JPH0528998A - Manufacture of artificial graphite electrode - Google Patents

Abstract

PURPOSE:To manufacture easily an artificial graphite electrode having low puffing, high strength, and high bulk density. CONSTITUTION:An artificial graphite electrode is manufactured by using coal base needle cakes, which are obtained after calcination at 1500-1700 deg.C, its true specific gravity being 2.150 or more, and using binder pitch, whose softening point is 100-150 deg.C, as a caking additive. The coal base needle cakes, which are obtained after the calcination at 1500-1700 deg.C, its true specific gravity being 2.150 or more, have small coefficient of thermal expansion, and is desirable as raw material cakes for artificial graphite electrode manufacturing, but kneadability and adhesiveness with the binder pitch are bad, and plenty of binder pitch is required. When plenty of binder pitch is used, such a defect is caused as the bulk density and strength of the electrode are reduced. The defect is eliminated by using the binder pitch having the softening point of 100-150 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an artificial graphite electrode, and more particularly to a method for producing a high strength, high density artificial graphite electrode with low puffing.

[0002]

2. Description of the Related Art In recent years, artificial graphite electrodes have been required to have high mechanical strength and excellent heat resistance in accordance with the severer conditions for using the electrodes. Coal-based needle coke having a low coefficient of thermal expansion is preferable as a raw material coke for manufacturing an artificial graphite electrode satisfying such conditions.

On the other hand, in the production of graphite electrodes, a method of using a rapid graphitization furnace instead of the conventional Acheson furnace has become popular in order to save energy in the manufacturing process.

When a graphite electrode is manufactured using coal-based needle coke, a puffing phenomenon may appear if a rapid graphitization furnace is used, and cracks occur in the electrode or cracks do not occur. However, the apparent specific gravity becomes small, and an electrode having insufficient strength is likely to be obtained. Although various proposals have been made to prevent such puffing,
There was a problem that the coefficient of thermal expansion deteriorates even if it is not very effective or even if it is effective in preventing puffing.

In addition, coal-based needle coke was previously
It has been proposed that calcination at a temperature of 00 ° C. or higher can reduce puffing [eg, JP-A-63-63].
No. 99290, and 12th Annual Meeting of the Carbon Society of Japan, pp. 156-157 (1985)]. This method is a method of causing puffing in advance at the stage of coke, and is a method of reliably reducing the puffing and not deteriorating the thermal expansion coefficient. However, on the other hand, in the case of producing an artificial graphite electrode using the coal-based needle coke obtained by this method, the moldability becomes poor when molded with a normal binder amount, and cracks easily occur in the electrode. Therefore, there is a drawback that a large amount of binder is required. In addition, the use of a large amount of binder causes a new problem that the bulk density and strength of the graphite electrode of the product are reduced. That is, the coal-based needle coke having a true specific gravity of 2.150 or more obtained by calcining at a temperature of 1500 ° C. or higher is effective in reducing puffing, as compared with coal-based needle coke currently commercially available. However, due to poor compatibility with the binder, a large amount of binder is required when used in the production of graphite electrodes, and using a large amount of binder reduces the bulk density and strength of the product electrode. There was a flaw.

[0006]

The present invention uses a coal-based needle coke having a true specific gravity of 2.150 or more obtained by calcining at a temperature of 1500 ° C. or more, which is effective in reducing puffing, and It is an object of the present invention to provide a method for manufacturing a high strength and high density artificial graphite electrode.

[0007]

The inventors of the present invention have conducted various studies to solve the above-mentioned problems, and as a result, the true specific gravity obtained by calcination at a temperature of 1500 ° C. or more is 2.150 or more. Coal-based needle coke has poor softness and adhesiveness when a binder pitch for ordinary artificial graphite electrodes is used because of the large number of pores in the coke itself, but the binder pitch has a high softening point. When using, good mating property and adhesiveness, a good molded product can be obtained without increasing the pitch amount, and by extension an excellent artificial graphite electrode with less puffing without lowering the strength and bulk density is obtained. It was possible to reach the present invention by finding out what can be obtained.

That is, the method for producing an artificial graphite electrode of the present invention is a method for producing a graphite electrode using coal-based needle coke having a true specific gravity of 2.150 or more obtained by calcination at 1500 to 1700 ° C. A binder pitch having a softening point of 100 to 150 ° C. is used as a binder.

The coal-based needle coke having a true specific gravity of 2.150 or more obtained by calcining at 1500 to 1700 ° C. used as a raw coke in the method of the present invention is, for example, a coal containing substantially no quinoline-insoluble matter. Tar, coal tar pitch, etc. are coked using a delayed coker to form coke, and the resulting coke is calcined at 1500 to 1700 ° C for 10 minutes or longer in a calcining furnace such as a rotary kiln, rotary hearth, or electric furnace to obtain a coke. The coke having a specific gravity of 2.150 or more can be easily produced.

If the calcination temperature of the coke is less than 1500 ° C., the effect of preventing puffing becomes insufficient, and if the calcination temperature exceeds 1700 ° C., the adhesiveness to the binder pitch and the like will be deteriorated. Inconvenience occurs.

The binder pitch used as a binder in the present invention may be coal-based or petroleum-based, and its softening point is 100 to 150.
The temperature should be ℃, preferably 110 to 130 ℃. This softening point refers to the value measured by the method described in JIS K2425. Conventionally, a binder pitch having a softening point of 90 ° C. or lower has been used as a binder pitch for producing an artificial graphite electrode. Therefore, the binder pitch used in the present invention has a softening point of 10 to 10 as compared with the conventionally used binder pitch. It is about 60 ° C higher.

If the softening point of the binder pitch is too low,
If the strength of the obtained graphite electrode is lowered and the softening point of the binder pitch is too high, the mating property becomes difficult. After all, the softening point of the binder pitch is preferably in the range of 100 to 150 ° C. in terms of the balance between tightness and strength of the production electrode.

The binder pitch used in the present invention preferably has a toluene insoluble content of 50% by weight or less, a quinoline insoluble content of 20% by weight or less, and a fixed carbon of 50% by weight or more. Further, the binder pitch may be a blend of two or more kinds of pitches so that the softening point is within the above range, but in that case, the respective pitches are sufficiently kneaded to be as uniform as possible. Is important.

Since the binder pitch having a high softening point is used as the manufacturing condition of the artificial graphite electrode in the present invention, its kneading temperature (T ¹ ) is the kneading temperature (T ² ) in the conventional manufacturing of the artificial graphite electrode. A slightly different temperature is used. The kneading temperature (T ¹ ) is preferably a temperature that satisfies the following formula. T ² −SP ² + SP ¹ ≧ T ¹ ≧ T ^{2 In the} formula, T ¹ T ² SP ¹ SP ² represents the following. T ¹ ... Kneading temperature in the present invention T ² ... Conventional kneading temperature SP ¹ ... Softening point of binder pitch of the present invention SP ² ... Softening point of binder pitch of conventional use

The softening point of the binder pitch used in the conventional production of the artificial graphite electrode is 90 ° C. or lower, and the kneading temperature in the production of the conventional artificial graphite electrode is several tens of degrees from the softening point of the binder pitch. Higher temperatures were used.

The conditions other than the softening point of the binder pitch and the kneading temperature in the production of the artificial graphite electrode of the present invention are essentially the same as the production conditions of the conventional artificial graphite electrode, and the type of the production apparatus and the production method. Various conditions can be used depending on the heat radiation state, the property of the aggregate, the particle size composition, and the like. Of course, the use ratio of the binder pitch in the present invention is essentially the same as in the conventional case.

[0017]

[Examples] Examples and comparative examples will be described in more detail below.

Example 1 Coal tar pitch having a quinoline insoluble content of substantially 0 was subjected to delayed coking to obtain raw needle coke having a volatile content of 6% by weight. This coke was calcined in an electric furnace (N ₂ atmosphere) at 1550 ° C. for 1 hour to obtain a calcined coke having a true specific gravity of 2.16.

The calcined coke was pulverized and sieved, and 100 parts by weight of coke obtained by blending the particle size according to a conventional method,
30 parts by weight of a coal-based binder pitch having a softening point of 110 ° C. and 2 parts by weight of iron oxide were added and kneading was performed at 130 ° C. Next, this is extruded and processed to a diameter of 25 m.
Make a test piece measuring mx 120 mm and
After raising the temperature to 1000 ℃ over time, 20 ℃
The temperature was raised to 2800 ° C. at a heating rate of / min, and the temperature was kept at 2800 ° C. for 30 minutes for graphitization. The diameter of the test piece before and after the graphitization was measured, and the puffing value (%) was calculated.

Further, the test piece after graphitization has a diameter of 2
It was cut to 0 mm × 100 mm in length, and the thermal expansion coefficient between 25 and 125 ° C. was measured. Further, its bulk density and bending strength were measured. The results are shown in Table 1.

Comparative Example 1 Using the calcined coke produced in Example 1 and a coal-based binder pitch having a softening point of 90 ° C., a kneading temperature of 110 ° C., and otherwise the same operation as in Example 1 A piece was prepared and the puffing value, the coefficient of thermal expansion, the bulk density and the bending strength were measured by the same method. The results are shown in Table 1.

Comparative Example 2 The raw coke produced in Example 1 was calcined at 1400 ° C. for 1 hour to obtain a calcined coke having a true specific gravity of 2.135. Using this calcined coke, a test piece was prepared in the same manner as in Comparative Example 1 except that the puffing value, the coefficient of thermal expansion, the bulk density and the bending strength were measured by the same method. The results are shown in Table 1.

[0023]

[Table 1]

As is clear from Table 1, the test piece of Comparative Example 1 has a low bulk density and a low bending strength. Also,
The test piece of Comparative Example 2 has a high puffing value.

[0025]

According to the method of the present invention, an artificial graphite electrode having a low puffing and a high strength and a high bulk density can be easily produced by simply using a binder pitch having a high softening point. be able to.

Claims (1)

Claim: What is claimed is: 1. A method for producing a graphite electrode using a coal-based needle coke having a true specific gravity of 2.150 or more obtained by calcination at 1500 to 1700 ° C. A method for producing an artificial graphite electrode, which comprises using a binder pitch having a softening point of 100 to 150 ° C.