In terms of magnetic field orientation, China is the only country in the world that adopts a two - step pressing and forming process. During orientation, a small - pressure vertical die - pressing is used for forming, and finally, a quasi - isostatic pressing is adopted. This is one of the most important features of China's sintered Nd - Fe - B industry.
Whether the production process is advanced or not directly determines the performance and quality of magnets. At present, the most advanced technologies are the Strip Casting (SC) technology, the Hydrogen Decrepitation (HD) technology and the Jet Milling (JM) technology. Small - capacity vacuum induction smelting furnaces (10 kg, 25 kg, 50 kg) have been replaced by large - capacity (100 kg, 200 kg, 600 kg, 800 kg) vacuum induction furnaces. The SC (Strip Casting) rapid - solidification casting - sheet technology has gradually replaced large - sized ingots (ingots with a thickness greater than 20 - 40 mm in the cooling direction). The HD (Hydrogen Decrepitation) technology and the JM (Jet Milling) have replaced jaw crushers, disc mills and ball mills (wet - process powder preparation), ensuring the uniformity of powder and being beneficial to liquid - phase sintering and grain refinement.
The quality monitoring of the production process is very important and can be controlled through detection methods such as SC - sheet - thickness measurement and JM - powder - particle - size distribution. High - quality products all depend on the control of the production process. However, customers must be very confused about how to judge the performance of the products they purchase. The National Institute of Metrology of China has successively developed various types of magnetic - parameter - measuring instruments for permanent - magnetic - material technology. The Pulsed - Field Magnetometer (PFM) is a testing instrument for testing ultra - high - coercivity permanent magnets, mainly to meet the needs of high - coercivity permanent magnets required in the field of electric vehicles and large - scale permanent - magnet motors.
According to the requirements of enterprises for manufacturing high - grade, medium - grade or low - grade sintered Nd - Fe - B, raw materials are purchased according to the raw - material components specified in national standards.
Customers can select the Nd - Fe - B grade they need according to the magnet parameters such as Br (remanence), Hcb (coercivity), Hcj (intrinsic coercivity) and (BH)max (maximum energy product). At the same time, these four parameters are the standards for determining whether the products are produced according to customer requirements.
