Wind's cast crop: after a record breaking year of new wind energy capacity in the U.S., manufacturers are clamoring for more metal castings.

Drive down a stretch of highway in Iowa past acres of cornfields or through the open ranchlands of Texas past miles of cattle and you might find yourself in the middle of one of the newest types of farms in the U.S.--the wind farm.

A far cry from the wooden windmills that have peppered the rural landscape of Europe for centuries, modern wind turbines are finding a place of their own among farms all over the world, as well as in the oceans and deserts. Wind energy is not as established in North America as it is in Europe, but the U.S. wind industry is in the throes of a record-breaking growth spurt due to rising gas prices and more supportive legislative policies.

Commercial wind turbines, which are constructed over acres of land in "wind farms," consist of several structurally and operationally integral metal castings that support these power-generating skyscrapers. Depending on their size, today's commercial wind turbines typically generate between 700 kWh and 2.5 MW of electricity a year. Currently, wind farms supply less than 1% of the nation's electricity, but by 2020, wind energy technology could provide 6% of the electricity--a share similar to hydropower (electricity produced by water) today.

Between 2004 and 2005, 2,431 MW of new wind energy was installed--a 35% increase in capacity that accounts for the most growth in the world (Table 1). Recent legislative decisions have signaled a more serious and committed approach to the development of wind energy as well, lending some stability to what has been a boom-and-bust market.

Wind energy could mean big business for some U.S. metalcasters. Wind turbines, which are growing in size every year, require large castings that weigh up to 50,000 lbs. (22,680 kg). Few metalcasting facilities can pour castings that size, but for those who do, wind energy's shining future is a breath of fresh air.

"We have wind casting orders of just one part for one customer to long-term commitments from other customers," said David Neil, president of ATI Casting Service (an Allegheny Technologies company), LaPorte, Ind. "But, when you're talking about a 36,000-1b. [16,329-kg] casting, even an order of 10 is a big deal."

Riding Out the Market

Worldwide, wind power generation has tripled over the last five years, with most of the capacity concentrated in Europe. The European market already has reached the 2010 target set by the European Commission of 40,000 MW installed capacity, while the U.S. currently has 9,149 MW.

"In Europe, they have set very aggressive targets for renewable energy," said Ross Bushman, president and COO of Cast-Fab Technologies Inc., Cincinnati, an iron casting supplier to the wind energy market.

The largest constraint to the U.S. wind market has been political. The success of the wind industry in the U.S. has depended greatly on the government-issued production tax credit (PTC), which provides a $0.019 per kWh credit for electricity produced commercially from a wind energy facility during the first 10 years of its production. The PTC was enacted in 1992 but must be renewed on a yearly basis. Three times in the last seven years, the PTC has been left to expire, and when the PTC expired, contracts were put on hold and investments trickled to a halt. In 2001 and 2003, new installations were near 2,000 MW, but because of expirations of the PTC, they dipped down to less than 500 MW in 2002 and 2004 (Fig. 1).

[FIGURE 1 OMITTED]

"European countries have made a strong, long-term commitment to alternative power," Neff said. "Because there has been no long-term commitment here, there are few manufacturing companies in the U.S."

However, a few recent legislative actions have indicated a growing commitment to wind energy. Congress recently extended the PTC to the end of 2007, providing a three-year window of stability. Additionally, high oil prices led to U.S. President George W. Bush's Advanced Energy Initiative, which he announced during his State of the Union Address on Jan. 31. The initiative promises $44 million of the 2007 budget to go to wind energy research, a $5 million increase over FY2006 levels.

With the extension of the PTC, the U.S. wind energy market is expected to have another record-breaking year in 2006, rather than the slow year that usually follows boom years. Wind turbine manufacturers are continuing to ramp up new projects and establish more contracts with their suppliers. Installations in 2006 are expected to top 3,000 MW compared to the nearly 2,500 MW installed in 2005. Although commercial wind turbines vary in energy capacity, 3,000 MW of electricity would mean 1,200 new 2.5 MW turbines (or 2,000 1.5 MW turbines).

Supplying a Booming Industry

A member of the American Wind Energy Association, ATI Casting Service has been involved in the wind industry for 15 years and produces cast ductile iron hubs, base plates, gearboxes and bearing housings for wind turbines. More than 20% of ATI Casting Service's production consists of wind castings, and Neil sees continued growth for the wind market beyond just the next few years.

"We see wind as a growth market for two reasons--the price of fuel is never going to go up because wind is free. And, unlike most other sources of electric generation, there is no need for water," Neil said. "Water is a shrinking resource, which makes wind practical. You can put a wind turbine out in the desert or the ocean."

Its status as clean energy will give the wind market staying power, predicts Bushman.

[ILLUSTRATION OMITTED]

"Access to cheaper, clean energy is something people all over the world want," he said. "Wind energy is not using natural resources--it's really just capturing the wind."

But the U.S.' late start in the wind industry means few manufacturing companies are located in the States.

"The negative about the wind industry is that other than a few American wind companies, most wind energy companies manufacture their turbines in Europe, where wind energy is more established," Nell said. "If we have a longer commitment to production tax credits, I believe the companies currently manufacturing in Europe would locate their manufacturing plants in the U.S. It would cut shipping costs, and the time to market would shrink."

Clipper Windpower Inc., Carpinteria, Calif., is one American wind energy company that manufactures its turbines in the U.S. Clipper started up in 2005 with the production of five prototype wind turbines, but plans are in the works to build 151 2.5 MW turbines in 2006 and more than 250 turbines in 2007. This would mean an additional 1,000 MW of installed capacity for the U.S. and thousands of tons of ductile iron castings to construct the turbines.

Depending on the size of the turbine, each wind mill consists of between 10 and 25 tons of ductile iron castings ranging in size from less than 200 lbs. to 50,000 lbs. (91-22,680 kg) (Fig. 2). It's a staggering number--only a few metalcasting facilities have the capability to pour such large components.

[FIGURE 2 OMITTED]

Hodge Foundry, Greenville, Pa., is one of a handful of North American metalcasting facilities that handles these monstrous castings. "We produce the center hubs and bed plate (or main frames), which attaches to the tower and supports the working generation components of the turbine," said Joe Simko, president. "These cast pieces range from 20,000 to 30,000 lbs. [9,072-'13,608 kg] and can be as large as 15 ft. [4.6 m] in diameter. In the next few years the trend will shift to larger pieces, which are already on the drawing board."

Metalcasting facilities are working hard to free up capacity and expand the capabilities for the large castings. In the meantime, U.S. wind turbine manufacturers shop around the world for casting suppliers.

"We buy castings from all over the world," said Fred Chase of Clipper Windpower. "We buy as many as we can in the U.S., but there are so few metalcasters that can make these large castings, and right now, the metalcasters we buy from are at capacity."

Chase said that in some instances, manufacturers are forced to forego purchasing a cast component because there's no one to supply it. "The support base (of the wind turbine) is better as a casting," he said. "But some manufacturers will use a welded support base because there are not enough metalcasters with the ability to cast a piece this size."

And, because of the historical boom-bust market of the U.S. wind industry, when the PTC is in effect, as it is now, wind companies rush to production, placing orders for as many castings as they can from as many casting facilities they need.

"When there is a PTC, there is a good level of business from wind energy companies ordering castings," Neil said.

Bushman sees a global trend of formal capacity commitments while the financial picture is strong. "There's such an interest worldwide in wind energy," he said. "As the world economy gets stronger, companies are trying to secure metalcasting capacity all over to ensure they'll get their orders filled in the coming year."

Standing Strong Against the Wind

Commercial wind energy capacity can range from 1 MW to 5 MW of power per turbine, and the turbines stand between 120-380 ft. (37-116 m) tall. Several castings are used in the construction of wind turbines, both as structural pieces and as part of the machine work (Table 2). The largest castings, such as the rotor hub, machine frame and baseplate, serve as the support system for the wind turbine's long, tall tower, gigantic rotor blades and machinery and gears.

Most of these large castings are ductile iron, which exhibits the highest strength of the cast irons, as well as good wear resistance and fatigue strength. In addition, ferritic ductile iron holds adequate mechanical properties while offering superiority over steel in machinability, castability, low temperature toughness and flexibility.

"We certainly can control the quality we want as well," Chase said. "And it is more reasonably priced than cast steel."

Cast-Fab Technologies produces castings for several different turbine companies, but most of the castings ultimately end up on either a 1.5 MW or 2.5 MW turbine. The castings, which include bearing housings, input housings, mid-plate casings and gearboxes, range in size from less than 100 lbs. (45 kg) to more than 30,000 lbs. (13,608 kg).

Orders for 2006 are up significantly from 2005, with all of Cast-Fab's manufacturing customers predicting solid to aggressive growth.

"In 2005, 15% of our casting sales were related to wind energy. In 2006, that percentage is forecast to jump to more than 25%," Bushman said. "Our long range plans are to continue to increase that market segment."

The majority of Cast-Fab's wind parts are made out of some of the more challenging ductile iron grades, such as the EN specification 1563. Many of the castings used for wind turbines, such as the 3,000-lb. (1,361-kg) bearing housing, are located far off the ground and susceptible to high-powered winds. This ferritic grade of ductile iron features the properties necessary to withstand the force of the wind without failure.

"Ductile iron has ideal physical properties for this application," Neil said. "It is known for its good tensile, elongation and yield properties, but a fourth property is what makes it so attractive for wind applications. That fourth property is its high impact strength at low temperatures. This physical property is measured via a Charpy V-notch impact test."

Achieving the proper properties for application in the wind industry is difficult, and requires a balance among chemistry, microstructure and mechanical properties. The castings must achieve high impact strength at low temperatures, so the metal must be modified to achieve lower silicon and phosphorous levels. The alloy also must have high nodularity without a high nodule count, so great care is taken during inoculation to achieve the optimal nodularity.

Critical components in wind applications are required to have an average minimum Charpy V-notch impact resistance of 10 Joules at -20c, in addition to achieving a minimum of 12% elongation, as required by the material specification DIN EN 1563, EN-GIS-400-18U-LT.

Wind turbine manufacturers, such as GE Energy, the country's leading wind energy company, prefer these properties to be met as-cast in the critical castings, and the components must pass rigid ultrasonic, magnetic and penetrant inspections.

Taking trepan specimans from bolthole locations on the rotor hub is also routine. "If the hubs show any evidence of a degenerated graphite structure beyond what is allowed, the hub is rejected," said Greg Bouse, engineer for materials and processes engineering of sand castings for GE Energy. "So we have checks in place from the test coupon and the component itself."

Accommodating Wind

As the U.S. wind industry continues to grow and more American manufacturers look for local suppliers, U.S. metalcasting firms like Hodge, ATI Casting Service and Cast Fab are finding ways to accommodate this growing market.

"Mission critical wind castings are a key component in our power generation market," Simko said. "Hodge Foundry is in the midst of a $2 million upgrade, which positions us well to handle the size and weight required in the future."

Cast Fab is in the process of expending significant capital throughout the facility, all with the thought in mind of improving speed and process. The firm's lean manufacturing efforts already have sparked some rearranging of paints flow to find more ways to gain efficiency.

"We're interested in this market, of course," Bushman said. "So we're working to be more efficient and make room for increased wind energy sales."

ATI Casting Service recently expanded its capacity to produce large castings. This expansion included the installation of new molding pits, a larger building and a new coreroom. The company also invested in tools to ensure the quality of these wind castings.

"This metal is very demanding, so it is required that we invest in the laboratory equipment to make sure we meet our quality targets," Neil said. ATI Casting Service has its own Charpy testing facilities on site, along with an image analyzer for the microstructure of the metal, and a new spectrometer has been ordered.

These investments are substantial, but with them these facilities can catch the wind market's strengthening current.

"Wind is certainly going to have a bright future," Chase said. "Not just as an alternative energy source, but as a real commercial source of energy."

RELATED ARTICLE: Collecting Energy is a breeze.

Wind power is attractive because it is a form of renewable energy that is replenished daily by the sun. Because only a tiny fraction of the potential energy from wind currently is captured by the U.S., the wind industry is expected to have several years of growth ahead. But cast components used in wind turbines must meet some strict guidelines because of their unique design and operation.

Wind power is created by the rush of air filling low-pressure areas caused by the warmth of the sun. The power in the wind is stronger at higher elevations. Wind can be five times stronger at the top of a 40-story building than the breeze rustling the leaves on the ground. So, the trend has been to make wind turbines bigger and taller to capture the largest amount of wind power possible.

Large, utility-scale turbines can have blades more than 130 ft. (40 m) king with a diameter of more than 260 ft. (79 m). The turbines are mounted on towers that can be 260 ft. (79 m) tall--nearly the length of a football field. Currently, wind turbines with 188-ft. (57-m) blades are being tested. These turbines stand nearly 400 ft. (122 m) tall.

Kinetic energy in the wind is converted to rotational motion by the rotor, which is usually a three-bladed assembly at the front of the turbine (Fig. A). The rotor turns a shaft, which transfers the motion into the large housing at the top of the tower, often called the nacelle.

[FIGURE A OMITTED]

Inside the nacelle, the slowly rotating shaft enters a gearbox that greatly increases the rotational shaft speed. The high-speed shaft is connected to a generator that converts the rotational movement into electricity at medium voltage (a few hundred volts). The electricity flows down thick electric cables inside the tower to a transformer, which increases the voltage of the electric power to the distribution voltage (a few thousand volts).

The distribution voltage power flows through underground lines to a collection point where the power may be combined with that of other turbines. Utility-scale turbines that produce 1.8 MW of power can supply enough electricity for 600 homes and cost over $1.5 million. But power generation is constantly growing as newer, bigger turbines are developed and produced. The newest turbines can generate up to 5 MW of power (Table A).

Table 1. Top Ten Nations That Added New
Wind Power Capacity in 2005

                          New
Country                capacity         % of Global
                         (MW)              Growth

U.S.                     2,431              20.7
Germany                  1,808              15.4
Spain                    1,764              15.0
India                    1,430              12.2
Portugal                  500               4.2
China                     498               4.2
Italy                     452               3.8
U. K.                     446               3.8
France                    367               3.1
Australia                 328               2.8
Total top 10            10,024              85.2
Rest of the world        1,745              14.8
World total             11,769             100.0

Table A. Wind Turbine Sizes Over the Years

                        1985   1990    1996    1999    2000     2005

Rotor diameter (ft.)      56     88     131     164     233      377
Rating (kW)              100    225     550     750   1,650    5,000
Annual MWh               220    550   1,480   2,200   5,600   17,000

Table 2. Weight Ranges for Ductile Iron Castings
Used in Wind Power Turbines

Castings                      Weight   Typical weight
                              range    for 1 MW wind
                              (tons)   turbine (tons)

Rotor hub                      4-25          4.5
Blade adopter--three pieces    -0.1          0.1
Frame--the machine body        6-19          --
Frame--the foundation          4-12          5.0
Bearing house-two pieces       0.1           0.2
Shaft                           1            --
Gears                          0.1           --
Jaw ring                       0.1           0.2
Brake disc                     -0.1          --

Total typical weight
  for 1 MW wind turbine                      10.0