Vented single screw for extruder
Part of the way along the extrusion barrel, the diameter of screw root is reduced to decompress the melt. At this point, a vent, through which the vapor escapes, is located in the barrel (when venting is not needed, the vent may be plugged and not used). Then, the vapor-free melt is sent towards the die and re-compressed by increasing the diameter of the screw root.
A dam or torpedo section is integrated on the screw just before the vent to make sure that melt does not escape through the vent. Due to the design and operation of the vented machines (a variable screw geometry and a high L/D ratio), it has been observed that these produce excellent mixing.