due to a combination of low silica level and coarse sand with a narrow distribution. Raising the seacoal level did not help.
Fixing the Problems Te main problems at Landers Foundry were a high
moisture requirement along with low density and specimen weight due to low silica content, high permeability due to coarse sand with a narrow and sharply peaking distribution, low fines, low green strength and high friability due to low active clay and high dead clay, and excessive carbon content. To correct the problems, Landers Foundry suspended
its carbon addition to allow the excessive carbon to gradu- ally burn off. Te seacoal and dead clay levels were diluted by adding a blend of sand designed to bring the silica level up and lower the clay. Cereal was added to reduce friability. At shakeout, the casting facility began adding 10-15% of a blend of new sand, 6% clay and 1.5% cereal. Te metalcast- ing facility also purchased additional sand testing equipment to complement its sand control program. Additionally, the base sand aggregate was changed to a sand with a broader distribution, but finding the correct granulometric distribution of the new sand fed into the sys- tem was difficult. On the Colombian market, new sand with four consecutive screening categories and AFS GFN higher than 58 was not available. Landers Foundry began to pur- chase sand from various suppliers and tested different mixes with the different types of sand available. Finally, an ideal sand mix was found. Now, the AFS fineness numbers range between 65 and 67, and the surface finish of the castings is substantially better, even with low levels of seacoal aggregate. After making the changes, the sand and molding problems
were remedied, and casting defects were greatly reduced. Scrap rate has dropped to 9% from 22% and continues to decrease. ■ To receive this digital magazine in the future, go to
www.globalcastingmagazine.com.
Mauricio Aycardi is director of operations for Landers Y Cia. S.A., Medellin, Colombia. Mary Beth Krysiak (deceased), Sand Technology Co. LLC, New Hudson, Mich., provided sand testing services and taught sand testing tech- niques at Landers. Cesare Frigo, director of SPACE, Pozzolo, Italy, provided sand plant and engineer- ing. Dean Martin, sales manager for Hunter Automated Machinery Corp., Schaumburg, Ill., provided automatic mold- ing machine and mold handling equipment.
解决问题
Landers 铸造厂的问题主要为水分含量高，硅砂含 量过低导致的型砂密度和样重不足，砂粒粗糙并且粒 度分布集中导致透气性过高，活性土含量偏低、死土 含量偏高和碳含量偏高导致微粒含量低、湿压强度低 和型砂过脆。
为了解决这些问题，Landers 铸造厂暂停了碳的 加入，使多余的碳慢慢烧掉。加入一种混合砂，增加 硅砂含量，降低膨润土含量，从而稀释了煤粉与死 土的含量。加入玉米淀粉以改善脆性。在落砂时加入 10-15%的混合砂、6%的膨润土与1.5%的玉米淀粉。 同时，增购型砂检测设备，完善了型砂控制系统。 同时，原砂更换为粒度分布更宽泛的砂，但是确定 加入系统中原砂的粒度分布比较困难。在哥伦比亚市 场，粒度分布连续四个筛目以上并且AFS粒度高于58 的新砂不存在。Landers 铸造厂开始从不同供应商采 购原砂并且测试了不同厂家的原砂混合而成的原砂， 最终找到一种理想的混合方式。现在，AFS粒度在65 与67之间，即使煤粉含量偏低，表面光洁度比原来也 有了根本改善。
在做了这些修正之后，型砂和砂型问题得到了解 决，铸件缺陷率大幅降低。废品率从22%降至9%并且 还在继续降低。■
请点击
www.globalcastingmagazine.com获取电子版 杂志.
Mauricio Aycardi是Lander公司的运营总监。Sand Technol- ogy公司的Mary Beth Krysiak提供了型砂测试设备并且培训了 Landers公司的型砂测试技术员。意大利Pozzolo SPACE公司的 主管Cesare Frigo提供了型砂设备和设计。Hunter Automated Machinery Corp公司的销售经理Dean Martin提供了自动造型设 备和砂处理设备.
The original test casting (far right) showed burn-in, rough casting surface, friable mold edges, and fins and flash. The most recent version of the same casting is shown, defect-free, on the far left.
最初的测试铸件（最 右）上可见到化学粘 砂、表面粗糙、型边 脆弱以及毛刺飞边等 缺陷，最左边的铸件 为最新铸造的同样铸 件，可见，缺陷已经 消失。
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION Summer 2011
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