Investigation of powder flow within a pharmaceutical tablet press force feeder - A DEM approach

Powder flow in rotary tablet presses, constituting one of the key machines in the tablet production chain, is today still considered as a black box. In this study, a discrete element approach is presented to assess the powder flow in a lab-scale rotary tablet press with a force feeder consisting of three paddle wheels of different shapes. Process conditions are chosen same as in reality and a model direct compression formulation with a poly-disperse particle size distribution is considered. Different means of process insights, e.g. tablet mass and API content, mass holdup in the different paddle wheel zones, particles' velocity, particle's segregation and mixing within the feeder, and residence time analysis, are presented. A direct link between the powder flow in the force feeder and the tablet quality attributes is established. Over the production time the particles filled into the dies have traveled different distances in the force feeder during which their particle properties might change. Thus over the die height differences in terms of particle size and particle properties due to particle attrition and over lubrication are identified. This intra-die variability is a direct consequence of the de-mixing in the force feeder and the shear forces exerted by the different paddle wheels. Modifications in terms of force feeder design, e.g. paddle wheel arrangement and blade shapes, are suggested as they could decrease the de-mixing side effect and enhance product quality. Finally, process understanding could be improved which helps in pharmaceutical development and increases the patient's safety. (C) 2019 Published by Elsevier B.V.