The development of an instrumented tamp-filling capsule machine II. Investigations of plug development and tamping pressure at different filling stations.

A previously described [Eur. J. Pharm. Sci. 10 (2000) 267] pneumatic tamping head with attached instrumentation, capable of recording tamping forces generated on a Bosch GKF tamp-filling machine with high precision was employed to investigate the development and density of plugs during capsule tamp-filling of two soft, ductile powders. The study aimed to make a contribution to control capsule fill weight by monitoring the tamping force. The results indicated that the tamping station utilised to measure the tamping force and that involved in the regulation of the pressure of the pneumatic chamber of the tamping head should preferably not be the same. A possible solution would be to install the instrumented pneumatic tamping head on tamping station 4, after which in all cases plugs had formed to their maximum length and density. A second pneumatic tamping head, without instrumentation, could be installed on tamping station 3, which would receive signals from the instrumentation, and as a result the inner chamber pressure of this second pneumatic tamping head could be changed to adjust fill weight. The cumulative tamping distance should be large enough to produce a force reading well above the limit set by the inner chamber pressure, but small enough to avoid overfilling of the capsules. The latter can be detected monitoring the variability of the tamping forces recorded. A larger standard deviation of the tamping forces obtained from tamping station 4 was found to be a strong indicator of overfilling.