Plastics Consultancy Network - Profile and sheet extrusion

The extrusion process may be very easily visualised perhaps the best examples are the meat grinder and the toothpaste tube. However the very simplicity of these examples belies the complexity of the process and extrusion technology is highly developed both as a science and as an art.

The extrusion line begins with the hopper which holds the plastic material (in either powder or granule form). The hopper continuously feeds the material to a heated barrel which contains a rotating screw. This screw transports the polymer to the die head and simultaneously the material is heated, mixed, pressurised and metered. Needless to say the detailed design of an extruder screw is extremely complex in order to perform all the above tasks. At the die the polymer takes up the approximate shape of the article and is then cooled either by water or air to give the final shape. As the polymer cools it is drawn along by haul-off devices and either coiled (for soft products) or cut to length (for hard products).