The sheet production extruder housing
The extruder can thus have for example at least three shafts parallel to the extruder axis and disposed in a cavity of an extruder housing along a circle or circular arc at equal central-angle distance, the extruder housing being provided on the radially interior and exterior sides of the cavity with concave circular segments parallel to the single screw extruder axis with the slip-on elements being guided on said segments. The cavity can also be of annular configuration.
The slip-on element has the smallest wall thickness in the area of the circular arc corresponding to the slip-on element core diameter. When the shaft transmits a torque, said shaft twists more than the slip-on elements which are harder and torsionally stiffer than the shaft. The slip-on element therefore absorbs this force in the particular area of the shaft. Upon this force transmission the ends at the lowest thickness of the slip-on element are exposed to the strongest load.That is, it is necessary to at least maintain a minimum wall thickness of the slip-on element in the area of the circular arc with the slip-on element core diameter.
According to the invention, the flight depth of the conveying or similar slip-on element is increased at high torque transmission of the shaft-to-hub connection. That is, at equal center distance the outside diameter of the slip-on element is greater and the core diameter of the slip-on element reduced by the same measure, which considerably increases the free conveying surface of the conveying element or working surface of the working element and thus the performance of the twin screw extruder. For this purpose, the slip-on element whose cross section comprises three circular arcs is configured in the area of the circular arc corresponding to the slip-on element core diameter without a shaft-to-hub connection with flat contact against the support shaft and/or provided at its ends with reinforcement segments.
This is obtained in the invention by providing no force transmission of the shaft-to-hub connection in this area. Thus, the cross-sectional area that the shaft-to-hub connection otherwise occupies in this area can be added to the cross-sectional area of the slip-on element in this area and thus the flight depth accordingly increased without impairing the strength of the support shaft.
The surface with which the support shaft and the slip-on element fit in the area of the slip-on element with the circular arc corresponding to the slip-on element core diameter can be a surface curved in a circular arc, or a plane surface, i.e. one corresponding in cross section to a straight line. Additionally and in the case of single-start slip-on elements, the slip-on element can be reinforced at its ends by preferably annular reinforcement segments in order to absorb the above-described great forces occurring at the ends of the slip-on element upon torque transmission.
The product flow is slowed down by the reinforcement segments, but this effect is partial and so slight that it does not play any part in practice. The inventive sheet production extruder has at least two support shafts, but it can also have a substantially larger number of support shafts.