Numerical simulation of powder flow in a pharmaceutical tablet press lab-scale gravity feeder

Abstract

The die filling process within a lab-scale rotary tablet press is simulated using the Discrete Element Method (DEM). The particle motion is captured as particles travel from the gravity feeder consisting of a chute connected to the shoe represented by a rectangular box to the dies/cavities of the turret. The particles fill the dies mostly due to gravity. The process conditions such as die table speed, die diameter as well as the material characteristics e.g. cohesion, coefficient of friction, coefficient of restitution, etc. influence the die filling process. The process conditions and material characteristics are systematically investigated by varying one of those parameters at a time while keeping other conditions constant. Eventually process conditions as well as material properties were changed simultaneously to analyze interaction relationships. The results give both qualitative (powder flow pattern from the feeder to the dies) and quantitative (tablet mass variation, mass flow rate etc.) insights into the die filling process. The numerical results indicate that faster die table speeds and smaller die diameters give rise to lower tablet mass with a significantly increased mass variation, which would eventually increase the challenges in meeting the specifications. On the other hand, cohesion between the particles significantly reduces the tablet mass and increases the mass variation. The influence of particle-wall friction coefficient on the particle rearrangement is analyzed both qualitatively and quantitatively, which shows that increasing the particle-wall friction reduces the dead zones within the shoe. The coefficient of restitution does not exhibit any influence on the die filling which may be attributed to the very confined space of the feeding system. Eventually this study emphasizes the importance of tablet blend characterization prior to tableting and provides operators with optimal process parameters and material attributes to ensure a high tableting process performance.