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A continuous process and a prototype for manufacturing rubber compounds

A continuous process and a prototype have been developed for manufacturing rubber compounds for car tyres, conveyor belts and technical rubber articles. The project investigated the possibility of using twin-screw extruders for a continuous production process of rubber compounds. The test runs with the basic and the prototype extruder could be carried out continuously. The condition in which the compound components were supplied caused an inaccurate feeding. Another problem was that in the most cases the high temperature of 120-140 C of the final product prevented that the addition of cross linking agents for the important curing process could not be carried through because of the required stock temperature of approximately 100 C. In spite of these problems the carbon black dispersion was good, which showed that the mixing intensity of the twin-screw extruder is as good as that of the internal mixer. The precise feeding is one of the most important factors for the success of the system. In spite of feeding problems the prototype extruder worked successfully. To investigate the possibility of increasing the dispersion of carbon black, the extruded profiles of the ZE 90 were fed into a second extruder. This pin convert extruder type GE 90 SC x 8 D belongs to Berstorff's new extruder generation. The most destinctive feature of this extruder type is the converting zone consisting of a multiple-flighted screw and liner section with a throttle element. This special design intensifies the shearing process which is most important for achieving a good dispersion of carbon black. The best results were achieved with the pin convert type extruder for additional mixing. About 10% increase of carbon black dispersion was measured. The most promising installation for the future was found to be a twin-screw extruder for pre-mixing, followed by a steel belt cooling conveyor and a pin-convert type extruder in which the thermosensitive additives are dosed and the final product can be extruded.

Reported by

Hermann Berstorff Maschinenbau GmbH
An der Breiten Wiese 3-5
30625 Hannover
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