Fibres are pulled from a creel through a resin bath and then on through a heated die. The die completes the impregnation of the fibre, 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 fibre direction other than at 0°. 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 mould for curing. This makes the process non-continuous, but accommodating of small changes in cross-section.
Resins: Generally epoxy, polyester, vinylester and phenolic.
Cores: Not generally used.
i) This can be a very fast, and therefore economic, way of impregnating and curing materials.
ii) Resin content can be accurately controlled.
iii) Fibre cost is minimised since the majority is taken from a creel.
iv) Structural properties of laminates can be very good since the profiles have very straight fibres and high fibre volume fractions can be obtained.
v) Resin impregnation area can be enclosed thus limiting volatile emissions.
i) Limited to constant or near constant cross-section components
ii) Heated die costs can be high.
Beams and girders used in roof structures, bridges, ladders, frameworks.
Published courtesy of David Cripps, Gurit