高Ni球墨铸铁排气歧管缩孔和缩松的消除

Elimination of Shrinkage Porosities and Cavities of High Ni Nodular Iron Exhaust Manifold

介绍了高Ni球墨铸铁排气歧管铸造工艺的改进过程。高Ni球墨铸铁w(Si)量较低,w(Cr)量较高,浇注温度高,缩松、缩孔倾向大。为消除缩松、缩孔,试验了4种工艺方案。方案1:铸件背面向上,在铸件顶面和侧面设置冒口,试图用冒口补缩来消除缩松、缩孔,结果缩孔更大。方案2:铸件背面向下,内浇道设在铸件侧面,结果缩松、缩孔仍然未能消除。方案3:仍采用方案2的浇注系统,在热节部位设置冷铁,结果缩松、缩孔消除,但放冷铁操作不便,铸件清理也较困难。方案4:采用具有鸭舌形冒口颈的冒口,使冒口颈在液态补缩结束后快速凝固封闭,防止凝固后期石墨化膨胀将铁液挤进冒口,充分利用石墨化膨胀进行补缩,结果缩松、缩孔消除。

The casting method improving process of a high-Ni nodular iron exhaust manifold was introduced. Since the high Ni nodular iron had lower Si content,high Cr content,and high pouring temperature to be adopted,therefore,its shrinkage defects （porosities and cavities） tendency was quite serious. In order to eliminate shrinkage defects, 4 casting methods were tried. Method 1 ：placing the back surface of the casting upwards,setting risers on the top and at the side of the casting with the purpose of using the risers feeding to eliminate shrinkage defects. However,the shrinkage defects became even bigger. Method 2：placing the back surface of the casting downwards,ingates were set at side of the casting. As the result, the shrinkage defects were still not eliminated. Method 3：using the same gating system as used in the method 2, setting chilis at hot spots of the casting. As the result, the shrinkage defects had been eliminated, but the operation of setting chills was inconvenient, and the casting cleaning was also quite difficult. Method 4：using risers with duck tongue-shaped neck to make the riser necks fast solidified and blocked after the liquid feeding ended to avoid the graphitization expansion in the late stage of solidification squeezing the iron melt into the risers and thereby to fully use the graphitization expansion for feeding. As the result,the shrinkage defects had been eliminated.