Plasticizing

Abstract

To mold plastic products, the plastic is plasticized, that is, it is melted. The plasticator is the device that does so. Different methods can be used. The common types are those found in the single-stage (or reciprocating) and the two-stage IMMs (Chap. 2). In the reciprocating type, plastic is fed through a screw and into a shot chamber (front of screw). In the two-stage plastic is fed into the first-stage screw, where it is plasticized prior to entering the second stage. In the first-stage plasticator the screw motion generates controllable low pressure [usually 50 to 300 psi (0.34 to 2.07 MPa)], which causes the screw to retract slightly, preparing the melt to enter the second stage. Depending on the plastic’s melt flow characteristics and pressure required in the mold cavity or cavities, the injection pressure at the nozzle is between 2,000 and 30,000 psi (14 and 200 MPa). Adequate clamping pressure must be used to keep the mold from opening (flashing) during and after the filling or packing of the cavities with the plasticized melt.