JPH0698477B2 - Control method for preventing outflow of slag in ladle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention prevents slag outflow in a ladle to prevent slag from flowing out together with molten steel when the molten steel is taken out from below a ladle filled with molten steel. Regarding control method.

[Conventional technology]

As is well known, in the steelmaking process, molten steel in a refined ladle is poured into a tundish of continuous casting by opening a sliding nozzle from a tap hole provided at the bottom of the ladle, and then poured from a tundish into a mold. A slab is being manufactured. What is important for producing clean steel in the above-mentioned work for injecting molten steel from the ladle is to prevent the slag floating on the molten steel in the ladle from flowing out. Efforts are being made.

The outflow of slag when pouring molten steel from the ladle into the tundish is (1) entrainment of the levitation slag layer into the vortex flow generated immediately above the ladle tap hole as the molten steel level in the ladle decreases.
And (2) it can be roughly divided into the outflow of the floating slag layer due to the delay in determining the end of pouring ladle. Therefore, the above (1),
As a method for preventing slag outflow due to (2), Japanese Patent Laid-Open No. 60-210352 has already proposed a slag outflow prevention method.

This method is called the floating valve method, and when the molten steel level in the ladle of which the specific gravity is adjusted decreases and a swirl occurs, the floating valve is positioned at the slag-molten steel interface just above the tap hole. This prevents the generation of vortex flow to prevent the slag from being entrained, and at the end of the injection, the floating valve is landed on the tap hole to block the tap hole and prevent the floating slag from flowing out.

According to this technique, it is possible to effectively prevent the generation of eddy currents and effectively prevent the slag from being caught.
The effect of preventing the outflow of slag at the end of injection is not sufficient. That is, when the refractory near the ladle tap hole and the refractory that constitutes the floating valve are melted and changed in shape, the tap hole cannot be reliably blocked and slag flows out at the end of pouring. There are often cases where

JP-A-62-203667 discloses a solution to this problem in which the float is positioned at the interface between the slag layer and the molten steel, and is lowered to follow the molten metal level drop to a predetermined height. A method is disclosed in which the descent is stopped at a point of time, a change in the buoyancy of the float thereafter is detected as a change in the tension of the float, and the tap hole of the ladle is closed based on this.

[Problems to be Solved by the Invention]

In the present invention, the timing of closing the tap hole is obtained only based on the change in the tension applied to the float held at a predetermined height. Therefore, when the refractory material near the tap hole melts and the shape changes, the positional relationship between the upper part of the tap hole and the detection point changes, the flow state of the molten steel changes, and timing deviation may occur. In addition, the state of molten steel flow changes depending on the state of thermal convection of molten steel or the opening of the tap hole, causing variations in the measured tension values, making it difficult to determine abrupt changes. I may make a mistake.

Therefore, an object of the present invention is to provide a slag outflow prevention control method that improves the above points.

[Means for Solving the Problems]

 The gist of the present invention is as follows.

(1) A method for preventing the outflow of sugag from a ladle 10 having a tap hole 12 at the bottom and having an outflow amount adjusting means 14 for adjusting the outflow amount of molten steel from the tap hole 12. ) After the rod-shaped object 18 is held above the molten metal surface,
When the molten steel level is lowered to a height where sufficient time is secured to prevent the adhesion of slag and molten steel when 18 is preheated and plunges into the molten steel, the rod-like object 18 is lowered and held above the molten metal level. Ii) after a sufficient time has elapsed to prevent the adhesion of slag and molten steel when plunging into the molten steel, the fishing force W ₀ of the rod-shaped object 18 is memorized, and iii) the level of the molten metal is the rod-shaped object 18 Of the rod-like object 18 is started to descend, and iv) the fishing force of the rod-like object 18 is equal to or less than a value obtained by subtracting the buoyancy of molten steel from the weight of the rod-like object 18. After that, it is assumed that the rod-shaped object 18 has reached the upper portion of the tap hole 12 and the descending is stopped to measure the position L of the rod-shaped object 18 at that time,
It is raised by a predetermined height and held. V) The difference ΔW between the fishing force W ₀ before the molten steel inrush and the fishing force W ₁ immediately before the slag flows out with respect to the position L when the rod-shaped object 18 reaches the tap hole 12. to previously obtain a more a relationship in advance historical data group regression _{equation, vi) W 1 = W 0} -ΔW against upper iv) the position L at the time of tapping hole 12 reaches the rod-like object 18 by the v) regression equation When the weight of the rod-shaped object 18 suddenly changes before reaching the fishing support force W ₁ just before the slag outflow obtained in step ₁ , the rod-shaped object 18 is moved down in synchronization with the molten metal lowering speed or more. , Vii) or before the weight of the rod-shaped object 18 suddenly changes.
v) With respect to the position L of the rod-shaped object 18 when reaching the tap hole 12, when the fishing support force W ₁ just before the slag outflow obtained by the above v) regression equation W ₁ = W ₀ −ΔW is reached, The rod-shaped object 18 is lowered at a speed equal to or higher than the descending speed, and viii) after the rod-shaped object 18 reaches the upper portion of the tap hole 12, the tap hole 12 is closed by the outflow amount adjusting means 14. A characteristic control method for preventing slag outflow in a ladle.

[Action]

The position when the rod-shaped object reaches the upper part of the tap hole in step iv) is known, and the position of the rod-shaped object and the upper part of the tap hole to obtain the timing to close the tap hole by rising to that position from that position. The positional relationship with and is always kept constant irrespective of the melting condition.

The timing of closing the sliding nozzle depends not only on the change in the fishing support force but also on the absolute value of the fishing support force. Therefore, even when the change is difficult to detect due to the change in the flow of the molten steel, the sliding nozzle can be reliably closed. If the metal or slag adheres to the rod-shaped object, it will cause disturbance and be affected. Therefore, in step ii) the adhesion is prevented as much as possible when it rushes into the molten steel by preheating. Further, even if the deposit adheres to the rod-shaped object due to insufficient preheating, the preheating sufficiently melts and removes the deposit without causing any problem.

In order to detect the state of melting loss, the rod-shaped object in the present invention is composed of a metal that is sufficiently heavier than molten steel and a refractory that covers it, and the total specific gravity is set to be sufficiently larger than that of molten steel. . Therefore, the rod-shaped object does not float near the surface of the molten steel. Moreover, its length is designed to be longer than the molten metal level at which vortex flow occurs, and when the molten metal level falls below that length, it is submerged in the molten steel in step iii), so that part of it is always molten steel. It comes out of the surface and prevents the generation of eddies.

In order to reduce the cost of the rod-shaped object, the length of the rod-shaped object is shortened, and near the molten metal surface level where the vortex is generated, the vortex is prevented by immersing part of the rod-shaped object in molten steel,
When the molten metal level becomes less than the length of the rod-shaped object, ii
i) The same effect can be obtained by performing the following operations.

In steps vi) and vii), the rod-shaped object descends in synchronization with the descending speed of the molten metal surface, reaches the upper portion of the molten metal outlet, and then the slag is closed by closing the molten metal outlet by means of the outflow adjusting means (sliding nozzle). It is possible to make maximum use of molten steel without causing it to flow out. In order to prevent the slag from flowing out more reliably, the descending speed of the rod-shaped object may be set higher than the descending speed of the molten metal surface. In this case, a slight amount of molten steel remains, but this is not a problematic level.

〔Example〕

FIG. 1 is a view showing a slag outflow prevention device in a ladle according to the present invention. Long nozzle 12 at the bottom of ladle 10
A sliding nozzle 14 is installed in the middle of the
The outflow amount of the molten steel 16 inside is adjusted. Reference numeral 17 represents a slag layer. The rod-like object 18 supported by the wire 28 above the long nozzle 12 is moved up and down by the winch 32 that is rotated by the rotation of the motor 20 to move up and down above the long nozzle 12. A load cell in the middle of the wire 28
24 is provided and the tension of the wire 28 is measured. The pulse generator 22 generates a pulse in response to the rotation of the winch 32, and the vertical position of the rod-shaped object 18 is measured by counting the pulse. The pulse from the pulse generator 22 and the signal from the load cell 24 are input to the sequencer 30, and the motor 20 and the sliding nozzle 14 are controlled according to the signal from the sequencer 30. In addition, 26 indicates a pot lid. At the time of preheating, the rod-shaped object 18 is set at a position between the pot lid 26 and the slag layer 17 and naturally preheated by the ambient temperature in the pot.

In addition, in order to prevent damage due to overheating, it is preferable to provide a pipe for passing a cooling medium around the load cell 24 and the wire 28.

Also, the function for adjusting the positions of the long nozzle 12 and the rod-shaped object 18 may be directed to the upper side of the wire 28.
Does not need to be set because it is set at a substantially predetermined position.

FIG. 2 is a diagram for explaining a control method of the apparatus of FIG. Further, FIG. 3 is a flowchart of control of the sequencer 30. An example of the control method according to the present invention will be described with reference to FIGS. 2 and 3 together with FIG.

When the ladle 10 containing the molten steel 16 is installed at a predetermined position, the sliding nozzle (SN) 14 is opened to start the extraction of the molten steel, and the arm 34 is swung to rotate the refractory stopper 18 to the nozzle. Located above twelve. After waiting for a predetermined time and waiting for the molten metal level to decrease to the extent shown in FIG. 2 (a) (step a in FIG. 3), the stopper 18 is lowered to the preheating position shown in FIG. 2 (a) and held. (Step b in FIG. 3). After a lapse of a predetermined time, the fishing support force that is the value indicated by the load cell 24 is stored as W ₀ . When the surface level drops to a predetermined value, for example 700 mm (Fig. 3, step c),
The stopper 18 is lowered at a speed sufficiently faster than the lowering speed of the molten metal level (step d in FIG. 3), and when the value indicated by the load cell 24 falls below a value obtained by subtracting the buoyancy of molten steel from the weight of the stopper 18 (third step). Step e) Assuming that the nozzle 12 has reached the upper part, the descending is stopped (FIG. 2 (b), step f in FIG. 3), and the vertical position L at this time is stored.

The level of the molten metal surface at which eddy currents are generated in molten steel is generally set to about 500 mm, and the above-mentioned 700 mm is a sufficiently higher level.

Next, the stopper 18 is 30 to 10 with respect to the position L above the nozzle 12.
It is raised by 0 mm and held (Fig. 2 (c), Fig. 3 step g). The rising stroke at this time must be within a range that does not hinder the pouring speed from the ladle.

CASE1 (Step h ₂ → Step j in Fig. 3) The value W from the load cell 24 is continuously monitored, and if there is a sudden change, it is assumed that the interface between the slag and the molten steel has reached near the lower end of the stopper 18 ( Fig. 2 (d)) After that, the stopper is synchronized with the lowering speed of the molten metal level or faster than that.
18 is lowered (Fig. 2 (e), Fig. 3 step h ₂ →
j). When the stopper 18 reaches near the zero point in the vertical direction (step k), the sliding nozzle 14 is closed and the molten steel is taken out (FIG. 2 (f)), FIG. 3 step 1).

FIG. 4 (a) shows the actual measurement value of the value W of the loadle when the operations of (a) to (d) in FIG. 2 are performed.

The period indicated by A is the state during preheating shown in FIG. The period indicated by B is a period in which the flow is descending from FIG. 2 (a) to FIG. 2 (b), and when reaching the upper portion of the nozzle, W rapidly decreases. The period indicated by C is a rising period from the position shown in FIG. 2B to the position shown in FIG. After that, the buoyancy decreases as the molten metal level decreases, and W gradually increases. W changes abruptly at the point indicated by D, which corresponds to the state shown in FIG. E represents the timing at which the closing of the sliding nozzle was started.

FIG. 5 (a) is an enlarged view near E in FIG. 4 (a).
As shown in the figure, normally, after this sudden change, the sliding nozzle is closed to complete the molten steel injection. Therefore, the outflow of slag can be prevented by closing the sliding nozzle after the rod-shaped object descends and reaches the upper portion of the tap hole upon confirmation of a sudden change.

The reason why the above W suddenly changes is that, as shown in FIG. 6 (a), a contracted flow occurs immediately before and immediately after the slag 17 on the molten steel 16 flows under the pan, and particularly immediately after the slag 17 flows under the pan, a rod-shaped object. Voids suddenly form around 18.
Due to this gap, the buoyancy is locally reduced and W rapidly increases.

The present invention utilizes the following phenomena.

CASE2 (step h ₁ → step j in FIG. 3) As shown in FIG. 4 (b) and FIG. 5 (b), unlike the case of FIG. 4 (a) and FIG. 5 (a) There may be a large deviation between the rod-shaped object 18 and the molten steel outlet (hole for tapping), or there may be no sudden change in the fishing support force W of the rod-shaped object 18 due to disturbances caused by changes in the flow of molten steel. As an effective relationship in such a case, the position L when the rod-shaped object 18 reaches the upper part of the molten steel outlet (melting hole) and the fishing support force W ₀ and the slag just before the rod-shaped object 18 rushes into the molten steel. Difference in fishing support force W ₁ just before the outflow Δ
It was found that there is a correlation with W = (W ₀ −W ₁ ) as shown in FIG. This relationship is further increased by aligning the molten steel outflow rate from the molten steel outlet of the steel type and ladle. Therefore, when there is no abrupt change in the fishing force W of the rod-shaped object 18, the position L when the rod-shaped object 18 reaches the upper portion of the molten steel outlet (melting hole) is set in advance according to the relationship shown in FIG.
On the other hand, the fishing support force W ₁ just before the slag flows out is measured, and the regression equation with ΔW which is the difference from the fishing support force W ₀ before the molten steel plunge is obtained. By this regression equation, ΔW is obtained at the time when the position L when the rod-shaped object 18 reaches the upper portion of the molten steel outlet (exit hole) is detected, and the fishing support force W ₁ immediately before the slag flows out.
It can be predicted by calculating W ₁ = W ₀ −ΔW.

In this case, when the fishing support force W becomes W ₁ , the rod-shaped object descends, reaches the upper part of the tap hole, and then the sliding nozzle is closed to complete the injection of molten steel while preventing the outflow of slag. be able to.

〔The invention's effect〕

As described above, according to the present invention, it is possible to prevent the generation of a vortex and prevent the outflow of slag,
By accurately grasping the timing of slag outflow, the effect of improving the yield can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of the present invention, FIG. 2 is a view for explaining control for preventing slag outflow, FIG. 3 is a flowchart of processing, and FIGS. 4 (a) and 4 (b) are FIG. 5 (a) and FIG. 5 (b) are partial enlarged views corresponding to FIGS. 4 (a) and 4 (b), respectively, and FIG. 6 (a) showing the time variation of the load cell value W in the method of the present invention. ) And (b) are views showing immediately after the slag flows out under the pan, and FIG. 7 is a view showing a relationship between the position L and the ΔW when the rod-shaped object reaches the tap hole. In the figure, 10 ... Ladle, 12 ... Long nozzle, 14 ... Sliding nozzle, 16 ... Molten steel, 17 ... Slag, 18 ... Stopper, 22 ... Pulse generator 24 ... Load cell.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideyoshi Yoshimura, 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Stock Co., Ltd. Inside the Kimitsu Works, Kaisha (56) Reference JP-A-3-5067 (JP, A)

Claims (1)

[Claims] 1. A ladle 10 having a tap hole 12 at the bottom and an outflow amount adjusting means 14 for adjusting the outflow amount of molten steel from the tap hole 12.
A method for preventing the outflow of slag from a slag, comprising: i) a rod-shaped object 18 after being held above the molten metal surface;
When the molten steel level is lowered to a height where sufficient time is secured to prevent the adhesion of slag and molten steel when 18 is preheated and plunges into the molten steel, the rod-like object 18 is lowered and held above the molten metal level. Ii) after a sufficient time has elapsed to prevent the adhesion of slag and molten steel when plunging into the molten steel, the fishing force W ₀ of the rod-shaped object 18 is memorized, and iii) the level of the molten metal is the rod-shaped object 18 Of the rod-like object 18 is started to descend, and iv) the fishing force of the rod-like object 18 is equal to or less than a value obtained by subtracting the buoyancy of molten steel from the weight of the rod-like object 18. After that, it is assumed that the rod-shaped object 18 has reached the upper portion of the tap hole 12 and the descending is stopped to measure the position L of the rod-shaped object 18 at that time,
It is raised by a predetermined height and held. V) The difference ΔW between the fishing force W ₀ before the molten steel inrush and the fishing force W ₁ immediately before the slag flows out with respect to the position L when the rod-shaped object 18 reaches the tap hole 12. to previously obtain a more a relationship in advance historical data group regression _{equation, vi) W 1 = W 0} -ΔW against upper iv) the position L at the time of tapping hole 12 reaches the rod-like object 18 by the v) regression equation When the weight of the rod-shaped object 18 suddenly changes before reaching the fishing support force W ₁ just before the slag outflow obtained in, the rod-shaped object 18 is lowered at a speed equal to or higher than the molten metal lowering speed, vii) or before the weight of the rod-shaped object 18 suddenly changes, i
v) With respect to the position L of the rod-shaped object 18 when reaching the tap hole 12, when the fishing support force W ₁ just before the slag outflow obtained by the above v) regression equation W ₁ = W ₀ −ΔW is reached, The rod-shaped object 18 is lowered at a speed equal to or higher than the descending speed, and viii) after the rod-shaped object 18 reaches the upper portion of the tap hole 12, the tap hole 12 is closed by the outflow amount adjusting means 14. A characteristic control method for preventing slag outflow in a ladle.