Fiberglass Reinforced Plastic Thermoset

Fiber reinforced plastic (FRP) is a thermoset plastic reinforced with fibers. Typically, a thermosetting plastic or thermoset is a liquid polymer that is cross-linked during molding process. A catalyst is added to the liquid polymer which causes the molecule chains to cross-link and create an irreversible solid material. The solid material is permanently hard and can’t be melted or remolded like thermoplastics. The thermoset plastic is a polymer matrix. Typically, the polymer is a vinyl ester, polyester or an epoxy thermosetting plastic. The fibers used as the reinforcement usually are glass, carbon, or aramid. Once the FRP is molded, the molecules crosslink and it becomes a solid substrate that is irreversible.

Liquid Composite Molding (a.k.a., cold molding and liquid compression molding) is a closed mold process which uses hydraulic press pressure to flow the liquid catalyzed resin (thermoset resin) through a fiber pack preloaded into a matched cavity/core molding die.

The mold has a positive and negative surface (top and bottom) waxed to a specified thickness. First, a fiber pack is laid into the mold. The fiber is used as the reinforcement. Many different types of fiber can be used depending on the part requirements. Next, a liquid catalyzed resin mix (the matrix) is poured over the fiber pack. Typically, the resin is either polyester, vinyl ester or an epoxy base. Finally, press-actuated pressure moves the resin mix throughout the fiber reinforcement and the catalyzed resin links together. The result is a solid part with two smooth sides.

The benefits of this process include:

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Resin Transfer Molding (RTM) is a closed molding process which uses hydraulic pressure to inject the liquid resin through a fiber pack preloaded into a matched cavity/core molding die. RTM offers the “best of both worlds” as this process allows for high surface finish with the structural additions, such as ribs and embosses.

Vacuum-Assisted RTM (Light RTM)is a closed molding process which uses vacuum pressure to pull the liquid resin through a fiber pack preloaded into a light structural cavity/core molding die or light structural cavity with a flexible core molding die.

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Open Molding (Spray-Up, Hand Lay-Up) processed products are manufactured by applying a mixture of resin and chopped fiber either sprayed or hand-laid onto a gel coated cavity only tool.

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