JPH0825812B2 - Conductive amorphous refractory - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrically conductive amorphous refractory used in a portion of a DC electric furnace electrode, etc., which requires high temperature and electrical conductivity.

[0002]

2. Description of the Related Art In a DC electric furnace, a DC arc is generated between a bottom electrode installed on the bottom of a furnace and a movable electrode charged through a furnace lid, and the heat of the DC arc melts iron scrap to produce steel. Is a furnace for refining. The bottom electrode is exposed to particularly high temperatures during energization and contacts molten steel. Moreover, after the molten steel is discharged, a chemical reaction occurs by coming into contact with the slag component generated by refining. Therefore, the vicinity of the bottom electrode of the furnace is significantly damaged. When this damage progresses, not only the life of the electric furnace is shortened, but also it is difficult to regenerate the electrode due to the residual molten steel (hot heel) after tapping, which makes it impossible to energize for the next operation. The harmful effect such as disappearance occurs. As a technique for preventing this, for example, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent No. 31688, there has been proposed a method for repairing an amorphous refractory material using dolomite or the like by spraying.

[0003]

However, since such a conventional spray material has no electrical conductivity, the entire surface of the furnace bottom electrode cannot be repaired at once, and an area capable of conducting electricity is secured. However, there is the inconvenience of having to repair the tapped side and the slag side alternately. Moreover, since the repair work is performed using water for the spray repair, there is a problem that the magnesia carbon bricks forming the bottom electrode part of the furnace are accelerated by spalling damage by quenching or carbon oxidation due to high temperature steam. It was

On the other hand, the magnesia carbon brick used for the lining of the furnace is a molded body, and it is difficult to apply it to complicated construction sites, etc., and it cannot be used for hot repair. .

The present invention has been made to solve the above-mentioned problems, and the magnesia carbon which can repair the entire surface of the bottom electrode by a hot repair work and which constitutes the bottom electrode part. It is an object of the present invention to provide a conductive amorphous refractory which does not promote damage to bricks.

[0006]

The amorphous refractory material according to the present invention is characterized in that the construction body itself has sufficient electric conductivity. That is, the volume resistivity is 1.0 × 10 ^-2 Ω · c
It is an irregular refractory material having electrical conductivity, which is composed of 20 to 70 wt% of a conductive material of m or less, 80 to 30 wt% of a refractory material, and a binder that forms a carbon bond by heating.

[0007]

The amorphous refractory material of the present invention has a volume resistivity of 1.0.
Conductive material 20 × 70 wt% or less × 10 ⁻² Ω · cm
%, A refractory material of 80 to 30 wt%, and a binder that forms a carbon bond by heating, and is an irregular refractory material having electrical conductivity.

In the present invention, the volume resistivity was investigated first in order to judge the electrical conductivity of various materials. The volume resistivity ρ has a length L (cm) and a cross-sectional area A.
When the electric resistance of a uniform substance of (cm ² ) is R, it is given as a proportional constant of the equation represented by R = ρ (L / A) (Ω). The smaller the value of ρ is, the better the electrical conductivity is. For example, iron (F
In e), ρ = 9.8 × 10 ⁻⁶ Ω · cm, but the volume resistivity of oxides used for general refractories is Al ₂
O ₃ ρ = 1 × 10 ¹⁶ Ω · cm, SiO ₂ ρ = 1 × 1
The value is 0 ¹⁵ Ω · cm, and ρ = 2 × 10 ⁸ Ω · cm for MgO, which is a very large value, and ordinary refractories have almost no electrical conductivity.

For the amorphous refractory material of the present invention, a conductive material having a volume resistivity of 1.0 × 10 ⁻² Ω · cm or less is used.
It is necessary to use ˜70 wt%. That is, when a material having a volume resistivity of more than 1.0 × 10 ⁻² Ω · cm is used, the minimum required amount of the refractory material is the balance of 30 wt%.
Even with a mixed amount of wt%, it is difficult to make the electrical conductivity of the construction body a satisfactory value. Also, the volume resistivity is 1.0 ×
Even when using a conductive material of 10 ⁻² Ω · cm or less, unless the mixing amount is 20 wt% or more, it cannot exist continuously in the irregular shaped refractory, and becomes a dispersed state. It is difficult to obtain satisfactory electrical conductivity. More specifically, the volume resistivity is 1.0 × 10 ^-2 Ω
The conductive material having a size of cm or less is 5 wt% or more in an aggregate portion of about 1 to 4 mm, which constitutes an amorphous refractory, and
It is preferable that the fine particles of 1 mm or less and the fine powder portion contain 10 wt% or more. The electrical conductivity after forming the construction body is determined by how the respective conductive materials are continuous. When used only for the aggregate part, the contact area between the aggregates is not so large, and no matter how small the volume resistivity of the conductive material is used, the electrical conductivity of the material itself will be the same as that of the construction body. It may not be reflected. On the other hand, when used only for fine particles and fine powder parts, for example, when only 0.3 mm particles are mixed, at least 10 particles come into contact with each other in order for electricity to flow the same distance as 3 mm particles as an aggregate. Then, the contact resistance increases accordingly.

As the conductive material having a volume resistivity of 1.0 × 10 ^-2 Ω · cm or less, most of the metals correspond to this, but at least the fire resistance as a refractory, molten steel, corrosion resistance to slag, etc. Need to be satisfied. That is, crushed carbon for electrodes, artificial / natural graphite, carbonaceous materials such as carbon black for fine powder, intrusive carbides such as titanium carbide and tungsten carbide, and metals forming them can be used. Among them, the carbonaceous material has a slightly higher volume resistivity, but is most preferable in terms of stability at high temperature, corrosion resistance against molten steel and slag, and economical efficiency.

The refractory material used for the amorphous refractory of the present invention is various materials used for general refractories, for example,
Alumina-silica-based natural and synthetic refractory materials, magnesia,
Basic refractory materials such as calcia and dolomite, and synthetic refractory materials such as alumina-magnesia and chromium-magnesia can be used. However, when the amorphous refractory material of the present invention is a baking material for the purpose of hot repair, it is necessary to pay attention to fluidity during hot work. That is, the baking material has to flow while hot due to the weight of the material itself, so that a good flow can fill the damaged portion and a repair work body having a high filling degree can be obtained. However, when a carbonaceous material is mainly used as the conductive material, the specific gravity of the carbonaceous material is about 1.4 to 1.7, which is considerably lightweight, so that the flow due to its own weight is not sufficient and the filling The density also tends to decrease. Therefore, in order to secure the fluidity of the entire baking material, it is necessary to use a refractory material having a specific gravity of 3.0 or more, and a refractory material having a specific gravity of less than 3.0 such as chamotte is preferable. Absent.

When the amorphous refractory material of the present invention is applied to the bottom electrode portion of a DC electric furnace, a basic material such as magnesia, calcia, dolomite, etc. is used in consideration of the corrosion resistance to the steelmaking furnace slag. preferable.

The amount of the refractory material used in the amorphous refractory material of the present invention must be in the range of 30 to 80 wt%. When considering only the electrical conductivity, it is better to use only the conductive material, but the corrosion resistance to molten steel or slag is poor, or wear damage due to insufficient strength occurs. Therefore, in order to obtain the effect as a refractory material, it is necessary to use at least 30 wt% of refractory material.
Furthermore, the refractory material has a length of 1 m for strengthening connective tissue.
It is preferable to use at least 10 wt% or more in the fine particles and fine powder portions of m or less. Further, when used as a baking material, it is necessary to use a refractory material having a specific gravity of 3.0 or more and 30 wt% or more from the viewpoint of hot fluidity.

On the other hand, in the amorphous refractory material of the present invention, in order to secure electric conductivity, as described above, at least 2
It is necessary to use 0 wt% of the conductive material, and the maximum mixing amount of the refractory material is 80 wt% which is the rest.

The amorphous refractory material of the present invention must use a binder that forms a carbon bond upon heating.
In order for the irregular-shaped refractory construction body to have good electric conductivity, it is of course necessary to use a conductive material as described above, but these conductive materials and refractory materials are combined. The binding system that does this is important. For example, in conventional spraying materials, etc., alumina cement, silicates, phosphates, etc. are used as binders, but these are all inorganic binders, have no electrical conductivity, and are in an amorphous refractory material. Even if a large amount of good conductive material is used, each particle will be bonded with an insulating binder, and the electrical conductivity as a construction object depends only on the direct contact of each particle. Therefore, in practice, it becomes a construction body that exhibits almost no electrical conductivity.

In the amorphous refractory material of the present invention, a binder which forms a carbon bond by heating is used on the assumption that it is used at high temperature. If it is a carbon bond,
It becomes possible to connect particles of all conductive materials through carbon having electric conductivity as a medium.

As the binder forming the carbon bond, coal-based or petroleum-based tar / pitch and various resins can be used. Of these, coal tar pitch and phenol resin are preferable because they have a large amount of residual carbon after heating and form a good carbon bond structure. However, in the case of coal tar pitch, the smoke generated during heating is remarkable, so it can be said that the phenol resin is the best in consideration of the environment.

The addition amount of the binder in the amorphous refractory is
It may not be the same depending on the method of construction of the irregular shaped material. For example, when importance is placed on the fluidity of a material such as a casting material or a baking material, the total amount of the conductive material and the refractory material should be 10
0, it is necessary to add 10 wt% or more, while
The material for stamping may be 3 to 8 wt%. The upper limit of the addition amount is also influenced by the specific gravities of the conductive material and the refractory material used. That is, when a conductive material such as a carbonaceous material having a low specific gravity is used, a relatively large amount of the binder is required in the weight ratio, but if it is added in excess of 50 wt%, the structure of the construction body is deteriorated. It is not preferable because it occurs 5
It should be kept at 0 wt% or less.

Further, preferably, the amount of the binder added should be set so that the amount of residual carbon after the binder is heated is at least 2 wt% or more. As described above, in order to connect the particles of the conductive material with carbon having electrical conductivity, it is preferable to adjust the residual carbon content of the binder in the connective tissue to be 2 wt% or more.

A small amount of metallic silicon or aluminum may be added to the electrically conductive amorphous refractory material of the present invention in order to prevent oxidation of carbon and improve hot strength.

The value of electric conductivity required for the amorphous refractory cannot be specified because it varies depending on the conditions under which the refractory is used. That is, even when applied to the bottom electrode of a DC electric furnace, the required electrical conductivity differs depending on the surface area of the bottom electrode, the distance from the movable electrode, the state of the iron scrap to be melted, and the like. But,
If the volume resistivity of the amorphous refractory is larger than 1.0 × 10 ³ Ω · cm, it is often impossible to conduct good current when used on the surface of the bottom electrode of a DC electric furnace. 1
The volume resistivity is preferably 0 ³ Ω · cm or less.
In the case of the amorphous refractory material having electrical conductivity of the present invention, 100
The volume resistivity of the construction body after reduction firing at 0 ° C. is 1.0
× 10 ³ Ω · cm or less. The volume resistivity of a conventional refractory material composed only of oxide-based refractory materials is 1 × 10 ¹⁵ to
The value is 1 × 10 ¹⁶ Ω · cm or more. By comparing these values, it is found that the amorphous refractory material of the present invention has a significantly reduced volume resistivity and that it has electrical conductivity. Recognize.

[0022]

EXAMPLES FIG. 1 shows examples of the present invention, conventional examples and comparative examples.

As the refractory material, the specific gravity of the grains is about 3.3.
Magnesia 5-1m using the magnesia clinker
m and magnesia 1 mm or less as shown in the figure, and as the total amount of refractory material, in Examples 1 to 6 of the present invention, 79.5 wt%, 74.5 wt% and 74.
5 wt%, 67 wt%, 60 wt%, 40 wt%, 100 wt% in the conventional example, and Comparative Examples 1 and 2
It was set to 84.5 wt% and 15 wt%, respectively.

As the conductive material, a carbonaceous material having a volume resistivity of less than 1.0 × 10 ⁻² Ω · cm is used, and the crushed carbon electrode product is 4 to 1 mm and the crushed carbon electrode product is 1 mm or less.
The proportions of natural scaly graphite 1 mm or less and carbon black 50 μm or less are shown in the figure, and the total amount of the conductive material is 20.5 wt.
%, 25.5 wt%, 25.3 wt%, 33 wt%, 4
0 wt% and 60 wt%, 0 wt% in the conventional example, and 15.5 wt% and 85 in Comparative Examples 1 and 2, respectively.
It was set to wt%.

Further, as the kind of the binder, the invention example 1 is used.
In 3 and 4 and 5, the addition amount of coal pitch and phenol resin was 5 wt% (remaining carbon amount 2.3 wt%) and 22 wt, respectively.
% (Residual carbon amount 4.6 wt%), 15 wt% (residual carbon amount 5.8 wt%), 24 wt% (residual carbon amount 5.6 wt%)
%), In the present invention example 2, the amount of coal pitch added is 8 wt% (residual carbon amount 4.6 wt%), in the present invention example 6, the amount of phenol resin is added 40 wt% (residual carbon amount 8 wt%), and magnesium sulfate in the conventional example Was added in an amount of 40 wt% (residual carbon amount of 0 wt%), and in Comparative Examples 1 and 2, the phenol resin was added in an amount of 12 wt% (residual carbon amount of 4 wt%) and 9 wt% (residual carbon amount of 3 wt%).

Next, a method of applying each material shown in the drawings (invention example 1: vibration molding material, invention example 2: stamp material, invention examples 3, 5 and 6: seizure material, invention example 4: pouring) Material, conventional example: stamp material, comparative example 1: cast material, comparative example 2: stamp material), a construction body was prepared and cut out to obtain a sample. The erosion test was carried out by using the rotating drum method by arc heating in a dry state of these samples.
An electric furnace slag was used as the erosion agent at this time. Further, the cut-out samples were heated at 1000 ° C. for 3 hours in a reducing atmosphere, and then the porosity and volume resistivity were measured.

In each of the examples of the present invention, the reducing atmosphere 10 is used.
The volume resistivity of the construction body after heating at 00 ° C. for 3 hours is 1.0 × 10 ³ Ω · cm or less as shown in the figure, which shows good electrical conductivity. Further, the amount of erosion loss after the erosion test is almost the same as that of the conventional magnesia stamp material, and the good corrosion resistance is maintained.

On the other hand, the conventional example does not contain a carbonaceous material as a conductive material at all, and therefore has a very large volume resistivity and no practical electrical conductivity.

Comparative Example 1 is a composition containing 15.5% of carbonaceous material, but its volume resistivity is considerably large, and it is difficult to put it into practical use as an electrically conductive refractory material. Comparative Example 2 contains 85% carbonaceous material and 15% refractory material.
Although it is a composition containing, although the volume resistivity is sufficiently low and good, it is inferior in erosion resistance to slag, and shows about 3 times the erosion amount of the conventional magnesia stamp material,
It is difficult to use as a refractory material.

Inventive Example 3 was used for hot repair of the bottom anode part of a DC electric furnace having a capacity of 60 ton, and was excellent in both electrical conductivity and corrosion resistance as a repair material. In addition, the present invention example 1 is a DC electric furnace having a capacity of 130 tons,
It was successfully used as a stamp material for the lining of the furnace bottom electrode without any problems.

[0031]

INDUSTRIAL APPLICABILITY As described above, the refractory material of the present invention has excellent electrical conductivity, good erosion resistance to slag, and excellent corrosion resistance as a repair material. It is also possible to repair the entire surface of the bottom electrode by the repair work.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an example of the present invention, a conventional example, and a comparative example.

Claims (4)

[Claims] 1. A conductive material having a volume resistivity of 1.0 × 10 ⁻² Ω · cm or less, 20 to 70 wt%, and a refractory material 8.
An electrically conductive amorphous refractory material comprising 0 to 30 wt% and a binder that forms a carbon bond by heating. 2. The refractory material according to claim 1, wherein the conductive material is 5 wt% or more in the aggregate portion and 10 wt% in the fine particle / powder portion.
Conductive amorphous refractory, which is characterized by containing at least 100%. 3. The refractory material according to claim 1, wherein the refractory material is contained in the fine particles / fine powder portion in an amount of 10 wt% or more. 4. The refractory material according to claim 1, wherein when the total amount of the conductive material and the refractory material is 100, the residual carbon content of the binder after heating is 2 wt% or more. Conductive amorphous refractory.