Reciprocating-Screw Injection Molding
n In this process the screw serves to both plasticate the feedstock and inject the melt into the mold. During part of the cycle, the screw rotates rapidly, moving backward as it accumulates a charge (shot) of melt in the forward and of the cylinder. A limit switch stops the rotation and two hydraulic rams, one on either side, push the screw forward, forcing the melt into the mold and holding melt pressure unit the gates freeze. The rams are withdrawn, screw rotation recommences, the mold opens to eject the parts, the mold closes, and a new cycle begins. Most new injection machines sold today (1993) are of this type.