JPH02310389A - Method for graphitizing baked-carbon electrode - Google Patents

Abstract

PURPOSE:To uniformly graphitize the entire carbon electrode and to stably produce an artificial graphite electrode having excellent performance when a carbon electrode is energized and heated to produce the artificial graphite electrode by interposing a graphite sheet and particulate graphite between the carbon electrode and a conductor guide electrode. CONSTITUTION:Coke as the essential material is formed with pitch, etc., as a binder, and the formed product is baked to obtain the conventional carbon electrode 3. Plural electrodes 3 are connected in series in a graphitizing furnace and covered with powdery coke 4, and the electrode 3 itself is energized by the guide electrode 2 and heated to graphitize the coke and to produce the artificial graphite electrode. In this case, plural graphite sheets 7 having a particulate graphite layer 6 on both ends are interposed between the electrode 3 to be graphitized and the conductor guide electrode 2 and pressed on each other, and the electrode is energized and graphitized. Consequently, both ends of the electrode 3 is not cooled by the heat release through the guide electrode 2, and the entire electrode 3 is uniformly graphitized, and an artificial graphite electrode having excellent performance is produced in good yield.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of graphitizing fired electrodes arranged in series through a guide electrode and by generating heat from the fired electrodes themselves. The present invention relates to a method for equalizing the temperature of the end portion of a fired electrode that is close to the electrode.

[Prior art] Artificial graphite electrodes are made by mixing coke powder with a pitch binder and extruding it into a cylindrical shape of a predetermined size.
It is produced by firing this once and then graphitizing it. As a means of graphitizing fired electrodes, the Acheson method, in which fired electrodes are arranged at intervals in a packed powder and indirectly heated with Joule heat generated by one energization, has been widely used, but recently it has been used to graphitize fired electrodes in series. Thermal graphitization method, in which the graphitization method is directly heated by energizing the graphitization layer by placing it on the surface of the graphitizer, has been successfully developed, and many proposals have been made.

FIG. 3 is a cutaway plan view of a graphitization furnace that shows the method. In FIG. 1, l indicates a refractory furnace wall, 2 indicates a guide electrode, and firing electrodes 3 are arranged in series. The surrounding area is filled with packed coke 4. 5 indicates a lining layer, and an example is shown in which the firing electrodes 3 are arranged in one row on the center line of the guide electrode 2 and graphitized by directly passing a current, but this also applies even if the firing electrodes 3 are arranged in multiple rows. I do not care.

The fired electrode itself is a heating element, and the rate of graphitization is determined by the temperature at which the fired electrode is heated.Therefore, many proposals have been made to ensure that the temperature is as uniform as possible without local overheating or variations between fired electrodes. is being done.

[Problems to be Solved by the Invention] Regardless of the method of connecting the guide electrode and the firing electrode, it is usually necessary to cool the exposed part of the guide electrode outside the furnace in order to ensure operational safety and protect the materials of attached parts.

Therefore, heat generated from the firing electrode close to the guide electrode is radiated to the outside of the furnace via the guide electrode. For this reason, the guide electrode side end of the fired electrode tends to be at a lower temperature than the central end, and the specific resistance after graphitization tends to decrease. There was a risk that cracks would occur in the parts, leading to a decrease in product yield.

Regarding the connection between the guide electrode and the firing electrode, some proposals have been made. In other words, there is a method of directly contacting the guide electrode and the firing electrode, but even though there is no problem with the electrical connection, it is possible to This is not a solution because the temperature difference becomes large, heat transfer from the fired electrode to the guide electrode is significant, and the degree of graphitization of the electrode in contact with the guide electrode decreases.

Next, there is a method of interposing a layer of graphite powder particles between the guide electrode and the firing electrode, but this method is effective in preventing local heat generation at the contact surface between the firing electrodes in the center of the graphitization furnace. When interposed between the connecting surface between the guide electrode and the firing electrode at both ends of the graphitization furnace, local heat generation is likely to occur, and the degree of graphitization on the electrode end surface becomes uneven due to uneven temperature, resulting in defects. The ratio was also high, and it was insufficient as a means to solve the problem of the graphitization furnace end.

[Means for solving the problem] In order to prevent the temperature of the firing electrode in contact with the guide electrode from decreasing, it is possible to interpose a medium that generates a large amount of heat here to generate heat and compensate for the heat loss. It will be done. The medium for this purpose is preferably one that is easy to handle and recover and is reusable.

The present inventors have solved the above problem in a graphitization method in which a plurality of fired electrodes arranged in series are heated with electricity in the axial direction from both ends via a guide electrode, and a graphite plate is placed between the guide electrode and the fired electrode, and both sides of the graphite plate are placed between the guide electrode and the fired electrode. The problem was solved by a method of graphitizing a fired carbon electrode, which is characterized by interposing graphite powder particles in the electrode and heating it with electricity in a press-contact state.

The guide electrode does not necessarily have to be solar irradiated in cross section, but it has the same diameter or larger area than the firing electrode, and is provided at both ends of the graphitization furnace, with part of it inside the furnace and part of it inside the furnace. Exposed outside the furnace. This exposed portion is air-cooled or water-cooled, and connected to a power supply cable at the cooling portion.

A sandwich layer consisting of a graphite plate having a layer of graphite powder particles on both ends is interposed between the connecting surface of the guide electrode in the furnace and the connecting surface of the facing firing electrode to establish an electrical connection.

At least one graphite plate is sufficient; if too many graphite plates are used, the throughput of the fired electrodes will be affected, and the effect will quickly become saturated, so about three graphite plates are sufficient. Of course, if you are doing it to adjust the distance, you don't have to worry about this number.

It is sufficient for the thickness of the graphite plate to be about 15 mm to 600 mm for reasons such as adjusting the length of the firing electrode and adjusting the length of the rows in a plurality of rows. If it is thinner than this, there are problems such as cracking and a decrease in the thickness accuracy of the graphite plate due to blurring during processing. On the other hand, making it thicker than 600 mm is not preferable because it results in a decrease in the amount of fired electrodes (processing amount), an increase in graphite plate manufacturing cost, and an increase in graphite plate inventory weight.

Further, it is necessary to provide a graphite powder layer on both sides of the graphite plate, and the thickness thereof is about 5 mm to 25 mm.

If it is thinner than this, it will be difficult to fill the powder layer evenly.
In addition, if the thickness is thicker than 25 mm, the filling work is easy, but the powder layer moves in the axial direction due to the expansion and contraction of the electrode during the graphitization process, so the layer does not thicken under pressure. It is difficult to maintain a uniform thickness, which tends to cause local heat generation, which poses problems in terms of equipment maintenance and quality.

The particle size of the graphite powder particles is suitably 5 mm or less.

It is usually sufficient to handle the graphite plate with the graphite electrode cut.
Therefore, the thickness can be selected arbitrarily.

As the graphite powder, graphite powder obtained by crushing a graphite electrode, carbon fiber, or the like can be used.

The graphitization furnace used in the method of the present invention has a furnace length of several tens of meters.
00m or more long, with several to 20 fired electrodes
Although the present invention is also arranged in series, the fact that the electrodes arranged at both ends can be stably graphitized by the method of the present invention has a great effect in terms of operational stability.

[Function] In the conventional method of filling only the conductive powder layer (actually graphite powder layer) between the guide electrode and the fired electrode and making the -C':4 gas connection, first the fired electrode is placed on the packed coke powder. Arrangement.

Graphite powder is filled between the end and the guide electrode, and then covered with packed coke. However, as the graphite powder layer becomes thicker, the filling of graphite powder may become too dense or wide when compressed from both sides. This is a problem in that the current path becomes non-uniform and local heat generation tends to occur in the fired electrode, and the electrode after graphitization tends to be damaged or cracked.

In the present invention, by selecting the thickness and resistivity of the graphite plate and the thickness of the graphite powder particle layer, the amount of heat generated at the joint can be controlled, and by interposing the graphite plate, the thickness of each graphite powder particle layer can be controlled. This prevents local heat generation within this layer, and fourth, the graphite plate has good thermal conductivity, so even if there is slight local heat generation in the graphite powder particle layer, it will not spread in the radial direction of the graphite plate. Since heat diffusion is easy, there is also a heat equalization effect in this direction.

These reduce the temperature gradient in the axial direction of the electrode and in the radial direction of the N end face at the junction with the guide electrode.

[Example J (Example 1) As shown in FIG. 1, graphite powder particles 6 / graphite plate 7 / graphite dressing particles 6 / graphite plate 7 / graphite powder particles 6 are placed between the guide electrode 2 and the firing electrode 3.
A sandwich layer was provided to make electrical connections.

540mmφX l 4 fired electrodes of 900mm Lσ
They were arranged in rows between guide electrodes, electrically connected by the sandwich layer, and graphitized under conditions of a maximum current of 68 KA, a maximum voltage of 30 V, a maximum power of 2040 KW, and a maximum contact force of 6 t.

The results are shown in Table 1.

(Example 2) In Example 1, one layer (
Therefore, the graphite powder particle layer was made into two layers, and graphitization was performed in the same manner. The results are shown in Table 1.

(Comparative Examples 1 to 3) Comparative Examples 1 to 3 were carried out in the same manner as in Examples 1 and 2, except that a layer of only graphite powder particles was used without using a sandwich layer for electrical connection. The results are shown in Table 1.

Sample 7a from the end surface of the graphitized electrode obtained in the above experiment (5 locations on the surface facing the guide electrode, see FIG. 1(b)), Sample 7b from the end surface of the other end of the same fired electrode, Sample 7C from the opposing surface of j5 and the central firing electrode adjacent thereto was cut out, and the highest average temperature reached in the graphitization process estimated from the graphitization degree of the sample and the temperature variation depending on the location within each sampling end surface were measured.

Sample size, diameter 20m sub-length rooms + degree of graphitization is the specific resistance ρ^ in a magnetic field with magnetic field strength A: 82 level
:ρ, and is an index that has a high correlation with the heat treatment temperature.

(The following is a blank space) [Effect J +1] By increasing the number of graphite discs and the number of conductive powder layers, the maximum temperature of the fired electrode end 7a adjacent to the guide electrode is lowered to the other position 7b. The temperature was close to that of , 7c, indicating that the temperature was equalized.

(2) When the graphite disc is not used and only the layer thickness of the conductive powder is increased, the average temperature of 7a is 7b.

7c, or the quality of the graphitized electrode became non-uniform because the temperature variation increased.

It was also determined that the crack defect rate would increase.

(3) Is the method of the present invention guided by abnormal heat generation near the guide electrode? It was also effective against wear-and-tear deterioration of 5itJj.

[Brief explanation of drawings]

FIG. 1(a) and FIG. 2 are cross-sectional views showing one embodiment of the present invention, and FIG. 1(b) is a view showing a sampling location. FIG. 3 is a plan view of a conventional graphitization furnace. 1. Furnace wall 2. Guide electrode 3, firing electrode 4. Packed coke 5, lining layer 6. Graphite powder 7, graphite plate

Claims (1)

[Claims] In a graphitization method in which a plurality of firing electrodes arranged in series are heated in the axial direction through a guide electrode from both ends, a graphite plate is interposed between the guide electrode and the firing electrode, and graphite powder particles are interposed on both sides of the graphite plate, A method for graphitizing a fired carbon electrode, which is characterized by heating with electricity in a pressurized state.