Rubber Terminologies

D

Damping:  The quality of an elastomer to absorb forced Vibrationsl energy.

Date Code: In hose identification , Any combination of numbers, letters, symbols or other methods used by manufacturer to identify the time of manufacture of a product.

Deburr : To remove ragged edges from the inside diameter of a hose end; an important fabrication step for assembling hose of fluropolymer in order to insure a good seal.

Deflashing: Any of various processes used to remove the waste edge from a moulded rubber part.

Dielectric properties: The ability if a material to resist puncture due to electric stress.

DeMattia Flex Test – This laboratory test to determine the flexible life of a material. It measures the rate of formation of cracks in a standard molded test bar.

Diffusion:The mixing of two or more substances due to the intermingling motion of their individual molecules.

Durometer: An instrument for measuring the hardness if a rubber, measure the resistance to the penetration of an indentor point into the surface of the rubber.

Dynamic: An application in which the seal is subjected to movement, or moving parts contact the seal.

Dynamic packing : A package employed in a joint whose members are in relative motion.

Dynamic seal: A seal required to prevent leakage past parts which are in relative motion.

Dielectric – Any insulating medium, which intervenes between two conductors and permits electrostatic attraction and repulsion to take place across it.

E

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 direction.

Elongation: Generally means ultimate elongation or percent increase in original length of a specimen been it breaks.

Extrusion: Distortion or flow under pressure of a portion of a seal into clearance between mating parts.

Explosive Decompression: Permeation of a gas into an elastomer under high pressure may not result in any long term effect provided the pressure is released gradually, allowing the gas to permeate out of the elastomer. However, if the pressure is released rapidly, the pressurised gas can expand suddenly, rupturing the elastomer in a catastrophic manner. Specific elastomer compounds are required to eliminate this effect, with the formulated materials tending to be very hard. 

Feather Edge: The sharp, thin edge on parts such as wiper seals and cups.

Flame resistance: The resistance to burning of material that will not Withstand combustion under ordinary conditions.

Flash: Excess rubber left around a rubber part after moulding, due to space between mating mould surfaces removed by trimming.

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.

Flexural strength: The ability of a material to flex without permanent distortion or breaking.

Flock: Fibrous filler sometimes used in rubber compounding.

Flow: Ability of heated plastic or uncured rubber, to travel in the mould and runner system during the moulding process.

Flow cracks: Surface imperfections due to improper flow and failures of stock to knit or blend with itself during the moulding operation.

Friction: Resistance to motion due to contact of surfaces.

G

Gamma Radiation: Electromagnetic disturbance emanating from a atomic nucleus.

Gasket: A device used to retain fluids under pressure or seal out foreign matter.Normally refers to static seal.

Gas permeability: The degree to which a substance resists permeation of gas under pressure.

Gates : The openings in an injection or transfer mould that ensures the even flow of material into the cavity.

Gate mark: A raised spot or small depression on the surface of an injection or transfer moulded part, where the gates interface the cavity.

Gland: The cavity into which an O ring is installed. Includes the groove and mating surface of the second part, which together confine the O- ring.

H

Heat aging: A test for degradation of physical properties as a result of exposure to high temperature conditions.

Heat deflection temperature:The temperature at which a standard plastic test bar deflect 0.010 in.under a static load of either 66 psi or 264 psi.

Hydrocarbon Solvents: Aromatic solvents having basic benzene structure,usually coat tar types such as benzene,toluene.

  Hysteresis: The difference between the amounts of energy absorbed when rubber is stretch and the amount of energy releases when it is then relaxed.

I

IRHD: International Rubber Hardness Degrees: 

Injection Moulding: Moulding in which the rubber of plastic stocks is heated and while in the flow able state is injected into the mould cavity.

Insert: Typically a metal or plastic components to which  rubber or plastic is chemically or physically bonded during the moulding process.

Knit Mark : A witness mark on moulded part, usually occurring at the midpoint between two transfer or injection sprue locations.Caused by the incomplete joining of the uncured rubber or plastic from each sprue during moulding.

Linear expansion: Expansion in any one linear dimension or the average of all linear dimension.

Low temperature flexibility:The ability of a rubber products 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, depression or projections in the insert.

Modulus:Tensile dress at specific elongation.

Modulus if Elasticity:  one of several measurements of stiffness or resistance to deformation, but often incorrectly used to indicate specifically static tension modulus.

Mould cavity: Hollow space or cavity in the mould, which is used to impart the desired form to the product being moulded.

Mould finish: The uninterrupted surface produced by intimate contact of rubber with mould surface with vulcanization.

Mould lubricant: A material usually sprayed onto the mould cavity surface prior to the introduction of the uncured rubber, to facilitate vthe easy removal of the moulded 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.

Non blooming : The absence of blooming.

O

Occlusion: The mechanical process by which vapours, gases, liquids or solid are entrapped within folds of a given substance during working for solidification, the materials so trapped.

Oil swell: The change in volume of a rubber article due to absorption of oil or other fluid.

O ring : A circle of material with round cross section vwhich effects a seal through squeeze or pressure.

Optimum cure: State of vulcanization at which the most desirable combination of properties which  attained.

Over cure: A degree of cure greater than the optimum, causing some desirable properties to be degraded.

Oxidation: The reaction od 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.

Oxygen Bomb: A camber capable of holding oxygen at an elevated pressure which can be heated to an elevated temperature.

Ozone resistance: Ability to withstand the deteriorating effect of ozone.

P

Parting line: The line on the surface of a moulded part where the mould plates meet.

Permanent set: The deformation remaining after a specimen bhas been stressed in tension for a definite period, released for a definite period.

Permeation:The diffusion of a medium through a rubber or plastic component.

Pimpled Rubber- A type of single layer rubber with a pimple surface facing upwards and outwards

( Table tennis bat) 

Plasticizer: A substance usually a heavy liquid  added to an elastomer to decrease stiffness improve low temperature properties and improving processing.

Plastometer:An instrument for measuring the plasticity of a raw or unvulcanized compounded rubber.

Polymer: A material formed  by joining together many individuals units of one or more monomers.

Polymerization: Chemical reaction whereby simple materials either one or more are converted to complete. Material which possesses properties entirely different from the original materials used to start the reaction.

Porosity : Quality or state of being porous .

Post cure: The second step in the vulcanization process for some specialized elstoners. Provides stabilization of parts and drives off decomposition products resulting from the vulcanization process.

Pot: The chamber, in the transfer or injection moulding where raw materials bus placed before it is transferred into the cavity.

Primer – A coating applied to the surface of a material, prior to the application of an adhesive to improve the performance of the bond.

R

Rebound: A measure of the resilience, usually as a percentage of vertical return of a body which has fallen and bounced.

Reciprocating seal: Seal used in linear motion application.

Reinforcement agents: Material dispersed in an elastomer to improve compression, shear or other stress properties.

Relative Humidity : The ratio of the quantity of water vapour actually present in the atmosphere, to the greatest amount possible at a given temperature.

RHC – The Rubber Hydrocarbon Content of a rubber, reclaim or compouns i.e Natural rubber is 92-95% hydrocarbon.

Rough Trim: Removal of superfluous material by pulling or picking usually the removal of a small portion of the flash or sprue which remains attached to the product.

Runner: The system for leading rubber and plastic materials into the gate of an injection mould.

Rubber Latex : A colloidal aqueous emulsion of an elastomer. The state of natural rubber as it comes from the tree, or as a result of emulsion polymerization for synthetic rubbers.

S

Scorching: Premature curing or setting up of a raw compound during processing.

Seal: Any device used to prevent the passage of a fluid gas,liquid.

Shelf aging: The change in a material properties which occur in storage with time.

Shelf Life: Length of time a moulded component or uncured compound can be stored without suffering significant loss of physical properties or processability

Shot Weight : The weight or charge of material required to fill a mould tool and produce a complete set of parts from the tool in one moulding cycle.

Spiral twist: A type of seal failure in reciprocating application  that results  from the twisting action that strains or ruptures the rubber

.

Stress relaxation: Decreasing stress with constant strain over a given time interval.

Static Seal: A gasket or O ring type application in which the seal is contained within two non moving gland walls. Except for pulsates caused by cycle pressure. does not move in its environment and there is no relative movement between the housing surfaces.

Surface finish: A numerically averaged value of surface roughness generally in units if micro inches or micro meters.

Swell: Increased volume of a specimen caused by immersion in a fluid

T

Thermal Expansion: Expansion caused by increase in temperature may be  linear or volumetric.

Tackiness: Stickiness. The degree of adhesion of material of identical nature to each other. Tack agents can be added to help make rubber fabrications easier to handle prior to vulcanising.

Tear Trim:The removal of remaining flash or sprue through picking or pulling which may leave a degree of flash still present on the split line to be removed by other methods if necessary

TGA:  Thermogravimetric Analysis it is a test procedure used to determine the thermal stability or composition of a material. Two modes are possible; determining the change of weight of a specimen while changing temperature at a given rate of the change of weight of a specimen with time at a fixed temperature.


U

UV Resistance: Ability to withstand decay duet to the damaging effect of the ultraviolet rays of the sun.

W

Weathering  – The surface deterioration of a rubber article during outdoor exposure.

Warping:A defect that results in a twisted or distorted rubber prodcut usually caused by incorrect temmperature.\

Wear strip: Added external material desingned to increase the external resistance to abrasion.

WEEE: Waste Electrical and Electronic Equipment Directive(WEEE) 2002/96/EC is often used in conjuction with RoHS. It sets collection, recycling and recovery targets for electrical goods.

Wrapped Cure: A vulcanizing process using a tensioned wrapper( usually of fabric) to apply external pressure.

V

Viscosity: The property of fluids and plastic solids which they resist an instantaneous change of shape.

Volume Change or Swell:measure of the swell or shrinkage of a material, seal or component resulting from immersion  in  a particular media for a specified period of time at a specified temperature. Expressed as a percentage of the original volume.

Y

Yerzley Resilience – Resilience as measured on a Yerzley oscillograph, determined by dividing the vertical height of the rebound of the first cycle of the oscillating system by the preceding vertical height of fall.

Yield Point – The first stress in a material less then a maximum attainable stress at which an increase ins train (elongation) can occur without an increase in stress.