Mathematical And Physical Simulation Of Transport Behavior During Ladle Teeming Process With Argon Injected Into Ladle Around The Tapping Hole

During continuous casting process, slag carry-over in ladle affects the cleanliness of steel and strand surface quality. Numerous studies show that the reduction of slag carry-over can improve the cleanliness of steel effectively. In the steelmaking and continuous casting process, the vortex is the most important reason for the slag flowing into tundish. Inspired by the ladle bottom argon blowing refining process, if a new technology of controlling slag carry-over by argon blowing around nozzle could be developed, the problem of leaving too much steel in the ladle during ladle pouring would be solved. Therefore, the transport behavior during continuous casting ladle teeming process with gas injected into ladle around the tapping hole is investigated and theoretical basis and guidance for developing the new technology are provided in this investigation.In this paper, taking a 145t ladle as the prototype, mathematical and physical simulations were used to study the transport behavior during ladle teeming process with argon blowing around nozzle. Based on the similarity principle, a water model was applied to study the process of vortex with and without argon blowing around nozzle and the influence of ladle slag layer thickness on the critical height of slag carry-over without argon blowing was studied. The effect of argon blowing on slag layer thickness and slag-steel interface behavior and the variation of critical height of slag carry-over with different gas flow rates were investigated. Based on water model experiment, mathematical simulation was employed to study the transport behavior during the ladle teeming process, the influence of different gas flow rates on the flow field and temperature field during this process and conflux vortex phenomena were discussed. The main results are as follows:(1) As argon is injected into ladle around the tapping hole during ladle teeming process, the conflux vortex is eliminated, accordingly reducing the quantity of slag carry-over caused by drain sink.(2) At the final stage of the ladle teeming process with argon blowing around nozzle, the phenomena such as the bubbling, the slag entrapment and the slag ring will appear at the steel slag interface and change with thickness of slag layer. When the slag layer thickness is between 0 and 10 mm, bubbles can get cross the slag layer, so that the bubbling does not exist. When the gas flow rate reaches a certain value, the slag ring appears. Moreover, the slag entrapment will appear with the gas flow rate increase s further. When the slag layer thickness is between 15 mm and 24 mm, not all bubbles can get across the slag layer, so that the bubbling is easily produced at the steel slag, even at smaller gas flow rates. With gas flow rate increasing, slag entrapment and slag ring appear successively. The bubbling dose the most significant effect on reducing the critical height of slag carry-over.(3) During ladle teeming process with gas injected into ladle around the tapping hole, when the slag layer thickness is 10 mm, the critical height of slag carry-over can be reduced with gas flow rate increasing. After the slag ring comes out, the critical height of slag carry-over will never change. When the slag layer thickness is 24 mm and before the bubble phenomenon appear, the critical height of slag carry-over can be reduced with gas flow rate increasing. After the bubble phenomenon coming out, the critical height of slag carry-over will increase and higher than the situation without gas blowing.(4) During ladle teeming process, circulation flow generates in the molten pool with and without argon blowing around nozzle. Without argon blowing, the center of circulation flow is next to ladle wall, which is ascribed to the density variation of the liquid steel with different temperature. With argon blowing, the center of circulation flow is next to the flow of argon, whose dynamic comes from buoyancy effect of argon. Argon blowing can decrease the temperature gradient of liquid steel in the molten pool.(5) At the final stage of ladle teeming process, argon blowing around nozzle can reduce circumferential rotation momentum of the liquid steel around the tapping hole as well as the critical height of slag carry-over. Circumferential rotation velocity of the steel around the nozzle decreases with the increase of the argon blowing rate.