Why does the aluminum coil curl after cooling at high temperature?

Aluminum coil after high temperature cooling will appear bending phenomenon, the reason is: Under general air-cooled conditions, the heat transfer coefficient of each part of the aluminum coil in contact with the air is flat, but because the wall thickness or shape is not the same, the heat dissipation speed of each part is unbalanced, resulting in the heat dissipation speed of the thick wall part or the hollow tube being slower than that of the thin wall part, and eventually the phenomenon of zigzagging to the hollow part or the part with thicker wall thickness when it is cooled.

The bending causes and processes are as follows:

1. the thin-wall part of the temperature drop fast, the first shrinkage force, thick wall part or hollow tube part of the temperature drop slowly, almost no shrinkage force;

2. the thin-wall part of the cross-sectional area is small, the contraction force is small, or is eliminated by the traction of the tractor;

3. leave the tractor, the temperature continues to drop;

4. The cross-sectional area of the thick wall part or the hollow tube part is large, and the shrinkage force is gradually generated as the temperature drops, and the temperature of the thin wall part has dropped significantly, and the shrinkage force is no longer generated or the shrinkage force is small;

5. The shrinkage force on the section of the aluminum coil is uneven, and it is bent along the extrusion direction to the thick wall part or the hollow tube part.