Fundamental investigations for the design of fluorine free mold powder compositions

摘要

The influence of the CaO/SiO_2 ratio on flux viscosity at 1300°C, break temperature and crystallization was investigated. The thermo-chemical software FactSage was used for the calculation of the viscosity, the equilibrium phase content and the liquidus temperature. Based on these results, two sample series with 8.8 wt% TiO_2, 5 wt% B_2O_3 and CaO/SiO_2 ratios from 0.8-1.2 were manufactured. Series M1 contained Li_2O which was replaced by a higher content of Na_2O for F-free mixtures in series M2. The viscosity and break temperature were determined through rotational viscometry, the crystallization temperature and crystalline fraction by a so called Furnace Crystallization Test, a macro style differential thermal analysis which enables a mineralogical investigation of the samples afterwards. The experiments exhibited that the break temperature, the liquidus temperature and the crystalline fraction rose with increasing C/S ratio while the viscosity decreased for both sequences.