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Full text of "Metallurgy Of Cast Iron"

20                         METALLURGY   OF   CAST   IRON.
either the coal is inferior to Connellsville coal or it has not been treated properly, and the coke has been allowed to waste. The amount of loss is due to several factors. One may be the indisposition of the coal to coke, and again it may be the fault of the ovens and their treatment.
The ash in coke is an impurity which, like phosphorus and sulphur, lessens the commercial value of the coke as the percentages increase. The ash in furnace and foundry coke generally ranges from nine to fourteen per cent. It may exceed this two to four per cent, or be as low as five per cent. The ash of coke generally includes the impurities found in Table 6, obtained by Mr. E. C. Pechin. The less ash coke contains the greater is its value, generally speaking,            !
although very low ash is not desirable in all cases. It is often beneficial in assisting the formation of a good slag. The coke made from washed coal contains less         JL&
ash and sulphur than that made from unwashed coal.
TABLE 6.—ANALYSES  OF  ASH IN  CONNELLSVILLE  COKE.
Silica........................................................................................   5.413
Alumina...................................................................................   3.262
Sesquioxide of iron..................................................................   0.479
Lime..........................................................................................   0.243
Magnesia...................................................................................   0.007
Phosphoric acid.......................................................................   0.012
Potash and soda.....................................................................Traces.
9.416
The chemical properties desirable in coke are, first, low sulphur and often low phosphorus, and second, high carbon. As a rule when adopting a new brand of coke, and often in the use of old ones, it will pay a founder to assure himself as to the chemical properties of the coke before using it. This is a practice which
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