Silica sol precision casting is a precision casting method that uses silica sol as a binder. Its products have the characteristics of precision and complexity, and are an advanced process of near net forming. To cast high-quality products such as hardware castings, textile castings, sewing castings, stainless steel castings, carbon steel castings, etc., we need to start from the following points.
1. Metal materials
The metal materials of silica sol precision casting enterprises mainly come from purchased materials, our own waste castings, and sprues. However, purchased metal materials are often loose and rarely pressed into cylindrical shapes. Materials of different materials are easily mixed together, such as 316 materials mixed with 304 or 430 materials. Therefore, precision casting enterprises should choose to purchase materials that are pressed into cylindrical shapes as much as possible, and analyze the chemical composition of each batch of purchased materials using spectral analysis, If possible, on-site consideration should be conducted on the supplier to evaluate whether their materials are labeled, protected, and stored in isolation.
2. Mold material
The performance indicators of mold materials mainly include: melting temperature and solidification temperature range, heat resistance, thermal expansion and contraction rate, strength, hardness, viscosity, flowability, coating and ash content, etc. Generally, precision casting enterprises find it difficult to test these performance indicators one by one. Therefore, when selecting suppliers, it is necessary to try to choose some formal enterprises with relatively complete quality management systems, and strictly evaluate and confirm the supplier. However, As one of the important performance indicators of the mold material, the shrinkage rate can be tested. The shrinkage rate directly affects the dimensional accuracy of the casting and the quality of the mold shell. Currently, the domestic method for measuring the linear shrinkage of circular cake specimens does not consider the influence of wax mold structure on the shrinkage rate. Referring to the step shaped specimen method used abroad, it is closer to the actual situation.
3. Silica sol
The physicochemical parameters of silica sol mainly include the content, density, Na2O content, pH value, kinematic viscosity, colloidal particle diameter, etc. These physicochemical parameters mainly affect the strength of the mold shell, the stability of the coating, and the powder liquid ratio of the coating. As it is difficult for general precision casting enterprises to detect these physicochemical parameters, on the one hand, it is necessary to strengthen the selection, evaluation, and confirmation of suppliers, and on the other hand, Different specifications of silica sol should be used for the surface layer and back layer, such as S-830 silica sol for the surface layer and S-1430 silica sol for the back layer.
4. Surface coating
Silicon sol precision casting enterprises generally choose zirconium powder as the surface coating. When zirconium powder contains oxide impurities, the decomposition temperature will decrease, and amorphous SiO2 will precipitate. Some elements in the metal undergo chemical reactions, causing defects such as "pitting" on the surface of the casting and deteriorating the surface quality of the casting. Moreover, the particle size and distribution of zirconium powder also have a direct impact on the powder to liquid ratio of the coating. Therefore, the selection of suppliers should be strictly controlled.
