Aluminum gravity casting can be divided into two types, one is multilayer, the other is solid, but at present, multilayer is widely used in the market. In the process of using, first immerse the module in the refractory, harden the refractory and dry it on the object of the module. It must be repeated several times until the thickness of the refractory coating reaches the standard. This is the composite material mentioned above. Shell technology, and then put aside for a period of time, so that it is completely hardened, and finally melted, so as to complete the effect of multi-layer shell.
In gravity casting aluminum, in fact, most multi-layer shells need to be filled with sand and filler, only a few do not need to be filled with sand and filler, as long as they are simply baked, they can be cast. When we use investment casting, we lose it. Generally speaking, due to the increase of the volume of the investment mold, in the process of baking and pouring, each part of the shell will control each other, but it is impossible to expand and contract uniformly. This may be due to the material of the metal shell and the chemical effect of relatively high temperature. Reaction. This means that due to the mechanical strength, temperature, heat resistance and vibration resistance of refractories, as well as the chemical stability under high temperature, there are still certain requirements for the size shrinkage and expansion of the shell. Therefore, the shell must also have certain air permeability, so that the inner shell does not exclude gas during the pouring process. They are closely related to the adhesives, refractories and casings used in the manufacturing process.