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Checking the Clay A second key independent variable


Fig. 3. This histogram for Hartley test results show 193 tests in an eight-hour period were within 3 points of the target.


the variation of return sand conductiv- ity or moisture. Figure 4 shows the conductivity fluctuations from muller batch to muller batch on one of Grede- St. Cloud’s molding lines. Te wide fluctuations occurred through October 2012 and then became much tighter in the following months. Te improvement


stemmed from the purchase of a new piece of equipment to replace a cooler moisture addition system that was not adding the right amount of water. Te data shows the new equipment made a positive impact on return sand conduc- tivity, which typically will improve varia- tion on compactibility at the mold line.


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 indepen- dent variable because most sand casting 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 equipment error. In the mixer, clay


March 2015 MODERN CASTING | 33


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