JPH0212398B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method for controlling induction heating, and particularly to a method for controlling the temperature of molten steel in a tundish in continuous casting.

B. Summary of the Invention The present invention provides induction heating control of the temperature of molten steel in a tundish, in which program control is performed during unsteady conditions, feedback control is performed during steady conditions, and when switching from feedback control to program control for pan replacement, By adjusting the timing of switching to program control based on the difference between the average value of input power and the input power at the start of program control and changes in molten steel weight, the temperature can be stabilized over the entire casting period, especially when changing the pot. This is to reduce the temperature fluctuation of molten steel.

C. Prior Art The surface quality of a slab in continuous casting is poorer in unsteady parts such as at the beginning and end of continuous casting, or when changing pots (joints) in continuous casting, than in steady parts. One of the causes of surface quality deterioration in unsteady parts is a decrease in the temperature of the molten steel in the tundish.The molten steel temperature in the tundish drops significantly in the early stages of casting, recovers in the middle, and then drops again at the end or when the pot is replaced.

Therefore, conventional methods have been used to continuously measure the temperature of the molten steel in the tundish, monitor the casting temperature, and adjust the heating amount of the induction heating furnace to keep the molten steel temperature constant. In order to avoid heating problems (inability to heat due to heating), methods are being used to adjust the input power using a specific pattern.

D. Problems to be Solved by the Invention Conventional heating power adjustment involved comparing the measured temperature with the target temperature and manually switching the taps to adjust the input power, which was a difficult operation. In addition, it is difficult to maintain the molten steel temperature constant over the entire range of unsteady and steady parts using a simple feedback control method that compares the measured temperature and target temperature, and it is especially difficult to stabilize the temperature in the unsteady part. It was hot.

E. Means for Solving the Problems In view of the above problems, the present invention performs feedback control in the steady state, performs program control in the unsteady state, and performs pan change when switching from feedback control to program control by changing the pan. If the difference between the average input power value and the input power at the start of program control is within a certain value, the system immediately switches to program control, and when it exceeds a certain value, it switches to program control when the weight of molten steel drops to a predetermined value. This is what I did.

F Effect During unsteady conditions, the temperature is stabilized by program control, and when the change in input power is too large when switching from feedback control to program control when changing the ladle, the input power is lowered at the start of program control due to a decrease in the weight of molten steel. to suppress temperature fluctuations during switching.

G. Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an apparatus configuration diagram. Tandaisuyu 1
The internal molten steel 2 is heated by AC power supplied to the inductor 3 of the induction furnace 1A, and this AC power is subjected to power control or voltage control by a power exchanger 4 consisting of an inverter INV and a converter CON. The control device 5 performs feedback control of the output power or voltage of the power exchanger 4 according to the input power command Es.

The input power command Es is switched by a changeover switch 6 into a command Ep for program control and a command Eo for temperature feedback control. Program control is performed during periods when the level of molten steel 2 changes significantly during unsteady conditions such as the initial stage of pouring when pouring from the ladle 7, the ladle replacement stage, and the final stage of casting.Temperature feedback control is performed when the program control is set. This is performed after a period of time or during steady state when the molten steel temperature reaches the target temperature, and is performed by comparing the measured temperature signal with the target temperature.

Program control obtains the amount of molten steel in the tundish 1 from its weight detector 8 (or molten steel depth detector), and sequentially reads data groups selected from the program data table 9 according to this detection signal and the target temperature θs. input power command Ep is obtained.

Temperature feedback control uses continuous thermometer 10.
The average calculation unit 11 detects the average temperature θa from the detected temperature θr, and converts this average temperature θa into the consumable thermometer 1.
The correction calculating unit 13 performs correction as needed according to the detected temperature θ _T according to No. 2, and the input power calculating unit 14 calculates the input power command Eo from the corrected average temperature θa ₁ and the target temperature θs.

The calculation in the input power calculation section 14 is performed by the following formula.

Eo=Ff (1+ΣKΔθ/θs) Here, Ef is the reference power, K is the proportionality constant, Δθ is the difference between the target temperature θs and the average temperature θa ₁ , and has the ratio of the difference Δθ between the actual temperature and the target temperature θs. The input power command Eo is obtained by correcting the reference power Ef at the sampling period.

The input power commands Ep and Eo by such program control and temperature feedback control are set by the limiter section 1.
5 is set as the command Es, and the pinch effect is suppressed.

FIG. 2 is a diagram showing the temperature control mode in FIG. 1. Start of casting into tandate 1 (time
At t ₁ ), program control is performed to read input power command Es commensurate with the weight of molten steel from table 9 to control input power and prevent a drop in molten steel temperature at the initial stage of casting (period T ₁ ). Specific time from start of casting
When the temperature of the molten steel reaches T ₁ (or the target temperature θs) (time t ₂ ), the switch 6 is switched to the Eo side for feedback control based on continuous measurement of the molten steel. next,
When a specific time (time t ₃ ) comes before the end of the ladle 7, the control is switched to program control again and power is input in accordance with the weight of the molten steel (period T ₃ ). The power input in this program control is such that the weight of molten steel starts to decrease when the ladle ends (time t ₄ ), and the input power follows this and is lowered to prevent overheating, and the next ladle starts pouring (time t 4 ).
As the weight of the molten steel increases at _t5 ), the input power is increased, and after a predetermined time or when the molten steel temperature reaches the target temperature (at time _t6) , the control is returned to feedback control.

The program control period for replacing the ladle is used to prevent the molten steel temperature from decreasing when the ladle is replaced, and the program control is similarly performed before the end of casting (time _t7 ).
In this case, at the end of casting (t ₈ ), the weight of the molten steel begins to decrease, and as all of the molten steel in the tundish 1 is discharged, the input power is also reduced.

As mentioned above, feedback control compensates for unsteady parts such as starting pouring and changing the pot using program control to compensate for temperature fluctuations due to unresponsiveness, and during steady-state conditions, feedback control compensates for temperature fluctuations with high accuracy. Take control. In Figure 2, ΔT shows the measured value on the deviation side between the target temperature and the molten steel temperature as a solid line, and the broken line shows the conventional measured value based only on feedback control, which shows that the temperature fluctuation is smaller compared to the conventional method. show.

In this embodiment, in the switching control of the changeover switch 6, the timing of switching from feedback control to program control at the time of pot replacement is adjusted to reduce temperature fluctuations at the time of switching. This will be explained in detail below.

In Fig. 2, the switch from feedback control to program control when replacing the pot is performed at a specific time (time _t3 ) before the pot ends, but at the time of this switch, the input power command Es has been switched from Eo to Ep. , if the difference between Eo and Ep is large, the molten steel temperature θ may temporarily rise.

Therefore, in this embodiment, the switching control shown in FIG. 3 is performed. In the feedback control state, calculate the average power Eo of the input power Eo from a predetermined time before the time to switch to program control by replacing the pot (step S ₁ ), and when the time to switch to program control comes (step S ₂ ), determines whether the difference between the average power Eo and the program data Eo at the switching time is smaller than a predetermined value Es (step _S3 ), and if it is smaller, immediately enters program control (step _S4 );
When the weight is large, feedback control is continued (step _S5 ), and this feedback control waits for the molten steel weight W to drop to the set weight Ws by replacing the ladle (step _S6 ), and when it has fallen to the set weight Ws, the program control ( Switch to step _S7 ).

Due to the switching control in steps _S5 to _S7 , the input power Ep under program control decreases with respect to the input power Eo under feedback control as the molten steel weight W decreases due to ladle replacement, and the difference between Eo and Ep decreases. is within the range of the set value Es, eliminating the temporary temperature rise when switching to program control. This switching mode is shown by a broken line in FIG. 2 where the switching occurs at timing _t9 .

In addition, the control of input power command Es and switching control of the changeover switch 6 by calculations of each part in the embodiments are not limited to being processed by a computer, but equivalent effects can be obtained by analog calculation means. Of course.

H. Effects of the Invention As described above, according to the present invention, temperature fluctuations in unsteady parts are reduced by switching between feedback control and program control, and furthermore, when switching to program control when replacing a pan, input using feedback control is performed. Since the difference in power is reduced, temperature fluctuations during switching can be further reduced, and high quality continuous casting can be obtained.

[Brief explanation of drawings]

FIG. 1 is a device configuration diagram showing an embodiment of the present invention;
Figure 2 is a diagram showing the control mode in Figure 1;
The figure is a control flowchart for switching from feedback control to program control when replacing a pot. DESCRIPTION OF SYMBOLS 1... Tunnel, 2... Molten steel, 4... Power converter, 5... Control device, 6... Changeover switch, 7... Ladle, 8... Weight detector, 9... Program data table, 10 ...continuous thermometer,
11...Average calculation unit, 12...Consumable thermometer, 1
3...Compensation calculation unit, 14...Input power calculation unit, 1
5...Limitsuta Club.

Claims (1)

[Claims] 1 Program control of the power input to the induction furnace of the continuous casting tundish during non-steady conditions, temperature feedback control by continuous measurement of the molten steel temperature in the tundish during steady conditions, and change of the pot from feedback control to program control by changing the pot. If the difference between the previous input power average value and the input power at the start of program control is within a certain value, the system immediately switches to program control, and if it exceeds a certain value, program control is activated when the weight of molten steel in the tundish drops to a predetermined value. An induction heating control method in continuous casting characterized by switching.