JP6962339B2 - How to repair the converter - Google Patents

Description

The present invention relates to a method for repairing a converter used in steelmaking.

The converter is composed of a furnace body and a trunnion ring, and the converter tilts by being rotated around a trunnion shaft provided on the trunnion ring. The furnace body and the trunnion ring are fixed by inserting the trunnion ring support neck through the upper support portion provided in the furnace body. As a result, the structure is such that the furnace body and the trunnion ring do not move relatively even if the converter tilts.

However, due to the long-term use of the converter, when the surface of the upper support part of the furnace body to which the trannyon ring support neck abuts is worn, a gap is created between the trannyon ring support neck and the upper support part of the furnace body, and the converter The furnace body and the tranny ring move relative to each other when tilting. Conventionally, when a gap is created between the trunnion ring support neck and the upper support part of the furnace body, measures have been taken to fill the gap by inserting a shim, but the contact surface of the upper support part due to wear. If it is rough, the shim cannot be fixed and there is a problem that it falls off when the furnace body is tilted. Therefore, when the contact surface of the upper support portion becomes rough due to wear, repair to smooth the surface is required.

As a technique for smoothing the contact surface of the upper support portion, there is a technique for cutting the contact surface of the upper support portion using a liquid jet cutting device. Patent Document 1 discloses a technique for cutting a reinforced concrete structure by ejecting a water jet or an abrasive jet mixed with an abrasive from a nozzle. Further, in Patent Document 1, elastic plates are provided on both sides of the nozzle to detect the degree of reflection of jet water, and it is assumed that this corresponds to the state of the portion to be cut during cutting, and the nozzle moving speed and the like are based on the detection result. It is also disclosed to control.

Japanese Unexamined Patent Publication No. 63-207595

Since the trunnion ring is used permanently in the converter, it is necessary to repair the converter without damaging the trunnion ring. Therefore, it is necessary to detect the cutting state of the upper support portion and end the cutting by the liquid jet cutting device immediately after the cutting of the upper support portion is completed. However, there is a problem that it is difficult to detect the cut state of the upper support portion because there is no space for directly observing the cut state or providing an elastic plate in the vicinity of the contact surface of the upper support portion. rice field.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for repairing a converter that can repair the main body of a trunnion ring without damaging it.

The features of the present invention for solving such a problem are as follows.
(1) A method for repairing a converter used for steelmaking. When cutting the upper support portion of a converter facing the upper support neck of a tranny ring with a water jet ejected from a nozzle, the upper support portion is cut. Below the position, a protective material having a hardness higher than that of the steel material used for the upper support portion is provided, and the temperature of the cut surface of the upper support portion cut by the water jet is measured to measure the cut surface. A method for repairing a converter, which terminates cutting by the water jet when the temperature of the water jet reaches a predetermined threshold value of 1 or more.
(2) The threshold value 1 is a threshold value for distinguishing between the temperature of the cut surface when the upper support portion is cut by the water jet and the temperature when the protective material is cut by the water jet (1). ) Is the method for repairing the converter.
(3) When the temperature of the cut surface becomes less than a predetermined threshold value 2, the moving speed of the nozzle is slowed down to raise the temperature of the cut surface in order to increase the cutting efficiency, and the temperature of the cut surface is raised. When the temperature reaches a predetermined threshold value 3 or higher, the moving speed of the nozzle is increased to lower the temperature of the cut surface in order to suppress the waviness of the cut surface, and the threshold value 2 and the threshold value 3 are set. Since the upper support portion is cut without being mistaken for cutting the protective material, the temperature is lower than the threshold value 1, and the threshold value 2 is a temperature lower than the threshold value 3 (1) or ( The method for repairing a converter according to 2).
(4) The method for repairing a converter according to (3), wherein the threshold value 2 is utilized for determining whether or not the upper support portion can be cut.
(5) The method for repairing a converter according to (3) or (4), wherein the threshold value 3 is utilized for determining whether or not waviness occurs on the cut surface of the upper support portion.

In the converter repair method of the present invention, the cutting state of the upper support portion, which is the cut portion, is grasped by measuring the temperature of the cut surface. As a result, the cutting state can be easily grasped even in the vicinity of the upper support portion of the furnace body where there is no space, and the contact surface of the upper support portion can be cut without damaging the main body of the trunnion ring to repair the converter.

It is a side view which shows an example of the converter 10 to repair by applying the repair method of the converter which concerns on this embodiment. It is a partial cross-sectional view (a) and a top view (b) of the part A of FIG. It is a partial cross-sectional view which shows the part A after the converter 10 has been used for a long time. It is a schematic diagram which shows the state which the contact surface of the upper support part 14 is cut by the liquid jet cutting equipment 80. It is a graph which conceptually shows the relationship between the temperature of the cut surface and the cutting time when the moving speed of the liquid jet cutting device 40 is controlled by the temperature of the cut surface.

The present invention will be described through embodiments of the present invention. FIG. 1 is a side view showing an example of a converter 10 to be repaired by applying the converter repair method according to the present embodiment. In FIG. 1, the arrow on the upper right indicates the vertical and horizontal directions of the converter 10.

The converter 10 is used for steelmaking and is composed of a furnace body 12 and a trunnion ring 20. The trunnion shaft 24 provided on the trunnion ring 20 is pivotally supported by a furnace body support frame (not shown), whereby the converter 10 can be tilted in the direction of the arrow 70.

The furnace body 12 has an upper support portion 14 and a lower support portion 16 having a rectangular cross section and provided with square holes penetrating in the vertical direction. The upper support portion 14 is provided on the peripheral surface above the furnace body 12 so as to project in the radial direction of the furnace body 12. The lower support portion 16 is provided on the peripheral surface below the furnace body 12 so as to project in the radial direction of the furnace body 12. The trunnion ring 20 has a ring-shaped main body 22, a trunnion shaft 24, an upper support neck 26, and a lower support neck 27. The trunnion shaft 24 is a cylindrical member, and is provided on the central peripheral surface of the main body 22 so as to project in the radial direction of the main body 22.

The upper support neck 26 is a rectangular member provided so as to project upward from the upper end surface of the main body 22 of the trunnion ring 20. The upper support neck 26 is provided with a square hole penetrating in the left-right direction. The lower support neck 27 is a rectangular member provided so as to project downward from the lower end surface of the main body 22.

The upper support neck 26 is inserted into the square hole of the upper support portion 14, and a wedge-shaped cotter 18 is inserted into the square hole of the upper support neck 26 in the left-right direction so as to sandwich the upper support portion 14. As a result, the furnace body 12 and the trunnion ring 20 are fixed in the vertical direction when the converter is not tilted. Further, the lower support neck 27 is fixed in the left-right direction by the lower support portion 16.

FIG. 2 is a partial cross-sectional view and a top view of part A in FIG. FIG. 2A is a partial cross-sectional view of part A. FIG. 2B is a top view of part A. As shown in FIG. 2A, the square hole of the upper support portion 14 is wider than the width of the corresponding upper support neck 26. By making the square hole of the upper support portion 14 wider than the width of the corresponding upper support neck 26 in this way, the upper support neck 26 can be reliably inserted into the square hole of the upper support portion 14. On the other hand, if the width of the square hole of the upper support portion 14 is wider than the width of the upper support neck 26, a gap is generated between the upper support neck 26 and the square hole. When a gap is created between the upper support neck 26 and the square hole, the furnace body 12 moves relative to the trunnion ring 20 when the converter 10 is tilted, and the movement causes an impact on the square hole of the upper support portion 14. Join. In order to avoid the occurrence of this impact, two shims 30 are provided in the gap between the square hole of the upper support portion 14 and the upper support neck 26. The two shims 30 fix the furnace body 12 and the trunnion ring 20 in the left-right direction when the converter 10 is tilted.

Further, recesses 28 are provided at two corners where the main body 22 and the upper support neck 26 are connected. By providing the recess 28 in the corner where the main body 22 and the upper support neck 26 are connected, the stress concentration in the corner when the converter is tilted is suppressed by the weight of the converter 10 and the weight of the molten steel, and the corner is cracked. Is less likely to occur. A protective material 29 having a hardness higher than that of the steel material used for the upper support portion 14 is provided in the recess 28 of the converter 10 to which the converter repair method according to the present embodiment is applied. As the protective material 29, for example, a cemented carbide obtained by mixing tungsten carbide (WC) and cobalt as a binder and sintering them is used. In order to further increase the hardness, a cemented carbide to which titanium carbide, tantalum carbide (TaC) or the like is added may be used as the protective material 29.

FIG. 3 is a partial cross-sectional view showing a part A after the converter 10 has been used for a long period of time. When the converter 10 is used for a long period of time, the contact surface where the upper support portion 14 comes into contact with the shim 30 is worn and the contact surface becomes rough. If the contact surface of the upper support portion 14 becomes rough, the shim 30 and the upper support portion 14 come into contact with each other at a point instead of a surface, so that the contact between the shim 30 and the upper support portion 14 becomes unstable. Further, when the shim 30 and the upper support portion 14 come into contact with each other at a point, the load of the furnace body 12 is concentrated on the point contact portion of the shim 30 when the converter 10 is tilted, and the shim 30 is deformed. Due to this unstable contact and deformation, the shim 30 may come off during tilting due to the vibration of the converter 10. Therefore, when the contact surface of the upper support portion 14 in contact with the shim 30 is worn and roughened, it is necessary to cut the contact surface and expose the contact surface to a smooth surface. When the contact surface of the upper support portion 14 is cut, the gap between the square hole of the upper support portion 14 and the upper support neck 26 becomes larger, but a thickened shim is provided in accordance with the cutting amount of the upper support portion 14. By newly providing it, the gap can be eliminated.

FIG. 4 is a schematic view showing a state in which the contact surface of the upper support portion 14 is cut by the liquid jet cutting equipment 80. FIG. 4A is a view seen from the direction of arrow B in FIG. FIG. 4B is a view seen from the cutting direction of FIG. 4A. Note that in FIG. 4B, equipment other than the nozzle is not shown.

In the converter repair method according to the present embodiment, the contact surface of the upper support portion 14 is cut by the liquid jet cutting equipment 80. The liquid jet cutting equipment 80 includes a liquid jet cutting device 40, a driving device 50, and a control device 60. The liquid jet cutting device 40 has a nozzle 42, an abrasive inlet 44, and an infrared sensor 45. High-pressure water 46 is sent to the nozzle 42, and a water jet is ejected from the tip of the nozzle 42 to cut the side surface of the upper support portion 14 facing the upper support neck 26. Further, when a water jet containing the abrasive 48 is ejected to cut the side surface of the upper support portion 14, the abrasive 48 is charged from the abrasive inlet 44.

The infrared sensor 45 measures the temperature of the cut surface of the upper support portion 14 that is cut by the ejection of the water jet. The infrared sensor 45 is an example of a device capable of measuring the temperature of the cut surface of the upper support portion 14 to be cut in a non-contact manner, and another device may be used as long as the device can measure the temperature of the cut surface in a non-contact manner. You may.

The drive device 50 moves the liquid jet cutting device 40 including the nozzle 42 in the cutting direction shown in FIG. 4A. The drive device 50 includes two columns 52, a drive motor 54, a screw shaft 58, and a pulley 56. The drive motor 54 is rotationally driven at a predetermined rotation speed. The pulley 56 transmits the drive of the drive motor 54 to the screw shaft 58. When the screw shaft 58 rotates at a predetermined rotation speed, the liquid jet cutting device 40 moves at a predetermined speed while ejecting a water jet from the nozzle 42, and cuts the contact surface of the upper support portion 14.

The control device 60 controls the operation of the liquid jet cutting device 40 and the operation of the drive device 50. The control device 60 receives temperature data from the infrared sensor 45 at predetermined intervals, for example, at intervals of 1 second, and controls the ejection of the water jet from the drive motor 54 and the nozzle 42 using the temperature data. The control device 60 is, for example, a computer including a CPU and a storage device, and the storage device stores in advance a program necessary for operating the liquid jet cutting device 40 and the drive device 50 and data used for the program. When the program is executed by the CPU of the control device 60, the upper support portion 14 is cut by the liquid jet cutting equipment 80.

As shown in FIG. 4B, the liquid jet cutting device 40 cuts the inside of the worn contact surface of the upper support portion 14. Due to the ejection of the water jet, frictional heat is generated on the cut surface of the upper support portion 14, so that the temperature of the cut surface rises. When the ejection pressure of the water jet is constant, when the moving speed of the liquid jet cutting device 40 becomes slow, the cutting by the water jet proceeds and the frictional heat increases, so that the temperature of the cut surface rises. On the other hand, when the moving speed of the liquid jet cutting device 40 is increased, the cutting by the water jet is slowed down, so that the frictional heat is reduced and the temperature of the cut surface is lowered. Further, when the hardness of the steel material to be cut increases, the frictional heat increases and the temperature of the cut surface rises, and when the hardness of the steel material to be cut decreases, the frictional heat decreases and the temperature of the cut surface decreases.

In the converter 10 repaired by the converter repair method according to the present embodiment, a protective material 29 having a hardness higher than that of the steel material used for the upper support portion 14 is placed below the cutting position of the upper support portion 14 to be cut. It is provided. The side surface of the upper support portion 14 is cut by the water jet, and when the water jet reaches the protective material 29, the protective material 29 having a hardness higher than that of the steel material used for the upper support portion 14 starts to be cut. The temperature rises. The storage device of the control device 60 has a threshold value 1 for distinguishing in advance the temperature of the cut surface when the steel material of the upper support portion 14 is cut by the water jet and the temperature when the protective material 29 is cut by the water jet. When the temperature indicated by the temperature data output from the infrared sensor 45 is equal to or higher than the threshold value 1, the control device 60 determines that the cutting of the steel material of the upper support portion 14 is completed, and cuts the liquid jet. End the cutting by the device.

In the converter repair method according to the present embodiment, cutting experiments of the steel material and the protective material 29 used for the upper support portion 14 are performed by ejecting a water jet at various moving speeds and various pressures, and these steel materials are used. A threshold value 1 for distinguishing the temperature of the cut surface when cut is set in advance. Then, the temperature of the cut surface is measured by the infrared sensor 45 while cutting the upper support portion 14 by the ejection of the water jet, and when the temperature indicated by the temperature data acquired from the infrared sensor 45 is less than the threshold value 1, the control device 60 Determines that the upper support portion 14 has not been cut, and continues cutting by the liquid jet cutting device 40. On the other hand, when the temperature indicated by the temperature data acquired from the infrared sensor 45 is the threshold value 1 or more, the control device 60 determines that the upper support portion 14 has been cut and ends the cutting by the liquid jet cutting device 40.

As described above, in the converter repair method according to the present embodiment, the cut state of the cut surface of the upper support portion 14 is easily grasped by measuring the temperature of the cut surface with the infrared sensor 45, and the temperature is predetermined. When the temperature exceeds the specified threshold value 1, it is determined that the upper support portion 14 has been cut, and the cutting by the liquid jet cutting device 40 is terminated. As a result, the converter 10 can be repaired by cutting the upper support portion 14 without damaging the main body 22 of the trunnion ring 20.

In the cutting of the upper support portion 14 by the water jet, if the moving speed of the liquid jet cutting device 40 is increased, the cutting of the upper support portion 14 by the water jet may be insufficient and a portion may not be cut. On the other hand, if the moving speed of the liquid jet cutting device 40 is made too slow, the water jet may hit the cut surface too much and the cut surface may be wavy.

As described above, since the temperature of the cut surface changes depending on the moving speed of the liquid jet cutting device 40, conversely, a threshold value of the temperature at which it can be determined whether or not the upper support portion 14 is sufficiently cut by the water jet. 2. And the threshold value 3 of the temperature at which it can be determined whether or not the cut surface is wavy due to the water jet hitting too much are set in advance, and the temperature data of the cut surface acquired from the infrared sensor 45, the threshold value 2 and the threshold value 3 are used. The control device 60 may control the moving speed of the liquid jet cutting device 40. The threshold value 2 and the threshold value 3 are set to a temperature lower than the threshold value 1 in order to favorably cut the upper support portion 14 without being mistaken for cutting the protective material 29. Further, the threshold value 2 is a temperature lower than the threshold value 3.

When controlling the moving speed of the liquid jet cutting device 40 using the temperature data of the cut surface, the control device 60 determines that cutting by the liquid jet cutting device 40 is insufficient when the temperature of the cut surface is less than the threshold value 2. Judging, the rotation speed of the drive motor 54 is lowered, and the moving speed of the liquid jet cutting device 40 is slowed down. As a result, the cutting time per unit length by the liquid jet cutting device 40 becomes long, and the upper support portion 14 can be cut by using the liquid jet cutting device 40.

The control device 60 determines that cutting by the liquid jet cutting device 40 is sufficient when the temperature of the cut surface is equal to or more than the threshold value 2 and less than the threshold value 3, and maintains the moving speed of the liquid jet cutting device 40 as it is.

Further, the control device 60 determines that when the temperature of the cut surface is equal to or higher than the threshold value 3, the water jet may hit the steel material too much and the cut surface may undulate, and the rotation speed of the drive motor 54 is increased to increase the rotation speed of the drive motor 54 to increase the rotation speed of the drive motor 54. Increase the movement speed of. As a result, the cutting time of the liquid jet cutting device 40 is shortened, and the amount of water jet that has hit the steel material too much is reduced. As a result, it is possible to suppress the occurrence of waviness on the cut surface cut by the water jet.

FIG. 5 is a graph conceptually showing the relationship between the temperature of the cut surface and the cutting time when the moving speed of the liquid jet cutting device 40 is controlled by the temperature of the cut surface. The vertical axis of FIG. 5 is the temperature (° C.) of the cut surface, and the horizontal axis is the cutting time (s).

The threshold value 1 in FIG. 5 is a threshold value of a temperature at which the temperature of the cut surface when the steel material of the upper support portion 14 is cut and the temperature of the cut surface when the protective material 29 is cut by a water jet can be distinguished. The threshold value 2 is a temperature threshold value that can be utilized for determining whether or not the upper support portion 14 can be cut by the water jet. Further, the threshold value 3 is a temperature threshold value that can be utilized for determining whether or not the cut surface of the upper support portion 14 is wavy due to excessive hitting of the water jet.

For example, at the start of cutting, the temperature of the cut surface is less than the threshold value 2, so the speed is 0.5 mm / min slower than the moving speed of the reference liquid jet cutting device 40 of 4.5 mm / min. As a result, the cutting time per unit length by the liquid jet cutting device 40 is increased, the cutting efficiency is increased, and the temperature of the joint surface is increased. If the temperature of the cut surface does not rise even after a predetermined time has elapsed by slowing down by 0.5 mm / min, the moving speed of the liquid jet cutting device 40 is further slowed down by 0.5 mm / min. The control device 60 repeats this operation until the temperature of the joint surface rises.

After that, when the temperature of the joint surface rises and the temperature of the cut surface becomes the threshold value 2 or more and less than the threshold value 3, the control device 60 maintains the moving speed of the liquid jet cutting device 40 as it is. After that, when the temperature of the joint surface further rises and the temperature of the joint surface reaches the threshold value of 3 or more, the control device 60 increases the moving speed of the liquid jet cutting device 40 by 0.5 mm / min. As a result, the cutting time per unit length by the liquid jet cutting device 40 is shortened, the amount of water jets hitting the joint surface is reduced, and the occurrence of waviness is suppressed. If the temperature of the cut surface does not decrease even after a predetermined time has passed by increasing the speed by 0.5 mm / min, the moving speed of the liquid jet cutting device 40 is further increased by 0.5 mm / min. The control device 60 repeats this operation until the temperature of the joint surface rises.

When the cutting by the liquid jet cutting device 40 is continued and the cutting of the upper support portion 14 is completed, the liquid jet cutting device 40 starts cutting the protective material 29. The hardness of the protective material 29 is higher than that of the steel material of the upper support portion 14. Therefore, the temperature of the cut surface rises sharply due to the difference in hardness. Since the temperature of the cut surface becomes the threshold value 1 or more due to this increase in temperature, the control device 60 determines that the cutting of the upper support portion 14 is completed, and finishes the cutting of the upper support portion 14 by the liquid jet cutting device 40. , Stops the ejection of the water jet from the nozzle 42.

As described above, in the converter repair method according to the present embodiment according to the present embodiment, the upper support portion 14 is cut by the liquid jet cutting device 40 when the temperature of the cut surface becomes a predetermined threshold value 1 or more. Is completed, and the cutting of the upper support portion 14 by the liquid jet cutting device 40 is completed. As a result, the cut state of the upper support portion can be detected even in the vicinity of the contact surface of the upper support portion where there is no space, so that the side surface of the upper support portion 14 is cut and rolled without damaging the main body 22 of the trunnion ring 20. The furnace can be repaired.

Further, a threshold value 2 that can be used for determining whether or not the upper support portion 14 can be cut and a threshold value 3 that can be used for determining whether or not the cut surface of the upper support portion 14 is wavy are set, and the temperature of the cut surface is set. , The threshold value 2 and the threshold value 3 may be used to control the moving speed of the liquid jet cutting device 40. As a result, the upper support portion 14 can be cut satisfactorily while suppressing the occurrence of waviness on the cut surface of the upper support portion 14.

The cutting conditions for cutting the upper support portion 14 using the liquid jet cutting device 40 are shown in Table 1 below. Further, the above-mentioned threshold value 1 was set to 90 ° C., the threshold value 2 was set to 50 ° C., and the threshold value 3 was set to 70 ° C. By controlling the moving speed of the liquid jet cutting device 40 by using the threshold values 1 to 3 and the temperature of the cut surface, the main body 22 of the trunnion ring 20 is not damaged and the cut surface in the upper support portion 14 is wavy. The upper support portion 14 could be cut while suppressing the above, and the converter 10 could be repaired.

Further, in the present embodiment, an example in which the control device 60 controls the operation of the liquid jet cutting device 40 and the operation of the drive device 50 is shown, but the present invention is not limited to this. For example, even if an operator controls the liquid jet cutting device 40 and the driving device 50 by using the temperature of the cut surface output from the infrared sensor 45 to cut the contact surface of the upper support portion 14 of the converter 10. good.

10 Rotating furnace 12 Furnace body 14 Upper support part 16 Lower support part 18 Cotter 20 Trunnion ring 22 Main body 24 Trunnion shaft 26 Upper support neck 27 Lower support neck 28 Recessed 29 Protective material 30 Sim 40 Liquid jet cutting device 42 Nozzle 44 Polishing agent Mouth 45 Infrared sensor 46 High-pressure water 48 Abrasive agent 50 Drive device 52 Strut 54 Drive motor 56 Pulley 58 Screw shaft 60 Control device 70 Arrow 80 Liquid jet cutting equipment

Claims (5)

It is a repair method for converters used in steelmaking.
The converter has a furnace body and a trunnion ring.
On the peripheral surface of the furnace body, an upper support portion having a square hole that protrudes and penetrates in the radial direction of the furnace body is provided.
The trunnion ring is provided at a corner where the trunnion ring main body, the upper support neck protruding from the trunnion ring main body and inserted into the square hole of the upper support portion, and the trunnion ring main body and the upper support neck are connected. It has a protective material that is arranged and has a higher hardness than the steel material used for the upper support portion.
When cutting the contact surface, the water jet ejected from the moving nozzle exposes the contact surface facing the upper support neck side of the square hole to a smooth surface.
The nozzle is arranged at a position facing the protective material across the upper support portion, and the water jet is ejected in the direction in which the upper support portion and the protective material are located.
The temperature of the collision position of the water jet on the upper support portion or the protective material is measured, and the temperature is measured.
When the temperature at the collision position becomes a threshold value of 1 or more that distinguishes between the temperature of the cut surface when the upper support portion is cut by the water jet and the temperature when the protective material is cut by the water jet. , A method for repairing a converter, which completes cutting by the water jet. In order to surface the contact surface facing the upper support neck side in the square hole to a smooth surface, the threshold value 1 is the case where the upper support portion is cut by the water jet when cutting the contact surface. The method for repairing a converter according to claim 1, which is a threshold value for distinguishing the temperature of the cut surface of the water jet and the temperature when the protective material is cut by the water jet. Wherein when the temperature of the cut surface becomes lower than the threshold value 2 to make the determination whether or not it can cut the upper support portion, the moving speed before Symbol nozzle slowed by raising the temperature of the cutting plane,
When the temperature of the cut surface reaches a threshold value of 3 or more used for determining whether or not the contact surface of the upper support portion is wavy, the nozzle moves to suppress the waviness of the cut surface. Increase the speed to reduce the temperature of the cut surface.
The threshold value 2 and the threshold value 3 are lower than the threshold value 1 because the upper support portion is cut without being mistaken for cutting the protective material, and the threshold value 2 is a temperature lower than the threshold value 3. The method for repairing a converter according to claim 1 or 2. The method for repairing a converter according to claim 3, wherein the threshold value 2 is utilized for determining whether or not the upper support portion can be cut. The method for repairing a converter according to claim 3 or 4, wherein the threshold value 3 is utilized for determining whether or not waviness occurs on the cut surface of the upper support portion.

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