1
- - Specification
METHOD OF STARTING TO SUPPLY MOLTEN STEEL
Field of the Invention
[OOO 11
The present invention relates to a method of starting to supply molten steel from a
ladle to a tundish in an operation of continuous casting, more particularly to a method of
.starting to supply mo6n steel while a lower end portion of a long nozzle is immersed in
molten steel in the tundish.
Related Art
[0002]
The molten steel decarbonized in the refining furnace is tapped into a ladle. In
the ladle, the molten steel is subjected to secondary refining and the like. The refined
molten steel together with the ladle is mounted onto the turret of the continuous casting
machine, and is set above a tundish. In the operation of continuous casting, a sliding
nozzle is installed directly under the upper nozzle that discharges the molten steel in the
ladle. To a lower portion (lower nozzle) of the sliding nozzle, a long nozzle is attached
via the support device. At this time, the long nozzle is set onto the sliding nozzle with a
little pressure against the sliding nozzle so that there is no gap between the lower portion
of the sliding nozzle and the long nozzle. Then, with the sliding operation of the sliding
plate of the sliding nozzle, the molten steel is supplied from the ladle to the tundish via the
long nozzle, to thereby pour the molten steel.
[0003]
Two types of pouring of the molten steel are in practice: so-called open pouring in
which molten steel is poured while the lower end portion (fkont-end portion) of the long - &.-7
nozzle is not immersed in the molten steel in the tundish; and immersion pouring in which
- . molten steel is poured while the lower end portion of the long nozzle is immersed in the
molten steel. Howeve-r , in the case of the open pouring, the slag formed on the molten
steel surface in the tundish is entrained, and the cleanliness of the molten steel may be
degraded because of the slag, the oxidant (inclusion), or the like. Therefore, because of
its ability to suppress the entrainment of slag, the immersion pouring (immersion opening)
is mainly practiced. Especially when a multitude of heats are continuously cast, the
immersion pouring has an advantage in that it is possible to prevent the contamination of
the molten steel at a joint portion between cast pieces caused by the slag, oxidant
(inclusion), or the like.
[0004]
- -
When starting to supply molten steel from the ladle to the tundish, the molten
steel in the ladle may be cooled to coagulate, leading to possible clogging in the nozzle.
Therefore, before the molten steel is poured into the ladle, sand-like filling (hereinafter,
also referred to as "filling sand") is previously filled in the upper nozzle, to thereby
prevent the molten steel from being immersed into a discharge hole (nozzle hole). When
the sliding nozzle is slid open at the time of starting to supply the molten steel, the filling
sand in the upper nozzle spontaneously falls (a hole is spontaneously opened
therethrough) to allow the molten steel to flow out.
[0005]
In the immersion opening, the filling sand falls through the inner hole of the long
nozzle to deposit on the molten steel surface. Therefore, after the deposited filling sand
is speedily discharged to the outside of the long nozzle by the falling flow of the molten
steel, it is necessary to pour molten steel into the tundish. If it is not possible to
favorably discharge the fallen and deposited filling sand, the filling sand remains in the
inner hole of the long nozzle. Its large remaining amount invites the clogging of the long
nozzle. As a result, the molten steel gushes from the connection portion between the
sliding nozzle and the long nozzle (molten steel leakage), and a nitrogen concentration in
the molten steel is increased (hereinafter, also referred to as "nitrogen pick up") by the air
that has flowed into the inner hole of the long nozzle through the gap produced in the
connection.portion. In the case of the immersion opening, the aforementioned trouble
may arise at the time of A replacement of a ladle, when the molten steel surface solidifies
(hereinafter, also referred to as "skinning") in the inner hole of the long nozzle to clog the
inner hole of the long nozzle.
Therefore, for example, Patent Document 1 discloses an invention in which, with
an inner diameter of a lower end portion to be immersed in molten steel in a tundish being
set to not less than 1.5 times and less than 2.25 times as long as the inner diameter of a
straight body portion formed at an upper portion of the long nozzle, the fallen and
deposited filling sand'k madz thinner at the start of casting for easier discharge to the
outside of the long nozzle, to thereby prevent the clogging from being produced in an
inner hole of the long nozzle..
, ,
[0007]
Patent Document 2 discloses a method in which, with an injection port of an
inactive gas into a nozzle being provided at a predetermined location of a ladle nozzle
(lower nozzle) or a long nozzle, and with a lower end portion of the long nozzle being
installed in a state of being immersed below a molten steel surface in a tundish, the ladle
nozzle and the long nozzle are opened while an inactive gas is being injected before the
ladle nozzle is opened.
Patent Document 3 discloses a method in which, when a lower end portion of a
long nozzle is kept waiting until a next ladle is attached while the lower end portion is
immersed and held in molten steel in a tundish, then a combustion thennogenic substance
that burns by contact with molten steel in the long nozzle or by the radiant heat from the
molten steel is charged into an inner hole of the long nozzle, a next ladle is attached to the
long nozzle, and the pouring of molten steel to the next ladle and the following ladles is
started.
Reference Document
Patent Document ... _ .. ,
[0009]
[Patent Document I]: Japanese Unexamined Patent Application, First Publication
NO. 2002-001496
Patent Document 2: Japanese Unexamined Patent Application, First Publication
NO. 2359-125250
Patent Document 3: Japanese Unexamined Patent Application, First Publication
NO. S63-137553
Disclosure of the Invetition .
Problems to be Solved by the Invention
[OO 1 01
. .
However, the aforementioned conventional techniques have the following
problems.
The technique described in Patent document 1 is effective to some degree for
prevention of the clogging of the long nozzle. However, there are still some cases where
the long nozzle is clogged by the fallen and deposited filling sand. As a method of
securely discharging the fallen and deposited filling sand to the outside of the long nozzle,
setting the size of the larger-diameter portion of the long nozzle to an extremely large
value can be conceived. However, in that case, the larger-diameter portion of the long -
nozzle may vibrate due to the flow of the molten steel in the tundish, resulting in a
possible leak of the molten steel from the connection portion between the sliding nozzle
and the long nozzle, possible bending damage of the neck portion (upper end portion) of
the long nozzle, or other possible failure.
[OO 1 11
The technique described in Patent document 2 is not capable of preventing the
production of skinning at the time of replacing a ladle. If skinning is produced, it is not
possible to remove the solidified molten steel by use of the inactive gas, inevitably leading - ;: -9
to the clogging of the long nozzle. Furthermore, there is also a problem in that a leak of
the inactive gas is likely to occur, which makes it difficult to control the internal pressure
of the long nozzle. *.
[0012]
The technique described in Patent document 3 is effective to some degree for
preventing skinning at the time of replacing a ladle. However, even in the case without
skinning, there is a problem in that, if the long nozzle has a large immersion depth, the
filling sand falls and deposits on the molten steel surface in the long nozzle, which
prevents immersion opening. Furthermore, although there is no skinning, the solidified
molten steel is attached to and remains on the inner wall surface of the long nozzle.
Therefore, when falling, the filling sand may be caught by the solidified molten steel.
This may invite unopenable deposition, which prevents a hole 'from being opened.
[00 131
The present invention has been achieved in view of the above circumstances, and
has an object to provide a method of starting to supply molten steel that is capable of
securely preventing the clogging of a long nozzle in the immersion pouring, to thereby
prevent troubles at the start of supplying molten steel from occurring.
Methods for Solving the Problem
[00 141
The present inventors have obtained knowledge that the factors inductive of the
clogging of the long nozzle are: solidified molten steel that clogs the inner hole of the long
nozzle like a plug at the time of replacing a ladle; and a frictional force acting on the
filling sand that has fallen and deposited on the molten steel surface in the long nozzle.
The present invention prevents the molten steel surface in the long nozzle fiom solidifying
at the time of replacing a ladle, and also minimizes the frictional force acting on the filling
sand that has fallen and deposited on the molten steel surface in the long nozzle, to thereby
prevent the clogging of the long nozzle.
[OO 1 51 2 - 3
As a result of devoted research in order to solve the aforementioned problems and
achieve the aforementioned object, the present inventors have adopted the following.
(1) An aspect o_f the present invention includes: a charge step of charging a
thermogenic gasification substance into a long nozzle from an opening of an upper end
portion of the long nozzle with a lower end portion thereof being immersed in molten steel
in a tundish; a connection step of, after the charge step, connecting the upper end portion
of the long nozzle via a seal member to a sliding nozzle that is in communication with a
discharge hole in a bottom surface of a ladle and controls a flow rate of the molten steel
flowing down from the ladle; an inner-pressure-of-the-long-nozzle check step of, after the
connection step, checking generation of a bubble on molten steel surface in the tundish;
and a fall step of, aftefihe inner-pressure-of-the-long-nozzle check step, allowing filling
sand in the discharge hole to fall into the long nozzle via the sliding nozzle, wherein an
immersion depth L of the lower end portion of the long nozzle with respect to the molten
steel surface in the charge step is 50 to 350 mm.
[00 1 61
(2) In the method of starting to supply molten steel as described above in (I), the
thermogenic gasification substance may be organic matter.
[00 171
(3) In the method of starting to supply molten steel as described above in (1) or
(2), a charge amount of the thermogenic gasification substance in the charge step may be
20 to 400 g.
[00 1 81
(4) In the method of starting to supply molten steel as described above in (1) or
(2), a lower nozzle may be connected directly under the sliding nozzle, and the upper end
portion of the long nozzle may be connected to the lower nozzle via the seal member in
the connection step.
[00 191
(5) In the method of starting to supply molten steel as described above in (3), a
lower nozzle may be connected directly under the sliding nozzle, and the upper end 3 "3
portion of the long nozzle may be connected to the lower nozzle via the seal member in
the connection step. , ,
- - &
Effects of the Invention
[0020]
According to the aspect as described above in (I), to prevent the molten steel
surface in the long nozzle fiom solidifjing at the time of replacing a ladle, a thermogenic
gasification substance is charged into the inner hole of the long nozzle before the long
nozzle is connected to the sliding nozzle of the ladle. Through the heat generated by the
thermogenic gasification substance and through the agitation effect on the molten steel by
the produced gas, a decrease in temperature of the molten steel surface in the long nozzle
is prevented. This prevents the solidification (skinning) of the surface of the molten steel
in the long nozzle. As a result, at the time of opening the sliding nozzle, it is made easy
to discharge the filling (filling sand) that has fallen and deposited on the molten steel
surface in the long nozzle.
[002 11
However, only by the prevention of solidification of the molten steel, it is not
possible to securely prevent the clogging of the long nozzle. This is because there are
cases where, with the frictional force acting between the filling sand that has fallen and
deposited on the molten steel surface in the long nozzle and the inner wall surface of the
long nozzle, the filling sand does not go down in the long nozzle, which prevents the
filling sand from being discharged to the outside of the long nozzle.
[0022]
FIG. 6 shows forces acting on filling sand 19 that has fallen and deposited on a
molten steel surface in a long nozzle 10. Note that the gravity and the buoyant force
acting on the filling sand 19 do not have an essential influence on the clogging of the long
nozzle 10. Therefore, in the following description, the gravity and the buoyant force
acting on the filling sand 19 are ignored.
Typically, if a molten steel static pressure 25 is loaded fiom above the granular a-3
filling sand 19 that is filled in the long nozzle 10 (with a cylindrical shape), the vertical
force is not transmitted downwardly as it is, but component forces directed laterally are
produced because the filling sand 19 is composed of granular bodies. Therefore, from
the top portion of the filling sand 19 to the bottom portion of the filling sand 19, the
molten steel static pressure 25 is more dispersed, a downward stress 26 that is directed
downwardly is decreased, and a lateral stress 27 that presses the inner wall of the long
nozzle 10 increases. With the increase in the lateral stress 27, there is an increase in a
frictional force 28 acting between the filling sand 19 and the inner wall surface of the long
nozzle 10. Therefore, there are cases where the molten steel static pressure 25 makes it
difficult to discharge the filling s a ~ d19 . As the filling sand 19 moves further downward
in the long nozzle 10,-the lateral stress 27 is further increased to increase the frictional
force 28. This makes it more difficult to discharge the filling sand 19.
COO231
Namely, the larger the immersion depth of the long nozzle is, the longer the
distance is from the molten steel surface in the long nozzle to the lower end of the long
nozzle, making it difficult to discharge the filling sand, which has fallen and deposited on
the molten steel surface in the long nozzle, to the outside of the long nozzle. Therefore,
in the present aspect, with an immersion depth L of the long nozzle at the start of pouring
the molten steel being set to 50 to 350 rnm, the gas produced from the aforementioned
thermogenic gasification substance is used to increase the inner pressure of the long
nozzle, to thereby lower the molten steel surface in the long nozzle to the lower end of the
long nozzle. The filling sand that has fallen and deposited on the previously-lowered
molten steel surface in the long nozzle is readily discharged to the outside of the long
nozzle by the pressure of the molten steel that falls following the filling sand.
[0024]
Here, if the immersion depth L of the lower end portion of the long nozzle is set
to less than 50 mm (especially, less than 40 mm), the slag of the molten steel surface in the
tundish is entrained by the entrainment flow that is induced by the molten steel discharged
from the lower end of the long nozzle, which deteriorates the quality of the molten steel. C-J
Therefore, this is not favorable. On the other hand, if the immersion depth L of the lower
, - .- end portion of the long nozzle is over 350 mm, the frictional force acting on the filling
sand that has fallen-and- d eposited on the molten steel surface in the long nozzle becomes
too strong, which makes it difficult to discharge the deposited filling sand to the outside of
the long nozzle. Furthermore, there is apprehension that the inner pressure may be
increased by the gas produced fiom the thermogenic gasification substance. To be more
specific, with an increase in inner pressure of the long nozzle, the long nozzle is swung
when the gas produced fiom the long nozzle is released. As a result, there is a leak of the
produced gas from the connection portion. This leads to a decreased inner pressure of
the long nozzle or other outcomes, which makes it impossible to control the inner
-
pressure. -
[0025]
Note that the inner pressure of the long nozzle is controllable by the immersion
depth or the charge amount of the thermogenic gasification substance. However, there
are cases where the gas produced from the thermogenic gasification substance leaks from
the connection portion between the lower portion of the sliding nozzle (or the lower
nozzle located thereunder) and the long nozzle, making it difficult to control the inner
pressure. Therefore, it is necessary to provide the connection portion with a seal
member.
[0026]
Furthermore, in the present invention, the inner pressure of the long nozzle with
an immersion depth of L mm is set to more than a value at which bubbles are recognizable
on the molten steel surface of the tundish. This is because of the following reasons.
The inner pressure, of the long nozzle with an immersion depth of L mm, at which bubbles
are recognizable on the molten steel surface of the tundish, is referred to as L mm iron
column. If the inner pressure of the long nozzle is roughly L mm iron column, that is, the
inner pressure of the long nozzle is substantially the same as the pressure by the iron
column (molten steel column) with a height of L mm, then the molten steel surface in the
long nozzle is lowered to the lower end (fiont end) of the long nozzle. Furthermore, if
the inner pressure of the long nozzle is above L mm iron column, then the gas in the long
- -nozzle is released to the outside of the long nozzle, and can be observed as bubbles on the
molten steel surface in $e tundish. If bubbles are recognizable, it is made clear that the
molten steel surface in the long nozzle is positioned at the lower end of the long nozzle,
which enables secure discharge of the filling sand. On the other hand, if bubbles are not
recognizable, this is conceivably caused by the situation where it is not possible to
discharge the filling sand or by a gas leak from the connection portion of the long nozzle
provided with the seal member (This produces a flow passage for a gas leak, directly
I leading to a nitrogen pickup of the molten steel). Because these failures invite
production stoppage or deteriorated quality (discarding as waste steel and reproduction of
alternatives), it is necessary ta address the failures. However, by checking that the inner _
pressure of the long nozzle has exceeded L mm iron column, it is possible to prevent these
failures from occurring.
100271
Therefore, in the method of starting to supply molten steel according to the
present invention, solidification of the molten steel surface in the long nozzle at the time
of replacing a ladle is prevented. Because the frictional force acting on the filling sand
that has fallen and deposited on the molten steel surface in the long nozzle is minimized,
the clogging of the long nozzle in the immersion pouring is securely prevented, making it
possible to prevent the troubles at the start of supplying molten steel from occurring.
Furthermore, at that time, the inner pressure of the long nozzle with an immersion depth of
L mm is configured to be above L mm iron column. Therefore, the gas released to the
outside of the long nozzle is observable as bubbles on the molten steel surface in the
tundish. Thereby, it is possible to visually check that the molten steel surface in the long
nozzle is positioned at the lower end of the long nozzle.
Brief Description of the Drawings
[0028]
FIG. 1 is a general view showing a facility that supplies molten steel according to +:-9
a first embodiment of the present invention.
FIG. 2 is a schematic view for explaining a procedure of a method of starting to
supply molten steel -acc_ording to the present embodiment.
FIG. 3 is a schematic view for explaining the procedure of the method of starting
to supply molten steel.
FIG. 4 is a schematic view for explaining the procedure of the method of starting
to supply molten steel.
FIG. 5 is a schematic view for explaining the procedure of the method of starting
to supply molten steel.
FIG. 6 is a schematic view for explaining a force acting on the filling sand that
has fallen and deposika on a surface of molten steel in a long nozzle.
FIG. 7 is an exemplary graph showing a correlation between the weight of a paper
tube that has been charged into an inner hole of the long nozzle as . a thermogenic ,
gasification substance and an amount of a generated gas.
Embodiments of the Invention
[0029]
Hereunder is a description of a method of starting to supply molten steel
according to an embodiment of the present invention, with reference to FIG. 1 to FIG. 5.
The following description is given on the precondition that the long nozzle is
provided upright so that its head is positioned on the upside and that its front-end portion
is positioned on the downside.
[0030]
As shown in FIG. 1, molten steel 5 in a ladle 1 that is set above a tundish 2 is
poured into the tundish 2 from a discharge hole 20 in the bottom surface of a ladle 1
through a long nozzle 10, and is then fed into a mold 3 where it is cast.
[003 11
As shown in FIG. 2, the long nozzle 10 has a cylindrical shape. In the long
nozzle 10, a flow passage 10a (inner hole) through which the molten steel 5 flows is
formed along its central axis. At the top portion of the long nozzle 10, a cone-shaped
recess portion lob is formed into which a lower end portion of a sliding nozzle 16 (or a
! lower nozzle 13 located_thereunder) is to be fitted. In the present embodiment, to secure
high airtightness between the sliding nozzle 16 (or the lower nozzle 13 located thereunder)
and the long nozzle 10, a seal member 12 is mounted on the cone-shaped recess portion
lob. As the seal member 12, a conventionally-used one such as fire mortar, ceramic
fibers, joint sealer such as fixed-shaped joint sealer may be used. Among these,
fixed-shaped joint sealer is a thin-plate-like refractory material that is previously formed
in a shape similar to the joint site and is excellent in workability and in detachability from
the mold.
The bottom portion of the ladle 1, an upper nozzle 17, the sliding nozzle 16, and
the lower nozzle 13 may be connected to each other with airtightness being previously
secured typically by use of mortar or the like, for use in an operation of continuous
, ,
casting. When the long nozzle 10 is used for the operation of continuous casting, it often
happens that the used long nozzle 10 is replaced with a new long nozzle 10.
Consequently, connection by use of mortar or the like is inconvenient. Therefore, a seal
member is mounted on the cone-shaped recess portion lob of the upper end portion 10d of
the long nozzle 10, and then the long nozzle 10 is connected to the sliding nozzle 16 (or
the lower nozzle 13 located thereunder), to thereby make it possible to secure airtightness.
[0032]
The long nozzle 10 with the seal member 12 set at its top portion is provided
upright in a state with a lower end portion 10c (front-end portion) being immersed in the
molten steel 5 in a tundish 2 (not shown in the figures).
Then, the thermogenic gasification substance 11 is charged fi-om the upper end
portion 10d of the long nozzle 10 into the flow passage 10a.
The thermogenic gasification substance 11 is a substance that, in receiving the
heat of the molten steel, is oxidized to generate heat and, at the same time, is gasified by
the atmosphere (oxygen) in the flow passage 10a. As the thermogenic gasification
substance 11, for example an organic material such as paper or wood, or a - 2.",7
carbon-containing material such as coal may be used. The charge amount of the
thermogenic gasification substance.11 may be approximately 20 to 400 g, as will be
described later. +
LO0331
Through the heat generated by the thermogenic gasification substance 11 and
through the agitation effect on the molten steel by the produced gas, a decrease in
temperature of a molten steel surface 21 in the long nozzle 10 is prevented, and
solidification (skinning) on the surface of the molten steel in the long nozzle 10 is deterred
(see FIG. 3).
[0034]
As shown in-F1G. 4, to the bottom portion of the ladle 1, the upper nozzle 17 for
discharging the molten steel 5 in the ladle 1 is attached. Furthermore, directly under the
upper nozzle 17, the sliding nbzzle 16 that controls the flow rate of the molten steel 5 at
the time of discharge is installed.
The sliding nozzle 16 includes: a fixed plate 15 that is fixed to the bottom portion
of the ladle 1 via a fixation metal mount (not shown in the figure); and a sliding plate 14
that slides with respect to a lower surface of the fixed plate 15. To the lower surface of
the sliding plate 14, the lower nozzle 13 is attached. Furthermore, in the fixed plate 15,
there is formed a nozzle hole 15a (discharge hole 20) that communicates with a nozzle
hole 17a (discharge hole 20) of the upper nozzle 17. In the sliding plate 14, there is
formed a nozzle hole 14a that communicated with a nozzle hole 13a of the lower nozzle
13.
[0035]
Before starting to supply the molten steel 5, the nozzle hole 15a of the fixed plate
15 is sealed by the sliding plate 14. In the nozzle hole 17a of the upper nozzle 17 and the
nozzle hole 15a of the fixed plate 15, granular filling sand 19 (filling) based on SiOz,
AlzOs, MgO or the like is filled.
[0036]
In the present embodiment, the long nozzle 10 with a gas G produced in the flow &-7
passage 10a is pushed upwardly by approximately 100 to 400 mm. Thereby, the lower
end portion of the sliding nozzle 16 (orthe lower nozzle 13 located thereunder) is fitted
into the recess portion 1_0b of the long nozzle 10. Thus, the sliding nozzle 16 (or the
lower nozzle 13 located thereunder) and the long nozzle 10 are connected to each other via
the seal member 12. An immersion depth L of the lower end portion 10c of the long
nozzle 10 after the connection is set to 50 to 350 mm.
At the time of pushing up the long nozzle 10, the molten steel surface 21 in the
long nozzle 10 is lowered relative to the long nozzle 10. However, due to the effect of
the charged thermogenic gasification substance 11, a decrease in temperature of the
molten steel is prevented. Therefore, the amount of the molten steel 5 attached to the
inner wall of the flow-passagc 10a is decreased, and hence, the attached molten steel 5 is
not likely to be an obstacle to a discharge of the filling sand 19 that falls and deposits at
the time of opening of the sliding nozzle 16.
[0037]
Through the above operation, the gas G produced from the thennogenic
gasification substance 11 is sealed in the flow passage 10a. This increases the pressure in
the flow passage 10a (the inner pressure of the long nozzle 10) to a value above L mm iron
column. As a result, the gas G in the flow passage 1Oa is released to the outside of the
long nozzle 10, and hence, is observable as bubbles B on the molten steel surface 21 in the
tundish 2.
Because an adjustment of the amount of the charged thermogenic gasification
substance 11 can bring about a situation where the pressure in the flow passage 10a is
above L mm iron column, it is preferable that the amount of the thermogenic gasification
substance 11 to be charged into the long nozzle 10 be previously determined based on the
tests on the actual device or the results of tentative calculation on the amount of the
produce gas. However, while it is not feasible that the inner pressure of the long nozzle
10 be far above L rnrn iron column (which is determined by the immersion depth L),
extremely too much amount of the produced gas generates splashes around the long nozzle
10, and hence, is not favorable. ,a -2
-5
[003 81
When the bubbles B released from the lower end of the long nozzle 10 are
recognized, a hydraulic e- cylinder (not shown in the figure), which is a drive mechanism
connected to the sliding plate 14, is driven and is slid horizontally the sliding plate 14.
Thereby, the nozzle hole 14a of the sliding plate 14 is communicated with the nozzle hole
15a of the fixed plate 15. As a result, the filling sand 19 filled in the nozzle hole 17a of
the upper nozzle 17 and the nozzle hole 15a of the fixed plate 15 simultaneously falls in
the flow passage 10a of the long nozzle 10, and then deposits on the molten steel surface
21 positioned at the lower end of the long nozzle 10 (see FIG. 5). The filling sand 19 that
has fallen and deposited on the molten steel surface 21 is readily discharged to the outside
of the long nozzle 10-by the pressure of the molten steel 5 that falls following the filling
sand 19.
[0039] . ,
The present inventors have confirmed that, if cellulose (paper) as organic material
or a carbon lump approximately 100 mass% of which can be gasified (one which is not
gasified but only carbonized due to insufficient oxygen and whose mass ratio is decreased
by approximately 20 to 50 percent) is used as the thermogenic gasification substance 11 in
the long nozzle 10 with a length of approximately 0.9 to 2 m and an inner diameter of
approximately 80 to 300 mm, then a charge amount of 20 g to 400 g allows the inner
pressure of the long nozzle 10 to exceed L mm iron column, and that there is no
significant splash around the long nozzle 10.
[0040]
FIG. 7 shows an exemplary correlation between the weight of the paper tube (a
piece of paper formed into a tube) charged into the'inner hole of the long nozzle 10 as the
therrnogenic gasification substance 11 and the amount of produced gas. At the time of
the test, the inner hole of the long nozzle 10 had a space volume of about 0.02m3, the long
nozzle 10 had an immersion depth of about 300 mm, and the paper tube had a combustion
rate of 40% (calculated based on the inner pressure of the long nozzle 10).
In the present test, if the inner pressure of the long nozzle 10 was less than 14.7 k-3
kPa, then bubbles B were not generated from the lower end of the long nozzle 10. On
I + ' the other hand, if the inner pressure of the long nozzle 10 was-above 58.8 kPa, then there
was abnormal generation of splashes around the long nozzle 10. Therefore, it is
preferable that the inner pressure of the long nozzle 10 be not less than 14.7 kPa and not
more than 58.8 kPa.
[004 11
In summary, an embodiment of the present invention is as shown below in (I) to
(5).
(1) A method of starting to supply molten steel 5, including: a charge step of
charging a thermogenic gasification substance 11 into a long nozzle 10 from an opening of
an upper end portion i6d of the long nozzle 10 with a lower end portion 10c thereof being
immersed in molten steel 5 in a tundish 2; a connection step of, after the charge step,
connecting the upper end po, rtio, n 10d of the long nozzle 10 via a seal member 12 to a
sliding nozzle 16 that is in communication with a discharge hole 20 in a bottom surface of
a ladle 1 qnd controls a flow rate of the molten steel 5 flowing down from the ladle 1; an
inner-pressure-of-the-long-nozzle- 10 check step of, after the connection step, checking
generation of a bubble B on molten steel surface 21 in the tundish 2; and a fall step of,
after the inner-pressure-of-the-long-nozzle- 10 check step, allowing filling sand 19 in the
discharge hole 20 to fall into the long nozzle 10 via the sliding nozzle 16, wherein an
immersion depth L of the lower end portion 10c of the long nozzle 10 with respect to the
molten steel surface 21 in the charge step is 50 to 350 mm.
[0042]
(2) In the method of starting to supply molten steel 5 as described above in (I),
the thermogenic gasification substance 1 I may be organic matter.
[0043]
(3) In the method of starting to supply molten steel 5 as described above in (1) or
(2), a charge amount of the thermogenic gasification substance 11 in the charge step may
be 20 to 400 g.
[0044] 4;u ,7
(4) In the method of starting to supply molten steel 5 as described above in (1) or
._ a -(2), a lower nozzle 13 may be connected directly under the sliding nozzle 16, and the
upper end portion 10d o_f the long nozzle 10 may be connected to the lower nozzle 13 via
the seal member 12 in the connection step.
LO0451
(5) In the method of starting to supply molten steel 5 as described above in (3), a
lower nozzle 13 may be connected directly under the sliding nozzle 16, and the upper end
portion 10d of the long nozzle 10 may be connected to the lower nozzle 13 via the seal
member 12 in the connection step.
[0046]
An embodiment of the present invention has been described above. However,
the present invention is not limited only to the structure according to the above
embodiment, but includes other embodiments and modifications that can be conceived
within the scope of the appended claims. For example, in the above embodiment, the
shape of the long nozzle 10 has been described as of straight type. However, the long
nozzle 10 may have an expanded-diameter portion at its lower end portion. Furthermore,
in the above embodiment, the lower nozzle 13 has been described as being installed
between the sliding nozzle 16 and the long nozzle 10. However, the sliding nozzle 16
and the long nozzle 10 may be connected directly to each other.
[Example 11
[0047]
The results of the tests conducted to verify the advantageous effects of the present
invention are listed in Table 1. The frequency of occurrence of clogging and the
propriety of adoption in actual device in the table were determined with reference to
comparative example 1. As for the frequency of occurrence of clogging, if the frequency
was improved over that of comparative example 1, it was evaluated as good. If the
frequency was similar to that of comparative example 1, it was evaluated as fair. If the
frequency became worse than that of comparative example 1, it was evaluated as bad.
Furthermore, as for the propriety of adoption in the actual device, if adoptable, it was
evaluated.as good. If adoptable but inferior to that of comparative example 1, it-was - .
evaluated as fair. If n ~atdo ptable, it was evaluated as bad.
As the long nozzle 10, a straight-type nozzle with an inner diameter of 100 mm
and a length of 1.5 m was used. However, only in comparative example 1, a long nozzle
10 with an inner diameter of the lower end portion being extended 1.4 times as long was
used.
[0048]
[Table I]
[0049]
Examples 1 6 3 are improved over comparative example 1 in the frequency of
occurrence of clogging, and hence, are adoptable in the actual device. However, in the
case of example 3, the amount of the thermogenic gasification substance 11 was so great
that there was abnormal generation of splashes around the long nozzle 10. Therefore, it
is required that measures be taken such as providing a shielding plate for shielding
splashes.
[OOSO]
On the other hand, comparative example 2 is improved over comparative
example 1 in the frequency of occurrence of clogging. However, there were cases where
the entrainment of slag was found at the lower end of the long nozzle 10. Therefore, its
adoption in the actual device is evaluated as bad. Comparative example 3 was similar to
comparative example 1 in the frequency of occurrence of clogging. However, there were
cases where a gas leaked from the connection portion between the long nozzle 10 and the
lower nozzle. Therefore, its adoption in the actual device was evaluated as bad.
Comparative example 4 as well as comparative example 5, to which the technique
according to patent document 3 was applied, showed worse results than comparative
example 1 both in the frequency of occurrence of clogging and the propriety of adoption
in the actual device. Especially in the case of comparative example 4, a skinning was
found in the investigation after the test. Additionally, the gas supply hole was clogged, - &-9
and there were cracks around the gas supply hole.
Furthermore, presumably due to a low inner pressure of the long nozzle 10, _ .- . -- - -
comparative example S,was not capable of discharging the filling sand 19, which had
fallen and deposited on the molten steel surface 21, to the outside of the long nozzle 10.
[OOS l]
Examples and comparative examples of the present invention have been
described above for the case where the lower nozzle 13 is installed between the sliding
nozzle 16 and the long nozzle 10. However, it has been confirmed that examples and
comparative examples in which the sliding nozzle 16 and the long nozzle 10 are directly
connected to each other also yield similar results.
Industrial Applicability
lo0521 , ,
According to the present invention, it is possible to provide a method of starting
to supply.molten steel that is capable of securely preventing the clogging of a long nozzle
in the immersion pouring, to thereby prevent troubles at the start of supplying molten steel
from occurring.
Reference Symbol List
100531
1 : ladle
2: tundish
3: mold
5: molten steel
10: long nozzle
10a: flow passage (inner hole)
lob: recess portion
10c: lower end portion
10d: upper end portion
1 1 : thermogenic gasification substance
12: seal member - - - -
13: lower no@e
14: sliding plate
15: fixed plate
16: sliding nozzle
17: upper nozzle
13% 14a, 15% 17a: nozzle hole
19: filling sand (filling)
20: discharge hole
2 1 : molten sfgel surface
25: molten steel static pressure
26: downward stress.
27: lateral stress
28: frictional force
B: bubble
G: gas
L: immersion depth

1. A method of starting to supply molten steel, the method comprising:
a charge step of charging a thermogenic gasification substance into a long nozzle
from an opening of an upper end portion of the long nozzle with a lower end portion
thereof being immersed in molten steel in a tundish;
a connection step of, after the charge step, connecting the upper end portion of the
long nozzle via a seal member to a sliding nozzle that is in communication with a
discharge hole in a boom surface of a ladle and controls a flow rate of the molten steel
flowing down fiom the ladle;
an inner-pressure-of-.the-long-nozzle check step of, after the connection step,
checking generation of a bubble on molten steel surface in the tundish; and
a fall step of, after the inner-pressure-of-the-long-nozzle check step, allowing
filling sand in the discharge hole to fall into the long nozzle via the sliding nozzle,
wherein an immersion depth L of the lower end portion of the long nozzle with
respect to the molten steel surface in the charge step is 50 to 350 mm.
2. The method of starting to supply molten steel according to claim 1,
wherein the thermogenic gasification substance is organic matter.
3. The method of starting to supply molten steel according to claim 1 or 2,
wherein a charge amount of the thermogenic gasification substance in the charge
step is 20 to 400 g.
4. The method of starting to supply molten steel according to claim 1 or 2,
wherein, in the connection step, a lower nozzle is connected directly under the
sliding nozzle, and the upper end portion of the long nozzle is connected to the lower .zu9
nozzle via the seal member.
5. The method of starting to supply molten steel according to claim 3, 20B
- .A%
iu b
wherein, in-theconnection step, a lower nozzle is connected directly under the
sliding nozzle, and the upper end portion of the long nozzle is connected to the lower
nozzle via the seal member.