Influence Of Electromagnetic Brake On Molten Steel Flow And Heat Transfer Solidification In Thin Slab Mold With High Casting Speed

The metallurgical transmission behavior of molten steel in thin slab continuous casting funnel mold（FM）is an important factor affecting the production of continuous casting machine and improving the quality of continuous casting slab.Aiming at the influence of multi-mode electromagnetic braking（MM-EMBr）on molten steel flow and heat transfer solidification behavior in the FM of thin slab continuous casting with high casting speed,the coupling relationship of multiple physical fields such as electromagnetic field,flow field and temperature field of the FM under different continuous casting process conditions was studied by physical simulation,numerical simulation combined with industrial tests.The influence law of MM-EMBr on molten steel flow and heat transfer solidification behavior of the FM was analyzed,the mechanism of electromagnetic field on metallurgical transmission behavior of molten steel in continuous casting FM was revealed,and the influence of FM copper wall reverse water supply cooling process on heat transfer was explored.The three-dimensional（3D）finite element numerical simulation analysis of the steady magnetic field of the MM-EMBr device is carried out using MAXWELL software in ANSYS.The effects of A,C,D,E and F five pairs of magnetic poles on the distribution of magnetic induction intensity in the FM under different current combinations,water channels and coil turns were studied.On the wide face of the FM,magnetic poles A,C,D and E are distributed on both sides of the upper and lower submerged entry nozzle（SEN）of the FM,and magnetic poles F is distributed directly below the SEN.The magnetic field distribution shape generated by the MM-EMBr device is similar to the"ω"shape.The magnetic induction intensity generated by the upper two pairs of A and C magnetic poles and the middle pair of F magnetic poles is strong,while the magnetic induction intensity of the lower D and E pairs of magnetic poles is weak.When the maximum current value of the magnetic pole coil turns is 1100-800 A,the maximum magnetic induction intensity generated by the magnetic poles is about 190 m T.The current intensity of the magnetic poles coil turns and the number of coil turns have great influence on the magnetic induction intensity of the EMBr device,but the water channels has little influence.The transient numerical simulation of steel/slag two-phase flow in FM was carried out by using FLUENT software Volume of Fluid（VOF）model,and the influence of continuous casting process parameters on the molten steel flow field in the FM was studied.When the submerged depth of SEN is 130～190 mm and the casting speed is between 4 and 6 m/min,the maximum surface velocity of the FM fluctuates between0.37～0.56 m/s,the maximum zone appears at the liquid level about 300～400 mm away from the SEN,and slag entrapment is easy to occur.The maximum velocity of the narrow face fluctuated in the range of 0.41～0.60 m/s.Through MHD module,the magnetic field and flow field of FM were coupled,and the transient numerical simulation is also carried out.The results show that the effect of MM-EMBr on restraining the flow of molten steel in FM is remarkable.When MM-EMBr is applied,the angle of molten steel jet at the outlet increases,the area of the flow path of molten steel increases,and the impact depth of molten steel and the velocity gradient of molten steel in the FM decrease.When the current intensity is 800-600 A,the whole liquid level becomes stable,the liquid level fluctuation value is basically less than 5 mm.When the current intensity reaches1100-800 A,the fluctuation value of the liquid level is basically about 3 mm.The liquid level is stable,and there is basically no entrapment slag at the liquid level.A 3D coupling mathematical model of magnetic field,molten steel flow field and temperature field in the FM was established under the MM-EMBr,and the influence of magnetic field on the flow and heat transfer solidification behavior of molten steel in the FM was analyzed.When the mushy zone coefficient A_mush ranges from 3.0×10⁸ to 9×10⁸kg/（m³·s）in the solidification heat transfer model of thin slab at high casting speed,the calculated thickness of solidified shell is in good agreement with the actual measured thickness of slab shell.Under the condition of no EMBr,the temperature gradient on the surface of the solidified shell is large,with the application of MM-EMBr,the temperature distribution of high temperature molten steel in the FM becomes orderly,the thickness of solidified shell at the FM outlet gradually thickens,and the surface temperature gradient of solidified shell becomes uniform.When the magnetic pole current intensity is 1100-800 A,the maximum solidified shell thickness at the FM outlet is 14.3 mm.The higher the casting speed,the larger the high temperature zone formed by upward moving stream near the narrow face.A 3D coupled heat transfer mathematical model of solidified shell,copper wall and cooling water was established under MM-EMBr,and the heat transfer behavior of copper wall under different water supply processes was calculated.After reverse water supply process is applied,the hot surface temperature of copper wall decreases significantly at110 mm below the top of the copper wall,the temperature decreases from 541.4℃in the forward water supply method to 420.2℃in the reverse water supply method,and the maximum temperature decreases by 121.2℃at most.The effect of cooling water flow rate and inlet water temperature on the cooling effect of copper wall is relatively small.The industrial test of thin slab continuous casting FM was carried out by means of nail board and large sample electrolysis under MM-EMBr.Industrial tests have shown that the MM-EMBr technology can significantly change the surface and internal quality of the slab.When the magnetic pole current intensity increases to 1100-800 A,the maximum surface velocity decreases from about 0.46 m/s without EMBr to about 0.26m/s.The surface velocity decreases obviously and becomes more stable and orderly.The greater the magnetic pole current intensity,the more obvious the crack rate and entrapment slag rate decrease.But when the current intensity rises to a certain level,the change of crack rate and entrapment slag rate is no longer obvious.EMBr has no obvious effect on the location of inclusion distribution,but the inclusion content decreases greatly at 1/4 of the 1/2 wide surface and the middle position of the FM,and the value is about half of that without EMBr.After the reverse water supply process is adopted,the temperature at the meniscus of copper wall decreases obviously,which greatly prolonging the service life of the copper wall.The industrial experiment shows that the numerical simulation results have high accuracy and can provide theoretical basis and reference for industrial production.Figure 119;Table 13;References 173...