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Glossary
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→ A

Abrasion

Wearing away by friction.

Abrasion Resistance

Ability to resist surface wear; term usually applied to adhesive coatings.

Accelerator

A substance that hastens a reaction or the solidification of an adhesive caused by a catalyst.

Acid

A chemical substance usually corrosive to common metals (iron, aluminum, zinc). Acids are generally divided into two classes: (a) Strong mineral or inorganic acids such as sulfuric, phosphoric, hydrochloric or nitric, (b) Weak organic or natural acids such as acetic (vinegar), citric (citrus fruit juices), oxalic and fatty acids (oleic, palmitic, stearic, etc.).

Acidity

A general term applying to substances on the acid side of neutral-principally the degree of acidity (1 - 7 on the Ph scale, 7 being neutral).

Acid Value

The acid value is the number of milligrams of potassium hydroxide necessary to neutralize the free acids in 1 gram of sample. With samples that contain virtually no free acids other than fatty acids, the acid value may be directly converted by means of a suitable factor to percent free fatty acids.>

Adhesive

A substance capable of holding materials together by surface attachment. Note- Adhesive is the general term and includes among other cement, glue, mucilage and paste. All of these terms are loosely used interchangeably.

Adhesive Batch

A homogenous quality of finished adhesive manufactured under controlled conditions at one tine or representing a blend of several manufactured units of finished adhesives of the sane formulation and processing.

Aggregate

A hard fragmented material used with an epoxy binder as a flooring or surfacing medium. Also a coarse filler used as a core for epoxy tools.

Aging

The change in properties of a material with time under stated conditions.

Alkali

A chemical substance which effectively neutralizes acid material so as to form neutral salts. A base. The opposite of acid. Examples, ammonia and caustic soda.

Alkalinity

A general term applying to substances on the base side of neutral-principally the degree of alkalinity (7 - 14 on the Ph scale, 7 being neutral).

Amine

Curing agent for epoxy resins that is any of a class of ammonia derivatives. The are derived from Ammonia (NH3) by replacement of 1, 2 or 3 hydrogen (H) atoms by univalent hydrocarbon radicals (R).

Artificial Weathering

The exposure of product to cyclic laboratory conditions involving changes in temperature, relative humidity, and ultra violet radiant energy, with or without direct water spray, in an attempt to produce changes in the material similar to those observed after continuous outdoor exposure. Note- The laboratory exposure conditions are usually intensified beyond those encountered in actual outdoor exposure in an attempt to achieve an accelerated effect.

ASTM

American Society for Testing Materials.

→ B

B-Stage

An intermediate stage in the reaction of certain thermosetting resins in which the material softens when heated and swells when in contact with certain liquids, but may not entirely fuse or dissolve. The resin in an uncured thermosetting system, is usually in this stage. Sometimes referred to as Resistol. ( See also A Stage; and C Stage.)

Baking Temperature

A temperature above 150°F.(65.6°C). Refers to curing materials at these elevated temperatures.

Binder

An adhesive substance, usually of liquid or molten form, used to create adhesion between aggregates, globules, etc. Distinguished from an adhesive in that it performs an internal adhesive function rather than a surface adhesive function.

Bisphenol A

A condensation product formed by the reaction of two molecules of phenol with acetone. This polyhydric phenol is the standard intermediate resin that is reacted with epichlorohydrin in production of epoxy resins.

Bisphenol F

A higher functionality liquid epoxy resin.

Body

The consistency of an adhesive; thickness; viscosity.

Bond

The union of materials by adhesives.

Bonding Operation

The curing of adhesives applied to details to effect the joining of parts into a single component.

Bonding Procedure

All operations connected with bonding, from the prefit of the formed details through their assembly for final bonding.

Bonding Process

All operations connected with the manufacture of assemblies whose parts are joined by adhesives.

Bond Strength

The unit load applied in tension, compression, flexure, peel, impact, cleavage, or shear, required to break an adhesive assembly with failure occurring in or near the plane of the bond. Note-The term adherence is frequently used in place of bond strength.

Brookfield Viscosimeter

An instrument for measuring the viscosity of formulated adhesives under standard conditions of temperature, speed and spindle

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→ C

C-Stage

The final stage in the reaction of certain thermosetting resins in which the material is relatively insoluble and infusible. Certain thermosetting resins in a fully cured state are in this stage.( See also A Stage; and B Stage.)

Cab-O-Sil

Trade name for anhydrous silica used as a thixotropic agent for adhesives, usually as a filler.

Calorie

A thermal unit. A calorie is that amount of heat required to raise the temperature of one gram of water, one degree centigrade.

Cast

(1) To form a plastic object by pouring a fluid resin into an open mold where it hardens. (2) Casting, the finished product.

Catalyst

A chemical substance added to thermosetting resin adhesives to speed up the cure time of these adhesives and to increase the cross linking of the synthetic polymer. A catalyst markedly speeds up the cure of an adhesive when added in minor quantity as compared to the amounts of the primary reactants.

Centigrade

A scale of temperature which features 0° and 100° as the freezing and boiling point of water respectively. To convert centigrade to Fahrenheit multiply by 1.8 and add 32, e.g., (100° x 1.8) + 32 = 212°F.

Centipoise

1/100th of a poise; (dyne-sec/cm2); a viscosity measurement unit.

Chalking

Formation of a dry powdery chalk-like appearance or deposit on the surface of a material. It is due to a breaking down of the material after being exposed to ultraviolet light, or other weathering.

Clarity

Degree of clearness in a cured epoxy system.

Closed-Cell Foamed Plastic

A cellular plastic in which there is a predominance of no interconnecting cells.

Coefficient Of Linear Thermal Expansion

Once cured, a measure of the change in length of an epoxy system over a given temperature range. It is expressed in inches per inch per degree C. ASTM D696-44.

Coefficient Of Thermal Expansion (CTE)

Change in a unit of length or volume that accompanies a unit change in temperature.

Cohesion

The state in which the particles of a single substance are held together by primary or secondary valence forces observed in the tendency of the substance to stick to itself. As used in the adhesive field, the state in which the particles of the adhesive (or the adhered) are held together.

Compressive Modulus

The ratio within the elastic limit of compressive stress to corresponding compressive strain (deformation per original length). It is expressed in pounds per square inch. ASTM D695-54.

Compressive Strength

Crushing load at the failure of a specimen divided by the original sectional area of the specimen.

Compressive Strength, Ultimate

The maximum load in pounds that can be carried per square inch of cross section of the material under test.

Conductive

Having the quality of power of conducting or transmitting heat, electricity, or static electricity.

Conductivity

Reciprocal of volume resistivity. Conductance of a unit cube of any material.

Contaminant

An impurity or foreign matter present in a bonded assembly which affects its usefulness.

Copolymer

A polymer formed by the reaction of two or more different monomers.

Coverage

A measure of the ability of the adhesive to be spread over adherend surfaces; the total amount of adhesive required per 1000 sq ft of bonded assembly.

Cross-Link

Tying together large molecules and hence changing the physical properties of material. Cross-linking usually involves formation of three dimensional molecular network and is customarily associated with thermosetting resins.

Cure

To change the physical properties of an epoxy by chemical reaction through polymerization, usually accomplished in the presence of heat and catalyst, alone or in combination.

Cure Cycle

The schedule of time periods at specified temperatures to which a reacting thermosetting plastic or rubber composition is subjected in order to reach certain specified properties.

Cure Period

The elapsed time the adhesive bond is required to remain at a specified cure temperature to produce a cure.

Curing Agent

A catalytic or reactive agent which when added to resin causes polymerization.

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→ D

Density

The ratio of a substance’s mass to its volume at a given temperature and pressure. Example-water at 25°C, 1 atmosphere of pressure =1.0 gr/cm3 = 8.35 lb. Per gallon.

Dielectric

A nonconductor of electricity; the ability of an adhesive to resist the flow of electrical current.

Dielectric Constant

When electrical energy is applied in a circuit, the insulating material of the electrical charge and releases it when the current is broken. Capacitance is the ratio of charge absorbed to the potential (voltage applied). Dielectric Constance is the ratio of an insulator's capacitance to that of dry air. (1.0). A dielectric constant of 5 means an insulator will absorb 5 times more electrical energy than air. The ratio of the parallel capacitance of a given configuration of electrodes with the epoxy system as the dielectric, the capacitance of the same electrode configuration with a vacuum as the dielectric (ASTM D150-5WT).

Dielectric Strength

The voltage which an insulating material can withstand before breakdown occurs, expressed in volts per Mil ((ASTM 149-61).

Diluent

A reactive or non-reactive additive whose primary function is to lower the viscosity and extend the material to which it was added.

Discoloration

Any change from an initial color possessed by a material, either due to environmental or internal conditions.

Dissipation Factor

The measure of electrical energy absorbed and lost in the insulating material when energy is applied in a circuit. 20-3060 has a dissipation factor of .01. This means that .01% of the energy being stored (capacitance) is lost. Dissipation factor is the ratio of the resistive component of a capacitor to the capacitive reactance of the capacitor. Also referred to as Loss Tangent (ASTM D150-59T).

Dry

To change the physical state of an adhesive of an adherend by the loss of solvent constituents by evaporation, absorption, or both.

Durometer hardness

The hardness of a material (usually applied to elastomerics) as measured by a shore durometer.

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→ F

Failure, Adhesive

The failure at the bond line between substrates and an adhesive; the adhesive separating entirely from the substrate.

Failure, Cohesive

Failure within the adhesive under a stress, resulting in a broken bond with all adhered surfaces still covered with adhesive.

Failure, Substrate

The failure of the substrate material itself, upon subjecting bonded adhered surfaces to a stress.

Fatigue

(1) A condition of stress created by repeated flexing or impact force upon the adhesive - adherend interface; (2) The failure or decay of mechanical properties after repeated stress applications. Fatigue tests provide information on the ability of an adhesive to resist the development of cracks which will bring about failure as a result of continued cyclic bonds.

Filler

A relatively non-adhesive substance added to an adhesive to make it less costly, or to improve physical properties, particularly hardness, stiffness, impact strength, workability, permanence, color, and electrical properties.

Film

The thin level application of an adhesive or coating to a surface or substrate. In the plastics industry, an optional term for a thermoplastic material having a thickness not greater than 0.010 inch.

Film adhesive

An adhesive that has been placed on a carrier or calendared into a thin film (0.002 to 0.016 inch).

Film forming

The property or ability of an adhesive substance to cast a dimensionally stable continuous film. Also refers to the relative strength of a cast adhesive film. Adhesives with good film-forming characteristics are those which tend to deposit more uniform films of high structural strengths.

Fisheye

Small globular mass which has not blended completely into the surrounding material and is particularly evident in a transparent or translucent material.

Flame Retardance

The ability of an epoxy system to resist combustion or burning. Some materials tend to extinguish themselves when subjected to a flame. Such materials are classified as self-extinguishing. ASTM D790-63.

Flash Point

The temperature at which the material gives off flammable vapor in sufficient quantity to ignite momentarily on the application of a flame under specified conditions.

Flexural Modulus

The ratio, within the elastic limit, of flexural stress to the corresponding strain. It is expressed in pounds per square inch. ASTM D790-63.

Flexural Strength

Ability of a material to withstand failure due to bending.

Flow

Movement of the epoxy during the curing stages before completely cured.

Forced Drying Temperatures

A temperature between room temperature and 150°F.(65°C).

Fusible

Capable of being melted or fused together by melting.

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→ G

Gallon, U.S

A volume equal to 231 cubic inches (3.7853 liters) measured at 25°C. (77°F).

Gel

The initial jelly-like solid phase that develops during the transition from a liquid to a solid. Note- In this state the epoxy is soft, flexible, and has no strength.

Gelation time

That interval of time, in connection with the use of synthetic thermosetting resins, extending from the introduction of a catalyst into a liquid adhesive system until the interval of gel formation.

Glass Transition Temperature (Tg)

Approximate midpoint of the temperature range over which a material undergoes a phase change from brittle to rubbery or vice versa.

Glue joint

The area of a bonded assembly where the adhesive and adherend are in contact.

Glue line

The adhesive layer between two adherends.

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→ H

Hardener

A substance or mixture of substances added to an adhesive to promote or control the curing reaction by taking part in it. The term is also used to designate a substance added to control the degree of hardness of the cured film.

Hardness

The resistance of surface indentation usually measured by a prescribed hardness tester.

Heat Distortion (Deflection) Temperature

The temperature at which a standard test bar (ASTM D-648)deflrcts 0.010 in. under a stated load of either 66 or 264 psi.. It is not usually considered to be beyond the maximum usable temperature, but is an indication of the maximum usable temperature when the material is load bearing at a given load. As the load decreases, the maximum usable temperature will increase.

Heat Sink

A contrivance for the absorption or transfer of heat away from a critical part or detail.

Humidity (Absolute)

The amount of moisture present in the atmosphere expressed in grams per cubic meter.

Humidity (Relative)

The ratio of the amount of moisture contained in the atmosphere to the amount of moisture that can be carried in the atmosphere at a given temperature. Relative humidity is expressed in percent, e.g., 75% R.H. at a given temperature means that the air is 75% saturated with moisture.

Hydrophilic

Capable of absorbing water.

Hydropholic

Capable of repelling water.

Hygroscopic

A property of absorbing and holding moisture.

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→ I

Iodine Value of Fats and Oils

The iodine value is a measure of the unsaturation of fats and oils and is expressed in terms of the number of centrigrams of iodine absorbed per gram of sample (% iodine absorbed).

Impact resistance

Relative susceptibility of adhesives to fracture by shock, e. g., as indicated by the energy expended by a standard pendulum-type impact machine in breaking a standard specimen in one blow.

Impact shock

A stress transmitted to the adhesive interface resulting from the sudden jarring or vibration of the bonded assembly.

Impact strength

(1)The ability of a material to withstand shock loading; (2) the work done in fracturing, under shock loading, a specified test specimen in a specified manner.

Impact test

Measures the energy necessary to fracture or break an adhesive joint as a result of a swinging pendulum or other impact device.

Impregnate

To fill the voids and spaces of an electrical unit with a compound; to provide liquid penetration into a porous or fibrous material; the dipping or immersion of a fibrous substrate into an adhesive liquid.

Inorganic

Applies to the chemistry of all elements and compounds not classified as organic (carbon); matter other than vegetable, such as earthy or mineral matter.

Inorganic pigments

Natural or synthetic metallic oxides, sulfides, etc., calcined during processing at 1200 to 2200°F. They impact heat stability, weathering resistance, color, etc., to adhesives.

Instron

An instrument utilized to determine the tensile and compressive properties of material.

Insulation Resistance

The ratio of the direct voltage applied to electrodes in contact with an epoxy system to the total current between them. It is dependent upon both the volume and surface resistance of the epoxy systems. ASTM D257-61.

Intermittent Operating Or Service Temperature

The temperature to which the epoxy system can be subjected for short periods of time without degradation of its properties.

Internal stress

Stress created within the adhesive layer by the movement of the adherends at differential rates or by contraction or expansion of the adhesive layer.

Izod Impact Strength

A measure of the brittleness of a material. Brittle materials will have low izod impact values (.15 for example). Tough materials will have high izod impact strengths (.60 for example). The Izod Impact Test is a destruetive test designed to determine the resistance of an adhesive to the impact of a suddenly applied force.

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→ J

Jig

A clamping device used to immobilize the bonded assembly until complete solidification of the adhesive film has taken place.

Joint

The location at which two adherends are held together with a layer of adhesive.

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→ K

Kinetic viscosity

The viscosity / density ratio.

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→ L

Lap joint

A joint made by placing one adherend partly over another and bonding together the overlapped portion.

Long time exposure

A relative term, found in most military specifications for adhesives, used normally to designate an exposure period of 192 hours duration to any desired medium or condition.

Loss factor

The product of the power factor and the dielectric constant.

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→ M

Mandrel

The core around which paper, fabric, or resin-impregnated fibrous glass is wound to form pipes or tubes.

Matrix

The part of an adhesive which surrounds or engulfs embedded filler or reinforcing particles and filaments.

Maximum Service Temperature

Highest recommended continuous use temperature based upon thermal endurance and historical data.

Melting point

The temperature at which a resin changes from a solid to a liquid.

Migration

A condition of extraction whereby a solvent, be it water or an organic solvent, selectively dissolves a portion of the adhesive film; the transferal of the plasticizer portion of an adhesive into the adherend resulting from the attraction of the adherend composition to the plasticizer used in the adhesive material composition.

Miscible

Capable of being mixed; mutually soluble in each other.

Modifier

Any ingredient added to an epoxy formulation that changes its properties.

Modulus in flexure

The ratio of the flexure stress to the strain in the adhesive over the range for which this value is constant.

Modulus of elasticity

The ratio of stress to strain in a material that is elastically deformed.

Moisture absorption

The pickup of water vapor from the air by an adhesive. This relates only to vapor taken from the air by a material and must be distinguished from water absorption which results in a weight gain due to water pickup by immersion.

Moisture Resistance

Having some resistance to high humidity. A moisture resistant adhesive will not be easily affected by moisture. Will not easily change its chemical and physical properties due to moisture. Should not be confused with "water proof."

Mold release

A liquid, powder, or other "slip agent" used to prevent adhesion to tools, molds or substrates during a bonding operation.

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→ N

Novolac

A phenolic resin which, unless a source of methylene groups is added, remains permanently thermoplastic.

Nylon

A generic name for all synthetic polyamides.

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→ O

OHM Unit

Unit of electrical resistance. Resistance of a circuit in which a potential difference of one volt produces a current of one ampere.

Opaque

Any material is opaque if no light can be transmitted through it.

Operating Or Service Temperature

The temperature at which an epoxy system can operate continuously without degradation of its properties.

Orange-Peel

Uneven surface somewhat resembling an orange peel.

Organic

Designating or composed of matter originating in plant or animal life or composed of chemocals of hydrocarbon origin, either natural or synthetic.

Overlap

A simple adhesive joint in which the surface of one adheremd extends past the leading edge of another.

Oxidation

The chemical reaction involving the process of combining with oxygen to form an oxide; the deterioration of an adhesive film due to atmospheric exposure; the breakdown of a hot-melt adhesive due to prolonged heating and oxide formation.

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→ P

Paste

An adhesive composition having a characteristic plastic-type consistency, a high order of yield value, low bond strength and higher viscosity.

Peel strength

Bond strength of an adhesive in pounds per inch width, using a standard peel test.

Pigment

The fine solid particle, usually inorganic, used in the preparation of colored products, and substantially insoluble in the vehicle. In contrast, a dye is soluble.

Pit

Small regular or irregular crater in a surface, usually with its width approximately of the same order of magnitude as its depth.

Poise

A unit of measurement for viscosity, a 100 centipoise = 1 poise; (dyne-sec/cm2);

Polurethanes

Synthetic polymers that may be either thermosetting or thermoplastic and range from soft and rubber-like to hard and brittle. They are usually made by the action of toluene diisocyanate or another diisocyanate with poyols, polyethers, polyesters, amines, or other materials containing active hydrogens.

Polyester

A resin formed by the reaction between a dibasic acid and a dihydroxy alcohol, both organic. Modification with multifunctional acids and/or bases and some unsaturated reactants permits cross linking to thermosetting resins. Polyesters modified with fatty acids are called alkyds.

Post-cure bonding

Post curing at elevated temperatures after parts have been removed from the autoclave or press to obtain higher heat-resistant properties of the adhesive bond.

Pot Life

The length of working time of a two component reactive system from the time of the addition of the curing agent in a specific mass (i.e. 100 grams). It is expressed in minutes.

Potting

Similar to encapsulating, except that steps are taken to insure complete penetration of all the voids in the object before the resin polymerizes.

Premix

An adhesive that has all the ingredients mixed to produce a joint and is then sealed or frozen for preservation until ready for use.

P.S.I.

Pounds per square inch; a unit measure of pressure.

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→ Q

Qualification tests

An investigation, independent of a procurement action, performed on an adhesive product to determine whether or not the product conforms to all requirements of the proposed application.

Quality assurance

The function of evaluating product quality and the procedures taken to ensure that the final product conforms to the specification requirements. It has for its purpose the continuing assurance of the customer that the product he receives is of, or better than, the quality level he expects.

Quality control

Monitoring and controlling the usefulness of the end product.

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→ R

Range

The difference between the extreme high and low test values from specimens cut from one test assembly.

Release agent

A material which is placed on tooling or other objects to prevent the adhesive from adhering to them during a bonding operation. The agent may be a mineral spray release or a plastic sheeting as Teflon.

Resin applicator

A device for applying or spreading an adhesive resin system.

Resin content

The amount of resin in a laminate expressed as a percent of total weight or total volume.

Resin-rich edge

Insufficient reinforcing material at the of the molded laminate.

Resin starved

Describing an area having an insufficient amount of resin.

Resistivity

The ability of a material to resist passage of electrical current either through its bulk or on a surface. The unit of volume resistivity is the ohm-cm, of surface resistivity, the ohm.

Rheology

Pertaining to viscosity behavior; the viscosity of an adhesive material under conditions of shear; the plastic flow properties of an adhesive interface.

Room temperature

As used in most specifications for adhesives and adhesive bonding, this term applies to temperatures within the range of approximately 75°F. +/- 5°F.

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→ S

JSaponification Value

The saponification value is the amount of alkali necessary to saponify a definite quantity of the sample. It is expressed as the number of milligrams of potassium hydroxide (KOH) required to saponify 1 gram of the sample.

Set

To convert an epoxy into a fixed or hardened state by chemical or physical action through polymerization.

Setting temperature

The temperature to which an adhesive or an assembly to be subjected to heat or pressure, or both, in order to set the adhesive.

Setting time

The period or time required for an assembly to be subjected to heat or pressure, or both, in order to set the adhesive.

Shear Strength

The shear force required to break a specimen divided by its cross-sectional area; the force being applied parallel to the cross-sectional area.

Shelf life

The period during which the manufacturer guarantees that an adhesive stored at some specified temperature will produce specified mechanical properties when used.

Shore A Hardness

The reading of a material's hardness on a durometer, the scale of which is 0-100, used on elastomers and other flexible materials. Consists of a pin point depression into the material, the material being at least 100 mils thick. A Shore A reading of 80 equal a Shore D reading of 30.

Shore D Hardness

The reading of a material's hardness on a durometer similar to the Shore A durometer, the scale of which 0-100, used on rigid and semi-rigid materials. Consist of a pin point depression into the material. Both the Shore A and Shore D instruments are made by the Shore Instrument Manufacturing Company, Inc., Jamaica, NY.

Shrinkage

The measure of shrinkage occurring during cure of an epoxy system. The term refers generally to linear shrinkage and is expressed in inches per inch. The decrease in volume, or contraction, of a material by the escape of any volatile substance, or by a chemical or physical change in the material.

Softening Range

The range of temperature in which a thermoplastic changes from a rigid to a soft state.

Solids contents

The percentage by weight of the nonvolatile matter in an adhesive.

Specific Gravity

The ratio of the weight of any volume of a mass or substance to the weight of an equal volume of water at given temperature. The specific gravity of a substance times the density of water equals the density of the substance. The density of water = 1.00

Stage

An early stage in the reaction of certain thermosetting resins in which the material is fusible and still soluble in certain liquids. (See also B Stage and C Stage)

Starved joint

A joint which has an insufficient amount of adhesive to produce a satisfactory bond.

Storage life

The period of time during which a packaged epoxy or curing agent can be stored under specific temperature conditions and remain stable for use. Sometimes called shelf life.

Stress

An applied force or pressure, as tension or shear, exerted on a body which produces a resultant strain on the material. The ability of material to withstand a stress depends on the strength of its cohesive force or molecular resistance.

Stripper

A compound used to remove undesirable foreign material from a surface. Such compounds should possess good penetration, rinse freely and not attack the substrate.

Stripping

The removal of undesirable substance from a surface by abrasive or chemical action.

Structural adhesive

An adhesive having sufficiently high mechanical properties, when cured, that it may safely be used for bonding parts in assemblies where human lives, valuable equipment, or both, are involved.

Substrate

A material upon the surface of which an epoxy is spread for any purpose, such as bonding or coating.

Surface Resistivity

The resistance to a current flow along the surface of an insulator material. Measure in ohms/cm.

Surface Tension

The property of a liquid which causes the surface to pull into the smallest area for a maximum volume, hence, drops are spherical. The fact that water drops on a wax surface do not spread out due to surface tension. If a wetting agent were to be added to the water the round droplet would spread out into a film because of the lowered surface tension.

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→ T
Titer Test

Definition: This method determines the solidification point of fatty acids.

Temperature, Curing

The temperature to which an adhesive or an assembly is subjected to cure the adhesive. Note-The temperature attained by the adhesive in the process of setting it may differ from the temperature of the atmosphere surrounding the assembly.

Tensile Modulus

A measure of stiffness, i.e., how much a material will bend, stretch or compress under a given load and still come back to its original size and shape. When measured in compression, it may be referred to as "compressive modulus". The same thing holds true for tension and flexural moduli. The modulus will be given in terms of pounds per inch and may be expressed exponentially, e.g. 8.8 x 104, which merely means 88,000 psi.

Tensile Strength

The pulling force necessary to break a given specimen divided by the cross sectional area. Units given in lbs./in/2(P.S.I.). It measures the resistance of a material to stretching without rupture. Normally is not used with reference to elastic materials which recover after elongation.

Thermal Conductivity

A measure of how rapidly heat is conducted through a material. To convert BTU/sq. ft./sec./in. to calories/sq. cm./sec./per cm., multiply by 1.2404.

Thermal decomposition

Breakdown of an adhesive caused by heat.

Thermal expansion (Coefficient of)

The fractional change in length (some times volume, specified) of a material for a unit change in temperature. Values for plastics range from 0.01 to 0.2 mils/inch.,°C.

Thermal Shock Resistance

The ability of a cured system to resist cracking or crazing under conditions of rapid and continuous thermal change. The 1/4 inch Olyphant Washer test is cycled over a temperature range of -55°C to +125°C, this temperature is normally used as the test condition unless otherwise stated.

Thermoplastic

A material which will repeatedly soften when heated and harden when cooled.

Thermosetting

Describes the property of an epoxy, to set or become rigid and non-meltable when heated with or without pressure.

Thixotropy

The property of certain gelatin systems of becoming fluid on agitation, and coagulating again when left at rest. This type material is called thixotropic

Time, Curing

The period of time during which an assembly or part may be subjected to heat or pressure, to cure the epoxy. It is the time between the addition of curing agent to the resin, and completed polymerization.

Trowel

To spread a high-viscosity adhesive material by spatula, knife, spreader bar, etc.

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→ U

Undercure

Results of a shortened cure cycle or the applied temperature is not sufficient to polymerize the adhesive.

Unfilled

No non-adhesive substance added to an adhesive.

Usable life

The maximum number of minutes or hours allowed to elapse between the time an adhesive is sampled for quality-assurance evaluation testing and the time the adhesive is cured.

Unsaponification Value

Unsaponifiable matter includes those substances frequently found dissolved in fatty acids and drying oils which cannot be saponified by caustic treatment, but which are soluble in the normal fat solvents. Included are the higher aliphatic alcohols, sterols, pigments, and hydrocarbons.

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→ V

Vapor degreasing

A cleaning process that employs the hot vapors of a chlorinated solvent to remove soils-particularly oils, grease and Waxes.

Viscosity

A measure of the fluidity of a liquid as determined by its internal fluid friction. The property of resistance to flow exhibited within the body of a fluid. The ratio of the shear stress existing between laminae of moving fluids and the rate of shear between these laminae; internal frictional resistance of an adhesive to flow (directly proportional to the applied force). Usually measured in centipoise.

1 cps = Water

400 cps = #10 Motor Oil

1,000 cps = Castor Oil

3,500 cps = Karo Syrup

25,000 cps = Hersheys Chocolate Syrup

Viscosity coefficient

The shearing stress tangentially applied that will induce a velocity gradient. A material has a viscosity of one poise when a shearing stress of 1 dyne/cm2 produces a velocity gradient of 1 cm/sec2.

Volatiles

Gaseous materials in an adhesive formulation that are driven off or liberated during the curing reaction.

Volume Resistivity

The ratio of the electrical resistance through a cross section A divided by the length through which the current flows. Measured in ohms/cm.

Volume Shrinkage (%)

Amount of dimensional change during cure.

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→ W

Water Absorption

Ratio of the weight of water absorbed by an adhesive to the weight of the same material in a dry condition.

Waviness, Surface

Wave-like unevenness, or out-of-plane in a surface.

Wetting

The relative ability of a liquid adhesive to display interfacial affinity for an adherend and to flow uniformly over the adherend surface. The more viscous a fluid, and the higher its surface tension, the more difficult it is for the liquid to "wet" materials. Wetting agents are added to help reduce surface tension, or viscosity and improve wetting properties.

Working Life

The period of time during which an epoxy after mixing with a curing agent, remains workable.

Working time

A measure of the interval of time during which an adhesive may be effectively applied to the adherend surface before adhesive setting retards flow and application properties of the adhesive.

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→ X

X axis

The horizontal directional flow of an adhesive or the horizontal directional flow of electricity through a conductive material or device.

→ Y

Y axis

The vertical directional flow of an adhesive or the vertical directional flow of electricity through a conductive material or device.

Yellowing

A color change in an unpigmented system, usually due to exposure to Ultraviolet rays or other weathering conditions.

Yield Strength

The load in pounds per square inch where the material under test begins to change dimensions and will not completely recover when the load is removed. Yield strength will normally be lower than ultimate strength. Generally speaking, the more rigid a material is, the closer will be yield and ultimate strengths. Furthermore, the more resilient a material is, the greater the spread between yield and ultimate strengths.

Young's modulus

The ratio of the tensile stress to tensile strain below the proportional limit.

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→ Z

Z axis

The third axis in a three dimensional configuration. The Z axis often refers to the height or thickness of a conductive material or device

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Harnessing the ability of wax molecules