According to the cause of the flat slab bending, we have taken the following treatment measures through discussion and analysis:
1. Increase the support area of the dummy bar head to the bottom of the flat slab. There are two main slab bending treatment measures taken:
- A 3mm thick aluminum silicate fiber board covering about 1 / 2 area of dummy ingot head is laid in the middle of dummy ingot head.
- In the bottom stage of flat ingot, decreasing the cooling strength and prolonging the cooling solidification time can reduce the
shrinkage stress and increase the feeding of molten aluminum. The circular arc at the bottom of the flat ingot becomes more gentle, the contact area between the bottom and dummy head increases, and the support area at the bottom increases.
2. In order to prevent aluminum leakage at the bottom center of the flat ingot, comprehensive preventive measures must be taken. These measures mainly include:
- Reducing the casting temperature, taking 3003 aluminum alloy flat ingot as an example, reducing the casting temperature from 690 ℃ to 700 ℃ to 680 ℃ – 690 ℃.
- In the initial stage of casting, controlling the distribution of liquid aluminum supply and diverting the high temperature molten aluminum from the center to the surrounding with a specially lengthened aluminum slag shovel can be adopted to reduce the thermal impact of high temperature aluminum liquid on the weak part of solidification forming, namely, the central area at the bottom of flat ingot
- The solidification time at the bottom of slab ingot should be prolonged appropriately, and the start-up and falling time should be delayed.
- At the beginning of casting, the descending speed is reduced from 40 ~ 45mm / min to 35 ~ 40mm / min, etc.
3. Since the cleanness of cooling water is related to the generation of slow bending, necessary measures should be taken to ensure the cleanness of cooling water and prevent the water hole of mould water jacket from being blocked by sediment and other impurities. Regularly clean the sediment in the cold water well, replenish clean fresh water in time, and filter the cooling water before it enters the water jacket.
4. Make preparation before casting. For example, check whether the water hole of the mould water jacket is unblocked, whether it is blocked by sediment and other impurities. If the water hole is blocked, it should be poked open with fine wire. Check whether the dummy bar head is placed stably with a level bar. If the dummy bar head is not placed stably, the method of filling thin copper sheet between the dummy bar head and the base can be used to adjust until the level bar shows stable. It should be specially emphasized that the dummy bar should be filled when filling the thin copper sheet.