Strong and resistant
at any wind force.

 

The process of generating electrical power from the wind is complex and demanding for all wind turbine parts, especially the material used in the blades. As of today, more than 50,000 rotor blades worldwide have been built using ArmaFORM® PET foam cores. Wind energy is one of our biggest markets, where ArmaFORM® PET is used in sandwich constructions for rotor blades, nacelles and spinners.

 

The rotor blades are the core element of the wind turbine

Modern rotor blades are made of sandwich composite structures, in which the core material is combined with glass fibres and resins. Balsa wood, PVC and PET foam are the most commonly used core materials in wind turbine applications. The rotor blades are the central wind turbine component and determine how much energy can be generated. Unsurprisingly, the trend is towards ever larger, more efficient rotor blades.

Today, the blades of an average onshore wind turbine are about 50 meters long; the latest offshore blades even exceed 80 meters. This makes great demands on the materials used in the composite structures of the ever-longer, consequently heavier blades: the high mechanical and wind loads require maximum core strength and rigidity without too much extra weight.

Beyond material performance, the OEMs' and blade manufacturers' choice of core materials is driven by processability, costs and availability. This is where Armacell comes into play. Key to the success of ArmaFORM® PET are its superior properties compared to previously dominant balsa wood, SAN and PVC core materials. These properties include, but are not limited to:

Mechanical strength and excellent fatigue properties: Composite sandwich structures in rotor blades are divided into two main groups: spar webs and shell panels. The main purposes of these sandwich sections are to keep the aerodynamic shape of the blade, which determines how well it can extract energy from the wind, and to prevent blade buckling. The crucial core material properties concerned are shear and compression strength. The gravity loads induced by the rotation of the rotor blade make high demands on the material’s fatigue properties. To resist the fatigue load, the core not only needs good compression and shear strength but also excellent fatigue properties. The fatigue threshold of ArmaFORM® PET is >60%. 

High temperature resistance and processing versatility: Higher curing temperature is translated into shorter cycle times and increased productivity, better mechanical properties in the laminate and peel strength. At +150°C, ArmaFORM® PET allows a processing time of days, at +180°C, a couple of hours with full vacuum. Modern wind turbine blades are usually made of fibreglass and epoxy resin, manufactured through a vacuum impregnation process and finished with surface coatings. ArmaFORM® PET is easy to process in infusion or pre-preg and is compatible with epoxy or polyester resin.

Limited density variation: The mechanical properties are all related directly to the density of the foam core; even small variations have a big impact. The extrusion process used to produce ArmaFORM® PET results in notably lower density variations than those of the batch process used for most other structural foam cores. We guarantee a density variation of less than ± 5 kg/m3. Our production features 100% inline density control of extruded boards.

Recyclability & sustainability: A wind turbine is designed to produce clean and green energy; in fact, during its operational phase, the turbine’s impact on the environment is minimal. But what happens afterwards, when the wind turbine is dismantled? The materials recyclability weighs more and more heavily in OEMs' and blade manufacturers' choice of core materials. Plastics such as PVC or SAN can only be recycled to a limited extent, if at all, so PET foams offer a more sustainable solution.

It was Armacell who paved the way, supplying the first PET foam to the wind turbine industry in 2006. But we did not stop there and have again made a major step in enhancing the sustainability of today’s rotor blades with the introduction of our PET GR grade. Unlike the standard PET foams on the market, PET GR is 100% made of post-consumer PET! Using ArmaFORM® PET GR instead of standard PET foam in the same rotor blades reduces the CO2 emission by -33%. The improvement is even greater compared to PVC, for example. Blades with a PVC core cause more than twice the CO2 emissions as ArmaFORM® PET GR during production. While ArmaFORM® PET made of virgin PET resin was used in the past, more and more wind turbine manufacturers are now switching to the even more sustainable and fully recyclable PET GR grade.

Highest quality at lowest environmental impact

To be compliant with the wind turbine industry's stringent quality requirements, Armacell has developed and implemented unique quality control systems that allow 100% quality control of important product properties. Several state-of-the-art inline systems have been implemented to control physical properties, optical aspects and dimensional tolerances. These tools enable statistical process control (SPC). An actively managed six-sigma process has continuously improved the process efficiency, with process capabilities of >6 sigma for certain key properties. Each individual board is digitised and identified with a unique serial number. Fully integrated ERP (enterprise resource planning) allows tracing each individual board down to the raw material batch used for its production. Besides these inline measurements and inspections, a series of tests are constantly carried out to guarantee highest quality and reliability.

 

Application: Rotor Blade / Nacelle / Spinner / Housing