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RECIPROCATING SCREW. An extruder system in which the screw when rotating is pushed backward by the molten polymer which collects in front of the screw. When sufficient material has been collected, the screw moves forward and forces the material at high velocity through the head and the nozzle into a mold.
REINFORCED PLASTICS. Plastics with some strength properties greatly superior to those of the base resin, resulting from the presence of high strength fillers embedded in the composition. The reinforcing fillers are usually fibers, fabrics, or mats made of fibers. The plastic laminates are the most common and strongest type of reinforced plastics. (See FILLER.)
REINFORCEMENT. A strong inert material that is bound into plastics to improve the strength, stiffness, and impact resistance. Reinforcements are usually long fibers of sisal, cotton, glass, etc., in woven or nonwoven form.
RESIN. Any of a class of solid or semisolid organic products of natural or synthetic origin. Resins generally are of high molecular weight and have no definite melting point. Most resins are polymers.
RESIN, LIQUID. An organic polymeric liquid which, when converted to its final state for use, becomes a solid.
RESINOID. (See NOVOLAK.)
RETARDER. (See INHIBITOR.)
RING GATE. Annular opening for entrance of material into cavity of injection or transfer mold.
ROTATIONAL MOLDING (OR CASTING). A method used to make hollow products from powdered plastics, plastisols, and lattices. Powdered plastics or plastisol is charged into a hollow mold that can be rotated in one plane or in two planes. Heat is applied to melt, fuse, or cure the polymer. Cooling is usually required before removing the casting.
ROVING. A form of fibrous glass in which spun strands (filaments) are woven into a tubular rope. Chopped roving is commonly used in preforming.
RUBBER. An elastomer capable of rapid recovery after being stretched to at least twice its length at temperatures from 0 to 150°F(-18 to 66°C); specifically, Hevea or natural rubber, which is the standard of comparison for elastomers.
RUNNER. In an injection or transfer mold, the channel, usually circular, that connects the sprue with the gate to the cavity.
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