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Bubbles, voids and porosity in extruded plastic nearly always point to the same thing. Something gassy stayed in the melt when it should have come out. Water vapour, trapped air or volatiles from the polymer and additives, all expanding as the product leaves the die.
The fix starts in the barrel. Vent ports with vacuum are there to strip that gas out before the melt reaches the die. If the venting is not doing its job, porosity follows.
Most of the time venting underperforms because the vacuum has been turned down to stop melt coming up the port. Or the vent has partly blocked and is not drawing properly. Either way, gas stays in and quality suffers.
A Screwtech Engineering vent port stuffer tackles both. Its self-wiping twin screws keep melt in the barrel and the port clear, and its precision tolerances allow full vacuum to be drawn. Moisture and volatiles come out, and the increased extruder pressure that follows improves porosity in the finished product.
The units are built from high quality stainless steel, with an oil filled gearbox and water cooled jacket for long life at high temperature, and an easy clean two-part vacuum chamber with separate seal housing.
If you are scrapping product because of bubbles or voids, the vent is a good place to look. Screwtech supplies vent port stuffers in various sizes for twin-screw and single-screw extruders. Speak to the team about your line.
For more information on What causes bubbles and porosity in extruded plastic? talk to Screwtech Engineering