The fiberglass pultrusion process, step by step

The creel rack holds 50 to over 300 spools of continuous fiber roving configured to deliver the precise number and type required by the profile design. For complex shapes, the creel also supplies continuous filament mat (CFM) or stitched multi-axial fabrics for off-axis strength.

Proper creel tension management is critical. Each roving must pay out at consistent tension to prevent dry spots (under-tensioned) or fiber breakage (over-tensioned). Modern systems use spring-loaded or pneumatic tensioners to maintain even pay-off as spool diameters decrease.

Fiber rovings and fabric reinforcements pass through precision-machined guide plates that arrange the fibers into the spatial configuration required by the die cross-section and pre-tension the fiber bundle to prevent tangling.

For profiles with multiple wall thicknesses (such as an I-beam with thick flanges and a thinner web) the guide plate routes more rovings to flange zones and fewer to the web, ensuring uniform fiber volume fraction throughout the cross-section.

Every fiber filament must be completely wetted by the resin system: any dry fibers create internal voids that reduce mechanical strength and durability. In injection systems, resin is injected under controlled pressure (3–8 bar) into a sealed chamber at the die entrance. This achieves near-zero emissions, minimal waste, and ±1% resin-to-fiber ratio control.

Open-bath systems submerge fibers in a resin trough: simpler and lower cost, but with higher styrene emissions and ±3–5% ratio control. Injection pultrusion is our standard process.

The resin-impregnated fiber bundle enters a precision-machined, chrome-plated steel die whose internal cavity defines the profile cross-section. The die has three independently controlled temperature zones: entry (100–130 °C to initiate cure), center (140–170 °C to complete cure), and exit (150–180 °C for controlled shrinkage release).

The exothermic peak temperature inside the profile must be carefully managed. If it runs too high, the resin develops internal stresses that cause surface crazing. Our dies incorporate thermocouple ports at multiple depths for real-time core temperature monitoring.

Two types of puller are used: reciprocating clamp pullers (hydraulic, for large profiles requiring up to 100 kN pull force) and caterpillar belt pullers (smoother, vibration-free, preferred for thin-walled profiles).

Pull speed determines the residence time inside the heated die and controls the degree of cure. Thick-walled profiles run at 0.3 m/min (longer heat penetration time), while small shapes reach 1.5 m/min. Our servo-driven pullers maintain ±0.5% speed accuracy.

A flying cut-off saw travels with the profile during the cutting stroke to maintain continuous production. Diamond-tipped blades cut through the abrasive composite; wet cutting with coolant suppresses dust and extends blade life.

After cutting, profiles are labeled, inspected for visual defects per ASTM D4385, measured for dimensional compliance, and staged for packaging or secondary fabrication (drilling, routing, bonding, painting).