Rubber Terminology

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Rubber Terminology
  • Abrasion : The wearing away of a surface by mechanical action, such as rubbing, scraping or erosion.
  • Abrasion Resistance : The wearing away of a surface by mechanical action, such as rubbing, scraping or erosion.
  • Absorption : The physical mechanism by which one substance takes up another substance (liquid, gas or vapor) into its interior.
  • Accelerated Life Test : Any set of test conditions designed to reproduce, in a short time, the deteriorating effect obtained under normal service conditions.
  • Accelerator : A substance which hastens the vulcanization of an Elastomer, causing it to take place in a shorter time or at a lower temperature.
  • Acid Resistance : With stands the action of acids.
  • Adhere : To cling or stick together.
  • Adhesion : Tendency of rubber to bond or cling to a contact surface.
  • After Cure : Continuation of vulcanization after the desired cure is effected and the heat source removed (Also Referred to as Post-Cure).
  • Aging : To undergo changes in physical properties with age or lapse of time.
  • Aging, Accelerated : Tests run on various rubbers to find out, in as short a period as possible, the destructive influence of light, oxygen, heat and ozone.
  • Air Curing : Vulcanization of a rubber product in air, as distinguished from in a press or steam vulcanizer.
  • Aniline Point : The lowest temperature at which equal volume of pure, fresh aniline and oil will completely dissolve in one another is the aniline point of the oil.
  • Antidioxidant : An organic substance which inhibits or retards oxidation.
  • Antiozonant : A substance that retards or prevents the appearance of cracks from action of ozone when the Elastomer is exposed under tension, either statically or dynamically, to air containing ozone.
  • Atmospheric Aging Resistance : Loss of physical properties due to the normal action of its surroundings (weather).
  • Atmospheric Cracking : Cracks produced in the surface of rubber articles.
  • Banbury (TM) Mixer : A specific type of internal mixer used to blend fillers and other ingredients with an Elastomer.
  • Batch : The product of one mixing operation.
  • Bench Test : A modified service test in which the service conditions are approximated, but the equipment is conventional laboratory equipment and not necessarily identical with that in which the product will be employed.
  • Bleeding : Migration to the surface of plasticizers, waxes or similar materials, to form a film or bead.
  • Blister : A raised spot in the surface, or a separation between layers, usually forming void or air-filled space in the vulcanized article.
  • Bloom : A dusty or milky looking deposit that sometimes appears on the surface of an molded product after molding and storage, caused by migration of a liquid or solid to the surface. Not to be confused with dust from external sources.
  • Bond : (a) Mechanical - purely physical attachment accomplished by such means as "through" holes, interlocking fingers, envelope design, riveting, etc.
    (b) Cold - adhesion of previously vulcanized Elastomer to another member through use of suitable contact cements.
    (c) Vulcanized - adhesion of an Elastomer to a previously primed surface using heat and pressure, thus vulcanizing the Elastomer at the same time.
  • Break : A separation or discontinuity in any part of an article.
  • Break-Out : Force to inaugurate sliding. Expressed in same terms as friction. An excessive break-out value is taken as an indication of the development of adhesion.
  • Brittleness : Tendency to crack when deformed.
  • Butyl : A copolymer of iso-butylene and isoprene.
  • Calender : A machine used to form a sheet of rubber between steel rollers.
  • Cell : A single small cavity surrounded partially or completely by walls.
  • Chemical Bonding : A method of bonding rubber to inserts by applying special adhesives to the insert prior to molding.
  • Coating : A uniform layer of chemical primers or adhesives to produce a chemical bond between the rubber and substrate. May also refer to special surface treatments that can be applied to rubber to achieve special properties.
  • Cold Flexibility : Flexibility following exposure to a predetermined low temperature for a predetermined time.
  • Cold Flow : Continued deformation under stress.
  • Cold Resistance : Able to withstand the effects of cold or low temperatures without loss of serviceability.
  • Commercially Smooth : Degree of smoothness of a surface of an article which is acceptable for use.
  • Compound : A term applied to a mixture of polymers and other ingredients to produce a usable rubber material.
  • Compression Molding : Molding process in which a preload of rubber compound is normally placed directly in the mold cavity, and compressed to shape by closure of the mold.
  • Compression Set : The amount by which a rubber specimen fails to return to its original shape after release of compressive load.
  • Conductive Rubber : A rubber capable of conducting electricity. Most generally applied to rubber products used to conduct static electricity.
  • Copolymer : A polymer consisting of two different monomers chemically combined.
  • Corrosion (Packing) : Corrosion of rigid member (usually metal) where it contacts packing. The actual corroding agent is fluid medium trapped in the interface.
  • Cracking : The sharp break or fissure in the surface. Generally due to excessive strain.
  • Creep : The progressive relaxation of a given rubber material while it is under stress. This relaxation eventually results in permanent deformation, or "set".
  • Cross-Linking Agents : A chemical, or chemicals, that bonds the polymer chains together to form a thermoset rubber product.
  • Cross-Section : A seal as viewed if cut at right angles to the molding line, showing internal structure.
  • Cure : See Vulcanization.
  • Curing Temperature : The temperature at which the rubber product is vulcanized.
  • Cylinder : Chamber in which piston, plunger, ram, rod or shaft is driven by, or against, the system fluid.
  • Degassing : The intentional, but controlled, outgassing of a rubber substance or other material.
  • Dielectric Properties : The ability of a material to resist puncture due to electric stress. The property is expressed in terms of "volts per MIL thickness".
  • Diffusion : The mixing of two or more substances (solids, liquids, gasses, or combinations thereof) due to the intermingling motion of their individual molecules. Gasses diffuse more readily than solids.
  • Durometer : (A) An instrument for measuring the hardness of a rubber; measures the resistance to the penetration of an indenter point into the surface of the rubber; (B) Numerical scale of rubber hardness.
  • Dynamic : An application in which the seal is subject to movement, or moving parts contact the seal.
  • Dynamic Seal : A seal required to prevent leakage past parts which are in relative motion.
  • Elasticity : The property of an article which tends to return to its original shape after deformation.
  • Elastomer : Any natural or synthetic material with resilience or memory sufficient to return to its original shape after major or minor distortion.
  • Elongation : Generally means "ultimate elongation", or percent increase in original length of a specimen when it breaks.
  • EPDM : (EPT, Nordel [TM, DuPont Co.]): Terpolymer of Ethylene-Propylene-Diene (noted for excellent ozone resistance).
  • Evaporation : The direct conversion from liquid to vapor state of a given fluid.
  • Extrusion : Distortion or flow, under pressure, of a portion of a seal into clearance between mating parts.
  • Flame Resistance : The resistance to burning of material that will not withstand combustion under ordinary conditions.
  • Flex Cracking : A surface cracking induced by repeated bending or flexing.
  • Flex Resistance : The relative ability of a rubber article to withstand dynamic bending stress.
  • Flock : Fibrous filler sometimes used in rubber compounding.
  • Flow : Ability of heated plastic, or uncured rubber, to travel in the mold and runner system during the molding process.
  • Fluid : A liquid or a gas.
  • Friction : Resistance to motion due to contact of surfaces.
  • Friction (Break Out) : Friction developed during initial or starting motion.
  • Fuel (Aromatic) : Fuel which contains benzene or aromatic hydrocarbons; causes little swell of rubber.
  • Gas Permeability : The degree to which a substance resists permeation of gas under pressure.
  • Gasket : A device used to retain fluids under pressure, or seal out foreign matter. Normally refers to static seal.
  • Gates : The openings in an injection or transfer mold that ensure the even flow of material into the cavity.
  • GRS : See SBR.
  • Hardness : Resistance to a disturbing force. Measured by the relative resistance of a material to an intender point of any one of a number of standard hardness testing instruments. (See Durometer).
  • Hardness, Shore (TM, Wilson-Shore Instruments) A : The rubber Durometer hardness as measured on a Shore (TM, Wilson-Shore Instruments) "A" Gauge. Higher numbers indicate harder materials; lower numbers, softer materials.
  • Heat Aging : A test for degradation of physical properties as a result of exposure to high temperature conditions.
  • Hydrocarbon Solvents - Aromatic : Solvents having basic benzene structure, usually coat tar types such as benzene, toluene orxylene.
  • Hypalon : DuPont trade name for chlorosulphonated polyethylene; an Elastomer.
  • Identification : Colored dots or stripes on seals for identification purposes; seldom used.
  • Immediate Set : The deformation found by measurement immediately after removal of the load causing the deformation.
  • Immersion : Placing an article into fluid, generally so it is completely covered.
  • Injection Molding : Molding in which the rubber or plastic stock is heated and, while in the flowable state, is forced or injected into the mold cavity.
  • Insert : Typically, a metal or plastic component to which rubber or plastic is chemically and/or physically bonded during the molding process.
  • Isoprene-acrylonitrite Rubber : A low-plasticity copolymer with around 34 per cent ACN.
  • Leakage Rate : The rate at which a fluid (either gas or liquid) passes a barrier. Total Leakage Rate includes the amounts that diffuse or permeate the material of the barrier as well as the amount that escapes around it.
  • Life Test : A laboratory procedure used to determine the amount and duration of resistance of an article to specific sets of destructive forces or conditions.
  • Linear Expansion : Expansion in any one linear dimension, or the average of all linear dimensions.
  • Low Temperature Flexibility : The ability of a rubber product to be flexed, bent or bowed at low temperature without cracking.
  • Mechanical Bond : A method of physically bonding rubber to inserts through the use of holes, depressions or projections in the insert.
  • Memory : The tendency of a material to return to original shape after deformation.
  • Mirror Finish : A bright, polished surface.
  • Modulus : Tensile stress at specific elongation. (Usually 100% elongation for Elastomers.)
  • Modulus of Elasticity : One of several measurements of stiffness or resistance to deformation, but often incorrectly used to indicate specifically static tension modulus.
  • Mold Finish : The uninterrupted surface produced by intimate contact of rubber with mold surface at vulcanization.
  • Mold Lubricant : A material usually sprayed onto the mold cavity surface prior to the introduction of the uncured rubber, to facilitate the easy removal of the molded part.
  • Mooney Scorch : The measurement of the rate at which a rubber compound will cure or set up by means of the Mooney Viscometer test instrument.
  • Mooney Viscosity : Measurement of the plasticity or viscosity of an uncompounded, or compounded vulcanized, Elastomer seal material by means of the Mooney Shearing Disk Viscometer.
  • Neoprene : (TM, DuPont) (GR-M) A polymer of chloroprene which is prepared from coal, salt and limestone.
  • Nitrile : (see also Buna-N) The most commonly used Elastomer for O-Rings because of its resistance to petroleum fluids, its good physical properties, and its useful temperature range.
  • Nominal Dimension : Nearest fractional equivalent to actual decimal dimension.
  • Non-aromatic : Straight chain organic structures, such as petroleum type solvents.
  • O-Ring : A torus; a circle of material with round cross section which effects a seal through squeeze or pressure.
  • Oil Resistant : Ability to vulcanize rubber to resist the swelling and deteriorating effects of various types of oils.
  • Oil Swell : The change in volume of a rubber article due to absorption of oil or other fluid.
  • Optimum Cure : State of vulcanization at which the most desirable combination of properties is attained.
  • Outgassing : A vacuum phenomenon wherein a substance spontaneously releases volatile constituents in the form of vapors or gases. In rubber compounds, these constituents may include water vapor, plasticizers, air, inhibitors, etc.
  • Over-Cure : A degree of cure greater than the optimum, causing some desirable properties to be degraded.
  • Oxidation : The reaction of oxygen on a compound, usually detected by a change in the appearance or feel of the surface, or by a change in the physical properties, or both.
  • Oxygen Bomb : A chamber capable of holding oxygen at an elevated pressure which can be heated to an elevated temperature. Used for an accelerated aging test.
  • Ozone Resistance : Ability to withstand the deteriorating effect of ozone (which generally causes cracking.)
  • PH : Determines the concentration of either an acid or a base.
  • Plasticity : When subject to sufficient shearing stress, any given body will be deformed. After stress is removed, if there is no recovery, the body is completely plastic. If recovery is complete and instantaneous, the body is completely elastic. A balance between the two is required.
  • Plasticizer : A substance, usually a heavy liquid, added to an Elastomer to decrease stiffness, improve low temperature properties, and improve processing.
  • Plastometer : An instrument for measuring the plasticity of a raw or unvulcanized compounded rubber.
  • Polymer : A material formed by joining together many (poly) individual units (mer) of one or more monomers; synonymous with elastomer.
  • Polymerization : Chemical reaction whereby simple materials, either one or more, are converted to complex material which possesses properties entirely different from the original materials used to start the reaction.
  • Polyurethane : An organic material noted for its high abrasion, ozone, corona and radiation characteristics
  • Porosity : Quality or state of being porous.
  • Post Cure : The second step in the vulcanization process for some specialized Elastomers. Provides stabilization of parts and drives off decomposition products resulting from the vulcanization process.
  • Rebound : A measure of the resilience, usually as a percentage of vertical return of a body which has fallen and bounced.
  • Register : The accurate matching of the plates in a mold.
  • Reinforcement Agent : Material dispersed in an Elastomer to improve compression, shear or other stress properties.
  • Relative Humidity : The ratio of the quantity of water vapor actually present in the atmosphere, to the greatest amount possible at a given temperature.
  • Resilience : Ability of an Elastomer to return to original size and shape after deforming forces are removed; generally expressed in per cent of the ratio of energy removed, to the energy used in compressing. (Resilient: having that capability.)
  • Rubber : See Elastomer.
  • Rubber Natural : Raw or crude rubber obtained from vegetable sources.
  • Rubber, Synthetic : Manufactured or man-made Elastomers.
  • SBR : Copolymer of Butadiene and Styrene; an all purpose type synthetic, similar to natural rubber. (Butadiene is a gaseous material of petroleum; Styrene, a reaction product of ethylene and benzene.)
  • Scorching : Premature curing or setting up of a raw compound during processing.
  • Seal : Any device used to prevent the passage of a fluid, gas or liquid.
  • Service : Operating conditions to be met.
  • Shelf Aging : The change in a material's properties which occur in storage with time.
  • Shore (TM, Wilson-Shore Instruments) A : See Durometer.
  • Shrinkage : 1) The ratio between a mold cavity size and the size of a product molded in that cavity, 2) Decreased volume of a seal, usually caused by extraction of soluble constituents by fluids followed by air drying.
  • Silicone Rubber : Elastomer that retains good properties through extra wide temperature ranges.
  • Size, Actual : Actual dimension of the product, including tolerance units.
  • Specific Gravity : Ratio of the weight of a given substance, to the weight of an equal volume of water, at any specific temperature.
  • Sphericity : The measure of a tolerance of a molded ball, or ground ball, in reference to a perfect sphere; also described as "roundness".
  • Static Seal : Part designed to seal between parts having relative motion. (See Gasket)
  • Statistical Process Control (SPC) : The use of statistical techniques on processes and their output, to establish process stability and increase capabilities.
  • Strain : Deflection due to force.
  • Stress : Force per unit of original cross section area.
  • Stress Relaxation : Decreasing stress with constant strain over a given time interval. (Viscoelastic response.)
  • Sun Checking : Surface cracks, checks or grazing caused by exposure to direct or indirect sunlight.
  • Surface Finish : A numerically averaged value of surface roughness, generally in units of microinches or micrometers.
  • Swell : Increased volume of a specimen, caused by immersion in a fluid (usually liquid).
  • Tack : The degree of adhesion of materials of identical nature to each other.
  • Tear Resistance : Resistance to growth of a cut or nick when tension is applied to the cut specimen.
  • Tear Strength : The force required to rupture a sample of stated geometry.
  • Temperature Range : Maximum and minimum temperature limits in which a seal compound will function in a given application.
  • Tensile Strength : Force, in pounds per square inch, required to cause the rupture of a specimen of rubber material. Terpolymer : A polymer consisting of three different monomers, chemically combined.
  • Thermal Expansion : Expansion caused by increase in temperature; may be linear or volumetric.
  • Thermoplastic : A plastic capable of being repeatedly softened by increase of temperature, and hardened by decrease of temperature.
  • Thermoplastic Rubber : Rubber that does not require chemical vulcanization and will repeatedly soften when heated and stiffen when cooled; and which will exhibit only slight loss of original characteristics.
  • Thermoset : An Elastomer or plastic cured under application of heat or chemical means, to make a product substantially infusible or insoluble.
  • Torque : The turning force of a shaft.
  • Torsion Strength : Ability of rubber to withstand twisting.
  • Transfer Molding : A method of molding in which material is placed in a pot, located between the top plate and plunger, and squeezed from the pot through gates (or sprues) into the mold cavity.
  • Ultimate Elongation : A measure of how far a material will stretch before breaking; expressed as a percentage of its original length.
  • Under Cure : Degree of cure less the optimum; may be evidenced by tackiness, loginess or inferior physical properties.
  • Vacuum : The term denoting a given space that is occupied by a gas at less then atmospheric pressure.
  • Vapour : The gaseous state of a fluid that normally exists as a liquid under atmospheric conditions, i.e. a gas whose temperature is below its critical temperature.
  • Vapour Pressure : The maximum pressure exerted by a liquid or a solid, heated to a given temperature in a closed container.
  • Vibration Dampening : The ability of an Elastomer to absorb vibrational or shock energy.
  • Viscosity : The property of fluids and plastic solids by which they resist an instantaneous change of shape, i.e. resistance to flow.
  • Void : The absence of material, or an area devoid of materials where not intended.
  • Volume Change : A change in the volume of a seal as result of immersion in a fluid; expressed as a percentage of the original volume.
  • Volume Swell : An increase in the physical size caused by the swelling action of a liquid.
  • Vulcanization : A thermosetting reaction involving the use of heat and pressure, resulting in greatly increased strength and elasticity of rubber-like materials.
  • Vulcanizing Agent : A material which produces vulcanization of an Elastomer.