RU77810U1 - METAL LEVEL CONTROL SYSTEM IN THE CRYSTALIZER - Google Patents

Abstract

The invention relates to continuous casting of metals, in particular, to regulating the level of liquid metal located in the mold of a continuous casting of metals.

The technical task of the utility model is to increase the reliability of the metal level control system in the mold, ensure the stability of the casting process, increase the casting seriality coefficient and eliminate ingot quality anomalies caused by the displacement of the steel flow due to overgrowing of the immersed nozzle.

The technical problem is achieved due to the fact that the system further comprises a unit for calculating the rate of change of the metal level in the mold and a unit for calculating the adaptive gain of the level controller, and the unit for calculating the rate of change of the level at the input is connected to the metal level sensor, and at the output it is connected to the adaptive calculation unit gain of the level controller, which in turn is connected at the input to the stop position sensor and the casting speed sensor, and at the output it is connected through the controller metal equal to a reference block which is in turn connected to the stopper position regulator, and the stopper drive actuator.

Description

The invention relates to continuous casting of metals, in particular, to regulating the level of liquid metal located in the mold of a continuous casting of metals.

In a continuous steel casting plant, the liquid metal that flows out of the casting ladle first flows in transit to an intermediate tank called an intermediate ladle.

One of the functions of this tundish is to orient the molten metal in the direction of a single swing mold or, more generally, in the direction of several swing molds of a continuous casting plant in which curing of workpieces (slabs, flat ingots, blooms, etc. . blanks).

Metal flows from the tundish directly into the mold. On the trajectory of its movement between the intermediate ladle and the mold, the liquid metal stream is enclosed in a pipe made of refractory material, called a pouring glass. The upper end of this pouring glass is attached to the bottom of the intermediate ladle, while its lower end passes through the meniscus and is immersed in liquid metal.

The main function of a pouring nozzle is to protect the liquid metal stream from being oxidized by atmospheric air, and also to prevent it from entraining a part of the slag covering the metal surface in the mold during the meniscus’s intersection, which may impair the cleanliness of the cast blanks.

One of the main parameters in obtaining defect-free products is the stability of the meniscus level in the mold. If this level stability is not satisfactorily provided, the crystallization of the metal is carried out under extremely variable conditions. So, it may turn out that the crystallized thickness of this billet is too small and there is a danger, more or less significant, of rupture of the hardened crust of the ingot. In this case, in the best case, a workpiece with a mediocre quality of the workpiece is obtained, and in the worst case, liquid metal can spill through the so formed

tearing and stopping the casting process and severe damage to this unit.

To ensure satisfactory control of the level of liquid metal in the mold of the continuous casting plant, it is necessary to use a special automatic system that could satisfy the spatial position of the said stopper. Such an automatic control system provides movement in the vertical plane of the said stopper, depending on the results of comparing the desired level in this case, the location of the meniscus and the actually changed level of this meniscus. This change in the actual level of the location of the meniscus of the liquid metal in the mold is usually achieved using an optical or inductive sensor. Such a sensor generates an electrical output signal, which after appropriate processing can be used to control the spatial position of said stopper.

A known method of automatic control of a continuous casting machine, comprising adjusting the level of the metal in the mold by measuring the speed of drawing the ingot [1].

However, this method does not allow you to accurately control the metal level due to slippage of the ingot relative to the pulling rolls, and also due to the significant inertia of the system caused by the large mass of the drawn ingot.

A device for dispensing molten metal, comprising a bath for molten metal and a metering chamber installed therein, is connected to the weighing device by means of the weighing lever and a stopper installed in the metering chamber with a drive for its movement mounted on the weighing lever [2].

There is also known a system for maintaining the metal level in the mold of a continuous casting plant, comprising a level meter, a converter, an adder, a comparison element, an amplifier, and an actuator, the second input of the adder connected to a level adjuster, and the second input of the comparison element connected to a feedback sensor kinematically connected to the stopper.

In addition, the system further comprises a follower drive and a block erosion compensation unit for the retaining pair, wherein the input of the follower drive is connected to the output of the adder, and its output shaft is connected via an erosion compensation sensor to a comparison element [3].

However, these systems do not allow sufficiently accurate control of the metal level in accordance with the given law due to the ingot slipping relative to the pulling rolls, as well as the large mass of the drawn ingot.

A device is known for measuring the level of metal in the mold of a continuous casting metal plant, comprising a two-arm lever pivotally mounted on a stationary rack, at one end of which a balanced weight is mounted, and hydraulic nozzles at the other end of the two-arm lever, the device is also equipped with a gas flow meter, a comparison unit, a setter , a measuring coil with a core, a recording device, a flow regulator, a dossel, a gas reducer and a compressed gas cylinder, and the point n is connected to a gas reducer, the output of which is connected to the throttle, the output of the throttle is connected to a gas flow meter, the output of which is connected to the first input of the comparison unit, the output of which is connected to the input of the flow regulator, the output of which is connected to the throttle, the second output of the comparison unit is connected to the master gas flow, a two-arm lever has a core with the ability to move it inside the measuring coil, the output of which is connected to a recording device [4].

A disadvantage of the known device is the low accuracy associated with intensive wear of the float. Attempts to reduce float wear by equipping it with a water cooling system led to the crystallization of metal on its surface.

A known method of automatic control of a continuous casting machine and a device for its implementation [5]. The device contains a halogen counter, an isotopic sensor, an electronic converter, a comparison unit, a constant signal generator, a logic unit, a metal flow controller and an actuator for the stopper drive.

Closest to the claimed technical solution and the achieved result is a system for maintaining the liquid metal level in a two-strand mold of a continuous casting plant, comprising a metal level sensor in the mold, connected through a converter, a comparison unit and

a regulator with an actuator, and the second comparison unit is connected to the master, and also to maintain predetermined and equal metal levels in two streams of the mold, the system additionally contains two comparison units, a converter, an amplifier and an actuator, the inputs of each of the additional comparison units connected to the inputs of the transducer of both streams of the mold, the input of one of the additional blocks of comparison is connected to the input of the amplifier channel regulating the position of the intermediate Nogo bucket, and the output of another additional comparator is connected to a reference channel stopper position regulating unit [6].

A significant drawback of these devices and systems is the low reliability of the stopper due to the ingress of fragments of oxide captures that are torn from the melt surface when the stopper is activated in the contact zone of the stopper pair, which significantly reduces the tightness of the closing of the stopper hole, which significantly reduces the tightness of the closure of the stopper hole and affects the accuracy of dosing.

The technical task of the proposed utility model is to increase the reliability of the metal level control system in the mold, ensure the stability of the casting process, increase the casting seriality coefficient and eliminate ingot quality anomalies caused by the displacement of the steel flow due to overgrowing of the immersed glass.

The stated technical problem is achieved due to the fact that the system further comprises a unit for calculating the rate of change of the metal level in the mold and a unit for calculating the adaptive gain of the level controller, the unit for calculating the rate of change of the level at the input connected to the metal level sensor and at the output connected to the calculation unit adaptive gain of the level controller, which in turn is connected at the input to the stop position sensor and the casting speed sensor, and the output is connected to Without a metal level controller with a comparison unit, which in turn is connected to a stop position controller and a stop actuator.

The object of the invention is a device designed for the practical implementation of the following system for controlling the level of metal in the mold. As will be understood from the description below, this utility model

consists in carrying out special processing of electrical signals emanating from the above-mentioned sensors before combining them, moreover, high-frequency and small-amplitude oscillations are excluded from these signals, after which these signals are combined into a single signal in the proper manner in this case.

The proposed utility model will be better understood from the description below, which provides links to the drawing — FIG. 1 and figures 1, 2, 3, 4. FIG. 1 is a functional diagram illustrating the operation of the metal level control system in the mold. Fig. 1, 2, 3 and 4 show the structural diagrams of the specific use of the proposed technical solution.

The metal control system in the mold contains:

Metal level sensor 1, stop position sensor 2, casting speed sensor 3, stop drive actuator 4, stop position adjuster 5, comparison unit 6, metal level regulator 7, comparison unit 8, metal level adjuster 9, metal level change speed calculation unit in the mold 10, the unit for calculating the adaptive gain of the level controller 11, the mold 12.

The system works as follows:

The metal level in the mold 12 is measured by a level sensor 1. An electric signal corresponding to the metal level is fed to the input of the comparison unit 8, where it is compared with a signal of a given level from block 9. The difference between the set and actual levels is fed to the input of the level 7 controller, which has a dynamically adjustable coefficient gain received from block 11. At one of the inputs of block 11, a signal of the rate of change of the metal level from block 10 is supplied (the derivative of the metal level in the mold is calculated). The other two inputs are fed with casting speed signals from the speed sensor 3 and the actual stopper position signal from the stop position sensor 2. The output level of block 7 is proportional to the gain calculated by block 11. The output signal of block 7 is compared in comparison block 6 with the signal of the actual stopper position . The difference of these signals is fed to the input of the stop position adjuster 5. The stop position regulator 5 gives a command to the actuator of the stop mechanism 4 to change the position of the stop.

The adaptive gain of the metal level controller 7 is calculated by block 11 based on the following conditions:

From the point of view of stability of continuous casting, it is important to prevent overgrowing of the casting cup, which occurs due to the deposition of steel deoxidation products in the channel of the dispenser cup and the submerged cup. The deposition rate and the degree of channel overgrowing can be estimated by the relative amount of stopper lifting during casting. In an ideal mode, during casting on one intermediate ladle, the stopper position should slowly go down, which is associated with the normal production of the stopper. However, in the real mode, especially when casting low-carbon, aluminum-graded steel grades, the stopper position has significant displacements in elevation height, which leads to a significant deterioration in the stability of level maintenance, a shift in the steel flow in the mold, erosion of the ingot crust, the need to switch to manual mode for break-in "stopper and emergency situations.

The system for maintaining the metal level in the mold operates in a dynamic mode, which is due to a large number of disturbing influences. Based on this, it can be concluded that in a normally configured system, with an optimal condition of the assembly, the stopper - dispenser cup - submerged cup, when the actual level deviates from the set level under disturbing action, in the future, under the influence of the control system, this difference should decrease. If the deviation of the actual metal level from the set level at the current time is greater than the same deviation in the previous measurement (evaluated in block 10), this serves as a prerequisite for increasing the adaptive gain. In this case, the quality of maintaining the level does not change, and the amplitude and front of the oscillations of the stopper increase. The rate of flow of metal into the mold becomes sharply variable, which reduces the likelihood of tightening the channel of the dispenser glass and the submerged glass and reduces the formation of deposits on the stopper. The gain value also depends on the relative position of the stopper. As the position increases (the stopper pops up), the gain increases, and when the stopper position decreases, in order to eliminate increased stopper production, the gain decreases. The amplitude and "front" of the stopper movement changes. As the position increases (stopper pops up), it is as if pumping the system, and the quality of maintaining the level remains the same. The stopper position also depends on the casting speed, therefore, block 11 also evaluates the speed value.

Based on the actual value of three quantities - the rate of change of the metal level, the stopper position and the casting speed, the block 11 calculates the gain for the metal level controller 7 at the current time.

Using the proposed technical solutions, we consider the examples shown in figures 1, 2, 3 and 4.

To improve the quality of maintaining the metal level in the mold, feedback on the rate of change of the level is introduced into the control system (see Fig. 1). The rate of change of level is calculated as the first derivative of the level of the metal in the mold. In automatic control theory, this is known as derivative control. Consider the structural diagram of the control object Wy - the metal level in the mold (Fig. 2)

From the analysis of the structural diagram, it is possible to determine the main disturbing influences that affect the quality of maintaining the metal level in the mold. These are:

1. the state of the pair "stopper-glass dispenser";

2. the diameter of the immersed glass;

3. casting speed;

4. grade and temperature of cast steel;

5. metal level in the tundish.

The last three indicators are determined by the requirements of technology, and during the casting process are maintained at the optimum level. From the point of view of stability of continuous casting, it is important to prevent overgrowing of the casting cup, which occurs due to the deposition of steel deoxidation products in the channel of the dispenser cup and the submerged cup. The deposition rate and the degree of channel overgrowing can be estimated by the relative amount of stopper lifting during casting. In an ideal mode, during casting on one intermediate ladle, the stopper position should slowly go down, which is associated with the normal production of the stopper. However, in the real mode, especially when casting low-carbon, aluminum-graded steel grades, the stopper position has significant displacements in elevation height, which leads to a significant deterioration in the stability of level maintenance, a shift in the steel flow in the mold, erosion of the ingot crust, the need to switch to manual mode for break-in "stopper and emergency situations.

The system for maintaining the metal level in the mold operates in a dynamic mode, which is due to a large number of disturbing influences. Based on this, we can conclude that in a normally configured system, with the optimal condition of the assembly, the stopper - dispenser cup - submerged cup, any change in the stopper position should lead to a change in the metal level in the mold.

It is proposed to use the second derivative of the metal level in the mold to assess the state of the control system and adjust the system (Fig. 3).

At times when the second derivative of the metal level is zero and has a modulo value greater than at the previous moment of time, you can increase the system gain or increase the task at the input of the level controller - (U (s) -Z (s) -dZ ( s) / dt) * Wz.

In this case, the quality of maintaining the level does not change, and the amplitude and front of the oscillations of the stopper increase. The rate of flow of metal into the mold becomes sharply variable, which reduces the likelihood of tightening the channel of the dispenser glass and the submerged glass and reduces the formation of deposits on the stopper. The value of the transfer function Wz depends mainly on the relative position of the stopper. As the position increases (the stopper pops up), the adaptive gain of the Wz function increases, and when the stopper position decreases, in order to exclude increased stopper production, the adaptive gain decreases. The value of Wz also depends on the time during which the second derivative is equal to zero, as well as on the magnitude of the module of this derivative, compared with the second derivative for the previous period of time.

Thus, the longer the system is open, or the stronger the disturbing effect, the stronger the effect on the stopper, which compensates for the disturbance. We get a metal level control system in the mold with feedback on the rate of change of the level and an adaptive regulator Wz, the parameters of which vary depending on the acceleration of the change in the metal level in the mold and the relative position of the stopper (Fig. 4).

The stopper in automatic mode is constantly in motion (exception - if the actual level coincides with the set). Any change in the position of the stopper should lead to a change in level, and not only to a change in level, but also to a change in the rate of change of level (second derivative). In the normal state of the stopper-cup dispenser assembly, the actual level should exponentially reach the predetermined level (if there is regulation with respect to the derivative). If the change in the actual level does not occur exponentially, the impact on the stopper sharply increases at such times, it begins to work out faster. The amplitude and "front" of the stopper movement changes. It turns out as if pumping the system, and the quality of maintaining the level remains the same. And this happens all the time.

The technical advantages of the proposed technical solution are to increase the accuracy and reliability of information about the position of the metal level in the mold, which allows for reasonable control of its operation mode, as well as in the simplicity of its industrial implementation. This ensures the stable operation of the system as a whole.

The advantages of the proposed system is also:

- more accurate stopper positioning for better control of metal flow;

- optimized time for working out the system command (electric cylinder + mechanism);

- smooth and precise control of the stopper mechanism without backlash and excessive friction;

- ease of manual stopper control for operators;

lack of sensitive electrical or electronic components operating in adverse conditions (harsh environment, high temperature during casting);

- uptime;

- lightweight maintenance;

- high potential for maintaining the mold at the beginning of the casting of metal.

References

1. US patent No. 4237960, 1980.

2. A.S. No. 839685, B22D 39/00, publ. in BI No. 24, 1981.

3. A.S. No. 603489, B22D 11/16, publ. in BI No. 15, 1978.

4. A.S. No. 1125096, B22D 11/16, publ. in BI No. 43, 11/23/1984.

5. A.S. No. 1295598, B22D 11/16, publ. 05/21/1985.

6. A.S. No. 538813, B22D 11/16, publ. in BI No. 46, 1976.

Claims (1)

A metal level control system in the mold, comprising metal level and stopper position sensors, a casting speed sensor, a metal level gauge and a comparison unit associated with an actuator, characterized in that it further comprises a metal level change rate calculation unit in the mold and an adaptive calculation unit gain of the level controller, and the unit for calculating the rate of change of the level at the input is connected to the metal level sensor, and at the output it is connected to the hell calculation unit the effective gain of the level controller, which, in turn, is connected at the input to the stop position sensor and the casting speed sensor, and at the output it is connected through the metal level controller to a comparison unit, which, in turn, is connected to the stop position controller and the actuator stopper drive.