Understanding effects of process parameters and forced feeding on die filling

Die filling is a critical step during pharmaceutical tablet production and is still not well understood due to the rather complex interplay between particle attributes, die orifice diameter and fill energetics. While shoe-die filling models have been used to simulate die filling conditions, they typically lack the sophistication of the actual production-scale, feeder-based die filling conditions. The relationship between tableting process parameters and filling into die orifices of different diameters by powders of different flowabilities requires critical examination and understanding. In this study, a special die filling contraption was designed and custom-made to simulate the effects of gravity, suction and feeder paddle assistance as present in modern rotary tablet presses. Die fill performance was studied using powders with different flow properties. Suction impact was greatest on die fill, in particular, for small orifice diameters and less permeable powders. Effect of paddle velocity on die fill was greater for compressible powders and larger orifice diameters. In comparison to suction and paddle velocity, forced feeding did not significantly affect die fill performance. Relationship between process parameters and die fill performance was found to be highly dependent on the material and orifice diameter.