Apparatus and Process for delivering molten steel to a continuous casting mold

Abstract

Apparatus and Process for delivering molten steel to a continuous casting mold with high inclusion removal capability and high mold pool flow optimization potential includes a tundish with a novel design and a metal distributor comprising a main chamber body connected to a vacuum device and tubes for metal exchange between the tundish, the distributor and the casting mold. At least one of the tubes has gas injection devices to perform gas lifting functions. The new design of the tundish enables it to receive all the steel in a ladle without leaving any heel and refining the steel to an extremely low inclusion level. The distributor is able to achieve an effective hydrostatic head relative to the mold metal level of the order of 10 −2 m or below in the submerged entry nozzle and obtain fully filled and stable flow with low disturbance inside the SEN and therefore is able to deliver the molten steel at low velocities at SEN exits with minimum turbulent disturbance and high flow, thermal and chemical homogeneity over the entire metal bath in the mold. The invention also makes it possible to leave no heels in either the tundish or the distributor when they are replaced. The invention is particularly useful for thin slab and strip casting processes where mold flow control is critical to the casting process.

1 . Apparatus for refining steel to low inclusion content and delivering the clean steel to a continuous casting machine, comprising: (a) a container for receiving steel from a ladle, and removing inclusions from steel, positioned on the side of the mold of the continuous casting machine, (b) a second container for delivering steel to a mold of a casting machine, connected to a vacuum device and having means to transfer the steel back to the first container and maintain the depth of its steel bath accurately, (c) conduits for exchanging steel between the first and the second container, and between the second container and the mold. 
     
     
         2 . The apparatus of  claim 1 , wherein the first container is a tundish having at least one internal part with openings at their bottom for dividing the said container into separate zones. 
     
     
         3 . The apparatus of  claim 2 , wherein argon stifling devices are installed in at least one zone of the tundish for creating a flow field with the adequate turbulent energy dissipation rate and increased transit time of steel. 
     
     
         4 . The apparatus of  claim 1 , wherein the second container is a distributor connected to a vacuum device to reduce its inner pressure to below the atmospheric level, has exits on the bottom to connect with submerged entry nozzles, and has a bottom surface that is tilted up towards the mold side so that steel flows back to the tundish when casting stoppage occurs. 
     
     
         5 . The apparatus of  claim 2 , wherein conduits are installed in the area of the tundish's final zone where inclusions are mostly removed, and connected at the other end to the distributor to act as flow paths for the molten steel between the tundish and the distributor. 
     
     
         6 . The apparatus of  claim 5 , wherein one or more conduits have gas injection devises at the bottom for creating bubbly gas-liquid flow inside the conduits and metal communication between the tundish, the distributor and the mold. 
     
     
         7 . The apparatus of  claim 4 , wherein the distributor further comprises a small reservoir which is made around the top of the down tubes with the top surface of the reservoir bank being higher than the bottom surface where steel enters the SEN. 
     
     
         8 . A method of delivering molten steel from a ladle to a mold of a continuous casting machine, comprising steps of receiving steel from the ladle to a first container positioned on the side of the mold whereby all the steel plus some slag in the ladle can be poured into the container, passing steel through the first container whereby the content of non-metallic inclusions in the steel is reduced, transferring the cleaner steel from the first container to a second container positioned above the mold, and delivering the steel from the second container to the mold. 
     
     
         9 . The method of  claim 8 , wherein the steel is received from the ladle by a tundish having more than one zones. 
     
     
         10 . The method of  claim 9 , wherein steel flows past at least an inclusion removal zone in the tundish with a flow field with the adequate turbulent energy dissipation rate distribution and long inclusion transit time, and a floatation zone with means promoting inclusions flow up to the steel surface. 
     
     
         11 . The method of  claim 10 , wherein the inclusion removal zone comprises flow channels with gas blowing devices at the bottom to create a series of fan-shaped bubbly plumes to provide efficient inclusion collide, agglomerate and float-up conditions. 
     
     
         12 . The method of  claim 11 , wherein clean steel after being refined in the inclusion removal zone is transferred to a distributor having a sloped bottom surface, a vacuum device, and conduits for steel flow between the tundish and the mold. 
     
     
         13 . The method of  claim 12 , wherein the clean steel is transferred to the distributor by one or more lifting tubes as a result of the vacuum maintained in the distributor above the mold. 
     
     
         14 . The method of  claim 12 , wherein the clean steel is transferred to the distributor by one or more lifting tubes having gas injection devises at the bottom to enhance the vacuum lifting effect. 
     
     
         15 . The method of  claim 12 , wherein the distributor has one or more than one conduits acting as down tubes to let steel flow back to the tundish and control the depth of the molten steel inside the distributor. 
     
     
         16 . The method of  claim 8 , wherein conditions of steel flowing from the second container to the mold is controlled and adjusted by means of vacuum pressure in the container, the vertical positions of the second and the first containers, the gas flow rate inside the lifting tube and the depths of the molten steel inside the first and the second containers.