ABSTRACT
Feeders are used in conjunction with extruders in the pharmaceutical
industry for both melt extrusion and wet granulation processes to accurately
meter solids and liquids. Feedstocks include pellets, powders, granules,
gases, and liquids. Materials are either continuously metered directly into
the extruder, or alternatively into a vessel to facilitate a premix that will then
be fed into the extruder. Feed streams are introduced into the extruder either
in a ‘‘starve-fed’’ manner, where the rate is set by the feeders and is independent of the extruder screw rpm; or alternatively via gravity, referred
to as ‘‘flood feeding,’’ where the hopper sits over the feed throat opening and the extruder screw rpm determines the throughput. Twin-screw extruders are
typically starve fed, and single-screw extruders are normally flood fed. Figure 1 shows a typical, continuous, starve-fed melt extrusion installation
with multiple feeders.
