Extrusion is a continuous process which is used to produce
both solid and hollow products that have a constant cross section. Examples are
tubing, pipes, profiles (like window frames,
curtain track), films,
sheets, insulated wires etc. Extrusion process is as
follows,
Operation procedure,
- Fill hopper with plastic material
- Plastic is then heated in the barrel gradually to the state that its’ able to flow sufficiently
- Melt plastic is forced by screw press through the die and cooling bath
- Letting the product cool and cut to length
Extrusion rates normally vary between nine and sixty
meters per minute. Thicker cross sections are extruded slowly because more time
is required for initial heating and later cooling. Extruder is the main object
in the extrusion process. Its main equipments are given in the figure.
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| Equipments of the extruder |
Functions of the extruder screw is convey the resin
through the extruder, mixing the ingredient together, build pressure in the
extruder (so that resin will be pushed through the die), impart mechanical
energy as part of the melting process. The screw can divide in to three zones
according to its function. They are feeding zone which pulls the polymer
pellets from the hopper, pre heat them and convey it to other zones, transition
zone which compress the material conveys from the feed zone and so it has
decreasing channel depth, metering zone which is a having
constant screw depth and very shallow flight depth as homogenize the melt and
supply to die.
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| Zones of the extrusion screw |
