Page 43 - Handbook of Plastics Technologies

INTRODUCTION TO POLYMERS AND PLASTICS

INTRODUCTION TO POLYMERS AND PLASTICS 1.29

FIGURE 1.25 Gas-assisted injection mold-
ing. 65

FIGURE 1.26 Coinjection molding. 66

1.6.2.5 Two-Shot Injection Molding. Two-shot or overmolding refers to a process
whereby either different colors or different materials are molded into one part. In this pro-
cess, the first material or color is injected, then the mold is rotated, and the second shot is
67
injected as depicted in Fig. 1.27. An alternative method is to use a retractable core. In
this case, the first material is injected, cooled to solidify, and then the core is retracted to
allow injection of the second material as shown in Fig. 1.28. Bonding is accomplished
through either strictly mechanical means or by adhesion between the two components
through diffusion of the chains. This can result in parts with two materials combined with-

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