Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
- ~1651~
~THOD OF APPLYING TO THE INT~RIOR FACES OF A
MT~T~TTURGIC~T CONTAINER A PROTECTIVF~ COATING COMPRISING
AT LEAST TWO LAYERS
BACKGROUND OF THE INVENTION
Field of the invention
The present invention concerns a method of applying
to the interior faces of a metallurgical container for
transferring liquid metal a consumable protective coating
comprising at least two layers.
The invention also concerns the coating obtained by
this method as well as the composition of this coating.
Description of the prior art
French patents 2 646 367 and 2 657 549 describe
various methods for applying to the interior faces of a
metallurgical container such as a casting ladle a
protective coating comprising at least two layers.
French patent 87757 describes a method for applying
to the interior faces of a casting ladle a coating
comprising two layers, this method comprising the
following steps:
A. A core is placed inside the metallurgical
container to be protected to create a molding space
between the interior walls of said container and the
exterior walls of the core.
B. A material made of up of heat-resistant
inorganic particles is introduced into the molding space
thus created, said particles being precoated with a
hardenable binder and/or mixed with a binder, said
material being dry or virtually dry.
C. After hardening of said material on the
interior walls of the container, the core is extracted
from the container, leaving in place a first or exterior
protective layer.
D. A second or interior layer is sprayed onto the
first or exterior protective layer by wet spraying a
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material made up of inorganic particles able to withstand
the temperature of the liquid metal.
E. The interior walls of the metallurgical
container are heated until the protective coating thus
deposited is perfectly dry.
In this method, the first layer is formed in the
space between the mold and the interior wall of the
container, whereas the second layer is sprayed.
The drawback of a method of this kind is that the
second layer is sprayed in the form of an aqueous sludge.
This layer is therefore wet; it is therefore
necessary to dry it carefully before pouring the liquid
metal into the container, to avoid all risk of explosion
resulting from the formation of hydrogen due to
decomposition of the water by the high temperature.
Moreover, because the second layer is wet, it
cannot contain any substances that are sensitive to water
such as quick lime, which has the function of purifying
oxides contained in the liquid metal.
The aim of the present invention is to overcome
these drawbacks.
SUMMARY OF THE INVENTION
In accordance with the invention, the method of
applying to the interior faces of a metallurgical
container for transferring liquid metal a consumable
protective coating comprising at least two layers
includes the following steps:
a. a permanent coating of said container has
sprayed onto it a first protective layer by wet spraying
a material made up of inorganic particles resistant to
the temperature of said liquid metal and a heatsetting
binder,
b. the layer thus obtained is heated to harden it,
c. a preheated or heater mold is introduced into
the interior of said metallurgical container to create a
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molding space between exterior walls of said mold and the
exterior surface of said first layer,
d. a powder material is introduced into the mold
space thus created, made up of inorganic particles
resistant to the temperature at which the liquid metal is
transferred, said particles being precoated with a
hardenable powder binder and/or mixed with a hardenable
powder binder, said material being dry or virtually dry,
e. after hardening of said powder material on said
exterior surface of said first layer due to the heating
effect of said preheated or heater mold, said preheated
or heater mold is extracted from said container to leave
therein a second exterior protective layer.
Thus, in accordance with the invention, only the
first layer is wet, whereas the second layer that will
come into contact with the liquid metal is virtually dry,
so that it can contain substances sensitive to water and
having purifying properties, such as quick lime.
In an advantageous version of the method, before
the preheated or heater mold is placed in position said
powder material is applied to the hardened first layer in
a bottom area of the container to form a second or bottom
layer and the lateral parts of the second layer are
formed after introducing the preheated or heater mold
into the container.
In a preferred version of the method the second
layer is formed of quick lime, a heatsetting binder and
optionally a flux.
The quick lime can therefore exert its purifying
properties in relation to oxides contained in the liquid
metal.
The heatsetting binder contained in this layer
ensures cohesion of the layer after hardening due to the
effect of the heat exerted by the preheated or heater
mold.
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The presence of a flux facilitates the sintering of
this layer due to the effect of the heating exerted by
the liquid metal so that cohesion of the layer is
maintained while the liquid metal remains in the
container.
The first layer preferably contains magnesium oxide
as its main constituent.
The particle sizes and the composition of the
inorganic particles of the first layer are preferably
chosen so that said layer is not sintered or is only
slightly sintered at the temperature at which the liquid
metal is transferred into the container.
Because of this, at the end of casting, the coating
can be very easily detached from the wall of the
container, which considerably facilitates cleaning of the
latter.
In another preferred embodiment of the invention
the second layer is mixed with 5% to 60% by weight of
substances that can generate an exothermic reaction.
This exothermic reaction melts the quick lime and
burns the carbon contained in the second layer.
Other features and advantages of the invention
emerge from the following description given by way of
non-limiting example with reference to the appended
drawings.
BRIFF DFSCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic view in cross-section of
a metallurgical container and the mold used to implement
the method of the invention, showing the step of spraying
the first coating layer.
Figure 2 is a view analogous to figure 1 showing
the stage of forming the second layer after introduction
of the heater mold into the container.
Figure 3 is a view analogous to figure 2 showing a
different embodiment of the second layer.
2165143
Figure 4 is a view in cross-section of the
container complete with its two layers and a gas burner
adapted to start the exothermic reaction in the second
layer.
Figure 5 is a view analogous to figure 4 showing
the gas burner in its in-service position inside the
container.
DETAITl~n DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the embodiments shown in the appended figures 1
through 5 a continuous casting ladle 1 comprises a metal
exterior jacket 2 and an interior coating 3 of refractory
bricks or cement.
In the bottom of the container 1 is a casting
orifice with a casting nozzle 4.
The method for applying to the interior faces of
the casting ladle 1 a consumable protective coating
comprising two layers comprises the following steps:
a. a permanent coating 3 of the container 1 has
sprayed onto it a first protective layer 5 by wet
spraying a material made up of inorganic particles
resistant to the temperature of the liquid metal and a
heatsetting binder (see figure 1),
b. the layer 5 thus obtained is heated to harden
it,
c. a preheated or heater mold 7 is introduced into
the interior of the metallurgical container to create a
molding space 8 between exterior walls of the mold 7 and
the exterior surface of the first layer 5 (see figure 2),
d. a powder material 9 is introduced into the mold
space thus created, made up of inorganic particles
resistant to the temperature at which the liquid metal is
transferred, said particles being precoated with a
hardenable powder binder and/or mixed with a hardenable
powder binder, said material being dry or virtually dry,
e. after hardening of said powder material on the
S~16~1~3
exterior surface of said first layer 5 due to the heating
effect of the preheated or heater mold 7, the preheated
or heater mold is extracted from the container to leave
therein a second or exterior protective layer 6.
In the example shown in figures 1 and 2 the mold 7
is metal and is heated internally by means of gas
burners 10.
In the version shown in figure 3, before fitting
the preheated or heater mold 7, said powder material is
applied to the hardened first layer 5 in the bottom part
of the container to form a bottom or second layer 6a and
the lateral parts of the second layer 6 are formed after
introducing the pre-heated or heater mold 7 into the
casting ladle 1.
The second layer 6 is preferably formed from quick
lime, a heatsetting binder and a flux.
The quick lime has a purifying function in relation
to oxides in the liquid metal in the ladle 1.
The binder provides the initial cohesion of the
layer 6 after hardening, the flux facilitates sintering
due to the effect of heat and maintains the cohesion of
the layer 6 throughout the time that the liquid metal
remains inside the ladle 1.
The first layer 5 preferably includes magnesium
oxide as the major constituent. The proportion of the
magnesium oxide is 75% by weight, for example.
The particle sizes and the composition of the
inorganic particles of the first layer 5 are preferably
chosen so that this layer is not sintered or is only
slightly sintered at the temperature at which the liquid
metal is transferred into the ladle 1.
Thus the layer 5 in contact with the permanent
coating 2 does not adhere to the latter with the result
that, at the end of casting, the coating is easily
detachable from the wall of the ladle, which facilitates
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cleaning it.
Usually, the mold 7 is preheated or is a heater
type mold that can produce a temperature between 400C
and 800C.
This hardens the layer 6 that comes into contact
with the liquid metal.
The second layer 6 can be formed of quick lime
precoated with a binder and/or mixed with an organic
and/or inorganic binder.
When the mold 7 is introduced into the
metallurgical container, the position and/or the
dimensions of the mold in the container are adjusted to
vary the thickness of the second layer 6.
In one embodiment of the method of the invention
- 15 the layer 6 that comes into contact with the liquid metal
and which contains quick lime is mixed with between 5% by
weight and 6~ by weight of elements that can generate an
exothermic reaction. These elements can be magnesium
and/or calcium to which are added calcium nitrate and/or
barium nitrate and/or aluminum nitrate and, for example,
calcium fluoride and/or magnesium fluoride and/or barium
fluoride.
After the mold 7 is removed, the exothermic
reaction to melt the quick lime and to burn the carbon of
the organic binder contained in the second layer 6 is
instigated, for example using gas burners 10.
This variant of the method of the invention is
shown in figures 4 and 5.
To give a non-limiting example, the composition for
the coating coming into contact with the liquid metal to
protect the interior of a liquid metal transfer container
comprises the following substances in the proportions by
weight indicated below:
Mg and/or Ca and/or Al 0 - 60%
SiO2 0 - 3.5
21~a l 43
Al23 0 - 4%
Quick lime 0 - 95%
MgO and/or chrome-magnesite 0 - 50%
Fe23 0 - 5%
Na2O 0 - 2.5%
Melting loss at 1 000C 0 - 5%
P 0 - 7%
H 0 - 0.5%
B2O3 0 - 3%
K2O 0 - 4%
H2O 0 - 3%
Total C 0 - 6%
Na 0 - 2.5%
K 0 - 1.80%
H2O of crystallization 0 - 3%
Ca(NO3)2 0 - 10%
(No3)2Ba 0 - 10%
MgF2 0-- 8%
CaF2 0 - 8%
BaF2 0 - 8%
