Evaluating the impact of stirrer design on powder behaviour in capsule filling using dyed lactose as tracer

Abstract

Ensuring temporal and spatial uniformity in the chamber of a capsule filling machine with vacuum drum is crucial for consistent dosing to in-row capsules. A stirrer must induce axial mixing to maintain a homogeneous powder bed and prevent accumulation in specific regions, primarily caused by the feeding system above the chamber. To achieve satisfactory filling, the performance of different stirrers was analysed using a tracer particle strategy. This contribution introduces a lactose dyeing process, preventing agglomerate formation and yielding minimal differences in powder properties. Four lactose grades, exhibiting diverse particle sizes and flow behaviours, were dyed with methylene blue. A comprehensive analysis of lactose properties, such as particle size, density, and flow behaviour, confirms minimal alterations post-dyeing. Tracers obtained through this process reveal that a spike-type stirrer induces more axial mixing compared to a wire-type stirrer. The dyed lactose tracers effectively contribute to understanding and optimising the capsule filling process.