JPH0722036B2 - Method for manufacturing hollow graphite electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a hollow electrode made of artificial graphite used in an electric steelmaking furnace.

[Conventional technology]

In the electric steelmaking furnace, in addition to the ordinary columnar artificial graphite electrode, a through hole along the central axis is drilled in the longitudinal direction of the electrode to suck inert gas for arc stabilization and minerals for component adjustment. A hollow electrode adapted to be embedded is used.

Conventionally, in order to manufacture a hollow electrode, a secondary step of machining a hole by a lathe is added to an ordinary cylindrical electrode once formed as a product form. However, since the electrode for steelmaking is a large material with a diameter of 400 mm or more and a length of over 500 mm, and the hole diameter is relatively small with a void ratio of the electrode total cross-sectional area / hollow cross-sectional area of 30 or more, There has been a problem in productivity, workability and economic aspects that a great deal of work is required for processing and a large amount of material processing loss occurs.

[Problems to be Solved by the Invention] The present invention provides a method for producing a hollow graphite electrode which solves the above-mentioned problems, and has a void ratio of 30 or more in total electrode cross-sectional area / hollow cross-sectional area. The first object is to improve productivity, workability, etc. by simultaneously forming relatively small hollow holes in the process of extrusion molding.

Conventionally, the ratio of the hollow cross-sectional area to the total cross-sectional area of the pipe is 1
When producing a graphite pipe with a void ratio of ~ 20, when the pipe-shaped hollow holes are baked with the coke packing material filled, the binder components that flow into the hollow due to melting are absorbed, and It is known that shrinkage and material deformation are prevented. However, when the electrode diameter is large and the diameter of the hollow holes is small like the hollow graphite electrode (the void ratio of the total cross-sectional area / hollow cross-sectional area is 30 or more), when the above method is adopted, the outflow amount of the molten binder is increased. Due to the small amount of packing material in the hollow holes, the pores are blocked due to sinter-fixing (coking) of the packing material.
It causes reduction and deformation. A second object of the present invention is to perform a firing treatment that does not cause clogging, shrinkage, deformation, etc. of hollow holes even when the void ratio of the electrode total cross-sectional area / hollow cross-sectional area is 30 or more. It is in.

[Means for Solving the Problems]

The method for producing a hollow graphite electrode according to the present invention to achieve the above object, the raw material paste is extruded into a hollow shape through a cylindrical nozzle having an axial mandrel, the hollow diameter of the molded body is smaller than the hole diameter. A structural feature is that a cylindrical or cylindrical filling rod made of a material having an outer diameter and volatilized or partially carbonized at a temperature of 400 ° C. or higher is inserted, followed by firing carbonization and graphitization.

Usually, a graphite electrode is produced by extruding a raw material paste obtained by kneading a raw material filler of coke powder particles with a binder made of tar pitch into a predetermined diameter, and then subjecting it to firing carbonization and graphitization treatment. Hollow holes are simultaneously formed during molding. Hollow extrusion molding is performed using an extrusion nozzle as shown in FIG. 1 (transverse sectional view) and FIG. 2 (front view). That is, this extrusion nozzle has a structure in which a mandrel 2 having a predetermined diameter that extends the center of the nozzle to the tip is mounted via a spider 5 on the opening side (curved portion) of a cylindrical nozzle 1 in which an insertion portion for pushing the raw material paste is curved and opened. Is designed to. The mandrel 2 is supported by a plurality of pieces of spiders 5, and the spiders 5 are detachably attached via a ring 6 along the opening so that the spider 5 can be used together with ordinary columnar molding. . In molding, the raw material paste extruded from the container of the extrusion device with the lid 3 covered is pressed into the nozzle of the cylindrical nozzle 1 from the opening side. The raw material paste progresses while forming hollow holes by the mandrel 2 during the press-fitting process. At this time, the paste structure once divided by the spider 5 is firmly bonded by the compression action due to the narrowing of the nozzle diameter, and the paste structure of the cylindrical nozzle 1 is retained. When approaching the tip, the lid 3 is removed and the extrusion is continued as it is to obtain a hollow molded body.

Then, as shown in FIG. 3, a cylindrical or cylindrical filling rod 8 having a diameter slightly smaller than the hole diameter, preferably about 1 to 5 mm, is inserted into the entire length of the hollow hole of the molded body 7. The filling rod 8 is made of a material that is volatilized or partially carbonized at a temperature of 40 ° C. or higher, and is preferably made of a material that is resistant to the expansion pressure generated during firing of the molded body. Examples of materials satisfying this requirement include paper, pulp, and thermosetting resins having a low residual carbonization rate. Therefore, a cylinder or a cylinder formed of these materials is preferably used, but when a paper cylinder is used, it is desirable to use one having a certain thickness.

The molded body in which the filling rod is inserted into the hollow hole is transferred to a firing furnace, and is fired and carbonized at a temperature of 1000 to 1300 ° C with the coke packing material encapsulated. At this time, when the filling rod is a paper cylinder, the inside of the cylinder can be filled with a packing material.

Although some carbides may remain in the hollow holes after the firing treatment, they can be easily scraped off by inserting the hollow holes with a keren rod and reciprocating them.

The fired and carbonized compact was then placed in a graphitization furnace at 2800 ° C.
Graphitization is performed at the above temperature to obtain a hollow graphite electrode.

[Action]

According to the above process, since normal hollow holes are formed at the same time as the outer diameter molding in the process of extruding the raw material paste, it is not necessary to perform complicated hole processing on the cylindrical graphite material. Next, in the firing step of the next step, the temperature range (200 to 350) in which the filling rod inserted in the hollow hole melts in the formed body structure.
It prevents the situation of flowing into the hollow at (° C) and absorbs part of it. Further, it effectively functions to prevent the contraction phenomenon and deformation of the hollow holes due to the thermal expansion of the molded body. The filling rod volatilizes or partly remains carbonized at a temperature of 400 ° C or higher at which the binder component is stabilized. At this time, the filling rod component that remains carbonized adheres to the inner surface of the hollow hole in a state where it can be easily peeled off, and thus can be easily removed by reciprocating the keren rod.

Through such a process action, a hollow graphite electrode having a highly accurate hollow hole without shrinkage or deformation can be manufactured with high productivity.

〔Example〕

 Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Example A raw material paste prepared by blending and kneading tar pitch as a binder with coke powder filler having a controlled particle size was extruded through an extrusion nozzle having a cylindrical nozzle shown in FIG. Diameter 374 mm, length 1
A hollow molded body having a hollow hole diameter of 818 mm, a hole diameter of 43 mm, and an electrode total cross-sectional area / hollow cross-sectional area of 75.8 was molded.

Next, insert a filling rod consisting of a cardboard cylinder with an outer diameter of 40 mm and a thickness of 5 mm into the entire length of the hollow hole of the molded body, put it in a firing furnace and wrap it up to 1300 ° C with the surrounding coke packing material. It was calcined at temperature.

After cooling, a Keren rod was inserted into the hollow hole of the firing electrode and lightly reciprocated to remove carbonized components adhering to the inner surface. When the hollow holes were inspected in this state, it was confirmed that normal through holes having a hole diameter of 8 to 40 mm were formed without being blocked, reduced, or deformed by the coke adhered matter.

The fired electrode was transferred to a graphitization furnace and subjected to graphitization treatment at 2800 ° C., whereby a good hollow graphite hole electrode was manufactured.

Comparative Example 1 A molded body having hollow holes formed in the same manner as in the example was placed in a firing furnace as it was, and a firing treatment was performed without filling the hollow holes. In this case, the pitch flowing out from the structure of the molded body was coke to block the hollow hole, and it was fixed in a state where it could not be scraped off by the keren rod.

Comparative Example 2 Baking treatment was performed in the same manner as in the example except that the hollow pores of the molded body were filled with coke grains having a grain size of 3 to 10 mm. In this case, the pitch component flowing out from the inside of the structure was absorbed by the coke grains and sintered and fixed, and most of the holes were closed. The adhered matter was extremely strong and could not be scraped off with a keren stick.

〔The invention's effect〕

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

(1) It is possible to smoothly and accurately form hollow holes in the electrode forming step. Therefore, the number of steps is reduced and the processing loss of the material is eliminated as compared with the conventional technique of manufacturing the hollow electrode by the secondary machining, so that the productivity and workability are improved, and the manufacturing cost can be reduced. it can.

(2) Even if the molded product has a relatively small diameter hollow hole with a void ratio of the electrode total cross-sectional area / hollow cross-sectional area of 30 or more, it is fired without causing the hollow holes to be blocked, reduced, or deformed. Can be performed. Therefore, a normal hollow graphite electrode can always be manufactured with high productivity.

[Brief description of drawings]

FIG. 1 is a cross sectional view illustrating an extrusion nozzle for molding 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, 2 ... Mandrel 3 ... Lid, 4 ... Tip 5 ... Spider, 6 ... Ring 7 ... Molded body, 8 ... Filling rod

Claims (2)

[Claims] 1. A raw material paste is extruded into a hollow shape through a cylindrical nozzle having an axial mandrel, and the formed body has an outer diameter slightly smaller than the diameter of the hollow hole of the formed body and is vaporized at a temperature of 400 ° C. or higher. A method for producing a hollow graphite electrode, characterized in that a cylindrical or cylindrical filling rod made of a material that is partially carbonized is inserted, followed by firing carbonization and graphitization. 2. The method for producing a hollow graphite electrode according to claim 1, wherein the ratio of total electrode cross-sectional area / hollow cross-sectional area is 30 or more.