Wind farm sizes are constantly increasing and the technical demand for parts is growing in response. To be able to meet these requirements in the future, the quality of parts and production processes must be continually optimized. Thus it is necessary to optimize the relationship between strengthening materials made of glass and carbon fibres, composite materials, matrix systems and production techniques. The SAERTEX® glass fibre non-crimp fabrics would not, as previously, be impregnated with epoxide resins, but with a newly developed PU resin manufactured Covestro.
Like epoxide resins, new PU resins are very lightweight. The web for a 45 m long wing would be produced in a mould at the German Centre for Aerospace´s laboratory in Stade. The spar cap would be constructed in a monolithic design with up to 44 layers of non-directional glass skins.
“The spar cap is the most important component of a rotor blade,” according to the SAERTEX® Director Sales & Marketing Marc Schrief. “It bears the entire force of the wind. The stiffer the spar cap, the better the yield results. This project has shown that we can match the construction of our interlaid scrims perfectly with the wishes of our clients. What has functioned so well with glass fibre can also be achieved with carbon. Then blades with a length of more than 100 metres become possible.”
Kim Klausen, Project Manager with Covestro, points out another very positive aspect: “Polyurethane gives us two clear advantages over epidoxide resins. Stability and durability are the decisive qualities of rotor blades. In this application a higher glass transition temperature and less shrinkage is obtained than with epidoxide. Besides, less heat is released by the reaction of the polyurethane.
SAERTEX® had performed a great deal of research and many tests on its own account in order to optimize the combination of glass fibre NCFs, core materials and PU resin. Thus SAERTEX® was able to validate the advantages of rapid infusion with PU resin through the optimized production of the skin. SAERfoam®, a core material certificated by the GL, also showed positive results in combination with PU resin.
SAERTEX® Director Sales & Marketing Marc Schrief looks confidently on the progress of the joint project: “As a first step we have increased productivity and been able to develop a more rapid infusion process through optimized manufacture of non-crimp fabrics. But we have further ideas and propositions for the wind industry: Balsa is not the material of the future from our point of view. As a natural product, balsa shows irregularities and in addition contains moisture. This absolutely does not happen with PU resins. Our structural core material SAERfoam® which uses ultra-light PU foam and with 3D glass bridges replaces balsa in the most innovative way.”
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