QT500-7井盖上表面缩凹形成机理及防治措施

球铁井盖用大平面朝上的浇注工艺,在其筋或筋与筋交汇处的上表面常会出现一些缩凹,严重影响井盖的质量,甚至造成较高的废品率。通过分析缩凹部位的微元体凝固过程及缩凹形成机理,比较了井盖结构改进前后热节圆直径的变化,结果认为：防止缩凹的关键是保证实现顺序凝固,保持浇注过程中补缩通道畅通。并从结构设计及铸造工艺设计两方面提出了防止球铁井盖上表面缩凹的措施,这些方法在生产实践中已得到检验。

Formation Mechanism and Prevention Methods of Depressions in the Top Surface of QT500-7 Manhole Covers

Depressions in surface occurs on the surface of the junction of ribs when ductile cast iron manhole cover is produced by a casting process with large section upside,which results in a higher casting defective rate.The paper analyzes the solidification process of a differential element and the shrinkage mechanism and compares the variation of hot spot circle diameter before and after modification.The results show that directional solidification to maintain a smooth feeding is critical to avoid the shrinkage.Some prevention methods were proposed from two aspects of structural design and casting processing which has been verified by production practice.