Powder filling into hard gelatine capsules on a tamp filling machine.

A series of pharmaceutical excipient powders used in capsule formulations as fillers have been filled into hard gelatine capsules on a Bosch GKF-400S tamp filling machine. These machines depend on pushing pins through a powder bed so that a unit dose is transferred into a dosing disc. This dose is then ejected into the capsule body. The results indicate that the range of powders that can be filled on this type of machine exceeds that applicable to a dosator nozzle system. Filling problems due to powder flooding could be solved by increasing the powder bed height in the powder bowl. The fact that such powders usually do not form a firm plug was not reflected in the coefficient of fill weight variation, and uniform filling could hence be achieved without problems. The influence of the powder bed height on the capsule fill weight increased with decreasing powder flow. The influence of the setting of the tamping pins on the capsule fill weight was comparatively small and further decreased with a decrease in powder flow. However, when a granulated product (Elcema G250) was filled, the tamping pin setting was more important than the influence of the powder bed height on the capsule fill weight. For moderate flowing powders the coefficient of fill weight variation appeared to be nearly independent of powder bed height or tamping pin setting. However, the filling performance of powders with poor flow properties could be adjusted by optimising both machine settings. Very complex relationships were found between the powder properties such as angle of internal flow, dynamic densification profile, Carr's compressibility index and particle size and shape, and the filling behaviour.