Note: Descriptions are shown in the official language in which they were submitted.
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This is a division of co~only assigned ~n~ n Paten-t
A~plication Serial No. 412,859 flled October 5, 1982.
BACXGROUN~ OF THE I~VENTION
The present invention relates to the treating of liquid metal
in a refining or holdin~ vessel by injection of gas through the
pouring outlet in the bottom wall of the vessel, which outle~ is
controlled by a slidable ga~e closure mechanism. This invention ~s
particularly applicable to the refining of steel in a ladle or
other holding vessel.
It is Xnown that various metal refining treatments may be
carried out in a vessel by the underbath injection of a gas through
the side wall or bottom wall of the vessel. Such treatments inclllde
desulfurizing, dephosphorizlng, deoxidation, and making alloy
addi*lons~ Heretofore,however,any required piping remained with
the vessel and was not detachable therefrom upon completion of the
metallurgical treatment.
A common method of injecting a treating gas into a liquid
metal bath is through a porous plug in the bottom wall of the
vessel. Gas will pass through the interstices of the porous plug
into the bath, but molten metal will not pass through the plu~.
Very high pressures are required to force sufficient quantities of
gas through the plug ~o accomplish the desired treatment. The
present invention avoids the problems inherent in the use of
porous plugs
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SUMMARY O~ TE-IE INVENTIOM
The present invention relates to a method of
preparing a bottom-pour vessel for subsurface gas treat-
ment through a nozzle well in its bot-tom wall. The method
includes the utilization of a removable underbath tuyere
for injection of the treating gases -through the pouring
opening oE the vessel and the utilization of a slidable
gate-type nozzle closure mechanism. The tuyere or
blowing nozzle is a dual concentric pipe, the central
passageway of which is adapted for blowing a treating
material therethrough, and the outer annular passageway of
which is adapted for blowing a coolant therethrough to
prevent deterioration of ~-he pipe duiing the trea~ilg
period. The tuyere extends through the pouring opening
in the slidable gate, and is anchored in a refractory
tuyere block fixed in the nozzle well.
Upon completion ol the metallurgical treatment
the tuyere and a portion of the tuyere block are remove~
from the nozzle well leaving a pouring opening controllahle
by the slidable gate.
Suitable slidable gate closure ~echanisms are
shown in Shapland U.S. Patent 3,501,068 issued March 17,
1970.
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BRIEF DESCRIPTION OF THE DRAWINGS
This invention is better understood by referring to the
following detailed description and the appended drawings, in which:
Figure 1 is a vertical cross-section of a hot metal vessel
taken through the pouring opening and showing the gas injection
apparatus in place.
Figure 2 is a vertical cross-section of a portion of Figure 1
on a larger scale.
Figure 3 is a plan view of a portion of the vessel depicted
in Figure 2 showing the nozzle well and gas injection àpparatus.
DETAILED DESCRIPTION
As shown in Figure 1, vessel or ladle 10 having a steel shell
12 is lined with refractory 14 and has a pouring opening in its
bottom wall. Situated within the pouring opening is a no~zle
block 16 which is made of a dense, wear-resistant refractory.
Central to the nozzle block is a vertical opening in which a
refractory tuyere block 18 is positioned. Both the nozzle block 16
and the tuyere block 18 are held in posi~ion by a mortar. The
nozzle block 16 is preferably tapered downwardly a~ surface 20
toward the pouring opening. Tuyere block 18 has a central orifice
in which a central dual concentric tuyere is sîtuated. The tuyere
consists of an outer metal pipe 24 and an inner or central metal
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pipe 26 spaced from the outer pipe by any convenient spacing means
to form an annular spac~ 28 between the pipes. The lower interior
portion of tuyere block lS is preferably provided with an internal
relief indicated at 30, which begins in the region of intersection
of the extended line of the tapered surface 20 with the center of
the tuyere block. A fixed refractory re~aining plate 32 engages
the bottom of the tuyere block 18 to hold it in the operati~e
position.
A slidable gate closure mechanism affixed beneath the pouring
opening consists of a slidable refractory plate 34 having an open
position and a closed position, means for operating the gate such
as a pneumatic or hydraulic cylinder 36 attached to plate 34, and
suitable suppor~ing means, not shown. Optionally, a pouring nozzle
39 may be attached to the bottom of the sliding gate to mini~ize
splash and spatter during the pouring operation.
Valve 40 connects outer tuyere pipe 24 to an external source
~; of coolant 42, and alternatively to an external source of oxygen 44.
Central tuyere pipe 26 is connected through valve 50 to oxygen
source 52, to a source of inert gas 54, and to the source 56 of
treating material. The treating material can be a solid addition
in a carrier ~as, a liquid or any desired treating gas.
The outer tuyere pipe ~4 is tightly cemented in~o the tuyere
block 18 only at the top where there is no inner relief.
In operation the nozzle block 16 is rammed into place in the
vessel lining 14 while the vessel is cold. The vessel is ~hen
heated to operating tempcrature by using conventional vessel
preheaters, after which the tuyere block 18 con~aining ~he tuyere
pipes 24 and 26 is placed into the nozzle brick and cemented into
place from the bottom of the vessel. The refractory suppor~ plate
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32 is fastened into position ~o retain the tuyere block in ~he
blowing position, after which the sliding gate closure apparatus
is installed. If desired, a moldable refractory such as gunnite can
be placed in region 58 around the tip of the tuyere block within
the furnace. The pipes 24 and 26 are connected to the sources of
gas supply, flow of a cooling gas from source 42 is initiated
through annulus 28. Inert gas from source 54 is started through
the central tuyere pipe 26, then liquid me~al is poured into the
vessel. Once the metal in the vessel reaches the required level,
approximately 70~ of the full level, then the gas trea~ment
commences. Normally oxygen will be blown through the central pipe
and cooling gas through the outer annulus. At the end of ~he
treatment oxygen is fed ~hrough both the central pipe 26 and the
annular space 28. The oxygen reacts wi~h the hot metal ~o burn
the pipes back into the tuyere blook and along with it the tip of
the refractory tuyere block. When ~he tuyere block is burnt back
as far as the annular relief 30, tuyere pipes 24 and 26 are no
longer connected to the tuyere block 1~, whereupon they are wi~hdrawn
and the sliding gate 34 is ~ctivated to close the pouring nozzle.
At this time the vessel is ready for further handling or treatment,
such as vacuum degassing, decanting, transport, or cas~ing.
The following is an example of making stainless steel in a
ladle utilizing the above-described inYention. In this case, the
refractory lining of the ladle. was magnesite containing in excess
of 95% MgO. The nozzle block and the tuyere block were also made
of plus 95~ MgO magnesite. Tuyere pipes 24 and 26 were made of
low-carbon steel. The cooling gas rom source 42 was carbon
~ioxide and the treating gas from source 56 was an oxygen-carbon
dioxide mixture. Sixteen tons of liquid steel containing Z0~
chromium,8% nickel and 1.3% carbon were poured into the ladle,
which had the invented apparatus situated in its pouring nozzle.
The oxygen-carbon dioxide mixture was blown in~o the molten metal
for sixty minutes, followed by an inert gas~o2 mixture for a short `
period, after which time the carbon content had been reduced to
0.005%. A mixture of finely divided lime and fluorspar was then
injected into the molten metal along with oxygen to desulfuri~e
and dephosphorize the metal. Oxygen alone was then blown ~hrough
both the central pipe 26 and the annular space 28 to burn back
the tuyere pipes and tuyere block to recess 30. The tuyere pipes
were removed and the slide gate 34 was immediately closedO The
ladle was then transported to a vacuum degassing station after
which the steel was cast into ingots. The resulting steel was a
chromium-containing stainless steel having a composi~ion of
18 chrome, 8 nickel stainless steel.
SUMMARY OF THE ACHIEVEMENT
OF THE OBJECTS OF THE INVENTION
From the foregoing, it is readily apparent that the present
invention provides a method and apparatus for metallurgically
treating molten metal in a refining or holding vessel by injection
of treating material through the sub-surface pouring nozzle.
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