Effect of Particle Size Distribution on the Preparation of Bonded NdFeB Permanent Magnet

In this paper, the effect of particle size distribution on the preparation of bonded NdFeB isotropic permanent magnets was investigated. Different particle size distribution of NdFeB powders was prepared by sieving method using standard test sieves of #100, #200, and #325 meshes. Varied distribution of particle size was mixed with 3 wt% of epoxy binder and compacted by uniaxial hydraulic pressing machine to produce bonded isotropic green body. Bonded NdFeB green body was cured by vacuum drying machine under temperature 100 °C for 4 hours with vacuum pressure of 10 mbar. The characterization performed were bulk density measurement, particle size analysis, microhardness Vickers, SEM image and hysteresis curve. We find that the hardness of bonded NdFeB magnets decreased as the particle size decreases. Contrary to common belief that the finer powder with sharply particle size distribution not always give the highest product characteristics. The optimum characteristics of bonded NdFeB was obtained by the mixture of #100+#200 meshes powders with bulk density, hardness, magnetic remanence, coercivity, and energy product of 5.87 g/cm3, 88 HV, 6.5 kG, 11.15 kOe, and 9.4 MGOe, respectively. Therefore, the middle range of particle size distribution is effective to obtain high quality bonded NdFeB permanent magnets.