Operation and Use of Co-kneaders

Every day, new polymer materials are created to meet increasingly specific needs, such as lighter, stronger, flame-retardant, anti-static materials that comply with new environmental standards. These complex materials require efficient mixing tools, enabling controlled and competitive manufacturing. Among continuous mixing processes, twin-screw extruders are widely used, but co-mixers also play an important role. A co-mixer is a modular, single-screw extruder with a double forward-backward rotation and oscillation movement. The screw threads are interrupted from place to place, and mixing fingers are attached to the barrel. The kinematics involved enable these fingers to sweep the screw channels through the thread interruptions, resulting in highly efficient mixing, with relatively low shear rates on average, inducing little heating. Co-mixers are therefore generally used for heat-sensitive polymers, such as PVC, or when high loading rates are required.

In this article, we'll start with a detailed presentation of the co-mixer configuration, explaining how it works, which is very different from that of a conventional single-screw extruder. We'll look at screw kinematics, the role of mixing fingers, flow modes, etc. The influence of operating parameters will then be discussed, before introducing some aspects of flow modeling in these particular extruders.