Characterisation of the flow behaviour of pharmaceutical powders using a model die–shoe filling system

In the pharmaceutical industry it is important to understand the factors that influence the flowability of a powder and to identify suitable experimental procedures which can be used to evaluate powders and guide the selection of process parameters. This paper determines the flowability of seven pharmaceutical powders using a model die–shoe filling rig. Dimensional analysis is employed to provide a framework for the interpretation of experimental results and to guide the development of procedures to extrapolate the results to other die and shoe geometries. It is demonstrated that the variation of mass delivered into a standard die as a function of shoe velocity provides a measure of flowability. Qualitative and quantitative studies were undertaken using a high-speed video system and by determining the critical shoe velocity, i.e. the shoe velocity above which incomplete filling occurs.