Definitions /Dictionary/Glossary - nptel

Pregel: An unintentional extra layer of cured resin on part of the surface of a reinforced plastic.
(Not relating to "gel coat.")
Preheating: The heating of compound prior to molding or casting in order to facilitate the
operation or to reduce the molding cycle.
Premix: A molding compound prepared prior to and apart from the molding operations and
containing all components required for molding: resin, reinforcement, fillers, catalysts, release
agents, and other compounds.
Pre-ply: Layers of prepreg material, which have been assembled according to a user specified
stacking sequence.
Prepreg: Ready to mold or cure material in sheet form which may be tow, tape, cloth, or mat
impregnated with resin. It may be stored before use. The resin is partially cured to a "B" stage
and supplied to the fabricator who lays up the finished shape and completes the cure with heat
and pressure.
Pre-Release: The premature release of the gel coat or laminate from the mold. Pre-release
causes cosmetic or dimensional problems.
Pressure Bag: A membrane which conforms to the inside of a laminate laid up on a mold. The
membrane or bag is then inflated applying pressure, which consolidates and densifies the
laminate.
Pressure: The force or load per unit area.
Pressure-Bag Molding: A molding technique in which a flexible bag is placed over the contact
layup in the mold, sealed, and clamped in place, and pressure applied by compressed air, which
forces the bag against the part while the part cures.
Primary Laminate: Laminate applied after the skin coat has cured. Generally thicker than the
skin coat.
Print Through: "Telegraphing" of the image of glass strands through the gel coat film.
Promoter: See Accelerator.
Proportional Limit: The maximum stress that a material is capable of sustaining without any
deviation from the proportionality of stress to strain (also known as Hooke's law).
Prototype: Process of creating a test part not intended for commercial release that establishes
design, material and fabrication parameters for a new product. May entail multiple iterations to
arrive at final/commercial part design.