Refractive Index
The deviation caused by the material when
a light beam passes through a transparent specimen.
Regrind
Resin that has been previously molded and ground
into small pieces for reprocessing. Regrind is usually
comprised of sprues, runners and unfilled parts.
Reinforcement
An inert fibrous or non-fibrous material
incorporated in a plastic to improve or modify mechanical or
physical properties.
Reinforced Plastic
A plastic with high-strength fibers
embedded in the polymer matrix, resulting in increased
strength properties superior to those of the base resin.
Reinforced Plastic A plastic composition in which fibrous
reinforcements are imbedded, with strength properties greatly
superior to those of the base resin.
Resin (Synthetic)
The term is use to designate any polymer
that is a basic material for plastics.
Rockwell
Rockwell hardness is the resistance of a material
to indentation of a defined steel ball. Three scales exist (R,
L and M) with different ball diameters and different levels of
loading for testing materials of different hardness.
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.
Runner Balancing
Developing a runner system which delivers the
required amount of melt to each cavity with the correct
pressure to finish filling all the cavities simultaneously at
the correct temperature for the part.
Runner Design
Using the runner as a flow control device
(positioning the gate and using the size of the runner to
control the filling pattern within the cavity) in addition to
getting the melt into the cavity.
Runner System
This term is sometimes used for the entire resin
feeding system, including sprues, runners and gates, in
injection molding.
Scrap
Any output of a mold that is not usable as the
primary product.
Screw
A rotating auger that uses a helical thread and a
varying channel depth to convey, melt, mix, and pump resin.
Consists of a feed section, transition zone, metering section
and in some cased a mixing zone/zones.
Shore
Shore hardness values are measured by using
calibrated durometers: Shore A for softest and Shore D for
harder materials. The material is penetrated with a steel rod
of predefined dimensions - different for Shore A and for Shore
D. The values show no correlation with other hardness
measurement values.
Short Shot
The amount of resin injected into a mold cavity at
a volume less than required to fill the mold.
Shot
One complete cycle of a molding machine.
Shrinkage
The percentage of reduction in overall part
dimensions. Shrinkage occurs during the cooling phase of the
process.
Shrinkage Allowance
The dimensional allowance which must be
made in molds to compensate for shrinkage of the plastic
compound on cooling.
Shut-Off Nozzle
A device attached to the front of the molding
machine barrel or hot manifold system. It opens to allow resin
flow into the mold cavity. It closes after injection to help
prevent drooling.
Single Cavity Mold
Produces one part with each cycle.
Sink
A depression on the part surface over a thick wall
feature i.e., a rib, boss, thick sprue gate or change in wall
section. Caused by the delayed cooling effects of the center
of the thick area. When the hot center cools, it shrinks and
pulls down the skin on the surface.
Sink Marks
An indentation on the surface of the part as a
result of significant local change in wall section. The mark
will occur in the thicker area.
Specific Gravity
The ratio of the density of a material as
compared to the density of water at standard atmospheric
pressure (1 ATM) and room temperature (73F).
Specific Heat
The amount of heat needed to raise one gram of
material one ŪC in temperature. Equals "heat capacity" or
"Cp."
Specific Volume
The volume of a unit of weight of a material;
the reciprocal of density.
Stabilizer
A substance used in the formulation of plastics
to help maintaining the properties of the material during
processing and service life.
Subgate
Entrance to the part from the runner located below
the parting line. On ejection the part breaks away from the
subgate.
Submolding
Break up of a full molding into component areas.
Surface Appearance
Distressed melt flow due to welding,
melding, splay, etc. will appear as surface imperfections.
Back
Next
