Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
This invention relates to a method of manufacturing long
or immersion type nozzles to be used for continuous casting -
hereinafter will be called as "casting nozzles" - having highly
stable quality, and high thermal shock- and corrosion-resistance.
Casting nozzles are very important and effective members
in the continuous casting, for improving the quality of cast
metal products. In response to the recent increasing demand
for high-quality steel material, continuous casting operations
using casting nozzles have been remarkably increased. As the
continuous casting process is locating at an early stage of
the steel production line, any trouble occurring in this process
may affect the subsequent processes remarkably. Accordingly,
the casting nozzles for use in this process have always been
required to have a long service life and a highly stable quell-
try. For instance, they are imposed such severe requirements
that the occurrence of troubles in the casting nozzles must
ye less than once per one or two thousands pieces of nozzles.
Besides that, the use of the continuous casting is extend-
Ed to the wide variety of steels, including the kinds of highly corrosive to the refractories. Also there is an increased use
of multi-ladle casting which requires long time continuous
operations. Therefore, there is an increased demand for the
development of casting nozzles having highly stable quality
and high reliability, as well as high thermal shock- and
corrosion-resistance.
According to our investigation of various troubles
occurred in actual operations which seem to have a relation-
ye
ship to the quality of casting nozzles, such troubles may be
classified into two major types, i.e.,
l). Occurrence of cracking or breakage which
seems to be often caused at the beginning
of casting operations.
2). Occurrence of pitting or boring on the
inner surface of the nozzles due to local
erosion which may be caused at the inter-
mediate stage of casting operations.
Detailed study of these defective nozzles and other
products of the same lot revealed that in the microscopic
tests, there is a tendency of lack of the uniform distribution
of the refractory constituent in one body of the casting nozzle
on one hand, while on the other hand in the physical and comma-
eel test results/ such as porosity, specific gravity, bending
strength and modulus of elasticity, considerably wide phlox
lion was observed in the results of measurements. This may
indicate that the cracking or abnormal erosion takes place at
the weak portion caused by the lack of uniform quality in the
body of the casting nozzles.
Generally, two counter plans are considered to avoid
such troubles:
l). Improving physical and chemical properties
such as antis palling or anti-corrosion
characteristics of the refractories used for
the casting nozzles.
2). Minimizing the fluctuation of the quality
in one body of the casting nozzle.
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Both coun~erplans are intending, after all, to minimize
the occurrence of the weak point described above.
As for the counter plan 1), efforts are being made to
raise the refractoriness, corrosion-resistivity and anti-
spelling characteristics of the material by controlling its composition and treatments. However, for the counter plan I
there has been found no effective procedures to minimize the
fluctuation of the quality, and this may be also fundamentally
important procedure to promote counterpl~n 1).
Next, we have studied the cause of the fluctuation of
the quality in connection with the manufacturing process of
the casting nozzles.
In the production of casing nozzles, flake graphite is
generally used as a refractory component for improving thermal
shock resistance of the products, and coal tar, pitch, phenol
resin or other organic substances are added as a binder to
the refractory materials.
Phenol resin is used as a binder for manufacturing cast
in nozzles as well as it is used for manufacturing other kinds
of fire bricks, such as those for converters, torpedo cars,
ladles, eta, because phenol resin has better mixing properties
at room temperature in case of liquid form, and assurance of
an improved working environment over the use of coal tar,
and also it gives to refractory material a high strength
after drying and after sistering.
For such refractories a liquid phenol resin of resow type
is generally used singly or in combination with a powdery
phenol resin of novolak type. Powdery phenol resin is used
substantially for increasing the strength of the refractories.
The addition of liquid phenol resin has been a convention-
at practice in the production of refractories containing flake
graphite. In the case of casting nozzles, however, cracking
occurs sometimes while molding, and also shows insufficient
and non-uniform mold packing and this may result in insufficient
strength of final products, so that it has been difficult to
obtain products of stable quality after molding or subsequent
sistering.
It was found by our study that such instability of the
quality is caused by uneven distribution of the liquid remaining
in the kneaded mixture. This liquid may come from, for instance,
organic volatile matter in the phenol resin, particularly
methylol in the resow type phenol resin, and free water, and
lo the condensation water which is generated in a large quantity
while drying the molded products.
If an excessive amount of liquid remains in the molded
products, cracks may-occur in the body thereof while drying
or sistering the same, and if the amount of remaining liquid
is too small, compression of the mixture may become difficult
at the stage of molding, and if the amount of liquid is local-
lye uneven, it is difficult to obtain molded products of dense
and uniform texture when the mixture is compressed by the
rubber press machine.
The ordinary method of improving above disadvantage is to
cure the kneaded mixture by placing the same in a room under
constant temperature and humidity for a long time/ for instance
several days. This method, however, still cannot eliminate
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the local difference in -the amount of liquid between the sun-
face and inner portion. Further, the kneaded mixture contain-
in a large amount of organic additives tends to solidify into
lumps, so that it is necessary to stir the mixture several
times while curing until the amount of liquid is reduced to
the desired values, and this requires troublesome operations.
Accordingly, an object of the present invention is to
provide a method of manufacturing nozzles for continuous
casting in which such disadvantages as mentioned above are
eliminated, and the casting nozzles having high antis palling
and corrosion resisting characteristics, and is highly stable
in quality are obtainable.
The present invention is directed particularly to the
manufacture ofcastingnozzles containing flake graphite as a
refractory component and also phenol resin as a binder.
Summary of the Invention
The method of manufacturing nozzles for continuous cast-
in according to the present invention comprises the steps of;
a) kneading refractory material containing flake
graphite with the addition of liquid phenol
resin as a binder;
b) drying said kneaded mixture by blowing hot air
while loosening said mixture into particles;
c) molding said dried mixture to the nozzle shape;
d) sistering by heating said molded refractory
material to form nozzle body.
Thus a-t the step b) of the method, dried mixture having
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uniformly distributed required amount of remaining liquid can
be obtained and the products of highly stable in quality can
be provided by the process of subsequent stops
In one type of said refractory material, the liquid
phenol resin of resow type is used independently as a binder,
and in another type of the refractory material, the liquid
phenol resin of resow type is used in combination with powdery
phenol resin of novolak type, and in a preferred embodiment of
this invention, about 5-20 percent by weight of liquid phenol
resin of resow type is added in the step a) independently or
in combination with the powdery phenol resin of novolak type.
retailed Description of the Invention
Flake graphite and other suitable refractory materials
are mixed together in the dry state, then 5-20 percent by
weight of liquid phenol resin is added to the mixture and
kneaded by the kneading machine.
In said refractory materials, for instance, alumina,
æirconia, silica, metallic silicon powder, aluminum powder,
boron nitride, silicon nitride, magnesia, spinet, and other
refractory materials generally used for making ordinary
casting nozzles may be included.
A powdery phenol resin may be added as required besides
the liquid phenol resin. the addition of the latter contra-
bytes to increase the strength of casting nozzles and also to improve their thermal shock resistance and corrosion no-
distance.
Addition of less than 5 percent by weight of liquid
phenol resin cannot ensure sufficient wetting of the material
powder in the kneading, and the use of more -than 20 percent
may cause formation of lumps or clods of the material during
kneading and the acquisition of uniform mixture may become
difficult and cause lowering of the thermal shock resistance
and corrosion resistance.
The kneading machines suitable for thy purpose of this
invention are, for instance, of the stirring type which may
not break flaky particles of graphite. Breakage of the flaky
particles of graphite adversely affects the product quality,
and particularly raise the modulus of elasticity unfavorably.
The kneaded mixture is then dried by blowing hot air of
about 30-90C while loosening the mixture into particles.
Air-flow type drier or rotary drum may be used suitably for
such purpose. Air-flow type drier includes, for instance,
a box type vessel having small holes on the bottom thereof
and the hot air is blown in-to the vessel from said holes. The
kneaded mixture is fed by the feeder into the vessel from the
inlet port thereof, then the mixture is dried uniformly by
the hot air while the same is blown up and loosened into
particles.
After the required amount of remaining liquid is attained,
the mixture is taken out from the vessel through the outlet
port.
In the rotary drum method, the kneaded mixture is fed
into the drum, and the hot air of about 30~90C is blown into
the drum, while the same is rotated then -the liquid in the
mixture is uniformly removed, besides, the mixture is stirred
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by this rotation and made into uniform composition and
divided into minute particles, -thus -the occurrence of cracking
or lamination in -the nozzle body can be prevented at the sub-
sequent molding process and the nozzle body having uniform qua
lily and required density can be obtained by the molding process
and the products of uniform quality can be obtained by Sinatra
in said nozzle body.
As mentioned above, in the drying process according to
the present invention, the kneaded mixture is dried by blowing
hot air while the mixture is being forcedly loosened, so
that the distribution of the liquid in the mixture can be
made uniform, and the desired amount of remaining liquid in
the mixture can be attained within a short time.
Example
30 parts by weight of flake graphite, 50 parts by weight
of sistered alumina, 10 parts by weight of fused silica and
10 parts by weight of reinforcing material and anti-oxidant
such as fine powder of silicon carbide, alumina, silica and
alumino-silicate were kneaded with the addition of 10 parts
by weight of liquid phenol resin.
The kneaded material was divided into two parts, and
the one was treated by the methodofthe present invention and
the other one was treated by the conventional method.
PA) Method of the Present Invention
A lump of 300kg of the kneaded mixture was fed by a belt
feeder, into the vessel of an air-flow type drier in which a
hot air of about 60C being blown at a rate of 60m3/min. from
the openings of about l-3mm diameter provided on the bottom
of the vessel.
The mixture taken out of the drier was then put into a
rotary drum in which a hot elf of about 60C being blown at a
rate of 60m3/min. The drum was rotated at lOrpm. The total
treating time or the method was two hours.
(B) Conventional Method
The kneaded mixture was cured in a thermohygrostatic
vessel kept at 20-30C temperature and 40-70 percent humidity
for seven days.
Mixtures treated by both methods were Jo adjusted that
they would have about log of final volatile matter content -
as measured with an infrared-heated moisture meter - and the
rate of weight decrease at 180C in five minutes would reach
1.7 percent in the average. Mixtures were then formed by the
use of a rubber press machine according to the ordinary method,
and fired in a reducing atmosphere.
Physical and chemical test results of the products made
by the both methods are shown in Table 1.
In the Table, modulus of quasi-elasticity E' is defined
by the following equation,
(Pro - PLY
E' = ---- I--------- (1)
48(~60 I
where P60 and P30 are 60 percent and 30 percent load respective-
lye of maximum load value Ppm in the stress-s~rain curve obtained
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by a three-point precision bending strength test made on a
square pillar specimen having a rectangular section; and
~60 and ~30 are strain values at the load Pro and P30 respect-
lively, and I is the moment of inertia of area of the specimen,
and L is the distance between the supporting points.
The reason of the use of the modulus of quasi-elasticity
for the evaluation of material quality is that the fire brick
materials containing considerable amount of flake graphite
shows relatively large plastic deformation and that a large
error would appear in the measurement of elasticity within
a very narrow elastic range. Actually, it was seen that the
evaluation based on the modulus of quasi elasticity including
the range of plastic deformation, can explain the quality of the
material more really.
Table 1
. . .. _. . .. _ .
Conventional Product of this
product invention
_ Standard Standard
Average deviation Average deviation
___ .......... .. .____
20 Bending strength 65 8 70 5
. _ . . ____ _ ___ . .__ .___ __ _
Modules of quasi-
elasticity E' 280 80 270 50
(kg/mm2 )
. .... .. __ .__ ___
Thermal shock no- -6 -6
distance parameter 2,320 x 10 2,593 x 10
M/E' . _._ _ __ _ . .. __ _ ___ __ _ _ _
Thermal shock test
(Repetition of ha - Cracks sometimes No crack occurs
in at 1,400C and occur at 5 repute- at over 7 repute-
water cooling prove- lions lions
dunes)
. .. _.. _
Hot-metal resistance
test, speed of Eros 0.4 0.3
soon (mm/hr)
_ ............. I . .... _ _ .... _ . .. 1
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Table 1 shows that the physical properties of the
products according to the present invention are substantially
similar to those of the conventional products, but in the
fluctuation of quality, the products according to the present
invention showed smaller values than those of the conventional
products, and in the thermal shock test and corrosion resistance
test, it was found that the products according to the present
invention showed better results than the conventional products.
In the performance tests, the casting nozzles made in
accordance with the present invention showed no spelling
trouble, which have occurred sometimes in the conventional
nozzles due to the quick temperature rise of the nozzles at
the beginning of the continuous casting.
The products of this invention also showed good corrosion
no instance, because, the speed of erosion became nearly uniform
over the whole inner surface of the casting nozzles due to
uniform quality so that no abnormal local corrosion occurred,
and the service life was eventually stabilized.
As described above, the casting nozzles made in accord-
ante with the present invention have not only an elongated
service lifeboat also have a stable service performance, so
that they may contribute greatly to the stabilization of the
continuous casting. Besides, the method ox the present in-
mention has an advantage ox shortening the time of the drying
process in comparison with the conventional method as stated
above.
What is claimed is:
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