Technology

Manufacturing process of welded can

3-piece cans comprise three main components; a can body, a can top end and a can bottom end.
While the body of 2-piece can is pressed and integrated with can bottom, that of 3-piece cans is made from a flat steel sheet (or blank sheet) cut into the can size which is rolled and side-seamed to form a cylindrical shape.
There are two types of side seaming methods, soldering and welding. Here, only the welded can is mentioned since the soldered cans have almost disappeared from the market.
Can body side seam of the welded can is sealed by “seam welding”, a type of electric resistance welding. Both ends of the blank sheet are superposed and welded with thermal resistance to form a cylindrical can body.
Thin copper wire is used for electrode.
As the steel substrate dissolves at the welding spot along the can body side seam, resulting in surface oxidization and degradation in corrosion resistance, repair coating is required on both the internal and external surfaces to prevent corrosion.
Welded side seam is repaired with OSS (outside side seam striping) coating on the outside to prevent rust, and with ISS (inside side seam striping) coating on the inside to protect the contents.
The welded can comes in various sizes and is widely used for beverage, food and aerosol products.

3ピース缶は、缶胴・上蓋・底蓋の3つの主要部分で構成

Can making process of 3-piece can (coating and printing)

3-piece cans are manufactured on three separate production lines; coating, printing and can making lines.

Coating process

*At least once each on the internal and exterior surfaces.

  1. Sheet feeder
    Feed sheets from sheet stack.
  2. Coater
    Apply coatings on the sheet.
  3. Sheet oven
    Dry and bake coatings at high temperature.
  4. Sheet piler
    Stack the sheets coming out of the oven.
Printing process

*The process is repeated according to the number of colors (coating is applied once in the final round of the process).

  1. Sheet feeder
    Feed coated sheets from sheet stack.
  2. Printer
    There are two printers, transferring ink to each sheet for printing.
  3. Coater
    Coat clear varnish on the surface.
  4. Sheet oven
    Dry and bake coatings at high temperature.
  5. Turn wheel
    Turn over the sheets for the downstream process.
  6. Sheet piler
    Stack the sheets coming out of the oven.
Can making process
  1. Sheet feeder
    Feed printed sheets from sheet stack.
  2. Slitter
    Cut sheets into a can size.
  3. Welder
    Weld can body side seam after rolling, and apply repair coating along the side seam.
  4. Oven
    Bake the coatings.
  5. Necker/Flanger
    Narrow down and flange can top.
  6. Seamer
    Seam can top end or bottom end with the can body.
  7. Air tester
    Blow air inside the can to check leakage.
  8. Palletizer
    Pile up cans on pallets.
  9. End seaming (by customers)

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