JP7683261B2 - metal melting furnace - Google Patents

Description

The present invention relates to a metal melting furnace.

Metal melting furnaces have been used in the past to apply a voltage to a material to be melted, such as a metal material, to melt the material. In such metal melting furnaces, in order to prevent damage to the refractory that constitutes the furnace side wall in contact with the material to be melted when melting the material, the material to be melted that is in contact with the refractory has been cooled and a coating layer has been formed on the surface of the refractory.

As disclosed in Patent Document 1 and other publications, various studies have been conducted on methods for cooling such furnace side walls.

JP 2013-127352 A

Furthermore, from the perspective of minimizing damage to refractories and reducing the frequency of maintenance, there was a demand for a metal melting furnace that could efficiently cool the side walls of the metal melting furnace.

In view of the problems with the above-mentioned conventional technology, one aspect of the present invention aims to provide a metal melting furnace that can efficiently cool the furnace side walls.

In order to solve the above problem, according to one aspect of the present invention,
A metal melting furnace for melting a material containing a metal component, comprising:
The metal melting furnace comprises:
an internal space for accommodating the object to be melted;
A furnace side wall defining a side surface of the internal space;
an electrode disposed in the internal space along a height direction;
The furnace side wall includes a refractory material disposed on the inner space side,
A metal jacket covering an outer surface of the refractory material,
The outer jacket has a plurality of plate-shaped protrusions arranged along a height direction on a surface facing the refractory,
The protrusion is fitted into a recess in a surface of the refractory facing the jacket ,
a height of the protrusion from the inner surface of the outer covering toward the internal space is 60% or more of a thickness of the refractory material,
The metal melting furnace is provided with three protrusions arranged along the height direction .

According to one aspect of the present invention, it is possible to provide a metal melting furnace that can efficiently cool the furnace side walls.

FIG. 1 is a cross-sectional view of a metal melting furnace according to one embodiment of the present disclosure taken along a horizontal plane perpendicular to the height direction passing through a protruding portion. FIG. 2 is a cross-sectional view taken along line AA' in FIG. FIG. 3 is a perspective view of the envelope. FIG. 4 is a diagram showing the temperature distribution in the inner space and the furnace side wall in Experimental Example 1. 5 is a graph showing the relationship between the boundary temperature between the material to be melted and the refractory material and the amount of heat dissipated from the surface with respect to the number of protrusions arranged in the height direction in Experimental Example 1. FIG. FIG. 6 is a diagram showing the temperature distribution in the inner space and the furnace side wall in Experimental Example 2. FIG. 7 is a graph showing the relationship between the height of the protrusion in Experimental Example 2 and the boundary temperature between the material to be melted and the refractory material and the amount of heat dissipated from the surface. FIG. 8 is a diagram showing the temperature distribution in the inner space and the furnace side wall in Experimental Example 3. FIG. 9 is a graph showing the relationship between the thermal conductivity of the outer cover and the amount of heat dissipated from the surface in Experimental Example 3.

The following describes a form for carrying out the present invention. However, the present invention is not limited to the following embodiment, and various modifications and substitutions can be made to the following embodiment without departing from the scope of the present invention.
[Metal melting furnace]
The metal melting furnace of this embodiment will be described with reference to the drawings. Fig. 1 is a horizontal cross-sectional view passing through the convex portion of the metal melting furnace of this embodiment. Fig. 2 is a cross-sectional view taken along line A-A' in Fig. 1. Fig. 3 is a perspective view of the outer casing.

The metal melting furnace of this embodiment is a furnace for melting a material to be melted that contains metal components, and the metal melting furnace of this embodiment can be, for example, a three-phase AC electrode type electric furnace. The material to be melted that contains metal components is not particularly limited, but examples include ores that contain metal components and various metal materials. In addition, the material to be melted may contain various additive components as necessary.

As shown in Figures 1 and 2, the metal melting furnace 10 of this embodiment can have an internal space 11 that contains the material to be melted, a furnace side wall 12 that defines the side of the internal space 11, and an electrode 13 that is arranged along the height direction of the internal space 11, i.e., vertically.

In Figures 1 and 2, the height direction refers to the Z-axis direction. And the horizontal plane corresponds to the XY plane.

Each component will be described below.
(1) Internal Space The internal space 11 is a space (area) for accommodating an object to be melted and melting the object by the electrode 13.

The internal space 11 may have, for example, a columnar shape, and preferably has a cylindrical shape as shown in FIG. 1. The columnar shape and cylindrical shape mentioned here do not have a strict geometrical meaning, but may be an approximately columnar shape or an approximately cylindrical shape, and may include a concave or convex part as necessary, and may be partially deformed from the columnar or cylindrical shape.

The internal space 11 is separated from the external space by a bottom refractory provided on the bottom side and a furnace side wall 12 provided on the side.
(2) Electrode The electrode 13 is a member for applying a voltage to the material to be melted contained in the internal space 11, and the shape is not particularly limited, but may have, for example, a columnar shape, and is preferably a cylindrical shape. The columnar shape and cylindrical shape here do not have a strict geometrical meaning, and may be an approximately columnar shape or an approximately cylindrical shape, and may be partially deformed as necessary.

The electrode 13 can be arranged, for example, so that the central axis of the electrode 13 is along the height direction, i.e., the Z-axis direction in Figures 1 and 2, and is preferably configured to be movable along the height direction.

The metal melting furnace 10 may have a plurality of electrodes 13, for example three as shown in FIG.
(3) Furnace Side Wall The furnace side wall 12 is provided on the side surface 11A of the internal space 11 and separates the side surface 11A of the internal space 11 from the external space.

The furnace side wall 12 may have a refractory material 121 arranged on the interior space 11 side, and a metal outer covering 122 covering an outer surface 121A of the refractory material 121 .
(3-1) Refractory The refractory 121 can be disposed on the inner space 11 side of the furnace side wall 12 as described above. The bottom refractory 14 can be provided so as to cover the bottom surface 11B of the inner space 11, and the refractory 121 and the bottom refractory 14 can be formed as an integrated member.

The material for the refractory material 121 can be any material that can withstand the temperature at which the material to be melted is melted, and can be, for example, various ceramics.

The refractory material 121 can have a cylindrical shape because it is arranged to cover the side surface 11A of the internal space 11. If the internal space 11 is cylindrical, the refractory material 121 can have a cylindrical shape.

The refractory 121 can have a recess 1211 on the outer surface 121A facing the outer sheath 122 described below, which fits into and accommodates the protrusion 1221 described below.

The size and shape of the recess 1211 can be selected so as to fit with the protrusion 1221 described below.
(3-2) Outer jacket The outer jacket 122 is disposed so as to cover the outer surface 121A of the refractory material 121. For this reason, the outer jacket 122 may have a tubular shape, for example, a cylindrical shape.

As mentioned above, in a metal melting furnace, when melting a material to be melted, in order to prevent damage to the refractory constituting the furnace side wall in contact with the material to be melted, the material to be melted that is in contact with the refractory is cooled and a coating layer is formed on the surface of the refractory. In order to form such a coating layer, it is necessary to efficiently cool the furnace side wall.

The inventors of the present invention have studied a method for efficiently cooling the furnace side wall and forming and maintaining the coating layer while the metal melting furnace is in operation, and have found that by providing a plate-shaped convex portion 1221 on the surface of the outer casing 122 facing the refractory material 121 and fitting the convex portion 1221 into a concave portion 1211 on the surface of the refractory material 121 facing the outer casing 122, heat can be removed via the convex portion 1221 and the outer casing 122, and the furnace side wall 12 can be efficiently cooled.
(3-2-1) Convex portion (shape and size of convex portion)
The convex portion 1221 can have a plate-like shape. A main surface 1221A of the convex portion 1221, i.e., a surface perpendicular to the height direction, can have a shape that is also called a circular sector shape, in which a part of a ring is cut off, as shown in Figures 1 and 3. The circular sector shape is a sector shape with an arc-shaped cutout on the center side, as shown in Figures 1 and 3, and can also be called an arch shape.

The size of the protrusion 1221 is not particularly limited and can be selected according to the size of the refractory material 121, etc.

The height L1221 of the protrusion 1221 protruding from the inner surface (inner peripheral surface) 122A of the outer jacket 122 toward the internal space 11 is preferably 20% or more of the thickness T121 of the refractory material 121, and more preferably 60% or more. In other words, it is preferable that 0.2≦L1221/T121, and more preferably that 0.6≦L1221/T121.

By making the height L1221 of the convex portion 1221 20% or more of the thickness T121 of the refractory material 121, the convex portion 1221 can be positioned close to the internal space 11, and the furnace side wall 12 and the molten material located near the furnace side wall 12 can be cooled particularly efficiently.

Note that L1221 only needs to be smaller than T121, but from the viewpoint of increasing the strength of the refractory material 121, it is preferable that L1221 is 90% or less. In other words, it is preferable that L1221/T121<1.0, and it is more preferable that L1221/T121≦0.9.

The height L1221 of the protrusion 1221 means the maximum thickness measured on a straight line connecting the center _O11 of the internal space 11 and the inner surface 122A of the outer cover 122 in a horizontal cross section perpendicular to the height direction as shown in Fig. 1. The thickness T121 of the refractory 121 means the maximum thickness measured on a straight line connecting the center O11 of the internal space ₁₁ and the outer surface 121A of the refractory 121 in a horizontal cross section perpendicular to the height direction as shown in Fig. 1.

The thickness T1221 of the protrusions 1221 (see FIG. 2 ) is not particularly limited, and can be selected according to the size of the height direction region in the outer sheath 122 where the protrusions 1221 are arranged, the number of the protrusions 1221 to be provided in the region, etc. For example, when the refractory material 121 and the outer sheath 122 have a thickness of about 100 mm, a thickness of about 70 mm is preferable because it reduces the boundary temperature and increases the amount of heat dissipated from the surface.
(Number of protrusions arranged along the height direction)
The outer cover 122 may have a plurality of protrusions 1221 on a surface facing the refractory material 121, i.e., an inner surface 122A. As shown in Fig. 2, the protrusions 1221 may be arranged along the height direction.

As shown in FIG. 2, the protrusions 1221 are arranged at intervals along the height direction. Therefore, the inner surface 122A of the outer cover 122 is exposed between the protrusions 1221.

The number of the convex parts 1221 arranged along the height direction is not particularly limited and can be set arbitrarily depending on the size of the metal melting furnace 10, etc., but it is preferable to have multiple parts, i.e., two or more, from the viewpoint of efficient cooling. However, it is considered that the amount of heat dissipated from the surface will be saturated even if an excessive number of convex parts are provided. In addition, if an excessive number of convex parts are provided, it may be difficult to form the concave parts 1211 provided in the refractory material 121 to fit the convex parts 1221, and the strength of the wall between the concave parts 1211 may be reduced. For this reason, it is preferable that the number of convex parts arranged along the height direction is five or less. In particular, it is preferable to provide three convex parts 1221 along the height direction. Note that Figs. 2 and 3 show an example in which three convex parts 1221 are provided along the height direction.

As described below, the convex portions can be provided spaced apart in multiple regions in the horizontal cross section, and the number of convex portions arranged along the height direction in each region can be different, but it is preferable from the standpoint of workability when attaching the outer sheath 122 that the number be the same.
(Regarding the height of the area in which the protrusions are arranged in the height direction)
The convex portions 1221 can be arranged along the height direction on the inner surface 122A of the outer cover 122. In this case, the height H1221 (see FIG. 2) of the region in which the convex portions are arranged in the height direction is not particularly limited. However, from the viewpoint of improving the cooling efficiency, it is preferable to provide the convex portions 1221 in the range from the bottom surface 11B of the internal space 11 to the water level line where the material to be melted in the internal space 11 is accommodated.

Since the material to be melted is usually placed within a range of 80% or less of the height of the internal space 11, it is preferable that the height H1221 of the region in which the convex portion 1221 is provided in the height direction be 80% or less of the height of the internal space 11. The lower limit of the height H1221 of the region in which the convex portion 1221 is placed in the height direction is not particularly limited, but it is preferable that it be 60% or more of the height of the internal space 11.

The height of the internal space 11 means the distance between the bottom surface 11B of the internal space 11 and the upper end of the refractory material 121.

The height H1221 of the area in which the convex portions are arranged refers to the distance from the bottom surface of the lowest convex portion 12211 to the top surface of the highest convex portion 12212.

It is preferable that the protrusions 1221 are arranged in the above-mentioned region so that the distances between the protrusions 1221 are equal.
(Regarding the area in which the convex portion is provided in the horizontal cross section)
In a horizontal cross section perpendicular to the height direction passing through the protrusion 1221, i.e., in the cross section shown in Fig. 1, the region in which the protrusion 1221 is provided is not particularly limited. For example, in the horizontal cross section, the protrusion 1221 can be provided in an annular shape along the inner surface 122A of the outer casing 122. However, in the horizontal cross section, it is preferable that the protrusion 1221 is disposed so as to cover at least the region of the furnace side wall 12 that is particularly required to be cooled, specifically, the region of the outer casing 122 that faces the electrode 13.

The region facing the electrode 13 may be, for example, a region B of the inner surface 122A of the outer casing 122 facing the refractory material 121, which is surrounded by a tangent line L1 and a tangent line L2 to the outer periphery of the electrode 13 passing through the center _O11 of the internal space 11, as shown in FIG.

However, the region where the protrusion 1221 is provided is not limited to the above region B, and the protrusion 1221 may be provided over a wider range. For example, as shown in Fig. 1, the protrusion 1221 may be provided in a region on the inner surface of the outer cover 122, which is sandwiched between lines L11 and L12, the angles between which are θ11 and θ12, respectively, between a line L passing through the center _O11 of the internal space ₁₁ and the center O13 of the electrode. Both lines L11 and L12 pass through the center _O11 of the internal space 11. It is also preferable that the relationship θ11 = θ12 is satisfied.

And, θ11 and θ12 are each preferably less than 60 degrees, more preferably 45 degrees or less, and even more preferably 30 degrees or less.

The lower limit of θ11 and θ12 is not particularly limited, but can be, for example, 5 degrees or more.

In a horizontal cross section perpendicular to the height direction and passing through the convex portion 1221, the region where the convex portion 1221 is not provided is a surface where the inner surface 122A of the outer cover 122 is exposed.
(About the material of the outer cover)
Since the outer cover 122 including the protrusions 1221 is a member for cooling the metal melting furnace 10, it is preferable that the outer cover 122 is made of a material having excellent heat transfer properties, and may be made of a metal, for example.

In particular, the outer cover 122 including the convex portion 1221 is preferably made of a metal with a thermal conductivity of 10 W/m·K to 200 W/m·K, and more preferably made of a metal with a thermal conductivity of 80 W/m·K to 200 W/m·K. This is because a thermal conductivity of 10 W/m·K or more allows the metal melting furnace to be cooled particularly efficiently. Also, a thermal conductivity of 200 W/m·K or less allows the use of readily available materials, thereby reducing the cost of the metal melting furnace.

The specific material of the outer sheath 122 is not particularly limited, but may be one or more selected from, for example, iron, Ni steel, Cu steel, copper, etc.

The protrusion 1221 can be configured to be removable from the outer sheath 122, but from the standpoint of ease of handling, etc., it is preferable that the protrusion 1221 is an integral member with the outer sheath 122.

According to the metal melting furnace of this embodiment described above, by providing a certain convex portion on the inner surface of the outer casing, heat can be transferred from the convex portion to the outer casing to remove heat, and the furnace side walls and the material to be melted can be efficiently cooled.

The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.
[Experimental Example 1]
A study was conducted on the change in temperature distribution depending on the number of protrusions 1221 arranged along the height direction on the inner surface 122A of the outer casing 122 facing the refractory material 121.

Specifically, a thermal fluid analysis simulation was performed for a three-phase AC electrode type circular electric furnace, which is a metal melting furnace 10 having three electrodes 13 as already explained using Figures 1 and 2, by changing the number of protrusions. The thermal fluid analysis was performed by steady-state analysis using AnsysFluent (ver. 20.2).

In any of the following experimental examples, in a horizontal cross section perpendicular to the height direction and passing through the protrusion 1221, the protrusion 1221 is arranged so as to cover at least the region of the outer cover 122 facing the electrode 13. Specifically, the protrusion 1221 is arranged in a region of the inner surface 122A of the outer cover 122, surrounded by straight lines L11 and L12 passing through the center _O11 of the internal space 11, which are drawn so that θ11 and θ12 in FIG. 1 are 30°. In a horizontal cross section perpendicular to the height direction and passing through the protrusion 1221, the protrusion 1221 is arranged in three regions as in the case of FIG. 1. In the same experimental example, the arrangement conditions of the protrusion 1221 in the three regions are the same.

The conditions for the convex portions 1221 arranged in the height direction are as shown in Table 1. In Experimental Examples 1-1 to 1-4, the number of convex portions 1221 arranged in the height direction was varied in the range from 0 to 5. The height H1221 (see FIG. 2) of the area in which the convex portions are arranged in the height direction was set to 180 mm. This height refers to the distance from the lower end surface of the convex portion 12211 located at the bottom, i.e., the bottom surface 11B of the internal space 11, to the upper end surface of the convex portion 12212 located at the top.

In each experimental example, the convex portions 1221 were arranged so that the distance between the convex portions in the height direction was uniform. The thickness of the convex portions 1221 was set so that the thickness of the convex portions 1221 and the distance between the convex portions were approximately equal.

Figure 4(E) shows the length of each part when performing the simulation. Figure 4(E) corresponds to the shape in experimental example 1-1 shown in Figure 4(A), but the length of each part is the same in the other experimental examples except for the change in the number of steps of the convex part. The unit of length of each part in Figure 4(E) is mm.

The conditions used in the thermal fluid analysis are shown in Tables 2 and 3.

Experimental examples 1-1 and 1-2 are comparative examples, and experimental examples 1-3 and 1-4 are working examples.

熱流体解析の結果を、図４（Ａ）～図４（Ｄ）、図５（Ａ）、図５（Ｂ）に示す。また、被熔融物と、耐火物との間の境界温度を、表１の境界温度の欄に示す。

The results of the thermal fluid analysis are shown in Figures 4(A) to 4(D), 5(A), and 5(B). The boundary temperature between the object to be melted and the refractory material is shown in the column for boundary temperature in Table 1.

Figures 4(A) to 4(D) show the temperature distribution in the internal space 11 and furnace side wall 12 in each experimental example. Figures 4(A) to 4(D) are temperature distribution diagrams in the parts corresponding to Figure 2, and in Figure 4(A) the internal space 11, refractory material 121, and outer casing 122 are numbered. The same parts in the other figures refer to the same components. The results of experimental example 1-1 are shown in Figure 4(A), the results of experimental example 1-2 in Figure 4(B), the results of experimental example 1-3 in Figure 4(C), and the results of experimental example 1-4 in Figure 4(D).

Figures 5(A) and 5(B) show the boundary temperature between the material to be melted and the refractory material and the amount of heat dissipated from the surface, respectively, relative to the number of protrusions arranged in the height direction. The lower the boundary temperature and the greater the amount of heat dissipated from the surface, the more sufficient the cooling is.

As is clear from the results in Figure 5 (A), it was confirmed that the boundary temperature tends to decrease by increasing the number of convex parts arranged along the height direction. Furthermore, in Experimental Examples 1-3 and 1-4, which are examples in which there are multiple convex parts, the boundary temperature was sufficiently reduced compared to Experimental Examples 1-1 and 1-2, which are comparative examples, and it was confirmed that the change in boundary temperature with an increase in the number of convex parts approaches a constant value.

In addition, from the results in Figure 5 (B), it was confirmed that the amount of heat dissipated from the surface was greatest when the number of protrusions was three.

This is believed to be because, depending on whether the temperature of the outer jacket is high or low relative to the heat-resistant material, there are heat extraction areas and heat inflow areas at the boundary between the two materials. Furthermore, when the number of protrusions is increased to five, the area of the heat inflow area increases compared to when there are three protrusions, and it is believed that the amount of heat extraction from the surface of the entire boundary decreases.
[Experimental Example 2]
A study was conducted on the change in temperature distribution due to the height L1221 of the protrusion 1221 protruding from the inner surface of the outer casing into the internal space.

In Experimental Examples 2-2 to 2-3, the number of convex parts arranged in the height direction was set to three, and the height L1221 of the convex parts and the ratio of the height of the convex parts to the thickness of the refractory material were set to the values shown in Table 4. Apart from the above, the thermal fluid analysis simulation was performed in the same manner as in Experimental Example 1. For comparison, the results of Experimental Example 1-1 are also shown as Experimental Example 2-1.

Experimental example 2-1 is a comparative example, and experimental examples 2-2 and 2-3 are working examples.

熱流体解析の結果を、図６（Ａ）～図６（Ｃ）、図７（Ａ）、図７（Ｂ）に示す。また、被熔融物と、耐火物との間の境界温度を、表４の境界温度の欄に示す。

The results of the thermal fluid analysis are shown in Figures 6(A) to 6(C), 7(A) and 7(B). The boundary temperature between the object to be melted and the refractory material is shown in the column for boundary temperature in Table 4.

Figures 6(A) to 6(C) show the temperature distribution in the internal space 11 and furnace side wall 12 in each experimental example. Figures 6(A) to 6(C) are temperature distribution diagrams in the parts corresponding to Figure 2, and in Figure 6(A) the internal space 11, refractory material 121, and outer casing 122 are numbered. The same parts in the other figures refer to the same components. The results of experimental example 2-1 are shown in Figure 6(A), the results of experimental example 2-2 in Figure 6(B), and the results of experimental example 2-3 in Figure 6(C).

Figures 7(A) and 7(B) show the boundary temperature between the material to be melted and the refractory material and the amount of heat dissipated from the surface as a function of the height of the protrusion, respectively. The lower the boundary temperature and the greater the amount of heat dissipated from the surface, the more sufficient the cooling is.

As is clear from the results of Figures 7(A) and 7(B), it was confirmed that increasing the height of the convex portion tends to decrease the boundary temperature and increase the amount of heat dissipated from the surface. However, it was also confirmed that when the height of the convex portion is increased, both the boundary temperature and the amount of heat dissipated from the surface approach a constant value.

From the results of Figures 7(A) and 7(B), it was confirmed that it is preferable for the height of the convex portion to be 60% or more of the thickness of the refractory material from the viewpoint of increasing the amount of heat transfer from the surface and particularly lowering the boundary temperature.
[Experimental Example 3]
Except for changing the material of the jacket, a thermal fluid analysis simulation was performed in the same manner as in Experimental Example 1. As the material of the jacket, Ni steel was used in Experimental Example 3-1, Cr steel in Experimental Example 3-2, iron in Experimental Example 3-3, and copper in Experimental Example 3-4.

The parameters of the modified outer shell are shown in Table 2.

The number of protrusions arranged along the height direction was three, and the height L1221 of the protrusions was 70 mm.

Experimental Examples 3-1 to 3-4 are all examples of the present invention.

The results of the thermal fluid analysis are shown in Figures 8(A) to 8(D) and 9.

Figures 8(A) to 8(D) show the temperature distribution in the internal space 11 and furnace side wall 12 in each experimental example. Figures 8(A) to 8(D) are temperature distribution diagrams in the parts corresponding to Figure 2, and in Figure 8(A) the internal space 11, refractory material 121, and outer casing 122 are numbered. The same parts in the other figures refer to the same components. The results of experimental example 3-1 are shown in Figure 8(A), the results of experimental example 3-2 in Figure 8(B), the results of experimental example 3-3 in Figure 8(C), and the results of experimental example 3-4 in Figure 8(D).

Figure 9 shows the normalized surface heat transfer rate against the thermal conductivity of the outer casing. The greater the surface heat transfer rate, the more sufficient the cooling is.

As is clear from the results in Figure 9, sufficient cooling was achieved regardless of the material of the outer casing, but it was confirmed that there was a tendency for the amount of heat dissipated from the surface to increase by increasing the thermal conductivity of the outer casing.

10 Metal melting furnace 11 Internal space 12 Furnace side wall 121 Refractory 1211 Concave portion 122 Outer cover 122A Inner surface 1221 Convex portion 13 Electrode

Claims (3)

A metal melting furnace for melting a material containing a metal component, comprising:
The metal melting furnace comprises:
an internal space for accommodating the object to be melted;
A furnace side wall defining a side surface of the internal space;
an electrode disposed in the internal space along a height direction,
The furnace side wall includes a refractory material disposed on the inner space side,
A metal jacket covering an outer surface of the refractory material,
The outer jacket has a plurality of plate-shaped protrusions arranged along a height direction on a surface facing the refractory,
The protrusion is fitted into a recess in a surface of the refractory facing the jacket ,
a height of the protrusion from the inner surface of the outer covering toward the internal space is 60% or more of a thickness of the refractory material,
The metal melting furnace has three convex portions arranged along the height direction . 2. The metal melting furnace according to claim 1 , wherein the outer casing is made of a metal having a thermal conductivity of 10 W/m·K or more and 200 W/m·K or less. 3. The metal melting furnace according to claim 1 , wherein in a horizontal cross section passing through said protrusion and perpendicular to the height direction, said protrusion is disposed so as to cover at least the region of said outer casing that faces said electrode.

Images