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Covestro and Saertex have developed materials for new process with manufacturing technology from Hubers.
Actively contributing to climate protection is a central element of the sustainability concept at Covestro, it explains. One of the key focal points in this commitment is the generation of power from renewable sources, and first and foremost from wind power. Numerous countries are now pursuing this sustainable form of power generation, although some state subsidies are being cut. As a result, the demand for cost-effective processes for manufacturing even bigger and more efficient wind turbines is greater than ever.
According to Covestro, the new process features a whole new approach to combining polyurethane resin with woven fibreglass. It explains how the partners have now successfully produced the prototype for a 45 meter-long spar cap at the Institute of Composite Structures and Adaptive Systems of the German Aerospace Center (DLR) in Stade. The spar is the core of the structural framework and has to accommodate the full wind load.
Kim Klausen, Head of Covestro’s Center of Excellence for Wind Power in Otterup, Denmark, says, “Stability and durability are the key properties for rotor blades.” He further explains, “Our polyurethane resin offers clear advantages over epoxy resins in this application: We achieve a higher glass transition temperature and low shrinkage. The reaction of the polyurethane resin also generates less heat.”
Marc Schrief, Managing Director at SAERTEX, adds, “Our woven fibreglass ensures the stability of the compound. They are thoroughly impregnated with the polyurethane resin and form a high-strength component. What’s more, they help to lower the weight of the rotor blades.” The 45 meter-long rotor blade would weigh eight metric tons overall. The spar cap made from polyurethane and glass fibres accounts for approximately a third of the total weight.
The half-shells for the rotor blades are manufactured using a vacuum infusion process. This involves placing core materials and woven fibreglass into a mould and sealing the structure hermetically with a film. After applying a vacuum, the infusion process begins with introducing the liquid polyurethane resin. Hübers explains it has developed a manufacturing technology that enables controlled mould filling.
“Our system uses pumps to actively convey the material. The use of sensors to control pump pressure ensures strict adherence to the planned pressure curve and thus to the material kinetics when filling the mould,” says Clemens Dieckmann, Project Engineer at Hübers.
Over the last few years, Covestro says the process sequence for manufacturing the rotor blade has been repeatedly optimised. For example, the infusion process can be completed in a relatively short space of time, thanks to the vacuum that is applied. The curing process starts when the mould is subsequently heated and is much faster than when using epoxy resins. There is no need for post-curing.
“That brings a considerable cost saving for manufacturers,” says Klausen. “Additional improvements in blade design and the intelligent use of composites, coatings and adhesives could help deliver even more weight savings.”
Covestro is exhibiting at the Wind Turbine Blade Manufacture conference from 30 November – 2 December 2015 in Düsseldorf, Germany, and is looking forward to talking with visitors.
Image provided by Covestro
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