| Mold is an important part of continuous casting machine, since superheated steel transfers to solid state and accomplishes the initial solidification process. The behavior of the meniscus plays a critical role in the surface quality of continuous casting slab. Exploring the mold flux lubrication behavior has a great significance in perfecting break-out prediction mold and improving strand surface quality. Because of the limitations of detection methods of mold flux and production conditions in steel plant, it is almost impossible to directly obtain the lubrication state directly. Therefore, it is particularly important to investigate mold flux lubrication behavior at meniscus through numerical simulation method. Based on the continuous casting mold for wide heavy slab in a plant, the present work established the hydrodynamic lubrication model of the mold flux in meniscus region and optimized the vibration parameters for that mold. The main research contents and conclusions were as follows:(1) Distribution law of the mold flux near meniscus region. Based on a3D thermo-mechanical coupling model for the copper mold and a transient heat-transfer mold for2D slab established in the paper, the temperature fields and normal deformation of the heated mold copper plates and the distribution of the slab surface temperature and the solidified shell thickness can be obtained. From the combination of all results above, the thickness distribution of mold flux can be derived. The shape of the flux channel is convergent since the thickness decreases along the casting direction. The liquid flux disappears at the location of200mm below the meniscus. The hydrodynamic lubrication model of the mold flux is established in the range of0-80mm below the meniscus on the basis of linear fitting the channel shape.(2) Theoretical research on the hydrodynamic lubrication behavior near meniscus region. Based on the hydrodynamic lubrication model, the distribution of relative velocity, pressure distribution and friction can be derived from momentum and mass balance equations. The results show that as the flux viscosity is0.1Pa-s and the mold vibration form is sinusoidal, the distribution of relative velocity in the flux funnel is continuously. The closer the shell boundary is to, the greater relative velocity gradient is. That velocity gradient increases with the increase vibration speed. The hydrodynamic lubrication formed in the positive-strip period could resist the molten steel hydrostatic pressure as the relative pressure is positive in that period. The flux is inhaled by the negative-pressure formed in negative-stripe period. The friction increases with the increase of distance below meniscus, the vibration speed and the vibration amplitude.(3) The study of the effect factors on the hydrodynamic lubrication behavior near meniscus region. The flux viscosity only influences the pressure and friction distribution. Under the condition that the upward strip speed is1.25m/min, as the viscosity increases from0.1Pa-s to1.0Pa-s, the maximum of positive pressure and the friction all improve. With the variation of casting speed, the distribution pattern of velocity, pressure and friction of mold flux in the channel keeps unchanged, although the values of them change. As the maximum upper vibration velocity of mold is1.25m/min and casting speed varies from0.8,1.0to1.2m/min. The pressure and the friction in the flux channel increase with the casting speed.(4) Study on optimizing criterion for vibration parameters. Analysis results of the hydrodynamic lubrication model show that the requirement of maintaining a good lubrication effect is to prolong the time for positive vibration with the peak upper vibration velocity as maximum as possible. On the premise of ensuring the smooth performance of mold, proper increase of non-sine factor, a, vibration frequency,f and amplitude, s is help to improve the hydrodynamic lubrication effect, demold the strand, heal the cracks and increase the consumption of mold flux. |
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