Modern aluminum cans may seem insignificant at first glance. After all, our interaction with them is limited to opening, drinking the contents, crushing, and throwing them away. However, few people know that creating an aluminum can demands a series of very advanced steps, with extreme levels of precision to guarantee the integrity and overall safety of both the container and the product inside.
Many Cans, Much Aluminum
Available numbers indicate that the world produces more than 180 billion aluminum beverage cans per year. Other sources do not hesitate to double that volume, but beyond the enormous differences, they agree on one thing: cans represent the main use of that metal worldwide. Obviously, to reach this point, the aluminum can had to make several evolutionary leaps. The first cans had serious limitations, starting with the obligation to use a dedicated opener, and quality problems in their internal lining, causing the unpleasant “metallic taste”.
Modern aluminum cans not only left all those problems behind, but they are also a true engineering marvel, combining cold forming techniques, chemical treatments, structural analysis, high-pressure packaging, precision folds, and much more, all from a small disc barely 0.3 millimeters thick.
How Aluminum Cans Are Made
For a general introduction, we couldn't find anyone better than Bill Hammack, the “Engineer Guy”. The initial aluminum disc is inserted into special molds and “stamped” until a cup 88 millimeters in diameter is obtained. That cup is reprocessed to a diameter of 65 millimeters, one of the standards for beverage cans. A series of additional processes are responsible for increasing the height of each can and making its walls even thinner. At this point the can acquires the classic dome-shaped bottom, which helps improve its integrity and reduce the amount of aluminum needed for its manufacture (a flat bottom consumes more material).
In the next phase, each can loses about six millimeters in height to obtain a straight, even edge, a condition necessary before sealing. However, it first receives its decoration (colors, patterns, logos, etc.), and an ultra-thin layer of epoxy on its interior, which protects the can from acidic contents and prevents the transfer of metallic flavor to the liquid.
The neck of an aluminum can seems simple at first, but it requires a total of eleven steps to prevent the aluminum from ending up wrinkled in that section. Over the years, manufacturers have reduced the diameter of the top lid. Bill tells us of a difference of six millimeters (from 60 mm to 54 mm), which translates to a saving of 90 million kilograms of aluminum per year, at least.
Pressure, and the Magic of the Double Seam
In previous generations, manufacturers soldered the lid of the aluminum can to the rest of the body, always with the risk of contaminating its contents. But everything changed with the appearance of the double seam: In its first phase, the machine folds the edges of both aluminum pieces (lid and body), forming an edge so they are hooked and interlocked. The second compresses that new edge, and with the help of a sealing compound that acts as a gasket, completely blocks the escape of gas.
In fact, the double seam is so effective that the pressure averages two atmospheres, but cans are designed to withstand up to six atmospheres, due to natural changes in the environment (mainly temperature). As if that were not enough, pressure completely changes the resistance of each can. While an empty can deforms using a couple of fingers (the final thickness of its walls does not exceed 75 microns), an adult man can stand on a pressurized can. This also helps in its transport and storage.
https://www.youtube.com/embed/GyY15Jkkg2AOpening and Recycling
So we return to the opening of aluminum cans. As we mentioned at the beginning, the first generations of cans needed an opener and two perforations. The “pull-tab” system was invented in the '60s, but solving one problem gave rise to another, with aluminum tabs and sharp edges thrown everywhere. The second solution was the “stay-on tab” system that debuted in the '70s, and is still used today, with an aluminum tab and a rivet that prevents its separation from the can.
Now, what about recycling? In general, aluminum cans use two types of alloys: 3004, softer and with approximately 1 percent manganese, and 5182, harder and suitable for lids, with 4.5 percent magnesium. The good news is that recycling rates for cans are close to 70 percent, and aluminum can be recycled infinitely.
In 2012, 92 percent of the cans sold in Switzerland were made with recycled metal. The Aluminum Association reports that almost 75 percent of all aluminum produced in history is still in use today, and it is shaping up as a solid candidate to replace PET, but it is no surprise that a transition on that scale will inevitably present new challenges.
Did you ever imagine that an aluminum can could be so complex? Leave a comment!
