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Quality control of materials for precision casting Feb 15, 2017

1, metal material

Precision casting enterprise metal materials mainly from outsourcing materials, the enterprise of scrap castings, pouring risers. The outsourcing of metal materials is often in bulk, very few pressed into a tube, different materials are easy to confuse together, such as 316 material mixed with 304 or 430 material. Therefore, the precision casting enterprises to choose as much as possible to purchase into a cylindrical material. The chemical composition of each batch of purchased material was analyzed using a spectral analyzer. If possible, the supplier should conduct field trips to evaluate whether the material is to be identified, protected and isolated.

For the enterprise scrap (waste castings, pouring risers) to be in addition to corrosion, to oil, sand and clean and dry treatment, control S, P ingredients. And, the scrap of different materials to be identified, protected, separated storage, can not be confused.

2, mold material

The performance indicators of the mold material are: melting temperature and solidification temperature range, heat resistance, thermal expansion and shrinkage, strength, hardness, viscosity, mobility, sanding and ash. General precision casting enterprises are difficult to test these performance indicators one by one. Therefore, in the choice of suppliers, as far as possible to choose some of the quality management system more perfect formal business, strict evaluation and confirmation of the supplier. However, as one of the most important performance indicators of mold material - shrinkage, you can test, the shrinkage of a direct impact on the casting of the dimensional accuracy and the quality of the shell. At present, the domestic round cake sample line shrinkage measurement method does not take into account the impact of wax structure on the shrinkage rate, it is best to refer to foreign countries using stepped sample method closer to the actual situation.

3, silica sol

The physical and chemical parameters of silica sol mainly include SiO2 content, density, Na2O content, pH value, kinematic viscosity and colloidal particle diameter. These physical and chemical parameters mainly affect the strength of shell, the stability of coating and the ratio of powder to powder. As the general precision casting enterprises are difficult to test these physical and chemical parameters, so on the one hand to strengthen the supplier's choice, evaluation and confirmation, on the other hand, the surface layer and back layer should choose to use different specifications of silica sol, Layer selection S-830 silica sol, back layer selection S-1430 silica sol.

Precision casting enterprises generally choose zircon powder as a surface coating. When the zirconium powder contains oxide impurities, the decomposition temperature will drop, precipitation of amorphous SiO2, and some elements of the metal chemical reaction, the casting surface "pitting" and other defects, deterioration of the casting surface quality. Moreover, the particle size and distribution of the zircon powder have a direct effect on the ratio of the powder to the coating. Therefore, the choice of suppliers should be strictly controlled.