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Sunday, February 1, 2009

Composite Fabrication : Pultrusion

Pultrusion process ia a continuous process, producing a profile of constant cross-section.
The fibres are pulled from a creel through a resin bath and then on through heated die.
Die completes the impregnation of fibre, controls resin content & cures to its final shape (as passes through die) and cured profile is automatically cut to length.
Fabrics may also be introduced into the die to provide fibre direction other than 0°.
A variant known as ‘pulforming’ allows for variation into cross-section where it pulls the materials through the die for impregnation, and then clamps them in a mould for curing (Process is non-continuous)

Pultrusion Process

Materials Options:
• Resins: Generally epoxy, polyester, vinylester and phenolic.
• Fibres: Any.
• Cores: Not generally used.

Main Advantages:
i) Can be a very fast i.e. Economic way of impregnating & curing materials.
ii) Resin content can be accurately controlled.
iii) Fibre cost is minimised, i.e. 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, i.e. limiting volatile emissions.

Main Disadvantages:
i) Limited to constant or near constant cross-section components
ii) Heated die costs can be high.

Typical Applications:
• Beams and girders used in roof structures, bridges, ladders, frameworks.

Pultrusion Machine