likened to a sponge, the residual magnetism is like the sponge absorbing water and absorbing saturation, and the magnetic force value of the magnet displayed at this time. It refers to the magnetic induction intensity of a magnet when it is magnetized by an external magnetic field in a closed-circuit environment until the technology is saturated and then the external magnetic field is removed.
Coercive force Hcb and intrinsic coercive force Hcj
The water in the sponge is absorbed to the maximum, and then the water is pressed out until there is no water in the sponge. The pressure used at this time is like coercive force. It is the value of the reverse magnetic field strength required to reduce the magnetic induction intensity to zero when the magnet is reversely magnetized. But at this time, the magnetization of the magnet is not zero, but the reverse magnetic field added and the magnetization of the magnet cancel each other out. At this time, if the external magnetic field is canceled, the magnet still has certain magnetic properties. The intrinsic coercive force is the reverse magnetic field strength required to reduce the magnetization of the magnet to zero.
Maximum energy product (BH)max
The sponge is saturated with water, and the total amount of water in it can be understood as the maximum magnetic energy product. It represents the magnetic energy density established in the two magnetic pole spaces of the magnet, that is, the static magnetostatic energy per unit volume of the air gap, which is the maximum value of the product of B and H, and its size directly indicates the performance of the magnet. So today I will talk to you about what determines the above performance of NdFeB strong magnets, how to improve the performance of magnetic materials through technical means, and how to avoid loss of magnetic material performance during use.
The raw material composition and production process of NdFeB strong magnets determine its innate magnetic properties, and after it becomes a strong magnetic product, its working environment (including temperature, humidity and other factors) will affect its innate magnetic properties. Improper use If so, permanent demagnetization will occur.
1. The influence of raw material composition on the strong magnetic properties of NdFeB
NdFeB strong magnetism, as the name implies, is a magnetic material made of rare earth metal neodymium, pure iron and boron using powder metallurgy technology. In order to further improve the magnetic properties of NdFeB, it can be based on the ternary system Nd-Fe-B Further add other elements, but the influence of the addition of elements on the performance of the magnet may be two-way, and the addition of elements should be determined according to the specific requirements of the magnetic material performance in the application of NdFeB strong magnetism.
2. The influence of production process on the strong magnetic properties of NdFeB
In order to obtain high-performance NdFeB permanent magnets, new technologies and processes are constantly emerging. In the production process of sintered NdFeB, the main problem is to prevent the precipitation of α-Fe phase and the oxidation of the alloy, and it is difficult to obtain the ideal microstructure. In order to solve these problems, new methods and processes are constantly emerging in practice, such as: Add anti-oxidant and lubricant, and prepare magnets by quick quenching strip method; steel ingot homogenization treatment and sheet casting process; dual-phase method preparation process; wet pressing molding process, etc.
The biggest advantage of adding anti-oxidant is to reduce the oxygen content of the final magnet, and at the same time, the magnetic powder can be ground finer, which is conducive to improving the coercive force. In addition, due to the reduced oxygen content, it is also conducive to improving the coercive force. Compared with the traditional technology, the intrinsic coercive force of the magnet added with anti-oxidant can be increased by about 160kA/m.
After adding the lubricant, the friction force between the magnetic powders becomes smaller, the fluidity of the magnetic powders is improved, the degree of orientation is increased, and the residual magnetism is increased.
The thickness of the NdFeB strip prepared by the stripping method is 0.25-0.35mm, which can completely eliminate the α-Fe phase. Because the anti-oxidation ability of the powder prepared by the stripping method is enhanced, the grain size of the magnet becomes smaller, and the coercive force is greatly improved.
3. The influence of the working environment on the strong magnetic properties of NdFeB
Temperature: NdFeB strong magnets have strict working temperature limits. When the working temperature is higher than the working temperature, the magnet may demagnetize. When it is higher than the Curie temperature, the magnet demagnetization will be irreversible.
Humidity: Sintered NdFeB is a magnetic material pressed and formed by powder metallurgy process. Its internal structure has gaps and is very easy to oxidize. Therefore, sintered NdFeB will be treated with coating for anti-corrosion. But the magnetosphere doesn’t fundamentally deal with the effects of ambient humidity on magnets. The drier the environment, the longer the magnetic energy of the magnet.