| The surface of continuously cast billets is characterized by the oscillation marks that form periodically at the meniscus zone due to mould reciprocation. The oscillation marks have an important influence on the surface quality of the billets because they are often the sites of transverse cracks and segregation happened, which is a disadvantage of the development of continuous casting toward near-net shape, high speed and high quality. Therefore, it is of significance to study how the oscillation marks form and how to decrease and eliminate the oscillation marks during continuous casing. This is what the paper concerned on.The paper is composed of three main parts. In the first part, a new oscillation marks formation mechanism was proposed. In which it is considered that the temperature fluctuation of early solidified shell caused by mould reciprocation is a key factor for the oscillation marks formation during continuous casting.The Initial Solidified Point (ISP) temperature fluctuation caused by mold reciprocation was measured by a method named as thermocouples column passed ISP one by one during experimental scale Tin continuous casting. The repeated experiments results show that the ISP temperature varied periodically along with mold oscillation, the fluctuation amplitudes are between 4 and 11℃. Based on the phenomenon, the reason caused the temperature fluctuation and its possible influence on early solidification is analyzed.Then a model experiment device, as a simulation of continuous casting early solidified process, was designed in order to measure the temperature fluctuation accurately. According to the experiments, the temperature fluctuation amplitudes of ISP decrease with the increasing of mold oscillation frequency, the decreasing of mold oscillation amplitude, cooling density, contact pressure between mold and solidifiedshell.A one-dimension heat transfer mathematic model on continuous casting early solidification process with a periodical boundary condition was developed to quantitatively study the temperature fluctuation. The mathematic model results show that when there was a temperature fluctuation in the inner mould wall, there were corresponding temperature fluctuations at every point in the molten steel, whose frequency is the same as the boundary condition and amplitude decreased along with the increasing depth whether there was mould flux between mould and steel or not. The influence depth of surface temperature fluctuation in molten steel is about 1~2 mm when there was no mould flux. The surface temperature fluctuation attenuated rapidly when there was mould flux. Therefore mould flux was helpful to improve the billets surface quality. In addition, high frequency and low amplitude mould oscillation, decrease the thermal conductivity of mould flux and increase the mould flux channel width are all helpful to decrease the influence on early solidified shell caused by surface temperature fluctuation. The mathematic model results were well consistent with the experimental results.Based on the phenomenon, the mechanism of how some technologies, including high frequency and low amplitude mold oscillation, soft-contact mold electromagnetic continuous casting, hot top mold and so on, improve surface quality of continuous casting billets is analyzed. Their common mechanism was the decreasing of the temperature fluctuation of early solidification shell.In the second part of the paper, by using a kind of special Amplitude-Modulated Magnetic Field (AMMF), i.e. a high frequency magnetic field (carrier wave) modulated by a low frequency periodic wave (modulate wave), a new Electromagnetic Continuous Casting (EMCC) technology, named as mold oscillation coupled with AMMF EMCC, was proposed based on the oscillation marks formation mechanism in which that dynamic pressure of mould flux channel play an important roll.Molten metal meniscus profile and mold flux channel width are measured underhigh frequency magnetic field with different intensities by model experiments, then the dynamic pressure in mold flux channel is calculated during one mold oscillation period. It is found that the high frequency magnetic field can decrease the dynamic pressure greatly, which may be one possible mechanism of improving the billets surface quality by soft-contact mold electromagnetic continuous casting. According to the calculation, the mold flux channel dynamic pressure can not be decreased unlimitedly by increasing magnetic flux density, there must be a most appropriate magnetic flux density in. order to get best billet surface quality.The distribution of electromagnetic force along with radius and time in cylinder shape liquid metal under continuous and amplitude modulated alternating magnetic field are deduced and calculated based on Maxwell equation. It is found that the frequency of electromagnetic force was the twice of the magnetic field under both continuous and amplitude modulated condition, and the amplitude of it changed in a square parabola type while amplitude of magnetic field changed in a linear type. Based on the study of mold flux channel dynamic pressure, a model to optimize design AMMF is be proposed.Continuous casting experiments results show that in the mold oscillation coupled with AMMF EMCC, imposition of AMMF duty part during mold oscillation positive strip can deduce the withdraw resistance and improve the billets surface. On the other hand, in the MOCAMMF technology, how to select the wave of AMMF to balance the lubrication effect and meniscus fluctuation in order to gain the best billets surface is a problem to be intensity studied.In the third part of the paper, another novel technology, named as Mould Oscillation-less Electromagnetic Continuous Casting (MOLECC) under AMMF was proposed in order to replace the huge mechanical mould oscillation system by AMMF imposing outside the mould in continuous casting.A high frequency AMMF power source that can produce rectangle, triangle and sine wave AMMF has been invented, and then the magnetic field inducted in the mould...
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