Heat transfer phenomena and mould flux lubrication in continuous casting of steel

University dissertation from Stockholm : Materialvetenskap

Abstract: Overall thermal resistance of the mould flux was measured tomake clear the influence of the mould flux properties on theheat transfer behavior in continuous casting, especiallythermal conductivity and the formation of air gaps in thisstudy. From the investigation of the effect of the mouldsurface temperature and physical properties of the mould fluxon heat transfer through the flux film, following knowledge hasbeen obtained. (1) When the temperature of the mould surfaceexceeded the solidification temperature of the mould flux, thecontact resistance for heat transfer disappeared together withdisappearance of air gaps. (2) An interfacial thermalresistance corresponding to an air gap of 20-50 µm wasobserved in the case of the solid mould flux. (3)Crystallization of the mould flux inhibited radiation heattransfer, which was equivalent to 20% of the total heatflux.With a heat transfer model and measuring physical propertiesof mould fluxes, numerical simulations for the heat transfer insteady state conditions were carried out. Assuming constantflux film thickness, surface temperature of the solid flux filmand heat flux at meniscus region was linked by the parameter,contact resistance of heat transfer. As a result, solidus ofmould flux determines the lower limit of heat flux atmeniscus.A mathematical model for flux infiltration is developed withintroduction of static pressure of metal inside the solidifyingshell. The characteristic of the model is calculatingdistribution of the liquid flux thickness, which has not beentried. Results of the calculation agree well with previousplant study of heat flux in the mould, mould flux consumptionand friction force acts on the shell.A new method of measuring the rupture strength of the mouldflux film was developed and provided the measurements to themathematical model of heat flux and lubrication. The resultssuggest that the solid flux film at meniscus region can bedestroyed by shear stress of liquid flux film athigh-speed-casting.Key words:Heat Transfer, Thermal Conductivity, ContactResistance, Mould Flux, Solidification, Lubrication,Infiltration, Friction, Shear Stress, Modeling,Crystallization, Rupture Strength, Solidus, High-Speed Casting,Viscosity, Elasticity, Uniform Cooling

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