The supply conduit
The extruder according to the invention is characterized in that the end of the supply conduit and ducts formed of the openings of the rotor are designed in such a way that the sum of the areas of the parts of the ducts visible at the end of the supply conduit remains substantially constant at each moment when the rotor rotates. An essential idea of the invention is that at the end of the conduit supplying material to the rotor, i.e. at the junction between the stator and the rotor, at each moment as the rotor rotates the sum of the areas of the rotor ducts visible at the end of the supply conduit remains substantially constant. Further, the idea of a preferred embodiment is that the width of the end of the supply orifice substantially equals the distance between the centres of the rotor ducts or a multiple of the distance.
In such a case, material is supplied at least temporarily from the supply conduit to a minimum of two different rotor ducts simultaneously. The idea of yet another preferred embodiment is that the end of the supply conduit comprises an extension, whereupon the end of the supply conduit has a greater cross-section than the rest of the supply conduit. Further, the idea of a preferred embodiment is that the extension at the end of the supply conduit has a volume substantially equalling the volume of the rotor ducts situated at the extension. The idea of yet another preferred embodiment is that the extension at the end of the supply conduit has an asymmetrical form, i.e. the extension tapers off at the end.
The invention has the advantage that the material to be fed along the supply conduit can flow evenly from the supply conduit via the rotor ducts, whereupon there will be no pumping effect in the flow of material . By means of the extension at the end of the supply conduit, the conduit itself can be made so small that the flow of mass through the supply conduit does not have to remain in the supply conduit for long, which prevents the harmful uneven warming of the material. When the volume of the extension at the end of the supply conduit and the corresponding volumes of the rotor ducts are made equal in magnitude, the material in the extension can be made to change entirely during the time the rotor openings move from one end of the extension to the other, whereupon the time the material remains in the single screw extruder will be as short as possible and narrow in distribution. When the extension at the end of the supply conduit is made asymmetrical, the rotating rotor makes the material rotate in the same direction, and the asymmetrical extension that tapers off towards the end forces the material to enter via the rotor openings, providing a more even flow of supply.