Mixing device in the screw antechamber of a twin-screw extruder

A mixing device for a counter-rotating twin-screw extruder for the extrusion of PVC, the mixing device comprising:

• parallel or conically arranged screws;
• a first screw and a second screw configured and arranged for mixing a melt stream, the first screw including an extension in the form of a mixing screw tip, at least one screw flight and at least one wing arranged substantially paraxially or helically wound on a tip core of the mixing screw tip, and a pitch (P) of the at least one screw flight is greater than a nominal diameter (ND) of the first screw;
• a first screw antechamber including a first melt channel with a cylindrical shape and configured and arranged to receive from the first screw;
• and
• a second screw antechamber including a second melt channel;
• wherein the first melt channel is arranged in a flow-connected manner via an elongated slot, the slot is formed by overlap of the first melt channel with the second melt channel, into which the second screw conveys;
• wherein the pitch (P) is twice to five times as large as the nominal diameter (ND), and in that the mixing screw tip extends over a length (L) in the direction of a longitudinal axis (B) which is equal to or greater than the nominal diameter (ND) of the first screw.