Analysis and optimization of flow behavior and impacting performance of the Nd-Fe-B particles in fluidized bed air jet milling using 3-D FDEM

Fluidized bed air jet milling is a key process for preparing high-performance Nd-Fe-B rare-earth (RE) permanent magnet particles, but its process parameter system and equipment structure are still in constant trial and error, which makes the magnetic particles size distribution and production efficiency upgrade slowly. In order to fill the technical gap in this industry, this paper studies the movement trajectory of airflow and magnetic particles in the fluidized bed air jet impacting chamber based on the method of finite element and discrete element coupling. Through the comparison analysis of the simulation value and the experimental results of the pressure in the impacting chamber, the error range is less than 5%, which verifies the effectiveness of the numerical simulation. Furthermore, the differences in magnetic particle size generated under four different classifying wheel speeds (2500–3100 rpm) were analyzed. From the simulation results, it can be seen that the classifying wheel speed plays a key role in the output of particles. The trend of particle size variation with classifying wheel speed in the simulation results is basically consistent with the experimental results, that is, the decrease in particle size is due to the increase in classifying wheel speed. However, when the classifying wheel reaches a certain speed, the difference in particle fineness change is significantly reduced. At the same time, the air jet trajectory in the milling is described by simulation, and the core impacting area is defined by combining the evolution law of the velocity, pressure, and turbulence kinetic energy of the air in the impacting area. This pioneering work provides a preliminary basis for the in-depth study of the structure optimization of air jet milling in the rare earth permanent magnet industry.