Calculation of effective pouring time of large castings

In production practice, the length of casting pouring time is directly related to many quality factors of castings. For example, for complex thin-walled parts, if the pouring time is too long, the casting is prone to defects such as insufficient pouring, cold shut, air hole, sand inclusion and so on; For large thick wall parts, if the pouring time is too short, there will be shrinkage (porosity), large casting stress, mold expansion (sand) and other defects. Therefore, the reasonable determination of pouring time has been paid more and more attention by casting technicians and is being studied continuously. Based on many years of factory practice and the analysis and research of a large number of data, the author has explored the calculation formula of effective pouring time of large castings that can be used for all kinds of metal materials, and can merge some unreasonable calculation formulas into a more perfect unified form for peer reference.

Practice has proved that compared with the traditional formula, it is not only more reasonable, applicable, simple and operable, but also saves the “guess and selection” process of some empirical coefficients. For most castings, fast pouring or slow pouring is caused by two important characteristic factors of the casting itself (Part g and δ) Determined. The effective pouring time can only be adjusted when the rising speed of liquid level is too fast or too slow due to the relatively high or low height of very few castings in the pouring position (such as large flat parts), but such castings are very few.

The calculated effective pouring time of large castings belongs to moderate pouring speed. When individual special castings need fast pouring, the calculated value can be taken as the lower control limit of effective pouring time; otherwise, when slow pouring is required, the upper control limit of calculated value can be taken. The fluctuation range of pouring time should be ± 10%.

To master the casting repair pouring time, it is necessary to flexibly grasp it according to the specific structure of the casting, the casting performance of the material, the temperature of the molten metal, and the setting of the riser, which is generally difficult to quantify.