Local mixing effects of screw elements during extrusion

An in-line method was applied to determine local residence time distribution (RTD) at two places in a completely filled corotating twin screw extruder. Axial mixing effects of different types of elements were evaluated. Paddles +90[degrees] induced flow patterns that appear to be circular, both upstream and downstream, whereas paddles -30[degrees] induced flow patterns that appear to be circular and mainly upstream. Transport and single-lead elements induced backflow. The results could be explained from pressure differences and direction of drag flow in the elements. All elements were characterized using an equivalent additional mixing length [lambda], dependent on the type of element and its position in the extruder, which may be practically useful for extrusion design. POLYM. ENG. SCI., 45:271-278, 2005. [c] 2005 Society of Plastics Engineers
INTRODUCTION In the last decades, interest has steadily grown in the use of corotating twin screw extruders in both food and nonfood applications [1-3]. The extruder is used for various [...]