In the production of motor magnets, the orientation magnetic field strength is the core parameter that affects the orientation degree and remanence consistency of the magnet. By precisely controlling the orientation magnetic field strength, the arrangement direction of the magnetic powder particles can be optimized and the uniformity of the magnet performance can be improved, thereby meeting the needs of efficient and stable operation of the motor.
The orientation magnetic field strength directly affects the easy magnetization axis arrangement of the magnetic powder particles. When the magnetic field strength reaches the anisotropy field of the magnetic powder (about 2-3 Tesla), the c-axis of the magnetic powder particles will be highly uniformly arranged along the magnetic field direction to form an anisotropic structure. If the magnetic field strength is insufficient, the magnetic powder particles are prone to orientation deviation, resulting in a decrease in orientation. Experiments show that for every 10% increase in magnetic field strength, the orientation degree can be increased by 5%-8%, but after exceeding the critical value, the improvement effect will gradually weaken.
Remanence (Br) is a measure of the residual magnetic induction intensity after the magnet is demagnetized, and its consistency depends on the uniformity of the orientation degree inside the magnet. During the magnetic field orientation process, if the magnetic field strength is unevenly distributed, the orientation degree of the magnetic powder in different regions will be significantly different, which will eventually lead to remanence fluctuations. For example, due to the magnetic leakage effect, the orientation degree of the edge area of the magnetic field is usually lower than that of the central area, resulting in a residual magnetic gradient. By optimizing the magnetic field design (such as using a multi-pole magnetic field generator), the residual magnetic fluctuation range can be controlled within ±2%.
Traditional steady magnetic field orientation is limited by the internal friction between magnetic powders, and it is difficult to achieve a high orientation degree. The high-energy pulse magnetic field provides positive orientation power for the magnetic powder through an ultra-high magnetic field with intermittent positive and negative orientation (peak intensity can reach more than 10 Tesla), and uses the pulse gap to release internal stress to avoid orientation destruction caused by magnetic condensation effect. Experimental data show that the orientation degree of magnets oriented by pulse magnetic field can reach more than 98%, and the residual magnetic consistency is improved by 15%-20%.
The magnetic field strength needs to match the molding pressure to achieve dual optimization of orientation degree and density. Under high magnetic field strength, magnetic powder is easy to align along the magnetic field direction, but it needs to be combined with high-pressure molding (such as 500-800 MPa) to compress the gap between magnetic powders and increase density. If the magnetic field strength is too high and the pressure is insufficient, pores are easily formed between magnetic powders, resulting in a falsely high orientation degree and a decrease in residual magnetism. By optimizing the magnetic field-pressure coupling parameters through finite element simulation (FEM), the magnet density can be increased to more than 7.6 g/cm3.
Magnetic field uniformity is a key factor affecting the orientation consistency of magnets. During the magnetic field orientation process, if the magnetic field gradient exceeds 5%, the orientation degree difference at different positions of the magnet can reach more than 10%. By using high-uniformity magnetic field generators such as Helmholtz coils or superconducting magnets, the magnetic field gradient can be controlled within 1%, thereby significantly improving the orientation consistency. In addition, magnetic field scanning technology (such as dynamic magnetic field compensation) can further eliminate local magnetic field distortion.
Although increasing the orientation magnetic field intensity can increase the orientation degree, excessive magnetic fields may cause abnormal growth of magnetic powder grains and reduce coercivity (Hcj). Studies have shown that when the magnetic field intensity exceeds the magnetic field threshold corresponding to the critical size of magnetic powder (about 50 nanometers), the coercivity will decrease by 10%-15%. Therefore, it is necessary to refine the magnetic powder particles through nanocrystallization processes (such as hydrogen explosion powder making) to match the magnetic field intensity with the grain size and achieve the coordinated optimization of orientation degree and coercivity.
In industrial production, real-time monitoring of the orientation magnetic field strength is crucial. By measuring the magnetic field strength online with a Gauss meter and detecting the orientation of the magnet with a hysteresis loop tester, a closed-loop control system of magnetic field strength-orientation can be established. When the orientation is detected to be lower than the set value, the system automatically adjusts the magnetic field generator parameters to ensure stable magnet performance. In addition, big data analysis technology can predict the trend of magnetic field fluctuations and optimize process parameters in advance.
By precisely controlling the orientation magnetic field strength, combined with high-energy pulse magnetic field, magnetic field uniformity optimization, and magnetic field-pressure coordinated control technologies, the orientation and remanent magnetization consistency of motor magnets can be significantly improved. In the future, with the further development of superconducting magnets, intelligent control and other technologies, the performance of motor magnets will move to a higher level, providing solid support for the efficiency and miniaturization of motors.
