JPH07268250A - Conductive antioxidant material - Google Patents

Abstract

PURPOSE:To enable the application of a conductive antioxidant material to an electrode chuck and improve the antioxidant effects of the material at high temps. by compounding a fire-resistant aggregate, a binder, a carbon black, and a polymer emulsion. CONSTITUTION:This material is obtd. by mixing 20-90wt.% fire-resistant aggregate, 2-30wt.% binder, 2-30wt.% carbon black, 0.05-10wt.% (solid) polymer emulsion, a graphite powder in an amt. of 20-70wt.% of the aggregate if necessary, and a water-sol. polymer in an amt. of 0.01-3wt.% of the sum of all the foregoing ingredients, adding 15-150wt.% water to the resulting mixture by pouring water from the outside, and subjecting the mixture to a homogenizing treatment. The material is applied to the side of an electrode for an arc furnace to form a dry coating film with a thickness of 100-200mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive antioxidant, and more particularly to a conductive antioxidant that can be suitably used as a antioxidant for graphite electrodes used in arc furnaces such as electric steelmaking furnaces. .

[0002]

2. Description of the Related Art Artificial graphite electrodes have been used in arc furnaces such as electric steelmaking furnaces. This graphite electrode is used under extremely harsh conditions that are affected by large current, high temperature, and splash of melt. In particular, a super-high temperature arc is generated at the tip of the electrode, and the temperature of the electrode is 400 ° C-
Since it is exposed to a high temperature of about 3,000 ° C., it is easily consumed by oxidation due to the oxidizing gas that has entered through the opening or the like in the furnace. Since the cost of this electrode in the steelmaking furnace is high, the consumption of this electrode causes a large economical loss. 50 to 70% by weight of this electrode is consumed by oxidation, and the consumption of the arc itself is small. further,
Since the tip of the electrode is tapered toward the tip due to oxidative consumption, oxidative consumption in the longitudinal direction is accelerated. Therefore, if the oxidation prevention from the side surface of the electrode is sufficient, the consumption of the electrode is reduced and the economic merit is large.

Therefore, various proposals have been made to prevent the oxidation of the electrodes. For example, there is a method of maintaining the electrode at an oxidation temperature or lower by cooling the electrode by jetting water. However, in this method, when a large amount of water enters the furnace, there is a risk of steam explosion and the cooling effect of the entire electrode is small, so a sufficient antioxidant effect cannot be expected. In addition, there is a method of forming a protective coating on the electrode to protect the electrode surface. For example, a method of forming a non-conductive antioxidant layer on the surface of a graphite electrode (Japanese Patent Laid-Open No. Sho 5 (1999) -58138).
9-51499), and further, a method of using a coating material in which alumina, silica fine particles and the like are dispersed in a colloidal solution of ultrafine silica particles (JP-A-3-45583). However, since all of these conventional coating materials are non-conductive, it is necessary to apply the coating while avoiding the chucked portion of the electrode in order to ensure the electric conduction to the electrode. Therefore, there are problems such as construction problems and insufficient prevention of oxidation in untreated portions.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent oxidative wear of graphite electrodes used in arc furnaces. A more specific object of the present invention is to solve the problems in conventional antioxidants for graphite electrodes,
In particular, it is an object of the present invention to provide a conductive antioxidizing material which can be applied to the electrode chuck portion during coating and which has an excellent antioxidizing effect at high temperatures.

[0005]

The conductive antioxidant of the present invention is characterized by containing a refractory aggregate, a binder, carbon black and a polymer emulsion. Hereinafter, the present invention will be described in detail. First, as the refractory aggregate in the present invention, oxides of silica, alumina, titania, zirconia, etc., SiC, B ₄ C, CrC, WC, T
iC, VC, ZrC, NbC carbide, TiN, VN,
NbN, Nitride such as ZrN, CrSi ₂ , TiSi ₂ , Z
One or more of silicides such as rSi ₂ or powders such as silicon are used. Further, boride powders such as ZrB ₂ , TiB ₂ and CrB, and metal powders such as Fe, Co, Ni, Cr and V can also be preferably used in combination with the above refractory powder. In particular, ZrB ₂ , B ₄ C, TiC, SiC and Si are suitable in terms of preventing oxidation of carbon and stability of the coating film against heat, and are preferably used.

[0006] The binder is not particularly limited as long as it can obtain an appropriate coating strength after drying, but is preferably an inorganic binder such as various silicates, phosphates and colloidal binders. Can be used. For example, as colloidal binder, colloidal silica or colloidal alumina,
Colloidal zirconia and the like can be preferably used. In particular, colloidal silica is most preferable in terms of water resistance after drying, adhesiveness, stability and price. Further, as the carbon black, one obtained by any manufacturing method such as a furnace method, an acetylene method, a thermal method or a contact method can be used. For example, these carbon blacks are preferably treated at a temperature of 2000 ° C. or higher, preferably 2500 to 3000 ° C., in an atmosphere substantially free of oxygen (for example, in N ₂ stream, in vacuum or in carbon powder). Graphitized carbon black is used. These graphitized carbon blacks preferably have a crystallite thickness Lc (Å) of the particle diameter (n
The value obtained by dividing by m) is in the range of 1.0 to 3.0.

The fourth component of the present invention is a polymer emulsion. Examples of the polymer emulsion include rubber latex and resin emulsion, and include a polymer emulsion obtained by an emulsion polymerization method or an emulsion obtained by re-emulsification of the polymer. Examples of the rubber latex include natural rubber latex and synthetic rubber latex. Examples of the synthetic rubber latex include butadiene polymer, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer,
Examples thereof include methyl methacrylate-butadiene copolymer and acrylate latex. Examples of resin emulsions include emulsions of polystyrene, styrene-acrylonitrile copolymer, polyvinyl chloride, ethylene-vinyl acetate copolymer, polymethylmethacrylate, polyethylene and the like. Of course, two or more of these may be used in combination. Of these polymer emulsions, styrene-butadiene copolymer latex,
Particularly, a carboxyl group-containing styrene-butadiene copolymer latex is preferably used.

The blending amounts of the above four essential components vary depending on the purpose, the kind of raw materials, etc., but in general, the refractory aggregate has a solid content of 20 to 90 wt% in the total amount of the four components.
%, Preferably 40-70 wt%, binder (solid content) 2-30 wt%, preferably 5-15 wt%, carbon black 2-30 wt%, preferably 10-20 wt%.
%, Polymer emulsion (solid content) is 0.05 to 10 w
t%, preferably about 0.05 to 3 wt%. When the solid content of the refractory aggregate is less than 20 wt%, the stability of the coating film is deteriorated by heat, cratering occurs, and the base material is easily oxidized. Further, when the solid content of the refractory aggregate exceeds 90 wt%, the fire resistance of the coating film becomes too high to oxidize the base material in a low temperature range of about 500 to 800 ° C. and it will not function as a coating film in the subsequent temperature range. . Further, the smaller the solid content of the binder is, the more preferable it is in terms of conductivity. If the solid content of the binder exceeds 30 wt%, the adhesive strength will be excellent, but a problem will occur in terms of conductivity, causing sparks. Further, the higher the content of carbon black, the more preferable it is in terms of electroconductivity.
When it exceeds wt%, the anti-oxidation slip is thickened, and the carbon black in the coating film burns hot to deteriorate the oxidation resistance performance. Carbon black content is 2wt
If it is less than%, the oxidation resistance is excellent, but desired conductivity cannot be obtained. Further, if the amount of the polymer emulsion (solid content) is less than 0.05 wt%, the sliding resistance is lowered, and if it exceeds 10%, the stability with time becomes insufficient.

Further, in the present invention, if necessary, components other than the above may be blended. For example, graphite powder can be blended as an antioxidant component. When the electrode wears out due to the operation of the arc furnace, a new electrode is connected to the upper part, and the electrode holder (grasping machine) is moved in the longitudinal direction of the electrode to re-grip, but at this time, the coating film and the electrode holder part come into contact and the coating film May be damaged. In such a case, by adding graphite powder to the coating film in order to prevent damage (peeling) of the coating film at the time of contact, sliding resistance can be improved and damage to the coating film can be reduced. Graphite powder is 2 for refractory aggregate
About 0 to 70 wt% (preferably 40 to 60 wt%) is added. Further, a water-soluble polymer such as an acrylic resin may be blended in an amount of about 0.01 to 3 wt% with respect to the total amount of the three components in order to improve stability over time, adhesiveness, and conductivity.

The respective components are usually compounded as follows. The conductive antioxidant of the present invention is prepared by adding water to a powder obtained by mixing the above components in the above specific weight ratio, and performing mixing and homogenization treatment. The amount of water added is
Although it varies depending on the coating operation mode, it is preferably 15 to 150 wt%, and most preferably 25 to 100 wt% in terms of the solid content of the conductive antioxidant composition component. The mixing and homogenizing treatment of the above composition components is carried out, for example, by adding a predetermined amount of the above mixed powder and water to an attritor device containing an alumina ball having the same volume as the mixed powder volume, and mixing for a predetermined time to perform the homogenizing treatment. To prepare a conductive antioxidant.
Here, there is no particular limitation on the mixing and homogenizing treatment device and method, and the mixture treatment may be carried out by an ordinary desk mixer, ball mill, roll mill or the like. The purpose of the mixing and homogenizing treatment is to make the composition distribution uniform, without making the composition in the applied coating film dependent on the coating film location. The conductive antioxidant thus obtained can be applied to the side surface of the arc furnace electrode, usually including the chuck portion in a thickness of about 100 to 200 μm (after drying). At the time of coating, the most suitable method can be selected from general coating film forming methods such as dipping, brush coating, spraying (spraying), and electrostatic coating. At this time, it is necessary to adjust the conductive antioxidant to a work viscosity suitable for each construction method.

[0011]

The present invention will be described in more detail with reference to the following examples. Examples 1 and 2 Two kinds of conductive antioxidants were obtained according to the following composition (solid content). (Formulation I) (Formulation II) Titanium carbide powder 35 wt% 35 wt% Graphite fine powder 25 〃 25 〃 Boron carbide powder 10 〃 10 〃 Carbon black 15 〃 15 〃 Inorganic binder (colloidal silica) (solid content) 15 〃 15 〃 Dispersant (acrylic resin + surfactant) +0.5 〃 +0.5 〃 SBR latex +0.5 〃 +3 〃 where the carbon black is a trade name: Mitsubishi Carbon Black CF-9 (manufactured by Mitsubishi Kasei Co., Ltd.) ) Was used as a dispersant and a mixture of an acrylic resin and a surfactant was used, and the addition amount of the component is the addition amount with respect to the total amount of the components. That is, 80 parts by weight of water was added to 100 parts by weight of the solid content of the compound I (Example 1) or the compound II (Example 2), and the mixture was mixed for about 24 hours by a wet pulverizer "Attritor" to obtain a uniform mixture. Conversion process,
Two types of conductive antioxidants were obtained.

<Volume Specific Resistance> Table 1 shows the results of measuring the volume specific resistance value (Ω · cm) by the following method.
The measurement results of the commercially available antioxidant A are also shown (Comparative Example 1). The volume resistivity measurement method is as follows. Carbon plate with known resistance (50 × 130
After coating a conductive antioxidant material with a predetermined thickness on the upper and lower surfaces of × 20 mmt (t: thickness), the coating is heated at a heating rate of 400 ° C./H and heated at a predetermined temperature (in the atmosphere) for 1 hour.
After holding for a period of time, a sample for resistance measurement was obtained. This sample was sandwiched between steel electrodes of a resistance measuring device and pressed at a total pressure of 1 t using an Amsler pressurizing device, and the volume resistivity of the coating film was calculated from the read resistance value by the following formula. ρ = S / H × (R−R ₀ ) ρ: Volume resistivity of coating film (Ω · cm) S: Current passing cross-sectional area of sample (cm ² ) H: Total thickness of coating layer (cm) R: Total resistance after treatment (Ω) R ₀ : Total resistance before treatment (Ω)

[0013]

[Table 1]

<Sliding resistance test> Further, the results of comparing the sliding resistance of the antioxidants shown in Formulations I (Example 1) and II (Example 2) are shown below. For comparison, a commercially available antioxidant A (Comparative Example 1) was similarly treated on a carbon plate.
As the sliding resistance test device, a wear test device manufactured by Shinko Seiki Co., Ltd. was used. Approximately 2 after drying the conductive antioxidant on the upper surface of the carbon base material (φ50 × 8 mmt) by a spray method.
After coating to obtain a film thickness of 00 μm,
It was naturally dried and used as a test piece for evaluation. This is set on a test stand with a motor and rotated at 50 rpm, and the coating surface is pressed against a steel ring (outer diameter / inner diameter = φ43 / φ33 mm) with a groove of 8 places at a load of 2000 kg and rotated 2000 times. The subsequent weight difference was measured and evaluated as the sliding resistance property. The results are shown in Table 2.

[0015]

[Table 2] By thus containing the latex in the coating layer, the sliding resistance can be remarkably improved, and the coating layer can be protected from rubbing that occurs when the electrode holder moves.

<Melting Experiment by Raw Material Melting Furnace> These antioxidants were applied to the surface of the graphite electrode rod (φ155 × 3750 mm) used in the raw material melting furnace (4 t) by a brush coating method to a thickness of about 200 to 300 μm (drying). It was applied to the latter) and a raw material melting experiment was conducted in an actual furnace. The raw material used for melting was magnesium oxide, and the time required for melting was about 3
It was 30 minutes. The results of the melting experiment are shown in Table 3. For comparison, a commercial antioxidant A (Comparative Example 1) is also shown. In each of Example 1 and Comparative Example 1, problems such as sparks did not occur, and there was no problem in operation. Regarding the anti-oxidation result, in Comparative Example 1 in which a commercial product was applied, 8.6% was consumed from the tip of the electrode and 10.6% was consumed from the side surface, for a total of 1
While the weight loss was 9.2%, in Examples 1 and 2, the oxidative consumption from the side was drastically reduced, and at the same time, the oxidative consumption from the tip was also reduced, and the weight loss rate was less than half that of the comparative example. And showed a good antioxidant effect.

[0017]

[Table 3]

[0018]

According to the present invention, it is possible to obtain a conductive antioxidant which can be applied to the electrode chuck portion and has excellent sliding resistance and antioxidant effect at high temperatures.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C09D 1/00 PCK PCN 1/04 PCM 5/02 PPT C09K 15/02 // C04B 111: 94

Claims (2)

[Claims] 1. A conductive antioxidant comprising a refractory aggregate, a binder, carbon black and a polymer emulsion. 2. The conductive antioxidant according to claim 1, which contains graphite powder.