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A-stage
This is a very early stage in the reaction of certain thermosetting resins where the molecular weight is low and the resin is still soluble in some liquids and still fusible.

Abrasion Resistance
The ability to withstand the effects of repeated wearing, rubbing, scraping, etc., that tend to remove material from its surface.

Absolute Viscosity
The tangential force on unit area of either of two parallel planes at unit distance apart when the space between the planes is filled with the fluid in question and one of the planes moves with unit differential velocity in its own plane. The C.G.S. unit for absolute (or dynamic) viscosity is poise (dyne-sec./sq. cm.). Centipoise (0.01) is often used.

Accelerator
A substance that hastens a reaction, particularly one which speeds up the vulcanization of rubber. Also known as Promoter.

Accumulator
A term used mainly with reference to blow molding equipment which designates an auxiliary ream extruder which is used to provide extremely fast parison delivery. The accumulator cylinder is filled with plasticated melt coming from the extruder between parison deliveries or “shots” and is stored or “accumulated” until the plunger is required to deliver the next parison.

Acrylic Resin .
A synthetic resin prepared from acrylic acid or from a derivative of acrylic acid,

Acrylonitrile
A monomer with the structure (CH2:CHCN). It is most useful in copolymers. Its copolymer with butadiene is nitrile rubber, and several copolymers with styrene exist that are tougher than polystyrene. It is also used as a synthetic fiber and as a chemical intermediate.

Acrylontrile Butadiene Styrene (ABS)
Acrylonytrile and styrene liquids and butadiene gas are polymerized together in a variety of ratios to produce the family of ABS resins.

Actuation
To put into mechanical action or motion.

Additive
A substance compounded into a resin to enhance or improve certain characteristics.

Adhesion Promoter
A coating which is applied to the substrate before it is extrusion coated with the plastic and which improves the adhesion of the plastic to the substrate.

Adhesive
A substance which applied as an intermediate is capable of holding materials together by surface attachment.

Affinity
The attraction for another substance.

Aging
The change of a material with time under defined environmental conditions, leading to improvement or deterioration of properties.

Air Gap
In extrusion coating, the distance from the die opening to the tip formed by the pressure roll and chill roll.

Air Ring
A circular manifold used to distribute an even flow of the cooling medium, air, onto a hollow tubular form passing through the center of the ring. In blown tubing, the air cools the tubing uniformly to provide uniform film thickness.

Air-assist Forming
A method of thermoforming in which a flow of air pressure is employed to partially pre-form the sheet immediately prior to the final pull down onto the mold using vacuum.

Alkyd Resin
Polyester resins made with some fatty acid as a modifier.

Alkyl
A general term for monovalent aliphatic hydrocarbon radicals.

Alloy
Composite material made up by blending polymers or copolymers with other polymers or elastomers under selected conditions, e.g., styrene-acrylonitryle copolymer resins blended with butadiene-acrylonitrile rubbers.

Allyl Resin
A synthetic resin formed by the polymerization of chemical compounds containing the group CH2=CH-CH2-. The principal commercial allyl resin is a casting material that yields allyl carbonate polymer.

Alpha-cellulose
Very pure cellulose prepared by special chemical treatment.

Amine
Any of a class of organic compounds derived from ammonia by replacement of hydrogen with one or more alkyl groups.

Amorphous
Latin meaning without form. Non-crystalline structure.

Amorphous Phase
Devoid of crystallinity – no definite order. At processing temperatures, the plastic is normally in the amorphous state.

Angle Press
A hydraulic molding press equipped with horizontal and vertical rams, and specially designed for the production of complex moldings containing deep undercuts.

Anneal
To prevent the formation of or remove stresses in plastics by cooling from a suitable temperature.

Annealing
A process of holding a material at a temperature mean, but below its melting point, the objective being to permit stress relaxation without distortion of shape. It is often used on molded articles to relieve stresses set up by flow into the molds.

Anti-friction Compounds
Materials specifically formulated to reduce or eliminate friction.

Antifogger
An additive that prevents condensation of moisture on glass and other transparent materials, such as windshields or lenses.

Antioxidants & Antiozonants
These additives are used to prevent the negative effects of oxygen and ozone on the resin materials.

Antistatic Agents
Methods of minimizing static electricity in plastic materials. Such agents are of two basic types: (1) metallic devices which come into contact with the plastics and conduct the static to earth. Such devices give complete neutralization at the time, but because they do not modify the surface of the material it can become prone to further static during subsequent handling; (2) chemical additives which, mixed with the compound during processing, give a reasonable degree of protection to the finished products.

Aramid
Any of a group of lightweight by very strong heat-resistant synthetic aromatic polyamide materials that are fashioned into fibers, filaments, or sheets.

Arc
1) A luminous glow formed by the flow of electric current through ionized air, gas or vapor between separated electrodes or contacts. 2) A portion of the circumference of a circle.

Arc Resistance
1) The resistance to the flow of current offered by the voltaic arc (i.e., if the carbons of an arc lamp are 1/32″ apart, the arc resistance will be 1-1/2 ohms). 2) The resistance of a material to the effects of an arc passing across its surface stated as a measure of the total elapsed time taken to form a conducting path (of material carbonizing by the arc flame) across the surface under prescribed conditions of applications of a high voltage, low current arc (as across an insulator).

Aromatic Hydrocarbons
Hydrocarbons derived from or characterized by presence of unsaturated resonant ring structures.

Asbestos
A gray, non-burning, non-conductive and chemical resistant material occurring in long fibers or fibrous masses, sometimes used as a filler for reinforcement.

Atactic
A polymer exhibiting no stereochemical regularity of structure.

Autoclave Molding
Modification of the pressure bag method for molding reinforced plastics. After lay-up, entire assembly is placed in steam autoclave at 50 to 100 psi. Additional pressure achieves higher reinforcement loadings and improved removal of air.

Automatic mold
A mold for injection or compression molding that repeatedly goes through the entire cycle, including ejection, without human assistance.

Average Molecular Weight (viscosity method)
The molecular weight of polymeric materials determined by the viscosity of the polymer in solution at a specific temperature. This gives an average molecular weight of the molecular chains in the polymer independent of specific chain length. Falls between weight average and number average molecular weight.

AWG
Abbreviation for American Wire Gauge, a standard system for designating wire diameter.

B-stage
This describes an intermediate stage of reaction where the material will soften when heated and swells in the presence of certain liquids, but may not completely fuse or dissolve. The resin is usually supplied in this uncured state.

Back Pressure
The viscosity resistance of a material to continued flow when a mold is closing. In extrusion, the resistance to the forward flow of molten material.

Backing Plate
In injection molding, a plate used as a support for the cavity blocks, guide pins, bushings, etc.

Baffle
A device used to restrict or divert the passage of fluid through a pipe line or channel. In hydraulic systems the device, which often consists of a disc with a small central perforation, restricts the flow of hydraulic fluid in a high pressure line. A common location for the disc is in a joint in the line. When applied to molds, the term is indicative of a plug or similar device located in a steam or water channel in the mold and designed to divert and restrict the flow to a desired path.

Bag molding
A method of applying pressure during bonding or molding, in which a flexible cover, usually in connection with a rigid die or mold, exerts pressure on the material being molded, through the application of air pressure or drawing of a vacuum.

Bakelite
The proprietary name for phenolic and other plastics materials produced by Bakelite Limited, but often used indiscriminately to describe any phenolic molding material or molding. The name is derived from that of Dr. Leo Hendrik Baekeland (1863-1944), a Belgian who, through his work on synthesis of phenolic resins and their commercial development in the early 1900’s, is generally considered to be the “father” of the plastic industry.

Base
The material woven (such as paper, woven cotton, glass fabric, or glass fiber mat, felted asbestos, aramid fibers, graphite and nylon fabrics) in the form of sheets or rolls which can be impregnated with resin to form laminated plastics.

Benzene Ring
The basic structure of benzene, the most important aromatic chemical. It is an unsaturated, resonant 6-carbon ring having three double bonds. One or more of the 6 hydrogen atoms of benzene may be replaced by other atoms or groups.

Binder
The organic or inorganic material which encapsulates and holds together the base in reinforced or otherwise heterogeneous composites.

Biocides & Fungicides
These additives act as pesticides and are used to inhibit the growth of fungus and other pests.

Bleed
To give up color when in contact with water or a solvent; undesired movement of certain materials in a plastic (e.g. plasticizers in vinyl) to the surface of the finished article or into an adjacent material. Also called Migration.

Blister
A raised area on the surface of a molding caused by the pressure of gases inside it on its incompletely hardened surface.

Block Copolymer
An essentially linear copolymer in which there are repeated sequences of polymeric segments of different chemical structure.

Blocking & Anticaking Agents
These additives are used to prevent the adhesion of two touching layers of film during fabrication and storage.

Bloom
A visible exudation or efflorescence on the surface of a material.

Blow Molding
Method of fabrication in which a warm plastic parison (hollow tube), is placed between the two halves of a mold cavity and forced to assume the shape of that mold cavity by use of air pressure.

Blow molding
A method of fabrication in which a parison (hollow tube) is forced into the shape of the mold cavity by internal air pressure.

Blow Pressure
The air pressure used to form a hollow part by blow molding.

Blow Rate
The speed at which the air enters the parison during the blow loading cycle.

Blowing & Foaming Agents
Upon addition to plastics or rubbers and then heating, this chemical generates inert gases which results in the resin assuming a cellular structure.

Blown Tubing
A thermoplastic film which is produced by extruding a tube, applying a slight internal pressure to the tube to expand it while still molten and subsequent cooling to set the tube. The tube is then flattened through guides and wound up flat on rolls. The size of blown tubing is determined by the flat width in inches as wound rather than by the diameter as in the case of rigid types of tubing.

Blowup Ratio
In blow molding, the ratio of the mold cavity diameter to the parison diameter. In blown tubing (film), the ratio of the final tube diameter (before gusseting, if any) to the original die diameter.

Bond Strength
1)The measure of the force required to separate objects or materials bonded together. 2) The strength of the bond between fiber and matrix. 3) The degree of attraction between adjacent atoms within a molecule, usually expressed in J/mol.

Boss
Protuberance on a plastic part designed to add strength, to facilitate alignment during assembly, to provide for fastening, etc.

Boston Round
A particular shape of container; cross section as well as shoulders are round.

Bottom Blow
A specific type of blow molding machine which forms hollow articles by injecting the blowing air into the parison from the bottom of the mold.

Bottom Plate
Part of the mold which contains the heel radius and the push-up.

Branched
In molecular structure of polymers (as opposed to Linear), refers to side chains attached to the main chain. Side chains may be long or short.

Breakdown
The disruptive discharge through insulation due to failure under electrostatic stress.

Breaker Plate
A perforated plate located at the rear end of an extruder head. It often supports the screens that prevent foreign particles from entering the die.

Breathing
The opening and closing of a mold to allow gases to escape early in the molding cycle. Also called Degassing. When referring to plastic sheeting, “breathing” indicates permeability to air.

Brighteners
Are used to add smoother or brighter coatings.

British Thermal Unit (BTU)
The quantity of heat required to raise the temperature of one pound of water 1°F from 58.5 to 59.5°F (its point of maximum density).

Brittle Temperature
A measure for judging the relative merits of materials for low temperature flexing or impact – i.e., the temperature at which materials rupture by impact under specified conditions.

Bubbler mold Cooling (injection molding)
A method of cooling an injection mold in which a stream of cooling liquid flows continuously into a cooling outlet normally positioned at the end opposite the inlet. Uniform cooling can be achieved in this manner.

Bulk Density
ASTM D1182-54 test method describes this measurement of mass per unit volume of a molding powder (in large volume determinations).

Bulk Density
The mass per unit volume of a molding powder as determined in a reasonably large volume. The recommended test method is ASTM D1182-54.

Bulk Factor
Ratio of the volume of loose molding powder to the volume of the same weight of resin after molding.

Bulk-molding compounds (BMC)
Bulk-molding compounds are used as a premix in composite manufacturing. A BMC consists of a mixture of resin, reinforcements, inert fillers, and other additives which form a puttylike preformed shape, rope or sheet.

Bushing (extrusion)
The outer ring of any type of a circular tubing or pipe die which forms the outer surface of the tube or pipe.

Butadiene
A gas, insoluble in water but soluble in alcohol and ether, obtained from the cracking of petroleum, from coal tar benzene or from acetylene produced from coke and lime. It is widely used in the formation of copolymers with styrene, acrylonitrile, vinyl chloride and other monomeric substances, where it imparts flexibility to the subsequent moldings.

Butadiene Styrene Plastics
A synthetic resin derived from the copolymerization of butadiene gas and styrene liquids.

Buttress Thread
A type of threading in which the thread sides terminate abruptly in threading gradually tapering down to the neck finish. Designed to withstand maximum force in one direction only. Cross section of thread is triangular.

Butylene Plastics
Plastics based on resins made by the polymerization of butene or copolymerization by butene with one or more unsaturated compounds, the butene being in greatest amount by weight.

C-stage
This term describes the final stage of the reaction where the material s relatively insoluble and infusible.

Calendering
A form of extrusion using two or more counter rotating rolls in which film and sheet is produced by squeezing a hot, viscous material between them.

Canvas
A cotton fabric weighing more than four ounces per square yard. (Used as the base material for NEMA grades C, CE and some L grade laminates.)

Capacitance
The property of an electric nonconductor that permits the storage of energy as a result of the separation of charge that occurs when opposite surfaces of the nonconductor are maintained at a difference of potential.

Carbon Black
A black pigment produced by the incomplete burning of natural gas or oil. It is widely used as filler, particularly in the rubber industry. Because it possesses useful ultraviolet properties. It is also used in polyethylene compounds intended for such applications as cold water piping and black agricultural sheet.

Carbonyl
Organic functional group occurring in aldehydes, ketones, carboxylic acids, esters and their derivatives.

Cast
To form a “plastic” object by pouring a fluid monomer-polymer solution into an open mold where it finishes polymerizing. (2) Forming plastic film and sheet by pouring the liquid resin onto a moving belt or by precipitation in a chemical bath.

Cast Film
A cast film is made by depositing a layer of plastic onto a surface then solidifying and removing the film from that surface. The plastic layer can be in molten form, in a solution, or in dispersion.

Catalyst
A substance which markedly speeds up the cure of a compound when added in minor quantity as compared to the amounts of primary reactants.

Cavity
Depression in a mold made by casting, machining, hobbing, or a combination of these methods; depending on number of such depressions, molds are designated as Single-Cavity or Multi-Cavity.

Cellular Plastics
Plastics containing numerous small cavities (cells), interconnecting or not distributed throughout the mass.

Celluloid
A thermoplastics material made by the intimate blending of cellulose nitrate with camphor. Alcohol is normally employed as a volatile solvent to assist plasticization, and is subsequently removed.

Cellulose
A natural high polymeric carbohydrate found in most plants; the main constituent of dried woods, jute, flax, hemp, ramie, etc. Cotton is almost pure cellulose.

Cellulose Propionate
An ester of cellulose made by the action of propionic acid and its anhydride on purified cellulose. It is used as the basis of a thermoplastic molding material.

Cellulose Triacetate
A cellulosic material made by reacting purified cellulose with acetic anhydride in the presence of a catalyst. It is used in the form of film and fibers. Films and sheet are cast from clear solutions on to “drums” with highly polished surfaces. The film, which is of excellent clarity, has high tensile strength, and good heat resistance and dimensional stability. Applications include book jackets, magnetic recording tapes, and various types of packaging. Cellulose triacetate sheet has somewhat similar properties to those of the film and is used to make such articles as safety goggles, map wallets and transparent covers of many kinds.

Celsius
Also referred to as Centigrade, is equal to the difference between the temperature in Fahrenheit less 32 and the quantity divisible by 1.8°C = (°F – 32) ÷ 1.8.

Cement
A dispersion of “solution” of unvulcanized rubber or a plastic in a volatile solution. This meaning is peculiar to plastics and rubber industries and may not be an adhesive composition.

Center Gated mold
An injection mold wherein the cavity is filled with resin through an orifice interconnecting the nozzle and the center of the cavity area. Normally, this orifice is located at the bottom of the cavity when forming items such as containers, tumblers, bowls, etc.

Centrifugal Casting
A method of forming thermoplastic resins in which the granular resin is placed in a rotatable container, heated to molten condition by the transfer of heat through the walls of the container, and rotated so that the centrifugal force induced will force the molten resin to conform to the configuration of the interior surface of the container. Used to fabricate large diameter pipes and similar cylindrical items.

Chalking
A powdery residue on the surface of a material often resulting from degradation.

Charge
The measurement or weight of material used to load a mold at one time or during one cycle.

Chlorinated Polyvinyl Chloride Plastics
Plastics based on chlorinated polyvinyl chloride in which the chlorinated polyvinyl chloride is in the greatest amount of weight.

Chlorofluorocarbon Plastics
Plastics based on polymers made with monomers composed of chlorine, fluorine, and carbon only.

Chromium Plating
An electrolytic process that deposits a hard film of chromium metal onto working surfaces of other where resistance to corrosion, abrasion, and/or erosion is needed

Circuit
In filament winding, the winding produced by a single revolution of mandrel or form.

Clamping Plate
A plate fitted to a mold and used to fasten the mold to a molding machine.

Clamping Pressure
In injection molding and in transfer molding, the pressure which is applied to the mold to keep it closed, in opposition to the fluid pressure of the compressed molding material.

Clarifier
An additive that increases the transparency of a material.

Co-extrusion
The process of combining two or more layers of extrudate to produce a multiple layer product in a single step.

Coalesce
To combine into one body or to grow together.

Coefficient of Expansion .
The fractional change in length (sometimes volume, specified) of a material for a unit change in temperature. Values for plastics range from 0.01 to 0.2 mils/in., C

Coefficient of Friction
Static: the ration of the limiting friction developed to the corresponding normal pressure if two surfaces move relative to each other.

Coefficient of Thermal Expansion
The unit change in dimension of a material for a unit change in temperature.

Cold Flow or Creep
A time-dependent strain of solids resulting from stress.

Cold Molding
The process of compression molding involving shaping an unheated compound in a mold under pressure then heating the article to cure it.

Cold Slug Well
Space provided directly opposite the spruce opening in an injection mold to trap the cold slug.

Cold Stretch
Pulling operation, usually on extruded filaments, to improve tensile properties.

Colorants & Pigments
Are additive used to change the color of the plastic. They can be a powder or a resin/color premix.

Composite
1)A structure or an entity made up of distinct components. 2) A complex material, such as fiberglass, in which two or more distinct, structurally complementary substances, especially glasses and polymers, combine to produce structural or functional properties not present in any individual component. 3) Reinforced laminates (i.e., canvas phenolic, glass epoxy, etc.).

Compound
These are chemical combinations of materials which include all the materials necessary for the finished product. They include BMC (Bulk Molding Compounds), SMC (Sheet Molding Compounds) and TMC (Thick Molding Compounds).

Compression Molding
The process of molding a material in a confined shape by applying pressure and usually heat.

Compression Ratio
In an extruder screw, the ratio of volume available in the first flight at the hopper to the last flight at the end of the screw.

Compressive Strength
The ability of a material to resist a force that tends to crush it.

Concentricity
For a container, the shape in which various cross sections have a common center.

Condensation
A chemical reaction in which two or more molecules combine with the separation of water or some other simple substance. If a polymer is formed, the condensation process is called Polycondensation. See also Polymerization.

Conditioning
The subjection of a material to a stipulated treatment so that it will respond in a uniform way to subsequent testing or processing. The term is frequently used to refer to the treatment given to specimens before testing.

Conductivity
The reciprocal of volume resistivity. It is the conductance of a unit cube of any material.

Conductor
A wire, or combination of wires not insulated from each other, suitable for carrying electricity.

Continuous Service Temperature
The highest temperature at which a material can perform reliably in long term application – long term being, however, inconsistently defined by the manufacturers.

Convergent Die
A die in which the internal channels leading to the orifice are converging (only applicable to dies for hollow bodies).

Conveyor
A mechanical device to transport material from one point to another, often continuously.

Cooling Channels
Channels or passageways located within the body of a mold through which a cooling medium can be circulated to control temperature on the mold surface.

Cooling Fixture
Block of metal or wood holding the shape of a molded piece which is used to maintain the proper shape or dimensional accuracy of a molding after it is removed from the mold until it is cool enough to retain its shape without further distortion. Also known as Shrink Fixture.

Copolymer
The chemical reaction of two different monomers with each other, result in a compound.

Copper Clad Laminate
Laminates (i.e., FR4) having copper foil bonded to one or both surfaces and intended primarily for use in printed circuits.

Core
The central member of a sandwich construction (can be honeycomb material, foamed plastic, or solid sheet) to which the face of the sandwich are attached; the central member of a plywood assembly. (2) A channel in a mold for circulation of heat-transfer media. (3) Part of a complex mold that molds undercut parts. Cores are usually withdrawn to one side before the main sections of the mold open. Also called Core Pin.

Core Drill
A device for making cooling channels in a mold.

Corona Resistance
A current passing through a conductor induces a surrounding electrostatic field. When voids exist in the insulation near the conductor, the high voltage electrostatic field may ionize and rapidly accelerate some of the air molecules, ionizing them, and thereby “eating” a hole in the insulation. Resistance to this process is called corona resistance.

Corrosion
Chemical action which causes destruction of the surface of a material by oxidation or chemical combination. Also caused by reduction of the electrical efficiency between a metal and a contiguous substance or to the disintegrating effects of strong electrical currents or ground return currents in electrical systems. The latter is known as electrolytic corrosion.

Corrosion Resistance
The ability to withstand the effect of oxidation.

Coupling Agents
A material that is used to form a chemical bridge between the resin and glass fiber or mineral fiber. By acting as an interface, bonding is enhanced.

Crater
A small, shallow surface imperfection.

Crazing
Small cracks near or on the surface of plastic materials.

Crazing
Fine cracks which may extend in a network on or under the surface or through a layer of a plastic material.

Creep
The dimensional change with time of a material under load. At room temperature it is also called cold flow.

Cross Laminate
A laminate in which some of the layers of material are oriented approximately at right angles to the remaining layers with respect to the grain or strongest direction in tension.

Cross-linking
The formation of chemical links between the molecular chains in polymers. This process can be achieved by chemical reaction, vulcanization, and electron bombardment.

Crosshead (extrusion)
A device generally employed in wire coating which is attached to the discharge end of the extruder cylinder, designed to facilitate extruding material at an angle. Normally, this is a 90 degree angle to the longitudinal axis of the screw.

Crystallinity
A molecular structure resulting from the formation of solid crystals with a geometric pattern.

Cull
Material remaining in a transfer chamber after mold has been filled. Unless there is a slight excess in the charge, the operator cannot be sure cavity is filled. Charge is generally regulated to control thickness of cull.

Cure
The process of changing properties of polymer into a more stable and usable condition. This is accomplished by the use of heat, radiation, or reaction with chemical additives.

Cure Cycle
The time periods at defined conditions to which a reacting thermosetting material is processed to reach a desired property level.

Curing Temperature
Temperature at which a cast, molded, or extruded product, a resin-impregnated reinforcing material, an adhesive, etc., is subjected to curing.

Curing Time
The period of time that a reacting thermosetting material is exposed to specific conditions to reach a specified property level.

Curtain Coating
A method of coating which may be employed with low viscosity resins or solutions, suspensions, or emulsions of resins in which the substrate to be coated is passed through and perpendicular to a freely falling liquid “curtain” (or “waterfall”). The flow rate of the falling liquid and the linear speed of the substrate passing through the curtain are co-ordinated in accordance with the thickness of coating desired.

Curvature
A condition in which the parison is not straight, but somewhat bending and shifting to one side, leading to a deviation from the vertical direction of extrusion. Centering of ring and mandrel can often relieve this defect.

Cut-off
The line where the two halves of a compression mold come together; also called Flash Groove or Pinch-off.

Cycle
The complete, repeating sequence of operations in a process of part of a process. In molding, the cycle time is the period, or elapsed time, between a certain point in one cycle and the same point in the next.

Cylindrical
Refers to the shape of a container which has a circular cross section parallel to the minor axis and a rectangular cross section parallel to the major axis.

Dash-pot
A device used in hydraulic systems for damping down vibration. It consists of a piston attached to the part to be damped and fitted into a vessel containing fluid or air. It absorbs shocks by reducing the rate of change in the momentum of moving parts of machinery.

Daylight Opening
Clearance between two platens of a press in the open position.

Deckle Rod
A small rod, or similar device, inserted at each end of the extrusion coating die which is used to adjust the length of the die opening.

Decomposition Product
The constituent elements or simpler compounds formed when a substance decays or decomposes.

Decorative Sheet
A laminated plastics sheet used for decorative purposes in which the color and/or surface pattern is an integral part of the sheet.

Deflashing
Covers the range of finishing techniques used to remove the flash (excess, unwanted material) on a plastic molding.

Deflection Temperature
The measure of temperature at which a specimen deflects 0.01 inches under a load of 264 lb/in2.

Degree of Polymerization
The number of structural units or mers in the “average” polymer molecule in a particle sample. In most plastics the DP must reach several thousand if worthwhile physical properties are to be had.

Delamination
The separation of a laminate along the plane of its layers. Also the separation of bonded insulation within the adhesive layer or at the adhesive interface.

Deliquescent
Capable of attracting moisture from the air.

Density
The equivalent property to specific gravity; measured by displacement.

Desiccant
Substance which can be used for drying purposes because of its affinity for water

Die Gap
The distance between the metal faces forming the die opening.

Die Lines
Vertical marks on the parison caused by damage of die parts or contamination.

Die Swell Ratio
The ratio of the outer parison diameter (or parison thickness) to the outer diameter of the die (or die gap). Die swell ratio is influenced by polymer type, head construction, land length, extrusion speed, and temperature.

Dielectric
1) Any insulating medium which intervenes between two conduits and permits electrostatic attraction or repulsion to take place across is. 2) A material having the property that energy required to establish an electric field is recoverable in whole or in part, as electric energy (see insulation for clarification).

Dielectric Constant
The ratio of the capacity of a condenser made with a particular dielectric material to the capacity of the same condenser with air as the dielectric. Measured at a frequency of 106 cycles per second.

Dielectric Constant (Permittivity or Specific Inductive Capacity)
The specific inductive capacity of a dielectric. That property of a dielectric which determines the electrostatic energy stored per unit volume for unit potential gradient.

Dielectric Heating (Electronic Heating)
The plastic to be heated forms the dielectric of a condenser to which is applied a high-frequency (20 to 80 mc.) voltage. Dielectric loss in the material is the basis. Process used for sealing vinyl films and preheating thermoset molding compounds.

Dielectric Strength
The voltage that an insulating material can withstand before dielectric breakdown occurs.

Dielectric Strength
Ability to retain precise shape and size.

Dimensional Stability
Ability of a plastic part to retain the precise shape in which it was molded, fabricated, or cast.

Dip Coating
Applying a plastic coating by dipping the article to be coated into a tank of melted resin or plastisol, then chilling the adhering melt.

Discoloration
Any change from the original color, often caused by overheating, light exposure, irradiation, or chemical attack.

Dispersion
Finely divided particles of a material in suspension in another substance.

Dissipation
Unusable or lost energy, as the production of heat in a circuit.

Dissipation Factor
The ratio of the power dissipated in watts in an insulating material to the product of the effective voltage and the current. Measured at a frequency of 106 cycles per second.

Divergent Die
A die in which the internal channels leading to the orifice are diverging (applicable only to dies for hollow bodies).

Dome
In reinforced plastics, an end of a filament wound cylindrical container.

Double-shot molding
A means of turning out two-color parts in thermoplastics materials by successive molding operations.

Draft
The degree of taper of a side wall or the angle of clearance designed to facilitate removal of parts from a mold.

Drape Assist Frame
In sheet thermoforming, a frame (made up of anything from thin wires to thick bars) shaped to the peripheries of the depressed areas of the mold and suspended above the sheet to be formed. During forming, the assist frame drops down, drawing the sheet tightly into the mold and thereby preventing webbing between high areas of the mold and permitting closer spacing in multiple molds.

Drape Forming

Method of forming thermoplastic sheet in which the sheet is clamped into a movable frame, heated, and draped over high points of a male mold. Vacuum is then pulled to complete the forming operation.

Draw Down Ratio

The ratio of the thickness of the die opening to the final thickness of the product.

Drawing
The process of stretching a thermoplastic sheet or rod to reduce its cross-sectional area.

Dry Coloring
Method commonly used by fabricators for coloring plastics by tumble blending uncolored particles of the plastic material with selected dyes and pigments.

Dry Strength

The strength of an adhesive joint determined immediately after drying under specified conditions or after a period of conditioning in the standard laboratory atmosphere. See Wet Strength.

Dry-blend
A free-flowing dry compound prepared without fluxing or addition of solvent. Also called powder blend.

Ductility
The extent to which a solid material can be drawn into a thinner cross section.

Dwell
A pause in the application of pressure to a mold, made just before the mold is completely closed, to allow the escape of gas from the molding material.

Dyes
Synthetic or natural organic chemicals that are soluble in most common solvents. Characterized by good transparency, high tinctorial strength, and low specific gravity.

Effect of Strong Acids
A descriptive notation to indicate the material’s performance.

Effective Thread Turns
The number of full 360 degree turns on a threaded closure that are actually in contact with the neck thread.

Ejector Pin (on Sleeve)
A pin or thin plate that is driven into a mold cavity from the rear as the mold opens, forcing out the finished pieces. Also Knockout Pin.

Ejector Return Pins
Projections that push the ejector assembly back as the mold closes; also called Surface Pins and Return Pins.

Ejector Rod
Bar that actuates the ejector assembly when mold is opened.

Elastic Deformation
The part of the deformation of an object under load which is recoverable when the load is removed.

Elastomer
A material which at room temperature stretches under low stress to at least twice its length and snaps back to the original length upon release of stress. See also Rubber.

Electroformed Molds
A mold made by electroplating metal in the reverse pattern on the cavity. Molten steel may be then sprayed on the back of the mold to increase its strength.

Electronic Treating
A method of oxidizing a film of polyethylene to render it printable by passing the film between the electrodes and subjecting it to a high voltage corona discharge.

Electroplating
The deposition of a layer of metal on a base of metal or conducting surface by electrolysis.

Elongation
The fractional increase in length of a material stressed in tension.

Embossing
Techniques used to create depressions of a specific pattern in plastics film and sheeting.

Emulsion
A suspension of fine droplets of one liquid in another.

Encapsulating
Enclosing an article (usually an electronic component or the like) in a closed envelope of plastic, by immersing the object in a casting resin and allowing the resin to polymerize or, if hot, to cool.

Endothermic Reaction
A chemical reaction in which heat is absorbed.

Entrance Angle
Maximum angle at which the molten material enters the land area of the die, measured from the center line of the mandrel.

Environmental Stress Cracking
The susceptibility of a thermoplastic article to crack or craze formation under the influence of certain chemicals and stress.

Epoxy Resins
Straight-chain thermosetting resins containing at least one three-membered ring consisting of two carbon atoms and one oxygenation.

Ester
The reaction product of an alcohol and an acid.

Ethylene Plastics
Plastics based on polymers of ethylene or copolymers of ethylene with other monomers, the ethylene being in greatest amount by mass.

Ethylene-vinyl Acetate
Copolymers from these two monomers form a new class of plastic materials. They retain many of the properties of polyethylene, but have considerably increased flexibility for their density – elongation and impact resistance are also increased.

Exotherm
The temperature/time curve of a chemical reaction giving off heat, particularly the polymerization of casting resins. (2) The amount of heat given off. The term has not been standardized with respect to sample size, ambient temperature, degree of mixing, etc

Exothermic Reaction
A chemical reaction in which heat is evolved.

Extender
A material added to a plastic compound used to reduce the amount of resin required per unit value.

Extrudate
The product or material delivered by an extruder, such as film, pipe, the coating on wire, etc.

Extrusion
The process of forming a continuous piece of plastic by forcing it through a shaping orifice with or without the presence of heat.

Extrusion
The method of processing plastic by forcing heat softened plastic through an opening of the desired shape of the cross-section of the finished product.

Fabric-Base Laminate
Laminated insulating material formed by bonding woven cloth (of fiberglass, cotton or synthetic fibers) with resin under heat and pressure.

Fabricating
The manufacture of plastic products by appropriate operations. This includes plastics formed into molded parts, rods, tubes, sheeting, extrusion and other forms by methods including punching, cutting, drilling, tapping, fastening or by using other mechanical devices.

Fahrenheit
Equals 1.8 multiplied to the sum of the temperature in Celsius and °F = 1.8 x (°C + 32).

Family Mold (injection)
A multi-cavity mold where each of the cavities forms one of the component parts of the assembled finished object.

Fiber
A thread or threadlike structure such as cellulose, wool, silk or glass yarn.

Fiber Show
Strands or bundles of fibers that are not covered by resin and that are at or above the surface of a reinforced plastic.

Fibre
1) A specific form of chemically jelled fibrous materials manufactured in sheets, rods and tubes. 2) Commonly used interchangeably with fiber.

Filament
1) Fiber characterized by extreme length. 2) The resistance wire through which filament current is sent in a thermionic tube to produce the heat required for electron emissions.

Filament Winding
Resin impregnated robbing or single strands of glass or other reinforcement wound in a pre-determined pattern onto a suitable form or mandrel and then cured.

Fill Point
The level to which a container must be filled to furnish a designated quantity of the content.

Fill-and-Wipe
Parts are molded with depressed designs; after application of paint, surplus is wiped off, leaving paint remaining only in the depressed areas.

Filler
A cheap, inert substance added to a plastic to make it less costly. Fillers may also improve physical properties, particularly hardness, stiffness, and impact strength. The particles are usually small, in contrast to those of reinforcements but there is some overlap between the function of the two.

Fillers & Reinforcements
Fillers are used to make a resin less costly. They can be inert or they can alter some properties of the plastic. Reinforcements are substances used to strengthen or give dimensional stability to a material.

Fillet
A rounded filling of the internal angle between two surfaces of a plastic molding.

Film
Films are flat materials that are extremely thin in comparison to its length and breadth. Typically, a film has a maximum nominal thickness of 0.25 millimeters.

Fin
The web of material remaining in holes or openings in a molded part which must be removed in finishing.

Finish
The plastic forming the opening of a container shaped to accommodate a specific closure. Also, the ultimate surface of an article.

Finish Insert
A removable part of a blow mold to form a specific neck of a plastic bottle. Sometimes called Neck Insert.

Fish Eye
A fault in transparent or translucent plastics materials, such as film or sheet, appearing as a small globular mass and caused by incomplete blending of the mass with surrounding materials.

FishPaper
1) A type of vulcanized fibre paper treated chemically for insulating purposes where high mechanical and electrical strength and flexibility are required. 2) A vulcanized fibre in thin cross-section.

Flake
Used to denote the dry, unplasticized base of cellulosic plastics.

Flame Retardant Resin
A resin which is compounded with certain chemicals to reduce or eliminate its tendency to burn. For polyethylene and similar resins, chemicals such as antimony trioxide and chlorinated paraffins are useful.

Flame Spraying
Method of applying a plastic coating in which finely powdered fragments of plastic, together with suitable fluxes, are projected through a cone of flame onto a surface.

Flame Treating
A method of rendering inert thermoplastic objects receptive to inks, lacquers, paints, adhesives, etc. in which the object is bathed in an open flame to promote oxidation of the surface of the article.

Flame, Fire & Smoke Retardants
Are added to the resin to retard these undesirable effects.

Flammability
Measure of the extent to which a material will support combustion.

Flange
A rib or rim for strength, for guiding, or for attachment to a pipe.

Flash
Extra plastic attached to a molding along the parting line; it must be removed before the part can be considered finished.

Flash Gate
Wide gate extending from a runner which runs parallel to an edge of a molded part along the parting line of a mold.

Flash Gate
A long, shallow rectangular gate

Flash Line
A raised line appearing on the surface of a molding and formed at the junction of mold faces.

Flash mold
A mold designed to permit excess molding material to escape during closing.

Flash Point
The lowest temperature at which a flammable liquid will produce a combustible vapor that will burn in the presence of a flame, under certain prescribed conditions of test.

Flexible Molds
Molds made of rubber or elastomeric plastics used for casting plastics. They can be stretched to remove cured pieces with undercuts.

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 strength of a material in bending, expressed as the tensile stress of the outermost fibers of a bent test specimen at the instant of failure.

Flocking
A method of coating by spraying finely dispersed powders or fibers.

Flow Line
A mark on a molded piece made by the meeting of two flow fronts during molding. Also called weld line.

Flow Marks
Wavy surface appearance of an object molded from thermoplastic resins caused by improper flow of the resin into the mold.

Fluidized Bed Coating
A method of applying a coating of a thermoplastic resin to an article in which the heated article is immersed in a dense-phase fluidized bed of powdered resin and thereafter heated in an oven to provide a smooth, pin-hole-free coating.

Fluorescent Pigments
By absorbing unwanted wavelengths of light and converting them into light of desire wavelengths, these colors seem to have an actual glow of their own.

Fluorine
The most reactive non-metallic element. A pale yellow gas which is both corrosive and poisonous, it reacts vigorously with most oxidizable substances at room temperature, and forms fluorides. It is used in the production of metallic and other fluorides, some of which are used to introduce fluorine into organic compounds, i.e., the fluorocarbons.

Fluorocarbon Plastics
Plastics based on polymers made with monomers composed of fluorine and carbon only.

Foaming Agents
Chemicals added to plastics and rubbers that generate inert gases on heating, causing the resin to assume a cellular structure.

Foil Decorating
Molding paper, textile, or plastic foils printed with compatible inks directly into a plastic part so that the foil is visible below the surface of the part as integral decoration.

Force Plate
The plate that carries the plunger of force plug of a mold and guide pins and bushings. Since it is usually drilled for steam or water lines, it is also called the Steam Plate.

Force Plug
The portion of a mold that enters the cavity block and exerts pressure on the molding compound, designated as Top Force or Bottom Force by position in the assembly; also called Plunger or Piston.

Formaldehyde
A colorless gas (usually employed as a solution in water) which possesses a suffocating, pungent odor. It is derived from the oxidation of methanol or low-boiling petroleum gases such as methane, ethane, propane, and butane. It is widely used in the production of phenol formaldehyde (phenolic), urea formaldehyde (urea), and melamine formaldehyde (melamine) resins.

Forming
The process whereby the current shape of a plastic is transformed to another desired configuration.

Formulation
1) A combination of ingredients before processing or made into a finished product. Also used as a synonym for a material, compound. 2) A selection of components of a product formula or mixture to provide optimum specific properties for the end-use desired.

Friction Coefficient
A number expressing the amount of frictional effect.

Furan Resins
Dark colored, thermosetting resins available primarily as liquids ranging from low-viscosity polymers to thick, heavy syrups.

Gasket
Piece used to make a joint fluid-tight.

Gate
In injection and transfer molding, the orifice through which the melt enters the cavity. Sometimes the gate has the same cross-section as the runner leading to it; often, it is severely restricted.

Gaylord
A large corrugated container usually sized to match the length and width dimensions of a pallet. Gaylord is actually a trade name that has become synonymous with this specific type of container.

Glass Cloth
Fabric used as insulating material base formed by weaving yarns comprising glass filaments and possessing high strength, heat resistance and dielectric properties.

Glass Fiber
Glass in fibrous form that has cooled to a rigid condition without crystallizing.

Glass Thread
A type of threading in which the thread sides gradually taper down to the neck finish. Cross section of threads are semi-circular.

Glass Transition
The reversible change in an amorphous polymer or in amorphous regions of a partially crystalline polymer from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one. NOTE – The glass transition generally occurs over a relatively narrow temperature region and is similar to the solidification of a liquid to a glassy state: it is not a phase transition. Not only do hardness and brittleness undergo rapid changes in this temperature region but other properties, such as thermal expansion and specific heat also change rapidly. This phenomenon has been called second order transition, rubber transition and rubbery transition. The word transformation has also been used instead of transition. Where more than one amorphous transition occurs in a polymer, the one associated with segmental motions of the polymer backbone chain or accompanied by the largest change in properties is usually considered to be the glass transition.

Gloss
The shine or luster of the surface of a material.

Graft Copolymers
A chain of one type of polymer to which side chains of a different type are attached or grafted (i.e., polymerizing butadiene and styrene monomer at the same time).

Granular Structure
Non-uniform appearance of finished plastic material due to retention of, or incomplete fusion of, particles of composition, either within the mass or on the surface.

Grit Blasted
A surface treatment of a mold in which steel grit or sand materials are blown to the walls of the cavity to produce a roughened surface. Air escape from mold is improved and special appearance of molded article is often obtained by this method.

Guide Pins
Devices that maintain proper alignment of force plug and cavity as mold closes.

Gum
An amorphous substance or mixture which, at ordinary temperatures, is either a very viscous liquid or a solid which softens gradually on heating, and which either swells in water or is soluble in it. Natural gums, obtained from the cell walls of plants, are carbohydrates or carbohydrate derivatives of intermediate molecular weight.

Gusset
A tuck placed in each side of a tube of blown tubing as produced to provide a convenient square or rectangular package, similar to that of the familiar brown paper bag or sack, in subsequent packaging.

Hardness
The resistance of a material to compression, indentation and scratching. There are several scales, and the data in the book gives both the scale used and the value on it.

Haze
The cloudy or turbid appearance of an otherwise transparent material caused by light scattered from within the specimen or from its surfaces.

Head Space
The space between the fill level of a container and the sealing plane.

Heat Chamber
In injection molding, that part of the machine in which the cold feed is reduced to a hot melt. Also Heating Cylinder.

Heat Deflection Temperature
The temperature at which a standard test bar (ASTM D648) deflects 0.010 in. under a stated load of either 66 or 264 psi.

Heat Distortion Point
The temperature in degrees Celsius at which a standard test bar (ASTM D648) deflects .010 in. under a stated load of either 66 or 264 psi, when the temperature is raised at a specific rate of increase.

Heat Loss
Power dissipated as heat.

Heat Sealing
A method of joining plastic films by simultaneous application of heat and pressure to areas in contact. Heat may be supplied conductively or dielectrically.

Heat Stabilizers
These additives increase the ability of the material to withstand the negative effects of heat exposure. They are used to increase the overall service temperature of the material.

Heat-Distortion Point
The temperature at which a standard test bar (ASTM D648) deflects 0.010 in. under a stated load of either 66 or 264 psi.

High-Pressure Laminates (molding pressure high)
Laminates molded and cured at pressures not lower than 1,000 psi. (Pressures of 1,000 to 2,500 psi are not uncommon.)

Hob
A master model in hardened steel used to sink the shape of a mold into a steel block.

Homopolymer
A polymer, consisting of (neglecting the ends, branch junctions, and other minor irregularities) a single type of repeating unit.

Honeycomb
Manufactured product consisting of sheet metal or a resin impregnated sheet material (paper, fibrous, glass, etc.) which has been formed into hexagonal-shaped cells. Used as core material for sandwich constructions.

Hoop Stress
The force per unit area in the wall of the pipe in the circumferential orientation due to internal hydrostatic pressure.

Hopper
Conical feed reservoir into which molding powder is loaded and from which it falls into a molding machine or extruder, sometimes through a metering device.

Hopper Dryer
A combination feeding and drying device for extrusion and injection molding of thermoplastics. Hot air flows upward through the hopper containing the feed pellets.

Hopper Loader
A curved pipe through which molding powders are pneumatically conveyed from shipping drums to machine hoppers.

Hot Gas Welding
A technique of joining thermoplastic materials (usually sheet) whereby the materials are softened by a jet of hot air from a welding torch, and joined together at the softened points. Generally a thin rod of the same material is used to fill and consolidate the gap.

Hot-runner mold
A mold in which the runners are insulated from the chilled cavities and are kept hot. Parting line is at gate of cavity, runners are in separate plate(s), so they are not, as is the case usually, ejected with the piece.

Hot-stamping
Engraving operation for marketing plastics in which roll leaf is stamped with heated metal dies onto the face of the plastics. Ink compounds can also be used. By means of felt rolls, ink is applied to type and by means of heat and pressure, type is impressed into the material, leaving the marking compound in the indentation.

Hydraulic
A system in which energy is transferred from one place to another by means of compression and flow of a fluid (e.g., water, oil).

Hydrocarbon Plastics
Plastics based on resins made by the polymerization of monomers composed of carbon and hydrogen only.

Hydrogenation
Chemical process whereby hydrogen is introduced into a compound.

Hydrolysis
Chemical decomposition of a substance involving the addition of water.

Hygroscopic
Tending to absorb moisture.

Immiscible
Descriptive of two or more fluids which are not mutually soluble.

Impact Bar (specimen)
A test specimen of specified dimensions which is utilized to determine the relative resistance of a plastic to fracture by shock.

Impact Modifiers
Are additive used to enhance the material’s ability to withstand the force of impact.

Impact Resistance
Relative susceptibility of material to fracture by stress at high speeds.

Impact Strength
Ability to withstand physical shock loading or work required to fracture under shock loading a specified test specimen in a specified manner.

Impregnate
1) To fill the voids and interstices of material with a compound (this does not imply complete fill or complete coating of the surfaces by a hole-free film). 2) The process of thoroughly soaking a material of an open or porous nature with a resin.

Impregnation
The process of thoroughly soaking a material such as wood, paper or fabric, with a synthetic resin so that the resin gets within the body of the material. The process is usually carried out in an impregnator.

Impulse Sealing
A heat sealing technique in which a pulse of intense thermal energy is applied to the sealing area for a very short time, followed immediately by cooling. It is usually accomplished by using an RF heated metal bar which is cored for water cooling or is of such a mass that it will cool rapidly at ambient temperatures.

Inert
Deficient in active properties; not affecting other substances when in contact with them such as inert gases not participating in any fashion in chemical reactions. Infrared – the band of light in the electromagnetic spectrum that lies between the visible light range and the radar range.

Infra-red
Part of the electromagnetic spectrum between the visible light range and the radar range. Radiant heat is in this range, and infra-red heaters are used in sheet thermoforming.

Inhibitor
A substance that slows down chemical reaction. Inhibitors are sometimes used in certain types of monomers and resins to prolong storage life.

Injection Blow Molding
Blow molding process by which the plastic parison to be blown is formed by injection molding.

Injection Molding
The process of forming a material by forcing it from a heated cylinder, under pressure, through a spruce into a cavity of a confined mold.

Injection molding Cycle
The complete time cycle of operation utilized in injection molding of an object including injection; die close and die open time.

Injection Molding Pressure
The pressure applied to the cross-sectional area of the molding cylinder.

Injection Ram
The ram which applies pressure to the plunger in the process of injection molding or transfer molding.

Insert
An integral part of a plastics molding consisting of metal or other material which may be molded into position or may be pressed into the molding after the molding is completed.

Instron
An instrument utilized to determine the tensile and compressive properties of material.

Insulation
Material having a high resistance to the flow of electric current, to prevent leakage of current from a conductor.

Intrinsic Viscosity
The intrinsic viscosity of a polymer is the limiting value of infinite dilution of the ratio at the specific viscosity of the polymer solution to its concentrate on moles per liter.

Ionomer Resins
A polymer which has ethylene as its major component, but containing both covalent and ionic bonds. The polymer exhibits very strong interaction ionic forces. The anions hang from the hydrocarbon chain and the reactions are metallic – sodium, potassium, magnesium. These resins have many of the same features as polyethylene plus high transparency, tenacity, resilience, and increased resistance to oils, greases and solvents. Fabrication is carried out as with polyethylene.

ISO
International Organization of Standardization.

Isomer
One of two or more compounds, radicals or ions that contain the same number of atoms of the same elements by differ in structural arrangement and properties.

Izod Impact Test
A test designed to determine the resistance of a plastics material to a shock loading. It involves the notching of a specimen, which is then placed in the jaws of the machine and struck with a weighted pendulum. See also Impact Strength.

Izod, Notched, LT
The energy required to break specimens in which there is a v-notch to create an initial stress point but measured at low temperature (minus 40°C).

Izod, Notched, RT
The energy required to break specimens in which there is a v-notched to create an initial stress point.

Jacket
A tough sheath to protect an insulated wire or cable, or to permanently group two or more insulated wires or cables.

Jet molding
Processing technique characterized by the fact that most of the heat is applied to the material as it passes through the nozzle or jet, rather than in a heating cylinder as is done in conventional processes.

Jetting
Turbulent flow of resin from an undersize gate or thin section into a thicker mold section, as opposed to laminar flow of material progressing radially from a gate to the extremities of the cavity.

Kelvin
The absolute temperature scale (metric). K = °C + 273.

Kirksite
An alloy of aluminum and zinc used for the construction of blow molds; it imparts high degree of heat conductivity to the mold.

Kiss-roll Coating
This roll arrangement carries a metered film of coating to the web; at the line of web contact, it is split with part remaining on the roll, the remainder of the coating adhering to the web.

Knockout Pin
A device for knocking a cured piece from a mold. Also called Ejector Pin.

Kraft Paper
1) Relatively heavy, high strength sulfate paper used for electrical insulating material. 2) Paper made from sulfate wood pulp, chiefly pinewood chips by digestion with a mixture of caustic soda.

L/D Ratio
A term used to define an extrusion screw which denotes the ratio of the screw length to the screw diameter.

Laminar Flow
Laminar flow of thermoplastic resins in a mold is accomplished by solidification of the layer in contact with the mold surface that acts as an insulating shell through which molten material flows to fill the remainder of the cavity.

Laminar Flow
Laminar flow of thermoplastic resins in a mold is accompanied by solidification of the layer in contact with the mold surface that acts as an insulating tube through which material flows to fill the remainder of the cavity. This type of flow is essential to duplication of the mold surface.

Laminate
1) (v) – To build up to desired shape or thickness.2) (n) – A material composed of successive layers of material, usually bonded together under heat and pressure.

Land
(1) The horizontal bearing surface of a semi positive or flash mold by which excess material escapes. See Cut-off. (2) The bearing surface along the top of the flights of a screw in a screw extruder. (3) The surface of an extrusion die parallel to the direction of melt flow.

Lattice Pattern
In reinforced plastics, a pattern of filament winding with a fixed arrangement of open voids.

Leach
To extract a soluble component from a mixture by the process of percolation.

Light Transmission
The amount of light that a plastic will allow to pass.

Light, UV Stabilizers & Absorbers
These additives increase the ability of the material to withstand the negative effects of light and UV exposure, thus increasing the service life of the material.

Light-resistance
The ability of a plastics material to resist fading after exposure to sunlight or ultra-violet light. Nearly all plastics tend to darken under these conditions.

Limiting Oxygen Index
The concentration of oxygen required to maintain burning. See ASTM Procedure D2863-74.

Linear Mold Shrinkage
The difference between the size of the part and the size of the mold cavity. Values given are often the average of a range.

Linear Molecule
A long chain molecule as contrasted to one having many side chains or branches.

Linear Thermal Expansion
The fractional change in length of a material for a unit change in temperature.

Liquid Injection
The process that involves an integrated system for proportioning, mixing, and dispensing two component liquid resin formulations and directly injecting the resultant mix into a mold which is clamped under pressure.

Loss Factor
The product of the power factor and the dielectric constant of a dielectric material.

Low Pressure Laminates
Laminates molded and cured in the range of pressures up to 400 psi

Lubricant
Internal lubricants, without affecting the fusion properties of a compound, promotes resin flow. External lubricants promote release from metals which aids in the smooth flow of melt over die surfaces.

Luminescent Pigments
Special pigments available to produce striking effects in the dark. Basically there are two types: one is activated by ultra-violet radiation, producing very strong luminescence and, consequently, very eye-catching effects; the other type, known as phosphorescent pigments, does not require any separate source of radiation.

Luminous Transmittance
The ratio of the luminous flux transmitted by a body of the flux incident upon it.

Machine Shot Capacity
Refers to the maximum weight of thermoplastic resin which can be displaced or injected by the injection ram in a single stroke.

Manifold
A term used mainly with reference to blow molding and sometimes with injection molding equipment. It refers to the distribution or piping system which takes the single channel flow output of the extruder or injection cylinder and divides it to feed several blow molding heads or injection nozzles.

Masterbatch
A concentration of a substance (an additive, pigment, filler, etc.) in a base polymer.

Mat
1) A randomly distributed felt of fibers, usually glass, used in reinforced plastics. 2) A nonwoven fabric of fibrous material used as a plastic reinforcement.

Melamine Plastics
Thermosetting plastics made from melamine and formaldehyde resins.

Melt Flow
Rate of extrusion of molten resin through a die of specified length and diameter. The conditions of the test (e.g. temperature and load) should be given. Frequently, however, the manufacturer’s data lists only the value, not the condition as well.

Melt Fracture
An instability in the melt flow through a die starting at the entry to the die. It leads to surface irregularities on the finished article like a regular helix or irregularly-spaced ripples.

Melt Index
The amount, in grams, of a thermoplastic resin which can be forced through a 0.0825 inch orifice when subjected to 2160 grams. forced in 10 minutes at 190 degrees C.

Melt Strength
The strength of the plastic while in the molten state.

Melt Temperature
The temperature of the molten plastic just prior to entering the mold or extruded through the die.

Melting Point
The temperature at which solid and liquid forms of a substance are in equilibrium. In common usage the melting point is taken as the temperature at which the liquid first forms in a small sample as its temperature is increased gradually.

Meniscus
The free surface of a liquid in a container, for example, water in contact with air confined in a capillary tube.

Mer
The repeating structural unit in any high polymer.

Metallizing
Applying a thin coating of metal to a non-metallic surface. May be done by chemical deposition or by exposing the surface to vaporized metal in a vacuum chamber.

Metering Screw
An extrusion screw which has a shallow constant depth, and constant pitch section over, usually, the last 3 to 4 flights.

Mica
A transparent, flaky mineral which splits into thin sheets and has excellent insulating and heat resisting properties, consisting of orthosilicates of aluminum or potassium; occurs naturally.

Modified
Containing ingredients such as fillers, pigments or other additives that help to vary the physical properties of a plastics material. An example is oil modified resin.

Modulus of Elasticity
The ratio of stress to strain in a material that is elastically deformed.

Moisture Resistance
The ability of a material to resist absorbing ambient moisture.

Moisture Vapor Transmission
The rate at which water vapor permeates through a plastic film or wall at a specified temperature and relative humidity.

Mold
(v.) To shape plastic parts or finished articles by heat and pressure. (n.) (1) The cavity or matrix into which the plastic composition is placed and from which it takes its form. (2) The assembly of all the parts that function collectively in the molding process.

Mold Release Agent
A lubricant used to coat a mold cavity to prevent adhesion of the molded piece when removed.

Moldability
The characteristics of being easy to mold without rupturing or developing flaws due o movement of the polymer during gelation.

Molding Cycle
(1) The period of time occupied by the complete sequence of operations on a molding press requisite for the production of one set of moldings. (2) The operations necessary to produce a set of moldings without reference to the time taken.

Molding Pressure
The pressure applied to the ram of an injection machine or press to force the softened plastic completely to fill the mold cavities.

Molding Shrinkage
The difference in dimensions, expressed in inches per inch, between a molding and the mold cavity in which it was molded, both the mold and the molding being at normal room temperature when measured.

Molecular Weight Distribution
The ratio of the weight average molecular weight to the number average molecular weight gives an indication of the distribution.

Monomer
The simple, unpolymerized form of a compound which is the building block of a polymer.

Mounting Plate
The part of the blow molding unit to which the mold is attached.

Movable Platen
The large back platen of an injection molding machine to which the back half of the mold is secured during operation. This platen is moved either by a hydraulic ram or a toggle mechanism.

Multi-cavity mold
A mold with two or more mold impressions, i.e., a mold which produces more than one molding per molding cycle.

Multiple Head Machine
A (blow molding) machine in which the plastic melt prepared by the extruder is divided into a multiplicity of separate streams (parisons) each giving ultimately a finished item.

Neck
The part of a container where the shoulder cross section area decreases to form the finish.

Neck Bead
A protruding circle on a container at the point where the neck meets the finish, the diameter of which usually equals the outside diameter of the closure.

Neck Insert
Part of the mold assembly which forms the neck and finish. Sometimes called Neck Ring.

Nest Plate
A retainer plate with a depressed area for cavity blocks used in injection molding.

Nonpolar
Having no concentrations of electrical charge on a molecular scale, thus, incapable of significant dielectric loss. Examples among resins are polystyrene and polyethylene.

Nonrigid Plastic
A non-rigid plastic is one which has a stiffness or apparent modulus of elasticity of not over 50,000 psi. at 25 degrees C when determined according to ASTM test procedure D747-43 T.

Notch Sensitivity
The extent to which the sensitivity of a material to fracture is increased by the presence of a surface in homogeneity such as a face notch, a sudden change in section, a crack, or a scratch. Low notch sensitivity is usually associated with ductile materials, and high notch sensitivity with brittle materials.

Nozzle
The hollow cored metal nose screwed into the extrusion end of (a) the heating cylinder of an injection machine or (b) a transfer chamber where this is a separate structure. A nozzle is designed to form under pressure a seal between the heating cylinder or the transfer chamber and the mold. The front end of a nozzle may be either flat or spherical in shape.

Nylon
The generic name for all synthetic fiber-forming polyamides; they can be formed into monofilaments and yarns characterized by great toughness, strength and elasticity, high melt point, and good resistance to water and chemicals. The material is widely used for bristles in industrial and domestic brushes, and for many textile applications; it is also used in injection molding gears, bearings, combs, etc.

O-ring
A ring used as a gasket.

Odorants & Deodorants
Odorants are used to add odor to materials, usually for safety reasons.

Offset
A printing technique in which ink is transferred from a bath onto the raised surface of the printing plate by rollers. Subsequently, the printing plates transfer the ink to the object to be printed.

Ohm
Practical unit of electric resistance.

Ohm’s Law
The strength of a direct current is directly proportional to the potential difference and inversely proportional to the resistance of the circuit.

Opaque
Descriptive of a material or substance which will not transmit light. Opposite of transparent. Materials which are neither opaque nor transparent are sometimes described as semi-opaque, but are more properly classified as translucent.

Orange Field
Said of injection moldings that have unintentionally rough surfaces.

Orientation
The alignment of the crystalline structure in polymeric materials so as to produce a highly uniform structure. Can be accomplished by cold drawing or stretching during fabrication.

Orifice
The opening in the extruder die formed by the orifice bushing (ring) and mandrel.

Orifice Bushing
The outer part of the die in an extruder head.

Outgassing
To remove occluded gases by heating.

Overcoating
In extrusion coating, the practice of extruding a web beyond the edge of the substrate web.

Oxidation
The addition of oxygen to a compound or the reduction of hydrogen.

Oxygen Index
See Limiting Oxygen Index.

Palletizing
A process of producing pellets.

Parison
The hollow plastic tube from which a container, toy, etc. is blow molded.

Parison Swell
In blow molding the ratio of the cross-sectional area of the parison to the cross-sectional area of the die opening.

Parting 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. Also called Release Agent.

Parting Line
Mark on a molding or casting where halves of mold met in closing.

Partitioned Mold Cooling
A large diameter hole drilled into the mold (usually the core) and partitioned by a metal plate extending to near the bottom end of the channel. Water is introduced near the top of one side of the partition and removed on the other side.

Pellet
A small ball or spherical shape.

Permanent Set
The increase in length, expressed in a percentage of the original length, by which an elastic material fails to return to original length after being stressed for a standard period of time.

Permeability
1) The passage or diffusion (or rate of passage) of a gas, vapor, liquid or solid through a barrier without physically or chemically affecting it. 2) The ability of a material to carry magnetism as compared to air which has a permeability of one.

Permittivity
Preferred term for dielectric constant. It is that property of a dielectic material that determined how much electrostatic energy can be stored per unit of volume when unit voltage is applied; the relative permittivity of most materials varies from 2 to 10, air having 1.

PH
An expression of the degree of acidity or alkalinity of a substance. Neutrality is pH -acid solutions being under 7 and alkaline solution over 7. pH meters are commercially available for accurate readings.

Phenolic Resin
1) A synthetic resin produced by the condensation of phenol with an aldehyde (usually formaldehyde). 2) Any of several types of thermoset plastics obtained by the condensation of phenol or substituted phenols.

Pigment
Any colorant, usually an insoluble powdered substance used to produce a desired color of hue.

Pinpoint Gate
A restricted orifice of 0.030 inches or less in diameter through which molten resin flows into a mold cavity.

Pitch
The distance from any point on the flight of a screw line to the corresponding point on an adjacent flight, measured parallel to the axis of the screw line or threading.

Plastic
1) High polymeric substances, including both natural and synthetic products, but excluding the rubbers that are capable in their manufacture of flowing under heat and pressure. 2) A material that contains an organic substance of large molecular weight, solid in finished state.

Plastic Deformation
A change in dimensions of an object under load that is not recovered when the load is removed; opposed to elastic deformation.

Plastic Memory
A phenomenon of plastic to return to its original molded form. Different plastics possess varying degrees of this characteristic.

Plasticity
The quality of being able to be shaped by plastic flow.

Plasticize
To soften a material and make it plastic or moldable, either by means of a plasticizer or the application of heat.

Plasticizer
Are usually low-melting solids or high-boiling organic liquids which, when added to hard plastics, impart flexibility. They have varying degrees of softening action and solvating ability resulting from a reduction of intermolecular forces in the polymer.

Plastisol
Mixtures of plasticizers and resins which can be converted to continuous films by applying heat.

Plate Dispersion Plug
Two perforated plates held together with a connecting rod which are placed in the nozzle of an injection molding machine to aid in dispersing a colorant in a resin as it flows through the orifices in the plates.

Plate-mark
Any imperfection in a pressed plastic sheet resulting from the surface of the pressing plate.

Platens
The mounting plates of a press to which the entire mold assembly is bolted.

Platform Blowing
A special technique for blowing large parts. To prevent excessive sag of the heavy parison the machine employs a table which after rising to meet the parison at the die descends with the parison but at a slightly lower rate than the parison extrusion speed.

Plug Forming
A thermoforming process in which a plug or male mold is used to partially preform the part before forming is completed using vacuum or pressure.

Plug-and-ring
Method of sheet forming in which a plug, functioning as a male mold, is forced into a heated plastic sheet held in place by a clamping ring.

Plunger
See Force Plug.

Pneumatic
Moved or worked by air pressure.

Poise
The unit of viscosity expressed as one dyne per second per square centimeter.

Polyamide
A polymer in which the structural units are linked by amide or thioamide groupings. Many polyamides are fiber-forming.

Polybutylene
A polymer prepared by the polymerization of butene as the sole monomer.

Polyester
A resin formed by the reaction between a dibasic acid and a dihydroxy alcohol, both organic. Modification with multi-functional acids and/or bases and some unsaturated reactants permit cross-linking to thermosetting resins. Polyesters modified with fatty acids are called Alkyds.

Polyethylene
A thermoplastic material composed by polymers of ethylene. It is normally a translucent, tough, waxy solid which is unaffected by water and by a large range of chemicals.

Polyimide Resins
A new group of resins recently introduced in the United States. The material is an aromatic polyimide made by reacting pyromellitic dianhydride with aromatic diamines. The polymer is characterized by the fact that it has rings of four carbon atoms tightly bound together, and the manufacturers claim that the new resin has greater resistance to heat than any other unfilled organic material yet discovered. Suggested applications include components for internal combustion engines.

Polyisobutylene
The polymerization product of isobutylene. It varies in consistency from a viscous liquid to a rubber-like solid with corresponding variation in molecular weight from 1,000 to 400,000.

Polyliner
A perforated longitudinally ribbed sleeve that fits inside the cylinder of an injection molding machine; used as a replacement for conventional injection cylinder torpedoes.

Polymer
High-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the mer: e.g. polyethylene, rubber, cellulose. If two or more monomers are involved, a copolymer is obtained.

Polymerization
A chemical reaction in which the molecules of a monomer are linked together to form large molecules whose molecular weight is a multiple of that of the original substance. When two or more monomers are involved, the process is called copolymerization or heteropolymerization. See also Degree of, Condensation, and Polymer.

Polymethyl Methacrylate
A thermoplastic material composed of polymers of methyl methacrylate. It is a transparent solid with exceptional optical properties and good resistance to water. It is obtainable in the form of sheets, granules, solutions, and emulsions. It is extensively used for aircraft domes, lighting, fixtures, decorative articles, etc.; it is also used in optical instruments and surgical appliances.

Polyolefin
A polymer prepared by the polymerization of an Olefin(s) as the sole Monomer(s).

Polyoxymethylene
A polymer in which the repeated structural unit in the chain is oxymethylene.

Polypropylene
A tough, lightweight rigid plastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst at relatively low pressures and temperatures.

Polystyrene .
A water-white thermoplastic produced by the polymerization of styrene (vinyl benzene). The electrical insulating properties of polystyrene are outstandingly good and the material is relatively unaffected by moisture

Polytetrafluoroethylene (PTFE) Resins
Members of the fluorocarbons family of plastics made by the polymerization of tetrafluoroethylene. PTFE is characterized by its extreme inertness to chemicals, very high thermal stability and low frictional properties. Among the applications for these materials are bearings, fuel hoses, gaskets and tapes, and coatings for metal and fabric.

Polyurethane Resins
A family of resins produced by reacting diisocyanate with organic compounds containing two or more active hydrogens to form polymers having free isocyanate groups. These groups, under the influence of heat or certain catalysts, will react with each other, or with water, glycols, etc., to form a thermosetting material.

Polyvinyl Acetal
A member of the family of vinyl plastics. Polyvinyl acetal is the general name for resins produced from a condensation of polyvinyl alcohol with an aldehyde. There are three main groups: polyvinyl acetal itself; polyvinyl butyl, and polyvinyl formal. Polyvinyl acetal resins are thermoplastics which can be processed by casting, extruding, molding and coating, but their main uses are in adhesives, lacquers, coatings and films.

Polyvinyl Carbazole
A thermoplastic resin, brown in color, obtained by reacting acetylene with carbazole. The resin has excellent electrical properties and good heat and chemical resistance. It is used as an impregnate for paper capacitors.

Polyvinyl Chloride (PVC)
A thermoplastic material composed of polymers of vinyl chloride; a colorless solid with outstanding resistance to water, alcohols, and concentrated acids and alkalies. It is obtainable in the form of granules, solutions, lattices, and pastes. Compounded with plasticizers it yields a flexible material superior to rubber in ageing properties. It is widely used for cable and wire coverings, in chemical plants, and in the manufacture of protective garments.

Polyvinyl Chloride Acetate
A thermoplastic material composed of copolymers of vinyl chloride and vinyl acetate; a colorless solid with good resistance to water, and concentrated acids and alkalies. It is obtainable in the form of granules, solutions, and emulsions. Compounded with plasticizers it yields a flexible material superior to rubber in aging properties. It is widely used for cable and wire coverings, in chemical plants, and in protective garments.

POM
The chemical abbreviation for Acetal, also known as Polyoxymethylene.

Postcure
Those additional operations to which a cured thermosetting plastic or rubber composition are subjected to enhance the level of one or more properties.

Postforming
The forming, bending, or shaping of fully cured, C-stage thermoset laminates that have been heated to make them flexible. On cooling, the formed laminate retains the contours and shape of the mold over which it has been formed.

Powder Molding
General term used to denote several techniques for producing objects of varying sizes and shapes by melting polyethylene powder, usually against the inside of a mold. The techniques vary as to whether the molds are stationary (e.g., as in variations on slush molding techniques) or rotating (e.g., as in variations on rotational molding).

Power Factor
In a perfect condenser, the current leads the voltage by 90 degrees. When a loss takes place in the insulation, the absorbed current, which produces heat, throws the 90 degree relationship out according to the proportion of current absorbed by the dielectric. The power factor is the cosine of the angle between voltage applied and the current resulting.

Preform
(n.) A compressed tablet or biscuit of plastic composition used for efficiency in handling and accuracy in weighing materials. (v.) To make plastic molding powder into pellets or tablets.

Preheat Roll
In extrusion coating, a heated roll installed between the pressure roll and unwind roll whose purpose is to heat the substrate before it is coated.

Preheating
The heating of a compound prior to molding or casting in order to facilitate the operation or to reduce the molding cycle.

Preimpregnation
The practice of mixing resin and reinforcement before shipping it to the molder.

Prepreg
A term generally used in reinforced plastics to mean the reinforcing material containing or combined with the full complement of resin before molding.

Pressure Forming
A thermoforming process wherein pressure is used to push the sheet to be formed against the mold surface as opposed to using a vacuum to suck the sheet against the mold.

Pressure Pads
Reinforcements or hardened steel distributed around the dead areas in the faces of a mold to help the land absorb the final pressure of closing without collapsing.

Pressure Roll
In extrusion coating, the roll which with the chill roll applies pressure to the substrate and the molten extruded web.

Processing
An average value is given rather than the temperature range often specified by the manufacturer.

Processing Aids
Some processing aids include thixotropic agents, flatting agents, and blocking and anticaking agents.

Processing Methods
The kind of processing (extruding, molding, casting, etc.) techniques recommended by the manufacturer.

Prototype mold
A simplified mold construction often made from a light metal casting alloy or from an epoxy resin in order to obtain information for the final mold and/or part design.

Pulp
A form of cellulose obtained from wood or other vegetable matter by prolonged cooking with chemicals.

Pulp molding
Process by which a resin-impregnated pulp material is preformed by application of a vacuum and subsequently oven cured or molded.

Purging
Cleaning one color or type of material from the cylinder of an injection molding machine or extruder by forcing it out with the new color or material to be used in subsequent production. Purging materials are also available.

Push Up
The bottom contour of a plastic container designed in such a manner as to allow an even bearing surface on the outside edge and to prevent the bottle from rocking.


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.

Reaction Injection
A process that involves the high pressure impingement mixing of two or more reactive liquid components and injecting into a closed mold at low pressure.

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.

Refractive Index, Sodium D
The ratio of the velocity and light in a vacuum to its velocity in the material.

Regrind
Waste material from injection molding, blow molding and extrusion operations, which has been reclaimed by shredding or granulating.

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 material with enhanced mechanical properties due to the addition of high strength fillers imbedded in the composition.

Reinforcement
Material used to reinforce, strengthen or give dimensional stability to another material; can be chopped, woven or braided.

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
A pseudosolid or solid organic material often of high molecular weight. It has a tendency to flow when subjected to stress, usually has a softening or melting range, and usually fractured conchoidally.

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

Resistance
Property of a conductor that opposed the current flow produced by a given difference of potential. The ohm is the practical unit of resistance.

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

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 spruce with the gate to the cavity.

Scar
A characteristic mark on plastic containers which is confined mostly to the bottom. It is caused by the pinch-off operation and is often referred to as the length of the pinch-off.

Scrap
Any product of a molding operation that is not part of the primary product. In compression molding, this includes flash, culls, runners, and is not reusable as a molding compound. Injection molding and extrusion scrap (runners, rejected parts, spruces, etc.) can usually be reground and remolded.

Sealing Plane
The plane on the inside of a bottle cap along the sealing surface.

Sealing Surface
The surface of the finish of the container on which the closure forms the seal.

Seizing
Act of holding or grasping suddenly or forcibly.

Self-extinguishing
A somewhat loosely-used term describing the ability of a material to cease burning once the source of flame has been removed.

Semipositive Mold
A mold which allows a small amount of excess material to escape when it is closed.

Semirigid Plastic
For purpose of general classification, a plastic that has a modulus of elasticity either in flexure or in tension of between 10,000 and 100,000 psi at 23 degrees C and 50% relative humidity when tested in accordance with ASTM Method D747 or D790 Test for Stiffness of Plastics.

Setting Temperature
The temperature to which a liquid resin, an adhesive, or products or assemblies involving either is subjected to set the resin or adhesive.

Setting Time
The period of time during which a molded or extruded product, an assembly, etc., is subjected to heat and/or pressure to set the resin or adhesive.

Shark Skin
A surface irregularity of a container in the form of finely-spaced sharp ridges caused by a relaxation effect of the melt at the die exit.

Shear Rate
The overall velocity over the cross section of a channel with which molten polymer layers are gliding along each other or along the wall in laminar flow.

Shear Strength
1) Ability of a material to withstand shear stress or stress at which a material fails in shear. 2) The maximum shear strength stress that a material is capable of sustaining.

Shear Stress
The stress developing in a polymer melt when the layers in a cross section are gliding along the wall of the channel (in laminar flow).

Sheet
Sheets are made of continuous phase plastic in a form in which the thickness is very small in proportion to length and width. The thickness is greater than 0.25 millimeters.

Sheet (thermoplastic)
A flat section of a thermoplastic resin with the length considerably greater than the width and 10 mils or greater in thickness.

Sheet Train
The entire assembly necessary to produce sheet which includes extruder, die, polish rolls, conveyor, draw rolls, cutter and stacker.

Shore Hardness
A method of determining the hardness of a plastic material using a scelroscope. This device consists of a small conical hammer fitted with a diamond point and acting in a glass tube. The hammer is made to strike the material under test and the degree of rebound is noted on a graduated scale. Generally, the harder the material the greater will be the rebound.

Short Shot
In injection molding, failure to fill the mold completely.

Shot
The yield from one complete molding cycle, including scrap.

Shot Capacity
The maximum weight of material which an accumulator can push out with one forward stroke of the ram.

Shrink Fixture
See Cooling Fixture.

Shrink Wrapping
A technique of packaging in which the strains in a plastic film are released by raising the temperature of the film thus causing it to shrink over the package. These shrink characteristics are built into the film during its manufacture by stretching it under controlled temperatures to produce orientation of the molecules. Upon cooling, the film retains its stretched condition, but reverts toward its original dimensions when it is heated. Shrink film gives good protection to the products packaged and has excellent clarity.

Shrinkage
Contraction of a container upon cooling.

SI Units
The International System of Units (Systems International) is a modernized version of the metric system established by international agreement. It provides a logical and interconnected framework for all measurements in science, industry and commerce. Officially abbreviated SI, the system is built upon a foundation of seven base units.

Side Draw Pins
Projections used to core a hole in a direction other than the line of closing of a mold, and which must be withdrawn before the part is ejected from the mold.

Silicone
One of the family of polymeric materials in which the recurring chemical group contains silicon and oxygen atoms as links in the main chain. At present these compounds are derived from silica (sand) and methyl chloride. The various forms obtainable are characterized by their resistance to heat. Silicones are used in the following applications: (a) Greases for lubrication. (b) Rubber-like sheeting for gaskets, etc. (c) Heat stable fluids and compounds for waterproofing, insulating, etc. (d) Thermosetting insulating varnishes and resins for both coating and laminating.

Silk Screen Printing
This printing method, in its basic form, involves laying a pattern of an insoluble material, in outline, on a finely woven fabric, so that when ink is drawn across it, it is able to pass through the screen only in the desired areas.

Single Cavity Mold
An injection mold having only one cavity in the body of the mold, as opposed to a multiple cavity mold or family mold which have numerous cavities.

Sink Mark
A shallow depression or dimple on the surface of an injection molded part due to collapsing of the surface following local internal shrinkage after the gate seals. May also be an incipient short shot.

Sintering
The partial welding together of powder particles at temperature near the melting point.

Sizing
The process of applying a material to a surface to fill pores and thus reduce the absorption of the subsequently applied adhesive or coating or to otherwise modify the surface. Also, the surface treatment applied to glass fibers used in reinforced plastics. The material used is sometimes called Size.

Skin
A relatively dense layer at the surface of a cellular material.

Slip Additive
A modifier that acts as an internal lubricant which exudes to the surface of the plastic during and immediately after processing. In other words, a non-visible coating blooms to the surface to provide the necessary lubricity to reduce coefficient of friction and thereby improve slip characteristics.

Slip Agent
An additive that provides surface lubrication during and immediately following processing of the plastic material. It acts as an internal lubricant which will eventually migrate to the surfaces.

Slip Forming
Sheet forming technique in which some of the plastic sheet material is allowed to slip through the mechanically operated clamping rings during a stretch-forming operation.

Slip-plane
Plane within transparent material visible in reflected light, due to poor welding and shrinkage on cooling.

Slurry
A watery mixture of insoluble matter.

Snap-back Forming
Sheet forming technique in which an extended heated plastic sheet is allowed to contract over a male form shaped to the desired contours.

Solvent
Any substance, usually a liquid which dissolves other substances.

Solvent Molding
Process for forming thermoplastic articles by dipping a male mold in a solution or dispersion of the resin and drawing off the solvent to leave a layer of plastic film adhering to the mold.

Specific Gravity
The density of any material divided by that of water at a standard temperature.

Specific Heat
The amount of heat required to raise a specified mass by one unit of a specified temperature.

Specular Transmittance
The transmittance value obtained when the measured transmitted flux includes only that transmitted in essentially the same direction as the incident flux.

Spherulites
Spherical crystalline body of radiating crystal fibers.

Spider
(1) In a molding press, that part of an injector mechanism which operates the ejector pins. (2) In extrusion, a term used to denote the membranes supporting a mandrel within the head/die assembly.

Spider Lines
Vertical marks on the parison (container) caused by improper welding of several melt flow fronts formed by the legs with which the torpedo is fixed in the extruder head.

Spin Welding
A process of fusing two objects together by forcing them together while one of the pair is spinning, until frictional heat melts the interface. Spinning is then stopped and pressure held until they are frozen together.

Spinneret
A type of extrusion die, i.e., a metal plate with many tiny holes, through which a plastic melt is forced to make fine fibers and filaments. Filaments may be hardened by cooling in air, water, etc., or by chemical action.

Spinning
Process of making fibers by forcing plastic melt through a spinneret.

Spiral Flow Test
A method for determining the flow properties of a thermoplastic resin in which the resin flows along the path of a spiral cavity. The length of the material which flows into the cavity and its weight gives a relative indication of the flow properties of the resin.

Spiral Mold Cooling
A method of cooling injection molds or similar molds wherein the cooling medium flows through a spiral cavity in the body of the mold. In injection molds, the cooling medium is introduced at the center of the spiral, near the spruce section, as more heat is localized in this section.

Splay
A defect in the surface of a molded part that is usually small in size, shiny, and may have the appearance of a lightly tinted or silver streaks.

Split-Ring Mold
A mold in which a split cavity block is assembled in a chase to permit the forming of undercuts in a molded piece. These parts are ejected from the mold and then separated from the piece.

Spray Coating
Usually accomplished on continuous webs by a set of reciprocating spray nozzles traveling laterally across the web as it moves.

Spray-up
Covers a number of techniques in which a spray gun is used as the processing tool. In reinforced plastics, for example, fibrous glass and resin can be simultaneously deposited in a mold. In essence, roving is fed through a chopper and ejected into a resin stream which is directed at the mold by either of two spray systems. In foamed plastics, very fast-reacting urethane foams or epoxy foams are used in liquid streams to the gun are sprayed on the surface. On contact, the liquid starts to foam.

Sprayed Metal Molds
Mold made by spraying molten metal onto a master until a shell of predetermined thickness is achieved. Shell is then removed and backed up with plaster, cement, casting resin, or other suitable material. Used primarily as a mold in sheet-forming processes.

Spreader
A streamline metal block placed in the path of flow of the plastic material in the heating cylinder of extruders and injection molding machines to spread it into thin layers, thus forcing it into intimate contact with the heating areas.

Spruce
The main feed channel that connects the mold-filling orifice with the runners leading to each gravity gate. Spruce is also the piece of plastic material formed in this channel.

Spruce Bushing
A hardened steel insert in an injection mold which contains the tapered spruce hole and has a suitable seat for the nozzle of the injection cylinder. Sometimes called an Adapter.

Spruce Gate
A passageway through which molten resin flows from the nozzle to the mold cavity.

Spruce Lock
In injection molding, a portion of the plastic composition which is held in the cold slug well by an undercut; used to pull the spruce out of the bushing as the mold is opened. The spruce lock itself is pushed out of the mold by an ejector pin. When the undercut occurs on the cavity block retainer plate, this pin is called the Spruce Ejector Pin.

Stabilizer
An ingredient used in the formulation of some plastics, especially elastomers, to assist in maintaining the physical and chemical properties of the compounded materials at their initial values throughout the processing and service life of the material.

Stabilizers & Surface
Some additives included in this category include antioxidants and antizonants, antistats, biocides and fungicides, heat stabilizers, light, and UV stabilizers and absorbers.

Staple
Refers to textile fibers of a short length, usually 1/2 to 3″, for natural fibers and sometimes larger for synthetics.

Stationary Platen
The large front plate of an injection molding machine to which the front plate of the mold is secured during operation. This platen does not move during normal operations.

Straight-sided Round
A round bottle with straight side walls from shoulder to base.

Stress Crack
A crack, either external or internal, in a plastic caused by tensile stresses less than its short-time mechanical strength.

Stretch Forming
A plastic sheet forming technique in which the heated thermoplastic sheet is stretched over a mold and subsequently cooled.

Striation
Rippling of thick parisons, caused by a local orientation effect in the melt by the spider legs.

Stripper-plate
A plate that strips a molded piece from core pins or force plugs. The stripper-plate is set into operation by the opening of the mold.

Structural Foam
The process of molding thermoplastics articles with a cellular core and integral solid skins in a single operation.

Submarine Gate
A type of edge gate where the opening from the runner into the mold is located below the parting line or mold surface as opposed to conventional edge gating where the opening is machined into the surface of the mold. With submarine gates, the item is broken from the runner system in ejection from the mold.

Surface Resistivity
The ratio of the potential gradient parallel to the current along its surface to the current per unit width of the surface.

Surface Resistivity
The electrical resistance between opposite edges of a unit square of insulating material. It is commonly expressed in ohms. (Also covered in ASTM D257-54T.)

Surface Treating
Any method of treating a polyolefin so as to alter the surface and render it receptive to inks, paints, lacquers, and adhesives such as chemical, flame, and electronic treating.

Surfactant
A compound that affects interfacial tensions between two liquids. It usually reduces surface tension.

Surfactants
The use of these chemicals allows the formation of an emulsion or intimate mixture of otherwise incompatible substances by modifying the surface properties and influencing the wetting and flowing properties of liquids.

Suspension
A mixture of fine particles of any solid with a liquid or gas. The particles are called the disperse phase, the suspending medium is called the continuous phase.

Sweating
Exudation of small drops of liquid, usually a plasticizer or softener, on the surface of a plastic part.

Syndiotactic
Having a stereochemical regularity where the molecules can be described in terms of alternation of configurational base units that are mirror images of one another.

Synergism
A term used to describe the use of two or more stabilizers in an organic material where the combination of such stabilizers improves the stability to a greater extent than could be expected from the additive effect of each stabilizer.

Tab Gated
A small removable tab of approximately the same thickness as the mold item, usually located perpendicular to the item. The tab is used as a site for edge gate location, usually on items with large flat areas.

Tack
Stickiness of an adhesive, measurable as the force required to separate an adherent from it by viscous or plastic flow of the adhesive.

Tackifiers
Additives used to enhance the adhesiveness or bonding ability of a material.

Tapered Cylinder
Refers to a particular shape of a container in which the circular cross section at the top is smaller in diameter than that at the bottom, or vice versa.

Tear Strength
1) Force required to initiate or continue a tear in a material under specified conditions. 2) The force acting substantially parallel to the major axis of the test specimen.

Tenacity (gpd)
The term generally used in yarn manufacture and textile engineering to denote the strength of a yarn or of a filament for its given size. Numerically it is the grams of breaking force per denier unit of yarn or filament size; grams per denier, gpd. The yarn is usually pulled at the rate of 12 in./min. Tenacity equals breaking strength (grams) divided by denier.

Tensile Bar (specimen)
A compression or injection molded specimen of specified dimensions which is used to determine the tensile properties of a material.

Tensile Modulus
(Also called modulus of elasticity). The ratio of nominal stress to the corresponding strain below the proportional limit of a material.

Tensile Strength
The longitudinal stress required to break a prescribed specimen divided by the original cross-sectional area at the point of rupture (usually expressed in lbs. Per square inch), within the gauge boundaries sustained by the specimen during the test.

Tensile Strength, Break
The maximum stress that a material can withstand without breaking when subjected to a stretching load.

Tensile Strength, Yield
The maximum stress that a material can withstand without yielding when subjected to a stretching load.

Thermal Conductivity
The rate of heat flow under steady state conditions through unit area per unit temperature gradient in a direction perpendicular to an isothermal surface.

Thermal Degradation
Deterioration by heat.

Thermal Expansion Coefficient
The fractional change in length (sometimes volume, specified) of a material for a unit change in temperature. Values for plastics range from 0.01 to 0.2 mils/in., degrees C.

Thermal Stress Cracking (TSC)
Crazing and cracking of some thermoplastic resins which results from over-exposure to elevated temperatures.

Thermionic
Relating to, using, or being the emission of charged particles (as electrons) by an incandescent material.

Thermoforming
Any process of forming thermoplastic sheet which consists of heating the sheet and pulling it down onto a mold surface.

Thermoplastics
Resins capable of undergoing a chemical reaction leading to a relative infusible and insolvable state.

Thermosets
Resins or plastic compounds, which in their final state are infusible and insoluble. After being fully cured, thermosets cannot be resoftened by heat.

Tie Bars
Bars which provide structural rigidity to the clamping mechanism often used to guide platen movement.

Tolerance
A specified allowance for deviations in weighing, measuring, etc., or for deviations from the standard dimensions or weight.

Top Blow
A specific type of blow molding machine forms hollow articles by injecting the blowing into the parison at the top of the mold

Torsion
Stress caused by twisting a material.

Tracking
A phenomenon wherein a high voltage source current creates a leakage or fault path across the surface of an insulating material by slowly but steadily forming a carbonized path.

Transfer Molding
A process of forming articles by fusing a plastic material in a chamber then forcing the whole mass into a hot mold to solidify.

Translucent
Descriptive of a material or substance capable of transmitting some light, but not clear enough to be seen through.

Transparent
Descriptive of a material or substance capable of a high degree of light transmission e.g., glass. Some polypropylene films and acrylic moldings are outstanding in this respect.

Tumbling
Finishing operation for small plastic articles by which gates, flash, and fins are removed and/or surfaces are polished by rotating them in a barrel together with wooden pegs, sawdust, and polishing compounds.

UL Temperature Index
The maximum temperature below which a material maintains its electrical and mechanical integrity over a reasonable period.

Ultimate Strength
Term used to describe the maximum unit stress a material will withstand when subjected to an applied load in a compression, tension, or shear test.

Ultrasonic Sealing
A film sealing method in which sealing is accomplished through the application of vibratory mechanical pressure at ultrasonic frequencies (20 to 40 KC.). Electrical energy is converted to ultrasonic vibrations through the use of either a magnetostrictive or piezoelectric transducer. The vibratory pressures at the film interface in the sealing area develop localized heat losses which melt the plastic surfaces effecting the seal.

Ultraviolet
Zone of invisible radiation beyond the violet end of the spectrum of visible radiation. Since UV wavelengths are shorter than the visible, their photons have more energy, enough to initiate some chemical reactions and to degrade most plastics.

Undercut
(a.) Having a protuberance or indentation that impedes withdrawal from a two-piece, rigid mold. Flexible materials can be ejected intact even with slight undercuts. (n.) Any such protuberance or indentation; depends also on design of mold.

Urea Plastics
Plastics based on resins made by the condensation of urea and aldehydes.

UV Stabilizer
Any chemical compound which, when mixed with a thermoplastic resin, selectively absorbs UV rays.

Vacuum Forming
A process whereby a heated plastic sheet is drawn against a mold surface by evacuating the air between it and the mold.

Vacuum Metallising
Process in which surfaces are thinly coated with metal by exposing them to the vapor of metal that has been evaporated under vacuum ( one millionth of normal atmospheric pressure).

Valley Printing
Ink is applied to the high points of an embossing roll and subsequently deposited in what becomes the valleys of the embossed plastic material.

Vent
In a mold, a shallow channel or minute hole cut in the cavity to allow air to escape as the material enters.

Vicat Softening Point
The temperature at which a flat ended needle will penetrate a specimen under a specific load using a uniform rate of temperature rise.

Virgin Material
A plastic material that has not been subjected to use or processing other than that required for its initial manufacture. It can be in the form of pellets, granules, powder, floc, or liquid.

Virgin Material
A plastic material in the form of pellets, granules, powder, flock, or liquid that has not been subjected to use or processing other than that required for its initial manufacture.

Viscosity
Internal friction or resistance to flow of a liquid. The constant ratio of shearing stress to rate of shear. In liquids for which this ratio is a function of stress, the term “apparent viscosity” is defined as the ratio.

Viscosity, Inherent
The logarithmic viscosity number determined by dividing the natural logarithm of the relative viscosity (sometimes called viscosity ratio) by the concentration in grams per 100 mls. of solution.

Viscosity, Relative (or Viscosity Ratio)
Determined by dividing the average efflux time of the solution by the average efflux time of the pure solvent.

Void
An unfilled space in a cellular plastic which is substantially larger than the individual cells. Can also be an empty space in any material or medium.

Volatiles
That portion of a substance that is readily vaporized.

Volume Resistivity
The measure of ratio of the potential gradient parallel to the current in the material to the current in density.

Vulcanization
The chemical reaction which induces extensive changes in the physical properties of a rubber and which is brought about by reacting the rubber with sulphur and/or other suitable agents. The changes in physical properties include decreased plastic flow, reduced surface tackiness, increased elasticity, much greater tensile strength, and considerably less solubility. More recently, certain thermoplastics, e.g., polyethylene, have been formulated to be vulcanisable. Cross-linking is encouraged, thereby giving resistance to deformation of flow above the melting point.

Warpage
A nonuniform change in internal stresses resulting distortion or warp of the material.

Water Absorption, 24 hours
The percentage of water absorbed by a material when immersed in water for 24 hours; water absorbed in a material chiefly affects its electrical properties.

Weir
A dam to divert water flow.

Weld Lines
A mark on a container caused by incomplete fusion of two streams of molten polymer. See Spider Lines.

Weld Mark
A mark on a molded plastic piece made by the meeting of two flow fronts during the molding operation.

Welding
Joining thermoplastic pieces by one of several heat-softening processes. In hot-gas welding, the material is heated by a jet of hot air or inert gas directed from a welding “torch” onto the area of contact of the surfaces which are being welded. Welding operations to which this method is applied normally require the use of a filler rod. In Spin-Welding the heat is generated by friction. Welding also includes heat sealing and the terms are synonymous in some foreign countries including Britain.

Wet Lay-up
A reinforced plastic manufacturing process where the polymer compound is applied as a liquid as the reinforcement is put into place.

Wet Strength
The strength of paper when saturated with water, especially used in discussions of processes whereby the strength of paper is increased by the addition, in manufacture, of plastic resins. Also, the strength of an adhesive joint determined immediately after removal from a liquid in which it has been immersed under specified conditions of time, temperature, and pressure.

Wet Winding
A fiber reinforcement material is coated with a polymer compound as a liquid prior to wrapping on a mandrel in the filament wound manufacturing process.

Wetting Agent
Wetting is produced when this surface active agent decreases the cohesion within a liquid. For wetting to occur, the adhesive force between the two phases (solid and liquid) is greater than the cohesive force within the liquid.

Whisker
A single-crystal, short fiber.

Wrinkle
An imperfection in reinforced plastics that has the appearance of a wave molded into one or more plies of fabric or other reinforcing material.


Youngs Modulus of Elasticity
The modulus of elasticity in tension. The ratio of stress in a material subjected to deformation.

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