for the majority of plastic resin processing in the U.S. by weight. It consists
of forcing molten plastic resin through a die, or orifice, under constant pressure
- a procedure similar to squeezing toothpaste from a tube. The process results
in a continuous length and uniform cross-section. The shape of the opening determines
its "profile". Since it is a continuous process, large volumes of resin
may be produced in a comparatively short time.
most important part of this process is the extruder. In the most common type of
extruder, the screw variety, dry resin is fed into a hopper on the machine and
enters the flutes of a long, motor-driven screw. The rotating action of the screw
serves the dual purpose of promoting the melting of the resin through pressure
and friction, as well as transporting the melt to the die ahead.
There are four
different classes of extrusion:
Extrusion - extruded profiles emerge from the die in a straight line.
The shapes are then either air- or water-cooled, cut to length, and are then basically
ready for use.
Common Applications: plastic pipe, window trim, housing siding, tubing
Sheet - also produced by passing a continuous resin melt through a die.
In this case, however, the die will be of a thin and slotted configuration.
Common Applications: packaging material, protective window films
film - a continuous extrusion where the molten resin is literally blown
into a tubular shape through a vertically mounted circular die.
Common Applications: trash bags, dry cleaning bags, grocery bags, other bags
- two or more resins of different colors or dissimilar properties may be combined
in a common product with this process.
Common Applications: drinking cups with white interior and color exterior