How tin cans are made

A can's welded side seam overlaps by just 0.3 to 0.5 mm, and rollers forge the two edges together.

stations: 9
things upstream: 59
raw sources: 21
steps from the ground: 8

The short version

A classic three-piece tin can is built from tinplate, which is steel sheet coated with tin. Coated sheets are cut to size, rolled into cylinders and welded down the side, and the seam is coated again. Beads stiffen the body, and a separate bottom is locked on by a double seam. The top goes on after filling.

Shear the coil into sheets

Coils of tinplate are sheared into flat plates. Tinplate is steel with a very thin layer of tin on both faces.

Goes in
Tinplate
Coat and print the sheets

While still flat, the plates are coated to keep the contents off the metal, and printed if the can will carry a design.

Goes in
Lacquer Ink
Slit into body blanks

The plates are cut into strips and then rectangles, one for each can body.
Roll and weld the seam

Each rectangle is rolled into a cylinder. Rollers squeeze a tiny overlap while current heats the metal to just below melting, which forges the edges together. Early cans were soldered with a tin-lead alloy, which could cause lead poisoning.

0.3–0.5 mm overlap
Repair the seam coating

Welding exposes bare iron and tin along the join, so the seam gets its own protective stripe of coating.

Goes in
Lacquer
Bead the body

Rollers press ribs into the wall, which stiffen a food can against the pressure and vacuum of processing.
Flange the ends

Rollers bend the rim of the cylinder outward so a separate end can be joined to it.
Fold the bottom on

A stamped disc is placed on the base. The edges of disc and body are curled together in a double seam, which locks them without any adhesive.
Inspect and stack

Empty cans are checked and stacked on pallets. The top is seamed on after the food goes in.

End of the lineTin can Next it goes into paint, condensed milk, baby formula and 3 more.

Worth repeating

The Dutch Navy reportedly carried salmon in tin-plated iron boxes as early as 1772.
Peter Durand obtained an English patent in 1810 for storing food in tin-coated iron cans for Frenchman Philippe de Girard.
When the American Can Company was founded in 1901, it was producing 90% of the tin cans in the United States.