Page 44 - Handbook of Plastics Technologies

INTRODUCTION TO POLYMERS AND PLASTICS

1.30 CHAPTER 1

FIGURE 1.27 Two-shot molding with rotating mold. 67

FIGURE 1.28 Two-shot injection molding with retractable core. 67
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out the need for an additional adhesive bonding step. In the case where direct adhesion
of the materials is desired, proper selection of compatible materials is required. Table 1.8
shows the bonding strength for a number of thermoplastic combinations for use in
multicomponent injection molding.

1.6.3 Thermoforming
Thermoforming is the heating of a thermoplastic sheet until it is soft and stretchable and
then forcing the hot sheet against the contours of a mold by mechanical (plug assist), vac-
uum, pressure, or a combination of all three. After cooling, the plastic sheet retains the
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mold's shape and detail. Thermoforming is still a rapidly growing processing method be-
cause of the range of products that can be formed and the relatively low cost of required
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tooling and equipment. Thermoformed products include dinnerware, cups, automotive
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parts, egg cartons, and blister packaging.
There are a wide variety of processes for thermoforming. One-step processes include
the following: 34
• Drape forming
• Vacuum forming

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