In this process polymer granules are fed from a hopper into a steel cylinder. As they enter the cylinder, the granules are forced to the heated outer edges of the vessel, where they are softened. A ram then forces the softened polymer through a narrow opening, or sprue, into a cooled mold which shapes the finished article. The use of plastics as replacements for glass containers is aided by a process combining traditions in both polymer and glass fabrication, blow molding. In this process a sealed tube of polymer, or parison, is placed inside a hollow mold.
Air is forced into the heated parison, expanding the polymer to fill the shape of the mold.
Here the glassblower's craft has its modern counterpart in polymer manufacturing machinery. Depending on the die used, extruders produce continuous cylinders of polymer or fine filaments, as in nylon production. Photo courtesy of Union Carbide Corporation. Nearly half of all polymer plastics are processed by extrusion. In this technique granular polymer is melted under heat and pressure, then forced through specially designed dies to yield a desired cross sectional shape.