PROCESSING GLASS-REINFORCED THERMOPLASTICS -2 Injection Molding

Reinforcements usually come in continuous or chopped fiber forms as in woven and nonwoven fabrics. Both thermoplastic (TP) and thermoset (TS) resins are used in RPs (Chapter 3). At least 90 wt% of all RPs use glass fiber (E-type) materials (Chapter 2). At least 55 wt% of all RPs use TPs even with their relatively lower properties compared to reinforced TSs (RTSs). Practically all reinforced TPs (RTPs) with short or long glass fibers are injection molded at very fast processing cycles producing... 

Recendy, storm doors have been constmcted of advanced thermoplastic composites. Stampable, glass-mat reinforced polypropylene sheet is used to create a high strength outer skin. These compression molded skins are welded together using a friction or ultrasonic process then injection molded with a polyurethane foam core to produce an insulated structure. New technology for window frames incorporate the pultrusion of frame channels to produce a thermoset composite channel that can be filled with fiber glass for further insulation enhancement (12,31,33,34,48,49,54—56,60—67). 

POLYCYCLO-ITEXYLENE-Dl METHYLENE TEREPHTHALATE. PCT is 1,4-cyclohexvlene-dimethylene terephthalate and is a high-temperature. semicrystalline thermoplastic polyester. PCT possesses excellent thermal properties. Injection molding is the predominant method of processing glass fiber-reinforced grades of PCT. It is widely used for... 

Fig. 11.30 Effect of preheating 50% by weight E-glass fiber-filled polyamide pulltruded pellets on fiber lengths at the screw tip of a 300-ton 23.86-oz reciprocating injection molding machine. [Reprinted by permission from C. G. Gogos, C. K. Yoon, and J. Brizzolara, Injection Molding Process Development for Long Fiber Reinforced Thermoplastics, SPE ANTEC Tech. Papers, 40, 384 (1994).]...

The process of injection molding (IM) is used principally for processing unreinforced or glass fiber reinforced thermoplastics (TPs) and thermosets (TSs) (Figure 4.1). Up to at least 90wt% of all plastics processed are TPs. There are many different types or designs of IM machines (IMMs) that permit molding many different products based on factors such as quantities, sizes (such as auto bumpers to medical micro products), shapes (simple to complex), product performances, and/or economics.1,150>157,173 176 476... 

In cavity-compression molding the cold powder or mold material is placed under pressure in a heated mold. The process is also called hot pressing. Glass-fiber-reinforced, unsaturated polyester resins are processed by the heated-cavity-compression molding method. The vulcanization of rubber can also be carried out using this method. High-fidelity records are pressed out of the thermoplasts PVC or poly(ethylene-co-vinyl acetate), while cheaper records are injection molded. 

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