JP5073269B2 - Method of cooling the iron shell of RH equipment - Google Patents

Description

  The present invention relates to a method for cooling an iron shell of an RH device.

As is well known, the RH apparatus includes a ladle charged with molten steel to be refined and a degassing tank provided on the upper side of the ladle. Two dip pipes immersed in the molten steel in the ladle are provided at the lower part of the degassing tank. An inert gas such as Ar gas is blown into one of the dip pipes, and the molten steel is placed in the degassing tank. By circulating, dehydrogenation of molten steel, denitrogenation, floating separation of inclusions, etc. are performed, and this refining is indispensable for the production of high cleanliness steel.
In the secondary refining in the RH apparatus, there is a case where the molten steel must be heated for operation. In such a case, oxygen is blown into it using an upper blowing lance inserted into the degassing tank. Then, an alloy metal such as Al is introduced into the degassing tank to raise the temperature of the molten steel (oxygen heat).

A degassing tank for performing such an operation includes an iron shell and a refractory disposed inside the iron shell. This refractory is composed of magnesia carbon brick, magcro brick, etc., and gradually melts and is damaged as the molten steel is refined.
When the refractory is melted or damaged, the thickness of the refractory decreases, and as a result, the iron skin located outside the refractory becomes hot, causing problems such as deformation, red heat, and perforations. May occur.
Therefore, the refractory inside the iron skin is replaced or the repair material is sprayed on the refractory regularly, but it is difficult to grasp the actual thickness of the refractory because of the operation. There is a risk of refining molten steel in a thin state. When refining with a thin refractory, deformation of the iron skin, red heat, and even the possibility of perforation increase, so cooling the iron skin of the RH device has been conventionally performed during secondary refining. ing.

For example, in the steel making furnace core cooling device of Patent Document 1, that is, the converter, the furnace body is cooled by mist while the temperature of the furnace body is measured by a measurement mechanism (thermocouple).
In the RH vacuum degassing furnace of Patent Document 2, gas is blown to the iron skin at the bottom of the lower tank while performing an operation without raising the temperature and measuring the iron skin temperature at the bottom of the degas tank. In this way, the iron skin is cooled. In particular, the flow rate of the cooling gas is controlled by the measured iron skin temperature.
In addition, as a technique for increasing the temperature of oxygen during secondary refining, there is a technique disclosed in Patent Document 3. In this technique, oxygen gas is injected into an RH vacuum degassing tank to raise the temperature of molten steel.
Special notice 5-027683 JP-A-10-287914 Japanese Patent No. 2722998

As described above, it is necessary to operate an RH apparatus that performs oxygen heating while cooling in order to prevent deformation, red heat, and perforation of the iron skin.
However, since the technique of Patent Document 1 is a cooling method for the iron skin of the converter, even if the technique is applied, the operation form is completely different between the converter and the RH apparatus. It is impossible to reliably cool the apparatus.
Even if the technique shown in Patent Document 2 (iron shell cooling for an RH device that does not perform oxygen heating) is applied, the operating conditions are different from those of an RH device that performs oxygen heating, and as a result, cooling is not appropriate. There is a risk of deformation of the iron skin.

On the other hand, as an operation of the RH apparatus that performs oxygen heating, there is one as shown in Patent Document 3, but this technique does not disclose cooling at all.
Although it is conceivable to apply the technique of Patent Document 2 to Patent Document 3, the operation shown in Patent Document 2 and the operation of Patent Document 3 are significantly different from each other. There is a possibility that the deformation of the material may occur.
Therefore, the present invention provides a method for cooling the iron shell of an RH device that can appropriately cool the RH device that performs secondary refining of molten steel while raising the temperature using oxygen gas to prevent iron-shell trouble. The purpose is to provide.

In order to achieve the above object, the present invention has taken the following measures.
That is, the present invention is a method for cooling an iron shell of an RH apparatus that performs an operation in which at least one charge for performing heating using oxygen gas is present, and the heating is performed using the oxygen gas with respect to the total number of charges. From the oxygen heating ratio indicating the ratio of the number of charges, the average amount of oxygen gas for heating, which is obtained by dividing the total amount of oxygen gas used for heating by the total number of charges, and the iron skin temperature of the RH device It is characterized in that the necessity / unnecessity of cooling is determined and cooling to the iron skin is performed based on the determination result.

First, the inventors of the present application have verified from various angles how the oxygen gas has an effect on the refractory in the RH operation in which the molten steel is heated using oxygen gas.
As a result, when heating the molten steel using oxygen gas,
(i) Since the atmospheric temperature rises due to the heat of oxidation reaction, the rate of damage to refractories is faster than when the molten steel is not heated.
(ii) Oxide gas is produced by reaction of metal or alloy attached to the refractory with oxygen gas, which causes damage to the refractory.
I came to know the phenomenon.

Therefore, the inventor pays attention to the oxygen heating ratio and the average heating oxygen gas amount, which are indicators of oxygen gas blowing, because oxygen gas greatly affects the damage of the refractory. The necessity / unnecessity of cooling of the iron skin was determined from the iron skin temperature of the RH apparatus.
The oxygen heating ratio indicates the ratio of the number of charges that have been heated with oxygen gas to the total number of charges. If oxygen gas is blown in, the temperature of the molten steel and the atmospheric temperature in the degassing tank will rise, so the oxygen heating rate will be the ratio of the degassing tank to the total charge by blowing oxygen gas. It shows how the temperature has increased and how often oxide damage has occurred.

The average amount of oxygen gas for heating is the total amount of oxygen gas used for heating, divided by the total number of charges. How high the temperature of the degassing tank is, or how much oxide is It indicates whether it occurred.
Even if it is an operation that performs oxygen heating by determining whether or not cooling is necessary from such oxygen heating ratio, average heating oxygen gas amount, and iron skin temperature, and performing cooling. It is possible to properly cool the iron skin and prevent trouble of the iron skin.
The most preferable technical means of the present invention is a method for cooling an iron shell of an RH apparatus that performs an operation in which at least one charge for performing heating using oxygen gas is present, wherein The oxygen heating ratio indicating the ratio of the number of charges heated by oxygen gas, the average amount of oxygen gas for heating, which is obtained by dividing the total amount of oxygen gas used for heating by the total number of charges, and iron of the RH device Create a control chart with skin temperature as a parameter and the control curve described in the control chart, and the ratio of the number of charges that were heated with oxygen gas to the number of charges from the start of operation to the charge Is the oxygen heating ratio, and the total amount of oxygen gas used for heating up to the charge divided by the number of charges from the start of operation to the charge is the average heating oxygen gas. On which the amount applied to the control chart and management curves were created, determines Y / N of furnace shell cooling from application result, there is performed a cooling of the furnace shell on the basis of the determination result.

  According to the present invention, in an RH device that performs secondary refining of molten steel while heating the molten steel using oxygen gas, it is possible to properly cool the iron skin and reliably prevent iron skin troubles. .

A method for cooling an iron shell of an RH device according to the present invention will be described below with reference to the drawings.
First, the RH device 1 will be described in detail.
As shown in FIG. 1, the RH apparatus 1 performs dehydrogenation, denitrogenation, decarburization, deoxidation, floating separation of inclusions, and the like of molten steel 2 that has been discharged from a converter. The RH apparatus 1 includes a ladle 3 in which molten steel 2 is charged, a degassing tank 4 that is disposed above the ladle 3 and degasses the molten steel 2 by circulating the molten steel 2 therein. have.
As shown in FIG. 2, the degassing tank 4 includes a canopy 5, an upper tank 6, and a lower tank 7. The upper tank 6 is provided with an exhaust port 8 for exhausting the gas in the degassing tank 4. Below the exhaust port 8 of the upper tank 6, there is provided an alloy chute portion 9 for introducing an alloy such as Si, Mn, or Al into the degassing tank 4. A lance 10 for blowing oxygen gas is inserted into the upper tank 6 through the canopy 5.

  The lower tank 7 is provided with two dip tubes 11, 11 protruding downward from the lower tank 7. The dip tubes 11 and 11 are immersed in the molten steel 2 charged in the ladle 3, and one of the two dip tubes 11 and 11 has an inert gas such as Ar gas. A blow-in port 15 is provided for blowing air. The lower tank 7 and the upper tank 6 are detachably connected. When the lower tank 7 and the upper tank 6 are connected, a processing space for processing the molten steel 2 is formed in the degassing tank 4. The upper tank 6 and the lower tank 7 have an iron skin 12 and a refractory 13 provided inside the iron skin 12. The refractory 13 is composed of magnesia carbon brick, magcro brick, or the like.

In the RH apparatus 1 described above, the dip tube 11 is immersed in the molten steel 2 in the pan 3, the gas in the degassing tank 4 is exhausted from the exhaust port 8, the inside of the degassing tank 4 is brought into a substantially vacuum state, and the blowing port 15, the molten steel 2 is circulated through the ladle 3 → the one dip pipe 11 → the degassing tank 4 → the other dip pipe 11 → the ladle 3, and hydrogen existing in the molten steel 2. The gas component is removed.
Hereinafter, the iron shell cooling method of the RH device 1 according to the present invention will be described in detail.
The iron shell cooling method of the present invention, when a plurality of charges for secondary refining of the molten steel 2 by the RH device 1 are collectively (all charges), at least one charge is oxygen gas using the lance 10. The present invention is applied to an operation in which the molten steel 2 is heated by blowing into the degassing tank 4 (hereinafter sometimes referred to as oxygen heating).

  When performing the secondary refining process of the molten steel 2 produced from the converter using the RH apparatus 1, the heat generated in the RH apparatus 1 is converted to iron through the refractory 13 attached inside the RH apparatus 1. It is transmitted to the skin 12. Therefore, the temperature of the iron skin 12 gradually increases with the progress of the process from the start of the process, and after a certain amount of time has passed, the temperature becomes substantially constant. Therefore, even if the thickness of the refractory 13 in the degassing tank 4 is thin, if the treatment time is short, the treatment is finished before the iron skin temperature rises, so iron reflecting the actual thickness of the refractory 13 The skin temperature will not be indicated. In such a case, relying only on the iron skin temperature overlooks that the remaining thickness of the refractory 13 is small, and the iron skin 12 cannot be cooled and trouble of the iron skin 12 occurs.

On the other hand, when oxygen is heated, the degassing tank 4 is heated by oxidation reaction and the ambient temperature becomes higher than usual, and a large amount of oxide is generated. Therefore, the refractory in the degassing tank 4 is heated by oxygen heating. No. 13 is more damaging than an operation that does not raise the temperature of oxygen.
Therefore, the timing at which the iron shell cooling is necessary cannot be determined only by the iron skin temperature, and there is a problem in that the cooling is delayed and the iron skin 12 is perforated.
Therefore, in this iron skin cooling method,
(i) `` Oxygen heating ratio '' indicating the ratio of the number of charges that were heated with oxygen gas to the total number of charges from the start of operation to the relevant charge
(ii) “Average amount of oxygen gas for heating” divided by the total number of charges divided by the total amount of oxygen gas used for heating
(iii) The necessity / unnecessity of the cooling of the iron skin 12 is determined from the three iron skin temperatures of the RH device 1, and the iron skin 12 is cooled based on the result.

In other words, even if the iron skin temperature is low, the degree of damage of the refractory 13 is estimated from the oxygen heating rate and the average heat-up oxygen gas amount, and based on these, cooling is started from a situation where the iron skin temperature is low. It is what is started.
The oxygen heating ratio and the average heating oxygen gas amount are calculated by equations (1) and (2).

Note that the total number of charges is the total number of charges performed after repairing the refractory 13 attached to the inside of the RH device 1 and before performing refractory repair again.
The oxygen heating ratio and the average heating oxygen amount defined by the formulas (1) and (2) indicate how much the temperature in the degassing tank 4 is increased, and oxide damage occurs. It is an index indicating whether or not In addition, even if the average amount of oxygen for heating is low, a high oxygen heating ratio indicates that the oxidation reaction has progressed in the degassing tank 4 and the refractory 13 has been damaged.
Hereinafter, the oxygen heating rate is sometimes referred to as the OB rate, and the average heating oxygen gas amount is sometimes referred to as the average OB amount.

As a means for measuring the iron skin temperature, a radiation thermometer (thermo viewer), a contact thermometer, a thermocouple, or the like may be used. A radiation thermometer that can reliably detect the temperature of the entire skin 12 is most preferable. The measurement of the iron skin temperature may be performed at any timing, such as during the secondary refining process, immediately after the process, or after a predetermined time after the process, and continuously throughout the process.
Further, in the iron skin cooling method according to the present invention, various known techniques can be adopted as specific iron skin cooling methods, and air, cooling water mist, spray, and the like are directly supplied from the injection pipe 14 to the iron skin cooling method. You may make it inject | pour into the skin 12, and you may arrange | position cooling piping (not shown) etc. previously to the iron skin 12 of the RH apparatus 1, and may cool indirectly by this cooling piping.

  When cooling is required for the iron skin 12 in a certain part of the RH device 1 based on the OB ratio, the average OB amount, and the iron skin temperature (details will be described in Examples), as described above, The air may be directly or indirectly cooled by injecting air into the 12 part. However, even if it is determined that cooling of the iron skin 12 is unnecessary, the cooling to the iron skin 12 is continued. That is highly preferred.

As Example 1, cooling to the vicinity of the alloy chute portion 9 provided in the upper tank 6 of the RH apparatus 1 will be described.
The portion to be cooled in this embodiment is a portion indicated by A in FIG. The refractory 13 affixed to the alloy chute portion 9 or the joint portion between the alloy chute portion 9 and the upper tank 6 is particularly damaged due to the oxidation reaction of the alloy powder, and the red heat trouble of the iron skin 12 is likely to occur. have.
Therefore, as a result of detailed examination of past operation data in the alloy chute 9, the inventors of the present application have determined a control chart (judgment chart) and a control curve for determining necessity / unnecessity of iron shell cooling as shown in FIGS. 3 and 4. It came to know (judgment curve). 3 and 4, the horizontal axis represents the average OB amount, and the vertical axis represents the iron skin temperature. For example, FIG. 3A shows an OB ratio of 10%, and FIG. 4A shows an OB ratio of 50%.

In FIG. 3 and FIG. 4, “○, ×” is the operation result, “○” is the case where the refractory 13 is sufficiently thick and there is no red heat of the iron skin 12, and “×” is a later inspection. The case where it is judged that the refractory 13 is thin or the iron skin 12 is red hot or distorted is shown, and the situation of “x” should be avoided.
Based on such a control chart, for example, when the OB ratio is 30% at a certain timing, attention is paid to FIG. 3C, and the average OB amount at that time is 160 Nm ³ / ch, and the iron shell of the alloy chute 9 If the temperature is 360 ° C., the iron skin 12 is not cooled. If the temperature is 380 ° C. or higher, the iron skin 12 is cooled.

  Table 1 shows the results of the iron shell cooling using FIGS.

[Example without trouble (i)]
Since the iron shell temperature of the alloy chute 9 exceeded 420 ° C. with an OB ratio of 20% and an average OB amount of 30 Nm ³ / ch, it was determined that iron skin cooling was necessary based on FIG. Therefore, as shown in Table 1, until the RH device 1 was stopped (1560 charge or more), it could be used without trouble of the iron skin 12 such as red heat.
The OB ratio and the average OB amount are values calculated for each charge. As for the iron skin temperature, the maximum temperature in one charge of the refining process is shown. The number of charges in the life of the iron skin indicates the timing when the furnace is stopped for repairing the refractory 13, and the iron skin 12 can be used further as it is. This condition is the same in the following examples.
[Examples without trouble (ii)]
Since the iron shell temperature of the alloy chute portion 9 exceeded 400 ° C. with an OB ratio of 60% and an average OB amount of 40 Nm ³ / ch, it was determined that iron skin cooling was necessary based on FIG. Therefore, as shown in Table 1, until the RH device 1 was stopped (1630 charge or more), it could be used without trouble of the iron skin 12 such as red heat.
[Examples without trouble (iii)]
Since the iron shell temperature of the alloy chute portion 9 exceeded 410 ° C. at an OB ratio of 50% and an average OB amount of 40 Nm ³ / ch, it was determined that iron skin cooling was necessary based on FIG. Therefore, as shown in Table 1, until the RH device 1 was stopped (1720 charges or more), it could be used without trouble of the iron skin 12 such as red heat.
[Example with trouble (i)]
Since the iron shell temperature of the alloy chute portion 9 was 390 ° C., it was used without cooling the iron shell 12 of the alloy chute portion 9, and then the red heat of the iron shell 12 was generated at the third charge, so the RH device 1 was stopped. The OB ratio at that time was 60%, and the average OB amount was 100 Nm ³ / ch. FIG. 4B shows that “cooling is necessary” under such conditions.
[Example with trouble (ii)]
Since the iron shell temperature of the alloy chute portion 9 was 380 ° C., the RH device 1 was stopped because red heat of the iron shell 12 was generated at the next charge when the iron shell 12 was used without cooling. The OB ratio at that time was 80%, and the average OB amount was 160 Nm ³ / ch. When FIG.4 (c) is seen, in such conditions, it is "I need to cool when the iron skin temperature is 370 degreeC or more."

As Example 2, cooling to the side wall of the upper tank 6 of the RH apparatus 1 will be described. In detail, it is cooling of the site | part shown by 1-2 span upper side of the attaching / detaching part of the upper tank 6, and B of FIG. The refractory 13 affixed to this portion is damaged by heating with a burner or oxygen heating, and there is a problem that the remaining thickness is lost and the iron skin 12 is apt to be red hot.
Therefore, as a result of detailed examination of past operation data on the side wall of the upper tank 6, the inventors of the present application have determined a control chart (judgment chart) and a control curve (determination chart) that determine the necessity / unnecessity of iron shell cooling as shown in FIG. 5. (Curve). In each diagram of FIG. 5, the horizontal axis represents the average OB amount, and the vertical axis represents the OB ratio. FIG. 5 (a) shows a condition under an iron skin temperature of 300 ° C., FIG. 5 (b) shows a condition under an iron skin temperature of 350 ° C., and FIG. 5 (c) shows a condition under an iron skin temperature of 380 ° C. is there.

In FIG. 5, “○, ×” is the operation result, “○” is refractory when the refractory 13 has a sufficient thickness and there is no red heat of the iron skin 12, etc. 13 shows a case where the thickness is judged to be thin or red heat or distortion occurs in the iron skin 12, and the situation of “x” should be avoided.
Based on such a control chart, for example, when it is desired to manage the iron skin temperature at 300 ° C. in a certain charge, paying attention to FIG. 5A, the average OB amount at that time is 50 Nm ³ / ch, and the OB ratio is 40 If it is%, the iron skin 12 is not cooled, and if it becomes 45% or more, the iron skin 12 is cooled.

  Table 2 shows the results of the iron shell cooling using FIG.

[Example without trouble (i)]
The RH apparatus 1 was operated at an OB ratio of 30%, and the iron skin temperature on the side wall of the upper tank 6 was 300 ° C. Thereafter, since the average amount of OB increased from 70 to 90 Nm ³ / ch, the iron skin was cooled based on FIG. Therefore, as shown in Table 2, until the RH device 1 was stopped (2,500 charges or more), the iron skin 12 such as red heat could be used without any trouble.
The OB ratio and the average OB amount are values calculated for each charge. As for the iron skin temperature, the maximum temperature in one charge of the refining process is shown. The number of charges in the life of the iron skin indicates the timing when the furnace is stopped for repairing the refractory 13, and the iron skin 12 can be used further as it is. This condition is the same in the following examples.
[Examples without trouble (ii)]
The RH device 1 was operated at an OB ratio of 30% and an average OB amount of 40 Nm ³ / ch, and the iron skin temperature on the side wall of the upper tank 6 was 350 ° C. Therefore, the iron skin cooling was performed based on FIG. Then, since the OB ratio fell to 20%, the iron skin cooling was stopped although the iron skin temperature was 370 ° C. based on FIG.

By stopping the iron shell cooling, the iron skin temperature gradually increased to reach 420 ° C., but iron skin troubles such as red heat did not occur in particular, and it could be used until the furnace was stopped (2450 charges or more).
[Example with trouble (i)]
In the operation of the RH apparatus 1, the OB ratio as an operation condition was 60%, and the average OB amount was 20 Nm ³ / ch. In particular, the use of the RH device 1 was continued as it was without cooling the iron skin (the iron skin temperature on the side wall of the upper tank 6 at that time was 380 ° C.). However, after the 10th charge treatment, the iron skin temperature reached 410 ° C. and the iron skin cooling was started. However, red iron fever of the iron skin 12 was generated by the next charge, and the furnace was unavoidably stopped.

Referring to FIG. 5 (c), “cooling is necessary” when the OB ratio is 60% and the average OB amount is 20 Nm ³ / ch.
In this embodiment, the control chart as shown in FIG. 5 is created and the necessity / unnecessity of the iron shell cooling is determined. However, the control chart (FIGS. 3 and 4) as in the first embodiment may be created. It is possible and there is no problem even if the iron shell cooling is performed based on such a figure.

As Example 3, cooling to the side wall (C in FIG. 2) of the lower tank 7 of the RH device 1 will be described. In addition to the molten steel 2 that circulates, this portion is susceptible to the oxidation reaction due to oxygen heating, and troubles such as red heat and perforation of the iron skin 12 are likely to occur.
Therefore, as a result of detailed examination of past operation data on the side wall of the lower tank 7, the inventors of the present application have determined that a control chart (judgment figure) and a control curve (judgment) that determine the necessity / unnecessity of iron skin cooling as shown in FIG. (Curve). The horizontal axis in FIG. 6 represents the OB ratio, and the vertical axis represents the iron skin temperature. This figure is the one when the cumulative value of the average OB amount reaches 100 Nm ³ / ch.

In FIG. 6, “○, ×” is the operation result, “○” is refractory when the refractory 13 has a sufficient thickness and there is no red heat of the iron skin 12, etc. 13 shows a case where the thickness is judged to be thin or red heat or distortion occurs in the iron skin 12, and the situation of “x” should be avoided. Note that “●” in FIG. 6 is an unfavorable result in terms of operation, such as the thickness of the refractory 13 being too thin than expected, although the iron shell 12 trouble did not occur. Therefore, it was judged that iron skin cooling was necessary.
[Example without trouble (i)]
In the operation shown in FIG. 7A, after 360 charges, the OB ratio was 65% and the average OB amount exceeded 100 Nm ³ / ch. Therefore, based on the control chart of FIG. Since the iron skin temperature was 385 ° C., the iron skin cooling was started. Therefore, after that, it was possible to use up to 410 charges without any problem and the furnace was shut down. Note that the OB ratio and the average OB amount here are values calculated and arranged every 10 charges. The iron skin temperature indicates the maximum temperature within 10 charges.
[Example with trouble (i)]
In the operation shown in FIG. 7B, the OB ratio was 63% at 270 charges, and the average OB amount exceeded 100 Nm ³ / ch. At that time, the iron shell temperature of the side wall of the lower tank 7 is 365 ° C., and iron shell cooling is necessary in view of FIG. However, the use of the RH device 1 was continued as it was. Then, the iron skin temperature exceeded 400 ° C. at 290 charge, and the iron skin cooling started from that point, but after 10 charges, the iron skin temperature rose to 465 ° C. and 12 holes in the iron skin occurred at 300 charge. .

  In this embodiment, the control chart as shown in FIG. 6 is created and the necessity / unnecessity of the iron shell cooling is determined. It is also possible to create such a control chart (FIG. 5), and there is no problem even if the iron skin is cooled based on such a chart.

It is a use mode figure of an RH device. It is sectional drawing of a RH apparatus. FIG. 6 is a control chart indicating whether or not iron shell cooling is used in Example 1; FIG. 6 is a control chart indicating whether or not iron shell cooling is used in Example 1; It is a control chart of necessity / unnecessity of iron shell cooling used in Example 2. FIG. 6 is a control chart showing whether or not iron shell cooling is used in Example 3; It is the figure which showed the operation condition of the RH apparatus concerning Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 RH apparatus 2 Molten steel 3 Ladle 4 Degassing tank 6 Upper tank 7 Lower tank 8 Exhaust port 9 Alloy chute part 11 Immersion pipe 12 Iron skin 13 Refractory 14 Injection pipe 15 Inlet

Claims (1)

A method for cooling an iron shell of an RH apparatus that performs an operation in which at least one charge for performing a temperature increase using oxygen gas is present,
An oxygen heating ratio indicating the ratio of the number of charges heated by the oxygen gas to the total number of charges, and an average amount of oxygen gas for heating by dividing the total amount of oxygen gas used for heating by the total number of charges; , Create a control chart with the temperature of the RH device as a parameter and a control curve described in the control chart,
The ratio of the number of charges that have been heated with oxygen gas to the number of charges from the start of operation to the charge is defined as the oxygen heating ratio, and the total amount of oxygen gas used for heating up to the charge, After dividing the number of charges from the start of operation to the number of charges up to the average amount of oxygen gas for heating, it is applied to the created control chart and control curve,
A method for cooling the iron shell of an RH device that determines whether or not the cooling of the iron skin is necessary from the applied result and performs cooling to the iron skin based on the determination result.

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