Progressively decreasing the volume of the solids bed has the result of keeping it
in contact with the interior wall of the barrel as a progressively larger portion of the one of the materials becomes plasticated. In a second section, all of the remaining unplasticated material is plasticated. A good indication that all material has been plasticated is that the single screw extruder maintains an essentially constant output of extruded material and that the amperage of the motor which powers the extruder remains essentially constant.