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Vent port flooding is when molten polymer comes up through the vent opening instead of staying in the barrel. It is messy, it wastes material and it nearly always ends with the line being stopped so someone can clear it.
The usual culprits are fairly well known. A high fill level under the vent means there is simply too much material in that part of the barrel. Pressure building upstream pushes melt towards the nearest way out. A screw configuration that does not properly decompress the melt at the vent zone leaves it nowhere to go but up. And a strong vacuum can draw melt up along with the gases.
Material type plays a part too. Some polymers and filled compounds foam or swell as volatiles come out, and that expansion lifts the melt into the port.
Traditionally, processors fight flooding by tweaking screw design, cutting throughput or turning the vacuum down. Each of those trades one problem for another. Lower output costs money. Less vacuum leaves moisture and volatiles in the product.
A vent port stuffer from Screwtech Engineering tackles flooding directly. Its self-wiping twin screws convey any rising material back into the barrel while letting gas escape. Precision tolerances mean full vacuum can still be drawn, so you do not have to compromise on degassing.
Because the stuffer takes care of the vent, the screw configuration becomes less critical and you can run at higher fill levels. Screwtech supplies stuffers in various sizes for twin-screw and single-screw extruders. Get in touch to find the right fit for your line.
For more information on What causes vent port flooding in extrusion? talk to Screwtech Engineering