Modeling die filling under gravity for different scales of rotary tablet presses

For tableting, die filling is an important process step as it directly influences the tablet weight and its variation, which is connected to the drug dose. However, the impact of process parameters and materials properties is not sufficiently understood until today, so process development and scale-up of this process require a considerable amount of powder and time. Therefore, the aim of this study is to develop a process-model to describe and predict the filling process. The investigation aims a fundamental understanding of the die filling process under gravity with special regard to the scalability from pilot scale to industrial scale rotary presses using a feed frame with one paddle. In this context, the applicability of a recently developed model for gravity filling is investigated [1]. At larger scales an evolving differential pressure in the dies, facilitating the filling process, was identified, which was covered by a model extension based on Bernoulli's equation. Finally, the model allows the calculation of the critical paddle speeds required for complete die filling under gravity at certain production rates and for several pharmaceutical excipients based on a few powder properties, machine and process parameters.