Ch-19 Forming and shaping plastics. Thermoplastic (TP) – Polymers that can be shaped when heated and regain original hardness & strength upon cooling – Have a linear or branched structure (weak secondary bonds ) – Process is reversible
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Thermoplastic (TP) – Polymers that can be shaped when heated and regain original hardness & strength upon cooling
– Have a linear or branched structure (weak secondary bonds)
– Process is reversible
– Acrylics, cellulosics, nylons, polyethylenes, polyvinyl chloride
• Thermoset (TS) – Polymers that become permanently set when heated
– Have a cross-linked structure (strong secondary bonds)
– Process is irreversible
– Epoxy, polyester, urethane, phenolics, silicones
• Elastomer (Rubber) – Elastic; low elastic modulus
– Tires, footwear, gaskets, flooring, weather stripping, hoses
Figure 19.1 Outline of forming and shaping processes for plastics, elastomers, and composite materials. (TP = Thermoplastics; TS = Thermoset; E = Elastomer.)
Figure 19.4 Extrusion of tubes. (a) Extrusion using a spider die (see also Fig. 15.8) and pressurized air. (b) Coextrusion for producing a bottle.
FIGURE l9.5 (a) Schematic illustration of the production of thin film and plastic bags from
tube-first produced by an extruder and then blown by air. (b) A blown-film operation. This
process is well developed, producing inexpensive and very large quantities of plastic film and
shopping bags. Source: (b) Courtesy of Wind Moeller 86 Hoelscher Corp.
Figure 19.10 Illustration of mold features for injection molding. (a) Two-plate mold with important features identified. (b) Four parts showing details and the volume of material involved. Source: Courtesy of Tooling Molds West. Inc.
Multicomponent injection molding (also called coinjection or sandwich molding): Car rear lights (different colors).
Insert molding: metallic components such as screws, pins, and strips are placed in the mold cavity prior to injection and then become an integral part of the molded product.
Figure 19.9 Typical products made by injection molding, including examples of insert molding. Source: (a) Courtesy of Plainfield Molding, Inc. (b) Courtesy of Rayco Mold and Mfg. LLC.
Figure 19.14 Schematic illustrations of (a) the extrusion blow-molding process for making plastic beverage bottles; (b) the injection blow-molding process; and (c) a three-station injection molding machine for making plastic bottles.
Figure 19.15 The rotational molding (rotomolding or rotocasting) process. Trash cans, buckets, and plastic footballs can be made by this process.
Figure 19.16 Various thermoforming processes for a thermoplastic sheet. These processes commonly are used in making advertising signs, cookie and candy trays, panels for shower stall, and packaging.
http://www.longmold.com/viewnews.php?id=85 to compare between the three types.
Figure 19.17 Types of compression molding – a process similar to forging: (a) positive, (b) semipositive, and (c) flash, which is later trimmed off. (d) Die design for making a compression-molded part with external undercuts.
Figure 19.18 Sequence of operations in transfer molding for thermosetting plastics. This process is suitable particularly for intricate parts with varying wall thickness.