The materials used to make the shells consist mainly of refractory materials and binders. At present, the refractory materials used in investment casting are primarily quartz, corundum, and aluminosilicate refractory materials. The most common binder is colloidal silicate solution (silicate sol), such as water glass and silica sol. Water glass shells are easier to deform and crack. And the dimensional accuracy and surface roughness of the castings are relatively poor compared with the silica sol shells. The stability of silica sol is better, it can stay for a long time, and no special hardener is needed for shell making. But the wetting ability of silica sol on the wax patterns is not good, and the hardening of the shells is a drying process that takes longer.
To improve the ability of the coating to wet the wax, it is necessary to remove the oil from the wax surface in advance. Moreover, the coating should be mixed well before applying it to the wax tree. And the viscosity and gravity of the coating should be optimized so that the coating can fill and wet the wax pattern well. While applying the coating, dip the wax tree into the coating and shake it up and down so that the coating can wet the wax patterns well and cover the wax surface evenly. After the wax tree is coated with refractory paint, it is sprinkled with refractory powder material, then dried and hardened, repeated many times until the refractory coating reaches the required thickness to form a multi-layer shell on the wax cluster.
For more information Custom water pump impeller, Alloy steel lost wax casting, Precision Investment Casting in Aerospace Applications, please get in touch with us!