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EXTRUSION MOULDING

Extrusion refers to a continuous process in which hot plastic melt is forced out
through a die or series of die that forms a profile which is sized, cooled and solidified
to required final dimensions. The word Extrusion comes from latin word extrudere
meaning 'to thrust out. It produces continuous, straight profiles having a constant
cross section which are cut to length. Production rates are measured in linear units,
such as feet/minute, ordinarily are reasonably high.
The die determines the final shape of product extruded which can be solid round,
square, hollow tubes, T, C or L shapes, etc. producing sheet, pipe, film, tubing and
profiles. Consider squeezing a toothpaste tube, its opening act as die and the paste
comes out in solid rod form. The change in the opening shape will change the shape
(cross section) of tube coming out.

In general, an extrusion system has several components:
lFeed hoppers and system for dosing the polymer and other desired
ingredients
lAn extruder to melt and mix the polymer and other ingredients
lA melt filtration system for removing contaminants
lAn adapter to connect the extruder to the die
lA die for forming the molten polymer into the desired shape
lA cooling mechanism (air ring, water bath, etc.) to freeze the molten
polymer into the final shape
lA puller to pull the polymer out of the die and through the cooling
mechanism.
The Extrusion Process: Plastic pellets from machine hopper are fed into an
extruder, comprising of a heated barrel surrounding rotating screw driven by a
motor. The screw forces the plastic pellets forward in the barrel which is melted by a
combination of heat from heaters fitted on barrel and friction inside barrel. The
molten plastic leaves the screw and travels through a screen pack to remove any
contaminants in the melt. A breaker plate, screen pack, and die are located at the
extruder outlet. These components serve to seal the interface between die and the
extruder, filter any contaminants, increase the flow resistance and plastication

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