Fused silica is produced by melting natural high-purity silica in an electric furnace at a temperature higher than 1760 ° C, followed by rapid cooling. This process converts crystalline SiO2 into an amorphous glass melt.
Fused quartz and products have three major characteristics:
1,Among all refractories, the coefficient of linear expansion is the smallest (the coefficient of thermal expansion at 1000 ° C is 0.05);
2,The thermal conductivity is the lowest, the thermal conductivity at 1000 °C is 0.836 W / (m · K) (0.02 cal / cm · s ° C);
3,the best thermal shock resistance (at 1200 ° C ~ water-cooled seismic resistance), 10 times No cracks are produced.
The coefficient of linear expansion is the smallest: the thermal expansion coefficient of fused silica is small, which is beneficial to prevent cracking and deformation of the shell during dewaxing and roasting, which is beneficial to ensure the dimensional stability of the casting. The shell has a high temperature creep resistance.
The lowest thermal conductivity: the thermal conductivity of the fused silica is lower, the wettability of most of the molten metal is poor, and the gap between the solidified layer and the inner surface of the shell is easy to occur, and the thermal conductivity is further reduced. It is conducive to the filling of thin wall castings.
The fused silica has high transparency at high temperatures, and can transmit heat through radiation, so that the casting can be cooled faster and the castings can be obtained more easily. When the casting cools, the quartz changes from high temperature type to low temperature type, and the volume changes suddenly, causing numerous cracks in the shell, and the strength drops sharply, which is favorable for shelling.
The best thermal shock resistance: fused silica has the best thermal shock resistance (in 1200 ° C ~ water-cooled seismic resistance), no cracks occur 10 times. Fused silica for investment casting, in which the mass fraction of SiO2 should be 99.5%.
The fused silica is acidic, and the shell can be removed by chemical sand cleaning such as alkali boiling or alkali explosion.