The role of high-quality pulverized coal suitable for the application of wet clay sand in the pouring process of sand castings:
① When high-temperature molten iron is injected into the sand mold, the pulverized coal will produce a large amount of reducing gas, prevent the molten iron from being oxidized, reduce the iron oxide on the surface of molten iron, and reduce the possibility of chemical reaction between metal oxide and molding sand;
② The pulverized coal begins to soften after being heated and has plasticity. Since the temperature range from softening to solidification is relatively wide and the time is relatively long, it can buffer the expansion stress caused by the heating of quartz particles in the sand mold, and reduce the sand inclusion defects of sand mold castings caused by the heating expansion of the sand mold;
③ After the pulverized coal is heated, it generates gas, liquid and solid three-phase colloid. The volume expansion of the colloid can partially block the pores between the sand particles on the surface of the sand mold, making it difficult for molten iron to penetrate;
④ The volatile components of hydrocarbons (mainly aromatics) generated by the heating of pulverized coal will undergo gas phase pyrolysis in a reducing atmosphere at a high temperature of 650~1000 ℃, thus separating a layer of shiny fine crystalline carbon, called “bright carbon” or “bright carbon”, on the interface between the molten metal and the sand mold, to protect the sand mold from being wetted by molten iron and difficult to penetrate into the pores of the sand particles, so as to obtain awith a smooth surface.