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In an intermeshing twin-screw extruder with the co-rotating screws, the extruded material is more evenly mixed and spends less time in the extrusion barrel than its single-screw counterpart. This decrease in dwell time is caused by an increase the material's speed down the barrel, which is allowed due to the elimination of back pressure.<ref name="Wolcott & Englund" /> Back pressure{{W|Back pressure}} is present in single-screw extruders because of the friction forces created by the screw. The utilization of two screws in this intermeshing extruder eliminates backpressure by displacing the material using the screws themselves and not friction.<ref name="Wolcott & Englund" /> This increase in material speed allows for a smaller energy input during forming and lower material temperature rise during extrusion, which produces better material properties in the final product and increased energy efficiency.<ref name="Wolcott & Englund" /> Furthermore, this design allows for increase materials efficiency as no compounding process is required when this forming process is used, which means no material can be lost between processes. | In an intermeshing twin-screw extruder with the co-rotating screws, the extruded material is more evenly mixed and spends less time in the extrusion barrel than its single-screw counterpart. This decrease in dwell time is caused by an increase the material's speed down the barrel, which is allowed due to the elimination of back pressure.<ref name="Wolcott & Englund" /> Back pressure{{W|Back pressure}} is present in single-screw extruders because of the friction forces created by the screw. The utilization of two screws in this intermeshing extruder eliminates backpressure by displacing the material using the screws themselves and not friction.<ref name="Wolcott & Englund" /> This increase in material speed allows for a smaller energy input during forming and lower material temperature rise during extrusion, which produces better material properties in the final product and increased energy efficiency.<ref name="Wolcott & Englund" /> Furthermore, this design allows for increase materials efficiency as no compounding process is required when this forming process is used, which means no material can be lost between processes. | ||
Despite the improvement in energy and materials efficiency, the twin-screw extruder is a very expensive upgrade from the single-screw extruder | Despite the improvement in energy and materials efficiency, the twin-screw extruder is a very expensive upgrade from the single-screw extruder. The economics that play into upgrading to this more efficient machine is discussed below. | ||
== Economic Analysis of Implementing Wood-plastic Composite Products == | == Economic Analysis of Implementing Wood-plastic Composite Products == |