JPS6374961A - Manufacture of artificial graphitic electrode - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

[Conventional technology]

Artificial graphite electrodes are produced by pulverizing, classifying, and mixing coke with a predetermined particle size as a filler, kneading this with a pitch binder, and then extruding, firing, and graphitizing. In the production of electrodes for use in electric power operations, a step is added in which the fired material is forcibly impregnated with tar pitch and re-fired.

This pitch impregnation-re-firing process has the effect of densifying the structure of the graphite electrode finally obtained and improving its strength and other physical properties, so it is an essential process in the manufacturing process today, where UHP operations are mainstream. It is said that However, this process requires complicated work and long processing time, which is a factor that increases manufacturing costs.

[Problem that the invention seeks to solve]

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 excellent strength performance as possible.

In general, the properties required of a binder component include strong cohesive strength, good wetting to fillers, and high carbonization yield after firing. The more suitable it is, the better the compatibility. For this reason, hard pitches with a softening point of 85°C or higher are commonly used in the production of graphite electrodes, but the progression of hard pitching tends to increase viscosity, and the temperature conditions in the kneading and forming processes must be increased. Excessive viscosity cannot be maintained.

However, there is a problem in that an extreme increase in the processing temperature in the above process leads to severe alteration of the pitch composition, which ultimately impedes stable operation.

Due to these circumstances, ultra-hard pitch with an extremely high softening point is not used as a binder, although its effectiveness is well recognized, and currently, a softening point of about 105°C is the limit of usable coal tar pitch. has been done.

[Means for solving problems]

The present invention provides a novel method for manufacturing an artificial graphite electrode that enables the use of a coal tar pitch binder with a softening point of 150° C. or higher without significantly modifying the conventional manufacturing process.

That is, the structure of the present invention is such that the filler coke contains fixed carbon 6 with a softening point of 150°C or higher as part of the binder component.
5 to 75% of finely powdered coal tar pitch (hereinafter referred to as "secondary binder") is mixed in advance, and the mixture is mixed into coal tar with a softening point of 85 to 105°C and a fixed carbon of 55 to 60%, which corresponds to the remainder of the binder component. It is characterized in that it is kneaded with 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 steady binder, the former being a cemented carbide pitch with a softening point of 150°C or higher and 65 to 75% fixed carbon, which was considered unusable in the prior art, and the latter being a cemented carbide pitch with a fixed carbon content of 65 to 75%. This is a hard pitch with a characteristic range that has been regularly used in the past.

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 the fine powder is adjusted to 100 mesh or less, preferably to such an extent that 50% or more of the whole powder 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 appropriately determined in consideration of the conditions of the kneading and molding processes, but in particular, the amount of the secondary binder is in the range of 50 to 70% by weight relative to the total binder component. When set to , 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 calcined 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.

[For production]

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 constant binder which is melted and liquefied 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 during the firing process when the temperature rises above the softening point and covers the filler coke powder. 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 action effectively increases the strength characteristics of the graphite electrode finally obtained.

〔Example〕

Petroleum coke with a particle size blend is used as a filler, and 5 to 20% by weight of fine powder (passed through a 200 mesh sieve, 55%) of a secondary binder with a softening point of 150°C and 70% fixed carbon is added to the filler.
The blending amount was changed stepwise within the range of 20% and mixed using a stirring mixer.

The above raw material mixture was charged into a Uniluna kneading machine together with a constant binder having a softening point of 98 DEG C. and 58% fixed carbon. 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 pressed into a shape with a diameter of 500 cm with a pressure of 50 kg/cm''.
A cylindrical molded product having a length of 1800 cm was obtained by extrusion from a nozzle of zx. Other molding conditions [amount of molding aid (lubricating oil),
The molding temperature] is shown in Table I together with the blending ratio of the binder component.

Table 1 Then, after firing the molded body in a firing furnace to 1000℃,
It was transferred to a graphitization furnace and graphitized at 3000°C.

Table H shows the apparent specific gravity during molding and the properties of the obtained artificial graphite electrode.

In addition, in the manufacturing process according to the conventional example, the characteristics were similarly measured for the material after firing, which was impregnated with tar pitch, re-fired, and graphitized, and is also listed in the table as a comparative example.

Table 2 From the results in the above table, it is clear that the examples of the present invention using 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 the pitch impregnation and re-firing treatment was applied. Ta.

〔Effect of the invention〕

The present invention has made it possible to use coal tar pitch with a softening point of 150'C or higher, which was conventionally considered impossible to use as a binder, through skillful improvements in the manufacturing process. Even without pitch impregnation and re-firing treatment, which is considered an essential step in the manufacturing process, it was possible to successfully impart the same strength improvement as when this application was applied, so the industrial effect is extremely large.

Claims (1)

[Claims] 1. Finely powdered coal tar pitch (secondary binder) with a softening point of 150°C or more 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 a binder. Softening point of the remainder of the ingredients: 85-1
05℃, coal tar pitch with 55-60% fixed carbon (
1. A method for producing an artificial graphite electrode, which comprises kneading the electrode with a steady-state binder), extrusion molding the electrode, and then firing and graphitizing it by a conventional method. 2. The method for manufacturing an artificial graphite electrode according to claim 1, wherein the ratio of the secondary binder 1 to the total amount of binder components is set to 50 to 70% by weight.