plastic material is designated with reference numeral 10 the single screw extruder 10 hereinafter simply called extruder comprises a tubular barrel 11 which is made up of three single tubular barrel assemblies 12 14 16 in the present embodiment the connection of the single assemblies 12 14 16 is achieved by respective flanges 17 the barrel 11 is divided in multiple functional longitudinal sections namely a filling zone 21 followed by a feed zone 22 a melting zone 23 a homogenizing zone 24 and finally a demoulding zone 25 in fig1 a the filling zone 21 forms the right end and the demoulding zone 25 forms the left end of the barrel 11 within the barrel 11 a screw 30 is coaxially and rotatably mounted therein for clarity reasons neither the screw drive nor the screw bearings are shown moreover for clarity reasons the diagram does also not show that the screw according to the present invention is formed as a barrier screw a more detailed description of the barrier screw follows hereinafter the screw 30 extends from the screw shaft and the filling zone 21 to the end of the homogenizing zone 24 in the assembly 12 of the barrel 11 an opening 27 is provided in the area of the filling zone 21 the opening allowing a connection from outside into the inner space of the barrel 11 for improving the feeding of initial material a funnel 28 is mounted on the opening 27 0038 fig1 a further shows that the assembly 12 comprises an inner liner 32 which is inserted into the tubular assembly 12 the liner 32 comprises axial grooves formed at its surface facing the screw 30 in fig1 a two of these.