The influence of mullite sand on casting quality in precision casting is mainly reflected in the following aspects:

I. Fire resistance

The refractoriness of mullite sand is usually above 1750℃, which makes it stable at high temperature without melting or deformation, thus ensuring that the casting mold maintains good shape and dimensional accuracy during pouring.

II. Chemical stability

The chemical composition of mullite sand mainly includes alumina (Al₂O₃) and silica (SiO₂), and contains a small amount of iron oxide (Fe₂O₃) and other impurities. Its low iron content (usually less than 1.2%) and low alkali metal oxide content (Nao+KO total less than 0.3%) are helpful to reduce the influence of chemical reaction on the casting surface and improve the surface smoothness of the casting.

III. Physical properties

Low expansion coefficient: the thermal expansion coefficient of mullite sand is small, which means that the size of the mold changes little when the temperature changes, further ensuring the dimensional accuracy of the casting.

High density: The density of mullite sand is generally about 2.5g/cm³. High density not only helps to improve the strength and stability of the mold, but also reduces the amount of materials and production costs.

Low dust content: the dust content of mullite sand is extremely low (usually between 0.01% and 0.03%), which helps to reduce the occurrence of casting defects such as sand holes and air holes and improve the surface quality and internal quality of castings.

IV. Particle size distribution

The particle size distribution of mullite sand also has an important influence on the quality of castings. According to different casting requirements, the grain size of mullite sand can range from coarse 8-16 mesh to fine -325 mesh. Reasonable particle size distribution can achieve good filling and permeability, and reduce the generation of pores and shrinkage cavities.

V. Shelling performance

Mullite sand should be easy to shell after casting without deformation. This not only improves the production efficiency, but also reduces the damage of castings caused by the difficulty of shelling.

VI. Reducing sand sticking.

The low dust content and good chemical stability of mullite sand are helpful to reduce the sand sticking phenomenon of castings. Sticking sand is a common defect in casting, which will increase the surface roughness of casting and make it difficult to clean it. The use of mullite sand can effectively reduce the incidence of sand sticking.

VII. Improve the yield

Due to the above advantages of mullite sand, the mold made of mullite sand can significantly improve the yield of castings. The casting has good surface smoothness and high dimensional accuracy, which reduces the need for subsequent processing.

VIII. Summary

Mullite sand in precision casting, through its high refractoriness, low expansion coefficient, low dust content and good chemical stability, significantly improves the surface smoothness, dimensional accuracy and yield of castings, while reducing common defects such as sand sticking and porosity. These characteristics make mullite sand an indispensable and important material in precision casting.