Elimination of a Restriction at the Entrance of Barrier Flighted Extruder Screw Sections

Barrier flighted screws have been used for many years to increase rates, to eliminate flow surging due to solid bed break up, to lower melt temperatures, and to minimize temperature fluctuations in the extrudate. For most barrier screws, the melt separation flight starts at a location where the melt pool starts to accumulate. However, if the start of melting occurs downstream from this point, compacted solid polymer can be wedged into the start of the barrier entrance. For some barrier screws, this wedging can lead to a restriction in the flow, decreasing the rate of extrusion by up to 30%. This paper will discuss the phenomenon and show how to eliminate the problem.