对铸铁件气孔和气缩孔防止措施的认识

Understanding of Measures to Prevent Blowhole and Shrinkage-Blowhole Defects of Iron Castings

气孔是由铁液内部的气体形成的。降低型砂、芯砂发气量、增加和增大排气眼、平稳浇注等常用气孔防止措施只能排除和减少铁液外围的气体和有限地减少进入铁液内部的气体,但未必能排除已进入铁液内部的气体,因此这些措施防止气孔的作用往往是有限的,并不能彻底消除气孔。排除铁液内部气体是防止气孔的关键,因而要尽量提高液面温度,使液面推迟形成氧化膜,使铁液内部气体在液面被氧化膜封闭之前有充分时间排出。对防止气孔应当注意的其它问题也进行了介绍,指出气缩孔的根源不是气孔而是缩孔,因此不可能采用防止气孔的方法,只能采用防止缩孔的方法消除气缩孔。还例举了防止气孔和气缩孔的实例。

The blowhole is formed from the gas inside the iron melt. The common-used measures to prevent blowhole such as reducing gas evolution of the molding sand and core sand, increasing number of venting holes, enlarging venting holes, pouring without turbulence, etc. could only remove or reduce the gas outside the iron meh and in a limited degree reduce the volume of the gas entering the iron meh, but couldn＇t remove the gas having entered the iron meh, theretbre the blowhole prevention effect of these measures was often limited and could not thoroughly eliminate blowholes. To remove out the gas inside the iron meh is the most important key measure to prevent the blowhole formation. And the key measure to remove out the gas inside the iron meh is to elevate as possible the top surface temperature of the iron meh inside the mold cavity in order to postpone the oxide fihn formation on the melt surface so that there is sufficient time for the gas inside the iron melt to escape through the top surface of the melt before the top surface being closed by the oxide fihn. Some other problems which should he pay attentions to prevent blowholes were introduced. It was pointed out that the shrinkage-blowhole is formed not from a blowhole, but from a shrinkage cavity, and therefore, it can be eliminated not by adopting blowhole-preventing measures, but only by adopting shrinkage-preventing measures. Some practical examples of blowhole prevention and shrinkage-blowhole prevention were given.