1. Pouring position and parting surface
According to the practical production experience for many years and the principle of accurate and reliable positioning of sand core, in order to ensure the accurate positioning of clay core, improve the dimensional accuracy, and facilitate the inspection of box size and wall thickness, three box molding process is adopted. The pouring position and parting surface are shown in Figure 1.
2. Core design
The core design is based on the principle of ensuring the dimensional accuracy, reducing the number of cores, improving the positioning accuracy and facilitating the operation of workers. The three-dimensional solid design software is used to optimize the core design, to avoid the interference between sand cores during assembly, and the positioning core head is designed to ensure its reliable positioning. The schematic diagram of clay core is shown in Figure 2.
3. Pouring system and cold iron design
The bottom injection gating system with filter device is adopted. The molten iron is introduced from the bottom dispersedly. The molten metal has less impact on the mold during the mold filling process, and the liquid level rises steadily, which is conducive to ensuring the casting quality of the rear inlet gas box. The design diagram of the gating system is shown in Figure 3.
3.1 Gating system design
According to the relevant data and production practice in recent years, the bottom flow rate, large flow rate and open gating system are adopted to make the hot metal filling stable and reduce the defects such as sand inclusion, secondary oxide slag and porosity. In this process design, the ratio of cross-sectional area of each unit is ∑ f straight: ∑ f horizontal: ∑ f inner = 1:2:3.
(1) Sprue: 1 φ 80mm sprue.
(2) Ingate: 16 35 mm ingates are used.
(3) Runner: 58 / 70 × 80mm trapezoidal runner, 2 in total.
3.2 Riser design
A total of 17 pieces of 120mm are set on the top of the casting × 180mm (high) cylindrical insulation riser plays the role of cavity exhaust and feeding.
3.3 Cold iron design
In order to prevent shrinkage and porosity defects at the intersection of relatively thick flange and wall thickness, external chill is designed in these parts, and the material is cast iron. The thickness of chill is designed according to 0.5-0.8 times of hot spot thickness. The schematic diagram of placement of chill is shown in Figure 4.
4. Melting and pouring design
Medium frequency furnace is used for smelting. In order to ensure that the casting quality meets the requirements of technical documents, the smelting and pouring process should be strictly controlled
(1) High purity pig iron, carbon scrap, recycled material and chemical material are used;
(2) Chemical composition control of original hot metal (%): C: 3.6-3.9; Si：1.45～1.55； Mn：0.15～0.20； P＜0.04； S≤0.020。
(3) Sandwich ball packing method and multi-stage inoculation were used to ensure the physical and chemical properties of the fuselage.
(4) Slag removal: high temperature static treatment is carried out in the furnace, and the temperature rises to 1500-1530 ℃ for 5-15min; If s content exceeds the process range, high temperature desulfurization treatment must be carried out to avoid secondary oxidation slag inclusion; Carry out slag removal in furnace and ladle to ensure the purity of molten iron.
(5) Pouring temperature control: the temperature of molten iron entering the mold cavity is controlled at 1350 ~ 1370 ℃, and the gun type thermometer is used to measure for many times to ensure that the temperature of molten iron entering the mold meets the process requirements.
4.5 simulation
The box casting process was simulated by using magma software.
4.5.1 flow field
The bottom pouring is open, and the pouring is stable. The specific structure and flow field are shown in Figure 5. From the hot metal filling, it can be seen that the pouring process is stable, without turbulence. At the same time, the velocity of hot metal in the cavity is less than 1m / s, which is in line with the process requirements.
4.5.2 temperature field
From the simulation of temperature field, it can be seen that the characteristics of temperature field after pouring are as follows: the temperature at the hot spot is higher, the temperature near the inner gate is higher, and the temperature field of the whole box is more uniform. The simulated photos of temperature field are shown in Fig. 6.
4.5.3 shrinkage prediction
Figure 7 is a simulation picture of shrinkage porosity. The density of the blue part in the picture is more than 95%. From the shrinkage porosity simulation results, it can be seen that the overall density of the box is high after solidification, and it has good internal quality.
4.5.4 simulation conclusion
After the casting process is calculated by the simulation, the casting process is smooth and turbulent. After the cold iron is reasonably set up, the solidification time of each hot spot is balanced and the tendency of shrinkage and loosening is small. Therefore, the casting technology of reasonable setting up pouring system and cold iron can be carried out.