Single Screw Extruder For Continuous
In a single screw extruder for continuous working and/or processing of flowable substances having at least two parallel, corotating shafts equipped with intermeshing screw elements whose face is limited by circular arcs corresponding to the outside twin screw extruder, the screw core diameter and at most the center distance of the screw elements, and guided on circular segments of the extruder housing that are parallel to the shafts, at least one screw element (1) has a plurality of concentric ring portions (8) spaced a distance apart and formed by grooves (12) turned into the screw element (1).
The ring portions permit additional dispersing surfaces to be gained. A substantial enlargement of dispersing surface can moreover be obtained if the screw portions between the ring portions are disposed at a progressive angular offset from each other with the same sense of rotation, for example at an angular offset by half the flight angle. The angularly offset screw portions form faces angularly offset in step-like fashion as additional dispersing surfaces.
The sheet production extruder can have only two screw shafts. However, it can also have at least three shafts disposed along a circle or circular arc with the same central-angle distance within a cavity of the extruder housing, the extruder housing being provided on the radially inner and outer sides of the cavity with concave circular segments parallel to the extruder axis, on which the screw elements are tightly guided, as described for example in EP-B-0788867. The inventive screw elements thus permit substance to pass through the ring of shafts from one side of the cavity to the other.
In the following, the inventive extruder will be explained in more detail with reference to the drawing, in which:
FIG. 1 shows a cross section through a twin-shaft extruder with screw elements closely intermeshing on the whole circumference;
FIGS. 2 a to 2 c show a side view, perspective view and view of the transverse profile of a first embodiment of the screw element;
FIGS. 3 a to 3 b show a side view, perspective view and view of the transverse profile of a second embodiment of the screw element; and
FIG. 4 shows a perspective view of a third embodiment of the twin screw extruder; and
FIG. 5 shows a perspective view of a fourth embodiment of the single screw extruder