Four key points to improve the precision of silica sol investment castings

Silica sol investment casting is a precision casting method using silica sol as a binder. Its products have precise and complex characteristics and are an advanced near-net forming technology. In order to forge high-quality products such as metal castings, textile castings, sewn castings, stainless steel castings, carbon steel castings, etc., we should start from the following points.

1. Metal material

The metal materials used by investment casting enterprises mainly come from purchased materials, waste castings and risers. The purchased metal materials are generally weighed in bulk, rarely pressed into the cylinder, and different materials can be easily mixed. If 316 material is mixed with 304 or 430 material. Therefore, precision casting companies should try their best to choose and buy suppressed tubular materials. The spectral analysis method is used to analyze the chemical composition of each purchased material. Suppliers shall consider on-site to assess whether materials are identified, protected, and stored in a safe manner, if possible.

2. Mold material

The key performance indicators of the mold are: melting temperature, solidification temperature range, temperature resistance, thermal expansion rate and shrinkage rate, strength, strength, viscosity, fluidity, coating, ash content, etc. It is difficult for general investment casting companies to test these performance parameters one by one. Therefore, when choosing a supplier, try to choose some formal companies with a complete quality certification system, and strictly evaluate and determine Ningbo silica sol casting suppliers. The shrinkage rate, as one of the important performance parameters of the mold material, can be tested. The shrinkage rate is directly related to the dimensional accuracy of the casting and the quality of the shell. The circular cake-like linear shrinkage measurement method currently used in my country does not consider the influence of the wax mold structure on the shrinkage rate, and the stepped shrinkage measurement method used overseas is closer to the specific situation.

3. Silica sol

The physical and chemical parameters of silica sol mainly include SIO2 content, density, Na2o content, pH value, kinematic viscosity, colloidal particle size, etc. These physical and chemical parameters critically affect the shell strength of the coating, the stability of the coating, and the powder-to-liquid ratio of the coating. Generally, these physical and chemical parameters cannot be detected by investment casting companies. On the one hand, strengthen the selection, evaluation, and determination of suppliers. On the other hand, silica sol of different specifications should be used layer by layer, such as s-830 silica sol for the surface, and s-1430 silica sol for the reverse layer.

4. Surface coating

Zirconium powder is generally used as the surface coating for silica sol precision castings. When the zirconium powder contains oxide impurities, the decomposition temperature decreases and amorphous Sio2 precipitates. Certain elements in the metal will undergo chemical changes, causing defects such as "pitting corrosion" on the surface of the casting, and deteriorating the surface quality of the casting. The particle size and distribution of zircon powder are directly related to the powder-liquid ratio. Therefore, the choice of suppliers should be strictly controlled. The application results show that the quality of Australian zircon powder is better.