The can wall is formed by welding. Three piece welded cans are only constructed from steel as aluminum is not suitable for welding.
As the material for the can wall, lightly coated Sn-plated steel sheets and Ni-plated steel sheets may be employed.
Two main types of base steel are commonly used in can manufacturing type L and type MR. Type L is very corrosion-resistant and is used in canning of very corrosive products e.g., apple juice, berries, prunes and pickles.
Type MR is more suitable for canning moderately to mildly corrosive products, e.g. grapefruit, peaches, peas, and corn.
In both the two-piece can and the three-piece can the outside surface of the can is provided with printing, in order to appeal to consumers for commercial value of the canned goods.
On the other hand the inside surface of the can is coated with resin so as to ensure the corrosion resistance of the can body.
The coatings and ink are normally dried by passing the sheets through a thermally heated oven where the temperature is in the range 150–205 °C.
Three piece cans usually are delivered to the packer with one end in place and the other shipped separately. After filling, the second end is double-seamed by closing machines, which can change the headspace air to a vacuum or inert gas, if required.
Presently, the three-piece cans are being widely used and other cans like two-piece cans, aluminum cans, and other flexible containers are slowly replacing them.
Three piece cans
