| With the development of high efficient continuous casting technology, it puts forward higher request for slab quality. The flow of liquid steel plays a decisive role for slab quality; and it directly affects heat transfer and inclusion floatation in mold and has a close relationship with surface and internal quality of slab. Therefore, it has great significance for further and deep study on liquid steel flow of mold to ensure continuous casting operation smooth and improve slab quality.Based on the submerged entry nozzle (SEN) design and optimization for 1# slab caster of the steel company, some research method issues for physical simulation of mold have been analyzed, and the method with consideration of solidified shell and flow mass balance for mold has been applied in the study. In the paper, it focuses on the change rule of flow characteristic in mold with condition of bias flow and change of casting parameters. The main research results in this paper are as follows:To reduce differences between physical model of mold and real caster, the physical simulation method with consideration of the solidified shell and the flow mass balance is putting forward. With consideration of shell in mold, the tapering of the shell in the mold enabled downward flow to facilitate more fluid being pushed into the upper recirculation zone, yielding more turbulence, higher velocities and greater level fluctuation at top surface. It will lead to smaller level fluctuation and lower velocity for thinner thickness mold section if ignore the solidified shell and the flow quality balance in mold, and the results of the physical simulation will be not very precise and have certain differences with real caster. The change rules of liquid flow for the different width and thickness mold with shell and without shell have been studied, and the solidified shell has different effect degree on different width and thickness mold.The effects of different turbulence model on flow and transport behavior for mold have been discussed. It found that the revised low Reynolds number model is suitable for high Reynolds number and low Reynolds number zone, can better handle the flow problem near the wall and have a better result for low Reynolds number zone. The dimensionless method has been used to analyze the main factors of fluid flow in the mushy zone, and the permeability model revised by switching function has been used to simulate the fluid flow and solidification process. The simulation results show that the permeability model used in the mushy zone has advantages for handling the flow and solidification process. In the mushy zone, the fluid flow plays a leading role at low solid fraction and the resistance force of dendrite increases gradually at high solid fraction, and it makes the simulation more accurate in the mushy zone.The characteristic of fluid flow for SEN has been analyzed to the relationship for the jet, the width of section and SEN parameters, and it will supply the theoretical basis for the SEN structural design and optimization. The bias flow phenomena of mold have been studied by numerical simulation method, and it will cause serious bias flow with uneven velocity distribution inside SEN for mold width direction and minor bias flow for mold thickness direction. In the same casting condition, it is more easily to make serious bias flow phenomenon for high speed situation. With deep studied of bias flow phenomena for SEN misalignment in mold, it will cause serious bias flow with SEN misalignment for mold width direction and minor bias flow for mold thickness direction. The change law of fluid flow for mold has been studied with condition of 10% and 20% area clogged for side port of SEN, and it will be more serious for the bias flow phenomena with the clogged area increased.Casting speed and casting temperature changes affect the fluid flow in mold. The simulation results indicate that the level fluctuation of top surface became large when the casting speed abruptly jumps or drops, which may lead to slag entrapment, and the level fluctuation can be controlled with gradually casting speed increased. Casting temperature changes affect the heat transfer behavior and the grown rates and uniformity of solidified shell for narrow face in mold.The experiment program has been established to design and optimize the parameters of SEN by physical simulation and numerical simulation methods. The effect of structural parameters of SEN and technical parameters on fluid flow has been studied, and the SEN and technical parameters of continuous casting for the section have been chosen. The 2# SEN of the experiment has been chosen for the thickness section of 230mm, and B2# SEN for the section of 160mm and 190mm with consideration of convenience of actual production.For the sake of unreasonable technical process and operation parameters at beginning period of production, some quality defects of slab for 1# caster appeared. To improve the quality of slab, some measures have been proposed to optimize the technical process and operation parameters. After the optimization, the statistics of slab quality indicated that hollow defects reduced gradually, subsurface blowhole and slag defect disappeared and longitudinal surface crack decreased a lot. The qualified rates of surface quality for slab is exceed 98%, and the surface quality of slab obviously improved. The situation of production indicated that it is reasonable of application of SEN design and optimization for mold of 1# caster, and design and optimization methods have good rationality and practicability. |
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