Depth profiling taper section

Finally, as pointed out earlier, extruder screws have tapered channel sections. The various shaped pressure profiles that can be obtained in simple non-parallel plate geometry explain the experimentally observed pressure profiles in screw extruders. For example, in a common metering screw (with a constant channel depth feed section, followed by a tapered section and a constant channel depth metering section), under normal conditions the pressure profile exhibits a maximum in the tapered section with the pressure dropping in the metering section to the die pressure. 

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