Fig. 3. This histogram for sand system test results show 193 tests in an eight-hour period were within 3 points of the target.
图3. 哈特利试验结果 的柱状图，表明8小时 测定数据中与目标值 偏差在±3点以内的数 据为192个。
conductivity, which typically will improve variation on compact- ibility at the mold line.
Checking the Clay
A second key independent variable in green sand is the amount of live clay present in the sand, which is identified with the methylene blue clay test at Grede-St. Cloud. Te amount of live clay, which is critical to binding a green sand mold, is considered an independent variable because most sand cast- ing facilities have an auger speed or weight they use to set the amount of clay to go into the muller. In Fig. 5, each dot represents the average of 30 methylene
blue clay tests. Te fluctuation shown here was caused by equip- ment error. In the mixer, clay is added via a mixer and when it stops, sometimes extra clay falls into the auger. Years ago, Grede-St. Cloud had installed a slide gate to prevent that from happening, but it was discovered the slide gate stopped working. Once the slide gate was fixed, the variation in live clay amount went back down. After keeping tabs on its live clay variations for some time,
Grede-St. Cloud moved to a mass balance system in which it calculates based on a formula of how much clay will be lost when running a specific job. Tat calculation is used to deter- mine how much new clay will be added for each job. Tis calculation is made for every job that runs through the facility. It has proven to significantly reduce variation in the methylene blue clay test results.
粘土的含量，Grede-St. Cloud公司用亚甲基蓝法测试 活性粘土含量。活性粘土的含量，对于湿型砂造型的粘 结作用是至关重要的，认为是独立的变量，因为大多数 砂型铸造厂都由自己螺旋输送器的速度或重量核定进入 混砂机的粘土量。
图5中，每个点代表30次亚甲基蓝法测试的平均值。 这里显示的波动表明，这是由设备故障引起的。在混砂 机中，粘土在混砂机停机时加入，有时过多的粘土落入 螺旋输送器。几年前，Grede-St. Cloud公司已经安装 了滑动闸门防止这种情况发生，但有时会出现滑动闸门 停止工作。一旦滑动闸门被固定住，活性粘土含量的数 值将下降。
经过一段时间持续记录活性粘土量的变化
后，Grede-St. Cloud公司启用了一套“质量平衡”系 统，用公式计算生产某项产品时损耗的粘土量。能由计 算确定每次作业需加入多少新粘土。企业生产的每种产 品都进行这样的计算。亚甲基蓝法测试的结果证明能显 著减少变异（图6）。
注意粒度分布
衡量湿型砂质量第三个关键的独立变量是粒度分布。 粒度分布是不容易控制的，因为新砂是由供应商提供， 不是在工厂内能改变的。但铸造厂应尽量控制粒度分
Fig. 4. Wide fluctuations in compactability at one molding line were solved in October 2012 with the installation of a new piece of equipment.
图4. 一条造型线上可紧实性波动幅度大的问题在2012年10月安 装新设备后得到解决。
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FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION June 2015
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