离心铸造大型汽缸套凝固过程的数值模拟及实验研究

本文以离心铸造280型柴油机汽缸套为对象进行了数值模拟及实验研究。计算采用了全隐格式的直接差分法,用热焓法处理潜热;在边界处理中考虑了模套外表面的对流换热及铸件内表面的辐射换热。同时,设计制造了一套柔性传动的刷一环测温装置,获得了实测温度场。数值计算结果与实测温度场基本吻合。由计算结果和对铸件本体的解剖可见:离心铸造汽缸套的凝固过程主要取决于传热的综合效应,在不同部位表现出不同程度的双向凝固,不存在明显的同时凝固区域;缩孔产生于临界固相率曲线封闭位置深入断面中心的情况下;缩松产生于固相率梯度很小的场所,特别是遍布于固相率梯度为负值的区域。改变与传热有关的工艺条件可以改变缸套的凝固方式,有可能控制或避免缩孔、缩松缺陷。

NUMERICAL SIMULATION AND EXPERIMENTAL INVESTIGATION ON THE SOLIDIFICATION PROCESS OF LARGE CYLINDER SLEEVES OF CENTRIFUGALLY CASTING

In this paper, the solidification process of centrifugally cast cylinder sleeves(model 280), used on marine Diesels is studied by means of numerical simulationas well as experimemt ally. Fully implicit DFDM is employed, and the latentheat release is handled with the enthalpy form. The convective heat transfer atthe outer surface of the mold and radiation heat transfer at the inner surface ofthe cylinder sleeve are considered in detail. The apparatus with the brush-ring andflexible drive is designed to obtain the temperature field of the cylinder sleeveunder real casting conditions. The computed temperature field of the cylinder sleeve during solidificationchecks fairly well with experimental results. It is seen that the solidificationprocess of centrifugally cast cylinder sleeves depends to a large extent on theheat transfer process that the casting-mold-ambieni system undergoes. Shrinkage porosity exists in the region where solid, fraction gradient is verysmall, especially in region with negative solid fraction gradient. Numericalsimulation indicates that shrinkage defects can be avoided by changing thetechnological conditions related to heat transfer of the casting-mold-ambientsystem.