JP3672220B2 - Nipple for electrode - Google Patents

Description

[0001]
[Industrial application fields]
TECHNICAL FIELD The present invention relates to an electrode nipple, and more particularly, to an improvement in an electrode nipple for connecting a graphite electrode for an electric steelmaking furnace to each other and preventing breakage of a connecting portion of the graphite electrode during operation of the electric steelmaking furnace.
[0002]
[Prior art]
In an electric steelmaking furnace, a graphite electrode is used, and an arc is blown between an electrode tip and a steelmaking raw material charged in the furnace to melt the raw material. Since the graphite electrode reaches a temperature of, for example, 3000 ° C. due to the arc, it is severely consumed. In order to compensate for the consumption, the graphite electrode is generally replenished by connecting sequentially from the upper part outside the furnace.
[0003]
As shown in FIG. 4, the graphite electrodes are connected by forming tapered sockets (female screw portions) 2 at both ends of the electrode pole 1, tapering the socket 2 toward both ends, and male threads at the tapered portions. It is carried out by screwing a nipple (graphite joint) 3 in which a portion is formed.
[0004]
Since the joints of graphite electrodes connected in this way are weak, if an impact (mechanical stress) is applied during operation due to the collapse of raw material scrap, etc., the bottom of the thread thread valley of the socket, especially a nipple with a large stress concentration It has been experienced that breakage occurs starting from the end of the screwed portion of the socket (A portion in FIG. 5).
[0005]
In particular, in the case of a large-diameter electrode, a temperature difference tends to occur in the radial direction, and electrode breakage due to thermal stress is also a problem. At the electrode connection, the nipple is significantly hotter than the electrode pole, and the coefficient of thermal expansion is larger than that of the electrode pole. Accidents may occur.
[0006]
If the connection breaks during operation, the lower electrode falls into the molten steel, delaying the work, sometimes suspending the furnace operation, reducing productivity, and the dropped electrode in the molten steel. Since problems such as deterioration of the quality of steel occur due to mixing, many proposals have been made for improvement of the electrode connecting portion in order to prevent an electrode breakage accident.
[0007]
For example, in order to prevent the electrode connection portion from being damaged due to mechanical stress, as shown in FIG. 6, the end portion of the nipple 3 is provided with a thinned portion 9 having a diameter of 50 to 80% of the diameter. An electrode joint having a structure in which the thinned portion 9 is screwed to the bottom of the socket 2 of the electrode pole 1 has been proposed. (Act No. 56-7115) This structure relieves stress concentration at the end of the threaded portion of the nipple and socket, and prevents cracks (lateral cracks) that occur in the plane perpendicular to the length of the electrode. Although it is quite effective to do this, as in recent years, a method in which a plurality of electric furnaces are provided to operate alternately is not a sufficient measure because the heating and cooling cycle of the graphite electrode is frequently performed.
[0008]
In order to prevent electrode breakage due to thermal stress, as shown in FIG. 7, it has also been proposed to provide a cut groove 10 in the longitudinal direction from the end face of the nipple 3. (Japanese Utility Model Publication No. 59-1357) This structure is effective in relieving the thermal stress in the circumferential direction of the electrode connecting portion and preventing cracks (vertical cracks) generated in the plane parallel to the length direction. However, there is no effect in preventing lateral cracking that occurs in a plane perpendicular to the length direction of the electrode.
[0009]
As shown in FIGS. 8 and 9, a space 11 having a spherical surface continuous with the tapered surface of the socket 3 is provided on the bottom surface of the socket 2 facing the end surface 3A of the nipple 3, and the inside of the nipple 3 from the end surface 3A thereof is provided. There has also been proposed a structure in which a plurality of slanted kerfs 12 are provided. (Japanese Utility Model Publication No. 62-24957)
[0010]
The purpose of this structure is to absorb and disperse the stress generated in the electrode connecting portion in the kerfs 12 and the voids 11 to prevent breakage of the electrode pole. It is not sufficient to prevent transverse cracks that occur in the plane perpendicular to the length direction.
[0011]
The inventors have reviewed the structure of the nipple that has been proposed in order to develop a connection structure that can eliminate the above-mentioned conventional problems in the connection part of the graphite electrode used in the electric steelmaking furnace, The structure in which the thinned portion 9 (FIG. 6) is provided on the end surface of the nipple facing the bottom surface of the socket is not only for preventing lateral cracks that occur on the surface perpendicular to the length direction of the electrode depending on the shape of the thinned portion, It has been found that it can function effectively for prevention of cracking.
[0012]
[Problems to be solved by the invention]
The present invention has been made as a result of repeated experiments and examinations on the relationship between the shape of the thinned portion and the occurrence of cracks based on the above knowledge, and the object thereof is the threaded portion of the nipple and the socket. For the electrode of graphite electrodes for electric steelmaking furnaces, which can relieve the stress generated at the end of the steel and absorb the thermal expansion difference between the nipple and the socket and effectively prevent the lateral cracking and vertical cracking of the electrode To provide a nipple.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, an electrode nipple according to the present invention is screwed into a socket in a graphite electrode nipple for an electric steelmaking furnace that is screwed into a socket formed at an end of an electrode pole and interconnects the electrode pole. The first feature is that a groove portion is provided around the circular end surface of the nipple facing the bottom surface of the socket when it is inserted, and a rising peripheral wall portion is formed by the groove portion and the end side surface of the nipple.
[0014]
In addition, in the nipple of the graphite electrode for an electric steelmaking furnace that is screwed into the socket formed at the end of the electrode pole and connects the electrode poles to each other, when the screw is inserted into the socket, the circular nipple face that faces the bottom of the socket A second feature is that a groove portion is provided around, and a space between the groove portion and the end side surface of the nipple is formed on a rising peripheral wall portion having an end face thickness of 1 to 30% of the diameter of the circular end face.
[0015]
Furthermore, in the above structure, the third and fourth characteristics are that the peripheral wall portion is formed continuously and that notches are formed in one or a plurality of locations of the peripheral wall portion.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol was attached | subjected about the same member as the prior art. In the present invention, as shown in FIGS. 1 and 2, a groove portion 5 is provided around the outer peripheral portion of the circular end surface 3 </ b> A of the nipple 3 facing the bottom surface 2 </ b> A of the socket 2, and the groove portion 5 and the end portion side surface 6 of the nipple 3 are provided. Is formed on the peripheral wall portion 4. With this configuration, the stress generated at the final end of the screwed portion between the socket and the nipple can be relaxed, and the thermal expansion difference between the electrode and the nipple can be absorbed to effectively reduce the breakage at the electrode connecting portion. it can.
[0017]
The end wall thickness t of the rising peripheral wall portion 4 is preferably 1 to 30% of the diameter D of the circular end surface 3A. By setting the thickness to 1 to 30%, regardless of the operating conditions, Longitudinal cracks can be reliably prevented. If the end wall thickness t of the peripheral wall portion 4 is less than 1% of the diameter D of the circular end surface 3A, the rising portion will be destroyed, and if it exceeds 30%, the effect of preventing lateral cracks and vertical cracks of the electrode will be reduced. To do.
[0018]
The depth of the groove 5 is not particularly defined, but considering the strength of the nipple 3, it is preferable in practice to have a length equal to or less than half the half length L / 2 of the nipple 3. Moreover, it is preferable that the bottom part of the groove part 5 is rounded. Furthermore, the width of the groove 5 is preferably 5 to 50 mm. 1 and 2, the groove 5 is formed in the nipple 3 in parallel with the axial direction. However, the groove 5 is not necessarily parallel if the purpose of reducing the stress concentration at the terminal end of the screw connection between the nipple and the socket can be achieved. It does not have to be formed.
[0019]
The central portion 7 of the circular end face 3A of the nipple 3 functions to maintain the end face strength of the nipple and facilitates handling of the nipple. The central portion 7 may be subjected to processing such as perforation and slit formation as necessary in order to adjust the degree of relaxation of stress during use of the electrode.
[0020]
The peripheral wall 4 of the circular end surface of the socket can be formed continuously as shown in FIGS. 1 and 2, but as shown in FIG. 3, the peripheral wall 4 is used to adjust the degree of stress absorption and dispersion. Notches 8 can also be provided at one or a plurality of portions of the portion 4. When notches 8 are provided at a plurality of locations, it is preferable to provide them in a radial manner.
[0021]
【Example】
Examples of the present invention will be described below.
Example 1
A nipple (end face diameter) in which sockets having a depth of 310 mm are formed at both ends of an electrode pole having an outer diameter of 762 mm (30 inches) and a groove 5 is continuously provided in the end face 3A as shown in FIGS. 292 mm) was screwed to connect the electrode poles.
[0022]
The groove 5 had a width of 20 mm and a depth of 100 mm, and a continuous peripheral wall having an end face thickness (t) of 30 mm was formed on the outermost edge of the circular end face of the nipple.
[0023]
When a connection type graphite electrode was attached to a 150 ton electric steelmaking furnace as described above and operated continuously for one month, the breakage accident rate of the electrode connection part was 3% or less.
[0024]
On the other hand, a socket with a depth H of 300 mm is formed at both ends of an electrode pole with an outer diameter of 762 mm (30 inches), and a normal nipple (end surface diameter 380 mm) that does not have a groove on the end face is screwed into the connection. As a result of conducting continuous operation for one month in the same furnace using the electrode pole, the failure rate of electrode connection exceeded 10%.
[0025]
In addition, as in the case of the electrode pole, the groove is 20 mm wide, 100 mm deep, and the end wall thickness (t) is 30 mm. The electrode pole is formed with a peripheral wall portion provided with notches having a width of 5 mm radially at three locations. It was installed in the furnace and operated continuously for one month, but the failure rate of electrode connection was 3% or less.
[0026]
【The invention's effect】
According to the present invention, in a graphite electrode for an electric steelmaking furnace, when a nipple is screwed into sockets formed at both ends of an electrode pole and the electrode poles are connected to each other for operation, the screwed portion between the socket and the nipple There is provided an electrode nipple that can relieve stress generated at the final end of the electrode and absorb a difference in thermal expansion between the electrode and the nipple to prevent a breakage accident at the electrode connecting portion.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an embodiment of an electrode nipple according to the present invention.
2 is an end view of the electrode nipple of FIG. 1. FIG.
FIG. 3 is a perspective view showing another embodiment of the electrode nipple according to the present invention.
FIG. 4 is a partial cross-sectional view showing connection of a conventional graphite electrode.
FIG. 5 is a partial cross-sectional view showing a crack occurrence state at a connection portion of a conventional graphite electrode.
FIG. 6 is a partial cross-sectional view showing a connection portion of a conventional graphite electrode.
FIG. 7 is a perspective view showing an example of a conventional electrode nipple.
FIG. 8 is a partial cross-sectional view showing a connecting portion of a conventional graphite electrode.
FIG. 9 is an end view of the nipple of FIG.
[Explanation of symbols]
1 Electrode pole 2 Socket
2A Bottom of socket 3 Nipple
3A Nipple end face 4 Peripheral wall part 5 Groove part 6 End part side face 7 Center part 8 Notch 9 Thinning part
10 Notch groove
11 void
12 kerf

Claims (4)

In a nipple of a graphite electrode for an electric steelmaking furnace that is screwed into a socket formed at the end of an electrode pole and connects the electrode poles to each other, a groove is formed on the circular end face of the nipple that faces the bottom of the socket when screwed into the socket. A nipple for an electrode, characterized in that a peripheral wall portion is formed around the groove portion and an end side surface of the nipple. In a nipple of a graphite electrode for an electric steelmaking furnace that is screwed into a socket formed at the end of an electrode pole and connects the electrode poles to each other, a groove is formed on the circular end face of the nipple that faces the bottom of the socket when screwed into the socket. A nipple for an electrode, characterized in that it is formed in a rising peripheral wall portion that is provided around and has an end wall thickness of 1 to 30% of the diameter of the circular end surface between the groove and the end side surface of the nipple. The electrode nipple according to claim 1, wherein the peripheral wall portion is formed continuously. The electrode nipple according to claim 1 or 2, wherein a notch is formed at one or a plurality of locations of the peripheral wall portion.

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