Compression and injection molding

Compression and injection molding are used with amino resins to produce articles such as radio cabinets, buttons, and cover plates. Because melamine resins have lower water absorption and better chemical and heat resistance than urea resins, they are used to produce dinnerware and laminates used to cover furniture. Almost ah molded objects use fillers such as cellulose, asbestos, glass, wood flour, glass fiber and paper. The 1997 U.S. production of amino resins was 2.6 billion pounds. 

Table 8-32 Comparison of resin transfer, compression, and injection molding RP processes...

Other applications are compression and injection molding. In order to mould it is necessary to heat the polymer to a temperature at which it will flow easily so that it can be introduced to the mould. Quite often this temperature needs to be quite high and often leads to charring and a poor product. 

Cellulose esters are used as plastics for the formation by extrusion of films and sheets and by injection molding of parts. They are thermoplastics and can be fabricated employing most of the usual techniques of (largely compression and injection) molding, extrusion, and casting. Cellulose ester plastics are noted for their toughness, smoothness, clarity, and surface gloss. 

AF polymers can be extruded, compression and injection-molded, solution or spray-coated as well as spin-coated from solution. A representative plot showing the dry-film thickness obtained by spin-casting from two different concentration AF solutions at different spin speeds is shown in Figure 2.8. It is possible to prepare multiple coats of AF using this technique. Although most of the solvent is removed in the spin-coating step the polymer must be heated above its glass transition temperature to ensure removal of the last traces of solvent. 

Tooling cost for the production of all polyurethane parts is much lower than that for making plastic parts by either compression or injection molding. The molds do not have to withstand the pressures involved when compression and injection molding is carried out. These lower molding costs can be used to prepare prototypes of a new concept for general evaluation prior to the expense of an injection molding die. 

However, the kind of technique used to mold these blends seems to be important in determining their mechanical properties. In fact, mechanical tests carried on injection molded samples [37] show, with respect to compression molded samples, a significant enhancement of the energy to break for all samples (Tables 20.2 and 20.3). Moreover the addition of 10wt% of SEBS to an 80 20 wt% sPS/HDPE blend involves in the injection molded samples an increase in both the energy at break and the Izod impact strength, whereas in the thermo-compressed samples no improvement is observed. Differences between compression and injection molded samples are widely acknowledged [38] and... 

In compression and injection molding operations the press operator demolds and trims the part. This same operator In a RIM... 

Low-cost molds for contact and low-pressure molding can be made from reinforced TS polyester or epoxy compounds with glass fiber and/ or mineral filler reinforcement. These constructions have also been used to make prototype molds for compression and injection molding, with the advantages that they can be produced quickly and at low cost (often in-house) and can readily be modified. Latest technology uses blocks of resin-based compounds that can be machined by computerized instructions, for production of protot5 e molds. 

Chopped strands, continuous and chopped strand mat, compression and injection molding, spraying, pressure bag, preform... 

Poly(p-Oxyben2oyl Systems) Homopolymer for Coatings Copolymers for Compression and Injection Molding... 

Development work has been going on for several years at The Carborundum Company on p-oxybenzoyl polymer systems. 3 The early work mainly focused on the homopolymer (EKONOLjI This polymer has excellent thermal stability and also very good friction and wear properties and has found use recently as an additive to PTPB for molded shapes and coatings. The homopolymer however is very difficult to fabricate by itself and this has led to the development of copolymer systems which retain the excellent thermal stability of the homopolymer but have sufficient flow for compression and injection molding. 

Transfer Molding. Transfer molding is intermediate between compression and injection molding. Whereas the compression mold has just one cavity for the finished product, the transfer mold also contains a preliminary auxiliary cavity. The resin is loaded into the auxiliary cavity ( pot ), preferably as a preheated perform, where it is heated to melt processing temperature. Then, a plunger forces the molten resin into the final mold cavity, where it cures to the finished product. 

Table 5.7 Comparison of properties of compression and injection- molded unfilled, and 40 and 50% CaC03 -filled PP untreated, 0.6 and 1.0% KR TTS-treated fillers. ...

Nylon, Type 11 Nylon, Type 12 Aromatic polyamide Partially aromatic Unfilled compression and injection molding oompound 30% glass fiber-reinforced... 

Thermoprocessing methods, snch as extrusion, melt compounding, compression, and injection molding, are the most commonly used technologies for industrial-scale production of nanocomposites. Currently, these technologies are also expected to promote... 

Denault, J., and Vu-Khauh, T. Tensile Behavior of Long Fiber Thermoplastic Composites Processed by Compression and Injection Molding. SPE ANTEC, pp. 891-95, May 1989. 

Isayev, A. I. and Modic, M., Self-reinforced melt processible polymer composites Extrusion, compression and injection molding, Poiym. compos. 5 158 (1987). 

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