JP3390773B2 - Conductive antioxidant for graphite electrodes - Google Patents

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, an extremely 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 penetrated through the openings in the furnace. For example, in a steelmaking furnace, the cost of the electrodes accounts for a large proportion, and the consumption of the electrodes 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. Furthermore, since the electrode is tapered toward the tip end 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 antioxidant material for a graphite electrode , which is capable of coating the electrode chuck portion at the time of coating and has an excellent antioxidant effect at high temperature.

[0005]

The conductive antioxidant for a graphite electrode of the present invention is characterized by containing a refractory aggregate, a binder and graphitized carbon black. Hereinafter, the present invention will be described in detail. First, as the refractory aggregate in the present invention, oxides such as silica, alumina, titania, zirconia, SiC, B ₄ C, CrC, WC, TiC,
Carbides such as VC, ZrC, NbC, TiN, VN, Nb
N, ZrN, etc. nitrides, CrSi ₂ , TiSi ₂ , ZrS
One or more of silicides such as i 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 are also preferably used in combination with the above refractory powders.
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 graphitized carbon black used in the present invention, carbon black obtained by a furnace method, an acetylene method, a thermal method, a contact method, or the like is used in an atmosphere in which oxygen is substantially absent (for example, in a N ₂ stream, 2000 ° C or higher, preferably 2500 to 3000 ° C in vacuum or in carbon powder)
The thing processed at the temperature of. That is, the graphitized carbon black preferably has a crystallite thickness Lc (Å)
The value obtained by dividing by the particle diameter (nm) is in the range of 1.0 to 3.0.

The blending amounts of the above-mentioned three essential components vary depending on the purpose, the kind of raw material, etc., but in general, the refractory aggregate has a solid content of 20 to 90 wt% in the total amount of these three components.
%, Preferably 40-70 wt%, binder (solid content) 2-30 wt%, preferably 5-15 wt%, graphitized carbon black 2-30 wt%, preferably 10-2.
It is used by blending so as to be about 0 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 and the base material is oxidized in a low temperature range of about 500 to 800 ° C and functions as a coating film in the higher temperature range thereafter. Will not do. Further, the smaller the solid content of the binder is, the more preferable it is in terms of conductivity. Further, when the content of the solid content of the binder exceeds 30 wt%, the adhesive force is excellent, but there is a problem in terms of conductivity, which causes sparks. Further, the higher the content of graphitized carbon black is, the more preferable it is in terms of conductivity.
If it exceeds 0 wt%, the antioxidant slip may be thickened,
The graphitized carbon black in the coating film burns hot, which may reduce the oxidation resistance. When the content of the graphitized carbon black is less than 2 wt%, the oxidation resistance performance is excellent but the desired conductivity cannot be obtained.

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 of the electrode comes into contact with the electrode holder and The membrane may be damaged. In such a case, by incorporating graphite powder into the coating film 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 in the following manner. 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 mixing and homogenizing the mixture. The amount of water added varies depending on the coating work mode, but is preferably 15 to 150 wt%, and most preferably 25 to 100 wt%, as applied to 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 of the applied coating film uniform regardless of the location of the coating film. 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 application, dipping method, brush application, spray (spray)
The most suitable method can be selected from general coating film forming methods such as a coating method and an electrostatic coating method. At this time, it is necessary to prepare the conductive antioxidant to a work viscosity suitable for each construction method.

[0010]

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) Titanium nitride powder 65 wt% Zirconium boride powder 5 wt% Graphitized carbon black 15 wt% (trade name: Mitsubishi carbon black # 4000B, manufactured by Mitsubishi Kasei Co.) Inorganic binder (colloidal silica) (solid content) 15 wt % Further, a mixture of an acrylic resin and a surfactant as a dispersant is added thereto in an amount of 0.5 wt% with respect to the total amount of the above.

(Formulation II) Titanium nitride powder 35 wt% Graphite fine powder 25 wt% Zirconium boride powder 10 wt% Graphitized carbon black 15 wt% (trade name: Mitsubishi Carbon Black # 4000B, manufactured by Mitsubishi Kasei Co.) Inorganic binder ( Colloidal silica) (solid content) 15 wt% Further, a mixture of an acrylic resin and a surfactant as a dispersant is added at 0.5 wt% with respect to the total amount of the above items. That is, Formulation I (Example 1) or Formulation II
80 parts by weight of water was added to 100 parts by weight of the solid content of (Example 2), mixed for about 24 hours by a wet pulverizer "Attritor", and homogenized to perform two kinds of conductive oxidation prevention. I got the material.

<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
A conductive antioxidant is applied to the upper and lower surfaces of × 20 mmt (t: thickness) to a predetermined thickness, and then heated at a heating rate of 400 ° C./H, and heated at a predetermined temperature (in the air atmosphere) for 1 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 Formula I (Example 1) and Formula II (Example 2) are shown below. For comparison, a commercially available antioxidant A 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 200 μm after drying the above conductive antioxidant on the upper surface of the carbon base material (φ50 × 8 mmt) by the spray method
After coating so as to obtain a film thickness of, the test piece for evaluation was naturally dried. 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 load of 10 kg and 8 kerfs on the circumference.
The weight difference after 000 rotations was measured, and the sliding resistance was evaluated. The results are shown in Table 2.

[0015]

[Table 2] In this way, by adding graphitized carbon black or graphitized carbon black and fine graphite powder in the coating layer, it is possible to significantly improve the sliding resistance,
The coating layer can be protected from rubbing that occurs when the electrode holder moves.

<Melting Experiment in 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 (after drying). ) And the raw material melting experiment was performed. The raw material used for melting was magnesium oxide, and the time required for melting was about 3 hours and 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 Formulation I (Example 1), Formulation II (Example 2) and Comparative Example 1, troubles such as sparks did not occur and there was no problem in operation. Regarding the antioxidant effect, in Comparative Example 1 in which a commercial product is applied, 11.0% from the tip of the electrode and 10.5% from the side surface.
While it was consumed and there was a total weight loss of 21.5%,
In Examples 1 and 2, the oxidative consumption from the side face was drastically reduced, and at the same time, the oxidative consumption from the tip part was also reduced, and the weight reduction rate was less than half that of the comparative example, showing 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 an excellent effect of preventing oxidation at high temperatures.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C09K 15/02 H05B 7/12 C H05B 7/12 C04B 111: 94 // C04B 111: 94 35/52 G (72) Inventor Hideyuki Hisa 404-2 Ninomiya, Ninomiya-cho, Kanagawa Prefecture (56) References JP-A-49-129238 (JP, A) JP-A-5-295298 (JP, A) JP-A-61-207484 (JP, A) JP 63-26822 (JP, A) JP 55-58259 (JP, A) JP 62-71638 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C09D 1/00-10/00 C09D 101/00-201/10 C04B 41/00-41/72 C04B 35/52-35/54 H01M 4/86-4/98 C25C 1/00-7/08 C25B 11 / 00-11/20 F27D 7/00-15/02 F27B 1/00-3/28 H01J 61/00-61/28 H05B 7/00-7/22

Claims (2)

(57) [Claims] 1. A conductive antioxidant for a graphite electrode, which comprises a refractory aggregate, a binder and graphitized carbon black. 2. The method according to claim 1, which contains graphite powder.
Conductive antioxidant for graphite electrodes .