Note: Descriptions are shown in the official language in which they were submitted.
CA 02406828 2002-10-21
WO 01/83138 PCT/BE01/00076
Refractory component and assembly with improved sealing for infection of an
inert
as.
[0001] The present invention relates to a refractory component used in the
processing of
a metal in the molten state, for example steel, fitted with a gas supply and
providing
improved sealing. In particular, the invention relates to such a component
used in
continuous casting of a metal in the molten state.
[0002] It is known that casting of a liquid metal is generally carried out by
means of an
installation comprising various refractory components forming a channel
between two
successive metallurgical vessels. These refractory components perform various
functions,
namely conveyance of the liquid metal, protection of the liquid metal against
cooling and
chemical attack from the surrounding atmosphere and, where appropriate,
regulation of
the rate of pouring of the liquid metal. These components may be, for example,
an inner
nozzle supported on a well block integral with the bottom of the upper
metallurgical
vessel, a submerged entry nozzle or a pouring shroud, a collector nozzle, or
the fixed or
mobile plates of a slide valve.
[0003] The joint surfaces between these various components forming a pouring
channel
all constitute points of potential ingress for the ambient air. In effect, by
virtue of the flow
of liquid metal through the pouring channel, substantial negative pressure is
generated
which is conducive to air ingress through these joint surfaces. The
detrimental effects of
such air ingress (nitrogen and oxygen) on the quality of the cast metal are
known, and
efforts have been made over a long period of time to remedy this.
[0004] One of the known solutions in the current state of the art involves
injecting an
inert gas, for example argon, into the joint surface between two adjacent
refractory
components in the pouring channel. This injection may be effected for example
via a
groove made for this purpose in the surface of at least one of the components.
To be
effective, this groove must as far as possible encircle the pouring orifice so
that the inert
gas which is under positive pressure can prevent any ingress of air into the
pouring
channel. Recently,. an improvement to this system was proposed in
international patent
application WO 98/ 17421, involving the additional injection of a sealing
agent in
suspension in a carrier fluid (which may be an inert gas) so that any sealing
defect liable
to appear between two adjacent surfaces during casting is immediately
eliminated.
[0005] Another known solution in the current state of the art entails
injecting an inert
gas directly into the pouring channel so as to form a protective barrier
against pollution
by the ambient air along the entire length of the pouring channel. In this
case, the
injection of inert gas into the liquid metal is generally carried out by
diffusion through a
porous wall of the component forming part of the pouring channel or, in
another known
variant, via one or more orifices in form of holes or slots arranged around
the pouring
channel.
.,
[0006] Furthermore, a method is also known wherein an inert gas is injected
directly into
the pouring channel in a manner such that the inert gas cooperates
mechanically with
the liquid metal. The purpose of this type of inert gas injection may be to
protect against
CONFIRMATION COPY
CA 02406828 2002-10-21
WO 01/83138 PCT/BE01/00076
2
erosion of certain refractory components located downstream of the injection
point and
which are particularly susceptible to the erosive action of the stream of
liquid metal, such
as for example the edges of the pouring orifice of the mobile plate of a slide
valve designed
to regulate the rate of flow. Another known effect of injecting an inert gas
into a pouring
channel is that it reduces problems of clogging of the pouring channel. In
effect,
problems due to the formation of alumina deposits against the walls of the
pouring
channel have been known for a long time, particularly in the case of casting
of
aluminium-killed steels. The inert gas thus injected downstream of a point
where this
type of clogging can occur mechanically, or even thermally, isolates the
liquid metal from
the pouring channel and, consequently, prevents or reduces the formation of
such
deposits.
[0007] Finally, it is also possible to inject a gas for the purpose of cooling
the refractory
component in question. It will be noted that the invention also relates to
components
used for the injection of gas into the bottom of a metallurgical vessel
containing a bath of
metal in the molten state, such as for example porous plugs.
[0008] For the purposes of the present patent application, the expression
"injection of.
gas" will therefore refer both to the direct injection of an inert gas into a
pouring channel
or into the bottom of a metallurgical vessel and to the injection of an inert
gas (or a
sealing agent in suspension in a carrier fluid as described in international
patent
application
WO 98/ 17421) into the joint surface between two adjacent refractory
components of a
pouring channel via a groove encircling at least partially the pouring orifice
of the liquid
metal, or to the injection of a cooling gas.
[0009] The refractory components designed for the injection of an inert gas
generally
include means of delivering the gas to the means of injection (via a groove or
the pouring
channel). However, assemblies of refractory components are known in which the
means
of delivery and means of injection of the gas are provided by adjacent inter-
communicating components (possibly they may even be separated by intermediate
refractory components, the essential feature being that the gas can be
transferred from
the means of delivery to the means of injection). For the purposes of the
present patent
application, where reference is made to a component equipped with means of
delivery and
means of injection of gas, this will refer equally to a component including
both means of
delivery and means of injection of gas or a component fitted with means of
delivering gas
and means of transfer and/or communication to means of injection which may be
provided by another refractory component.
[0010] The means of delivery generally include an inlet aperture opening on
the outside
wall of the refractory component and connected to a gas delivery line. This
delivery line is
connected to the fixed gas supply circuit of the casting installation,
possibly via flexible
pipes protected against thermal radiation. Conventionally, during the
fabrication of said
refractory component, a metal connector is mounted in the inlet aperture; the
connector
and the material then form an integral assembly upon sintering of the
constituent
CA 02406828 2002-10-21
WO 01/83138 PCT/BE01/00076
3
refractory material of the component. The connector can then be connected to
the gas
delivery line by screwing (either the connector is fitted with a male threaded
part
projecting beyond the component onto which the female end of the line is
screwed, or the
connector has a female thread into which the male-threaded end of the line is
screwed),
by welding or by various means of mechanical coupling. These means of gas
delivery are
not entirely satisfactory in that, firstly, it is not obvious that a threaded
joint can be made
airtight, and particularly a joint that will remain airtight at the very high
temperatures to
which the installation is subjected during casting operations and, secondly,
by virtue of
the difference between the coefficients of expansion of the metal of which the
connector is
made and the refractory material, it is inevitable that the sealing tightness
between the
connector and the refractory will gradually deteriorate. The negative effects
of this loss of
sealing tightness are three-fold: firstly, the quantities of gas to be
injected are that much
greater (the high price of inert gases such as argon is well known), secondly,
as indicated
above, given that the whole of the pouring channel is under negative pressure
relative to
the ambient environment, there is a risk that air will be drawn in through
these defective
joints and, thirdly, in case of loss of sealing tightness, precise control of
the quantity of
gas actually injected into the system is lost and it becomes impossible to
establish a
perfectly reproducible system.
[0011] Various attempts have been made to improve this situation, such as for
example
"packing" the refractory component in a metal casing incorporating an aperture
at the
connector, welding to ensure mechanical retention of the connector and improve
the gas
tightness. A number of drawbacks associated with this "improvement" have
already been
reported. For instance, as the connector is integral with the metal casing, it
has a
tendency to work loose from the refractory material and to move about in its
seating,
which gives rise to losses of inert gases and, as indicated above, ingress of
air into the
liquid metal.
[0012] More recently, a very simple device was proposed in European patent
application
EP 703,023 for the delivery of inert gas to an inner nozzle, wherein the
external surface of
the refractory component receiving the gas feed simply incorporates a gas
inlet aperture
against which a connection fitting connected to an inert gas delivery line is
held in
compression. Where appropriate, it may even be possible to provide a seal
between the
fitting and the inlet aperture.
[0013] Although this device greatly improves the situation, the applicant
observed that it
was not yet wholly satisfactory in that sealing tightness between the
connection fitting
and the gas inlet aperture at the surface of the component was not totally
assured, even
when a seal is engaged between the fitting and the aperture.
[0014] A refractory component provided with means of injecting or conveying
gas and
means of delivering said gas from an external wall of the component to said
means of
injection, the means of delivery of the gas comprising a part of enlarged
cross-section
extending from an external wall of the component and a part of reduced cross-
section
communicating, at one end, with the inner end of the part of enlarged cross-
section and,
CA 02406828 2002-10-21
WO 01/83138 PCT/BE01/00076
4
at the other end, with the means of injecting or conveying gas, the said
component also
comprising a seal fitted against the inner end of the part of enlarged cross-
section, said
seal, comprising an orifice at least partially in register with the
communicating orifice
between the parts of enlarged and reduced cross-section is known from FR-A-
2,763,012.
[0015] By virtue of this particular arrangement of the refractory component,
the gas
delivery line can be engaged more deeply into said component so that, when an
appropriate seal is fitted therein, sealing tightness is assured not only at
the
communication between the two parts of the means of delivery, but also at the
walls of
the part of enlarged cross-section. A very substantial improvement in sealing
tightness
compared with the device disclosed in European patent application 703,028
(reduction of
the consumption of inert gas, reduction of air ingress, and precise control of
the quantity
of gas injected) was observed. However, it is desirable to still improve the
sealing
tightness.
[0016] According to the invention, the seal presents a cross-section
substantially similar
to the cross-section of the enlarged part. Thus, when the seal is placed in
compression in
an appropriate manner, it bears not only on the end of the part of enlarged
cross-section,
but also on the side walls of the latter, thereby providing an even tighter
seal.
[0017] It is advantageous that the thickness of the seal does not exceed the
depth of the
part of enlarged cross-section, otherwise, under the effect of compression by
the gas
delivery line, the plastic seal will bear on the rim of the outer orifice of
the means of
delivery as it deforms, and sealing tightness will no longer be assured at the
inner end of
the part of enlarged cross-section.
[0018] According to a particular embodiment of the invention, the inner end of
the part of
enlarged cross-section forms a surface presenting an orifice, the said parts
of enlarged
and reduced cross-section communicating via this orifice. In this way, it is
possible to
use a gas delivery line of essentially tubular form.
[0019] Advantageously, the part of enlarged cross-section consists of a bore
of
substantially circular cross-section which is easy to make.
[0020] Provision can also be made so that the surface forming the inner end of
the part of
enlarged cross-section is fiat and essentially orthogonal to the axis of the
bore. Not only
is this arrangement easy to achieve, but its sealing tightness will be
improved where it is
made by the pressing of parallel elements.
[0021] According to a particular aspect of the invention. The thickness of the
seal does
not exceed the depth of the part of enlarged cross-section. It is to be noted
that the seal
can be made integral with the component.
[0022] Advantageously, the seal presents a cross-section substantially similar
to the
cross-section of the enlarged part. Thus, when the seal is placed in
compression in an
appropriate manner, it bears not only on the end of the part of enlarged cross-
section,. but
also on the side walls of the latter, thereby providing an even tighter seal.
It is essential
that the thickness of the seal does not exceed the depth of the part of
enlarged cross-
section, otherwise, under the effect of compression by the gas delivery line,
the plastic
CA 02406828 2002-10-21
WO 01/83138 PCT/BE01/00076
seal will bear on the rim of the outer orifice of the means of delivery as it
deforms, and
sealing tightness will no longer be assured at the inner end of the part of
enlarged cross-
section.
[0023] Preferably, the seal takes the form of a washer. Provision may be made
however
5 for a stack of such washers depending on the required thickness of the seal.
The person
skilled in the art will readily determine the optimal thickness of the seal.
[0024] Advantageously, the seal is made of a plastic material so that, at
operating
temperatures, it is able to deform su~ciently when pressure is exerted on it
to form a
tight seal with the bottom wall and with the side walls of the end of the part
of enlarged
cross-section. Clay and graphite are materials potentially suitable for such
use, graphite
being the preferred choice.
[0025] According to another of its aspects, the invention relates to an
assembly including
a refractory component as described above and a gas delivery line, wherein one
end of the
gas delivery line is engaged in the part of enlarged cross-section which holds
the seal in
compression at the inner end and against the side walls of the part of
enlarged cross-
section. The advantages of such an assembly have already been described above.
[0026] According to a particular embodiment of the invention, the refractory
component
is fitted with a metal casing (in the case of an inner nozzle for example) or
band (in the
case of a slide valve plate for example) covering it at least partially in the
area of the gas
delivery means. It is thus possible to form a solid attachment between the
delivery line
(by welding or screwing) and the casing or band, thereby avoiding accidental
loss of
sealing tightness in case of vibration for example.
[0027] Advantageously, the end of the line engaged in the part of enlarged
cross-section is
configured so as to form a tight joint with the seal. For example, the end may
be shaped
as a cone or truncated cone so that it "keys" into the joint. As a variant,
the end of the
line may be threaded to enable the line to "screw" into the joint. Provision
may also be
made fox a self tapping end so that a perfectly fitting thread is formed in
situ in the seal
and the line/seal joint is totally tight. According to this variant, it is
advantageously the
action of screwing the end of the line into the seal that compresses said seal
towards the
side walls of the part of enlarged cross-section.
[0028] Finally, according to a most particular embodiment of the invention,
the part of
enlarged cross-section is su~ciently deep so that, under the effect of thermal
expansion
of the end of the line engaged in the part of enlarged cross-section, the
compression of the
seal increases. In effect, once the line is made solid with the casing or
band, its only
possibility of expansion is towards the end of the part of enlarged cross-
section where the
seal is located.
(0029] In order to better explain the invention, two embodiments given by way
of a non-
limitative example are described below with reference to the attached diagrams
in which
- figure 1 is an axial sectional view of an inner nozzle;
- figure 2 is an enlarged view of the circle I in figure 1.
- figure 3 is an axial sectional view of a slide valve plate.
CA 02406828 2002-10-21
WO 01/83138 PCT/BE01/00076
6
[0030] Figure 1 shows an inner nozzle 1 comprising a refractory body 2 forming
a pouring
channel 3 and a plate 4. The inner nozzle 1 also includes means of injecting
gas, for
example an inert gas such as argon, into the pouring channel 3. These means of
injecting
gas are formed for example by a sleeve 5 in porous material mounted in a
groove 6 formed
in the refractory body 2. The groove 6 is connected to means of delivery of
gas (7, 8). As
shown in figure l, these means of delivery may emerge at the upper surface of
the plate 4.
Also shown is part of the gas delivery line 9, together with a metal casing 10
surrounding
the plate 4 of the inner nozzle.
[0031] Figure 2 shows the details of the connection between the gas inlet and
the means
of delivery of the gas at the plate 4 of the inner nozzle. These means of
delivery of gas
include a part of enlarged cross-section 7 and a part of reduced cross-section
8
communicating via an orifice 11. The inner end of the part of enlarged cross-
section is
fitted with a seal 12 for example in graphite. Also shown is one end of the
gas delivery
line 9 engaged in the part of enlarged cross-section 7. It can be seen that
the line 9 is
made solid with the casing 10 by means of a circular weld 13.
[0032] Figure 3 shows a refractory plate 14 of a slide valve presenting an
orifice 15 for the
pouring of metal. The plate is provided with a circular groove 16
circumscribing the
pouring orifice 15 and forming with the surface of the refractory part (not
shown) adjacent
to the plate 14 a channel for the injection of a gas between these adjacent
parts. The
groove 16 is connected to gas delivery means including a portion of enlarged
cross-section
17 and a portion of reduced cross-section 18 communicating via an orifice 21.
Also
shown is the gas delivery line 19 engaged in the part of enlarged cross-
section and made
solid with the metal band 20 of the plate 14 by a spot weld 23. When the plate
is in
service, under the effect of the temperature to which the assembly is raised,
the part of
the line 19 between the spot weld 23 and its inner end expands towards the
inner end of
the enlarged part 1'7 and compresses the seal 22.
CA 02406828 2002-10-21
WO 01/83138 PCT/BE01/00076
7
References:
1. Inner nozzle
2. Refractory body
3. Pouring channel
4. Plate
5. Porous sleeve
6. Groove
7. Part of enlarged cross-section
8. Part of reduced cross-section
9. Gas delivery line
10. Metal casing
11. Communication orifice
12. Seal
13. Weld
14. Plate
15. Pouring orifice of the plate
16. Gas circulation groove
17. Part of enlarged cross-section
18. Part of reduced cross-section
19. Gas delivery line
20. Metal band
21. Communication orifice
22. Seal
23. Weld
