4.1 water glass binder is used for coating, quartz powder is used for surface layer powder, and bauxite is used for reinforcement layer powder.
4.2 shell making and hardening process
A. drying before hardening: the precision casting of driving wheel is large and smooth, and after surface coating is directly sanded with sand, the gel film will produce serious cracking or wrinkle, which will affect the surface quality of the shell due to the hardening of interface and rapid penetration hardening. During the drying process before hardening, the binder components can diffuse and homogenize from the inner layer with high concentration to the outer layer with low concentration to disperse the accumulation of Na2O and water in the shell, so as to ensure that the shell can be hardened evenly during hardening. In addition, the sol produced by natural drying before hardening is not in liquid but completely gel transformed in the sodium silicate solid formed by dehydration and concentration of sodium silicate. Therefore, such gel has high elasticity, good density, high hardness and strength, and is not easy to peel, crack, pulverized and peel off.
From the comparison in the actual production process, the surface quality of large complex parts with large flat surface such as the driving wheel after drying is much better than that of the shell hardened immediately after sanding.
b. Wire mesh reinforcement after the fifth layer of mold shell is hardened and dried, the following three purposes can be achieved by weaving metal mesh on the inner and outer surfaces of the mold shell with iron wire: ① prevent the wax mold and pouring system of precision casting from breaking at the welding surface due to the significant increase of the weight of the whole module when making the mold shell after five layers; ② Further improve the overall strength of the shell Prevent defects such as pouring fire escape and deformation of precision castings; ③ Use Φ 6mm iron wire is used to make lifting rings, so that the module can be dewaxed (the gate rod has been removed), loaded into the furnace, roasted and transported.