Pultrusion is a manufacturing process which is used to produce continuous lengths of fiber reinforced composite materials having constant cross-section. The reinforcement is usually pulled through a bath of low viscosity resin, and then enters a heated die to form and cure the part. Resin injection may also be used in the front of the die instead of a bath to mitigate concerns of resin contamination. Usually die injection results in a cleaner work environment and less health and safety concerns. While pultrusion has often been associated with low cost glass fiber composites, pultrusion of carbon fiber composites are gaining in application. The use of carbon fiber tow as opposed to woven and commingled reinforcements has added a new level of performance, coupled with advances in pultrusion processing. Advances in online braiding and pull-winding (circ winding) are enabling the development of high performance lower cost composite profiles which were traditionally produced using prepreg table rolling processes. Further advances in processing through the development of curved profiles and tapering will provide even greater expansion of this manufacturing method.
Thermoset pultrusion resins are generally low viscosity two part systems which require mixing at the specified ratio before they are added to a resin bath or injection apparatus. The mixed resin viscosity is usually developed for ambient temperature wet-out of the reinforcing fibers. A series of pultrusion resins are offered with some having extremely fast cure/production capability, while others are developed with aerospace mechanical performance.