Tin-free steel

This material is produced by electronically coating mild steel plate with a chromium/chromium oxide film. By placing an inert layer on the surface of the same low-carbon steel used for electrolytic tin-plating, it is at least partially protected against oxidation and dissolution.

The chrome layer acts as corrosion barrier. The oxide layer recues chrome surface oxidation and covers discontinuities in the surface. The process was developed in Japan and one version, known as Hi-Top is being made in the United Kingdom.

The chromium/chromium oxide layer is even thinner than the thinnest tin coatings normally used, and must be lacquered before it can be used in the manufacture of containers.

The cost if tin-free steel is lower than of tinplate, but is increased by the necessity for lacquer coating.

Tin-free steel has found fairly wide usage, typically examples being daw-redraw containers and fixed ends for processed food cans.
Tin-free steel

Tinplate cans

Tin is the oldest available metals and centuries of use have established its non-toxic nature. Tinplate is the common term for a steel sheet with a protective coating of tin.

This combination of materials gives the following properties: a shiny, metallic appearance, formability, possessing a gas barrier, rigidity and providing adequate protection against corrosion and solderability.

Tinplate, the first material used to make metal cans and canisters, consists of a thin sheet of steel, coated with tin. The purpose of the tin coat is to reduce the risk of corrosion.

Modern tinplate for cans is produced from steel strip with tin applied by continues electro-deposition.

There are three can types:
*The three piece can evolved from original concept
*The two piece draw/redraw can
*The draw/wall-ironed can

The two main advantages of tinplate cans are that they are cheaper than aluminum cans and are also magnetic.

This latter feature enables tinplate cans to be transported through leak-testing baths on magnetized conveyor rather than magnetic pucks having to be individually fitted.
Tinplate cans