JPH07268248A - Conductive antioxidant material - Google Patents

Abstract

PURPOSE:To enable the application of a conductive antioxidant material to an electrode chuck part and improve the antioxidant effects of the material at high temps. by compounding a fire-resistant aggregate, a colloidal binder, and a carbon black. CONSTITUTION:This material is obtd. by mixing 20-90wt.% fire-resistant aggregate, 2-30wt.% colloidal binder. 2-30wt.% carbon black, a graphite powder in an ant. of 20-70wt.% of the aggregate, 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. The cost of this electrode in the steelmaking furnace occupies a high proportion, and the oxidation consumption of the electrode causes a large economical loss.
50 to 70% by weight of this electrode is consumed by oxidation, and its consumption by 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.

Further, a method using a frit (glaze) is also known. For example, Japanese Patent Laid-Open No. 72211/1978 discloses a matrix containing a glaze material having a melting point of 1,000 ° C. or less and a refractory bone. An antioxidant composition is disclosed that requires the use of a material. However,
When these frits are used, in addition to the above problems, the coating film shrinks when the matrix softens and shrinks at 1,000 ° C. or less, and film defects such as peeling and (penetration) cracks easily occur. However, there is a problem that a sufficient antioxidation effect cannot be obtained unless a film thickness of about 1 mm is secured after melting. Therefore, in order to secure the film thickness of about 1 mm, it is necessary to repeat the coating work many times, which means that the work efficiency is very poor.

[0005]

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.

[0006]

The conductive antioxidant of the present invention is characterized by containing a refractory aggregate, a colloidal binder and carbon black, and is substantially free of glass frit. Hereinafter, the present invention will be described in detail.
First, examples of the refractory aggregate in the present invention include oxides such as silica, alumina, titania, zirconia, SiC, and B.
₄ C, CrC, WC, TiC, VC, ZrC, NbC and other carbides, TiN, VN, NbN, ZrN and other nitrides,
One or more of silicides such as CrSi ₂ , TiSi ₂ and ZrSi ₂ or powders such as silicon are used. Also, ZrB
₂ , boride powder such as TiB ₂ , CrB, Fe, Co, N
Metal powders such as i, 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. Colloidal silica, colloidal alumina, colloidal zirconia or the like can be preferably used as the colloidal binder. In particular, colloidal silica is most preferable in terms of water resistance after drying, adhesiveness, stability and price. Further, as the carbon black used in the present invention, carbon black obtained by any of the furnace method, the acetylene method, the thermal method, the contact method and the like can be used.

The conductive antioxidant of the present invention contains the above-mentioned three components as essential components and substantially does not contain glass frit. Glass frit, when contained in a coating film, softens and shrinks at a predetermined temperature to form an impermeable glass film, which may be effective in preventing oxidation, but may cause cracking, peeling, etc. during the shrinking process of the coating film. There is a problem that coating film defects are likely to occur. In addition, in the case of an electrode rod having a high temperature of 3000 ° C. or more at the tip of the arc, an electrode holder (a gripping machine, generally made of steel alloy is used) when the continuous operation is started.
In some cases, the temperature may rise to 400 ° C or higher, and the glass frit component in the coating and the oxide of the steel alloy cause a welding phenomenon at the contact area with the coating, leaving a welding layer and causing sparks. There is a problem. Examples of such glass frit include alkali metal, alkaline earth metal silicate, borate, and phosphate. In the present invention, it is necessary that such a glass frit is not substantially contained in order to prevent the above problems from occurring.

The amounts of the above three essential components of the present invention are:
Generally, the refractory aggregate has a solid content of 20% by weight in the total amount of these three components, although it varies depending on the purpose and the type of raw material.
-90 wt%, preferably 40-70 wt%, and the binder (solid content) wt% is 2-30 wt%, preferably 5-
15wt%, carbon black weight% is 2-30wt%
%, Preferably about 10 to 20 wt% is used by blending. When the solid content of the refractory aggregate is less than 20 wt%, the stability of the coating film is deteriorated due to heat and cratering occurs and the base material is easily oxidized. The solid content of the refractory aggregate is 90
If it exceeds wt%, the fire resistance of the coating becomes too high and 500
The base material is oxidized in a low temperature range of about 800 ° C., and it does not function as a coating film in the subsequent temperature range. Further, the smaller the solid content of the binder, the more preferable it is in terms of conductivity, but it is 2 wt%.
When it is less than the above range, there is no adhesive force and the film is easily peeled off. Further, if 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. Furthermore,
The higher the content of carbon black, the more preferable it is in terms of conductivity, but if it exceeds 30 wt%, the antioxidant slip will be thickened, or the carbon black in the coating film will be burned hot to reduce the oxidation resistance. When the content of carbon black is less than 2 wt%, the oxidation resistance is excellent, but desired conductivity cannot be obtained.

Further, in the present invention, if necessary, components other than the above may be added as antioxidant components. 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 (gripping 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 part, 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 is improved and damage to the coating film can be reduced. About 20 to 70 wt% (preferably 40 to 60 wt%) of graphite powder is added to the refractory aggregate. Further, in order to improve stability over time, adhesiveness, and conductivity, a water-soluble polymer such as an acrylic resin is added to the total amount of the above three components in an amount of 0.01
It is also possible to mix about 3 wt%.

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 homogenize the distribution of the composition components in the coating film so that the composition in the applied coating film does not depend on 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 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 prepare the conductive antioxidant to a work viscosity suitable for each construction method.

[0011]

The conductive antioxidant of the present invention can be applied to the electrode chuck portion of the arc furnace electrode, and in particular, the oxidation consumption of the electrode from the side surface of the electrode is drastically reduced, and further the oxidation consumption from the tip portion is also reduced. As a result, the weight loss rate is significantly reduced,
It showed a good antioxidant effect.

[0012]

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). (Compound I) Silicon fine powder 65 wt% Zirconium boride powder 5 wt% Carbon black 15 wt% (trade name: Mitsubishi carbon black CF-9, manufactured by Mitsubishi Kasei Co., Ltd.) 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.

(Formulation II) Silicon fine powder 30 wt% Graphite fine powder 30 wt% Zirconium boride powder 10 wt% Carbon black 15 wt% (trade name: Mitsubishi Carbon Black CF-9, manufactured by Mitsubishi Kasei Co.) Inorganic binder (colloidal) Silica) (solid content) 15 wt% To this, a mixture of an acrylic resin and a surfactant as a dispersant is further 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> The results of measuring the volume specific resistance value (Ω · cm) by the following method are shown in Table 1.
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)

[0015]

[Table 1]

<Melting Experiment with 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 2.

[Table 2] In each of Examples 1 and 2 and Comparative Example 1, no trouble such as sparking occurred and there was no problem in operation. Regarding the antioxidant effect, in Comparative Example 1 in which a commercial product was applied, 8.5% was consumed from the electrode tip part and 10.2% from the side surface, and the total was 1
While the weight loss was 8.7%, in Examples 1 and 2, the oxidative consumption from the side face was drastically reduced, and further the oxidative consumption from the tip part was also reduced. As a result, the weight loss rate was the same as that of the comparative example. It was less than half and showed a good antioxidant effect.

[0017]

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. ⁶ Identification code Office reference number FI technical display area C09K 15/02 // C04B 111: 94

Claims (2)

[Claims] 1. A conductive antioxidant containing a refractory aggregate, a colloidal binder and carbon black, and substantially free of glass frit. 2. The conductive antioxidant according to claim 1, which contains graphite powder.