Dynamic Performance of Single-Screws of Different Configurations

Abstract

A 45 mm diameter single-screw “transparent” extruder was employed for an investigation on the dynamic performance of screws of different configurations. The extruder had eight glass windows installed along the entire metal barrel which enabled visual observation to be easily made. It was demonstrated, with this extruder, that pressure profile appeared to be an important factor for screw performance such as throughput rate, residence time, mixing characteristics, break-up of solid-bed, etc. The full-flight screw had the lowest pressure profile among all the screws tested, and its performance was found to be generally inferior to that of the mixing screws. The Darnell and Mol solid plug flow theory was shown to be applicable only to the mixing screws for the solid flow behaviour in the entire solid conveying section. The secondary flight of the barrier screw was found to effectively suppress solid bed break-up, but only at low screw speed. A screw with a Maddock mixing device was found to have the highest throughput rate. Other findings were believed to be of practical significance in the screw design.