The methods of reducing casting deformation by mullite powder in the casting process are mainly reflected in the following aspects:

I. Optimizing material ratio and microstructure

By accurately mixing mullite powder with other refractories (such as high-temperature calcined bauxite powder, alumina powder, etc.), a stable microstructure can be formed, which effectively inhibits creep and deformation at high temperature. For example, multi-level particle size design is adopted to form a composite structure with large particle skeleton support, medium particle filling and small particle lubrication, which significantly improves the compactness and dimensional stability of the core and reduces shrinkage and deformation during sintering.

II. Controlling the thermal expansion of cores and molds

Mullite powder has low thermal expansion coefficient, which can effectively reduce the deformation of core and shell at high temperature. By adding mullite powder, the high-temperature expansion coefficient of the shell can be reduced, and its high-temperature yield can be improved, thus reducing the deformation of the casting.

III. Improving the strength of cores and molds

Mullite powder can enhance the high-temperature strength of core and shell, and keep them stable during high-temperature pouring. For example, adding mullite powder into ceramic core, combined with the synergistic effect of toughening agent, pore-forming agent and plasticizer, can significantly improve the thermal shock resistance and overall toughness of the core and reduce the risk of cracking caused by thermal stress.

IV. Improving the permeability and concession of the mould shell

The addition of mullite powder can improve the permeability of the mold shell, reduce the gas accumulation and expansion pressure during pouring, and thus reduce the deformation risk of the casting. At the same time, by adjusting the formula and process parameters, the high-temperature yield of the shell can be improved, so that it can better adapt to the shrinkage of the casting during the cooling process.

V. Reducing sintering shrinkage

Mullite powder can form stable mullite whiskers during sintering, which can improve the strength and dimensional stability of the mold shell and reduce sintering shrinkage. For example, by adding mullite phase transformation promoter (such as aluminum fluoride trihydrate), mullite whiskers can be generated in the mold shell, which significantly reduces the sintering shrinkage.

VI. Process optimization

In the design of casting process, the temperature distribution of cavity and gating system should be controlled reasonably to make them cool evenly and reduce the residual stress inside the casting. In addition, the deformation can be further reduced by optimizing the preparation process of core and shell, such as adopting multi-layer coating and controlling baking temperature and time.

VII. Integrated core and shell technology

Using one-step forming technology of core shell can reduce the problems of core deformation, deviation and fracture caused by different thermal expansion in traditional liquid precision forming methods. This integrated technology combined with advanced manufacturing technology (such as stereo lithography, gel casting, etc.) can significantly improve the dimensional accuracy and stability of cores and shells.

Through the above method, mullite powder can effectively reduce the deformation of castings in the casting process and improve the quality and dimensional accuracy of castings.