JP3488053B2 - Continuous casting method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control technique for simultaneously and accurately realizing a constant value control of a molten metal level in a mold and a constant value control of a slab drawing speed in continuous casting of metal.

[0002]

2. Description of the Related Art When casting metal by continuous casting, in order to improve the quality of the slab and stabilize the operation, it is necessary to keep the molten metal level in the mold constant and the casting speed constant. is important. Conventionally, in continuous casting of metals, in order to perform the constant value control of the molten metal level in the mold and the constant value control of the slab withdrawal speed at the same time, it is roughly classified into (1) "metal level in the mold" as shown in Fig. 4. A constant value control of the slab is realized by controlling the slab withdrawal speed, the molten metal static pressure is changed by controlling the level of the molten metal in the tundish, and the injection flow rate is changed to indirectly control the slab withdrawal speed. "Slab withdrawal speed control method for constant value control" or (2) "Slab withdrawal speed is made constant and the inflow rate of molten metal in the mold is controlled by an inflow rate changing mechanism such as a stopper or a sliding nozzle. Two techniques of "molten metal inflow control method, which realizes constant value control of the molten metal level in the mold by changing the inflow amount" have been used.

[0003]

In the above technique (1), the molten metal level in the mold is linearly affected by the withdrawal of the cast piece, so that the controllability is high, and the small mold size causes a large fluctuation in the molten metal surface in the mold. Even in the continuous billet casting, it is possible to satisfactorily control the molten metal level in the mold.

However, in general, one tundish has a plurality of strands, and in reality, the rate of erosion of the nozzle that flows the molten metal from the tundish into the mold varies depending on the strand. Therefore, the molten metal inflow rate into the mold is different for each strand, and the slab drawing rate is different accordingly, so in a continuous casting facility with multiple strands per tundish, only the level of the molten metal in the tundish is controlled. As a result, there is a problem in that it is impossible to perform constant value control of the slab drawing speed for all strands.

On the other hand, in the above technique (2), i) there is a time delay for the molten metal to reach the mold from the tundish, ii) the injection flow rate of the molten metal has an integral effect on the level of the molten metal in the mold. Iii) It has a high speed and a high degree of controllability because, for example, the opening of the flow rate changing mechanism such as a stopper or a sliding nozzle at the operation end and the flow rate of the molten metal are generally in a non-linear relationship. Since the control device must be used, there is a problem that the equipment cost increases.

In addition, since the materials such as stoppers and sliding nozzles used as a mechanism for changing the amount of molten metal flowing into the mold must be expensive materials that can withstand melting loss, and high-precision machining must be performed, running costs increase. There was a problem of doing. In addition, especially in small-section billet continuous casting, the diameter of the nozzle etc. becomes small and nozzle clogging due to solidification of the molten metal is likely to occur, so it is very difficult to apply the flow rate changing mechanism. is there.

When a stopper, a sliding nozzle or the like uses a flow rate changing mechanism for changing the flow rate by changing the shape of the flow channel, turbulence is generated in the molten metal flow depending on the opening degree, so that the immersion nozzle is especially used. There is a problem that the injection flow varies during open casting that is not used.

[0008]

Means for Solving the Problems The present invention advantageously solves the above problems, and the gist thereof is (1) the level of molten metal in a mold for each strand as described in the claims. The constant value control of the casting is performed by controlling the casting speed, and the constant value of the casting speed is controlled by controlling the molten metal inflow amount in the mold, and further, the molten metal inflow amount in the mold is controlled. A continuous casting method characterized in that the level of molten metal in the tundish is controlled so that the opening of the mechanism for changing the amount of molten metal inflowing into the mold is constant. (2) When a single tundish has a plurality of strands, the average value of the target tundish inner surface level of each strand is determined, and the average value is adopted as the target tundish inner surface level. (1) The continuous casting method as described above. (3) In a continuous casting device for injecting molten metal into a mold from a molten metal ladle via a tundish, the level of the molten metal in the mold (hereinafter referred to as the molten metal level) is detected and the molten metal level is kept at a constant value. Control means (referred to as a loop) for controlling the pinch roll for pulling out the slab to detect the withdrawal speed of the slab from the pinch roll, and from the tundish in the mold so as to keep the withdrawal speed constant. Means for controlling the opening of the molten metal inflow amount changing mechanism in the mold for controlling the inflow of the molten metal into the mold by the opening thereof (referred to as a loop)
And a control for controlling the opening degree of the molten metal inflow amount changing mechanism in the tundish that controls the inflow of the tundish molten metal from the molten metal ladle according to the opening degree so that the opening degree of the molten metal inflow amount changing mechanism in the mold becomes a constant value. And a means (referred to as a loop).

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing a continuous casting apparatus according to the present invention. The figure shows, from above, a molten metal ladle containing molten metal 1,
The molten metal inflow amount changing mechanism 2 for changing the molten metal outflow amount when the molten metal flows out from the pan to the tundish at the bottom portion thereof, the long nozzle 3 thereunder, and the tundish 4 continue below.

At the bottom of the tundish 4, there is a case in which a molten metal inflow amount changing mechanism 5 for changing the amount of molten metal flowing out from the tundish 4 to the mold 7 is provided, and a dipping nozzle is provided thereunder. Continue to mold 7. Below the mold 7 is a pinch roll 9 for pulling out the solidified slab. The rotation speed of the pinch roll determines the drawing speed of the slab.

In the case of the present invention, the molten metal level detector 8 in the mold 7 detects the molten metal level, and the pinch roll 9 is used to keep the molten metal level in the mold constant from the detection signal.
There is a control means (loop) 11 for controlling the.

Further, the casting speed is detected from the number of rotations of the pinch roll 9, and the amount of the molten metal flowing into the mold 7 from the tundish 4 is changed from the detection signal so that the casting speed becomes constant. There is a control means (loop) 12 for controlling the opening degree of the changing mechanism 5.

Furthermore, the molten metal inflow amount changing mechanism 2 for changing the amount of molten metal flowing out from the molten metal ladle 1 to the tundish 4 is opened so that the opening degree of the molten metal inflow amount changing mechanism 5 in the mold becomes constant. There is a control means (loop) 14 for controlling the degree.

By using the control means in three stages in this manner, the problem of the conventional technique (2) is solved, and high-speed and high-level control is possible.

On the other hand, when one tundish has a plurality of strands, the opening degree of the molten metal inflow amount changing mechanism 5 in each mold of each strand is detected, and its average value,
It has a calculator 13 for calculating a target tundish level in the bath based on the minimum and maximum values.

FIG. 2 shows a transition chart of each element such as the molten metal level in the mold obtained by the control system of the following three patterns depending on the presence or absence of each loop. (A) Control by loop only (B) Loop + loop control (C) Loop + loop + loop control (the present invention) (The following method (d) is adopted as the control method of the strand opening)

(A) is a pattern in which the molten metal level in the mold is controlled to a constant value only by controlling the casting speed. Incidentally, casting
At the start of production, early increase the level of molten metal in the tundish
In order to maintain a certain level, usually at the start of casting, use a pot
The melt flow rate from the tundish to the tundish rather than in the steady state
It is set, and FIG. 2 is a diagram based on that. Since
The same assumptions apply to (B) and (C) below. As the casting time elapses, the stopper melts and the amount of molten metal flowing out of the tundish into the mold increases temporarily. Along with this, the drawing speed increases temporarily to keep the molten metal surface level in the mold constant. As a result, the slab, which is the optimum solidification time for light reduction, passed through the light reduction roll zone, and the center segregation deteriorated.

Further, in (B), the casting speed data is reflected on the opening of the molten metal inflow amount changing mechanism (usually, a stopper or a sliding nozzle is used) in the mold in order to make the casting speed constant in the above pattern. ing. When the stopper melts and the casting speed tends to increase, the opening is decreased to reduce the inflow amount of the molten metal in the mold, and the increase in the drawing speed is suppressed.

That is, the signal passed through the low-pass filter 10 having the actual slab drawing speed is used as the detection end, and the flow rate changing mechanism 5 such as the stopper 6 or the sliding nozzle independently installed in each strand is used as the control end. Performs constant value control of the slab drawing speed.

In this control, the low-pass filter 10 cuts the high-frequency region speed fluctuation that is generated by the molten metal level control in the mold by the slab withdrawal speed of the control loop 11 and is superimposed on the slab withdrawal speed. It accurately controls and controls fluctuations in the slab withdrawal speed due to stopper melting loss and changes in the tundish melt level.

In the control loop of the flow rate changing mechanism in this control, a low speed control system is sufficient as compared with the conventional technique (2), and the opening degree of the molten metal inflow amount changing mechanism in the mold, which is the operating end, is sufficient. A narrower range is sufficient for the manipulated variable itself. Shi
However , in (B), in the case of the operation without using the immersion nozzle, the opening degree of the molten metal inflow amount changing mechanism in the mold is excessively narrowed, and the injection flow into the mold is varied, resulting in poor operation and quality. It will be in a stable state.

In comparison, in (C) according to the present invention,
Compared to (B), the flow rate change mechanism opening degree is used as the detection end, and the molten metal outflow amount from the molten metal ladle to the tundish is adjusted by a control loop in which the molten metal inflow amount from the molten metal ladle to the tundish is used as the operating end. The level of molten metal in the tundish is controlled, and the molten metal static pressure applied to the nozzle that flows the molten metal from the tundish to the mold is controlled, thereby controlling the flow rate of the molten metal that flows from the nozzle of each strand, and The control is performed so that the flow rate changing mechanism installed at the position is maintained near a certain target opening.

By this control, it becomes possible to selectively use a control range having a high linearity in the control range of the flow rate changing mechanism such as a stopper and a sliding nozzle having nonlinearity, and not only the control accuracy is improved. Design of stoppers, stoppers or sliding nozzles
Running cost can be reduced by relaxing processing accuracy.

The detection end of the control loop is a track record of the opening degree of the flow rate changing mechanism for each strand, and one or more values are the operation end, but various meanings can be given by performing appropriate calculation. It is possible to control the level of the melted tundish. The following are four calculation examples.

FIG. 3 (a) shows that the flow rate changing mechanism of all the strands is controlled as a whole by controlling the average of the opening of all the strands to the median value of the controllable range or a certain specified value similar to it. Arithmetic for use in good range. FIG. 3B shows that the minimum controllable opening of all the strands is controlled to a value obtained by adding a margin to the controllable lower limit opening, so that the flow rate changing mechanism of all the strands can be set to the control lower limit opening. Arithmetic for use in higher range. FIG. 3C shows that the flow rate changing mechanism of all the strands as a whole is controlled by controlling the maximum value of the opening of all strands to a value obtained by subtracting a certain margin from the controllable upper limit opening. Operation for use in the lower range. FIG. 3D is a calculation for controlling the opening to an optimum value as a whole by controlling the opening by controlling the opening within the controllable upper and lower limits by combining the above three calculations.

As described above, according to the present invention, the level of the molten metal in the mold and the casting speed can be stably maintained for a long time in continuous casting. Further, no particular variation in the molten metal was observed in the injection flow during open injection from the tundish into the mold.

[0027]

The effects obtained by the present invention described above are as follows. (1) While realizing the molten metal level control in the mold at the same level as the slab withdrawal speed control method, it is possible to control the slab withdrawal speed constant value for each strand as in the molten metal inflow control method. (2) Compared with the molten metal inflow control method, a low-speed control loop can be used to control the flow rate changing mechanism, and the required control range of the flow rate changing mechanism can be narrowed, resulting in a large equipment cost. Can be reduced to (3) The required control range of the flow rate changing mechanism can be narrowed as compared with the molten metal inflow control method, and the flow rate changing mechanism can be selectively used within an appropriate control range. The running cost can be reduced because the flow rate changing mechanism can be designed easily and the processing accuracy can be relaxed.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a device of the present invention.

2A is a chart obtained as a result of control using only a loop, FIG. 2B is a chart obtained as a result of control employing a loop + loop, and FIG. 2C is a book employing loop + loop + loop. It is a chart obtained as a result of control of the invention.

3 (a) to 3 (d) are diagrams showing a calculation logic for obtaining an opening degree of a molten metal inflow amount changing mechanism in a mold adopted in the present invention.

FIG. 4 is a diagram showing an example of a conventional stationary surface level control device for a molten metal level in a mold in continuous casting.

FIG. 5 is a diagram showing an example of a conventional stationary control device for the molten metal level in the mold and the drawing speed in continuous casting.

[Explanation of symbols]

1 Molten iron ladle 2 Molten metal inflow amount changing mechanism 3 Tundish 4 Tundish 5 Molten metal inflow amount changing mechanism 6 Stopper 7 Mold 8 Mold level detector 9 pinch roll 10 Low pass filter 11 Control means (loop) 12 Control means (loop) 13 Computing device 14 Control means (loop) 15 Tundish inner surface level detector

Continuation of the front page (56) Reference JP-A-63-97347 (JP, A) JP-A-62-24848 (JP, A) JP-A-62-183951 (JP, A) JP-A-56-141954 (JP , A) JP-A-54-77229 (JP, A) International Publication 97/014521 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22D 11/00-11/22 B22D 37 / 00,39 / 00,39 / 02

Claims (3)

(57) [Claims] 1. A constant value control of the molten metal level in the mold is performed for each strand by controlling the slab drawing speed, and a constant value control of the slab drawing speed is controlled by the inflow amount of the molten metal in the mold. Further, the target molten metal level in the tundish is calculated from the opening so that the opening of the molten metal inflow changing mechanism for controlling the molten metal in the mold is constant. A continuous casting method, characterized in that the opening degree of the molten metal inflow changing mechanism in the tundish is controlled so that the level of the molten metal in the dish is reached. 2. When a plurality of strands are provided in one tundish, the opening degree of the molten metal inflow amount changing mechanism in each mold of each strand is detected, and the target value is determined from the average value, the minimum value and the maximum value. The continuous casting method according to claim 1, wherein the molten metal surface level in the dish is obtained. 3. A continuous casting apparatus for injecting molten metal into a mold from a molten metal pot through a tundish, detects the level of the molten metal in the mold (hereinafter referred to as the molten metal level), and determines the molten metal level. Control means for controlling the pinch roll that pulls out the slab so as to maintain a constant value (called a loop)
And, detecting the withdrawal speed of the slab from the pinch roll, of the molten metal inflow amount change mechanism in the mold that controls the inflow of the molten metal from the tundish into the mold so that the withdrawal speed becomes a constant value A control unit (referred to as a loop) for controlling the opening degree, an arithmetic unit for obtaining a target tundish molten metal surface level such that the opening degree of the molten metal inflow control mechanism in the mold becomes a constant value, and an arithmetic unit determined by the arithmetic unit Control means (called a loop) for controlling the opening degree of the molten metal inflow amount changing mechanism in the tundish that controls the molten metal inflow amount from the ladle to the tundish according to the target level in the tundish A continuous casting device characterized in that