GLOSSARY OF TERMS

A

Abrasion Resistance: The ability of a material to withstand mechanical actions such as rubbing, scraping, or erosion, that tend progressively to remove material from its surface. [Top of Page]

Acceptable Runner / Cavity Ratio: Runner systems designed for high pressure drops to minimize material usage and increase frictional heating in the runner. [Top of Page]

Additive: A substance compounded into a resin to enhance or improve certain characteristics. [Top of Page]

Adhesive Assembly: The process of joining two or more plastic parts by means of an adhesive. [Top of Page]

Aging: The process of, or the results of, exposure of plastics to natural or artificial environmental conditions for a prolonged period of time. [Top of Page]

Air Burn: A patch or streak of brown or black material on the component caused by air or gases that have not been properly vented from the mold and have caused the material to overheat and burn. [Top of Page]

Ambient Temperature: The temperature of a medium surrounding an object. The term is often used to denote prevailing room temperature. [Top of Page]

Amorphous: Devoid of crystallinity or stratification. Most plastics are amorphous at processing temperatures. Material assumes more random molecular structure when cooling. [Top of Page]

Anisotropy: The tendency of a material to react differently to stresses applied in different directions. [Top of Page]

Annealing: The process of relieving internal stresses of molded plastic articles by heating to a predetermined temperature, maintaining this temperature for a predetermined length of time, and slowly cooling the articles. [Top of Page]

ANSI: Abbreviation for American National Standards Institute. [Top of Page]

Antiozonants: These additives are used to prevent the negative effects of ozone on the resin materials. [Top of Page]

Antistatic Agent:Additive used to improve the electrical conductivity of the plastic part so that any charge can readily go to ground and not remain in the part. Artificially balanced runner system: balancing a runner system by adjusting the pressure drop of a long large diameter runner against a short small diameter runner. Since pressure drop over the small diameter runner will be much more affected by heat loss than the large diameter runner, an artificially balanced runner system will work with a set range of molding conditions. The width of this range of molding conditions determines the stability of the molding. [Top of Page]

Ash Content:The solid residue remaining after a substance has been incinerated or heated to a temperature sufficient to drive off all combustible or volatile substances. [Top of Page]

Aspect Ratio: Ratio of total flow length to average wall thickness. [Top of Page]

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. [Top of Page]

ASTM: ASTM: [Top of Page]

B

Back Pressure: The resistance of the molten plastic material to forward flow. In molding, back pressure increases the temperature of the melt, and contributes to better mixing of colors and homogeneity of the material. However, as back pressure increases, so does cycle time. [Top of Page]

Backflow: Molten resin flows back out of the mold, returning to the runners. [Top of Page]

Backing Plate: A plate used as a support for the mold cavity block, guide pins, bushings, etc. [Top of Page]

Balanced Runner: A runner system designed to place all cavities at the same distance from the sprue. [Top of Page]

Barrel: The section of a molding machine that contains the feed screw, also the section where resin heating and mixing occurs. [Top of Page]

Binder: A resin or other material used to hold particles together. The binder is the continuous phase in a reinforced plastic, which provides mechanical strength or ensures uniform consistency, solidification, or adhesion to a surface coating. Typical binder materials include resin, glue, gum and casein. [Top of Page]

Black Specks: A specific kind of inclusion/contamination often associated with heat-degraded materials. [Top of Page]

Blast Finishing: The process of removing flash from molded objects and/or dulling their surfaces, by impinging upon them with sufficient force to remove the flash. [Top of Page]

Blister: TAn imperfection on the surface of a plastic article caused by a pocket of air or gas beneath the surface. [Top of Page]

Blocking & Anticaking Agents: These additives are used to prevent the adhesion and agglomeration of ingredients within a resin compound. [Top of Page]

Bloom (also know as Migration): An undesirable cloudy effect or whitish powdery deposit on the surface of a plastic article or to the surrounding environment caused by the exudation of an ingredient such as a lubricant, stabilizer pigment, plasticizer, or other non-bonded component. [Top of Page]

Blow Molding: Method of fabrication in which a warm plastic 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 internal pressure. This process forms hollow articles such as bottles, tanks, etc. [Top of Page]

Blowing & Foaming Agents: Additives for plastics or rubbers that generate inert gases within the resin matrix when heated. The resulting part construction will contain a cellular structure. [Top of Page]

Blushing: The tendency of a plastic article to turn white or chalky in areas that are highly stressed. [Top of Page]

Boss: A raised feature of a molded part designed to add strength, facilitate alignment during assembly or for attachment to another part. [Top of Page]

Branching: The modification of the molecular structure of a polymer derived from the growth of a new polymer chain from an active site on an established chain, in a direction different from that of the original chain. [Top of Page]

Breakdown Voltage: The voltage required, under specific conditions, to cause failure of an insulation material. see Dielectric Strength. [Top of Page]

Brighteners: Are used to add smoother or brighter coatings or finishes. [Top of Page]

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. [Top of Page]

Broken Mold Marks: Part surface defects caused by mold damage. [Top of Page]

B-stage: This describes an intermediate stage of a thermoset resin 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. [Top of Page]

Bubbles: Air or gas pockets that have formed in the material of the component. Bubbles may vary in size. [Top of Page]

Bulk Density: A measurement of mass per unit volume of materials (such as powders) that describes the effects of the particle packing density. [Top of Page]

Bulk Factor: The ratio of the volume of any given mass of loose plastic material to the volume of the same mass of the material after molding. [Top of Page]

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. [Top of Page]

Burned:Showing evidence of excessive heating during processing or use of a plastic, as evidenced by blistering, discoloration, distortion or destruction of the surface. [Top of Page]

C

Casting: The process of forming solid or hollow articles from fluid plastic mixtures or resins by pouring or injecting the fluid into a mold or against a substrate with little or no pressure, followed by solidification and removal of the formed object. [Top of Page]

Cavity: A depression, or a set of matching depressions, in a plastics-forming mold which forms the outer surfaces of the molded articles. [Top of Page]

Charge: The amount of material used to load a mold at one time or during one cycle. The measurement or weight of material necessary to fill a mold during one cycle. [Top of Page]

Charpy Impact Test: A destructive test of impact resistance, consisting of placing a test coupon in a horizontal position between two supports, then applying a blow of known magnitude. If the specimen does not break, a new specimen is put in position and the magnitude is increased until the specimen breaks. [Top of Page]

Chopped Strand: A type of fiber reinforcement consisting of strands of individual glass fibers which have been chopped into short pieces. [Top of Page]

Clamp: The part of an injection molding machine incorporating the platens that provides the force necessary to hold the mold closed during injection of the molten resin and open the mold to eject the molded part. [Top of Page]

Clamping Area: The largest rated molding area an injection press can hold closed under full molding pressure. [Top of Page]

Clamping Force: The force applied to the mold to keep it closed, in opposition to the fluid pressure of the compressed molding material within the mold cavity and the runner system. [Top of Page]

Clamping Plate: A plate fitted to a mold and used to fasten the mold to a platen. [Top of Page]

Clamping Pressure: The pressure applied to the mold to keep it closed during the molding cycle. [Top of Page]

Clarifiers: Additive used in resins to improve transparency or translucency. [Top of Page]

Closed-loop Control: System for monitoring and automatically adjusting injection molding process conditions such as temperature, pressure and time. The automatic changes keep part production within preset tolerances. [Top of Page]

Coefficient of Thermal Expansion (CTE): The change in length of a material for a unit change in temperature, per unit of length. [Top of Page]

Co-Injection: Simultaneous or near simultaneous injection of multiple materials. See multi-shot molding. [Top of Page]

Cold Flow Lines:Imperfections within the part wall due to thickening or solidification of resin prior to full cavity fill. [Top of Page]

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

Color Concentrate (also know as Colorant, Pigment): A plastic compound which contains a high percentage of pigment, to be blended in appropriate amounts with the base resin so that the correct final color is achieved. [Top of Page]

Colorant (also know as Color Concentrate, Pigment): A plastic compound which contains a high percentage of pigment, to be blended in appropriate amounts with the base resin so that the correct final color is achieved. [Top of Page]

Composite: A structural non-homogenous material consisting of a combination of materials. Typically, one of the materials is a strengthening agent, the other being a thermoset or thermoplastic resin. [Top of Page]

Compound: A mixture of resin(s) and additives usually formed in a separate machine downstream forn the primary reactor. [Top of Page]

Compounding: The process required to mix polymer(s) with all of the additives that are necessary to provide the end user with a finished grade with suitable properties. [Top of Page]

Compression Molding: A method of molding in which the molding material, generally preheated, is placed in an open heated mold cavity, the mold is closed with a top force, pressure is applied to force the material into contact with all mold areas. [Top of Page]

Compressive Strength: The ability of a material to sustain a force in a direction opposite of tension. [Top of Page]

Conditioning: Subjecting a material to standard environmental and/or a non-standard stress state prior to testing or use. [Top of Page]

Constant pressure gradient: pressure drop per unit length. The constant pressure gradient principle says that the most efficient filling pattern is when the pressure gradient is constant along the flow path. [Top of Page]

Continuous Service Temperature:The highest temperature at which a material can perform reliably in long term application - as defined by the manufacturer. [Top of Page]

Controlled frictional heating:runners designed to deliver a higher melt temperature to the cavity. This results in lower stress levels in the part without causing material degradation due to long exposure to elevated temperatures in the barrel. [Top of Page]

Conversions (Commonly Used in Injection Molding): KPa x 0.145 = psi MPa x 145 = psi °C x 1.8 + 32 = °F Liters/min x 0.2642 = Gal/min Inches x 25.4 = mm Flow rate = ((# of cavities) x (volume per cavity))/(injection time) [Top of Page]

Cooling Channels:Channels located within the body of a mold through which a cooling medium is circulated to control the mold surface temperature. [Top of Page]

Cooling time:the elapsed time required for the melt to reach its Vicat softening temperature. [Top of Page]

Copolymer:The chemical reaction of two different monomers with each other, result in a unique new polymer. [Top of Page]

Core:A protrusion, or set of matching protrusions, in a plastics forming mold which forms the inner surfaces of the molded articles. [Top of Page]

Corona Treatment:Impingement of AC power on a component to bombard with free radicals thus improving the ability to bond to a surface. [Top of Page]

Corrosion Resistance:A broad term applying to the ability of plastics to resist degradation in many environments, usually die to oxidation. [Top of Page]

Corrosion Resistance:A broad term applying to the ability of plastics to resist many environments. [Top of Page]

Coupling Agents:A material that is used to form a chemical bridge between the resin and an additive such as glass fiber or mineral fiber. By acting as an interface, bonding is enhanced. [Top of Page]

Crack/Splits/Chips:A physical separation or tearing of the part. [Top of Page]

Crazing:Defect in plastics articles characterized by distinct surface cracks or minute frost-like internal cracks, resulting from stresses within the article which exceed the tensile strength of the plastic. [Top of Page]

Creep:Due to its viscoelastic nature, a plastic subjected to a load for a period of time tends to deform more than it would from the same load released immediately after application, and the degree of this deformation is dependent of the load duration. [Top of Page]

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. [Top of Page]

Cryogenic Processes:Reduction of parts to very low temperatures usually associated with liquid nitrogen. Commonly used to create assemblies or to deflash or degate a part. [Top of Page]

Crystal:A homogeneous solid having an orderly and repetitive three-dimensional arrangement of its atoms. [Top of Page]

Crystallinity:A state of molecular structure in some resins attributed to the existence of solid crystals with a definite geometric form, Such structures are characterized by uniformity and compactness. [Top of Page]

CSA:Abbreviation for the Canadian Standards Association. [Top of Page]

C-stage:This term describes the final stage of the reaction where a thermoset material is relatively insoluble and infusible. [Top of Page]

Cure Cycle:The time periods at defined conditions to which a reacting thermosetting material is processed to reach a desired property level. [Top of Page]

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. [Top of Page]

Custom Molder:A firm specializing in the molding of items or components to the specifications of another firm which handles the sale of distribution of the item, or incorporates the custom molded components in one of its own products.. [Top of Page]

Cycle Time:The time required by an injection molding system to mold a part and return to its original position/state. [Top of Page]

Cycle:complete, repeating sequence of operations for injection molding a part. [Top of Page]

D

Damping: The effect on a mass that causes decreasing amplitude. [Top of Page]

Deflection Temperature: The measurement of temperature at which a specimen deflects to a set point under a defined load. [Top of Page]

Degassing: The momentary opening and closing of a mold during the early stages of the cycle to permit the escape of air or gas from the heated compound. [Top of Page]

Degradation: A deleterious change in the chemical structure, physical properties or appearance of a plastic caused by exposure to heat, light, oxygen, weathering or other external influence. [Top of Page]

Delamination: When the surface of a finished part separates. Strata or fish-scale-type appearance may be visible where the layers may be separated. [Top of Page]

Density: Mass per unit volume of a substance. [Top of Page]

Design Review: A review of a blueprint, of an application, to be molded in a plastic material, with recommendations given for design, material, processing, tooling. [Top of Page]

Diaphragm Gate: Used in symmetrical cavity filling to reduce weld-line formations and improve filling rates. [Top of Page]

Dielectric Strength: The voltage that an insulating material can withstand before dielectric breakdown occurs. See Breakdown Voltage. [Top of Page]

Differential Cooling: Occurs when one area of the part cools at a different rate or when the mold surfaces are at different temperatures. Warping can result from differential cooling. [Top of Page]

Dimensional Stability: Retention of the precise shape of the part. [Top of Page]

Direct Gate:A sprue that feeds directly into the mold cavity. [Top of Page]

Discoloration: Any change from the designated color of the material or component. [Top of Page]

Dispersion Aids: Flow alteration components placed at the entry point of an additive to aid in mixing or dispersing actions of a compounding process. [Top of Page]

Dominant Flow Path:At the juncture of two confronting flows the dominant flow will reverse the direction of the other. [Top of Page]

Draft: A Slight taper in a mold wall designed to facilitate removal of the molded object from the mold. [Top of Page]

Drag Marks: A form of deep scratch or scratches on the surface of the component usually caused by the ejection of the part. [Top of Page]

Drooling:The extrudation or leakage of molten resin from nozzle or nozzle sprue bushing area while filling or shooting the mold. [Top of Page]

Drying: The removal of moisture from the resin pellets by exposure to certain time and temperature. All Hydroscopic Material must be dried prior to molding. [Top of Page]

Durometer:An instrument used for measuring the hardness of a material. [Top of Page]

Dwell: A pause in the applied pressure to a mold during the injection cycle just before the mold is completely closed. This dwell allows any gases formed or present to escape from the molding material. [Top of Page]

E

Edge gate: Entrance to the part from the runner located on the parting line. [Top of Page]

Ejection Pin Marks: A residual mark on the part caused by the profile of the ejection pin. [Top of Page]

Ejection Pin: A rod, pin or sleeve that pushes a molded part off of a core or out of a cavity of a mold. [Top of Page]

Ejector Return Pins: Projections that push the ejector assembly back as the mold closes. Also called surface pins or return pins. [Top of Page]

Ejector Rod: A bar that actuates the ejector assembly when the mold opens. [Top of Page]

Elastic Memory: A characteristic of certain plastics evidenced by their tendency to revert to a previously existing shape or dimension. [Top of Page]

Elasticity: The ability of a material to quickly recover its original dimensions after removal of a load that has caused deformation. [Top of Page]

Elastomer: A rubber-like material which at room temperature can be stretched repeatedly to at least twice its original length and, upon immediate release of the stress, will return with force to its approximate original length. [Top of Page]

Element: A triangle defined by at least three nodes, creating the basis for the finite element analysis. [Top of Page]

Elongation, Break: The increase in distance between two gauge marks at the break point divided by the original distance between the marks. A zero value in the field indicates that it measured less than one. [Top of Page]

Elongation, Yield: The increase in distance between two gauge marks at a yield point divided by the original distance between the marks. A zero value indicates that it measured less than one. [Top of Page]

Engineering Plastics: A broad term covering plastics, with or without fillers or reinforcements, which have improved mechanical, chemical and thermal properties over commodity grades of resins. [Top of Page]

Extender: A filler material added to a plastic compound used to reduce the amount of resin required per unit value. [Top of Page]

Extrudate:The product or material delivered from an extruder, for example, film, pipe profiles. [Top of Page]

Extrusion: The process of forming continuous shapes by forcing a molten plastic material through a die. [Top of Page]

F

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. [Top of Page]

Family mold: A mold that produces non-identical parts simultaneously from multiple cavities. [Top of Page]

Fan Gate: A gate used to help reduce stress concentrations in the gate area by spreading the opening over a wider area. Less warping of parts can usually be expected by the use of this type of gate. [Top of Page]

Fatigue Strength: The maximum cyclic stress a material can withstand for a given number of cycles before failure occurs. [Top of Page]

Fill pattern: The contours of the advance of the material as the cavity fills(see flow pattern). [Top of Page]

Fill pressure: The pressure required to fill the cavity. [Top of Page]

Fill Time (also known as Injection):Time required to fill the cavity or mold. See injection. [Top of Page]

Fill: The packing of the cavity or cavities of the mold as required to give a complete part or parts that are free of flash and porosity. [Top of Page]

Filler: A relatively inert substance added to a plastic compound to reduce its cost and/or to improve physical properties, particularly hardness, stiffness and impact strength. [Top of Page]

Fines: In the classification of powdered or granular materials such as molding compounds according to particle size, fines are the portion of the material composed of particles which are smaller than a specified size. [Top of Page]

Finish: The surface texture and appearance of a finished article. [Top of Page]

Finite element analysis: the solution of simultaneous equations for each element with resulting pressure, temperature and elapsed time at each node. [Top of Page]

Flame Retardant: Having the ability to resist combustion (A flame retardant plastic is considered to be one that will not continue to burn or glow after the source of ignition has been removed.) [Top of Page]

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. [Top of Page]

Flash: Any excess material that is formed with and attached to the component along a seam or mold parting line. [Top of Page]

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 elements of the specimen. [Top of Page]

Flexural Strength, Yield:The measure of resistance of the material to fracture during bending. [Top of Page]

Flexural Strength: The maximum stress in the outer fiber at the moment of crack or break. In the case of plastics, this value is usually higher than the tensile strength. [Top of Page]

Flow Balancing: Modifying flow paths, particularly runner sections, so that all flow paths within a mold fill in equal time with equal pressure. [Top of Page]

Flow Leader: Local increase in thickness to encourage flow in a particular direction. [Top of Page]

Flow Marks: Wavy surface appearances on a molded part caused by improper flow of the melt into the mold. [Top of Page]

Flow Pattern: The contour the melt takes sequentially as it fills the cavity.(See Fill Pattern.) [Top of Page]

Flow Rate: The volume of material passing a fixed point per unit time. [Top of Page]

Foaming Agent:Any substance which alone or in combination with other substances is capable of producing a cellular structure in a plastic mass. [Top of Page]

Fracture: The separation of a body, usually characterized as either brittle or ductile. [Top of Page]

Freeze off: The temperature of the material is reduced to the point that it blocks an area it would fill if it were hotter. [Top of Page]

Frictional heating: Heat generated by the friction of the chains of molecules slipping past each other or over a surface. [Top of Page]

G

Gate Blush: A blemish or disturbance in the gate area of an injection molded article. [Top of Page]

Gate Trim: Remnant of plastic left over from cutting the component from the runner or sprue, usually to be cut flush with the edge of the component. [Top of Page]

Gate: The channel through which the molten resin flows from the runner into the cavity. [Top of Page]

Glass Fibers: A family of reinforcing materials for reinforced plastics based on single filaments of glass. [Top of Page]

Glass transition: Change in an amorphous polymer from viscous to hard and relatively brittle. [Top of Page]

H

Hardener: A substance or mixture of substance added to a material to increase or control the curing reaction by taking part in it. [Top of Page]

Hardness: The resistance of a material to compression, indentation and scratching. [Top of Page]

Haze: The cloudy appearance of a material caused by light scattered from within the specimen or from its surface [Top of Page]

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. [Top of Page]

Hesitation effect: Occurs in parts of varied thicknesses. The flow moves preferentially into a thicker area causing an adjacent thin area to freeze off while the thicker area fills. Gates should be positioned as far as possible from where the flow divides into thick and thin flow paths. [Top of Page]

Homopolymer: Plastic that results from the polymerization of a single monomer. [Top of Page]

Hopper Dryers: Auxiliary equipment that removes moisture from resin pellets. [Top of Page]

Hot-Runner Mold (also known as Insulated Runner or Runnerless Molding): A mold in which the runners are insulated from the chilled cavities and are kept hot. Hot-runner molds make parts that have no scrap. See insulated runner, Runnerless molding. [Top of Page]

Hygroscopic: Readily absorbs moisture. [Top of Page]

I

Impact Modifiers: Additive used to enhance the material's ability to withstand the force of impact. [Top of Page]

Impact Resistance: The resistance of plastic articles to fracture under stresses applied at high speeds. [Top of Page]

Impact Strength: The ability of a material to withstand shock loading. [Top of Page]

Injection (also known as Fill Time): Time required to fill the cavity or mold. See fill time. [Top of Page]

Injection Blow Molding: Blow molding process by which the plastic parison to be blown is formed by injection molding. [Top of Page]

Injection Molding Pressure: The pressure applied to the cross-sectional area of the molding cylinder. [Top of Page]

Injection Molding: The method of forming objects from granular or powdered plastics, most often of the thermoplastic type, in which the materials is fed from a hopper to a heated chamber in which it is softened, after which a ram or screw forces the material into a mold. Pressure is maintained until the mass has hardened sufficiently for removal from the mold. [Top of Page]

Injection Pressure: The pressure on the face of the injection screw or ram when injecting material into the mold, usually expressed in PSI. [Top of Page]

Insert Molding: Insert molding is the process of molding plastic around preformed metal inserts. This process is compatible with both thermoplastic and thermoset materials. [Top of Page]

Insert: A removable part of the mold imparting increased resistance to wear, heat transferability, or changeable part shape to that area of the mold. [Top of Page]

Insulated Runner (also known as Hot-Runner Mold or Runnerless Molding): A mold in which the runners are insulated from the chilled cavities and are kept hot. Hot-runner molds make parts that have no scrap. See hot runner mold, runnerless molding. [Top of Page]

Isobar: A line of equal pressure. Any point along an isobar sees the same cavity pressure as any other point along the same isobar. [Top of Page]

Isochrone: A line of equal time. Any point along an isochrone is filled at the same time as any other point along the same isochrone. [Top of Page]

Isotherm: A line of equal temperature. Any point along an isotherm is at the same temperature as any other point along the same isotherm. [Top of Page]

Izod Impact Strength: A measure of impact strength determined by the difference in energy of a swinging pendulum before and after it breaks a notched specimen held vertically as a cantilever beam. [Top of Page]

Izod Impact Test: Test to determine impact strength of a sample by holding a sample bar at one end and broken by striking. Sample specimen can be either notched or unnotched. [Top of Page]

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). [Top of Page]

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

J

Jetting: A turbulent flow in the melt caused by an undersized gate or where a thin section rapidly becomes thicker. [Top of Page]

Jig: A tool for holding parts of an assembly during the manufacturing process. [Top of Page]

K

K-Factor: A term sometimes used for thermal insulation value or coefficient of thermal conductivity.< [Top of Page]

Knit Lines: Where melted material flows together to form a line or lines that may cause weakening or breaking of the component. [Top of Page]

Knockout Pin: A pin that ejects a molded article from the mold. [Top of Page]

L

Land (Gate Area): Gate dimension parallel to the direction of melt flow. [Top of Page]

Land Area: The area of surfaces of a mold which contact each other when the mold is closed. [Top of Page]

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. [Top of Page]

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. [Top of Page]

Linear Thermal Expansion: The fractional change in length of a material for a unit change in temperature. [Top of Page]

Liquid Injection Molding (LIM): 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. [Top of Page]

Low Temperature Flexibility: The ability of a plastic to be bent without fracture at reduced temperatures. [Top of Page]

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. [Top of Page]

M

Machine Shot Capacity: Refers to the maximum volume of thermoplastic resin which can be displaced or injected by the injection ram in a single stroke. [Top of Page]

Mar Resistance: The resistance of glossy plastic surfaces to abrasive action. [Top of Page]

Masterbatch: A concentration of a substance (an additive, pigment, filler, etc.) in a base polymer. [Top of Page]

Material Safety Data Sheets: Documentation regarding the toxicity or hazards associated with contact with some substances. The manufacturer of the plastic prepares these data sheets. [Top of Page]

Mechanical Property: Properties of plastics which are classified as mechanical include abrasion resistance, creep, ductility, friction resistance, elasticity hardness, impact resistance, stiffness and strength. [Top of Page]

Melt Flow Rate: A measure of the molten viscosity of a polymer determined by the weight of polymer extruded through an orifice under specified conditions of pressure and temperature. Particular conditions are dependent upon the type of polymer being tested. [Top of Page]

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. [Top of Page]

Melt Index: The amount of a thermoplastic resin, measured in grams, which can be forced through a specified orifice within ten minutes when subjected to a specified force. (ASTM D-1238) [Top of Page]

Melt Strength: The strength of the plastic while in the molten state. This is a pertinent factor in extrusion, blow molding and drawing of molten resin from a die. [Top of Page]

Memory: The tendency of a plastic article to revert in dimension to a size previously existing at some stage in its manufacture. [Top of Page]

Metallizing: A term covering all processes by which plastics are coated with metal. [Top of Page]

Migration (also know as Bloom): An undesirable cloudy effect or whitish powdery deposit on the surface of a plastic article caused by the exudation of a compounding ingredient such as a lubricant, stabilizer pigment, plasticizer, etc. [Top of Page]

Mineral Reinforcements: Inorganic substances used as filler for plastics. Some common examples are: clay, mica, talc. [Top of Page]

Minimum Specifications: The minimum values, usually of mechanical properties, that a compound must meet by Quality Assurance prior to shipment. [Top of Page]

Modulus in Compression: The ratio of compressive stress to strain within elastic limits of the material. [Top of Page]

Modulus in Flexure: The ratio of the flexure stress to strain, within elastic limits of the material. [Top of Page]

Modulus in Shear: The ratio of shear stress to strain within elastic limits of the material. [Top of Page]

Modulus of Elasticity: The ratio of stress to corresponding strain below the proportional limit of a material in tensile testing. [Top of Page]

Modulus of Resilience: The energy that can be absorbed per unit volume without creating a permanent distortion. [Top of Page]

Modulus: Derived from the Latin world meaning "small measure", modulus is the ratio of stress to strain in the linear region of the s-e curve. [Top of Page]

Moisture Absorption: The pick-up of moisture from the environment by a material. [Top of Page]

Mold (n): A hollow form or matrix into which a plastic material is placed and which imparts to the material its final shape as a finished article. [Top of Page]

Mold (v): To impart shape to a plastic mass by means of a confining cavity or matrix. [Top of Page]

Mold Changer: An automated device for removing one mold from a machine and replacing it with another mold. [Top of Page]

Mold Frame: A series of steel plates which contain mold components, including cavities, cores, runner system, cooling system, ejection system, etc. [Top of Page]

Mold Release Problems: Excess use of mold release may leave parts oily and weaken the material. [Top of Page]

Mold Release: In injection molding, a lubricant used to coat the surface of the mold to enhance ejection of the molded article or prevent it from sticking to the tool. [Top of Page]

Mold Temperature: The temperature at which the mold is maintained. Often the most important benefit of raising mold temperature is that it allows a slower injection rate without the plastic getting too cold. [Top of Page]

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

Molding Cycle: The period of time occupied by the complete sequence of operations on a molding press requisite for the production of one set of molded articles. [Top of Page]

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. [Top of Page]

Molding sensitivity: The variability of the pressure to fill the cavity and temperature of the melt at the part as influenced by changes in injection time and barrel melt temperature. [Top of Page]

Molding window: The range of molding conditions under which a part can be successfully molded. [Top of Page]

Mold-Temperature-Control Unit: Auxiliary equipment used to control mold temperature. Some units can both heat and cool the mold. Others, called chillers, only cool the mold. [Top of Page]

Molecular Weight: The sum of the atomic weights of all atoms in a molecule. Especially in plastics an average molecular weight is reported. [Top of Page]

Molecular Weight: The sum of the atomic weights of all atoms in a molecule. Especially in plastics an average molecular weight is reported. [Top of Page]

Molecule: The smallest unit quantity of matter which can exist by itself and retain all of the properties of the original substance. [Top of Page]

Monomer: A relatively simple molecular structure, usually containing carbon and of low molecular weight, which can react to form a polymer by combination with itself or with other molecules and energy. [Top of Page]

Moving Platen: The platen of an injection molding machine that is moved by a hydraulic ram or mechanical toggle. [Top of Page]

Multi-Cavity Mold: A mold having two or more impressions for forming finished items in one machine cycle. [Top of Page]

Multidirectional flow: flow direction changes during filling resulting in orientation in different directions which can cause flow marks, stresses and warping. [Top of Page]

Multiple cavity mold: Produces more that one identical part with each cycle. [Top of Page]

Multi-Shot Molding: The injection of two-or-three materials, in sequence, into a single mold during a single molding cycle. The injection molding machine is equipped with two-or-three plasticators. (see also co-injection.) [Top of Page]

N

Naturally balanced runner system: Each succession of runner is identical to the runners in the same succession in all other flows in the mold. [Top of Page]

Nest Plate: A retainer plate in the mold with a depressed area for cavity blocks. [Top of Page]

Non-Fill (also known as Short Shot): Failure to completely fill the mold or cavities of the mold. Edges may appear melted. [Top of Page]

Non-Return Valve: Screw tip that allows for material to flow in one direction and closes to prevent back flow and inject material into the mold (check valve). [Top of Page]

Notch Sensitivity: The extent to which the sensitivity of a material to fracture is increased by the presence of a surface notch or sudden change in section. [Top of Page]

Nozzle: Hollow metal hose screwed into the extrusion end of the heating cylinder of an injection machine designed to form a seal under pressure between the cylinder and the mold. [Top of Page]

Nucleating Agent: Additive used in a polymer to increase crystallization rate by providing additional sites for crystal growth (i.e. Talc). This results in faster cycle time. [Top of Page]

O

Odorants & Deodorants: Odorants are used to add odor to materials, usually for safety reasons.Top of Page

Opaque: Not able to transmit light. [Top of Page]

Orange Peel: A surface finish on a molded part that is rough and splotchy. Usually caused by moisture in the mold cavity or poor heat transfer properties. [Top of Page]

Orientation: The arrangement of the molecules of the melt. If the molecules are orientated, they are aligned with each other; if non-orientated they are not in alignment. In general, orientated material shrinks more than non-orientated material. [Top of Page]

Over Molding: A process in which a mold cavity is first partially filled with one plastic and then a second shot is injected to encapsulate the first shot. [Top of Page]

Overpack: Melt will fill the easiest flow path first and will continue to pack this area while material reaches the other areas. This is a cause of warping created by unbalanced flow. [Top of Page]

Oxygen Index: A flammability test based on the principle that a certain volumetric concentration of oxygen is necessary to maintain combustion of a specimen after it has been ignited. [Top of Page]

P

Packing: The filling of the mold cavity or cavities as full as possible without causing undue stress on the molds or causing flash to appear on the finished parts. Over-packing or under-packing results in less than optimum fill. [Top of Page]

Part Picker: An auxiliary unit usually mounted on fixed platen, which reaches into the open mold to grab parts and remove them prior to next molding cycle. Also called a robot, the device is used when you do not want to drop parts from mold upon ejection. See robot. [Top of Page]

Partially-balanced runner system: Composed of both naturally and artificially balanced runners. [Top of Page]

Parting line: Mark on the part indicating where the two halves of the mold met in closing. [Top of Page]

Peeling: An open blister. [Top of Page]

Pellets: Tablets or granules of uniform size, consisting of resins or mixtures of resins with compounding additives which have been prepared for molding operations by extrusion and chopping into short segments. [Top of Page]

Photodegradation: Degradation of plastics due to the action of light. [Top of Page]

Pigment (also know as Colorant, Color Concentrate): A plastic compound which contains a high percentage of pigment, to be blended in appropriate amounts with the base resin so that the correct final color is achieved. [Top of Page]

Pinpoint Gate: A restricted gate of 0.030 in or less in diameter, this gate is common on hot-runner molds. [Top of Page]

Piston: see ram. [Top of Page]

Pit: An imperfection, a small crater in the surface of the plastic. [Top of Page]

Plastic Deformation: A change in dimensions of an object under load that is not recovered when the load is removed. [Top of Page]

Plastic: A material that contains as an essential ingredient one or more organic polymeric substances of large molecular weight, is solid in its finished state, and, at some stage in its manufacture or processing into finished articles, can be shaped by flow. [Top of Page]

Plasticity: The ability of a material to withstand continuous and permanent deformation by stresses exceeding the yield value of the material without rupture. [Top of Page]

Plasticize: A substance or material incorporated in a material (usually a plastic or an elastomer) to increase its flexibility, workability or extensibility. [Top of Page]

Platens: The mounting plates of a press on which the mold halves are attached. [Top of Page]

Plate-Out: An objectionable coating gradually formed on metal surfaces of molds during processing of plastics due to extraction and deposition of some ingredient such as pigment, lubricant, stabilizer or plasticizer. [Top of Page]

Plots: Graphical representations of analysis results. [Top of Page]

Poisson's Ratio: The constant relating the changes in dimensions which occur when a material is stretched. It is obtained by dividing the change in width per unit length by the change in length per unit length. [Top of Page]

Polymer Structure: A general term referring to the relative positions, arrangement in space, and freedom of motion of atoms in a polymer molecule. [Top of Page]

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. [Top of Page]

Polymerization: A chemical reaction in which the molecules of a simple substance (monomer) are linked together to form large molecules whose molecular weight is a multiple of that of the monomer. [Top of Page]

Preform: A plastic pre- shaped part produced by injection molding systems in the first step of a two-stage injection molding and blow molding process used to produce bottles or containers. The preform is subsequently re-heated and stretch blown through a blow molding process into the final container shape. [Top of Page]

Pressure Pads: Reinforcements of 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. [Top of Page]

Processing Aids: Additives specifically used to improve the injection process. [Top of Page]

Proportional Limit: The greatest stress which a material is capable of sustaining without deviation from proportionality of stress and strain. (Hooke's Law). [Top of Page]

Prototype Tool: A preliminary mold built upon which the final mold will be based. [Top of Page]

Pulled Gate: Area where the part was connected to the sprue or runner that has been drawn out or stretched from the surface. See strings. [Top of Page]

Purging: In extrusion or injection molding, the cleaning of one color or type of material from the machine by forcing it out with the new color or material to be used in subsequent production, or with another compatible purging material. [Top of Page]

R

Raised Ejector Site: Where the ejector site is either heightened or raised above the surface of the component. [Top of Page]

Ram: Not able to transmit light. [Top of Page]

Reaction Injection Molding (RIM): 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. [Top of Page]

Reagent Resistance: The ability of a plastic to withstand exposure to chemicals. [Top of Page]

Recovery Time: The length of time for the screw to rotate, create a shot, and return to original position. [Top of Page]

Regrind: Waste material such as sprues, runners, excess parison material and reject parts from injection molding, blow molding and extrusion, which has been reclaimed by shredding or granulating. Regrind is usually mixed with virgin compound at a predetermined percentage for remolding. [Top of Page]

Reinforced Plastic: A plastic composition in which fibrous reinforcements are imbedded, with strength properties greatly superior to those of the base resin. [Top of Page]

Release agent: A material sprayed on the mold which facilitates removing the part. [Top of Page]

Resin (Synthetic): The term is use to designate any polymer that is a basic material for plastics. [Top of Page]

Restricted Gate: A very small orifice between runner and cavity in an injection mold. When the part is ejected, this gate readily breaks free of the runner system. Generally, the part drops through one chute and the runner system through another leading to a granulator and scrap reclaim system. [Top of Page]

Retainer Plate: The plate on which demountable pieces, such as mold cavities, ejector pins, guide pins and bushings are mounted during molding. [Top of Page]

Retractable Cores: Used when molding parts in cavities not perpendicular to the direction in which the part is ejected from the mold. The cores are automatically pulled from the mold prior to the mold opening and reinserted when the mold closes again and prior to injection. See side draw pins. [Top of Page]

Rib: A reinforcing member of a molded part

Ring Gate: Used on some cylindrical shapes. This gate encircles the core to permit the melt to first move around the core before filling the cavity. [Top of Page]

Robot: Automated devices for removing parts upon ejection from an open mold rather than letting the parts drop. Also see parts picker. Robots also can perform secondary functions, such as inspection, degating, precise placement of parts on a conveyor, etc. [Top of Page]

Rockwell Hardness: A measure of the surface hardness of a material. A value derived from the increase in depth of an impression as the load of a steel indenter is increased from a fixed minimum value to a higher value and then returned to the minimum value. The values are quoted with a letter prefix corresponding to a scale relating to a given combination of load and indenter. [Top of Page]

Runner Balancing: Developing a runner system which delivers the required amount of melt to each cavity with the correct pressure to finish filling all the cavities simultaneously at the correct temperature for the part. [Top of Page]

Runner Design: Using the runner as a flow control device (positioning the gate and using the size of the runner to control the filling pattern within the cavity) in addition to getting the melt into the cavity. [Top of Page]

Runner System: This term is sometimes used for the entire resin feeding system, including sprues, runners and gates, in injection molding. [Top of Page]

Runner: In an injection mold, the feed channel, usually of circular cross section, which connects the sprue with the cavity gate. The term is also used for the plastic piece formed in this channel. [Top of Page]

Runnerless molding (also known as Hot-Runner Mold or Insulated Runner): A mold in which the runners are insulated from the chilled cavities and are kept hot. Hot-runner molds make parts that have no scrap. See hot runner mold, insulated runner. [Top of Page]

S

Scrap: Any output of a mold that is not usable as the primary product.Top of Page

Screw Travel: The distance the screw travels forward when filling the mold cavity. [Top of Page]

Shear rate: The rate at which a layer of melt slides over the layer below. Shear rate is velocity-related rather than force- related. [Top of Page]

Shear Strength: The maximum load required to shear the specimen in such a manner that the moving portion has completely cleared the stationary portion. Sheet Sheets are distinguished from films in the plastics industry only according to their thickness. In general, sheets have thicknesses greater than.040". [Top of Page]

Shear stress: The shearing force divided by the area. It is always a maximum at the outside of the flow channel. As it is force-related, it depends on the viscosity of the material, which in turn depends on the material and molding conditions. The maximum allowable stress level is usually taken as 1% of the tensile strength of the material. High shear stress is unimportant at gates, and in sprues and runners. [Top of Page]

Short Shot (also known as Non-Fill): Failure to completely fill the mold or cavities of the mold. Edges may appear melted. [Top of Page]

Shot Capacity: Generally based on polystyrene, this is the maximum weight of plastic that can be displaced or injected by a single injection stroke. Generally expressed as ounces of polystyrene. [Top of Page]

Shot: One complete cycle of a molding machine. [Top of Page]

Shrinkage Allowance: The dimensional allowance which must be made in molds to compensate for shrinkage of the plastic compound on cooling. [Top of Page]

Shrinkage: Contraction upon cooling of all or areas of the part. Shrinkage occurs less is disorientated material and more across chains of molecules than along their lengths. Lower pack area have lower areas of orientation and shrinkage. [Top of Page]

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. See also retractable cores. [Top of Page]

Sink Mark: An indentation on the surface of the part as a result of significant local change in wall section. The mark will occur in the thicker area. [Top of Page]

Skin: A relatively dense layer at the surface of the material. [Top of Page]

Slide: Projection in the mold used to form the geometry of the part, which is not in the direction of the closing of the mold and must be withdrawn before the part can be ejected. [Top of Page]

Slip Agent: Additive used to provide lubrication during and immediately following processing of plastics. [Top of Page]

Solvents: Substances with the ability to dissolve other substances. [Top of Page]

Specific Gravity: The ratio of the density of a material as compared to the density of water at standard atmospheric pressure (1 ATM) and room temperature (73F). [Top of Page]

Specific Volume: The volume of a unit of weight of a material; the reciprocal of density. [Top of Page]

Spiral Flow: Test performed by injection molding a sample into a spiral mold and used to compare the processability of different resins. [Top of Page]

Splay Marks: Scan or surface defects on molded part caused by abnormal racing of the melt in the mold. [Top of Page]

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

Sprue Bushing: A hardened-steel insert in the mold that accepts the nozzle and provides an opening for transferring the melt. [Top of Page]

Sprue Gate: A passageway through which melt flows from the nozzle to the mold cavity. [Top of Page]

Sprue Lock: The portion of resin retained in the cold-slug well by an undercut. This lock is used to pull the sprue out of the bushing as the mold opens. The sprue lock itself is pushed out of the mold by an ejector pin. [Top of Page]

Sprue: The feed opening provided in injection molding between the nozzle and cavity or runner system. [Top of Page]

Stabilizer: An agent used in compounding some plastics to assist in maintaining the physical and chemical properties of the compounded materials at suitable values throughout the processing and service life of the material and/or the parts made therefrom.Top of Page

Stack Molds: Two or more molds of a similar type that are positioned one behind the other to allow for additional parts to be manufactured during a cycle. [Top of Page]

Stationary Platen: The large front plate of an injection molding press to which the front plate of the mold is secured. This platen does not move during normal operation. [Top of Page]

Stiffness: The capacity of a material to resist elastic displacement under stress. [Top of Page]

Strain: In tensile testing, the ratio of the elongation to the gage length of the test specimen, that is, the change in length per unit of original length. [Top of Page]

Stress Concentrators: abrupt changes in geometry of the part serve as the focus of high stresses. Various means can be devised to relieve the abruptness of the geometric changes and thus the stresses. [Top of Page]

Stress Cracking: There are three types of stress cracking: 1. Thermal stress cracking is caused by prolonged exposure of the part to elevated temperatures or sunlight. 2. Physical stress cracking occurs between crystalline and amorphous portions of the part when the part is under an internally or externally induced strain. 3. Chemical stress cracking occurs when a liquid or gas permeates the partís surface. All of these types of stress cracking have the same end result: the splitting or fracturing of the molding. [Top of Page]

Stress Relaxation: The decay of stress at a constant strain [Top of Page]

Stress: The force producing or tending to produce deformation in a body measured by the force applied per unit area. [Top of Page]

Stress-Crack: External or internal cracks in a plastic caused by tensile stresses less than that of its shorttime mechanical strength. Note: The development of such cracks is frequently accelerated by the environment to which the plastic is exposed.

Stress-Strain Curve: The curve plotting the applied stress on a test specimen versus the corresponding strain. Stress can be applied through shear, compression, flexure, or tension. [Top of Page]

Striations: Marks evident on the molded-part surfaces that indicate melt flow directions or impingement. [Top of Page]

Strings: Strings of material due to poor gate cut off. see pulled gate. [Top of Page]

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. [Top of Page]

Structural Foam Molding: The process of molding thermoplastics articles with a cellular core and integral solid skins in a single operation. [Top of Page]

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, whereas conventional edge gating has the opening machined into the surface of the mold. See tunnel gate. [Top of Page]

Subgate: Entrance to the part from the runner located below the parting line. On ejection the part breaks away from the subgate. [Top of Page]

Suck-back: When the pressure on the sprue is not held long enough for the melt to cool before the screw returns. Some of the melt in the cavities or runner system may expand back into the nozzle and cause sinks marks on the finished part. [Top of Page]

T

Tab Gate: A small removable tab about the same thickness as the molded item, but usually perpendicular to the part for easy removal. [Top of Page]

Tackifiers: Additives used to enhance the adhesiveness or bonding ability of a material. [Top of Page]

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

Tensile Strength, Break: The maximum stress that a material can withstand without breaking when subjected to a stretching load. [Top of Page]

Tensile Strength, Yield: The maximum stress that a material can withstand without yielding when subjected to a stretching load. [Top of Page]

Tensile Strength: The maximum tensile stress sustained by the specimen during a tension test. [Top of Page]

Thermal Conductivity: Ability of a material to conduct heat. [Top of Page]

Thermal Degradation: Deterioration of the material by heat, characterized by molecular scission. [Top of Page]

Thermal Shut-Off: Material freezes causing blockage. [Top of Page]

Thermoelasticity: Rubber-like elasticity exhibited by a rigid plastic resulting from an increase in temperature. [Top of Page]

Thermoforming: The process of forming a thermoplastic sheet into a three-dimensional shape by clamping the sheet in a frame, heating it to tender it soft and flowable. Then applying differential pressure to make the sheet conform to the shape of a mold or die positioned below the frame. [Top of Page]

Thermoplastic Elastomers: The family of polymers that resemble elastomers in that they can be repeatedly stretched without distortion of the unstressed part shape, but are true thermoplastics and thus do not require curing. [Top of Page]

Thermoplastic: Material that will repeatedly soften when heated and harden when cooled. [Top of Page]

Thermoset: A polymer that doesn't melt when heated. Thermoset polymers "set" into a given shape when first made and afterwards do not flow or melt, but rather decompose upon heating. They are often highly cross-linked polymers, with properties similar to those of network covalent solids, i.e., hard and strong. [Top of Page]

Tie-Bar Spacing: The space between the horizontal tie-bars on an injection molding machine. Basically, this measurement limits the size of molds that can be placed between the tie-bars and into the molding machine. [Top of Page]

Time scan: Effects of mold and melt temperature and injection time changes on pressure, stress and temperature at the end of flow. [Top of Page]

Toggle: A type of clamping mechanism that exerts pressure by applying force on a knee joint. A toggle is used to close and exert pressure on a mold in a press. [Top of Page]

Tonnage: The measure by which injection molding machines are typically categorized, representing the clamping force of the injection molding machine. [Top of Page]

Tool: In injection molding, the term sometimes used to describe the mold. [Top of Page]

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. [Top of Page]

Transition Temperature: The temperature at which a polymer changes from (or to) a viscous or rubbery condition (or from) a hard and relatively brittle one. [Top of Page]

Tunnel Gate: See submarine gate. [Top of Page]

U

UL Temperature Index: The maximum temperature below which a material maintains its electrical and mechanical integrity over a reasonable period. [Top of Page]

Ultimate Elongation: In a tensile test the elongation at rupture. [Top of Page]

Ultimate Strength: Term used to describe the maximum unit stress a material will withstand when subjected to an applied load in a compression, tension, flexural, or shear test. [Top of Page]

Undercut: A protuberance or indentation that impedes withdrawal from a two-piece rigid mold. [Top of Page]

Underflow: The dominant flow of two confronting flows, over the other. The lesser flow reverses direction giving poor surface appearance and structural strength. Underflow should be avoided by positioning gates so that the flow fronts meet at the end of filling. [Top of Page]

Unidirectional Flow Pattern: Plastic flowing in one direction with a straight flow front throughout filling. [Top of Page]

Uniform Cooling Time: Cooling time the same throughout the part to avoid warping. [Top of Page]

V

Vacuum Forming: A process whereby a heated plastic sheet is drawn against a mold surface by evacuating the air between it and the mold. [Top of Page]

Valve Gating: A type of gate where a pin is held in the gate or channel by spring tension. As the injection stroke moves forward, this gate compresses the plastic in the runner. When this pressure build-up is sufficient to overcome the spring tension, the pin is then pushed back (pulled) and the fast decompression of the melt fills the cavity at extremely high speed. [Top of Page]

Vent: A shallow channel or opening cut in the cavity to allow air or gases to escape as the melt fills the cavity. [Top of Page]

Vented Barrel: Special barrel unit with a vent port over the compression section of the screw to permit escape of gases prior to injecting melt into mold. Often used when molding moisture-sensitive resins. [Top of Page]

Vertical Flash Ring: The clearance between the force plug and the vertical wall of the cavity in a positive or semi-positive mold. Also the ring of excess melt which escapes from the cavity into this clearance space. [Top of Page]

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. [Top of Page]

Virgin Material: Any plastic compound or resin that has not been subjected to use or processing other than that required for its original manufacture. [Top of Page]

Viscoelasticity: This property, possessed by all plastics to some degree, dictates that while plastics have solid-like characteristics such as elasticity, strength and form-stability, they also have liquid-like characteristics such as flow depending on time, temperature, rate and amount of loading. [Top of Page]

Viscosity: Resistance to flow of a liquid. [Top of Page]

W

Warpage: ADistortion caused by nonuniform internal stresses. [Top of Page]

Water Absorption: The amount of water absorbed by a plastic article when immersed in water for a stipulated period of time. All plastics will absorb moisture to some extent. [Top of Page]

Weld Line: Where melted material flows together during molding to form a visible line or lines on a finished part that may cause weakening or breaking of the component. [Top of Page]

Wisps: Similar to stringing but smaller in size. These also may occur as slight flashing when the mold is over packed or forced open slightly. Mold-parting-line wear or misalignment can also cause wisps. [Top of Page]

Vertical Flash Ring: The clearance between the force plug and the vertical wall of the cavity in a positive or semi-positive mold. Also the ring of excess melt which escapes from the cavity into this clearance space. [Top of Page]

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. [Top of Page]

Y

Yellowness Index: A measure of the color on the yellow scale. [Top of Page]

Yield Point: In tensile testing, yield point is the first point on the stress-strain curve at which an increase in strain occurs without an increase in stress. [Top of Page]

Yield Strength: The stress at which a material exhibits a specified limiting deviation from the proportionality of stress to strain. [Top of Page]

Young's Modulus: The ratio of tensile stress to tensile strain below the proportional limit. [Top of Page]