Characterization of a downer reactor for particle rounding

Abstract

The gradual shift of rapid prototyping towards additive manufacturing (AM) implies higher demands on the available material. So far, most of the processes as laser beam melting (LBM) rely on polyamide as PA12. To overcome limitations and to address this lack of suitable polymer material with a fine particle size, Schmidt et al. [1] have established a wet-grinding process which allows the production of very fine polymer particles. Since the ground product shows a rather bad flowability, further treatment is necessary to enable the use of this material in AM. A rounding of the chiseled particles can improve the flowability [2]. This treatment changes the morphology of the particles by surface tension forces in the molten state [3]. To accomplish rounding of the polymer powder, a downer reactor in semi-industrial scale has been established and will be characterized in this article. Main topics are the powder dispersion, the inlet geometry and its influence on the gas flow behavior inside the downer. This was achieved by combining basic simulation and experimental data. Furthermore, the heat distribution and agglomeration in the gas phase were investigated as important parameters of the process. Finally, a proof of concept by rounding wet ground PBT material was successfully conducted. The product was investigated to obtain data about a change in particle size and polymeric structure.