Flow Visualization and Performance of a Non-Intermeshing Counter-Rotating Twin Screw Extruder

Abstract

Abstract A laboratory modular twin screw extruder with transverse and tangential apex windows for flow visualization is described. The machine is operated as a tengential twin screw extruder with right- and left-handed screw elements. Screw characteristic curves, Q-Δ p, were measured and compared for polyethylene in matched and staggered flight screw configurations with right-handed screw elements. Configurations with matched screw elements are better pumps. We have introduced left-handed screw elements into each screw configuration. This reduces the total pressure developed. Again matched screw element configurations are better pumps. Pressure profiles are measured along the length of the extruder. For right-handed screws, the pressure rises monotonically. Left-handed screw elements produce regions of decreasing pressure. Flow visualization investigations allow us to locate the position and follow the mechanism of the melting process. Using colored markers, we were able to see that in most (but not all cases) there was no inter-screw transfer of material.