JPH0561025B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a device for controlling a constant level of molten steel in a mold in continuous casting equipment. Note that in the description of each figure below, the same reference numerals indicate the same or corresponding parts.

[Prior art and its problems]

Maintaining a constant level of the molten steel (also referred to as hot water) injected into the mold from the tundish into the mold (hereinafter referred to as the mold molten level) is to prevent overflow or breakout of molten steel from the mold (slab outer shell). This is extremely important not only to prevent molten steel from flowing out through breaks in the solidified shell, but also to maintain quality by preventing horizontal cracking of slabs. Therefore, in order to prevent abnormalities in the quality of cast products, a control method that suppresses mold level fluctuations as much as possible is required, but realistically, the casting speed (the speed at which the slab is withdrawn from the mold) is constant and the flow rate into the mold is constant. In controlling the mold level at a constant level with little change in the inlet area (also called nozzle opening) of the molten steel injection nozzle,
If the charge is too long, the inside of the nozzle will become clogged, making it impossible to maintain stable controllability. In addition, such clogging may suddenly peel off, causing a sudden change in the mold level, which not only makes the control unstable, but in the worst case, the control diverges and requires operator intervention. Conventional mold level control methods of this type include the following. (a) A method in which the amount of molten steel injected from the tundish into the mold is kept constant and the casting speed is controlled by feedbag. (b) A method in which the casting speed is kept constant and the amount of molten steel injected from the tundish into the mold is controlled by feedbag. Since the control method (a) changes the casting speed, it is unfavorable in terms of the quality of the cast product, and has the drawback that it is not suitable for the recent continuous casting operation in which several charges are cast continuously. There are two types of control methods as described in (b) above. That is, one method is PID control that uses the mold surface level as the control variable, and the other method uses the tundish molten steel head (difference in the surface level between the tundish and the mold), casting speed, and mold surface level deviation as parameters. The amount of change in each parameter is converted into an opening change from the opening calculated by the molten steel nozzle inlet opening calculation, and the opening change is used for control that combines feedback control and feedforward control. be. The former control method has the disadvantage that it cannot adequately cope with disturbances such as nozzle clogging and peeling. The latter control method is effective against fluctuations in the mold level due to changes in the tundish molten steel head and casting speed; ) is very small relative to the casting speed, so the control action against peeling of the nozzle is slow and there is a risk of overflow of molten steel. Another method for removing blockages is to superimpose a vibrated signal on the normal operation signal for the operating end, but this method depends on the timing of applying weight.
This has been difficult to do automatically due to the risk of overflow or breakout.

[Purpose of the invention]

The present invention eliminates the above drawbacks, automatically detects nozzle clogging, and corrects the control parameters of the regulator, thereby preventing the clogging from increasing and making control more stable than responsiveness. Mold level control that can stabilize control with responsiveness by automatically detecting peeling of the surface level control device and nozzle clogging and correcting the nozzle opening command value and controller control parameters. The purpose is to provide equipment.

[Key points of the invention]

First, to explain the main points of the control compensation by clogging detection according to the first invention of the present application, this control compensation method uses the mold level level signal as the control amount, and the molten steel inflow hair value area (nozzle In feedback control using the stroke of the stopper that changes the opening (opening degree) as the manipulated variable, the casting speed ((rate of slab withdrawal from the mold, amount of slab pulled out calculated from the cross-sectional area of the slab pulled from the mold) and , when the nozzle opening and the amount of molten steel flowing into the mold calculated from the tundish molten steel head are in balance, the ideal nozzle opening is determined from the relationship that there is no fluctuation in the mold level, and this value and the nozzle opening are This is a compensation method that detects clogging based on the difference from the actual value and performs gain correction.In other words, the amount of molten steel injected from the tundish into the mold via the nozzle per unit time is as follows:
It is expressed by equation (1). K F (distance to the water surface level). On the other hand, the amount of molten steel drawn out as slabs from the mold per unit time (casting speed) is expressed by the following equation (2). A・V...(2) Where A: Mold cross-sectional area (cross-sectional area of the slab from the mold), V: Speed at which the slab is pulled out from the mold. If the amount of molten steel flowing into the mold and the amount of molten steel withdrawn from the mold are equal, there will be no fluctuation in the mold level. Therefore, assuming that Equation (1) = Equation (2), the ideal nozzle opening value F is determined by the following equation (3). You are asked to do so. F=A・V/K・√2......(3) However, for the stopper control device (cylinder control panel described later) that controls the nozzle opening, the stroke of the stopper is used as the amount that replaces the nozzle opening. Since it is a manipulated variable, it is necessary to convert it into a stopper stroke to obtain the nozzle opening degree F calculated using equation (3). This conversion method can be calculated using the stroke/opening characteristic (function f) as shown in equation (4) below, which is determined in advance from the structure of the equipment. ST1=f(F)...(4) Here ST1: Ideal stopper stroke value. Ideal stroke value ST obtained from formula (4)
If there is a steady deviation between the actual stroke value ST (ST1) and the actual stroke value ST (ST2), it can be determined that the nozzle is clogged. That is, ΔST=ST1−ST2...(5) where ΔST: Stroke change amount corresponding to the amount of nozzle clogging, ST2: Actual stroke value. That is, when the stroke difference ΔST is ΔST<−k (k is positive and is the clogging determination value), in other words, when the absolute value of ΔST is equal to or greater than k, it can be determined that the clog is present. When clogging is detected in this way, if the gain of the PID controller, which is the regulator in the mold level control device, is increased by the stroke change amount ΔST, the actual stroke value of the stopper will be compared to when there is no clogging. The vibration waveform follows the stroke command value in a superimposed manner, making clogging less likely and making it possible to remove clogging. Next, the main points of the control compensation by detecting peeling of a clogged nozzle according to the second invention of the present application will be described. Disturbance factors for mold level control include stopper stroke, tundish molten steel head, casting speed, and flaking due to nozzle clogging.In order to detect this flaking, it is necessary to control the mold molten metal while there is no change in disturbance factors other than flaking. Peeling may be determined when a sudden change occurs in the surface level. When separation is detected in this way, the stopper control device (cylinder control panel) superimposes a signal corresponding to the width of sudden mold level fluctuation, that is, the amount of change in the mold level within a predetermined period of time, on the stroke command value. The stroke of the stopper is modified to close the nozzle opening to quickly settle the mold level, and at the same time, the gain of the P (proportional) operation of the PID controller is lowered, and the I
(Integral) By increasing the operating time, hunting due to peeling can be suppressed. To summarize the above, the main points of the first invention of the present application are:
Molten steel is temporarily stored in a tundish, from which the molten steel is injected into the mold through a nozzle, and slabs are pulled out of the mold for continuous casting. Controls the molten steel level in the mold (mold level). The apparatus includes a nozzle opening varying means (stopper operation cylinder) for varying the opening of the nozzle, and a nozzle opening varying means for controlling the nozzle opening so that the actual value of the nozzle opening matches the command value of the nozzle opening. Continuous casting equipped with a nozzle opening control means (cylinder control panel) that controls the mold level, and a regulator (PID controller) that outputs a nozzle opening command value to the nozzle opening control means to maintain a constant mold level. For the equipment's mold level control device, there is a means (pinch rolls, etc.) to measure the casting speed at which the slab is pulled out of the mold, and a means to measure the level difference between the molten steel level in the tundish and the mold level (the tundish molten steel head). ), the casting speed, the tundish molten steel head, the mold level and the actual nozzle opening are input, and the ideal value of the nozzle opening is calculated from the casting speed and the tundish molten steel head. , detecting that the absolute value of the deviation between the ideal nozzle opening value and the actual nozzle opening value exceeds a predetermined determination value, and determining that the nozzle is clogged;
Controller compensation means (opening degree calculator, opening stroke calculator, subtractor, clogging compensation determiner, PID) that increases the proportional gain of the controller according to the absolute value of the deviation.
(parameter compensator, etc.). Then, the gist of the second invention of the present application is that instead of the regulator compensation means of the first invention, each of the casting speed, tundish molten steel head, mold surface level, and nozzle opening actual value is input, and each of these values is inputted. The time change in the amount is monitored, and if a sudden change is detected only in the mold surface level, it is determined that the nozzle is clogged and has peeled off, and the nozzle opening specified value and adjuster are adjusted according to the amount of time change in the mold surface level. The present invention is based on the provision of regulator compensation means (peeling compensation determiner, PID parameter compensator, etc.) that reduces the proportional gain of the regulator and increases the integration time of the regulator.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described based on FIGS. 1 and 2. FIG. 1 is a block diagram showing the configuration of an embodiment of the apparatus of the present invention, and FIG. 2 is an explanatory diagram of the detailed structure of the nozzle inlet. In FIG. 1, molten steel 2 is injected into a tundish 1 from a ladle (not shown), passes through an upper nozzle 3A from the tundish 1, passes through an immersion nozzle 3, is cast into a mold 4, and is poured into a tundish 1. As it solidifies, a solidified shell is formed, and the cast slab 5 is pulled out by pinch rolls 8 from the lower open end of the mold. In this case, the amount of molten steel 2 injected from the tundish 1 into the mold 4 is varied by a stopper 6 that opens and closes the molten metal inlet of the upper nozzle 3A in the vertical direction (stroke direction). The structure of this part is shown in FIG. 2, where the hot water inlet area to the nozzle (nozzle opening degree F) is represented by the hatched area, and this is a value determined corresponding to the stroke ST of the nozzle. 7 is a mold hot water level meter that detects the hot water level in the mold 4, and a PID controller 18 as a regulator inputs the mold hot water level signal 7a from the level meter 7, and controls this so as to keep it constant. A PID calculation is performed on the difference between the signal value 7a and the target hot water level set inside the controller 18, and this adjustment output signal is given to the cylinder control panel 11 as a stroke command value 18a. As a result, the cylinder control panel 11 changes the actual stroke value ST2 to the command value 18.
The actual stroke value ST2 of the stopper 6 (therefore, the nozzle opening degree) is varied via the stopper operating cylinder 10 so as to match the temperature a, so that the mold surface level becomes constant. 9 is a pinch roll drive device for driving the pinch roll 8. The stopper 6 operates in synchronization with the rise and fall of the stopper operation cylinder 10, and the actual stroke value ST2 of the cylinder 10 is reset to zero in the fully closed state.
Using that position as a reference point, plus and minus signed values are input to a subtracter 14 and a peeling compensation determiner 16, which will be described later. The slab drawing speed signal V is sent from the pinch roll drive device 9 to the tundish molten steel head total 1.
9, the tundish molten steel head h is taken into the opening degree calculator 12, and the ideal nozzle opening value F is calculated using the calculation formula (3).The result is passed through the opening/stroke converter 13, and the stopper stroke ideal value
The value converted to ST1 and the actual stroke value coming from the cylinder control panel 11 as a stopper control device
ST2 is subtracted by a subtractor 14, and the stroke difference ΔST is inputted to a clogging compensation determination unit 15 to determine whether or not compensation is to be performed. That is, the clogging compensation determiner 15
Then, the stroke difference signal ΔST from the subtractor 14
When the calculated value is below the lower limit (ΔST<-k) or the absolute value of ΔST is greater than or equal to k, the timer is monitored, and if the condition of being below the lower limit still holds true even after time has elapsed. , when the PID parameter compensator 17 increases the proportional gain P of the PID controller 18 by a predetermined amount according to the value of the stroke difference ΔST, the stopper movement amount (stroke change) becomes more severe compared to the state before the gain increase. That is, the rate of change of the actual stroke value ST2 becomes faster, and it converges to the stroke command value 18a oscillatingly. As a result, the nozzle is gradually removed from the clogged state, and when the nozzle returns to normal, the proportional gain P is returned to its normal value. Further, removal of the clog is performed using the removal compensation determination device 16. That is, in addition to the actual stroke value ST2, the slab withdrawal speed V, the tundish molten steel head h, and the mold level level 7a from the mold level meter are input to the determiner 16. When it is determined that there is a sudden change in the hot water level 7a, the slab withdrawal speed V and the actual stroke value
If there is no change in ST2 or tundish molten steel head h, it is determined that separation has occurred, the PID parameter compensator 17 is activated, the P operation gain in the PID controller 18 is lowered, and the integral time of the I operation is lengthened. , a response of mold level control in response to separation by forcibly superimposing a signal corresponding to the mold level level fluctuation amount within a predetermined time on the stroke command value 18a for the cylinder control panel 11 in the direction of decreasing the actual stroke value. Try to improve your sexuality.

【Effect of the invention】

As is clear from the above description, according to the first invention of the present application, the ideal value of the nozzle opening is calculated from the casting speed and the tundish molten steel head, and the absolute value of the deviation between the ideal value of the nozzle opening and the actual value of the nozzle opening is calculated. By detecting that the value exceeds a predetermined judgment value and determining that the nozzle is clogged, the proportional gain of the regulator is increased in accordance with the absolute value of the deviation, thereby changing the actual stroke value of the stopper from vibration. By making the shape that looks like a superimposed waveform follow the stroke command value, that is, by manipulating the nozzle opening with a slight hunting effect, it is possible to make the nozzle less likely to clog and to remove the clog, thereby stabilizing the control. . Further, according to the second invention, changes over time in each value of the casting speed, tundish molten steel head, mold level and nozzle opening actual value are monitored, and sudden changes are detected only in the mold level. It is determined that the nozzle is clogged and has peeled off, and the nozzle opening command value and the proportional gain of the regulator are reduced according to the amount of time change in the mold level, and the integral time of the regulator is increased, thereby quickly reducing the mold level. It is possible to stabilize control by suppressing hunting caused by peeling.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the detailed shape of the nozzle inlet. 1: tandate, 2: molten steel, 3A: upper nozzle, 4: mold, 5: slab, 6: stopper,
7: Mold water level meter, 8: Pinch roll,
9: Pinch roll drive device, 10: Stopper operation cylinder, 11: Cylinder control panel, 12: Opening degree calculator, 13: Opening degree/stroke converter, 14: Subtractor, 15: Clogging compensation determiner, 16: Peeling Compensation determiner, 17: PID parameter compensator, 18: PID
Controller, 19: Tundish molten steel head meter.

Claims (1)

[Scope of Claims] 1. Molten steel surface in the mold of equipment that temporarily stores molten steel in a tundish, injects the molten steel from the tundish into a mold through a nozzle, and continuously casts slabs by pulling them out from the mold. The level control device includes a nozzle opening varying means for varying the opening of the nozzle, and a nozzle opening varying means for adjusting the nozzle opening so that the actual value of the nozzle opening matches a command value of the nozzle opening. A mold for continuous casting equipment, comprising: a nozzle opening control means for controlling the molten steel; and a regulator for outputting a nozzle opening command value to the nozzle opening control means so as to maintain a constant molten steel level in the mold. The molten metal level control device includes: means for measuring a casting speed at which slabs are pulled out from the mold; means for measuring a level difference between the molten steel level in the tundish and the molten steel level in the mold; The speed, the level difference, the molten steel level in the mold, and the actual value of the nozzle opening are input, and the ideal value of the nozzle opening is calculated from the casting speed and the level difference. Detecting that the absolute value of the deviation of the actual nozzle opening value exceeds a predetermined judgment value, determining that the nozzle is clogged, and increasing the proportional gain of the regulator in accordance with the absolute value of the deviation. A mold level control device for continuous casting equipment, characterized in that it is equipped with a regulator compensation means for controlling the temperature. 2. A device for controlling the level of molten steel in the mold of equipment that temporarily stores molten steel in a tundish, injects the molten steel from the tundish into a mold through a nozzle, and pulls slabs from the mold for continuous casting. a nozzle opening degree variable means for varying the opening degree of the nozzle; and a nozzle opening degree control for controlling the nozzle opening degree variable means so that the actual value of the nozzle opening degree matches a command value of the nozzle opening degree. and a regulator that outputs a nozzle opening command value to the nozzle opening control means so as to keep the molten steel level in the mold constant. , means for measuring the casting speed at which the slab is pulled out from the mold; means for measuring the level difference between the molten steel surface level in the tundish and the molten steel surface level in the mold; the casting speed, the level difference, The molten steel level level in the mold and the actual value of the nozzle opening are input, and changes over time in these quantities are monitored, and a sudden change is detected only in the molten steel level in the mold. It was determined that the peeling was caused by a clogged nozzle.
Adjuster compensation means for reducing the nozzle opening command value and the proportional gain of the adjuster and increasing the integration time of the adjuster in accordance with the amount of time change in the molten steel surface level in the mold; A mold level control device for continuous casting equipment featuring: