Pultrusion is a manufacturing technique used to make parts with a constant cross-section. The material is pulled through the die, which closely controls the profile dimensions. The resulting end product is a composite profile with a high fiber ratio.
Fiber rovings (sometimes along with fabrics) are drawn from the rear of the machine, guided into position, passed through a resin bath, and then through preforming tooling. The thermoset materials will need time to cure as they are pulled through the curing die.
The material is cured into a solid shape as it moves through the die, and it has cured by the time it completes its trip and exits as a solid, cured profile. The process results in long lengths of composite.
During pultrusion, glass-reinforced textiles or fibers are pulled through a resin bath in a controlled process known as wet-out.
The process is monitored to ensure total-wetting out of the emerging reinforced fiber. Afterward, excess resin is removed to expel any trapped air before the impregnated glass-reinforced textiles are passed through a heated die to cure the combination of resins, catalysts, and any other fillers.
Why use pultrusion resins? Resins are at the core of the pultrusion process and are used to coat the fibers and hold them together, enabling them to withstand damaging external factors such as corrosion.
Therefore, resins offer structural and thermal stability to the resulting composite. Depending on your project's needs, different resins can be used to meet your specifications. Once the composite is fully cured, it can be cut into the required length or shape.
Some of the most commonly used resins in pultrusion include:
Epoxy ─ This is a popular option due to its low shrinkage rate. These have thermochemical integrity and are ideal for reinforcing and bonding Fiber Reinforced Polymer (FRP) components. This resin boasts excellent performance in high-heat environments and strong corrosion resistance.
In addition to the usually higher cost, the disadvantage is that epoxy resins have high viscosity and sometimes require a post-cure. They also have poor UV resistance.
Vinyl ester ─ This is a popular pultrusion resin due to its exceptional moisture and corrosion resistance. It also has strong chemical resistance properties and is commonly used in the production of coastal and marine products.
The faster a pultrusion resin cures, the quicker the turnaround and production rate. According to the European Pultrusion Technology Association (EPTA):
Phenol resins are the oldest known resin systems created by the condensation of phenols and formaldehyde. Such resins are often dark-colored, from yellow to dark red, and are found in many industrial products. As water is released during curing, there is a risk of cracks and pores forming. This may cause considerable processing problems. There is very low flammability, but high flue gas emissions.
Since phenolics are the most suitable when it comes to thermal insulation and fire resistance, they are often applied together with other resins so the resulting product can be both durable and fire-safe.
Polyurethane (PU) is a two-component thermoset resin commonly used in pultrusion. The main properties of PU are high impact and fatigue resistance, low shrinkage & a line speed comparable to that of unsaturated polyesters. PU-based pultruded profiles are ideal for applications that require high structural performance.
Combinations of glass fibers and thermoplastics are another option to improve specific properties such as surface slip characteristics, subsequent deformation during heat exposure, abrasion resistance, and chemical stability. Polyethylene, polypropylene, and polyamide are used as matrix materials.
E, C, or S glass filaments are an important part of the reinforcing structure and are bundled by melt spinning to form rovings with a weight between 600 and 9600 tex. These form a unidirectional reinforcement in the pultrusion direction. The filaments are surrounded by silane sizing, which enhances bonding to the matrix. Textured roving is used where increased transverse strength may be achieved, as it is not a fully unidirectional arrangement.
There are three main types:
Custom fiberglass pultrusions come in many configurations you can consider. Depending on application requirements, many combinations of resin types and reinforcements can be used to adjust physical and chemical properties and UV resistance.
Pultrusion enables rapid, cost-effective, high-volume, continuous manufacturing of pultruded profiles that are strong, durable, long-lasting, and lightweight.
The right manufacturer will be able to work with you to advise on profiles that are the best fit for your project/s to optimize performance and your value-to-cost. Contact Tencom today.