In the process of making aluminum sheet coil, in order to help change its shape, we need to heat it at high temperature, in the high temperature state it will be relatively soft, its shape is also easier to some changes, after the shape is adjusted, it can be lowered to its temperature, so that it maintains a certain degree of hardness, but some cases, after the completion of high temperature cooling, aluminum coil will appear some curling problem, what is the reason for this?
Cooling will appear bending phenomenon, the reason is: general air-cooled conditions, the aluminum coil of the various parts of the heat transfer coefficient of contact with air are equal, but because the wall thickness or shape is not the same, the parts of the uneven heat dissipation speed, resulting in thick-walled or hollow tube of the heat dissipation speed than the thin-walled part of the slow, eventually causing it to appear in the cooling to the hollow part or wall thickness of the thicker part of the phenomenon of bending.
Bending causes and processes are as follows.
1, the thin-walled part of the temperature drop quickly, the first contraction force, the thick-walled part or hollow tube part of the temperature drop slowly, almost no contraction force.
2, the thin-walled part of the cross-sectional area is smaller, resulting in a smaller contraction force, or traction eliminated by the traction machine traction force.
3, leaving the traction machine, the temperature continues to fall.
4, thick-walled part or hollow tube part of the cross-sectional area is larger, with the temperature drop gradually produce a larger contraction force, the thin-walled part of the temperature has dropped significantly, no longer produce contraction force or contraction force is smaller.
5, the aluminum coil cross-sectional shrinkage force is uneven in size, along the extrusion direction to the thick-walled part or hollow tube part of the bending.