Since the casting temperature of
AZS brick is about 1800 degrees, the casting mold can be sandy. The raw materials of the sand mold are natural sand and quartz sand. Different particle size gradations enhance the strength of the sand plate. The quartz sand uses fine sand and surface. There are two kinds of sand, and the silicon content is above 99%. The casting surface of each sand mold board must be painted with a certain thickness of surface sand to prevent impurities from polluting the mold. There are many types of binders for sand molds. Generally, water glass is used because the source of water glass is stable, inexpensive, easy to wash, and has no peculiar smell, and the sand mold made of water glass high-purity silica sand can meet the following technical requirements:
1) Good air permeability
The gas precipitated from the melt of the zirconium corundum brick can permeate out of the gaps between the silica sand particles in the molding wall.
2) Good thermal shock resistance
The thermal shock generated by the zirconium corundum brick during casting can make the temperature of the inner and outer walls of the sand mold vary greatly, but the sand mold is relatively stable under heating conditions because its refractoriness is not less than 1690 degrees, and it is between 20-450 degrees. The linear expansion coefficient is about 0.03mm/degree, so it can withstand the static pressure of the high-temperature melt stream without breaking.
3) Have good thermomechanical properties
The strength of the sand mold decreases after heating. The soft load test shows that it starts to soften at about 320 degrees and breaks down at 400 degrees.
4) No chemical sticky sand is produced on the surface of zirconium corundum brick
After the AZS melt contacts the sand mold, it cools and hardens rapidly. The surface of the sand mold is fused into a thin layer of sodium silicate or silica sand, which does not react with AZS. The amount of water glass added is proved by experiments to be 5.7%, and less will reduce the refractoriness of the sand mold, and more will not be shaped.
The made relatively large green sand molds often crack during the transportation process in the furnace. In order to make it have a certain strength, several holes are often inserted in the sand mold, and then carbon dioxide is charged into it.
Silicic acid has a low solubility and forms a precipitate, so the green sand mold can have a certain strength in a short time. The finished sand mold should be dried in a resistance furnace to make it have a certain strength for casting. The upper limit of the drying temperature is about 400 degrees.
