Note: Descriptions are shown in the official language in which they were submitted.
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BOTTOM POURING NOZZLE FOR ARRANGEMENT IN THE BOTTOM OF A
METALLURGICAL VESSEL
The invention concerns a bottom pouring nozzle for arrangement in or at a
bottom of a
metallurgical vessel, having an upper end, particularly for fitting in a
metallurgical vessel or
onto a sliding gate of a metallurgical vessel and having a lower end, whereby
in between
both ends a throughflow channel is arranged having at least a lower pouring
opening at the
lower end, whereby the radially outermost surface of the wall of the
throughflow opening is
surrounded by a gastight housing. Furthermore, the invention concerns a method
of using a
bottom pouring nozzle.
Especially with steel melts, the molten metal is poured from a metallurgical
vessel into a
mould. Such a metallurgical vessel can for instance be a casting ladle (also
called ladle) or a
so called distrubutor (also known as intermediate vessel or tundish). For
example, the liquid
metal is poured from the ladle into the tundish and from the tundish into the
mould of a
continuous casting installation. It runs through the bottom of the ladle or
tundish through a so
called bottom pouring nozzle (also called nozzle).
Disadvantageous is the adhering of material onto the wall of the bottom
pouring nozzle
accumulated during throughflow. This reduces the cross sectional area, so that
flow ratios
and steel quality is detrimentally influenced because of turbulences. This
accumulated
material can also break free and cause inclusion related defects in the steel.
To prevent the adhering of material onto the wall, mostly an inert gas such as
Argon is
supplied in the throughflow opening. Too much gas can also negatively affect
the steel
quality, for instance the formation of pinholes in steel, which lead to
surface defects during
the rolling of steel.
A material for a bottom pouring nozzle is for instance described in WO
2004/035249 Al. A
bottom pouring nozzle in a metallurgical vessel is disclosed in KR 2003-
0017154 A or in US
2003/0116893 Al. The use of inert gas is relied upon in the latter document,
with the aim to
reduce the adhering of material nozzle (so called Clogging) to the inner wall
of the bottom
pouring nozzle, similar to what is described in JP 2187239. A mechanism using
a regulated
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gas supply is known in detail from WO 01/56725 Al. Nitrogen is supplied
according to
Japanese publication JP 8290250. JP 3193250 discloses a method for monitoring
the
adhering, particularly the sticking of material by means of a plurality of
temperature sensors
arranged after another alongside the bottom pouring nozzle. The supply of
inert gas inside a
bottom pouring nozzle is further known from JP 2002210545, JP 61206559, JP
58061954
and JP 7290422.
From some of these publications it is also known, in addition to the supply of
inert gas, to
prevent air aspiration by using housings around a part of the bottom pouring
nozzle. In this
case, for instance in JP 8290250, an inert gas excess pressure is partially
obtained. JP
11170033 discloses a housing around the slide valve of a bottom pouring nozzle
to prevent
air aspiration. According to the forementioned publications, the throughflow
of the metal melt
through the bottom pouring nozzle is regulated by sliding valves. These valves
slide
perpendicular to the throughflow direction of the metal and can shut off the
bottom pouring
nozzle. Another possibility for regulating the throughflow is the so called
stopper plug (also
called stopper rod), for example as is known from JP 2002143994.
The arrangement of an additional housing around the valve of a bottom pouring
nozzle is
described in Korean publication KR 1020030054769 A. The gas that is present in
the
housing is being evacuated by means of a vacuum pump. JP 4270042 describes a
similar
housing. Herein, as well as in other previously mentioned publications, a non
oxidizing
atmosphere is obtained. The housing has an opening, through which inert gas
can be
supplied. A further arrangement, in which gas is evacuated from the housing
partially
surrounding the bottom pouring nozzle, is known from JP 61003652.
Further bottom pouring nozzles are for instance known from DE 10 2004 057381.
Herein, it is
attempted to prevent clogging by means of a regulated inert gas supply or by
means of a
nearly complete sealing of the entire bottom pouring nozzle wall surface and
the related
prevention of air aspiration through the wall of the bottom pouring nozzle.
It is the object of the present invention to further improve upon the known
techniques, to
minimize the adhering of depositions in the nozzle of a bottom pouring nozzle
in a simple and
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effective manner, without influencing the quality of the metal melt,
particularly the solidified
metal.
The object is solved in accordance with one aspect of the invention by a
bottom pouring
nozzle having an upper end and a lower end, whereby a throughflow channel is
arranged in
between both ends, with at least one lower outflow opening arranged at the
lower end,
whereby a radially outermost surface of a wall of the outflow opening is
surrounded by a
gastight housing which housing encases the lower end with the at least one
outflow opening
in a gastight manner such that an overpressure or an underpressure is
obtainable in the
complete volume inside the gastight housing when the pouring nozzle is
arranged in or at a
bottom of a metallurgical vessel.
Surprisingly, it was shown that good results could be obtained with the bottom
pouring nozzle
for arrangement in a bottom of a metallurgical vessel, having an upper end,
particularly for
fitting on a metallurgical vessel or onto a sliding gate of a metallurgical
vessel and having a
lower end, whereby in between both ends a throughflow channel is arranged
having at least
a lower pouring opening at the lower end, whereby the radially outermost
surface of the
(refractory) wall of the throughflow opening is surrounded by a gastight
housing, by not only
having the circumference of the bottom pouring nozzle, thus the radially
outermost wall of the
throughflow channel being surrounded by a gastight housing, but by having the
housing also
encasing the lower end of the bottom pouring nozzle having at least one
pouring opening in a
gastight manner. Gastight obviously does not mean totally leak free, but
essentially stopping
the ingress of gasses, mainly atmospheric oxygen and nitrogen.
It will clearly be understood for a skilled person that the bottom pouring
nozzle, the sliding
valve (or a stopper rod enclosure) and a further upper nozzle, which is
surrounded by a
casing and which is arranged in the bottom of the metallurgical vessel above
the sliding valve
are connected together gastightly thus establishing a system of a completely
sealed nozzle.
A method of using a bottom pouring nozzle is an object of the invention, for
example with the
use of a bottom pouring nozzle according to the invention, characterized in
that, the bottom
pouring nozzle is fitted to a slide valve or a stopper rod closure of a
metallurgical vessel and
whereby prior to opening if the slide valve or the stopper rod enclosure a
vacuum is obtained
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or an inert gas flushing with consequent inert gas excess or an overpressure
is obtained
after which the slide valve or stopper rod enclosure are opened.
Argon can be used as an inert gas. Oxygen can at least partially be removed
out of the
bottom pouring nozzle in this manner, through which an oxygen deficiency or a
lower oxygen
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partial pressure is obtained. The overpressure or particularly the vacuum
(underpressure)
exists in the complete volume inside the gastight housing.
The definition of "in the bottom pouring nozzle" thus means the space inside
the housing or
the outer wall thereof and including the internal volume and voids of the
total pouring
channel.
Said under- or overpressure also exists in the throughflow channel prior to
the inflow of the
steel melt. During flow of the steel melt in the bottom pouring nozzle,
particularly in the
throughflow channel, after the opening of the slide valve or the stopper rod
closure, the
housing melts when it comes into contact with the molten steel in the region
of the at least
one outflow opening, so that the steel melt can flow into the lower placed
container. The
bottom pouring nozzle can either be operated under vacuum or with inert gas
after opening
A type of bottom pouring nozzle is the so called immersion nozzle, known in
the art as
SEN/SES (Submerged Entry Nozzle/Submerged Entry Shroud). It is dipped with its
lower
end in the steel melt in the lower metallurgical vessel, whereby the housing
melts when in
contact with liquid steel, thus enabling a free throughflow.
It is advantageous that the housing comprises several gastight connected
housing parts,
particularly arranged on top of each other. Particularly, the housing is made
of a metal, such
as steel, so that it has sufficient strength but still melts when contacting
the steel melt. The
metal of the housing is selected such that it can be melted by metal in the
receiving vessel.
It can be advantageous, that the housing comprises a lower housing part made
of steel,
which surrounds the lower end of the at least one throughflow opening in a
gastight manner
and that a gastight housing part is arranged thereupon as an integrated
component of the
wall, so that the throughflow opening is closed by a kind of cap, due to which
the periphery
(the wall) of the bottom pouring nozzle has a gastight layer, particularly
surface, that can be
considered as a housing part according to the invention.
It can be advantageous, that the housing comprises a lower housing part made
of steel,
which is inserted in the lower end with the at least one throughflow opening
in a gastight
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manner and that a gastight housing part is arranged thereupon as an integrated
component
of the wall, so that the throughflow opening is closed by a plug, due to which
the periphery of
the bottom pouring nozzle has a gastight layer, particularly surface, that,
including the plug,
can be considered as a housing part according to the invention.
It can be advantageous to apply a layer of ablative material, such as a paper
cover known to
one skilled in the art to prevent the adherence of slag or dross which is
typically present
floating on the surface of the section of metal housing to be immersed, thus
speeding the
melting of said housing.
It is efficient to arrange a getter material, particularly of at least one
metal from the group of
Silicon, Calcium, Titanium, Aluminium, Magnesium or Zirconium inside the
housing. This
allows the free oxygen present in the housing to form a compound therewith.
The refractory material of the wall could have a low porosity of 2 to 13 %,
preferably lower
than 10 '%. Such material, for example carbon impregnated alumina graphite
material, could
have sufficient sealing capacity in the meaning of the invention. Standard
refractory materials
have a porosity of more than 16 %.
It is also advantageous, to have a heating arranged in the wall of the
throughflow channel, in
order to preheat the bottom pouring nozzle prior to use and to prevent or
reduce thermal
shocks.
It is preferred that a layer of ablative material, such as a paper is arranged
around the outer
surface of the bottom pouring nozzle. Furthermore it could be advantageous
that the outer
circumference of the wall, below the gastight housing, is surrounded by an
insulating cement
seal at its upper end, whereby the cement seal preferably comprises a heat
resistant
castable cement, preferably at least one of alumina, aluminosilicate,
magnesia. Further it is
prefered that the outer circumference of the wall, below the gastight housing,
is surrounded
by an insulating material, especially ceramic paper or fiber cloth made of
ceramic fibers at its
lower end. The insulating material can be arranged immediately below the
insulating cement
seal.
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It is also preferred that below the gastight housing, especially between the
gastight housing
and the wall gas channels are arranged in longitudinal direction of the
nozzle.
An inventive sliding valve for use with a bottom pouring nozzle and especially
for use with an
above defined bottom pouring nozzle, comprising a gastight outer housing,
characterized in
that the gastight housing comprises at least one gas inlet and at least one
gas outlet. The at
least one gas inlet can be used for pumping inert gas like Argon into the
housing and the at
least one gas outlet can be used for establishing a vacuum within the housing.
An advantageous method is, after opening of the slide valve or the stopper rod
closure to
either have
a. an inert gas overpressure is obtained, in case an underpressure was present
prior to
opening or
b. an underpressure is obtained, in case an overpressure was present prior to
opening.
It is especially advantageous, that the underpressure amounts to 1 up to
1013mbar,
particularly 150 to 1013mbar and the overpressure amounts to 1013 up to
1500mbar or
more, that means, above atmospheric pressure.
First a vacuum (underpressure) can be obtained especially with a bottom
pouring nozzle for
use with a casting ladle and later on, after opening, an inert gas
overpressure. For a bottom
pouring nozzle for use in a tundish, it is advantageous to obtain an inert gas
overpressure
first, and a vacuum after opening.
The invention is explained in the drawings by way of example. The drawings are
showing as
follows
Fig. 1 a bottom pouring nozzle for a tundish
Fig. 2 a further bottom pouring nozzle for a tundish
Fig. 3 a third kind of a bottom pouring nozzle for a tundish
Fig. 4 a bottom pouring nozzle for a casting ladle
Fig. 5 a further bottom pouring nozzle for a casting ladle
Fig. 6 the arrangement of a bottom pouring nozzle to a tundish and
Fig. 7 the arrangement of a bottom pouring nozzle to a casting ladle.
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The bottom pouring nozzle according to Fig. 1 has a throughflow channel 1 with
several
outflow openings 2 in the side. The wall 3 of the throughflow channel 1 is
essentially made of
a mixture of aluminium oxide and graphite. A fitting collar 4 is arranged at
its upper end for
arrangement to a slide valve which is the main body of the sealed system. The
outer
circumference of the wall 3 is surrounded by an insulating cement seal 5 at
its upper end,
under which an insulating material 6, for example ceramic paper or fiber cloth
made of
ceramic fibers is arranged. A gastight housing 7 is arranged onto the cement
seal 5 and the
insulating material 6. This encases the entire bottom pouring nozzle all the
way up to the
fitting collar 4 and only has an opening 8 for the supply of inert gas
(Argon). The inert gas
may be introduced in a slit between gastight housing 7 and the insulating
material 6 for
purging purposes. A so called slag band 9 made of zirconium graphite 9 is
fitted above the
outflow openings 2. The outflow openings 2 are closed by the housing 7.
Fig. 2 shows a similar Bottom pouring nozzle. It has a cap 10 which is made,
for example, of
steel, at its lower end, which closes the outflow openings 2. At least above
the cap 10 at
least the surface of the wall 3 is gastight, thus establishing a gastight
housing part. A layer of
an ablative material 10' is arranged at the outer surface of the cap 10, for
example made of
paper. The ablative material could also cover the total outer surface of the
bottom pouring
nozzle.
Fig. 3 shows an arrangement similar to Fig. 1, whereby an annular slit 27 is
arranged within
the wall 3 and which is connected with opening 8. Herewith it is possible to
introduce Argon
into the wall 3 ant to establish an overpressure.
The bottom pouring nozzle for a casting ladle (Fig. 4) principally constructed
in a similar
manner, but it has a straight throughflow opening 1' and an outflow opening 2'
arranged in
the centre of the lower end. A similar arrangement is shown in Fig. 5, whereby
the outflow
opening 2' is closed by a plug 28 and whereby at least the outer surface of
the wall 3 is made
gastight. Plug 28 can melt or burn or dissolve by influence of the metal melt
which is
arranged in the metallurgical vessel, thus releasing outflow opening 2'. For
example plug 28
can be made of steel or of stainless steel or of copper.
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The arrangement of a bottom pouring nozzle as a lower nozzle 11 of a tundish
12 is shown in
Fig. 6. The tundish 12 has a lining 13 composed of a plurality of layers to
protect the tundish
wall 14. In the bottom of the tundish 12, an upper nozzle 15 is arranged, in
which electrode
materials 16 are embedded and whereby the outer side 29 of the upper nozzle 15
is formed
gastight. At its upper end, the upper nozzle 15 is surrounded by a well block
17 for
protection. At the lower end of the upper nozzle 15, underneath the bottom of
the tundish 12,
a slide valve 18 is fitted, surrounded by a gastight slidegate housing 19,
which at its upper
end is connected in a gastight manner with the outer side 29 of the upper
nozzle 15 and
which at its lower side is connected in a gastight manner with the gastight
housing 7. An inlet
20 for inert gas and a connection 21 for a vacuum pump is provided in the
slidegate housing
19.
Fig. 7 shows the arrangement of a bottom pouring nozzle to a casting ladle 22
as well as the
tundish 12 arrangement underneath. The inside of the tundish contains apart
from the outlet
23 also so called baffles 24, that mechanically calm the steel melt, in order
to prevent too
heavy turbulences. The bottom pouring nozzle from Figure 4 is arranged to the
casting ladle
opening (sliding valve) 25. The inlet for inert gas as well as the connection
for a vacuum
pump are not shown in Fig. 7 for simplicity.
One skilled in the art will understand that the general mechanical
arrangements of the
described components of the invention employed to transfer molten metal from
the ladle to
tundish and then from the tundish to mould are very similar and share common
shapes and
functions. The casting ladle 22 itself comprises a multi layered lining 26 on
its inside.
Prior to casting, the slide valve 25 is closed, a vacuum is obtained in the
throughflow channel
1', FIG 4, of a casting ladle, in order to remove oxygen. A vacuum is obtained
in this manner,
in throughflow channel 1', in the wall of the bottom pouring nozzle, in
between the inner wall
surrounding the throughflow channel 1' and the outer housing and an
underpressure
(vacuum) is obtained in the slide valve 25 as well. During inflow of the steel
melt in the
throughflow channel 1' the gastight housing 7 melts in the region of the
throughflow opening
2' when it comes into contact with the molten steel, so that the steel melt
can flow into the
lower arranged vessel (tundish 12). The underpressure is regulated for example
in a range of
700 to 800 mbar, the subsequent overpressure was set to a maximum of 1500
mbar.
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A bottom pouring nozzle is also arranged at the outlet of the tundish 12.
Herein an
overpressure is obtained using an argon pressure of maximum 1500 mbar. The
gastight
housing 7 melts in the region of the outflow opening 2 during inflow of the
steel melt in the
throughflow channel 1, so that the steel melt can flow into the lower arranged
vessel. The
gas is being pumped out of the bottom pouring nozzle, so that a vacuum is
obtained.
