Porosity is a main defect in aluminum alloy castings, which is also thought to be severe in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring. Fu...Porosity is a main defect in aluminum alloy castings, which is also thought to be severe in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring. Fundamental experiments were carried out to evaluate the effect of process parameters such as the melt treatment, the cooling rate and the density of expanded polystyrene （EPS） foam on porosity in A356.2 bar casting. The effect of melt treatment including degassing and refining was investigated. The effect of cooling rate was also evaluated by changing the mold packing material such as the silica sand, the zircon sand and the steel shots. Gas entrapment due to the turbulent metal flow during mold filling in conventional molding process results in porosity. Mold filling sequence in lost foam process is different from that in conventional molding process. The effect of molten metal flow was estimated by comparing the density of the casting by conventional sodium silicate molding with that by lost foam process. Density measurement was conducted to analyze the extent of porosity in the casting. Source of the porosity in lost foam process can be divided into two factors, i.e. turbulence in molten metal flow and entraining residue or gas from the pattern during pouring.展开更多
The velocity profile determined by the gas pressure in the gas gap during molten metal filling in Lost Foam Process was numerically simulated. The results show that the molten metal flows forward in a circular-arc sha...The velocity profile determined by the gas pressure in the gas gap during molten metal filling in Lost Foam Process was numerically simulated. The results show that the molten metal flows forward in a circular-arc shape from the ingate, which is different from that in traditional green sand casting.展开更多
The effects of modification, grain refinement, polystyrene pattern, pouring temperature and reduced pressure degree on aluminum alloy porosity in lost foam casting (LFC) process were studied. The results show that the...The effects of modification, grain refinement, polystyrene pattern, pouring temperature and reduced pressure degree on aluminum alloy porosity in lost foam casting (LFC) process were studied. The results show that the solidification rate of LFC process is slower than that of resin sand process or clay sand process. The effect of modification and grain refinement on the aluminum alloy casting density in LFC is greater than that on resin sand process. Through α Al phase refinement process with 0.2%Ti for aluminum melt, the subversive effect of Sr modification in LFC process is decreased greatly, and the aluminum casting density in LFC process is nearly equal to that in resin sand process. To decrease the porosity of aluminum castings in LFC process, lower density of polystyrene pattern, higher pouring temperature (760～780 ℃) and lower reduced pressure degree (≤20 kPa) should be applied.[展开更多
Lost foam casting (LFC) is regarded as a cost-effective, environment-friendly vital option to the conventional casting process for production of near-net shape castings with high quality. Effect of vacuum on the solid...Lost foam casting (LFC) is regarded as a cost-effective, environment-friendly vital option to the conventional casting process for production of near-net shape castings with high quality. Effect of vacuum on the solidification process and microstructure of LFC magnesium alloy were explored. The results indicate that vacuum plays a very important role in the heat transfer during mould filling and solidification periods, it increases the cooling rate of the filling melt, but greatly decreases the cooling rate of the casting during solidification period, and the solidification time of the casting is greater than that without vacuum. The microstructure of LFC magnesium alloy is rather coarse. Compared with that without vacuum, the microstructure of the LFC magnesium alloy under vacuum is more refined and has less precipitatedβ-phase, which is formed at the grain boundry and around the Al-Mn compound particle.展开更多
文摘Porosity is a main defect in aluminum alloy castings, which is also thought to be severe in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring. Fundamental experiments were carried out to evaluate the effect of process parameters such as the melt treatment, the cooling rate and the density of expanded polystyrene （EPS） foam on porosity in A356.2 bar casting. The effect of melt treatment including degassing and refining was investigated. The effect of cooling rate was also evaluated by changing the mold packing material such as the silica sand, the zircon sand and the steel shots. Gas entrapment due to the turbulent metal flow during mold filling in conventional molding process results in porosity. Mold filling sequence in lost foam process is different from that in conventional molding process. The effect of molten metal flow was estimated by comparing the density of the casting by conventional sodium silicate molding with that by lost foam process. Density measurement was conducted to analyze the extent of porosity in the casting. Source of the porosity in lost foam process can be divided into two factors, i.e. turbulence in molten metal flow and entraining residue or gas from the pattern during pouring.
文摘The velocity profile determined by the gas pressure in the gas gap during molten metal filling in Lost Foam Process was numerically simulated. The results show that the molten metal flows forward in a circular-arc shape from the ingate, which is different from that in traditional green sand casting.
文摘The effects of modification, grain refinement, polystyrene pattern, pouring temperature and reduced pressure degree on aluminum alloy porosity in lost foam casting (LFC) process were studied. The results show that the solidification rate of LFC process is slower than that of resin sand process or clay sand process. The effect of modification and grain refinement on the aluminum alloy casting density in LFC is greater than that on resin sand process. Through α Al phase refinement process with 0.2%Ti for aluminum melt, the subversive effect of Sr modification in LFC process is decreased greatly, and the aluminum casting density in LFC process is nearly equal to that in resin sand process. To decrease the porosity of aluminum castings in LFC process, lower density of polystyrene pattern, higher pouring temperature (760～780 ℃) and lower reduced pressure degree (≤20 kPa) should be applied.[
基金Project (2005037697) supported by China Postdoctoral Science Foundationproject (Y04850-61) supported by Creative Program of Nanjing University of Aeronautics and Astronautics
文摘Lost foam casting (LFC) is regarded as a cost-effective, environment-friendly vital option to the conventional casting process for production of near-net shape castings with high quality. Effect of vacuum on the solidification process and microstructure of LFC magnesium alloy were explored. The results indicate that vacuum plays a very important role in the heat transfer during mould filling and solidification periods, it increases the cooling rate of the filling melt, but greatly decreases the cooling rate of the casting during solidification period, and the solidification time of the casting is greater than that without vacuum. The microstructure of LFC magnesium alloy is rather coarse. Compared with that without vacuum, the microstructure of the LFC magnesium alloy under vacuum is more refined and has less precipitatedβ-phase, which is formed at the grain boundry and around the Al-Mn compound particle.
