Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02356350 2001-06-20
WO 00/40358 PCTBE99/00170
REFRACTORY ASSEMBLY.
Description
The invention concerns a device for regulating the flow rate of a pouring,
notably of an
installation for pouring a molten metal, such as steel or cast iron.
It concerns more particularly the injection of an inert fluid such as argon,
in a
refractory assembly used in a regulating device of this type. This fluid is
designed to
cooperate mechanically with the molten metal.
Devices for regulating the flow rate have a pouring channel, downstream from
which
two refractory plates, each with an orifice, are usually interposed. These
plates are
essentially perpendicular to the axis of the channel and one of the plates can
slide
relative to the other, toward one side of the channel. In the pouring
position, the
aperture of the sliding plate coincides essentially with the axis of the
pouring and the
respective apertures of the plates mutually communicate. On the other hand, in
the
pouring stop position the aperture of the sliding plate is offset at a
distance from the
other plate and the two plates thus close off their mutual aperture.
In the known regulating devices, a means of injection is generally distributed
over the
entire periphery of the channel for injecting the said fluid all around the
axis of the
channel. The radial injection of the fluid thus permits a uniform and
axisymmetric
injection.
However, it can be provided that the sliding plate is slightly offset relative
to the other
plate, in an intermediate position between the said pouring and stop positions
to
furnish a moderate or low pouring flow rate. The molten metal then encounters
an
obstacle formed by the edge of the aperture of the sliding plate with regard
to the axis
of the channel. An erosion of this orifice generally results. Moreover, solid
deposits
can form on the edge of the aperture, above the sliding plate, in a zone of
recirculation
of the molten metal.
The present invention is intended to improve this situation.
It then concerns a refractory assembly used in a regulating device of the said
type and
having, downstream form the pouring channel, at least two refractory plates
essentially
perpendicular to the axis of the channel and equipped with the respective
orifices. One
of the plates is designed to slide relative to the other plate toward one side
of the
channel, from a pouring position in which the respective orifices essentially
communicate to a pouring stop position in which the plates essentially close
off their
mutual orifice. The refractory assembly also has injection means essentially
upstream
form the plates for a fluid capable of cooperating mechanically with the
molten metal to
avoid deposits in the said recirculation zone.
According to a general characteristic of the invention, the refractory
assembly has an
internal nozzle with an essentially cylindrical, hollow form upstream from the
plates.
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The internal wall of this nozzle delimits the said pouring channel. The
injection means
are designed to inject the fluid in directions essentially radial to the
nozzle, in an
angular sector less than 360° and opposite the side of the channel with
regard to the
sliding plate when it is in the closure position. The molten metal is thus
perturbed
locally by the injected fluid and mechanically (even thermally) isolated, from
the wall in
the recirculation zone.
The said angular sector is preferably less than or equal to about 270°,
so as to
concentrate the fluid flux more intensely in the zone of molten metal
recirculation. For
some applications, the angular sector is preferably close to 120°.
According to an advantageous optional characteristic of the invention, the
internal
nozzle has in an essentially transversal section a recess that communicates
with the
interior of the pouring channel and forms a crown of angular sector less than
360°.
The fluid is then injected through this recess.
This recess preferably accommodates an insert e$ected in a porous refractory
material,
in which the fluid is injected toward the inside of the pouring channel.
Other advantages and characteristics of the invention will appear from reading
the
following detailed description and an examination of the attached drawings:
- figure 1 is a partial schematic view, in longitudinal section, of a
refractory assembly
for a regulating device according to the invention;
- figure 2 is a view in longitudinal section of an internal nozzle of the
device, according
to a preferred implementation mode of the invention;
- figure 3 is a cross-sectional view of the nozzle shown in figure 2.
The attached drawings and the following detailed description essentially
contain
elements of a certain nature. They could not only serve to better understand
the
present invention, but also contribute to its definition, if necessary.
Reference is first made to Figure 1, which schematically shows a refractory
assembly
for a regulating device for a molten metal pour (arrows C), notably in a steel-
making or
metallurgical installation.
The refractory assembly in the example described has three refractory plates,
one of
which, designated as 1, can slide between the other two, 2 and 3. The three
plates 1, 2
and 3 are essentially superposed and perpendicular to the pouring axis ~Z,
vertical in
the example described. Upstream from the plates, it has an internal refractory
nozzle
4, designed to be seated at least partially in a pouring hole that has a
bottom wall of a
continuous casting distributor (not shown) in the example described. The
internal
nozzle 4 constitutes an element of the pouring channel that connects the
pouring
distributor to an ingot mold of the installation.
The internal nozzle 4 is of an essentially cylindrical, hollow general form,
its internal
wall 43 (figure 2) delimiting a pouring channel 7. More particularly, the
nozzle 4 is of
an essentially truncated conical form. The pouring channel 7 communicates with
an
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aperture 20 of the upstream refractory plate 2.
In the example described, the upstream plate 2 and the downstream plate 3 are
fixed
with regard to the internal nozzle 4, while the intermediate plate 1 can slide
from a
pouring position toward a pouring stop position (toward the right of Figure 1,
as
shown). thus, displacement of the aperture 10 of the sliding intermediate
plate 1,
essentially along the horizontal X-X axis, allows regulating the pouring flow
rate.
Indeed, in the pouring position the aperture 10 communicates with the orifice
20 of the
upstream plate 2 on the one hand and with the aperture 30 of the downstream
plate 3
on the other. In the pouring stop position, the orifice 10 is offset toward
the right of
figure 1 and a portion of refractory plate 11 in the vicinity of the orifice
10 (shown to
the left of the orifice 10 in Figure 1) sensibly closes o$'the orifice 20 of
the upstream
plate 2 on the one hand and the orifice 30 of the downstream plate 3 on the
other.
Thus, when the orifice 10 of the sliding intermediate plate 1 is offset
relative to the
pouring channel 7 along the axis X-X, the flow rate of pouring decreases, up
to the
point that the pouring is interrupted when the sliding plate 1 is in an
extreme position
corresponding to the said pouring stop position. on the other hand, when the
axis of
the orifice 10 is substantially merged with the pouring axis, the flow rate of
pouring is
maximal.
In an intermediate position of the plate 1, the molten metal encounters a
first obstacle
corresponding to the upper wall of the part 11 of the sliding plate 1, in the
vicinity of
orifice 10. The respective apertures 20 and 10 of plates 2 and 1, sensibly
offset relative
to each other, form an essentially curved-in pouring trajectory C. The metal
stagnates
in the zone 6 called the udead zone of recirculation". In a metallurgical
installation of
molten steel, for example, solid deposits of alumina and solidified steel can
form in this
zone 6, capable of perturbing the displacement of the sliding plate 1, even
obstructing
the orifice 20 of the upstream plate 2.
The general idea is to inject a fluid capable of cooperating mechanically with
the
molten metal so as to create a local turbulence and/or a sleeve protecting the
walls of
the nozzle in order to counteract the formation of a deposit. This fluid is
chosen so as
not to react chemically with the molten metal. In practice, an inert gas such
as argon
is injected.
In the Down regulating devices, this injection is generally made all around
the pouring
axis Z-Z. A circular aperture is provided that extends over 360° of the
pouring channel
for injecting the gas radialy. However, this axisymmetric injection in no way
resolves
the problem posed by the recirculation in zone 6 and the resulting deposit.
One of the goals of the present invention is to furnish a localized injection
of the fluid
capable of cooperating mechanically with the molten metal in order to limit,
even
eliminate the recirculation of molten metal in the said zone 6.
According to a preferred embodiment of the present invention, the internal
nozzle 4 has
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a recess 40 in its internal wall 43, which extends over an angular sector less
than
360°, in a plane essentially perpendicular to the axis of the nozzle
~Z. An insert 5
made of a porous refractory material is located in this recess; the inert gas
is injected
in it (arrows F). The flux of injected gas creates a turbulence localized in
the zone 6 of
potential deposition, and protects the wall by the formation of a thermally
insulating,
gaseous sheet.
Preferably, the angular sector on which the recess 40 of the internal nozzle 4
extends is
close to 120° in the example described (Figure 3). In particular, the
recess 40
presents, in a cross section of the nozzle (Figure 3), a form of crown or
collar of angular
cross section A less than 270° and close to 120° in the example.
As shown in Figure 2, the internal nozzle 4 has a circular slot 41 for
supplying the
fluid from the external connector 46 up to the injection zone 5. The slot 41
is
prolonged locally by an orifice 42 that communicates with the recess 40 and
through
which the gas is injected (arrow F). the gas F is introduced into the pores of
the insert
5 by being directed essentially in a transversal plane and in an angular
sector close to
120°, toward the center of the channel 7.
Thus, a localized injection of the fluid advantageously makes it possible to
limit, even
prevent the formation of a deposit in the zone 6, in particular, when the
pouring
trajectory is essentially curved inward, the sliding plate 1 being in an
intermediate
position (Figure 1), defining a pouring flow rate less than the maximum flow.
Of course, the present invention is not limited to the implementation form
described
previously by means of example. It also extends to other variants.
Another implementation form consist of seating a metal pipe in the body of the
nozzle,
connecting the external connector 46 directly to the slot 41.
It should be understood that the injection of fluid can also be effected
through a
plurality of orifices arranged in a plane essentially perpendicular to the
axis of the
nozzle 4 and distributed over an angular sector less than 360°, e.g.,
close to 120°.
In a variant, the nozzle 4 can have a slot in a plane essentially
perpendicular to its axis
Z-Z, and which extends over an angular sector less than 360°, according
to a general
characteristic of the invention.
The injection of fluid is effected in both cases with regard to a zone of the
channel
capable of containing a zone of molten metal recirculatian. This recirculation
forms
principally on the side of the channel opposite the side 45 (Figure 1) toward
which the
plate 1 slides from its pouring position toward its stop position.
It is to be noted that in the USP 4,632,283, a refractory assembly is
disclosed having
injection means in the upstream plate 2 for injecting the fluid through a
portion of the
plate 2 distant relative to the sliding plate 1 in its stop position (to the
left of the orifice
20, as shown in figure 1) in order to orient the injected flux essentially in
the direction
of displacement of the sliding plate 1.
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However, the upstream plate 2, having such injection means, requires a boss
(also
named spigot) on its upper surface, around its orifice 20. This boss, which
has a slot,
a plurality of orifices or even a porous insert for injecting the fluid,
extends toward the
internal nozzle, with a significant height along the axis of pouring ~Z to
effect an
5 effective injection of the fluid. It is also necessary to provide a
homologous recess in a
lower part of the nozzle for accommodating this boss.
The applicant found that, surprisingly, the molten metal undergoes a loss of
heat in
circulating from the internal nozzle to the upstream plate 2. This loss of
heat is
greater, the higher the boss. Thus, an excessively high boss causes the
formation of
solid deposits on the intermediate plate 1, which is exactly the contrary of
the effect
sought in USP 4,632,283. An injection of fluid from the nozzle, according to
the
invention, permits limiting this heat loss.
It is also possible to equip the refractory assembly according to the
invention with an
intermediate sliding plate 1 having a porous refractory insert and secondary
injection
means (arrows F~ in the direction of sliding of the plate 1 from its stop
position to its
pouring position (from the right to the left in Figure 1) in order to
eliminate a possible
deposition associated with the recirculation of metal above the upper face of
a part 31
of the downstream plate 3 in the proximity of its orifice 30 (to the right of
the orifice 30,
as shown in Figure 1). This secondary injection extends preferably over an
angular
sector less than 360°.
In addition, a porous insert or any other means of injection of the fluid can
also be
located in the downstream plate 3, on the side opposite the closure of the
sliding plate
1 in order to protect the zone under the sliding plate, to the left of its
pouring aperture
from a possible recirculation.
In the example described, the refractory assembly has three superposed
refractory
plates, one of the plates, the intermediate one, sliding between the other
two. In a
variant, only two refractory plates 1 and 2 can be provided downstream from
the
nozzle 4. The lower plate 1 is then designed to slide relative to the plate 2
toward a
side 45 of the channel. The sliding plate 1 is generally located below the
fixed plate 2,
while the principal injection of fluid is always done from the side of the
channel
opposite the side 45, toward which the sliding plate 1 is displaced from its
pouring
position to its stop position.
In another variant of the refractory assembly according to the invention, the
internal
nozzle 4 and the upstream plate 2 are made of a single monoblock refractory
piece.
The internal nozzle 4 is a refractory piece that is generally part of the
upper zone of the
refractory assembly designed to connect a continuous casting distributor to an
ingot
mold of the pouring installation. In a variant, this nozzle can be part of a
refractory
assembly connecting a pouring ladle to the distributor, or an electric furnace
to a
pouring ladle.
