铸件鼠尾形成机理的分析

鼠尾的形成是由于铸型型腔局部表面干砂层受热膨胀，当膨胀力大于滑移阻力时，干砂层产生了剪切滑移。滑移的阻力主要来自相邻的干砂层。阻力随干砂层长细比的增加而急剧减小。提高型砂的热强度，减少干砂层的长细比，能有效增加鼠尾产生的临界应力σc，有效防止鼠尾的产生。当干砂层长细比小于1/2或热压应力不大于水分饱和凝聚区的湿压强度时，绝不可能产生鼠尾。

ANALYSIS OF FORMING MECHANISM OF RATTAIL ON CASTING

The formation of the rat tail is because that the partical dry molding sand layer on the internal surface of mould cavity is heated to high temperature and expanses. When the expansion force is bigger than the total slipping resistance, the hot molding sand layer slips and bulges. The majority of resistance comes from the neighboring hot molding sand layer. The resistance decreases intensely when the slenderness ratio of the hot molding sand layer increases. The increase of molding sand's hot strength and the decrease of the slenderness ratio of the hot molding sand layer can increase the critical stress effectively and prevent rat tail effectively. When the slenderness ratio is less than 1/2 or the hot compression stress is not bigger than the wet compression strength of the molding sand, the rat tail should never come into being.