A cold feed rubber extruder has been rebuilt into a pin barrel extruder with two rows of pins. A comparative experimental study has been made of the initial cold feed extruder, the extruder with a screw with slices in two flights, and the extruder with pins as well as Slight slices. An experimental study of pumping characteristics (Q – Δp screw curves) and of flow patterns obtained from feeding black and white compound with curatives to the extruder with subsequent vulcanization after steady state is achieved. Longitudinal and transverse sections of the rubber compound cured in the flights are studied. It is shown that introducing slices into screw flights reduces pumping capability. The subsequent introduction of pins has little effect on pumping. The flow marker studies show that introduction of slices into screw flights significantly enhances mixing. Both the improved mixing and poorer pumping is due to backflow through the slices. The introduction of pins is shown to again greatly increase mixing. The results of this study are used to discuss the performance and design of commercial pin barrel extruders for the rubber industry.

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