Twin screw extruder screw design - one, two, three
Twin screw extruders mix, devolatilize and perform reactions in a continuous manner with the end product being either a pellet or extruded part. Whether the screw rotation is co-rotating or counterrotating the twin screw extruder performs the same basic process tasks: feeding, melting, mixing, venting, and developing die/localized pressure. Modular screws and barrels make an infinite number of process configurations possible.
There are, however, only three families of screw elements: (1) flighted, (2) mixing, and (3) zoning. Flighted elements feed and forward material past barrel ports, through mixers and out of the die. Mixers can be dispersive and/or distributive, depending upon the amount of elongational acceleration or shear versus the number of melt divisions in the design. Zoning elements isolate two operations within the extruder, such as for providing a vent seal. Screws can be shear intensive or passive, based upon the elements used and machine operating conditions.
Example: typical process schematic
