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Glossary

A

Abrasion Resistance

The ability of rubber to resist surface wearing caused due to mechanical action

Abrasion

The process of wearing down due to friction

Accelerator

A chemical compound that speeds up the vulcanization of rubber

Aging

The change in physical and chemical characteristics of an elastomer that has been exposed to a particular environment over time

Alloy

A composite material produced by blending polymers or copolymers with other polymers under selected conditions to achieve unique physical properties

Abrasion Resistance

The ability of rubber to resist surface wearing caused due to mechanical action

Annealing

A process of holding a material at a temperature near, butbelow, its melting point, to relieve stress caused by material flow into the mold, without distortion of shape.

Antioxidant

Any organic compound that slows the process of oxidation

ASTM

American Society for Testing and Materials. An organization for issuing standard specifications on materials, including metals, compounds and alloys.

Axial Seal

Also called face seal. The expansion/compression takes place on the top and bottom surfaces of the seal’s cross section.

B

Base Line

The mark from which all features are dimensioned.

Barrel

The part of an extruder inwhich the feed screw is located

Batch Number

The unique number assigned to a particular batch of rubber compound or finished parts made in any given production run, to aid traceability.

Blast Finishing

The process of removing flash from molded objects and/or dulling their surfaces, by continuous blasting/rubbing using media such as crushed apricot pits, walnut shells or plastic pellets, thus creating sufficient friction to remove the flash

Bleeding

The release of excess plasticizer or other compound elements onto the surface of a rubber product. This happens when rubbers contain inappropriate levels of plasticizers which are not fully compatible.

Blemish

Anything affecting the appearance of a compound, such as a mark, deformity, or injury.

Blister

An imperfection on the surface of a rubber part caused by accumulation of air or gas beneath the surface.

Bloom

A whitish powdery surface visible on the rubber surface post molding/curing caused by the exudation of certain compound components (such as antiozonants, lubricants, stabilizer pigment, plasticizers, etc.). This discoloration DOES NOT affect material performance in any way.

Bond

A bond is a force that holds the elastomer to some other object. A bond can be mechanical or chemical. Mechanical bonding includes physical fixing without any molecular cross-bridging. Chemical bonding involves molecular bridging or vulcanization with heat and pressure to bond an elastomer with the primed surface.

Bore

A hole machined in a component, which permits the passage of a shaft/tube.

C

Clearance (in a sealing system)

The space between components inmechanical systems which allows for manufacturing, thermal, and dynamic variations in the size and position of the components.

Chemical bonding

A method for bonding rubber to other part/parts by applying special adhesives to the part prior to molding

Coefficient of Thermal Expansion

Determines the amount of linear dimensional change for a particular elastomer, which is temperature dependent

Compound

A mixture of a polymer and associated chemical ingredients such as catalysts, plasticizers, antioxidants, lubricants, etc. necessary to produce a finished rubber material.

Compression Molding

A molding process in which the uncured rubber compound is placed directly into the mold cavityand compressed to its final shape.

Compression Set

The permanent deformation experienced by a rubber material when compressed for a period of time. The term is commonly used in reference to a test conducted under specific conditions wherein the permanent deformation, expressed as a percentage, is measured after a prescribed period of time. This is to test the effectiveness of the seal in terms of retaining its dimensions. Low compression sets are desirable.

Cooling Channels

Channels located within the body of a mold through which a cooling medium is passed to control the mold surface temperature

Cross-linking Agents

A chemical or chemicals that bond the polymer chains of a rubber together during the molding process

Cure

The process (heating) after which raw stock (elastomer compounds) are turned into finished rubber parts.

Clearance (in a sealing system)

The space between components inmechanical systems which allows for manufacturing, thermal, and dynamic variations in the size and position of the components.

Chemical bonding

A method for bonding rubber to other part/parts by applying special adhesives to the part prior to molding

Coefficient of Thermal Expansion

Determines the amount of linear dimensional change for a particular elastomer, which is temperature dependent

Compound

A mixture of a polymer and associated chemical ingredients such as catalysts, plasticizers, antioxidants, lubricants, etc. necessary to produce a finished rubber material.

Compression Molding

A molding process in which the uncured rubber compound is placed directly into the mold cavityand compressed to its final shape.

Compression Set

The permanent deformation experienced by a rubber material when compressed for a period of time. The term is commonly used in reference to a test conducted under specific conditions wherein the permanent deformation, expressed as a percentage, is measured after a prescribed period of time. This is to test the effectiveness of the seal in terms of retaining its dimensions. Low compression sets are desirable.

Cooling Channels

Channels located within the body of a mold through which a cooling medium is passed to control the mold surface temperature

Cross-linking Agents

A chemical or chemicals that bond the polymer chains of a rubber together during the molding process

Cure

The process (heating) after which raw stock (elastomer compounds) are turned into finished rubber parts.

D

Deflashing

Any process used to remove extra rubber (flash) from a molded rubber part

Damping

The ability of an elastomer to absorb forced vibrational energy

Delamination

Separation of two or more surfaces in a composite material.

Diaphragm Seals

Regulator seals used in gas controls, valves, actuators, regulators, pumps and metering equipment.

Die

Molds through which the uncured elastomer is pushed out in the desired shape during the extruding process.

Die Cut Gaskets

Press cut and hand cut gaskets in all types of rubber, most commonly reported using the Shore ‘A’ scale

Durometer

Standard rubber industry test instrument which uses an indenter to measure the hardness of specimen rubber. The hardness of rubber is most commonly reported by a durometer using the Shore ‘A’ scale

Dynamic Seal

A seal used in an environment that subjects it or a mating surface to movement

E

Elasticity

A rubber’s ability to return to its original size and shape after removal of the stress causing deformation such as stretching, compression, or torsion.

Elastic Limit

Maximum stress that a material will stand before permanent deformation occurs

Elastomer

Any of various polymers having the elastic properties of rubber

Elongation

Generally referred to in terms of tensile (pull apart) testing. Elongation is the increase in length of a test specimen, expressed as a percentage of its original (unstretched) length; relative to a given load at the breakpoint

EMI

Electromagnetic interference

Extrusion

When a part is forced from its groove (die) by high continuous or pulsating pressure

F

FDA

Food & Drug administration

Face Seal

Also called axial seal. The expansion/compression takes place on the top and bottom surfaces of the seal’s cross section.

Feed

The area or opening where rubber is injected or transferred into the mold cavity

Filler

Fine material used to reinforce or modify elastomer physical properties, like hardness, curing time, tensile, etc. Typical examples are carbon black, calcium carbonates, clay, silica, etc.

G

Gland

The space in mechanical systems where the seal is installed. It consists of the seal groove and any additional space required for proper seal compression.

Gasket

A static sealing device used to retain fluids under pressure or to seal out foreign matter

H

Hardness

A measurement of resistance to penetration of a rubber sampleby an indenter. Higher values indicate harder materials and vice versa. The hardness of rubber is most commonly reported by durometer using the Shore ‘A’ scale a

I

Insert

A term referring to a metal or plastic component, placed/inserted into a mold cavity prior to the start of the molding cycle, to which rubber is chemically and/or physically bonded during the molding process

Injection Molding

A molding method in which a rubber is heated and forced under pressure into the mold cavity

J

JIT

Just in Time manufacturing, an efficient manufacturing technique developed by the Japanese automotive industry in the 1950’s to reduce inventory as far as possible.

L

LSR

“Liquid silicone rubber”. Used in injection molding of high-quality parts, offering low compression set and great stability and temperature resistance.

Laser Etching

Physically marking a component with a laser, often to uniquely identify each individual component with a unique serial number.

M

Mechanical bond

A method of physically/mechanically attaching the rubber to another object like a metalinsert

Mating Surfaces

Points where different parts of an assembly meet.

Memory

Ability of an elastomer to return to its original size and shape after deformation

Modulus

A measure of resistance of a material to deformation. is measured by the force required to reach a predetermined compression or extension

Mold

Typically made from steel. The rubber part is formed within the machined cavity

Mold Cavity

The hollow space of the mold in which the uncured rubber compound is compressed to give the desired cured finished product

N

Nominal Dimension

The mean dimension of a molded article, from which small dimensional deviations/tolerances (plus and minus) are permitted

Non-fill

An unintentional void or absence of material in the part

O

Oil Resistant

Ability of vulcanized rubber to resist swelling and other detrimental effects of exposure to various oils

O-Ring

A doughnut-shaped object, or torus, that functions as a seal, blocking the passage of liquids or gases, by being compressed between the two mating surfaces comprising the walls of the cavity (gland) into which the ring is installed

Orange Peel

A surface finish on a molded part that is rough and splotchy. Usually caused by moisture in the mold cavity

Oscillating Seal

Most commonly used in faucet valves, in this application the inner or outer member of the gland moves in an arc around the axis of a shaft. Movement is limited to a few turns in one direction and a few turns in the return direction (i.e. faucet on, faucet off)

Outgassing

Primarily occurring in vacuum situations, the volatile (evaporative) components of some rubber compounds may become vaporized in the vacuum and released (outgassed) by the compound into the surrounding environment

Overflow

A designed escape reservoir for rubber compound used to insure mold cavity fill and also allowance for excess compound

Overflow Groove

A groove around the periphery of a mold cavity used to accept any excess material from the cavity during molding. Additional material beyond that which is required to fill the cavity is usually introduced into the cavity to ensure that the part is completely formed and to minimize the presence of entrapped air and voids

Oxidation

The reaction of oxygen with a rubber compound, typically resulting in surface cracking of the rubber material. As oxidation involves the transfer of electrons, reduction in the physical strength of elastomers may also occur from exposure to the oxidizing agent

P

Plasticizer

A chemical agent added to the rubber compounding batch to soften the elastomer for processing, and to improve its physical properties like increase elongation, reduce hardness, improve tack

Parting line

The line visible on the finished molded part, indicating the location where the mold plates were connected

Polymer

A long molecular material chainformed by the chemical combination of many similarly structured, small molecular units

Post-curing

The process of baking or heating parts after they are molded. This process helps to improve the heat and compression set resistance of specific elastomers (e.g. silicones and fluorocarbons)

Q

Quad Ring

Solid elastomeric ring seal with a four lobed cross-section, used similar applications as o-rings, but offering better seal efficiency and lower friction compared to standard o-rings

R

Reinforcing Agent

Fillers like carbon black which are added to the rubber compound batch mix to improve physical properties of the elastomer such as tensile strength

Radial Seal

Seals wherein the compression is applied perpendicular to the seal center-line

Resilience

The capability of elastomers to returnto their original size and shape after deformation

Rubber

A common name for both naturally occurring and synthetically made elastomers

S

Scorching

Premature curing of compounded rubber stock during processing or storage, which if not done might adversely affect material flow and plasticity during subsequent molding and curing processes

Synthetic Rubber

Man-made elastomers such as Silicone, EPDM, FKM, Nitrile, Fluorocarbon, etc.

Seal

Any device used to prevent leakages in the form of passage of a fluid (gas or liquid) or fine particles

Shore A

A hardness scale used to measure the hardness of molded rubber. The Shore A scale is most effectively used to measure rubber with a hardness from 10 to 95 Shore A. For materials harder than 90 to 95 Shore A, the Shore D scale is recommended (see also durometer)

Shrinkage

The linear contraction upon cooling of a molded rubber

Static Seal

A seal that does not move in its environment, except for pulsations caused by cycle pressure

T

Tear Resistance

Resistance to the development of a cut in the seal when tension is applied

Tack

The degree of adhesion of materials of identical nature to each other

Tear Strength

The force required to rupture a material specimen

Tensile Strength

The extension force per cross-sectional area required to fracture a material specimen

Terpolymer

A polymer resulting from the chemical combination of three monomers

Thermal Expansion

expansion in the elastomer caused by temperature increases

Thermoplastic Elastomer (TPE)

A material which exhibits combined characteristics of both plastic (processing properties) and rubber (physical properties).

Thermoset

A material, either rubber or plastic, which when thermally processed undergoes an irreversible chemical reaction to achieve its final state

V

Viscosity

The measure of the resistance of a material to flow under stress

Volume Change

The measure of the swell or shrinkage of a material resulting from immersion in a particular media/chemical agent for a specified time period at a specified temperature

W

Weathering

The detrimental effect on an elastomer after outdoor exposure