JP2003260552A - Method of casting molten steel into mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the fluctuation of a molten steel level in a mold accompanying the change of a cast piece drawing rate even if the cast piece drawing rate is changed during casting of a continuous casting of steel. <P>SOLUTION: In a method of casting a molten steel wherein the molten steel 4 is cast while a molten steel cast quantity is controlled from a tandish (turn dish) to the mold by controlling the opening of a nozzle gate 9 disposed in a molten steel supply channel 16 from the tandish (turn dish) 1 to the mold 2, when the cast piece drawing rate is changed, the opening of the nozzle gate is changed to the opening equivalent to an opening after the cast piece drawing rate is changed 1 to 10 seconds before the cast piece drawing rate is changed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injecting molten steel into a mold in continuous casting in which the amount of molten steel injected from a tundish into the mold is controlled by changing the opening of a nozzle such as a sliding nozzle. .

[0002]

2. Description of the Related Art In continuous casting, the amount of molten steel once poured into a tundish is adjusted by a nozzle gate such as a sliding nozzle and then poured into a mold through a dipping nozzle. If the molten steel level in the mold fluctuates, it may cause product defects such as the inclusion of mold powder.Therefore, the nozzle gate controls the molten metal level in the mold so that it does not fluctuate. It has not been possible to completely prevent surface fluctuations.

One of the causes of the fluctuation of the molten metal surface in the mold is the fluctuation of the molten steel injection amount, which is caused by the intentional change of the slab drawing speed or the clogging of the immersion nozzle due to the adhesion of alumina to the inner wall of the immersion nozzle. It is caused by or blockage. In addition, bulging of the slab in the secondary cooling zone may cause fluctuations in the molten metal surface in the mold. In the present invention, a method for controlling the fluctuation of the molten metal surface caused by the fluctuation of the molten steel injection amount due to the change of the cast slab drawing speed will be considered. In addition, since the molten steel injection amount that passes through the nozzle gate is changed when the slab drawing speed is changed, the opening of the nozzle gate is always adjusted, which causes the fluctuation of the molten metal surface in the mold.

Conventionally, in continuous casting, many methods have been adopted in which the level of molten metal in the mold is measured by a vortex distance meter or the like, and the opening of a sliding nozzle or a stopper is adjusted based on the information to control the variation of molten metal. There is. For example, in Japanese Unexamined Patent Publication No. 2000-141003, the level of molten metal is continuously measured after the start of injecting molten steel into the mold, and the rising speed of the molten metal is calculated from the measured value of the molten metal level. A method of adjusting the amount of molten steel injected into the mold based on the deviation between the mold and the reference speed has been proposed, and Japanese Patent Application Laid-Open No. 10-216914 discloses a melt level sensor for main control and both ends 2 near the mold short side.
By using the melt level sensor installed at a certain location, it is possible to grasp whether the melt surface condition near the short side of the mold is a one-sided flow phenomenon or a ripple phenomenon, and based on the grasped result, change the opening of the sliding nozzle and change the slab drawing speed. A method of controlling the level of molten metal is proposed, and Japanese Patent Laid-Open No. 4-59160 discloses that a molten metal level meter is installed at two positions on the left and right of a position having a width of 1/4 from the short side of the mold, and the level of molten metal A casting method has been proposed in which surface variation is detected and the opening degree of a sliding nozzle is appropriately adjusted.

[0005]

[Problems to be Solved by the Invention] However, the above 3
Each of the methods proposed in the two publications is a method of injecting while adjusting the opening of the sliding nozzle based on the measured value of the molten metal surface level in the mold, which causes a control delay due to the feedback control. That is, it is a method of adjusting the nozzle opening so as to reduce the fluctuation of the molten metal level after the fluctuation of the molten metal level in the mold. It is not possible to suppress the fluctuation of the molten metal surface that occurs.

The present invention has been made in view of the above circumstances, and an object of the present invention is to perform continuous casting of steel.
It is an object of the present invention to provide a method for injecting molten steel into a mold, which can significantly reduce the fluctuation of the molten metal level in the mold due to the change in the slab drawing speed even if the slab drawing speed is changed during casting.

[0007]

In order to solve the above-mentioned problems, the present inventor uses a water model experiment and numerical flow analysis to determine the time until the change in the molten metal surface flow in the mold with respect to the movement of the sliding nozzle, That is, the delay time of the molten metal surface flow in the mold with respect to the movement of the nozzle gate was investigated.

As a result, a change in the flow of the molten metal in the mold begins to occur simultaneously with the operation of the sliding nozzle, but when the nozzle gate is activated, the time required for the fluid particles passing through the nozzle gate to reach the molten metal in the mold, that is, the traveling time ( It was found that the largest variation occurs after Tp). Further, it was found that at least twice as long as the traveling time (Tp) was required until the change in the melt surface flow disappeared and the steady state was settled.

In this case, the traveling time (Tp) can be determined by, for example, Teshima et al. (Iron and steel) if the casting conditions (the cross-sectional size of the slab, the drawing speed of the slab, the shape of the immersion nozzle, the immersion depth of the immersion nozzle) are known. , 79 (1993), p576) and the like. Therefore, the delay time of the change in the flow of the molten metal in the mold with respect to the operation of the sliding nozzle can be predicted by calculation.

By using this phenomenon, the nozzle gate opening of the sliding nozzle or the like is changed before the change of the cast slab drawing speed in response to the increase or decrease of the cast slab drawing speed planned during the operation. You can avoid it.
That is, casting conditions (slab cross-sectional size, slab drawing speed,
The shape of the immersion nozzle, the immersion depth of the immersion nozzle), and the traveling time (Tp) calculated from the beginning, by adjusting the nozzle opening of the sliding nozzle, etc. due to the change of the withdrawal speed of the ingot, the withdrawal speed of the ingot It is possible to suppress the fluctuation of the molten metal surface in the mold due to the change of. Within the practical range of continuous slab casters, this traveling time (Tp)
It was found from the calculation result that it was 1 to 10 seconds.

The present invention has been made on the basis of the above-mentioned examination results. A method for injecting molten steel into a mold in continuous casting according to the first invention is based on a nozzle gate installed in a molten steel supply passage from a tundish to the mold. By adjusting the opening, in the molten steel pouring method of pouring molten steel while controlling the molten steel pouring amount from the tundish into the mold, when changing the slab withdrawal speed, when changing the slab withdrawal speed 1 second to 10 seconds before, the opening of the nozzle gate is changed to an opening corresponding to the opening after the slab drawing speed is changed. Molten steel in a mold in continuous casting according to the second invention. The pouring method according to the first aspect of the invention is characterized in that the opening of the nozzle gate is automatically changed in response to a change in the slab drawing speed scheduled during continuous casting.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic view of a slab continuous casting machine used in carrying out the present invention.

In FIG. 1, the opposite long sides 20 of the mold,
The opposing short sides 21 of the mold, which are installed inside the long side 20 of the mold.
A tundish 1 whose outer shell is covered with a steel skin 22 and whose inside is covered with a refractory material 23 is arranged at a predetermined position above a mold 2 constituted by and the bottom of the tundish 1 has a fire resistance. The upper nozzle 8 is installed by being fitted to the object 23, and is in contact with the lower surface of the upper nozzle 8 so that the upper fixing plate 1
0, sliding plate 11, lower fixed plate 12, and rectifying nozzle 13
And a dipping nozzle 14 having a pair of discharge holes 15 in the lower part is disposed in contact with the lower surface of the sliding nozzle 9, and a molten steel supply flow channel 16 from the tundish 1 to the mold 2 is provided. Has been formed.

The sliding plate 11 is a reciprocating actuator 1.
7 and is moved by the operation of the reciprocating actuator 17 between the upper fixed plate 10 and the lower fixed plate 12 while being in contact with these fixed plates, and the sliding plate 11 and the lower fixed plate 12 are moved. The amount of molten steel passing through the molten steel supply passage 16 is controlled by adjusting the area of the opening to be formed. That is, in such a molten steel supply device including the upper nozzle 8, the sliding nozzle 9, and the immersion nozzle 14, the sliding plate 11 serves as a nozzle gate for adjusting the molten steel injection amount. Reciprocating actuator 1
7 is electrically connected to the casting control device 19, the opening of the sliding plate 11 by the reciprocating actuator 17 is transmitted to the casting control device 19, and conversely, the opening of the sliding plate 11 becomes a predetermined value. As described above, the casting control device 19 controls.

Below the mold 2, a plurality of pinch rolls 3 for pulling out the cast slab 5 to be cast below the mold 2 are installed, and the slab withdrawing speed by the pinch rolls 3 is controlled by the casting control device 19. Controlled. In FIG. 1, only one pinch roll 3 is shown and the other pinch rolls are omitted.

A swirl range finder 18 for detecting the position of the molten steel level 6 in the mold 2 is installed directly above the molten steel level 6 and the swirl range finder 18 melts the molten metal. The detected value of the surface 6 is transmitted to the casting control device 19.

In the continuous casting machine thus constructed, the molten steel 4 is poured from the tundish 1 into the mold 2 as follows.

First, the molten steel 4 is poured from a ladle (not shown) into the tundish 1, and when the amount of molten steel in the tundish 1 reaches a predetermined amount, the sliding plate 11 is opened and the molten steel 4 is put into the mold 2 Inject into. The molten steel 4 injected into the mold 2 is the mold 2
To form a solidified shell 7. Then, when a predetermined amount of molten steel 4 has been injected into the mold 2, the pinch roll 3 is driven to start extraction of the slab 5 having the unsolidified molten steel 4 inside with the outer shell as the solidified shell 7. After the drawing is started, the slab drawing speed is increased to a predetermined slab drawing speed. The mold powder 2 is provided on the molten steel surface 6 for the purpose of preventing the molten steel 4 from oxidizing and lubricating the solidified shell 7.
Add 4.

During this period, the molten steel level control by feedback control by the eddy current type distance meter 18, that is, the position of the molten steel level 6 is detected by the vortex type distance meter 18, and the sliding nozzle 9 is detected based on the measured value of the molten steel level. Inject while adjusting the opening.

When it is necessary to change the slab withdrawal speed during continuous casting by changing the ladle or tundish in continuous casting, the casting control device 19 controls the pinch roll 3
1 to 10 seconds before the signal for increasing or decreasing the slab drawing speed is transmitted to the reciprocating actuator 17, a signal is transmitted to the reciprocating actuator 17 so as to change the nozzle opening of the sliding plate 11. In response to this signal, the nozzle opening of the sliding plate 11 is changed to the nozzle opening corresponding to the increase or decrease of the cast strip drawing speed. Casting control device 19
1 to 10 seconds after the instruction to change the nozzle opening is sent to the reciprocating actuator 17 so as to change the rotation speed of the pinch roll 3, whereby the slab drawing speed by the pinch roll 3 is changed. Be changed. If the withdrawal speed of the slab reaches the specified speed after the change, the eddy current type distance meter 1
Return to the molten steel level control by the feedback control of 8.

In this case, the timing for changing the nozzle opening of the sliding plate 11 is in the range of 1 to 10 seconds from the timing for starting the change of the slab drawing speed, but more precisely, it is only the traveling time (Tp). It is preferable to do the above. The traveling time (Tp) can be calculated from the casting conditions (the slab cross-sectional size, the slab drawing speed, the shape of the immersion nozzle, the immersion depth of the immersion nozzle).

Further, the nozzle opening after changing the slab drawing speed is based on the molten steel injection amount corresponding to the slab drawing speed, the molten steel depth in the tundish 1, the immersion depth of the immersion nozzle 14, the immersion It can be empirically determined by the inner diameter of the nozzle 14. It is not necessary to match the opening instruction value when the nozzle opening is changed with the true nozzle opening after the slab drawing speed is changed, and thereafter the molten steel level control by feedback control by the eddy current type distance meter 18 As a result, the nozzle opening is automatically controlled to be accurate.

By injecting the molten steel 4 from the tundish 1 into the mold 2 in this manner, it is possible to extremely reduce the fluctuation of the molten steel molten metal surface 6 due to the change in the slab drawing speed. It is possible to stably cast a high-quality slab 5 that does not involve 24 or the like.

In the above description, the example of the sliding nozzle 9 having a three-plate structure is given, but the present invention can be applied to a sliding nozzle having a two-plate structure in accordance with the above. In addition, a rotary sliding nozzle (also referred to as a "rotary nozzle") that uses a circular fixed plate and a sliding plate, and the sliding plate rotates in a circumferential direction around the center point thereof.
The present invention can be similarly applied to the above. Further, even in the case of the stopper type, the present invention can be applied along the above.

[0025]

EXAMPLES In order to confirm the effects of the present invention, low carbon steel was cast using the slab continuous casting machine shown in FIG. 1 and the width position of the 1/4 slab from the short side of the mold when the sliding nozzle was operated. The fluctuation of the molten metal surface was measured. The thickness of the slab is 200
mm, the slab width is 1600 mm, the immersion nozzle used is a two-hole nozzle with a pool bottom, and the discharge angle is 25 downwards.
The nozzle inner diameter is 90 mmφ. Adjusting the opening of the sliding nozzle of 3 plates, the molten steel injection amount is 5.5ton /
It was changed from min to 4.8 ton / min over about 40 seconds, and the fluctuation of the molten metal surface in this case was measured. The eddy current type distance meter was installed at a width position of 1/4 slab from the short side of the mold.

The traveling time (Tp) under these casting conditions was calculated. In Fig. 2, the traveling time (T
The conceptual diagram used when calculating p) is shown. As shown in FIG. 2, in calculating the traveling time (Tp),
The passage of fluid particles was obtained by dividing the passage into four passages.

The path is from the lower surface of the sliding plate of the sliding nozzle to the discharge hole. The distance between them is 0.58m
And the inner diameter is 90 for molten steel injection amount of 4.8 ton / min.
The average flow velocity in the immersion nozzle of mm is 1.8 m / s. Therefore, the traveling time (T1) in the route is 0.
It will be 31 seconds.

The path of molten steel in the mold was determined by the above-mentioned empirical formula of Teshima et al., And the trajectory of the discharge flow and the maximum flow velocity colliding with the short side of the mold were calculated. That is, the path is from the discharge hole to the collision point of the mold with the short side, and the distance between them is 1.1 m.
And the path is from the point of collision to the short side of the mold to the point of rise to the molten steel surface, and the distance between them is 0.47.
It was calculated as m. Taking the maximum flow velocity of collision with the short side of the mold as the representative flow velocity of molten steel in the route and the route, this was calculated to be 0.275 m / s. When the route and the traveling time in the route were obtained from the molten steel flow velocity, the traveling time (T2) was 4.00 seconds and the traveling time (T3) was 1.71 seconds.

The route is from the rising point to the surface of the molten steel to the position where the eddy current range finder is installed, and the distance between them is 0.4 m. The flow velocity of the molten steel was 0.275 m / s, which was assumed to be equivalent to the route and the route, and the traveling time (T4) in the route was 1.45 seconds.

From these calculations, the traveling time (Tp) required for the fluid particles passing through the nozzle gate to reach the molten metal surface in the mold was 7.47 seconds, which is the sum of the traveling times of the routes.

FIG. 3 is a diagram showing the measurement results of the molten metal level when the slab drawing speed is changed at the same time as the opening of the sliding nozzle is changed. From 7 to 8 seconds after changing the opening of the sliding nozzle, the fluctuation amount of the molten metal surface became large, and the fluctuation of the molten metal surface did not become small for about 80 seconds.

On the other hand, FIG. 4 is a diagram showing the measurement result of the molten metal level fluctuation when the slab drawing speed is changed after 7.5 seconds have elapsed after changing the opening of the sliding nozzle. In this case, it was observed that the molten metal level was stable during the measurement period.

From these results, by changing the opening of the sliding nozzle in advance by the method of the present invention,
It was confirmed that fluctuations in the molten metal surface at the time of changing the withdrawal speed of the slab can be suppressed.

[0034]

According to the present invention, in the continuous casting of steel, when the molten steel is supplied from the tundish to the mold, the opening of the nozzle gate used for adjusting the molten steel injection amount is set to 1 to 10 seconds. The change in the molten steel level due to the change in the casting speed can be minimized, and as a result, high quality casting without entrainment of mold powder can be achieved. It is possible to stably cast the piece, which has an industrially beneficial effect.

[Brief description of drawings]

FIG. 1 is a schematic view of a slab continuous casting machine used when carrying out the present invention.

FIG. 2 is a conceptual diagram used when calculating a traveling time (Tp).

FIG. 3 is a diagram showing a measurement result of a molten metal surface level when the slab drawing speed is changed at the same time when the opening of the sliding nozzle is changed.

[Fig. 4] After changing the opening of the sliding nozzle,
It is a figure which shows the measurement result of the molten-metal level fluctuation at the time of changing a slab drawing speed after 7.5 second progress.

[Explanation of symbols]

1 tundish 2 molds 3 pinch rolls 4 Molten steel 5 slab 6 Molten steel surface 7 solidification shell 8 upper nozzle 9 sliding nozzles 11 Sliding plate 14 Immersion nozzle 16 Molten Steel Supply Channel 17 Reciprocating actuator 18 Eddy current range finder 19 Casting control device

Continued front page    (72) Inventor Jun Kubota             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 4E004 MB04 MB09 MB15 NA01 NB01                       NC01 PA04

Claims (2)

[Claims] 1. A molten steel injection method for injecting molten steel while controlling the injection amount of molten steel from the tundish into the mold by adjusting the opening of a nozzle gate installed in the molten steel supply passage from the tundish to the mold. When changing the slab drawing speed, 1 second to 10 seconds before the start of changing the slab drawing speed, the opening of the nozzle gate is changed to an opening corresponding to the opening after the slab drawing speed is changed. The method for injecting molten steel into a mold in continuous casting, characterized in that 2. The continuous casting according to claim 1, wherein the opening of the nozzle gate is automatically changed in response to a change in the withdrawal speed of the slab that is scheduled during the continuous casting. Method of pouring molten steel into a mold.