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. |