Mold fluxes play an important role in the steel continuous casting process. Mainly, they must prove adequate lubrication between the solidified steel shell and the copper mold. Thus, the knowledge of mold flux viscosity with the temperature is a relevant property for industry applications in order to prevent operation problems and product defects. On the other hand, for environmental reasons, the replacement of fluorine by non-pollutants compounds, is one of the objectives in the design of new compositions for these slags. In this paper, the viscosity is calculated in the range: 1250-1400 °C applying two models based on their chemical composition and another one using the differential thermal analysis technique. The results obtained with this model showed a good correlation with respect to other traditional models using the chemical composition of the mold flux to estimate the viscosity. The aim is to observe the effect of different oxides on the viscosity of mold fluxes. One of the mold powders was designed with a chemical composition similar to a commercial one (containing 10 wt% of fluorine), while the others powders were fluorine-free (containing boron and lithium). It should be noted that a fluorine-free powder with a viscosity similar to the powder with fluorine was produced replacing 10 wt% fluorine by 4 wt% Li2O and 6 wt% B2O3.
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