ABSTRACT
A hydrodynamic hybrid between nonintermeshing devices and the positive conveying screw pump is the co-rotating intermeshing and self-wiping extruder. The co-rotating geometry is open to cross-flow at the intermesh except for the wiping flight, and therefore the screws have an open path from feed to discharge. Screw extrusion is a highly developed technology for melting polymers, mixing process aids, additives, or other polymers, and pressurizing the mixed melt to downstream transport, pelletizing, or profiling devices. The intermediate concentrated solutions can be preconcentrated in light-duty, high-volume twin-screw devolatilizing extruders before final processing in a high-power, staged devolatilizer. Large-diameter twin-screw solution concentrators consisting of a short, back vented extruder discharging into a smaller, close-coupled finishing devolatilizer are used when large solution volume charges are affected by the flash devolatilization. The long aspect ratios of devolatilization extruders and limited back-mixing in screw-type elements substantiate the application of one-dimensional mass transport models.
