CompositesWorld
Issue link: https://cw.epubxp.com/i/841219
NEWS CompositesWorld.com 35 PU-infused Wind Blades 45m long spar cap, the primary structural element of a wind blade. At this point, two final project partners were invited to participate: reinforcements and core materials supplier SAERTEX (Saerbeck, Germany) and process engineering specialist and equipment supplier Hübers Verfahrenstechnik Maschinenbau (Bocholt, Germany). "We received a request from DLR to provide unidirectional [UD] glass fiber reinforcements," recalls SAERTEX account manager Alexander Winter. "ese UDs are a material we commonly supply into wind blade spars," he notes. ey comprise two layers: a stabi- lization layer of 90° fibers, weighing only a few grams per square meter, and the unidirectional 0° layer, which provides strength along the length of the spar. "e fabric used in the spar cap demo project was one we had specifically developed for a 45m spar," says Winter. It featured a 1,182-g/m 2 areal weight and 670-mm width. SAERTEX has made this type of noncrimp fabric (NCF) with glass fiber as heavy as 4,000 g/m 2 and as light as 230 g/m 2 . It also can slit this type of fabric into widths that range from a few centimeters up to 3m. "For many fabrics, the normal production width is 50 or 100 inches [1.3 or 2.5m]," says Winter, "but UDs are typically 200-600 mm in width." To help speed layup, especially for blade skins, SAERTEX also kits fabrics for a variety of manufacturers — e.g., 100 cut and labeled NCF pieces per box. "We selected glass fibers with a sizing that is compatible with the Covestro PU resin," Winter recalls. Covestro also completed smaller-scale infusion tests in advance (see Step 1, p. 34). Like other infusion resins used in wind blade construction, PU requires the metering, mixing and dispensing (MMD) of two 5 The resin infusion is completed in 46 minutes. 7 The mold is closed to help prevent heat loss. 6 Insulation blankets are then placed over the infused laminate. 8 The finished spar cap is demolded.