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Cans are certainly one of the most common forms of product packaging known to man. From soft drinks to tennis balls and gunpowder, they all come in cans. The production of cans is, therefore, one of the more prolific global industries, with billions of units produced all over the world every year. The average can production line is a fairly extensive and complex one, consisting of a large number of stages, each facility geared to produce a range of, but typically not all, types of cans. For this reason, it is difficult to describe a single, definitive can-making process, but a basic layout of an aluminum can plant will be able to detail the general procedure.
In most cases, a can production line starts with a extrusion section. Here, raw aluminum stock is drawn out to form a continuous cylinder of the correct diameter for the specific can. The cylinder is then drawn through to a combination trimming and forming machine that cuts the cylinder into shorter blanks. The same machine may also be configured to close the bottom of the can, form screw tops, and emboss custom patterns on the blank.
From the trimmer, the blanks are then transported via a conveyor to the washing section of the can production line. The blanks are then washed several times with a powerful alkaline solution to remove any contaminants accumulated during the extrusion and trimming stages. From the washing plant, the cans are again transported by conveyor to an annealing oven, which heats the cans to a specific temperature to remove any hardening and brittleness imparted by extrusion and trimming. Re-softening the cans in the annealing oven is an essential part of the process if the finished cans are to remain flexible.
After annealing, the cans are transported to an accumulator, which collects the cans so that they may be fed in a controlled fashion to the next two stages of production. These are the internal coating machine, which sprays a sterile coating onto the inside surface of the cans, and a lacquer curing oven, which sets the coating. From the curing oven, the cans are passed through to the first of the coloring processes. This process involves the printing of a special auto detection strip on the can which prevents cans from “skipping” the next steps in the process. This includes two base coat applications and a four-, five-, or six-color printing process that imparts the desired design on the can.
Once the cans are dyed, they are moved to a drying oven to set the coloring. After the cans have cooled, they are sent to the last stage of the can production line where they are capped in readiness for distribution. In some cases, the can production line can include an extra step — can latexing — on demand. In this step, a ring of latex is added to the base of the can as an additional content-protection measure and shelf-life extender.