Experiments and Modelling of Air Pressure Effects on Powder Flow for Die Fill on Rotary Presses

Tablet production using high speed rotary presses involves powder handling and dosing operations that need to be performed consistently to ensure weight and content uniformity as well as efficiently for achieving high production rates. Research into the flow through the feed frames of rotary presses identified gravity and suction fill mechanisms where a low pressure is created in the die during the filling process.

Experiments with increased complexity have been carried out to characterise:

• Hopper discharge into a controlled pressure chamber
• Gravity and suction die fill mechanisms using a linear shoe-die system
• Powder flow through a model rotary powder feeder into a controlled pressure chamber

Corresponding numerical modelling have been carried out using a coupled discrete element model (DEM) and computational fluid dynamics (CFD). The paper presents flow rules developed using the coupled model for the three problems above. The potential impact of the experimental results and flow models is significant for the design of die fill operations on tablet presses and other powder dosing processes.