Study On Vibration Demoulding Technology Of Continuous Casting

Iron and steel industry is the pillar industry of national economy.Continuous casting is an efficient,green production method of billet which is widely used.In continuous casting production,in order to continuously demould the ingot from mould,the vibration applied to the mould will result in the formation of unwanted oscillation marks on the surface of the billet.Oscillation marks are the origin of transverse cracks,micro-cracks and alloy element segregation on the surface of the billet.The defects such as inclusion of slag and bubbles are also easy to appear at the oscillation marks,which seriously affect the quality and productivity of the billet and the subsequent sheet rolling and increase the work load of the subsequent finishing process.To reveal the formation mechanism of oscillation marks and to eliminate or reduce the oscillation marks are the urgent task to be solved and many researches are focused on continuous casting.The oscillation marks occur in steel-slag-mold interface near the meniscus and are the result of the heat-fluid-solid coupling.To reveal the formation mechanism of oscillation marks and its influencing factors,the principal problems are studied in this paper by analyzing the multi-field coupling problem in steps.By the simulation analysis of fluid-thermal coupling,fluid-solid coupling and multi-phase fluid-dynamics,the initial solidification process near the meniscus,the formation of oscillation marks and the influence of the mould vibration on oscillation marks were studied.On the basis of these researches,three types of schemes of novel vibration demoulding devices with high frequency inertial excitation vibration were proposed.The new devices can effectively reduce the formation of oscillation marks and ensure the good lubrication between the surface of billet and mould.The main work is as follows:(1)The basic morphology characteristics of oscillation marks are analyzed,and the existing theories on the formation mechanism of oscillation marks and the control methods of oscillation marks are summarized.(2)The formation mechanism of oscillation marks is studied.By using the multi-phase fluid-thermal coupling simulation method,the solidification simulation of billet shell and its primary solidification structure on the meniscus interface during the positive sliding time within one vibration period were carried out.The effects of degree of superheat,convective heat transfer coefficient,pulling speed and other factors on the solidification process were analyzed;The formation process of the concave oscillation marks was simulated by multi-phase hydrodynamics method and the effects of the amplitude and frequency of the mould-vibration on this formation were analyzed;The formation process of overflow oscillation marks was simulated by fluid-structure coupling method,and the effects of the amplitude and frequency of the mould-vibration on the formation process were analyzed;Based on the simulation analysis of the formation process of the above two kinds of basic oscillation marks,the method to reduce the oscillation marks by high frequency and small amplitude vibration demoulding is proposed.(3)The mathematical physical model of slag lubrication analysis under tension was established and the multi-phase hydrodynamic simulation was carried out.The lubrication mechanism of the mould interface under the conditions of high frequency and small amplitude vibration and the effect of interface tension on slag lubrication was analyzed,which provides a foundation for the design of new vibration demoulding device for continuous casting.(4)Three types of schemes of novel vibration demoulding devices with high frequency inertial excitation vibration of continuous cast were proposed.The vibration system modeling was carried out,the rotor self synchronous conditions,the method for the calculation of equivalent friction force during the process of continuous casting,the method for frequency range selection of excitation vibration for three kinds of apparatus,and the determining methods of the optimal stiffness ratio and mass ratio for double body vibration system were given.The related design theory and method were preliminarily established.(5)The effectiveness of the new demoulding device on suppressing oscillation marks is verified by simulation.The formation mechanism of oscillation marks and the design theory and method of new vibration demoulding device presented in this thesis have great theoretical significance and practical value for controlling oscillation marks and improving the surface quality of billet.