AbstractUsing simulation, the steady state performance and transient behavior of starved extrusion screws are described. At steady state the filled length of the extruder is controlled by the relative resistance of the screw and die to flow, the flow index of the extrudate, and the feed rate to the extruder. For transient situations, small variations in the composition or feed rate of the material being extruded can significantly alter the extruder's output and filled length. Because of the broader residence time distribution of a twin screw extruder compared to a single screw extruder, the magnitude of the transient effects are seen to be smaller for twin screw extruders. The predicted output transients for extruders operated in the starved condition are of significantly lower magnitude than that for extruders operated in a filled condition. The implications of these effects on the design and operation of extrusion systems are discussed.
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