Krauss-Maffei: Twin-screw extruder with 36 L/D

Krauss-Maffei, Germany, is showcasing a new generation of counter-rotating twin-screw extruders with 36 L/D processing units, incorporating a radically new processing technology for PVC. The new 36 L/D extruders have two venting zones. In this double-venting process, the dry blend is fed to the processing unit, where it is compressed and preheated as usual. By the time it reaches the first venting zone, after 15 D, the material is compressed, but still powdery. In this zone, air that entered along with the material is allowed to escape via two long vents in the barrel. Then follows a further compression phase before the melt reaches the second venting zone, where a vacuum extraction system removes the remaining air and volatile constituents. The ratio of mechanical energy to heat energy applied to the melt is thus significantly reduced. As a result, although 36 L/D machines have 17% higher output, compression values in the restricted flow zone are much lower than in 26 L/D extruders. This innovation significantly reduces wear on the screws and barrel.

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