Study On Abnormal Mold Level Fluctuation In Slab Continuous Casting Process

In the continuous casting process of steel,the stability of the mold level plays an important role in improving the quantity and quality of the steel.Abnormal mold level fluctuation is frequently observed in high speed casting,which is proved to deteriorate product quality severely.It is obviously significant to analyze and study the abnormal mold level fluctuation of molten steel.In this study the molten steel level in the mold is observed on line by using electromagnetic sensor.The obtained mass mold level fluctuation data(different steel grades,casting speeds,slab widths and physical parameters of mold slag)are analyzed by Iba Analyzer for the frequency and amplitude.The effects of the process parameters including five grades of steel(extra low carbon steel,low carbon alloy steel,low carbon steel,medium carbon steel and peritectic steel),casting speed(0.78?1.26m/min),slab width(910?1290mm),physical properties of slag(surface tension and viscosity)are researched.The following conclusions are obtained:(1)Effect of steel gradeIn the process of continuous casting of different steel grades,the abnormal mold level fluctuation widely exists,in peritectic steel the occurrence probability is highest by 15.6%.In peritectic steel,with the increase of carbon content,the main frequency and equivalent amplitude of the abnormal mold level fluctuations firstly increases and then decreases.(2)Effect of casting speed/slab widthAt w=1260mm,in the production of various grades of steel,increasing casting speed,the main frequency of the abnormal mold level fluctuation and the equivalent amplitude increases.At v1.2m/min,increasing slab width,the main frequency of the abnormal mold level fluctuation changes little,the equivalent amplitude of increases slowly,however in peritectic steel the frequency has an abrupt jump at w=1000mm.(3)Effect of physical parameters of mold slagIn the production of various grades of steel,the main fluctuations of the abnormal mold level fluctuation is positively related to the surface tension of slag;on the other hand,the viscosity of slag is negative related to the main frequency of abnormal mold level fluctuation.(4)New abnormal mold level fluctuation mechanismBased on these results and the principle that the natural frequency of the steel in mold is controlled by its interface tension,a new mechanism is proposed.Abnormal mold level fluctuation mainly caused by the bulgings that passing through the rollers,and when this frequency approaches the natural frequency of the molten steel in mold,a resonance occurs and resulting in large amplitude(abnormal)fluctuation of mold level.Based on this mechanism,a new equation for the natural frequency of molten steel that considering the above mentioned parameters is proposed.The improved process based on this mechanism is proved to be effective on decreasing the abnormal mold fluctuations.