Note: Descriptions are shown in the official language in which they were submitted.
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PATENT APPLICATION
~A~ PERMEABL~ WELL NOZZLE
TO ALL WHOM IT MAY CONCERN:
Be it known that we: James D. ~ngel, citizen
of the United States and residing at 3444 Maplespring
Drive, Can~ield, Ohio, U.S A. and Han K. Park, citi~en of
the United States and res:iding at 1812 Taper Drive,
Pittsburgh, Pennsylvania, U.S.A., have invented certain
new and useful improvements in ~ GAS PERMEABLE WELL NOZZLE
of which the following is a specification.
sACKGRoUND OF THE INV NTION
The present invention relates generally to
refractory elements used in metallurgical operations and
more particularly to an improved well nozzle for use in a
tundish, ladle or like vessel in the continuous casting of
steel. Heretofore, the benefits of bubbling an inert gas
such as argon through a porous refractory element in a
tundish well nozzle have been recognized, particularly, as
an aid in eliminating unwanted inclusions in the steel,
preventiny air aspiration and in minimizing the deposition
of aluminum-type inclusions on the walls of the refractory
casting elements. If uncheckedj, such aluminum oxide
depositions will aventually cause completP blockage of the
casting element.
In order to provide inert gas to the bore of the
tundish well nozzle, it has been common practice to
provide a pressed and fired porous refractory member of a
generally cylindrical shape having an axial bore and an
outer sidewall surface. The sidewall is machined to
closely receive a metal can therearound. The outer
sidewall of the porous refractory member and the inside
surface of the steel can define an open annular region
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therearound for the introduction of a pressurized inert
gas. The top and bottom portions of the porous re*ractory
sidewall are joined to the can with a refractory cement
along the contacting surfaces to prevent gas leakage
therealong. When properly operating, inert gas introduced
to the metal can enters the open annular region and
permeates the porous refractory member to exit as a fine
dispPrsion of bubbles in the molten metal stream passing
through the axial boxe of the well nozzle.
Unfortunately, it has been observed that the
refractory cement seal at the joint between the porous
refractory member and metal can eventually fails causing
inert gas leakage along the top joint. When such a joint
failure occurs, the inert gas takes the path of least
resistance and generally flows along the failure path
rather than permeating through the porous refractory to
the bore, as required for proper operation.
The preisent invention solves the shortcomings of
the prior art by providing a porous well nozzle for a
metallurgical vessel such as a tundish in which the
likelihood o~ inert gas leakage along the metal can is
virtually eliminated. In addition, the well nozzle o-E the
invention provides a novel construction in which the inert
gas sealing joint is not dependent upon a refractory to
metal cement seal, thus eliminating the problem caused by
differing thermal expansion coefficients between ceramics
and metals, which is inherent in prior art well nozzles.
Still further, the present invention provides a gas
permeable well nozzle which is less expensive to
manufacture than prior nozzles because it employs less of
the more costly porous refractory material, requires
shorter firing times and requires no labor intensive
external machining.
SUMMARY OF THE INVENTION
Briefly, the present invention is directed to a
gas permeabLe inner nozzle or well nozzle for use in a
metallurgical vessel such as in a well block of a tundish.
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The novel well nozzle is generally cylindrical in shape
and includes a gas permeable or porous refractory member
having an axial bore therethrough, defining an entry end
at an upper end portion and an exit end at a lower end
5 thereof. The porous member is preferably formed of a
pressed and fired ceramic refractory material having a
high resistance to molten metal erosion such as alumina,
zirconia or magnesia, which may be present either as a
single phase or as a carbon bonded system. A castable
member of a pourable or castable refractory cement
material is cast around the outside of the gas permeable
member having an open gas annulus defined therebetween.
The castable member has upper and lower end portions which
extend beyond the gas annulus and directly contact and
15 bond with t~e outer surfaces of the porous refractory
member to form qas impermeable joints along the upper and
lower end portions thereof. A transverse gas inlet
channel extends through the castable member to communicats
at one end with the gas annulus. A metal can, preferably
of steel, is positioned around the castable member and
includes a gas fitting which communicates with a second
end of the gas inlet channel to permit introduction of
pressurized inert gas therethrough.
The castable refractory member which defines the
gas annulus along the porous refractory member forms a
very tenacious chemical bond, upon curing, thus, creating
a gas impermeable joint between the two refractory
members. Preferably, the major refractory constituents of
the porous member and the castable member are identical so
as to provide matched thermal expansion rates and thus
lessen the opportunity for thermally induced cracking
along the gas impermeable joints between the two members.
For example, the porous refractory member may be of a
pressed and fired alumina material and the castable member
may be a mixture of alumina and a cementitious material,
preferably consisting of about 95~ by weiqht alumina and
about 5% by weight cementitious calcia, plus minor
impurities. The predominant hydraulic bonding phase in
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this system is calcium aluminate. The castable mixture is
poured around the porous refractory member with a wax
sleeve previously applied on the outer sux~ace of the
porous member. After drying and moderate temperature
5 curing at about 700-800F, the castable portion sets and
forms a bond with the gas p~rmeable refractory along the
joint areas while the wax s:Leeve melts and vaporizes to
form the open gas annulus in the region formerly occupied
bv the wax sleeve~
In addition to alumina, compatible matched
refractory materials which may be used to form the gas
permeable member and castable member also include zirconia
and magnesia, wherein the castable member contains
preferably about 95% by weight of the mathed refractory
material and ~bout 5~ by weight cement, preferably calcium
oxide, plus incidental impurities.
As a further embodiment, the above mentioned
refractory materials, namely, alumina, zirconia and
magnesia may be individually employed in a matched, carbon
bonded system for manufacture of both the porous and
castable or pourable members. A carbonaceous resin or
pitch binder forms a strong carbon bond within and between
the respective members. In the carbon bonded embodiment,
volatile hydrocarbons in the castable or pourable member
are driven off during a conventional preheating treatment
of the tundish and the member undergoes a further firing
treatment during normal use.
BRIEF DB~CRIPTION OF THE DRAWINGS
~igure 1 is a partially fragmented, cross-
sectional side elevation view of a tundish, with aconventional sliding gate valve and attached submerged
casting nozzle, showing a prior art well nozzle in place
in the tundish;
Figure 2 is a cross-sectional side elevation
view of a gas permeable well nozzle of the prior art,
similar to that depicted in Figure l; and
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Figure 3 is a cross-sect:ional side elevakion
view of ~ gas permeable well nozzle according to the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to t]he drawings, Figure 1 shows a
partially fragmented section of a conventional tundish 2
which is used in continuous steel casting operations to
hold molten metal prior tlD delivery to a continuous
casting machine (not shown). The tundish has a well block
area 4 and may include a cylindrical member 6 positioned
around the discharge orifice of the tundish for the
purpose of improving the quality of the metal being cast
therefrom. A conventional well noz~le 8 is cemented into
the well block area 4 and contains an axial bore 10
therethrough. A conventional sliding gate valve 12 is
fitted to the bottom of the tundish 2 to control the flow
of molten metal exiting therefrom. A slideable refractory
plate 14 m~ves between two stationary refractory plates to
control the metal flow, all in a well-known manner. A
conventional collector nozzle 16 is fitted to the bottom
stationary plate of the sliding gate valve 12 and directs
the stream of molten metal to a submerged pouring nozzle
18 which, in turn, directs the molten metal to the
continuous casting mold (not shown). A conduit 20
supplies pressurized inert gas, such as argon~ to the well
nozzle 8 for emission as a fine dispersion of inert gas
bubbles to the axial bore 10, all of which is well-known
in the steelmaking art.
A porous well nozzle 8', typi~al of the prior
art, is also depicted in Figure 2 and is similar to the
nozzle 8 shown in Figure 1. The prior art well nozzle 8'
includes a gas permeable, porous re~ractory portion 22 of
a pressed and fired refractory material, such as alumina,
for exampleO The porous portion 22 is encased by a metal
can 24, usually of a steel material. An annular gas slot
26 is defined between the outside surface of the porous
refractory portion 22 and the metal can 24. The metal can
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also includes a threaded fitting 28 which communicates at
one end with the annular slot 26 and is adapted to be
fitted to an inert gas supply line such as the conduit 20
of Figure 1 to supply pressurized inert gas to the annular
slot 26.
The steel can 24 is joined to an upper end
region of the porous refractory portion 22 by way of a
joint 30 formed by a thin layer of refractory cement which
creates a barrier to pre~ent the escape of inert gas from
the annular ~lot 26. During operation, at elevated steel
casting temperatures, it has been observed that the
refractory cement joint 30 may begin to fail and
thereafter permits the pressurized inert gas ~o leak from
the annular slot 26 along the periphery of the steel can
24. Thus, instead of having the desired ~ine dispersion
of inert gas bubbles around the bore lo', the inert gas
will short circuit, taking the path of least resistance
and escape around the upper edges of the steel can where
the refractory cement 30 has failed. It is theorized that
this premature and undesirable failure of the refractory
cement joint 30 occurs because o~ the differences in the
thermal expansion coefficients of th~ steel can 24 and thP
porous refxactory portion 22, since the refractory
material expands at a much lower rate than the steel
material. Of course, when short circuiting of the inert
gas ~low occurs, the desired action of the inert gas along
the axial bore 10' ceases and the well nozzle can no
longer perform its intended gas distribution function.
This common problem is aliminated by the gas
permeable well nozzle 40 of the present invention shown in
Figure 3. The well nozzle 40 of the invention includes a
gas permeable porous refractory member 42 o~ a genPrally
cylindrical shape with an axial bore 44 formed
therethrough. Due to the novel configuration of the
present well nozzle 40, the porous refractory member 42
has a smaller wall thickness and diameter than its prior
art counterpart depicted in Figure 2, previously
identified as porous portion 22. Because of this decrease
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in physical size, l~ss of the more expensive sized
refractory grains are used in the manufacture of the
porous member 42 and the tim~ required for firing the
re~ractory is also reduced. Thus, the porous re~ractory
member 42 is less expensive to manufacture than the larger
porous portion 22 of the prior art due to decreased
material and energy costs.
A pourable or castable refractory member 46
having a generally cylindrical shape surrounds the porous
lo refractory member 42. An open gas annulus 48 is
positioned intermediate the members 42 and 46 and includes
a transverse channel 49 which is adapted to be placed into
communication with a remotely positioned supply of
pressurized inert gas. In operation, the pressurized
inert gas fills the annulus 48 and permeates the porous
refractory member 42. The gas exits along the sidewall of
the axial bore 44 as a fine dispersion of inert gas
bubbles~ in the molten stream of metal passing
therethrough.
The annulus 48 is formed by the so-called "lost
wax~ method of casting, well-known in the refractory and
foundry arts. A wax sleeve or coating of wax is applied
around the outer surface of the fired porous refractory
member 42 by hot dipping, for example, to form the gas
annulus 48. The upper and lower joint areas 54 and 56 are
preferably masked prior to wax application by taping the
surface of the porous member 42~ which prevents the wax
from adhering to th~se areas. The wax coated piece 42 is
then placed in a cylindrical mold having the configuration
of the pourable or castable member 46. The tape covering
the masked areas 54 and 56 is removed prior to pouring the
castable material so as to provide a wax free bonding
surface along the upper and lower areas 54 and 56. A wax
core is also inserted into the mold in contact with the
wax sleeve for formation of the transverse channel 49D
The castable or pourable refractory material is poured
into the mold and assumes the cylindrical shape of the
mold, substantially as depicted in Figure 3. The castable
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member 46 sets in the mold and assl~mes a green strength
after a given time period after which the green part is
dried and then subjected to a thermal curing treatment to
harden the castable member 46 and to f~rm the bonded
joints 54 an~ 56. During the curing treatment at about
7000-8000F, the previously applied wax melts and volatizes
off to produce the open gas annulus 48.
A metal closure or can 50, preferably of steel,
is positioned around the cured castable member 46 and held
in place by a mechanical fit. ~he cain 50 includes a
thread2d gas conduit fitting 52 which communicates with
the transverse channel 49 ancl is adapted to be attached to
an inert gas supply conduit, such as a gas pipe 20 of
Figure l.
The gas permeable porous re~ractory member 42 is
constructed of a pressed and fired re~ractory material
such as alumina, zirconia or magnesia, all of which
exhibit good erosion resistance in molten steel. After `
curing, the upper portions of the porous member 42 and
castable member 46 form a high streng~h bonded joint 54
along their interface. A similar strong bonded joint 56
is formed along the lower portions of the contacting ~
surfaces of the porous member 42 and castable member 46. `
In a presently preferred embodiment, the porous
25 member 42 is made from a refractory material selected from -~
alumina, zirconia or magnesia. The porous member is
pressed and fired all in a well-known manner. The
castable member 46 is constructed of a matched refractory
system containing a high percentage of one of alumina,
zirconia or magnesia plus a small percentage of a
refractory cement component. A preferred dry mix ratio
for the castable member is about 95% by weight refractory
material and about 5% by weight cement, preferably calcium
oxide cement. In practice, the use of like refractory
materials in the members 42 and 46 provides matched
thermal expansion rates in the porous and castable
members. Such matched thermal expansion properties serves
to maintain the integrity of the gas impermeable joints 54
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and 56 during service and prevents cracking and subsequent
leakage of inert gas therebetween. It will be ~urther
appreciated, that the joint provided by the cementitious
material in the castable member 46 creates a strong bond
with the refractory material of the porous refractory
member 42. The resulting ~oints 54 and 56 are much
stronger than the prior art joint 30 between the
refractory ~ement and the metal can. In addition, the
close matching of thermal expansion rates of the members
o 42 and 46 provides further resistance to thermally induced
cracking at the bonded joints 54 and 56.
Since castable me~)er 46 is poured around the
porous member 42, there is no need for time consuming and
costly machining operations to fit the parts together as
previously called for in the prior art. The castable
refractory mixture making up member 4~ in the wet, unset
condition is flowable and conforms to any surface
irregularities which may be present on the outer surface
of the porous member 42. ~he wax sleeve employed to form
the open gas annulus 48 likewise accommoda~es any surface
imperfections or irreyularities which may be present on
the outer surface of the member 42.
It will be further appreciated that in the prior
art construction of Figure 2, a gas seal is established by
the application of a thin layer of refractory cement to
joint 30 between the sur~ace of the refractory portion 22
and the metal can 24. The improved gas impervious joint
54 of the present invention is robust because of the
relatively great thickness of castable member 46, coupled
with the concept of matching the thermal expansion
coefficients of the refractory materials employed so as to
permit the members 42 and 46 to expand and contract in
unison without separating along the joint 54.
The present invention also contemplates the use
of matched carbon bonded refractory systems, in which case
the previously described cementitious constituent in the
castable member 46 is not used. A resin or pitch
carbonaceous binder in an amount of between about 2% 30% i-
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2 ~ 3 9 2
by weight is preferably employed in the refractory mix and
formulated as a pourable materlal which is cast into place
around a like carbon bonded refractory porous member 42
which has been previously pressed and fired. Refractory
systems ~uch as carbon bonded alumina, carbon bonded
zirconia and carbon bonded magnesia ~re well-known in the
art and provide good steel erosion resistance and superior
thermal shock resistance. The carbon bonded refractory
systems also form strong joints 54 and 56 as previously
described. The metal can 50 holds the unfired, pourabl~
carbon bonded refractory in place and prevents handling
damage to the pourable member 4~ prior to thermal
treatment which occurs during use. During conventional
tundish preheat operations, the volatile hydrocarbon
materials are driven off from the pourable member 46 such
that the member 46 is cured as the tundish is preheated
prior to start-up of metal teeming. The much higher
temperatures which occur during continuous steel casting
then provide a further firing treatment to the carbon
bonded refractory pourable member 46. Such carbon bonded
refractories also exhibit improved, longer life inert gas
sealing along the joints 54 and 56 due to the fact that
the refractories employed in the carbon bonded systems are
matched. Therefore, the previously discussed balanced
thermal expansion and contraction properties between the
porous refractory member 42 and the pourable refractory 46
are likewise achieved in the carbon bonded refractories.
While specific embodiments of the invention have
been described in detail, it will be appreciated by those
skilled in the art that various modifications and
alternatives to those details could be developed in light
of the overall teachings of the disclosure. The presently
preferred embodiments described herein are meant to be
illustrative only and not limiting as to the scope of the
invention which is to be given the full breadth of the
appended claims and any and all equivalents thereof.
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