Composite Glossary

 

A 

ACCELERATOR

An additive to polyester resin that speeds up the cure and is usually used in conjunction with a promoter. See Promoter

 

ACETONE

A ketone group solvent that is used to dissolve polyester resins. Used to a large extent for clean up of tools in fiberglass operations.

 

ADHESIVE

A bonding substance that creates a molecular attraction, holding two surfaces together.

 

AIR DRY

A resin or paint that dries through the loss of solvent or monomer.

 

AIR-INHIBITED RESIN

Resin that cures with a tacky surface due to their air inhibiting their cure in a thin surface layer.

 

ADDITIVE

Any number of materials used to modify the properties of polymer resins. Categories of additives include reagents, fillers, viscosity modifiers, pigments and others.

 

ALLIGATORING

A visible cosmetic defect in the exposed gel coat that looks like wrinkled or alligator skin.

 

ANTIMONY TRIOXIDE

Fire retardant additive for use with resins containing chloride or bromine.

 

ARAMID

Aromatic polyamide used to make high strength fibers, commonly known as Dupont KevlarTM.

 

ARCING

A spray gun stroke that moves the gun through an arc, thus changing the spray angle throughout the stroke. An arcing stroke should be avoided for proper spraying technique.

 

AUTOCLAVE MOLDING

Molding technique where a vacuum bagged composite lay-up is placed in a pressure chamber and heated to cure. A pressure of 50 to 100 psi consolidates the laminate.

 

AUTO-IGNITION TEMPERATURE

The temperature at which a substance experiences ignition in the absence of a spark or flame.

 

B

 

BAG MOLDING

An airtight film used to apply atmospheric force to a laminate. See Vacuum Bag Molding and Pressure bag.

 

BARCOL HARDNESS

A measure of surface hardness made with a Barcol Impressor instrument in accordance with ASTM D-2583. The harness value can be used as an indication of the degree of cure of FRP laminates.

 

BENZOYL PEROXIDE (BPO)

An initiator for curing polyester resin. BPO is used with aniline accelerators or where heat is used to cure the resin.

 

BI-DIRECTIONAL

Reinforcing fibers that are arranged in two directions, usually at right angles to each other.

 

BINDER

A resin soluble adhesive that secures the random fibers in chopped strand mat or continuous strand roving.

 

BLEEDER PLY

Layer of porous material placed in a vacuum bag to absorb excess resin and allow air and gas to escape.

 

BOND STRENGTH

Stress required (as measured by load/bond area) to separate a layer of material from another material to which it is bonded. Also, amount of adhesion between bonded surfaces.

 

BREAKOUT

Separation or breakage of fibers when edges of a composite part are drilled or cut.

 

BRIDGING

Fabric reinforcement extended over a curved edge that does not come into contact with rest of the composite.

 

BUCKLING

Failure mode usually characterized by fiber deflection rather than breaking.

 

BULK MOLDING COMPOUND (BMC)

Premixed blend of thermosetting resin, reinforcements, catalysts and fillers for use in compression, transfer, or injection molding process.

 

BLISTER

A void formed within a composite that may be the result of either trapping air in a laminate, or chemical action within the laminate.

 

C 

 

CASTING

The process of pouring a mixture of resin, fillers and/or fibers into a mold as opposed to building up layers through lamination. This technique produces different physical properties from laminating.

 

CARBON FIBER

A high strength-reinforcing fiber used in lightweight structural composites. Produced by pyrolysis of an organic precursor fiber in an inert atmosphere at temperatures above 1800oF. Material can also be graphitized by heat treating above 3000oF. See Graphic fiber.

 

CAST POLYMER

Non-reinforced composite (resin used without reinforcing fibers). Combines polymers, fillers and additives as composites to meet specific applications requirements.

 

CATALYST

Technically considered an initiator, catalyst is the colloquial name given to the substance added to the resin or gel coat to initiate the cure. The most common catalyst used in the composites industry are MEKP and BPO.

 

CATALYST INJECTION

Plural components spray equipment that mixes catalyst and resin at the spray gun or applicator.

 

CAULK

An elastic material used to protect joints or connections from external elements, particularly moisture.

 

CAVITY

The space between a male and female mold set in which the part is formed. Sometimes used to refer to a female mold.

 

CENTIPOISES

A unit of measure used to describe the viscosity of a liquid. Viscosity is measured with a Brookfield Viscometer for most polyester resin applications.

 

CHALKING

A surface phenomenon indicating degradation of a cosmetic surface. Chalking is a powdery film that appears lighter than the original color.

 

CHOPPED STRAND MAT

A fiberglass reinforcement consisting of short strands of fiber arranged in a random pattern and held together with a binder. Mat is generally used in rolls consisting of oz/ft2 material to 2 oz/ft2 material.

 

CLOTH

A fiberglass reinforcement made by weaving strands of glass fiber yarns. Cloth is available in various weights measured in ounces per square yard or Kg/m2.

 

COLOR STABILITY

The ability of a surface coating or pigment to resist degradation due to environmental exposure.

 

COMPOSITE

A material made of distinct components. For example; a reinforcing fiber in a resin matrix where the combined properties are superior to the individual materials.

 

COMPRESSION MOLD

A closed mold, usually of steel, used to form a composite under heat and pressure.

 

COMPRESSIVE MODULUS

A mechanical property description that measures the compression of a sample at a specified load. Described in ASTM D-695.

 

COMPRESSIVE STRENGTH

The stress a given material can withstand when compressed. Described in ASTM D-695.

 

CONNECTION

Where two panels are attached to each other or a panel is attached to the building.

 

CONTACT MOLDING

Refers to the use of a single or open mold onto which resin and reinforcement materials can be applied. Contact molding is characterized by one finished cosmetic side.

 

CONTINUOUS FILAMENT STRAND

A fiber bundle composed of many glass filaments. Also when referring to gun roving, a collection of string like glass fiber or yarn, which is fed through a chopper gun in the spray up process.

 

CONTINUOUS STRAND ROVING

A bundle of glass filaments which are fed through a chopper gun in the spray up process.

 

CONTINUOUS LAMINATING

An automated process for forming panels and sheeting in which fabric or mat is passed through a resin bath, brought together between covering sheets, and passed through a heating zone for cure. Squeeze rolls control thickness and resin content as the various plies are brought together.

 

CORE

A low-density material used between two FRP skins. Examples of core materials are end-grain balsa wood, urethane foam, PVC foam and various honeycomb materials.

 

CRAZING

Cracking of gel coat or resin due to stress.

 

CROSS-LINKING

The chemical bonding of molecules which in polymers occurs in the curing transition from a liquid to a solid.

 

CURE

The completion of the cross-linking process during which a composite develops its full strength.

 

CURING AGENT

An initiator or catalyst that initiates polymerization when added to a resin.

 

CURE TIME

Time between introduction of catalyst or initiator to a polymer and final cure.

 

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