Extrudate Profile 50 parts Silica 2+1
127 133/140 153 ºC Temperature
The extrudates developed voids at the higher rpms. These could be seen forming in the melt stream about 10-20 cm away from the die. The voids did not blow through the surface. Although the experiment was not designed to study this in detail, there did not appear to be a relationship to mixing procedures, additive, or silica level, except the drop temperature of the 1st pass. Whenever the melt temperature reach the mid 130’s small voids were seen in a cooler 2+1 mix. Since the additives give less heat build up the voids were reduced slightly. Whether these voids could be explained by ethanol coming of from the coupling agent or from water in the stock is unknown but both are suspected. Stocks that were mixed in the 1+1 mix, where temperatures of 180 C were reached, did not show any porosity up to extruder temperatures in excess of 150C. Previous unpublished work that the author has done with water in a carbon black stock showed that porosity of this type could be expected at about 0.1% water in the compound.
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