Application, Material, Process – Three Aspects To Appreciate The New Highlights Of Pultrusion

 

Pultrusion products are increasingly in demand for a wide variety of applications due to their superior customizability and durability. Markets&Markets, a market research firm, predicts that the global pultrusion market will be worth $3.4 billion by 2024, growing at a compound annual growth rate of 4%.

 

The pultrusion process originated in the early 1950s to create FRP (fiber reinforced plastic) profiles with constant cross-sections. More than 70 years later, manufacturers and material suppliers are exploring ways to revolutionize the process. Industry leaders gathered at the 2021 Pultrusion Conference hosted by the Composites Fabricators Association to share the latest breakthroughs in the pultrusion industry. Ahead of the conference, Composites Manufacturing magazine provides some highlights on developments in pultrusion applications, manufacturing, and materials.

 

Pultrusion Production Workshop

 

Application Highlight: Wind Turbines

 

One of the main advantages of pultrusion materials is their strength in long-span applications. This is one of the reasons why pultrusion has become what Vestas Group expert Sascha Erbslöh, a well-known wind turbine manufacturer, calls the “material of choice” for wind turbine structures, most notably the spar caps that serve as the skeleton of rotor blades.

 

Erbslöh said, “Pultruded CFRP spar caps are inherently more efficient than those made using the older open mold wet lay-up process. The main advantage is that all the fibers are in the right direction. In theory, using the open mold process, you can also lay down several unidirectional fiber layers, but if you impregnate all these fibers, there is always the possibility of wrinkles. If you use pultrusion, this phenomenon can be almost completely avoided.”

 

Wind Turbine Blades (Source: Composites Manufacturing)

 

Erbslöh expects demand for pultrusion technology to increase significantly as the wind energy market continues to grow. The U.S. Department of Energy projects that U.S. wind power will increase from 113.43 GW in 2020 to 224.07 GW in 2030 and 404.25 GW in 2050.

 

This growth requires another key feature: rapid manufacturing repeatability. This is another clear advantage of pultrusion. “You can assemble it from pre-manufactured parts in a very controlled way. For the most critical parts, this is very advantageous.”

 

The DOE report adds that the increase in rotor diameter has played a major role in improving turbine efficiency. Pultrusion is a key technology in manufacturing the next generation of larger and more efficient offshore wind turbine rotors.

 

In addition, Erbslöh said, manufacturers are focusing on how to improve the lightning protection of CFRP parts. Although CFRP parts have good structural properties, they face challenges in protecting against lightning strikes. “It’s best to use all-glass fiber and non-conductive materials,” he said. “It certainly takes detailed engineering and high-fidelity, multi-physics simulation to build a good lightning protection system, and there’s a lot of work to do to ensure that.”

 

Material Highlight: Advanced Glass Fiber

 

While carbon fiber has been the reinforcement of choice for many composite manufacturers seeking strength and stiffness, manufacturers are finding that advanced glass fibers can also meet the higher strength requirements of pultruded structural materials.

 

Patrick Haller, product director at Owens Corning, noted that improving the performance of reinforcements can have a significant impact on the tensile and flexural modulus and strength of the part. While many manufacturers focus on tuning resins to achieve specific properties, innovations in how glass fibers are made, the chemistry that goes into the glass fibers and their coatings are also helping manufacturers get stronger reinforcements.

 

Haller called Owens Corning’s High Performance Glass (HP Glass) the third step in glass fiber reinforcements, following E-glass and ECR Glass. “The real improvement is in the mechanical properties, with 10% higher strength and modulus in tension and bending than ECR glass,” he explains. “Corrosion resistance is also improved, especially in alkaline media.”

 

Higher-performance glass fibers play a significant role in ensuring that structural components maintain their stiffness and strength over longer spans, such as wind turbine blades. “Many pultruded parts are structural in nature. They can be things like I-beams, scaffolding surfaces, or railings. By increasing the elastic modulus by 8% to 12%, you can either make the part thinner or use it over a longer span, which can reduce system weight, reduce system cost, broaden design flexibility, and so on.”

 

In addition to improving product strength, fiber reinforcement changes can also improve processing performance. “Our standard products provide fast, uniform filament saturation to reduce resin usage and increase molding speeds,” Haller said. “Using the same chemistry on higher-performance products provides the same molding results. In addition, by using new products and redesigning, glass fiber can be reduced, and processors will spend less time setting up processes for new products or changing materials.”

 

Improved performance is just one of the many benefits of pultruded products. The innovations described here and on display at the 2021 Pultrusion Conference highlight pultrusion’s ability to create high-quality, complex FRP shapes with consistent, repeatable mechanical properties. It’s exciting to see innovation in this growing composites market segment.

 

Manufacturing Highlight: Compressive Flow Forming

 

Durability is a major benefit of pultruded products and one of the reasons they appeal to wind turbine manufacturers. But perhaps no application is more important than medical implants, which must last a lifetime.

 

Suprem, a Swiss supplier of continuous fiber reinforced thermoplastic (CFRTP) materials, has been driving manufacturing advances to support more durable medical products made from CFRTP. The pultrusion process is the first step in creating fracture-resistant rods.

 

Pultruded Continuous Fiber Reinforced Thermoplastic Rods For Medical Applications (Source: Suprem)

 

Suprem worked closely with its sister company icotec to develop carbon fiber reinforced polyetheretherketone (PEEK) rods for use in icotec’s compression flow molding (CFM) process. The pultruded carbon fiber reinforced PEEK rods were remolded by CFM into medical implants, structural bearings, fasteners, etc., that are less than ½ inch.

 

Thermoplastics appear to be the ideal answer to this unique challenge, as they provide the critical fracture toughness, rigidity, and heat, moisture, and corrosion resistance necessary for in vivo use. This has the potential to end the long-standing susceptibility of metal implants to corrosion. For example, corrosion in artificial hip joints has been linked to metal poisoning, which can lead to bone tissue death and implant failure.

 

However, pultruding thermoplastics presents some technical challenges, as these polymers tend to have higher viscosities than thermosets. For example, materials such as epoxies or vinyl esters have lower viscosities, making it easier to impregnate continuous fibers without disturbing fiber alignment and forming voids. To address these issues, Suprem has also developed a process that can pultrude high-performance fibers with a high content and uniform distribution in high-viscosity thermoplastics.