石墨化膨胀引起制动鼓粘砂缺陷的防止措施

Measures to Prevent Graphitization Expansion-Caused Penetration Defect of Brake Drum

介绍了制动鼓铸件的生产情况,对冒口下部铸件表面粘砂缺陷的原因进行了分析。采用MAGMA软件对凝固过程进行模拟,结果显示:冒口颈凝固早于铸件最大热节,冒口颈邻近的铸件表层开始凝固时间与铸件最大热节接近,该处的表层强度不足以抵抗热节中心石墨化膨胀产生压力,而且冒口与铸件之间的型砂强度较低,以上情况导致铁液从铸件热节溢出进入砂层而形成粘砂缺陷。防止措施为:加大冒口颈厚度,让铸件热节石墨膨胀压力释放到冒口中。生产结果显示:铸件不再产生上述粘砂,铸件返修率下降至零。

The production situation of brake drum casting was introduced,the reason causing metal penetration defect on the casting surface area under the riser was analyzed. By using MAGMA software,the solidification process was simulated. The result showed：the riser neck solidified earlier than the biggest hot spot of the casting,the beginning time of casting surface area adjacent to the riser neck was near to the biggest hot spot of the casting,the strength of the surface layer of casting in that area was not enough to resist the graphitization expansion pressure from the hot spot center,and further more,the strength of the molding sand between riser and casting was relatively lower. Above situation led to that the iron melt overflowed from the hot spot of casting,entered into sand layer and caused metal penetration defect formation. The measures to avoid defect were：increasing thickness of the rise neck to allow the graphitization expansion pressure releasing into the riser. As the result,the penetration defect no more occurred with the castings,and the repairing rate of casting decrease to zero.