Residence time distribution of a continuously-operated capsule filling machine: Development of a measurement technique and comparison of three volume-reducing inserts.

This paper presents the measurement and analysis of the residence time distribution (RTD) of a tamping-pin capsule filling machine. The tamping speed and the amount of material inside the powder bowl proved to have a significant effect on the RTD. Various inserts into the powder bowl that reduce the volume and alter mixing and transport in the bowl were experimentally investigated. To obtain the RTD, a tracer-based measurement method was applied and a sophisticated data processing strategy was developed. The tracer-based method also allowed investigations of stagnant zones in the powder bowl, another important aspect in continuous manufacturing (CM). The suitability of tracer material was assessed based on a detailed characterization of bulk and tracer material. Characteristic parameters of the RTD were extracted and compared, proposing a systematic strategy for selection of a suitable insert.