Fabrication Process
Modern cans are generally produced through a mechanical cold forming process that starts with punching a flat blank from very stiff cold-rolled sheet. This sheet is typically alloy 3104-H19 or 3004-H19, which is aluminium with about 1% manganese and 1% magnesium to give it strength and formability. The flat blank is first formed into a cup about three inches in diameter. This cup is then pushed through a different forming process called "ironing" which forms the can. The bottom of the can is also shaped at this time. The malleable metal deforms into the shape of an open-top can. With the sophisticated technology of the dies and the forming machines, the side of the can is significantly thinner than either the top and bottom areas, where stiffness is required. A single can-making production line can turn out up to 2400 cans per minute.
Plain lids (known as shells) are stamped from a coil of aluminium, typically alloy 5182-H48, and transferred to another press that converts them to easy-open ends. This press is known as a conversion press which forms an integral rivet button in the lid and scores the opening, while concurrently forming the tabs in another die from a separate strip of aluminium. The tab is pushed over the button, which is then flattened to form the rivet that attaches the tab to the lid.
Finally, the top rim of the can is trimmed and pressed inward or "necked" to form a taper conical where the can will later be filled and the lid (usually made of an aluminium alloy with magnesium) attached.
Aluminium cans are coated internally to protect the aluminium from oxidizing. Despite this coating, trace amounts of aluminium can be degraded into the liquid, the amount depending on factors such as storage temperature and liquid composition. Chemical compounds used in the internal coating of the can include types of epoxy resin. Companies use "epoxy resin (made from BPA) to manufacture coatings for the interior of beer and beverage cans."
Read more about this topic: Beverage Can
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