One of the most common is rigid polyurethanefoam, which is used for flotation, insulation or as a core material. Flexible foams are used for seating, pads and soft grips in a variety of recreational industries. Non-foaming urethanes can be formulated into waterproof coatings, rigid plastics or elastomeric (rubber-like) materials.
Catalysts
By balancing catalysts, inhibitors and accelerators, manufacturers can change or control a resin’s cure profile in terms of shelf life, pot life, gel time, cure temperature and viscosity.
Methyl ethyl ketone peroxide (MEKP), benzyl peroxide (BPO) and other catalysts and high temperature initiators are available.
Core Materials
Used in sandwich composite construction, core materials add stiffness and strength to a product with only minimal weight increase. Reinforced laminate skins applied to both sides of the core take the loading. The core’s purpose is to keep the skins a specified distance apart. Increasing core thickness geometrically increases the stiffness of the core structure.
Commonly used core materials include balsa wood, PVC foam, urethane foam, core mat and honeycomb.
Gel Coats and Pigments
Gel coats are specially modified resins with greater impact and abrasion resistance as well as better surface appearance. Pigmented gel coats provide a finished color to fiberglass parts. Standard are Iso, Iso-NPG and tooling grades. Also available are specialty gel coats designed for pattern work, fire retardancy, cultured marble clear, and other applications.
Other coatings include polyurethanes and those that provide a temporary protective finish.
Specialty Resins
Epoxies, phenolics and other specialty resins are used in pultrusion and other molding processes where their physical properties such as temperature resistance can best be utilized.
Epoxies have high heat resistance, long pot life, superior adhesion and other specialized properties. Since epoxies do not contain styrene, they also are lower in odor and much less flammable than polyester or vinyl ester resins.
Specialized Reinforcements
Yarns, rovings and filaments can be reprocessed to create specialized reinforcements tailored to specific end use applications where their physical properties can best be utilized. They are primarily made from fiberglass, as well as carbon, KEVLAR® and other fibers.
Woven Fabrics are traditional materials available in a variety of styles, weights and weaves. Weight is measured in square yards.
In Stitched or Knitted Fabrics, fibers are laid down flat (not woven or crimped) and stitched together. Not crimping the fibers results in better physical properties. This process can be used to produce unidirectional, biaxial, triaxial and quadraxial fabrics with reinforcements placed exactly where they are needed.
Braided Fabrics are designed for cylindrical shapes. They can also be made as socks to slip over a core material.
Other specialized reinforcements include anti-reflective (AR) glass,milled fibers and prepregs ( fiber saturated with resin ).
Primary Reinforcements
Glass manufacturers classify chopped strand mat, continuous strand mat, woven roving, gun roving, pultrusion roving, and chopped strands as Primary Reinforcements. All share the same raw material – fiberglass – that is produced when molten glass is pulled through bushings.
Chopped Strand Mat is made up of randomly oriented fibers, 1.5 -2 inches long, held together by a styrene-dissolvable binder in a rolled mat form. When the binder dissolves, the material conforms to very tight radii. It is primarily used to add stiffness and bulk as a tooling fabric, reinforce gel coat and reduce print-through, or increase inter-laminar strength when placed between layers of woven fabric. Weight is measured in ounces per square foot.
Continuous Strand Mat has long, continuous fibers held together by non-styrene-dissolvable binder. When saturated with resin, the material retains its shape. It is most often used in RTM and pultrusion processes.
Woven Roving is a loose fabric that drapes easily, conforms to compound curves, and has a heavy weave pattern that transfers through gel coat when placed near the surface. Its strength is due to a high glass-to-resin ratio, making it ideal for contact molding or used as the last laminate layer in boats and large structures. Chopped strand mat can be bonded to the back for greater reinforcement. Weight is measured in ounces per square yard.
Gun Roving is cylindrical in shape and finished with a special sizing that provides good chopping characteristics without fluffing. It is used with a chopper gun in Spray-Up Molding.
Pultrusion and Filament Winding Rovings are also cylindrical in shape, with a finish suitable for their respective molding processes.
Chopped Strands are short lengths of fiberglass used in SMC (Sheet Molding Compounds) and BMC (Bulk Molding Compounds) applications, for reinforcing stucco products, or as reinforcements for thermoplastic and thermoset injection molding.
Polyester and Vinyl Ester Resins
Polyester and vinyl ester resins are commonly used in Hand Lay-Up and Spray-Up Open Molding. They are also used in Resin Transfer Molding and other Closed Mold processes.
Due to its low cost and easy handling, polyester is the most popular resin used with fiberglass . General purpose (GP) resins usually are orthopolyester or a blend. Isopolyester resins (also called tooling resins) have higher physical properties and smaller shrinkage factors, and come in different viscosities and gel times. Fire retardant and casting (cultured marble) versions are also available.
With their high corrosion resistance, vinyl ester resins are used in applications subjected to water and contaminants. Using vinyl ester resin has helped the marine industry improve product durability.
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