Short answer. Most pultrusion defects trace to a few causes: cure that is too early or too late, poor wet-out, trapped air, a worn or dirty die, or fibre in the wrong place. Use the table to go from symptom to likely cause to first check.
| Symptom | Likely causes | First checks |
|---|---|---|
| Surface cracks, rough skin | Cure too early or too fast; die too hot at entry; high shrinkage | Lower die temperature at entry; reduce speed or change catalyst; check resin |
| Soft or sticky profile | Under-cure | Raise die temperature or lower speed; check catalyst level |
| White patches, dry fibre | Poor wet-out; fibres bypass the resin | Bath level, fibre tension, pre-former, resin viscosity |
| Blisters and voids | Air trapped; moisture in fibre; resin too viscous | Fibre drying, resin degassing, entry design |
| Fibre show-through (bloom) | No surface veil; resin-poor surface; die finish worn | Add a surface veil; check die polish; resin content |
| Dimensional drift, bow or twist | Uneven cure; unbalanced fibre layout; wrong die allowance | Reinforcement symmetry; die temperature; post-die cooling |
| Sticking and stick-slip marks | Die surface dirty or worn; wrong release agent; cure too early | Clean and re-polish; check release agent and cure |
| Pulling force rising | Resin gelling too early; die build-up; excess fibre | Die temperature; clean the die; fibre count |
| Delamination | Poor bond between layers; contamination | Mat and roving balance; resin cleanliness |
Mould (die) problems
| Problem | What it causes | Remedy |
|---|---|---|
| Worn or scratched working surface | Rough finish, sticking, rising pull force | Re-polish and re-plate; protect during cleaning |
| Blocked or fouled entry | Dry spots and fibre pile-up | Clean at set intervals; adjust the entry taper |
| Heater or thermocouple fault | Uneven cure and drift | Check zones against setpoints; replace sensors |
| Misalignment on the line | Twist, uneven wear, higher force | Re-align the die to the puller and creel |
| Design faults (radii, wall thickness) | Cracks and voids at corners | Rework the die or the section |
Good practice
- change one variable at a time and record die temperatures, speed and resin batch;
- keep a clean-down and re-polish schedule for the die;
- log the first 100 m of every run for later comparison.
Background: the pultrusion process step by step and pultrusion die design.
Send us your requirement
Guangdong Haikuo Composite Materials Co., Ltd. (Huizhou, Guangdong) designs pultrusion moulds in-house and produces custom FRP profiles. Send a drawing, a sample or just the application and the environment, and we will tell you what is feasible.
Email: helena@frphk.cn | Phone: +86 189 5198 8522