Cold rolling the aluminum sheet applied, to:
- increase its strength to a given level;
- get the given state of the material;
- to give the surface of the aluminum sheet a higher quality;
- compress the sheet to a very small thickness.
Aluminum sheet for cans of beer
for instance, aluminum sheet, which is used for the manufacture of beer cans, cold rolled sheet of thickness 2,5 mm to a thickness of 0,25 mm. This can be done for four or five passes through a single rolling stand, or in a single pass through a cluster rolling stand.
Aluminum alloys can be rolled down to a thickness of about 0,05 mm. For pure (low alloyed) aluminum, cold rolling can be used to achieve a thickness of up to 0,0025 mm or 2,5 μm!
can be reduced by about a first pass through a single stand cold rolling the material thickness 50 %. Subsequent passages may decrease in thickness and a similar lower magnitude.
Letter, which is intended to cold rolling to a thickness of about 1 mm, They are usually subjected to a preliminary hot rolled to a thickness of 3-6 mm.
To the extent that, as the hardening - strain hardening - aluminum increases, more efforts are needed, to laminating sheet to reduce its thickness. Above a certain level of hardness of the metal begins to crack, if you do try compressing it further.
Intermediate annealing the cold-rolled sheet
This imposes practical limits on the reduction of the sheet thickness by cold rolling, which can be achieved with a continuous series of passes. If further reduction of the sheet thickness, then it must be subjected to intermediate annealing for softening the metal, so that he could continue to cold rolling.
The degree of cold rolling, which can be achieved after (or without) annealing is calculated as follows, to a cold-rolled sheet was given properties - strength and / or plastic. This may be the final state of its material, or may require additional machining, for example, annealing, to achieve a given state of the material.
Less compression - better surface
In order to obtain a reflective surface cold rolled aluminum sheet, at last pass perform its minimum compression. The most shining surface obtained by applying well-polished working rollers.
A typical cold rolling mill with a single roll stand may sheet at about 1500-1850 meters per minute for each passage.
The heating of the metal during cold rolling
Although the sheet enters the rolling mill "cold" – at room temperature, rolling friction and pressure can raise the temperature to 80 degrees Celsius or higher. This excess heat must be removed by an appropriate coolant, which can also play the role of lubrication.
Cluster rolling stand
For cold rolling cluster rolling stand - tandem mill - the same principles are valid, and that the cold rolled through a single roll stand. Tandem rolling mill gives some thickness reductions per pass and therefore easily outperforms single roll stand.
Coiling the aluminum sheet into the bay
Length list, who wound up in a bay, It depends on the diameter of the bay and the sheet thickness. The coil with an inner radius 255 mm and an outer radius 1220 mm can accommodate 760 layers of sheet, rolled to a typical thickness 1,25 mm. One such bay comprise aluminum sheet longer than three kilometers. Workpiece for this sheet could be thick ingot 610 mm and length 7,3 m.
Flat-rolled greater thickness 6 mm is usually not wound into coils, and supply chopped to length.
Source: The Aluminum Association, www.aluminum.org