JP2005224847A - Method for controlling molten steel level in mold in continuous casting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling molten steel level in a mold in a continuous casting apparatus by which a stable operation is realized. <P>SOLUTION: In the method for controlling the molten steel level in the mold in the continuous casting apparatus, the molted steel level is stabilized by periodically varying a stopper for opening/closing an immersion nozzle in an opening direction and a closing direction on the way of the molten steel level control which controls the opening/closing the immersion nozzle corresponding to the detected value of the molten steel level during casting, thereby preventing the growth of material deposited on the immersion nozzle, and the operation, that the automatic operation is once interrupted during automatic control, the stopper is forcibly operated in the opening direction in a short time just before being operated in the closing direction, the stopper is operated in the closing direction till pushing against the upper part of the immersion nozzle, thereafter when the stopper is opened to be returned to the original position, the nozzle opening degree is set to be less by a fine value (D value) than the position of the operating end before interrupting the automatic control, then the automatic control is started again, is periodically performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for controlling the molten steel level in a mold of a continuous casting facility, and more specifically, in a steel type with many clogs, by reducing the fluctuation of the molten metal surface, it is possible to prevent deterioration of the quality of the slab to be manufactured and to prevent manual intervention The present invention relates to a method for controlling the molten steel level in the mold for the purpose of stable operation.

Conventionally, molten steel is poured into a tundish from a ladle, and the molten steel in the tundish is poured into a mold to continuously produce slabs. The slab is continuously produced by automatically controlling a stopper that adjusts the molten steel injection amount installed in the tundish based on the detected molten steel level. By the way, the molten steel is poured from the tundish through the immersion nozzle into the mold, but deposits such as Al ₂ O ₃ inclusions and SiO ₂ deposit on the inlet side of the immersion nozzle and on the inner wall of the molten steel flow path. Even if the opening of the stopper with respect to the nozzle is constant, the flow rate of the molten steel may fluctuate greatly.

In particular, even in high-precision control devices that are controlled within ± 3 mm during steady state with steel types that are not clogged with nozzles, generally in the case of aluminum killed steel or aluminum silicon killed steel, the molten steel components contain the same in the tundish. Due to the deposition of Al ₂ O ₃ or the like on the stopper and the nozzle portion, nozzle clogging and clogging of the clogging occur irregularly and the injection amount changes suddenly, resulting in a large fluctuation in the molten steel level in the mold. For example, a slab including a fluctuation of the molten metal surface level exceeding 5 to 10 mm is a cause of a large deterioration in quality that is treated as a slab quality rank reduction or scrap slab, which is said to be disqualified.

  For example, Japanese Patent Application Laid-Open No. 59-35867 (Patent Document 1) describes a control technique for unstable disturbance to molten steel level control in a mold, specifically, disturbance due to nozzle clogging and separation. In addition, the molten steel supply control in continuous casting that reduces nozzle clogging and delamination by periodically vibrating the stopper in the opening and closing directions in a short time and applying shock waves to the supplied molten steel flow A method has been proposed.

JP 59-35867 A

  However, with the shock wave in the technique described in Patent Document 1, the effect of suppressing the growth of nozzle clogging is small, and large peeling occurs due to the growth of nozzle clogging over a long period of time, resulting in fluctuations in the molten steel surface level due to peeling. To do. Further, in Patent Document 1, the period is preferably about 10 seconds. However, in such a short period, fluctuation occurs because the opening / closing operation itself is frequently performed, and the fluctuation amount exceeds ± 3 mm. It has become. In addition, it is impossible to prevent the clogging growth, and eventually the clogging will become a big clogging, and the clogging removal work (shaking) by manual intervention will be required. is there.

  In order to solve the above-mentioned problems, the inventors have intensively developed, and as a result, the molten steel level in the mold that controls the molten steel level in the mold of the continuous casting equipment by changing the injection amount using the stopper of the refractory. About the control device, in steel types with a lot of molten steel level fluctuation due to nozzle clogging and subsequent peeling, rather than periodically opening and closing the stopper for a short time and generating shock waves to suppress nozzle clogging growth, During automatic control, once the automatic operation is interrupted and the stopper is forcibly operated in the opening direction for a short time, the clogging of the nozzle and stopper is grown by forcibly and periodically pressing the stopper under the nozzle. The amount of peeling when clogging is reduced and the level fluctuation due to clogging is reduced. .

  Further, the opening stroke after closing does not return to the operation end position before opening and closing, but rather the nozzle opening that is smaller by a minute value (hereinafter referred to as D value) than the operation end position before interruption of automatic control, that is, slightly before ( D value), and restarting the automatic control again suppresses the rise fluctuation of the molten metal surface due to clogging due to the opening and closing operation, and keeps the molten metal surface level fluctuation within ± 3 mm equivalent to the steel type without nozzle clogging. It has been found that can be.

The gist of the invention is that
(1) In-mold molten steel level control of continuous casting equipment, in the middle of continuous mold in-mold molten steel level control in which the opening and closing of the immersion nozzle is controlled to follow the detected value of the molten steel level during casting. Molten steel in the mold in which the stopper that opens and closes the immersion nozzle is periodically changed in the opening and closing directions in a short time to prevent the growth of deposits on the immersion nozzle and to stabilize the molten metal surface level. In the level control method, the automatic operation is temporarily interrupted during automatic control, and the stopper for a short time immediately before being operated in the closing direction is forcibly operated in the opening direction. When returning to the original position, after the nozzle opening is set to a minute value (D value) smaller than the operation end position before the interruption of the automatic control, the automatic control is restarted periodically. Continuous casting equipment The molten steel in the mold level control method.

(2) The in-mold molten steel level control method for continuous casting equipment according to the above (1), wherein the open / close cycle is set to more than 30 seconds and within 5 minutes.
(3) The method for controlling the molten steel level in the mold of the continuous casting facility according to (1) or (2), wherein the D value is varied depending on the steel type.

  As described above, according to the present invention, the operation of the immersion nozzle and the stopper portion is performed by periodically performing the operation in the closing direction until the stopper is forcibly pressed against the upper portion of the immersion nozzle after being once opened in the opening direction. The clogging growth is greatly reduced, and the amount of peeling when the nozzle clogging is peeled off is also greatly reduced. Therefore, the level fluctuation due to clogging peeling is small, and the level fluctuation amount that was difficult with conventional products with large adhesion is ± 3 mm. Can be achieved and prevention of deterioration of slab quality can be achieved.

  In addition, in the past, automatic control is temporarily interrupted to remove this clogging, and the stopper is manually operated to eliminate the clogging work (shake) that causes an opening / closing impact to the clogged part. A significant improvement in slab quality can also be achieved without large level fluctuations. As described above, according to the present invention, it is possible to achieve a stable operation by improving the slab quality and eliminating manual intervention by improving the molten steel level control in the mold of the continuous casting equipment. .

Hereinafter, the present invention will be described in detail.
The present invention relates to a molten steel level control device in a mold that controls the molten steel level in a mold of a continuous casting facility by changing the injection amount using a refractory stopper. By reducing the level fluctuation of the steel grade to improve the level control accuracy, eliminating the manual work (shaking) to remove the clogging, and eliminating the large fluctuation of the molten metal level due to the intervention of manual operation. This is a method for controlling the molten steel level in the mold of a continuous casting facility that improves the quality of the slab by setting the same molten metal surface level fluctuation within ± 3 mm.

  As a specific method, in the case of a steel grade that has a large fluctuation in the molten steel level in the mold due to nozzle clogging and subsequent peeling, for example, aluminum killed steel or aluminum silicon killed steel, the automatic operation is temporarily interrupted during automatic control and opened once. After moving in the direction, the short-term stopper as the main operation is forcibly pressed until it is pressed against the upper part of the immersion nozzle, then it is opened and then returned to its original position, and immediately after that, the automatic operation is performed periodically. It is. The stroke in the closing direction is set such that the distance between the stoppers is 0 mm (fully closed position) or about several mm from the fully closed direction, thereby suppressing the growth of clogging according to the present invention and positively releasing the clogging periodically. Can be obtained.

  If this operation cycle is long, clogging grows and has no effect, and if it is short, it causes disturbance of the molten metal surface level. Further, if the automatic control interruption period is too long, it causes fluctuations in the level of the molten metal surface due to the opening and closing of the stopper. In addition, in the present invention, the initial opening operation is not performed for the generation of shock waves, but in order to reduce the downward movement of the molten metal surface by closing the stopper and performing the opening operation. The operation in the closing direction of the operation is performed to reduce the lowering of the molten metal surface due to the opening / closing operation.

Furthermore, according to the opening / closing operation of Patent Document 1, the level of the molten metal rises due to the clogging after opening / closing. Accordingly, in the present invention, the fluctuation of the molten metal level due to the main operation can be suppressed by stopping at the D value which is a stroke a little before the opening position at the time of automatic interruption and making it automatic again. . In addition, since this clogging condition depends on the molten steel component of the steel type, it is preferable that the D value varies depending on the steel type. The D value is preferably 10 to 50% with respect to the stopper opening during steady level control with little fluctuation of the molten metal surface. That is, a component that easily adheres. For example, aluminum killed steel, etc. has a large increase in the flow rate due to peeling because the volume of the deposit (peeling amount) is large, so the amount returned to the original opening is reduced, and the D value is set to 50%. It is desirable that the steel type that does not easily adhere and relatively does not require Al ₂ O ₃ deoxidation be in the direction of 10%.

Hereinafter, the present invention will be specifically described with reference to the drawings.
FIG. 1 is a conceptual diagram constituting a molten steel level control device in a mold of a continuous casting facility according to the present invention. As shown in this figure, the continuous casting equipment is provided with a tundish 3 for pouring and collecting molten steel 1 from a ladle 2 by means of a ladle molten steel discharge operation end 4 and an immersion nozzle 5 attached to the lower part of the tundish 3. ing. And the immersion nozzle 5 configured as described above injects steel with a stopper 8 provided in the tundish 3. In that case, the molten steel level 7 in the mold 6 is detected by the molten steel level meter 9, and the control output to the operation end is performed by the level control calculation 11 via the molten metal level meter signal processing device 10, and this control output Is controlled so as to stabilize the molten steel level 7 in the mold 6 by moving the stopper 8 up and down via the stopper drive control device 12 and the stopper drive device 13.

However, Al ₂ O ₃ or the like adheres and grows on the upper part of the immersion nozzle 5 below the stopper 8 due to the molten steel component, and the clogging 15 on the upper part of the immersion nozzle 5 occurs. The clogging 15 at the upper part of the nozzle grows large and then peels off at irregular timings, resulting in a large fluctuation in the molten metal surface level. Therefore, in the present invention, the level control calculation unit 11 shown in FIG. Reference numeral 14 denotes a slab.

  FIG. 2 is an operation schematic diagram showing the stopper opening / closing mechanism according to the present invention. As shown in this figure, during automatic control, the automatic operation is temporarily stopped at point A, the stopper is forcibly opened and closed for a short time, and immediately after that, automatic operation is performed again at point B, for example, f This period is performed every 30 seconds to 5 minutes. The opening / closing operation is performed in a short time from the start to the end. For example, the period e is performed within a short time of 1 second or less. The closing stroke b of the stopper is such that the distance between the stopper and the nozzle is 0 mm (fully closed position) when closed, or a few mm from the fully closed direction, thereby suppressing clog growth and periodically small. A positive clogging release effect can be obtained.

  In addition, in order to reduce the drop of the molten metal surface when the stopper is opened from the closed state, if the stopper is opened from the first position as shown in section a and then closed from the open position, the amount of decrease in the molten metal surface level is affected. Hateful. Furthermore, depending on the steel type, the molten steel components are different, and the amount of clogging per unit time therefor is different, so the amount of separation due to opening and closing operations is different, and the molten metal surface may rise due to separation, so it opens after c section is closed. Sometimes, when the position is opened with respect to the position immediately before the opening / closing operation, when it is stopped automatically by the D amount slightly before and again automatically, an increase in the level of the hot water when clogging is removed by this opening / closing operation can be suppressed. This D value is preferably variable so that the amount of peeling may vary depending on the steel type. Note that this operation diagram is an example of the present invention, and the clogging of the lower part of the stopper and the peeling thereof are forced and periodic operation of the stopper to suppress the growth of the clogging and consequently reduce the peeling amount. It does not depart from the scope of the invention.

  FIG. 3 is a diagram showing an actual molten steel surface control chart and results thereof, and FIG. 3 (a) shows a strand molten steel surface control chart and results thereof to which the present invention is not applied, and FIG. b) shows the control chart of the molten steel surface of the strand to which the present invention is applied and the result. As shown in FIG. 3A, the control result of the molten steel surface of the strand to which the present invention is not applied shows that the molten metal surface level fluctuates more than the level target value. On the other hand, as shown in FIG. 3B, the control result of the molten steel surface of the strand to which the present invention is applied shows almost no clogging growth, and the level fluctuation due to peeling after nozzle clogging is greatly within ± 3 mm. It can be seen that the quality of the slab is greatly improved as compared with the case where it is not applied.

  FIG. 4 is a diagram showing the opening / closing of the stopper and the fluctuation of the hot water level. FIG. 4A shows the opening / closing of the stopper and the fluctuation level of the molten metal surface level when the present invention is not applied. As shown in FIG. 4A, it can be seen that the hot water level fluctuates greatly. On the other hand, FIG. 4 (b) shows the opening / closing of the stopper and the fluctuation level of the molten metal surface level when the present invention is applied. As shown in FIG. 4 (b), it can be seen that the hot water surface level fluctuates slightly with respect to the level target value by once opening and closing and stopping at the D value.

It is a conceptual diagram which comprises the molten steel level control apparatus in a mold of the continuous casting installation by this invention. It is an operation | movement schematic diagram which shows the opening / closing mechanism of the stopper which concerns on this invention. It is a figure which shows the control chart of the molten steel surface of a strand, and its result. It is a figure which shows the fluctuation | variation of a stopper opening / closing and a hot-water surface level.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molten steel Ladle 3 Tundish 4 Ladle molten steel discharge operation end 5 Immersion nozzle 6 Mold 7 Molten steel level 8 Stopper 9 Molten steel level meter 10 Hot water level meter signal processing device 11 Level control calculation 12 Stopper drive control device 13 Stopper drive device 14 Slab 15 Clogging at the top of the immersion nozzle


Patent applicant: Nippon Steel Corporation and 1 other
Attorney Attorney Shiina and others 1

Claims (3)

In the mold control of the molten steel in the mold of the continuous casting equipment, the immersion nozzle is controlled during the control of the molten steel level in the continuous mold by controlling the opening and closing of the immersion nozzle according to the detected value of the molten steel level during casting. A molten steel level control method in the mold in which the stopper for opening and closing is periodically changed in the opening direction and the closing direction in a short time to prevent the growth of deposits on the immersion nozzle and to stabilize the molten metal surface level. In the automatic control, the automatic operation is temporarily interrupted, and the stopper for a short time immediately before the operation in the closing direction is forcibly operated in the opening direction. Continuous casting equipment characterized in that when returning to the position, the nozzle opening is set by a minute value (D value) smaller than the operation end position before interruption of automatic control, and then the automatic control is restarted periodically. Mold Molten steel level control method. The method for controlling the molten steel level in the mold of a continuous casting facility according to claim 1, wherein the opening and closing cycle is 30 seconds to 5 minutes. The method for controlling a molten steel level in a continuous casting facility according to claim 1 or 2, wherein the D value is varied depending on the steel type.

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