What is pultrusion?
Pultrusion is a continuous manufacturing process in which fibres are pulled through a resin bath and then through a heated die, producing a cured composite profile with a constant cross-section. The word combines pull and extrusion: in extrusion material is pushed through a die, in pultrusion it is pulled.
How it works
- Fibre feed: glass-fibre rovings and mats, sometimes carbon fibre, come off creels.
- Impregnation: the fibres pass through a bath of resin, usually polyester, vinyl ester or epoxy.
- Shaping and curing: in a heated die the profile takes its shape and the resin cures.
- Pulling: a puller draws the profile continuously out of the die.
- Cutting to length.
Because most fibres run lengthwise, a pultruded profile is much stronger along its length than across it.
Properties
| Property | In practice |
|---|---|
| Light | Roughly a quarter of the weight of steel for the same dimensions |
| Corrosion resistant | Does not rust; resists salt and many chemicals |
| Electrically non-conductive, non-magnetic | Suitable around electrical installations |
| Low thermal conductivity | Little thermal bridging |
| Lower stiffness than steel | Deflection often governs the design |
Uses in construction
- Gratings, stairs, platforms and handrails in wet or aggressive environments
- Cable trays and ladders
- Beams and decks for footbridges and cycle bridges
- GFRP reinforcing bars in concrete where corrosion is a risk
- Window and curtain wall profiles with low heat transfer
- Carbon-fibre plates for strengthening existing structures
Working tips
- Cutting: use a diamond or carbide blade; ordinary metal-cutting blades wear quickly.
- Dust: wear a respirator (at least FFP2), eye protection and gloves, and extract dust at source.
- Seal cut edges: coat cut ends with resin or the manufacturer’s sealer so moisture cannot wick along the fibres.
- Connections: bolt and bond, don’t weld. Keep to the manufacturer’s edge distances.
- Design: use the manufacturer’s load tables or have an engineer do the calculations; steel rules of thumb do not apply.
Related terms
- GRP
- Polyester
- Carbon fibre laminate
- Resin
- Plastics
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.