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carbon contained in both the coke and briquetted SiC. Comparing carbon recovery with and without the free carbon in SiC included as a carbon input illustrates the relative propensities for carbon pickup from either the coke or SiC (Figs. 3 & 4). Fig. 3 clearly indicates greater carbon recovery for 65% SiC when excluding free carbon in the SiC as an input, while Fig. 4 indicates approximately equal carbon recover- ies for the two grades when including free carbon in the SiC as an input. Te differences shown by Figs. 3 & 4 taken together then predict and account for the additional 0.6% greater melt yield for 65% SiC that is not accounted for by the difference in slag weight percentage alone. Te excellent melt yields for these


trials are a reflection of the minuscule iron oxide contents of the slags, which average less than 2% of the total slag weight. Furthermore, since the slag weights are small percentages of the


total charge weights, the resultant iron losses are exceedingly small at approxi- mately 0.1% of the total iron charged for both grades of SiC. Te two grades of briquetted SiC


had approximately equal performances when gauged by all performance metrics other than melt yield and slag weight. Tis was likely due to the mass balance based on calcium standardiz- ing all metrics other than melt yield. Calcium was used as the basis for the mass balance for the following reasons: • The calcium input derives in substantial amounts from several different sources. Although the calcium inputs are insubstantial relative to the iron content, they are substantial relative to all elements other than iron.


• The sources of calcium for both grades of the briquetted SiC are the same, so even if the actual measured amounts of calcium entering the cupola are not totally accurate, the measurement errors would apply


equally to both grades of SiC. The relative differences in calcium introduced by each grade of SiC would be a valid metric.


• It can be assumed 100% of all cal- cium entering the cupola exits as slag. Long running steady-state melt


conditions for the two grades of SiC were desired because of the assumption that, relative to shifting iron chemistry, transitioning from (flushing out) the slag composition in the cupola takes much longer when switching from one grade of SiC to another. However, this assumption was challenged by the demarcations between SiC grades in Figs. 1 & 2, as both graphs indicate abrupt changes in short periods of time when changing from one grade of SiC to another.


Te research summarized in this article was overseen by AFS Division 8 Melting Methods and Materials and funded by AFS. Te divi- sion would like to acknowledge the support of Sy Katz, Katz & Associates, West Bloomfield, Mich., and Bill LaFramboise, proprietor of Auburn Analytical Labs, Midland, Mich.


June 2012 MODERN CASTING | 39


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