防止首饰铸造缩松缺陷的工艺措施

Technological Measures of Preventing Shrinkage Porosity in Jewelry Castings

采用差热分析仪、体视显微镜、扫描电镜、微区能谱分析仪等手段对石膏型首饰铸件的缩松缺陷进行分析。结果表明,首饰铸件缩松是凝固枝晶生长过程中枝晶间被孤立的金属液池得不到补缩而形成的。合金性质、铸件结构、浇注系统、铸型温度、浇注工艺等是首饰铸件枝晶状生长和缩松缺陷的影响因素。为防止缩松缺陷,生产时要优先选择熔点适宜、凝固温度范围较窄的合金,同时优化首饰铸件结构,合理设置浇注系统,避免结构差别过大的铸件同时浇注。另外,合理控制铸型温度及浇注温度,并借助离心浇注或真空吸铸等方式为金属液提供足够的补缩压力。

DTA,stereo microscope,SEM and micro-area EDS were used to observe and analyze the shrinkage porosity in the gypsum mold jewelry castings.The results show that during the solidification process,the crystal grows in dendritic form and the shrinkage porosity generated in the dendrite gaps is caused by insufficient feeding of external liquid metal.Some parameters,such as alloy properties,casting structure,pouring system,mould temperature and pouring process,have significant impact on the dendritic growth and shrinkage porosity.To avoid shrinkage porosity defect in jewelry casting,alloy materials with suitable melting point and narrow solidification range should be selected preferentially,and jewelry structure and pouring system should be optimized,and castings with markedly different structures should not be poured at the same time,meanwhile,the mould temperature and pouring temperature should be controlled reasonably,and sufficient feeding force should be provided by centrifugal pressure casting or vacuum suction casting.