Filling is a common operation across all industries, although fill weights and tolerances vary widely. The pharmaceutical industry often requires milligram doses to be filled accurately and at high speed, in order to meet the stringent criteria and high throughput requirements of tablet manufacture. By contrast, the bulk chemicals and minerals industries may load powders into 20 ton containers, employing a much longer filling process and without the regulatory pressures governing accuracy.
The factors that influence filling efficiency will depend on the type of equipment being used. Some systems are purely gravity driven, whilst others rely on force-feeding. In many applications, such as tablet manufacture on a rotary press, the powder fills the dies through a combination of gravity and force-fed flow. The influence of each of the two mechanisms will depend on the geometry of the feedframe, the flow rate through the press and the characteristics of the powder. It is easy to see, with wide variation in each of these variables that this is a complex process and remains challenging to model from knowledge of a limited number of particle properties and process parameters.
At large scale, such as filling of bags or bulk containers, the process might be volumetric filling or one based on mass. In both cases, it is typical that augers or rotary valves directly attached to the bottom of the feed hopper are employed. In this configuration, the factors that control filling efficiency may be different to those in tablet manufacture, however, efficiency across all scales and in all processes will depend on the compatibility of the material properties with the conditions imposed in the processing environment.
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