Extrusion is a manufacturing process used to make pipes, hoses, drinking straws, curtain tracks, rods, and fibre.
Materials such as polystyrene, nylon, polypropylene and polyethene can be used in this process. These are thermoplastics – this means when they are heated and then pressured in a mould they can be formed into different shapes and sections.
A machine used to extrude materials is very similar to the injection moulding machine. A motor turns a thread which feeds granules of plastic through a heater.
The polymer resin is heated to a molten state by a combination of heating elements and shear heating from the extrusion screw. The screw, or screws as the case with twin screw extrusion, forces the resin through a die, forming the resin into the desired shape.
The shape of the die determines the shape of the tube. The extrusion is then cooled and forms a solid shape. The tube may be printed upon and cut at equal intervals.
A “caterpillar haul-off” (called a “puller” in the US) is used to provide tension on the extrusion line which is essential for overall quality. The caterpillar haul-off must provide a consistent pull, or it will result in a distorted product or variation in lengths.
The configuration of the interior screws is a driving force dependent on the application. Mixing elements or convey elements are used in various formations. Extrusion is common in the application of adding colourant to molten plastic thus creating a specific custom colour.
The extrusion is then cooled and forms a solid shape. The tube may be printed upon and cut at equal intervals. The pieces may be rolled for storage or packed together.
Shapes that can result from extrusion include T-sections, U-sections, square sections, I-sections, L-sections and circular sections.
Did you know? One of the most famous products of extrusion is fibre optic cables.
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