This category includes establishments primarily engaged in manufacturing aluminum (including alloys) castings, except die-castings, which are classified in SIC 3363: Aluminum Die-Castings.
331524 (Aluminum Foundries)
Aluminum foundries create castings by pouring heated, liquefied metal into hollowed-out molds. As the molten metal cools, it hardens and assumes the shape created by the mold's cavity. Aluminum foundries typically work with metal purchased in the form of ingots from primary producers or from secondary aluminum recyclers. Some foundries located in close proximity to primary smelters obtain aluminum in molten form.
Aluminum foundry shipments grew to $4.41 billion in 2000, up from $4.22 billion in 1999 and from $3.91 billion in 1997. Although industry shipments grew steadily throughout the late 1990s, employment declined slightly from 35,234 in 1998 to 35,108 in 2000.
The largest user of aluminum castings is the automotive industry. Overall automotive content doubled in the 1990s, as car companies incorporated more aluminum to help reduce vehicle weight and meet federally mandated fuel efficiency standards. In the late 1990s, 92.5 percent of all aluminum used in the automotive industry was in the form of castings. The second largest market for aluminum was in containers and packaging such as food containers, beverage cans, and institutional and household foil. Building and construction were the third largest market for cast aluminum products.
A total of 625 establishments were involved in aluminum casting in the late 1990s. Only 276 of these companies employed 20 or more workers. With 81 companies, California had the greatest number of aluminum foundries in the United States, followed by Ohio with 80, and Pennsylvania with 45.
Aluminum is the most abundant metal in the earth's crust, but it never occurs naturally in isolation. It is a component of many gem stones such as rubies, turquoise, and jade, and it exists in the mineral bauxite. Clays with high aluminum content were used to make pottery in prehistoric times, and aluminum compounds were used by several ancient civilizations as well. The ability to break the chemical bonds between aluminum and other elements to produce the isolated metal was first discovered during the 1800s.
Bauxite, the source for virtually all modern aluminum, was first discovered in Lex Baux, France in 1821. Advances made during the nineteenth century in chemistry and electrolysis made practical the commercial production of aluminum metal from bauxite. In 1855, aluminum cost $115 per pound, but improvements in chemical production led to price reductions. By 1859, the price had dropped to $17 per pound.
Although falling prices permitted the introduction of some aluminum products such as surgical instruments and novelty items, aluminum was still too expensive to gain widespread industrial use. The most important breakthrough came later in the century when Charles Martin Hall of the United States and Paul L. T. Haroult of France independently developed commercial aluminum production methods based on electrolysis. As a result, by the turn of the twentieth century, aluminum prices had dropped to $0.33 per pound.
One of the most famous aluminum castings in the United States was placed on the tip of the Washington Monument in 1884. The first aluminum household utensils were created during the 1890s and gained popularity during the early 1900s. By the mid-1960s, more than half of the cookware on the U.S. market was aluminum.
In 1903, aluminum reached new heights when Wilbur and Orville Wright launched the Kitty Hawk Flyer. Its converted engine contained 30 pounds of aluminum parts.
During World War I, items such as canteens, mess kits, ammunition cases, and tent pins were made from cast aluminum. The emerging automotive industry required engines, manifolds, crankcases, oil pans, and valve covers. World War II increased aluminum casting demands by the military, and brought growing needs within the aeronautic industry.
Modern Casting Techniques. During the mid-twentieth century, aluminum foundries relied on several different casting technologies to meet the diverse demands of their customers. The casting techniques are differentiated by the type of mold used and the process by which the molds are filled. One of the most common types of casting is called "sand casting." Sand castings are created using molds formed from precise blends of sands, clays, and moisture. After a mold is formed, molten aluminum is poured into it. When the aluminum hardens, the sand is removed. The advantages of sand casting are its versatility and low cost for producing small quantities. Its principle disadvantage is its slowness compared to other casting methods.
Shell mold casting is a type of sand casting that relies on a thin mold made of preformed, baked sand. Plaster mold casting is similar to sand casting but molds are fabricated from plaster instead of sand. Plaster mold casting produces products with an improved surface finish.
Permanent mold castings employ molds made of iron or steel into which aluminum is poured. Although aluminum die-casting also uses permanent steel molds, it differs from permanent mold casting by using pressure to force the molten aluminum into the dies, instead of relying on gravity. Permanent mold casting technology produces the strongest castings.
Investment casting is a complex type of casting in which two or more permanent molds are assembled with an intervening wax lining or in which a wax shape is formed and dipped into a special liquid ceramic. When dried, the ceramic creates a shell around the shape. In both cases, the wax is heated and drained to create a hollow for the liquid aluminum. Because the melted wax is drained out of the mold, investment casting is sometimes referred to as the "lost wax" method. After cooling, the mold is broken and an exact aluminum replica of the former wax image remains. One advantage of investment casting is its ability to duplicate intricate patterns.
One of the most recently developed casting processes is called expendable pattern casting, sometimes referred to as "lost foam casting" or "evaporative foam pattern casting." Expendable pattern casting employs a polystyrene pattern made from fused polystyrene beads surrounded by a special sand pack. When liquid aluminum is poured into the mold the polystyrene vaporizes. This procedure yields a casting of the same dimensions as the pattern. Thus, the process holds many advantages such as a reduction in finishing costs and an improved ability to make more complicated designs. According to one estimate, production cost savings associated with expendable pattern casting are as much as 50 percent over traditional casting techniques.
Why Aluminum? Many industrial users favor aluminum because of its physical and chemical properties. Aluminum reflects light, conducts heat and electricity, and weighs only one-third as much as an equal volume of steel. It is also nonmagnetic, nontoxic, and naturally resistant to corrosion. Cast aluminum products are made of pure aluminum or aluminum alloys. Pure industrial aluminum is defined as aluminum containing less than 1 percent impurities. Many of the alloys incorporated into aluminum are added to improve the mixture's hardness, tensile strength, or corrosion resistance. Binary aluminum alloys are made of aluminum and one other element, while complex alloys contain two or more other elements. The most frequently used metals in aluminum alloys include copper, magnesium, manganese, and zinc. Another element often alloyed with aluminum is silicon. Alloys of aluminum with silicon have a lower melting point, which results in improved castability.
Aluminum foundry shipments grew from $3.91 billion in 1997 to $4.41 billion in 2000, while the cost of materials increased from $1.72 billion to $1.84 billion. Although employment between 1998 and 2000 decreased from 35,234 workers to 35,108 workers, the cost of payroll increased from $1.05 billion to $1.14 billion.
The driving force for aluminum castings in the United States is the automobile industry's efforts to conform with the Corporate Average Fuel Economy (CAFE) governmental regulations. According to a study commissioned by the Aluminum Association, the average North American passenger car or light truck contained 183 pounds of aluminum parts in 1991. By 1996, the aluminum content per vehicle had increased more than 80 percent to 248 pounds. Indeed between 1977 and 1999, the average aluminum content per vehicle rose by 150 pounds per vehicle—4.3 percent per year. Approximately 63 percent of the total amount of aluminum in 1999 model cars was recycled metal.
Another trend in the automotive industry fueling the use of aluminum castings was the growing popularity of light trucks (including pick-up trucks, sport utility vehicles, and minivans) in the late 1990s. On average, light trucks in 1999 contained 256 pounds of aluminum, compared to 241 pounds for passenger cars. While the average passenger car had gained 8 pounds of aluminum between 1996 and 1999, the average light truck gained 34 pounds of aluminum. Analysts for the Aluminum Association predict that the demand for aluminum in the automotive sector should slow somewhat in the early twenty-first century. Nevertheless, aluminum should continue to play a still greater role in the automotive industry, especially in closure panels, body structures, chassis and suspension components, and engine blocks.
Other traditional markets such as computers, office machines, and small engines, will also continue to provide aluminum with opportunities for long-term growth. Recent advances in the refrigeration and air conditioning market sectors should spur increased aluminum sales as well.
In an effort to save energy, natural resources, and landfills, more Americans are recycling. In the late 1990s, 33 percent of the total supply of aluminum was recycled, and approximately two-thirds all beverage cans were recycled. This growth was made possible by the increase in recycling centers—there are now more than 10,000 throughout the nation. Moreover, almost 90 percent of automotive aluminum in the late 1990s was reclaimed and recycled. The aluminum industry continues to support and promote recycling.
Aluminum foundries are still experiencing difficulties in complying with the U.S. Environmental Protection Agency (EPA) policies on the treatment and disposal of used aluminum potliners. The agency classified the potliner contaminants (arsenic, cyanide, and fluoride) as hazardous waste in 1989 and revised the levels in 1996. In response, the casting industry began investigating ways to reduce the amount of waste generated through programs such as sand reclamation and reuse. Some governmental jurisdictions instituted studies to evaluate potential applications for foundry waste. Proposed uses included: fill for highway embankments, sub-base materials for concrete slabs, and raw material for making construction products such as bricks.
One of the largest aluminum foundries in the United States is CMI International, Inc. of Southfield, Michigan. CMI is a major producer of machine-cast and molded parts primarily for the automotive industry. Its products include intake manifolds, cylinder heads, engine blocks, suspension and chassis systems, and drive train components. The foundry also produces castings for trucking, mining, and construction equipment. Other industry leaders were Wabash Alloys of Wabash, Indiana; Columbia Aluminum Corporation of Vancouver, Washington,; General Housewares Corporation, headquartered in Terre Haute, Indiana, with 500 workers and $119 million in sales.
Aluminum foundries employ a wide variety of skilled and unskilled workers. Typical employees with specialized skills include technicians, engineers, and chemists. Other specialists include patternmakers (who produce the patterns necessary to create castings), molders (who make the sand molds), and coremakers (who make sand cores). Aluminum foundries also employ many workers with skills not specific to metal-casting. These include industrial hygienists, electricians, and millwrights.
A total of 35,108 people were employed at aluminum foundries in 2000. Of this total, 29,553 were production workers, who were employed an average of 40 hours a week and earned an average wage of $13.67 per hour. In the late 1990s, Ohio employed the largest number of foundry workers in the United States, followed by Wisconsin with 3,627, and California with 2,676.
According to the American Foundrymen's Society (AFS), approximately 25 universities in the United States offered Cast Metals Studies programs. In addition, the Cast Metals Institute, established by the AFS in 1957, provided ongoing training to individuals within the industry.
Among employees in aluminum foundries, burns have been one of the leading causes of work-related injuries. To help protect workers from the inherent dangers involved in handling hot, liquid metal, the Aluminum Association's recommended safety precautions include the use of shields and the establishment of areas in which personnel must wear protective equipment. Special protective clothing for workers directly exposed to molten aluminum is deemed essential because some types of fabrics are subject to igniting or melting upon contact with the liquid metal. As a result, industry standards require wrist to ankle coverage and mandate the use of special footwear, gloves, headgear, and safety glasses.
Ongoing research efforts within the cast aluminum industry have been aimed at alleviating specific casting problems and producing castings of a better quality. Because aluminum shrinks as it cools, casting were sometimes prone to "hot tears," a type of fracture caused by the stresses created during solidification. Breaks in the finished product caused by insufficient metal flow during the casting process can lead to another problem. These types of deficiencies are known as "shrinkage cracks."
One of the biggest challenges, however, has been the elimination of hydrogen-induced porosity in cast products. Under certain conditions, hydrogen, which was soluble in aluminum, can cause tiny pores within a casting's metal structure. According to Hans J. Heine, International Editor of Foundry Management & Technology, these tiny holes represent "a primary cause for rejection of an aluminum casting."
To help reduce hydrogen-induced porosity, a method was developed to pass nitrogen gas through the molten aluminum solution. The nitrogen was not soluble in aluminum and the action of its presence helped the mixture release trapped hydrogen prior to casting. Some researchers experimented with refinements using argon, freon, and chlorine. Although these methods were deemed effective, industry analysts judged them to be too expensive. Another promising method of reducing hydrogen-induced porosity involved degassing the molten aluminum under a partial vacuum. Pressurized conditions caused the gas to float to the surface of the molten mixture.
To produce castings with specific qualities, sometimes heat treatments are used. When a cast product is heated and cooled under precise conditions, it develops a uniform internal structure, removes stresses, and improves its strength, stability, and hardness. One type of heat treatment, called annealing, involves heating a casting to a temperature above the point where its metal crystals would melt and then cooling it to recrystallize the metal.
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Ducker Research Company. "Report on Aluminum Content in 1999 North American Passenger Cars and Light Trucks: Executive Summary," 28 December 1999. Available from http://www.aec.org/ducker_report.htm .
Kirgin, Kenneth H. "Nonferrous Foundries Vie for Continued Growth." Modern Casting, September 1996, 40.
United States Census Bureau. "Aluminum Foundries," 29 October 1999. Available from http://www.census.gov .
United States Census Bureau. "Statistics for Industries and Industry Groups: 2000." Annual Survey of Manufacturers. February 2002. Available from http://www.census.gov .