球墨铸铁件表层球化不良的原因分析

Analysis of the Causes of Nodular Iron Parts Poor Spheroidization

从固化剂、涂料、冷速、回用砂4个方面分析了球墨铸铁件表面层球化不良缺陷形成的原因,提出了相应的防止措施,得出以下结论:(1)采用低S固化剂可以很明显地降低球化不良表面层厚度,减少型砂中的w(S)量和适当提高铸件表层的w(Mg)量,有助于减薄球化不良表面层厚度;(2)冷铁周围、薄壁处冷却速度较快,可减少铁液与型砂中S的反应时间,铸型表面铁液中的有效Mg或有效RE的含量会损耗较少,有利于避免出现石墨球化不良缺陷;(3)使用新砂、低S固化剂在一定程度上能改善球墨铸铁件表面层的石墨形态,Si-Mg合金涂料对铸件表面层的石墨形态有明显改善作用。

The reasons for the formation of spheroidized defects in the surface layer of nodular iron castings were analyzed from four aspects:curing agent,coating,cooling rate and recycled sand. The corresponding prevention measures were proposed and the following conclusions were drawn:(1)Using low S curing agent could obviously reduce the thickness of the spheroidized surface layer,reduce the amount of w(S)in the molding sand and appropriately increase the amount of w(Mg)in the surface layer of the casting. It helped to reduce the thickness of the spheroidized surface layer.(2)The cooling rate around the cold iron and the thin wall was faster,which could reduce the reaction time of S in the molten iron and the molding sand. The consumption of effective Mg or effective RE in the molten iron on the surface of the mold was reduced,which was beneficial to avoid the bad spheroidization of graphite.(3)Using new sand,low S curing agent could improve the graphite morphology of the surface layer of nodular iron parts to a certain extent. Si-Mg alloy coating had a significant improvement on the graphite morphology of the surface layer of castings.