glosary

 

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

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

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

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

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

Antioxidant: 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.

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.

Assembly: The process of joining parts by any of several methods.

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.

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

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

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.

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.

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

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.

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.

Brighteners: Are used to add smoother or brighter coatings or finishes.

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.

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.

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.

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.

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.

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

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.

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

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.

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

Co-Injection: Simultaneous or near simultaneous injection of multiple materials.

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

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.

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.

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

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

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

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.

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

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

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.

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

Cycle: complete, repeating sequence of operations for injection molding a part.

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

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.

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.

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.

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

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

Ejector Rod: A bar that actuates the ejector assembly when the mold opens.

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

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

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.

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

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

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.

Finish: The surface texture and appearance of a finished article.

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

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.

Flow Pattern: The contour the melt takes sequentially as it fills the cavity.

Flow Rate: the volume of material passing a fixed point per unit time.

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

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

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.

Homopolymer: Plastic that results from the polymerization of a single monomer.

Impact Modifiers: Additive used to enhance the material´s ability to withstand the force of impact.

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

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

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.

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.

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

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.

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

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

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

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.

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

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.

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

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

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

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

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.

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

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.

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.

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.

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

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

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

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.

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

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.

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.

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 parts surface. All of these types of stress cracking have the same end result: the splitting or fracturing of the molding.

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

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.

Thermoplastic: material that will repeatedly soften when heated and harden when cooled.

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.

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

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.

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.

Unidirectional Flow Pattern: Plastic flowing in one direction with a straight flow front throughout filling.

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