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Making Aluminum Cans

What we do
Raw Materials

The raw material of the aluminum beverage can is, of course, aluminum. Aluminum is derived from an ore called bauxite. The bauxite is refined and then smelted, and the resulting molten aluminum is cast into ingots The aluminum base, for beverage cans consists mostly of aluminum, but it contains small amounts of other metals as well. These are typically 1% magnesium, 1% manganese, 0.4% iron, 0.2% silicon, and 0.15% copper. A large portion of the aluminum used in the beverage can industry is derived from recycled material. Twenty-five percent of the total American aluminum supply comes from recycled scrap, and the beverage can industry is the primary user of recycled material. The energy savings are significant when used cans are remelted, and the aluminum can industry now reclaims more than 63% of used cans.

The Manufacturing Process

Cutting the blank

1 The modern method for making aluminum beverage cans is called two-piece drawing and wall ironing. The process begins with an aluminum ingot which was cast to be about 30 inches (76 cm) thick, then rolled into a thin sheet. The first step in the actual manufacture of the can is to cut the sheet into a circle, called a blank, that will form the bottom and sides of the can. Each blank is 5.5 inches (14 cm) in diameter. Some material is necessarily lost between each circle, but manufacturers have found that minimum aluminum is lost when the sheets are wide enough to hold two staggered rows of seven blanks each. About 12-14% of the sheet is wasted, but can be reused as scrap. After the circular blank is cut, it is “drawn” or pulled up to form a cup 3.5 inches (8.9 cm) in diameter.

Redrawing the cup
Redrawing the cup

2 The small cup resulting from the initial draw is then transferred to a second machine. A sleeve holds the cup precisely in place, and a punch lowered swiftly into the cup redraws it to a diameter of about 2.6 inches (6.6 cm). The height of the cup increases simultaneously from the initial 1.3 to 2.25 inches (3.3 to 5.7 cm). The punch then pushes the cup against three rings called ironing rings, which stretch and thin the cup walls. This entire operation—the drawing and ironing—is done in one continuous punch stroke, which takes only one fifth of a second to complete. The cup is now about 5 inches (13 cm) high. Then another punch presses up against the base of the cup, causing the bottom to bulge inward. This shape counteracts the pressure of the carbonated liquid the can will contain. The bottom and lower walls of the can are also a little thicker than the upper walls, for added strength.

Trimming the ears

3 The drawing and ironing process leaves the can slightly wavy at the top. These small ripples in the metal are called “ears.” “Earing” is an unavoidable effect of the crystalline structure of the aluminum sheet. Aluminum companies have studied this phenomenon extensively, and they have been able to influence the placement and height of the ears by controlling the rolling of the aluminum sheet. Nevertheless, some material is lost at this stage. About a quarter inch is trimmed from the top of the can, leaving the upper walls straight and level.

Cleaning and decorating

4 The drawing and ironing process leaves the outer wall of the can with a smooth, shiny surface, so it does not require any further finishing such as polishing. After the ears are trimmed, the can is cleaned and then imprinted with its label. After the can is decorated, it is squeezed in slightly at the top to a make a neck, and the neck is given an out-ward flange at the very top edge, which will be folded over once the lid is added.

The lid
The lid

5 The lid is made of a slightly different alloy than the aluminum for the base and sides of the can. The inward bulge of the bottom of the can helps it withstand the pressure exerted by the liquid inside it, but the flat lid must be stiffer and stronger than the base, so it is made of aluminum with more magnesium and less manganese than the rest of the can. This results in stronger metal, and the lid is considerably thicker than the walls. The lid is cut to a diameter of 2.1 inches (5.3 cm), smaller than the 2.6-inch (6.6 cm) diameter of the walls. The center of the lid is stretched upward slightly and drawn by a machine to form a rivet. The pull tab, a separate piece of metal, is inserted under the rivet and secured by it. Then the lid is scored so that when the tab is pulled by the consumer, the metal will detach easily and leave the proper opening. To ensure that the cans are made properly, they are automatically checked for cracks and pinholes. One in 50,000 cans is usually found to be defective.

Filling and seaming

6 After the neck is formed, the can is ready to be filled. The can is held tightly against the seat of a filling machine and a beverage is poured in. The lid is added. The upper flange formed when the can was given its neck is then bent around the lid and seamed shut. At this point, the can is ready for sale.

Byproducts/Waste

Some aluminum is lost at several points in the manufacturing process—when the blanks are cut and the ears are trimmed—but this scrap can be reused. Cans which have been used and discarded by consumers can also be reused, and as mentioned above, recycled material makes up a significant percentage of the aluminum used for beverage cans. The savings from recycling are quite significant to the industry. The major expense of the beverage can is in the energy needed to produce the aluminum, but recycling can save up to 95% of the energy cost. Can producers also try to control waste by developing stronger can sheet so that less aluminum goes into each can, and by carefully controlling the manufacturing process to cut down on loss through earing. The lid of the typical can is smaller in diameter than the walls in order to conserve the amount of aluminum that goes into it, and as world-wide demand for beverage cans continues to grow, the trend is to make the lid even smaller.

The Future

Worldwide production of aluminum beverage cans is steadily increasing, growing by several billion cans a year. In the face of this rising demand, the future of the beverage can seems to lie in designs that save money and materials. The trend towards smaller lids is already apparent, as well as smaller neck diameters, but other changes may not be so obvious to the consumer. Manufacturers employ rigorous diagnostic techniques to study can sheet, for example, examining the crystalline structure of the metal with X-ray diffraction, hoping to discover better ways of casting the ingots or rolling the sheets. Changes in the composition of the aluminum alloy, or in the way the alloy is cooled after casting, or the thickness to which the can sheet is rolled may not result in cans that strike the consumer as innovative. Nevertheless, it is probably advances in these areas that will lead to more economical can manufacture in the future.