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form precise compound curves. In the mid-1970s Alcoa Industries became interested
in aluminum VAWT blades and systems as potential product lines and investigated methods
for reducing blade manufacturing costs. Working with Sandia engineers, the company
developed an extrusion process for Darrieus blades in which partially molten bars of
aluminum are forced through an airfoil-shaped die, after which the shaped structure cools
and solidiies. This process dramatically reduced the cost to manufacture VAWT blades,
produced long sections of uniformly high quality material, and controlled the airfoil shape
to very close tolerances.
Extruded aluminum blades were irst lown on the 17-m VAWT, and extrusion con-
tinues to be used today to manufacture VAWT blades. Figure 3-21 shows a steel extrusion
die and extruded aluminum sections for a large VAWT airfoil. The leading and trailing-
edge sections in Figure 3-21(b) are joined together before the complete airfoil is given its
curved shape.
Figure 3-21. Extrusion of
aluminum VAWT blades.
(a) Steel die used to form the
leading-edge section of an airfoil
integrally with its interior spars.
(b) Leading- and trailing-edge
extrusions prior to being joined
and bent to their inal, curved
shape. ( Courtesy of Sandia
National Laboratories )
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