Extrusion - Single-screw extrusion (part 1)

Extrusion is by far the most important polymer shaping process. The basic principle of single-screw extrusion is the use of a screw that rotates inside a cylindrical barrel. A continuous process, extrusion is used to manufacture finished products or semi-finished products of constant cross-section (films, sheets, tubes, profiles, etc.) by passing them through a tool called a die. In this case, the main functions of the process are to melt the solid polymer, then pressurize and mix the molten polymer, in order to feed the die under the right conditions, which will give the manufactured product its shape. In addition to shaping, extrusion is also used for granulation, compounding and polymerization. Extrusion leads the way ahead of injection molding and other transformation processes, with some 1.7 million tonnes of material consumed per year (France, 1999 figures).

The very principle of extrusion is a very old one, if we trace it back to Archimedes' screw, and has been widely used for a very long time, particularly in the food industry (sausage and pasta production). In the case of synthetic materials, the process was first applied to rubber in the early twentieth century, and has since been widely developed in the field of thermoplastics.