With the increasing use of insulating aluminum coils in construction and automobile use, the shape of aluminum foil is becoming more and more diverse and complex, but the cooling material in the aluminum insulating volume will appear hollow or thick-walled on the cooling bed. The thick part has a zigzag appearance. The following are the reasons for the zigzag:
1. Under general air cooling conditions, the heat transfer coefficient of all parts in contact with the insulation and air is flat. However, due to different wall thicknesses or shapes, the heat dissipation of each part is uneven, so thick-walled or hollow tubes are used for cooling. Slower than thin wall;
2. Choose partial high-pressure aerosol cooling because there are two heat transfer media, air and water, and the heat transfer coefficient of water is better than that of air, which can increase the cooling speed;
3. The high-pressure air atomizes the water, adds water and the profile contacts the appearance of the product, plus the destruction of water and high-temperature profiles when the steam film occurs, improving the heat transfer efficiency;
4. The high-pressure aerosol nozzle has a strong direction, the aerosol angle is about 25°~30°, and can be partially cooled without affecting other parts of the aluminum foil.
The reason why the aluminum foil bends when cooling is because the heat transfer coefficients of various parts of the aluminum foil in contact with the air are different, resulting in uneven heat dissipation speeds in each part, causing the heat dissipation speed of the thick-walled part or hollow tube to be slower than that of the thin-walled part, ultimately causing the aluminum foil to When cooling, it will bend toward hollow parts or thicker wall parts.
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Specifically, the temperature of the thin-walled part of the aluminum foil drops quickly and shrinkage occurs first, while the temperature of the thick-walled part or the hollow tube part drops slowly and there is almost no shrinkage force. When the temperature continues to drop, the thick-walled part or the hollow tube part gradually produces greater shrinkage force as the temperature decreases, while the temperature of the thin-walled part has dropped significantly and no longer produces shrinkage force or the shrinkage force is small, resulting in the aluminum coil section being damaged. The shrinkage force is uneven, causing the aluminum foil to bend toward the thick-walled part or the hollow tube part along the extrusion direction.
