Flow Characteristics Of The Molten Steel And Optimization Of Flow Control Device In A Single-strand Slab Caster Tundish

In the resent years, with the people’s increasingly strict requirement for steel quality, much more attention has been paid to the cleanness of steel by metallurgist all over the world. Tundish plays an important role in the continuous casting process. Metallurgical effect of the tundish will directly affects the cleanness of steel and products’ quality. The long-term production practice and research proves that the capacity and structure of tundish have a great influence on tundish metallurgical effect as well as the flow control device. However, it’s not clear about the issues like how the streamlines behavior of the molten steel and tundish structural parameters effect the flow mode of the molten steel in tundish. This can lead a problem that the mixed model for widespread adoption can not evaluate how the short-circuiting flow of the molten steel affect the flow mode in tundish at present. For example, the mixed model can not evaluate how the Residence Time Distribution curve with double peaks reflect the flow mode of the molten steel in tundish.Based on above issues, the thesis makes research on a 30 tons single-strand slab continuous caster tundish of Baosteel Group Xinjiang Bayi Iron & Steel Limited Liability Company. The physical and mathematical simulation methods are currently being used successfully to obtain and analyze the Residence Time Distribution curve, especially the RTD curve with double peaks which reflect the flow mode of the molten steel in tundish. On this basis, a new method to characterize the melt flow in tundish was presented according to the Mixed Model. With this new method, the characterization results of flow mode for the molten steel in tundish which include short-circuiting flow were analyzed, to further elaborate the mechanism of the molten steel flow in tundish. On the basis of the above-mentioned mechanism research, applying the orthogonal experimental design with four factors and five levels(L25(54)) and range analysis to optimize the structure of flow control device in tundish. From the physical and numerical simulation, the key issues can be summarized as follows:(1) The research found that appearance of double peaks in the RTD curves indicates that short-circuiting flow phenomena appeared in the tundish fluid flow system. However, the Mixed Model takes no account of the effects of short-circuiting flow. To further elaborate flow mode of the molten steel flow in tundish practically, it can be divided the overall fluid flow region into two regions in tundish, namely the available region and dead region.(2) Previous researches indicated that all other parameters such as bath height, inlet volumetric flow rate, inlet-exit distance, exit flow control device(stopper rod or nozzle), submergence depth of the ladle shroud, they have no influence on the shape of the RTD curve. In this research, the ratio of width to length(W/L) in tundish is a key factor to control the short-circuiting flow in the tundish fluid flow system. With increasing the ratio of(W/L) in tundish, the wide-side walls play an important roles to retard the short-circuiting flow on the inlet-outlet plane straight towards the outlet, the short-circuiting flow disappeared gradually, the shape of RTD curves change from double peaks to single peak gradually. When the ratio of(W/L) in tundish is 0.30, the short-circuiting flow in tundish disappeared completely, the RTD curve shows a single peak completely.(3) Under more favourable conditions which without the short-circuiting flow at the ratio of(W/L) in tundish is 0.30, the structure of flow control device in tundish were optimized by orthogonal experiment and range analyses. Two optimization schemes are as follows: ① taking the mean residence time as index: the ladle shroud-weirs distance(A) is 1090 mm, the weirs-bottom distance(D) is 350 mm, the weirs-dams distance(B) is 640 mm, the height of dams(C) is 410 mm; ② taking the volume fraction of plug flow as index: the ladle shroud-weirs distance(A) is 1090 mm, the weirs-dams distance(B) is 440 mm, the height of dams(C) is 360 mm, the weirs-bottom distance(D) is 150 mm.