Pultrusion is a manufacturing process for producing continuous lengths of reinforced polymer structural shapes with constant cross-sections. Raw materials are a liquid resin mixture (containing resin, fillers and specialized additives) and flexible textile reinforcing fibers. The process involves pulling these raw materials (rather than pushing, as is the case in extrusion) through a heated steel forming die using a continuous device.
The reinforcement materials are in continuous forms such as rolls of fiberglass mat and reels of fiber glass roving. As the reinforcements are saturated with the resin mixture in the resin bath and pulled through the die, the gelation, or hardening of the resin is initiated by the heat from the die and a rigid, cured profile is formed that corresponds to the shape of the die.
While Pultrusion machine design varies with part geometry, the basic Pultrusion process concept is described in the following animation.