COMPOSITES EUROPE 2012 Blog

Every movement must be just right when the blade and rotor hub of a wind turbine are married together at a dizzy height.  Because screwing the rotor blade onto the rotor hub 100 metres above the ground represents a major bonding technology challenge. Heavy-duty threaded bushes are bonded into the fibre-reinforced flange on the blade holder of each blade – and the bond must be absolutely rock solid.

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To ensure their suitability when used in wind energy systems, the epoxy resin adhesives used must be suitably certified by Germanischer Lloyd (GL). This is because rotor blades must withstand extreme stresses. The larger the unit, the higher the demands on the fatigue strength of the rotor blades manufactured from composites. In the near future, experts predict 10 megawatt systems with 80 metre long wind vanes.

The enormous rotor blades consist of two half shells, that are produced in suitable moulds from cross-linked hard foams and inserted balsa woods, which are subsequently stuck together. The balsa wood is cultivated in plantations in Ecuador and is harvested after six years. From a one metre long tree trunk, rectangular timber sections are cut and stuck together to make 1.22 metre long and five centimetre wide ashlars. These blocks are then cut into boards against the grain and finely sprayed with a resin solution to protect them against moisture.

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Block material is usually used for the manufacture of ultra firm, lighter weight carbon composites.  This involves the curing of a combination of epoxy resins, micro glass spheres and a curing agent in an autoclave.  When curing the pre-impregnated carbon fibres, a composite laminate is produced in the same shape as the original model.  This in turn forms the basis for the pertinent carbon component.  Epoxy based composite materials have become the norm especially for high speed use, for example in Formula 1.

Block materials are also becoming the norm not only in high-tech applications, such as those for speedy runabouts, but also in other industries.  In addition to the customary automobile industry, examples can also be found in railway and ship building as well as in aviation.  In addition, companies in the wind energy sector are increasingly relying on the blocks that are stuck together from slabs in defined standard sizes.  At the Composites Europe Trade Fair, which will take place in Stuttgart from 27 to 29 October 2009, high-tech as well as routine applications will be on display.

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