Recently published figures for the United Kingdom show that an average of about 50% of the main thermoplastics consumed (polyolefins, PVC and polystyrenes) is finally extruded. These figures do not take into account the very important application of extrusion machines in the manufacture of polymers where extruders are used as reactors, melt pumps, compounders, devolatilisers and so on. The large majority of all thermoplastics materials now produced will have been extruded at some stage of manufacture. It should also be borne in mind that other plastics processes, not usually associated with extrusion, employ extruders for auxiliary functions. For example, extruders are used in both blow moulding and injection moulding to plastify the polymer.
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