AN IMPROVED PROCESS FOR THE MANUFACTURE OF BESSEMER STEEL FROM PHOSPHORETIC PIG-IRON
Year: 1879

page_text: LETTERS PATENT to Sidney Gilchrist Thomas, of 3, Queen's Road Villas,
Queen's Road, Battersea, in the County of Surrey, for the Invention of "AN
IMPROVED PROCESS FOR THE MANUFACTURE OF BESSEMER STEEL FROM
PHOSPHORETIC PIG-IRON."
Sealed the 8th August 1879, and dated the 2nd April 1879.
PROVISIONAL SPECIFICATION left by the said Sidney Gilchrist Thomas at
the Office of the Commissioners of Patents on the 2nd April 1879.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Queen's Road, Battersea,
in the County of Surrey. "AN IMPROVED PROCESS FOR THE MANUFACTURE OF
BESSEMER STEEL FROM PHOSPHORETIC PIO-IRON."
My Invention relates to an improved process for the manufacture of Bessemer
steel from phosphoretic pig-iron. When pig-iron is blown in the Bessemer con-
verter in the manner now practiced as is well known the blow is stopped and the.
converter is turned down when the flame drops, which happens almost concurrently
with the disappearance of the so called carbon lines from the spectrum. If this is
not done the metal is greatly wasted, and great importance is attached to not
overblowing the metal. Even if the metal is overblown phosphorus is not
removed.
By my improved process I proceed as follows:-I use a converter lined with a
basic (preferably calcareous) material, which I prefer to be the lime bricks described
by me in the Specifications of former Patents, Nos. 44227, and 289 and 9087
I also produce a highly basic calcareous slag (a condition I have before
described as necessary for the removal of phosphorus) which I prefer should contain
over 35 per cent. of lime and magnesia together by adding to the contents of the
converter bases equal in weight to from two and a half to four times the weight of
the silicon and phosphorus contained in the pig treated. The bases added will
generally amount to from two to three cwt. for every ton of pig-iron treated, and
should consist of lime or of lime mixed with iron ore with or without the addition
of common salt according to the character of the pig treated. I do not stop the
blow when the flame drops and the so called carbon spectrum lines disappear, but I

page_text: continue it afterwards even to the extent of six minutes where the metal is of a
highly phosphoretic nature. The time to stop the blow is indicated by the appear-
ance of dense and copious brown smoke from the chimney of the converter in con-
junction with white smoke round the edge of the flame, or the stopping point may
be regulated by taking test ingots after the drop of the flame and after cooling in
water, hammering them under a steam hammer, if their hardness indicates that too
much phosphorus remains the blow is continued.
I find that in the presence of an earthy basic slag and a basic lining the phospho-
rus protects the iron after the carbon is gone, while it is itself oxidised and almost
completely removed.. My Invention is particularly useful when blowing pig-iron
containing over half a per cent. of phosphorus.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Sidney Gilchrist Thomas in the Great Seal Patent Office on the 1st
October 1879.
SIDNEY GILCHRIST THOMAS, of 3, Queen's Road Villas, Queen's Road, Battersea,
in the County of Surrey. "AN IMPROVED PROCESS FOR THE MANUFACTURE OF
BESSEMER STEEL FROM PHOSPHORETIC PIG IRON."
My Invention relates to an improved process for the manufacture of Bessemer
steel from phosphoretic pig-iron. When pig-iron is blown in the Bessemer converter
with a silicious lining, in the manner now practised, as is well known, the blow is
stopped and the converter is turned down to add the spiegel when or almost imme-
diately after the flame drops, which happens almost concurrently with the dis-
appearance of the so called carbon lines from the spectrum. If this is not done the
metal is greatly wasted, and much importance is attached to not overblowing the
metal except in some instances of a very silicious pig, when the blow is occasionally
continued for some forty seconds, while even if the metal is overblown even for
many minutes the phosphorus is not removed. By my improved process I proceed
as follows:-I use a converter lined with a basic, preferably calcareous or magnesian
material, which I prefer to be the magnesian lime bricks described by me in a
former Patent, No. 908 in the year 1878. I also produce a highly basic calcareous
slag which should contain over 45 per cent. of lime and magnesia together; by
adding to the contents of the converter bases equal in weight to from four to six
times the weight of the silicon and phosphorus contained in the pig or metal
treated.
The bases added must (as before described by me) consist of lime or of lime
mixed with a little iron ore, with sometimes (though it is not often necessary) the
addition of a little common salt. I prefer to add a great part of the lime in very
fine powder, which may be readily introduced by degrees, from an iron hopper or
cylinder with a strong air-tight cover or valve into the blast pipe through a stop-
cock, and so by the tuyères into the bath of molten metal (as has been before pro-
posed for blowing in charcoal dust, etc.). This blowing in of lime-dust should
continue throughout the operation. The remainder of the lime I throw into the
vessel in small pieces before the metal is run into the converter. I do not however
stop the blow when the flame drops and the so-called carbon spectrum lines dis-
appear, but I continue it from one (1) to five (5) minutes. The time to stop the
blow is generally indicated by the appearance of dense and copious brown smoke
from the chimney of the converter in conjunction with white smoke round the edge
of the flame, but the stopping point is better and more exactly regulated by taking
small test samples out of the vessel and examining their fracture. The first test is
taken one to three minutes after the drop, when the blower judges from the appear-
ance of the flame the metal is nearly or quite dephosphorised. The test ingot is
slightly cooled to set it, and then while still hot rapidly hammered out; it is then
plunged in water till cold and broken under the hammer. If the fracture exhibits
a leaden bluish white color and long facets indicating the presence of phosphorus
the vessel is turned up and blown again for as long a time as the blower thinks
necessary. It is then again turned down and either sampled again (if the blower
judges it desirable) and if necessary again blown, or if the first sample showed that
the metal was nearly dephosphorised, it may after the second blowing be at once
finished with spiegel without taking a further sample. If the first sample shows
the characteristic silver white fracture and round or polygonal facets of good steel
the metal is of course not blown further but finished and poured at once.
I find an
overblow of two (2) to three (3) minutes generally sufficient.
I do not claim the overblowing of Bessemer metal except when treating phospho-
retic pig-iron in combination with the use of a calcareous or magnesian lining to
the converter and the addition of large quantities of lime so as to produce a highly

page_text: calcareous slag in which the phosphorus may be removed as herein described. I
do not find overblowing beneficial in removing phosphorus under any other
conditions.
In witness whereof, I, the said Sidney Gilchrist Thomas, have hereunto set
my hand and seal, this Sixteenth day of September, in the year of our Lord
One thousand eight hundred and seventy nine.
SIDNEY G. THOMAS.
(LS)