Stock shapes compression molding

Reinforced PPS compounds may be extruded into profile shapes or sheets under carefully controlled processing conditions using a 24 1 to 28 1 LID standard metering screw with 3 1 compression ratio and a heated die clamp. Typical barrel temperature set points are about 285 to 310°C (545 to 590°F). Some extruded rods and sheets of reinforced PPS compounds are used as stock for machining small quantities of parts, as is compression-molded stock. Thermoforming of extruded sheet may be performed using conventional techniques at temperatures above the crystalline melting point of PPS of 285°C (545°F) [133]. 

Compression molding is the method by which massive (700 kg), cylindrical (billet), rectangular, and sheet shapes of PTFE are produced. The blocks and cylinders can be solid or annular and are by far the heaviest objects produced from any fluoropolymer. The height of a cylinder can exceed 1.5 m. These billets are cut (skived) into wide thin films (<0.5 mm thick) or sheets (7 mm thick). Sheets, blocks, and cylinders are utilized as stock shapes for machining more complex shapes. The same principles are applied to mold any shape. 

Isostatic molding is a suitable alternative to compression and automatic molding techniques for the production of PTFE parts with complex shapes in a wide range of sizes. Compression molding can supply a stock shape which can be machined to obtain the desired shape. The drawback to this option is the... 

Due to the specialty nature and niche applications for polyamide-imide parts, many of these low-volume pieces are machined from preformed stock shapes. Toray, based in Japan, is producer of polyamide-imide resin that it converts to polyamide-imide parts and stock shapes, largely for the Asian markets. In the United States, Quadrant EPP supplies extruded Torlon polyamide-imide rod and plate stock as well as compression-molded ingots and shapes. Drake Plastics extrudes custom profiles in addition to standard shapes from Torlon resins. Injection-molded Torlon polyamide-imide stock shapes are available through Parkway Products. 

Measurement of a number of properties requires sheet stocks of PFA, from which specimens are punehed out and conditioned before testing. The sheet is prepared by using a chase in the shape of a picture frame with the adequate depth to produce a finished thickness of 1.5 0.25 mm. A fairly thick (0.13-0.18 mm) aluminum foil is sprayed with a high-temperature mold release agent before being placed smoothly over a flat steel plate (>1 mm thick). The chase is then placed over this plate-assembly. An amount of polymer sufficient to produce the sheet is placed in the middle of the chase in the form of a mound. A second sheet of aluminum foil is placed on top of the polymer granules and the top steel plate is added to the assembly, which is then put in a preheated (380 5°C) compression molding press. 

Compression molded PBI stock shapes are commercially available under the trade name Celazole U-60. High temperature and high pressure are needed to compression mold PBI. PBI stock shapes can be further machined into specific parts. With the highest among thermoplastics at about 427°C... 

Sheet stock can be produced using variations of the physical mechanics used by other processes. Simple drape forming uses the force of gravity-induced creep to allow a preheated blank to form over an open male mold. Vacuum may be applied to either a male or female mold to improve the formabUity and improve detail. In an approach similar to other compressive processes, pressure forming squeezes heated material between two mold halves to produce a crisply finished shape. Finally, two sheets may be heated and formed outward against the walls of a closed mold to produce hollow shapes. 

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