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The ZS-EG twin-screw degassing unit from Coperion represents part of its range of degassing solutions for compounding and extrusion processes.

Coperion has made a number of improvements to its ZS-EG side degassing units.

The screw set has been optimised and the standard models of the ZS-EG are designed for an absolute vacuum of up to 50 mbar.

Lower degassing pressure is available on request and the ZS-EG is now fitted with a variable-speed screw drive as standard.

Compared to an open-vent dome, the twin-screw side degassing unit is said to offer many advantages.

It can be fitted at low cost to a combi barrel segment of the ZSK twin-screw extruder.

By replacing an atmospheric venting barrel with a combi barrel it can be retro-fitted in order to make full use of the performance of ZSK technology.

It delivers effective degassing, even with high air or moisture content of the bulk material at acceptable residence times so that plant throughput can be raised by 10 to 15 per cent.

It can improve compound quality and consistency as no material can fall back into the processing unit from the vent.

It can lower production costs through reduced cleaning and maintenance times as well as through lower wear.

It can also simplify machine control through simple operation and reduce accident risks, particularly during start-up.

The ZS-EG has deep-cut co-rotating twin screws to deliver its high venting capacity.

Due to the direction of rotation, it keeps the product within the processing zone.

The large free cross section of the flow channel ensures low gas velocities.

Quick-release connections allow the ZS-EG to be dismantled easily for cleaning and maintenance.

Typical applications for twin-screw degassing units include the manufacture of glass-reinforced or highly filled compounds, wood plastic compounds (WPC) or thermoplastic elastomers (TPE).

For example, Solvay Advanced Polymers in the US manages higher throughput when processing polyphthalamide (PPA) through the use of a twin-screw degassing unit as the gas flow channel is constantly open.

The new ZS-EG generation has increased plant output due to lower downtime for cleaning and maintenance.

Bayer Material Science achieves high and uniform product quality in the manufacture of polycarbonate compounds at its facility in Krefeld using a ZS-EG, since material cannot accumulate in the twin-screw degassing unit and fall back into the processing zone.

Downtime for maintenance and colour changes has dropped, while the availability of the compounding plant has increased.

Production costs are also lower since colour changes are easier and quicker.

Solvay and Bayer are said to have both benefited from the increased machine safety offered by the current ZS-EG configuration.

Twin-screw side degassing has advantages in the manufacture of wood plastic compounds (WPC).

The moisture contained in the wood flour escapes very quickly due to the high temperatures in the processing section.

In order to vent this gas stream safely, WPC plants from Coperion are equipped with both an atmospheric and a vacuum side vent.

Degassing takes place safely and without dust formation to achieve maximum throughput.

Coperion Werner and Pfleiderer

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