Improvements in or relating to the "Thomas" Metallurgical Process.
Year: 1893

page_text: Date of Application, 23rd Mar., 1893
Complete Specification Left, 29th Nov., 1893-Accepted, 24th Feb.,
1894
PROVISIONAL SPECIFICATION.
Improvements in or relating to the "Thomas" Metallurgical
Process.
1, HERMANN WILD of Peine in the German Empire, Manager of the Technical
Department of The "Peiner Walzwerk" Joint Stock Company do hereby declare
the nature of this invention to be as follows:-
In addition to the methods which have been generally employed hitherto for
ascertaining the time or duration of the blowing or blistering operation in
"Thomas" process, in minutes or seconds or by the number of revolutions of the
blowing machines, and in addition to "sampling "both in the preliminary and in
the final stages, (the usual blowing process being, by the way, generally kept up
too long by way of precaution or for the sake of greater safety) it is according
to this invention proposed, for the purpose of determining exactly the duration of
the final or supplemental blowing, to ascertain the quantity of iron contained in the
slag and to reduce the time of such supplemental blowing (down to say one minute
and a half or less) so that, by the time that dephosphorization has made sufficient
progress, the quantity of iron contained in the slag becomes reduced to a minimum.
By such means the quantity of burnt iron in the converter is diminished
(i.e. brought down to 2 per cent. or less) the slag becomes richer in phosphoric
acid, but poorer in oxides of iron, and this fact prevents re-phosphorization.
Furthermore, blocks of far better appearance and greater density than hitherto,
are thus obtained, with the result that the general output of finished goods, in
rolling mills for example, is greatly increased, while the quantity of waste is
a considerable diminution in the
materially reduced. A further result is
consumption of lime, dolomite, ferromanganese, spiegel-iron, etc.
101 Mo 1802
W. P. THOMPSON & BOULT,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in or relating to the "Thomas" Metallurgical
Process.
I, HERMANN WILD of Peine in the German Empire, Manager of the Technical
Department of The "Peiner Walzwerk" Joint Stock Company do hereby declare
the nature of this invention and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement :-
The determination of the most suitable and correct period of duration of the
"overblow" is a matter of great importance in the process known as the "Thomas
process " for the manufacture of iron and steel; inasmuch as, if the same be
inaccurately determined, the charge is more considerable, the dephosphorisation
less, and the consumption of coal, dolomite, ferromanganese and spiegeleisen
greater.
Further, when the most suitable and correct duration of the overblow is deter-
mined with accuracy, ingots of greater density and finer appearance are obtained,
whereby in the rolling-mills, the output of finished work is enhanced, and waste
considerably decreased. Lastly the durability of the soles and linings of the
converters is augmented.

page_text: According to the methods hitherto adopted for determining the time of duration
for the overblow in the "Thomas" process, the revolutions of the blowing machine
were counted, or assays were made before and after completion.
The taking of samples, the forging, the critical examination of the fracture for
the proportion of phosphorus, the subsequent chemical analysis, for phosphorus,
carbon and manganese-which last, be it observed in passing, notwithstanding all
the trouble bestowed and pains taken about them, can not be thoroughly carried
out with all the rapidity which is desirable-all these tests fail, nevertheless to give
the results with the desired accuracy.
The estimation of the results from forging and fracture tests, both of the
sample-materials taken before and after the overblow, for the determination of
the phosphorus is very uncertain and inaccurate; and before the chemical analyses
with their results can be made available, several other charges will already have
been passed through the converter and finished by the process. In order, therefore,
to obtain adequate dephosphorisation, the charges, because of the uncertainty as
to the exact and most favourable stage of dephosphorisation are in general blown
too long for the sake of the assumed safety.
Should the chemical analysis show still too much phosphorus to be present, the
blowing, in order to bring the excess into the slag or cinder in the form of
phosphoric acid, is naturally continued for some time longer, and the test will then
again show a further reduction in the proportion of phosphorus. By this
suppression of the old methods, the error, which has naturally arisen since the
introduction of the "Thomas" process, is the result and has gradually led the
makers astray.
The bath is regularly too much blown; too much iron oxide is formed in the
"Thomas" slag whereby considerable additions of spiegeleisen and manganese, etc.,
are counteracted and nullified; and rephosphorisation takes place, attended by an
uncertain amount of carburation.
Hitherto, the former has mostly been set down to the presence of some silicic
acid and silicon in the flux; but, through the researches made in Peine, and the
now regular and most successful carrying out of this improved process, I have been
led to the conclusion that rephosphorisation is a result of overblowing, aided by
subsequent action of the carbon, whether it be of the spiegeleisen and ferro-
manganese, or of the Derbyshire carburation-mass, upon the "Thomas" slag or
cinder in the converter and pan.
In the great heat of the fluid bath the carbon reduces a portion of the iron
oxide, as well as also a portion of the phosphorus from the lime phosphate of the
"Thomas" slag or cinder, and the phosphorus is found again in the bath in the
form of iron phosphuret.
"
I find as a certain fact, that in a blast-furnace where phosphorus earths are
reduced by carbon phosphuretted metals are produced. Consequently a
" Thomas
slag must be worked off with as small a proportion of iron as possible, and this
follows on complete control and determination of the overblow.
By my improved process, which forms the subject of this invention, the accurate
determination of the most suitable and correct time of duration of the overblow
is attained, and thus the defects of the process hitherto adopted are effectually
remedied.
The improved process is carried out in the following way; viz.: The first charge
is blown in the manner hitherto known and practised; the necessary quantitative
and qualitative tests are previously taken; the carbon, phosphorus, and manganese,
in the finished product, are severally determined, and the "Thomas" slag is
analysed in regard to its proportion of iron. On the supposition that the quality
of the finished product is satisfactory, comparison is made of the proportion of iron
contained in the several slags with each other, and should they be found to differ,
the attempt must be made still further to reduce the lowest proportion found, by
a reduction of the time of overblow, as far as it may eventually be possible, i.e., so
long as the samples and tests continue to give good results.

page_text: Inasmuch as the analysis for iron, and determination of its proportion in the slag
can be quickly effected, I am enabled to come to a rapid conclusion as to the
proper working of the following charge.
In Peine, the lowest proportion of iron varies between 6 and 12 per cent.,
according to the higher or lower temperature of the working of the charge.
In the case of other blast-furnaces, the same results cannot be adopted off-hand,
as the figures depend upon the varying proportions of the furnace, and accordingly
they must be determined in each separate case, by actual experiment.
The results of this improved process, as already stated in the introductory part
of this Specification, are:-
Shorter duration of overblow than hitherto, and consequent reduction of waste;
More even quality of the charge;
More valuable slag;
Ingots of better appearance and greater density, and consequent proportionate
increase in output of finished products in the rolling mills, and
Considerable decrease of waste."
The consumption of lime, dolomite, ferromanganese, spiegel iron etc. is also
thereby considerably lowered.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
The process for determining of a suitable duration of "overblow" in the
dephosphorisation of iron, consisting in the determination by analysis of the
proportion of iron contained in the slag formed by the first or any preceding
charge, in the ordinary series or succession of charges and to found the duration
of the subsequent charge or charges on the basis of such analytical determination.
Dated this 29th day of November 1893.
W. P. THOMPSON & BOULT,
Agents for the Applicant..