Electric furnace

Abstract

To provide an electric furnace capable of improving the service life of a refractory wall.SOLUTION: The electric furnace includes a furnace body 20 including a melting chamber 21 in which a metallic material is melted, and electrodes for melting the metallic material in the melting chamber 21, the furnace body 20 includes a sidewall 21W constituting the melting chamber 21, the sidewall 21W includes an outer skin 23 and a fireproof wall 24 located on an inner circumferential side of the outer skin 23, and at least a part of the sidewall 21W includes a cooling portion 25 including a support surface 25S1 that presses an upper surface 24S of the fireproof wall 24. The support surface 25S1 presses the upper surface 24S of the fire wall 24 from a first end 24E1 on the outer skin 23 side to a position on the second end 24E1 side with respect to a midpoint 24E2 between the first end 24P and the second end 24E2 on the inner peripheral side.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an electric furnace. [Background technology]

[0002] An electric furnace for melting metal materials includes a side wall that surrounds molten steel, which is the molten metal material. The side wall includes a refractory wall that contacts the molten steel and a cooling section arranged above the refractory wall. The refractory wall is made of a refractory material such as refractory bricks. The cooling section is, for example, a metal water-cooled panel. For example, Patent Document 1 describes a furnace wall structure of an electric furnace that includes an iron water-cooled panel and a copper water-cooled panel as an example of a cooling section. Patent Document 1 illustrates a configuration in which the water-cooled panel is arranged on the outer periphery of the upper surface of the refractory wall relative to the inner periphery end. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-322470 Summary of the Invention [Problem to be solved by the invention]

[0004] The refractory bricks that make up the refractory wall have low thermal conductivity. Therefore, the temperature of the inner peripheral portion of the refractory brick, which is closer to the molten steel, is higher than that of the outer peripheral portion, which is farther from the molten steel. This temperature difference causes a difference in the amount of thermal expansion between the inner and outer peripheral portions of the refractory brick. Furthermore, because a water-cooled panel is disposed above the outer peripheral portion of the refractory brick, when thermal expansion occurs in the refractory brick, the upper surface of the outer peripheral portion of the refractory brick is pressed down by the water-cooled panel. On the other hand, no water-cooled panel is disposed above the inner peripheral portion of the refractory brick. Therefore, cracks are likely to occur starting from the boundary between the inner peripheral portion of the refractory brick, which has a small amount of thermal expansion and is pressed down from above by the water-cooled panel, and the outer peripheral portion, which has a large amount of thermal expansion and is not in contact with the water-cooled panel. [Means for solving the problem]

[0005] An electric furnace for solving the above problem comprises a furnace body having a melting chamber in which a metal raw material is melted, and an electrode for melting the metal raw material in the melting chamber, the furnace body having a side wall that constitutes the melting chamber, the side wall having an outer shell and a fire-resistant wall located on the inner side of the outer shell, at least a portion of the side wall having a cooling section having a support surface that presses against the upper surface of the fire-resistant wall, the support surface pressing against the upper surface of the fire-resistant wall from a first end on the outer shell side to a position closer to the second end than the midpoint between the first end and a second end on the inner side.

[0006] According to the above configuration, in the portion of the side wall that includes the cooling section, at least a portion of the inner circumferential side of the fire wall, which is subject to a large thermal load, is supported by the support surface of the cooling section. This reduces the amount of thermal expansion of the inner circumferential side of the fire wall, which is prone to relatively large thermal expansion, in the portion of the side wall that includes the cooling section, thereby suppressing cracks on the upper surface of the fire wall and the resulting damage and detachment of the fire wall. As a result, the life of the fire wall can be improved, thereby reducing the frequency of repairs. In the above electric furnace, the cooling section may have an inner circumferential surface that faces the inner circumferential side, and the inner circumferential surface may protrude inward as it extends downward.

[0007] An electric furnace for solving the above problems comprises a furnace body having a melting chamber in which a metal raw material is melted, and an electrode for melting the metal raw material in the melting chamber, the furnace body having a side wall that constitutes the melting chamber, the side wall having an outer shell and a fire-resistant wall located on the inner periphery of the outer shell, at least a portion of the side wall having a cooling section having a support surface that presses down on the upper surface of the fire-resistant wall, the cooling section having an inner periphery surface that faces the inner periphery, and the inner periphery surface protruding inward as it extends downward.

[0008] If the cooling section has an inner surface that protrudes inward as it extends downward, as in the cooling section of the above configuration, the support surface of the cooling section also protrudes inward. Therefore, in the portion of the side wall that includes the cooling section, the support surface protrudes inward, which effectively holds down the inner portion of the fire wall, which is prone to relatively large thermal expansion, thereby reducing the amount of thermal expansion of the inner portion. This prevents cracks from occurring on the upper surface of the fire wall, and the resulting damage and detachment of the fire wall. As a result, the lifespan of the fire wall can be improved, reducing the frequency of repairs.

[0009] In the electric furnace, the portion of the side wall that includes the cooling section may further include a monolithic refractory material provided across the refractory wall and the cooling section. According to the above configuration, by covering the cooling section with a spray material, contact and sparks between the metal raw material supplied to the furnace body and the cooling section can be more reliably suppressed.

[0010] In the electric furnace, the inner peripheral surface of the cooling section facing the inner peripheral side may include an inclined surface that slopes upward so as to approach the outer shell. With this configuration, since the inner peripheral surface slopes from the end of the support surface toward the outer peripheral side of the furnace body, contact and sparks between the metal raw material supplied to the furnace body and the cooling section can be more reliably suppressed.

[0011] In the electric furnace, the cooling section may include a bottom wall including the support surface and an inner wall including the inner peripheral surface, and the bottom wall and the inner wall each may have an outer plate forming an outer surface and a flow path forming member disposed inside the outer plate. With the above configuration, a cooling section excellent in strength and cooling efficiency can be realized with a simple structure.

[0012] In the electric furnace, the side wall may be configured to include the cooling section over the entire circumferential direction. With this configuration, cracks on the upper surface of the refractory wall can be suppressed over the entire circumferential direction of the side wall, and the resulting damage and falling off of the refractory wall can be suppressed. As a result, the life of the refractory wall can be improved over the entire circumferential direction of the side wall, thereby reducing the frequency of repairs.

[0013] The electric furnace may further include a shaft serving as a supply path for supplying the raw metal material to the melting chamber, the furnace body being disposed in the side wall and including a shaft connection port to which the shaft is connected, and the cooling unit may be disposed in a portion of the side wall facing the shaft connection port. Even if a cooling unit with a larger support surface is disposed in the portion of the side wall facing the shaft connection port to hold down the inner peripheral portion of the fire-resistant wall, the cooling unit is unlikely to come into contact with the raw metal material being supplied to the melting chamber. Therefore, if the cooling unit is disposed in the portion of the side wall facing the shaft connection port, the cooling unit can effectively prevent the raw metal material being supplied to the melting chamber from coming into contact with the cooling unit while suppressing the occurrence of cracks on the upper surface of the fire-resistant wall.

[0014] In the electric furnace, the furnace body may be configured to include a tapping hole and a slag discharge port that are arranged opposite each other in the circumferential direction of the side wall, the tapping hole, the slag discharge port, and the shaft connection port are arranged at different positions in the circumferential direction of the side wall, and the refractory wall and the cooling section are located continuously between the tapping hole and the slag discharge port in a portion of the side wall that faces the shaft connection port. With this configuration, it is possible to suppress cracks in the refractory wall and the resulting damage and falling off of the refractory wall in the entire portion of the side wall between the tapping hole and the slag discharge port and that faces the shaft connection port.

[0015] In the electric furnace, the upper surface of the refractory wall may be made of a shaped refractory material, and a monolithic refractory layer may be disposed at least partially between the support surface and the upper surface of the refractory wall, and the support surface may press the upper surface of the refractory wall via the monolithic refractory layer. According to the above configuration, the force applied to the cooling section due to thermal expansion of the monolithic refractory material constituting the refractory wall can be reduced by the monolithic refractory layer.

[0016] In the electric furnace, the thickness of the monolithic refractory layer may be set based on the height and thermal expansion coefficient of the monolithic refractory located below the monolithic refractory layer, and the temperature rise of the monolithic refractory during use of the electric furnace. According to the above configuration, a sufficient thickness can be ensured for the monolithic refractory layer to reduce the force applied to the cooling section due to the thermal expansion of the monolithic refractory.

[0017] In the electric furnace, the monolithic refractory layer may be made of a stamped material. With this configuration, the durability of the monolithic refractory layer can be ensured. [Effects of the Invention]

[0018] According to the present invention, the life of the fire-resistant wall can be improved. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a top view of an electric furnace. [Figure 2] FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. [Figure 3] FIG. 3 is an enlarged cross-sectional view of a main part of the side wall. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a main part of a side wall in a state where the fire-resistant wall has been damaged and repaired with a spraying material. [Figure 5] FIG. 5 is an enlarged cross-sectional view of a main part of a comparative example, showing the configuration of a side wall in which only the outer periphery of the upper surface of the fire-resistant wall is pressed by a cooling portion. [Figure 6] FIG. 6 is an enlarged cross-sectional view of a main part showing a modified example of the side wall in which a chamfered portion is provided on the inner circumferential side of the cooling portion. [Figure 7] FIG. 7 is a schematic diagram showing a cross-sectional structure of the cooling section shown in FIG. [Figure 8] FIG. 8 is an enlarged cross-sectional view of a main part showing a modified example of the side wall in which a monolithic refractory layer is provided between the upper surface of the fire-resistant wall and the support surface of the cooling section. DETAILED DESCRIPTION OF THE INVENTION

[0020] [Overall configuration] An embodiment of an electric furnace according to the present invention will be described below with reference to FIGS. As shown in Fig. 1, electric furnace 10 includes furnace body 20 and shaft 30. Furnace body 20 includes melting chamber 21. Metal raw material is supplied to melting chamber 21 from shaft 30. The top of melting chamber 21 is closed by furnace lid 22 (see Fig. 2), but Fig. 1 does not show furnace lid 22.

[0021] The furnace body 20 includes a side wall 21W that constitutes the melting chamber 21. The furnace body 20 also includes a tapping port 21A, a slag discharge port 21B, and a shaft connection port 21C. The tapping port 21A is an opening for tapping molten steel, which is obtained by melting raw metal materials, from the melting chamber 21. The slag discharge port 21B is an opening for discharging slag (slag) generated as the raw metal materials are melted from the melting chamber 21. The shaft connection port 21C is an opening to which the shaft 30 is connected. The side wall 21W may include blowing holes for blowing oxygen, carbon, etc. into the melting chamber 21.

[0022] The tapping hole 21A, the slag discharge port 21B, and the shaft connection port 21C are arranged at different positions in the circumferential direction of the side wall 21W. For example, in the furnace body 20, the tapping hole 21A and the slag discharge port 21B are arranged opposite each other in the circumferential direction of the side wall 21W. Molten steel produced in the melting chamber 21 is discharged from the tapping hole 21A by tilting the furnace body 20. Slag produced in the melting chamber 21 is discharged from the slag discharge port 21B by tilting the furnace body 20.

[0023] The side wall 21W includes a first portion 21W1 and a second portion 21W2. The first portion 21W1 is a portion located between the tapping opening 21A and the slag discharge opening 21B in the circumferential direction of the side wall 21W, and is a portion where the shaft connection opening 21C is disposed. The second portion 21W2 is a portion located between the tapping opening 21A and the slag discharge opening 21B in the circumferential direction of the side wall 21W, and is a portion facing the shaft connection opening 21C. That is, the tapping opening 21A, the shaft connection opening 21C, the slag discharge opening 21B, and the second portion 21W2 are arranged in this order in the circumferential direction of the side wall 21W.

[0024] 2, the shaft 30 is a cylindrical member having an internal space. The internal space of the shaft 30 is connected to the melting chamber 21 via the shaft connection port 21C. That is, the shaft 30 serves as a supply path for supplying the metal raw material M1 to the melting chamber 21.

[0025] The shaft 30 has a charging port and an exhaust port for exhausting gas generated in the melting chamber 21. As an example, the exhaust port is located between the charging port and the connecting portion with the shaft connecting port 21C.

[0026] The electric furnace 10 includes a pusher 40. The pusher 40 pushes the metal raw material M1 in the shaft 30 toward the melting chamber 21, thereby moving the metal raw material M1 from the shaft 30 to the melting chamber 21. The operation of the pusher 40 is controlled by a drive device (not shown).

[0027] The electric furnace 10 includes electrodes 50. The electrodes 50 are located inside the melting chamber 21 of the furnace body 20, penetrating the furnace lid 22. The number of electrodes 50 may be one or more. As an example, the electric furnace 10 includes three electrodes 50. The electrodes 50 are, for example, graphite electrodes. When AC power is supplied to the electrodes 50, an arc discharge is induced inside the melting chamber 21.

[0028] After being inserted into the shaft 30, the metal raw material M1 is pushed out from the shaft 30 into the melting chamber 21 by the pusher 40. The metal raw material M1 pushed out into the melting chamber 21 is melted by an arc discharge induced by the electrode 50. As a result, molten steel M2 is produced in the melting chamber 21. Slag S derived from the metal raw material M1 is produced on the surface of the molten steel M2.

[0029] The top of the melting chamber 21 is closed by a furnace lid 22. Therefore, gas generated as the metal raw material M1 melts is discharged from the exhaust port through the shaft 30. The gas passing through the shaft 30 preheats the metal raw material M1 located inside the shaft 30. In other words, by discharging the gas generated as the metal raw material M1 melts from the shaft 30, the energy required to preheat the metal raw material M1 located inside the shaft 30 can be reduced.

[0030] [Side Wall Configuration] As shown in FIG. 3 , the second portion 21W2 of the side wall 21W includes an outer skin 23, a fireproof wall 24, a cooling section 25, and a spraying material 26. In the side wall 21W, the fireproof wall 24 and the cooling section 25 are located on the inner circumferential side of the outer skin 23. The cooling section 25 is located above the fireproof wall 24. The spraying material 26 is an example of a monolithic refractory that covers the inner surfaces of the fireproof wall 24 and the cooling section 25, spanning the fireproof wall 24 and the cooling section 25. Note that the configuration of the side wall 21W is not limited to a configuration in which the second portion 21W2 of the side wall 21W includes the cooling section 25, as long as at least a portion of the side wall 21W includes the cooling section 25. In other words, "at least a portion of the side wall 21W includes the cooling section 25" means that the cooling section 25 is provided on at least a portion of the side wall 21W in the circumferential direction.

[0031] 3 also illustrates an undamaged state in which the fireproof wall 24 constituting the side wall 21W has not been damaged by the thermal load from the molten steel M2 since it was formed. The undamaged state includes, for example, a state in which the fireproof wall 24 has been formed on the side wall 21W and has not been used or has just started to be used, and a state in which part or all of the fireproof wall 24 has been replaced and has not been used or has just started to be used.

[0032] The outer skin 23 is, for example, an iron shell. The refractory wall 24 is composed of a shaped refractory material such as multiple layers of refractory bricks. Examples of refractories that make up the refractory bricks include alumina (Al2O3), magnesia (MgO), magnesia-carbon (MgO-C), and spinel-based refractories. The upper surface 24S of the refractory wall 24 is composed of a shaped refractory material. In addition, in the refractory wall 24, a stamping material made of magnesia or the like, or a filling material made of a spinel-based refractory or the like may be provided on the inner periphery (particularly the lower side) of the refractory bricks. The cooling section 25 is made of iron or copper, or an alloy containing iron or copper. The cooling section 25 is preferably made of copper or a copper alloy, which has particularly high thermal conductivity. The spraying material 26 is made of an inorganic material used as a refractory material, for example, magnesia.

[0033] The cooling section 25 is configured, for example, by a water-cooled cooling panel with a water channel provided therein. The cooling section 25 is arranged above the molten metal surface MS, which is the surface of the slag S or molten steel M2. The cooling section 25 includes a first cooling section 25A located above the fire-resistant wall 24 and a second cooling section 25B located above the first cooling section 25A. The first cooling section 25A contacts the fire-resistant wall 24, for example.

[0034] The first cooling section 25A receives stress from the fire-resistant wall 24 when the fire-resistant wall 24 thermally expands. It is preferable that the first cooling section 25A be fixed to the outer skin 23 by a fixing means stronger than that of the second cooling section 25B so that the first cooling section 25A can withstand the stress from the fire-resistant wall 24. The first cooling section 25A is fixed to the outer skin 23 by, for example, bolts at multiple locations. The second cooling section 25B is fixed to the outer skin 23 by a cotter.

[0035] The first cooling section 25A is located closer to the molten steel M2 than the second cooling section 25B, and is therefore preferably made of a metal material with higher thermal conductivity than the second cooling section 25B. This makes it easier for the first cooling section 25A to be cooled by cooling water, thereby reducing the thermal load on the first cooling section 25A. For example, the first cooling section 25A is made of copper or a copper alloy, and the second cooling section 25B is made of iron or an iron alloy (steel).

[0036] The thickness of the second cooling section 25B is configured to be thinner than the thickness of the upper end of the fire-resistant wall 24 from the viewpoint of reducing the weight of the furnace body 20. In addition, the first cooling section 25A has a shape that protrudes inward as it extends downward, so as to connect the lower end of the second cooling section 25B and the upper end of the fire-resistant wall 24.

[0037] Cooling section 25 has support surface 25S1 that supports upper surface 24S of fire-resistant wall 24. Support surface 25S1 is the lower surface of first cooling section 25A. Support surface 25S1 has inner peripheral end 25E. Upper surface 24S has first outer peripheral end 24E1 that faces outer skin 23, and second inner peripheral end 24E2. In a cross-sectional view perpendicular to the circumferential direction of side wall 21W, a point on upper surface 24S where the distance from first end 24E1 and the distance from second end 24E2 are equal is defined as midpoint 24P, and the distance from first end 24E1 to second end 24E2 is defined as length L.

[0038] Support surface 25S1 presses down on upper surface 24S of fire-resistant wall 24 from first end 24E1 to at least a position closer to second end 24E2 than midpoint 24P. In other words, inner peripheral end 25E of support surface 25S1 is located on upper surface 24S of fire-resistant wall 24 closer to second end 24E2 than midpoint 24P.

[0039] That is, in a cross-sectional view perpendicular to the circumferential direction of side wall 21W, support surface 25S1 presses down on upper surface 24S of fire wall 24 from first end 24E1 to a position at least 50% closer to second end 24E2 than 50% of length L. In other words, upper surface 24S of fire wall 24 is pressed down by support surface 25S1 of cooling section 25 over an area that is greater than 50% of the entire upper surface 24S of fire wall 24 from the outer periphery.

[0040] It is preferable that as large an area as possible of the upper surface 24S, from the outer periphery to the inner periphery, be held down by the support surface 25S1. Therefore, it is preferable that 60% or more of the area of ​​the entire upper surface 24S from the outer periphery is held down by the support surface 25S1, and it is even more preferable if 70% or more of the area is held down by the support surface 25S1. Furthermore, the effect of the present invention is even greater if nearly the entire area (almost the entire area) of the upper surface 24S from the outer periphery to the inner periphery is held down by the support surface 25S1. Therefore, it is even more preferable that 80% or more of the area of ​​the entire upper surface 24S from the outer periphery is held down by the support surface 25S1, and it is particularly preferable if 90% or more of the area is held down by the support surface 25S1.

[0041] In this embodiment, support surface 25S1 is disposed so as to overlap second end 24E2 on the inner periphery side of upper surface 24S of fire wall 24. That is, support surface 25S1 presses the entire upper surface 24S of fire wall 24 so as to contact a portion of upper surface 24S of fire wall 24 that includes second end 24E2 on the inner periphery side. Support surface 25S1 is disposed, for example, so that inner periphery side end 25E of support surface 25S1 overlaps second end 24E2 on the inner periphery side of upper surface 24S of fire wall 24. In this case, contact between cooling portion 25 and metal source material M1 and the generation of sparks can be more effectively suppressed than in a configuration in which support surface 25S1 protrudes more inward than fire wall 24, for example.

[0042] The cooling section 25 has an inner peripheral surface 25S2 facing the inner peripheral side. The inner peripheral surface 25S2 includes an inclined surface 25AS. The inclined surface 25AS is a surface of the inner peripheral surface 25S2 that is provided in the first cooling section 25A. The inclined surface 25AS protrudes toward the inner peripheral side as it extends downward. In detail, the inclined surface 25AS is inclined toward the outer peripheral side so as to approach the outer skin 23 as it extends upward from the inner peripheral end 25E of the support surface 25S1, which is the lower surface. The lower end of the inner peripheral surface 25S2 is covered with the spray material 26.

[0043] By making the portion of inner circumferential surface 25S2 that is configured by first cooling portion 25A into inclined surface 25AS, inner circumferential surface 25S2 retreats toward the outer periphery as it moves upward, thereby preventing contact and sparks between unmelted raw metal material M1 and cooling portion 25. In addition, by covering the lower end of inner circumferential surface 25S2 with spray material 26, contact and sparks between unmelted raw metal material M1 and cooling portion 25 are more reliably prevented.

[0044] In the second section 21W2, the refractory wall 24 and the cooling section 25 are positioned continuously between the tapping port 21A and the slag discharge port 21B. In FIG. 1 , the positions of the refractory wall 24 and the cooling section 25 in the second section 21W2 are indicated by dots. For convenience, the dots indicating the positions of the cooling sections 25 are shown as being continuous in the circumferential direction in FIG. 1 . However, in this embodiment, the cooling section 25 is formed by arranging multiple cooling panels, each having a width of approximately 500 mm to 1000 mm in the circumferential direction. In this embodiment, these individual cooling panels are referred to as the first cooling section 25A and the second cooling section 25B. Furthermore, the same configuration as the refractory wall 24 and the cooling section 25 of the second section 21W2 is also provided between the slag discharge port 21B and the shaft connection port 21C.

[0045] Second portion 21W2 of side wall 21W faces shaft connection port 21C through which metal raw material M1 is supplied to melting chamber 21. Therefore, even if the thickness of the lower end of cooling portion 25 is equal to the thickness of the upper end of fire-resistant wall 24, contact between unmelted metal raw material M1 and cooling portion 25 and sparks are unlikely to occur.

[0046] [Repair method] The inner peripheral portion of the fire wall 24 is more susceptible to heat from the molten steel M2 and is therefore more susceptible to damage than the outer peripheral portion of the fire wall 24. Therefore, as the operation period elapses from the undamaged state shown in FIG. 3, damage gradually occurs in the inner peripheral portion of the fire wall 24.

[0047] As shown in Fig. 4, if damage occurs to a portion of the fire wall 24 located on the inner circumferential side, the damaged portion is removed and then the portion from which the fire wall 24 was removed is filled with spray material 26, thereby repairing the side wall 21W. In other words, by improving the lifespan of the fire wall 24, the total amount of spray material 26 used for repairs during long-term operation can be reduced. In Fig. 4, the outline of the damaged portion of the fire wall 24 and the position of the second end 24E2 on the inner circumferential side are indicated by dashed lines.

[0048] Furthermore, because end 25E of support surface 25S1 is positioned to overlap second end 24E2 of upper surface 24S of fire-resistant wall 24, during repair work the position of end 25E of support surface 25S1 can be used as an indicator for the position of second end 24E2 of fire-resistant wall 24 before damage. By performing repair work using the position of end 25E on the inner periphery of support surface 25S1 as an indicator, it is possible to ensure a thickness equivalent to that of fire-resistant wall 24 before damage without providing an excessively thick spraying material 26.

[0049] [Operation of the embodiment] FIG. 5 illustrates a comparative example of a conventional configuration in which only the outer peripheral side of upper surface 24S of fire-resistant wall 24 is pressed by cooling section 25. FIG. 5 also illustrates a case in which inner peripheral surface 25S2 of cooling section 25 is formed solely by a vertical surface perpendicular to support surface 25S1, without including inclined surface 25AS. In this case, inner peripheral end 25E of support surface 25S1 is located radially outward of midpoint 24P of upper surface 24S of fire-resistant wall 24. As an example, in the configuration illustrated in FIG. 5, in a cross section perpendicular to the circumferential direction of side wall 21W, the width of support surface 25S1 is 50% or less of the width of upper surface 24S. Note that the width of upper surface 24S in a cross section perpendicular to the circumferential direction of side wall 21W refers to the length L (see FIG. 3) from first end 24E1 to second end 24E2. For example, in the conventional configuration, the width of support surface 25S1 is about 20% to 30% of the width of upper surface 24S. That is, in the conventional configuration, only an area of ​​about 20% to 30% of the entire upper surface 24S of fire-resistant wall 24 from the outer periphery is pressed down by support surface 25S1 of cooling section 25.

[0050] In this case, the amount of thermal expansion of the fire wall 24 is large, and the deformation amount of the inner circumferential side of the fire wall 24 that is not pressed by the cooling portion 25 is larger than the deformation amount of the outer circumferential side that is pressed by the cooling portion 25, which has a small amount of thermal expansion. As a result, a bending stress acts on the fire wall 24, causing the inner circumferential side to bulge upward while the outer circumferential side is supported by the cooling portion 25, with the inner circumferential side being the boundary at the inner circumferential end 25E of the support surface 25S1. As a result, a crack C occurs at the boundary between the inner circumferential side of the fire wall 24 that is not pressed by the cooling portion 25 and the outer circumferential side of the fire wall 24 that is pressed by the cooling portion 25. In this case, the portion of the fire wall 24 that is inner circumferentially closer to the crack C is damaged. Furthermore, the starting point P of the crack C is positioned so as to overlap with the inner circumferential end 25E of the support surface 25S1.

[0051] In this embodiment, the inclined surface 25AS is configured to protrude inward as it extends downward, so that the support surface 25S1 also protrudes inward. The support surface 25S1 presses the upper surface 24S of the fire-resistant wall 24 from the first end 24E1 to at least a position closer to the second end 24E2 than the midpoint 24P. This allows the support surface 25S1 to press the inner portion of the fire-resistant wall 24, which has a large amount of thermal expansion, thereby reducing bending stress acting on the fire-resistant wall 24. This prevents crack C from occurring at the position where the inner end 25E of the support surface 25S1 overlaps the upper surface 24S of the fire-resistant wall 24, and also prevents damage and detachment of the fire-resistant wall 24. Since the cooling unit 25 presses the entire upper surface 24S of the fire-resistant wall 24, the overall thermal expansion of the fire-resistant wall 24 is reduced.

[0052] Furthermore, in the second portion 21W2, the fire wall 24 and the cooling portion 25 are positioned continuously between the steel tapping port 21A and the slag discharge port 21B, so that the upper surface 24S of the fire wall 24 is supported by the cooling portion 25 throughout the second portion 21W2. That is, the occurrence of a crack C having an origin P on the upper surface 24S of the fire wall 24 is suppressed throughout the second portion 21W2.

[0053] [Effects of the embodiment] According to the above embodiment, the following effects can be obtained. (1) Support surface 25S1 presses down on top surface 24S of fire wall 24 from first end 24E1 to at least a position closer to second end 24E2 than midpoint 24P. That is, in the portion of sidewall 21W including cooling section 25, at least a portion of the inner circumferential side of fire wall 24, which is subject to a high thermal load, is supported by support surface 25S1. This reduces the difference in thermal expansion between the inner and outer circumferential sides of fire wall 24 compared to a configuration in which only the outer circumferential side of fire wall 24 is pressed down by cooling section 25. This reduces the occurrence of cracks C on top surface 24S of fire wall 24 and the resulting damage and falling of fire wall 24. As a result, the lifespan of fire wall 24 can be improved. Furthermore, the reduction in repair frequency during long-term operation reduces the total amount of spraying material 26 used for repair.

[0054] The above-described effect can be more effectively achieved by supporting surface 25S1 over 60% or more, preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more of the entire area of ​​upper surface 24S from the outer periphery. In particular, if support surface 25S1 is configured to overlap second end 24E2 of upper surface 24S of fire-resistant wall 24 at second portion 21W2 of sidewall 21W, the entire inner peripheral portion of fire-resistant wall 24, which is subject to a high thermal load, is supported by support surface 25S1. This effectively supports the inner peripheral portion of fire-resistant wall 24, which is prone to relatively large thermal expansion, thereby reducing the amount of thermal expansion of the inner peripheral portion. Furthermore, supporting surface 25S1 supports the entire upper surface 24S of fire-resistant wall 24, thereby reducing the overall thermal expansion of fire-resistant wall 24. Furthermore, the amount of cooling received by cooling unit 25 on upper surface 24S can be uniform.

[0055] (2) If the inner peripheral surface 25S2 of the cooling section 25 is configured to protrude inward as it extends downward, the support surface 25S1 of the cooling section 25 also protrudes inward. Therefore, in the portion of the side wall 21W where the cooling section 25 is provided, the support surface 25S1 protrudes inward, thereby effectively supporting the inner peripheral portion of the fire wall 24, which is prone to relatively large thermal expansion. This reduces the amount of thermal expansion of the inner peripheral portion. This reduces the difference in thermal expansion between the inner and outer peripheral sides of the fire wall 24, thereby suppressing the occurrence of cracks C on the upper surface 24S of the fire wall 24 and the resulting damage and detachment of the fire wall 24. As a result, the lifespan of the fire wall 24 can be extended. Furthermore, by reducing the frequency of repairs during long-term operation, the total amount of spraying material 26 used for repairs can be reduced.

[0056] (3) Covering the cooling section 25 with the spray material 26 can more reliably prevent contact and sparks between the cooling section 25 and the metal raw material M1. In addition, the spray material 26 functions as a heat insulator, reducing the thermal load that the cooling section 25 receives from the heat source in the furnace.

[0057] (4) Inner peripheral surface 25S2 of cooling section 25 includes inclined surface 25AS, and inclined surface 25AS is inclined toward outer skin 23 as it extends upward, thereby more reliably suppressing contact and sparks between unmelted raw metal material M1 and cooling section 25. Also, compared to a configuration in which inner peripheral surface 25S2 has a vertical surface, such that first cooling section 25A has a rectangular outer shape in cross section, the cooling efficiency of first cooling section 25A can be improved.

[0058] (5) Even if cooling unit 25 with enlarged support surface 25S1 is disposed on the portion of side wall 21W facing shaft connection port 21C to press down on the inner peripheral portion of fire-resistant wall 24, it is unlikely to come into contact with raw metal material M1 supplied to melting chamber 21. Therefore, if cooling unit 25 is disposed on the portion of side wall 21W facing shaft connection port 21C, cooling unit 25 can prevent the occurrence of cracks C on upper surface 24S of fire-resistant wall 24 while preventing contact between cooling unit 25 and raw metal material M1 supplied to melting chamber 21.

[0059] (6) In the second portion 21W2, the fire wall 24 and the cooling section 25 are located continuously between the steel tapping port 21A and the slag discharge port 21B, thereby suppressing the occurrence of cracks C in the fire wall 24 and the resulting damage and falling off of the fire wall 24 throughout the entire second portion 21W2.

[0060] (7) By arranging inner circumferential end 25E of support surface 25S1 so that it overlaps with inner circumferential second end 24E2 of upper surface 24S of fire-resistant wall 24, it is possible to suppress contact between cooling portion 25 and metal source material M1 and the generation of sparks, while also achieving the effect of (1). Furthermore, if fire-resistant wall 24 is damaged and repaired using spray material 26 or the like, the position of inner circumferential end 25E of support surface 25S1 can be used as an indicator of the position of inner circumferential second end 24E2 of fire-resistant wall 24 before the damage. Therefore, repairs can be easily performed without providing an excessively thick spray material 26 to achieve the same thickness as fire-resistant wall 24 before the damage.

[0061] [Example of change] Although the present invention has been described above using the embodiments, the present invention is not limited to the configurations of these embodiments. The scope of the present invention is determined based on the description of the appended claims, and all configurations in which some of the components shown in the embodiments have been omitted or modified, or in which such improvements have been made, are included within that scope.

[0062] For example, the above embodiment can be modified as follows: The following modifications can be implemented in combination with each other within the scope of technical compatibility. As long as the occurrence of cracks C in the refractory wall 24 can be suppressed throughout the entire second portion 21W2, the entire upper surface 24S of the refractory wall 24 does not have to be supported by the cooling unit 25 throughout the entire second portion 21W2. For example, in a portion of the second portion 21W2 between the tapping port 21A and the slag discharge port 21B, a portion of the upper surface 24S of the refractory wall 24 may not be pressed by the support surface 25S1 of the cooling unit 25. Alternatively, the cooling unit 25 may be provided only in the second portion 21W2 of the side wall 21W. In this case, the cooling unit 25 is disposed only in a portion of the side wall 21W that is unlikely to come into contact with the raw metal material M1 supplied to the melting chamber 21. This more reliably prevents contact between the cooling unit 25 and the raw metal material M1 supplied to the melting chamber 21.

[0063] As long as the inner peripheral surface 25S2 protrudes inward as it extends downward, the support surface 25S1 may also protrude inward. The position of the support surface 25S1 relative to the upper surface 24S of the fire wall 24 is not limited. For example, the support surface 25S1 may press the upper surface 24S of the fire wall 24 from the first end 24E1 to the midpoint 24P, or may press any position from the first end 24E1 to the midpoint 24P toward the outer periphery. Furthermore, the outer peripheral portion of the upper surface 24S of the fire wall 24 is a portion that is relatively less susceptible to thermal load from the molten steel M2. Therefore, for example, the support surface 25S1 of the cooling unit 25 may not be in contact with the first end 24E1 of the upper surface 24S of the fire wall 24, which is located on the outer periphery.

[0064] The shape of inner circumferential surface 25S2 can be changed to any shape as long as support surface 25S1 is configured to press down on upper surface 24S of fire-resistant wall 24 from first end 24E1 to at least a position closer to second end 24E2 than midpoint 24P. For example, as long as contact and sparks between cooling portion 25 and unmelted metal raw material M1 can be prevented, inclined surface 25AS of first cooling portion 25A of inner circumferential surface 25S2 of cooling portion 25 can be made vertical.

[0065] Instead of the inclined surface 25AS, the inner peripheral surface 25S2 may include a surface of any shape that protrudes inward as it extends downward. For example, the inner peripheral surface 25S2 may include a curved surface such as an arcuate surface that approaches the outer skin 23 as it extends upward, or a discontinuous surface with multiple steps.

[0066] In the cooling section 25, if contact with the unmelted metal raw material M1 and sparks can be prevented, the spray material 26 may be configured to cover only the inner surface of the fire-resistant wall 24 without covering the inner peripheral surface 25S2 of the cooling section 25. Alternatively, a monolithic refractory material such as mortar or cement may be used instead of the spray material 26.

[0067] As long as contact and sparks between cooling portion 25 and unmelted metal raw material M1 can be prevented, for example, inner peripheral end 25E of support surface 25S1 may protrude further inward than inner peripheral second end 24E2 of upper surface 24S of fire-resistant wall 24. In this case, upper surface 24S of fire-resistant wall 24 is supported by support surface 25S1 up to inner peripheral second end 24E2.

[0068] In the above example, the cooling unit 25 is disposed in the second portion 21W2 of the side wall 21W, which is the portion facing the shaft connection port 21C. Alternatively, for example, in an electric furnace 10 that does not have a shaft 30 serving as a supply path for supplying the metal raw material M1 to the melting chamber 21, the side wall 21W may be provided with the cooling unit 25 along the entire circumferential direction. In this case, the occurrence of cracks C on the upper surface 24S of the fire wall 24 and the resulting damage and falling-off of the fire wall 24 can be suppressed along the entire circumferential direction of the side wall 21W. As a result, the life of the fire wall 24 can be improved along the entire circumferential direction of the side wall 21W, thereby reducing the frequency of repairs.

[0069] In the above embodiment, a configuration is exemplified in which the support surface 25S1 is arranged so as to overlap with the second end portion 24E2 on the inner periphery of the upper surface 24S of the fire-resistant wall 24, but the support surface 25S1 does not necessarily have to be arranged so as to overlap with the second end portion 24E2 on the inner periphery of the upper surface 24S.

[0070] As shown in FIG. 6, for example, the first cooling section 25A may include a lower chamfered portion 25R1 and an upper chamfered portion 25R2 at an inner corner. The lower chamfered portion 25R1 connects the support surface 25S1 and the inclined surface 25AS in an arc. The upper chamfered portion 25R2 connects the upper surface of the first cooling section 25A and the inclined surface 25AS in an arc. As an example, the first cooling section 25A is positioned so that the inner tip of the lower chamfered portion 25R1 does not protrude further inward than the second end 24E2 of the upper surface 24S. In the example shown in FIG. 6, the inner end 25E of the support surface 25S1 is located at the boundary between the lower chamfered portion 25R1 and the support surface 25S1. The inner end 25E of the support surface 25S1 is located closer to the second end 24E2 than the midpoint 24P and further outward than the second end 24E2 of the upper surface 24S.

[0071] The configuration shown in FIG. 6 is also an example of a configuration in which inner peripheral surface 25S2 of cooling section 25 protrudes inward as it extends downward. Therefore, support surface 25S1 of cooling section 25 also protrudes inward, making it possible to suitably hold down the inner peripheral portion of fire wall 24, which is prone to relatively large amounts of thermal expansion. The configuration shown in FIG. 6 is also an example of a configuration in which support surface 25S1 holds down the upper surface 24S of fire wall 24 from first end 24E1 to at least a position closer to second end 24E2 than midpoint 24P. Therefore, it is possible to hold down at least a portion of the inner peripheral portion of fire wall 24, which is prone to relatively large amounts of thermal expansion.

[0072] FIG. 7 shows a cross-sectional view of the first cooling section 25A shown in FIG. 6. In this case, the first cooling section 25A includes a bottom wall portion 251 including a support surface 25S1 and an inner wall portion 252 including an inclined surface 25AS. The bottom wall portion 251 includes an outer plate portion 251A that forms the outer surface and a flow path component 251B that is arranged inside the outer plate portion 251A. The inner wall portion 252 includes an outer plate portion 252A that forms the outer surface and a flow path component 252B that is arranged inside the outer plate portion 252A. The outer surface of the outer plate portion 251A of the bottom wall portion 251 corresponds to the support surface 25S1. The outer surface of the outer plate portion 252A of the inner wall portion 252 corresponds to the inclined surface 25AS.

[0073] The flow path forming members 251B, 252B are formed by welding a plurality of partition plates welded to the outer plate portions 251A, 252A to each other, thereby forming flow path spaces 253A, 253B through which the cooling water flows. The flow path forming member 251B of the bottom wall portion 251 has internal spaces that are alternately connected on one side at both ends in the panel width direction. This allows the cooling water to flow in a serpentine manner within the flow path space 253A in the bottom wall portion 251. Note that the panel width direction refers to the depth direction of the paper in FIG. 7. Therefore, the ends in the panel width direction refer to the ends on the front side of the paper and the ends on the back side of the paper. Similarly, the flow path forming member 252B of the inner wall portion 252 has internal spaces that are alternately connected on one side at both ends in the panel width direction, from top to bottom. This allows the cooling water to flow in a serpentine manner within the flow path space 253B. This configuration allows the first cooling section 25A, which has excellent strength and cooling efficiency, to be realized with a simple structure.

[0074] The flow path forming members 251B, 252B are partition plates that form flow path spaces 253A, 253B through which the refrigerant flows. Alternatively, for example, metal hollow pipes welded to the inside of the outer plate portions 251A, 252A in a serpentine state may be used as the flow path forming members 251B, 252B. In this case, the space inside the hollow pipe corresponds to the flow path spaces 253A, 253B.

[0075] As shown in Fig. 8, a monolithic refractory layer 27 may be disposed between the support surface 25S1 of the cooling section 25 and the upper surface 24S of the fire wall 24. The monolithic refractory layer 27 may be made of a stamping material made of alumina, magnesia, or the like. Note that the monolithic refractory layer 27 may be made of a monolithic refractory material other than the stamping material, but it is preferable to use the stamping material in terms of durability (corrosion resistance).

[0076] Here, an example of the configuration of the refractory wall 24 will be described. The refractory wall 24 includes first bricks 24A, second bricks 24B, and third bricks 24C as shaped refractories, and a covering portion 24D as unshaped refractory. The first bricks 24A are stacked adjacent to the inner peripheral surface of the outer skin 23. The first bricks 24A are, for example, refractory bricks made of magnesia-carbon. The second bricks 24B are stacked adjacent to the inner peripheral surfaces of the stacked first bricks 24A, excluding the upper bricks. The second bricks 24B are refractory bricks made of magnesia. The third bricks 24C are stacked adjacent to the inner peripheral surfaces of the second bricks 24B. The third brick 24C is stacked on top of the second brick 24B and the third brick 24C adjacent to the inner peripheral surface of the second brick 24B so as to be adjacent to the inner peripheral surface of the upper first brick 24A. The covering portion 24D is provided so as to cover the inner peripheral surface of the lower portion of the stacked third bricks 24C. The covering portion 24D is made of, for example, a stamping material made of magnesia or the like, or a fill material made of a spinel-based refractory or the like.

[0077] In this case, the upper surface 24S of the fire wall 24 is formed by the upper surface of the first brick 24A that is the uppermost of the multiple first bricks 24A and the upper surface of the third brick 24C that is the uppermost of the multiple third bricks 24C. That is, the upper surface 24S of the fire wall 24 in this case is a discontinuous surface with a step. In this case, in a cross-sectional view perpendicular to the circumferential direction of the side wall 21W, the point on the upper surface 24S where the horizontal distance from the first end 24E1 of the first brick 24A is equal to the horizontal distance from the second end 24E2 of the third brick 24C is defined as the midpoint 24P. The horizontal distance from the first end 24E1 to the second end 24E2 is defined as the length L.

[0078] The monolithic refractory layer 27 is provided on the uppermost third brick 24C among the plurality of third bricks 24C so as to contact the upper end portion of the inner circumferential surface of the first brick 24A. In this case, the support surface 25S1 includes a portion that presses the upper surface 24S via the monolithic refractory layer 27, which has a lower density than the monolithic refractory (particularly the third brick 24C in this example) that constitutes the fire wall 24. This allows the monolithic refractory layer 27 to reduce the force applied to the cooling section 25 due to the thermal expansion of the monolithic refractory that constitutes the fire wall 24. In other words, the monolithic refractory layer 27 functions as a buffer layer that reduces the force applied to the cooling section 25 due to the thermal expansion of the fire wall 24. By reducing the force applied to the cooling section 25, for example, the force applied to the fixing bolts 28 that fix the cooling section 25 to the outer shell 23 can be reduced, thereby preventing breakage of the fixing bolts 28.

[0079] The fire wall 24 shown in FIG. 3 of the above embodiment corresponds to a state in which a third brick 24C is arranged in place of the monolithic refractory layer 27 in the portion where the monolithic refractory layer 27 is arranged in FIG.

[0080] When the monolithic refractory layer 27 is provided, it is sufficient that the monolithic refractory layer 27 is disposed at least partially between the support surface 25S1 of the cooling section 25 and the upper surface 24S of the fire wall 24. When the monolithic refractory layer 27 is provided, it is preferably provided on the inner circumferential side of the upper surface 24S of the fire wall 24, where the amount of thermal expansion is likely to be large. For example, it is preferably provided so as to cover the second end 24E2 of the upper surface 24S of the fire wall 24. Furthermore, for example, the monolithic refractory layer 27 may be configured to be provided at least between the inner circumferential end 25E of the support surface 25S1 and the upper surface 24S of the fire wall 24. Even with such a configuration, the occurrence of cracks C near the inner circumferential end 25E of the support surface 25S1 can be suppressed.

[0081] Furthermore, the monolithic refractory layer 27 may cover not only the top surface of the uppermost third brick 24C but also the top surface of the uppermost first brick 24A. In other words, the monolithic refractory layer 27 may cover the entire top surface 24S of the fire wall 24 made of a monolithic refractory.

[0082] The thickness of the monolithic refractory layer 27 is set based on the height and thermal expansion coefficient (linear expansion coefficient) of the monolithic refractory located below the monolithic refractory layer 27 in the fire wall 24, and the temperature rise of the monolithic refractory when the electric furnace 10 is in use. In the example of FIG. 8 , the thickness of the monolithic refractory layer 27 is set based on the construction height H and thermal expansion coefficient of the third brick 24C, which is the monolithic refractory located below the monolithic refractory layer 27 and is prone to thermal expansion, and the temperature rise of the third brick 24C when the electric furnace 10 is in use. In this case, the thermal expansion amount of the third brick 24C in an unconstrained state can be calculated from the construction height H, thermal expansion coefficient, and temperature rise of the third brick 24C. The thickness of the monolithic refractory layer 27 is preferably greater than the thermal expansion amount of the monolithic refractory located below the monolithic refractory layer 27 when in an unconstrained state. This ensures a sufficient thickness for the unshaped refractory layer 27 to reduce the force applied to the cooling portion 25 due to thermal expansion of the shaped refractory material that constitutes the fire wall 24.

[0083] The cooling section 25 may press the upper surface 24S of the fire wall 24 via a member other than the monolithic refractory layer 27. For example, the cooling section 25 may be configured to include a water-cooled panel and a metal plate located at the bottom of the water-cooled panel, and the metal plate may be configured to contact the entire upper surface 24S of the fire wall 24. In this case, the water-cooled panel may be configured to be located closer to the outer periphery than the inner edge of the metal plate. [Explanation of symbols]

[0084] M1…metal raw material 10...Electric furnace 20…Furnace body 21…Dissolution chamber 21A…Tapping port 21B...Dregs outlet 21C...Shaft connection port 21W…Side wall 23…Outer skin 24…Fireproof wall 24E1…First end 24E2…Second end 24P…midpoint 24S…Top surface 25…Cooling section 25A…1st cooling section 25AS…Slope surface 25B…Second cooling section 25E…End 25R1…Bottom chamfer 25R2…Top chamfer 25S1…support surface 25S2…Inner surface 251...Bottom wall 251A,252A…Outer panel part 251B, 252B...flow path component 252...Inner wall 253A, 253B...flow path space 26...Spraying material 27…Unshaped refractory layer 28...Fixing bolt 30...shaft 40...Extrusion section 50...electrode

Claims

1. The furnace body includes a melting chamber in which a metal raw material is melted, and an electrode for melting the metal raw material in the melting chamber, the furnace body includes a side wall that defines the melting chamber, The side wall includes an outer shell and a fire-resistant wall located on the inner circumferential side of the outer shell, At least a portion of the side wall includes a cooling portion having a support surface that presses against an upper surface of the refractory wall; The support surface presses the upper surface of the fire-resistant wall from a first end on the outer skin side to a position closer to the second end than a midpoint between the first end and a second end on the inner periphery side. Electric furnace.

2. the cooling portion has an inner peripheral surface facing the inner peripheral side, The inner peripheral surface protrudes inward as it extends downward. The electric furnace according to claim 1.

3. The furnace body includes a melting chamber in which a metal raw material is melted, and an electrode for melting the metal raw material in the melting chamber, the furnace body includes a side wall that defines the melting chamber, The side wall includes an outer shell and a fire-resistant wall located on the inner circumferential side of the outer shell, At least a portion of the side wall includes a cooling portion having a support surface that presses against an upper surface of the refractory wall; the cooling portion has an inner peripheral surface facing the inner peripheral side, The inner peripheral surface protrudes inward as it extends downward. Electric furnace.

4. The portion of the side wall including the cooling portion further includes a monolithic refractory provided across the refractory wall and the cooling portion.

4. An electric furnace according to claim 1.

5. The inner peripheral surface includes an inclined surface that is inclined so as to approach the outer skin as it goes upward. The electric furnace according to claim 2 or 3.

6. the cooling portion includes a bottom wall portion including the support surface and an inner wall portion including the inner circumferential surface, The bottom wall portion and the inner wall portion each have an outer plate portion that forms an outer surface, and a flow path forming member that is arranged inside the outer plate portion. The electric furnace according to claim 5.

7. The side wall is provided with the cooling portion over the entire circumferential direction.

4. An electric furnace according to claim 1.

8. a shaft serving as a supply path for supplying the metal raw material to the melting chamber; The furnace body is disposed on the side wall and includes a shaft connection port to which the shaft is connected, The cooling portion is provided in a portion of the side wall that faces the shaft connection port.

4. An electric furnace according to claim 1.

9. The furnace body has a tapping port and a slag discharge port arranged opposite to each other in the circumferential direction of the side wall, The tapping port, the slag discharge port, and the shaft connection port are arranged at different positions from each other in the circumferential direction of the side wall, In the portion of the side wall facing the shaft connection port, the refractory wall and the cooling section are continuously located between the steel tapping port and the slag discharge port. The electric furnace according to claim 8.

10. The upper surface of the fire resistant wall is made of shaped refractory material, a castable refractory layer disposed at least partially between the support surface and the upper surface of the refractory wall; The support surface presses the upper surface of the refractory wall via the monolithic refractory layer.

4. An electric furnace according to claim 1.

11. The thickness of the monolithic refractory layer is set based on the height and thermal expansion coefficient of the monolithic refractory located below the monolithic refractory layer, and the temperature rise of the monolithic refractory when the electric furnace is in use. The electric furnace according to claim 10.

12. The monolithic refractory layer is made of a stamping material. The electric furnace according to claim 10.

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