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Green Sand Control Best Practices


Regular sand tests performed at Grede-St. Cloud helped identify variations and reduce their causes to achieve better operation.


AL JACOBSON, GREDE-ST. CLOUD, ST. CLOUD, MINNESOTA 湿型砂质量控制的最佳方法


Grede-St. Cloud公司对型砂进行常规的性能检测,有助于确定型砂性能参数的 变化,排除其产生的原因,让作业状况更好。


美国明尼苏达州圣克劳德市, Grede-St. Cloud公司,阿尔•雅各布森 G


reen sand control in a metalcasting facility relies on reducing the variation in key measurable aspects of sand properties. All metalcasting facilities make good sand at times and bad sand at times. Success-


ful plants make good sand most of the time. Reducing variation in green sand systems consists of determin-


ing the key independent variables, finding a method to quantify current variation and implementing improvements to reduce varia- tion and monitor the results. Grede-St. Cloud, a green sand molding operation producing


iron castings, operates two molding lines, each with its own sand system. For each line, daily tests are used to quantify variation within the sand system and make corrections as needed to keep within the optimal performance range.


Monitoring Compactibility Key independent variables are those aspects of the sand system


that can be adjusted easily. For instance, the level of compactability (one of the key independent variables in green sand control) can be adjusted simply by setting the system to target a lower or higher number. Te operator has total control. At Grede-St. Cloud, a 3-ram manual tester (rammer method) and an automatic compactibility tester are used. Te automatic tester is in the sand system on the muller itself, while the sand lab performs the 3-ram test from the sand at the mold. Although some facilities may opt to only run the automatic tester, also including a manual test in the lab at some frequency will help check the accuracy of the automatic tester. Additionally, sand properties can change during the time it comes out of the muller to when it reaches the mold. Testing automatically at the muller and then manually at the mold can tell you how much your sand is drying out or losing compactibility from muller to mold. Te current variation in a sand system can be quantified by defining it with a standard deviation. Fig. 1 shows a standard deviation for compactibility using the 3-ram testing method at Grede-St. Cloud. Each data point represents the average of 30 3-ram tests. Tirty tests are used because that is considered a sta- tistically sound sample size. As seen in the chart, the metalcasting operation was running in control in May and early June but then veered out of control in July. Tis alerted Grede to investigate for equipment malfunctions. Grede found and repaired the mechani-





用湿型砂工艺的铸造厂对型砂质量的控制有 赖于减少影响型砂性能的关键指标的变化。 铸造厂在型砂制备时可能时好时坏,而优秀


的铸造厂在绝大部分时间内都能保证型砂质量。 减少湿型砂系统的变化,包括确定关键的独立变量, 找到方法来量化当前的变量并实施改进以减少变差、监 测结果。 Grede-St. Cloud公司采用湿型砂造型工艺生产铸铁 件,有两条造型线作业,每条线都有自己的型砂系统。 对每线都进行日常的检测以确定型砂系统内的变化,并 根据需要进行修正以保持性能在最佳的范围内。


监控可紧实性


重要的独立变量,是型砂系统中一些易于调整的部 分。例如,可紧实性的水平(湿型砂控制中重要的独立 变量之一)可以简单地通过将系统目标值设置得低一点 或高一点来进行调整。操作者完全可以控制。 Grede-St. Cloud公司使用3锤制样机(用锤击法人 工测定)和可紧实性自动测试仪。自动测试仪是砂处理 系统装在混砂机中,而在型砂实验室中使用3锤制样机 检测,在造型时取样。虽然有些铸造厂可以选择只运行 自动测试仪,但是,也要在实验室中按某种频次人工检 测,有助于校准自动测试仪的准确度。另外,型砂从 混砂机放出到用于造型的这段时间内,性能可能有所改 变。混砂机自带的自动测试仪和人工检测造型时的取 样,可以告诉你从混砂机到造型线这段时间型砂失水而 损失的可紧实性。


型砂系统当前参数的变化在可以通过确定标准偏差 予以量化。图1所示为Grede-St. Cloud公司使用3锤制 样机测试的型砂可紧实性的标准偏差曲线。每个数据点 代表30次3锤制样机测试值的平均值。采用30次测试数 据的平均值是因为统计上这样的取样数量是合理的。从 图中可以看出,在5月到6月初铸造厂的生产运行是受控 的,但随后在七月转向失控。这些数据提示Grede公司 检查是否出现设备故障。 Grede公司发现并维修了系统 的机械故障,在这之后,系统回归受控状态。根据同一 时间段自动测试仪绘制的图表也确认了3锤制样机测试


62 | FOUNDRY-PLANET.COM | MODERN CASTING | CHINA FOUNDRY ASSOCIATION June 2015


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