Melting and sintering characteristics of carbon-free mold fluxes

This study systematically investigates the effects of basicity (CaO/SiO₂) and key constituents on the melting behaviour and sintering characteristics of carbon-free mold fluxes. As the CaO/SiO₂ ratio increases, both the melting temperature and time of mold fluxes increase, while the sintering rate and volumetric shrinkage decrease. With increasing Al₂O₃ content, the melting temperature and time first decrease and then increase with CaO/SiO₂ ratios below 1.0, and both parameters exhibit a continuous increase when the ratio is above 1.0. Moreover, the increase of Al₂O₃ content leads to a reduced sintering rate and volumetric shrinkage. Higher F⁻, TiO₂ and MnO contents result in reduced melting behaviour, along with increased sintering characteristics. With increasing MgO and BaO content, the melting temperature and time first decrease and then increase, whereas the sintering rate and volumetric shrinkage show an opposite trend. XRD analysis indicates that carbon-free mold fluxes with lower sintering rates exhibit more complex phase compositions. The optimal compositional range for carbon-free mold fluxes is determined to be having CaO/SiO₂ ratio of 1.0–1.1, Al₂O₃ content of 3–9 wt-%, F⁻ content of 3–6 wt-%, and TiO₂, MnO, MgO and BaO contents each at 6 wt-%, 6 wt-%, 3 wt-% and 3 wt-%, respectively.