Study On The Method Of Heat Transfer Characterization And Heat Transfer Of Mold Fluxes

Mold flux is a key functional material used in the continuous casting process, which has a very important function of controlling the heat transfer from strand to mould. It has been confirmed that change the heat-transfer character of mold flux through changing its chemical composition is very effective, and that will reduce the longitudinal crack of cracking sensitivity steel. But it is a difficulty to study the heat transfer properties of mold flux because of that the test methods of heat-transfer character are not perfect at present. The heat flux simulator of mold slag film comprehensively considered the comprehensive heat-transfer phenomenon of the heat-transfer of molten slag and solid slag, as well as the interface heat-transfer between solid slag film and simulate copper mould, it also has many advantages, such as conveniency, dependable, low test cost, and it has a widely application prospect. However, the parameters that can be used to characterize the mold flux's heat-transfer properties have not been built perfectly.This paper take advantage of the heat flux simulator of mold slag film, put the plant acquisition slag flim and the slag film which acquired by simulator contrast, the research shows that structure of the slag film which acquired by simulator at 45s is near with the one which nearby the practical mould meniscus at 45s, and the heat flux density changes slowly after 45 second, so the 45s is determined as the time of heat flux mearurement and solid slag film acquisition of simulator. And through analyzing the characteristic curve of heat-flux density change with time, setting up the characteristic methods which based on the simulator.Characterization parameters are:â‘ the maximum heat-flux characterize the heat-transfer of liquid slag;â‘¡the time of air gap formation steadily characterize the velocity of slag reduce heat transfer at meniscus;â‘¢the average heat-flux density between t1 and t2 reflects the heat-transfer capability of slag at meniscus;â‘£the average heat-flux density between t2 and 45s characterize the heat-transfer capability of slag after air gap formed stably;⑤t1-45s characterize the total heat-transfer capability of slag, which is corresponding to actual heat flux data obtained from practical production. And proving the rationality of characteristic method through comparison analyze test parameters of slags employed for casting medium carbon steel (MC) and low carbon steel (LC) under the same caster type.Based on setting up the heat-transfer characteristic method of slag which on account of simulator, the effect of the chemical composition of mould slag (R, CaF₂, Na₂O, Al₂O₃, MgO, Li₂O, MnO, and use NaF replace CaF₂ offer F- and replace Na2O offer Na⁺) on slag film structure and heat-transfer property has been studied. Effect of basicity and chemical composition of mold fluxes on the formation time of stable air gap and all kinds of heat flux density has been obtained under the current slag system conditions.And the study shows that: Thickness and crystallization ration of slag film is related to the formation time of stable air gap. Thicker slag film or higher crystallization ration is beneficial to form stable air gap at the area of meniscus. It is to say heat flux can be reduced rapidly at meniscus. And the effect of thickness is greater than crystallization ration of slag film. Similarly, thickness and crystallization ration of slag film are key factors that could affect each kind of heat flux density. It is also that the effect of thickness is greater than crystallization ration of slag film. The main factors that could influence thickness of slag film are melting point, viscosity and crystallization capacity of the slag. Mold slag with lower melting point and viscosity is more likely to form thinner slag film, on the contrary, the crystallization capacity promoted.The effect of physical properties of mold slag (melting point and viscosity) on heat-transfer property and slag film structure has also been researched in the paper. The results indicate thatâ‘ Increase both melting point and viscosity of slag would be beneficial to reduce the heat-transfer capability of slag. It is because that thickness of slag film increased with increasing melting point and viscosity.â‘¡The influence on crystallization ratio by melting point is not obviously, but the crystallization tendency reduced by increasing the viscosity of slag.