Abstract
Die filling is an important process step in manufacturing of tablets. An important mechanism in the die filling process is suction that is developed with the downward motion of the bottom punch once the die is covered by powder. However, the contribution of suction to the die filling performance is still poorly understood. Hence, the present study aimed to experimentally investigate the flow behaviour of powders during suction filling. Four different types of pharmaceutical powders were used and a model suction filling system was developed. Effects of filling and suction velocities, as well as powder properties, on the efficiency of die filling were systematically investigated. Cohesive and free-flowing powders behaved differently at various filling-to-suction velocity ratios. The filling behaviour of cohesive powders was improved at high filling-to-suction ratios due to acceleration-induced densification. Free-flowing powders performed better at low filling-to suction ratios.