Note: Descriptions are shown in the official language in which they were submitted.
CA 02219930 1997-10-31
WO 96!34838 . PCT/US96/05654
APPARATUS FOR DISCHARGING MOLTEN METAL
IN A CASTING DEVICE AND METHOD OF USE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the art of casting aluminum killed
molten steel and related ferrous alloys. The invention is directed toward
tubes such as casting shrouds, nozzles (including submerged entry nozzles
and submerged entry shrouds) and the like through which the molten metal
passes during a continuous casting process. Typically these tubes are used
in a continuous casting process for pouring the molten metal from a ladle
into a tundish or from a tundish into a casting mold. The tubes of the
present invention are made from a composition which is effective in
preventing the deposition of non-metallic inclusions, especially alumina
(A1203), on the interior surface of the tube as the metal passes
therethrough. In addition, the tubes made from this material also have a
surprising thermal shock resistance. The invention is more particularly
directed toward submerged entry nozzles and submerged entry shrouds
which resist clogging caused by the deposition of aluminum oxide therein
and which also have a surprising thermal shock resistance.
2. Background Information
' It is well known that aluminum metal or alloys thereof may be added
to molten steel in order to remove dissolved oxygen. The aluminum
removes the oxygen from the steel by reacting with the oxygen to produce
solid A1203, most of which floats to the top of the rinolten steel where it
can
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be easily removed. However, a small amount of AI203 remains in the steel.
The AI203 which remains in the steel is known to accumulate and form a
deposit on the inner surface of casting shrouds and nozzles as the molten
metal passes therethrough. Although the reasons for this phenomenon are
not completely understood, it is believed that the deposition occurs due to ,
the presence of alumina in the refractory material of the nozzle which
comes in contact with the molten steel containing residual alumina from the
aluminum killing process.
The deposition of alumina is particularly troublesome in the.nozzles
and shrouds associated with a tundish which is used in a continuous
casting process. In this type of process, the molten steel is teemed from
a ladle through a nozzle or shroud into a tundish. The tundish includes a
plurality of holes in the bottom which are connected to nozzles for the flow
of molten steel therethrough into the casting machine. In order to
accomplish this objective, it is important that the nozzles be able to provide
a regular flow of molten metal to the casting machine. Typically, such
casting machines operate at a specific casting rate. Obviously, it is
important that the supply of molten metal which flows through the nozzles
to the casting machine must remain as constant as possible during the
casting procedure. Thus, nozzles which become partially or wholly
occluded due to the deposition of alumina within the bore of the nozzle will
cause serious problems in the casting procedure.
Various techniques are known in the prior art for avoiding the above-
noted clogging problems. However, none of these have been totally
satisfactory for a variety of reasons. For example, it is known in the art to
provide a nozzle with a plurality of openings in the internal surface for the
,
passage of an inert gas into the bore while the metal is flowing
therethrough. In operation, gas is injected through these openings into the
bore and this gas minimizes contact between the molten metal and the
2
CA 02219930 2004-04-05
nozzle surface, thus preventing interaction between the metal and the nozzle
which, in turn, prevents clogging from taking place. Typically, the openings
constitute a highly porous surface which may be in the form of a porous
sleeve within the bore of the nozzle. A nozzle of this type must include a
complex and costly internal structure in order for the inert gas to reach the
openings or pores within the internal portion of the nozzle. Thus, the
manufacturing steps and costs associated with such a nozzle make this type
of nozzle undesirable. In addition, the use of such nozzles is known to
produce defects such as pinholes in the steel product due to the large amount
of inert gas which is required to avoid the clogging problem.
Another approach to solve the clogging problem involves the
fabrication of the nozzle from a material which inherently does not interact
with the molten metal to form deposits of alumina. However, there are only a
limited number of materials which are capable of functioning in this manner
and which have the refractory properties which are needed in the environment
of the molten metal casting apparatus. In particular, it is difficult to find
a
material which has the required thermal shock resistance needed for nozzles
and the like through which molten metal flows.
U.S. Patent Nos. 5,244,130; 5,046,647; 5,060,831 and 5,083,687
disclose various types of materials which are used to make nozzles and the
like for casting molten metal.
U.S. Patent No. 5,244,130 (Ozeki et al.) provides an improved
nozzle which is said to overcome the problems associated with other
prior art nozzles. Ozeki et al. mention two types of prior art nozzles over
which their invention is said to be an improvement. The first prior art nozzle
is made from graphite and calcium zirconate (zirconia clinker) containing
23%-36°~ CaO. Ozeki et al. mention that the calcium oxide contained in
the
3
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calcium zirconate does not sufficiently move toward the surface of the
nozzle bore through which the steel flows and consequently the calcium
oxide does not come into sufficient contact with the non-metallic inclusions
such as a alumina, and for this reason, this prior art nozzle is not effective
in preventing the accumulation and deposition of alumina within the nozzle.
The second type of prior art nozzle discussed in U.S. Patent No.
5,244,130 is similar to the first, but additionally includes calcium
metasilicate (CaO.Si02). It is said the that presence of the calcium
metasilicate in the second type of prior art nozzle overcomes the problems
noted with respect to the first type of prior art nozzle due to the combined
effects of calcium zirconate and calcium metasilicate which allows the
calcium oxide in each particle of zirconia clinker to move toward the
surface. However, Ozeki et al. also note with respect to the second type
of prior art nozzle that the calcuim metasilicate has a low content of
calcium oxide which is insufficient to adequately replenish the calcium
oxide which reacts with the alumina in the molten steel; thus making it
impossible to prevent clogging of the nozzle for a long period of time. In
order to overcome this problem, Ozeki et al. use crystal stabilized calcium
silicate (2CaO.Si02 and 3CaO.Si02).
The nozzles disclosed by Ozeki et al. include graphite in the amount
of 1 O-35 wt. °i6 which is added to improve oxide resistance, wetting
resistance against molten steel and to increase thermal conductivity.
Graphite in amounts which exceed 35°~ are avoided since such large
amounts of graphite degrade corrosion resistance. There is no suggestion
for adding flake graphite to improve the thermal shock resistance which is
not surprising since the zirconia clinker used by Ozeki et al. is said to have
a low thermal expansion coefficient.
4
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U.S. Patent No. 5,083,687 (Saito etal.) provides an improved nozzle
for overcoming the above-noted clogging problem. Saito etal. mention that
one type of prior art nozzle which, was designed to avoid the clogging
problem uses an inner lining made from a material containing 90-50 wt.
°~
Mg0 and 10-50 wt.°r6 C. However, it is noted in the specification
that
such materials containing graphite (C) and Mg0 suffer from cracking due
to a large thermal expansion coefficient as compared to conventional
nozzles made from alumina and graphite. Saito et al. also note that nozzles
containing Mg0 and C exhibit inferior anti-spalling. In view of these
undesirable features associated with refractories containing Mg0 and
carbon, particularly the poor thermal shock resistance associated with the
presence of Mg0 in the composition, Saito et al. concluded that nozzles
which includes these ingredients would be unacceptable. Thus, Saito et al.
avoid any material which contains Mg0 as a material for making the nozzle.
Instead, they use a composition containing boron nitride, zirconium oxide
and a sintering assistant containing SiC and BBC.
U.S. Patent No. 5,046,647 (Kawai et al. ) discloses two types of
improved nozzles for dealing with the clogging problem. One nozzle is
made from Zr02, C and Si02. Kawai et al. emphasize that Ca0 and Mg0
should be avoided, or at best, can be tolerated in small amounts so that the
sum of Ca0 and Mg0 is less than 1 °~. Kawai et al. also describe a
second
type of nozzle containing Ca0 and Si02 in which the ratio of Ca0 to Si02
is limited to 0.18 to 1.86. No Mg0 is disclosed for use in this second type
of nozzle which is not surprising in view of the lack of thermal shock
resistance noted in the prior art when Mg0 is included in the composition
of the nozzle.
Patent No. 5,060,831 (Fishier et a/. ) discloses a material for covering
a casting shroud such as a tundish nozzle used for casting steel. The
5
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composition includes Ca0 and a zirconium oxide carrier. There is no
suggestion for including Mg0 in the composition.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a casting element
such as a nozzle or the like which does not become clogged with alumina
when used in a process for casting aluminum killed ferrous metal alloy,
especially aluminum killed steel.
It is a further object of this invention to provide a casting element
such as a nozzle or the like which combines the aforementioned clogging
resistance with enhanced thermal shock resistance.
It is a further object of the present invention to provide a method for
casting aluminum killed ferrous metal, especially aluminum killed steel
which utilizes the casting element of the present invention.
These and other objectives are accomplished by providing a tubular
casting element containing doloma (i.e., doloma or CaO.MgO) and flake
graphite in a carbon matrix or network derived from a binder resin by
heating the resin under carbonizing conditions. It has been discovered that
tubular casting elements such as a nozzle made from the above material
avoids the clogging problem. In addition, it has also been discovered that
the selection of doloma as the refractory material for such casting elements
combined with flake graphite results in a casting element having highly
desirable thermal shock resistance so that the molten metal can flow
through the casting element without cracking with a minimum or absence
of preheating of the casting element being necessary. The thermal shock ,
resistance obtained with the doloma refractory is surprising in view of the
prior art observation that nozzles which include Mg0 have an unacceptable
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'WO 96/34838 PCT/I1S96/05654
level of thermal shock resistance which causes them to crack when used
in a casting process.
Although the present invention is more particularly directed to
nozzles used in continuous casting procedures, the invention is not limited
to such nozzles but is more generally applicable to any tube or the like
through which molten metal flows and which is susceptible to clogging as
described above. Thus, while the following descriptive material refers to
nozzles used in casting procedures, it will be understood that the
description applies equally well to related devices which are susceptible to
the aforementioned clogging problem.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a sectional view illustrating an embodiment of the nozzle
of the present invention.
Figure 2 is a vertical section illustrating another embodiment of the
nozzle according to the present invention.
Figure 3 is a graph which illustrates the relationship between the
parameter R~ and the probability of failure.
DETAILED DESCRIPTION OF THE INVENTION
AND PREFERRED EMBODIMENTS
The nozzles of the present invention are made by substituting
dolomalgraphite in place of the AI203/graphite used in prior art nozzles. It
has been discovered that the doloma avoids the clogging problem
~ associated with alumina/graphite tubes because the doloma causes the
production of soluble reaction products which do not clog the nozzle.
' 25 Doloma is a well known and commercially available refractory material
which is currently used for a variety of refractory applications due to its
7
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heat resistant capability. It is made by calcining dolomite to convert the
MgC03 to Mg0 and the CaC03 to CaO. Sintering is then performed on the
calcined dolomite to densify the grain. Typically, the doloma is sold in
pulverized form which can be shaped into a variety of structures.
The nozzles of the present invention are made by mixing doloma
powder with graphite, preferably flake graphite, with sufficient liquid resin
binder to form agglomerates. Generally, 9-13 °~ by weight, preferably
about
9%Z-10%Z °~6 by weight of liquid resin binder (based on the weight of
the
solids blend) is sufficient to form agglomerates in the mixing process.
The agglomerates are pressed isostatically in a mold at ambient
temperature to shape the material into the desired form. The shaped mass
is baked in a curing oven where the temperature is gradually increased to
harden (cure) the resin: Next the formed mass is carbonized (coked) in a
furnace at a carbonizing temperature greater than 850°C (e.g., 1800-
2400°F) in an inert gaseous atmosphere which is unreactive with the
resin
(e.g., nitrogen or argon) to fully carbonize the resin and form a carbon
network or matrix which holds the doloma and graphite together.
Resins which have sufficient green strength to bind the refractory
materials and which can be carbonized to form a carbon network are well
known to those skilled in the art. Many synthetic resins are known to be
useful for forming refractory materials such as nozzles and can be used in
the present invention. In general, it is known that these resins form a
carbon network after the carbonizing or coking step. The carbon network
holds the article together so that it resists breaking. Thus, the amount of
resin should be enough to provide a sufficient amount of carbon network
to accomplish this well known objective. Excessive amounts of carbon
network should be avoided. Thus, it is preferable that the amount of
carbon network should be no more than the amount which is required to
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'WO 96/34838 PCT/L1S96/05654
hold the finished article together so that it resists breaking. Generally, the
carbon network constitutes 4-7 wt. % of the finished nozzle, preferably
about 5-6°~6 (e.g., 6°~6).
If solid resin is used, it should be dissolved in a solvent to form a
liquid binding resin composition. Typically, resins which are known for use
in forming nozzles have a high coking value in the range of about 45°~-
50% to produce sufficient carbon network after carbonization. Also, curing
the resin should avoid a condensation reaction since the water produced by
such a reaction would be expected to react with the calcium oxide in the
dolomite to produce the corresponding hydroxide which occupies a higher
volume and thereby causes the structure to come apart. Thus, resins
which are known for use with other calcium oxide containing refractory
materials can be used in the present invention. The binding resin will
produce a carbon network after the carbonizing or coking step which is
sufficient so that the nozzle resists breaking. It is known that some weight
loss of the resin occurs during the carbonization step. This weight loss
results in some open porosity. Ideally, the weight loss which accompanies
the thermal treatments does not result in an open porosity greater than
16%.
A preferred resin is phenol-formaldehyde resin. Such resins are well
known and are produced by the reaction of phenol and formaldehyde.
Preferably, the resin system contains formaldehyde and phenol in a ratio of
0.85 formaldehyde to phenol. The reaction between the phenol and
formaldehyde is normally acid catalyzed so that the resulting resin must be
buffered, dewatered and have the free phenol adjusted. The preferred
~ levels are pH about 7.0, water below 0.1 °~ and free phenol between
0.2-
0.9°x. The resin should then be put into solution with solvent.
Suitable
solvents include primary alcohols such as methyl, ethyl, isopropyl and
furfuryl alcohol; glycol such as ethylene glycol; ketones such as methyl
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ethyl ketone and methyl isobutyl ketone; aldehyde such as furfuraldehyde
and acetaldehyde; dibasic esters and dimethyl formamide. Preferably the
solvent is a furan compound, preferably furfuraldehyde or a solution of
furfuryl alcohol and furfuraldehyde. In practice, the resin solution includes
a basic co-reactant such as triethylene tetramine, diethylene tetramine,
ethylene diamine or tetraethylene pentamine. Other suitable co-reactants
include diamines having an amine value of 10001100 and the equivalent
molecular weight of 30 t 2.
As an alternative to the B staged phenolic novolak-furfural solution,
the invention may use a phenolic novolak dissolved in glycol and methyl
alcohol but this resin is less desirable.
Another alternative binder system involves the use of furfural and a
powdered phenolformaldehyde resin, mixed until the furfural picks up the
solid, powdered resin and the resulting plasticized resin then causes the
raw materials to roll up into agglomerates. A tumble dryer is subsequently
used to densify the agglomerates. This process results in agglomerates
with excellent properties.
The graphite used is preferably natural flake graphite with a carbon
content of not less than about 94°x. Preferably the flake size should
be
described by a normal distribution curve centering around 250 microns.
Although minor amounts of impurities may be tolerated in the graphite, it
is preferable to minimize such impurities. Preferably the graphite should be
substantially free from contaminates and residual flotation compounds and
the water content should be less than 0.5°~. An analysis of a preferred
flake graphite is shown in Table 1.
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WO 96/34838 . PCT/iTS96/05654
TAB LE
7
Specie wt.
Carbon 95 t 1
Ca0 0.15
' 5 Mg0 0.06
AI203 0.87
Si02 2.7
Fez03 1.0
r
Other 0.22
~
i0 The graphite is in the form of a powder so that it can form
agglomerates with the doloma powder and resin and so that these
agglomerates can then be molded into a fixed shape for carbonization.
Preferably the particles are 0.044-0.3mm in diameter.
The doloma is also in the form of a powder which can form
15 agglomerates with the graphite and resin. Preferably the doloma is small
enough to pass through a 14 mesh screen and large enough to be held on
a 100 mesh screen (U.S. standard meahl. However, when screening the
doloma to obtain the appropriate si:e range for this invention, it is not
absolutely necessary to remove all of the material which would pass
20 through the 100 mesh screen. For example, it is acceptable to include up
to about 10 wt.% of the fines which would eventually pass through the
100 mesh screen if the screening process were continued for a very long
period of time. In addition, doloma ball mill fines may also be included. Ball
mill fines are small enough to pass through a 325 U.S. standard mesh and
25 can be defined as particles having a surface area-to-weight ratio of
' 2300 Cm2/gm to 2800 Cm2lgm. A suitable doloma is a powder having
particles ranging in size from 0.15mm to 1.4mm in diameter and which may
further include dolomite ball mill fines. Minor amounts of impurities may be
tolerated in the dolomite. However, it is preferable to minimize such
11
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impurities. Preferably, the doloma should contain a minimum of 56.5%
CaO, 41.5°h Mg0 and a maximum of 2% other impurities with a
maximum
of 1 °~6 Fe2O3. An analysis of a preferred doloma is shown below in
Table
2.
g TABLE 2
Specie Wt. 96
Ca0 56.7
Mg0 41.2
A1203 0.5
Si02 0.4
Fe203 1.2
Preferably the density of the doloma is from 3.25 to 3.28
grams/cubic centimeter. Thus, the doloma should be sintered until the bulk
density of the grain is a minimum of 3.25 grams/cubic centimeter.
Preferably the total porosity, open and closed, should not exceed 59~. The
preferred particle size distribution of the doloma fraction contained in the
nozzle is 150 microns - 1300 microns with the ball mill fines having a
statistical mean particle diameter of 7.2 microns. In another preferred
embodiment, the doloma includes a fraction having a particle size range
from 0.15mm - 1.4mm in diameter (coarse fraction) and a ball mill fines
fraction. In this preferred embodiment, the coarse fraction of doloma
should be in the range from about 32 wt. °~6 to about 43 wt. °i6
with respect
to the solids blend. The solids blend includes all the solid material (e.g.,
graphite and doloma) and excludes the resin, solvent and resin co-reactant.
In this preferred embodiment, the ball mill fines fraction may range from 20-
25 wt. % of the solids blend.
The solids blend used in the present invention may further include
other oxides which are compatible with Ca0 and MgO. Such oxides
include silica (Si02), zirconia (ZrOz), hafnia (Hf02), ceria (Ce02), titanic
12
CA 02219930 2004-04-05
(Ti02) and magnesia (Mg0). These oxides should be below 25 wt. % of the
solids blend, preferably no more than 10 wt. °~ and most preferably no
more
than 5 wt. °~. The amount of Mg0 may exceed 1 °~ (e.g., more
than 1 °h up to
10°~ or more than 1 °~ up to 5%). In addition, effective amounts
of known
antioxidants used in refractory nozzles may also be included in the solids
blend. Suitable antioxidants can include the metal powders of aluminum,
silicon, boron, calcium and magnesium or the carbides of silicon, calcium,
zirconium, boron, tantalum and titanium. Some low melting oxides such as
boric oxide, sodium borate or any combination of glass formers - aluminum,
silicon, boron, phosphorous and zirconium oxides can be added to the body in
order to form a protective layer on the surtace to ban the ingress of oxygen
into the body. This oxygen will destroy the bond carbon, and therefore, must
be prevented from doing so by some barrier layer. The additions of metals or
glass forming oxides or carbides accomplish this. These materials are added
in antioxidant effective amounts to protect the nozzle from oxidation
particularly when the nozzle is hot.
The nozzles and related articles of this invention are made by
conventional molding techniques. First, the solid blend containing the
doloma, graphite and optional metal oxide additives and optional
antioxidant additives are mixed. Next, the resin is added to the dry
solid blend and the ingredients are mixed in an agglomerating mixer to
form agglomerates. Preferably the agglomerates have a normal size
distribution centered around 400 microns with no agglomerates being greater
than about 2000 microns and none being finer than about 150 microns.
The agglomerates are formed in the mixing operation when the solids
blend is wet blended with the resin. For example, in a preferred embodiment,
the agglomerates are formed by wet mixing the solids blend with the
resin solution along with the co-reactant. Densification of the agglomerates
occurs during the mixing operation through viscosity enhancement of the
resin which occurs when the volatile liquids evaporate and the resin and co-
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reactant react with each other. Preferably, the bulk density of the
agglomerates should not be less than 1.65 grams/cubic centimeter, more
preferably from 1.9-2.1 grams/cubic centimeter. Such agglomerates, when
pressed at 10000 PSI, will form an article having a bulk density of 2.37- '
2.45 grams/cubic centimeter. ,
The agglomeration is best performed at ambient temperature with
only a gradual and limited amount of warming which occurs due to the
mixing and slight exothermic reaction which occurs as the resin cures.
Preferably the material being agglomerated should not be allowed to exceed
a temperature more than about 140°F and the rate of temperature
increase
should be no more than about 3°F per minute.
The agglomerates are placed in a mold (e.g., rubber mold) and
formed at high pressure, e.g., 8500 PSI (580 bar) to 25000 PSI (1700 bar)
to form the shaped structure having a bulk density in the range of 2.35-
2.45 grams/cubic centimeter which is a preferred density for operation in
a metal casting procedure. An isostelic press with rubber tooling may be
used for the molding operation. After molding, the shaped structure is
heated in the absence of oxygen (e.D., in an atmosphere of nitrogen or
argon) at a high temperature (e.g., 975-1375°C) until the resin bond is
converted to a carbon bond. The articles in this coked state will have the
required physical characteristics to permit successful use as nozzles and the
like for casting molten metal.
There may be wide variation in the amount and proportion of the
solid materials which are used to form the nozzles and similar articles of
this invention. Generally, the doloma (including ball mill fines) can vary
from 30-70°~ based upon the weight of the solids blend. Unless
otherwise
stated, all percentages given herein are percentages by weight. -
14
CA 02219930 2004-04-05
There should be at least about 25 wt. °h graphite in the solids
blend.
There is no upper limit to the amount of graphite as long as there is
sufficient
doloma to avoid the clogging problem. However, it is preferred to limit the
graphite to no more than 45°l° to avoid excessive erosion
associated with
nozzles containing a large amount of graphite. Thus, a preferred embodiment
of this invention, the graphite can vary from about 25 wt. °r6 to about
45 wt.
based upon the weight of the solids blend, more preferably about 30°~
to
about 45°r6 by weight. However, in order to combine the anticlogging
advantage with the desired thermal shock resistance required for adequate
performance, the graphite content should be greater than 33°~ (e.g.,
greater
than 35°~) to about 43°r6, preferably about 37-43% and most
preferably about
38% and the doloma should be in the range of 37-63 wt. °~ based upon
the
weight of the solids blend.
The thermal shock resistance property of the nozzles of this invention
is very significant since it allows the nozzles to be used without having to
undergo an extensive and time consuming pre-warming procedure.
When molten steel which can vary from 2850-3100°F depending on the
grade, hits a cooler tube, the interior of the tube begins to expand at a
faster
rate than the outer parts of the tube. This generates a tensile "hoop stress"
in
the outer parts of the tube. The tube will crack if this stress exceeds the
tensile fracture strength of the material. Air will be admitted to the steel
stream
when the tube cracks and this will result in unwanted oxidation.
A parameter which is used to evaluate thermal shock resistance is
shown in the formula below:
R~ _ ~ ~
azE
CA 02219930 2004-04-05
In the above formula: G is the surface fracture energy; a is the linear
coefficient of thermal expansion and E is Young's modulus which is the ratio
of stress-to-strain in the elastic region of the stress-to-strain curare.
For the purposes of the present invention, adequate thermal shock
resistance is achieved when the probability of failure (i.e., cracking) is
below
an acceptable level. Figure 3 is a graph which shows the relationship between
the probability of failure on the vertical axis and the Rgt value on the
horizontal
axis. For practical purposes, an acceptable thermal shock resistance is
obtained when the Rst value is about 25 or higher, since such RSt values are
associated with a probability of failure which is less than 10'2. Such values
begin to be achieved when the graphite content is more than about 33% since
it has been observed that when the graphite content is 33% with 62% doloma,
the R~ value is 24.6. There is a distinct improvement in the thermal shock
resistance when the graphite level is greater than 35 wt. °l° of
the solids blend.
The nozzles of the present invention may be formed entirely of the
above described composition like the embodiment shown in figure 1. Figure 1
shows a nozzle indicated generally by reference numeral 1. The entire nozzle
is made from the refractory material of this invention which is shown by
reference numeral 2.
Figure 2 shows an alternative embodiment wherein only the inner
portion of the nozzle is made from the refractory material of this invention.
Thus, figure 2 includes an inner lining 3 made from the refractory material of
this invention while the outer material 4 may be less expensive material which
does not come in contact with the molten metal. Figures 1 and 2 show an
inner bore 5 within the nozzle for the passage of molten metal therethrough.
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The following examples illustrate preferred embodiments of the
invention which have acceptable thermal shock resistance values.
a
T ABLE
3
Example Example Example Example Example Example
1 2 3 4 5 6
Graphite 38 30 38 30 45 38
0.3mm-
0.15mm dia.
Graphite 0 8 0 8 0 7
0.15mm-
0.044mm
Doloma 7 7 37 37 0 12
0.42mm-
0.15mm
Doloma 30 30 0 0 37 25
1.4mm- -
0.15mm
Doloma 25 25 25 25 25 25
Ball Mill
Fines
Liquid Resin10 10 10 10 10 10
Basic ~ 1 ~ 1 ~ 1 1 1 ~ 1
Coreactant ~ ~
2S Examples 1-6 were made from the compositions shown in Table 3
which shows the parts by weight for each ingredient used therein. In
examples 1-6, the dry ingredients (graphite, doloma and ball mill fines) are
dry
mixed to form a blend which is then wet mixed with the resin and co-reactant.
Mixing is continued to form agglomerates of the cured resin and solid
particles. These agglomerates are placed in a rubber mold and formed at high
pressure (e.g., 8500-25000 ~PSI). Next, these parts are then heated in the
absence of oxygen until the resin is converted to a carbon bond. The parts in
this coked state have desirable physical properties to permit successful use
as
t
pouring tubes. These properties are shown below in Table 4.
3S
17
SUBSTITUTE SHEET (RULE 26)
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TABLE
4
Example6campleExampleExample ExampleExample
1 2 3 4 5 6
r
Bulk 2.28 2.29 2.26 2.26 2.23 2.20
t t t t t t
Density0.05 0.05 0.06 0.06 0.05 0.05
$ Apparent15.4 1 S.1 16.1 16.0 16.3 16.7
t t t t t
Porosity2% t2% 2% 2.0% 2.0% 2.0%
Room 70o 70o soo sso t soo sso
t t t t t
Temp. 200 200 200 200 200 100
MOR
(psi)
Rst 38.1 36.4 36.4 35 41 40
. ,
All of the above examples have R,~ values well in excess of 25.
However, lowering the amount of graphite from 38~ of the solids blend to
33°6 of the solids blend results in an R,~ value of only24.6 compared
to an R,~
value of 38.5 when the amount of graphite is 3896. This distinction is
illustrated by a comparison between the composites A and B formed by
pressing and carbonizing the compositions shown below in Table 5 which
indicates the parts by weight of each ingredient.
TABLE 5
Example A Example B
Graphite 38 33
0.3mm-01.5mm
dia.
Doloma 30 30
1.4mm-0.59mm
Doloma 7 'I 2
0.42mm-0.15mm
3p Doloma 25 25
BMF
Resin 10 10 .-
Coreactant 1 '1
18
SU$STITU~~ SHEET (RULE 2<3j
CA 02219930 1997-10-31
WO 96/34838 PCT/US96/05654
The physical properties of the composites A and B are shown below in
Table 6.
TABLE 6
' S Example A Example B
Coefficient of 6.8x10-C-' 8.7x10-C-'
Themnal Expansion
Younp's Modulus 1.65 2.33
GPA
1 /2 b, E, 1~ 19 107
Rst 38.5 24.6
ft can be seen from the R,~ values in Table 6 and the graph of figure 3
that the probability of failure for composite A is very low at about 1 tube in
1428 tubes while the probability of failure for composite B is much higher at
about 1 tube in 100 tubes.
While the present invention has been described in terms of certain
preferred embodiments, one skilled in the art will readily appreciate that
various modifications, changes, omissions and substitutions may be made
without departing from the spirit thereof. It is intended, therefore, that the
present invention be limited solely by the scope of the following claims:
19
SUBSTITUTE SH~fT (RULE 26~
