Process Encyclopaedia
Polymer extrusion
Overview
Unlike metal extrusion, polymer extrusion is a continuous process. A useful variation of the process called co-extrusion can be used (for example, to coat wires in-line for electrical cables).
Polymer extrusion is sometimes used as a 'melter' for feeding other shaping processes such as injection moulding or blow moulding.
Materials and shapes
Mainly used for thermoplastics, but can be used with rubbers and some thermosets.
Complex shapes with constant cross-section can be easily formed.
Because of shrinkage, die design can be difficult (and hence expensive) if good dimensional accuracy is required.
Near-net-shape process, only the ends of the extrusion are wasted.Economics
The cost of the machines is high - well over £50,000.
Die design can be expensive; the actual dies usually cost a few thousand pounds to produce and need replacing after 10-100km of extrusion.
Depending on size, parts can be extruded at rates from 1-60m/minute.
Because of the high costs, it is usually only economic to produce lengths over 10km - although there is little competition for many of the possible shapes.Typical products
Channels, pipes, sheet, architectural mouldings, cables, coated wires.