③ broken, milling
The purpose of milling is to crush a large alloy ingot or quick-setting chip to a certain size of powder. At present, the method of hydrogen explosion + jet milling is mainly used. The melting of the alloy ingot or quick-setting chip into the furnace, evacuated to 10-2 Pa or less, and then filled with high-purity hydrogen, the hydrogen pressure to 105 Pa or so, about 20-30 min, you will hear Crack sound, and stove temperature will rise. Hydrogen hydrogen alloy formed after the burst, a hydrogen burst, referred to as hydrogen burst, that is, HD (Hydrogen decrepitation). The hydrogenation of the magnet occurs exothermically, thus raising the temperature of the furnace. The HD treatment breaks the magnet into particles in the 45-355 mm range, mostly particles of about 125 mm. If after repeated hydrogen absorption - dehydrogenation cycle, the powder particles can be further reduced to 10 mm below. HD equipment used is hydrogen broken furnace.
The further use of HD powder jet mill (Jet Milling, referred to as JM), secretion can be broken up to 2 ~ 5 mm, the size of the powder can be used directly to manufacture sintered magnets. Air mill powder is the use of airflow to accelerate the powder particles to supersonic collision with each other and broken. Common equipment for jet milling is a jet mill. HD + JM has become an important milling method of sintered magnets. The picture below shows the hydrogen broken furnace and airflow mill powder machine.
Hydrogen broken furnace Air mill powder machine
④ magnetic orientation and pressure type
Powder magnetic field orientation is one of the key process technologies for manufacturing high performance sintered magnets. The purpose of the magnetic field orientation is to orient the easy magnetization direction (c-axis) of each powder particle in the same direction to make an anisotropic magnet, and then the maximum remanence Br in the direction of the c-axis orientation of the powder particles increases the magnet The maximum energy product. The orientation of the powder Chengdu has an important influence on the remanence Br and the maximum energy product (BH) max of the magnet. Powder pressure has two purposes: First, according to user needs will be pressed into a certain shape and size of the powder compact; the second is to maintain the orientation of the crystal obtained in the magnetic orientation. At present, there are three types of pressing methods commonly used: molding method, molding plus cold isostatic pressing and rubber molding (plus cold isostatic pressing). Pressure-type process is the main process of magnetic oxygen absorption, so the molding process has strict anti-oxidation measures, requiring magnetic powder weighing or pressing process under the protection of inert gas. The equipment used in this process is a forming press as shown below.
Article from NdFeB Industry Network