Analysis of Different Pouring Methods in Precision Casting on Castings

Analysis of Different Pouring Methods in Precision Casting on Castings

There are various types of defects in investment casting, and the factors that affect the quality of castings exist in every process related to casting production. The characteristics of large castings are large size, namely large volume, heavy weight, more liquid poured, relatively thick wall thickness, and some shapes are simple and some are complex; Castings from different fields have different requirements. Today, precision casting manufacturer Tianyao Metal will talk to you about the analysis of different casting methods on casting types.

1、 Dispersed bottom pouring

Advantages: It is beneficial for the metal liquid to smoothly fill the mold; Reduce oxidation of molten metal, with low impact force on the mold and core; Prevent sand flushing, reduce turbulence, and reduce gas entrapment; Beneficial for the discharge of gas from the mold cavity: Beneficial for slag removal: Avoiding excessive temperature differences between different parts, beneficial for reducing casting shrinkage stress, beneficial for reducing deformation of long and thin castings, and beneficial for preventing crack defects from occurring.

Disadvantages: If the filling time is too long, the metal liquid will come into contact with the air for a long time during the rise of the mold cavity, and the surface is prone to generate oxide skin (which needs to be quickly poured to overcome); The high temperature at the bottom of the casting is not conducive to shrinkage (it has little effect on gray cast iron parts).

2、 Rapid pouring

Advantages: The rising speed of molten iron is fast, and it is not easy to oxidize. The baking time of molten iron on the mold cavity is short, reducing the possibility of coating cracking and peeling, and reducing the occurrence of defects such as slag inclusion in castings; Prevent insufficient pouring and cold insulation defects; Increase the air pressure inside the mold cavity, forcing the gas to be easily discharged from the mold, making it less prone to defects such as pores in the casting. The temperature difference between different parts of the casting is small, preventing cracks from occurring.

Disadvantages: Low strength sand molds are prone to sand flushing defects, which have a relatively small impact on high-strength sand molds such as resin sand. The cross-sectional area of the pouring system is increased, and the yield of the casting process is reduced.

3、 Determination of Reasonable Casting Time

The commonly used pouring time in production represents the pouring speed. For castings, a long pouring time means a slow pouring speed; conversely, it means a fast pouring speed. The appropriate pouring time should be determined based on comprehensive considerations such as casting quality, wall thickness, structure, and technical requirements. The pouring time is related to factors such as casting structure, material, mold conditions, pouring temperature, etc. Each casting has a reasonable pouring time corresponding to it. There is no perfect calculation formula for pouring time, which is generally determined based on various empirical formulas, charts, and casting quality. After determining the pouring time, calculate the cross-sectional area of each unit of the pouring system according to the selected cross-sectional ratio.

4、 High temperature pouring

Advantages: Good fluidity, can avoid casting defects that are easily formed due to bottom injection, and can obtain castings with clear contours; Can avoid cracks and cold insulation defects: can avoid defects such as pores and pinholes (the pouring temperature should be appropriately increased according to the casting wall thickness and structural shape, not the higher the better).

Disadvantage: prone to sand sticking defects; Easy to produce sand flushing defects; A particularly thick and large piece can easily cause tissue to become coarse; Thick and large ductile iron parts tend to have shrinkage and porosity: increasing the tendency for graphite to float.

5、 Conclusion

For large cast iron parts produced using high-strength molds, adopting a dispersed and bottom pouring pouring method in the pouring process, supplemented by appropriately increasing the pouring speed and pouring temperature, can greatly reduce the occurrence of hole defects (pores, slag holes, iron beans), crack defects (hot cracks, cold cracks), surface defects (cold shuts, insufficient pouring), and structural and performance defects (incubation decline) in the casting, improve the yield of the casting, reduce waste loss, and reduce mechanical processing losses caused by internal defects in the casting process.

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