Pultrusion is a continuous low pressure molding process using fiber reinforcements and thermosetting resins matrices. The fiberglass reinforcements are drawn through a resin bath or injected with resin in which all fibers are thoroughly impregnated with the liquid resin system. The wet-out fiber is formed to the desired geometric shape and pulled into a heated steel die. Once inside the die, the resin cure is initiated by controlling at precise elevated temperatures. The composite laminate solidifies in the exact cavity shape of the die, as it is continuously "pulled" by the pultrusion machine, thus getting the name – Pultrusion.
Virtually any constant cross-section can be pultruded dependant upon wall thickness and complexity of the cross-section of the profile.
Most commonly utilized resins are standard thermosetting resins such as polyesters, vinyl esters, epoxies, phenolics and urethanes during the pultrusion manufacturing process. However, thermoplastic resins can also be utilized in the Pultrusion process.
Typical reinforcements used are fiberglass roving, continuous strand mat, woven and stitched fabrics. Other reinforcing materials such as carbon and aramid fibers, which are more costly, can be utilized during the Pultrusion process to increase the modulus/stiffness of the composite member.
For most applications, internal coloration, surfacing veils, and various UV stabilized additives eliminate the need for secondary painting applications. However, to improve the weathering properties or the appearance of a pultruded profile during outdoor exposure, coatings are highly recommended. Most commonly used coatings are Acrylics and Urethanes.