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Glossary: Technical Terms
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A
- Abrasion Resistance
- The ability of a material to withstand mechanical actions such as rubbing, scraping, or erosion, that tend progressively to remove material from its surface.
- Additive
- In the plastics industry: materials added in minor amounts to basic resins or compounds to alter
properties.
- Adhesive Assembly
- The process of joining two or more plastic parts by means of an adhesive.
- Aging
- The process of, or the results of, exposure of plastics to natural or artificial environmental
conditions for a prolonged period of time.
- Alloy
- A term used in the plastics industry to denote blends of polymers or copolymers with other polymers
or elastomers. - i.e. ABS/Polycarbonate.
- Ambient Temperature
- The temperature of a medium surrounding an object. The term is often used to denote prevailing
room temperature.
- Amorphous
- Random molecular chain orientation. Most plastics are amorphous at processing temperatures.
- Anisotropy
- The tendency of a material to react differently to stresses applied in different directions.
- Annealing
- The process of relieving stresses in molded plastic articles.
- ANSI
- Abbreviation for American National Standards Institute.
- Antifogging Agents
- Additives which prevent or reduce the condensation of water on a plastic film in the form of small
droplets which resemble fog.
- Antioxidant
- Additives which inhibit oxidation at normal or elevated temperatures.
- Antistatic Agents
- Chemicals which impart a slight to moderate degree of electrical conductivity to plastic compounds,
thus reducing the accumulation of electrostatic charges on finished articles.
- Application
- The act of applying or putting to use. What the molded plastic article will be in its final form.
- Arc Resistance
- The ability of a plastic material to resist the action of a high voltage electrical arc, usually
stated in terms of time required to render the material electrically conductive.
- Ash Content
- The solid residue remaining after a substance has been incinerated or heated to a temperature
sufficient to drive off all combustible or volatile substances.
- Assembly
- The process of joining parts by any of several methods.
- ASTM
- Abbreviation for
American Society for Testing and Materials.
B
- Back Pressure
- The resistance of the molten plastic material to forward flow. In molding, back pressure increases the temperature of the melt, and contributes to better mixing of colors and homogeneity of the material.
- Balanced Runner
- In injection molding, a runner system designed to place all cavities at the same distance from
the sprue.
- Barrel
- That part of an extruder inside which the feed screw is located.
- Black Specks
- A specific kind of inclusion/contamination often associated with degraded materials.
- Blast Finishing
- Generally referred to as adding a non-polished surface on a mold.
- Blister
- An imperfection on the surface of a plastic article caused by a pocket of air or gas beneath the
surface.
- Bloom
- An undesirable cloudy effect or whitish powdery deposit on the surface of a plastic article caused
by the exudation of a compounding ingredient such as a lubricant, stabilizer pigment, plasticizer,
etc.
- Blow Molding
- The process of forming hollow articles by expanding a hot plastic element called a parison against
the internal surfaces of a mold.
- Blushing
- The tendency of a plastic article to turn white or chalky in areas that are highly stressed.
- Boss
- A protuberance provided on an article to add strength, facilitate alignment during assembly or
for attaching the article to another part.
- Branching
- The growth of a new polymer chain from an active site on an established chain, in a direction
different from that of the original chain.
- Breakdown Voltage
- The voltage required, under specific conditions, to cause failure of an insulation material. See
Dielectric Strength.
- Brittleness Temperature
- The temperature at which plastics and elastomers rupture by impact under specified conditions.
- Bulk Density
- The density of a modking material in loose form expressed as a ratio of weight to volume.
- Bulk Factor
- The ratio of the volume of any given mass of loose plastic material to the volume of the same
mass of the material after molding.
- Burned
- Showing evidence of excessive heating during processing or use of a plastic, as evidenced by blistering,
discoloration, distortion or destruction of the surface.
C
- Cavity
- A depression, or a set of matching depressions, in a plastics-forming mold which forms the outer
surfaces of the molded articles.
- Charge
- The amount of material used to load a mold at one time or during one cycle.
- Charpy Impact Test
- A destructive test of impact resistance, consisting of placing the specimen in a horizontal position
between two supports, then applying a blow of known magnitude. If the specimen does not break,
a new specimen is put in position and the magnitude is increased until the specimen breaks. (ASTM
D-256, Method B)
- Chopped Strand
- A type of fiber reinforcement consisting of strands of individual glass fibers which have been
chopped into short pieces.
- Clamping Area
- The largest rated molding area an injection press can hold closed under full molding pressure.
- Clamping Force
- In injection molding, the pressure which is applied to the mold to keep it closed, in opposition
to the fluid pressure of the compressed molding material within the mold cavity and the runner
system.
- Clamping Pressure
- In injection molding, the pressure applied to the mold to keep it closed during the molding cycle.
- CTE
- Coefficient of Thermal Expansion: The change in length of a material for a unit change in temperature,
per unit of length.
- Coextrusion
- The process of extruding two or more materials through a single die with two or more orifices
arranged so that the extrudates merge and weld together into a laminar structure before chilling.
- Colorants
- Dyes or pigments which impart color to plastics.
- Color Concentrate
- A plastic compound which contains a high percentage of pigment, to be blended in appropriate amounts
with the base resin so that the correct final color is achieved.
- Composite
- An article or substance containing or made up of two or more different substances.
- Compound
- A mixture of resin and the ingredients necessary to modify the resin to a form suitable for processing
into finished articles.
- Compounding
- The step of mixing base resins with additives such as stabilizers, fillers, pigments into a form
suitable for processing into finished articles.
- Compression Molding
- A method of molding in which the molding material, generally preheated, is placed in an open heated
mold cavity, the mold is closed with a top force, pressure is applied to force the material into
contact with all mold areas, and heat and pressure are maintained until the molding material has
cured. This process is most often used with thermoset.
- Compressive Strength
- The load sustained by a test specimen in a compressive test divided by the original area of the
specimen.
- Conditioning
- Subjecting a material to standard environmental and/or stress history prior to testing.
- Copolymer
- This term usually, but not always, denotes a polymer of two chemically distinct monomers.
- Core
- A protrusion, or set of matching protrusions, in a plastics forming mold which forms the inner
surfaces of the molded articles.
- Corrosion Resistance
- A broad term applying to the ability of plastics to resist many environments.
- Crazing
- An undesirable defect in plastics articles characterized by distinct surface cracks or minute
frost-like, internal cracks, resulting from stresses within the article which exceed the tensile
strength of the plastic, generally caused by chemical attack.
- Creep
- Due to its viscoelastic nature, a plastic subjected to a load for a period of time tends to deform
more than it would from the same load released immediately after application, and the degree of
this deformation is dependent of the load, load duration, and environment temperature.
- Cross-Linking
- The setting up of chemical links between the molecular chains.
- Cryogenic
- Pertaining to very low temperatures.
- Crystal
- A homogeneous solid having an orderly and repetitive three dimensional arrangement of its atoms.
- Crystallinity
- A state of molecular structure in some resins attributed to the existence of solid crystals with
a definite geometric form, Such structures are characterized by uniformity and compactness.
- CSA
- Abbreviation for the Canadian Standards Association.
- Custom Molder
- A firm specializing in the molding of items or components to the specifications of another firm
which handles the sale of distribution of the item, or incorporates the custom molded components
in one of its own products.
- Cycle Time
- In a molding operation, cycle time is the time elapsing between a particular point in one cycle
and the same point in the next cycle.
D
- Damping
- Variations in properties resulting from dynamic loading conditions.
- DTUL
- Abbreviation for Deflection Temperature Under Load Degassing In injection molding, the momentary
opening and closing of a mold during the early stages of the cycle to permit the escape of air
or gas from the heated compound.
- Degradation
- A deleterious change in the chemical structure, physical properties or appearance of a plastic
caused by exposure to heat, light, oxygen, weathering, or a chemical.
- Design Review
- A review of a blueprint, of an application, to be molded in a plastic material. Recommendations
given for design, material, processing, tooling.
- Density
- (Absolute) Mass per unit volume of a substance.
- Dieletric Strength
- A measure of the voltage required to puncture a material, expressed in volts per mil of thickness
(ASTM D-149)
- Dimensional stability
- The ability of a plastic part retain the precise shape in which it was molded.
- Draft
- Degree of taper of the cavity/core side walls, allowing the part to be removed easily from the mold.
- Drying
- The removal of moisture from the resin pellets by exposure to certain time and temperature. All
Hydroscopic Material must be dried prior to molding.
- Durometer
- An instrument used for measuring the hardness of a material.
E
- Ejector Pin
- A rod, pin, sleeve or bar which pushes a molding off of a core or out of a cavity of a mold.
- Elasticity
- The ability of a material to quickly recover its original dimensions after removal of a load that
has caused deformation.
- Elastic Memory
- A characteristic of certain plastics evidenced by their tendency upon reheating to revert to a
shape or dimension previously existing during their manufacture.
- Elastomer
- A material which at room temperature can be stretched repeatedly to at least twice its original
length and, upon immediate release of the stress, will return with force to its approximate original
length.
- Engineering Plastics
- A broad term covering all plastics, with or wirhout fillers or reinforcements, which have mechanical,
chemical and thermal properties suitable for use, in construction, machine components and chemical
processing equipment.
- Extrudate
- The product or material delivered from an extruder, for example, film, pipe profiles.
- Extruder
- A machine for producing more or less continuous lengths of plastics sections such as rods, sheets,
tubes, and profiles.
- Extrusion
- The process of forming continuous shapes by forcing a molten plastic material through a die.
F
- Family Mold
- A multiple cavity mold containing variously shaped cavities, producing different parts.
- Fatigue Strength
- The maximum cyclic stress a material can withstand for a given number of cycles before failure
occurs.
- FDA
- Abbreviation for Food and Drup Administration, the U.S. agency under the Department of Health,
Education and Welfare which is concerned with the safety of products marketed for consumer use.
- Filler
- A relatively inert substance added to a plastic compound to reduce its cost and/or to improve
physical properties, particularly hardness, stiffness and impact strength.
- Film
- Films are distinguished from sheets in the plastics industry only according to their thickness.
- Fines
- In the classification of powdered or granular materials such as molding compounds according to
particle size, fines are the portion of the material composed of particles which are smaller than
a specified size.
- Finish
- The surface texture of a finished article.
- Flame Retardant
- Having the ability to resist combustion (A flame retardant plastic is considered to be one that
will not continue to burn or glow after the source of ignition has been removed.)
- Flame Retardants
- Additives that reduce the tendency of plastics to burn.
- Flash
- The thin, surplus of material which if forced into crevices between mating mold surfaces during
a molding operation remains attached to the molded article.
- Flexural Modulus
- The ratio, within the elastic limit, of the applied stress on a test specimen in flexure to the
corresponding strain in the outermost fibers of the specimen.
- Flexural Strength
- The maximum stress in the outer fiber at the moment of crack or break. In the case of plastics,
this value is usually higher than the tensile strength.
- Foaming Agent
- Any substance which alone or in combination with other substances is capable or producing a cellular
structure in a plastic mass.
- Forming
- A general term encompassing processes in which the shape of plastic pieces such as sheets, rods
or tubes is changed to a desired configuration.
- Fracture
- The separation of a body, usually characterized as either brittle or ductile.
G
- Gate
- In injection molding, the channel through which the molten resin flows from the runner into the
cavity.
- Gate Blush
- A blemish or disturbance in the gate area of an injection molded article.
- Glass Fibers
- A family of reinforcing materials for reinforced plastics based on single filaments of glass.
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