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Covestro, Saertex and Hübers have developed a new technology for the manufacture of rotor blades for wind power plants which has allowed them to successfully produce a prototype of a 45 metre-long spar cap.
It has been made based on a new approach to combining polyurethane resin with woven fibreglass.
“Stability and durability are the key properties for rotor blades,” explains Kim Klausen, head of Covestro’s Center of Excellence for Wind Power in Otterup, Denmark “Our polyurethane resin offers clear advantages over epoxy resins in this application and we achieve a higher glass transition temperature and low shrinkage. The reaction of the polyurethane resin also generates less heat.”
The spar is the core of the structural framework and has to accommodate the full wind load.
“Our woven fibreglass ensures the stability of the compound,” says Saertex MD Marc Schrief. It is thoroughly impregnated with the polyurethane resin and forms a high-strength component, also helping to lower the weight.”
The 45 metre-long rotor blade would weigh eight metric tons overall with the spar cap accounting for approximately a third of the total weight.
The half-shells for the rotor blades are manufactured using a vacuum infusion process which involves placing core materials and woven fibreglass into a mold and hermetically sealing the structure with a film. After applying a vacuum, the infusion process begins with introducing the liquid polyurethane resin. Hübers has developed a manufacturing technology that enables controlled moUld filling based on pumps and sensors to control pump pressure and ensure strict adherence to the planned pressure curve and material kinetics when filling the mould.”
Over the last few years, the process sequence for manufacturing rotor blades has been repeatedly optimised. The infusion process, for example, can be completed in a relatively short space of time, due 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 and there is no need for post-curing.