Title of Invention

ANTI-ALUMINA-BUILDUP REFRACTORIES FOR CASTING NOZZLES

Abstract A continuous casting nozzle comprising a refractory material comprising a refractory aggregate including 20 mass% or more of CaO component, and 10 mass% or more of clinker particle, each of said clinker containing CaO as a mineral phase on the basis of 100 mass% of the entire composition, the refractory material being applied to a portion to be in contact with molten steel, wherein at least a part of only the surface of the CaO exposed from the surface of said corresponding clinker particles is formed with a CaCO3 film after the nozzle is molded and burned.
Full Text ANTI-ALUMINA-BUILDUP REFRACTORIES FOR CASTING NOZZLES
TECHNICAL FIELD
The present invention relates to refractories applicable to a nozzle for continuous casting
of steel, such as immersion nozzle, upper nozzle, sliding nozzle, lower nozzle or long nozzle,
and more particularly to refractories applicable to an inner hole portion of such a casting nozzle
to be in contact with molten steel, to prevent alumina buildup thereon.
BACKGROUND ART
Responding to recent requirements stricter quality control of steel products, a good deal of
effort has been made to reduce non-metallic inclusions, such as alumina which builds up on ah
inner hole portion of a nozzle for continuous casting of steel. Moreover, in terms of casting
operations, the buildup of alumina and others which arises from long hours of casting is likely to
cause clogging of the inner hole portion and difficulties in continuing the casting operation,
which hinders the improvement in productivity.
As one of measures against the alumina buildup, there has been known a technique in
which argon gas is injected from the inner surface of a nozzle into molten steel to prevent the
alumina buildup in physical manner. In this technique, if the argon gas is injected at an
excessive amount, bubbles of the injected argon gas will be incorporated into molten steel to
form pinholes in slabs. Thus, due to the restriction in the allowable injection amount of argon
gas, this method cannot be exactly used as a sufficient measure for preventing the alumina
buildup.
There has also been known a technique intended to provide an anti-alumina-buildup
function to refractories themselves. For example, in view of inducing the reaction between
alumina attached on a refractory nozzle and CaO contained in the refractories to form a
low-melting-point or fusible substance, Japanese Patent Publication No. 61-44836 discloses a
casting nozzle using refractories containing a combination of graphite, and either one of sintered
calcia, fused calcia and another ceramic material containing a CaO component. While such
CaO-containing refractories can exhibit an anti-alumina-buildup effect in some cases, it is likely


to cause increase in alumina buildup depending on the circumstances.
Further, when applying refractories containing CaO as a mineral phase to a casting nozzle,
the CaO is likely to undesirably hydrated due to a hydration reaction with water absorbed
therein. While Japanese Patent Laid-Open Publication No. 10-5944 discloses a technique of
adding CaCO3 as aggregate to prevent the hydration, the CaCO3 aggregate is pyrolytically
decomposed to have a high porosity, and the resulting irregularity of an effective or operative
surface of a casting nozzle leads to undesirable alumina buildup thereon.
DISCLOSURE OF INVENTION
In view of the above problems concerning the measures against aluminum buildup on
CaO-containing refractory nozzles, it is therefor an object of the present invention to provide
refractories for casting nozzles capable of bringing out an excellent effect of suppressing the
alumina buildup on an operative surface, and an effect of preventing the hydration of CaO due
to a hydration reaction.
Through various research on achieving this object, based on analyses of the phenomenon
of alumina attachment/buildup on an operative surface of CaO-containing refractories, it was
found that metal is first attached on the surface of the refractories, and alumina is then attached
on the metal.
According to the observation of a portion of the surface having the metal attached thereon,
the portion of the refractory surface had a large irregularity. Based on this fact, it is verified
that this irregularity generates stagnation in molten flow to accelerate the accretion of metal
thereon, and the accreted metal blocks the dispersion of CaO from refractories constituting a
casting nozzle (hereinafter occasionally referred to as "nozzle") to preclude alumina attached on
the metal from being converted to a fusible substance.
Using the above knowledge that the alumina buildup is caused by the penetration of metal,
such as molten steel, into the refractory matrix in advance of alumina, the inventor found that
the penetration of molten steel into the matrix of refractories constituting a nozzle and including
clinker particles each including CaO as a mineral phase can be suppressed by forming CaCO3
on at least a part of the surfaces of the CaO exposed outside from the surfaces of the


corresponding clinker particles, so as to achieve an enhanced anti-alumina-buildup function, and
finally accomplish the present invention. While it is preferable to form CaCO3 on all of the
surfaces of the CaO exposed outside from the surfaces of the corresponding clinker particles, the
CaCO3 may be formed on only a part of the surfaces of the CaO to obtain the
anti-alumina-buildup accordingly.
Specifically, the present invention provides refractories applicable to a casting nozzle,
primarily an inner hole portion of the nozzle, which comprises refractory aggregate including 20
mass% or more of CaO component, and 10 mass % or more of clinker particles each containing
CaO as a mineral phase, on the basis of 100 mass % of the entire composition. In these
refractories, at least a part of the surfaces of the CaO exposed from the surfaces of the
corresponding clinker particles is formed v/ith a CaCO3 film.
A function to be contained from the formation of CaCO3 on at least a part of the exposed
surfaces of the CaO will be described below based on reaction formulas.
CaCO3 on the surface of the clinker is decomposed by a heat load from molten steel to
release CO2 gas.
CaCO3 → CaO + CO2
The released CO2 reacts with aluminum in the molten steel to form alumina on the
operative surface of the nozzle.
4Al + 3CO2 → 2Al2O3 + 3C
The formed alumina reacts with CaO to form a fusible substance so as to smooth the
operative surface. This prevents the accretion of metal while facilitating the continuous supply
of CaO to alumina attached on the operative surface, to suppress/prevent the alumina buildup.
As above, the suppression of the alumina buildup can be achieved only if CaCO3 is
allowed to exist only on the surface of the clinker particle so as to maintain the smoothness of
the operative surface. When using CaCO3 as aggregate as in the aforementioned Japanese
Patent Laid-Open Publication No. 10-5944, the smoothness of an operative surface cannot be
maintained because the CaCO3 aggregate itself has a high porosity.
The formation of CaCO3 on the surface of CaO exposed outside from the surface of the
clinker particle in the refractories additionally provides a function of preventing the hydration of


CaO due to a hydration reaction. To facilitate the reaction between alumina precipitated in
molten steel and the CaO in the nozzle itself, to form a fusible substance, the CaO may be
contained in the refractories at 20 mass% or more on the basis of 100 mass% of the entire nozzle
composition.
In the present invention, the aggregate may include 20 mass% or more of CaO component,
and 10 mass% or more of clinker particles each containing CaO as a mineral phase, on the basis
of 100 mass% of the entire composition. The aggregate may be used together with another
refractory aggregate without any problem.
In view of the anti-alumina-buildup effect, a clinker particle containing CaO as a mineral
phase, so-called free-CaO, at 10 mass% or more, preferably 20 mass% or more, more preferably
30 mass% or more, specifically calcia-magnesia clinker including calcia clinker and dolomite
clinker, may be preferably used to facilitate the formation of the CaCO3 film on the surface of
CaO in the clinker particle.
Any combination of CaZrO3 clinker or CaO-SiO clinker, which contains no CaO as a
mineral phase; material containing CaO-based compound as a primary component;
carbon-based material, such as graphite or carbon black; and magnesia-based or zirconia-based
material commonly used with refractories, may be additionally used as aggregate according to
need.
The following technique may be used to form the CaCO3 film on at least a part of the
surfaces of the CaO exposed outside from the surfaces of the corresponding clinker particles.
(1) A nozzle molded integrally with the refractories is subjected to a heat treatment under a
CO2 atmosphere at a temperature of 300 to 850°C. Alternatively, the molded nozzle is
subjected to a heat treatment at a temperature of greater than 850°C, and then cooled under a
CO2 atmosphere in the temperature range of 300 to 850°C.
(2) The molded nozzle is burnt in a conventional process, and is then subjected to a heat
treatment under a CO2 atmosphere at a temperature of 300 to 850°C, again.
CaCO3 may be formed on the surface of the clinker particle to have a thickness in the
range of 0.07 to 7 µm, preferably 0.1 to 5 µm, more preferably 0.5 to 5 µm. If the thickness is
less than 0.1 urn, the amount of CO2 to be generated from thermal decomposition will be


reduced, and consequently the amount of alumina to be formed on the operative surface will be
reduced. While the thickness of less than 0.1 µm causes deterioration in the anti-hydration
effect, if the thickness is at least 0.07 µm, a practically acceptable level can be maintained
because the alumina buildup will occur only in a significantly limited area, and the deterioration
in the anti-hydration effect is not significant unless the nozzle is left in nonuse for a long period
of time. If the thickness is greater than 5 µm, the surface of the clinker will have an increased
porosity after the release of CO2 likely to case difficulty in obtaining smoothness in the
operative surface. However, if the thickness is 7 µm or less, a practically acceptable level can
be remained because the alumina buildup caused by the increase porosity in the operative
surface occurs only in a partial area. In this case, the anti-hydration effect is not particularly
deteriorated. The thickness of the CaCO3 film can be controlled by adjusting at least one of the
CO2 concentration, time and temperature for inducing the reaction between CaO and CO2.
CaCO3 is thermally decomposed at a temperature of about 900°C or more. Thus, where a
preheat temperature of the nozzle is set at 900°C or more, the release of CO2 before the inflow
of molten steel is likely to spoil the anti-alumina-buildup effect. As one measure against this
problem, an antioxidant may be applied on the CaCO3 film. Specifically, this antioxidant is
fused to form a glass layer on the CaCO3 film, and the glass layer acts to suppress the release of
CO2 until the inflow of molten steel, so as to allow the anti-alumina-buildup effect to be
adequately brought out.
Preferably, the refractories of the present invention primarily designed to obtain the
anti-alumina-buildup effect are applied to a surface of continuous casting refractories to be in
contact with molten steel. In this case, the refractory use as an inner hole portion may be
integrally molded together with other nozzle component materials, or may be formed as
sleeve-shaped refractories and inserted into or adhesively bonded to a refractory nozzle body.
In the present invention, the CaCO3 film is formed only on the surface of CaO exposed
outside from the surface of the clinker particle. Thus, the increase in porosity due to
decomposition of CaCO3 can be minimized to achieve approximately no deterioration in
strength after decomposition of CaCO3.
Thus, the refractories of the present invention are applicable to not only an inner hole


portion but also an nozzle body. In addition, nozzle body and the inner hole portion may be
formed using the same material to provide enhanced productivity. The refractories of the
present invention may also be applied as a baffle for preventing uneven molten steel flow in the
nozzle.
BEST MODE FOR CARRYING OUT THE INVENTION
A preferred embodiment of the present invention will now be described in connection of
Examples.
Table 1 shows the composition of a compound for use in forming refractories of the
present invention, the conditions of a treatment for forming CaCO3, and characteristics of
obtained refractories, together with Comparative Example.

* Alumina buildup test: O; no buildup, A: buildup only in a part of the surface, X: buildup in
50% or more of the entire surface
An appropriate amount of phenol resin as organic binder was added to each of the
materials as shown in Table 1, and the mixture was homogenously kneaded. The obtained

compound was subjected to a cold isostatic pressing (CIP) process under a pressure of 1000
Kg/cm , and burnt under a reduction atmosphere at a temperature of 1000°C.
In Comparative Example, the burnt product was directly cooled. In Inventive Examples 1
to 7, when a temperature in a furnace was reduced to 850°C during the course of the cooling,
CO2 was supplied into the furnace to form a CaCO3 film on the surfaces of CaO exposed outside
from the surfaces of respective dolomite clinker particles.
The thickness of the CaCO3 film was measured by observing the cut section of the clinker
particle using a scanning electron microscope, and controlled by adjusting the partial pressure
and supply time of CO2.
In the alumina buildup test, molten steel of low-carbon aluminum-killed steel with 0.2% of
aluminum dissolved therein was maintained at 1570°C, and a rod-shaped sample was immersed
into the molten steel. After 60 minutes, the sample was pulled out to evaluate the amount of
alumina buildup. In Table 1, O indicates a sample having no alumina buildup, A indicated a
sample having alumina buildup only in a part of the surface, and x indicates a sample having
alumina buildup in 50% or more of the entire surface.
The hydration test was performed by measuring the bending strength of a sample after
being maintained under a temperature of 35°C and a relative humidity of 70% for 3 days, and
expressing the measured bending strength value as an index on the basis of 100 of the bending
strength of the sample before the test. An index closer to 100 indicates a better result or less
deterioration in the strength.
As compared to Comparative Example, all of Inventive Examples 1 to 7 have better results
in both the alumina buildup test and the hydration test. The anti-alumina-buildup and
anti-hydration effects from CaCO3 were observed in Inventive Examples 1 to 7 having a film
thicknesses of 0.07 µm to 7 µm. An optimal film thickness was in the range of 0.1 to 5 µm as
in Inventive Examples 2 to 6. Among them, Inventive Examples 3 to 6 having a film thickness
of 0.5 to 5 µm had particularly good results.
As mentioned above, in the continuous casting refractories including clinker particles each
containing CaO as a mineral phase, the CaCO3 film formed on the surfaces of the CaO exposed
outside from the surfaces of the respective clinker particles releases CO2 gas through thermal


decomposition to smooth the operative surface so as to prevent the accretion of metal thereon,
so that CaO is continuously supplied to alumina attached on the operative surface to prevent the
alumina buildup. In addition, the CaCO3 film effectively prevents the hydration of CaO due to
a hydration reaction so as to provide enhanced operational efficiency and steel quality in
continuous casting.
INDUSTRIAL APPLICABILITY
The present invention is applicable as anti-alumina-buildup refractories for use in inner
hole portions of various nozzles for continuous casting of steel.


WE CLAIM:
1. A continuous casting nozzle comprising a refractory material comprising a
refractory aggregate including 20 mass% or more of CaO component, and
10 mass% or more of clinker particle, each of said clinker containing CaO
as a mineral phase on the basis of 100 mass% of the entire composition,
the refractory material being applied to a portion to be in contact with
molten steel, wherein at least a part of only the surface of the CaO
exposed from the surface of said corresponding clinker particles is formed
with a CaCO3 film after the nozzle is molded and burned.
2. An anti-alumina-buildup continuous casting nozzle as defined in claim 1,
wherein said CaCO3 film has a thickness ranging from 0.1 to 5 µm.
3. An anti-alumina-buildup continuous casting nozzle as defined in claim 1,
wherein said portion to be in contact with molten steel is the surface of
the inner hole of the nozzle.


A continuous casting nozzle comprising a refractory material comprising a
refractory aggregate including 20 mass% or more of CaO component, and 10
mass% or more of clinker particle, each of said clinker containing CaO as a
mineral phase on the basis of 100 mass% of the entire composition, the
refractory material being applied to a portion to be in contact with molten steel,
wherein at least a part of only the surface of the CaO exposed from the surface
of said corresponding clinker particles is formed with a CaCO3 film after the
nozzle is molded and burned.

Documents:

443-KOLNP-2005-ABSTRACT-1.1.pdf

443-kolnp-2005-abstract.pdf

443-KOLNP-2005-CANCELLED PAGES.pdf

443-KOLNP-2005-CLAIMS-1.1.pdf

443-kolnp-2005-claims.pdf

443-kolnp-2005-correspondence.pdf

443-kolnp-2005-correspondence1.1.pdf

443-kolnp-2005-description (complete).pdf

443-kolnp-2005-examination report.pdf

443-kolnp-2005-form 1.pdf

443-kolnp-2005-form 18.1.pdf

443-kolnp-2005-form 18.pdf

443-KOLNP-2005-FORM 2-1.1.pdf

443-kolnp-2005-form 2.pdf

443-kolnp-2005-form 26.1.pdf

443-kolnp-2005-form 26.pdf

443-kolnp-2005-form 3.1.pdf

443-kolnp-2005-form 3.pdf

443-kolnp-2005-form 5.1.pdf

443-kolnp-2005-form 5.pdf

443-kolnp-2005-granted-abstract.pdf

443-kolnp-2005-granted-claims.pdf

443-kolnp-2005-granted-description (complete).pdf

443-kolnp-2005-granted-form 1.pdf

443-kolnp-2005-granted-form 2.pdf

443-kolnp-2005-granted-specification.pdf

443-KOLNP-2005-OTHERS-1.1.pdf

443-kolnp-2005-others.pdf

443-KOLNP-2005-PA.pdf

443-KOLNP-2005-PETITION UNDER RULE 137.pdf

443-KOLNP-2005-REPLY TO EXAMINATION REPORT.pdf

443-kolnp-2005-reply to examination report1.1.pdf

443-kolnp-2005-specification.pdf

443-KOLNP-2005-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf

443-kolnp-2005-translated copy of priority document1.1.pdf


Patent Number 248947
Indian Patent Application Number 443/KOLNP/2005
PG Journal Number 37/2011
Publication Date 16-Sep-2011
Grant Date 14-Sep-2011
Date of Filing 17-Mar-2005
Name of Patentee KROSAKIHARIMA CORPORATION
Applicant Address 1-1, HIGASHIHAMA-MACHI, YAHATANISHI-KU, KITAKYUSHU-SHI, FUKUOKA, 806-8586
Inventors:
# Inventor's Name Inventor's Address
1 HOOVER, DONALD BRUCE HILLOCK LANE 1710, YORK, PA 17403
2 OGATA, KOJI C/O KROSAKIHARIMA CORPORATION, 1-1, HIGASHIHAMA-MACHI, YAHATANISHI-KU, KITAKYUSHU-SHI, FUKUOKA, 806-8586
PCT International Classification Number B22D 11/10
PCT International Application Number PCT/JP2003/010474
PCT International Filing date 2003-08-19
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2002-239940 2002-08-20 Japan