In the process of making aluminum coil, in order to help change its shape, we need to heat it at high temperature. At high temperature, it will be softer and its shape is easier to change. After the shape is adjusted After that, its temperature can be lowered to maintain a certain hardness, but in some cases, after the high-temperature cooling is completed, the aluminum coil will have some curling problems. What is the reason for this?
There will be bending phenomenon during cooling. The reason is: under the general air cooling condition, the heat transfer coefficient of each part of the aluminum coil in contact with the air is the same, but because of the different wall thickness or shape, the heat dissipation speed of each part is not balanced, resulting in The heat dissipation rate of the thick-walled part or hollow tube is slower than that of the thin-walled part, which eventually causes it to bend towards the hollow part or the part with thicker wall thickness when cooling.
The reason and process of bending are as follows:
1. The temperature of the thin-walled part drops quickly, and the shrinkage force is generated first, and the temperature of the thick-walled part or the hollow tube part drops slowly, and there is almost no shrinkage force;
2. The cross-sectional area of the thin-walled part is small, and the contraction force generated is small, or it is eliminated by the traction force of the traction machine;
3. Leaving the tractor, the temperature continues to drop;
4. The thick-walled part or the hollow tube part has a large cross-sectional area, and gradually produces a larger shrinkage force as the temperature drops, and the temperature of the thin-walled part has dropped significantly, and no shrinkage force is generated or the shrinkage force is small;
5. The shrinkage force on the section of the aluminum coil is uneven, and it bends toward the thick-walled part or the hollow tube part along the extrusion direction.