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Single-screw extruder with production benefits

To increase the economic efficiency of single-screw extruders, processing equipment manufacturer Troester has introduced an alternative to current designs featuring gearboxes. The RotoSpeed PXS is said to provide an increase of melt throughput via higher screw speeds compared to similarly sized gear-driven extruders.

The unit operates at 800 rpm and its developer, Tim Pohl, R&D director at the company, says the 45-mm extruder is capable of providing the same output as a 60-mm extruder operating at normal speed. The unit includes a proprietary screw design for pulsation-free inflow of material. This gives a linear conveying behavior over the screw speed range and helps control melt temperature.

The line features four individual three-phase asynchronous motors transmitting power through a single pinion shaft onto a central drive gear. Noise generation of the CMG Drive is said to be substantially lower than existing gearbox-driven extruders. As this type of drive is a coaxial system with hollow shaft, a coupler to a gearbox drive is unnecessary. It allows the screw to be removed quickly from either end by means of a quick-change clamp and hinged flange.

Output for the 45-mm diameter screw unit, when running at 800 rpm, ranges from 120 to 155 kg/hr for medium- and high-density PE, up to 150 kg/hr for LDPE and PP, and up to 160 kg/hr for flexible PVC.

The PXS, which targets cable and pipe extrusion, competes head on with the Reifenhauser REItorque (formerly called REI-Compakt) direct-drive gearless single-screw extruder (June 2003 MP/PI). Instead of using four small motors to drive the single-drive gear, Reifenhauser relies on a single linear motor, first supplied by Etel (Mitiers, Switzerland). It has since switched to motors from Siemens. Pohl says the single linear motor concept is supplied by an outside vendor, which he won't name but appears to be gearbox manufacturer K.& A. Knodler (Ostfildern Ruit, Germany).

Hans-Peter Krukenberg, Reifenhauser sales director for profit center extruders, believes the linear-motor concept provides fewer points that could break down, and offers better energy savings and less heat generation. Reifenhauser GmbH & Co. Maschinenfabrik, Troisdorf, Germany; +49 2241 481256; www.reifenhauser.com; Troester GmbH & Co. KG, Hanover, Germany; +49 511 8704285; www.troester.de

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