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Pultrusion is a manufacturing process for converting reinforced fibers and liquid resin into a fiber-reinforced plastic, also known as fiber-reinforced polymer (FRP).
The pultrusion process allows the continuous production of FRP structural shapes in an automated, energy-efficient process by pulling fiberglass rovings through a resin bath or resin impregnator that completely saturates the reinforcements. The resin hardens from the heated steel pultrusion die, resulting in a strong, lightweight final product that follows the shape of the die.
Pultrusion machine design can vary as part geometry can differ. The two main types of pulling systems used to create FRP profiles are reciprocating (hand-over-hand) and continuous (cat-track).
The rovings of fiber reinforcements are positioned by the creels for continuous feeding onto the guide plate. To ensure strength and quality, the fiber reinforcements must be positioned accurately within the finished composite.
The resin impregnator is optimally designed to completely saturate the fiber reinforcements in a resin bath or wet out that consists of either epoxy, polyurethane, polyester or vinyl ester. Fillers and other additives such as colors, fire inhibitors and UV retardants can be included to improve the lasting performance of the composite.
As the reinforcements exit the resin impregnator, they’re passed through “pre former” tools, designed to squeeze out surplus resin and organize the fiber reinforcements into the correct shape. During this process, additives such as continuous strand materials and protective surface veils are often included to improve the structure, resistance to corrosion and finish of the final product.
After this process, the resin-impregnated fiber passes through the steel die for polymerization. The die is heated at a consistent temperature to cure the thermosetting resin, resulting in a solidified polymer.
The hardened FRP is then pulled towards the saw by the pulling system for accurate cutting to the desired length. The pull locks are custom-made of urethane to ensure cured profiles aren’t cracked, distorted or deformed by the pulling system.