JPH0771727B2 - Casting end control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling a pouring speed at the end of pouring of a continuous casting machine. More specifically, the present invention relates to a control method in which a deceleration speed pattern of an optimum casting speed is selected in advance and the speed at the end of casting is decelerated according to the pattern.

(Prior Art) In a continuous casting machine, molten steel in a tundish is continuously cast to produce a slab. However, in order to maintain the quality of the slab at the end of casting, it is necessary to appropriately reduce the casting speed and stop the casting while leaving a predetermined small amount of molten steel in the tundish.

Until now, deceleration control at the end of casting has often relied on manual operation. However, manual control has the drawback that the quality of the bottom portion of the slab becomes unstable due to fluctuations in the casting speed, and the work load is large.

Therefore, an automatic control method of pouring end based on the principle shown in FIG. 6 has been proposed. The upper graph of the figure shows the change of the molten steel amount W in the tundish with the passage of time t. After the end of the molten steel supply indicated by the arrow X, the molten steel amount W gradually decreases.

At the time ta when the steel amount W decreases to Wa, the casting speed V
The deceleration control (the lower graph in the figure) is started. That is,
With a weighing scale attached to the tundish,
When it is detected that it becomes equal to Wa, the casting speed V is decelerated from the steady speed Vc by a constant deceleration for a predetermined time and then maintained at a constant value (graph abc).

After that, when it is detected that the steel amount W further decreases and becomes equal to the predetermined value Wc at the time tc, the casting speed V is further reduced and maintained at a constant value again (graph cde).
The casting is stopped at the time te when the steel amount W further decreases and the predetermined value We is detected.

As described above, in the conventional method for controlling the end of pouring shown in FIG. 6, the residual steel amount W in the tundish is determined by the predetermined values Wa, Wc,
The points at which We are reached are controlled as the deceleration start point, re-deceleration start point, and pouring stop point, respectively.

Therefore, in the control method described above, the casting speed Vc in the steady state is
If is small, it takes a long time to start or stop deceleration,
The efficiency is poor (see Fig. 7). The same applies when the size of the slab is small.

On the other hand, when the velocity Vc and the slab size are large, the time of the portion (bc, de) maintained at a constant velocity after deceleration becomes extremely short (see FIG. 8).

As described above, in the conventional casting end control method, the temporal change pattern of the casting speed V is not constant. For this reason, it is inevitable that the end control will take longer than necessary and that the quality of the bottom portion of the cast slab will vary.

Therefore, the applicant of the present application has already applied for a casting end control method that eliminates the above-mentioned drawbacks of the conventional automatic control method for the end of pouring and shortens the time required for the end control as much as possible while maintaining high slab quality. Proposed in No. 60-263462.

That is, prior to the end control, a target casting speed pattern is selected in advance, and if the speed is decelerated according to this pattern, an expected casting amount from deceleration start to stop is calculated. The deceleration control is started when the amount of molten steel in the tundish becomes equal to this calculated value. Therefore, according to this method, the pouring speed can be controlled substantially faithfully to the previously selected pattern.

More specifically, this pouring end control method is a pouring end control method for controlling the pouring speed at the end of pouring at the end of pouring of a continuous casting machine in which molten metal in a tundish is continuously cast into slabs. That is, the pattern of the temporal change of the casting speed from the start of deceleration to the stop of casting, which is the target in deceleration control, is determined in advance, and the prediction from the start point of deceleration to the stop point of casting in the pattern Calculating the casting weight, and at the time when the measured amount of molten metal weight in the tundish matches the calculated predicted casting weight, start the deceleration control of the casting speed according to the above pattern, and change the casting speed. And controlling according to the pattern.

Further, in order to match the residual molten metal amount at the time of pouring stop with a predetermined value while faithfully following the pattern when there is a change in the pouring speed, etc., the target casting in the deceleration control is performed. After the casting speed pattern is determined, the difference between the casting speed specified in the pattern and the actual casting speed is detected at a predetermined cycle, and the change in the predicted casting weight based on the detected difference in the casting speed. It is characterized by calculating the amount, correcting the casting speed pattern in accordance with the amount of change in the predicted casting weight, and controlling the casting speed with the corrected pattern.

Furthermore, when the slab size changes after the target casting speed pattern is determined in deceleration control, it is detected that the slab size change is detected periodically after the pattern is determined. Calculate the amount of change in the predicted casting weight based on the change in the slab size, correct the pattern of the casting speed according to the amount of change in the predicted casting weight, and adjust the casting speed with the corrected pattern. And controlling.

As described above, in the method proposed in Japanese Patent Application No. 60-263462, the target pattern for deceleration is determined in advance before entering the deceleration control. Further, the predicted casting weight from the start of deceleration to the stop when the control is performed according to this target pattern is calculated, and the deceleration control is started at the time when the measured molten metal weight in the tundish matches the calculated value.

Further, in this control method, the control accuracy is improved by making a correction according to the casting speed and the slab size.

(Problems to be Solved by the Invention) However, in the case of a continuous casting machine having two or more molds, such correction may not be sufficient. This problem will be described below by taking the case of having two molds as an example.

As the pouring end control method, there are a conventional manual control method and a control method based on the remaining pouring length, in addition to the method of calculating the predicted pouring weight based on the speed pattern described above. The manual control method is a method in which the operator manually sets the pouring speed. In the control method based on the remaining casting length, the remaining casting length is calculated in advance from the request for the length of the product slab and the deceleration control is performed so that the casting is completed at this length.

In the case of a continuous machine having two molds, in the case where the cast strands of the two molds are both subjected to a predetermined speed pattern as described above to calculate the predicted casting weight and to control the casting end (auto stop) In some cases, only one of them is used for the predicted casting weight (auto stop) based on the speed pattern, and the other is used for manual control or control by the remaining casting length. In the case of the latter two cases, casting of the strand on the mold side by manual or remaining length is completed quickly,
The casting end time may be significantly different from that of the strand using the auto stop.

However, if the timing of the end of casting is greatly deviated in both cast strands in this way, it is not sufficient to correct the strand using speed pattern predictive casting weight control (auto stop) only by the method of the above patent application. Next, accurate control faithful to the set speed pattern cannot be performed.

Therefore, an object of the present invention is to control the pouring end of at least one mold with a predicted pouring weight (hereinafter referred to as auto stop) based on a preset speed pattern in a continuous casting machine having two or more molds, and When the mold end control is selected from auto stop, manual control, and remaining length control, the mold control using auto stop is set to a preset speed pattern regardless of other mold control methods. It is an object of the present invention to provide a pouring end control method that can be faithfully executed with high accuracy.

(Means for Solving the Problems) Thus, the gist of the present invention is that the molten metal in the tundish is continuously cast into two or more molds to form slabs at the end of casting. A pouring end control method for controlling the pouring speed by decelerating, wherein a pattern of temporal change of the pouring speed from the start of deceleration to the stop of pouring, which is a target in the deceleration control of at least one mold, is determined in advance. And calculating the predicted casting weight from the deceleration start time to the pouring stop time in the pattern, and after determining the casting speed pattern targeted in the deceleration control, the casting specified in the pattern To detect the difference between the speed and the actual casting speed and the change in the slab size, and to calculate the change in the predicted casting weight based on the detected changes in the casting speed and the slab size. Selecting a suitable correction formula from among a plurality of correction formulas respectively corresponding to the casting completion control method for molds other than the above-mentioned mold, and calculating the change using the selected correction formula; The pouring speed is controlled according to the pattern by starting deceleration based on the predicted pouring weight corrected for the change, and the pouring end control method is characterized by:

(Operation) The predicted pouring weight in the mold in which the pouring end control is performed by the predicted pouring weight control is first calculated by the preset speed pattern and the set slab size.

Further, the amount of change in the predicted casting weight, that is, the amount of correction is calculated based on the detected casting speed and slab size. For the correction formula at this time, depending on whether the other mold control method is, for example, auto stop, manual control, or remaining length control, there are a plurality of correction formulas suitable for each control method. Select from among the available. Specific examples of correction formulas suitable for each case will be described in detail in the following description of the embodiments.

Therefore, no matter how the other mold control method is selected, the mold pouring end control using the predicted pouring weight control can be performed with high accuracy faithfully to the set speed pattern.

(Example) Next, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram of an example of an apparatus for carrying out the control method according to the present invention, and shows a case where the present invention is applied to a continuous casting facility for molten steel having two molds.

The tundish 10 of the continuous casting equipment 1 continuously casts the molten steel injected from the ladle 11 into the first and second molds 12 and 13 to produce cast pieces 14 and 15. While the molten steel is continuously supplied from the ladle 11, the casting is carried out at a substantially constant casting speed.However, when the molten steel is completely supplied from the ladle 11 and the casting is near the end, the pouring is decelerated and controlled. , A predetermined weight of molten steel is left in the tundish 10 and stopped.

This pouring end control according to the present invention will be described below.

The speed pattern determination and predicted casting weight calculation management unit 2 is composed of, for example, a host computer,
It manages the number of charges to be cast, the size of the slab, the type of steel, the number of slabs, etc. The management unit 2 determines an appropriate deceleration speed pattern from these values and the like. It is preferable that the management unit 2 stores a large number of speed patterns, and selects an appropriate one from these. The management unit 2 outputs the slab size and the determined speed pattern to the weight calculation unit 3 and the control calculation unit 4.

FIG. 2 is a graph V = of the change pattern of the casting speed into the first mold 12 determined by the management unit 2 with respect to time t.
V (t) is shown.

Casting speed pattern V = 1st mold 12 side strand
V (t) starts deceleration from the steady casting speed Vc at A ₁ point,
Stops at A ₅ after passing A ₂ , A ₃ , and A ₄ (in graph V
Times corresponding to A _{1 to} A ₅ are represented by t ₁ to t ₅ , respectively.

From A ₁ to A ₂ , V decelerates at a predetermined deceleration K ₁ , and A ₂ to A ₃
Until that time, the predetermined speed V ₁ is maintained for the predetermined time T ₁ . Start deceleration again from A ₃ (predetermined speed K ₂ ) and reach the predetermined speed V ₂
It is maintained at a constant speed for ₂ hours (A _{4 to} A ₅ ).

The above pattern V includes deceleration K ₁ , K ₂ , maintenance speeds V ₁ , V ₂ ,
It is determined by the maintenance times T ₁ and T ₂ and the steady speed Vc.
Therefore, the management unit 2 determines the parameters K ₁ , K ₂ , V ₁ , V ₂ , T ₁ , and T ₂ according to the steady speed Vc, the dimension (cross-sectional area) S of the slab 14, and the like, together with Vc and S. Output.

Here, the reason for using the pattern shown in FIG. 2 and the selection of the value of each parameter by the management unit 2 will be briefly described.

In order to finish casting in a short time and improve work efficiency,
It is preferable that the total deceleration control time Tt is short. For this purpose, T ₁ and T ₂ must be short and K ₁ and K ₂ must be large.
However, the range of possible values of these parameters has the following restrictions. Therefore, the management unit 2 selects these parameters so that Tt is as short as possible within the limit range.

When K ₁ and K ₂ are large (that is, when the casting speed is rapidly reduced), it becomes difficult to control the molten metal level of the mold 12. Therefore, there is a practical upper limit (for example, 1.0 m / min ² ) to the possible values of K ₁ and K ₂ .

Further, if the deceleration period (t _{1 to} t ₂ ) continues for too long, blowing up (upwelling of the molten metal) occurs. To prevent this
It is necessary to set T ₁ to a predetermined value (for example, 0.5 to 1.0 min) or more. Outside there is a similar reason for the T _2, in order to stabilize the quality of the slab 14 the bottom portion, a fixed time-lapse V ₂ (e.g.
2 min or more) It is necessary to cast. The lower limit of T ₂ is a value determined by the characteristics of the continuous casting machine 1, steel grade, and the like.

If it is assumed that the second mold 13 is controlled to be finished by auto-stop like the first mold 12, the casting speed pattern V'to the second mold 13 is usually determined to be the same value as V described above. To be done.

On the other hand, when the control based on the remaining casting length is used for the casting completion control of the second mold 13, the management unit 2 determines the speed different from the above V from the length to be further cast into the second mold 13 from the present time. The pattern V'is determined and output. The speed pattern V'in this case may be directly determined by the operator.

In this way, the management unit 2 outputs the velocity patterns V, V ′ of the first and second molds 12, 13 and the slab dimensions (cross-sectional areas) S ₁ , S ₂ to the weight calculation unit 3 and the control calculation unit 4. .

The weight calculation unit 3 which receives these values from the management unit 2
The predicted casting weight W ₁ into both molds 12 and 13 from the deceleration start time t ₁ of the first mold 12 side strand to the stop time t ₅ is calculated by the following formula (both molds 12 and 13 perform automatic stop control). Assuming that).

W ₁ = W ₁₁ + W ₁₂ W ₁₁ and W ₁₂ are predicted casting weights of the first and second molds 12 and 13 in the period from t ₁ to t ₅ , respectively. Therefore, W ₁₁ and W ₁₂ are given by the following equations.

Here, G is the density of the molten steel.

Since V and V ′ are time variables, more accurately, V
Where it should be described as (t), V ′ (t), for convenience,
Also referred to simply as V and V '.

Similarly, the first and second deceleration start times t ₃ to t ₅
The predicted casting weight into the molds 12 and 13 is calculated by the following formula.

W ₃ = W ₃₁ + W ₃₂ Here, W ₃₁ and W ₃₂ are predicted casting weights to the first and second molds 12 and 13, respectively, in the above period (from t ₃ to t ₅ ).

The weight calculator 3 outputs the predicted casting amounts W ₁ and W ₃ to the control calculator 4.

The speed setting unit 6 starts deceleration when W = W ₁ + W ₅ or W = W ₃ + W _5, and stops at W = W ₅ .

Deceleration control based on speed pattern A) When both strands are predicted cast weight control (auto stop).

When switching to the auto stop control mode, there may be a difference between the target speed pattern (target speed) and the actual speed. For example, when the actual speed is high, if the basic pattern is stopped, the residual steel amount may become insufficient at the end of casting. Therefore, it is necessary to determine the deceleration start weight by subtracting the overcasting amount caused by the difference between the target speed and the actual speed of the other strand from the current weight.

The same applies when the speed is changed during casting.

The same applies to the slab size, but the size may be changed during casting, but since it cannot be predicted, it is necessary to correct the excess or deficient casting amount in the same manner as the speed fluctuation when the size change occurs.

The first deceleration start point t ₁ is determined by the control calculation unit 4 as follows.

The automatic control condition, that is, (a) the pouring speed setting is in the automatic control state.

(B) The speed pattern has been set by the management unit 2.

(C) The weight of molten steel in the tundish 10 is not less than a predetermined value.

(D) Casting is in progress.

Control operation unit 4 at the time point t ₀ everything was confirmed that it is satisfied starts calculation of W _n (prediction casting weight corrected for variations of the slab dimensions and casting speed) by the following equation .

(The following formula (1) is a formula for the first mold 12,
The same applies to the calculation formula for the second mold 13. ) Where W: measured tundish weight by weight scale 5, W ₅ : amount of molten steel to be left in the tundish 10 at the pouring end point, S ′ _{1 to} S ′ ₂ : casting of the first and second molds 12 and 13 Actual size of each piece, G: Specific gravity of molten steel V: Speed according to set speed pattern V _P : Actual pouring speed (see Fig. 2 and 3). The first mold 12
V ′ and V ′ _P in the calculation formula (1) are the values on the second mold 13 side.

Here, since V _P and V ′ _P are time variables,
Where it should be written as V _P (t) and V ′ _P (t), for convenience,
Hereinafter, they are also simply referred to as V _P and V ′ _P.

The control calculation unit 4 always calculates W _n by the formula (1) after t ₀ , and is set at time t ₁ when W _n1 = W ₁₁ · S ′ ₁ / S ₁ (2) Start deceleration according to the speed pattern. (Here, S ₁ is the value used to calculate the speed pattern V as described above.) The control calculation unit 4 instructs the speed setting unit 6 to calculate the speed pattern V,
The output of the speed according to V'is started, and the casting speed is controlled according to the pattern. That is, the speed control unit 7 controls each speedometer.
The speed of the pinch rollers 16 and 17 is controlled to the target value input from the speed setting unit 6 as a feedback signal of the input from 18 and 19.

Similarly, the second round of deceleration point (Re deceleration start _{point) t 3, W n1 = W} 31 · S '1 / S 1 and became a time point t _3, performs the same deceleration control as described above.

B) When the second mold side is manually controlled and only the first mold side is automatically stopped.

When the other strand is manually controlled, it is impossible to predict how fast and when it will stop. For this reason, for example, when casting is performed at a high speed, there are cases in which the remaining weight for auto-stop is insufficient or a certain holding time cannot be secured.

Furthermore, when the other strand stops first, the remaining weight of the tundish is used only by the own strand, and therefore the deceleration stop should be performed after the remaining weight becomes considerably small.

Therefore, until the other strand is stopped, both strands can be calculated by the same correction formula as the automatic stop, but after the other strand is stopped, it is necessary to remove the term of the other strand from the deceleration timing calculation formula.

As shown in FIG. 4, the second mold side of the manual control is the first
The casting is finished at a time point t _x before the casting time point t _{5 of the} mold (in FIG. 4, t _x is the first and second deceleration points t ₁ , t ₃
Between) is shown).

Therefore, in this case, the deceleration point changes the correction method of predicting casting weight used in the case of entering the time domain prior to t _x, in the case the control of the first mold 12 entering the time domain of t _x after .

(1) When the deceleration point falls within the time range before t _x , as in the case of the first deceleration point t _{1 in} FIG. 4, it is assumed that the second mold 13 is also controlled according to the set speed pattern V ′. Then, the first mold 12 is controlled by using the equations (1) and (2) in the above item A).

(2) When the deceleration point as 2nd deceleration point t ₃ of FIG. 4 enters the time zone of t _x after a correction operation is performed for casting pieces strands performing casting only the first mold. That is, at the first deceleration start point t ₁ , W is When it becomes, the time is t ₁ . The second deceleration start point t ₃ is Be time point t ₃ .

(The meanings of the symbols are as described above, and V _P and V are the values on the first mold side.) C) The second mold side is the casting end control based on the remaining length (hereinafter referred to as the strand strip), 1 When the mold side is set to auto stop.

Basically, it is the same as when other strands are manually controlled.However, in the case of strand stop, the future schedule (scheduled amount of casting weight) of that strand is known, so auto-stop with the remaining weight after subtracting that amount in advance. It is possible to

Therefore, the remaining casting amount of the other strand is calculated and corrected.

As shown in FIG. 5, the casting end control on the second mold 13 side is performed by the speed pattern V'determined based on the remaining casting length.
Accordingly, the casting is finished first on the second mold side.

Also in this case, the deceleration point is the time t _x at which the casting of the second mold 13 ends.
The correction calculation method of the predicted casting weight of the first mold is changed between before and after t _x .

(1) When the deceleration point is before t _x like the first deceleration point _{1 in} FIG. 5, the remaining casting amount Ws (the shaded area in FIG. 5) is calculated from the remaining casting length of the second mold. Indicates the residual casting amount after t ₁ ) is calculated in advance. This residual casting amount Ws is determined by the second mold 13
Since it is cast from the first mold 12, the cast amount from the first mold 12 is a value obtained by subtracting the residual cast amount Ws.

Therefore, the first deceleration start point t ₁ of the first mold 12 is It will be the time when.

At the second deceleration start point t ₃ , W is It will be the time when. (The meanings of the symbols are as described above.) (2) When the deceleration start point is after t _x , as at t ₃ in FIG. 5, it is the same as described in B) (2) above. Correction calculation is performed. That is, the predicted casting weight is calculated assuming that the single-strand casting is performed using only the first mold 12. The details are the same as (2) in the description of the item B) above.

(Effect of the Invention) In the present invention, in the pouring end control of the continuous casting machine having two or more molds, at least one of the molds is controlled based on the predicted pouring weight (auto stop control) to start deceleration. The target speed pattern V ₁ is determined in advance, and the predicted casting weights W ₁ and W ₃ from the deceleration start times t ₁ and t ₃ to the stop t ₅ are calculated assuming that the pattern V ₁ is followed. To be done.

The other mold is controlled by selecting one from a plurality of control methods (for example, auto stop, manual control, remaining casting length control).

The predicted casting weight from the deceleration points t ₁ and t ₃ to the end point t ₅ of the mold of the auto stop control is corrected based on the measured casting speed and the casting dimension. According to the invention, this correction is
The correction formula is selected from a plurality of correction formulas in accordance with another mold control method used and is performed.

Therefore, according to the present invention, it is possible to always control the mold of the auto stop control with high accuracy, faithfully to the set speed pattern, regardless of how to control the other mold.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of a system when the control method according to the present invention is carried out in a two-mold continuous casting machine; FIG. 2 is a graph of an example of a target speed pattern in the system of FIG. FIG. 3 is a graph of tundish weight, target speed pattern, and actual pouring speed when both molds are set to auto stop in the apparatus of FIG. 1; FIG. 4 and FIG. A graph of the target speed pattern and the actual casting speed when the second mold is controlled manually and the remaining casting length is controlled in the apparatus shown in the figure; FIG. 6 is a graph showing the principle of the conventional control method; And FIGS. 7 and 8 are graphs of examples of changes in the actual pouring speed under the control method of FIG. 1: Continuous casting machine, 10: Tundish 11: Ladle, 12, 13: Mold 14, 15: Slab, 16, 17: Pinch roller 18, 19: Speedometer, 2: Management section 3: Weight calculation section, 4: Control calculation unit 5: Scale, 6: Speed setting unit 7: Speed control unit

Claims (2)

[Claims] 1. A pouring end control method for controlling the pouring speed at the end of pouring at the end of pouring of a continuous casting machine in which molten metal in a tundish is continuously cast into two or more molds to form cast pieces. , Predetermining a pattern of temporal change in the casting speed from the start of deceleration to the stop of casting, which is a target in the deceleration control of at least one mold, and After calculating the predicted casting weight of the casting and determining the target casting speed pattern in deceleration control, the difference between the casting speed specified in the pattern and the actual casting speed and the change in the slab size To detect the change in the predicted casting weight based on the changes in the detected casting speed and slab size. A suitable correction formula is selected from among a plurality of corresponding correction formulas, the change in the predicted cast weight is calculated using the selected correction formula, and the predicted cast weight corrected for the change is calculated. Controlling the pouring speed according to the pattern by starting deceleration based on the above. 2. A method of controlling pouring completion of a mold other than the above-mentioned mold 1 is a method of presetting a pouring speed pattern similarly to the above-mentioned mold 1 and controlling according to the pattern, a manual control method, or The casting control method according to claim 1, wherein the control method is based on the remaining casting length.