1. Defect analysis of original process plan
In the original process, two blind risers are set at positions a and B in Fig. 1, and the blind risers are sand mold risers. Due to the low feeding efficiency of sand mold riser and insufficient feeding liquid, shrinkage porosity occurs. The process is simulated and analyzed again by simulation software, and the shrinkage and micro shrinkage criteria are checked, which shows that there is an obvious tendency of shrinkage defects. The simulation results are shown in Figure 2.
A large number of slag inclusion defects appeared in a and C of the test castings in Fig. 1. The preliminary judgment is mainly related to the gating system setting
(1) The original process is set with 2 units ϕ 60 mm inner gate, 1 ϕ 100 mm sprue, 1 for ladle ϕ 70 mm nozzle. During the pouring process, the sprue is not filled with molten steel, the molten steel is seriously oxidized, and a large amount of slag enters into the mold cavity.
(2) Set 2 ϕ The flow velocity of the inner gate reaches 0.8 m / s, the molten steel is sprayed into the mold cavity, the molten steel splashes to form slag inclusion, and the oxide slag adheres to the upper box with the flow of molten steel.
(3) The inner gate is set on two flanges. When the liquid steel is filled with the third flange, it will flow backward and form oxide slag.
By checking the tracking particle criterion in the simulation software, the whole slag inclusion is all retained at a and C in Fig. 1, which is consistent with the defect location of the real object. The specific filling results are shown in Fig. 3.
2. Process optimization and simulation analysis
After detailed analysis of the principle of shrinkage porosity, slag inclusion, porosity and other casting defects, the original process was optimized and verified by software simulation. The specific process adjustment is as follows:
(1) The original riser A and B are combined into an oval heating riser to improve the feeding capacity of the riser and solve the shrinkage defects. The simulation results are shown in Figure 4.
(2) The sprue was modified to ϕ The 100 mm sprue is changed to 80 mm to ensure that the molten steel is always filled with the sprue during the filling process and reduce the secondary oxidation of the molten steel.
(3) The slag collecting sprue is set to introduce the first strand of molten steel into the slag collecting sprue to ensure the purity of molten steel entering the cavity.
(4) Four ϕ In order to ensure the smooth flow of molten steel, the flow rate of inner gate should be kept at 0.5 m / s.
(5) The inner gate is respectively set on three flanges and connected by dichotomy to ensure that the flow of each inner gate is uniform and the liquid level rises smoothly without turbulence.
The process scheme of the optimized gating system is shown in Figure 5. The filling process is verified by software simulation. Through the analysis of secondary oxide slag and particle tracking results, the whole mold filling process is stable and oxide slag is greatly reduced. The simulation results are shown in Figure 6.