Fabrication compression molding

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. 

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). 

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). 

Some plastics, such as the TSs and in particular the TS-RPs (RTSs), can produce products with exceptionally tight tolerances that practically meet zero tolerances. In injection or compression molding of relatively thin to thick and complex shapes, tolerances can be held to less than 0.001 in. or to even zero, as can also be done using hand layup RP fabricating techniques. 

After synthesis, the modified carborane-siloxane gums were fabricated into shaped components using standard siloxane vulcanization and fabrication technology. Di-chlorobenzyl peroxide (1% by wt) was used as the cross-linking agent and mixed into the polymer formed in scheme 7. Shaped rubber components were readily prepared by compression molding operations at 70°C. Postcure operations were typically at 120°C for 24 hours. 

Jiang and Zhu (2000) and Qiu and Zhu (2001) have reported the fabrication of multilayered devices composed of stacks of compression-molded disks of alternating compositions. One type of disk is either P(SA-EG) or P[SA-co-TMAgly)-Z>-EG] and the other is a pH-sensitive, protein-loaded blend of, for example, poly(methacrylic acid) and polyethoxazoline. The release of model proteins, myoglobin, bovine serum albumin, and FITC-dextran, and compounds such as brilliant blue have been studied and pulsatile release profiles have been demonstrated (Jiang and Zhu, 2000 Qiu and Zhu, 2001). 

A thin molding of an acetylene-terminated phenylquinoxaline, fabricated by compression molding at 316°C for 26 hr and at 371°C for 5 hr, gave tensile strength of 103 MPa (15,000 psi), tensile modulus of 2.62 GPa (380,000 psi) and elongation of 5% (46). Preliminary unidirectional graphite fiber laminate properties are reported in Table VI. 

An important step in the manufacture of any plastic product is the fabrication or the shaping of the article. Most polymers used as plastics when manufactured are prepared in pellet form as they are expelled from the reactor. These are small pieces of material a couple of millimeters in size. This resin can then be heated and shaped by one of several methods. Thermoset materials are usually compression molded, cast, or laminated. Thermoplastic resins can be injection molded, extruded, or blow molded most commonly, with vacuum forming and calendering also used but to a lesser extent. 

Compression molding (Fig. 16.7) is practically the oldest method of fabricating polymers and is still widely used. The polymer is placed in one half of a mold and the second half compresses it to a pressure of about 1 ton/in. The powder is simultaneously heated, which causes the resin to cross-link. 

Techniques commonly used to manufacture advanced composites from prepregs, which are available in unidirectional fiber or fabric form, include compression molding, vacuum-bag autoclave molding, stamp molding, thermoforming, and on-line (in situ) consolidation [3]. In compression and vacuum-bag autoclave molding techniques, the prepreg is cut to the dimensions of the structure, and the fiber directions are oriented to obtain the required... 

Compression molding A fabrication method in which a polymeric material, mostly a thermoset (a plastic or an elastomer), is compressed in a heated mold for a specific period of time. 

Fabrication techniques include compaction and sintering, direct compression molding, hot stamping, forging, and hot plate or spin welding (13). 

Amino resins are fabricated principally by transfer and compression molding. Injection molding and extrusion are used on a limited scale. Urea resins are not recommended for outdoor exposure. The resins show rather high mold shrinkage and some shrinkage with age. The melamines are superior to the ureas insofar as resistance to heat and boiling water, acids, and alkalis is concerned. 

Polystyrene, 20% by weight glass, 32% for fabric laminate, epoxy silane compression molded at 500°F. 

Polymeric chips have been fabricated with various methods, as developed from the plastics industry. These processes include casting, injection molding, laser ablation, imprinting, and compression molding. The physiochemical properties of various polymeric materials and their molding methods have been summarized in a recent review article [7],... 

Besides PMMA, compression molding was also used to fabricate microstructures on PC chips (1 mm thick). High temperature (188°C) and pressure (11 metric ton pressure applied by a hydraulic press) were used. Before bonding, the hydrophobic channel surface was treated with UV irradiation (220 nm) to increase surface charge, which would assist aqueous solution transport. The molded chip was thermally bonded to another PC wafer. During use, the bonded chip did not yield to a liquid pressure up to 150 psi (134°C, 4 metric ton, 10 min) [938],... 

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