Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
Refractory Element, Assembly and Tundish for Transferring Molten Metal
BACKGROUND OF THE INVENTION
(1) Field of the Invention
[0001] The present invention relates to the continuous casting of steel and
particularly to the problem of steel reoxidation. In particular, the invention
relates
to a tundish comprising an assembly comprising a nozzle and a surrounding
refractory element preventing or limiting steel reoxidation, and preventing
oxidation products from entering a casting channel. The invention also relates
to
an assembly comprising a nozzle and a surrounding refractory element
preventing or limiting steel reoxidation, and preventing oxidation products
from
entering a casting channel. According to other of its aspects, the invention
also
relates to such a surrounding refractory element and to a continuous steel
casting process.
[0002] With growing demands for quality and property control, cleanliness of
steel becomes more and more important. Issues like controlling the chemical
composition and the homogeneity have been supplanted by concerns generated
by the presence of non-metallic inclusions. Especially the presence of
aluminum
oxide and spinel inclusions is considered as harmful both for the production
process itself as for the steel properties. These inclusions are mainly formed
during the deoxidation of the steel in the ladle, which is necessary for
continuous
casting. Incomplete removal of the non-metallic inclusions during secondary
metallurgy and reoxidation of the steel melt cause nozzle clogging during
continuous casting. The layer of clogged material contains generally large
clusters of aluminum oxide. Its thickness is related to the amount of steel
cast as
well as to the cleanliness of the steel. Nozzle clogging results in a
decreased
productivity, because less steel can be cast per unit of time (as result of
the
decreasing diameter) and due to replacement of nozzles with concurrent casting
interruptions. Besides clogging, the presence of reoxidation products may give
rise to erosion of the nozzle and to the formation of inclusion defects in the
steel.
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SUBSTITUTE SHEET (RULE 26)
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(2) Description of Related Art
[0003] Several solutions have been developed in the art to prevent steel
reoxidation.
In particular, the molten metal stream is generally shrouded with a pouring
shroud
during its transfer from a casting vessel to a downstream vessel (or mold) to
prevent
direct contacts between the poured steel and the surrounding atmosphere. Argon
is
often injected directly at the surface of a pouring nozzle so as to shield the
molten metal
stream. The surface of the steel melt in a metallurgical vessel (for example a
tundish) is
generally covered with a liquid slag layer so as to prevent direct contacts
between the
steel and the surrounding atmosphere. Alternatively (or in addition), the
atmosphere
above the tundish can be made inert (by the use of an oxygen scavenger or of
an inert
gas such as argon).
[0004] Further solutions have been developed in the art to remove non-metallic
inclusions and reoxidation products when they are present in the tundish.
These
solutions consist generally in facilitating the flotation of these inclusions
and reoxidation
products so that these are captured by the floating slag layer. For example,
dams,
weirs, baffles and/or impact pads can be used to deflect upwardly the molten
metal
stream in the tundish. Inert gas bubbling devices can also be used to float
out
inclusions and reoxidation products.
[0005] Other solutions also exist for making the inclusions and oxidation
product
harmless. For example calcium based alloys can be used to eliminate some of
the
problems generated by the presence of aluminum oxide inclusions.
[0006] All these prior art solutions have contributed to improve the general
cleanliness
of the steel. However, some of the prior art solutions can, in turn, generate
new defects
in the steel (as in gas bubbling, or the use of a calcium-based alloy), can be
expensive
(as in the use of an inert atmosphere) or environmentally unacceptable. For
these
reasons, it would be desirable to propose an alternative solution which would
solve the
above problem, which would be economical and would not raise environmental
problems.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention is based on the hypothesis that, even though the
steel
can be made relatively clean, it is impossible to keep it clean up to the mold
in normal
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conditions. In particular, reoxidation of the steel by chemical reaction
between the
refractory elements (generally metal oxide) used in the continuous casting
(vessel
lining, slag, nozzles, stoppers, etc.) can also generate reoxidation products.
Another
potential source of reoxidation is the oxygen permeating through these
refractory
elements or through a permeable joint between the bottom wall lining and the
nozzle
inlet or even the oxygen desorbed from the refractory element.
[0008] An object of the present invention is therefore to solve the above
problems by
preventing the reoxidation products from reaching a casting nozzle and/or from
forming
in the immediate vicinity of or in the casting nozzle.
[0009] According to the invention, this object is achieved by the use of a
surrounding
refractory element, an assembly of a nozzle and a surrounding refractory
element, or an
assembly of a nozzle and a surrounding refractory element housed in a tundish,
in
which the element has a base having a main surface, a bottom and a periphery
surrounding the main surface, in which the periphery has an exterior surface,
and
interior surface and an upper face, and the intersection of the bottom of the
base and
the exterior surface of the periphery contains at least one point at which the
angle of
intersection is not a right angle.
[0010] It is already known in the art to provide a surrounding element around
the
pouring orifice of a tundish. FR-A-2394348 for example discloses a ring
intended to
retain the steel in the tundish until a sufficient level and thereby a
sufficient thermal
mass is reached in order to avoid the entry of "cold" steel into the pouring
orifice. The
prior art however fails to disclose an element with a base and a periphery,
and the
intersection of the bottom of the base and the exterior surface of the
periphery contains
at least one point at which the angle of intersection is not a right angle.
[0011] JP-A1-2003-205360 discloses a tundish for the continuous casting of
steel.
The well block of this tundish is comprised of two elements. The nozzle is
located inside
the bottom part of the well block. An additional refractory element is
positioned above
the upper part of the nozzle to cover and protect the cement joint between the
nozzle
and the well block. However, this document fails to disclose a refractory
element with a
base and a periphery, and the intersection of the bottom of the base and the
exterior
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surface of the periphery contains at least one point at which the angle of
intersection is
not a right angle.
[0012] W02007/009667 discloses an element for use in conjunction with a nozzle
in a
metallurgical vessel. However, this document does not disclose a refractory
element
with a base and a periphery in which the intersection of the bottom of the
base and the
exterior surface of the periphery contains at least one point at which the
angle of
intersection is not a right angle.
[0013] Thanks to the particular arrangement according to the present
invention, the
reoxidation products and/or inclusions present in the metallurgical vessel and
which
tend to accumulate on the bottom surface of the vessel and are carried down by
the
molten steel stream cannot reach the inlet of the nozzle.
[0014] It must be understood that the element surrounding the nozzle can be of
any
appropriate shape. In function of the metallurgical vessel design; it can be
circular, oval
or polygonal; its main orifice can be central or eccentric. In an alternate
embodiment of
the invention, appropriate shapes for the element may exclude circular shapes.
The
element surrounding the nozzle can also be cut off so as to accommodate those
cases
when one or more tundish walls are close to the pouring orifice. The main
surface of
the element can be planar or not (it can be frusto-conical, rippled,
inclined). The nozzle
can be an inner nozzle (for example in case the molten steel flow is
controlled with a
slide gate valve or if the installation is equipped with a tube or calibrated
nozzle
changer) or a submerged entry nozzle or SEN (for example in the case of
stopper
control). The metallurgical vessel or tundish can be equipped with one or more
of such
assemblies. The assembly can be supplied as a one-piece pre-assembled article
(for
example, co-pressed) or as separated articles.
[0015] As the element surrounding the nozzle need not be circular, and as the
element
may be placed in a vessel that does not have circular symmetry, it may be
important to
align the element with the nozzle, and therefore with the nozzle's
surroundings, to
produce desired flow patterns in the vicinity of the nozzle. Accordingly, the
element and
the nozzle may be constructed with matching visual indicators or markings
that, when
aligned or placed in contact, produce the desired geometrical arrangement of
the
element and the nozzle. Alternatively, the element and the nozzle may be
constructed
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with mating geometries so that, when these geometries are mated, the desired
geometrical arrangement of the element and nozzle, and of the combined element
and
nozzle with their surroundings, is produced. The mating geometries may be a
matching
recess and protrusion, a matching groove and lip, a matching peg and bore, a
matching
notch and protrusion, a matching dimple and mogul, a matching ridge and
groove,
aligned threaded receivers, aligned key or bayonet receivers, or matching non-
circular
surface geometries such as oval or polygonal faces. The mating geometry of the
element may be placed within its main orifice or on the bottom of the base.
The
element, considered alone, may contain, within its main orifice or on its
base, one or
more orienting geometries, such as pegs, bores, protrusion, recesses, notches,
bevels,
dimples, moguls, ridges, grooves, housings for screw or bayonet fittings, or
shaped or
threaded receiver portions. The bore of the element may be asymmetric, oval or
polygonal in shape.
[0016] In certain embodiments of the invention, the element and the nozzle may
constitute a single piece.
[0017] According to the present invention, the refractory element comprises a
base
having a main surface and a periphery surrounding the main surface; the upper
face of
the periphery being higher than the main surface of the refractory element.
Thereby, a
kind of deflecting trap is created in the area surrounding the nozzle. It must
be
understood that the upper face of the periphery does not need to be planar. It
can be
waved or have different heights along the periphery (for example higher in
area of the
periphery close to a vessel lateral wall and lower on the other side). The
periphery may
contain one or more interruptions or openings. The periphery may contain
stepped
changes in height, or may contain gradual changes in height. The upper face of
the
periphery may have a sawtooth configuration, a semicircular notch
configuration, a
square notch configuration, a wave configuration, a semicircular protrusion
configuration
or may contain one or more steps. The upper face of the periphery may be in
communication with an outwardly protruding lip. The upper face of the
periphery may
be in communication with an inwardly protruding lip. The upper face of the
periphery
may be in communication with a plate or dome structure containing at least one
port.
The periphery may contain one or more ports; these ports may be circular, oval
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polygonal in shape, and the ports may have horizontal axes, axes directed
upwards and
inwardly, axes directed downwards and inwardly, or axes that are not
perpendicular to
the external surface of the periphery. The ports may be configured to have
axes that
are mutually tangent to a circle within the periphery. Pairs of ports may be
configured to
have axes that intersect each other at a circle within the periphery. The
ports may be
flared. In the inventive combination of a tundish, a nozzle and a refractory
element, the
level of at least one portion of the outer periphery of the refractory element
is higher
than the surface of the bottom wall of the tundish. Thereby, a second obstacle
is
created around the nozzle tundish preventing the inclusions or reoxidation
products to
reach its inlet. This type of arrangement is particularly advantageous.
[0018] The periphery of the refractory element of the present invention may
take the
form of a wall with measurements that are related to other measurements of the
element by particular ratios or ranges of ratios. In certain embodiments, the
maximum
height of the wall, measured from the bottom of the base, has a ratio of 1:1
to 6:1, or
1.1:1 to 6:1, to the minimum height of the wall, measured from the bottom of
the base.
In certain embodiments, the maximum height of the wall, measured from the
bottom of
the base, has a ratio of 0.1:1 to 10:1, or 0.1:1 to 8.5:1, or 0.2:1 to 8.5:1,
or 0.5:1 to 8.5:1,
to the maximum exterior diameter of the base. In certain embodiments, the wall
has a
minimum thickness of 2 mm, 5 mm, or 10 mm. In certain embodiments, the wall
has a
maximum thickness of 60 mm, 80 mm, or 100 mm. In certain embodiments, the base
has a maximum thickness of 100 mm or 200 mm.
[0019] The periphery of the refractory element of the present invention may
take the
form of a wall that has an exterior surface that has a portion that is not
vertical. In
certain embodiments, the entire exterior surface of this wall is not vertical.
In certain
embodiments, the entire wall forms an obtuse angle with the main surface, as
measured
from the interior of the element. In certain embodiments, the angle between
the bottom
surface of the base and the exterior surface of the wall has an angle lying
within the
ranges of 45 degrees to 89.5 degrees and 90.5 degrees to 135 degrees. In
certain
embodiments, the angle between the bottom surface of the base and the exterior
surface of the wall may vary around the circumference of the element. In
particular
embodiments, the element has non-vertical outer walls, and the element
partially
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encloses a volume with a cross-section that decreases in size with decreasing
distance
to the nozzle or to a port in which the nozzle may be located. The walls may
take the
form of a cylinder with an axis that is not orthogonal to the horizontal
plane. The walls
may take the form of the radial surface of a truncated cone with a projected
vertex
below the plane of the main surface. The walls may take the form of the radial
surface
of a truncated cone with a projected vertex above the plane of the main
surface. The
upper face of the periphery may form a circle, oval, or polygonal figure in a
plane that is
not parallel to the plane of the main surface.
[0020] The interior of the wall of the refractory element and the base of the
refractory
element may communicate, separately or together, with one or more vanes. A
vane
may be disposed so that a projection of the plane of the vane intersects the
axis of the
nozzle. A vane may also be disposed so that no projection of a plane of the
vane
intersects the axis of the nozzle. The vanes may have surfaces and edges; the
surfaces may be planar, may be curved in one or two dimensions, and may be
smooth
or have grooves. The edges of the vanes may be chamfered or have a sawtooth
configuration, a semicircular notch configuration, a square notch
configuration, a wave
configuration, a semicircular protrusion configuration or may contain one or
more steps.
[0021] The exterior of the wall of the refractory element may communicate with
one or
more vanes. A vane may be disposed so that a projection of the plane of the
vane
intersects the axis of the nozzle. A vane may also be disposed so that no
projection of
a plane of the vane intersects the axis of the nozzle. The vanes may have
surfaces and
edges; the surfaces may be planar, may be curved in one or two dimensions, and
may
be smooth or have grooves. The edges of the vanes may be chamfered or have a
sawtooth configuration, a semicircular notch configuration, a square notch
configuration,
a wave configuration, a semicircular protrusion configuration or may contain
one or
more steps.
[0022] The surrounding refractory element may be made from a gas-impervious
material. To be regarded as gas-impervious, such material has an open porosity
(at the
temperature of use) which is lower than 20% (thus lower than the open porosity
of
conventional lining material which is typically higher than 30%). For
refractory materials,
the permeability is generally related to the porosity. Therefore a low
porosity material
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has a low permeability to gases. Such a low porosity can be obtained by
including
oxygen scavenger materials (e.g. antioxidants) in the material constituting
the
surrounding element. Suitable materials are boron or silicon carbide, or
metals (or
alloys thereof) such as silicon or aluminum. In certain embodiments, they are
used in
an amount not exceeding 5 wt /0. Alternatively (or in addition), products
generating
melting phase (for example B203) can also be included in the material
constituting the
surrounding element. In certain embodiments, they are used in an amount not
exceeding 5 wt.%. Alternatively or (in addition), materials forming more
voluminous
new phases (either upon reaction or the effect of the temperature) and closing
thereby
the existing porosity can also be included in the material constituting the
preformed
element. Suitable materials include compositions of alumina and magnesia.
Thereby,
steel re-oxidation in the area surrounding the nozzle is prevented. In certain
embodiments of the invention, the refractory material has a permeability value
less than
15cD, 20cD, 25cD or 30cD, according to standard ASTM testing. A material that
may
be used contains 0.5-1%, or 1-5% silica, 0.005% to 0.2% titania, 75% to 95%
alumina,
0.1% to 0.5% iron (III) oxide, 0.5% to 1% magnesia, 0.1% to 0.5% sodium oxide,
0.25%
to 2% boron oxide, and 1 /0 to 10% of zirconia + hafnia. A suitable material
may have a
loss on ignition value of 0 to 5%.
[0023] The element, the nozzle or a layer of the element or the nozzle may be
made
from a gas-impervious material. The nozzle or element may be made from
refractory
oxides (alumina, magnesia, calcia) and may be isostatically pressed. To be
regarded
as gas-impervious in the sense of the present invention, a 100 g sample of the
candidate material is placed in a furnace under argon atmosphere (a gentle
stream of
argon is continuously blown (about 1 I/min) into the furnace) and the
temperature is
raised to 1000 C. The temperature is then raised progressively to 1500 C (in 1
hour)
and is then left at 1500 C for 2 hours. The loss of weight of the sample
between
1000 C and 1500 C is then measured. This loss of weight must be lower than 2%
for
qualifying the material as gas-impervious. Thereby, not only the inclusion or
reoxidation
products cannot reach the nozzle but, in addition, they cannot form in the
nozzle or the
element. This particular combination provides thus a synergistic effect
according to
which a perfectly inclusion- and reoxidation product-free steel can be cast.
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[0024] The material constituting the nozzle or element can be selected from
three
different categories of materials:
a) materials which do not contain carbon;
b) materials essentially constituted of non reducible refractory oxides in
combination
with carbon; or
c) materials comprising elements which will react with the generated carbon
monoxide.
Preferably, the selected material will present two or three of the above
categories.
[0025] Examples of suitable material of the first category are alumina,
mullite, zirconia
or magnesia based material (spinel).
[0026] Suitable materials of the second category are for example pure alumina
carbon
compositions. In particular, these compositions should contain very low
amounts of
silica or of conventional impurities which are usually found in silica (sodium
or
potassium oxide). In particular, the silica and its conventional impurities
should be kept
under 1.0 wt. %, preferably under 0.5 wt. %.
[0027] Suitable materials of the third category comprise for example free
metal able to
combine with carbon monoxide to form a metal oxide and free carbon. Silicon
and
aluminum are suitable for this application. These materials can also or
alternatively
comprise carbides or nitrides able to react with oxygen compound (for example
silicon
or boron carbides).
[0028] In certain embodiments of the invention the selected material will
belong to the
second or third categories; in certain embodiments of the invention the
selected material
will belong to the second and third categories.
[0029] A suitable material constituting the layer which will not produce
carbon
monoxide at the temperature of use can comprise 60 to 88 wt. % of alumina, 10
to 20
wt. % graphite and 2 to 10 wt. % of silicon carbide. Such a material contains
oxygen
getters such as non-oxide species such as nitrides or carbides, or non-
reducible oxides,
which can react with any oxygen present.
[0030] In a variant, only a liner present at the steel contacting surface
(inside and
outside of the nozzle) is made from such a material. In another variant, the
nozzle and
the surrounding element are made integral (one-piece).
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[0031] In case the joint between the surrounding element and the nozzle is not
perfectly tight, it might be advantageous to provide a mortar joint which is
made from a
gas impervious mortar. Conventional mortars have an open porosity of 30 to
50%.
According to this advantageous embodiment, the mortar should have an open
porosity
of less than 20%. The mortar may be made of a composition similar to, and
processed
in similar fashion to, the element or nozzle.
[0032] According to another of its aspects, the invention relates to a
particular
surrounding refractory element which is used in the assembly according to the
invention. This surrounding element comprises a main orifice adapted for
matching
engagement with at least a portion of the outer surface of the nozzle, a main
surface
surrounding the main orifice and an outer periphery surrounding the main
surface, the
level of the upper face of the periphery being higher than that of the main
surface.
Advantageously, the surrounding refractory element is made from a gas-
impervious
material. Thereby, steel re-oxidation in the area surrounding the nozzle is
prevented.
For example, a particularly suitable composition to this end is essentially
comprised of a
high alumina material comprising at least 75 wt.% of A1203, less than 1.0 wt.%
of Si02,
less than 5 wt.% of C, the reminder being constituted of refractory oxides or
oxides
compounds that cannot be reduced by aluminum (particularly aluminum dissolved
in
molten steel) at the temperature of use (for example calcia and/or spinel. A
particularly
suitable material is the CRITERION 92SR castable available from VESUVIUS UK
Ltd.
This material is a high alumina low cement castable material reinforced with
fused
alumina-magnesia spinel. A typical analysis of this product is the following:
A1203 92.7 wt.%
MgO 5.0 wt.%
CaO 1 .8 wt.%
5i02 0.1 wt.%
Other 0.4 wt.%
[0033] According to yet another of its aspects, the invention is directed to a
process for
the continuous casting of steel which comprises pouring the molten steel
through an
element, or a combination of a nozzle and an element, as above described.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
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[0034] The invention will now be described with reference to the attached
drawings in
which
[0035] ¨ Fig. 1 shows a cross-section of the bottom wall of a metallurgical
vessel
provided with an assembly according to the invention;
[0036] ¨ Fig. 2 and 3 show respectively top and perspective views of a
surrounding
element according to the invention;
[0037] ¨ Figs. 4 and 5 show skulls collected at the end of the casting
operations in the
upper part of the nozzle;
[0038] ¨ Fig. 6 is a cross-section of an element according to the invention;
[0039] ¨ Fig. 7 is a cross-section of an element according to the invention;
[0040] ¨ Fig. 8 is a cross-section of an element according to the invention;
[0041] ¨ Fig. 9 is a perspective view of an element according to the
invention;
[0042] ¨ Fig. 10 is a cross-section of an element according to the invention;
[0043] ¨ Fig. 11 is a cross-section of an element according to the invention;
[0044] ¨ Fig. 12 is a cross-section of an element according to the invention;
[0045] ¨ Fig. 13 is a perspective view of an element according to the
invention;
[0046] ¨ Fig. 14 is a cross-section of an element according to the invention;
[0047] ¨ Fig. 15 is a perspective view of an element according to the
invention;
[0048] ¨ Fig. 16 is a cross-section of an element according to the invention;
[0049] ¨ Fig. 17 is a cross-section of an element according to the invention;
[0050] ¨ Fig. 18 is a cross-section of an element according to the invention;
[0051] ¨ Fig. 19 is a cross-section of an element according to the invention;
[0052] ¨ Fig. 20 is a perspective view of an element according to the
invention;
[0053] ¨ Fig. 21 is a perspective view of an element according to the
invention;
[0054] ¨ Fig. 22 is a perspective view of an element according to the
invention;
[0055] ¨ Fig. 23 is a perspective view of an element according to the
invention;
[0056] ¨ Fig. 24 is a perspective view of an element according to the
invention;
[0057] ¨ Fig. 25 is a perspective view of an element according to the
invention;
[0058] ¨ Fig. 26 is a perspective view of an element according to the
invention;
[0059] ¨ Fig. 27 is a perspective view of an element according to the
invention;
[0060] ¨ Fig. 28 is a perspective view of an element according to the
invention;
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[0061] ¨ Fig. 29 is a perspective view of an element according to the
invention;
[0062] ¨ Fig. 30 is a cross-section of an element according to the invention;
[0063] ¨ Fig. 31 is a cross-section of an element according to the invention;
[0064] ¨ Fig. 32 is a schematic perspective view of an element according to
the
invention;
[0065] ¨ Fig. 33 is a schematic perspective view of an element according to
the
invention;
[0066] ¨ Fig. 34 is a top view of an element according to the invention;
[0067] ¨ Fig. 35 is a top view of an element according to the invention;
[0068] ¨ Fig. 36 is a cross section of an element and a metallurgical vessel
according
to the invention;
[0069] ¨ Fig. 37 is an elevation of a portion of a raised outer periphery of
an element
according to the invention;
[0070] ¨ Fig. 38 is an elevation of a portion of a raised outer periphery of
an element
according to the invention;
[0071] ¨ Fig. 39 is an elevation of a portion of a raised outer periphery of
an element
according to the invention;
[0072] ¨ Fig. 40 is an elevation of a portion of a raised outer periphery of
an element
according to the invention;
[0073] ¨ Fig. 41 elevation of a portion of a raised outer periphery of an
element
according to the invention; and
[0074] ¨ Fig. 42 is a perspective drawing of an element according to the
invention.
DETAILED DESCRIPTON OF THE INVENTION
[0075] The bottom wall 3 of a metallurgical vessel (here a tundish) is
generally
constituted of a permanent lining 33 made from refractory bricks or castable
material. A
working layer 32 of castable material is generally present above the permanent
lining
33. The surface 31 of the working layer will contact molten steel during the
casting
operations. A layer of insulating material 34 is normally present under the
permanent
lining 33 in order to protect the metallic envelope 35 of the metallurgical
vessel.
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[0076] A nozzle 1 goes through the bottom of the tundish and serves to the
transfer of
the molten steel from the tundish to the continuous casting mold. The nozzle
is provided
with an inlet 11 opening into a bore defining thus a passage 2 for the molten
steel. The
upper edge of the inlet is depicted as reference 12. Fig. 1 shows a submerged
entry
shroud or SES but, as explained above other kind of nozzles (such as an inner
nozzle)
are also encompassed within the scope of the present invention. In the case of
a SEN,
the continuous casting operation is generally provided with a guillotine 37 to
break the
nozzle 1 and terminate casting operations. Generally, the SEN is maintained in
position
by a ramming mass 36.
[0077] The surrounding refractory element 4 surrounds the inlet portion 11 of
the
nozzle 1. The surrounding element 4 is comprised of a main surface 41
surrounding a
main orifice 40. The main surface has been represented frusto-conical at Figs.
1 and
planar at Figs. 2 and 3, but, as explained above, other arrangements are
possible. A
raised outer periphery surrounds the main surface 41; the raised outer
periphery has an
interior face 105. The upper face 42 of the periphery is higher than the level
of the main
surface 41.
[0078] As can be seen on Fig. 1, it is advantageous to have the upper face 42
of the
periphery rising higher than the surface 31 of the tundish.
[0079] A mortar or cement joint at the junction 5 between the refractory
element 4 and
the nozzle 1 can be provided for further tightness improvement.
[0080] A trial has been performed to illustrate the effect of the invention.
The solidified
steel skull remaining in the inner nozzle at the end of casting operations has
been
collected and cut vertically in the middle. Fig. 4 (given by way of
comparison) shows
such a skull collected in a conventional installation (without the surrounding
refractory
element) and Fig. 5 shows such a skull collected in an installation according
to the
invention.
[0081] The skull 20 of Fig. 4 shows significant disturbance in the region 21,
21'
indicating the presence of alumina deposit on the inner wall of the nozzle.
This alumina
deposit is responsible for the clogging of the nozzle with all the detrimental
consequences explained above. The skull 20 of Fig. 4 shows also an enlarged
portion
in the region 22, 22' indicating a severe erosion of the nozzle inlet.
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[0082] The skull 20 shown on Fig. 5 corresponds to the inner shape of the
nozzle
indicating thereby that the nozzle has neither been subjected to erosion nor
to alumina
clogging.
[0083] Fig. 6 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, both of the angles
shown in
the cross-section representation are obtuse angles. In this embodiment, the
height of
the raised outer periphery is constant.
[0084] Fig. 7 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, both of the angles
shown in
the cross-section representation are obtuse angles. In this embodiment, the
height of
the raised outer periphery varies around the course of the element's
circumference.
[0085] Fig. 8 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, both of the angles
shown in
the cross-section representation are obtuse angles. In this embodiment,
portions of the
raised outer periphery with a fixed height are joined by height transition
segments 44.
[0086] Fig. 9 shows a perspective view of an element 4 of the present
invention having
main orifice 40. A raised outer periphery is joined to the base; the raised
outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
all angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
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plane of the upper face of the raised outer periphery and the plane of the
bottom face of
the base of the element are not parallel.
[0087] Fig. 10 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, both of the angles
shown in
the cross-section representation are acute angles. In this embodiment, the
height of the
raised outer periphery is constant.
[0088] Fig. 11 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, both of the angles
shown in
the cross-section representation are acute angles. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference.
[0089] Fig. 12 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, both of the angles
shown in
the cross-section representation are acute angles. In this embodiment,
portions of the
raised outer periphery with a fixed height are joined by height transition
segments 44.
[0090] Fig. 13 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
all angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are acute. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
plane of the upper face of the raised outer periphery and the plane of the
bottom face of
the base of the element are not parallel.
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[0091] Fig. 14 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, one of the angles
shown in
the cross-section representation is an acute angle; the other angle shown is
an obtuse
angle. In this embodiment, the height of the raised outer periphery is
constant around
the course of the element's circumference. The plane of the upper face of the
raised
outer periphery and the plane of the bottom face of the base of the element
are parallel.
[0092] Fig. 15 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are acute, obtuse and, at two points,
are right
angles. In this embodiment, the height of the raised outer periphery varies
around the
course of the element's circumference. The plane of the upper face of the
raised outer
periphery and the plane of the bottom face of the base of the element are not
parallel.
[0093] Fig. 16 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, one of the angles
shown in
the cross-section representation is an acute angle; the other angle shown is
an obtuse
angle. In this embodiment, the height of the raised outer periphery varies
around the
course of the element's circumference. The plane of the upper face of the
raised outer
periphery and the plane of the bottom face of the base of the element are not
parallel.
[0094] Fig. 17 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, one of the angles
shown in
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the cross-section representation is an acute angle; the other angle shown is
an obtuse
angle. In this embodiment, the height of the raised outer periphery varies
around the
course of the element's circumference. The plane of the upper face of the
raised outer
periphery and the plane of the bottom face of the base of the element are not
parallel.
[0095] Fig. 18 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, one of the angles
shown in
the cross-section representation is an acute angle; the other angle shown is
an obtuse
angle. In this embodiment, the raised outer periphery has two portions of
constant
height; these portions are joined by two height transition segments 44. The
planes of
the constant height portions of the upper face of the raised outer periphery
and the
plane of the bottom face of the base of the element are parallel.
[0096] Fig. 19 shows a cross section of an element 4 of the present invention,
in which
base 102 contains main orifice 40 and base bottom face 104. A raised outer
periphery
is joined to the base; the raised outer periphery has an exterior face 106 and
an upper
face 42. Angles 108 are formed between element base bottom face 104 and
exterior
face 106 of the raised outer periphery. In this embodiment, one of the angles
shown in
the cross-section representation is an acute angle; the other angle shown is
an obtuse
angle. In this embodiment, the raised outer periphery has two portions of
constant
height; these portions are joined by two height transition segments 44. The
planes of
the constant height portions of the upper face of the raised outer periphery
and the
plane of the bottom face of the base of the element are parallel.
[0097] Fig. 20 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
plane of the upper face of the raised outer periphery and the plane of the
bottom face of
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the base of the element are not parallel. An element fin 120 protrudes from
the interior
face 105 of the raised outer periphery of the element. The fin surface nearest
main
orifice 40 is at an angle from the vertical.
[0098] Fig. 21 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
plane of the upper face of the raised outer periphery and the plane of the
bottom face of
the base of the element are not parallel. Two element fins 120 protrude from
the interior
face 105 of the raised outer periphery of the element.
[0099] Fig. 22 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
plane of the upper face of the raised outer periphery and the plane of the
bottom face of
the base of the element are not parallel. Three element fins 120 protrude from
the
interior face 105 of the raised outer periphery of the element.
[00100] Fig. 23 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
plane of the upper face of the raised outer periphery and the plane of the
bottom face of
the base of the element are not parallel. An element fin 120 protrudes from
the interior
face 105 of the raised outer periphery of the element. The fin surface nearest
main
orifice 40 is vertical.
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[00101] Fig. 24 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
plane of the upper face of the raised outer periphery and the plane of the
bottom face of
the base of the element are not parallel. An element fin 120 protrudes from
the interior
face 105 of the raised outer periphery of the element. The fin extends
upwardly above
the maximum height of the upper face 42 of the raised outer periphery of the
element.
[00102] Fig. 25 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
plane of the upper face of the raised outer periphery and the plane of the
bottom face of
the base of the element are not parallel. An element fin 120 protrudes
inwardly from the
interior face 105 of the raised outer periphery of the element as well as
outwardly from
the exterior face 106 of the raised outer periphery of the element. The fin
extends
upwardly above the maximum height of the upper face 42 of the raised outer
periphery
of the element.
[00103] Fig. 26 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
plane of the upper face of the raised outer periphery and the plane of the
bottom face of
the base of the element are not parallel. An element fin 120 protrudes
outwardly from
the exterior face 106 of the raised outer periphery of the element.
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[00104] Fig. 27 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery varies around the course of the element's
circumference. The
plane of the upper face of the raised outer periphery and the plane of the
bottom face of
the base of the element are not parallel. An element fin 120 protrudes
inwardly from the
interior face 105 of the raised outer periphery of the element. The fin
extends upwardly
above the maximum height of the upper face 42 of the raised outer periphery of
the
element.
[00105] Fig. 28 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery is constant around the course of the element's
circumference.
The plane of the upper face of the raised outer periphery and the plane of the
bottom
face of the base of the element are parallel. A plurality of lateral ports 124
extends from
interior face 105 of raised outer periphery of the element to the exterior
face 106 of the
raised outer periphery of the element. These ports may be cylindrical, or may
be flared
at one end or at both ends.
[00106] Fig. 29 shows a perspective view of an element 4 of the present
invention
having main orifice 40. A raised outer periphery is joined to the base; the
raised outer
periphery has an exterior face 106 and an upper face 42. In this embodiment,
angles
formed between the bottom face of the base of the element and the exterior
face of the
raised outer periphery of the element are obtuse. In this embodiment, the
height of the
raised outer periphery is constant around the course of the element's
circumference.
The plane of the upper face of the raised outer periphery and the plane of the
bottom
face of the base of the element are parallel. A plurality of paired lateral
ports 128
extends from interior face 105 of raised outer periphery of the element to the
exterior
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face 106 of the raised outer periphery of the element. These ports may be
cylindrical,
or may be flared at one end or at both ends. These ports may be directed so
that the
longitudinal axes of each of a pair of ports intersect at a circle within the
volume partially
enclosed by the element, i.e., the volume partially enclosed by the interior
face 105 of
the raised outer periphery of the element.
[00107] Fig. 30 shows a cross section of an element 4 of the present
invention, in which
base 102 contains main orifice 40. A raised outer periphery 140 is joined to
the base;
the raised outer periphery has an exterior face 106. In this embodiment an
externally
directed rim 132 is in communication with the exterior face 106 of the raised
outer
periphery of the element. In the embodiment shown, externally directed rim 132
is
horizontal; it may be directed above or below the horizontal in other
embodiments.
[00108] Fig. 31 shows a cross section of an element 4 of the present
invention, in which
base 102 contains main orifice 40. A raised outer periphery 140 is joined to
the base;
the raised outer periphery has an interior face 105. In this embodiment an
internally
directed rim 134 is in communication with the interior face 106 of the raised
outer
periphery of the element. In the embodiment shown, the internally directed rim
takes a
truncated conical form; it may be horizontal in other embodiments.
[00109] Fig. 32 shows a schematic perspective view of an element 4 of the
present
invention, in which base 102 contains main orifice 40. A raised outer
periphery 140 is
joined to the base. In the embodiment shown, the raised outer periphery has a
gap.
[00110] Fig. 33 shows a schematic perspective view of an element 4 of the
present
invention, in which base 102 contains main orifice 40. A raised outer
periphery 140 is
joined to the base. In the embodiment shown, the raised outer periphery has
two gaps.
[00111] Fig. 34 shows a top view of an assembly of an element 4 of the present
invention with a nozzle 1. The top view depicts the main surface 41 of the
element and
the outer periphery surrounding the main surface of the element; the interior
face 105 of
the raised outer periphery is visible, as is the upper face 42 of the raised
outer
periphery. The interior of the main orifice 40 of the element has a non-
circular geometry
configured to mate with the exterior geometry of nozzle 1. In the embodiment
shown,
the respective geometries are hexagonal. The corresponding geometries
constrain the
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positioning of the element 4 about the nozzle, so that vertical and horizontal
asymmetries of the element can be properly positioned within a metallurgical
vessel.
[00112] Fig. 35 shows a top view of an assembly of an element 4 of the present
invention with a nozzle 1. The top view depicts the main surface 41 of the
element and
the outer periphery surrounding the main surface of the element; the interior
face 105 of
the raised outer periphery is visible, as is the upper face 42 of the raised
outer
periphery. The interior of the main orifice 40 of the element has a non-
circular geometry
configured to mate with the exterior geometry of nozzle 1. In the embodiment
shown,
indentations on the interior of main orifice 40 accept protrusions on the
surface of
nozzle 1. The corresponding geometries constrain the positioning of the
element 4
about the nozzle, so that vertical and horizontal asymmetries of the element
can be
properly positioned within a metallurgical vessel.
[00113] Fig. 36 shows a cross section of an element 4 and the walls 152 of a
metallurgical vessel according to the invention. The nozzle and the floor of
the
metallurgical vessel have been omitted for clarity. A stopper rod 154 is
positioned to be
moved vertically to permit or interrupt flow through main orifice 40. The
interior face 105
and the exterior face 106 of the raised outer periphery of the element are
indicated.
Gaps 162 between the element and the metallurgical vessel wall are indicated.
The
distance 164 between the interior face 105 and the main orifice 40 is also
indicated.
The asymmetric design on the element embodiment shown permits gaps of the same
size between each metallurgical vessel wall 152 and the top of the element, as
well as
permitting constant, or nearly constant, distances between the interior face
105 and the
main orifice 40, while allowing the stopper rod 154 to be positioned closer to
one
metallurgical vessel wall than to the other.
[00114] Fig. 37 shows a portion 170 of the raised outer periphery of element
4. The
upper face 42 of raised outer periphery of the element contains a plurality of
square
notches.
[00115] Fig. 38 shows a portion 170 of the raised outer periphery of element
4. The
upper face 42 of raised outer periphery of the element contains a plurality of
semicircular protrusions.
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[00116] Fig. 39 shows a portion 170 of the raised outer periphery of element
4. The
upper face 42 of raised outer periphery of the element is formed in a sawtooth
pattern.
[00117] Fig. 40 shows a portion 170 of the raised outer periphery of element
4. The
upper face 42 of raised outer periphery of the element contains a plurality of
semicircular notches.
[00118] Fig. 41 shows a portion 170 of the raised outer periphery of element
4. The
upper face 42 of raised outer periphery of the element is formed in a wave
pattern.
[00119] Fig. 42 is a perspective drawing of an element 4 of the present
invention, in
which base 102 contains main orifice 40 and in communication with raised outer
periphery 140. Raised outer periphery 140 houses upper face 42. The maximum
external dimension of the base of the element 202, the minimum external
dimension of
the base of the element 204, the maximum external dimension of the top of the
element
206, the minimum external dimension of the top of the element 208, the
thickness of the
base of the element 222, the thickness of the raised outer periphery of the
element 224,
the maximum exterior height of the element 232, the maximum interior height of
the
element 234, the minimum exterior height of the element 236, and the minimum
interior
height of the element 238 are indicated.
[00120] A refractory element according to the present invention, therefore,
may
comprise a base having a bottom and a main surface, a main orifice passing
through
the main surface, and a periphery surrounding the main surface, wherein the
main
orifice has an interior face, wherein the periphery has an interior face, an
exterior face
and an upper face, wherein the upper face of the periphery is higher than the
main
surface of the refractory element, wherein the periphery intersects the bottom
of the
base, and wherein the exterior face of the periphery forms an angle other than
a right
angle with the bottom of the base in at least one point in their intersection.
The exterior
face of the periphery may form a right angle with the bottom of the base at
two points in
their intersection, may form an acute angle with the bottom of the base at all
points in
their intersection, or may form an obtuse angle with the bottom of the base at
all points
in their intersection. The plane of the exterior face of the periphery and the
plane of the
bottom of the base may be non-parallel planes. The upper face of the periphery
comprises an upper level and a lower level joined by two transitional non-
vertical, non-
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horizontal portions. The main surface of the element may have a geometry
selected
from the group consisting of circular, oval, truncated circular, truncated
oval, and
polygonal geometry. The element may also comprise one or more fins extending
from
the inner face of the periphery, or one or more fins extending from the
exterior face of
the periphery. The element may comprise one or more ports passing from the
exterior
face to the interior face of the periphery. The element may comprise a feature
on its
surface, for example on the interior face of the main orifice or on the bottom
of the base,
which may be a marking, a recess, a protrusion, a groove, a lip, a peg, a
bore, a notch,
a dimple, a mogul, a ridge, a threaded receiver, a key receiver, a bayonet
receiver, a
bevel, and a non-circular geometry, or any other device or feature which would
constrain movement of the element around an axis. The refractory element of
the
invention may be composed of single pieces or of multiple pieces. The
refractory
element of the invention may be produced from a high alumina material
comprising at
least 75 wt.% of A1203, less than 1.0 wt.% of Si02, and less than 5 wt.% of C.
The
refractory element may be constructed so that the periphery of the element has
a
thickness equal to or less than 100 millimeters, and the base of the element
has a
thickness equal to or less than 100 millimeters.
[00121] An assembly of a refractory element and a nozzle according to the
invention
may be composed of a single piece or multiple pieces. The refractory element
may
comprise a main orifice having a non-circular geometry, and wherein the
refractory
nozzle comprises an exterior radial surface having a non-circular geometry
configured
to mate with the refractory element. The refractory element comprises a main
orifice
interior face having a mating feature, wherein the refractory nozzle comprises
an
exterior radial surface having a corresponding mating feature configured to
engage with
the main orifice interior face mating feature. The mating feature of the
nozzle and the
mating feature of the element, when engaged, may prevent rotational motion of
the
element around the longitudinal axis of the bore of the nozzle.
[00122] An assembly of a refractory element and a nozzle according to the
present
invention may be deployed in a metallurgical vessel for the casting of molten
metal. In a
typical deployment, the refractory nozzle may have an inlet portion forming a
passage
through the bottom wall of the metallurgical vessel and a refractory element
as
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previously described surrounding the inlet portion of the nozzle, wherein the
inlet portion
of the nozzle has a top outer edge, wherein the inlet portion of the nozzle
has a
longitudinal axis, wherein the main orifice of the element is adapted for
matching
engagement with at least a portion of the outer surface of the nozzle, wherein
the main
surface of the base of the element has a lowest level, the lowest level being
lower than
the top outer edge of the nozzle inlet portion, and wherein at least a portion
of the
periphery of the refractory element is higher than the surface of the bottom
wall of the
tundish. The element may comprise a gas impervious refractory material. The
nozzle
or the element may comprise a gas impervious refractory material. A gas
impervious
mortar may be used between the nozzle and the refractory element.
[00123] A process for the continuous casting of steel may comprise pouring the
molten
steel from a ladle into a metallurgical vessel housing an assembly of a
refractory
element and a nozzle as described above, and thence into a casting mold.
[00124] Numerous modifications and variations of the present invention are
possible. It
is, therefore, to be understood that within the scope of the following claims,
the
invention may be practiced otherwise than as specifically described.
