The pultrusion process is one of the most cost-effective methods for the production of composite materials. It is a continuous process that produces little waste material. In the pultrusion process for thermoset resins, fiber reinforcement is pulled through a resin impregnation area to coat the reinforcement with resin, through preform plates to begin to shape the fiber/resin bundle, and through a heated die to cure the resin. A cured part in the desired shape that requires no further processing exits from the die. Although the process appears to be simple, numerous process variables such as pull speed, die temperature, quality of fiber/resin wet-out, and fiber volume can affect the quality of pultruded composites. In order to take full advantage of the pultrusion process, the effect each process variable has on mechanical properties must be completely understood. Because it is a cost-effective method for the production of advanced composites, the pultrusion process has tremendous potential for traditional composite applications as well as currently expanding applications such as infrastructure revitalizaiton.
The pultrusion process also offers a unique combination of characteristics. Due to the continuous nature of the pultrusion process, composites of any desired length can be produced. The pultrusion process can be used to fabricate profiles with simple or complex geometry; however, the part must have a constant cross-section down the length of the part. Travel through the die results in all surfaces of a pultruded composite being smooth, finished surfaces. Process speeds vary depending on the type of resin and the profile geometry, but faster line speeds are desirable to increase process efficiency and economics. Pultrusion can produce composites with higher fiber volume and, thus, higher mechanical properties than many processes can achieve. The automated nature of the process produces composites with more uniform properties that are not highly dependant on operator skill as they are for some processing methods such as hand lay-up or VARTM. Commercial applications for pultruded composites include standard structural shapes like I-beams and channel sections, nonconductive ladder rails and tool handles, grating, and window framing.
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Pultrusion Scene (gif image)