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The companies produced a prototype of a 45 meter-long spar cap. The spar is the core of the structural framework and has to accommodate the full wind load.
Numerous countries are now pursuing wind 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.
Together with Saertex, a manufacturer of non-woven fiberglass, and Hübers as partner for the process technology, Covestro has developed an innovative technology for manufacturing rotor blades in line with precisely these requirements. The new process features a whole new approach to combining polyurethane resin with non-woven fiberglass. 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.
Advantage for polyurethanesAccording to Kim Klausen, Head of Covestro’s global Center of Excellence for Wind Power in Otterup, Denmark: "Stability and durability are the key properties for rotor blades.” He further explains: “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 non-woven fiberglass 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 fibers accounts for approximately a third of the total weight.
Vacuum infusion processThe half-shells for the rotor blades are manufactured using a vacuum infusion process. This involves placing core materials and non-woven fiberglass into a mold and sealing the structure hermetically with a film. After applying a vacuum, the infusion process begins with introducing the liquid polyurethane resin. Hübers Verfahrenstechnik Maschinenbau GmbH has developed a manufacturing technology that enables controlled mold 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 mold,” says Clemens Dieckmann, project engineer at Hübers.
Cost savings thanks to efficient productionOver the last few years, the process sequence for manufacturing the rotor blade has been repeatedly optimized. 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 mold is subsequently heated and is much faster than when using epoxy resins. There is no need for post-curing.
More information: www.covestro.com - www.saertex.com
Wind energy is really dependant on public policy. Areas of activies change in time and space really quickly. But the wind energy industry continues to innovate especially in the field of Offshore...