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Pultrusion is a manufacturing process integral to composite production, involving the continuous pulling of reinforcing fibers through a resin bath and then through a shaping die, where they are cured and formed into a constant cross-sectional profile.

In a pultrusion process, fibers are pulled from a creel through a resin bath and then on through a heated die. The die completes the impregnation of the fiber, controls the resin content and cures the material into its final shape as it passes through the die. This cured profile is then automatically cut to length. Fabrics may also be introduced into the die to provide fiber direction other than at 0 degrees. Although pultrusion is a continuous process, producing a profile of constant cross-section, a variant known as “pulforming” allows for some variation to be introduced into the cross-section. The process pulls the materials through the die for impregnation, and then clamps them in a mold for curing. This makes the process non-continuous, but accommodating of small changes in cross-section.

Source: Pultrusion: The basics

Advantages to pultrusion include:

1. This can be a very fast, and therefore economic, way of impregnating and curing materials.
2. Resin content can be accurately controlled.
3. Fiber cost is minimized since the majority is taken from a creel.
4. Structural properties of laminates can be very good since the profiles have very straight fibers and high fiber volume fractions can be obtained.
5. Resin impregnation area can be enclosed thus limiting volatile emissions.

The disadvantages include that the process is limited to constant or near constant cross-section components, and costs for heated dies can be high.

Source: Pultrusion: The basics