JPH03230492A - Manufacture of hollow graphite electrode - Google Patents

Abstract

PURPOSE:To smoothly form a precise hollow hole by extrusion-molding the raw material paste into a hollow shape via a cylinder nozzle, inserting a specific filling bar material into the hollow hole of a molding, and baking, carbonizing and graphitizing it. CONSTITUTION:The raw material paste extruded with a cover 3 covered is pressed into a nozzle 1 from the opening section side of the cylinder nozzle 1 with an axis mandrel 2. The raw material paste proceeds while a hollow hole is formed by the mandrel 2 during the pressing process. The paste composition is firmly bound by the compression action based on the narrowed nozzle 1. The cover 3 is removed near the tip section of the nozzle 1, and extrusion is continued to obtain a hollow molding 7. A filling bar material 8 is inserted into the hollow hole of the molding 7. The filling bar material 8 has the outer diameter slightly smaller than the hole diameter of the hollow hole, it is made of a material vaporized or partially carbonized at the temperature 400 deg.C or above, and it is formed into a cylinder or a columnar shape. This molding is put in a baking furnace to be baked, carbonized and graphitized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a hollow electrode made of artificial graphite for use in an electric steelmaking furnace.

[Conventional technology]

In electric steelmaking furnaces, in addition to the usual cylindrical artificial graphite electrode, a through hole is drilled along the central axis in the longitudinal direction of the electrode, and inert gas for arc stabilization and minerals for composition adjustment are blown into the electrode. A hollow electrode is used.

Conventionally, in order to manufacture hollow electrodes, a secondary step of machining holes using a lathe was added to an ordinary cylindrical electric bridge that was first formed as a product. However, electrodes for steelmaking have a diameter of 400 mm or more and a length of 1
It is a large material exceeding 500+ sm, and the hole diameter is relatively small with a void ratio of 30 or more (total cross-sectional area of the electrode/hollow cross-sectional area), so it takes a considerable amount of time to process the hole and also causes a large amount of material processing loss. There were problems in terms of productivity, workability, and economy.

! [Problems to be Solved by the Invention] The present invention provides a method for manufacturing a hollow graphite electrode that eliminates the above problems, and provides a method for manufacturing a hollow graphite electrode in which the ratio of the total cross-sectional area of the electrode to the hollow cross-sectional area is 30 or more. The first purpose is to improve productivity, workability, etc. by simultaneously forming small hollow holes during the extrusion process.

Conventionally, the ratio of the hollow cross-sectional area to the total cross-sectional area of the pipe is 1.
When manufacturing a graphite pipe with a void ratio of ~20, when the hollow holes formed in the pipe shape are filled with coke backing material and fired, the binder components flowing into the hollows due to melting are absorbed, and the binder components flowing into the hollow holes are absorbed. It is known that shrinkage, material deformation, etc. can be prevented. However, when the above method is adopted when the electrode diameter is large and the diameter of the hollow holes is small (the void ratio of total cross-sectional area/hollow cross-sectional area is 30 or more), such as a hollow graphite electrode, the amount of molten binder flowing out is reduced. As the amount of banking material in the hollow hole increases, the amount of banking material in the hollow hole is small, leading to blockage, shrinkage, deformation, etc. of the hole due to sintering and fixation (coking) of the backing material.The second object of the present invention is to completely disconnect the electrode. Even when the void ratio (area/hollow cross-sectional area) is 30 or more, the firing process is performed without causing blockage, reduction, deformation, etc. of the hollow pores.

[Means to solve the problem]

A method for producing a hollow graphite electrode according to the present invention to achieve the above object is to extrude a raw material paste into a hollow shape through a cylindrical nozzle having an axial mandrel, and fill a hollow hole in a molded product with a hole slightly smaller than the hole diameter. The structure is characterized in that a cylindrical or cylindrical filling rod material having an outer diameter and made of a material that volatilizes or partially carbonizes at a temperature of 400° C. or higher is inserted and then fired to carbonize and graphitize.

Normally, graphite electrodes are manufactured by extruding a raw material paste obtained by kneading a raw material filler of coke powder with a binder made of cool pitch to a predetermined diameter, and then subjecting it to firing carbonization and graphitization treatment. Hollow holes are formed at the same time during molding. Hollow extrusion molding is performed using an extrusion nozzle as shown in FIG. 1 (cross-sectional view) and FIG. 2 (front view). That is, this extrusion nozzle has a structure in which a mandrel 2 of a predetermined diameter is attached to the opening side (curved part) of a cylindrical nozzle 1 whose insertion part into which the raw material paste is pushed is curved and which extends from the center of the nozzle to the tip via a spider 5. It is designed to. The mantle 2 is supported by a plurality of spiders 5, and the spiders 5 are removably attached via a ring 6 along the opening so that it can be used in combination with ordinary cylindrical molding. . For molding, the raw material paste extruded from the container of the extrusion device is press-fitted into the nozzle from the opening side of the cylindrical nozzle l with the lid 3 covered.

The raw material paste advances while forming hollow holes by the mandrel 2 during the normal process. At this time, the paste structure once divided by the spider 5 is firmly combined by the compression action based on the narrowing of the nozzle diameter, and is formed into the cylindrical nozzle 1. When the tip is reached, the lid 3 is removed and extrusion is continued to obtain a hollow molded body.

Then, as shown in FIG. 3, a cylindrical or cylindrical filler rod 8 having a diameter slightly smaller than the hole diameter, preferably about 1 to 5 mm smaller, is inserted into the entire length of the hollow hole of the molded body 7. The filling rod material 8 is preferably made of a material that volatilizes or partially carbonizes at a temperature of 400° C. or higher, and is resistant to the expansion pressure generated during firing of the compact. Examples of materials that satisfy this requirement include paper, pulp, and thermosetting resins with a low carbonization residual rate. Therefore, cylinders or cylinders made of these materials are preferably used, but when using a paper cylinder, it is desirable to use one with a certain degree of wall thickness.

The molded body with the filling rod inserted into the hollow hole is transferred to a firing furnace, and heated to a temperature of 1,000 to 130
Calcined and carbonized at a temperature of 0°C.

At this time, if the filling rod material is a paper cylinder, the inside of the cylinder may be filled with a backing material.

Although some carbide may remain in the hollow hole after firing, it can be easily scraped off by inserting a scraping stick into the hollow hole and moving it back and forth.

The fired and carbonized compact is then placed in a graphitization furnace for 280 minutes.
Graphitization treatment is performed at a temperature of 0° C. or higher to obtain a hollow graphite electrode.

[For production]

According to the above process, normal hollow holes are formed at the same time as the outer diameter is formed during the extrusion process of the raw material paste, so there is no need to perform complicated hole processing on the cylindrical graphite material. Then, in the next firing step, the filling rod inserted into the hollow hole is heated to a temperature range (2 o
0~350'C), it prevents the situation from flowing into the hollow space and also absorbs a part of it. Furthermore, it functions effectively to prevent shrinkage and deformation of the hollow pores due to thermal expansion of the molded body. The filled rod material evaporates or remains partially carbonized when the temperature reaches 400° C. or higher, at which time the binder component becomes stable. The filling rod material components remaining carbonized at this time are attached to the inner surface of the hollow hole in a state where they can be easily peeled off, so they can be easily removed by moving the scraper back and forth.

Through these process actions, a hollow graphite electrode having highly precise hollow holes without shrinkage or deformation can be manufactured with high productivity.

〔Example〕

Examples of the present invention will be described below in comparison with comparative examples.

Example A raw material paste made by blending cool pitch as a binder with coke powder filler whose particle size has been adjusted is extruded through an extrusion nozzle equipped with a cylindrical nozzle shown in Fig. 1 on the front of a container to form the outside of the electrode. Diameter 374 mm
, length 1818mm.

A hollow molded body was molded with a hollow hole diameter of 43 mm and a void ratio of total electrode cross-sectional area/hollow cross-sectional area of 75.8.

Next, a filling rod made of a cardboard cylinder with an outer diameter of 40 mm and a thickness of 5 mm was inserted into the entire length of the hollow hole of the molded body, and this was placed in a firing furnace and the surrounding area was covered with coke backing material for 13 minutes.
Firing treatment was carried out at temperatures up to 00°C.

After cooling, a keren rod was inserted into the hollow hole of the fired electrode and moved back and forth lightly to remove carbonized components adhering to the inner surface. When the hollow hole was inspected in this state, it was found that a normal through hole with a hole diameter of 38 to 40 mm was formed without blockage, shrinkage, deformation, etc. due to coke deposits.

The above fired electrode was transferred to a graphitization furnace and subjected to graphitization treatment at 2800° C., thereby producing a good hollow graphite electrode.

Comparative Example 1 A molded article with hollow holes formed in the same manner as in the example was put into a firing furnace as it was, and firing treatment was performed without filling the hollow holes with anything. In this case, the pitch flowing out from the structure of the molded body turned into coke, blocked the hollow holes, and was stuck in such a state that it could not be scraped off with a scraper.

Comparative Example 2 A sintering treatment was performed in a state in which the hollow holes of a molded body blow-molded in the same manner as in the example were filled with coke grains having a grain size of 3 to 10 mm. In this case, the pitch components flowing out from within the structure were absorbed by the coke grains and sintered and fixed, blocking most of the pores. The stuck matter was extremely strong and could not be scraped off with a scraper.

〔Effect of the invention〕

According to the present invention, the following effects are brought about.

(1) Hollow holes can be formed smoothly and accurately in the electrode forming process. Therefore, compared to the conventional technology of manufacturing hollow electrodes through secondary machining, the number of steps is reduced and there is no processing loss of material, improving productivity and workability, and reducing manufacturing costs. can.

(2) Even if the molded body has relatively small-diameter hollow pores with a void ratio of total electrode cross-sectional area/hollow cross-sectional area of 30 or more, the firing process will not cause any clogging, shrinkage, or deformation of the hollow pores. It becomes possible to do this. Therefore, a normal hollow graphite electrode can always be manufactured with high productivity.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view illustrating an extrusion nozzle for forming a hollow electrode used in the present invention, and FIG. 2 is a front view thereof. FIG. 3 is a cross-sectional view of a hollow molded body showing an embodiment of the present invention. 1... Cylindrical nozzle 3... Lid 5... Spider 7... Molded body 2... Mandrel 4... Point 6... Ring 8... Filling rod material

Claims (1)

[Claims] 1. Extrusion of the raw material paste into a hollow shape through a cylindrical nozzle having an axial mandrel, the hollow hole of the molded product having an outer diameter slightly smaller than the hole diameter, and at a temperature of 400°C or more. 1. A method for producing a hollow graphite electrode, which comprises inserting a cylindrical or cylindrical filling rod made of a material that volatilizes or partially carbonizes, and then subjecting it to firing carbonization and graphitization treatment. 2. The method for manufacturing a hollow graphite electrode according to claim 1, wherein the ratio of the total electrode cross-sectional area to the hollow cross-sectional area is a void ratio of 30 or more.