MODEL STUDIES OF HYDRODYNAMIC CHANGES OF STEEL FLOWS IN MOLD OF SLAB CCM DURING SUBMERGED NOZZLES REPLACEMENT

The analysis results of trends and modern techniques of research in the field of steel continuous casting are highlighted which are aimed at finding and eliminating of factors that have a negative impact on the surface quality of continuous cast billets. It is shown that the existing concept of creating quick change systems of submerged nozzles, which are used on the slab CCM, leads to the formation at the each stream of machine during serial casting of 20 heates of substandard portion of the billet with 30 – 40 m of length, formed as a result of unstable hydrodynamic conditions in the mold. The research results are given for the physical model of changes of trajectory and speed of the metal flows into the CCM mold, which are related with submerged nozzles replacement in the process of serial casting of steel. Recommendations to reduce duration of the negative impact of this factor on the con­ditions of cast billet formation are offered. Using control-measuring system with strain gauge transducer, it was found that the fluid flows velocity difference at the opposite narrow walls of the mold model, causing a violation of the thermal conditions of crust formation of con­tinuous casting billet, in the case of once-through submerged nozzles can reach 2.0 – 2.3 and for non-pressure hollow-bottom nozzles with two lateral holes separated by divider – 1.2 – 4.0. Information about the trajectory symmetry breaking of circulation circuits of melt flows in the mold, caused by conducting of operation of outworn submerged nozzle replacing, also was obtained using high speed video materials. During the research the visualization of water flows trajectories, which simulated the molten steel in the mold model, was provided by intro­duction of air through a channel of model of stopper-monoblock of the tundish, so that the input of argon during casting was simulated. The obtained information allowed to develop a new principle of construc­tion of system of submerged nozzles quick change which consists the combined and parallel implementation of individual stages of refracto­ries replacement by its structural elements (manipulator, teeming and pushing devices). It allowed to reduce the time required to replace a outworn submerged nozzle and to increase the yield during the produc­tion of slab billets on CCM.