Figs. 1 & 2. For overall melt yield and slag weight as a percentage of charge weight, high purity (65%) SiC outperformed 36% SiC.
Figs. 3 & 4. The graphs showing carbon recovery (Fig. 3 WITH & Fig. 4 WITHOUT the free carbon in SiC included as a carbon input) illustrate greater carbon pickup from coke by the higher-purity 65% SiC.
weight as a percentage of charge weight. The higher purity 65% SiC offered a yield increase of 1.7% over 36% SiC. A review of the standard deviation differences showed the increase was statistically significant. The performance of 65% SiC
3
was superior to that of 36% SiC when gauged by melt yield and slag weight. The mass balance based on calcium and corroborated by the
38 | MODERN CASTING June 2012
Results and Conclusions Figs. 1 & 2 show high
correlations between the grade of SiC and both the melt yield and the slag
zero degrees of freedom for carbon and other elements (the carbon out- puts/inputs ratio was 105.3% before limestone carbonates and 101.3% after limestone carbonates) shows that the greater impurity (gangue) content of 36% SiC relative to 65% SiC makes no contribution to melt yield. If the impurity content of SiC is defined as all of its solid constitu- ents plus moisture that are deducted from the contained SiC and free carbon, then the 1.1% difference in slag weight as a percentage of charge weight between the two grades of SiC closely approximates the dif-
ference in impurity contents added between the two grades. It is important to note the 0.6%
discrepancy between the 1.7% greater melt yield and 1.1% lesser slag weight as a percentage of total charge weight for 65% SiC rela- tive to 36% SiC. This distinction between melt yield and slag weight as a percentage of total charge weight is necessary because cupola slag has no solubility/capacity for carbon other than un-dissolved particles of coke or briquetted SiC, while spout iron does have capacity to pick up carbon, including the free
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