Glossary

Plastics Glossary - R

Radio frequency heating A heating and drying process utilizing radio frequency energy to generate heat in a dielectric material (non-metallic) by molecular friction

Radio frequency heating A heating and drying process utilizing radio frequency energy to generate heat in a dielectric material (non-metallic) by molecular friction.

Ram travel The distance the ram travels to force the resin through the heating cylinder (barrel) and into the mold of a plunger injection molding machine.

Ram The portion(Rod, plunger, or screw) of an injection machine that moves backward and forward to deliver the shot of resin to the nozzle and mold. The screw in a reciprocating screw machine.

Random Distribution Arrangement of particles in a mixture so that the probability of a single particle being at any one location is the same as that of its being at any other location.

Rao Birefringence Viscometer Couette-type viscometer that is used for low-viscosity fluids.

Rapid Prototyping Casting void-free parts for fast-curing polyurethanes for quick mold turnarounds.

Reaction injection molding A process that is applied to polyurethane, epoxy, and other liquid chemical systems. Mixing of two or four components in the proper chemical ratio is accomplished by high pressure impingement type mixing head from which the mixed material is delivered into the mold at low pressure.

Reagent Resistance The ability of a plastic to withstand exposure to chemicals.

Reciprocating screw injection molding An extruder-type screw rotates within a cylinder, which is typically driven by a hydraulic drive mechanism. Plastic material is moved through the heated cylinder via the screw flights and the material becomes fluid. The injection nozzle is blocked by the previous shot, and this action causes the screw to pump itself backward through the cylinder. (During this step, material is plasticated and accumulated for the next shot.) When the mold clamp has locked, the injection phase takes place. At this time, the screw advances, acting as a ram. Simultaneously, the non-return valve closes off the escape passages in the screw and the screw serves as a solid plunger, moving the plastic ahead into the mold. When the injection stroke and holding cycle is completed, the screw is energized to return and the non-return valve opens, allowing plastic to flow forward from the cylinder again, thus repeating the cycle.

Reciprocating screw A combination melting, softening, and injection unit in an injection molding machine. Another term for the injection screw. Reciprocating screws are capable of turning as they move back and forth.

Regrind As defined by ASTM D5033, is “a product or scrap, such as sprues and runners, that has been reclaimed by shredding and granulating for use in-house, and that may be dry blended by the molder with the same grade of virgin material.”

Reheat blow molding For critical containers for foods, cosmetics, carbonated beverages, etc., this process gives many resins improved physical properties. In biaxial orientation, parisons are stretched lengthwise by an external gripper, or by an internal stretch rod, and then stretched radially by blow air to form the finished container against the walls of the mold. This aligns the molecules along two planes - a configuration that gives substantially better barrier properties.

Reinforced plastic mold Designed to form a structure manufactured with any epoxy- or polyester-based resin with reinforcing fibers, strands, metallic, ceramic, or mineral extenders. There are hard and soft tooling. Hard tooling is manufactured from electroformed nickel, cast aluminum, or machined steel. Use for long-run, high-surface finish requirements, and high-cure temperatures. Soft tooling is manufactured from cast plastics, rubber, or reinforced plastics.

Reinforced plastics Molded, formed, filament wound or shaped plastic parts consisting of resins to which reinforcing fibers, mats, fabrics, etc. have been added before the forming operation. Strength properties are improved.

Reinforcement A material used to reinforce, strengthen, or give dimensional stability to another material. Materials added to plastic, usually to make it tougher or stronger.

Relative humidity The percent of moisture in the air relative to the greatest amount the air can hold at a given temperature.

Relative Viscosity Viscosity of a liquid in terms of the viscosity of some standard liquid, such as water at 20˚C.

Relative Volatility Volatility of one component divided by volatility of the other components; the pressure ration for components following Raoult’s law.

Release agent See Mold release agent.

Repeatability The ability of a system or mechanism to repeat the same motion or achieve the same points when presented with the same control signals. The cycle-to-cycle error of a system when trying to perform a specific task.

Resin content The amount of resin in a laminate expressed as either a percent of total weight or total volume.

Resin Natural or synthetic plastic characterized by being polymeric in structure. Most resins are of high molecular weight and consist of long-chain or network molecular structure. Usually resins are more soluble in their lower molecular weight forms.

Resin-rich area Localized area filled with resin and lacking reinforcing material.

Resin-rich content Localized area filled with resin and lacking reinforcing material.

Resin-starved area Localized area containing excess reinforcement and insufficient resin.

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, or surface resistivity, the ohm.

Resolving Power Ability of a microscope to produce separate images of particles very close together.

Restricted gate A small opening between the cavity and runner in an injection or transfer mold. To aid separation, the gate breaks cleanly after the piece is ejected.

Reverse pressure Suction used to draw cooling water through a mold.

Reverse temperature profile A set of barrel temperature settings starting higher in the rear and declining toward the front of the barrel. This is the reverse of normal.

Revolutionary method of change Method of changing machine settings in large increments, quickly finding the outer bounds of the process window.

Reynolds Number (Re, dimensionless) Measure of the degree of turbulence of a fluid flowing in a pipe; diameter times velocity times density and divided by absolute viscosity.

Rhe Unit of fluidity; 1 rhe=1 poise-1

Rheological Properties Flow properties of a system, e.g. plastic flow, thixotropy, and pseudoplasticity.

Rheology Study of the deformation and flow of matter.

Rheopectic Pertaining to a fluid whose apparent viscosity increases with time to some maximum value at any constant rate of shear.

Rib Configuration designed into a plastic part to provide lateral, horizontal, or other structural support. Long, thin intersecting walls that are used to reinforce the outer walls of the plastic part.

Rigid reinforcement An extremely stiff material such as glass, carbon fibers, or minerals that is blended with the resin to give it improved stiffness and strength.

Rigidity Reciprocal of mobility.

RIM (Reaction Injection Molding) Involves the injection of liquid polyurethane systems into a mold. The components then polymerize within the mold.

RIM mold Molds for reaction injection molding may be constructed from epoxy, nickel aluminum, or steel, depending upon the expected life of the mold. They should be designed to constrain a foaming pressure of 30-50 psi. For molding with a dense outer skin, it is important to use a temperature-controlled metal mold.

Ring gate Used on cylindrical shapes, this gate encircles the core to permit the melt to first move around the core before filling the cavity.

River-Water Die-Away Test Proposed test to determine the biodegradability of surface-active agents.

Robotics Refers to equipment that works automatically or by remote control.

Rockwell hardness A test for hardness (resistance to indentation) of a material in which a hardened steel ball or diamond point is pressed into the material under test.

Roller Mill Two or more rolls, usually revolving at different speeds, between which the materials to be mixed are passed.

Rotational Flow Flow that exhibits appreciable vorticity.

Rotational mold see Mold, Rotational

Rotational molding In rotational molding, or rotomolding, a product is formed from fine powder within a closed mold which is rotated in a heating chamber and then a cooling chamber. While the mold is slowly turning and tumbling, it is heated by forced hot air in an oven. As the mold wall heats, the resin begins to stick to the inside of the mold forming a hollow part.

ROV ( Refined Oil Viscosity) Viscosity of lamp oils and napthas as measured by a Saybolt Thermo-viscometer.

RRIM Reinforced Reaction Injection Molding.

RTM (Resin Transfer Molding) Is a closed mold process for molding fiberglass products. It does not require metal molds or high pressure mold closing systems. It is ideal for part volumes from 500 to 10,000 parts per year.

Runner Pullur A pin, hole, or undercut used to pull the runner off the stationary side of the mold as it opens.

Runner System This term is sometimes used for the entire resin feeding system, including sprues, runners and gates, in injection molding.

Runner In an injection mold, the feed channel, usually of circular cross section, that connects the sprue with the cavity gate. The term is also used for the plastic piece formed in this channel. The channels that connect the sprue with the gate of the mold.

Rupture Stress Shear stress .