| As one of key equipment in continuous casting, tundish plays a very important role in continuous casting operation and ensuring the quality of steel strands. Reasonable state of molten steel flow is advantageous to extension of residence time of the molten steel in tundish and uniformity of temperature and composition. And it also helps reducing slag entrapment, promoting the separation of inclusions floating and improving casting product quality. In order to improve the yield, reduce the cost by minimizing the amount of residual steel in tundish, the steel plant has modified the inner structure of its tundish. However, after the transformation, the volume of tundish and the effective height of liquid level were reduced. This would be unconducive to the floating exclusion of inclusion in steel liquid, thereby affecting the cleanliness of molten steel and cast slab quality. By means of numerical simulation and hydraulic model test, the inclusion floatation ratio of the tundish before and after modification was tested, and the capability of inclusion removal was compared between the different flow control devices and the working conditions. This subject optimized the flow control devices. And the influence of the parameters of the dam and weir on the flow field and the inclusion floating rate of the tundish were analyzed. Through comparison of modified tundish and original tundish, the thesis determined whether the new tundish put into use reach or exceed the original tundish on capability of inclusion removal.Scheme NTGA7 and NTA5 is the optimal solution after numerical simulation. Under the scheme NTGA7, the removal ratio of inclusions whose diameters are equal to or less than 40?m is higher than that of the original tundish. The removal ratio of inclusions which have size of 70?m and above is very close to original tundish. Particle size between 50?m and 70?m is a little bit worse. The scheme TGA7 and TA2 are optimal flow control devices in original tundish, tested on hydraulic model. Under the two schemes, 65?m inclusions have decreased by 3.4% and 0.5%. The former's inclusion exclusion ability is slightly higher, but the latter is more convenient for slag discharge, and it has less fluctuation of liquid level and lower costs. After the transformation of the tundish, the optimal flow control device is the NTA4. Compared with the tundish before optimization, it reduces the content of 65?m and 90?m inclusions by 7.3% and 13.1%.After the transformation, the new tundish have a significant reduction of inclusion floating exclusion capacity in different steel flux, different liquid level. For the optimized flow control devices(TA2 and NTA4), the inclusions of 65?m and 90?m in the tundish are increased by 14% and 36.2% respectively compared with the original tundish. And the liquid level fluctuation is more severe than the original tundish when it's changing the ladle, causing more prone to roll slag. At the same steel flux and liquid level height(steel flux 9.45t/min, liquid level 1020mm), the liquid level fluctuation of new tundish is almost 2 times than that of original tundish.While liquid level is dropping due to changing ladle, inclusion removal ability of tundish is significantly higher than that of the normal casting. While liquid level is rising, the inclusion removal ability is lower than the normal casting condition. And inclusion removal ability decreases with the increase of steel flux. Liquid level fluctuation also increased severely with the increase of steel flux. But the larger steel flux can increase the liquid level to the normal state of casting more quickly. It can shorten the length of the affected slab. |
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