JP2003129123A - Method for estimating minor diameter of vacuum vessel in vacuum degassing apparatus and method for controlling height - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for estimating a minor diameter of a vacuum vessel, which can accurately estimate the minor diameter when the vacuum vessel is worn, and provide a method for controlling height using it. SOLUTION: This method for estimating the minor diameter of the vacuum vessel comprises previously determining the relation between an internal pressure of the vacuum vessel and a surface level of a molten metal in a ladle when the vacuum vessel is not worn on several minor diameters of the vacuum vessel, measuring the surface level of the molten metal and the pressure in the vacuum vessel after the pressure in the vacuum vessel reaches a predetermined pressure in degassing treatment; and estimating the minor diameter of this time of the vacuum vessel from these value; or storing these data while relating them with charge numbers, and estimating the minor diameter of the vacuum vessel based on these stored data. A method for keeping an immersion length of a dip tube in a constant range, includes controlling elevation of the ladle or the vacuum vessel, based on the estimated minor diameter and pressure in the vacuum vessel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating the inner diameter of a vacuum tank in a vacuum degassing apparatus, and a method for controlling the height of a ladle or vacuum tank of the vacuum degassing apparatus.

[0002]

2. Description of the Related Art Steel sheets requiring workability and steel wires requiring ductility, if carbon (C) or nitrogen (N) is contained therein, the workability and the ductility are deteriorated. It is necessary to reduce the contents of these elements as much as possible. Also,
In order to prevent hydrogen-induced cracking, steel plates for structural steel plates and steel products for line pipes are required to reduce the content of hydrogen (H) contained in the steel as much as possible.

The above elements (C, N and H) are C + O.
= CO, 2H = H_TwoAnd 2N = N _TwoThe degassing reaction of
Thus, the molten steel, which is the liquid phase, shifts to the gas phase side. At that time,
In order to proceed these reactions, the reaction product C
O, H_TwoAnd N_TwoIt is necessary to reduce the partial pressure of.
Therefore, when producing the above steel, the vacuum degassing method
Has been adopted. Generally used as a vacuum degassing method for molten steel
The method that can be used is the RH degassing method.

FIG. 1 is a partial vertical sectional view showing an example of the structure of an RH degassing apparatus. In the figure, the RH degassing apparatus is provided with a ladle 2 for accommodating the molten steel 1 and a dip pipe mounting portion 3a at two lower portions, and a vacuum exhaust pipe 5, an alloy addition pipe 6 and a lance 7 at the upper portion. And a vacuum drive unit (not shown) for moving one of the ladle 2 and the vacuum chamber 3 up and down. The immersion pipe 4 is attached to the immersion pipe mounting portion 3a provided in the lower portion of the vacuum chamber 3, and the vacuum exhaust unit (not shown) is connected to the vacuum exhaust pipe 5 provided in the upper portion of the vacuum chamber 3. .

Incidentally, the ladle 2 and the vacuum chamber 3 (the dipping pipe mounting portion 3
(including a) has a refractory material lined therein, and is repeatedly used until the lined refractory material wears and reaches a use limit. When the refractory material wears and reaches the limit of use, a new refractory material is lined in the ladle 2 and the vacuum chamber 3. The dip pipe 4 is made of a refractory material, and is repeatedly used until the refractory material is worn and reaches the use limit, and is replaced when the use limit is reached.

In the degassing process, two dipping tubes 4 are dipped in the molten steel 1 housed in the ladle 2, and reflux is carried out from a tuyere (not shown) provided on the inner wall of one dipping tube 4. Blow in the gas for use. Further, the inside of the vacuum chamber 3 is decompressed by a vacuum exhaust unit (not shown) connected to the vacuum chamber 3. As a result, the molten steel 1 is sucked up from the one immersion pipe 4 into the vacuum chamber 3 and returned from the other immersion pipe 4 to the ladle 2 to melt the molten steel 1
The ladle 2 is circulated between the ladle 2 and the depressurized vacuum chamber 3. The molten steel 1 is degassed by the above degassing reaction during this circulation.

Further, in order to prevent the temperature of the molten steel 1 from decreasing during the degassing process, oxygen gas is blown from the lance 7 toward the molten steel 1 in the vacuum chamber 3.

By the way, the pressure in the vacuum chamber 3 is generally the amount of gas in the vacuum chamber 3 (total amount of reflux gas, oxygen gas, gas generated by degassing reaction, leak gas, etc.) and vacuum exhaust. The degassing process is usually performed at a pressure of, for example, about 1 kPa depending on the capacity of the part. When the pressure in the vacuum tank 3 is set as described above, the amount of the molten steel 1 sucked up from the ladle 2 into the vacuum tank 3 is also determined accordingly, and the molten steel 1 in the ladle 2 The level 1a is lowered. In addition, Ti, Cr alloy,
The composition of molten steel 1 may be adjusted by adding Mn alloy or the like. At this time, since the pressure in vacuum chamber 3 temporarily increases, the molten metal 1 ladle 1 ladle 2 rises. To do.

During this degassing process, the lower part of the immersion pipe 4 is immersed in the molten steel 1 from the molten steel surface 1a of the molten steel 1 housed in the ladle 2. It is important to keep the dipping length from to within a certain range. That is,
When the immersion length of the immersion pipe 4 is increased and the flange 4a provided on the upper part of the immersion pipe 4 is immersed in the molten steel 1, the water cooling pipe (not shown) provided on the flange 4a is melted and damaged.
May cause steam explosion. On the other hand, when the immersion length of the immersion pipe 4 is shortened, the length of the portion of the immersion pipe 4 that is exposed to the atmosphere is increased, so that the amount of the atmosphere entering from the side wall of the immersion pipe 4 is increased and the composition of the molten steel 1 is adversely affected. And the efficiency of the degassing process becomes poor. Further, the immersion pipe 4 may be sucked with slag, and the immersion pipe 4 may come out of the molten steel 1. In this case, the degassing process must be interrupted.

Therefore, during the degassing process, it is necessary to control the height of the ladle 2 or the vacuum tank 3 to keep the immersion length of the immersion steel 4 of the molten steel 1 from the molten metal surface 1a within a certain range. .

Japanese Unexamined Patent Publication No. 9-49013 discloses a method of controlling the elevation of the immersion pipe in order to keep the immersion length of the immersion pipe constant. In this method, the up / down correction amount of the vacuum tank (or ladle) is HV (mm), and the vacuum degree in the vacuum tank is P (To
rr), the inner diameter of the immersion pipe is Dl (mm), and the specific gravity of the molten steel is ρ
(G / cm ³ ), the inner diameter of the ladle is DL (mm), and the outer diameter of the dip tube is DO (mm), only the elevation correction amount HV defined by the following equation (1) is used for the vacuum tank or the ladle. Is moved up and down to keep the immersion length of the immersion tube constant regardless of changes in the degree of vacuum in the vacuum chamber.

HV = (760-P) × 13.6 × Dl ² / {ρ (DL ² -DO ² + Dl ² )} ··· (1) In addition, this method is used in the lower part of the vacuum chamber without the chamber bottom. The target is a vacuum degasser having one straight barrel type dip tube with the same inner diameter as the inner diameter of the vacuum tank, but such a control method should also be applied to the above-mentioned RH degasser. You can

However, in the above equation (1), the elevation correction amount HV is calculated based on the vacuum degree P in the vacuum chamber, the inner diameter DI of the dip tube, the outer diameter DO of the dip tube and the inner diameter DL of the ladle. However, according to paragraphs 0026 and (2) of the publication,
The dimensions such as the inner diameter DL of the immersion tube are set to constant values. That is, in the above method, when the refractory material lined on the inner surface of the repeatedly used vacuum chamber is worn, the increase in the inner diameter of the vacuum chamber due to this wear is not taken into consideration.

Therefore, when the vacuum chamber is large or the number of times of repeated use is small, the error of the elevation correction amount HV calculated by the equation (1) is small. However, if the vacuum chamber is small, or if it is repeatedly used many times, the increase in the inner diameter due to the wear of the vacuum chamber has a large effect on the control, and the above control method causes a large error and causes the operation to stop. Could be.

The HV obtained by the above equation (1)
Is a value obtained with the height relationship between the vacuum tank and the ladle being constant, so that the volume of the immersion pipe immersed in the molten steel when the immersion pipe is moved up and down by HV. Increases and decreases are not considered. Therefore, the control error becomes large as described above.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is, in a vacuum degassing apparatus, a method for estimating an inner diameter of a vacuum chamber, which can accurately estimate the inner diameter when a refractory material lined in the vacuum chamber is worn, And a method for controlling the height of a ladle or a vacuum chamber that can accurately maintain the immersion length of the immersion tube within a certain range even when the vacuum chamber is small or the number of repeated uses is large. It is in.

[0017]

The gist of the present invention resides in the following (1) method for estimating the inner diameter of a vacuum chamber in a vacuum degassing apparatus and (2) a height control method in a vacuum degassing apparatus.

(1) A ladle for containing molten metal, a vacuum tank provided with a dip tube at the bottom and connected to an evacuation unit, and an elevating / lowering drive unit for elevating either one of the ladle and the vacuum tank. The vacuum of the vacuum degassing apparatus, which is equipped with a vacuum degassing apparatus, in which a dipping tube is immersed in molten metal contained in a ladle to circulate the molten metal between the ladle and a vacuum chamber under reduced pressure to perform degassing treatment. A method for estimating the inner diameter of a vacuum tank in a vacuum degassing apparatus, characterized in that the inner diameter of the tank is estimated by any of the following A to C or D to F. A. The pressure in the vacuum tank and the level of molten metal in the ladle when the dipping pipe is immersed in the molten metal contained in the ladle and the height relationship between the ladle and the vacuum tank is constant. The relationship with and is obtained in advance for a plurality of inner diameters of the vacuum chamber. B. During the degassing process, the molten metal level in the ladle and the pressure in the vacuum tank at that time shall be measured after the molten metal contained in the ladle reaches the vacuum tank. taking measurement. C. Based on the relationship between the level of the molten metal in the ladle and the pressure in the vacuum tank measured in B, and the previously determined pressure in the vacuum vessel and the level of the molten metal in the ladle. Estimate the inner diameter of the vacuum chamber at the time the surface level was measured. D. The inner diameter of the vacuum chamber is estimated for a plurality of charges by the inner diameter estimation methods A to C and stored. E. The relationship between the number of charges and the inner diameter of the vacuum chamber is obtained in advance based on the inner diameter of the vacuum chamber in the plurality of charges stored in the above D. F. At the time of degassing, the current inner diameter of the vacuum chamber is estimated based on the current number of charges and the relationship between the number of charges previously obtained in E and the inner diameter of the vacuum chamber.

(2) A ladle for accommodating molten metal, a vacuum tank provided with a dip tube at the bottom and connected to a vacuum exhaust unit, and an elevating / lowering drive unit for elevating or lowering one of the ladle and the vacuum tank. And a vacuum degassing apparatus for performing degassing treatment by immersing the dipping tube in the molten metal contained in the ladle and circulating the molten metal between the ladle and the depressurized vacuum tank. A method of controlling the height of a pan or vacuum chamber, the method comprising:
The inner diameter of the vacuum chamber estimated in D to F by measuring the pressure in the vacuum chamber and estimating the difference between the lower end position of the immersion pipe and the initial lower end position of the immersion pipe when the immersion length of the immersion pipe is constant. And height control in a vacuum degassing device, characterized in that the ladle or the vacuum tank is moved up and down in order to correct the difference in the lower end position of the immersion pipe obtained based on the measured pressure in the vacuum tank. Method.

In the present invention, the inner diameter of the vacuum chamber means the inner diameter of the space formed by the refractory material lined in the vacuum chamber.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for estimating the inner diameter of a vacuum chamber in a vacuum degassing apparatus according to the present invention will be described with reference to FIGS. 2 to 4 in the case of degassing molten steel using the RH degassing apparatus shown in FIG. 4 will be described. Note that the configuration of the RH degassing device shown in FIG. 1 has already been described, and will be omitted.
FIG. 2 is a vertical cross-sectional view showing a state of molten steel when the pressure in the vacuum chamber is atmospheric pressure. In Figure 3, the vacuum chamber is depressurized,
It is a longitudinal cross-sectional view showing a state in which a part of the molten steel has been sucked up inside the immersion pipe and the immersion pipe attachment portion. FIG. 4 is a vertical cross-sectional view showing a state where the inside of the vacuum tank is further decompressed and a part of the molten steel is sucked up into the vacuum tank.

2 to 4, the inner radius of the vacuum chamber 3 is R ₁ , the inner radius of the immersion pipe mounting portion 3a and the immersion pipe 4 is R ₂ , the outer radius of the immersion pipe 4 is R ₃ , and the ladle is ladle. The inner radius of 2 is R ₄ , the length of the dip tube 4 is A, and the length of the dip tube mounting portion 3 a is B.

[0023] In FIG. 2, molten metal surface level of the molten steel 1 in the ladle 2 (i.e., the pressure in the vacuum chamber 3 is melt-surface level when the atmospheric pressure) to the initial level L _0, dipping from an initial level L ₀ It is assumed that the distance from the upper end of the flange 4a formed at the upper part of the tube 4 to A _{1 is} the distance from the initial level L ₀ to the lower end of the immersion tube 4, that is, the immersion length of the immersion tube 4 is A ₂ . Further, the distance between the lower end of the dipping tube 4 and the bottom of the ladle 2 at this time is H ₀ .

In FIGS. 3 and 4, the level of the molten metal 1 sucked into the immersion pipe 4 and the immersion pipe mounting portion 3a or the vacuum tank 3 is defined as the molten metal level L ₁ and the ladle 2 is used. The level of the molten steel 1 in which the level of the molten steel is lowered is defined as the level of the molten metal L _2, and the amount of increase in the level of the molten metal L _{1 from} the initial level L ₀ is X ₁ , and the amount of the molten metal level L ₂ is decreased from the initial level L _0. The amount is X ₂ , and the difference between the molten metal level L ₁ and the molten metal level L ₂ is X. In addition, the lower end of the dipping pipe 4 and the ladle 2 at this time
Let H be the distance from the bottom of. All these units are expressed in mm.

When the pressure in the vacuum chamber 3 is reduced, part of the molten steel 1 contained in the ladle 2 is immersed in the dip pipe 4 and the dip pipe mounting portion 3a.
It is sucked up inside. That is, when the pressure in the vacuum chamber 3 decreases (the degree of vacuum rises), as shown in FIG. 3, the molten metal level in the dip tube 4 and the dip tube mounting portion 3a becomes the initial level L.
_The amount of rise X ₁ rises from ₀ to the level L ₁ , and the level of the molten metal in the ladle 2 falls from the initial level L ₀ by the amount X ₂ to reach the level L ₂ .

Further, when the pressure inside the vacuum tank 3 is reduced, a part of the molten steel 1 contained in the ladle 2 is sucked up into the vacuum tank 3 through the immersion pipe 4 and the immersion pipe attachment portion 3a. That is, as shown in FIG. 4, the level of the molten metal in the vacuum tank 3 rises from the initial level L ₀ by the amount of increase X ₁ to the level of the molten metal level L ₁ , and the level of the molten metal in the ladle 2 is initially set. The level is lowered from the level L ₀ by the descending amount X ₂ to reach the level of the molten metal level L ₂ . At this time, in the states of FIGS. 2 to 4, the following two relationships are established.

One of them is. The total amount of the amount of molten steel 1 present inside the vacuum chamber 3, the amount of molten steel 1 present inside the immersion pipe 4 and the immersion pipe mounting portion 3a, and the amount of molten steel 1 present inside the ladle 2 is shown in FIG. 2 to 4 are the same in all states.

The other one is, as shown in FIGS. 3 and 4, the molten metal level L in the immersion pipe 4 and the immersion pipe mounting portion 3a.
₁ , or the molten steel differential pressure represented by the difference X (L ₁ −L ₂ ) between the molten metal level L ₁ in the vacuum tank 3 and the molten metal level L ₂ in the ladle 2, is the atmospheric pressure and the vacuum tank. It is equal to the difference with the pressure in 3.

Therefore, in the state of FIG. 3, the pressure in the vacuum chamber 3 is set to P ₁ (kPa), and the density of the molten steel 1 is d (g / g /
cm ³ ), the following expressions (2) and (3) are established from the above relationship.

2R ₂ ² · X ₁ = (R ₄ ² −2R ₃ ² ) · X ₂ · (2) X ₁ + X ₂ = (101-P ₁ ) · (760/101) · (13.6 / d ) · (3) From these equations (2) and (3), the descending amount X ₂ can be obtained by the following equation (4).

X ₂ = (101-P ₁ ) ・ (760/101) ・ (13.6 / d) ・ {2R ₂ ² / (R ₄ ² -2R ₃ ² + 2R ₂ ² )} ・ ・ (4) Also In the state of FIG. 4, the pressure in the vacuum chamber 3 is set to P
_{When 2} (kPa) is set, the following expressions (5) and (6) are established from the above relationship.

R ₁ ² · (X ₁ −BA ₁ ) + 2R ₂ ² · (B + A ₂ ) = (R ₄ ² −2R ₃ ² ) · X ₂ ·· (5) X ₁ + X ₂ = ( 101-P ₂ ) ・ (760/101) ・ (13.6 / d) ・ ・ (6) From these equations (5) and (6), the descending amount X ₂ can be calculated by the following equation (7). .

X ₂ = {(101-P ₂ ) ・ (760/101) ・ (13.6R ₁ ² / d) + (B + A ₁ ) ・ (2R ₂ ² -R ₁ ² )} / (R ₁ ² -2R ₃ ² + R ₄ ² ) ··· (7) Therefore, for example, the design value is used as the size of the vacuum degassing device to be used, and the amount of molten steel 1 contained in the ladle 2 and the initial stage of the dipping pipe 4 are set. If the initial level L ₀ is set according to the immersion length A ₂ of the above, the initial level of the molten steel 1 stored in the ladle 2 during degassing is determined by the above equations (4) and (7). The amount of decrease X ₂ from the level L ₀ , in other words, (L ₀ −
X ₂ ), the level L ₂ of the molten metal in the ladle 2 is set to the vacuum tank 3
It can be calculated by the pressure inside.

The above equations (4) and (7) are the height control method in the vacuum degassing apparatus having the straight barrel type immersion pipe described in the prior art, and the RH with two immersion pipes 4 is used. This is merely applied to the height control of the degassing device, and does not consider the increase in the inner diameter due to the wear of the vacuum chamber 3 that is repeatedly used.

Therefore, in the present invention, the inner diameter due to wear of the vacuum chamber 3 is estimated by either of the following two methods.

One of them is a method of estimating the inner diameter of the vacuum chamber 3 by the following AC.

A. The pressure in the vacuum tank 3 and the pressure in the ladle 2 in a state where the dipping pipe 4 is immersed in the molten steel 1 housed in the ladle 2 and the height position relationship between the ladle 2 and the vacuum tank 3 is constant. The relationship with the molten metal level of the molten steel 1 is calculated in advance for a plurality of inner diameters of the vacuum chamber 3.

That is, in the state shown in FIGS. 2 to 4, the initial value (for example, a design value) and a value near the use limit due to wear are used as the inner diameter of the vacuum chamber 3 of the vacuum degassing apparatus to be used. From the atmospheric pressure to a pressure lower than the pressure at which the degassing process is performed, the descending amount X ₂ is calculated based on the above equations (4) and (7), and the vacuum chamber 3
Internal pressure and level L ₂ of ladle ₂ (= initial level L
The relationship with ₀ -falling amount X ₂ ) is obtained in advance.

The inner diameter of the vacuum chamber 3 is the initial value and the vacuum chamber 3
The relationship between the pressure in the vacuum chamber 3 and the level L ₂ of the molten metal in the ladle 2 is determined in advance for as many cases as possible between the inner diameter near the use limit of 1) and the inner diameter of the ladle 2.

FIG. 5 shows the pressure in the vacuum chamber 3 and the molten metal level L in the ladle 2 which are obtained by using the equations (4) and (7).
It is a diagram showing an example of the relationship between the decrease amount X ₂ of ₂ and molten metal surface. In the figure, when the inner radius R ₂ of the vacuum chamber 3 is 700 mm, which is the design value (straight line V ₁ ), it is close to the use limit of 1
Three cases are shown: a case of 000 mm (straight line V _n ) and an intermediate case (straight line V _i ). As described above, the inner diameter of 3 of the vacuum chamber is close to the design value (for example, 700 mm) and the usage limit. A plurality of cases (for example, 1000 mm) will be calculated.

As can be seen from the figure, as the pressure in the vacuum chamber 3 decreases from the atmospheric pressure (101 kPa), the level L ₂ of the molten metal in the ladle 2 gradually drops along a straight line S, and the vacuum chamber 3 When the internal pressure becomes lower than approximately 25 kPa, the molten metal level L ₂ in the ladle 2 sharply drops like the straight lines V ₁ , V _i and V _n . In the case of the figure, part of the molten steel 1 reaches the inside of the vacuum tank 3 at the time of about 25 kPa, so that the molten metal level L ₂ in the ladle 2 drops sharply from this time. The amount of decrease of the molten metal level L ₂ in the ladle 2 at the pressure lower than approximately 25 kPa is the straight line V ₁ (the inner radius R _{2 of the} vacuum chamber 3).
Is 700 mm), the straight line V _n and the straight line V
_n (when the inner radius R ₂ of the vacuum chamber 3 is 1000 mm).

B. In the degassing process, after the time when a part of the molten steel 1 stored in the ladle 2 reaches the vacuum tank 3, the molten steel 1 level L ₂ in the ladle ₂ and the vacuum at that time The pressure P ₂ in the tank 3 is measured.

As described above, when the degassing process is started, the pressure in the vacuum tank 3 is reduced, and the molten metal level L in the ladle 2 is lowered.
₂ is, for example, the straight lines S and V ₁ (or V _i , V in FIG. 5)
_n ). In the case of FIG. 5, in a region where the pressure in the vacuum tank 3 is lower than approximately 25 kPa, when the inner diameter of the vacuum tank 3 is different, the molten metal level L ₂ in the ladle ₂ is a straight line V ₁ , a straight line V _i or a straight line V 2. Different as _n .

Therefore, after a part of the molten steel 1 in the ladle 2 reaches the vacuum chamber 3 as shown in FIG. 4, in other words, in the case of FIG. Pressure is almost 2
When it becomes lower than 5 kPa, the molten metal level L ₂ in the ladle ₂ and the pressure P ₂ in the vacuum tank 3 at that time are measured.

The method of measuring the molten metal surface level L ₂ is not limited to any particular method. However, it is difficult to directly observe and measure the molten metal level L ₂ because steam, dust, and the like are present above the molten metal 1 contained in the ladle 2 and the temperature is high. is there. Even if there is a detector that can be directly observed, the environment above the ladle 2 is bad as described above, and therefore the life of the detector is extremely short and not practical.

In the method for estimating the inner diameter of the vacuum chamber 3 according to the present invention, it is not necessary to continuously measure the molten metal level L ₂ during the degassing process, but it is sufficient to measure the molten metal level L ₂ at least once at the above-mentioned time point. Therefore, for example, a steel bar having a known length is inserted into the molten steel 1 from the upper portion of the ladle ₂ to measure the molten metal level L ₂ . That is, a steel bar having a known length is prepared, the steel bar is inserted into the molten steel 1 until the upper end thereof coincides with the upper end position of the ladle 2, and after a predetermined time has elapsed, the steel bar is taken out and the length thereof is measured. . The portion of the steel bar inserted into the molten steel 1 melts, and the portion above the molten metal surface of the molten steel 1 remains, so the molten metal level L ₂ is measured by measuring the length of this remaining portion.

The pressure P ₂ in the vacuum chamber 3 when the molten metal level L ₂ is measured is measured by the pressure gauge (vacuum gauge) provided in the vacuum exhaust unit.

The molten metal level L ₂ and the pressure P ₂ may be measured each time degassing is performed, that is, every charge, or when it is desired to estimate the inner diameter of the vacuum chamber 3. If the molten metal level L ₂ and the pressure P ₂ are measured for each charge, the inner diameter of the vacuum chamber 3 described in C below can be estimated for each charge.

C. Surface level in ladle 2 measured in B above
Bell L_TwoAnd the pressure P in the vacuum chamber 3 _TwoAnd in A above
Obtained pressure P in the vacuum chamber 3_TwoAnd molten steel 1 in ladle 2
Level L_TwoBased on the relationship with_TwoBut
The inner diameter of the vacuum chamber 3 at the time of measurement is estimated.

As described above, the vacuum chamber 3 has a resistance to the inner surface.
Fire is lined. The vacuum chamber 3 is made of refractory material.
Used repeatedly until its inner diameter reaches its limit
Be done. That is, the inner diameter of the vacuum chamber 3 that is repeatedly used
Increases due to the wear of refractory as the number of charges increases.
I hear Therefore, equation (4) described above or
Based on formula (7), the amount of downward movement of the molten metal in the ladle 2 X_TwoSeeking
However, the actual amount of descent X _TwoThere is an error between and.

Vacuum chamber 3 increased by wear of this refractory
The inner diameter of the molten metal is the level L in the ladle 2 measured in B above.
₂ and the pressure P ₂ in the vacuum tank 3 and the relationship between the pressure in the vacuum tank 3 and the level of the molten metal in the ladle 2 which are obtained in advance in A.

That is, FIG.
In the above, the point z indicating the level L ₂ of the molten metal in the ladle 2 measured at B and the pressure P ₂ in the vacuum tank 3 at that time is entered, and the point z of the straight lines V _{1 to} V _n is the most If you select a straight line,
When the selected straight line is the inner radius of the vacuum tank 3 at that time, it represents the relationship between the pressure in the vacuum tank 3 and the molten metal level in the ladle 2.

By the way, the inner diameter of the vacuum tank 3 after wear, more specifically, the inner diameter of the refractory material lined on the inner surface of the vacuum tank 3 after wear, is calculated from the lower portion of the vacuum tank 3 to the molten steel 1 in the vacuum tank 3. The surface level L ₁ is not always the same. Therefore, the inner radius of the vacuum chamber 3 estimated as described above represents the average inner radius of the worn portion.

From the above A to C, it is possible to estimate the inner diameter of the vacuum chamber 3 when the level L ₂ of the molten metal in the ladle 2 is measured.

The inner diameter estimating method according to A to C is a method of estimating the inner diameter of the vacuum tank 3 at that time by using the measured molten metal level L ₂ in the ladle 2. Therefore, this is an effective method at the beginning of the operation of the RH degasser. However, if the inner diameter of the vacuum chamber 3 is estimated and stored for a plurality of charges as described above and the stored data is used, the refractory lined in the vacuum chamber 3 reaches the use limit and is newly lined. during the vacuum processing after the, even without measuring the molten metal surface level L ₂ of the ladle 2, it is possible to estimate the internal diameter of the vacuum chamber 3.

That is, another method of estimating the inner diameter of the vacuum chamber 3 is a method of estimating the inner diameter of the vacuum chamber 3 by the following D to F.

D. The inner diameter of the vacuum chamber 3 is estimated and stored for a plurality of charges by the inner diameter estimating methods A to C.

As described above, the vacuum chamber 3 is repeatedly used until the refractory material lined on the inner surface of the vacuum chamber 3 is worn and reaches the limit of use. Therefore, the inner diameter of the vacuum chamber 3 is estimated by the above-mentioned A to C for a plurality of charges from when the new refractory is lined up to when the usage limit is reached,
The estimated value is stored in association with the number of charges. Here, the number of charges refers to the number of times vacuum processing is repeatedly performed from the time when a new refractory is lined in the vacuum chamber 3.

The estimation of the inner diameter of the vacuum chamber 3 by A to C may be performed for each charge or may be performed for a plurality of charges. Also, after the new refractory is lined in the vacuum chamber 3, the A
The estimation by ~ C may be repeated, and the estimated average value of the inner diameter may be stored in association with the number of charges.

E. Based on the inner diameter of the vacuum chamber 3 in the plurality of charges stored in D, the number of charges and the vacuum chamber 3
The relationship with the inner diameter of is obtained in advance.

When the inner diameter of the vacuum chamber 3 is estimated for each charge and stored in D, the relationship between the number of charges and the estimated inner diameter of the vacuum chamber 3 is used. When the inner diameter of the vacuum tank 3 is estimated and stored for each of a plurality of charges, the inner diameter of the vacuum tank 3 of the charge whose inner diameter of the vacuum tank 3 is not estimated is set to the inner diameter of the vacuum tank 3 estimated before and after that. The above relationship is obtained by performing a proportional calculation based on the difference between and the number of charges in between.

F. At the time of degassing, the current inner diameter of the vacuum chamber 3 is estimated based on the current number of charges and the relationship between the number of charges previously obtained in E and the inner diameter of the vacuum chamber 3.

During the degassing process, it is not necessary to measure the molten metal level L ₂ in the ladle 2. However, the current number of charges after the new refractory is lined in the vacuum chamber 3 is stored. Then, the inner diameter of the vacuum chamber 3 corresponding to the current number of charges is estimated to be the inner diameter of the current vacuum chamber 3 based on the relationship between the number of charges previously obtained in E and the inner diameter of the vacuum chamber 3.

As described above, the inner diameter of the vacuum chamber 3 can be estimated from the above A to C or D to F. Based on the estimated value of the inner diameter of the vacuum chamber 3 and the limit value of use, the vacuum chamber 3
It is possible to judge the usage limit of the above, that is, the replacement time of the refractory material lined in the vacuum chamber 3. Since the estimated inner diameter of the vacuum tank 3 is the average inner diameter of the vacuum tank 3 increased due to wear as described above, the use limit value of the inner diameter of the vacuum tank 3 is set to a value corresponding to this average inner diameter. To do. Further, if the inner diameter of the vacuum chamber 3 estimated from the above D to F is used, the height control described below can be performed accurately.

Next, the height control method of the present invention will be described.

[0066] The height control method of the present invention, the height of the ladle 2 or the vacuum chamber 3 so as dipping length A ₂ of the dip tube 4 is within a predetermined range from the melt surface level L ₂ of the ladle 2 Is a method of controlling.

That is, by using the inner diameter of the vacuum chamber 3 estimated by the inner diameter estimating method of the vacuum chamber 3 described above, the immersion length A ₂ (see FIGS. 2 to 4) of the immersion pipe 4 is constant during the degassing process. For example, the vacuum chamber 3 is moved up and down so as to be within the range as follows.

As described above, the vacuum chamber 3 is used during the degassing process.
Even if the pressure in the chamber fluctuates, the molten steel 1 existing inside the vacuum chamber 3
, The total amount of the molten steel 1 present inside the dip tube 4 and the dip tube mounting portion 3a, and the amount of the molten steel 1 present inside the ladle 2 are equal in all the states of FIGS. 2 to 4. . Also,
2 to 4, the immersion pipe 4 and the immersion pipe mounting portion 3a
Level L ₁ inside or level L inside the vacuum tank 3
₁ and the level L ₂ of the molten metal in the ladle 2 X (= L ₁ −L
_The molten steel differential pressure represented by ₂ ) is equal to the difference between the atmospheric pressure and the pressure in the vacuum chamber 3.

Using the above relationships, the index Q relating to the molten steel amount in the state of FIG. 2 can be expressed by the following equation (8), and the index Q relating to the molten steel amount in the state of FIG. It can be expressed by equation (9).

Q = (R ₄ ² -2R ₃ ² + 2R ₂ ² ) ・ A ₂ + R ₄ ²・ H ₀・ ・ (8) Q = 2R ₂ ²・ X + (R ₄ ² -2R ₃ ² + 2R ₂ ² ) · A ₂ + R ₄ ² · H ··· (9) In the equations (8) and (9), if the immersion length A ₂ of the immersion pipe 4 is equal, the following equation (10) is obtained. To establish.

R ₄ ² · H ₀ = 2R ₂ ² · X + R ₄ ² · H ··· (10) Therefore, the movement amount (H ₀ −H) of the lower end of the immersion pipe 4 is expressed by the following equation (11). expressed.

H ₀ -H = (2R ₂ ² / R ₄ ² ) × X (11) Here, as described above, the dip tube 4 and the dip tube mounting portion 3
Since the difference X between the level L ₁ of the molten metal in a and the level L ₂ of the molten metal in ladle 2 is equal to the difference between the atmospheric pressure and the pressure in vacuum chamber 3, the above equation (11) is (12) can be expressed.

H ₀ -H = (2R ₂ ² / R ₄ ² ). (101-P ₁ ). (760/101). (13.6 / d) .. (12) In the formula (12), H ₀ -H is the amount of movement of the lower end of the immersion pipe 4 from the initial position when the immersion length A ₂ of the immersion pipe 4 is constant. In other words, it is the amount of movement from the initial position of the lower end of the immersion pipe 4 required to keep the immersion length A ₂ of the immersion pipe 4 constant.

Therefore, in the case of the state of FIG. 3, the pressure P ₁ in the vacuum chamber 3 is measured during the vacuum processing, and the lower end of the dip tube 4 is moved by the equation (12) using this pressure P _1. By determining the amount and moving the vacuum chamber 3 up and down by this amount of movement, the immersion length of the immersion tube 4 can be made substantially constant.

Further, in the state of FIG. 4, the movement amount of the lower end of the dipping tube 4 is obtained as follows.

That is, in the state of FIG. 4, the index Q relating to the molten steel amount can be expressed by the following equation (13).

Q = R ₁ ² · (XB-A + A ₂ ) + 2R ₂ ² · (A + B) + (R ₄ ² −2R ₃ ² + 2R ₂ ² ) · A ₂ + R ₄ ² · H .. (13) Here, the index Q relating to the amount of molten steel after the molten steel 1 reaches the boundary between the vacuum chamber 3 and the immersion pipe mounting portion 3a is
Since the amount of molten steel existing inside the and the immersion pipe mounting portion 3a is constant, this is excluded, and if the immersion length A ₂ of the immersion pipe 4 is constant, the following formula (14) simplifies. Can be expressed as

Q = R ₁ ² · X + R ₄ ² · H (14) On the other hand, when the molten steel 1 reaches the boundary between the vacuum chamber 3 and the immersion pipe mounting portion 3a, the lower end of the immersion pipe 4 moves. Since the amount (H ₀ −H) is expressed by the above formula (11), the position of the lower end of the immersion pipe 4 at this time can be expressed by the following formula (15).

H = H ₀ · (2R ₂ ² / R ₄ ² ) · X ₀ ··· (15) However, X ₀ in the equation (15) is that the molten steel 1 is the vacuum tank 3 and the immersion pipe mounting portion 3 a. Level L when reaching the boundary
₁ and the level L ₂ of the molten metal in the ladle 2,
The equation (14) can be expressed as the following equation (16).

Q = R ₁ ² · X ₀ + R ₄ ² · {H ₀ − (2R ₂ ² / R ₄ ² ) · X ₀ } (16) The above equations (14) and (16) are Since they are equal, the next (1
Equation 7) is established.

R ₁ ² * X + R ₄ ² * H = R ₁ ² * X ₀ * R ₄ ² * {H _0- (2R ₂ ² / R ₄ ² ) * X ₀ } ... (17) Therefore, The movement amount (H ₀ −H) of the lower end of the immersion pipe 4 is expressed by the following equation (18).

H ₀ -H = {R ₁ ² · X- (R ₁ ² -2R ₂ ² ) · X ₀ } / R ₄ ² · (18) Here, as described above, in the vacuum chamber 3 a Level L ₁
And the level L ₂ of the molten metal in the ladle 2 are equal to the difference between the atmospheric pressure and the pressure P ₂ in the vacuum chamber 3. The difference X ₀ between the molten metal surface level L ₂ of the molten metal surface level L ₁ and the ladle 2 when the molten steel 1 has reached the boundary between the vacuum chamber 3 and the immersion pipe mounting portion 3a is atmospheric pressure and the molten steel 1 Is equal to the difference between the pressure P ₃ in the vacuum chamber 3 when the boundary between the vacuum chamber 3 and the dip tube mounting portion 3a is reached. Therefore, the equation (18) can be expressed as the following equation (19).

H ₀ -H = {R ₁ ² · (101-P ₁ )-(R ₁ ² -2R ₂ ² ) · (101-P ₃ )} · (13.6 / d · R ₄ ² ) · (760 / 101) ··· (19) In the formula (19), H ₀ −H is the amount of movement of the lower end of the immersion pipe 4 from the initial position when the immersion length A ₂ of the immersion pipe 4 is constant. Is. In other words, it is the amount of movement from the initial position of the lower end of the immersion pipe 4 required to keep the immersion length A ₂ of the immersion pipe 4 constant.

Therefore, in the case of the state of FIG. 4, the pressure P ₂ in the vacuum chamber 3 is measured during the vacuum processing, and this pressure P ₂ and P ₃ obtained in advance are used. Using the inner diameter estimated by the above D to F as ₁ , the above (1
The amount of movement of the lower end of the dip tube 4 is calculated by the equation 9). In addition,
The pressure P ₃ in the vacuum tank 3 when the molten steel 1 reaches the boundary between the vacuum tank 3 and the immersion pipe mounting portion 3a is the straight line S and the straight line V in FIG.
₁ (V _i , V _n ) is the pressure at the intersection, (4)
It can be obtained in advance by the formula or the formula (7).

The vacuum chamber 3 is moved by the amount of movement thus obtained.
By moving up and down, even if the vacuum chamber 3 is worn,
The immersion length of the immersion tube 4 can be set within a substantially constant range.

Although the vacuum chamber 3 is moved up and down in the above description,
Instead of raising and lowering the vacuum chamber 3, raising and lowering of the ladle 2 can be performed in the same manner as above.

The estimation of the inner diameter of the vacuum chamber 3 has been described with reference to FIG. 5, but data corresponding to the figure may be used instead of the figure.

[0088]

EXAMPLE After the molten steel 1 blown in a converter is tapped in a 75-ton ladle 2, the dipping pipe 4 of the RH degassing apparatus having the structure shown in FIG. It was immersed in the molten steel 1 contained in the ladle 2 and degassed without controlling the height of the vacuum chamber 3. The degassing treatment was performed for 20 minutes after the pressure inside the vacuum tank 3 was reduced and the pressure inside the vacuum tank 3 reached 1 kPa. At this time, 100 m from the tuyere (inner diameter 20 mm x 12) provided on the inner wall of one dipping tube 4
³ (normal) / h of argon gas was blown, and the temperature of the molten steel 1 in the ladle 2 was measured during the degassing process, and oxygen gas was supplied from the lance 7 so that the molten steel temperature could be maintained at approximately 1600 ° C. Blown in. The main dimensions of the RH degasser used are as follows.

The inner radius R ₁ of the vacuum chamber 3 is 700 mm, and the inner radius R _{2 of} the immersion pipe mounting portion 3 a and the immersion pipe 4 is 160.
mm, the outer radius R _{3 of} the immersion pipe attachment portion 3 a and the immersion pipe 4: 460
mm, the length of the dip tube attaching portion 3a B: 670 mm, length of the dip tube 4 A: 900 mm, ladle 2 of the radius _R 4,: _1160mm.

Prior to the degassing treatment, the amount X ₂ of drop of the molten metal 1 contained in the ladle 2 from the initial level L ₀ was calculated by the above equations (4) and (7). .

The amount of molten steel 1 contained in the ladle 2 at this time was 75 tons (density d = 7 (g / cm ³ ),
The initial immersion length A ₂ of the immersion tube 4 is set to 300 mm,
The measurement was performed for the inner radius R ₁ of the vacuum chamber 3 of 700 mm (design value) and 1000 mm (usage limit). Relationship between the pressure in the vacuum chamber 3 and the molten metal surface level L ₂ and descent amount X ₂ of molten metal surface in the ladle 2 at this time is as shown in Figure 5 of the.

In the degassing process, the length is 1500 when the pressure in the vacuum chamber 3 during each charging is 15 kPa.
Insert the mm of steel bar in the molten steel 1 measured melt surface level L _2, the pressure in the vacuum chamber 3 is 15 kPa, and plotted in Figure 5 points molten metal surface level L _2, the vacuum chamber 3 at that time The inner diameter of was estimated for each charge.

In this way, degassing treatment is performed,
Since the inner diameter of the vacuum tank 3 was estimated to be 1000 mm, which is the limit of use, in the degassing process of 300 charges, the refractory material in the vacuum tank 3 was replaced with a new refractory material, and the length A was 70 mm.
A 0 mm dip tube 4 was attached to the above device. Further, the relationship between the number of charges and the inner diameter of the vacuum chamber 3 was obtained based on the estimated inner diameter of the vacuum chamber 3.

Thereafter, the degassing process was performed in the same manner as described above while controlling the height of the vacuum chamber 3 based on the equations (12) and (19). However, the level L ₂ of the molten metal in each charge was not measured, and the inner diameter of the vacuum tank 3 in each charge was estimated from the relationship between the number of charges and the vacuum tank 3 which was obtained in advance, and the estimated inner diameter was calculated as described above. Used in equation (19). Then, the immersion pipe 4 withdrawn from the molten steel 1 was observed after the vacuum treatment of each charge was completed, and the immersion length immediately before the immersion pipe 3 was withdrawn from the molten steel 1 was estimated based on the degree of discoloration. As a result, the estimated immersion length was 450 to 550 mm.

For comparison, the height of the vacuum chamber 3 is set by the above equations (12) and (19) while setting the target value of the immersion length to 200 mm and keeping the inner diameter of the vacuum chamber 3 constant for all charges. Controlled. In this case, since the slag existing above the molten steel 1 in the ladle 2 began to be sucked up from the dipping pipe 4 at an early stage after the refractory material in the vacuum tank 3 was replaced with a new refractory material, the operation was stopped. did.

[0096]

According to the method for estimating the inner diameter of a vacuum chamber of the present invention, the inner diameter when the vacuum chamber is worn can be accurately estimated, so that the limit of use of the refractory lined in the vacuum chamber is limited. It can be accurately determined. Further, according to the height control method of the present invention, the immersion length of the immersion tube can be accurately maintained within a certain range even when the vacuum chamber is small or the number of repeated uses is large.

[Brief description of drawings]

FIG. 1 is a partial vertical cross-sectional view showing an example of the configuration of an RH degassing device.

FIG. 2 is a vertical cross-sectional view showing a state of molten steel when the pressure in the vacuum chamber is atmospheric pressure.

FIG. 3 is a vertical cross-sectional view showing a state where a part of molten steel is sucked up inside the dip tube and the dip tube mounting portion.

FIG. 4 is a vertical cross-sectional view showing a state where a part of molten steel is sucked up in a vacuum chamber.

FIG. 5 is a diagram showing an example of the relationship between the pressure in the vacuum chamber, the level L ₂ of the molten metal in the ladle, and the amount X ₂ of lowering of the molten metal in the ladle, which are calculated.

[Explanation of symbols]

1: molten steel, 2: Ladle, 3: vacuum chamber, 4: immersion tube, 5: vacuum exhaust pipe, 6: Alloy addition tube, 7: Lance.

Claims (3)

[Claims] 1. A ladle for accommodating molten metal, a vacuum tank provided with a dip pipe at the bottom and connected to a vacuum exhaust unit, and an elevating / lowering drive unit for elevating or lowering one of the ladle and the vacuum tank. The vacuum tank of the vacuum degassing apparatus, which comprises a dipping tube immersed in the molten metal contained in the ladle and circulates the molten metal between the ladle and the depressurized vacuum tank to perform degassing treatment. The method of estimating the inner diameter of the, the pressure in the vacuum tank in a state in which the immersion pipe is immersed in the molten metal contained in the ladle and the height position relationship between the ladle and the vacuum tank is constant. The relationship between the molten metal level in the ladle and the molten metal level is obtained in advance for multiple inner diameters of the vacuum tank, and during degassing, part of the molten metal contained in the ladle is in the vacuum tank. Level of molten metal in the ladle after Measuring the pressure in the vacuum chamber, and the pressure of the molten metal surface level and the vacuum chamber of the measured ladle,
A vacuum characterized by estimating the inner diameter of the vacuum tank at the time when the level of the molten metal is measured based on the relationship between the pressure in the vacuum chamber and the level of the molten metal in the ladle that is obtained in advance. Method for estimating inner diameter of vacuum chamber in degassing device. 2. The inner diameter of the vacuum chamber is estimated and stored for a plurality of charges by the inner diameter estimating method according to claim 1.
The relationship between the number of charges and the inner diameter of the vacuum chamber is obtained in advance based on the inner diameters of the vacuum chambers in the plurality of stored charges, and the current number of charges and the previously determined charge are used during degassing. A method for estimating the inner diameter of a vacuum chamber in a vacuum degassing apparatus, comprising estimating the inner diameter of the current vacuum chamber based on the relationship between the number and the inner diameter of the vacuum chamber. 3. A ladle for containing molten metal, a vacuum tank provided with a dip pipe at the bottom and connected to a vacuum exhaust unit, and an elevating / lowering drive unit for elevating or lowering one of the ladle and the vacuum tank. And a ladle of a vacuum degassing device for degassing by immersing a dipping tube in molten metal contained in a ladle and circulating the molten metal between the ladle and a vacuum chamber under reduced pressure. Or a method of controlling the height of the vacuum chamber, measuring the pressure in the vacuum chamber, the lower end position of the immersion pipe and the initial lower end position of the immersion pipe when the immersion length of the immersion pipe is constant The difference is obtained based on the inner diameter of the vacuum chamber estimated in claim 2 and the measured pressure in the vacuum chamber, and the ladle or the vacuum chamber is moved up and down to correct the difference between the obtained lower end positions of the immersion tubes. A method for controlling height in a vacuum degassing device, comprising: