Formation of macrosegregation of 5 t steel ingots cast in sand molds with and without water-cooled copper tube is simulated by solving macroscopic mass, momentum, species and energy conservation equations with the con...Formation of macrosegregation of 5 t steel ingots cast in sand molds with and without water-cooled copper tube is simulated by solving macroscopic mass, momentum, species and energy conservation equations with the consideration of shrinkage formation. Predicted macrosegregation pattern of the ingots shows a fair agreement with the experimental data. Both calculations and experiments reveal that some positive segregation patches are formed at the bottom of ingot. With the water-cooled copper tube inserted in the sand mold, the ingot cast has a less intensive macrosegregation. Mechanisms of macrosegregation formation are numerically analyzed. Explanations regarding the influences of fluid flow and temperature change upon the segregation formation are provided.展开更多
Cast shape during investment casting process dictates properties and service life of the casting. These properties are the function of cast part parameters (both static and dynamic), part geometry and hence mold geome...Cast shape during investment casting process dictates properties and service life of the casting. These properties are the function of cast part parameters (both static and dynamic), part geometry and hence mold geometry, nature and type of metal being cast, properties (extrinsic and intrinsic) and processing parameters (rate of heating, rate of cooling, rate of pouring). Improper and inadequate manipulation and modification of mold properties degrade the properties and life of casting altogether. A mathematical model is developed using standard transport equations incorporating all heat transfer coefficients (HTCs) to determine the effect of external mold heating on the properties of the final casting and a simulation is performed in C++ to validate it against experimental results. Pure iron is casted in investment molds of silica sand with zircon coating. Airflow near the mold surfaces was partially restricted due to geometry of the molds and arrangement of the pieces around a tree. The variations in heat transfer coefficient contribute towards total heat transfer out of mold surface. External heating is found to be very effective for improved casting properties. The mold heat transfer profile is found to be in good agreement with experimental values validating the effectiveness of mold heating.展开更多
Effect of two-stage sintering parameters such as heating rate, top sintering temperature and holding time, sintering temperature and holding time at the second stage on relative density, transverse rupture strength(TR...Effect of two-stage sintering parameters such as heating rate, top sintering temperature and holding time, sintering temperature and holding time at the second stage on relative density, transverse rupture strength(TRS) and microstructures of powder injection molded Ti(C, N)-based cermets were investigated, by means of Archimedes’s method, three-point bending test and micrographic analysis. The results show that the optimum sintering cycle for powder injection molded Ti(C, N)-based cermets comprises rapid heating (10℃/min) at low temperatures, slow heating (5℃/min) at intermediate temperatures, holding at the highest sintering temperature (1420℃) for a short time (10min), and holding at the second stage (1360℃) for a longer time (6h) to avoid grain coarsening, and that its TRS reaches 624MPa, and there are little pores in their microstructures.展开更多
基金supported by "High-end CNC machine tools and basic manufacturing equipment" Major Science and Technology Project of China(No.2009ZX04014-081)Post-Doctor Project of China (No.20080431162)Young Expert Science Foundation of Harbin University of Science and Technology(No.2008XQJZ005)
文摘Formation of macrosegregation of 5 t steel ingots cast in sand molds with and without water-cooled copper tube is simulated by solving macroscopic mass, momentum, species and energy conservation equations with the consideration of shrinkage formation. Predicted macrosegregation pattern of the ingots shows a fair agreement with the experimental data. Both calculations and experiments reveal that some positive segregation patches are formed at the bottom of ingot. With the water-cooled copper tube inserted in the sand mold, the ingot cast has a less intensive macrosegregation. Mechanisms of macrosegregation formation are numerically analyzed. Explanations regarding the influences of fluid flow and temperature change upon the segregation formation are provided.
文摘Cast shape during investment casting process dictates properties and service life of the casting. These properties are the function of cast part parameters (both static and dynamic), part geometry and hence mold geometry, nature and type of metal being cast, properties (extrinsic and intrinsic) and processing parameters (rate of heating, rate of cooling, rate of pouring). Improper and inadequate manipulation and modification of mold properties degrade the properties and life of casting altogether. A mathematical model is developed using standard transport equations incorporating all heat transfer coefficients (HTCs) to determine the effect of external mold heating on the properties of the final casting and a simulation is performed in C++ to validate it against experimental results. Pure iron is casted in investment molds of silica sand with zircon coating. Airflow near the mold surfaces was partially restricted due to geometry of the molds and arrangement of the pieces around a tree. The variations in heat transfer coefficient contribute towards total heat transfer out of mold surface. External heating is found to be very effective for improved casting properties. The mold heat transfer profile is found to be in good agreement with experimental values validating the effectiveness of mold heating.
文摘Effect of two-stage sintering parameters such as heating rate, top sintering temperature and holding time, sintering temperature and holding time at the second stage on relative density, transverse rupture strength(TRS) and microstructures of powder injection molded Ti(C, N)-based cermets were investigated, by means of Archimedes’s method, three-point bending test and micrographic analysis. The results show that the optimum sintering cycle for powder injection molded Ti(C, N)-based cermets comprises rapid heating (10℃/min) at low temperatures, slow heating (5℃/min) at intermediate temperatures, holding at the highest sintering temperature (1420℃) for a short time (10min), and holding at the second stage (1360℃) for a longer time (6h) to avoid grain coarsening, and that its TRS reaches 624MPa, and there are little pores in their microstructures.
