18.3 Injection molding
Injection molding IS essentially the same process as hot chamber die casting (Fig. 18.5; also Section 11.12). Just as in extrusion, the barrel (cylinder) IS heated to promote melting. However. with-injection molding machines, a far greater portion of the heat transferred to the polymer is due to frictional heating. The pellets or granules are fed into the heated cylinder, and the melt is forced into a split-die chamber, either by a hydraulic plunger or by the rotating screw system of an extruder.