Improvement method of shrinkage casting defects of special alloy gray cast iron

1. Improve the temperature field of castings

Through the simulation of the overall temperature field of the casting with the help of magma simulation software, the position of the runner in the casting is improved according to the simulation results, and the corresponding chilling measures are taken in the key areas and the thick wall areas where the shrinkage and porosity problems occur, so that the overall temperature field of the casting is uniform, the sequential solidification is realized, and the shrinkage and porosity risk is reduced. Comparing the temperature fields of schemes a and B, scheme B has a more uniform temperature field distribution at the hole where shrinkage occurs, and the hot spot in the key area is reduced, which effectively reduces the risk of shrinkage during solidification shrinkage, as shown in Figure 1.

(a) Scheme A
(b) Scheme B
(c) Temperature field of scheme A
(d) Temperature field of scheme B

2. Monitor the fluctuation trend of key parameters

Due to its particularity in the casting process, the method of setting control points and control parameters is usually used to monitor the casting quality. The metrological data of the production process can be analyzed by using the control chart method. After the casting has shrinkage defects, the conventional statistical analysis is used to make trend statistics on the data only. When the upper and lower limits of the data fluctuation specification are very small, the fluctuation and abnormal trend of its process parameters cannot be completely seen, so the potential failure factor cannot be found. By using the method of mean range (Xbar-R) control chart to compare and analyze the key parameters of the casting, it is found that the pouring temperature, silicon content, copper content and chromium content of the casting fluctuate greatly in the upper and lower limits of the control within a certain period of time (as shown in Figure 2), which intensifies the shrinkage tendency during solidification. By adjusting the pouring temperature and controlling the addition of Si, Cu and Cr elements, the shrinkage porosity tendency is effectively reduced.

(a) Mean range diagram of pouring temperature
(b) Mean range diagram of Si element
(c) Mean range diagram of Cu element
(d) Mean range diagram of Cr element

Through the implementation of improvement measures, Pt was carried out after the anatomical processing of the body, and the PT test results were not displayed, as shown in Figure 3. The improvement effect was obvious, and there was no repetition in the later production process.