general machinery. The casting weights range from 3 to 50 kg. The specification of cast iron covers HT250, HT300, QT450-15 and QT550-7. The thinnest casting wall thickness achieved is less than 4.5 mm. Compared with centrifugal castings, less melt is
needed for small and medium castings at less frequent intervals. However, there are more types of castings with additional specifications. Following are the difficulties Jintang discovered in applying the shortcut technology: • Because less melt is needed, dispensing, shipping and holding are difficult. The melt is susceptible to solidi- fication and sticking to the tank wall due to decreas- ing
temperature.Therefore, the traditional method using a cupola with medium frequency induction furnace was restored.
• Since there is no solidification process of the melt, its metallurgical properties are different from the remelt pig iron. If no proper measures are taken, the mechanical properties will decrease, especially for gray cast iron.
• Compared with the remelting of pig iron, the iron produced by the new technology has higher carbon content. Therefore, it is good for the production of ductile iron and vermicular cast iron, which requires higher carbon content, but not for gray cast iron. During the beginning of the application of the new
technology, a 6-ton tank was used to ship the melt. In the workshop, a 5-ton, 500-kw medium frequency induc- tion furnace is used for holding, and two 2-ton, 1,100- kw medium frequency induction furnaces are used for further heating. Because less melt is required, sticking of the melt occurred in 30% of cases. Including the use of the holding furnace, the total cost was higher than with a single medium frequency induction furnace. Meanwhile, substantial D-type graphite and white fractures appeared on casting edges. Therefore, the new technology had to be suspended while the shipping and treatment of the melt was redesigned. The following steps were taken to come to a solution: • The crane and hook of the ladle were modified; the 6-ton tank was replaced with a 20-ton tank, so the temperature decrease problem in shipping was solved and cost was reduced.
• The gas from the blast furnace was burned to heat the ladle above 800C, which was effective in preventing the melt from sticking to the ladle.
• The tank was covered with both a lid and insulation material.
• Overheating temperature and holding time were increased in the workshop. Meanwhile, good inoculation agents and immediate inoculation were adopted.
• More ductile and vermicular iron castings were arranged in production. By adopting these measures, the rate of sticking was
lowered to 0.9% or less, the usage of the melt increased to 70% or more, power consumption decreased from 700 kWh/ton to 350-400 kWh/ton, and the cost of castings decreased by 330 yuan per ton. Today, the casting quality
有：HT250,HT300,QT450-15,QT550-7，铸件壁厚最 小4.5mm。
相对于离心球墨铸铁管生产，普通中小型铸件具有铁 水需求量小、生产连续性差、铸件品种杂、铸铁牌号多 的特点，短流程铸造工艺具有较大难度，主要表现在以 下几方面：
1．由于铁水需要量小，高炉铁水的分配、运输、保温 难度大，往往因为铁水降温严重造成粘包，不但不能 降低成本，反而造成成本大幅升高，以至最后因得不 偿失，仍恢复到化冷料的常规工艺。
2．高炉铁水未经过凝固，冶金性能与生铁二次熔化的 铁水存在差异，如果不采取适当措施，会造成铸件性 能下降，尤其是灰铁铸件，受影响更大。 3．与生铁二次熔化相比，高炉铁水含碳量高，更适合 生产球墨铸铁、蠕墨铸铁等高碳当量的品种。 在采用短流程铸造工艺初期，铸造生产采用6t铁水 包运送高炉铁水，铸造车间配备1台5t中频电炉作为 保温炉，功率500kW，升温采用2台2t中频炉，功率 1100kW。由于铸造车间铁水使用量小，造成6t铁水包 粘包铁比例约30%，加上保温炉费用，成本比中频炉化 铁还要高，而且在灰铁铸件中大量出现D型石墨及边角 白口，短流程工艺被迫停用。
针对以上情况，重新设计了高炉铁水运输及 铁水处理方案：
（1）改造铸造车间熔炼跨天车及铁水包龙门钩，将原 来的6t小容量铁水包单独运输，改为与铸管共用20t 铁水包集中运输，既减少了铁水降温，又减少了运输 费用。
（2）利用高炉煤气，建设铁水包烘烤间， 铁水包温度始终保持在800℃以上，防止冷包接铁水。 （3）铁水包加盖并覆盖100～200mm保温材 料。 （4）铸造车间增加铁水过热温度、适当延长高温保温 时间、优选孕育剂、采用瞬时孕育等强化孕育措施。 （5）尽量多安排球墨铸铁、蠕墨铸铁订单。 通过以上措施，高炉铁水粘包比例降低到0.9%，高 炉铁水使用比例提高到70%以上，铸造铁水电耗从原来 的700kWh/t降低到350～400kWh/t，铸件成本降低 330元/t。产品质量稳定，达到了汽车行业对铸件的要 求。同时电炉熔炼效率得以大幅提高。在设备条件未改 变的情况下，熔炼时间从60分钟/炉降低到40分钟/炉， 炉衬寿命由原来的150炉提高到近300炉，年增加铁水 供应量7,800t。
三．注重高炉生产的技术进步
短流程铸造工艺的特点在于节能减排，如果没有高炉 生产的技术进步，高炉生产的高能耗、高排放会抵消甚 至超过短流程铸造工艺在铸造生产环节产生的节能减排 效果。也就是说，从整个流程来看，不一定节能减排。
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION Fall 2011
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