What is vacuum venting in extrusion?

Vacuum venting is the process of pulling unwanted gases out of polymer melt while it is in the extruder barrel. A vent port is opened part way along the barrel, a vacuum pump is connected, and air, water vapour and volatile compounds are drawn off before the melt reaches the die.

For it to work, the screw configuration has to drop the pressure at the vent zone so the melt opens up and releases its gas. The vacuum then does the rest. The stronger the vacuum, the more moisture and volatiles come out.

That is the theory. In practice, a strong vacuum on an open port tends to pull melt up along with the gas. So processors often run less vacuum than they want, and accept some gas left in the product.

A vent port stuffer lets vacuum venting work properly. Screwtech Engineering stuffers sit on the vent and use a self-wiping twin-screw design to keep melt in the barrel. Their precision tolerances mean full vacuum can be drawn, removing moisture and volatiles without losing process material.

Screwtech units are made from high quality stainless steel, with an easy clean two-part vacuum chamber and separate seal housing. The oil filled gearbox with water cooled jacket gives long life at high temperature.

Various sizes are available to suit twin-screw and single-screw extruders. If your vacuum venting is not delivering, talk to Screwtech Engineering.

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