Extrusion

Extrusion, process for shaping materials—especially metals, but also such nonmetals as rubber, plastic, and glass—by forcing them through a small orifice or die. Hydraulic or mechanical rams are employed to apply pressure to a billet (square chunk) of the material to be shaped. Some metals, such as copper and steel, must be kept hot during extrusion, aluminum may be extruded cold. In extruding plastics, the raw material, in the form of tiny pellets, is heated and forced through dies by a long feed screw. In the extrusion of nylon, rayon, and other synthetic fibers, filaments of the material are extruded by centrifugal force from tiny dies called spinnerets. They may then be spun and woven into cloth in the same way as natural fibers.