The largest mass-produced rotor blade in the world has a length of 37.5 m and is manufactured with leading-edge production methods. Both, the manufacturer’s personnel and the materials used must meet the highest demands with regard to quality. As a matter of principle, materials are subjected to in-house incoming inspection and additional intermediate tests before entering the production process.

The quality of the finished product has also continuously been improved such that, at present, rotor blades are provided with so-called ‘erosion-protection foils’ — special self-adhesive polyurethane films which are applied during the final stage of production. The rotor blades consist of two shells made from glass fiber and epoxy resins, which are assembled and painted. An initial long-term test completed in 1998 showed that the application of a protective foil allowed the maintenance intervals of the bonded surface to be extended to at least four years. By comparison, nonprotected rotor blades had a maintenance interval of two to two-and-a-half years due to erosion problems occurring much earlier. Although erosion-protection is an additional cost-factor, it allows the manufacturers to achieve a quality standard with which they can be associated. Indeed, erosion-protection not only extends the maintenance interval but also improves the public image of the manufacturer of the wind power plant.

At present, all leading German manufacturers fit their rotor blades with protection foils. Typically, a polyurethane film 300 mm wide is applied to the center, starting at the tip, over a length of 22 m, and then bonded to the sides. A combination of a particularly tough thermoplastic polyurethane elastomer film and high-quality acrylic adhesive provides excellent protection from erosion.

In the manufacture of rotor blades, it is important that the protective foils can conform to slightly deformed surfaces. These pressure-sensitive polyurethane films have been used for some years in the aircraft and automobile industries, where they have been coated with high-quality, low-bake or polyurethane paints at later stages. The protective material used for rotor blades is 0.36 mm thick, highly transparent, and resistant to UV light and, if staining does ever occur after long-term exposure to adverse ambient conditions, it will be hardly perceptible.

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