Industry and process description

The aluminum forming industry is a manufacturing industry in which aluminum or aluminum alloys are made into semifinished aluminum products using hot or cold working processes. The aluminum forming manufacturing operations include the rolling, drawing, extruding, and forging of aluminum. In the U.S., the industry consists of about 300 plants owned by about 150 companies. The industry employs about 30,000 workers.

As well as the aluminum forming manufacturing operations of rolling, drawing, extruding, and forging, there are associated processes, such as the casting of aluminum alloys for subsequent forming, heat treatment, cleaning, etching, and solvent degreasing.1-6

Surface treatment of aluminum (such as cleaning, etching, and solvent degreasing) is any chemical or electrochemical treatment applied to the surface of aluminum. Such surface treatment is considered to be an important part of aluminum forming. For the purposes of government regulation, surface treatment of aluminum is considered to be an integral part of aluminum forming whenever it is performed at the same plant site at which aluminum is formed, and such operations are not considered for government regulation under the Electroplating and Metal Finishing provisions of U.S. 40 CFR parts 413 and 433.

Casting aluminum when performed as an integral part of aluminum forming and located on site at an aluminum forming plant is considered an aluminum forming operation and hence is covered under these government guidelines.

When aluminum forming is performed on the same site as primary aluminum reduction the casting shall be regulated by the nonferrous metals guidelines if there is no cooling of the aluminum prior to casting. If the aluminum is cooled prior to casting then the casting shall be regulated by the aluminum forming guidelines. The major aluminum forming processes are briefly described in the narrative below.

5.1.1 Casting

Before aluminum alloys can be used for rolling or extrusion and subsequently for other aluminum forming operations, they are usually cast into ingots of suitable size and shape.

The aluminum alloys used as the raw materials for casting operations are sometimes purchased from nearby smelters and transported to the forming plants in a molten state. Usually, however, purchased aluminum ingots are charged together with alloying elements into melting furnaces at the casting plants. Several types of furnaces can be used, but reverberatory furnaces are the most common.

At many plants, fluxes are added to the metal to reduce hydrogen contamination, remove oxides, and eliminate undesirable trace elements. Solid fluxes such as hexachloroethane, aluminum chloride, and anhydrous magnesium chloride may be used, but it is more common to bubble gases such as chlorine, nitrogen, argon, helium, and mixtures of chlorine and inert gases through the molten metal.

The casting methods used in aluminum forming can be divided into three classes: direct chill casting, continuous casting, and stationary casting.

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