Comparison of two paddle wheel geometries within the filling chamber of a rotary tablet press feed frame with regard to the distribution behavior of a model powder and the influence on the resulting tablet mass

Objective: The purpose of this study was to compare the influence of two different paddle wheel geometries on the distribution behavior of a model powder within the filling chamber of the modified feed frame of a rotary tablet press. Moreover, both paddle wheels were compared regarding their influence on the resulting tablet mass during the tableting process. Significance: Insights are provided regarding the influence of the paddle wheel geometry on the powder distribution to optimize the die filling process. Materials and methods: Avicel PH 102 served as model powder. A laser triangulator was used to scan the powder surface level within the feed frame and, combined with the determination of the angle position of the paddle wheel, an in-house written software was used to calculate the powder surface profiles and filling levels. Two experimental setups, one based on the filling chamber filled with a defined amount of powder (offline) and one using the filling chamber during tableting (inline) were applied. Results: Both paddle wheel geometries caused a significantly different distribution behavior of the powder within the filling chamber. The tablets obtained with the round rod filling wheel showed significantly higher tablet masses and significantly lower standard deviations. The inflow of powder into the filling chamber appeared to be improved with the round rod filling wheel. Conclusions: Under the applied experimental conditions, the round rod filling wheel showed obvious advantages compared to that with flat rods in terms of the uniformity of tablet masses and the extent of die filling.