Fused Silica Spare Parts with Heat Resistance

The use of fused silica material in investment casting shell has been increasing year by year in developed countries such as the United States and Japan, especially in the surface layer of silica sol shell. It has made great breakthrough in the use and price ratio with zircon material, and is an ideal engineering application material.

Fused silica is made by melting natural high-purity silicon dioxide in an electric furnace at a temperature above 1760 ºC, and then cooling rapidly. This process transforms crystalline silica into amorphous glass melt.

The melting temperature of fused silica is about 1713 ºC, the thermal conductivity is low, and the thermal expansion coefficient is almost the smallest of all refractory materials, so it has extremely high thermal shock stability. Therefore, the fused silica mold shell is rarely broken due to temperature changes during baking and pouring. It is an ideal refractory for investment casting, which can be used as refractory for surface or back coating, and as sanding material.

Fused silica can improve the shell performance partially or completely. The small thermal expansion coefficient of fused silica is beneficial to prevent the shell from cracking and deformation during dewaxing and baking, and to ensure the dimensional stability of castings. The purity of fused silica is high, and the stability of the coating is good; The high-temperature creep resistance of the shell is improved.

When the temperature of fused silica is low, its thermal conductivity is poor, and its thermal capacity is only half of that of zircon sand. Most of the liquid metal has poor wettability on it, which makes it easy to generate gaps between the metal solidification layer and the inner surface of the mold shell. The thermal conductivity is further reduced, which is conducive to the filling of thin wall castings. At high temperature, fused silica has high transparency, and can conduct heat through radiation, making its thermal conductivity exceed that of aluminum silicate shells. And make the casting cool faster, making it easier to obtain a sound casting.

When the casting cools down, the quartz transforms from a high-temperature type to a low-temperature type, and at the same time, the volume undergoes a sudden change, causing countless cracks in the mold shell and a sharp decrease in strength, which is conducive to the peeling process. Fused silica is acidic and can be removed by chemical sand cleaning methods such as alkali boiling and alkali explosion.