The Advantage of Silica Sol Precision Casting is High Precision
Silica sol precision casting is a precision casting method using silica sol as a binder. Its products are characterized by precision and complexity. It is an advanced process of near-net-shape forming. If we want to cast fine products such as hardware castings, textile castings, sewing castings, stainless steel castings, and carbon steel castings, we must start from the following points.
1. Metal materials
The metal materials of precision casting enterprises mainly come from purchased materials, waste castings of the enterprise, and pouring and risers. The purchased metal materials are often in bulk, and few are pressed into a cylinder. 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 pressed into a cylinder as much as possible, and analyze the chemical composition of each batch of purchased materials by spectral analysis. If possible, the supplier should be considered on the spot to evaluate whether its materials are marked, protected, and stored in isolation.
2. Mold material
The performance indicators of mold material mainly include: melting temperature and solidification temperature range, heat resistance, thermal expansion rate and shrinkage rate, strength, hardness, viscosity, fluidity, coating and ash content, etc. It is difficult for general precision casting enterprises to test these performance indicators one by one. Therefore, when selecting suppliers, it is necessary to choose some formal enterprises with relatively complete quality management systems as much as possible. Strict evaluation and confirmation by suppliers are required. However, as one of the important performance indicators of mold material, shrinkage rate can be tested. Shrinkage rate directly affects the dimensional accuracy of castings and the quality of mold shells. At present, the domestic round cake sample line shrinkage determination method does not consider the influence of wax mold structure on shrinkage rate. Referring to the step-shaped sample method adopted abroad, it is closer to the actual situation.
3. Silica sol
The main physical and chemical parameters of silica sol are: SIO2 content, density, Na2o content, pH value, kinematic viscosity, colloidal particle diameter, etc. These physical and chemical parameters mainly affect the shell strength, coating stability and coating powder-liquid ratio. Since it is difficult for general precision casting companies to detect these physical and chemical parameters, on the one hand, it is necessary to strengthen the selection, evaluation and confirmation of suppliers. On the other hand, different specifications of silica sol should be selected for the surface layer and the back layer, such as S-830 silica sol for the surface layer and S-1430 silica sol for the back layer.
4. Surface coating
Silica sol precision casting companies generally choose zircon powder as the surface coating. When zircon powder contains oxide impurities, the decomposition temperature will drop and amorphous Sio2 will be precipitated. Certain elements in the metal react chemically, causing defects such as “pitting” on the surface of the casting, which deteriorates the surface quality of the casting. Moreover, the particle size and distribution of zircon powder also have a direct impact on the coating powder-liquid ratio. Therefore, the selection of suppliers should be strictly controlled.
Silica sol precision casting’s anti-deformation ability and process requirements
Silica sol precision casting is a kind of precision casting that produces high-quality products. Such products have been widely used in industrial production. Silica sol precision casting has good stability performance, its product value adaptation range is wider, and the stable storage time is longer. The workload required for silica sol precision casting during storage is relatively small, so it can adapt to high shear stress mixing, and the interlayer drying time of the product is further shortened. However, they can shorten the interlayer drying time of such enhanced silica sol to 1h.
Silica sol precision casting has strict requirements on the shell making environment and wind speed. For castings with slender holes, the interlayer drying time needs to be appropriately extended. Polymeric additives can better help reduce the defects of shells and castings. The effect of the additives in the manufacturing process of silica sol precision casting will no longer be limited to helping the shell to quickly establish wet strength, and it will also effectively improve the quality of its investment casting. The surface quality of the silica sol shell is good and its high temperature strength is high. The high temperature deformation resistance of silica sol precision casting is strong. The product requires a process with relatively high precision. In practice and theory, we should strengthen the understanding of precision casting technology, continuously supplement its professional tests, and enrich its practical experience.
When using silica sol precision casting, the foam model must be liquefied and decomposed during the filling process, and its product will produce a lot of small molecular gases and foam ash. At that time, these substances are harmful to the human body. In daily work, operators must strictly follow their operating manuals to perform.
