How do I remove moisture from plastic during extrusion?

Moisture in plastic is bad news. It turns to steam in the barrel, leaves bubbles and voids in the product, and with some polymers it breaks down the material itself. Drying the raw material helps, but it is not always enough, and it is not always practical with recycled or filled feedstock.

That is why extruders have vent ports. Part way along the barrel, the screw configuration drops the pressure and opens the melt up, and a vacuum pump draws off water vapour and other volatiles. Done properly, it is one of the most effective ways to get moisture out.

The catch is that a strong vacuum on an open vent can pull melt up with the gas. To avoid flooding, many processors run the vacuum lower than they would like. Less vacuum means less moisture removed, and you are back to bubbles.

A vent port stuffer from Screwtech Engineering solves that trade off. Its self-wiping twin screws push any rising melt back into the barrel, while precision tolerances allow full vacuum to be drawn. So you get proper moisture removal without losing product out of the vent.

Screwtech stuffers are built from high quality stainless steel with an oil filled gearbox and a water cooled jacket, made for long life at high temperature. The two-part vacuum chamber is easy to clean.

Various sizes are available to suit twin-screw and single-screw extruders. If moisture is causing quality problems on your line, speak to Screwtech Engineering about getting your venting working properly.

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