Magnetic Properties and Particle Flowability of Neodymium Magnetic Granules

Abstract

In this study, sintered Nd–Fe–B magnets with high residual flux densities and magnetic coercivities were manufactured by filling a die cavity with granulated Nd–Fe–B magnetic powder during pressing. In the binder-bound granules prepared by a spray drying method, the bonding force between the primary particles was relatively strong. However, the magnets obtained from these granules could not achieve high residual magnetic flux densities because it was difficult to align each particle in these granules along the magnetization easy axis through magnetic field pressing. Therefore, a weak liquid bridge force was utilized for particle binding. After preparing the liquid-bound granules containing 0.25 mass% terpineol, which does not evaporate easily at room temperature (∼293 K) but undergoes debinding on baking, the angle of repose of the magnetic powder (representing its flowability index) decreased from 63° to 44.2°, while the deterioration of its magnetic properties was considerably suppressed. As a result, the residual magnetic flux density of the sintered magnet was equal to 99.3% of the value obtained for the non-granulated powder. In addition, the liquid-bound granules exhibited high filling rates and low weight variations, demonstrating their applicability for mass production.

Figure Measurement of angle of repose; (a) original powder, (b) liquid-bound granule with 2.0 mass% terpineol and (c) optical image of liquid-bound granule (b).