精铸型壳“墨点”和铸件“黑皮”分析

Ink-point in Shell Mold and Black-face in the Investment Castings

以锆石砂粉为面层、高岭石系耐火材料为背层制成的精铸型壳浇注不锈钢铸件,经常在铸件表面出现大面积“黑皮”和相互孤立的凹陷疤痕,严重影响铸件质量。通过生产现场跟踪调查,结合俄歇能谱分析等手段,对缺陷部位化学组成和形成原因进行分析探讨。指出:铸件表面的疤痕与型壳表面“墨点”直接相关;而“黑皮”主要是型壳面层中的氧化铁与铸件表面氧化产生的各种金属氧化物反应生成的尖晶石型复杂化合物。在此基础上,提出了防止此类缺陷的措施。

Severe-area black-face and concave scar often appear in surface of the investment castings, especially stainless steel castings, using shell mold made of ZrO2 as face layer and kaolinite refractory as back layer, which is severely detriment to the quality of the investment castings. Chemical properties and formation of defect position have been analyzed by energy diffusion analyzer based on worksite investigation. It is revealed that surface scar in the castings is remarkably relevant to the ink-point in shell-mold, and the blackface is composed of spinel complicated compound, which is created by reaction between Fe2O3 in face-layer and different metal oxidizer from oxidation on surface of castings. Based on above mentioned analysis, the counter-measures eliminating these defects were expounded.