Study On Melting And Rheological Properties Of Fluoride-Free Mold Fluxes

Mold fluxes play a key role during the continuous casting process. The current used mold fluxes generally contain fluorine bearing materials such as fluorite and cryolite etc, which can volatilize at operational temperatures, polluting both the plant air and cooling water. Airborne fluoride could potentially be a health and safety issue. Waterborne fluoride forms hydrofluoric acid (HF), which can cause plant corrosion. Developing and using fluoride-free (F-free) mold powders is of importance to the environmental protection.In this paper, fluoride-free mold fluxes are developed basing on CaO-SiO2-TiO2 slag system. The relationship between the melting and viscosity properties of F-free mold fluxes and fusing reagents, binary basicity and TiO2 content is investigated. Effect between TiO2 and carbon materials in F-free mold fluxes is researched by studying the crystalline phase. Experimental research on the relationship between carbon materials and melting rate is also carried out. At last, the absorptive rate of the F-free mold powders on Al2O3 and the properties stability after absorbing inclusions are measured by rotating cylinder method. All the studies provide a basal direction for producing F-free and titanium-bearing mold fluxes. The experimental result indicates that:(1) In F-free and titanium-bearing mold fluxes, the order of the effect on lowering melting point are Li2O > B2O3 >MgO> MnO>Na2O. The increase of TiO2 content and CaO/SiO2 ratio will heighten the melting point. The order of the effect on lowering viscosity are Li2O>B2O3>Na2O>MgO>MnO. The viscosity will reduce rapidity by increasing CaO/SiO2 ratio. When the content of titanium is 6% in mass, the viscosity shows the minimum. Na2O, Li2O and B2O3 can reduce the surface tension, while TiO2, MnO, MgO and CaO will enhance the surface tension. Li2O, MnO and B2O3 can reduce the break temperature. The increase of MgO content and CaO/SiO2 ratio will heighten the break temperature. The effect of Na2O and TiO2 on the break temperature are also obtaind.(2) The effect of the carbon materials on melting rate in F-free mold fluxes are similar to which in traditional mold fluxes. The order of ability to lower melting speed is: fine graphite (500 mu)>fine graphite (300 mu) >intermediate super carbon black, semi-reinforcing carbon black and carburetant >graphite.(3) Due to feeblish dynamic conditions during CC process, it is very difficult to...