What is pultrusion?

With pultrusion of composites, continuous fibre is pulled through a resin bath or has resin injected on to it. The wetted fibre is then pulled through a heated die (~ 150°C), which is in the shape of the component. In addition to shaping the fibre the die also acts to control the amount of resin and initiate curing. On exiting the die, the material is automatically cut to the required length.

Glass fibre is the most commonly used reinforcement material. While carbon fibres can be included in pultrusions their high stiffness requires more robust pultrusion equipment. Polyester (isophthalic) is the most common resin used although Vinyl ester is used for applications where corrosion resistance is a priority. If the desired properties of the component include good fire, smoke and toxicity performance then urethane methacrylate resin can be used.

This process is fast and economic and is the method of choice for much of the construction industry. A high fibre volume fraction can be accurately controlled allowing pultruded parts to be used in structural applications. Health and Safety issues can be controlled by enclosing the resin impregnation area with suitable extraction. The capital equipment cost is high but modularity in changing the dies to produce different profiles allows for flexibility.

Some of the key points of this method include: