Uniformity discrimination analysis part 1: Powder deposition characteristics in rectangular shallow die using feed shoe with circular cross-section

The process of die filling is a significant unit operation in many industries. The inhomogeneity of distribution such as, mass, bulk density, and pressure distribution might cause many tablet and compact quality issues, such as lamination, capping, and distortion. No systematic investigations have been done to evaluate pressure distribution characteristics in dies with small aspect ratio (<0.5). In order to evaluate the pressure distribution during filling of shallow dies, factors influencing powder deposition were studied in this research. The factors included, particle size and shape, particle size distribution, and circular cross section feed shoe speed. The second generation pressure deposition tester (PDT-II) was used to measure powder's pressure distribution characteristics. A battery powder mixture (BPM) and microcrystalline cellulose (Avicel PH102) were used to fill rectangular shallow die 32×30 mm in dimension and 6.5 mm deep. The feed shoe speeds of 20 and 100 mm/s were used to fill the die. Symmetry analysis, variance metrics, Gini coefficient, and contour plots were used to quantify the deposition characteristics. The results showed that (1) contour plots were the most reliable method for measuring powder deposition characteristics, (2) Avicel generated more symmetrical pressure distribution vs. BPM (symmetry index=3%); (3) based on contour plot analysis, 20 mm/s feed shoe speed for Avicel led to the more uniform pressure distribution (64.4% uniformity at +/- 50 Pa resolution) among all.