Orientation and Magnetization of Sintered NdFeB Magnetic Steel
Orientation is an important process in the production of sintered neodymium iron boron magnetic steel
The magnetism of magnets originates from magnetic ordering (arranging magnetic domains in an orderly manner in one direction), and sintered neodymium iron boron is formed by pressing magnetic powder in a mold. Place the magnetic powder into a mold with a given shape, apply a strong magnetic field through an electromagnet, and apply a certain pressure to the magnetic powder through a press, so that the easy magnetization axis of the magnetic powder is aligned. After the pressing is completed, demagnetize the blank and then demold it to obtain a blank with good orientation of easy magnetization direction. Subsequently, cut it into magnetic steel products of specified size according to the user's needs.
Powder orientation is a key process for preparing high-performance neodymium iron boron permanent magnets. The good orientation of the magnet during the blank production stage is influenced by various factors, including the strength of the orientation magnetic field, the shape and size of the powder particles, the molding method, the relative direction of the orientation field and molding pressure, and the loose packing density of the orientation powder.
The magnetic declination generated in the post-processing stage has a certain impact on the magnetic field distribution of the magnet steel
Magnetic declination refers to the angle between the direction of magnetic field lines and the orientation plane of the magnet. The ideal state of magnetic declination is perpendicular to the orientation plane, but during post-processing, due to the operation of adhesive and cutting techniques, there may be a certain angle between the cutting direction and the polarity plane. After subsequent magnetization, the magnetic field strength of the orientation plane will be lower than the normal magnetic field strength.
Magnetization is the final step in sintering neodymium iron boron to obtain magnetism
The magnet blank is cut to obtain the size required by the user, and then subjected to anti-corrosion treatment such as electroplating to become the finished magnetic steel product. However, at this time, the magnet itself does not display magnetism to the outside world and needs to be magnetized to "magnetize" the magnet.
The equipment we use to magnetize magnetic steel is a magnetizer, also known as a magnetizer. The magnetizer first charges the capacitor with a high DC voltage (i.e. energy storage), and then discharges it through a very small resistance coil (magnetizing fixture). The peak value of the discharge pulse current is very high, reaching tens of thousands of amperes. This current pulse generates a strong magnetic field inside the magnetizing fixture, which can permanently magnetize the magnet placed in the magnetizing fixture.
Unexpected situations may also occur during the magnetization process, such as magnetization unsaturation, magnetization machine pole explosion, and magnet breakage.
🔸 Unsaturation of magnetization is mainly due to insufficient magnetization voltage, and the magnetic field generated by the coil cannot reach 1.5 to 2 times the saturation magnetization strength of the magnet.
🔸 If it is multipolar magnetization, magnets with thicker orientation directions are also difficult to magnetize to saturation because the distance between the upper and lower poles of the magnetizer is too large, and the magnetic field strength generated by the poles is not strong enough to form a normal closed magnetic circuit. The magnetic field passing through the magnet cannot penetrate the magnet, so it will cause magnetic pole confusion and insufficient magnetic field strength.
🔸 The explosion of the magnetizing pole is mainly due to the set voltage being too high, exceeding the safe voltage of the magnetizing machine.
Unsaturated magnets or demagnetized magnets are more difficult to saturate because the original magnetic domains are chaotic and do not display magnetism to the outside. To saturate, one only needs to overcome the resistance of the displacement and rotation of their own magnetic domains. However, when the magnet is not fully saturated or has demagnetized but not completely demagnetized, there is a reverse magnetic field region inside it. Whether it is forward magnetization or reverse magnetization, there are some magnetization regions that need to be magnetized in the opposite direction, requiring additional overcoming of the intrinsic coercivity of the reverse magnetic field region. Therefore, a stronger magnetic field than the theoretical magnetization field is needed.