The spin-flow necking process, which devolved from the 2-piece canmaking industry in principle, has been developed into a patented version specifically designed for the production of 3-piece cans by Cantec. This spin-flow necking process has an adjustable degree of forming per rotation to adapt it to specific material properties and combines a maximum diameter reduction with an attractive neck geometry (smooth neck) for SR and - especially important - for DR material. Can diameters can thus be reduced by up to 13 mm.
A modified flow pressing process forms the neck between two inner tooling components, which rotate together with the can body, and an outer shaping roller. The number of shaping rotations depends on diameter reduction and material. It can be adjusted at infinitely variable increments up to a nominal rotary speed of up to 25 rotations per can. Specially developed high-precision clamping tools ensure that the can body securely follows these rotations. Upper tool and lower tool are centered relative to each other during the necking process so that radial forces can be transmitted without deformation. An accurately concentric neck geometry achieved without timeconsuming adjustments is the result.

A 3-piece can with a nominal diameter of 83 mm is an excellent example to demonstrate the savings potential of this technology. The calculation is based on the assumption that the can body remains totally unchanged (interior diameter, height, sheet gauge, lacquering, side coating). The slight loss of volume in the headspace caused be the neck is compensated the fact that spin-flow necking increases the height
of the can by 1.0 – 1.5 mm. Savings are solely due to the smaller ends.
In our example the welded can body is necked from 83.4 mm to 72.9 mm, which equals a diameter reduction of 10.5 mm. Savings with regard to the ends are due to a smaller nominal diameter (step 1), a smaller seam (step 2) and the reduced sheet gauge of the end (step 3).

The actual savings with regard to the ends will differ slightly from case to case because both the initial situation as well as the type (EOE, standard) and dimensions of end and seam will be different. But even in the worst case savings of 20 - 25 % should always be possible for the ends.
Apart from such direct savings, other savings are due to a higher degree of sheet utilisation if a higher number of blanks can be stamped out of sheets with the same dimensions.
If the cans are to be stackable, the other end of their bodies must be necked, too, and closed with a bottom with the corresponding diameter. This results in additional savings potentials.
The shaping of the can described above modifies its look. Although this may be desirable for marketing reasons, it must be coordinated with the canner whose canning and seaming equipment must be able to process different diameters, too.
The possibilities offered by linear sheet gauge reduction without can geometry modification have been exhausted to a large extent and only minor progress can be expected in the future. The ratio of savings to increased risk is becoming more and more unfavourable. Major material savings can only be achieved by modifying the can geometry.