JPS6261383B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the level of molten steel in a mold in continuous casting, and more specifically, to a method for controlling the level of molten steel in a mold during continuous casting, and more specifically, to control the level of molten steel when changing the slab width by moving a short piece of the mold during continuous casting. This invention relates to a level control method.

In continuous casting, in order to control the injection rate of molten steel from the tundish and to maintain a constant level of molten steel in the mold (hereinafter referred to as the molten metal level), generally speaking, as shown in Fig. 1, The level of the molten steel 3 in the mold 1 is detected by the installed molten steel level detector 2 in the mold 1, and the injection speed of the molten steel 3 injected from the tundish 4 is controlled so that the molten steel level is constant. A control method is implemented by adjusting the opening degree of the injection hole 4a using a sliding nozzle 5 or a nozzle stopper (not shown) installed in the tundish 4.

FIG. 2 is a block diagram showing the control mechanism shown in FIG. , is compared with a pre-stored target value for the level of the molten metal in the mold. If there is a difference from the target hot water level (hereinafter referred to as the target hot water level), a signal is sent from the level controller 6 to the opening controller 7 of the sliding nozzle 5, and the opening level is adjusted. The opening degree of the sliding nozzle 5 is adjusted by the controller 7, and the rate of injection of molten steel from the tundish 4 into the mold 1 is appropriately controlled.

The opening controller 7 detects the target sliding nozzle opening and the sliding nozzle opening detector 8
The driving device 9 of the sliding nozzle 5 is compared with the actual value of the opening degree of the sliding nozzle detected in the
It has a function of automatically correcting and controlling the sliding nozzle opening degree by giving a drive command signal to the target sliding nozzle opening degree.

As described above, the mold level was appropriately controlled by detecting the level of the molten metal in the mold, changing the opening of the sliding nozzle, and controlling the rate of injection of molten steel from the tundish.

By the way, as is well known, in recent years, in continuous casting, in order to improve productivity, the width of the slab has been frequently changed during casting, and the speed of changing the width has tended to become even faster. To change the slab width, for example, as shown in FIG. 2, a pressing device 14 using a hydraulic or electric cylinder is connected to the mold short piece 1a, and the pressing device 14 is driven to move the short piece 1a in the width direction of the slab. This is done by moving. When changing the width of the slab, the volume inside the mold changes significantly. Therefore, the control method shown in Fig. 2 cannot accurately control the level of the molten metal to follow the volume change, and the slab width changes. This has been a major obstacle in changing the width of the slab, as it can deteriorate quality and cause problems such as breakouts.

The present invention eliminates the above-mentioned drawbacks, and even if there is a change in mold internal volume when changing slab width,
The purpose of this is to control the level of hot water in the mold, and its gist is that in a continuous casting method in which the width of the slab is changed by moving the short piece of the mold during continuous casting, the position of the set short piece is used as a reference. A mold width change signal obtained by detecting the amount of movement of the short piece from the position,
The mold internal volume change is calculated over time from the measured casting speed signal and the slab thickness that is set in advance or actually measured from the casting conditions, and the opening degree of the sliding nozzle is adjusted based on the calculated value. The present invention is a method for controlling the level of molten steel in a mold, which is characterized by controlling the injection rate of molten steel into a tundish.

Next, one embodiment of the present invention will be described with reference to FIG.

In FIG. 3, a mold 1 includes a detector 2 for detecting the level of molten metal in the mold and a short piece position detector 10.
A sliding nozzle 5 is also installed in the tundish 4, and the injection speed of molten steel can be adjusted by adjusting the nozzle opening.

As the hot water level detector 2, for example, one using a thermocouple embedded in the mold 1 or one using an electromagnetic level sensor may be used alone or in combination. In addition, the short piece position detector 10 detects the amount of movement of the short piece 1a from the set position,
In other words, it is a device that detects the width change amount, a device that directly detects the position of the short piece 1a, or a device that directly detects the position of the short piece 1a, or
4 may be detected, and the position of the short piece may be detected from the amount of movement of the pressing device 14. In the experience of the present inventors, in the case where a stepping cylinder is used as the pressing device 14, there is a mechanism that counts command pulses issued to the stepping cylinder and detects the amount of movement of the stepping cylinder from the counted pulses. It was effective because it enabled highly accurate position detection.

A casting speed detector 11 detects the casting speed by detecting the speed of the slab 15 pulled out from the mold 1 using, for example, a rotational speed detector of a roll (pinch roll) for pulling the slab.

Now, in this embodiment, the mold width change signal a from the short piece position detector 10 and the casting speed signal b from the casting speed detector 11 are transmitted to the computing device 1.
2 is input. The calculation device 12 has set slab thickness,
That is, the thickness of the slab being cast is input in advance from, for example, casting command conditions, or the thickness of the slab 15 pulled out from the mold 1 is actually measured and the actual value is input, and the thickness of the slab and the above-mentioned slab thickness are input. From the mold width change signal a and the casting speed signal b, a mold internal volume change (hereinafter simply referred to as a volume change) is calculated over time. Next, an embodiment of the volume change calculation method using the arithmetic unit 12 will be described. Equation (1) below shows a calculation formula for calculating the molten steel acceptable volume (hereinafter referred to as possible volume) V in the mold when molten steel 3 is poured into the mold 1 up to the target level.

V (m ³ /min) = W _(n) × D _(n) × U (m / min)
...(1) However, V: Possible volume W: Mold width D: Slab thickness U: Casting speed Therefore, if the possible volume V due to the change in mold width W when changing the slab width is calculated every predetermined time, The possible volume corresponding to the amount of change is determined and compared with each other to calculate the amount of change in the possible volume V, that is, the volume change referred to in the present invention. FIG. 4 is a graph showing the change in volume when the width of the slab is changed under the condition that the casting speed is constant, and the range X represents the time when the width is expanded, and the range Y represents the time when the width is decreased. As can be seen from FIG. 4, the shorter the calculation unit time Δt, the more the calculated volume change is expressed in a continuous straight line.
Capable of accurately calculating volume changes over time.

The calculated value of the volume change calculated over time by the arithmetic unit 12 is input to the opening controller 7 of the sliding nozzle 5 via the adding device 13, and the sliding nozzle is adjusted based on the calculated value. The opening degree of the riding nozzle is adjusted to control the injection speed of molten steel poured from the tundish 4 into the mold 1. For example, when the width is expanded, the possible volume increases sequentially, and the volume change changes in the positive direction as shown in FIG. 4, so the opening degree of the sliding nozzle 5 is controlled in the direction of increasing it. In the embodiment shown in FIG. 3, the calculated value of the volume change is inputted from the arithmetic unit 12 to the adding device 13, and the signal from the level controller 6 is also inputted thereto. As described above, the level controller 6 compares the target hot water level with the actual hot water level measured by the hot water level meter 2, and if a difference occurs, a signal corresponding to the difference is generated. If the melt level differs from the target melt level due to a disturbance factor other than a change in the mold width or casting speed when changing the width, the addition device 13 causes the arithmetic device 12 to
The command signal sent to the opening controller 7 is automatically corrected by adding the signal (variation value) from the level controller 6 to the calculated value.

As described above, in the present invention, the volume change is calculated over time from the mold width change signal, the casting speed signal, and the set slab thickness based on the set position of the short piece 1a, and the molten steel injection rate of the tundish is based on this calculated value. By implementing the present invention, the opening degree of the sliding nozzle can be immediately adjusted even when the width is changed due to rapid volume changes, and it is possible to control the molten metal level in the mold without disturbing it. Summer. Therefore, according to the present invention, even when changing slab width during casting, it is possible to control the level of molten steel in the mold in a very stable manner, which improves slab quality and stabilizes operations. The effect is huge.

In the experience of the present inventors, when the width is changed at a speed of 20 mm/min, the measured hot water level fluctuates by ±20 mm with respect to the target hot water level using the conventional control method shown in Figure 2. However, in the implementation of the present invention, ±
The result was 10 mm or less, confirming that extremely high-precision hot water level control is possible. In addition, in the present invention, even if the width change speed was higher than 20 mm/min, the accuracy hardly changed, but with the conventional control method, the difference between the target level and the measured level became even larger, and It was not possible to change the width.

As described above, the practical effects of the present invention are extremely large.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a tundish and mold that control the level of molten steel in the mold, Fig. 2 is a block diagram showing a conventional method for controlling the level of molten steel in the mold, and Fig. 3 is a mold according to the present invention. FIG. 4, which is a block diagram showing a method for controlling the level of molten steel, is a chart showing the volume change situation when changing the width. 1... Mold, 2... Molten steel level level detector in the mold, 3... Molten steel, 4... Tandate, 5...
Sliding nozzle, 6... Level controller, 7
... Sliding nozzle opening degree controller, 9 ... Sliding nozzle drive device, 10 ... Short piece position detector, 11 ... Casting speed detector, 12 ... Arithmetic device, 13 ... Addition device, 14 ... Pressing device, 1
5...Slab.

Claims (1)

[Claims] 1. In a continuous casting method in which the strip width is changed by moving a mold short piece during continuous casting, the mold width change signal obtained by detecting the amount of short piece movement from the reference position using the set short piece position as a reference, and the actually measured mold width change signal. Calculate the change in mold internal volume over time from the casting speed signal and the slab thickness that is preset from the casting conditions or is actually measured, and adjust the opening degree of the sliding nozzle based on the calculated value, A method for controlling the level of molten steel in a mold, characterized by controlling the injection rate of molten steel in a tundish.