JPS6045026B2 - Mold content steel level control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to controlling the level of molten steel in a mold while keeping a constant steel billet drawing speed in continuous casting equipment.

Maintaining a constant level of molten steel injected into the mold from the tundish is extremely important in terms of quality, not only to prevent overflow or breakout, but also to prevent transverse cracking of the slab and the formation of surface inclusions.

Therefore, it is necessary to minimize fluctuations in the molten steel level.
High controllability and stability are required. There are three methods for controlling this molten steel level: (1
) Control the flow rate of molten steel from the tundish by keeping the billet drawing speed constant.

(2) The flow rate of molten steel from the tundish into the mold is fixed and the copper piece drawing speed is controlled. (3) Control by a combination of (1) and (2) above. Method (1) is preferable in terms of the quality of the slab because the billet drawing speed is constant;
It is easy to predict the end time of casting, and it is easy to schedule the end of charging even in continuous casting. However, in reality, wear and tear on the tundish nozzle and occurrence of nozzle clogging cause changes in flow characteristics, making control using this method difficult. In method (2), the controllable range of the slab drawing speed is limited. In other words, the upper limit cannot be made too large due to the relationship with the cooling capacity and quality of the slab, and if the speed is too low, it will lead to a decrease in operational capacity. In order to keep the drawing speed within this range, it is necessary to minimize changes in the flow rate of molten steel from the tundish, and in reality there are many constraints on the operating pattern, etc. Method (3) has the disadvantage that control is complicated. J In any case, in order to maintain the quality of the slab, the change in the level of molten steel in the mold should be ±5 to
It is necessary to keep it within 10wt. The present invention utilizes method (1) by understanding the degree of nozzle wear and nozzle clogging.
) to control the molten steel level.
An object of the present invention is to provide a highly accurate molten steel level control method by calculating the cross-sectional area of a tandate nozzle from the amount of change in molten steel in the mold and the amount of slab movement, and applying this calculated value to molten copper level control. is to provide. The main points of the present invention will be briefly explained.

The amount of molten steel flowing from the tundish into the mold within a unit time is equal to the sum of the amount of movement of the slab and the amount of change in molten steel within the mold within the same time. This relationship is expressed as in equation (1). Here, S: Nozzle cross-sectional area g: Gravitational acceleration h: Height from the tundish molten metal level to the molten steel level W: Slab width D: Slab thickness L: Slab movement amount Δx: Change in molten steel level within the mold Now, let the tandate nozzle opening setting value be Sm, and S
If the difference d between m and the nozzle cross-sectional area is defined as in equation (2),
If d is normal, it should be a value close to O.

However, if the tundish nozzle is worn out, the actual nozzle cross-sectional area is larger than the nozzle opening setting value Sm, and becomes d - k (k is a positive constant). Similarly, if the tandate nozzle is clogged,
The nozzle cross-sectional area is smaller than the nozzle opening setting, which is only βm, and d>k. In the present invention, by determining the nozzle opening setting value so that this d becomes O, it is possible to excellently control the level of molten steel in the mold. An embodiment of the present invention will be described below with reference to FIG.

Molten steel is tanned from a ladle (not shown). After being poured into the tundish 1, the molten steel passes through the tundish nozzle 3, the immersion nozzle 4, and is cast into the mold 5. As the molten steel solidifies in the mold 5, it is cast from the lower open end of the mold. It is pulled out as piece 6. The problem in this invention is the degree of clogging of the tundish nozzle 3.
Another issue is how to correct it online when a deviation between the set opening degree and the actual opening degree has occurred due to wear and tear.

When the billet movement amount calculation device 12 receives a signal from the timing generator 11 that issues a signal at regular intervals, the billet movement amount calculation device 12 generates a pulse generator 10 attached to the drive roll 9 for drawing billets.
Input the number of pulses corresponding to the amount of slab movement and calculate the amount of slab movement within unit time. For example, there is a relationship such that as the slab drawing speed increases, the number of pulses from the pulse generator increases.

Therefore, the slab movement amount calculating device 12 calculates the movement amount of the slab by counting the number of pulses from the timing generator 11 which emits pulse signals at regular intervals. The molten copper change amount calculating device 14 receives the molten steel level value in the mold from the molten steel level detector 8 when receiving the signal from the timing generator 11 as described above, and calculates the difference ΔX from the previous value.

The nozzle opening calculation device 15 is the same as the slab movement amount calculation device 1.
2 and the slab specification storage device 13, the slab width W1 and slab thickness D. ．． By inputting a constant K specific to the steel type, the tundish nozzle opening degree is calculated so that the molten steel level is constant.

The slab drawing speed at this time is fixed at the optimum drawing speed for casting the slab. The nozzle opening degree S1 output from the nozzle opening degree calculation device 15 is obtained from equation (3). Here, K is a constant corresponding to the steel type, and changes depending on, for example, the viscosity and specific gravity of the copper type.

The opening correction calculation device 16 is the same as the molten steel change amount calculation device 14.
Input the output ΔX1, the slab width W1 being poured at the time, the slab thickness D, and the constant K from the slab specification storage device 13, and calculate the tundish nozzle opening correction amount for the change in the level of molten steel in the mold. do. This opening degree correction amount ΔS1 is obtained by equation (4). This ΔS1 is the correction amount determined from the change in the molten steel level, that is, the opening correction amount of the tundish nozzle when the molten steel level is kept constant. Adder 1, 18
is the nozzle opening degree S which is the output of the nozzle opening degree calculation device 15
1 and the opening correction amount ΔS1 which is the output of the opening correction calculation device 16, and outputs the tundish nozzle opening S2 which is corrected for the change in the molten steel level.

The relationship between S2, S1, and ΔS1 is as shown in equation (5). The cross-sectional area calculation device 17 is the same as the slab movement amount calculation device 12.
The output L of the molten steel and the output ΔX of the molten steel change calculation device 14 are input, and the slab width W1 and slab thickness D are input from the slab specification storage device 13, and the nozzle cross-sectional area S3 at that point is calculated using the formula (6
). Nozzle cross-sectional area S calculated by equation (6)
3 shows the nozzle cross-sectional area itself that has changed at that point in time even when nozzle wear or nozzle clogging occurs. The subtracter 19 inputs S2, which is the output of the adders 1 and 18, and S3, which is the output of the cross-sectional area calculating device 17, and calculates the difference ΔS2 between the two.

That is, iν B −6

'II. This ΔS2 is expressed by the formula (2) in the previous explanation.
This corresponds to d, and in this control device plays a role as a control parameter regarding abnormalities such as tundish nozzle wear and nozzle clogging. If there is no abnormality in the nozzle, ΔS2 naturally takes a value close to 0. In the adder 20, the output S2 of the adder 18 and the subtracter 19
The tundish nozzle opening setting value S4 is determined by inputting the output ΔS2.

That is, S4 is expressed as in equation (8). This S4 is a nozzle opening setting value that takes into account abnormalities in the tundish nozzle, and this setting value S4 is sent to the nozzle opening setting device block to adjust the nozzle opening.

FIG. 2 is a flow diagram of the operation of the present invention. That is, in block 25, the number of pulses is taken in by starting the timing generator 11, and in block 26, processing corresponding to the slab movement amount calculation device 12 that calculates the slab movement amount L is performed. Blocks 27 and 28 perform processing corresponding to the molten steel level detector 8 which takes in the molten steel level and calculates Δx, and the molten steel change amount calculation device 14.

Blocks 29 and 30 read D, W, and K and calculate S1, and 31 corresponds to the opening correction calculation device 16.
The block 32 corresponds to the adder 18, the block 33 corresponds to the cross-sectional area calculating device 17, the block 34 corresponds to the subtracter 19, and the block 35 corresponds to the adder 20. According to the present invention, by correcting the nozzle opening degree in consideration of changes in the cross-sectional area of the nozzle due to wear and tear of the tundish nozzle or nozzle clogging, it is possible to achieve good control of the molten steel level in the mold without changing the flow characteristics. becomes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a flowchart explaining the present invention in detail.

7... Nozzle opening setting device, 8... Molten steel level detector, 10... Pulse generator, 1
1... Timing generator, 12... Slab movement amount calculation device, 13... Slab specification storage device,
14... Molten steel change calculation device, 15...
・Nozzle opening degree calculation device, 16...Opening degree correction calculation device, 1
7... Cross section calculation device, 18... Adder 1, 19... Subtractor, 20... Adder O unit 2.

Claims (1)

[Claims] 1. In a system for controlling the level of molten steel in a mold in continuous casting equipment, the change in the level of molten steel in the mold is measured, and the amount of billet movement is calculated from the number of rotations of a drive roll for pulling out a billet,
The molten steel in the mold is characterized in that the cross-sectional area of the tundish nozzle is calculated from the amount of movement of the slab and the amount of change in the molten steel in the mold, the set value of the tundish nozzle opening degree is corrected, and the molten steel level is controlled. Level control method. 2. The molten steel level in the mold as set forth in claim 1, characterized in that the tundish nozzle opening correction value is calculated from the amount of change in the molten steel level in the mold to correct the tundish nozzle opening. Control method.