Blog Glossary

LSR and Injection Molding Glossary

Abrasion: the process of scraping or wearing away.

Abrasion Resistance: the ability of a material to resist mechanical wear; an attribute of Liquid Silicone Rubber (LSR).

Absorption: the uptake of a substance.

Accelerator: a chemical that speeds the vulcanization of an elastomer, so that it takes place in a shorter period of time or at a lower temperature.

Adhesion: the action or process of binding to a surface or object; for LSR, the tendency to stick to a contact surface, resulting from chemical or physical interlocking.

After Cure: the uncontrolled continuation of vulcanization after the desired cure is effected and after removal of the heat source; note: not the same as Post Cure.

Aging: the change of the characteristics of LSR or other materials after exposure to light or heat.

Ambient Temperature: the surrounding temperature relative to the given point of application.

American Society of Testing Materials (ASTM): an international standards organization which evaluates and publishes standards for materials and processes.

Assembly Injection Molding: see Two Shot Injection Molding.

Autoclave: a strong, heated container used for chemical reactions and other processes involving high pressures and temperatures.

Backrind: the distortion at the parting line, usually in the form of a ragged indentation.

Bake-Out: the process whereby a vacuum system is heated for a given time at a predetermined temperature to de-gas components such as gauges, fittings, valves, seals, etc.

Batch: a quantity or consignment of goods produced at one time.

Blister: a raised spot or bubble on a material’s surface, or a separation between layers, usually forming a void or air-filled pocket in the vulcanized article.

Bloom: a dusty or milky-looking deposit caused by migration of a liquid or solid to the surface; may occur after curing when excess additives are blended within the rubber; also known as bleeding.

Break-Out: the amount of frictional force required to start a body in motion over a surface.

Bundesinstitut für Gesundheitlichen Verbraucherschutz und Veterinärmedizin (BgVV): German Federal Institute for Consumer Health Protection and Veterinary Medicine; in 2002, the BgVV dissolved into two entities: the Bundesinstitut für Risikobewertung (BfR) and the Bundesamt für Verbraucherschutz und Lebensmittelsicherheit (BVL).

Bundesinstitut für Risikobewertung (BfR): German Federal Institute for Risk Assessment; the scientific agency responsible for assessing the safety of food, feed, substances, and products.

Bundesamt für Verbraucherschutz und Lebensmittelsicherheit (BVL): German Federal Office of Consumer Protection and Food Safety; like the FDA in the US, the BVL makes recommendations applicable for medical and food applications.

Catalyst: the chemical that triggers or accelerates the cure of LSR; does not usually become a component of the end product.

Cavity: the hollowed-out portion of a set of molds that will be used in shaping a container as it is formed on a bottle machine.

Chemical Bonding: an attraction between atoms or molecules, resulting in the formation of a chemical compound.

Coefficient of Thermal Expansion: describes the expansion of an object with changes in temperature and may be linear or volumetric; the coefficient of linear thermal expansion is the change in length per unit of length for a one degree rise in temperature; the coefficient of volumetric thermal expansion is the change in volume divided by the product of the original volume and the change in temperature.

Compound: the mixture of polymers and other ingredients to produce a usable rubber material.

Compression Modulus: the ratio of compression stress (force) to the resulting compression strain (noted as a percentage of the original specimen thickness).

Compression Molding: a thermoset molding technique in which the uncured LSR compound is put in a heated, open mold cavity and the mold is closed under pressure (often in a hydraulic press); the material flows to completely fill the cavity and pressure is maintained until curing is complete.

Compression Set: the amount by which a rubber specimen fails to return to its original shape after the release of a compression load; the numerical value is the percentage of the amount compressed that does not return.

Co-Polymer: a polymer consisting of two different monomers chemically combined.

Cracking: the sharp breaks or fissures in a rubber surface caused by excessive strain and/or exposure to detrimental environmental conditions, such as ozone, weather, or ultraviolet (UV) light; also known as crazing.

Creep: the increasing deformation of a rubber material under a constant compressive load; also known as cold flow.

Cross-link: bonds that link one polymer chain to another.

Cure: the heat- or mixing-induced process whereby long chains become cross-linked by a vulcanizing agent to form three-dimensional elastic structures. This reaction transforms soft, weak, non-cross-linked materials into strong elastic products; also known as Vulcanization.

Cure Date: the date when the rubber product was molded (e.g., 1Q01 means the 1st quarter of the year 2001).

Cure Moderator: a substance that delays or controls the rate of the cure.

Daylight Opening: the distance between two edges of the open mold.

Deflashing: the various processes used to remove the waste edge from a molded part.

Dielectric Strength: the maximum electric field that a material can withstand without breaking down.

Durometer: an instrument for measuring the hardness of rubber by its resistance to surface penetration of an indenter point; also the numerical scale indicating the hardness of rubber (e.g., Shore A Durometer).

Elasticity: the property of an article which tends to return to its original shape after deformation or the extent to which it tends to do so.

Elastomer: any synthetic or natural material with resilience or memory sufficient to return to its original shape after major or minor distortion.

Elongation: generally, “Ultimate Elongation,” or the percent of increase in original length of a specimen at time of break.

Endothermic: a reaction that requires heat; absorbing heat.

Exothermic: a reaction that releases heat such as vulcanization or cure; releasing heat.

Fiber Reinforced: describes a structural matrix of materials used in polymers to gain structural support.

Filler: the chemically inert, finely divided material added to the elastomer to aid in the processing and improvement of physical properties.

Flash: the excess rubber remaining around a rubber part after molding due to space between mating mold surfaces.

Food and Drug Administration (FDA): the US body which regulates medical and food applications.

Gate: the point of rubber entry into a mold cavity.

Goniometer: an instrument used for the precise measurement of angles.

Hardness: resistance to a distorting force, measured by the relative resistance of the material to an indented point of a standard hardness-testing instrument.

Hardness, Shore A: rubber durometer hardness as measured on a Shore “A” gauge; higher numbers indicate harder material (e.g., 30 shore is soft, 90 shore is hard).

Heat Resistance: the capacity of a rubber compound to undergo exposure to a specified level of elevated temperature while retaining a large majority of its original properties.

High Cure Rubber (HCR): rubber that is processed on a rubber mill having much higher viscosity than liquid silicone rubber (LSR); belongs to the HTV family.

High Temperature Vulcanization (HTV): high-temperature-curing rubbers.

Hydrolysis: the chemical breakdown of a compound due to its reaction with water.

Hydrophilic: having a tendency to mix with or be wetted by water.

Hydrophobic: having a tendency to repel or fail to mix with water.

Hysteresis: the phenomenon in which the value of a physical property lags behind the changes in the effect causing it.

Injection Molding: a process in which preheated rubber is injected under pressure from the heating chamber through a series of runners and sprues and into a closed, heated mold cavity, where it is then vulcanized; injection molding is ideal for high-volume, high-precision production of molded rubber parts.

In-Mold: refers to the processing of two materials within the same mold to form a component with parts of multiple materials; see Two Shot Injection Molding.

Innovation: the introduction of something new, whether an idea, method, or device. Innovation can involve the creation of a new idea or method, or a creative change to an existing idea or process. Specifically, the creation of more effective products, processes, or methods and making them available to markets and society at large.

Liquid Injection Molding (LIM™): refers to the processing of liquid silicone rubber (LSR).

Liquid Silicone Rubber (LSR): the silicone rubber utilized in the LIM™ process; the liquid form of HTV.

Low Temperature Flexibility: the ability of an elastomeric product to resist cracking or breaking when flexed or bent at low temperatures.

Material Safety Data Sheet (MSDS): a form containing data regarding the various properties of a particular substance.

Maximum Cure: the point at which an elastomer has reached its highest degree of cure.

Mechanical Bond: a form of adhesion in which material physically locks into the crevices of the surface of another material.

Melt Flow Index: a measure of the ease of flow for the melt of a thermoplastic polymer.

Millable Gum Rubber: rubber that is processed on a rubber mill having a much higher viscosity than liquid silicone rubber (LSR); as also known as high consistency rubber.

Mismatch: the misalignment of the halves coming together in a mold.

Modulus: the tensile stress at a specified elongation (usually 100% elongation for elastomers).

Modulus of Elasticity: the ratio of the stress (force per unit area) to the strain (increase in length per initial length) as measured on a rubber specimen; also known as Young’s Modulus (E).

Mold: to shape or process a material into a usable form (verb); the metal tools, usually steel or aluminum, machined and assembled so as to create openable cavities for the purpose of shaping and vulcanizing rubber (noun).

Mold Cavity: a hollow space within the mold in which uncured rubber is shaped and vulcanized; also known simply as a Cavity.

Mold Finish: an uninterrupted surface produced by the intimate contact of rubber with the surface of the mold at vulcanization.

Mold Shrinkage: the dimensional loss in a molded rubber product that occurs during cooling, after it has been removed from the mold.

Monomers: the unit of a chemical compound that is polymerized into a polymer.

Mooney Viscometer: a shearing disk device used to gauge the viscosity of a rubber sample under heat and pressure. Named for developer Melvin Mooney, this was once the standard tool for determining processing characteristics, but has now largely been replaced by the Rheometer.

Moving Die Rheometer (MDR): an instrument used to measure the cure degree of liquid silicone rubber (LSR) and rubber by a percentage of maximum torque, utilizing heated die.

Multi-Component Injection Molding: see Two Shot Injection Molding.

Nitrile Butadiene Rubber (NBR): a material with a wide temperature resistance that is resistant to oil, fuel, and other chemicals.

Occlusion: the mechanical process by which vapors, gases, liquids, or solids are entrapped within the folds of a given substance during working or solidification.

Oil Resistant: the ability of a vulcanized rubber to resist the swelling and deterioration effects of various types of oils.

Oil Swell: the change in volume of a rubber article due to absorption of oil or other fluids.

Oscillating Disk Rheometer (ODR): an instrument used to measure the cure degree of liquid silicone rubber (LSR) and rubber by a percentage of maximum torque, utilizing an oscillating rotor.

Outgassing: a vacuum phenomenon wherein a substance spontaneously releases volatile constituents in the form of vapors or gases. In rubber compounds, this may include water vapor, plasticizers, air, inhibitors, etc.

Over Cure: when a longer than optimum vulcanization causes some properties to be thermally degraded. There are two types of over cure: (a) the material continues to harden, the modulus rises, and both tensile strength and elongation fall; and (b) the rubber begins to break down, the material softens, and the modulus, tensile strength, and elongation all decrease.

Overflow: a spot for excess material during molding.

Over-Molding: see Two Shot Injection Molding.

Parting Line: the place at which two (or more) parts of the mold meet.

Permanent Set: the deformation remaining after a specimen has been stressed in tension for a definite period and released for a definite period.

Permeability: the rate at which a liquid or gas under pressure passes through a solid material by diffusion and solution. In rubber terminology, it is the rate of gas flow expressed in atmospheric cubic centimeters per second through an elastomeric material one centimeter square and one centimeter thick (atm cc/cm squared / cm/sec).

Pigment: the material, usually a powder or paste, used to color rubber.

Polymer: a material formed by the joining of many (poly) individual units (mer); i.e., of one or more monomers.

Post Cure: the controlled continuation of vulcanization (usually in an oven) to complete the curing process; provides stabilization of parts and drives off decomposition products resulting from the vulcanization process.

Pot Life: the period of time after mixing a two component system wherein the material retains sufficiently low viscosity for processing.

Purging: the flushing or removing of material.

Resilient: being capable of returning to original size and shape after deformation.

Reversion: the condition in an elastomer caused by thermal or chemical attack whereby chemical bonds are broken with a resulting loss in physical properties.

Rheometer: a cure meter which determines the state of cure for a given time and temperature by measuring the viscosity of the vulcanizing rubber; typically either an Oscillating Disk Rheometer (ODR) or a Moving Die Rheometer (MDR).

Room Temperature Vulcanization (RTV): generally silicone rubber, which after mixing will cure when exposed to air at low temperatures; comes as a soft paste or a viscous liquid.

Rubber, Natural: raw or crude rubber obtained from vegetable sources.

Rubber, Synthetic: manufactured elastomers.

Runner: the distribution system within a ; connects the Sprue to the Gates.

Styrene Butadiene Rubber (SBR): material with very good resilience and tensile strength, but poor ozone and oil resistance.

Screw: the rotating component of an injection molding machine which delivers the material into the mold.

Scorching: the premature curing or setting up of raw compounding during processing.

Shore A Durometer: an instrument used to gauge soft to medium hard rubber based on its resistance to a frustum (truncated) cone indenter point; most accurate for materials below 90 Shore A.

Shore D Durometer: an instrument used to gauge hard rubber based on its resistance to a sharp 30° angle indenter point; most accurate for materials at or above 90 Shore A.

Shrinkage: the decreased volume of material; usually caused by extraction of soluble constituents by fluids followed by air-drying.

Silicone Rubber: an elastomer that retains beneficial properties through an extra wide temperature range.

Specific Gravity: the ratio of the weight of a given substance to the weight of an equal volume of water at a specified temperature.

Sprue: the initial entry point of rubber into a mold. In a simple molding.

Weld Lines: the point at which two different flow fronts meet in the molding process.

Young’s Modulus (E): a measure of material stiffness; defined as the ratio of the stress to the strain (increase in length relative to initial length) as measured on a rubber specimen; also known as Modulus of Elasticity; not the same as tensile modulus.