In the casting process, the sprue cup needs to withstand complex working conditions such as high temperature, molten metal scouring and thermal shock, so its material selection is very important. The following is the stress on the selection of sprue cup materials:

I. Fire resistance

The sprue cup material must have high refractoriness to withstand the long-term action of high-temperature molten metal without melting or softening. Common refractory materials include high alumina silicate, refractory clay, alumina, etc. The fire resistance of these materials is usually between 1670℃ and 1770℃.

II. Thermal shock resistance

The sprue cup will undergo rapid temperature change during use, so it needs to have good thermal shock resistance to prevent cracking or peeling caused by thermal stress. For example, high aluminosilicate materials have excellent thermal shock resistance, while aluminum titanate composites have extremely low expansion coefficient (expansion coefficient ≤ 1x10-6 at 0-1000℃), which is an ideal material for high temperature, thermal shock resistance, corrosion resistance and other key parts.

III. Slag corrosion resistance and corrosion resistance

The sprue cup needs direct contact with high-temperature molten metal, so the material must have good slag corrosion resistance and corrosion resistance to prevent it from being corroded by impurities in molten metal. Both high aluminosilicate materials and alumina materials have good slag corrosion resistance and can effectively resist the corrosion of molten metal.

IV. Mechanical strength

The sprue cup will be impacted and washed by molten metal during use, so it needs to have sufficient mechanical strength. High alumina silicate materials and refractory clay materials have high strength and wear resistance after being fired at high temperature.

V. Coefficient of thermal expansion

The thermal expansion coefficient of the material should be as low as possible to reduce the dimensional change caused by temperature change, thus ensuring the dimensional stability of the sprue cup. For example, the thermal expansion coefficient of high-density calcium silicate material is less than 0.3% within 3 hours at 850℃, and it has good dimensional stability.

VI. Surface smoothness

The inner surface of the sprue cup should be smooth to reduce the flow resistance of molten metal and avoid vortex or splash. After firing, the surfaces of high aluminosilicate materials and alumina materials are smooth and free of impurities, which can effectively improve the fluidity of molten metal.

VII. Material Cost and Machinability

On the premise of meeting the performance requirements, the cost and machinability of materials are also important considerations. For example, high-density calcium silicate material is an ideal substitute for aluminum titanate material, although its performance is excellent, but its cost is low. In addition, the materials should be easily processed into the required shapes and sizes to meet the requirements of different casting processes.

VIII. Chemical stability

The sprue cup material should not react chemically with molten metal to ensure the purity of molten metal and the service life of the sprue cup. For example, aluminum titanate composite material does not react with non-ferrous metals and does not infiltrate, which is an ideal material for high temperature casting.

IX. Summary

The selection of sprue cup material needs to comprehensively consider the factors such as refractoriness, thermal shock resistance, slag corrosion resistance, mechanical strength, thermal expansion coefficient, surface smoothness, cost and machinability. Common materials include high-alumina silicate, refractory clay, alumina, aluminum titanate composite and high-density calcium silicate. These materials have their own advantages in different casting processes and application scenarios, and need to be selected according to specific needs.