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Planetary roller extruders are machines from the plastic industry and belong to the superordinate group of extruder. It was invented by Ludwig Wittrock in the early 1950s and was initially widely used in the PVC calendering industry. Today, the planetary roller extruder covers the entire range of compounding and reaction technology.

Construction of the planetary roller extruder

At the planetary roller extruder a central spindle is driven on which the individual spindles, to be varied in their number, roll off. The rotating planetary spindles are additionally guided via an internally toothed liner. The heating-cooling takes place both via the central spindle and via the cylinder assembly. While the central spindle is rotating, the planetary spindles catch the material and by meshing of the spindle teeth with the corresponding tooth gaps, the supplied material is rolled out into thin layers and brought forward by means of the helix. The repeated thin-layer rolling-out with the planetary spindles and the large heat exchanging surface of the extremely thin-walled cylinder assembly ensure optimal plastification, dispersion and homogenization.

Standard planetary roller extruder for the plastic industry

To provide an idea of the contact surface area of a planetary roller extruder, we regard the standard size of a calender feeding extruder. With one revolution of the central spindle, this planetary roller extruder exchanges approx. an area of two tennis courts per minute.

Special features

The manufacture of cylinder liners by means of deep erosion offers various advantages compared with the conventional production methods drawing, whirling or grinding. On the one hand and exact geometry of the involute toothing also in hardened material, on the other hand a minimal wall thickness of the cylinder liner. Especially this minimization of the wall thickness together with the repeated thin-layer rolling-out enable the most exact and gentle material compounding of all (compounding) extruders. With this system, even material mixtures with high viscosity differences can be easily processed.

A further special feature is the modular design of the planetary roller extruder. At the modular construction, several cylinder assemblies are coupled one behind the other and thus the procedural path is multiplied or the process technology is adapted to the respective requirements. As a result, the planetary roller extruder, in contrast to other conventional compounding extruders, has the possibility of connecting in series process chains. During one process, several reactions (such as degassing, injecting liquids or adding fillers and solid components) can be run in sequence.

Fields of application

Due to their exact and gentle material compounding, planetary roller extruders can be used in following fields of application:

• Plastics industry: all PVC formulations, ABS, TPO, TPU, filled polyolefins, prepex, rubber processing, elastomer adhesives
• Colour industry: epoxy, polyester, acrylic and similar lacquers
• Chemical industries: mixtures with endothermic and exothermic reactions
• Food industry: all thermal sensitive formulations, cocoa-sugar dispersions, ice cream, special malts
• Pharmaceutical industry: pelletizing of hydrophobic and lipophilic agents
• Special applications: sludge compounding, wood plastic composite

References

• Polymer-Aufbereitung und Kunststoff- Compoundierung / Harald Rust, Klemens Kohlgrüber, Michael Bierdel / Hansa Fachbuch / 1. Auflage 10/2019
• Erwin Baur, Sigrid Brinkmann, Tim A. Osswald, Ernst Schmachtenberg: Saechtling Kunststoff Taschenbuch / 30. Auflage. 11/2007
• Fachkunde Kunststofftechnik, Lernfelder 1 bis 14 / 2. Auflage 2010
• Friedrich Johannaber, Kunststoff-Maschinenführer, Hanser Verlag / 4. Auflage. 12/2003