JPH043883A - Hearth bottom electrode - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hearth bottom electrode that is used by being attached to the hearth bottom in an electric furnace such as a direct current arc furnace or a direct current furnace.

[Conventional technology]

Steel rods are generally used as conventional hearth bottom electrodes. Such a furnace bottom electrode is installed in a penetrating manner in the furnace bottom, and is used by cooling its protrusion outside the furnace or the connection portion with a current-carrying conductor outside the furnace.

[Problem to be solved by the invention]

When melting, scouring, etc. are performed in a furnace under the above usage conditions, the bottom electrode melts from the top to a considerable depth. The lowest part of the molten part gradually lowers as the bottom refractory is eroded and worn from the upper surface due to repeated operations of the furnace. Then, the melting depth of the furnace bottom electrode became too deep and it fell out from the furnace bottom.
In order to prevent accidents in which molten metal inside the furnace leaks out of the furnace,
The temperature of the electrode should be extremely strictly controlled through the cooling described above, the thickness of the furnace bottom should be strictly controlled, or a backup cooling system should be prepared in case there is an abnormality in the electrode cooling system. There have been problems with a number of troublesome safety measures, such as having to be used.

The present invention was made to solve the problems (technical problems) of the prior art described above, and when used by being attached to the bottom of the furnace,
We provide an electrode for the bottom of a furnace that eliminates the worry of melt dropping at the normal operating temperature of the furnace, simplifies electrode temperature management, eliminates the need for the above-mentioned backup cooling system, and greatly simplifies safety measures. The purpose is to

[Means to solve problems]

In order to achieve the above object, the present invention takes the measures as described in the claims above, and its effects are as follows.

[Effect]

The hearth bottom electrode is used by being attached to the hearth bottom in a penetrating manner. When operations such as melting or 1-refining are performed in the furnace in this state, the furnace bottom electrode does not melt and maintains a solid state.

〔Example〕

The drawings showing the embodiments of the present application will be described below.

In Fig. 1, reference numeral 1 indicates the hearth bottom of a DC arc furnace, and it is composed of a hearth bottom plate 2 made of a metal material such as a steel plate and forming the outer shell of the hearth bottom, and a refractory 3 lined on the upper surface of the hearth bottom plate 2. It is. 4 indicates a location where the molten metal formed above the furnace bottom 1 is kept.

Next, reference numeral 5 denotes a holding plate for the bottom electrode, which is made of a strong metal plate, such as a steel plate. Reference numeral 6 denotes a hearth bottom electrode, which is integrally fixed to the holding plate 5. The electrode 6 is made of a material whose components are 85 to 65% molybdenum and the remainder an oxide containing zirconium oxide as a main component.

The thickness is, for example, 200 to 250 φ. A conductor 8 for supplying electricity is connected to a lower end 6a of the hearth bottom electrode 6 that protrudes outside the furnace via a connecting terminal 7. Reference numeral 9 denotes an insulator interposed between the annular receiver 1112a on the furnace bottom plate 2 and the peripheral edge of the holding plate 5, and is used to electrically insulate between the furnace bottom plate 2 and the furnace bottom electrode 6. . Reference numeral 10 denotes a cooling device, which blows out a cooling gas such as air as shown by an arrow 11 to cool the furnace bottom plate 2, the holding plate 5, the lower end 6a of the electrode 6, the insulator 9, etc.

In the above DC arc furnace, the melted raw material (
For example, scrap) is charged, and as is well known, by supplying electric power between the upper electrode and the bottom electrode 6 (not shown),
The above raw materials are melted to become molten metal (for example, molten steel).

The electrode 6 does not melt at the normal temperature at which the raw materials are melted, for example, 1700° C. during operation of the above-mentioned furnace (for example, it does not melt up to about 2000° C.). Therefore, temperature control to prevent the electrode 6 from melting is simple. Further, as described above, since the electrode 6 does not melt, as the furnace is repeatedly operated, the refractory 3 is melted and damaged as shown by the two-dot chain line 13, and the electrode 6 protrudes. Therefore, if this happens, intermediate repair can be easily performed by stamping magnesia (MgO) around the electrode 6.

Next, FIG. 2 is a graph showing the relationship between the component proportions of the materials constituting the electrode and various characteristics of the electrode with respect to the electrode used as the hearth bottom electrode, that is, the hearth bottom electrode 6 as described above. As is clear from the electrical resistivity of molybdenum M
The smaller the proportion of o is, the larger the proportion is, and when the proportion of molybdenum is less than 65%, the electrode has a diameter of 20 µΩ and is not suitable as an electrode for an arc furnace in normal operation. Thermal shock resistance decreases as the proportion of molybdenum decreases, and when the proportion of molybdenum is 65% or less, it becomes undesirable as an electrode for the above-mentioned arc furnace. The oxidation index increases as the proportion of molybdenum increases, and when the proportion of molybdenum exceeds 85%, it becomes undesirable as an electrode for the above-mentioned arc furnace. Therefore, the bottom electrode for arc furnaces operating normally as described above should contain 85 to 65% molybdenum.
It is preferable that the material be formed of a material having a component ratio in which the balance is an oxide mainly composed of zirconium oxide ZrO2. The electrical resistivity of such electrodes is in the range of 8 to 20 .mu..OMEGA..

The above-mentioned furnace bottom electrode is manufactured from materials having the above-mentioned components by a sintering method in an inert gas at normal pressure (atmospheric pressure) or high pressure, or by the HIP method.

Next, FIG. 3.4 shows a structure (a structure called the Keller type) in which a plurality of relatively small diameter electrodes 6e are used at the bottom of the arc furnace. As the electrode 6e in such a structure, it is preferable to use a hearth bottom electrode made of the above-mentioned material.

In the figure, reference numeral 15 denotes a connecting body made of a conductive material.The upper flange 15a of the connecting body is fixed to the holding plate 5e with a plurality of electrodes 6e by nuts 16, and the connecting terminal 7e is attached to the outer periphery of the lower part. The connecting body 15 is formed hollow and supplies cooling gas to the lower end of the electrode and the holding plate 5e.
A plurality of blow-off holes 17 are provided for blowing air toward the air. 1
8 is a cooling gas supply pipe connected to the lower end of the connector 15.

It should be noted that parts that are considered to have the same or equivalent structure as those in the previous figure in terms of function are given the same reference numerals as in the previous figure with the letter e, and redundant explanations are omitted.

Next, in this specification, the bottom of the furnace includes not only a place where molten metal is present on the upper side during operation of the furnace, but also a place where molten metal is present on the side,
In other words, it refers to a location that comes into contact with molten metal, and the furnace bottom electrode may be used by being attached to such a location.

〔Effect of the invention〕

As described above, in the present invention, the hearth bottom electrode is 85 to
Since it is made of a material containing 65% molybdenum and the remainder zirconium oxide as its main component, when the furnace bottom electrode is attached to the furnace bottom 1 and used, the operating temperature of a normal furnace can be maintained. In this case, the electrode 6 can maintain a solid state and there is no need to worry about the melt falling off. Therefore, the temperature control of the electrode can be relatively rough compared to the conventional technique, and the preliminary cooling for electrode cooling required in the conventional technique can be avoided. This has the advantage of greatly simplifying safety measures, such as eliminating the need for a system.

Furthermore, since the hearth bottom electrode of the present invention is made of the materials with the above-mentioned components, when used in the above-described manner,
Its low electrical resistivity makes it possible to use small-diameter products, its high high-temperature oxidation resistance allows it to be used for a long time, and its low reactivity with molten metal and slag makes it possible to reduce the composition of molten metal. Due to the ability to maintain a constant level and high thermal shock resistance,
It has many effects, including the ability to melt high melting point materials.

[Brief explanation of drawings]

The drawings show an embodiment of the present application, and FIG. 1 is a vertical sectional view showing the bottom structure of an arc furnace in which a bottom electrode is used, and FIG.
The figure is a graph showing the relationship between the component ratio of constituent materials of the hearth bottom electrode and various characteristics of the hearth bottom electrode, Figure 3 is a similar diagram to Figure 1 showing different embodiments, and Figure 4 is the FIG. 3 is a plan view showing the arrangement relationship of a plurality of electrodes in the illustrated example. 1... Hearth bottom, 6... Hearth bottom electrode. Figure Figure Figure Number? Figure 8e

Claims (1)

[Claims] An electrode for the hearth bottom that is used by being attached to the hearth bottom in a penetrating manner, and the hearth bottom electrode is made of 85 to 65% molybdenum,
An electrode for a furnace bottom, characterized in that the remaining part is formed of a material whose component is an oxide mainly composed of zirconium oxide.