Vacuum innovation in blade production

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Dutch blade manufacturer Aerpac is embarking upon a 7200 square metre expansion of its main production facilities at Almelo. Once building work is complete, capacity for series production will be doubled, says the company. The original 8000 square metre facility, completed just two and a half years ago, is too small to cope with production now that the company's share of world wind turbine rotor blade sales has risen 15%, adds Aerpac. It recently won an order to replace the blades on the 94 turbines which make up the wind farm of American Kenetech machines in north Holland (Windpower Monthly, July 1998).

The expansion has also been technologically driven. All the new production lines to be installed in the NLG 6 million extension will be fitted with Aerpac's high-tech Resin Infusion Moulding (RIM) system. Described by Aerpac as "an important innovation in production technology" the RIM system allows epoxy resin to be infused under vacuum throughout the entire blade structure rather than being applied layer by layer to the glass fibre.

Because it eliminates all traces of air from the process and consequently produces a laminate with the transparency of glass, the RIM system improves inspection opportunities and may eventually make it possible to manufacture blades using more environmentally friendly materials, such as wood, at a competitive price, the company believes.

More immediately, alongside the quality control benefits of a transparent laminate, Aerpac project manager Hendrik Jan Zwanenburg identifies two advantages of the new method. First, an increased level of impregnation leads to greater structural homogeneity. "Glass fibre is a woven material consisting of bundles of glass. These bundles, or rovings, are in turn made up of tiny filaments. The vacuum process allows us to use a thinner resin, which is sucked into the interior of the rovings, impregnating the separate filaments," he says

Second, because the vacuum technology eliminates any trace of air between the laminate and the gel coating there is a significant decrease in the blade's erosion sensitivity. While erosion symptoms cannot be completely eradicated, the RIM system means they can be further reduced.

The first vacuum impregnated Aerpac APX 43 blade has been delivered to turbine manufacturer Nordex Balcke-Dürr and mounted on a N 43 unit in Germany. Within the next few months all Aerpac blades will be produced with the new technology.

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