Pultrusion, like RTM, has been used for decades with glass fiber and polyester resins, but in the last ten years the process also has found applications in the advanced composites industry. In this relatively simple, low-cost, continuous process, the reinforcing fiber (usually roving, tow or continuous mat) is typically pulled through a heated resin bath, then formed into specific shapes as it passes through one or more forming guides or bushings. The material then moves through a lengthy heated die, where it takes its net shape and cures. Further downstream, after cooling, the resulting profile is cut to desired length. Pultrusion yields smooth finished parts that do not require post-processing.
A wide range of continuous, consistent, solid and hollow profiles are pultruded, and the process can be custom-tailored to fit specific applications. Pultruders are currently developing ways to create variable cross-sectional shapes by manipulating resin chemistry, temperature and die characteristics. New resins for pultrusion, such as polyurethanes, are yielding tougher finished parts.