Extruder basket-type

Another continuous extrusion press that finds increasing but specialized application, mostly in the pharmaceutical industry, is the basket-type extruder (Figure 317). This type of equipment is similar to the radial discharge extruder except that material is fed into the extrusion zone by gravity... 

Forces developing in basket-type machines are similar to those described for screw extruders except that the additional compressive force of the screw(s) is not present. These devices generally result in the least compaction of all extrusion apparatuses and, therefore, the number of applications is rather limited. Attractive features for the pharmaceutical industry are low energy input coupled with minimal temperature rise in the mass, high porosity, and quick dissolution of the product. 

These studies point towards the need to optimize moisture content of the wet mass and extrudate by careful selection of formulation ingredients and type of extruder. A basket or gear/roll extruder is preferred for a very dense and moist wet mass, as it generates little shear and rise in temperature, while an axial or radial screw extruder which increases granule density and hardness is desirable for a wet mass which is less cohesive with poor binding. 

Figure 12.16. Two types of extrusion pelleting equipment, (a) Screw-type extruder for molten plastics The die is turned 90° in the illustration from its normal position for viewing purposes. The extruded material is cooled and chopped subsequently as needed, (b) Ring extruders material is charged with screw conveyors to the spaces between the inner rolls and the outer perforated ring, the ring rotates, material is forced through the dies and cut off with knives. (Walas, 1988). (c) BEPEX basket extruder (Courtesy of Hoso Kawa. BEPEX Gmblh).

Basic types of extruders include both screw extruders such as axial endplate, radial screen, and basket designs, as well as pelletization equipment described above, such as rotary cylinder or gear and ram or piston extruders (Fig. 21-136). See Newton [Powder Technology ana Pharm. Processes, Chulia et al. (eds.), Elsevier, 1994, p. 391]> Pietsch (Size Enlargement by Ag omeraUon, Wiley, 1992), and Benbow and Bridgwater (Paste Flow and Extrusion, Oxford University Press, 1993). 

One problem with this type of continuous reactor is the potential for catalyst loss during the removal of the reaction liquid. With a powdered catalyst this loss can be minimized by the use of an appropriate filter on the exit line inside the reactor. Catalysts made from granular or extruded supports can be placed in a basket... 

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