Compression molds

Fine Powder Resins. Fine powder PTFE resins are extremely sensitive to shear. They must be handled gendy to avoid shear, which prevents processing. However, fine powder is suitable for the manufacture of tubing and wire insulation for which compression molding is not suitable. A paste-extmsion process may be appHed to the fabrication of tubes with diameters from fractions of a millimeter to about a meter, walls from thicknesses of 100—400 )J.m, thin rods with up to 50-mm diameters, and cable sheathing. Calendering unsintered extmded soHd rods produces thread-sealant tape and gaskets. 

Compression-molded specimens property data on extmded wire specimens are similar. At 23°C... 

Sample 250-pm compression-molded films of Teflon PFA 340 from G.E. resonance transformer 2 MeV capacity, at a current of 1 m A. 

PCTFE plastic is available in products that conform to ASTM 1430-89 Type 1 (Grades 1 and 2) and is suitable for processing into parts that meet MIL-P 46036 (Federal Specification LP-385C was canceled 1988). Standards for fabricated forms are available for compression molded heavy sections (AMS-3645 Class C), thin-walled tubing, rod, sheet, and molded shapes (AMS-3650). PCTFE plastics have been approved for use in contact with food by the FDA (55). 

Eoamable compositions in which the pressure within the cells is increased relative to that of the surroundings have generally been called expandable formulations. Both chemical and physical processes are used to stabilize plastic foams from expandable formulations. There is no single name for the group of cellular plastics produced by the decompression processes. The various operations used to make cellular plastics by this principle are extmsion, injection mol ding, and compression molding. Either physical or chemical methods may be used to stabilize products of the decompression process. 

Type of polymer Extmsion Expandable Eroth Compression mold Injection Sintering... 

Manufacture of friction elements includes the impregnation of fabrics and subsequent lamination, the wet-dough process, and the dry-mix process. Elements from the last two are prepared by compression-molding the formulation for up to an hour at 150—175°C. Thick brake elements require a carefully controUed heating-and-cooHng cycle to minimize stresses created by expansion and contraction (see Brake linings and clutch facings Fillers). 

Wet System Compression M olding. Wet system compression molding was the first high volume method for manufacturing reinforced plastic parts, in such appHcations as the Chevrolet Corvette, industrial trays, tote boxes, luggage, refrigerator liners, and other commercial appHcations. 

Hybrid Processes. There are also hybrid processes that have evolved to meet specific product needs. As an example, automotive leaf springs utilize a filament winding system to prepare impregnated fiber bundles that are then compression molded to final configuration. 

Acrylics processed by compression-molding techniques give dentures as satisfactory and dimensionally stable as the estimated 5% of the dentures made with special resins and elaborate processing equipment (208). Promising fiber-reinforced dentures have been reported (209—212). 

Anode electrode assembly, electrode panel between compression molded gaskets. 

Cathode electrode assembly, electrode panel between compression molded gaskets. A range of gasket, electrode materials, and electrode geometries is available... 

Molding and injection Compression ratio Compression molding pressure (lbf/in. ) Compression molding temperature (°C) Injection molding pressure (Ibf/in. ) Injection molding temperature (°C) Molding qualities Mold (linear) shrinkage (in./in.) Specific volume (Ib )... 

Arc Extinguishing Plastics 1964 E Injection or compression molded and extruded Fuse tubing, lightning arrestors, circuit breakers, panel boards... 

A plate used for holding plugs in place in compression molding. 

Sheet molding compound (SMC) consists of randomly oriented chopped fibers in a matrix of resin and filler. SMC is produced in the continuous manner shown in Figure 1-16. Note that the polyethylene film protects the roller system from getting gummed up with the resin-filler paste. The rug-like rolls of SMC are then used in compression molding machines to create large parts such as the sides of cars and trucks. 

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