Double-sheet foil production involves three distinct rolling processes: rough rolling, intermediate rolling, and finishing rolling. These processes are differentiated by the thickness of the rolled sheets. The exit thickness of roughly rolled sheets is either equal to or greater than 0.05mm, while intermediate rolled sheets measure between 0.013mm to 0.05mm. Finally, sheets that undergo finish rolling result in single and double rolled products with exit thickness less than 0.013mm.
During the rough rolling process, thickness control is achieved by regulating the rolling force and applying post-tension. As such, the processing rate for rough rolling is slow. This process shares similarities with the rolling of aluminum sheets and strips. However, it has peculiarities that make it unique, such as the specific control requirements for thickness and the associated rolling forces.
When it comes to making aluminum strips thinner, the key lies in the rolling force. As a result, automatic control methods for plate thickness rely on maintaining a constant roll gap through AGC. Even if the rolling force shifts, the thickness can be achieved by adjusting the roll gap, thereby ensuring consistency in the sheet and strip. However, aluminum foil rolling is a different story altogether. As the thickness of the material is incredibly thin, the elastic deformation of the rolls is easier to produce than plastic deformation. Consequently, the rolling force can no longer play the same role as it does in plate rolling. Instead, rolling aluminum foil occurs without a roll gap under constant pressure conditions. The thickness is adjusted by manipulating the tension and rolling speed. Therefore, it's important to note that the process for rolling aluminum strips and aluminum foil is fundamentally distinct.
Stack rolling is a widely adopted method for producing ultra-thin aluminum foil. The process is specifically used for aluminum foils with a thickness below 0.012mm, as it is hard to roll out such thin sheets using single-sheet rolling techniques. One of the primary reasons for this is that the rolls tend to become elastic and flatten out. In contrast, when using the double-rolling technique, a lubricating oil is added between two sheets of aluminum foil, and they are rolled together. This can significantly reduce the number of broken strips and enhance labor productivity.
Apart from allowing for the production of extremely thin aluminum sheets that cannot be rolled out using the single-sheet technique, stack rolling makes it possible to create single-sided smooth aluminum foil. Batches of aluminum foil ranging from 0.006mm to 0.03mm in thickness can be produced using this method. Overall, stack rolling is highly crucial in the production of aluminum foil, and it has significantly improved the quality and quantity of aluminum foil that can be manufactured.
The speed effect in the aluminum foil rolling process refers to the phenomenon where the foil material's thickness reduces as the rolling degree increases. Although the exact mechanism behind the speed effect is not yet fully understood, it is believed to be influenced by three main factors. Further research is required to gain a comprehensive understanding of the speed effect and its underlying reasons.
b. As the rolling speed increases, the friction between the work roll and the rolling material undergoes a change. This change causes an increase in the amount of lubricating oil introduced into the system, leading to a different lubrication state between the roll and the rolling material. Consequently, the coefficient of friction decreases, resulting in a thicker oil film and a corresponding decrease in the thickness of the aluminum foil.
When the rolling speed increases in a rolling mill equipped with cylindrical bearings, the roll neck will experience a floating effect within the bearing. As a result, the two rolls, which are mutually loaded, will move closer to each other. This change occurs due to the interactive nature of the rolls and their interaction with the bearings.
When high-speed aluminum foil is rolled, the material undergoes softening during processing. This is due to the high velocity of the rolling mill, which increases the temperature of the deformation zone. The metal in this zone can reach temperatures of up to 200°C, creating an environment similar to intermediate recovery annealing. Consequently, the rolled material becomes work-softened.