Injection Molding Glossary

The ability of a material to withstand mechanical actions such as rubbing, scraping, or erosion, that tend progressively to remove material from its surface.

Runner systems designed for high pressure drops to minimize material usage and increase frictional heating in the runner.

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

The process of joining two or more plastic parts by means of an adhesive.

The process of, or the results of, exposure of plastics to natural or artificial environmental conditions for a prolonged period of time.

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.

A term used in the plastics industry to denote blends of polymers or copolymers with other polymers or elastomers. – i.e. ABS/Polycarbonate.

The temperature of a medium surrounding an object. The term is often used to denote prevailing room temperature.

Devoid of crystallinity or stratification. Most plastics are amorphous at processing temperatures. Material assumes more random molecular structure when cooling.

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.

Abbreviation for American National Standards Institute.

Additive used to reduce degradation from oxygen attack at normal or elevated temperatures. Sources such as heat, age, chemicals, and/or stress may accelerate oxygen attack.

These additives are used to prevent the negative effects of ozone on the resin materials.

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.

The act of applying or putting to use. What the molded plastic article will be in its final form. 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.

The solid residue remaining after a substance has been incinerated or heated to a temperature sufficient to drive off all combustible or volatile substances.

Ratio of total flow length to average wall thickness. Assembly: The process of joining parts by any of several methods.

Abbreviation for American Society for Testing and Materials.

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.

molten resin flows back out of the mold returning to the runners.

A plate used as a support for the mold cavity block, guide pins, bushings, etc.

A runner system designed to place all cavities at the same distance from the sprue.

The section of a molding machine that contains the feed screw, also the section where resin heating and mixing occurs.

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.

Additives that are used to inhibit the growth and colonization of fungus, bacteria, and other pests.

A specific kind of inclusion/contamination often associated with heat-degraded materials.

The process of removing flash from molded objects and/or dulling their surfaces, by impinging upon them with sufficient force to remove the flash.

An imperfection on the surface of a plastic article caused by a pocket of air or gas beneath the surface.

These additives are used to prevent the adhesion and agglomeration of ingredients within a resin compound.

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.

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.

Additives for plastics or rubbers that generate inert gases within the resin matrix when heated. The resulting part construction will contain a cellular structure.

The tendency of a plastic article to turn white or chalky in areas that are highly stressed.

A raised feature of a molded part designed to add strength, facilitate alignment during assembly or for attachment to another part.

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.

Are used to add smoother or brighter coatings or finishes.

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.

Part surface defects caused by mold damage. Bubbles: Air or gas pockets that have formed in the material of the component. Bubbles may vary in size.

A measurement of mass per unit volume of materials (such as powders) that describes the effects of the particle packing density.

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.

Showing evidence of excessive heating during processing or use of a plastic, as evidenced by blistering, discoloration, distortion or destruction of the surface.

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.

A depression, or a set of matching depressions, in a plastics-forming mold which forms the outer surfaces of the molded articles.

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.

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.

A type of fiber reinforcement consisting of strands of individual glass fibers which have been chopped into short pieces.

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.

The largest rated molding area an injection press can hold closed under full molding pressure.

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.

A plate fitted to a mold and used to fasten the mold to a platen.

The pressure applied to the mold to keep it closed during the molding cycle.

Additive used in resins to improve transparency or translucency.

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.

The change in length of a material for a unit change in temperature, per unit of length.

Simultaneous or near simultaneous injection of multiple materials.

Imperfections within the part wall due to thickening or solidification of resin prior to full cavity fill.

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. Colorant (also known 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.

A mixture of resin(s) and additives usually formed in a separate machine downstream from the primary reactor.

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.

The ability of a material to sustain a force in a direction opposite of tension.

Subjecting a material to standard environmental and/or a non-standard stress state prior to testing or use.

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.

The highest temperature at which a material can perform reliably in long term application – as defined by the manufacturer.

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.

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)

Channels located within the body of a mold through which a cooling medium is circulated to control the mold surface temperature.

the elapsed time required for the melt to reach its Vicat softening temperature.

The chemical reaction of two different monomers with each other, result in a unique new polymer.

A protrusion, or set of matching protrusions, in a plastics forming mold which forms the inner surfaces of the molded articles.

Impingement of AC power on a component to bombard with free radicals thus improving the ability to bond to a surface.

A broad term applying to the ability of plastics to resist degradation in many environments, usually die to oxidation.

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.

A physical separation or tearing of the part.

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.

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.

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

Reduction of parts to very low temperatures usually associated with liquid nitrogen. Commonly used to create assemblies or to deflash or degate a part.

A homogeneous solid having an orderly and repetitive three-dimensional arrangement of its atoms.

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.

Abbreviation for the Canadian Standards Association.

This term describes the final stage of the reaction where a thermoset material is relatively insoluble and infusible.

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.

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.

The time required by an injection molding system to mold a part and return to its original position/state.

Complete, repeating sequence of operations for injection molding a part.

The effect on a mass that causes decreasing amplitude. Deflection Temperature: The measurement of temperature at which a specimen deflects to a set point under a defined load.

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.

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.

When the surface of a finished part separates. Strata or fish-scale-type appearance may be visible where the layers may be separated.

Mass per unit volume of a substance.

A review of a blueprint, of an application, to be molded in a plastic material, with recommendations given for design, material, processing, tooling.

Used in symmetrical cavity filling to reduce weld-line formations and improve filling rates.

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

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.

Retention of the precise shape of the part.

A sprue that feeds directly into the mold cavity. Discoloration: Any change from the designated color of the material or component.

Flow alteration components placed at the entry point of an additive to aid in mixing or dispersing actions of a compounding process.

At the juncture of two confronting flows the dominant flow will reverse the direction of the other.

A Slight taper in a mold wall designed to facilitate removal of the molded object from the mold.

A form of deep scratch or scratches on the surface of the component usually caused by the ejection of the part.

The extrudation or leakage of molten resin from nozzle or nozzle sprue bushing area while filling or shooting the mold.

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

An instrument used for measuring the hardness of a material.

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.

entrance to the part from the runner located on the parting line.

A residual mark on the part caused by the profile of the ejection pin.

A rod, pin or sleeve that pushes a molded part off of a core or out of a cavity of a mold.

Projections that push the ejector assembly back as the mold closes. Also called surface pins or return pins.

A bar that actuates the ejector assembly when the mold opens.

A characteristic of certain plastics evidenced by their tendency to revert to a previously existing shape or dimension.

The ability of a material to quickly recover its original dimensions after removal of a load that
has caused deformation.

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.

a triangle defined by at least three nodes, creating the basis for the finite element analysis.

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.

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.

A broad term covering plastics, with or without fillers or reinforcements, which have improved mechanical, chemical and thermal properties over commodity grades of resins.

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

The product or material delivered from an extruder, for example, film, pipe profiles.

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.

A mold that produces non-identical parts simultaneously from multiple cavities.

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.

The maximum cyclic stress a material can withstand for a given number of cycles before failure occurs.

the contours of the advance of the material as the cavity fills. (See flow pattern)

the pressure required to fill the cavity.

Time required to fill the cavity or mold.

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.

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.

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.

The surface texture and appearance of a finished article.

The solution of simultaneous equations for each element with resulting pressure, temperature and elapsed time at each node.

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.)

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

Any excess material that is formed with and attached to the component along a seam or mold parting line.

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.

The measure of resistance of the material to fracture during bending.

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.

Modifying flow paths, particularly runner sections, so that all flow paths within a mold fill in equal time with equal pressure.

Local increase in thickness to encourage flow in a particular direction.

Wavy surface appearances on a molded part caused by improper flow of the melt into the mold.

The contour the melt takes sequentially as it fills the cavity.

The volume of material passing a fixed point per unit time.

Any substance which alone or in combination with other substances is capable of producing a cellular structure in a plastic mass.

The separation of a body, usually characterized as either brittle or ductile.

the temperature of the material is reduced to the point that it blocks an area it would fill if it were hotter.

Heat generated by the friction of the chains of molecules slipping past each other or over a surface.

A blemish or disturbance in the gate area of an injection molded article.

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.

The channel through which the molten resin flows from the runner into the cavity.

A family of reinforcing materials for reinforced plastics based on single filaments of glass.

Change in an amorphous polymer from viscous to hard and relatively brittle.

A substance or mixture of substance added to a material to increase or control the curing reaction by taking part in it.

The resistance of a material to compression, indentation and scratching.

The cloudy appearance of a material caused by light scattered from within the specimen or from its surfaces.

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.

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.

Plastic that results from the polymerization of a single monomer.

Auxiliary equipment that removes moisture from resin pellets.

Auxiliary equipment for automatically loading resin pellets into machine hopper.

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.

Readily absorbs moisture.

Additive used to enhance the material’s ability to withstand the force of impact.

The resistance of plastic articles to fracture under stresses applied at high speeds.

The ability of a material to withstand shock loading.

Time required to fill the cavity or mold.

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

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

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.

The pressure on the face of the injection screw or ram when injecting material into the mold, usually expressed in PSI.

Insert molding is the process of molding plastic around preformed metal inserts. This process is compatible with both thermoplastic and thermoset materials.

Aa removable part of the mold imparting increased resistance to wear, heat transferability, or changeable part shape to that area of the mold.

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.

A line of equal pressure. Any point along an isobar sees the same cavity pressure as any other point along the same isobar.

A line of equal time. Any point along an isochrone is filled at the same time as any other point along the same isochrone.

A line of equal temperature. Any point along an isotherm is at the same temperature as any other point along the same isotherm.

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.

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.

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 4000).

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

A turbulent flow in the melt caused by an undersized gate or where a thin section rapidly becomes thicker.

A tool for holding parts of an assembly during the manufacturing process.

A term sometimes used for thermal insulation value or coefficient of thermal conductivity.

Where melted material flows together to form a line or lines that may cause weakening or breaking of the component.

A pin that ejects a molded article from the mold.

Gate dimension parallel to the direction of melt flow.

The area of surfaces of a mold which contact each other when the mold is closed.

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.

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

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

The ability of a plastic to be bent without fracture at reduced temperatures.

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.

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

The resistance of glossy plastic surfaces to abrasive action.

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

Documentation regarding the toxicity or hazards associated with contact with some substances. The manufacturer of the plastic prepares these data sheets.

Properties of plastics which are classified as mechanical include abrasion resistance, creep, ductility, friction resistance, elasticity hardness, impact resistance, stiffness and strength.

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.

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.

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 0-1238)

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.

The tendency of a plastic article to revert in dimension to a size previously existing at some stage in its manufacture.

A term covering all processes by which plastics are coated with metal.

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.

Inorganic substances used as filler for plastics. Some common examples are: clay, mica, talc.

The minimum values, usually of mechanical properties, that a compound must meet by Quality Assurance prior to shipment.

The ratio of compressive stress to strain within elastic limits of the material.

The ratio of the flexure stress to strain, within elastic limits of the material.

The ratio of shear stress to strain within elastic limits of the material.

The ratio of stress to corresponding strain below the proportional limit of a material in tensile testing.

The energy that can be absorbed per unit volume without creating a permanent distortion.

Derived from the Latin word meaning “small measure”, modulus is the ratio of stress to strain in the linear region of the s-e curve.

The pick-up of moisture from the environment by a material.

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.

To impart shape to a plastic mass by means of a confining cavity or matrix.

An automated device for removing one mold from a machine and replacing it with another mold.

A series of steel plates which contain mold components, including cavities, cores, runner
system, cooling system, ejection system, etc.

Excess use of mold release may leave parts oily and weaken the material.

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.

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.

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

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.

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

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.

The range of molding conditions under which a part can be successfully molded.

Auxiliary equipment used to control mold temperature. Some units can both heat and cool the mold. Others, called chillers, only cool the mold.

The sum of the atomic weights of all atoms in a molecule. Especially in plastics an average molecular weight is reported.

The smallest unit quantity of matter which can exist by itself and retain all of the properties of the original substance.

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.

The platen of an injection molding machine that is moved by a hydraulic ram or mechanical toggle.

A mold having two or more impressions for forming finished items in one machine cycle.

flow direction changes during filling resulting in orientation in different directions which can cause flow marks, stresses and warping.

produces more than one identical part with each cycle.

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)

Each succession of runner is identical to the runners in the same succession in all other flows in the mold.

A retainer plate in the mold with a depressed area for cavity blocks.

Failure to completely fill the mold or cavities of the mold. Edges may appear melted.

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).

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.

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.

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.

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

Not able to transmit light.

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.

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.

opening.

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.

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.

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.

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- or under-packing results in less than optimum fill.

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.

Composed of both naturally and artificially balanced runners.

Mark on the part indicating where the two halves of the mold met in closing.

An open blister.

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.

Degradation of plastics due to the action of light.

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.

A restricted gate of 0.030 in or less in diameter, this gate is common on hot-runner molds.

See ram.

An imperfection, a small crater in the surface of the plastic.

A change in dimensions of an object under load that is not recovered when the load is removed.

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.

The ability of a material to withstand continuous and permanent deformation by stresses exceeding the yield value of the material without rupture.

To render a material softer, more flexible and/or more moldable by the addition of a plasticizer.

A substance or material incorporated in a material (usually a plastic or an elastomer) to increase its flexibility, workability or extensibility.

The mounting plates of a press on which the mold halves are attached.

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 orplasticizer.

graphical representations of analysis results.

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.

A general term referring to the relative positions, arrangement in space, and freedom of motion of atoms in a polymer molecule.

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.

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.

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.

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.

Additives specifically used to improve the injection process.

The greatest stress which a material is capable of sustaining without deviation from proportionality of stress and strain. (Hooke’s Law).

A preliminary mold built upon which the final mold will be based.

Area where the part was connected to the sprue or runner that has been drawn out or stretched from the surface.

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.

Where the ejector site is either heightened or raised above the surface of the component.

The forward motion of the screw in the plasticator barrel that forces the melt into the mold cavity.

The ability of a plastic to withstand exposure to chemicals.

The length of time for the screw to rotate, create a shot, and return to original position.

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.

A plastic composition in which fibrous reinforcements are imbedded, with strength properties greatly superior to those of the base resin.

a material sprayed on the mold which facilitates removing the part.

The term is use to designate any polymer that is a basic material for plastics.

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.

The plate on which demountable pieces, such as mold cavities, ejector pins, guide pins and bushings are mounted during molding.

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.

A reinforcing member of a molded part.

Used on some cylindrical shapes. This gate encircles the core to permit the melt to first move around the core before filling the cavity.

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.

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 ahigher 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.

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.

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.

This term is sometimes used for the entire resin feeding system, including sprues, runners and gates, in injection molding.

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.

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.

Any output of a mold that is not usable as the primary product.

The distance the screw travels forward when filling the mold cavity.

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

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″.

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`)/0 of the tensile strength of the material. High shear stress is unimportant at gates, and in sprues and runners.

Failure to completely fill the mold or cavities of the mold. Edges may appear melted.

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.

One complete cycle of a molding machine.

The dimensional allowance which must be made in molds to compensate for shrinkage of the plastic compound on cooling.

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.

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.

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.

A relatively dense layer at the surface of the material.

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.

Additive used to provide lubrication during and immediately following processing of plastics.

Substances with the ability to dissolve other substances.

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).

The volume of a unit of weight of a material; the reciprocal of density.

Test performed by injection molding a sample into a spiral mold and used to compare the processability of different resins.

Scan or surface defects on molded part caused by abnormal racing of the melt in the 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.

A hardened-steel insert in the mold that accepts the nozzle and provides an opening for transferring the melt.

A passageway through which melt flows from the nozzle to the mold cavity.

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.

The feed opening provided in injection molding between the nozzle and cavity or runner system.

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.

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.

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.

The capacity of a material to resist elastic displacement under stress.

In tensile testing, the ratio of the elongation to the gage length of the test specimen, that is, thechange in length per unit of original length.

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.

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 pats surface. All of these types of stress cracking have the same end result: the splitting or fracturing of the molding. [jacc/] Stress Relaxation: ::
The decay of stress at a constant strain.

The force producing or tending to produce deformation in a body measured by the force applied per unit area.

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

The curve plotting the applied stress on a test specimen versus the corresponding strain. Stress can be applied through shear, compression, flexure, or tension.

Marks evident on the molded-part surfaces that indicate melt flow directions or impingement.

Strings of material due to poor gate cut off. See pulled gate.

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.

entrance to the part from the runner located below the parting line. On ejection the part breaks
away from the subgate.

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.

A small removable tab about the same thickness as the molded item, but usually perpendicular to the part for easy removal.

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

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

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

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

The maximum tensile stress sustained by the specimen during a tension test.

Ability of a material to conduct heat.

Deterioration of the material by heat, characterized by molecular scission.

Material freezes causing blockage.

Rubber-like elasticity exhibited by a rigid plastic resulting from an increase in
temperature.

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.

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.

Material that will repeatedly soften when heated and harden when cooled.

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 moldingmachine.

Effects of mold and melt temperature and injection time changes on pressure, stress and temperature at the end of flow.

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.

The measure by which injection molding machines are typically categorized, representing the clamping force of the injection molding machine.

In injection molding, the term sometimes used to describe the mold.

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

The temperature at which a polymer changes from (or to) a viscous or rubbery condition (or from) a hard and relatively brittle one.

See submarine gate.

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

In a tensile test the elongation at rupture.

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.

A protuberance or indentation that impedes withdrawal from a two-piece rigid mold.

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.

Plastic flowing in one direction with a straight flow front throughout filling.

Cooling time the same throughout the part to avoid warping.

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

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.

A shallow channel or opening cut in the cavity to allow air or gases to escape as the melt fills the cavity.

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.

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.

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

Any plastic compound or resin that has not been subjected to use or processing other than that required for its original manufacture.

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.

Resistance to flow of a liquid.

An unfilled space within a solid material.

Distortion caused by nonuniform internal stresses.

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.

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.

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.

A measure of the color on the yellow scale.

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.

The stress at which a material exhibits a specified limiting deviation from the proportionality of stress to strain.

The ratio of tensile stress to tensile strain below the proportional limit.