JP3186959B2 - Automatic casting start method for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for controlling the level of molten metal in a mold in continuous casting, and more particularly, to the ability to shift the molten steel level in the mold to a steady state from the start of casting without a sudden level change. Automatic casting start method.

[0002]

2. Description of the Related Art In continuous casting, as is well known, a lower portion of a mold is closed by inserting a dummy bar into a mold at the start of casting, and molten steel is poured on the lower portion.
In order to shift from this state to the steady casting state, the level of the molten steel in the mold must be raised to the target level in the steady state, and the dummy bar must be pulled out at the casting speed. At this time, if the molten steel level in the mold fluctuates rapidly, stable operation may be impaired as a cause of breakout or deterioration of cast slab quality. For this reason, in order to automatically start casting, it is necessary to control the rise of the molten steel level to smoothly shift to the molten steel level in a steady state.

In order to solve such technical problems, the following methods have been conventionally proposed. (A) The molten steel surface is detected at at least two points in the lower part of the mold, thereby estimating the molten metal rising speed, correcting the molten steel injection amount so that the molten metal rising speed is equal to the casting speed, and Level is 2 from target steady level
A method of starting drawing of the slab at a point when the position of the molten steel reaches 0 mm lower position, and immediately after the molten steel surface level has settled to a substantially steady state, is shifted to a steady state level control (Japanese Patent Application Laid-Open No. Sho 62-179859). reference).

(B) A plurality of thermocouples mounted in the height direction of the lower part of the mold are used to measure the temperature distribution in the vertical direction, thereby estimating the level of the molten steel level in real time to raise the level of the molten steel level and determine the level in advance. When the molten steel level rises to the measured level, the molten steel level measured by the level gauge used for level control in the steady state is used to smoothly change to the target steady level. A method of performing feedback control with a surface level command value to shift to a steady level (see Japanese Patent Application Laid-Open No. 1-254361).

(C) The molten steel injection start point is detected, the opening of the sliding nozzle is preset controlled, the molten steel level is raised, and the height of the molten steel level is detected stepwise. The above-mentioned preset control is corrected based on the value to control the rising speed of the molten steel level, and after the molten steel level reaches a predetermined level, the molten steel level is controlled to a predetermined height by feedback control based on a measured value of the level gauge. A method in which the process is shifted to start pulling out the dummy bar (see JP-A-2-41745).

(D) Prior to the start of the pinch roll, a level command value is set in advance so as to have a molten steel level rise speed substantially equal to the casting speed at the time of the start of the pinch roll, and the molten steel is made to follow the level command value. A method in which the level of the molten metal is raised to suppress the influence of the subsequent pinch roll activation on the molten steel level, and the target level is smoothly shifted to a steady target level (see Japanese Patent Application Laid-Open No. 5-329605).

[0007]

However, the above-mentioned conventional method has the following problems. That is,
In the method (A), since the molten steel level at the time of starting the pinch roll is almost the same as the target level, the level fluctuation caused by the error between the drawing speed at the start of the pinch roll and the level rise rate is reduced. However, there is a problem that the level control is maintained even after shifting to the steady state level control. (B),
In the method (C), when shifting to the steady casting state, the effect on the molten metal level caused by starting the pinch roll is only dealt with by feedback control, and no special consideration is given. Therefore, when the pinch roll is activated and casting starts, a step-like disturbance acts on the feedback control system of the molten steel level, causing fluctuations in the molten steel level, and the molten steel level is stable and steady. There is a problem that it is difficult to shift to the surface level.

On the other hand, the method (D) is based on the methods (A) and (B)
In order to solve the problem of the method (C), an automatic casting start method for stably shifting the molten steel level from the start of casting to a steady state without a sudden level change has been proposed. In this method, as shown in FIG. 5, since there is a delay from when the pinch roll activation level is reached to when the pinch roll is actually activated, the opening of the sliding nozzle, which has been corrected by the mass balance control processing so as to balance the casting speed, is reduced. ,
There is a problem that the pinch roll breaks from the balance point before starting. In addition, since the opening speed of the sliding nozzle is controlled so as to balance the initial casting speed, if the initial speed is set to be high, the level of the molten metal before the pinch roll is activated is also increased, which makes it difficult to control the molten metal level. is there.

The present invention has been made to solve the problem of the method (D), in particular, to prevent the deviation of the opening of the sliding nozzle from the balance point caused by the delay in the start of the pinch roll, and to further reduce the initial speed. It is an object of the present invention to propose an automatic casting start method for continuous casting that can suppress the rate of rise of the molten metal level even when the casting speed is high.

[0010]

According to the present invention, there is provided an automatic casting start method for continuous casting, in which a molten steel level in a mold is shifted to a steady state from the start of continuous casting. The molten steel supply speed is controlled by the sliding nozzle opening so that the molten steel supply speed matches the casting speed at the start of pouring from the molten metal rising speed in the mold until the molten metal level reaches the starting level of the pinch roll, Next, when the molten metal level reached the activation level of the pinch roll, the pinch roll was activated, and the supply speed of the molten steel was fixed until the pinch roll was actually activated, and the pinch roll was activated. Then, the supply speed of the molten steel is changed from the fixed value so that the molten metal level reaches the target level at a predetermined speed. There By controlling so as to balance, characterized in that to prevent the deviation from the balance point of the sliding nozzle opening generated by the pinch rolls start delay (claim 1).

As another method, when the casting speed is increased to a predetermined speed in two stages, the casting surface level at the start of casting reaches the starting level of the pinch roll. The supply speed of the molten steel is controlled by the opening of the sliding nozzle so that the supply speed of the molten steel matches the casting speed of the second stage, and then the pinch roll is activated when the molten metal level reaches the activation level of the pinch roll. While fixing the supply speed of the molten steel until the pinch roll is actually started, and further changing the supply speed of the molten steel after the start of the pinch roll from the fixed value, and subsequently from the molten metal rising speed in the mold. The supply speed of molten steel is controlled by the opening of the sliding nozzle so that the supply speed of molten steel matches the casting speed of the second stage. The casting speed is increased when the speed increase to the casting speed is reached, and after the speed increase, the molten steel supply speed is gradually increased so that the molten metal level reaches the target level at a predetermined speed. When the surface level reaches the target level, the casting speed and the supply speed of the molten steel are controlled so as to be balanced, so that even when the initial speed is high, the metal surface rising speed is suppressed (claim 2).

The method according to claim 1 of the present invention will be described with reference to FIG. That is, in the method according to the first aspect, the control section includes an open loop (waiting for a rise in the molten metal level at a predetermined opening degree), a section for balancing the casting amount (initial speed) and the injection amount, and a start delay of the pinch roll. And a section for smoothly shifting the target level to the steady level.

Here, is the same section as in the conventional method. That is, as in the conventional method, the sliding nozzle opening is controlled to an opening that balances with the initial speed by the interval. In the conventional method, it moves to the section after that,
If there is a delay in starting the pinch roll, the level of the molten metal rises at the same speed as the process even after shifting to the section, so the sliding nozzle opening is corrected, and as a result, the balance with the initial speed is lost I will.

In the present invention, in order to prevent this, a section is provided immediately after the section in which the casting amount (initial speed) and the injection amount are balanced to compensate for the start-up delay of the pinch roll. In this section, feedback control (for example, PID control) is performed with the target level = the actual molten metal level in order to maintain the opening of the sliding nozzle at the opening of the section. By doing so, the deviation between the target level and the actual molten metal level is always zero, so that it is not necessary to correct the opening of the sliding nozzle. As a result, when the pinch roll is actually started, the inflow and outflow of molten steel are balanced, and thereafter, the section shifts to the section where the molten metal level is set at the steady target level.

Next, a method according to a second aspect of the present invention will be described with reference to FIG. In the conventional method, when the opening speed of the sliding nozzle is corrected so as to be balanced with the initial speed, if the initial speed is set to be high, the level of the molten metal rises, and the level control of the molten metal becomes difficult. In the present invention, in order to prevent this, the initial speed is increased in two stages, so that even when the initial speed is high, the metal surface rising speed is suppressed.

In the following, the sections will be described in order.
As in the case of FIG. 1, this is a section in which a rise in the molten metal level is waited for in a predetermined opening degree pattern. When the level of the molten metal in the mold reaches, for example, L0000, the process shifts to a section for controlling the rising speed of the molten metal. At this time, the opening of the sliding nozzle is corrected so that the rising speed of the molten metal level matches the casting speed of the second stage. Correction logic for sliding nozzle opening (1)
To (3).

ΔMV = Kp * (E _n −E _n−1 ) + Ki * E _n Equation (1) ΔMV: Sliding nozzle opening correction amount for each control cycle Kp, Ki: control gain (PI control) E _n: deviation (n: time),

[0018] E _n = SV over PV ...... (2) the formula SV: target level PV of the section: Jitsuyumen level

SV = VO * t + L0000 Expression (3) VO: Casting speed of the second stage t: Elapsed time since entering the section L0000: → Switch level

SV ′ = (VO−VP) * + L′ 000 Equation (4) SV ′: Target level in section VO: Second stage casting speed VP: First stage casting speed t: Section Elapsed time after entering L'000: → 'switch level

Subsequently, the level of the molten metal is set to a predetermined level L000.
Is reached, the casting speed is reduced to X% of the initial speed (X is 50%
Activate the pinch roll with (approximately before and after). However, since a start delay occurs in the pinch roll, in this section, the molten steel supply speed is fixed by setting the target level of the equation (1) = the actual molten metal level and setting the opening degree correction to zero. Further, when the pinch roll is actually started, the sliding nozzle opening is corrected in the section 'so that the casting speed is continuously matched with the casting speed of the second stage. The sliding nozzle opening correction logic is expressed by the formulas (1), (2) and (4), and the calculation of the target level is different from that of the section.

Thereafter, when the level of the molten metal reaches L00, the casting speed is increased to the second stage casting speed, and after increasing the molten steel level, the molten steel level reaches the target level L0 at a predetermined speed. The supply speed is gradually increased in the section, and thereafter, when the molten metal level reaches the target level L0, the opening of the sliding nozzle is corrected so that the casting speed and the supply speed of the molten steel are balanced. According to this method, even when the initial speed is set to be high, the level rise speed is reduced by ', and the subsequent level control becomes easy.

As described above, according to the present invention, when the molten steel level in the mold is shifted from the start of casting to a steady state, the level of the molten steel level in the mold is increased before the start of the pinch roll at the same casting speed as when the pinch roll is activated. A method that controls the molten metal level to have a speed and compensates for the delay in starting the pinch roll, and then suppresses the influence on the molten steel level by the subsequent activation of the pinch roll to stably shift to the steady state level. is there. Therefore, according to the present invention, it is possible to further stabilize automatic casting in continuous casting.

[0024]

【Example】

Example 1 FIG. 3 shows the result of applying the invention of claim 1 to continuous casting of a slab having a mold size of 90 mm and a thickness of 1000 mm. In the present embodiment, the pinch roll activation command is output from the controller when the molten metal level reaches -75 mm, but there is a delay of about 1.5 seconds before the pinch roll is actually activated. In the present invention, a pinch roll activation command is output to the controller in advance, and the opening is not corrected for 1.5 seconds as the target level = the actual molten metal level (section in FIG. 1). Thus, when the pinch roll is actually activated in the section shown in FIG. 1, the balance of the molten metal level is maintained, and thereafter, the molten metal level smoothly reaches the steady target level.

On the other hand, in the conventional method, since the sliding nozzle opening deviates from the balance point before the pinch roll actually starts in the section, the molten metal surface descends and hunts thereafter.

Embodiment 2 An embodiment according to claim 2 of the present invention will be described below. FIG. 4 shows the result of applying the invention of claim 2 to continuous casting of the same slab as in Example 1. In this embodiment, the casting speed is set to 0.6 m when the level of the molten metal reaches -120 mm.
/ Min, and thereafter, when the casting speed reached -75 mm, the pinch roll was activated in two stages at 1.2 m / min (initial speed). In addition, the opening correction in the section 'in FIG.
To minimize it (because the sliding nozzle opening is almost balanced with the initial speed in the section), the control gain in the above equation (1) is Kp = 0.2, Ki = 0.
(Integration time is equivalent to infinity).

As a result, up to the section of FIG.
In (initial speed), the molten metal surface rises at a speed of 20 mm / sec, but since the drawing starts at 0.6 m / min in the section '区間, the molten metal surface rising speed is about 10 mm / sec.
c, the subsequent control becomes easy. Also,
When reaching 1.2 m / min (initial speed) at −75 mm, the inflow amount and the initial speed are balanced.

On the other hand, in the conventional method, the initial speed is 1.2 m /
When it is set to min, the level rise speed is increased at a rate of 20 mm / sec until the pinch roll starts, and the level change after the start of the pinch roll cannot be suppressed because the rise speed is too fast.

[0029]

As described above, according to the method of the first aspect of the present invention, during the pinch roll activation delay time, the target level is set to the actual molten metal level, and the sliding nozzle opening is not corrected. Since the deviation of the opening degree of the sliding nozzle from the balance point, which is caused by the roll activation delay, can be prevented, it is possible to suppress the fluctuation of the molten metal level in the mold at the start of casting. According to the method of the second aspect of the present invention, since the pinch roll is activated in two stages, even when the initial speed is high, the mold rising level in the mold can be suppressed. This can be performed easily and accurately. Therefore, according to the method of the present invention, breakout, overflow and the like can be reliably prevented, which greatly contributes to the stability of the operation of continuous casting.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a method according to claim 1 of the present invention.

FIG. 2 is an explanatory diagram showing a method according to a second aspect of the present invention.

FIG. 3 is a diagram illustrating a control result according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a control result according to the second embodiment of the present invention.

FIG. 5 is a diagram showing an example of a control result according to a conventional method.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B22D 11/18 G05D 9/12

Claims (2)

(57) [Claims] In an automatic casting start method for shifting the molten steel level in a mold to a steady state from the start of casting in continuous casting, the level of molten metal in the mold is increased until the level of the molten metal at the start of casting reaches a starting level of a pinch roll. The supply speed of the molten steel is controlled by the opening of the sliding nozzle so that the supply speed of the molten steel from the surface rising speed matches the casting speed at the start of casting, and then when the molten metal level reaches the starting level of the pinch roll, With the pinch roll activated, the supply speed of the molten steel is fixed until the pinch roll is actually activated, and after the pinch roll is activated, the molten steel supply speed is determined from the fixed value at the molten metal level in advance. Automatic casting of continuous casting characterized by controlling the supply speed of molten steel so as to reach a target level at a set speed. How to get started. 2. An automatic casting start method for shifting the molten steel level in a mold to a steady state from the start of casting in continuous casting, wherein the casting level is increased to a predetermined speed in two stages. The supply speed of molten steel is controlled by the opening of the sliding nozzle so that the supply speed of molten steel matches the casting speed of the second stage based on the rising speed of the molten metal in the mold until the start level of the pinch roll is reached. Activating the pinch roll when the surface level reaches the activation level of the pinch roll,
The supply speed of the molten steel is fixed until the pinch roll is actually started, and after the pinch roll is started, the supply speed of the molten steel is changed from the fixed value, and the supply speed of the molten steel is continuously determined from the molten metal rising speed in the mold. The supply speed of molten steel is controlled by the opening of the sliding nozzle so that the speed matches the casting speed of the second stage, and the casting speed is increased when the level of the molten metal reaches the speed increase to the casting speed of the second stage. After increasing the speed, after gradually increasing the molten steel supply speed so that the molten metal level reaches the target level at a predetermined speed, when the molten metal level reaches the target level, the casting speed and the molten steel supply speed are increased. An automatic casting start method for continuous casting, characterized in that control is carried out so as to be balanced.