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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


G


30 40 50 70


100 140 200 270 pan


Total


reen sand control in a metalcasting facility relies on reducing the variation in key


measurable aspects of sand proper- ties. All metalcasting facilities make good sand at times and bad sand at times. Successful plants make good sand most of the time. Reducing variation in green


sand systems consists of deter- mining the key independent variables, finding a method to


Multiplier for GFN


0.20 0.30 0.40 0.50 0.70 1.00 1.40 2.00 3.00 9.50


Percent of Total


2.11% 3.16% 4.21% 5.26% 7.37%


10.53% 14.74% 21.05% 31.58%


30 | MODERN CASTING March 2015


quantify current variation and implementing improvements to reduce variation and monitor the results. Grede-St. Cloud, a green sand molding operation producing iron castings, operates two mold- ing lines, each with its own sand system. For each line, daily tests are used to quantify variation within the sand system and make correc- tions as needed to keep within the optimal performance range.


Table 1. Comparison of GFN to Surface Area Sieve Size


Multiplier for Surface Area


40 60 90


130 190 270 400 600 900


2680


Percent of Total


1.49% 2.24% 3.36% 4.85% 7.09%


10.07% 14.93% 22.39% 33.58%


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


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