GLOSSARY OF TERMS
C

Carbon: element that provides the backbone for all organic polymers. Graphite is a more ordered form of carbon. Diamond is the densest crystalline form of carbon.

Carbon-Carbon: composite material consisting of carbon or graphite fibers in a carbon or graphite matrix.

Carbon Fiber: fiber produced by the pyrolysis of organic precursor fibers, such as rayon, polyacrylonitrile (PAN), and pitch, in an inert environment.

Casting: 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.

Catalyst: substance that changes the rate of a chemical reaction without itself undergoing permanent change in composition or becoming a part of the molecular structure of the product. A substance that markedly speeds up the cure of a compound when added in minor quantity as compared to the amounts of primary reactants. For this industry, used synonymously with initiator. See also Initiator, Accelerator, Curing Agent, Hardener, and Promoter.

Catastrophic Failures: totally unpredictable failures of a mechanical, thermal, or electrical nature.

Caul Plates: smooth metal plates, free of surface defects, the same size and shape as a composite lay-up, used immediately in contact with the lay-up during the curing process to transmit normal pressure and temperature, and to provide a smooth surface on the finished laminate.

Cavity: space inside a mold in which a resin or molding compound is poured or injected. The female portion of the mold. That portion of the mold that encloses the molded article (often referred to as the die). Depending on the number of such depressions, molds are designated as a single cavity or multiple cavity.

Centrifugal Casting: production technique for fabricating cylindrical composites, such as pipe, in which composite material is positioned inside a hollow mandrel designed to be heated and rotated as resin is cured.

C-glass: glass with a soda-lime-borosilicate composition.

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

Chemical Size: surface finish applied to a fiber that contains some chemical constituents other than water.

Chopped Strand Mat: fiberglass reinforcement consisting of short strands of fiber arranged in a random pattern and held together with a binder.

Clamping Pressure: in injection molding and transfer molding, the pressure that is applied to the mold to keep it closed in opposition to the fluid pressure of the compressed molding material.

Cloth: fiberglass reinforcement made by weaving strands of glass fiber yarns.

Coefficient of Elasticity: reciprocal of Young’s modulus in a tension test.

Coefficient of Thermal Expansion (CTE): how much a material shape will change for each degree of temperature change.

Cohesion: the propensity of a single substance to adhere to itself. The internal attraction of molecular particles toward each other. The ability to resist partition of itself. The force holding a single substance together.

Cold Flow: the distortion that takes place in materials under continuous load at temperatures within the working rage of the material without a phase or chemical change.

Compaction: the application of a temporary vacuum bag and vacuum to remove trapped air and compact the lay-up; also in SMC machines for removal of air prior to roll-up.

Compatibility: the ability of two or more substances combined with one another to form a homogeneous composition of useful plastic properties; for example, the suitability of a sizing or finish for use with certain general resin types.

Composite: chemical or mechanical bonding of dissimilar materials such as glass fiber and polyester resin, whose cumulative properties are superior to the individual materials.

Composite Material: a combination of two or more materials (reinforcing elements, fillers, and composite matrix binder). The constituents retain their identities; that is, they do not dissolve or merge completely into one another although they act in concert. Normally, the components can be physically identified and exhibit an interface between one another.

Compound: the intimate admixture of a polymer with other ingredients, such as fillers, softeners, plasticizers, reinforcement, catalysts, pigments, or dyes. A thermoset compound usually contains all the ingredients necessary for the finished product, while a thermoplastic compound may require subsequent addition of pigments, blowing agents, and so forth.

Compression molding: a process where a mold is open when the material is introduced and shapes the material by the pressure of closing and by heat. All Schmelzer Industries veils are appropriate for use in compression molding.

Compressive modulus: ratio of compressive stress to compressive strain below the proportional limit. Theoretically equal to Young’s modulus determined from tensile experiments.

Compressive strength: the ability of a material to resist a force that tends to crush or buckle. The maximum compressive load sustained by a specimen divided by the original cross-sectional area of the specimen.

Condensation polymerization: a chemical reaction in which two or more molecules combine, with the separation of water or some other simple substance.

Conductivity: reciprocal of volume resistivity. The electrical or thermal conductance of a unit cube of any material (conductivity per unit volume).

Conformability: Ability of the mat to conform to difficult shapes without causing wrinkles or leaving excessively resin-rich or glass-rich radii, which may craze. Schmelzer Industries offers fiberglass veils with excellent conformability.

Contact molding: Refers to the use of a single or open mold onto which layers of polymer and reinforcement materials can be applied. Contact molding is characterized by one finished cosmetic side. Cure is either at room temperature using a catalyst-promoter system or by heating in an oven, without additional pressure.

Continuous Filament Yarn: yarn formed by twisting and or plying tow or more continuous filaments into a single continuous strand.

Continuous Laminating: 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.

Continuous Strand: fiberglass mat of very long individual fibers with a regular crossed pattern loosely held together with a binder.

Copolymer: a long-chain molecule formed by the reaction of two or more dissimilar monomers.

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. The central member, usually foam or honeycomb, of a sandwich construction to which the faces of the sandwich are attached or bonded. The central member of a plywood assembly. A channel in a mold for circulation of heat transfer media. A device on which prepreg is wound.

Corrosion resistance: the ability of a material to withstand contact with ambient natural factors or those of a particular artificially created atmosphere, without degradation or change in properties. For metals, this could be pitting or rusting; for or organic materials, it could be crazing. Schmelzer Industries uses corrosion resistant “A” glass to prevent corrosive substances from marring your composite.

Coupling agent: any chemical substance designed to react with both the reinforcement and matrix phases of a composite material to form or promote a stronger bond at the interface.

Crazing: cracking of gel coat or resin due to stress. Region of ultra-fine cracks, which may extend in a network on or under the surface of a resin or plastic material. May appear as a white band. Often found in a filament-wound pressure vessel or bottle.

Creel: a device for holding the required number of roving balls (spools) or supply packages of reinforcement in desired position for unwinding onto the next processing step, that is, weaving, braiding, or filament winding.

Creep: the change in dimension of a material under load over a period of time, not including the initial instantaneous elastic deformation. The time-dependent part of strain resulting from an applied load.

Creep, rate of: rate of the slope of the creep-time curve at a given time. Deflection with time under a given static load.

Cross-Linking: setting up of chemical bonds between molecule chains which occurs in all thermosetting resins during cure. Styrene monomer is a cross-linking agent in polyester resins.

C-Stage: the final stage in the reaction of certain thermosetting resins in which the material is practically insoluble and infusible.

CTE: see Coefficient of Thermal Expansion.

Cure: completion of the cross-linking process during which a composite develops its full strength. Cure may be accomplished by addition of curing (cross-linking) agents, with or without heat and pressure.

Cure cycle: the time/temperature/pressure cycle used to cure a thermosetting resin system or prepreg.

Cure Time: period between introduction of the catalyst to a polymer and final cure.

Curing agent: a catalytic or reactive agent that, when added to a resin, causes polymerization. Also called hardener.

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