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Page 41
In the Siemens process pieces of ore of the size of beans or peas,
mixed with lime or other fluxing material, form the charge, which is
introduced into a rotating furnace; and when this charge has become
heated to a bright-red heat, small coal of uniform size is added in
sufficient quantity to effect the reduction of the ore.
The size of the pieces of the material employed prevents the intimate
mixture of the particles of iron with the particles of carbon, and
hence we would, on theoretical grounds, anticipate just what practice
has proved, viz., that the reduction is incomplete, and the resulting
metal being charged with oxides is red-short. In practice, blooms made
by this process have been so red-short that they could not be hammered
at all.
It would be impracticable in this process to employ ore and carbon in
as fine particles as Wilson does, as a very large portion of the
charge would be carried off by the draught, and a sticking of the
material to the sides of the rotating furnace could scarcely be
avoided. I do not imagine that a division of the material into
anything like the supposed size of molecules is necessary; we know
that the graphitic carbon in the pig-iron employed in puddling is not
so finely divided, but it is much smaller particles than bean or pea
size, and by approximating the size of the graphite particles in pig
iron, Wilson has succeeded in obtaining good results.
If we examine the utilization of the heat developed by the combustion
of a given quantity of coal in this process, and compare it with the
result of the combustion of an equivalent amount of fuel in a blast
furnace, we shall soon see the theoretical economy of the process. The
coal is burned on the grate of the puddling-furnace, to carbonic acid,
and the flame is more fully utilized than in an ordinary
puddling-furnace, for besides the ordinary hearth there is the second
or rear hearth, where additional heat is taken up, and then the
products of combustion are further utilized in heating the retorts in
which the ore is partly reduced. After this the heat is still further
utilized by passing it under the boilers for the generation of steam,
and the heat lost in the gases, when they finally escape, is very
small. In a blast furnace the carbon is at first burned only to
carbonic oxide, and the products of combustion issue mainly in this
form from the top of the furnace. Then a portion of the heat resulting
from the subsequent burning of these gases is pretty well utilized in
making steam to supply the power required about the works, but the
rest of the gas can only be utilized for heating the blast, and here
there is an enormous waste, the amount of heat returned to the furnace
by the heated blast being very small in proportion to the amount
generated by the burning of that portion of carbonic oxide expended in
heating it, and the gases escape from both the hot-blast and the
boilers at a high temperature.
In the direct process under consideration the fuel burned is more
completely utilized than in the puddling process, to which the cast
iron from the blast furnace is subjected to convert it into wrought
iron.
The economy claimed for this process, over the blast furnace and
puddling practice for the production of wrought iron, is that nearly
all the fuel used in the puddling operation is saved, and that with
about the same amount of fuel used in the blast furnace to produce a
ton of pig iron, a ton of wrought iron blooms can be made. I had no
opportunity of weighing the charges of ore and coal used, but I saw
the process in actual operation at Rockaway, N.J. The iron produced
was hammered up into good solid blooms, containing but little cinder.
The muck-bar made from the blooms was fibrous in fracture, and showed
every appearance of good iron. I am informed by the manager of the
Sanderson Brothers' steel works, at Syracuse, N.Y., that they
purchased blooms made by the Wilson process in 1881-1882, that _none_
of them showed red-shortness, and that they discontinued their use
only on account of the injurious action of the titanium they contained
on the melting pots. These blooms were made from magnetic sands from
the Long Island and Connecticut coasts.
[Illustration: NEW PROCESS FOR MAKING WROUGHT IRON FROM THE ORE.]
The drawing given shows the construction of the furnace employed. I
quote from the published description:
"The upper part, or deoxidizer, is supported on a strong
mantel plate resting on four cast iron columns.
"The retorts and flues are made entirely of fire-brick, from
special patterns. The outside is protected by a wrought iron
jacket made of No. 14 iron. The puddling furnace is of the
ordinary construction, except in the working bottom, which is
made longer to accommodate two charges of ore, and thus
utilize more of the waste heat in reducing the ore to metallic
iron.
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