A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
A
Abraded
Worn away by friction
Abrasion
Wear due to friction
Abrasion Resistance Index (ARI)
A measure of abrasion resistance of a urethane elastomer relative to a standard urethane elastomer under the identical conditions. ARI is expressed as a percentage.
Abrasion Tester
A machine for determining relative abrasion resistance
Accelerated Life Test
Amethod designed to approximate in a short time the deteriorating effects obtained under normal service conditions
Accelerator
Asubstance used too increase the rate of a chemical reaction; synonymost with the term catalyst
Acid Number
The value given to trace residues of acids in the finished polyol
Acid Resistance
The ability to resist the action of identified acids within specified limits of concentration, temperature and time.
Activator
Seldom used term nowdays for curavative or chain extender. Sometimes mistakenly used to mean catalyst
Additive
Amaterial which does not effect the chemical reaction but is included to alter the final product such as pigments, fillers, flame retardants, plasticizers. Maybe liquid or solids
Adhesion
The adhering, cling, bonding or sticking of two material surfaces to one another, such as polyurethane to polyurethane, polyurethane to metal, polyurethane to rubber
Adhesion Failure
The separation of two bonded surfaces in the adhesive layer due service conditions
Adhesive
A material which, when applied, will cause two surfaces in contact with each other to stick together
Adhesive Coating
A coating applied to a surface to increase its bond to an adjoining surface
Aftercure
A continuation of the stabilization process after the cure has been carried to the desired degree for a predetermined length of time. May be conducted at room or elevated temperatures
Aging
To undergo changes in physical properties with age or elapse of time
Aging (Shelf)
Aging during storage. Temperature is assumed to be room temperature, humidity is not controlled.
Air Bomb Aging
A means of accelerating changes in the physical properties of material by exposing them to the action of air at elevated temperatures and pressure
Air Checks
The surface markings or depressions which occur due to air trapped between the material and the mold or pouring surfcae (see bubble)
Air Oven Aging
A means of accelerating a change in the physical properties of polyurethane compounds by exposing them to the action of air at an elevated temperature at atmospheric pressure. Generally done in a temperture controlled, forced air oven.
Aliphatic
A chain-like molecule comprising of carbon and hydrogen, without the presence of benzene ring
Alloy
A composite material produced by blending polymers or copolymers with other polymers under controlled conditions to achieve enhanced physical properties.
Ambient Temperature
The environment tempewratrure surrounding the objecy under consideration
Amine
A group of organic compounds containing,N, NH or NH2 group
Amine Catalyst
A group of amine containing organic compounds that cause specific beneifical urethane-related chemical reactions. May be reactive or non-reactive ( to isocyanates)
Amine Equivalent
An analysis value determined for isocyanate materials to express their reactive strength, used in some methods for calculating 'stoichiometric balance' of a formula . The value secured has an inverse relationship to the strength of the chemical as the larger the value, the weaker is the reactive strength of the isocyanate per unit of weight. The method of analysis may be obtained by request to one of the major chemical companies supplying the isocyanate.
Aniline
A key starting material used to make MDI, MOCA, a few speciailty crosslinkers
ANSI
American National Standards Institute
Anti-static
See static conductive
Antidegradant
An additive used to retard (delay) deterioration caused by oxidation, ozone, light, radiation, in any combination. The additive may reactive or non-reactive.
Antiflex Cracking Agent
An additive used to retard (delay) cracking caused by cyclic deformation.
Antioxidant
A compounding ingredient used to retard deterioration caused by oxygen
Antiozonant
A compounding ingredient used to retard deterioration caused by ozone
Antislip Surface
A specially treated surface tobtain greter than normal traction
Aperature
The clear opening size, as in length, width or diameter of an opening. Apertures may also involve special shapes such as rectangular ( oblong) or triangular configurations
Aromatic
Molecules that include at least one bemzene ring
Artifical Weathering
Exposure to cyclic laboratory conditioins involving changes in temperature, relative humidity, and radiant energy, with a without direct water spray, attempting to produce changes in material similar to that observed after long-term continuous outdoor exposure.
ASME
American Society of Mechanical Engineers
ASTM
American Society for Testing and Materials
Average Modulus
The total change of stress divided by the total strain
B
Backrind
A molding defect in which the urethane elastomer adjacent to a parting line shrinks below the surface of the molded product, leaving the part with an irregular parting line.
Banbury mixer
A specific type of internal mixer used to incorporate filler and other ingredients in polyurethane or plastic matrix
Batch
The product of one mixing or blending operation-no size limit.
Batch Mixing
The process of simultaneously mixing the entire amount of the fotmula required in one container
Batcher
A person who prepares mixtures of urethane chemicals before they are cast
Bench Marks
Two marks of a known separation applied to a tensile test specimen to measure the strain of the specimen during extension.
Bench Test
A modified service test in which the service conditions are approximated in the laboratory
Bending Force
The force required to bend a given cross-section under prescribed conditions
Bending Modulus
That force required to induce bending aroiund a specified radius and, hence a measure of stiffness
Bleeding
Migration to the surface of plasticizer, waxes or similar materials to form a film or beads. See also Bloom.
Blemish
A mark, deformity or injury which impairs appearance but not to the degree where the urethane component would not otherwise perform its intended function
Bloom
A discoloration or change in appearance of the surface of a polyurethane product caused by migration of a liquid or solid to the sutrface. Examples: sulfur bloom, wax bloom. Not to be confused with dust on the surface from external sources
Blow-up
A blister between plies of a dual durometer article
Bond
See adhesion
Boss
Aprotuberance designed to add strength, faciltate alignment, provide fastenings, etc.
Brand
A mark or symbol identifying or describing a product and/or manufacturer: may be embossed, inlaid or pad printed
Breaking strength
The tensile strength which polyurethane first ruptures
Brittle Point
The highest temperature at which a urethane elastomer will fracture under a shock load.
BTU
Btitish Thermal Unit, the amount of energy required to heat one pound of water one degree Fahrenheigt
Buffer Catalyst
A catalyst, usually a very alkaline amine, that has beenpartially or wholly neutralized with acid so that the reaction would not be affected by the extreme alkalinity of the catalyst
Buffing
The grinding of a vulcanizate (urethane) producing a roughened textured surface.
Buffing Marks
The characteristic surface condition after a secondary buffing operation
Bulk Storage
A series of tanks large enough in capacity that bulk shipments (tank wagon or railcar) can be off loaded and stored on the premises. Can be above or below ground
Bulking Agent
A matetrial or chemical added to another that increases the qualtity of the mixture without changing the chemical activityof the total mass. Can be solid or liquid.
Bumping
A process used in compression molding consisting applying and releasing pressure to the gelling urethane elastomer to force air bubbles out of the mold.
Butt Seam
A seam made by placing the pieces to be joined edge to edge
C
Castfilm
A film made by depositing a layer of polyurethane in solution, or in a dispersion onto a surface, solidifying and removing the film from the surface
Casting
The process of filling (pouring) open molds with liquid (uncured) polyurethane
Castor oil
A naturally occuring triol derived from the castor bean used to make low durometer, water resistance urethanes
Catalys Balance
The ratio between amine catalysts and organotin catalysts
Catalyst
The ingredient in a polyurethane formulations which initiates a chemical reaction or increases the rate of chmemical reaction. Maybe reactive or no-reactive.
cc
Abbreviation for cubic centimeter, a metric system unit of volume
CD Curve
Abbreviation for compression-Deflection Curve
Cement
A mixture of polymeric compounds or elastomers used as an adhesive or sealant
Cemented Edge
An application of cement around the edge of a fabricated product with or with or without internal reinforcement for protection or adhesion
Centipoise
1/100 of a poise, a unit of viscosity
Centrifigal Casting
A molding process whereby the mold is spun and the liquid, uncured urethane is poured into the spinning mold through an oipen at the center the spinning mold slinging it outwards against the internal cavities of the mold. A useful molding process for complex shapes and thin sections
CFM
Abbreviation for Cubic Feet per Minute
Chain Reaction
Lengthening of the main chain (backbone) of polymer molecules by end-to-end attachment
Charging
Aterm used to describe the filling of machine or day tanks with various quantities of chemicals
Chaulking
Formation of a powery surface due to disintergration of surface binder or elastomer due to weathering or other destructive environments
Checking
Short, shallow cracks on the surface generally due to the effect of destructive action of severe environmental conditions
Chute Lining
Highly abrasion resistant elastomeric (polyurethane) lining a chute to protect the metal chute from abrasive wear
Clicker Press
A mechanical press used to die cut test samples for physical testing or articles of commerence from flat sheets of elastomer
Coefficient of Friction
kenetic,The ratio of the force required to maintain movement of an object in motion across a surface to the weight of that object. A dimensionless number
Coefficient of Friction
static,The ratio of the force required to initiate movement of an object at rest across a surface to the weight of that object. A dimensionless number
Coefficient of Thermal Expansion
The average expansion per degree over a stated temperature range, expressed as a fraction of the initial dimension.
Cog
A tooth on the rim of a wheel or polyurethane product
Cohesive
Tendency of a material to stick to itself
Cold Flex
See low temperture flexing
Cold Flexibility
The relative ease of bending following exposure to lowtemperature
Cold flow
Continued deformation under stress, See creep
Cold splice/bond
Usually the joining of two or more substraits together, using a two-part cement that is chemically cutred withiut using supplemental heat from an external source.
Commericially smooth
A degree of smoothness of an article which is acceptable in accordance with industry practice.
Component
A separtely metered stream of liquid which is introduced directly into the mixing head
Compound
a mixture of a polymer(s) and other materials to give the desired chemical and physical properties in the elastomeric components of a polyurethane product
Compound Standard
A control or reference compound prepared according to a prescribed formula and mixing procedure.
Compounding in the head
A procedure whereby two or more prepolymers and/or curatives and/or other components are metered into the mixing head of a urethane dispensing machine at a predetermined ration and stoiciometry to achieve a desired polyurethane compound. An efficient method of switching urethane compounds (formulation) on the fly; requires specialized equipment. May be applied to quasi or one shot sytems,also.
Compression Molding
A molding process whereby liquid, uncured urethane is poured into the bottom half of a mold, allowed to gel, followed by the placement of top half of the mold and placed under great pressure in a press.
Compression Set
The deformation in a material remaining after it has been subjected to and released from a compressive force
Conditioning (Environmental)
The storage of a urethane sample, under specified conditions of time, temperature and humidity prior to testing.
Conditioning (Mechanical)
The prescribed program of deformation of a urethane sample prior to testing.
Conductive Elastomer
An elastomer capable of conducting (generally static) electricity).
Conductivity
The quality of power of conducting or transmitting heat or electiciry
Control
A material ora product of known characteristics included in a series of tests to provide a basis for evaluation ofm other products
Copolymer
A substance consisting of molecules characterized by the repetition of two or more types of momomeric units
cps
Abbreviation for centipoise
CPS
Aqbbreviation for cycles per second
Crack, Flex
A fissure starting in the surface of a urethane elastomer caused by cyclic deformation (bending).
Cracking
A sharp break or fissure in the surface generally due to excessive strain
Crater
A small shallow surface imperfection
Crazing
Slight break in the surface of a material
Creep
The deformation occuring with elapsed time in both cured and partialy cured polyurethane, in a body under stress in addition to immediate elastic deformation
Cross Linking
The formation of chemical links between molecular chains
Crude Isocyanate
Undistilled isocyanate containing several different polymeric isocyanates,generally dark brown in color
Crystallization
A change in physical properties resulting from the crystalline reoientation caused by temperature
Curative
See curing agent
Cure
The process which completes the chemical reaction. The term also refers to the state of completeness of the chemical reaction
Cure Date
The date a urethane part was molded usually cast into the part.
Cure Temperature
The temperature at which the elastomer product is cured
Curing Agent
Chemicals with a functionality of two or more that react with isocyanate groups that chain extend the molecule to very large molecular weights
Cut Resistance
The ability of polyurethane to withstand the cutting action of sharp objects
Cycle Time
The amount of time required to complete a molding cycle from start to finish
D
DABCO®
Is a registered trademark used for triethylenediamine, a very powerful Accelerator or catalyst of the tertiary Amine family.
Dam
A device installed within a mold to prevent the flow of material into areas of the mold cavity to reduce, alter, or eliminate a portion of the cast part, of which the mold is intended to produce.
Damping
See hysteresis.
Day Tanks
A slang expression generally meaning either Batch Tanks or machine tanks used for one day’s production run. The tanks size may vary significantly from manufacturer to manufacturer.
Deflashing
A variety of process used to remove excess material from the edges of a cured part.
Deformation
Any change of form or shape produced in a body by a stress.
Degradation
A deleterious change in the chemical structure of a material.
Degree of Polymerization (DP)
The number of structural units or mers in the 'average' polymer molecule in a particular sample.
Delamination
The separation of layers of material in a multilayer material
Demolding Time
The time between pouring the liquid into the mold and the removal of the article from the mold. This is usually kept to the minimum possible time in which the partially cured object can be handled without damage so as to reuse the molds.
Density
The weight of a specified volume of material (resin, curative, finished part). In some countries this is expressed as pounds per cubic foot; in others it is expressed as grams per cubic centimeter or kilograms per cubic meter. For ordinary practical purposes, density and specific gravity may be regarded as equivalent.
Desiccant
A compound used to irreversibly remove moisture from other materials (typically liquids).
Dew point
The temperature at which a vapor begins to condense.
Diameter
The length of a straight line passing through the geometric center to the periphery of an object.
Dibutyltin Di-Ethyl Hexoate
Is a powerful catalyst of the organotin group. This is one of the best.
Dibutyltin Diacetate
Is a powerful catalyst of the organotin group.
Dibutyltin Dilaurate
Is a powerful catalyst of the organotin group. It is sometimes used for adhesives.
Die Cutting
The process whereby shaped articles are stamped out of a sheet of by the impact of a die against the sheet. Polyurethanes frequently form the acking material for Die Cutting applications.
Dielectric strength
The measure of electric potential strength of a polyurethane product. Measure of its ability as an insulating compound to resist passage of a disruptive discharge produced by an electric stress. Measured as volts per mil of thickness.
Differential Scanning Calorimetry (DSC)
An analytical technique where the heatflow is monitored during a steady heating of the sample. This technique can be used to obtain glass transition temperatures (Tg), melt transition temperatures (Tm) and als
Differential Thermal Analysis (also Thermal Gravimetric Analysis TGA)
Is an examination technique whereby the material may be heated to destruction while a temperature profile recording is being taken. In TGA the weight of the sample is monitored du
Diisocyanate
One of the major components of a polyurethane, often referred to as the ‘resin’ side. Diisocyanates may be in monomeric form or in prepolymer form and can be characterized as ‘aromatic’ or ‘aliphatic’. Major diisocyanates used in the polyurethane industry include TDI, MDI, PPDI, NDI as well as the aliphatics H6-MDI, IPDI and HDI.
Diluent
A liquid used to extend or reduce the viscosity of another material without changing the reactivity of the original material other than by the dilution occurring.
Dimensional Stability
Ability of a plastic part to retain the precise shape in which it was molded, fabricated, or cast.
Dimer
A substance (comprising molecules) formed from two molecules of a monomer.
Diol
A polyol having two reactive hydroxyl (OH) groups attached to each molecule.
Dip coat
A coating on a surface obtained by dipping the material to be coated into the coating materials.
Discharge Orifice
The port or opening through which the chemicals are discharged. This term is usually restricted to the final discharge of the mixed materials rather than to intermediate points opening into the mixing chamber, which are normally called metering ports or metering tubes'.
Discoloration
The gradual darkening of urethane due to a photochemical reaction. It is faster in sunlight than in artificial light, although it occurs in both. Discoloration without exposure to light can indicate excessive temperature exposure.
Dispersion
The application of high shearing forces to distribute one or more liquids or fine solids into a “mother” liquid in ensure uniformity and stability over time.
Dumbbell
A specimen with lesser width at the middle of its length than at its ends used in testing materials physical properties.
Durometer
An instrument for measuring the hardness of polyurethane. Measures the resistance to the penetration of an indentor point into the surface.
Durometer hardness
The resistance to indentation under conditions which do not puncture the elastomer surface. The most frequently used device is the spring-loaded Shore Durometer. The scale runs from zero hardness for a liquid, to 100 for a hard plane surface, such as glass. Usually reported as a Shore A (softer scale) or Shore D (harder scale) hardness.
Dynamic fatigue
Loss in properties of a material when continually subjected to flexing and or cyclic stress.
Dynamic Properties
Mechanical properties exhibited under repeated cyclic deformations.
E
Ejector Pins
Internal mold pins that, when activated ejects the part from the mold. Generally used only in complex molds.
Elastic Limit
The point of deformation beyond which a material will permanently deform rather than elastically recover.
Elastic Modulus
A ratio between the force applied to cause the deformation and the resistance to that force by the material being deformed. It can be determined for samples in tension as well as compression.
Elasticity
The property of a material whereby the material tends to return it very nearly to its original dimensions after significant deformation.
Elastomer
Polymers which resist and recover from deformation produced by force. Similar to behavior to natural rubber. Commonly called rubber, polymer, co-polymer, vulcanizates. Most cast polyurethanes are elastomers.
Elastomeric properties
The chemical and physical properties of an elastomer.
Elongation
The percent of its original length to which a specially shaped sample will stretch before breaking.
Embossing
Operation of transferring a design to a polyurethane surface.
Equivalent Weight
Is the molecular weight of a chemical divided by the number of reactive (functional) groups. For example, the molecular weight of pure TDI is 174, the number of reactive groups is two (it is a diisocyanate) so the equivalent weight is 174/2 or 87. In a formulation, the number of equivalents of isocyanate must be balanced against the number of equivalents of curative in order to achieve stoichiometric balance. Isocyanate resins typically are provided with a %NCO instead of an equivalent weight. Amines typically have an isocyanate equivalent weight given. Some curatives can be used for both epoxies and polyurethanes with differerent equivalent weights for each.
Exotherm
The heat liberated by some of the chemical reactions occurring in the urethane formation. Urethane reactions fall in the general class of exothermic reactions, which have heat as a by-product.
Extender
See plasticizer and fillers
Extensometer
A device for determining elongation of a specimen as it is elongated (strained) in a testing machine.
Extraction test
A test in which certain components are separated from a solid by immersing the solid in a liquid solvent under suitable conditions, then analyzing the solvent for foreign components (i.e. plasticizers).
Extruded
Forced through die of tubing machine in either solid or hollow cross section (i.e. hollow tubing or solid rod).
Extrusion
A process whereby heated or unheated plastic forced through a shaping orifice becomes a continuously formed piece.
F
Fatigue
The weakening or deterioration of a material caused by a repetition of stress or strain.
Filler
An inert material added to the formulation to change the final physical properties. Fillers can be used to increase the density of the product without significantly adding to the cost, or they are used to assist in a cost reduction. The solid fillers often result in higher load bearing properties but lower tensile and tear strengths. Fillers are usually solid, particulate materials, such as glass, silica, or clays.
Film
A thin sheet of polyurethane.
Filter
A device to remove unwanted particles of material from the liquid streams of chemicals. For trouble free operation all lines should be properly filtered.
Fire resistant
Retards the burning action of fire or flame.
Fisheye
A small globule that has not blended completely into the surrounding material.
Fixed Calibration Time
The practice of metering the various fluid streams during a fixed time interval such as 6 seconds or 1 minute in order to calibrate and set the liquid streams to a desired total flow rate per minute as well as to a desired ratio with each other.
Fixed Ratio
The condition of having all components with a fixed throughput so that ratio variations are not possible.
Fixed Throughput (Fixed Flow rate)
A term used to describe a machine with one or more pumps directly connected to the drive motors so that no variation in flow rate is possible.
Flame performance
The manner in which cured polyurethane after being ignited will burn and/or self extinguish.
Flame retardance
Intensity of flame diminished by fire retardant ingredient(s) in the polymer compound.
Flame Retardant
Generally, a flame retardent material is an additive that imparts a certain degree of flame retardancy to a finished article, i. e. the will burn less rapidly or lose less weight on burning. (Also Fire Retardant)
Flame test
A means, under specific condition, for establishing the (standardized) flame performance of a polyurethane product.
Flammability
Describes the relative burnability of the material in a specified situation. Meanings vary according to the test method used.
Flange
A raised edge on a polyurethane article.
Flash
Material protruding from the surface of a molded part, appearing at the mold parting line or mold vent points. Usually very thin, and removed by some method from the finished part.
Flat Blade Impeller
A mixing blade that is characterized by a generally single plane shape or flat appearance. It may be solid, perforated with various patterns, or may be irregular in contour.
Flex cracking
A surface cracking induced by repeated bending or flexing.
Flex Fatigue
The loss of physical properties of a sample undergoing continuous flexing of a specified magnitude, duration and rate.
Flex life
The relative ability of a polyurethane article to withstand dynamic bending stresses.
Flex life test
A laboratory method used to determine the life of a plastic product when subjected to dynamic bending stresses.
Flexibility
The ability to be bent repeatedly without cracking.
Flexible Mold Material
The rubber like material used for molding very intricate shapes and contours. These materials can be any elastomers but are more usually urethane or silicone based. The usual compounds are liquids which are poured over the 'master', allowed to gel, then removed and oven cured to maximum tensile strength before use to provide flexible molds.
Flexometer
A laboratory testing apparatus that subjects test specimens to repeated deformation in tension, compression shear or bending or any combination thereof.
Flow Marks
Visible flow lines on molded products caused by imperfect flow of the gelling liquid urethane elastomer as it is being cast. Can occur in compression molded urethane elastomers.
Flow-Rate
A term which refers to the quantity of chemicals delivered to the discharge nozzle or metering port in a specified time interval, usually expressed in pounds per minute per component, in the USA. 'Total flow rate' would be the quantity of mixed
Formula/Formulation
The list of ingredients and their proportions to each other which must be used to make a particular product.
Free Monomer
The weight percent of monomeric isocyanate, usually in a prepolymer resin.
Friction
The resistance to motion of an object due to the contact between two surfaces.
Friction
coefficient of ,The ration between the force pressing the surfaces together and the force required to move it.
Full Recirculation
A term applied to a urethane machine designed to permit all fluid components to be circulated between the tank and the mixing head during the 'idle' or non-production time. For 'full recirculation' the valve that diverts the flow to the mixing chamber should be immediately adjacent to the chamber so that stagnant areas are eliminated.
Fully Automatic Solvent Flush
The solvent flush cycle initiated automatically by the machine.
Functionality
The number of reactive groups attached to a single molecule. An amine or polyol with a functionality of 2 would be a diamine or a diol. An amine or polyol with a functionality of three would be a triamine or a triol.
Fungicide
An agent that destroys fungi or inhibits their growth.
G
Gel
The initial semi-solid stage that develops during the solvation of a (solid) resin by a plasticizer.
Gel point (or Gel time)
The stage at which a liquid begins to exhibit pseudo-elastic properties. The gel time of a polyurethane is dependent on both the temperatureand the mass. Gel times are usually reported on a 100g mass at an indicated temperatu
Glass Transition Temperature
The temperature at which a polymer changes from having rubbery characteristics to glassy ones. Physical properties often change rapidly with small temperature changes in the vicinity of the glass transition temperature.
Glycol
Is the generic terms for polyols having a functionality of 2, also termed diols.
Ground finish
Surface produced by grinding or buffing.
Guard Thermostat
An extra thermostat in the electrical circuit of a heating system, used as a safety control over the maximum temperature of the heating source.
H
Handbatching
,The mixing together premeasured components in a urethane formula by means of a spatula then pouring into a mold. Sometimes a mechanical mixer is used such as a drill motor/mixer blade.
Hardening
An Increase in resistance to indentation
Hardness
Property or extent of being hard; usually expressed in Shore A or D units
Haze
The cloudy appearance of a transparent casting
Hazing
A dull funish
Heat Degradation
Change in chemical and/ or physical properties due excessive exposure to heat
Heat History
A combination of time and temperature a urethane prepolymer has been subjected to.
Heat Of Reaction
See Exotherm
High Shear Mixing
The mixing together of urethane components in a high-speed close tolerance mixing chamber
Homogenous
Uniform Composition
Humid Aging
An accelerated laboratory test under conditions of high humidity and temperature to determine the suitability of amaterial to specific end use
Hydorxyl Equivalent Weight
The number of grams of sample required so that one gram equivalent weight of hydroxyl ( 17.008) will be present in the sample
Hydrolytic Stability
The ability to resist the deterioration by the effects of water
Hydrophillic
An Affinity fo water
Hydrophobic
A repellency for water
Hydroxyl Number
A number that indicates the number of hydroxyl groups available for reaction in a polyol.
Hysteresis Loop
The area under the stress-strain curve
Hysteresis Loss
A loss of mechanical energy due to successive deformation and relaxation
Hystersis
A loss of energy due to successive deformation and relaxation of an elastomer. Ameasurement of the area between the deformation and relaxation stress-strain cutves
I
Immediate Set
The amount of deformation measured immediatelyafter removal of the load causing the deformation
Impact
The single instantaneous stroke or contact of a moving body with another either moving or atb rest, such as a large mass of heavy material dropping on a polyurethane product
Impact Energy
The effective combination of force (mass of the body and height) when one body falls on another
Impact Force
The energy power of impact
Impact Resistance
The realtive ability to withstand mechanical or physical blows without loss of protective properties
Impulse
An application of force in a manner to produce sudden strain or motion
Indentation
(1) The extent of deformation by the indentor point of any one of a number of standard hardness testing instruments; (2) A recess in the surface of a polyurethane component
Inhibitor
A material used to delay a chemical reaction.
Injection Molding
A method frequently utilized in the manufacturing of polyurethane products. While this method is extremely cost effective when producing hugequantities, the properties of injection molded polymers (thermoplastics) do not offer the superior characteristics of open cast (thermoset polyurethane
Insert
Generally, a metal or plastic component to which a urethane elastomer is chemically and/or physically bonded during the molding process.
International Rubber Hardness Degrees (IRHD)
An alternate method to Shore hardness of measuring hardness of rubber or urethane elastomer articles.
ISO
The abbreviation for the International Organization for Standardization
Isocyanate
The group name of chemical compounds having one or more NCO groups attached to the main chemical chain
Isomer
Any one of two or more chemical compounds having the same kind of atoms in their structure, but arranged in a different way
Isomer Ratio
The ratio between two or more isomers. 80/20 TDI is an example (80% 2,4 isomer; 20% 2,6 isomer of TDI)
J
Jaws
Clamps to hold a specimen when applying stres to a specimen on a Universal Testing Machine (Instron)
Jig
A fixture used to accurately position parts during the manufacturing process-welding jig, hole positionong jig
Joint
The area where two ends of a compnent are fastened together by chemical and/ or mechanical means. See also splice
K
Ketone
Compounds in which a carbonyl group is bound to two alkyl or two aryl groups, or to one alkyl and one aryl group
Kinetic Energy
Energy that matter pocesses by virtue of its motion
Knit Line
A line where two or steams of curing, liquid urethane come together in complex and/or large molds to form a visible boundary
Know How
Technical background information required in order to properly operate a specific process
L
Laminate
A product made by bonding together two or more layers of material
Laminated
Build up from thinner layers
Lap
A part that extends over itself or a like part
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
Lateral
Coming from the side
Life test
A laboratory procedure used to determine the resistance of a polymer article to a specific set of destructive forces or conditions
Light Resistance
The ability of polyurethane elastomer to resist changing color when exposed to sunlight or UV light. Related to the type of isocyanate (aromatic or aliphatic) used in the system.
Linear Molecule
A long chain molecule as contrasted by one having many side chains or branches. In castable urethanes, can becontrolled, within limits, by isocyanate index
Logy
Very slow recovery of an extended elastomer.
Longitudinal
A lengthwise direction
Longitudinal seam
A seam joining two materials in the length of the finished product
Low temperature flexibility
The ability of a polyurethane to be bent or flexed at lowm temperatures without loss of serviceability
Low temperature flexing
The act of bending a product under conitions
M
Machine Tanks
Compnent tanks mounted on a urethane dispensing machine frame with metering pumps either inside or outside said tanks
Mass Effect
The influence of the size of the pour to the maximum exotherm, The larger the mass, the heat heat is retained in the casting which, in extreme cases, can cause degradation of the polymer
Masterbatch
A preliminary mixture of two or more compound ingredients for purposes of more through dispersion or better processing, and which later become part of the final compound in a subsequent mixing operations
MDI
The abbreviated term for diphylmethane diisocyanate
Memory
The tendency of an elastomer to return to its original shape after the deformation force has been removed.
Mer
The repeating structural unit of any high polymer
Mil
one thousandth of one inch, 0.001"
Mirror Finish
A bright, polished surface appearance
Mismatch
A part defect caused by misaligned mating mold cavities.
Mix
A urethane compound
ml
The abbreviation for milliliter
Mn (Number-Average Molecular Weight)
The total weight of all molecules divided by the total number of molecules
Modulis of Elasticity
The ratio of stress to strain in an elastomer
Modulus
A coefficient or numerical measure of some property
Mold Mark
An indentation or embossment on the surface of a molded product caused by irregularties in the mold surface
Mold Release Agent
One of many chemical compounds whixh, when applied to a mold surface prevnts the cured urethane part from sticking to the mold.
Mold Shrinkage
The dimensional difference between the part and its mold when measured at normal room temperature.
Molding
The practice of pouring liquid urethane into a mold, curing then demolding the part form its mold
Monomer
A relatively simple compound which can react to form a polymer
MSHA
Abbreviation For Mine Safety and Health Administration
Mw (Weight-Average Molecular Weight)
The sum of the total weights and molecules of each size multiplied by their respective weights divided by the total weight of all molecules
N
Naphthenic Oil
A hydrocarbon processing oil containing more 30% by mass of naphthenic hydrocarbons. Commonly used as a low cost plasticizer in polyether cast urethane elastomers.
NCO
Abbreviation for the isocyanate chemical group, contains nitrogen double bonded to carbob which is double bonded to oxygen
NDI
Abbreviation for 1,5-napthalene diisocyanate
Nitrogen
An inhert, anhydrous gas commonly used to blanket urethane chemicals to prevent harmful moisture absorption
Nominal
An Approximate amount, normal or expected value of a parameter
Non-fill
A defect resulting from the lack of material completely filling the entire mold cavity.
Nozzle
The discharge opening or tip of a mixing head
Number of Components
Ambiguous term to describe the number of reactive fluid streams that enter the final mixing zone in a urethane dispensing machine. Usually excludes air, solvent flush and color streams.
O
Off-Register
See mismatch
OH groups
See hydroxyl group.
OH number (Hydroxyl Number),
Is the number of milligrams of KOH (potassium hydroxide) that is chemically equivalent to the activity of a specified weight (in grams) of the polyol. This number is used in calculating the equivalent weight of the water and po
Oil proof
Not adversely affected by exposure to oil.
Oil resistant
Withstands the deterioration effect of oil(generally refers to petroleum) on the physical properties
Oligomer
A polymer consisting of only a few monomer units such as in dimer, a trimer, a tetramer etc. & their mixtures
Open cast
The method of manufacture utilized to obtain maximum wear characteristics in polyurethane modules.
Open molding
A term which refers to the practice of pouring into a cavity having a closed bottom and sides but an open top. The mold may be shallow or deep. It is generally not the most economical way to mold a product but may have an Application where minimum internal mold pressures are required.
Optimum cure
The time and temperature of fusion at which a desired combination of properties is attained in an elastomer.
Organosol
A suspension of a finely divided plastic in a plasticizer with a volatile organic solvent.
Outgassing
The release of volatile constituents (usually under high vaccum) in the form of vapor or non condensable gasses from cured urethane or liquid urethane components such as prepolymers, polyols, plasticizers or color dispersions.
Oven
A low pressure hot air chamber equipped with precise temperature controls, used for the purpose of post curing open cast polyurethane products.
Overcure
An excess of curing time/temperature leading to the loss of optimal physical properties.
Oxidation
The addition of oxygen to a compound or the reduction of hydrogen.
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.
Oxygen bomb aging
A means of accelerating change in the physical properties of polymer compounds by exposing them to the action of oxygen at an elevated temperature and pressure.
Ozone resistant
Withstands the deteriorating effects of ozone (generally cracking).
P
Paraffinic Oil
A hydrocarbon oil composed mainly of alkanes.
Parting line
A ridge on the part where mold plates meet.
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 material layer.
Permeation Rate
The flow rate of a gas, under specified conditions, through a predetermined area divided by that area.
pH
An expression of the degree of acidity or alkalinity of a substance. Neutrality is pH7 - acid solutions being under 7 and alkaline solutions over 7. Accurate pH meters are commercially available.
PHR (phr)
Abbreviation for parts per hundred and is used to indicate proportions of components in a system. Commonly used for purposes of compounding prepolymers, curing systems and to ratio urethane dispensing machines.
Pimple
A small crater in the surface of a molded product with width about the same as its depth.
Pin impeller
A rotating mixing blade generally characterized as having a straight, relatively sturdy, central shaft parallel to the direction of liquid flow and a series of smaller, round, square or hexagonal shaped "pins" mounted on the central shaft at right angles to the central shaft and generally perpendicular to the liquid flow. There are many variations of this involving pin mounting angles other than 90 degrees (different diameter pins, different quantity of pins, different spacing between pins, etc). It is usually classed as a low shear mixing device.
Pin mixer
A mixing head utilizing a pin impeller.
Plastic
A material that contains as an essential ingredient one or more organic polymeric substances of large molecular weight, is solid in its finished state, can be shaped by flow.
Plasticity
A measure of the resistance to shear of an uncured elastomer; (2) a measurement of resistance to shear with heat history.
Plasticizer
A compounding ingredient which can change the physical and chemical properties and processibility of a polymeric compound.
Plastisol
A dispersion of a powderous polymer in a plasticizer
Plate finish
A finish resulting from contact with commercially smooth but not polished heated pouring table.
Poise
A measure of the specific viscosity of a fluid. It is measured by the force required to move one plate in relation to another plate when the space between is filled with the fluid. A material with a viscosity of 1 poise requires 1 gram of force to move the plate 1 centimeter in 1 second. Since most of the fluids used in urethane foam have viscosities that vary with the temperature, any statement regarding the viscosity of these fluids must be qualified with the temperature of the hid at which the data was taken. centipoise, which is 1/1OOth of a poise, is more commonly used in the foam industry particularly since water is approximately 1 centipoise at 20 degrees C and thus provides a physical comparison with which we are all familiar.
Poly isocyanates
Isocyanate compounds having more than one isocyanate (NCO) group attached to the molecule. See functionality.
Polyester
A polymeric compound, with the reactive hydroxyl groups containing ester linkages. Is one of the families of compounds that can be prepared with reactive hydroxyl groups and thus can be used as a polyol in the preparation of urethane foam. This is a large family and a wide variety of compounds can be used. As a family, these compounds are characterized by the presence of -C-O-groups in the molecule. This type of bond is more susceptible to attack by water (hydrolysis) than is the single oxygen present in the polyether type. Polyester polyols are generally more expensive, in the USA, than polyether polyols.
Polyether
A polymeric compound, with the reactive hydroxyl groups containing ether linkages. Is one of the families of compounds that can be prepared with reactive hydroxyl groups and thus can be used as a polyol in the preparation of urethane foam. This is a large family and a wide variety of compounds can be used. As a family, these compounds are characterized as having ether groups -C-0-C-in the molecule. This type of molecular joint is less susceptible to hydrolysis than the type characteristic of polyesters. In general polyethers are less expensive than polyesters in the USA.
Polymer
A macromolecular material formed by the chemical combination of monomers having either the same or different chemical composition. A high-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the mer; e.g., polyethylene, rubber, cellulose. Synthetic polymers are formed by addition or condensation polymerization of monomers. If two or more monomers are involved, a copolymer is obtained. Some polymers are elastomers, some plastics.
Polymeric isocyanates
Is generally used to refer to those isocyanates containing products that consist of a mixture of isocyanate compounds containing more than two isocyanate groups in the molecule. This type is being widely used in the rigid foam field where good heat resistance and high char strength is required. This type of isocyanate reacts with polyol with less heat generation than with 'pure' diisocyanates; hence there is less tendency for scorching of the foam.
Polymerization
The process that converts monomers into polymers.
Polyol
A chemical compound with more than one reactive hydroxyl group attached to the molecule.
Polyol mix
The product resulting from premixing many of the compatible minor ingredients into the polyol component. This is usually done in order to reduce the final number of components required to be metered and introduced into the mixing head and to improve the Accuracy of the compounding when some of the minor ingredients would be difficult to meter individually because of very small quantities or very high viscosity. This also allows time to mix some materials that are difficult to mix in the short length of time available in the final mixer. This product is also called 'masterbatch' and 'premix'.
Polyurethanes
Are a family of chemical compounds that can be prepared by the reaction of an isocyanate containing material with a hydroxyl containing material.
Porosity
The presence of numerous small holes or cavities in an elastomer. Typically caused by moisture in cast urethane elastomer systems.
Positive displacement
A term which refers to those pumps that are so designed that substantially all of the material displaced from the suction side of the pump is delivered to the outlet side of the pump. In other words internal recirculation is at a minimum and what little there is, is constant over a fairly wide range of conditions. In normal practice some limitation in use is necessary. Under some conditions, a pump that is positive metering with a 1000 cps material, may slip rather badly with 100 cps material. Under other conditions, a pump that is designed to be positive metering with a 1 cps material may transfer enormous quantities of energy in the form of heat to material of 1000 cps.
Positive metering
The ability to control the flow rate of a particular fluid to an Accuracy of approximately 1% of the total flow regardless of temperature or pressure fluctuations downstream from the metering device. This is difficult to achieve in normal practice at all times under any conditions. It can be achieved economically if certain design rules and limitations of use are practiced. There is a certain amount of ambiguity in the term since many piston pumps can be classified as positive metering for total quantity delivered, while the amount delivered per second may vary, and many gear or vane pumps can be positive metering both for total quantity delivered and for quantity per second delivered.
Positive proportioning
A term which refers to the condition in which two or more fluid streams are positively metered with respect to an absolute standard and are maintained in an exact ratio with each other continuously.
Positive tracking
A term used to describe the condition existing when the flow rate is changed in two or more fluid circuits simultaneously while still maintaining positive proportioning. For Accuracy positive tracking is normally stated as a plus or minus variation from a standard flow level and for a specific viscosity material.
Post cure
The period of cure after the product has been removed from the mold. In many cases, accelerated curing at elevated temperatures is utilized.
Pot life
The period of time during which a reacting polymeric compound remains suitable for its intended use after having been mixed with a reaction-initiating agent.
Potting
The process of encapsulating or imbedding a device by pouring a casting compound into a cavity in which the device has been fixed and curing the compound in place, As a result the device is imbedded completely in a plastic polymer, either solid or foamed. The compounds are usually thermosetting and vacuum may be used with the solid polymers in order to avoid entrapped gases.
Pouring head
A mixing head designed only to dispense liquid mixtures.
Pre-heat
A term normally applied to the technique of bringing molds or cavities to the desired temperature level prior to pouring. This is a fairly critical factor and must be accomplished with reasonable Accuracy and reproducibility for best quality cont
Premix
A term often used synonymously with masterbatch or polyol mix to indicate the mixture resulting from blending many of the minor ingredients in with the polyol in an effort to reduce the final number of components or to allow more time for mixing or blending those chemicals that may not be readily miscible in the short period of exposure to the final mixing. See polyol mix.
Premix tank
A term used to indicate tanks that are used for making batches of premix separately from the machine and also those tanks on the machine that are used in the premix flow circuit.
Prepolymer
A chemical intermediate, manufactured by reacting all the isocyanate with a portion (or all) of the polyol.
Pressure balance
A term used to describe the condition existing in an 'on-off' fluid metering circuit when the pressure during the 'on' cycle is exactly the same as the pressure during the 'off' cycle. This condition is normally required for best quality foam production, as most commercial foam machines have rubber hoses in the circuit plus places that could trap gas and act as accumulators. Under these circumstances if the pressure were permitted to change, a surge or lag of material could occur immediately after switching 'on' (mix cycle) which would cause an imbalance in the stoichiometric ratio of the chemicals, and poor quality foam or 'initial spot' during at least a portion of the cycle would result. Generally the shorter the 'on' time, the more critical is the pressure balance, depending on the design and capacity of the impeller and mixing chamber.
Pressure balance valve
A valve located somewhere in the return line between the mixer and the tank and used to help in balancing pressures. In some cases this valve is built into the mixing head, and in others it is separate and located on the tank. For some materials, particularly isocyanates, the construction of the valve is important, and it should be of a type that does not accumulate small particles. In most cases a filter is installed just prior to the valve to ensure more trouble free performance. The closer the valve is to the mixing head, the better is the performance. regulators are sometimes used for pressure balance instead of valves.
Pressure cut-off switch
A switch actuated by movement of a diaphragm or bourdon tube located near the pump in the flow circuit and arranged to cut off the power to the pump drive motor. This device protects the fluid circuit against damage from over press
Pressure developing
A technique used to gain more positive control of metering when a water-thin (1 cp) viscosity liquid must be metered at extremely small flow rates. This situation is encountered often when total prepolymer systems are used for filling very small cavities. With this technique a special needle valve or pressure regulator is installed in the flow circuit of the catalyst system between the metering pump and the mixing head and as close to the mixing head as possible. A back-pressure (between the valve and the pump) of at least 5 psig is maintained at all times. Very small inner diameter metering tubes must be used in the mixing head to keep the system liquid full at all times, but they must not be so small as to cause the pressure to rise during the 'on' cycle
Pressure gauge
A device for measuring and indicating pressure. It is not safe or practical to operate a urethane foam machine without accurate pressure gauges in all flow circuits.
Primary alcohol groups
Are reactive groups present in certain polyol molecules. Primary alcohol groups react faster than secondary alcohol groups. Usually, the higher the percentage of primary alcohol groups in the formulation, the less catalyst is required for curing. The term 'primary hydroxyl groups' is often used interchangeably.
Process Oil
A hydrocarbon oil used as a plasticizer in elastomers and classified as allaphatic, aromatic or naphthenic according to its chemical structure.
PTMEG
Poly Tetra Methylene Glycol
PU
The abbreviation for Polyurethane
Pumper
A term occasionally used to describe a metering unit.
Pumping impeller
A mixing blade designed to positively move the liquids being mixed through the mixing zone and through the discharge orifice by means of the force exerted by the pumping action designed into the mixing blade itself.
Q
Qualification conformance inspection
The examination of samples from a production run to determine conformance to a given specification.
Qualification inspection test
The examination of samples from a typical production run to determine conformance to a given specification for approval to become a supplier
Quasi-prepolymer (Quasi-system)
Quasi-prepolymers are defined as NCO-terminated products prepared from diisocyanates and polyols with NCO contents between 16 and 25 percent. These products can be processed like one-shot elastomers and yield elastome
R
Ratio control
The ability to change and regulate the ratio or proportion between 2 or more fluid components . This introduces versatility to a machine, enabling it to be used with several different formulations. A fixed ratio machine can be built that will work with only one formula under precise operating conditions, but these are rarely requested. raw materials-a term often used to describe the chemical ingredients used in manufacturing urethane foam. The term is generally applied to the chemicals as received from the chemical manufacturers prior to any premixing.
Rebound Test
The method of determining the resilient properties of a cured elastomer by measuring the rebound of a steel ball or pendulum from a defines height. Expressed as a percent.
Recipe
A written document detailing the composition, amount and process procedure for the making an elastomer.
Recovery
The degree an elastomeric material returns to its original dimensions after being stressed.
Register
The accurate matching of mold sections.
Regulator
A fluid control device usually consisting of a housing, a spring loaded diaphragm and a means for adjusting the spring tension. This can be used to control either the upstream or downstream pressure.
Reinforcement
The strengthening member of a polyurethane component.
Reinforcement agent
An ingredient in a polymeric compound used to increase its chemical and physical properties.
Reinforcing element
The strengthening members of polyurethane component or product.
Reproducibility
The ability to produce the same result at repeated intervals. This is a very important consideration in buying chemicals or machinery, since lack of reproducible control over any production variable can result in the production of poor quality foam.
Resilience value
A measure of the 'rubberiness' or elasticity of the product, in compression. One of the methods for measuring this is the 'Ball Rebound Test'.
Resin
Certain materials produced by chemical synthesis.
Resistance
The property or ability of matter to withstand the effects of force, pressure, heat or chemical action.
Rheology
Is the study of flow and deformation of matter
Ribbon blender
A type of internal mixer used to mix powders and liquids into a dry powderous viscous or liquid mass.
Rotor
A term sometimes used to describe a mixing blade or impeller
Run tanks
A term sometimes used to describe the machine tanks that form part of the metering system in order to distinguish them from bulk storage or premix tanks.
S
Sample
A piece of material removed for ewvaluation or testing
Scraper
Seam
The place where twomedges of fabric or elastomer are adjecent to each other to form a single ply of layer
Semi-cure
A partial or incomplete cure
Service Test
A test in which the product is made to operate under expected field conditions
Service Test
See bench test
Set
The amount of deformation remaining after complete release of the load producing the deformation. Can be tensile or compression.
Shape Factor
Ratio of loaded area to unloaded area of a urethane part under compression
Sheeting
A form (shape) of plastic or elastomer in which the thickness is very small in proportion to the length and width and in which the material is a continuous phase. Sometimes called sheetstock.
Shelf Storage Life
The period of time prior to use during which the product retains its intended performanace parameters
Shock Load
The sudden application of an external force.
Shore Hardness
Shrinkage
The dimensional difference between a molded part cooled to room temperature and its actual mold dimensions
Sink
A collapsed blister or bubble leaving a depression in the product
Skive
A cut made on an angle to the surface to produce a 6tapered or feathered cut
Specification
A detailed description of specific requirements
Specimen
A piece cut from a sample to test
Specimen (Test)
A piece of an elastomer appropriately shaped and prepared so that it is ready for testing.
Spread
To apply a thin coat of a liquid material over a surface determined by means of a knife, bar or doctor blade
Sprew
See Flash
Static Conductive
Capabillity to conduct static electricity
Static Electricity
Electrical potential between two objects
Static Friction
Then resistance which must be overcome to start a body in mtion
Stiffness
Resistance to flexing
Stoichiometry
the science of relative proportions of urethane components-closely realted to ratio
Strain
Deformation resulting from a force applied to abody
Stress0Strain
The relationshiop of force and deformation in a body during compression, extension or shear
Stretch
An increase in length
String Time
The time between pouring mixed urethane liquid into a container and the time it begins to form sting when touched with an object such as a spatula. Closely related to gel time
Sun Check
Fine cracks and crazing of an elastomeric surface primarily due to the sun's ultraviolet rays
Swelling
The increase in volume of an elastomer immersed in a liquid or exposed to a vapor over a set of defined conditions such as time, temperature, concentration and pressure.
T
Tack
Temporary adhesion
TDI
Abbreviation for toluene diisocyanate
Tear Propagation
Continuation of tear
Tear Strength
The load to tear apart an elastomer, expressed in pounds per linear inch
Tensile Set
The extension remaining after a specimen has been stretched and then allowed to relax in a specified manner. Expressed as a percentage of the original length.
Tensile Stess
The force applied to stretch a test piece (specimen)
Tensile Strength
The maximum force, stress,applied to a specimen at rupture
Tension
Stress on a material tending to cause extension of the material
Tension Fatigue
A fracture, caused by crack growth, of a component or test specimen subjected to repeated tensile deformation.
Terathane
DuPont trademark for polytetramethlene glycol (PTMEG)
Thermoplastic
Capable of being repeatedly soften by heating and cooling and in the soften state can be shaped by flow
Thermoset
A material that can undergo a chemical reaction bythe action of heat or catalyst,leading to a relatively infusible and cross-linked state. Thermoset polyurethane is not altered by elevated temperatures until reaching the decomposition point
TODI
Abbreviation for O-tolidine diisocyanate
Tolerances
The limiting values for a dimension
Trapped Air
Air which is enclosed in a product or between a product and a mold surface during cure
U
Ultimate elongation
Elongation at rupture.
Ultimate strength
The force required to rupture a specimen.
Ultimate tensile
Tensile stress at rupture.
Undercure
A less than optimal state of cure which may be evidenced by tackiness or inferior physical properties.
UV Stabilizer (Ultraviolet)
Any chemical compound which, when admixed with a resin, selectively absorbs UV rays. ultraviolet-zone of invisible radiations beyond the violet end of the spectrum of visible radiations. Since UV wavelengths are shorter than th
V
Viscoelasticity
A combination of viscous and elastic properties in an elastomer, with the relative contribution of each being dependent on time, temperature, stress and strain rate.
Viscosity
The resistance of a fluid to flowing readily. For example, a low viscosity material would flow readily from a container on being poured, while a high viscosity material would only pour slowly from a tipped container. The lower the number, the thinner the liquid.
Void
The absence of material or an area devoid of materials where not intended. See also blister and sink.
Vulcanizate
The product of molecular chain extension (growth) and crosslinking of a urethane elastomer.
W
Warpage
Dimensional distortion in a molded product.
Water Absorption
The amount of water absorbed by an elastomer under a set of specified test conditions. Expressed as a percent of the original dry weight of the test specimen or article.
Weathering
Surface deterioration, evidenced by cracks and crazing of an elastomer, during outdoor exposure.
Y
Yield point
The stress in a material at which a substantial increase in strain occurs with a minimum increase in stress.
Yield strength
The stress at which a material exhibits a specified limiting permanent set. Determined by a measurable value of plastic yielding of the material, above which the material is considered to be damaged and below which the damaging effects are considered to be negligible.
Young's modulus
Stress per unit strain for perfectly elastic material.
Z
Zero load
A reference load applied in taking an initial reading and prior to determining compressibility or extensibility.
