Extrusion - Twin-screw extrusion processes

The extrusion process involves the continuous manufacture of finished or semi-finished products, or the transformation of materials, within a screw/sleeve system. Single-screw extrusion refers to a single screw rotating inside a cylindrical barrel (see [18] in Techniques de l'Ingénieur), while double-screw extrusion refers to two screws, generally parallel, rotating inside a barrel with a figure-of-eight cross-section. However, under the very general term of bivis extrusion, we find machines of very different designs and with a variety of specific applications. While counter-rotating machines, derived from internal mixers for the rubber industry or dough kneading, appeared around 1880, corotating extruders were born around 1935 in Italy. Since then, this technology has gone from strength to strength, and is currently experiencing unprecedented growth. In the following article, after presenting the different types of twin-screw extruder, we will describe in detail the technical characteristics and operating modes of the two main families of machines: corotating extruders and counter-rotating extruders.