Study Of The Linear Expansion Coefficient Of Gradient Sand Mould For Titanium Alloys

In titanium alloy sand casting,the property of the sand mould have a great effectionthe quality of castings,especially the linear expansion coefficient of the sandmould.Unsuitable contraction of the sandwill lead to excessivecasting deformation, andcausethe shape of the castings dimension tolerance.Different linear expansion coefficient gradient sandmoulds are prepared by zirconsand, quartz sand and magnesium olivine sand in different proportion, the effects thatcompaction, particle size, water content of glass and heat hardening temperature haveon the liner expansion coefficient of the sand are studied in this article.Based on thelinear expansion coefficient measurement and combined with gas permeability andcompressive strength, we determined the water-glass content of the zircon sand、quartzsand and magnesium olivine sand in the gradient sand, respectively3%、4%and5%.The hardening temperature is800℃.The linear expansion coefficient of zircon sand,quartz sand and magnesium olivine sand increasein a certain rangewith the water-glasscontent increasing, the liner expansion coefficient of zircon sandmaximum value is8.916×10^-6/℃when the water-glass content is3%; The liner expansion coefficient ofquartz sand maximum value is9.013×10^-6/℃when the water-glass content is4%; theliner expansion coefficient of magnesium olivine sandmaximum value is9.013×10^-6/℃when the water-glass content is5%.The liner expansion coefficient ofzircon sand and quartz sand decreased when thehardening temperatureelevatedin the expansion stage, reaching a maximum value at thehardening temperature of500℃, respectively4.97×10^-6/℃and8.572×10^-6/℃. Theliner expansion coefficient of magnesium olivine sand becomes larger and larger withthe hardening temperature increasing, reaching a maximum value of9.576×10^-6/℃atthe hardening temperature is900℃.We get25distribution values of the liner expansion coefficient from roomtemperature to1200℃by using water glass zirconium sand, quartz sand andmagnesium olivine sand to prepared different proportions of gradient sandmould. At600℃, the liner expansion coefficient gradient change interval is （4.286¹0.253）×10^-6/℃. At1200℃, the liner expansion coefficient gradient change interval is（-15.977^-0.807）×10^-6/℃.