Glossary
A— D
Abrasion
 The wearing away of a surface by rubbing or scraping.
Adhesion
 The state in which two surfaces are held together by interfacial forces which may consist of valence forces, or interlocking action, or both.
Air Locks
Surface depressions on molded part caused by trapped air between the mold surface and the plastics material.
Autoclave
 A device for applying pressure and heat to a tool. (Might be compared to a modern pressure cooker.)
Bag-Molding
 Application of fluid pressure, usually air or vacuum, to a flexible membrane or bag enclosing the material to be molded.
Blending
Mixing of various ingredients of a molding composition, or of several batches of the same type, to ensure uniform distribution of all particles. Called dry blending or wet blending depending on condition.
Bubble
 A globule of air or other gas trapped within a plastic.
Cast
To form a plastic material into a definite shape by pouring it into a mold and letting it harden without applying external pressure. Can be accomplished with or without application of external heat either before or after pouring.
Casting
 The finished product of a casting operation. (Should not be used as synonym for molding.)
Cross-laminated
A laminate in which some, usually alternate, layers of material are oriented at right angles to the strongest direction in tension.
Cure
 To change the physical properties of a material by chemical reaction, which may be condensation, polymerization or vulcanization: usually accomplished by the action of heat and catalysts, alone or in combination with or without pressure.
Curing Agent
 A reactive chemical which causes a resin to cure. Also called hardener.
Delamination
An area over which initial adhesion between I materials has been lost.
Diluent
Any material which reduces the concentration of the fundamental resin; usually a liquid added to the resin to afford lower viscosity in order to facilitate working with the system.
Dimensional Stability
Ability of a product to retain its exact shape and dimensions under ordinary conditions of use.
Draw

To stretch a sheet of plastic material to fit a mold, to cup.

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E - L
Elongation
 The increase in length of a material under tension.
Endothermic
Indicating a reaction which absorbs heat.
Exothermic
 Indicating a reaction which liberates heat.
F.R.P.
Fiberglass reinforced plastic.
Fiber Pattern
Denotes the thread size and weave of glass cloth.
Filler
Inert material added to a plastic composition for purposes of reducing cost, modifying mechanical properties, to serve as a base for color effects, or to serve as a heat sink.
Flexible Molds
Molds that can be stretched to remove cured plastics.
Flexural Strength
The strength of a material in bending.
Gel
1. The name given to any gelatinous solid mass produced from a solution of a colloid body.
2. The "stage" at which a polymerizing resin composition thickens to a semi-solid state.
Gel Time
The time in minutes required for a specific quantity of mixed resin and hardener to become unworkable (gelled).
Heat Distortion Point
The temperature at which a test bar deflects under a given flexural load and a prescribed amount of heat.
Hygroscopic
The ability to absorb and retain atmospheric moisture.
Inert
 Not chemically reactive.
Impregnate
 To saturate reinforcement with plastic.
Laminate
 To unite sheets of material by a bonding material. Normally used in reference to flat sheets.
Lay-Up

The arrangement of reinforcing material (glass cloth) and the resin in its uncured state.

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M - R
Mil
.001 inch.
Mold
 The cavity or matrix into or on which the plastic composition is placed and from which it takes its form.
Mold Release
An agent used to prevent a plastic from sticking to the mold.
Mold Shrinkage
The immediate shrinkage a molded part undergoes when removed from a mold and cooled to room temperature.
Parallel laminated
A laminate in which all the layers of material are oriented parallel with respect to the strongest direction in tension.
Plastic
Anyone of a large and varied group of materials which consists of or contains as an essential ingredient an organic substance of large molecular weight and which, while solid in the finished state, at some stage in its manufacture has been or can be formed (cast, calendered, extruded, molded, etc.) into various shapes by flow usually through the application singly or together of heat and pressure.
Post-Cure
In certain resins complete cure and ultimate mechanical properties are attained only by exposure of the cured resin to higher temperatures. This second stage is the post-cure and is necessitated by the fact that the higher temperatures would resul1 in excessive reaction if used throughout the entire cure.
Polyurethane
 Thermosetting plastics used for flexible molds, protective coatings and abrasion resistant casting applications.
Pot Life
Regarding a resin mix, the time period between complete catalyzation and initial gelation, during which time the mix is said to be usable. Also called "working life".
Reinforcement
Material used primarily for strengthening a plastic product, i.e., fibrous glass, cotton, etc., which is impregnated with the plastics mixture. (Should not be used synonymous with filler.)
Room Temperature
 25° C (77° F)
Resin

A class of solid or semi-solid organic products of natural or synthetic origin, generally of high molecular weight with no definite melting point. (Resins are generally water-insoluble and have little or no tendency to crystallize. However, certain resins such as some polyvinyl alcohols and polyacrylates are readily dispersible in water; and others such as polyamides and polyvinylidene chloride are readily crystallized.)

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S — Z
Spline
To prepare a surface to its desired contour by working a paste material with a flat-edged tool. The procedure is similar to screeding of concrete.
Spray Up
 The technique of using a spray gun to prepare a reinforced plastic article.
Sprue
The main opening into a mold cavity through which a plastic material is introduced into the mold.
Starved Area
The area in a reinforced plastic part that did not have sufficient plastic to wet the reinforcement completely.
Tack
 Stickiness.
Thermal Conductivity
The ability of a material to conduct heat.
Thermoforming
Shaping a plastic material by heating it to its softening point and cooling it on a mold.
Thermoset
 A plastic which when cured changes into a substantially infusible or insoluble product.
Thixotropic Liquids
Liquids which reduce their viscosity as the agitation is increased, i.e., ketchup, latex paint.
Thixotrophy
 The property by which some compositions become semi-solid at rest and liquefy again on agitation.
Viscosity
The resistance of a liquid to flow. Thickness.
Voids
 Gas or air pockets trapped within a material.
Working Life
Same as "gel time", but may also be defined for other sizes of resin-hardener mixtures. That is, the working life of a one-pint unit is usually longer than the working life of a one-quart unit.

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