Fabrication of cans - Best tin can manufacturer
Rimmed three-piece can construction involves several stages;
Forming a tube and welding or soldering the seam of the sides
Joining the bottom end to the tube
Printing or attaching labels to the can
Filling the can with content; sterilization or retorting is required for many food products
Joining the wall and top "end".
Double seam rims are crucial to the joining of the wall to a top or bottom surface. An extremely tight fit between the pieces must be accomplished to prevent leakage; the process of accomplishing this radically deforms the rims of the parts. Part of the tube that forms the wall is bent, almost at its end, turning outward through 90 degrees, and then bent further, toward the middle of the tube, until it is parallel to the rest of the tube, a total bend of 180 degrees.
The outer edge of the flat piece is bent against this toward the middle of the tubular wall, until parallel with the wall, turning inward through 90 degrees. The edge of bent portion is bent further through another 90 degrees, inward now toward the axis of the tube and parallel to the main portion of the flat piece, making a total bend of 180 degrees. It is bent far enough inward that its circular edge is now slightly smaller in diameter than the edge of the tube. Bending it yet further, until it is parallel with the tube's axis, gives it a total bend of 270 degrees. It now envelops the outward rim of the tube.
Looking outward from the axis of the tube, the first surface is the unbent portion of the tube. Slightly further out is a narrow portion of the top, including its edge. The outward-bent portion of the tube, including its edge, is still slightly further out. Furthest out is the 90-degree-bent portion of the flat surface.
The combined interacting forces, as the portion of the flat surface adjacent to the interior of the tube is indented toward the middle of the tube and then outward forward the axis of the tube, and the other bent portions of the flat piece and the tube are all forced toward the axis of the tube, drives these five thicknesses of metal against each other from inside and out, forming a "dry" joint so tight that welding or solder is not needed to strengthen or seal it. Illustrations of this process can be found on pages 20-22 of the FAO Fisheries Technical Paper 285 "Manual on fish canning" located here.( http://www.fao.org/3/t0007e/t0007e.pdf )
Design and manufacture
Steel for can making
The majority of steel used in packaging is tinplate, which is steel that has been coated with a thin layer of tin, whose functionality is required for the production process. The tin layer is usually applied by electroplating.
Two-piece steel can design
Most steel beverage cans are two-piece designs, made from 1) a disc re-formed into a cylinder with an integral end, double-seamed after filling and 2) a loose end to close it. Steel cans are made in many different diameters and volumes, with opening mechanisms that vary from ring pulls and tab openers, to wide open mouths. Modern can making lines may produce up to 1000 cans per minute.
Drawn-and-ironed (DWI) steel cans
The process of re-forming sheet metal without changing its thickness is known as ‘drawing’. Thinning the walls of a two-piece can by passing it through circular dies is called ‘ironing’. Steel beverage cans are therefore generally referred to as drawn-and-ironed, or DWI, cans (sometimes D&I). The DWI process is used for making cans where the height is greater than the diameter, and is particularly suited to making large volumes of cans of the same basic specification.
Steel can wall thicknesses are now 30% thinner and weigh 40% less than 30 years ago, reducing the amounts of raw materials and energy required to make them. They are also up to 40% thinner than aluminium.
Steel is a ferrous metal and is therefore magnetic. For beverage packaging this is unique. This allows the use of magnetic conveyor systemsto transfer empty cans through the filling and packing processes, increasing accuracy and reducing potential spillage and waste. In recycling facilities, steel cans may be readily separated from other waste using magnetic equipment including cross-belt separators, also known as overband magnets, and drum magnets.
Printing on steel cans
In the retail environment, beverage cans both contain the product and carry branding and other point-of-sale messages. New printing techniques permit many different finishes, with high-resolution printing operating at 48 or even 60 lines per cm. This ensures consistency and accuracy for packaging designers and brand managers.
Thermostatic print uses temperature-sensitive pigments that change colour according to whether the can is hot or cold. This property encourages a longer customer interaction with the product packaging as they wait for the colour to change.
Matte printing gives steel cans a premium feel and stands out from more traditional gloss finishes. Scratch-resistant lacquers ensure the print is undamaged during filling, distribution, retail and consumption.