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dimensions related to the molding aggregates thermal expansion at the time of solidification (Fig. 5). Zircon sand, which exhibits low expansion, was used to modify the expansion profile of the molding aggregate and therefore change the core dimensions at the critical or solidus temperature of the adjacent metal. Te peak expansion for


silica with 10% zircon is similar to baseline silica sand. However, from 20% zircon onwards, a reduc- tion in the alpha-beta phase transition peak expansion can be seen with silica with 40% zircon having the lowest peak of 0.005 in./in., which is lower than base- line silica by 56%. Te 100% silica sand has the


Fig. 8. The comparison of the shrink rule with actual and predicted dimensions for baseline silica is shown.


greatest amount of expansion at the alpha/beta quartz, A/B transforma- tion and a distinct transformation point to cristobalite. Te various blends of silica sand with zircon sands


show a reduced amount of A/B peak transfor- mation that reduce the core dimensions at the adjacent metal’s critical temperature reducing the predicted diameter of the casting section. Although the cases in


this research are restric- tive, it provides solid insight into more accurate predictions of final cast- ing dimensions based on molding aggregates. Fur- ther studies will be under- taken to address large core mass and low metal mass situations where the core retains more strength and


may restrict metal contraction.


Tis article is based on a paper (16-076) that was presented at the 2016 CastExpo in Minneapolis.


40 | MODERN CASTING July 2016


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