Radio Frequency Welding - A method of welding thermoplastics using a radio frequency field to apply the necessary heat. Also known as high frequency welding.

Ram Travel - The distance the injection ram moves in filling the mold, in either injection or transfer molding.

Rayon - The generic term for fibers, staple, and continuous filament yarns composed of regenerated cellulose but also frequently used to describe fibers obtained from cellulose acetate or cellulose triacetate. Rayon fibers are similar in chemical structure to natural cellulose fibers (e.g., cotton) except that the synthetic fiber contains shorter polymer units. Most rayon is made by the viscose process.

Reciprocating Screw - An extruder system in which the screw when rotating is pushed backwards 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 through the head and die at a high speed.

Recycled Plastic - A plastic prepared from used articles which have been cleaned and reground.

Reformulated Plastic - Recycled plastic that has been upgraded to alter or improve performance capability or to change characteristics through use of plasticizers, fillers, stabilizers, pigments, etc.

Regrind - Plastic that is re-introduced into the production stream.

Reinforced Molding Compound - Compound supplied by raw material produced in the form of ready-to-use materials; as distinguished from premix.

Reinforced Plastics - A plastic with high strength fillers embedded in the composition, resulting in some mechanical properties superior to those of the base resin.

Reinforcement - A strong inert material bound into a plastic to improve its strength, stiffness, and impact resistance. Reinforcements are usually long fibers of glass, sisal, cotton, etc. - in woven or non-woven form. To be effective, the reinforcing material must form a strong adhesive bond with the resin.

Relative Humidity - Ratio of the quantity of water vapor present in the air to the quantity which would saturate it at any given temperature.

Relative Viscosity - The relative viscosity of a polymer in solution is the ratio of the absolute viscosities of the solution (of stated concentration) and of the pure solvent at the same temperature.

Release Agent - A lubricant, often wax, used to coat a mold cavity to prevent the molded piece from sticking to it, and thus to facilitate its removal from the mold.

Relief Angle - The angle of the cutaway portion of the pinch-off blade measured from a line parallel to the pinch-off land.

Reprocessed Plastic - A thermoplastic prepared from scrap industrial plastic by other than the original processor.

Resiliency - Ability to quickly regain an original shape after being strained or distorted.

Resin - Any of a class of solid or semi-solid organic products of natural or synthetic origin, generally of high molecular weight with no definite melting point. Most resins are polymers.

Resin Pocket - An apparent accumulation of excess resin in a small, localized section visible on cut edges of molded surfaces.

Resistivity - The ability of a material to resist passage of electrical current either through its bulk or on a surface. The unit of volume resistivity is the ohm-cm., of surface resistivity, the ohm.

Restricted Gate - A very small orifice between runner and cavity in an injection or transfer mold. When the piece is ejected, this gate breaks cleanly, simplifying separation of runner from piece.

Retainer Plate - The plate on which demountable pieces, such as mold cavities, ejector pins, guide pins, and bushings are mounted during molding; usually drilled for steam or water.

Rheology - Study of the deformation and flow of matter in terms of stress, strain and time.

Rib - A reinforcing member of a fabricated or molded part.

Rigid Plastics - For purpose of general classification, a plastic that has a modulus of elasticity either in flexure or in tension greater than 100,000 psi at 23 degrees C and 50% relative humidity when tested in accordance with ASTM Methods D 747 or D 790 Test for stiffness of plastics.

Rigid PVC - Polyvinyl chloride or a polyvinyl chloride/acetate copolymer characterized by a relatively high degree of hardness; it may be formulated with or without a small percentage of plasticizer.

Rigid Resin - Having a modulus high enough to be of practical importance, e.g., 10,000 psi or greater.

Rockwell Hardness - A common method of testing a plastic material for resistance to indentation in which a diamond or steel ball, under pressure, is used to pierce the test specimen. The load used is expressed in kilograms and a 10-kilometer weight is first applied and the degree of penetration noted. The so-called major load (60 to 150 kilograms) is next applied and a second reading obtained. The hardness is then calculated as the difference between the two loads and expressed with nine different prefix letters to denote the type of penetrator used and the weight applied as the major load.

Rosin - The hard resin, amber to black in color, left after the distillation of turpentine.

Rotational Molding - A method used to make hollow articles from plastisols and lattices. Plastisol is charged into a hollow mold capable of being rotated in one or two planes. The hot mold fuses the plastisol into a gel after the rotation has caused it to cover all surfaces. The mold is then chilled and the product stripped out.

Round Square - Particular shape of a container which has sides of equal width with well-rounded corners and shoulders.

Rubber - An elastomer capable of rapid elastic recovery after being stretched to at least twice its length at temperatures from 0 to 150 degrees F, at any humidity. Specifically, heavy or natural rubber, 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.