Why are soda cans cylinders, and how does the tab work?

A cylinder combines the useful traits of a sphere and a cube. It stands on a table, fits a hand, packs fairly well and resists the pressure of a fizzy drink. The tab is a lever held by a rivet on the lid. Lifting it pops open a pre-scored section of metal, and on modern cans the tab stays attached. [1] [2]

A sphere uses the least material for a given volume and spreads stress evenly, but it would roll off tables and is inefficient to pack and ship. A cube packs with no wasted space, but its edges are weak points that need thicker walls, and it is awkward to hold and drink from. A cylinder looks like a sphere from above and a cuboid from the side. According to the Christian Science Monitor, cylinders fill about 90 percent of the space in a box. [2] [1]

A flat metal disk is pressed into a shallow cup and then a taller one. The bottom is pushed inward into a dome. That dome lets the can resist more pressure than a flat base would, and it also stops the can from bulging and rocking. The top is narrowed into a neck, and the lid is joined to the body with a double seam after filling. Modern aluminum walls are under a tenth of a millimeter thick, yet the cans hold pressure of up to about 90 pounds per square inch. [1] [2] [3]

The pressure of the drink itself adds strength to the thin sides, which is why an unopened can is hard to crush and an empty one is easy. Soda is pressurized with carbon dioxide and juice with nitrogen. Because of this internal pressure, soda cans do not need the corrugations seen on unpressurized food cans. The lid is made from a stiffer alloy with more magnesium and is considerably thicker than the walls. [1] [2] [4]

The center of the lid is drawn upward into a rivet, and a separate metal tab is secured under it. The lid is scored in the shape of the opening. Lifting the tab makes the rivet act as a fulcrum, and the tab then pivots to push in the scored section, which releases the pressure. The scored piece folds underneath the lid and out of the way. Bill Hammack describes the tab as a first-class lever, like a seesaw. [4] [2] [5]

Early flat-top cans had no tabs and needed two openings, one for drinking and one for venting. Ermal Fraze's rivet-based pull-off tab came next, but the detached tabs littered beaches and roadsides and were sometimes swallowed. 99% Invisible reports that a physician, Lee Rogers, swallowed one in 1974 and publicized the risk. Daniel F. Cudzik of Reynolds Metals is generally credited with the stay-on tab. The sources differ on the date, giving 1975 and 1976, and cans used it in the United States by 1977. [2] [6] [4]