A thermoplastic process whereby pellets, granules, or powder
are melted and forced through a die under pressure to form a given, continuous
shape. Typical shapes extruded are flat films and sheets, filaments and fibers,
strands for pelletizing, and webs for coating and laminating. Also used for
forming composite preformed materials from mixtures of a matrix powder and
short fibers suitable for MMCs. Widely used for continuous production of film,
sheet, tube, and other profiles; also used in conjunction with blow molding.
Thermoplastic or thermoset molding compound is fed from a hopper to a screw and
barrel where it is heated to plasticity then forwarded, usually via a rotating
screw, through a nozzle possessing the desired cross section. Production lines
require input and takeoff equipment that can be complex.
Low tool cost, numerous complex profile shapes possible,
very rapid production rates, can apply coatings or jacketing to core materials
(such as wire).
Familiar products manufactured
by extrusion include: pipes, ingot,
guttering, window sills and insulation