According to the structure and size requirements of turbine guide and the characteristics of K438 alloy, vacuum investment casting is selected for pouring development, with vacuum degree<3 Pa. The selection of vacuum melting and vacuum casting solidification can effectively avoid air entrainment in the pouring process. The top-pouring gating system can directly fill the mold cavity. In order to avoid the under-casting defects at the exhaust edge, the top-pouring gating system is selected.
| Preheating temperature/℃ | Pouring temperature/℃ | Pouring time/s | Shell – casting heat transfer coefficient/W · m ^ – 2 · K ^ – 1 | Shell-air heat transfer coefficient/W · m ^ – 2 · K ^ – 1 |
| 1050 | 1480 | 5 | 800 | 10 |
The pouring cup is mainly used to receive the metal liquid from the ladle, prevent the metal liquid from splashing and overflowing, reduce the erosion of the liquid flow on the cavity wall and have the slag retaining function. Due to the deep internal liquid depth, the pool gate cup consumes more molten metal, which is not conducive to the production rate of the investment casting of the turbine guide, so the funnel gate cup is selected. The selection of circular runner in the gating system design can reduce the heat lost by the metal melt in the gating system, and make the metal melt fill the entire cavity of the guide by setting the appropriate pouring speed. The inner runner guides the liquid metal to flow smoothly into the mold cavity, controls the filling speed and direction, and adjusts the temperature difference and solidification sequence of various parts of the investment casting of the turbine guide. In order to avoid serious spraying when the liquid metal flows into the mold cavity, it is necessary to adjust the gate ratio when designing the inner runner so that the cross runner is used as the flow resistance section, so that the liquid metal can be filled smoothly during the pouring process. The pouring system is shown in the figure.
The designed gating system and casting are simulated and analyzed by ProCAST. In the simulation software, the investment casting material of turbine guide is K438 alloy, and the casting material is RE ⁃ FRACTORY contained in the material library_ Mullite, thickness is defined as 10.5mm. The investment casting and mold shell of the turbine guide are divided into about 100000 triangular meshes and about 700000 tetrahedral meshes. The simulation parameters of investment casting of turbine guide are shown in the table.