Pultrusion

The pultrusion process is used to produce composites of uniform cross -section with exceptional longitudinal strength and rigidity. The process was first used in the 1950’s to produce simple items such as rod stock. Since then, developments in process and material technology mean that highly complex profiles of considerable dimensions can now be manufactured using this method.

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Expressed simply, the process involves drawing reinforcements, impregnated with activated resin through a forming guide, which pre-shapes the material. Using continuous rovings, which are usually the predominant reinforcement present, the material is pulled through a heated die, which activates the catalyst, thus curing the resin. The cured profile then passes a flying saw attachment and is automatically cut to the required length.

The reinforcement is wetted out either by the use of a resin bath, or by resin injection at the front of the die. The resin bath system is still the most common, though resin injection is gaining in popularity and is more environmentally friendly as it drastically reduces styrene emissions.

The curing system used in the pultrusion process usually consists of a combination of peroxides. A highly reactive peroxide, known as a ‘kicker’, is used for initial cure, in combination with medium or low reactivity peroxides to achieve a more gradual through cure. This dual system ensures that profiles achieve optimal cure, with low residual styrene contents.

The cured profile is pulled through the die using either reciprocating pullers or a continuous caterpillar track system. The reinforcement most commonly used in the pultrusion process is glass, though carbon and polyaramid fibers can also be used successfully. Resin systems for pultrusion include polyesters, vinyl esters, epoxies and methacrylate resins, with polyesters being the most common.

Pultrusion resins in the Crystic range are designed to achieve the balance of properties necessary to optimize the process.