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Extrusion Troubleshooter - Graphic
Prevent Streaks & Specks From Vented Extruders
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By Chris Rauwendaal, President
Rauwendaal Extrusion Engineering Inc.
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In normal operation, the partially filled length (inset) has a melt pool at the pushing side of the flight, a gas pocket ahead of the melt pool, and a melt film along the barrel but not on the screw.
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Appearance problems start with a drop in barrel pressure. The filled length of the screw then shortens, leaving melt film to degrade slowly on the now empty screw surface. The next time barrel pressure increases, the partially empty flight will become filled. Shear action will scour degraded particles off the screw.
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