1. The thermal conductivity of graphite exceeds that of steel and other metal materials, especially in the manufacturing of precision casting, the thermal conductivity decreases with the increase of temperature. Therefore, graphite can be used to ensure that the reaction with oxygen at high temperature, forming a reducing atmosphere, protecting the high temperature metal injected into the mold from oxidation. In addition, graphite's high temperature resistance enables it to lose little weight under ultra-high temperature arc burning.

2, graphite has good plasticity, lubrication and high temperature strength. In the high temperature production of precision casting, graphite is almost an adiabatic body with good chemical stability and does not react with acid, base and organic solvents. By using this property, the filling ability of the thin wall cavity of the mold shell can be increased, and the local heat dissipation ability of the mold shell can be changed, so as to change the cooling and solidification sequence of the casting.

3, the thermal shock resistance of graphite is high, the volume change is small when the temperature changes, the mold shell is not easy to crack. In the process of calcination of the shell, the oxidation escapes, forming uniform dispersed micropores in the shell, thus increasing the permeability and collapsibility of the shell. Therefore, in the manufacture of precision casting shell process, such as cast iron, non-ferrous metal sand mold and metal mold casting, graphite is very common.

2. What kind of zirconium sand should be used in manufacturing precision casting?

Zircon sand is a mineral consisting mainly of zirconium, silicon, and oxygen that crystallized from magma during the formation of igneous rocks. Zircon sand is mostly born in seaside sand, obtained after separation by water separation, electric separation, magnetic separation and other mineral processing, brittle, fracture shell, is an indispensable material in the manufacture of precision casting. Zirconium sand used in manufacturing precision casting should have the characteristics of good thermal conductivity, small thermal expansion, high refractoriness, and melting point up to 3000℃ or more. It has a strong chilling effect on castings, which can refine metal structure and improve mechanical properties. As a surface layer material, it has the function of refining grain and is a good shell refractory.

Casting grade zirconium sand is used for the thick wall of large steel castings and the veil of various alloy steel castings, as well as the coating and paste of sand resistance. In the production of investment castings such as stainless steel, it can be used as the preparation of surface layer and sand spreading material, which can effectively prevent the chemical sand adhesion and mechanical sand clamping, which is beneficial to the surface finish of the castings, refine the surface structure of the castings and improve the dimensional accuracy.