By designing the test device by pouring method, the thermophysical parameters of glass quartz sand used in actual sand mold casting production are tested, and the heat transfer coefficient of sand mold casting mold interface is obtained by using the reverse module in ProCAST software. The results are analyzed and compared. Combined with the turbine blades produced in the factory, the gating system is improved, and the flow field, flow field and The stress field in temperature field is simulated and analyzed, the rationality of gating system is verified, the location of shrinkage cavity and porosity casting defects in sand casting process is predicted, and the stress and deformation of hydraulic turbine blade are analyzed. The main work and research conclusions are as follows:
(1) Using the pouring method, through the self-designed test device, the temperature change curve of sodium silicate sand mold is measured, and the thermophysical parameters of sodium silicate sand are measured combined with the inverse algorithm. The mathematical model of thermal conductivity and specific heat of sodium silicate sand under this process condition is established.
(2) Using the reverse module in ProCAST software and taking the temperature change value of the mold measured by the pouring method as the known quantity, the change curve of the interface heat transfer coefficient between sand mold casting and mold with temperature is obtained, and the influence of different interface heat transfer coefficients on the simulation results is analyzed. By using the calculated interface heat transfer coefficient to simulate the temperature field, the simulation curve of mold temperature change is obtained, and then compared with the measured temperature value, It is concluded that the calculated interfacial heat transfer coefficient is basically in line with the reality.
(3) According to the two-dimensional wood model diagram of hydraulic turbine blade, the three-dimensional modeling is carried out by UG. According to the design principle of pouring and riser, the pouring system and riser of the blade are designed by modulus method, and the flow field in the sand casting process is simulated and analyzed by ProCAST software. The irrationality of the traditional stepped pouring system is pointed out, and then the pouring system is improved by adopting the bottom pouring system, The simulation results of flow field and temperature field show that the improved gating system has stable mold filling and no turbulence. Through the simulation of temperature field of hydraulic turbine blade, it is predicted that the positions of shrinkage cavity and porosity in the solidification process of blade are all located at the riser, which further explains the rationality of sand casting process. The stress field simulation analysis shows that the maximum deformation at the sharp corner of the discharge edge of the turbine blade reaches 50mm. It is necessary to add a certain amount of process reverse deformation in advance in the actual production.
Through the pouring method, the thermophysical parameters of sodium silicate sand mold are measured. The key of the test is to ensure one-dimensional heat transfer. However, due to the limitation of test conditions, it is difficult to achieve one-dimensional heat conduction in the real sense. If the test device is improved and better thermal insulation materials are used, the errors in the test process can be further eliminated. In addition, only the interfacial heat transfer coefficient of sand casting mold is studied, and the interfacial heat transfer coefficient of sand casting cold iron can be further studied.
Although the improved turbine blade gating system is reasonable in the simulation analysis and there is no turbulence, it still needs to be verified by the actual production, because there is still a certain gap between the simulation and the actual production. The sand mold casting defects predicted by temperature field simulation can also be verified by actual production.