A comparison study on viscosity and heat transfer property of fluorine-bearing and fluorine-free mold flux for casting silicon steel

A comparison study was conducted on viscosity and heat transfer property of the traditional fluorine-bearing (F-bearing) mold flux and the newly designed fluorine-free (F-free) mold flux for casting silicon steel. The results showed that the viscosity of F-free mold flux is lower than that of F-bearing mold flux, as the apparent activation energy of F-free mold flux is also lower than that of F-bearing mold flux confirmed by the kinetics results for viscous flow, which meant that the energy barrier of F-free mold flux that the migration of ion clusters needs to overcome is smaller, and thus leads to a lower viscosity of F-free mold flux. Besides, the research results of the heat transfer suggested that the comprehensive heat transfer coefficient of F-free mold flux is lower than that of F-bearing mold flux in all directions. One reason is that the true density of F-free mold flux increases from glassy state to crystalline state, while that of F-bearing mold flux is opposite. Another reason is that the air gap gets increased due to the volume shrinkage of F-free mold flux from glassy state to crystalline state and the solidification of the molten steel. These introduce a larger thermal resistance of F-free mold flux than that of F-bearing mold flux. Through the comparison, the designed F-free mold flux shows a better lubrication and capacity to control the heat transfer than the traditional F-bearing mold flux.