JP2023117512A - Furnace cover and furnace cover cooling method - Google Patents

Abstract

To provide a furnace cover capable of suppressing the generation of heat cracks in an inner wall therein, and a furnace cover cooling method.SOLUTION: A furnace cover covering an opening upper end face of a container comprises: a hollow cooling chamber provided therein; a nozzle provided for injecting cooling water toward an inner wall inside the cooling chamber; and an annular drainage provided over all the circumference of a lower end part of the cooling chamber; and an exhaust port connected to the drainage. In the inner wall side of the drainage, the inner diameter thereof is larger than the opening inner diameter of the container, and the inner wall side of the drainage lower than a position in which the inner diameter is made maximum has a cylindrical shape with the same inner diameter or is diameter-reduced downward. Also provided is a furnace cover cooling method in which cooling water is injected to the inner wall inside the cooling chamber from the nozzle to cool the inner wall, and the cooling water injected to the inner wall is drained from the exhaust port to the outside of the furnace cover via the drainage.SELECTED DRAWING: Figure 1

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a furnace lid covering an upper end surface of an opening of a container such as a pot smelting furnace or an electric furnace, and a method of cooling the furnace lid.

Furnace lids of containers containing hot molten metal, such as pot refining furnaces and electric furnace containers, may be deformed or melted due to high heat during refining. As a countermeasure, a spray type furnace lid is known, which cools the furnace lid by injecting cooling water into a hollow cooling chamber formed therein. The spray type furnace lid cools the inner wall surface of the furnace lid with water jets, so that a large cooling effect can be obtained with a small flow rate compared to the water cooling jacket method. However, the area below the water level of the wastewater accumulated on the bottom of the furnace lid is not exposed to the spray water and can only be cooled slowly due to the slow flow speed toward the wastewater outlet. may lead to A water leak may cause a steam explosion due to contact with the high-temperature molten metal in the container, which poses a serious safety problem.

As a countermeasure to this, Patent Document 1 discloses a method of providing an outer peripheral drainage groove and allowing the drainage to naturally fall into the outer peripheral drainage groove. Patent Literature 2 discloses a method of installing a nozzle for accelerating a drainage flow in a drainage channel. Patent Literature 3 discloses a method of sucking and discharging waste water with a vacuum pump and a method of installing a water cooling jacket at the bottom inside the furnace lid.

JP-A-7-260367 JP-A-10-246576 JP 2017-116186 A

The above prior art has the following problems.

In the method of Patent Document 1, by providing a drainage groove on the outer periphery of the furnace lid, it is possible to suppress the accumulation of waste water on the bottom surface of the furnace lid, and it is possible to prevent insufficient cooling from occurring at the bottom surface of the furnace lid. . However, since the drainage ditch protrudes toward the outer peripheral surface of the furnace lid, it may interfere with the suspension arms of the furnace lid and surrounding equipment. For this reason, it is difficult to provide a drainage groove over the entire circumference of the furnace lid, resulting in insufficient cooling in places where no drainage groove is provided.

In the method of Patent Document 2, by providing a nozzle that accelerates the flow of waste water, it is possible to suppress accumulation of waste water in the drainage channel. However, in order to obtain a sufficiently high flow velocity, a large amount of water is required in addition to the spray water, which inevitably leads to an increase in the size of the wastewater treatment apparatus.

In the method disclosed in Patent Document 3, in which waste water is sucked and discharged by a vacuum pump, it is possible to suppress accumulation of waste water on the bottom surface of the furnace lid by sucking and discharging the waste water with the vacuum pump. However, a vacuum pump that sucks and discharges such a large amount of waste water has strict device specifications and is expensive.

In the method of installing a water-cooling jacket inside the lower part of the furnace lid disclosed in Patent Document 3, the water-cooling jacket cools the furnace lid, thereby solving the problem of insufficient cooling of the bottom portion of the furnace lid. However, when a new small water channel is provided inside the furnace so as to cover the stagnant water part at the bottom of the furnace lid, it is necessary to pump the cooling water to increase the flow rate in order to obtain a sufficient cooling effect. If the small waterway is damaged during operation, for example by splashing molten metal, the pressure of pumping will cause a large amount of cooling water to spout, creating a safety risk. In the case of spray cooling and stagnant water, there is no risk of blowout because the pressure inside the furnace lid is atmospheric.

In addition to the above, there is a method known to increase the width of the drainage channel by enlarging the outer diameter of the furnace cover in order to lower the water level of the drainage. However, it causes interference with surrounding equipment, and the weight of the furnace lid is significantly increased, which increases the size of the lifting device for the furnace lid, resulting in high equipment cost.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a spray cooling type furnace lid and a cooling method for the furnace lid that suppresses the occurrence of heat cracks on the inner wall of the furnace lid.

The furnace lid according to the present invention, which advantageously solves the above problems, is constructed as follows.

[1] A hollow cooling chamber provided in the furnace lid covering the upper end surface of the opening of the container, a nozzle provided for injecting cooling water toward the inner wall in the cooling chamber, and the cooling chamber An annular drainage channel provided in the circumferential direction at the lower end, and a drainage port connected to the drainage channel, the inner diameter of the inner wall side of the drainage channel being larger than the inner diameter of the opening of the container. The inner wall side of the drainage channel below the position where the inner wall side has the maximum inner diameter is a furnace cover that has a cylindrical shape with the same inner diameter or has a diameter that decreases downward.
[2] In the above [1], the inner wall side above the position where the inner wall side of the drainage channel has the maximum inner diameter is a furnace lid that forms an inclined surface whose inner diameter increases downward.
[3] In the above [1] or [2], the position where the inner diameter on the inner wall side of the drainage channel is maximum is the furnace lid below the water surface of the maximum water level of the cooling water existing in the drainage channel. .
[4] In any one of the above [1] to [3], there is further provided an outer peripheral drainage ditch connected to the branch of the drainage channel and arranged outside the drainage channel and at a position lower than the drainage channel. and at least the inside diameter of the inner wall side other than the branching portion of the drainage channel is larger than the inside diameter of the opening of the vessel.
[5] In any one of the above [1] to [4], the maximum inner diameter of the inner wall side of the drainage channel is set based on the water surface position of the maximum water level of the cooling water existing in the drainage channel. is the lid.
[6] In the above [5], when the furnace lid is attached to the container containing the molten metal, the setback of the inner wall of the furnace lid satisfies the equation (1): is.
(setback amount)/(height of molten metal surface)>0.10 Expression (1)
Here, in the above formula (1), the setback amount is the amount of outward displacement of the lower end of the inner wall side of the drainage channel with respect to the upper end of the opening of the container, and the height of the molten metal surface is the upper end of the opening of the container. It is the distance from the end face to the molten metal surface.

A furnace lid cooling method according to the present invention, which advantageously solves the above problems, is configured as follows.
[7] Using the furnace lid according to any one of [1] to [6] above, cooling the inner wall by injecting cooling water from the nozzle to the inner wall in the cooling chamber, and injecting it to the inner wall This is a cooling method for the furnace lid, in which the cooling water for cooling is drained out of the furnace lid from a drain port through a drainage channel.

When attaching the furnace lid to the upper end surface of the opening of the container, the present invention displaces the inner wall side of the annular drainage channel provided at the lower end of the hollow cooling chamber to the outside of the opening of the container, that is, the inner wall side of the drainage channel. The inner diameter is formed larger than the inner diameter of the container opening, and the inner wall side of the drainage channel below the position where the inner diameter is maximized is made cylindrical or the diameter is reduced toward the inside of the container to reduce the water level of the drained water. Therefore, heat cracks can be suppressed by reducing the heat load.
In addition, since the present invention does not require a vacuum pump and a large amount of wastewater treatment equipment, the equipment cost can be kept down. be.

1 is a schematic horizontal sectional view showing one embodiment of a furnace lid of the present invention; FIG. 1 is a schematic vertical cross-sectional view of the outer peripheral portion showing one embodiment of the furnace lid of the present invention, (a) is a cross-sectional view along AA in FIG. 1, and (b) is a cross-sectional view along BB in FIG. 1, and (c) is a cross-sectional view taken along the line CC of FIG. It is a conventional furnace lid, (a) is a schematic horizontal sectional view, and (b) is a schematic longitudinal sectional view. It is a schematic diagram explaining the relationship between the setback of the inner wall and the molten steel surface (molten metal surface) seen from the height of the water surface of the drainage channel. It is a graph which shows the relationship between the amount of setback/height of a molten steel surface (molten metal surface), a visible molten steel area ratio, and a drainage water level.

A furnace lid according to an embodiment of the present invention is for covering the upper end surface of the opening of a container such as a ladle refining furnace or an electric furnace. Molten steel, which is an example of molten metal, is contained in the container. An example of the furnace lid according to this embodiment is shown in FIGS. 1 and 2. FIG. The furnace lid of this embodiment forms a hollow cooling chamber, and the cooling chamber has a structure including a cooling function by cooling water, a drainage function for draining cooling water, and a radiant heat reduction function for reducing radiant heat of molten steel. An example of a conventional furnace lid is shown in FIG. In the cooling chamber of the conventional furnace lid, the cooling water sprayed on the inner wall 7 is collected through the drainage channel 1 to one drainage port 1A. The inner wall side of the drainage channel 1 has a cylindrical shape with the same inner diameter, which matches the inner diameter of the upper end of the opening of the container 20 . A furnace lid suspension arm 3 is provided on the outer circumference of the furnace lid. The furnace lid suspension arms 3 are used to lift the furnace lid, and the four furnace lid suspension arms 3 protrude from the four sides of the furnace lid. In the example shown in FIG. 1, only two of the four furnace lid suspension arms 3 are shown.

<Cooling function>
As shown in FIG. 2( c ), the furnace roof of this embodiment forms a hollow cooling chamber surrounded by an inner wall 7 , an outer wall 8 and a bottom wall 11 . A plurality of nozzles 13 are provided within the cooling chamber. A pipe for supplying cooling water is connected to the nozzle 13, and the cooling water is jetted from the nozzle 13 toward the inner wall 7 in the cooling chamber to cool the inner wall 7. As shown in FIG.

<Drainage function>
As shown in FIGS. 1 and 2(b), the lower end of the cooling chamber, which is the bottom surface of the furnace lid (the portion surrounded by the inner wall 7, the outer wall 8, and the bottom wall 11), has an annular drainage channel 1 all around. It has become. Cooling water jetted from the nozzle 13 to the inner wall 7 is accumulated. The cooling water 15 collected in the drainage channel 1 is directed to the drainage port 1A connected to the drainage channel 1 via the drainage channel 1, and is drained out of the furnace lid from the drainage port 1A.

Further, as shown in FIGS. 1 and 2(a), it is preferable that a peripheral drainage groove 2 is partially connected to the drainage path 1 formed at the lower end of the cooling chamber. That is, the drainage channel 1 has a branched portion 4 to which the outer peripheral drainage groove 2 is connected and a non-branched portion 5 to which the outer peripheral drainage groove 2 is not connected. The outer peripheral drainage groove 2 is provided outside the drainage channel 1 and at a position lower than the drainage channel 1.例文帳に追加Thus, the water level in the drainage channel 1 of the furnace lid can be lowered by providing the outer peripheral drainage channel 2 . Thereby, the cooling effect of the inner wall 7 of the furnace lid can be improved.

Further, as an example of the present embodiment, it is preferable to form the outer peripheral drainage groove 2 only on the side of the furnace lid opposite to the side on which the container is attached and detached. In the example shown in FIG. 1, the outer drainage groove 2 is formed only in the left half of the furnace lid. As a result, when the container (pot) is moved from the right side to the left side of the furnace lid and the furnace lid is attached to the container, it is possible to prevent the outer peripheral drainage groove 2 from interfering with the container and damaging the outer peripheral drainage groove 2. can be done.

<Radiation heat reduction function>
As shown in FIGS. 2(b) and 2(c), an enlarged diameter portion 9 is formed on the inner wall 7 side of the drainage channel 1 of the furnace lid. This enlarged diameter portion 9 has an inner diameter larger than the inner diameter of the opening of the container 20, and below the position 10B where the inner diameter is the maximum (that is, the lower part 10 of the enlarged diameter portion), the inner diameter of the inner wall 7 side of the drainage channel 1 is It has the same cylindrical shape, or the inner diameter of the drain channel 1 on the inner wall 7 side becomes smaller as it goes downward. When the lower portion 10 is cylindrical with the same inner diameter, the upper end is the position 10B where the inner diameter becomes the maximum.

Specifically, the enlarged diameter portion 9 is divided into an “upper portion” 10A above the position where the inner diameter is maximum and a “lower portion” 10 below the position 10B where the inner diameter is maximized. 10A has an inner diameter on the inner wall 7 side of the drainage channel 1 that increases downward, and has an inclined surface (substantially truncated cone surface). On the other hand, the lower portion 10 of the expanded diameter portion is cylindrical (vertical surface) having the same inner diameter on the inner wall 7 side of the drainage channel 1 in the examples of FIGS. 2(b) and 2(c). The position 10B where the inner wall 7 side of the drainage channel 1 has the maximum inner diameter is preferably below the maximum water level of the cooling water (drainage) 15 accumulated in the drainage channel 1 . Furthermore, it is more preferable to be above the water surface of the minimum water level of the cooling water 15 accumulated in the drainage channel 1 .

In addition, the lower part 10 of the expanded diameter portion is not a cylindrical shape having the same inner diameter on the inner wall 7 side of the drainage channel 1, but an inclined surface (substantially truncated) in which the inner diameter on the inner wall 7 side of the drainage channel 1 decreases as it goes downward. conical surface). Further, the upper portion 10A of the enlarged diameter portion is not limited to an inclined surface as long as it has a shape such that the inner diameter of the furnace lid increases as it goes downward.

By making the upper portion 10A of the enlarged diameter portion an inclined surface, the angle of the inner wall 7 can be made substantially perpendicular to the angle of the nozzle 13 (the angle of cooling water sprayed from the nozzle 13), and the heat removal efficiency is improved. can be raised. In addition, by forming the upper portion 10A of the enlarged diameter portion into an inclined surface shape, it is possible to suppress accumulation of waste water (cooling water) as compared with the case where the upper portion 10A is formed into a stepped shape.

In this embodiment, the enlarged diameter portion 9 described above is formed on the entire circumference of the drainage channel 1 on the inner wall 7 side, that is, on both the branched portion 4 and the non-branched portion 5 . However, since it is the non-branched portion 5 where the outer peripheral drainage groove 2 is not provided that the drainage tends to accumulate, the enlarged diameter portion 9 should be formed at least on the inner wall 7 facing the non-branched portion 5 of the drainage channel 1. Just do it. That is, the outer peripheral drainage groove 2 is connected to the branch portion 4 of the drainage channel 1, and the inner wall 7 side of the branch portion 4 of the drainage channel 1 may be cylindrical with the same radius as the inner diameter of the opening of the container. By making the inner wall 7 side of the branch portion 4 provided with the outer peripheral drainage groove 2 cylindrical with the same inner diameter as the upper end of the opening of the container, the furnace lid can be easily manufactured and repaired. In addition, since the upper end surface of the opening of the vessel overlaps the bottom wall 11 of the furnace lid to a large extent, it is possible to improve the insulation between the molten steel and the outside air.

In this embodiment, especially in the non-branched portion 5 of the drainage channel 1 where the outer peripheral drainage groove 2 is not provided, the enlarged diameter portion 9 is formed by shifting the lower end of the drainage channel 1 on the inner wall 7 side to the outside of the container as shown in FIG. Form. Here, in the following description, the outward displacement of the lower end of the drain channel 1 on the inner wall 7 side with respect to the upper end of the opening of the container is referred to as a setback 12 .
Due to this setback 12, when the furnace lid is attached to the vessel 20, part of the radiant heat emitted from the molten steel surface (molten metal surface) 14 is blocked by the edge of the upper end of the opening of the vessel 20, and the drainage path 1 does not reach the inner wall 7 side. This effect becomes more pronounced toward the bottom.

In addition, in the inner wall 7 of the furnace lid of the present embodiment, the portion above the water level 18 of the cooling water 15 (drainage pool water) accumulated in the drainage channel 1 is strongly cooled by the cooling water spray, so that heat cracks is unlikely to occur. On the other hand, the effect of blocking the radiation heat emitted from the molten steel surface (molten metal surface) 14 is more pronounced in the portion below the water level 18 of the stagnant water.
Therefore, from the viewpoint of cooling and heat load, heat cracks are most likely to occur in the inner wall 7 (iron shell) portion of the water level height 18 of the pooled water in the drainage channel 1, and it is important to lower the water level height. .

The water level 18 of the pooled water in the drainage channel 1 is determined by the flow rate at which the pooled water flows into the branch 4 (the range where almost no drainage is collected) where the outer drainage ditch 2 is located, which corresponds to a square weir. Yes, according to Torricelli's theorem, the deeper the water level, the higher the outflow velocity.
For this reason, if the lower part 10 of the enlarged diameter part 9 of the inner wall 7 of the furnace lid is inclined outward, that is, if the inner diameter is increased downward, the outflow velocity increases. The horizontal area at the location is smaller, resulting in a higher water level for the same outflow.
On the other hand, the inner diameter of the lower part 10 of the enlarged diameter portion 9 of the inner wall 7 of the furnace lid is not changed, that is, it is vertically downward, or the inner diameter is decreased, that is, it is inclined inward of the container 20, and the water level is increased. It is possible to lower the water level by widening the horizontal area at a deeper position.

Further, in the present embodiment, the position 10B where the inner diameter of the enlarged diameter portion 9 is maximum (the position of the maximum inner diameter) is based on the maximum water level height 18 of the cooling water 15 (drainage stagnant water) accumulated in the drainage channel 1. set. Assuming that the position of the outer wall 8 of the furnace lid is constant, the larger the inner diameter of the inner wall 7, the more the effect of reducing the heat load of the inner wall 7, that is, the area 17 where the molten steel surface 14 is blocked by the edge of the vessel increases. While it is effective, there is a contradictory relationship that the channel of the drainage channel 1 becomes narrower and the water level rises, and the position of the inner wall 7 has an optimum value. In addition, between the setback 12 amount of the inner wall 7 and the height of the molten steel surface (molten metal surface) 14 (the distance 19 from the upper end surface of the opening of the container to the molten steel surface (molten metal surface) 14), There is a correlation.

Therefore, the molten steel (molten Regarding the relationship between the ratio of the visible molten steel area 16, which is the surface area of metal), and the water level height 18 (drainage water level) of the pooled water (drainage water level), the case where the outer drainage ditch 2 is installed (Fig. 1) and the conventional drainage channel 1 FIG. 5 shows the results of the investigation in the case (FIG. 3). Here, the amount of setback 12 is the amount of outward displacement of the lower end of the inner wall 7 side of the drainage channel 1 with respect to the upper end of the opening of the container 20, that is, the difference between the inner diameter of the opening of the container 20 and the maximum inner diameter 10B of the expanded diameter portion 9. It means the distance of the difference (radius difference) (Fig. 2(c), Fig. 4). In either case, the ratio of the visible molten steel area 16 decreases as the (setback 12 amount)/(distance 19) increases to 0.20.
However, since the water level 18 of the stagnant water rises accordingly, the visible molten steel area 16 rather increases when the (setback 12 amount)/(distance 19) exceeds 0.20. Therefore, in FIG. 5, the optimum value of (setback 12 amount)/(distance 19) is 0.20.
From the viewpoint of reducing the heat load on the inner wall, the visible molten steel area 16 is preferably 90% or less. 19) is 0.10, the visible molten steel area 16 is 90%. Therefore, the setback when the furnace lid is attached to the container containing the molten metal is set within a range that satisfies the following formula (1) in order to reduce the heat load on the inner wall.
(setback amount)/(height of molten metal surface)>0.10 Expression (1)

In addition, when the outer drainage ditch 2 is installed, the water level 18 of the drainage pool water in the drainage channel 1 is low, so the ratio of the visible molten steel area 16 is higher when the outer drainage ditch 2 is installed. can be lowered.

ｖ（ｙ）：排水の水面の高さｈから深さｙにおける流出速度
ｇ：重力加速度
Ｗ：排水路から２カ所の流出 流出断面の幅 ２８１ｍｍ
Ｑ：流出量
排水量＝給水量：１８０ ｔ／ｈ
その結果、排水水位ｈは９６．８ｍｍ、可視溶鋼面積の割合は１００％（セットバックなし）であった。炉蓋の内壁において、排水の水面高さ位置で微小のヒートクラックが観察された。これは、水位９６．８ｍｍから下の内壁は、スプレー水による強冷却を受けられず、熱負荷を受けたためと考えられる。 In the conventional furnace lid and the furnace lid of the above-described embodiment, the inner wall surface of the furnace lid was cooled and the effect thereof was confirmed.
(1) Conventional furnace cover (Fig. 3)
The heat transfer coefficient on the inner wall of the furnace lid is 6,000 to 7,500 W/m ² ·K, and the heat transfer coefficient on the wastewater pool is 600 to 2,500 W/m ² ·K. It has a higher cooling capacity than stagnant water in drainage channels.
The maximum water level h of stagnation in the drainage channel was calculated as follows.

v (y): Outflow velocity g at depth y from height h of water surface of drainage: Gravitational acceleration W: Outflow from drainage channel at two locations Width of outflow cross section 281 mm
Q: Outflow amount Wastewater amount = Water supply amount: 180 t/h
As a result, the drain water level h was 96.8 mm, and the percentage of visible molten steel area was 100% (no setback). On the inner wall of the furnace lid, minute heat cracks were observed at the height of the water surface of the waste water. It is considered that this is because the inner wall below the water level of 96.8 mm could not be strongly cooled by the spray water and received a heat load.

(2) Furnace cover of the above embodiment (Figs. 1 and 2)
A nozzle for injecting cooling water is installed in the hollow part of the furnace lid, a peripheral drainage groove is installed, and an enlarged diameter part is formed at the lower end of the inner wall (inner wall side of the drainage channel) to expand the inner diameter of the furnace lid. The upper portion of the enlarged diameter portion was inclined downward, and the lower portion 10 of the enlarged diameter portion was cylindrical. (Amount of setback)/(Height of molten metal surface) was 0.20.
As a result, the drainage water level was 120.0 mm, and the ratio of the visible molten steel area was evaluated as 76%. No heat cracks occurred on the inner wall of the furnace cover.

1 Drainage channel 1A Drain port 2 Peripheral drainage groove 3 Furnace lid suspension arm 4 Branched part 5 Non-branched part 7 Inner wall 8 Outer wall 9 Expanded diameter part 10 Lower part of expanded diameter part 10A Upper part of expanded diameter part 10B The inner diameter of the expanded diameter part is maximum 11 bottom wall 12 setback 13 nozzle 14 molten steel surface (molten metal surface)
15 Cooling water accumulated in the drainage channel (drainage accumulated water)
16 Surface area of molten steel (molten metal) that can be seen from the water surface height of the drainage pool: Visible molten steel area 17 Area where the molten steel (molten metal surface) is blocked by the edge of the container 18 Water level height of the drainage pool 19 Opening of the container Distance from the upper end surface of the part to the molten steel surface (molten metal surface) 20 Container

Claims (7)

A hollow cooling chamber provided in the furnace lid covering the upper end surface of the opening of the container;
a nozzle provided for injecting cooling water toward the inner wall of the cooling chamber;
an annular drainage channel provided in the lower end of the cooling chamber in its circumferential direction;
a drain port connected to the drain channel;
with
The inner diameter of the inner wall side of the drainage channel is larger than the inner diameter of the opening of the container, and the inner wall side of the drainage channel below the position where the inner diameter of the inner wall side is the maximum is cylindrical with the same inner diameter. or downwardly tapering. 2. The furnace lid according to claim 1, wherein the inner wall side above the position where the inner wall side of the drainage channel has the maximum inner diameter forms an inclined surface whose inner diameter increases downward. 3. The furnace lid according to claim 1 or 2, wherein the position at which the inner wall side of the drainage channel has the maximum inner diameter is below the water surface of the maximum water level of the cooling water present in the drainage channel. Furthermore, it has an outer peripheral drainage ditch connected to the branched portion of the drainage channel, arranged outside the drainage channel and at a position lower than the drainage channel, and at least on the inner wall side other than the branched portion of the drainage channel. 4. Furnace lid according to any one of claims 1 to 3, wherein the inner diameter is larger than the inner diameter of the opening of the vessel. 5. The furnace lid according to any one of claims 1 to 4, wherein the maximum inner diameter of the inner wall side of the drainage channel is set based on the water surface position of the maximum water level of the cooling water present in the drainage channel. 6. The furnace lid according to claim 5, wherein the setback of the inner wall of the furnace lid satisfies equation (1) when the furnace lid is attached to the vessel containing the molten metal.
(setback amount)/(height of molten metal surface)>0.10 Expression (1)
Here, in the above formula (1), the setback amount is the amount of outward displacement of the lower end of the inner wall side of the drainage channel with respect to the upper end of the opening of the container, and the height of the molten metal surface is the upper end of the opening of the container. It is the distance from the end face to the molten metal surface. Using the furnace lid according to any one of claims 1 to 6, the inner wall is cooled by injecting cooling water from the nozzle to the inner wall in the cooling chamber, and the cooling water injected to the inner wall is A method for cooling a furnace lid, in which water is drained out of the furnace lid from a drain port through a drainage channel.

Images