Calculation of the Ore Mixture or Burden for a Blast Furnace. [Volume: 8, Issue: 3, 1889, pp. 130-143]

130

UNITED STATES ASSOCIATION OF

[VOL. 8,

Calculation of the Ore Mixture or Burden for a Blast
Furnace.
[Translated from the German of Prof. Ledebur for the JOURNAL OF THE
UNITED STATES ASSOCIATION OF CHARCOAL IRON WORKERS, by E. K.
Landis, B. S.]
As the production of any desired iron is closely connected with
the temperature of formation and the melting point of the accompanying slag, the first task in the production of the iron must be
to so proportion the burden as to produce a slag of corresponding
properties, i. e., of correct chemical composition. This object is
attained in an empirical way by melting different experimental
mixtures- which is best done in a crucible-until the desired result is obtained. A shorter method is by calculation-stoichiometrically or by atomic weights.
In order to employ the latter method one must clearly know
which composition of slag is most suitable for the production of
the kind of iron to be made, under the conditions given, whether
coke or charcoal is used, high or low heats of blast, etc. Authentic
analyses of furnace slags which have been produced under known
conditions must form the basis of calculation in all these cases
when one tries to form the burden in such a way that the slag produced may resemble one of the normal slags chosen. Owing to
the great number of elements in a blast furnace slag and the multiplicity of composition of the materials smelted, it is not always
feasible, from the ores and fluxes at hand, to calculate a burden
'whose composition in all parts will conform exactly to that of a
given normal slag, so it suffices to form a slag which at least essentially, will show a fusibility corresponding to the requirements of
the case. Here comes in before everything else the ratio of silica
to the bases, in the second place the ratio of alumina to the
stronger bases (CaO, MgO), finally also whenever feasible, the inverse ratio of the last two named bases. In practice it is frequently observed that this inverse ratio of CaO to MgO (lime to
magnesia) is by no means equal for the fusibility of the slag; a
slag high in MgO and low in CaO is, for the same oxygen ratio,
generally less fluid than in the reverse case. In the calculation, not
only the composition of the slag, but also its amount in proportion