A final annealing stage removes the lubricating oil, thus making the foil receptive to printing inks and adhesives.Ī number of quality issues can arise from the manufacturing process, including the following : The addition of lubricants to the aluminium surfaces also maintains the workability of the material. During the rolling process, the aluminium stock requires annealing to maintain workability. This is done so that the two webs of foil support each other and are less likely to tear when rolled. Foil gauges under 25 µm are often passed through the work rolls in two webs at a time. The rolling process can be viewed as a form of extrusion. This means the required width for the final foil product must be set at the beginning of the process. Each time the foil stock passes through the rolling mill, it is squeezed, its thickness is reduced and its length increases, but its width remains the same. This pressure ensures a uniform gauge (thickness) across the resulting aluminium foil sheet (known as a web). The work rolls are paired with heavier backup rolls which exert very high pressure on the work rolls to ensure stability. The work rolls have finely ground and polished surfaces to ensure a flat, even foil with a bright finish. Since it is heated during production, continuous-cast reroll stock does not need to be re-annealed when being made into foil.Īfter the foil stock has been manufactured, it must be further processed on a rolling mill. The system continuously feeds, casts, chills and coils the reroll stock. A typical continuous-casting production line runs directly from the furnace to a winding reel. The most economical means of manufacturing reroll stock, however, is via continuous casting. When being rolled to foil, ingot-rolled stock must be re-annealed (reheated) between mill passes to overcome work hardening and restore workability. Continuous casting or ‘hot-strip’ casting to produce aluminium reroll stock and ultimately, aluminium foil.īecause it has been established for longer, the rolling-mill method of producing reroll stock is still widely used.
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December 2022
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