Glossary of Terms

Abrasion:

Wearing away by friction.

Acid Resistant:

Withstands the action of acids.

Adhere:

(1) To cling or stick together.  (2) To cause to Cling or Stick together.

Adhesion:

(1) Basically, the adhering, clinging, bonding or sticking of two material surfaces to one another, such as rubber to rubber, rubber to glass, rubber to metal, rubber to wood, rubber to fabric, rubber to cord, rubber to wire, etc.  (2) Refers to the strength of bond between cured rubber surfaces or cured rubber surface and a non-rubber surface.

Adhesion Failure:

(1) The separation of the two surfaces with a force less than specified.  (2) The separation of the two adjoining surfaces due to service conditions.

Adhesive:

A material which, when applied, will cause two surfaces in contact with each other to stick together.

Adhesive Coating:

A surface layer applied to any product to increase its adherence to an adjoining surface.

Aging:

(1) Natural deterioration by oxygen, ozone, heat and light.  (2) Testing to measure rate of deterioration.

Aging, Air Oven:

A means of accelerating the change in physical properties of rubber compounds by exposing them to the action of air at an elevated temperature.

Air Checks:

Surface markings or depressions due to trapping air between the material being cured and the mold or press surface.

Air Curing:

The vulcanization of a rubber product in air as distinguished from vulcanizing in a press or steam vulcanizer.

Ambient Temperature:

The environment temperature surrounding the object under consideration.

Backing:

A layer or liner of material on the underside of sheeted product for mechanical reinforcement.

Banbury Mixer:

A specific type of internal mixer used to incorporate fillers and other ingredients.

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.

Binder:

The component of any non-homogenous rubber product that holds it together.

Bleeding:

Migration to the surface of plasticizers, waxes, or similar materials to form a file or beads.  (See Bloom)

Blemish:

A mark, deformity, or injury which impairs the appearance.

Blisters:

A raised spot on the surface or a separation between layers usually forming a void or air-filled space in the vulcanized article.  (See Bubbles, Sinks, Voids)

Bloom:

A coating or efflorescence creating a discoloration or change in appearance of the surface of a rubber product caused by the migration of a liquid or solid to the surface.  Examples:  Sulfur Bloom, Wax Bloom.  Not to be confused with dust on the surface from external sources.

Blowing Agent:

Mixed with a rubber compound, this material decomposes when heated to form the gases, which create sponge rubber.

Brittle Point:

The highest temperature in a series of low temperatures at which a rubber specimen fractures on sudden impact.

Bubbles:

Usually referring to surface blisters.  (See Blisters)

Buffing:

To grind the surface producing a roughened or a velvety surface.  Usually done to produce dimensional conformance.

Butt Joint:

A juncture of two edges formed or cut at a right angle to the surface plane without lap.

Calendered:

Continuously sheeted or plied up rubber compound or fabric that is fractioned or coated with rubber compound on a machine equipped with three or more heavy, internally heated or cooled rolls revolving in opposite directions.

Cellular Rubber:

Sponge rubber.

Cemented Edge:

An application of cement around the edge of a fabricated product with or without internal reinforcement for protection or adhesion.

Chalking:

Formation of a powdery surface condition due to disintegration of surface binder or elastomer due in turn to weathering or other destructive environments.

Checking:

Short, shallow cracks on the surface generally due to effect of destructive action of environmental conditions.

Closed Cell:

A cell totally enclosed by its walls and hence not interconnected with other cells.

Coefficient Friction:

The ratio between the force pressing the surfaces together and the force required to move it.

Coefficient of
Thermal Expansion:

Average expansion per degree over a stated temperature range, expressed in a fraction of initial dimension.  May be linear or volumetric.

Cold Flex:

Act or instance of bending or bowing a rubber product under conditions of cold environment.

Cold Flexibility:

Flexibility following exposure to a predetermined low temperatures for a predetermined time.

Cold Flow:

Continued deformation under stress.  (See Creep and Drift)

Cold Resistant:

Withstands the effect of cold or low temperatures without loss of serviceability.

Compound:

An uncured mixture of a rubber polymer and other ingredients.  (Fillers, Vulcanizing Agent, etc.)

Compressibility:

The property of exhibiting compression under load.  In case of sheet material the percent loss of thickness when subjected to a given load applied by a disc or given diameter for a predetermined short time and at a predetermined temperature as defined in ASTM F-36.

Compressible:

Exhibiting compression under stress.  Sometimes limited to products which exhibit volume compression; thus, rubber products containing no voids are said to be “incompressible.”

Compression:

Reduction in one dimension as the result of application of stress.  May or may not be accompanied by increase in other dimensions.

Compression Modulus:

The ratio of the compressive stress to the resulting compressive strain (the latter expressed as a fraction of the original height or thickness in the direction of the force.)  Compression modulus may be either static or dynamic.

Compression Set:

The deformation which remains in rubber after it has been subjected to and released from a specific compressive stress for a definite period of time at a prescribed temperature.  Compression set measurement is for the purpose of evaluating creep and stress relaxation properties of rubber.

Conductive:

A rubber having qualities of conducting or transmitting heat or electricity.  Most generally applied to rubber products used to conduct static electricity.  (See Conductivity)

Conductivity:

Quality or power of conducting or transmitting heat or electricity.

Contraction:

Opposite to elongation or to expansion.

Control:

A product of known characteristics, which is included in a series of similar service or bench tests to provide a basis for evaluation of one or more unknown products.

Corrosion:

Chemical deterioration of RIGID member (usually metal) where it contacts gasket or packing.  The actual corroding agent is medium trapped in the interface.

Corrosion-Inhibiting:

A property which actively inhibits corrosion of adjacent metal faces.

Corrosive:

A property which is assumed to promote corrosion of the rigid member by a trapped medium.

Cracking:

A sharp break or fissure in the surface.  Generally due to excessive strain.

Crazing:

A surface effect on rubber articles characterized by multitudinous minute cracks.

Crease:

A wrinkle or fold.

Creep:

The deformation occurring with the lapse of time, in both cured and uncured rubber, in a body under stress in addition to the immediate elastic deformation.  Some related terms and properties are stress-relaxation, hysteresis, damping, flow compression set, and viscosity.  (See cold flow and drift)

Creep Relaxation:
(Flange Gasket)

The type of relaxation encountered in bolted flange joints, i.e., loss of stress accompanied by constantly decreasing compressed thickness.

Crystallization:

A change in physical properties resulting from the crystalline reorientation caused by temperature and/or elongation.

Curing:

Vulcanization.  Chemical process which converts raw rubber compounds to rubber.  Usually (not always) involves heat.  In most rubbers, a one-step process in hot mold or stream; in some (including silicone) the initial cure is followed by a post cure in an oven to develop optimum properties.

Damping:

(1) The progressive reduction of amplitude in free vibration.  (2) The friction of any kind in a free vibration system causing the motion to decrease gradually to the vanishing point.

Date Code:

Any combination of numbers, letters, symbols or other methods used by a manufacturer to identify the period of manufacture of the products.

Deformation:

Any change of form or shape produced in a body by a stress.

Delamination:

Separation or splitting, usually as lack of adhesion in plied goods.

Density:

The ratio of the mass of a body to its volume.

Depression:

A place or part that is depressed; a hollow.

Die Cut:

Shaped articles punched from a sheet of rubber with a die.

Dielectric:

The electrical potential strength of non-conducting properties of a rubber product.  (See Dielectric Strength)

Dielectric Strength:

The measure of electric potential strength of a rubber product.  Measure of its ability as an insulating compound to resist passage of a disruptive discharge produced by an electric stress.  Measure as volts per mil of thickness.

Diffusion:

(1) Commonly used to express the flow or loss of a gas under pressure through a rubber layer.  (2) The striking through as in “fractioning.”

Dip Coat:

A thin coat on a surface obtained by dipping the material to be coated into the coating material.

Dished:

A depressed surface distortion of a flat or curved section of a rubber product.

Drift:

(1) Continued deformation under strain.  (2) The change in a given durometer reading after a period of time.

Dry:

(1) Absence of tack, no adhering properties.  (2) To remove moisture.

Durometer:

An instrument for measuring the hardness of rubber.  Measures the resistance to the penetration of an indentor point into the surface of rubber.

Durometer Hardness:

An arbitrary numerical value which measures the resistance to penetration of the indentor point of the durometer.  Value may be taken immediately or after a very short specified time.

Dynamic Modulus:

The ratio of stress to strain under vibratory conditions.  It is calculated from data obtained from either free or forced vibration tests, in shear, compression or elongation.  It is usually expressed in p.s.i. for unit strain.

Dynamic Resilience:

The percentage of the vibrational energy which persists in the second of two successive free vibrations: Also called “vibrational resilience.”

Elasticity:

The property of an article which tends to return it to its original shape after deformation.

Elastic Limit:

(1) The greatest stress which a material is capable of developing without a permanent deformation remaining upon complete release of the stress.  (2) In rubber the elastic limit as above defined is very low and sometimes practically non-existent.  Usually this term is replaced by various load limits for specific cases in which the resulting permanent deformations are not zero but negligible.  (See Yield Point)

Elastomer:

Macromolecular material that returns rapidly to approximately the initial dimensions and shape after substantial deformation by a weak stress and release of stress.

Elongation:

Increase in length expressed numerically as a fraction or percentage of initial length.

Embossing:

Operation of transferring a design to a rubber or rubber-like surface.

Expanded Rubber:

Cellular rubber having closed cells made from a solid rubber compound.

Expansion:

The increase in any linear dimension or in volume.

Extrusion:

Process of shaping uncured rubber compounds into continuous form by forcing the material through a die.

Fabric Impression:

Marked with the imprint of fabric used as a wrapper during vulcanization.

Fatigue:

The weakening or deterioration of a material caused by a repetition of stress or strain.

Feathered Edge:

A gradually and completely tapered edge or cut of a rubber product.

Fire Resistant:

Retards the burning action of fire or flame.

Flame Resistant:

See fire resistant.

Flange Gasket:

A gasket employed in a flange joint.

Flex Cracking:

A surface cracking induced by repeated bending or flexing.

Flex Life:

The relative ability of a rubber article to withstand dynamic bending stresses.

Flexing Life Test:

A laboratory method used to determine the life of a rubber article when exposed to dynamic bending stresses.

Flex Test:

A laboratory method used to evaluate the resistance of an article to repeated bending.

Flexibility:

Opposite of stiffness.

Flow Cracks:

Surface imperfections due to improper flow and failure of stock to knit or blend with itself during the molding operation.

Flow Lines:

See flow marks.

Flow Marks:

Similar to flow cracks, but the depressions are not quite as deep.

Fungicide:

A material that prevents or retards the growth of fungi.

Gasket:
(Mechanical)

A deformable material clamped between essentially stationary faces to prevent the passage of matter between an opening or joint.

Gasketing:

Material in bulk form from which gaskets may be cut.

Gauge:

(1) The measure or thickness of the individual elements making up a rubber product.  (2) A device for measuring.  (See Thickness)

Grain:

The effect on a rubber compound due to processing it through a tubing machine, calender, or mill.

Gravity:

See specific gravity.

Ground Finish:

Surface produced by grinding or buffing.  (See Buffing)

Hardness:

Property or extent of being hard.  Measured by extent of failure of the indentor point of any one of a number of standard hardness resting instruments to penetrate the product.

Heat Resistance:

The property or ability of rubber articles to resist the deteriorating effects of elevated temperatures.

Homogeneity:

Uniformity of composition throughout the material.

Homogeneous:

Of uniform composition throughout.

Immediate Set:

The deformation found by measurement immediately after removal of the load causing deformation.

Impact:

The single instaneous stroke or contact of a moving body with another, either moving or at rest, such as a large lump of material dropping on a chute liner.

Impression:

Design formed during vulcanization in the surface of any rubber article by a method of transfer, such as fabric impression or molded impression.

Indentation:

(1) The extent of penetration by the indentor point of any one of a number of standard hardness testing instruments.  (2) A recess in any surface of a rubber article.

Inhibit:

To prevent or retard.

Laminated:

Built up from thinner layers.

Lamination:

A single thickness of material used in laminating a product to the required thickness before vulcanization.  (See also Laminated)

Lap:

A part that extends over itself or like part, usually by a desired and predetermined amount.

Lap Seam:

A seam made by placing the edge of one piece of material extending flat over the edge of the second piece of material.

Length:

A lineal dimension, usually the longer or longest dimension of the product.

Life Test:

A laboratory procedure used to determine the amount and duration of resistance of a rubber article to a specific set of destructive forces or conditions.  (See Accelerated Life Test)

Light Resistance:

Withstands the deleterious action of light, such as cracking.

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.

Low Temperature Flexing:

Act or instance of repeated bending or bowing a rubber product under conditions of low temperature.  (See Cold Flex)

Migration:

The transfer of an ingredient in a rubber compound from one layer to an adjacent layer or to the surface.

Migration Stats:

When staining occurs on the area of an object adjacent to the rubber article, it is known as “migration stain.”

Mildew:

Growth on organic matter produced by fungi, generally in textile components of rubber articles.  Usually cause deteriorating of the textile.

Mildew Inhibited:

The article contains material to prevent or retard mildew.

Mildew Resistant:

Withstands the action of mildew growths and their deteriorating effect.

Modulus:

In the physical testing of rubber, it is the ratio of stress to strain: that is, the load in pounds per square inch or kilograms per square centimeter of initial cross sectional area necessary to produce a stated percentage elongation.  It is a measure of stiffness.

Moisture Absorption:

The absorption of moisture by a rubber or textile product.

Mold Lubricant:

The material used to coat the surfaces of a mold to prevent the rubber adhering to the metal during vulcanization.

Mold Marks:

Indentations or ridges embossed into the skin of the molded product by irregularities in the mold surface.

Mold Release:

See mold lubricant.

Mold Scratches:

See mold marks.

Mold Skin:

The surface of a molded product formed by contact with the mold.

Off-Gauge:

Not conforming to thickness specified.

Oil Resistant:

Withstands the deteriorating effect of oil (generally refers to petroleum) on the physical properties.

Oil Swell:

The change in volume of a rubber article due to absorption of oil.

Open Cell:

A cell not totally enclosed by its walls and hence interconnected with other cells.

Oven:

A low pressure, hot air chamber used for the purpose of heating, drying, baking or vulcanizing rubber products.

Over-Cure:

A degree of cure greater than the optimum.

Oxidation:

The reaction of oxygen on a rubber product, usually detected by a change in appearance or feel of the surface, or by a change in the physical properties.

Ozone Cracking:

Surface cracks, checks or crazing caused by exposure to an atmosphere containing ozone.  (See also Ozone Resistant)

Ozone Resistant:

Withstands the deteriorating effects of ozone, generally cracking.

Permanent Set:

(1) Permanent set is the deformation remaining after a specimen has been stressed in tension a prescribed amount for a definite period and released for a definite period.  (2) In creep determinations, permanent set is residual, unrecoverable deformation after the load causing the creep has been removed for a substantial and definite period of time.

Permeability:

The quality or condition of allowing passage of liquids or gases through a rubber layer.

Pin Hole:

A small puncture in any surface of a fabricated product.

Pit:

A surface depression.

Plasticizer:

A material which, when incorporated in rubber or a polymer, will change its hardness, flexibility, processability and plasticity.

Ply Separation:

Delamination of plies caused by lack of adhesion.

Pock Marks:

Uneven blister-like elevations, depressions or pimpled appearance.  (See also Air Checks and Blisters)

Polymer:

A very long chain of units of monomers, prepared by means of an addition and/or condensation polymerization.  The units may be the same or different.  There are co-polymer, di-polymers, quadric-polymers, high polymers, etc.  Natural rubber is a polymer of Isoprene.

Porosity:

Quality or state of being porous due to presence of globular structural voids.

Press Marks:

Irregularities in the surface of a vulcanized product caused by the press ends or by corresponding irregularities in the press surface.

Press Mold:

The cavity in which a rubber product is shaped.  Also includes the body containing the cavity which can be removed from the press.

Pressure:

A force or thrust applied over the surface as hydraulic pressure to a rubber product.  Usually referring to pressure against a diaphragm.

Recovery:
(Sheet Gasketing)

The percent decrease compressed deformation during a specified time interval and at a specified temperature, following release of load, as defined by ASTM F-36.

Reinforcement:

(1) The strength members, consisting of fabric, cord, and/or metal, of a rubber product.  (2) The non-rubber elements making up a rubber product.  (3) The non-rubber compounding ingredients which impact increased tensile strength or other desirable properties.

Relative Humidity:

The ratio of the quantity of water vapor actually present in the atmosphere to the greatest amount possible at the given temperature.

Resilience:

(1) In metals and some other materials, resilience is the amount of energy stored up in a deformed body and as no loss of energy is contemplated, it is also the amount of energy recoverable when the force producing the deformation is removed.  (2) In rubber or rubber-like materials subjected and relieved of stress, resilience is the ratio of energy given up on recovery from deformation to the energy required to produce the deformation.  Resilience for rubber is usually expressed in percent.  (See also Dynamic Resilience)

Resistance:

The property or ability of matter to withstand the effects of force, pressure, heat or chemical action.

Resistant:

Having resistance.

Reversion:

(1) The change which occurs in vulcanized rubber, as the result of aging or overcuring in the presence of air or oxygen, usually resulting in a semi-plastic mass.  (2) It is the basis of rubber reclaiming processes and is aided by the use of swelling solvents, chemical plasticizers and mechanical disintegration to obtain a workable mass.

Rubber:

A material that is capable of recovering from large deformations quickly and forcibily, and can be, or already is, modified to a state in which it is essentially insoluble (but can swell) in boiling solvent, such as benzene, methyl ethyl ketone, and ethanol-toluene azeotrope.  A rubber in its modified state, free of diluents, retracts within 1 minute to less than 1.5 times its original length after being stretched at room temperature (18ºC to 29ºC) to twice its length and held for 1 minute before release.

Rubberized:

Coated with a rubber compound.

Scratch:

Surface blemish, a sharp or ragged mark, on finished item by a scored or scratched mold, matrix or press platens or the finished product being cut after cure.

Seal
(Mechanical)

Any material or device which prevents or controls the passage of matter across the separable members of an assemble.

Service Test:

A test in which the packing is made to operate under service conditions in the actual equipment.

Set:

Retention of strain following release of stress.  The opposite of retraction.

Skrinkage:

A decrease or contraction in dimension.

Silicone:

Chemically, polyorganosiloxane.

Silicone Rubber:

A synthetic rubber made by adding suitable compounding ingredients to a silicone polymer.

Sink Blisters:

See Sinks.

Sinks:

A collapsed blister or bubble leaving a depression in the product.

Skin:

A relatively dense layer at the surface of a cellular material.

Skive:

A cut made on an angle to the surface to produce a tapered or feathered cut.

Skive Edge:

An edge that has been cut with a skive.

Specific Gravity:

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

Sponge Rubber:

Cellular structure produced by adding gasifying substance to rubber compound, expanding and curing in heated mold.  Cells may be open (interconnecting) or closed.

Staining:

The discoloration imparted to the surface finished in contact with a rubber product.

Static:

(1) Electrical potential charge produced through motion or rubbing rubber against unlike materials.  (2) Not moving, non-dynamic.

Static Conducting:

Quality or power of conducting or transmitting electrical static charge.  (See Conductivity)

Stretch:

An increase or elongation in dimension.

Sun Checking:

Surface cracks, checks, or crazing caused by exposure to direct or indirect sunlight.  (See Ozone Cracking)

Surface Void:

A void on the surface of a product.  (See Voids)

Swelling:

Increase in volume, usually caused by immersion in a liquid.

Tacky:
(Rubber Surface)

Tending to adhere.

Tear:

To separate or pull apart by force.  In measuring tear resistance of rubber, the specimen is usually nicked with a sharp blade and then the force to tear the rubber is measured.

Tear Resistance:

The property of a rubber article to resist tearing force.

Temperature:

The degree of heat or cold as measured in terms of degrees centigrade or Fahrenheit.

Template:

A gauge or pattern used as a guide for cutting or finishing.

Tensile Strength:

The maximum tensile stress applied during stretching a specimen to rupture.

Tensile Stress:

The applied force per unit of original cross-sectional area of a specimen.

Thermal Contraction:

Contraction caused by decrease in temperature.

Thermal Expansion:

Expansion caused by increase in temperature.  May be linear or volumertric.

Thickness:

(1) The measure of thickness of the complete rubber product.  (2) See Gauge.

Torsion:

(1) Deformation by twisting.  (2) The internal restoring couple or twisting moment in a piece of rubber subject to a twisting motion.

Trapped Air:

Air which is trapped in a product or in a mold during cure.  Usually causes a loose ply, or a surface mark, depression or void.

Trim:

The removal of superfluous parts from a molded product.  Usually removal of parting line flash or fee sprues.

Trimming:

Act of removing superfluous parts from a product.

Tuber:

An extrusion machine.

Tubing:

Process of producing continuous shapes, hollow or not, by extrusion.

Ultimate Elongation:

Elongation at rupture.

Under-Cure:

A degree of cure less than the optimum.  (See Cure)

Unicellular Rubber:

Sponge rubber containing closed cells.

Viscosity:

A manifestation of internal friction opposed to mobility.  The property of fluids and plastic solids by which they resist an instantaneous change of shape, i.e., resistant to flow.

Voids:

The absence of material or an area devoid of materials where not intended.  (See also Blister, Bubbles, Sinks)

Volume Compressibility:

Reduction in physical size affected by imposing a load.

Volume Expansion:

Expansion in volume.

Volume Swell:

Increase in physical size caused by the swelling action of a liquid.

Vulcanization:

Act or process of treating an elastomer or compound of same to improve its useful properties, usually accomplished by application of heat.

Water Absorption:

The process of assimilating or soaking up water.

Weak Spot:

A limited structural defect in a product which degrades the physical characteristics or strength.

Wrinkle:

A corrugation, ridge, crease or fold in the reinforcement member or the tube or covers.

Young’s
Modulus of Elasticity:

(1) In may non-rubber materials Young’s Modulus may be taken in tension or compression, the values being approximately the same.  It is the ratio of strain.  (2) In rubber, the assumption that tension modulus equals compression modulus is valid only for extremely small deformations and for certain shapes, such as specified in ASTM D-797-64, “Standard Method of Test for Young’s Modulus in Flexure of Natural and Synthetic Elastomers at Normal and Subnormal Temperatures”, and ASTM D-1053-65 (Sec. 7), “Standard Method of Measuring Low-Temperatures, Stiffening of Rubber and Rubber-Like Materials by Means of a Torsional Wire Apparatus.”