The name pultrusion combines the words, “pull” and “extrusion”. Pultrusion technology represents the only method currently capable of producing automatically structural composite parts on a continuous basis and of unlimited length.
In the pultrusion process, reinforcing materials in the form of dry unidirectional fibers, woven or non-crimp fabrics are continuously pulled from creel racks. This collation of dry reinforcing fibers then passes through forming cards, before entering a heated steel mold. Resin is applied to the preform, either by pulling through a wet-bath or by injecting the resin directly into the die. Due to this pulling, the fiber filaments are in tension when curing in the heated die. While in tension, the fibers have higher strength values and are more aligned, allowing good compaction and more fibers fitting into a given gravity. The mold forms and compact the material into the final geometry. A pair of hydraulically-activated gripping plates is used to alternately grab and pull the material through the system at a constant speed. The profiles then periodically cut with a cut-off saw.
Human interface, for example by hand-lay-up is eliminated and therefore the quality is not a function of motivation of factory technicians. Within the composites industry, pultrusion is one of the fastest rising processes for composite parts because it is a highly cost-effective fabrication method. The process of pultrusion is not nearly as basic as it may appear. Therefore, the seminar explains step by step how to pultrude a T-shape profile with resin transfer molding and why trial and error is the only true method of improving the process.
Zürich University of Applied Sciences, Austria