Pultrusion

Pultrusion continuously pulls fiber and resin through a heated die to form constant cross-section composite profiles with high stiffness, corrosion resistance, and high throughput.

Overview

Pultrusion is a continuous composites process that pulls fiber reinforcements saturated with resin through a heated steel die to create constant cross-section profiles. The process delivers long, straight parts with consistent fiber volume fraction, good mechanical properties, and excellent corrosion resistance. Think structural shapes, channels, tubes, and custom profiles produced in continuous lengths or cut-to-length.

Pultrusion makes sense when you need high volumes of prismatic parts, strong directional stiffness along the length, and repeatable cross-sectional geometry at competitive cost. Typical profiles have moderate complexity in 2D, with features defined entirely in the die; holes, notches, and cutouts require secondary machining. You trade off geometric freedom and thickness variation for low part cost per foot and stable properties. Expect some limits on sharp inside corners, thick sections, and very tight dimensional or surface-finish requirements. For straight, run-of-the-mill structural profiles, ladder rails, and framing members, pultrusion is often the most economical composites route once you commit to a die.

Common Materials

  • E-glass / polyester
  • E-glass / vinyl ester
  • E-glass / epoxy
  • Carbon fiber / epoxy
  • Carbon fiber / vinyl ester
  • Aramid fiber / epoxy

Tolerances

±0.010" on cross-sectional dimensions for standard profiles; length, bow, and twist controlled by agreed QC limits.

Applications

  • Structural channels, angles, and I-beams for corrosive environments
  • Ladder rails and safety handrails
  • Cable trays and instrument supports
  • Window, door, and curtainwall lineals
  • FRP rebar and reinforcing rods
  • Utility poles, crossarms, and structural tubes

When to Choose Pultrusion

Use pultrusion for long, straight, constant cross-section composite parts where you need high directional stiffness, corrosion resistance, and medium-to-high production volumes. It excels when the part geometry can be fully defined in a 2D die profile and you can amortize die cost over long production runs. For low-volume, highly 3D, or heavily featured parts, other composites processes are usually more appropriate.

vs Resin Transfer Molding

Choose pultrusion over RTM when your part is a straight, constant cross-section profile and you need high throughput with minimal labor per foot. RTM suits more complex 3D shapes and local thickening, but for structural beams, rails, and lineals, pultrusion usually delivers lower cost and more consistent fiber alignment.

vs Vacuum-Assisted Resin Transfer (VARTM)

Pick pultrusion instead of VARTM when you’re making standardized structural profiles in significant volume and can invest in a dedicated die. VARTM is better for large, non-prismatic parts like panels or blades, while pultrusion wins on repeatability, cycle time, and material utilization for long, uniform shapes.

vs Prepreg Layup with Autoclave

Use pultrusion over autoclave-cured prepreg when you need cost-effective, continuous profiles rather than aerospace-grade, highly optimized laminates. Autoclave layup offers superior control and very high performance for complex geometries, but pultrusion provides plenty of strength and stiffness at far lower piece price for straight beams, rods, and sections.

vs Filament Winding

Select pultrusion instead of filament winding when your part is prismatic with a defined 2D profile, not primarily a pressure vessel or axisymmetric tube. Filament winding excels at circumferential strength and complex winding patterns; pultrusion is better when you want linear stiffness, flat webs, and flanges along the length.

vs Compression Molding (Composites)

Choose pultrusion over composite compression molding when your production is focused on long, continuous profiles rather than discrete, closed-mold parts. Compression molding handles 3D features and thicker sections well, but requires a cycle per part; pultrusion runs continuously, driving cost down for standardized structural shapes.

Design Considerations

  • Keep cross-sections constant along the length; avoid tapers, variable wall thickness, or features that would require a split or adjustable die
  • Use generous inside corner radii and avoid very sharp edges to reduce die wear and resin-rich stress concentrations
  • Align primary load paths with the pultrusion direction and clearly specify required mechanical properties along and across the length
  • Define acceptable tolerances for width, thickness, bow, twist, and surface finish up front so suppliers can design appropriate dies and process controls
  • Minimize holes, notches, and cutouts in the profile; plan these as secondary machining operations and consolidate features where possible
  • Standardize on existing die shapes (channels, angles, I-beams, tubes) when you can, to avoid custom die cost and speed up quoting