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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