JPH0220591B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method of manufacturing an artificial graphite electrode for use in an electric steelmaking furnace. [Prior art] Artificial graphite electrodes are made by crushing, classifying, and blending coke with a predetermined ratio of particle sizes as a filler, mixing this with a pitch binder, and then extruding it.
It is manufactured through various processes such as firing and graphitization,
In electrode manufacturing for UHP (Ultra High Power Operation),
A step of forcibly impregnating tar pitch into the material after the above-mentioned firing treatment and re-firing is added. This pitch impregnation and re-firing process has the effect of densifying the structure of the final graphite electrode and improving its strength and other physical properties, so it is an essential process in today's manufacturing process where UHP operations are the mainstream. It is said that However, this process requires complicated work and long processing time, which is a factor that increases manufacturing costs. [Problems to be Solved by the Invention] Originally, the mechanical strength that governs the quality characteristics of graphite electrodes is greatly influenced by the inherent strength of filler coke and binder pitch. Therefore, when the components of filler coke are the same, the key to improving electrode strength is to use a binder with as good strength performance as possible. In general, properties required of binder components include strong cohesive strength, good wettability to fillers, and high carbonization yield after firing. The more suitable it is, the better the compatibility. For this reason, the production of graphite electrodes requires 85
Hard pitches having a softening point of .degree. However, there is a problem in that an extreme increase in processing temperature in the above process leads to severe deterioration of the pitch composition, which ultimately impedes stable operation. Due to these circumstances, ultra-hard pitch, which has an extremely high softening point, is not used as a binder, although its effectiveness is well recognized;
Approximately 105℃ is considered the limit for coal tar pitch that can be used. [Means for Solving the Problems] The present invention provides a novel artificial graphite electrode that makes it possible to use a coal tar pitch binder with a softening point of 150°C or higher without significantly modifying the conventional manufacturing process. A manufacturing method is provided. That is, the structure of the present invention is such that the filler coke has a softening point of 150°C or higher as part of the binder component.
Finely powdered coal tar pitch containing 65 to 75% fixed carbon (hereinafter referred to as "secondary binder") is mixed in advance, and the mixture is mixed with the remainder of the binder component, which has a softening point of 85 to 105°C and has a fixed carbon content of 55 to 60%. It is characterized in that it is kneaded with coal tar pitch (hereinafter referred to as a "steady binder"), extruded, and then fired and graphitized by a conventional method. The binder component of the present invention consists of a secondary binder and a stationary binder. This is a hard pitch with a characteristic range that is regularly used from . The secondary binder is mixed in advance in the form of a fine powder with the filler coke powder that has been crushed, classified, and mixed in particle size. The particle size range of fine powder is 100 mesh or less,
Preferably, the preparation should be such that at least 50% of the total amount passes through a 200-mesh sieve. The mixture of filler coke and secondary binder is kneaded with a constant binder and then extruded. The proportion of the secondary binder and the steady binder to be used is determined as appropriate in consideration of the conditions of the kneading and molding processes, but in particular the amount of the secondary binder should be in the range of 50 to 70% by weight relative to the total amount of binder components. When set, the strength improvement effect becomes noticeable. At this time, as the ratio of secondary binder used increases, the viscosity necessary for extrusion molding tends to be insufficient. The problem can be avoided by controlling the The formed body extruded to a predetermined size is then fired and carbonized (800 to 1200°C) in a conventional manner, and then transferred to a graphitization furnace and graphitized (2500 to 3000°C) to obtain a graphite electrode. [Function] According to the present invention, in the kneading step (130 to 140°C), the secondary binder is sufficiently kneaded with the filler coke by the melted and liquefied stationary binder while maintaining a stable solid state. The secondary binder is not affected by heat during the subsequent extrusion molding process (100 to 135°C), but it gradually liquefies as the temperature rises above the softening point in the firing process, covering the filler coke powder. Then, it rapidly carbonizes while forming mutual bonds. The binder bond described above is extremely dense and strong due to its high carbonization yield compared to a steady binder, and this effect effectively increases the strength characteristics of the graphite electrode finally obtained. [Example] Petroleum coke with a particle size blend is used as a filler,
Add to this a fine powder of a secondary binder with a softening point of 150℃ and 70% fixed carbon (passed through a 200 mesh sieve, 55%) in varying amounts in stages from 5 to 20% by weight, and mix with stirring. Mixed in a machine. The above raw material mixture has a softening point of 98℃ and a fixed carbon content of 58%.
The mixture was put into a Werner kneading machine together with a constant binder. The amount of constant binder used was adjusted so that the total amount of binder components added to the filler coke was 30% by weight. After sufficiently kneading at a kneading temperature of 140°C, each kneaded product was transferred to an extrusion press, and the diameter ^was
It was extruded from a 500 mm nozzle to obtain a cylindrical molded body with a length of 1800 mm. Other molding conditions [amount of molding aid (lubricating oil), molding temperature] are shown in the table together with the blending ratio of the binder component.

[Table] The compact was then fired in a firing furnace to 1000°C, then transferred to a graphitization furnace and graphitized at 3000°C. The apparent specific gravity during molding and various properties of the obtained artificial graphite electrode are shown in the table. In addition, in the manufacturing process according to the conventional example, the properties of the material after firing were impregnated with tar pitch, re-fired, and graphitized were also measured in the same manner, and are also listed in the table as a comparative example.

[Table] From the results in the table above, it is clear that the examples of the present invention that use a secondary binder in combination have improved properties such as tissue density, elastic modulus, and bending strength compared to the conventional examples. . In particular, it was observed that the bending strength of Example 3, in which the amount of secondary binder was 50% by weight based on the total amount of binder components, increased significantly and became equivalent to that of the comparative example in which pitch impregnation and re-firing treatment was applied. Ta. [Effects of the Invention] The present invention has made it possible to use coal tar pitch, which has a softening point of 150°C or higher, which was conventionally considered impossible to use as a binder, through skillful improvement of the manufacturing method, and has made it possible to use it in combination with a stationary binder. by current
The industrial effect is extremely large, as it has succeeded in imparting the same strength improvement as when this method is applied without performing pitch impregnation and re-firing treatment, which is an essential step in the UHP electrode manufacturing process.

Claims (1)

[Scope of Claims] 1. Finely powdered coal tar pitch (secondary binder) with a softening point of 150°C or higher and 65 to 75% fixed carbon is mixed in advance with filler coke as part of the binder component, and the mixture is used as the binder component. An artificial graphite electrode characterized by being kneaded with coal tar pitch (stationary binder) with a softening point of 85 to 105°C and 55 to 60% fixed carbon (stationary binder), which corresponds to the remainder of manufacturing method. 2. The method for producing an artificial graphite electrode according to claim 1, wherein the ratio of the amount of secondary binder to the total amount of binder components is set to 50 to 70% by weight.