1. Field of the Invention
The present invention relates generally to extruders and, more particularly, to a twin-screw extruder having an inlet head section provided with an internally grooved surface.
2. Description of the Prior Art
Both single screw and twin screw corotating intermeshing extrusion mechanisms are used in the food processing industry and convey material from an inlet to a die by virtue of having the material slip on the surface of the screw or screws. However, in single screw mechanisms, the head or barrel wall of the extruder can produce insufficient resistance to prevent the extrudate from spinning at the barrel wall and thus material will stick on the screw surface and not be conveyed forward.
In order to prevent the extrudate from sticking to the single screw and spinning at the head wall, the inside bore of the single screw extruder head is often grooved with helical grooves which are configured to propel the extrudate toward the die. These grooves act to increase the friction between the wall and the extrudate so as to prevent the extrudate from spinning at the head wall, and thus tend to provide a cleaning of the single screw. Further, because the helical grooves serve as an extension of the screw helix, the capability of the mechanism to propel the extrudate toward the die increases, thus providing an increase in the capacity of the single screw mechanism.
In co-rotating twin screw mechanisms with fully intermeshing screws, there is an interaction of one screw flight with the flow channel in the adjoining screw. Thus, if any extrudate sticks to the screw surfaces, the adjacent screw crest wipes the material from the companion screw flank as the two screws intermesh and the adjacent screw thus transports the extrudate forward. Because of this interaction between the screws, it has not in the past been thought necessary to provide anti-rotational mechanisms in the barrel walls in order to achieve a self-cleaning construction.