This article was updated on the 11th September 2019.
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Rolled products – that is, sheet, plate and foil – constitute almost 50% of all aluminum alloys used. In North America and Western Europe, the packaging industry consumes the majority of the sheet and foil produced to make beverage cans, foil containers and foil wrapping. Sheet is also used extensively in building for roofing and siding, in transport for airframes, road and rail vehicles, and in marine applications including offshore platforms and superstructures and hulls of boats.
While relatively little is currently used in the manufacture of high volume production automobiles, aluminum sheet used for body panels has been growing rapidly in recent years. A market that could in the future match the approximate 2.4 million tons used for packaging in the USA in 2016. Plate is used for airframes, military vehicles and bridges, ship superstructures, cryogenic and chemical vessels and as tooling plate for the production of plastic products. Foil applications other than packaging include electrical equipment, insulation for buildings, lithographic plate and foil for heat exchangers.
The starting stock for most rolled products is a DC (Direct Chill semi-continuous cast) ingot. The size of the ingot depends on the size of the DC unit available, the hot rolling mill capacity, the volume required for a particular end use and to some extent the alloys being cast. Ingots up to and over 20 tons in weight, 500-600 mm thick, 2000 mm wide and 8000 mm long can be produced.
The DC ingot is usually cooled after casting to room temperature. It is then reheated to around 500°C prior to successive passes through a hot rolling mill where it is reduced to about 4-6 mm in thickness
The strip from the hot rolling mill is coiled for transport to the cold mill which might be on the same site or elsewhere. Cold mills are available in a wide range of types and sizes; some are single stand, others have three stands and some are five-stand. Cold rolling speeds vary but modern mills operate at exit speeds as high as 3000 meters per minute and the alloys may be cold rolled to a thickness of around 0.05 mm.
Developments in the Aluminum Rolled Products Industry
In recent years, much effort has been made by the aluminum industry and mill producers to ensure that cold rolled products have the specific characteristics required for satisfactory end use and that they can be economically competitive with rival materials such as steel.
Control of Properties
Properties such as strength, formability, toughness and corrosion resistance are controlled primarily by alloy choice, rolling deformation schedule and thermal treatments before, during and after rolling.
Surface Finish, Flatness and Gauge Uniformity
Other requirements such as surface finish, flatness and gauge uniformity have been achieved by careful attention to the mechanics and chemistry of the rolling process. This has been shown to be very important in the production of beverage cans and will play an increasing role in the manufacture of car body parts.
Hot and Cold Rolling
In hot rolling, a knowledge of the influence of the starting stock surface condition, surface condition of the rolls and lubrication used has been necessary, as have the effect of corresponding parameters in the cold mill. The full understanding of the effect of roll coatings, arcs of contact, and so on has been achieved by detailed studies.
In modern installations concerned with high volume production, for instance in the canning industry, stringent flatness requirements are achieved by combinations of mill control and the use of tension levelers. Gauge control is achieved in much the same way as flatness, by continuously measuring outgoing strip thickness and adjusting the roll bite accordingly.
Source: The European Aluminium Association.
For more information on this source please visit The European Aluminium Association.