The purpose of the present project is the development of a continuous process and a corresponding test equipment for the manufacture of rubber compounds applied in the tyre manufacturing industry, the conveyer belt industry, the drive belt (V-belt) industry and for the manufacture of technical rubber articles.
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 which was confirmed by the analysis of records obtained. 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 approx. 100 °C.
In spite of the aforementioned problems the carbon black dispersion was good, which showed that the mixing intensity of the twin-screw extruder is as well as that of the internal mixer.
The presice feeding is one of the most decisive factors for the success of the system. In spite of feeding problems the prototype extruder worked successfully and showed that the mixing intensity of the twin-screw extruder was as good as that of the internal mixer.
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 to achieve 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 will therefore 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.
The production of rubber compounds for the aforementioned purposes has so far been effected discontinuously with internal mixers connected in series. These internal mixers, however, can only incorporated the fillers such as carbon black etc. to an extent of approx. one third in one mixing cycle, in order to avoid an overheating of the compound.
The aim is to incorporate all components without a damaging temperature increase. This objective is to be reached by developing a process and a test equipment which will increase the surface/volume ratio by at least ten times compared to internal mixers in order to improve the mixing effect and the temperature control.
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