Mold Filling Analysis and Solidification Analysis with the Measurement of Interfacial Heat Transfer Coefficient in Expendable Pattern Casting Process for Aluminum Alloys
| Autor: | Chen, Jui-Chin, 陳瑞琴 |
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| Rok vydání: | 1998 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 86 This thesis research is to study the fluid flow and heat transfer phenomena for the evaporative pattern casting (EPC) of A356 aluminum alloy. For fluid flow phenomena, numerical simulation method is employed to simulate the flow pattern of molten aluminum during the filling of casting. For solidificatio for the evaporative pattern casting (EPC) of A356 aluminum alloy. For fluid flow phenomena, numerical simulation method is employed to simulate the flow pattern of molten aluminum during the filling of casting. For solidification and heat transfer phenomena, temperature measurement in an unidirectional heat transfer system along with the Inverse Method are used to measure the interfacial heat transfer coefficient between the casting and the binder-free sand. The measured interfacial heat transfer coefficient is then applied to solidification model to predict the temperature variation in a EPC casting. A corresponding EPC casting is made and temperature measurements are taken to compare with the simulated results.For the filling of a EPC casting, one major difficulty to simulate the fluid flow phenomena is how to taken into account the effect of the strong back pressure generated by the evaporation of the polystyrene pattern on the flow pattern. In this study, free surface boundary conditions are modified along with the incorporation of a back force (approximately 260 cm/sec2) to handle this back pressure problem. For the experimental measurement of interfacial heat transfer coefficient; h, a major difficulty is how to design and fabricate an unidirectional heat transfer condition for EPC casting. In this study, a CO2 sand mold is used to fix the thermocouples and heat insulating transfer system. Furthermore, temperature measurements are made for two EPC castings; one rectangular and the other one stepwise. The measured temerature data are compared with the simulated ones. Possible reasons besides the interfacial heat transfer heat transfer coefficient are discussed if discrepancy exists between the two results.Temperature measurements from a stepwise EPC casting poured horizontally from the side reveal that molten aluminum makes contacts with the thermocouples in the order of S#1, S#2, S#3, and S#4. This flow pattern differs from the flow pattern usually observed in gravity casting. With the modified free surface boundary conditions and back force introduced in this study, the simulated flow pattern in the stepwise casting shows uniform expansion in all three directions, which is consistent with the measured flow pattern. For the measurement of interfacial heat transfer coefficient, the value calculated from the Inverse Method is again verified in the unidirectional heat transfer system. With reference to the surface temperature of casting, the values of h can be categorized into three ranges. The value of h is approximately 0.012 cal/sec.cm2.℃for temperature above the liquidus temperature. It becomes 0.006 cal/sec. cm2.℃for temperature below the eutectic temperature. Foe the temperature in between, the value of h is approximately 0.008 cal/sec. cm2.℃. For the simulation of solidification heat transfer in EPC casting, it is found in this study that other than h, the thermal conductivity of sand and the dependence of latent heat released mode on cooling rate also have significant effects on the results of the simulation. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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