Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
1998-12-22
2001-09-11
Sample, David R. (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S089000, C501S090000, C501S101000, C501S119000, C501S120000, C501S121000, C501S127000, C266S165000, C266S280000, C266S284000
Reexamination Certificate
active
06288001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monolithic refractory material, and particularly to a monolithic refractory material having a low moisture content, excellent casting workability, and both corrosion resistance and spalling resistance. Particularly, this material is suitable as a casting monolithic refractory material for lining a torpedo ladle car.
2. Description of the Related Art
In a steel making process, a torpedo ladle car is used as a transport container for transporting a hot metal from the blast furnace to the converter, and a pre-processing bath for removing impurities such as silicon, sulfur, phosphorus, and the like, from the hot metal.
Although lining of the torpedo ladle car is generally carried out by brick laying, casting of a monolithic refractory as a lining has recently been investigated.
A material for lining the torpedo ladle car is required to have corrosion resistance which allows the material to resist the severely corrosive slag by-produced from the flux used in the above-described pre-processing of a hot metal, and resistance to spalling (referred to as “spalling resistance” hereinafter) in a working environment in which the outer periphery is confined by a shell.
From this viewpoint, an alumina-SiC-graphite brick provides excellent corrosion resistance due to the prevention of wetting with a slag, which is caused by the effect of the SiC and graphite contained therein, and maintains the high spalling resistance due to low thermal expansion, low elastic modulus, and high heat conductivity, thereby exhibiting excellent practicability.
However, in an attempt to produce a casting material by adding equal amounts of SiC and graphite of the same type as brick, a large amount of water is required for ensuring casting workability because of the low water wettability of graphite, and thus the final resultant product has an extremely high porosity, and very low practicability.
Namely, for a monolithic refractory material, it is necessary to ensure sufficient workability by adding a small amount of water, and to ensure durability close to the durability of brick. It is difficult to satisfy both of these requirements.
In order to solve the above problem, a method (refer to Japanese Unexamined Patent Publication No. 6-166574) has been previously proposed, in which an oxide such as alumina or the like, which has excellent water wettability, is ground and adhered to graphite. However, the raw material cost of the monolithic refractory is increased due to the processing cost, thereby limiting practical use of this method.
Another known method comprises applying a mechanical impact to artificial graphite or crystalline graphite (refer to Japanese Unexamined Patent Publication Nos. 8-183666 and 301667). This method also has the same economic problem as the above-described conventional technique.
Other methods are also known, in which anthracite (refer to Japanese Unexamined Patent Publication No. 8-83667) or amorphous graphite is used. It is difficult, however, to obtain an effect on the corrosion resistance and the spalling resistance by adding such materials to brick in the same manner as crystalline graphite.
As described above, at present, there is no economical casting refractory material for lining torpedo ladle cars having a low moisture content and excellent casting workability, and both corrosion resistance and spalling resistance.
SUMMARY OF THE INVENTION
In consideration of the above-described disadvantages of known materials, an object of the present invention is to provide a monolithic refractory material having a low moisture content and excellent casting workability, and both corrosion resistance and spalling resistance, without using an expensive special carbon material.
Another object of the present invention is to provide a casting monolithic refractory material suitable for lining a high-temperature vessel such as a torpedo ladle car.
In order to achieve these and other objects, the present invention provides a graphite-containing monolithic refractory material comprising (i) at least one component selected from the group consisting of alumina and alumina-magnesia spinel, (ii) artificial graphite and (iii) pitch powder, and wherein the following conditions are satisfied:
(a) the amount of the artificial graphite that has an average particle size of not less than about 100 &mgr;m to not more than about 1 mm is from about 5 to about 15 wt %;
(b) the amount of the pitch powder is from about 0.5 to about 6 wt %;
(c) the total amount of the at least one component selected from the group consisting of alumina and alumina-magnesia spinel having a particle size of more than about 1 mm to not more than about 10 mm is from about 35 to about 50 wt %;
(d) the total amount of the at least one component selected from the group consisting of alumina and alumina-magnesia spinel having a particle size of more than about 100 &mgr;m to not more than about 1 mm is X (wt %) [wherein X is a value satisfying the following equations (1) and (2)]:
15−1.5
Y≦X≦
30−1.5
Y
(1)
x>
0 (2)
(where in the equation (1), Y represents the amount (wt %) of artificial graphite having an average particle size of not less than about 100 &mgr;m to not more than about 1 mm); and
(e) the total amount of the at least one component selected from the group consisting of alumina and alumina-magnesia spinel having a particle size of not more than about 100 &mgr;m is from about 15 to about 35 wt %.
In embodiments of the graphite-containing monolithic refractory material of the present invention, (e) the amount of the at least one component selected from the group consisting of alumina and alumina-magnesia spinel having a particle size of not more than about 100 &mgr;m is preferably from about 17 to about 35 wt %.
In embodiments of the graphite-containing monolithic refractory material, (e) the amount of the at least one component selected from the group consisting of alumina and alumina-magnesia spinel having a particle size of not more than about 100 &mgr;m is preferably from about 15 to about 30 wt %, and (f) the refractory material comprises an amount of silicon carbide having an average particle size of not more than about 100 &mgr;m is preferably from about 4 to about 15 wt %.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described in further detail below.
The inventors carried out various experiments for finding a carbon raw material that does not need a large amount of water and that has the ability to improve both the corrosion resistance and spalling resistance, and for optimizing the whole particle size configuration to decrease the necessary amount of water added, leading to achievement of the present invention.
The additives that can be used in the present invention, including pitch powder, artificial graphite, and silicon carbide (SiC), other additives, and the main components of the present invention including alumina and alumina-magnesia spinel, are described herein with respect to the actions, effects, desirable particle size ranges, and desirable amounts of the additives and main components.
Additives
Pitch Powder
The graphite-containing monolithic refractory material (also represented by the “monolithic refractory material” hereinafter) typically contains from about 0.5 to about 6 wt % of pitch powder.
As a result of a corrosion test using pig iron and hot metal pre-processing slag, slag penetration was suppressed by adding a smaller amount of pitch powder as compared to the amount of other carbon-containing materials, and a large effect of improving the corrosion resistance was obtained. In a table test, the use of an alumina-pitch material produced evaluation results equivalent to an alumina-SiC-graphite brick in use.
As a result of evaluation in an actual furnace, it was found that at least sufficient corrosion resistance can be obtained by adding a small amount of pitch.
However, with the addition of an amount of less than about 0.5 wt %
Iida Masakazu
Kiyota Yoshisato
Komatsubara Noboru
Kumagai Masato
Nanbu Masao
Kawasaki Steel Corporation
Oliff & Berridg,e PLC
Sample David R.
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