JP2010159921A - Method of detecting molten metal surface of molten metal stirring device and method of determining immersion position of stirring member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of detecting a molten metal surface within a molten metal container having excellent detection accuracy without providing a specific sensor. <P>SOLUTION: In the method of detecting the molten metal surface, a current value of a lifting/lowering motor for lowering a stirring member immersed in molten metal within the molten metal container and used and lifting/lowering speed of the stirring member are measured. A current value when the stirring member is lowered at constant speed Vc is determined as a steady-state current value Ic. A measurement current value Ir which is a current value when the stirring member is continuously lowered is determined. A difference &Delta;I (=Ic-Ir) between the steady-state current value Ic and the measurement current value Ir is determined. Time when the difference &Delta;I indicating reduction amount of the current value exceeds a predetermined value is determined as molten metal surface detection time ta which is time when the stirring member reaches the molten metal surface. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for detecting a molten metal level in a hot metal container that detects when the stirring member reaches the molten metal level in the molten metal container, and a method for determining the immersion position of the agitated member based on the method.

Of the processes for manufacturing steel products, in the steelmaking process, refining treatment is performed to reduce impurities in the hot metal. For example, in an electric furnace which is a kind of steelmaking furnace, a desulfurization process is performed to reduce sulfur (S) contained in the hot metal after melting the raw material. Conventionally, a slag raw material blended and adjusted to have a high basicity excellent in a desulfurization reaction has been used for the desulfurization treatment. A high basicity slag produced by dissolving a slag raw material has low fluidity. Therefore, fluorite (CaF ₂ ) is added to the slag to improve the fluidity, and the slag and molten iron that have secured the fluidity are reacted to desulfurize.

  However, if fluorite is used extensively to ensure the fluidity of slag, environmental problems such as fluorine (F) leaching into rainwater are feared when secondary use of slag after desulfurization treatment is as a roadbed improvement material. . Therefore, there is a method to secure the fluidity of slag by keeping the basicity low, and to compensate the decrease in the desulfurization reaction due to keeping the basicity low by mechanically stirring the hot metal and slag in the hot metal vessel. Has reached.

  When hot metal and slag are mechanically agitated, the contact frequency and contact interface area of both increase, and the desulfurization reaction is promoted. The effect of promoting the desulfurization reaction by mechanical stirring is greatly influenced by the position of the stirring member immersed in the hot metal. In particular, in chromium-containing hot metal containing chromium, since chromium is an element that lowers the activity of S, desulfurization reaction does not proceed easily, and a relatively large amount of desulfurizing agent is required. It will be necessary. If the immersion position of the stirring member with respect to the hot metal is too deep, only the hot metal is stirred and the slag is hardly stirred, so that a sufficient desulfurization effect cannot be obtained. On the contrary, if the immersion position of the stirring member in the hot metal is too shallow, only the hot metal in the vicinity of the slag and the molten metal is stirred, and the hot metal existing in the deep position in the hot metal container and the slag are hardly in contact with each other. The effect cannot be obtained. Furthermore, since the stirring member jumps up the hot metal in the vicinity of the hot water surface and increases the splash, the wear of the refractory in the hot metal container is accelerated and the steelmaking yield is lowered. In order to obtain a sufficient desulfurization effect, it is necessary to immerse the stirring member in an appropriate position with respect to the hot metal. Usually, the immersion position of the stirring member with respect to the hot metal is determined based on the position of the hot metal surface by detecting the hot metal surface. Therefore, in order to know the position of the hot water surface, the hot water surface detection for detecting when the stirring member reaches the hot water surface is important.

  The hot water level detection method uses a method of judging the brightness change of the hot water level when the stirring member is immersed in the molten iron by visual observation or imaging with a camera, or using a non-contact hot water level sensor using a microwave or the like. There is a method of judging. However, there is a problem from the viewpoint of work load and labor saving because the operator must constantly monitor the hot water level with visual inspection. In addition, in the determination by the camera, there is a problem that the detection accuracy varies depending on the properties, generation amount and distribution state of the slag floating on the hot metal surface. Although the hot water level sensor is excellent in measurement accuracy, it is installed in the vicinity of the hot metal container or in a high place in the building, so there is a problem that the life is reduced due to high heat or vibration, and it is also expensive.

  For such problems, measure the current value of the lifting motor that drives the stirring member up and down after the stirring blade member of the stirring member is completely immersed in the hot metal and until the stirring shaft member is further immersed in the hot metal. In addition, it has been proposed to detect the total sinking position of the stirring blade member by detecting the bending point of the gradient in which the decrease in the current value due to the buoyancy of the hot metal acting on the stirring member indicates a discontinuous change (Patent Document) 1). In addition, a method of detecting the current fluctuation of the stirring motor when the stirring member is inserted into the hot metal while rotating the stirring member, and detecting the level of the molten metal level based on the detection raising and lowering position of the stirring member at that time, and the stirring member contacted the hot metal when lowered It has been proposed to detect the ground current at the time and detect the level of the molten metal by the detection lift position of the stirring member at that time (see Patent Document 2).

Japanese Patent No. 2957999 JP 2003-65684 A

  However, the technique disclosed in Patent Document 1 has the following problems. Since the stirring member is designed on the basis of various ideas, the shape thereof is not uniform and various types are formed. Therefore, some stirring members do not have a very large difference between the volume per unit length of the stirring blade member and the volume per unit length of the stirring shaft member. In addition, after agitation, a large amount of slag adheres to the agitation shaft member, and the volume difference between the agitation blade member and the agitation shaft member becomes small, but especially in stainless steel that is difficult to desulfurize, a large amount of desulfurization agent is added. Therefore, the slag adhesion of the stirring shaft member is extremely large. In such a stirring member, there is no significant difference in the effect of buoyancy on the stirring blade member and the stirring shaft member. If there is no significant difference in the buoyancy acting on the stirring blade member and the stirring shaft member, it will be difficult to detect the difference in the gradient of the current value decrease of the lifting motor, so it is possible to accurately detect the entire time of the stirring blade member There is a problem that you can not.

  Further, the technique disclosed in Patent Document 2 has the following problems. In the method of detecting the current fluctuation of the stirring motor when the stirring member is inserted into the hot metal while rotating the stirring member, when the rotating stirring member comes into contact with the molten metal surface, the hot metal near the molten metal surface is sprinkled up to generate a large amount of splash. . This splash wears the refractory in the hot metal container and lowers the steelmaking yield. In addition, since the outer periphery of the stirring blade member approaches a circular shape as the use progresses, the resistance decreases and the accuracy decreases. In the method of detecting the ground current when the stirring member comes into contact with the molten metal surface, the grounding current detection sensor must be provided on the stirring member that comes into contact with the hot metal and becomes high temperature.

  An object of the present invention is to provide a hot water level detection method for a hot metal stirring device excellent in detection accuracy and a method for determining a dipping position of a stirring member based on the method without providing a special sensor.

The present invention relates to a hot water level detection method for a hot metal stirring device for detecting when a stirring member used by dipping in hot metal in a hot metal container descends from above and reaches the molten metal level.
Measure the current value of the motor that drives the stirring member up and down,
Obtain the current value when the stirring member descends at a constant speed as the steady current value,
Next, obtain the current value when the stirring member descends as the measured current value,
Find the difference between the steady current value and the measured current value,
It is a hot water level detection method for a hot metal stirring device, characterized in that a time when the difference becomes equal to or greater than a predetermined value is determined as a hot water level detection time when the stirring member reaches the hot water level.

Further, the present invention is a method for determining the immersion position of the stirring member for determining the position in the immersion depth direction of the stirring member used by immersing in the hot metal in the hot metal container.
The hot water level detection method is used to determine when the hot water level is detected, and from the lower end position of the stirring member at the time of hot water level detection, the stirring member is lowered by a predetermined distance to determine the immersion position in the hot metal. This is a method for determining the immersion position of the stirring member.

  Further, the present invention is a desulfurization treatment of a chromium-containing hot metal containing 5% by mass or more of chromium, and performs the detection of the molten metal surface or the immersion position of the stirring member by using the molten metal surface detection method or the immersion position determination method. It is a mechanical stirring method characterized by stirring hot metal.

  According to the present invention, the current value of the motor that drives the stirring member to move up and down is measured, and the difference between the steady current value when the stirring member is lowered at a constant speed and the measured current value when the stirring member is subsequently lowered is determined. When the difference is equal to or greater than a predetermined value, it is determined that the hot water level is detected, so no special hot water level detection sensor is required. Further, since the motor current value that is easy to detect is used as an index, and the time when the stirring member that can clearly grasp the fluctuation reaches the molten metal surface is detected, high detection accuracy can be obtained.

  Further, according to the present invention, when the molten metal level is detected by the molten metal level detection method, the stirring member is further lowered by a predetermined distance from the lower end position of the stirring member at the time of molten metal level detection and immersed in the hot metal. Therefore, the immersion position of the stirring member can be determined with high accuracy. As a result, for example, when the hot metal in the hot metal container is stirred for desulfurization, the immersion position of the stirring member with respect to the hot metal can be accurately positioned at a position preferable for stirring, and the desulfurization rate is highly stabilized. be able to.

It is a timing chart which shows the outline | summary of the hot_water | molten_metal surface detection method in the hot metal container which is embodiment of this invention. It is a figure which shows the structure of the hot metal stirring apparatus 10 in which the hot_water | molten_metal surface detection method is used. FIG. 3 is an enlarged view showing a configuration of a hot water surface detection unit 16. It is a figure which shows the state which the stirring member 17 descend | falls and arrives at the hot_water | molten_metal surface 12a. It is a graph which compares and shows the distance from the reference | standard position of the stirring member 17 based on the hot_water | molten_metal surface detection method and the hot_water | molten_metal surface detection by visual hot_water | molten_metal surface determination to the hot_water | molten_metal surface 12a. It is a figure which shows the outline | summary of the immersion position determination method of the stirring member which is embodiment of this invention. It is a graph which shows the result of having carried out the desulfurization process of the hot metal of stainless steel by the mechanical stirring with the hot metal container.

  FIG. 1 shows an outline of a method for detecting a molten metal level in a hot metal container according to an embodiment of the present invention. The line graph in FIG. 1A is a current value of a motor that drives the stirring member to move up and down, and is a time transition of the current value when the stirring member descends in the hot metal container. The line graph in FIG. 1B is a time transition of the ascending / descending speed of the stirring member corresponding to the current value of the motor. Since the ascending / descending speed is a moving speed in the descending direction, it is represented with a minus sign (−). The graph of FIG.1 (c) is a timing chart showing the hot_water | molten_metal surface detection time ta by the hot_water | molten_metal surface detection method (henceforth only a hot_water | molten_metal surface detection method) in the hot metal container which is this embodiment.

  In the hot water level detection method, the current value of the motor when the stirring member descends is measured, and based on the fluctuation of the current value, the time of hot water level detection when the stirring member reaches the hot water level is determined. In the hot water level detection method shown in FIG. 1, the motor current value 49A in a state where the stirring member descends at a constant speed Vc = −3 m / min is obtained as the steady current value Ic. After obtaining the steady current value Ic, the current value Ir when the stirring member continues to descend is obtained as the measured current value Ir. A difference ΔI (= Ic−Ir) between the steady current value Ic and the measured current value Ir is obtained, and the time when the difference ΔI is equal to or greater than a predetermined value is determined as the hot water level detection time ta. In FIG. 1, the predetermined value is set to 1.5 A, and the time when the measured current value Ir decreases by 1.5 A or more from the steady current value Ic is determined as the hot water level detection time ta.

  FIG. 2 shows a configuration of the hot metal stirring device 10 in which the molten metal level detection method is used. Hereinafter, the hot metal stirring device 10 will be described, and the molten metal level detection method will be described in detail. The hot metal stirring device 10 is a device that mechanically stirs the hot metal 12 in the hot metal container 11, and includes a stirring unit 13 that stirs the hot metal 12, a support unit 14 that supports the stirring unit 13, and a lift that drives the stirring unit 13 up and down. It includes a drive unit 15 and a hot water level detection unit 16 for detecting the hot water level.

  The stirring unit 13 includes a stirring member 17 and a stirring motor 18 that rotationally drives the stirring member 17. The stirring member 17 includes a stirring shaft member 19 and a stirring blade member 20. The stirring blade member 20 may be referred to as an impeller 20. The stirring member 17 is immersed in the hot metal 12 in the hot metal container 11 and is rotated by the stirring motor 18 to stir the hot metal 12.

  The support unit 14 includes a support base 21, a support column 22, a shelf plate 23 provided on the support column 22, and a support arm 24. The support base 21 includes a leg portion 21a and a table portion 21b, and is fixed on the reference surface 25 by the leg portion 21a. A support column 22 is provided on the upper surface of the table portion 21b so as to extend in the vertical direction. The support arm 24 extends in the horizontal direction, and its one end 24a is formed in a tubular shape. The support column 22 is inserted into the tubular portion of the support arm 24, and the support arm 24 is guided by the support column 22 and can move in the vertical direction. The stirring member 17 is rotatably supported by the other end 24b of the support arm 24 on the side opposite to the side where the impeller 20 of the stirring shaft member 19 is provided. The stirring motor 18 is provided on the support arm 24 and rotates the stirring member 17.

  The elevating drive unit 15 includes a winch 26 provided on the upper surface of the table 21b of the support base 21, a front pulley 27 and a rear pulley 28 provided on the shelf board 23, a moving pulley 29 provided on the support arm 24, It includes a wire 30, a deflector roll 31, a wire fixture 32, and a lifting motor 34 connected to the winch 26 via a speed reducer 33. The winch 26 can switch the rotation direction between forward and reverse. The elevating motor 34 connected via the speed reducer 33 rotates the winch 26 in the forward direction or the reverse direction, so that the wire 30 can be wound or unwound. The wire 30 exiting from the winch 26 passes through a front pulley 27 and a rear pulley 28, circulates around a movable pulley 29 on the support arm 24, and passes through a deflector roll 31 to a wire fixture 32 provided on the shelf plate 23. The tip is fixed. When the elevating motor 34 drives the winch 26 to rotate in the forward direction, the winch 26 winds the wire 30, and the support arm 24 to which the movable pulley 29 is attached is guided by the support column 22 and is lifted and supported by the support arm 24. The stirring member 17 to be moved up. When the elevating motor 34 rotationally drives the winch 26 in the reverse direction, the winch 26 rewinds the wire 30 and the agitating member 17 supported by the support arm 24 is lowered, contrary to the above. In this way, the stirring member 17 can be raised and lowered within the hot metal container 11.

  FIG. 3 shows an enlarged configuration of the hot water surface detection unit 16. The hot water level detection unit 16 includes an ammeter 35, a speedometer 36, an encoder 37, and a detector 38. The ammeter 35 measures the current value of the lifting motor 34 and outputs the measurement result to the detector 38. The speedometer 36 detects the rotational speed of the winch 26, converts it to the ascending / descending speed of the stirring member 17, and outputs it to the detector 38. The encoder 37 detects the rotation angle and the number of rotations of the winch 26, converts the winding length and rewinding length of the wire 30 into the ascending / descending distance of the stirring member 17, and outputs it to the detector 38. The detector 38 includes a storage unit 41 and a calculation unit 42. The memory | storage part 41 memorize | stores the electric current value of the raising / lowering motor 34 measured when the stirring member 17 descend | falls at the constant speed Vc as a steady-state electric current value Ic. After storing the steady current value Ic, the measured current value Ir of the elevating motor 34 when the stirring member 17 continues to descend is obtained, and the calculation unit 42 calculates the difference ΔI (= Ic−Ir) from the steady current value Ic. To do. The detector 38 is set so as to determine when the difference ΔI is equal to or greater than a predetermined value as the hot water level detection time ta.

  FIG. 4 shows a state in which the stirring member 17 descends and reaches the molten metal surface 12a. When the stirring member 17 descends in the hot metal container 11, the lower end of the impeller 20 reaches the molten metal surface 12a. The impeller 20 is formed of a refractory material and has a specific gravity smaller than that of the hot metal 12. Therefore, when the stirring member 17 is lowered even after the lower end of the impeller 20 reaches the molten metal surface 12 a, the buoyancy of the molten iron 12 acts on the impeller 20, that is, the stirring member 17. Due to the buoyancy acting on the stirring member 17, the load applied to the lift motor 34 via the wire 30 is reduced, and the current value of the lift motor 34 is reduced. By detecting the fluctuation in which the current value decreases as the difference ΔI, the molten metal level detection time ta can be determined.

  Hereinafter, the hot water level detection by the detector 38 will be described. The steady current value Ic of the elevating motor 34 measured in a state where the stirring member 17 descends at the constant speed Vc can be determined as follows, for example. The operator operates the stirring member 17 so as to descend at the constant speed Vc, and after confirming that the agitation member 17 is in the constant speed descending state based on the output of the speedometer 36, inputs the signal to the detector 38. The detector 38 receives the signal and stores the current value measured by the ammeter 35 in the storage unit 41 as the steady current value Ic. After storing the steady current value Ic, the measured current value Ir of the elevating motor 34 that further lowers the stirring member 17 is measured at intervals of 1 second, for example. Every time the measured current value Ir is obtained, the calculation unit 42 obtains a difference ΔI from the steady current value Ic. The detector 38 determines that the molten metal level detection time ta is when the amount of decrease in the current value obtained by the difference ΔI is equal to or greater than a predetermined value.

  A predetermined value as a threshold value of the current decrease fluctuation amount can be determined as appropriate. By reducing the predetermined value within a range in which error determination can be prevented, the molten metal level detection time ta can be detected with higher accuracy. Since the influence of the acting buoyancy varies depending on the configuration of the hot metal stirring device, the predetermined value cannot be determined in general, but is preferably selected and set within the range of 1.0A to 2.0A. If the predetermined value is less than 1.0 A, there is a possibility that a minute fluctuation in the current value when the impeller 20 is lowered is erroneously detected. If the predetermined value exceeds 2.0 A, there is a risk of detection after passing through the true hot water surface position, and the detection accuracy is lowered.

  If the position of the support arm 24 where the stirring member 17 rises and stops is determined, and the length of the stirring member 17 in the ascending / descending direction is obtained, the reference position of the stirring member 17 above the molten metal surface in the hot metal container 11 can be determined. . By detecting the hot water level detection time ta when the stirring member 17 reaches the molten metal surface 12a, the descending distance of the stirring member 17 from the reference position of the stirring member 17 to the hot water surface detection time ta is obtained by the encoder 37. The distance to the hot water surface 12a can be determined.

  FIG. 5 shows a comparison of the distance from the reference position of the stirring member 17 to the molten metal surface 12a based on the molten metal surface detection method and the molten metal surface detection by visual molten metal surface determination. The data shown in FIG. 5 shows the distance from the reference position to the molten metal surface 12a when the stirring member 17 is lowered from the reference position to the molten iron 12 in the molten metal container 11 and the molten metal surface is detected by the molten metal surface detection method, and the visual molten metal surface. The distance from the reference position to the hot water surface 12a when the arrival time of the hot water surface is determined by the determination is compared. The distance between the hot water level detection method and the visual hot water level determination has a high correlation. Moreover, the standard deviation calculated | required about the difference of the distance obtained by the hot_water | molten_metal surface detection method and visual hot_water | molten_metal surface determination was 26.0 mm. For example, when stainless steel hot metal is desulfurized by mechanical stirring, the immersion depth of the stirring member 17 that provides an empirically good desulfurization rate is 500 mm. The immersion depth is a distance from the upper end of the impeller 20 immersed in the molten iron 12 to the molten metal surface 12a. Since the standard deviation is as small as 5.2% with respect to the target immersion depth of 500 mm, it can be said that the accuracy of position determination is sufficiently high. Therefore, it can be seen that the molten metal level detection method can sufficiently withstand practical use as an alternative to visual determination.

  FIG. 6 shows an outline of the method for determining the immersion position of the stirring member according to the embodiment of the present invention. 6A shows a state where the stirring member 17 reaches the molten metal surface 12a, and FIG. 6B shows a state where the stirring member 17 is positioned in the hot metal. The stirring member immersing position determination method for determining the immersion position of the stirring member 17 with respect to the molten iron 12 (hereinafter simply referred to as the immersion position determining method) is performed by determining when the molten metal surface is detected by the above-described molten metal surface detection method. The stirring member 17 is further lowered by a predetermined distance Lb from the lower end position of the stirring member 17 and immersed in the hot metal 12 for positioning.

  Hereinafter, the immersion position determination method will be further described. The length of the impeller 20 in the ascending / descending direction is defined as an impeller width W. In the state immersed in the hot metal 12, the distance from the upper end of the impeller 20 to the molten metal surface 12a is defined as the immersion depth D. The distance obtained by adding the impeller width W and the immersion depth D is defined as the immersion position of the stirring member 17. For each steel type and slag to be melted, an immersion position where the desulfurization rate can be maximized empirically is obtained as a predetermined distance Lb. The hot water level detection method is used to determine when the hot water level is detected, and the stirring member 17 is further lowered by a predetermined distance Lb from the lower end position of the stirring member 17 at the time of hot water level detection and immersed in the hot metal 12 for positioning. The unwinding length of the wire 30 corresponding to the predetermined distance Lb can be obtained by the encoder 37.

  This operation is based on the determination at the time of detecting the molten metal level by the detector 38, and after the molten metal level is detected, the operator drives the lifting motor 34 so that the wire 30 of the winch 26 is rewound by a length corresponding to a predetermined distance Lb. This can be achieved. Further, between the detector 38 and the lift motor 34, the lift motor 34 is driven so as to rewind the wire 30 by a length corresponding to a predetermined distance Lb according to the molten metal level detection signal and the output of the encoder 37. It can also be realized by providing a control device for controlling. As a result, the stirring member 17 can be accurately and reproducibly positioned at the immersion position Lb preferable for the stirring of the desulfurization reaction.

FIG. 7 shows the result of desulfurization treatment of stainless steel hot metal with mechanical stirring in a hot metal container. The results of FIG. 7 show that the desulfurization rate when the stirring member is positioned and desulfurized according to the above-described immersion position determination method, and the molten metal surface position in the hot metal container is always at a constant position with respect to the reference position of the stirring member. It is assumed that there is a desulfurization rate when the desulfurization treatment is performed by positioning the stirring member according to the assumed hot water surface position. In the dipping position determination method, the stirring member 17 was lowered and positioned by a distance Lb from the lower end position of the stirring member 17 when the molten metal surface was detected. In the method based on the assumed hot water surface position, the stirring member 17 is moved down by the distance Lb from the lower end position of the stirring member 17 when reaching the assumed hot water surface position. Therefore, in the case of the assumed hot water surface position, the immersion position of the stirring member 17 is not necessarily the position at the distance Lb from the true hot water surface position. Here, the desulfurization rate refers to the value given by the formula (1) expressed as a percentage. In the formula (1), [% S] represents the sulfur content in the hot metal.
Desulfurization rate = (Before desulfurization [% S] −After desulfurization [% S]) / Before desulfurization [% S] (1)

  The horizontal axis in FIG. 7 is the basic unit of calcium oxide (CaO), which is a component of desulfurized slag. The data indicated by the circle symbols in FIG. 7 indicate the desulfurization rate when the desulfurization treatment is performed by positioning the stirring member by the dipping position determination method. Further, the data indicated by the square symbols indicate the desulfurization rate when the desulfurization treatment is performed by positioning the stirring member according to the assumed hot water surface position. When the desulfurization treatment is performed according to the assumed hot water surface position, the desulfurization rate varies greatly in the range of 20% to 80%. On the other hand, when the desulfurization treatment is performed by the dipping position determination method, the desulfurization rate is highly stabilized in the range of about 60% to 90%. Thus, according to the immersion position determination method, the stirring member 17 can be accurately and reproducibly positioned at the immersion position Lb where the molten iron and slag can be suitably stirred for desulfurization. It becomes possible to stabilize.

DESCRIPTION OF SYMBOLS 10 Hot metal stirring apparatus 11 Hot metal container 12 Hot metal 17 Stirring member 34 Lifting motor 35 Current meter 36 Speedometer 37 Encoder 38 Detector

Claims (3)

In the hot water level detection method of the hot metal stirring device for detecting when the stirring member used by dipping in the hot metal in the hot metal container descends from above and reaches the molten metal level,
Measure the current value of the motor that drives the stirring member up and down,
Obtain the current value when the stirring member descends at a constant speed as the steady current value,
Next, obtain the current value when the stirring member descends as the measured current value,
Find the difference between the steady current value and the measured current value,
A hot water level detection method for a hot metal stirring device, characterized in that a time when the difference becomes a predetermined value or more is determined as a hot water level detection time when the stirring member reaches the hot water level. In the method for determining the immersion position of the stirring member for deciding the position in the immersion depth direction of the stirring member used by immersing in the hot metal in the hot metal container,
The hot water level detection method according to claim 1 is used to determine when the hot water level is detected,
A method for determining a dipping position of a stirring member, wherein the dipping position in the hot metal is determined by lowering the stirring member by a predetermined distance from the lower end position of the stirring member at the time of detecting the molten metal surface.   In the desulfurization treatment of the chromium-containing hot metal containing 5% by mass or more of chromium, the method of claim 1 or 2 is used to detect the molten metal surface or determine the immersion position of the stirring member and to stir the chromium-containing hot metal. A mechanical stirring method.

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