375807 The Influence of Unconfined Yield Strength on the Filling of Tablet Dies and Capsules

Thursday, November 20, 2014: 5:21 PM
210 (Hilton Atlanta)
Kerry D. Johanson, Material Flow Solutions Inc., Gainesville, FL

The filling of a tablet press die cavity is generally based on gravity feed into a very small cavity and the use of feed frames to induce the flow of material into small orifices.  The same is true for capsule filling devices; in some cases the filling is done by gravity, while in other cases external feed frames and tamping or suction devices aid the filling process.  In all cases, the ability of the powder to fill these cavities is dependent on the cohesive nature of the material.  Feed frame devices can help overcome some cohesive flow problems, but the addition of cohesion will always result in failure to produce reliable filling at some point.  Thus, it is important to understand the relationship between bulk cohesion and tablet weight variation.  We measured the weight variation of commercially produced capsules and compared it to the bulk strength of the powder within the capsules.  This was done by measuring the weight of capsules and then directly measuring the bulk strength of the small sample of material in each capsule.  Results of these measurements indicate that the tablet weight variation increased as the bulks strength increased.  At a critical strength value the weight variation was skewed to lighter values, indicating that bulk strength tends to limit the filling process such as to produce under-filled tablets and capsules.  We developed a theoretical strength based model that describes the filling capacity of capsules and tablets as a function of the cohesive flow properties.  This model was compared to the observed capsule data and showed good agreement.

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See more of this Session: Solids Handling and Processing I
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