The fifth process of magnet production: isostatic pressing

The density of green compacts pressed in the magnetic field directional forming process is about 3.2-3.8g/cm³, while the ideal density of NdFeB magnets after sintering should be about 7.5g/cm³. Therefore, when pressing relatively large cylinders and squares, they need to be put into an isostatic press to increase the density of green compacts through isostatic pressing due to large shrinkage, easy cracking, deformation and size deviation caused by missing angles, after isostatic pressing, the density of the green compact is 4.5 g/cm. At present, magnet manufacturers have to go through isostatic pressing except for low-performance small columns (Ф less than 10mm), which are not hydrostatically pressed and directly put into the sintering furnace. In order to prevent oil immersion and surface oxidation, the isostatic green compact must be vacuum packaged and stripped before entering the furnace.

The working principle of the isostatic press is Pascal's principle. The green body put into the soft mold sleeve is put into a closed super-high claw container, and the hydraulic oil is continuously pressed into the sealed container through the booster pump to make the hydraulic pressure in the sealed container continuously increase. The general use pressure is100 ~ 630MPa. The high-pressure liquid uniformly acts on the surface of the rubber sleeve, and compresses the pellets in the rubber sleeve to form it. Since isostatic pressing is characterized by equal pressure in all directions, the formed blank has uniform density, uniform structure and isotropy.

Source: magnet manufacturers Youlian Magnetic Industrywww.youliancy.com