METHOD FOR MANUFACTURING HIGH-DENSITY ARTIFICIAL GRAPHITE ELECTRODE

Abstract

Provided is a method for manufacturing a high-density artificial graphite electrode without substantially changing a particle size or a proportion of needle coke used, increasing an amount of binder pitch, or performing extrusion molding at a high molding pressure. The method for manufacturing a high-density artificial graphite electrode is kneading binder pitch into needle coke, performing extrusion molding thereof, and then calcining and graphitizing thereof, wherein needle coke obtained by performing coke shape changing treatment for at least some of pulverized needle coke to be used, thereby increasing a ratio of an enveloping perimeter/a perimeter by 1% or more as compared with a value before the changing is used. Here, the enveloping perimeter is a length of a perimeter when apexes of convex portions of the pulverized needle coke are connected to each other via the shortest distance, and the perimeter is a length of a perimeter of a particle.

Claims

1. A method for manufacturing a high-density artificial graphite electrode by pulverizing needle coke, kneading the pulverized needle coke with binder pitch, extrusion molding thereof, and then calcining and graphitizing thereof, the method comprising pulverizing needle coke, and then performing coke shape changing treatment for some or all of the pulverized needle coke, thereby increasing a ratio of an enveloping perimeter/a perimeter (E.sub.A/L.sub.A) of the needle coke after the shape changing treatment by 1% or more as compared with a value (E.sub.0/L.sub.0) before the shape changing treatment as a reference, wherein the enveloping perimeter is a length of a perimeter when apexes of convex portions of a particle of the needle coke are connected to each other via the shortest distance, and the perimeter is a length of a perimeter of the particle of the needle coke.

2. The method for manufacturing a high-density artificial graphite electrode according to claim 1, wherein the needle coke has a true specific gravity of 2.00 or more, a CTE of 1.30×10.sup.−6/° C. or less, a nitrogen content of 0.6 wt % or less, and a sulfur content of 0.6 wt % or less.

3. The method for manufacturing a high-density artificial graphite electrode according to claim 1, wherein the needle coke for which the shape changing treatment is performed is pulverized needle coke having a particle size of 500 μm or less.

4. The method for manufacturing a high-density artificial graphite electrode according to claim 1, wherein the binder pitch has a softening point of 70° C. to 150° C. and an amount of β resin of 15 to 30 wt %.

5. The method for manufacturing a high-density artificial graphite electrode according to claim 2, wherein the needle coke for which the shape changing treatment is performed is pulverized needle coke having a particle size of 500 μm or less.

6. The method for manufacturing a high-density artificial graphite electrode according to claim 2, wherein the binder pitch has a softening point of 70° C. to 150° C. and an amount of β resin of 15 to 30 wt %.

Description

DESCRIPTION OF EMBODIMENTS

[0023] A manufacturing method of the present invention is characterized by using needle coke obtained by performing coke shape changing treatment for some or all of pulverized needle coke product kneaded with binder pitch, thereby increasing a ratio of an enveloping perimeter/a perimeter (E.sub.A/L.sub.A) of the needle coke after the shape changing treatment by 1% or more as compared with a value (E.sub.0/L.sub.0) before the shape changing treatment as a reference.

[0024] In this case, although the pulverized needle coke whose shape is changed may be the whole thereof, only some of the pulverized needle coke may be subjected to the changing treatment. 1 wt % or more, preferably 5 wt % or more, more preferably 20 wt % or more of the pulverized needle coke may be subjected to the changing treatment. A particle size of the pulverized needle coke to be subjected to the shape changing treatment is not particularly limited, but fine particles are more effective, and for example, it is preferable to perform the changing treatment to pulverized needle coke having a particle size of 500 μm or less. 130 μm or less, and more preferably 75 μm or less is preferable.

[0025] The method for performing the coke shape changing treatment, thereby increasing the ratio of the enveloping perimeter/the perimeter (E.sub.A/L.sub.A) of the pulverized needle coke after the shape changing treatment by 1% or more as compared with the value (E.sub.0/L.sub.0) before the shape changing treatment as a reference will be described.

[0026] Bulk needle coke is pulverized into fine particles by a crusher, for example, a jaw crusher, a hammer crusher, a roll crusher or a double roll crusher, and then classified in accordance with the particle size. Further, after the particles are finely pulverized by a roller mill or a tube ball, they are classified in accordance with the particle size.

[0027] Some or all of the classified fine particles or fine powder of the needle coke is subjected to coke shape changing treatment. In this shape changing treatment, various devices can be used as long as they can perform desired shape changing treatment. For the shape changing treatment, for example, a commercially available spheroidizing device can be used, of which an air flow type, a mechanical type, and a high-speed stirring type spheroidizing device are commercially available, and these can be arbitrarily selected.

[0028] Also, the measurement of the enveloping perimeter and the perimeter of the fine particles and the fine powder particles of the needle coke subjected to the shape changing treatment is performed using a shape image analysis device, a particle distribution image analysis device, or an image analysis particle size distribution meter that can measure the enveloping perimeter and the perimeter of the fine particles and the fine powder particles.

[0029] The present invention is characterized by increasing the ratio of the enveloping perimeter/the perimeter (E.sub.A/L.sub.A) of the pulverized needle coke subjected to the coke shape changing treatment by 1% or more as compared with the value (E.sub.0/L.sub.0) before performing the shape changing treatment as a reference. This makes it possible to significantly increase a bulk density (BD) of a molded product, and thus the bulk density after calcining or graphitizing. When the bulk density and the molding pressure are considered, it is desirable that the ratio be preferably increased by 3% or more, more preferably 5% or more.

[0030] Further, a shape changing rate (R) can also be represented by the following mathematical expression.

[00001]$\begin{array}{cc}R=\frac{\left(E_A\text{/}{L}_A\right)-\left(E_0\text{/}{L}_0\right)}{\left(E_0\text{/}{L}_0\right)}\times 100& \left[\mathrm{Math}.1\right]\end{array}$

[0031] In a case in which the changing rate (R) before and after the changing treatment of the enveloping perimeter/perimeter has a difference of less than 1%, many needle-like forms derived from a crystal structure of the needle coke remain. Therefore, in the molded product obtained by combining the needle coke having a plurality of particle sizes, kneading it with the binder pitch, and performing extrusion molding thereof, voids generated due to the needle-like forms derived from the crystal structure of the needle coke remain, which causes cracks due to thermal shock.

[0032] The needle coke used is not particularly limited, and coal-based needle coke and petroleum-based needle coke can be used.

[0033] A true specific gravity of the needle coke is 2.120 to 2.170 g/cm.sup.3, preferably 2.125 to 2.165 g/cm.sup.3, and more preferably 2.130 to 2.160 g/cm.sup.3.

[0034] A CTE of the needle coke is 0.8 to 1.4×10.sup.−6/° C., preferably 0.85 to 1.3×10.sup.−6/° C., and more preferably 0.9 to 1.25×10.sup.−6/° C.

[0035] An apparent density of the needle coke is 2.090 to 2.140 g/cm.sup.3, preferably 2.110 to 2.135 g/cm.sup.3, and more preferably 2.125 to 2.130 g/cm.sup.3.

[0036] A nitrogen content in the needle coke is 0.60 wt % or less, preferably 0.55 wt %, and more preferably 0.45 wt % or less. A sulfur content in the needle coke is 0.60 wt % or less, preferably 0.45 wt % or less, and more preferably 0.30 wt % or less.

[0037] The binder pitch serving as a binder to be used preferably has a softening point of 70 to 150° C. and includes 15 to 30% of a β resin. If the softening point is lower than 70° C., it has a too low viscosity and is likely to enter into a deep portion of pores in the needle coke, and thus effects of the present invention become insufficient. If the softening point exceeds 150° C., a temperature of a kneader for kneading must be raised and the viscosity of the binder pitch must be forcibly lowered, and thus it is disadvantageous in terms of production efficiency. A more preferable softening point is 80 to 130° C.

[0038] For the binder pitch, the same kinds of binder pitch, for example, those having the same softening point may be used in at least two sub-divided kneading stages, and different kinds of binder pitch, for example, those having different softening points may be used in a first kneading stage and a second kneading stage. By changing the softening point, a diameter of the pores in the needle coke into which the binder pitch infiltrates and an amount of the infiltrating binder pitch can be adjusted.

[0039] Also, if necessary, impregnating pitch is impregnated after the calcining, secondary calcining is performed, and then the graphitizing is performed.

[0040] The needle coke is sieved and further pulverized, the binder pitch or the like is mixed thereinto, and kneading, molding, calcining, pitch impregnating, secondary calcining, and graphitizing at a high temperature of about 2500° C. is performed, and thus the artificial graphite electrode can be obtained. According to the manufacturing method of the present invention, a high-density artificial graphite electrode with few voids can be obtained without increasing the molding pressure.

EXAMPLES

[0041] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative examples, but the present invention is not limited to these Examples.

Examples 1 to 7

[0042] For the needle coke, coal-based needle coke having a true specific density of 2.15 and a pore volume of 0.136 cc/g measured by a mercury porosimeter was used.

[0043] This needle coke was pulverized with a jaw crusher, and after 8 to 16 mesh (Me′) (2.38 to 1.0 mm) sieving, coke on and below the sieve was mixed and pulverized with a hammer crusher and sieved to 48 to 200 Me′ (325 to 74 μm) and 200<Me′ (74 μm or less).

[0044] Among these particle sizes, powder of 200 Me′ or less was subjected to shape changing treatment using a high-speed stirring type powder spheroidizing device manufactured by Seishin Enterprise Co. Ltd. The shaping treatment was carried out under four conditions with the same coke blending ratio (Examples 1, 3, 4, and 5). Further, in Examples 2, 6 and 7, cokes having the same particle size that had not been subjected to the shape changing treatment was blended in, and the effect of the shape changing treatment was compared therebetween.

[0045] A degree of the shape changing treatment was measured using a particle shape image analysis device PITA-04 manufactured by Seishin Enterprise Co. Ltd. In order to show the degree of the shape changing treatment that had been performed, a shape changing rate (R), obtained by calculating the ratio of the enveloping perimeter/the perimeter (E.sub.A/L.sub.A) of 200<Me′ after the shape changing treatment referenced to a ratio of an enveloping perimeter/a perimeter (E.sub.0/L.sub.0) of 200<Me′ before the shape changing treatment, is shown in Table 1.

[0046] After the particle sizes were blended such that the particle size distribution became 40% (8 to 16 Me′), 35% (48 to 200 Me′), and 25% (200<Me′) from the largest particle size, 100 parts of this needle coke was kneaded with 27 parts of the binder pitch (BP). The binder pitch used had a softening point of 97° C. and includes 20% of a β resin.

[0047] A molding pressure for the kneaded product in an extrusion molding machine was adjusted such that an extrusion speed thereof is constant at 7 cm/min for a size of 20 mmφ×100 mm, and the pressure at that time was defined as the molding pressure. An extruded product was calcined at 900° C. and then graphitized at 2500° C.

[0048] A bulk density (BD) was measured for each of the extruded products, the sample after the calcining at 900° C., and the sample after the graphitizing.

[0049] The results are shown in Table 2.

Comparative Example 1

[0050] A graphite electrode was manufactured in the same manner as in the examples except that surface changing treatment was not performed by a high-speed stirring type powder spheroidizing device. The results are also shown in Tables 1 and 2.

TABLE-US-00001 TABLE 1 200 < Me′ 8 to 16 Me′ 48 to 200 Me′ Shape changing Untreated Untreated Untreated treated E.sub.0/L.sub.0 E.sub.A/L.sub.A R (%) Compara 40% 35% 25%   0.866 1.0 example 1 Example 1 40% 35% 25% 0.955 10.3 Example 2 40% 35% 12.5%   12.5% 0.911 5.1 Example 3 40% 35% 25% 0.951 9.8 Example 4 40% 35% 25% 0.971 12.1 Example 5 40% 35% 25% 0.959 10.7 Example 6 40% 35% 17.5%   7.5% 0.894 3.2 Example 7 40% 35% 22.5%   2.5% 0.875 1.1 (Remarks) Values of E.sub.0/L.sub.0, E.sub.A/L.sub.A, and R indicate shape characteristics of coke 200 < Me′.

TABLE-US-00002 TABLE 2 Molding Calcining Graphitizing Pressure BD BD BD CTE E.sub.0/L.sub.0 E.sub.A/L.sub.A R (%) [MPa] [g/cm.sup.3] [g/cm.sup.3] [g/cm.sup.3] [× 10.sup.−6/° C.] Compara 0.866 1.0 13.5 1.481 1.443 1.443 1.32 example 1 Example 1 0.955 10.3 8.9 1.537 1.495 1.495 1.26 Example 2 0.911 5.1 10.6 1.513 1.485 1.485 1.27 Example 3 0.951 9.8 9.2 1.538 1.502 1.502 1.26 Example 4 0.971 12.1 6.7 1.607 1.580 1.580 1.21 Example 5 0.959 10.7 7.6 1.562 1.529 1.529 1.29 Example 6 0.894 3.2 10.9 1.501 1.470 1.470 1.30 Example 7 0.875 1.1 12.1 1.488 1.455 1.455 1.31

INDUSTRIAL APPLICABILITY

[0051] According to the manufacturing method of the present invention, it becomes possible to lessen the voids as compared with the case in which needle coke having a plurality of particle sizes is sorted by classification in accordance with the particle size and then combined in order to lessen the causative voids with the purpose of preventing cracks in an artificial graphite electrode due to thermal shock accompanying an increase in diameter thereof. As a result, this manufacturing method can contribute to increasing the density of the artificial graphite electrode so that the pressure in the extrusion molding process can be reduced, and it can contribute to a great deal of energy saving. Accordingly, the artificial graphite electrode manufactured by the manufacturing method of the present invention can be suitably used for a large artificial graphite electrode corresponding to a large high-load electric furnace.