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Nickel key component in wind turbine castings
by Dean Jobb
Nickel Magazine, June 2007 -- Efforts to reduce carbon emissions and
mitigate the effects of global warming are generating increasing demand worldwide for clean energy produced
from wind – and creating a promising new market for nickel.
The massive components of wind turbines -- rotor hubs, gearbox housings, base plates, gears and shafts –
are cast in ductile iron, which has the advantage of being about 10% lighter than carbon steel. The metal
must meet demanding standards for impact resistance, and that’s where nickel plays a key role.
“Turbine manufacturers are looking for a ductile iron alloy that has certain critical properties,
including good impact strength at low temperatures (in northern climates),” says Rick Gundlach, senior
metallurgical engineer for Stork Climax Research Services in Wixom, Michigan, U.S.A. “These mechanical
properties would be difficult to achieve with a conventional ductile iron that doesn't contain nickel.”
Conventional ductile iron contains 2 or 3% silicon, which strengthens the metal but has the drawback of
making it brittle at low temperatures. Adding between 0.5 and 1% nickel to the casting process (GGG 40.3)
reduces the need for silicon and enables the iron to meet the minimum impact resistance specified for wind
turbine components at a temperature of minus 20°C.
“The wind energy engineers don't want a brittle material, they want toughness at low temperatures,” says
James Mullins, technical director for the Ductile Iron Society of North America. “Nickel is one of the few
elements that strengthens the iron but doesn't embrittle it.”
The addition of such a small amount of nickel may seem insignificant, but consider the size of the
components being cast. Rotor hubs are ring-shaped castings with a central hole to accommodate rotor blades
and other components that are large enough for a man to walk through. Each one can weigh up to 1,600
kilograms. Between 32 and 45 tonnes of ductile iron castings are used to build a 4.5-megawatt turbine
windmill capable of powering 1,500 homes. Larger turbines are under development and even larger turbines are
anticipated in the future.
So a single turbine assembled from 45 tonnes of castings would contain close to half a tonne of nickel.
Only about 20 manufacturers worldwide can produce castings of that size “and they're using truckloads of
nickel,” Mullins notes.
“There has been a tremendous push to produce a lot of these wind turbines,” adds Gundlach, who is under
contract to do quality control testing for two U.S. foundries. “They can’t make them fast enough.”
Turbines are increasing in number as well as in size. The American Wind Energy Association (AWEA)
estimates that wind power will generate 31 billion kilowatt-hours of electricity in the United States in
2007, with America’s capacity expected to grow at a rate of up to 30% a year. But overall, North America has
been slow to embrace wind energy. In Europe, where commercial wind generation is firmly established,
nickel-treated ductile iron has been used to make turbines since the mid-1990s.
The U.S. government has extended its tax credit for wind power producers to the end of 2007, adding
stability to what had been a boom-and-bust market for turbines. Four turbine factories opened new American
plants in 2006, AWEA reports, and established European manufacturers are setting up branch plants to supply
the growing U.S. market.
American foundries are re-tooling to provide the needed castings. Cast-Fab Technologies of Cincinnati,
Ohio, for instance, sells more than a quarter of its casting output to wind producers, according to
Engineered Casting Solutions Magazine.
“There’s such a demand for wind turbine generators that the people producing them can’t find enough
foundry supply to make the castings,” notes Gundlach. “We’ve not seen a new market like this in a long
time.”
Dean Jobb is a Halifax, Nova Scotia-based freelance writer.
Photos: iStock and General Electric
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