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accelerated life test: a method designed to approximate in a short time the deteriorating effects obtained under normal service conditions,

adhesion: the strength of bond between cured rubber surfaces or a cured rubber surface and a non-rubber surface.

air checks: the surface markings or depressions which occur due to air trapped between the material being cured and the mold or press surface.

air oven aging: a means of accelerating a change in the physical properties of rubber compounds by exposing them to the action of air at an elevated temperature at atmospheric pressure. ANSI: the abbreviation for the American National Standards Institute.

ASME: the abbreviation for The American Society of Mechanical Engineers.

ASTM: the abbreviation for the American Society for Testing and Materials.

atmospheric cracking: small fissures in the surface of rubber articles caused by exposure to atmospheric conditions.


backing: a layer or liner of material on the underside of a sheeted product to provide mechanical reinforcement.

bare back: the textile face of an article which is free of any treatment or covering.

bleeding: surface exudation. See also bloom.

blemish: a mark, deformity, or damage which impairs the. appearance.

blister: a raised area on the surface or a separation between layers usually creating a void or air- or gas-filled space in a vulcanized article. See void.

bloom: 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.

blow: a soft area caused by porosity below the surface.

buffing: grinding a surface to obtain dimensional conformance or surface uniformity.


calendar: a machine equipped with three or more heavy, internally heated or cooled rolls revolving in opposite directions, which is used for continuously sheeting or plying up rubber compound, or frictioning or coating fabric with rubber compound.

calender stop: a mark left on the surface of rubber sheet or sheeting due to interruption of calender roll motion.

CBS: the abbreviation for cloth both sides, used to describe a sheet consisting of a ply of fabric on each surface with a layer of rubber between them.

chalking: the formation of a powdery surface condition due to disintegration of surface binder or elastomer by weathering or other destructive environmental conditions.

checking: the short, shallow cracks on the surface of a rubber product resulting from damaging action of environmental conditions.

Cl: the abbreviation for cloth-inserted. indicating a sheet of rubber containing one or more plies of fabric covered with rubber. cloth -both-sides sheet: see CBS.

cloth impression: see fabric impression. cloth-inserted sheet: see CI.

cloth-one-side sheet: see COS.

cold flow: continued deformation under stress. See creep.

commercially smooth: a degree of smoothness of an article which acceptable in accordance with industry practice.

compressed asbestos sheet: a sheet prepared from a rubber cc pound containing a high percentage of asbestos fiber and vola solvent by the use of a special calender (sheeter) in such a man that the solvent is volatilized and the compound is caused to build as an oriented sheet on one roll of the sheeter.

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

compression set: the deformation which remains in rubber after has been subjected to and released from a specific compress stress for a definite period of time at a prescribed temperature. Cc Compression set measurements are used to evaluate the creep and stress relaxation properties of rubber.

conductive: having the ability to conduct or transmit heat electricity. In rubber products, it generally relates to the capability conducting static electricity.

cork-composition sheet: sheet made from cork granules treated with a binder.

COS: the abbreviation for cloth one side, similar to CI sheet except that one fabric ply is exposed at the surface. Generally not friction on the exposed side.

count: in fabric, the number of warp ends, the number of filling picks. or both in a square inch of fabric.

crack: a sharp break or fissure in a surface. Usually caused by strain and/or environmental conditions.

crazing: a surface effect on rubber articles characterized multitudinous, minute cracks.

creep: the deformation, in either cured or uncured rubber under stress, which occurs with lapse of time after the immediate deform ation See cold flow.

creep relaxation: in a flange gasket. loss of stress accompanied constantly decreasing compressed thickness. This type of relaxation is encountered in bolted flange joints. cure: the act of vulcanization. See vulcanization.

cure time: the time required to produce vulcanization at a given tem perature.


damping: (1) the progressive reduction of amplitude in a freely vibrating system; (2) any kind of friction in a freely vibrating 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 time of manufacture of a product.

diaphragm: a packing attached between rigid members in relative motion which absorbs the motion through its own deformation.

diaphragm sheet: sheet. generally of fabric reinforced rubber, fro which flat diaphragms may be cut. die cut: shaped by punching from a sheet of rubber with a die.

dielectric strength: the measure of a product's ability to resist passage of a disruptive discharge produced by an electric stress.

diffusion: a flow or loss of a gas under pressure through a rubber layer.

drift: a change in a given hardness value after a specified period of time.

durometer: an instrument for measuring the hardness of vulcanized rubber and plastic.

durometer hardness: an arbitrary numerical value which measures the resistance to indentation of the blunt Indentor point of a durometer. Value may be taken immediately or after a very short specified time.


elastomer: a macromolecular material which, in the vulcanized state, at room temperature can be stretched repeatedly to at least twice its original length and which, upon release of the stress, will immediately return to approximately its original length.

elongation: an increase in length expressed numerically as a fraction or percentage of the initial length.


fabric impression: a pattern in a rubber surface formed by contact with fabric during vulcanization.

flange gasket: a gasket employed in a flange joint.

flex life: the relative ability of a rubber or plastic product to withstand cyclical bending stresses.

flex test: a laboratory method used to evaluate the resistance of a rubber product to repeated bending.

flow crack: a surface imperfection caused by improper flow and failure of stock to knit or blend with itself during the molding operation.

flow mark: a surface imperfection similar to flow crack, but the depression of which is not quite as deep.

friction: a rubber adhesive compound applied to and impregnating a fabric.

friction coating: a rubber covering applied to the weave of a fabric simultaneously with impregnation.

friction surface: the exposed portion of a rubber product formed by a layer of rubber-impregnated fabric as distinguished from a product having the fabric completely covered with a layer of rubber.

full-face gasket: a gasket covering the entire flange surface and drilled with bolt holes.


gasket (mechanical): a deformable material clamped between essentially stationary faces to prevent the passage of matter through an opening or joint.

ground finish: a surface produced by grinding or buffing. See buffing.


hydraulic packing: a slab packing composed of superimposed fine textile frictioned plies. Used mainly for piston rings.


low temperature flexibility: the ability of a rubber product to be flexed, bent, or bowed at low temperatures without loss of serviceability.


"M" value: an empirical design constant of a flange gasket used in the ASME Code for Unfired Pressure Vessels. The code equation defines this term as the ratio of residual gasket load to fluid pressure at leak. modulus: in the physical testing of rubber, the load necessary to produce a stated percentage of elongation, compression. or shear.

Modulus: in the physical testing of rubber, the load necessary to produce a stated percentage of elongation. Compression, or shear.


oil resistant: having the ability to withstand deteriorating effects of oil (generally petroleum) on the physical properties.

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 cracking: the surface cracks, checks, or crazing caused by exposure to an atmosphere containing ozone.


packing: a deformable material used to prevent or control the passage of matter between surfaces which move in relation to each other.

paper finish: that finish resulting from curing in contact with paper or film.

permanent set: the amount by which an elastic material fails to return to its original form after deformation.

permeability: the quality or condition of allowing passage of liquids or gases through a layer.

plate finish (sheet): a commercially smooth surface, the usual result of vulcanization between press plates or platens.

pock marks: uneven blister-like elevations, depressions. or pimpled appearance. See air checks and blister.

porosity: the condition of containing numerous small holes or voids.

press lap: the mark of the area of overlap of one press cure length on the next.

press length: the length of a product which can be vulcanized at one time in a press, limited to the length of the press.

press mark: an irregularity in the surface of a vulcanized product caused by the press ends or by corresponding irregularities in the press surface.


RAC: the abbreviation for The Rubber Association of Canada.

RMA: the abbreviation for The Rubber Manufacturers Association, Inc.


SAE: the abbreviation for the Society of Automotive Engineers.

seal: any material or device which prevents or controls the passage of matter across the separable members of a mechanical assembly.

sensitivity: in a diaphragm, the absence of resistance to displacement by light fluid pressures.

separator diaphragm: a diaphragm between two fluids at substantially the same pressure and, hence, under little or no stress.

set: the amount of strain remaining after complete release of a load producing a deformation.

shape factor: the ratio of the area of one load face to the combined area of those surfaces free to expand laterally when a rubber is under compression.

shear modulus: the ratio of the shear stress to the resulting shear strain (the latter expressed as a fraction of the original thickness of the rubber measured at right angles to the force.) Shear modulus may be either static or dynamic.

shelf storage life: the period of time prior to use during which a product retains its intended performance capability.

skim coat: a layer of rubber material laid on a fabric but not forced into the weave. Normally laid on a frictioned fabric. Sometimes called skim.

slab: a thick sheet.

spread fabric: a fabric coated with a rubber cement by a spreading process and then dried to remove the solvent.

square woven: a cloth or duck having practically the same count or tensile strength in both the warp and filling.


tensile strength: the maximum tensile stress applied while stretching a specimen to rupture. trapped air: air which is enclosed in a product or between a product and a mold surface during cure. (Usually causes a loose ply or cover or a surface mark, depression, or void.)


void: the absence of material or an area devoid of materials where not intended. See blister.

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