JP3558029B2 - Method for detecting abnormal behavior of slab during continuous casting and method for controlling casting conditions - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of detecting abnormal behavior of a slab, particularly in casting of a billet or the like in continuous casting, and a condition of oscillation and mold powder (hereinafter simply referred to as “powder”) based on the abnormal behavior detected by this method. The present invention relates to a method for controlling casting conditions such as the input amount of the above.
[0002]
[Prior art]
The continuous casting equipment is provided with an oscillation device that pours powder between the molten steel and the mold and moves the mold at a predetermined frequency and stroke so that the molten steel in the mold does not fuse to the inner surface of the mold. The oscillation device reduces friction between the mold and the molten steel to prevent breakout and to prevent seizure flaws on the slab surface. Japanese Patent Publication No. 3-56824 proposes a method for improving the surface properties of a continuous cast slab, in which the vibration of a mold is performed with a non-sine waveform to thereby more effectively prevent breakout and seizure.
[0003]
However, when a round billet, a square billet, or a small-diameter bloom is continuously cast, vibration of a slab due to mold oscillation, so-called shaking, may occur. This is because, when the mold is oscillated, the solidified slab located downstream from the mold is linked to the oscillation stroke and frequency due to the frictional force between the inner surface of the mold and the solidifying molten steel in the mold. This is because they may be cast while shaking in the shape.
[0004]
A pinch roll for holding the slab is installed on the downstream side immediately below the mold and the slab is drawn out at a predetermined torque or speed. This can be prevented by increasing the force, that is, the rolling force on the slab. However, if the rolling force by the pinch roll is increased more than necessary, it may cause the cross-sectional shape of the slab to deteriorate. In particular, in a round billet, it is desirable to increase the roundness as much as possible to make it a perfect circle for the reason described later. Therefore, the rolling force is at least a force that can prevent the slab from falling and hold it.
[0005]
In recent years, the casting of round billets has been carried out at higher speeds from the viewpoint of improving productivity and preventing the temperature of molten steel in the ladle and molten steel in the tundish, and cooling the slab located directly below the mold. A slab cooled by a water spray or a mist spray of a mixture of water and air needs to be cooled with a minimum amount in order to prevent cracks on the slab surface due to rapid cooling.
[0006]
In this case, the surface temperature of the slab whose surface located downstream from the mold has solidified is higher than in the past, and the entire slab is softer. Therefore, it is desirable that the pinch roll holding the soft slab be held with a minimum rolling force so as not to deteriorate the sectional shape of the slab.
[0007]
This is because when the round slab is processed into a pipe by a seamless mill in the next process, the shape of the round slab greatly affects the uneven wall thickness and drilling efficiency of the pipe, and the rolling property when transported to the seamless mill. Therefore, a round billet as close to a perfect circle as possible is required. Therefore, in order to ensure roundness, it is necessary to slightly reduce the pressure with a pinch roll.
[0008]
[Problems to be solved by the invention]
However, when the rolling force of the pinch roll is reduced, the restraining force of the slab by the pinch roll is weakened, and the shaking phenomenon of the slab appears as described above due to the influence of the mold oscillation. When the shearing phenomenon appears, the frictional force between the pinch roll and the slab changes, or the slab is rubbed by the pinch roll, so that a flaw is generated on the surface of the slab.
[0009]
Further, when cutting a continuously cast slab to a predetermined length, relative movement occurs between the cutting torch and the slab, and the properties of the cut surface deteriorate. This is because when the slab is cut with a cutting flame composed of gas and oxygen from the torch blow tube while the slab is clamped, the blow tube and the torch bogie main body cause abnormal behavior of the slab due to shank of the slab. This is because they do not always move in tune with (Shakuri).
[0010]
In other words, the vibration of the main body of the torch and the vibration of the blow tube do not match the time period and the amount of vibration of the blow tube due to the minute vibration of the slab due to the shank. As a result, the cutting properties of the cut surface deteriorate. The appearance of the shearing phenomenon is due to the fact that the friction between the surface of the molten steel in the mold and the inside of the mold is increasing in the mold, and the amount of powder flowing between the molten steel and the mold is properly adjusted. It can be said that it is not.
[0011]
The present invention has been made in view of the problem that occurs due to the above described shearing phenomenon, and a method for detecting abnormal behavior of a slab during continuous casting, and an oscillation based on the detection by this method. It is an object of the present invention to provide a method for controlling the casting conditions such as the conditions and the amount of powder input.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the method for detecting an abnormal behavior of a slab during continuous casting according to the present invention is directed to a method of moving a slab in a casting direction and a counter casting direction during continuous casting performed while performing mold oscillation. After the pulse in the casting direction continued for several pulses to several tens of pulses, when one or several pulses were detected in the anti-casting direction , an abnormal behavior that was oscillation of the slab caused by oscillation occurred. It is decided to judge. This makes it possible to accurately detect the abnormal behavior of the slab, that is, the occurrence of the shearing. Then, after detecting the abnormal behavior of the slab, the abnormal behavior of the slab can be eliminated by controlling the conditions of the oscillation and the casting conditions such as the amount of powder input based on the amount of the behavior.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for detecting an abnormal behavior of a slab during continuous casting according to the present invention measures a movement amount of a slab in a casting direction and a counter casting direction during continuous casting performed while performing mold oscillation, and a pulse in the casting direction is measured. After a few pulses to several tens of pulses have been detected, when one or several pulses are detected in the anti-casting direction, it is determined that an abnormal behavior, which is vibration of the slab caused by oscillation, has occurred. At this time, the abnormal behavior of the slab, that is, the shearing, has been found by experiments of the present inventor to be a minimum of about 0.1 mm. Thus, if the measurement is performed with a resolution of 0.01 to 0.2 mm per pulse, the abnormal behavior of any size can be measured.
[0014]
That is, as shown in FIG. 1, in the continuous casting equipment including the tundish 1, the sliding gate 2, the immersion nozzle 3, the mold 4, and the like, the slab 5 continuously cast as described above is cut into a predetermined length. A cutting machine 6 (generally a gas type torch) is provided. Since the cutting machine 6 needs to cut the hot cast and solidified slab 5 without stopping the casting, the torch carriage 6a to which the torch blowing pipe 6c is attached comes out at the casting speed. And a clamp device 6b for cutting to a predetermined length while moving in synchronism with.
[0015]
As a length measuring device for measuring the cutting length at the time of cutting by the cutting device 6, a roll called a measuring ring 7 which is in direct contact with the cast piece 5 is usually employed. The measuring roll 7 is a roll supported so as to be freely rotatable, has appropriate friction so as not to slip on contact with the slab 5, and rotates in synchronization with the movement of the slab 5, A rotation sensor 8 for measuring the amount of rotation is provided on the axis of the roll.
[0016]
The rotation sensor 8 employs a pulse generator usually called a pulse generator. Hereinafter, the rotation sensor 8 is referred to as a pulse generator 8. The pulse generator 8 can output 1,000 to several thousand pulses per rotation, and its detection resolution is selected according to the precision required for length measurement. Usually, the required precision for length measurement in continuous casting equipment is 0.1 pulse. About 5 to 1 mm is sufficient.
[0017]
By the way, since the casting 5 that is continuously cast and comes out of the mold 4 is pulled out only in the pouring direction, the rotating direction of the measuring roll 7 is always only one direction (hereinafter referred to as “forward direction”). ). However, for some reason, the casting may be stopped for several tens of seconds to several minutes or tens of minutes, and then, for example, when the casting is restarted, the slab 5 shrinks with a decrease in temperature. The measuring roll 7 is reversed. In such a case, the pulse generator 8 that can measure only the amount of movement in the normal rotation direction also counts in the normal rotation direction even in the case of reverse rotation.
[0018]
Therefore, in general, a two-phase output type pulse generator 8 that can determine the direction of a pulse is used. However, even when the two-phase output type pulse generator 8 is used, the purpose of use of the This is a length measurement for cutting into lengths, and since it is only necessary to have the necessary precision for measuring the cut length, as described above, one pulse usually has a resolution of about 0.5 to 1 mm. Things have been adopted.
[0019]
However, when the abnormal behavior of the slab, that is, the shearing phenomenon, occurs, no matter how the two-phase output type pulse generator 8 is used, the abnormal behavior of the slab, that is, the shearing phenomenon, can be detected in the above-described normal usage. Can not. In addition, since the minimum amount of the shearing action is about 0.1 mm, it is detected by the pulse generator 8 of the measuring roll 7 used for length measurement for cutting the normal slab 5 to a predetermined length. Can not.
[0020]
Therefore, in the method for detecting an abnormal behavior of a slab during continuous casting according to the present invention, for example, a high-resolution two-phase output type pulse generator 8 in which one pulse has a resolution of 0.01 mm to 0.2 mm is used. In this way, a fine shark amount is accurately detected.
[0021]
That is, in the method for detecting abnormal behavior of a slab during continuous casting according to the present invention, the two-phase output pulse sent from the high-resolution pulse generator 8 is taken into the abnormal behavior determining circuit 9, and the abnormal behavior determining circuit 9 detects the abnormal behavior. As shown in FIG. 3B, the magnitude of the amount (shear amount) and its movement, that is, one pulse or several pulses in the anti-casting direction after several to several tens of pulses continue as shown in FIG. Is detected, that is, if the detected two-phase pulse is a reverse rotation pulse in the anti-casting direction, and if it begins to exist in the normal rotation pulse in the casting direction, the The abnormal behavior of the piece 5 is determined. According to the method for detecting an abnormal behavior of a slab 5 at the time of continuous casting according to the present invention, it becomes possible to detect the shear behavior of a slab of at least about 0.1 mm with high accuracy.
[0022]
Further, the method for controlling casting conditions during continuous casting according to the present invention includes detecting the abnormal behavior of a slab by the above-described method for detecting abnormal behavior of a slab during continuous casting according to the present invention, and then detecting the detected abnormal behavior amount. (1) As shown in FIG. 2 (a), the oscillation frequency (solid line) is increased, the amplitude (dashed line) is reduced, and the amount of powder input (dashed line) 2) As shown in FIG. 2 (b), the casting speed (two-dot chain line) and the oscillation frequency (solid line) are reduced, and the oscillation amplitude (dashed line) and the powder It increases the input (dash-dot line).
[0023]
That is, in the method of controlling casting conditions during continuous casting according to the present invention, the abnormal behavior of the slab 5 detected as described above is analyzed by the abnormal behavior determining circuit 9 and the abnormal behavior is determined based on the analyzed abnormal behavior amount. That is, in order to eliminate the shearing force, the oscillation frequency and amplitude, the powder input amount, and, if necessary, the pouring speed are calculated in proportion thereto.
[0024]
Then, based on the data calculated and calculated, the steady state (the oscillation frequency is linked to the casting speed, and the amplitude is a value determined in advance by the casting size and the steel type, so as to become the value calculated and calculated. Since the quality of the powder deteriorates due to entrainment in the molten steel in the mold, the powder is usually controlled with a minimum amount of injection in order to prevent seizure.) A control signal is transmitted to the oscillation control device 10 and the powder supply control device 13 in order to correct the amplitude value, the amount of powder input from the powder supply device 12 and, if necessary, the pouring speed, thereby causing a shaking phenomenon. To stop.
[0025]
In FIG. 1, 11a is an oscillation table, 11b is a stepping cylinder, 11c is a stepping motor, and 11d is a drive unit, and these constitute the oscillation device 11. Reference numeral 14 denotes a pinch roll, and reference numeral 15 denotes a transport roller.
[0026]
When an abnormal behavior (shaking phenomenon) as shown in FIG. 3 (b) is detected by the method of the present invention, the steady state is proportional to the amount of abnormal behavior by the method of the present invention as shown in FIG. 3 (a). When the oscillation frequency was increased and the amplitude was decreased, and the amount of powder injected into the mold was increased from the steady state in proportion to the abnormal behavior amount, the result was shown in FIG. 3 (b). As such, the abnormal behavior has ceased.
[0027]
That is, according to the present invention, since the excessive frictional force between the shell of the molten steel in the mold and the inner surface of the mold is eliminated, the seizure is avoided immediately before the seizure. In addition, it is possible to prevent breakout more effectively while preventing quality deterioration due to excessive powder input.
[0028]
FIG. 3 (c) shows that thermocouples are embedded in a mold in order to prevent breakout, and the temperature behavior of these thermocouples is monitored during casting, and an abnormal temperature or an abnormal temperature rise rate occurs. This is an abnormality determination signal by a breakout prediction device that predicts a breakout or issues an alarm in the case, and the occurrence position of the abnormality determination signal and the detection position of the abnormal behavior according to the present invention shown in FIG. It turns out that it is.
[0029]
【Example】
Hereinafter, the results of experiments performed to show the effects of the method for detecting abnormal behavior of a slab and the method for controlling casting conditions during continuous casting according to the present invention will be described.
FIG. 1 is a diagram showing a schematic configuration of a continuous casting machine for carrying out the method of the present invention. Explaining the case of the round cast slab, the molten steel injected into the mold 4 from the tundish 1 can control the level of the molten metal in the mold 4 by appropriately controlling the opening of the sliding gate 2 of the immersion nozzle 3. Has been stabilized.
[0030]
The oscillation device 11 is operated at a predetermined amplitude (stroke) and a frequency in synchronization with the casting speed at the same time as the casting is started by a signal from the oscillation control device 10. The start of pouring is guided by a dummy bar (not shown), and the dummy bar is removed after the last-stage pinch roll 14, and thereafter, only the slab 5 is pulled out.
[0031]
A high-resolution pulse generator 8 is installed on a measuring roll 7 for counting the cutting length for cutting into a predetermined length by a cutting machine 6, and its two-phase output is taken into an abnormal behavior judging circuit 9 to cause abnormal behavior. Is analyzed. The content of this analysis is the determination of the absolute value of the abnormal behavior amount and its direction (forward direction pulse and reverse direction pulse). The analysis is based on the frequency linked to the casting speed, the casting size, and the amplitude (stroke) set by the steel type The change is notified to the oscillation device 11 that is being operated.
[0032]
FIG. 3 shows that, as described above, when the abnormal behavior shown in (b) occurs, the frequency and amplitude of the oscillation as shown in (a) are proportional to the amount of abnormal behavior obtained by the above-described analysis. The abnormal behavior was eliminated by making the amplitude smaller than the normal value, increasing the frequency, and increasing the amount of powder injected into the mold 4 from the normal state in proportion to the abnormal behavior amount. It is a case.
[0033]
In FIG. 3, the two-phase pulses for detecting the normal rotation and the reverse rotation detected by the high-resolution pulse generator 8 of the measuring roll 7 are represented as A-phase and B-phase, respectively (see FIG. 3B). This is a two-pulse signal having a phase difference of degree, in which case the A phase appears earlier in time and the B phase appears later by 90 degrees. This case indicates that the pulse generator 8 is rotating in the normal rotation direction. However, this indicates that the pulse generator 8 has reversed when the B phase appears first, and at this time, it indicates that the slab 5 is abnormally behaving in a so-called sheared state.
[0034]
FIG. 4 shows an example in which the casting speed is also controlled. In this case, when the pulse generator 8 of the measuring roll 7 shown in FIG. 3 detects the shearing phenomenon while operating at the casting speed of 3 m / min, the casting speed is reduced to 3 m as shown in FIG. / Min rapidly decreases from 0.5 m / min to 0.5 m / min, the amplitude of the oscillation is increased from a stroke of 4 mm to 8 mm as shown in FIG. 4 (a), and the frequency is shown in FIG. 4 (b). As described above, the casting speed is reduced rapidly from 200 (cycles / minute) to 25 (cycles / minute) as well as the casting speed is reduced, and this state is maintained for 10 seconds, and thereafter, at the predetermined rate during the return time, respectively. This is an example of a return in conjunction with the casting speed.
[0035]
As described above, when the abnormal behavior of the slab, that is, the shaking phenomenon, occurs, the amplitude and frequency of the oscillation and the pouring speed are changed from the steady state in proportion to the amount of the abnormal behavior that has occurred, thereby constraining the inside of the mold. The phenomenon could be eliminated. As described above, as a result of performing various casting tests, the abnormal behavior amount of the slab and the termination thereof, that is, the casting speed, the mold powder amount, the oscillation frequency, the oscillation frequency to reduce the risk of breakout, FIG. 2 is a graph of the relationship with the amplitude.
[0036]
【The invention's effect】
As described above, according to the present invention, {circle around (1)} shank of a slab occurs during casting, and if it is permitted, a flaw on the slab surface is generated. In the worst case, a breakout will occur immediately below the mold, and (2) if the slab is shaking against the cutting torch of the cutting machine that is cutting to a predetermined length, The quality of the cut surface deteriorates because the slab always shrinks, and if it is bad, it can not be processed well when marking or marking the cut surface to identify the slab cut in the subsequent process By reducing the problem, the cross-sectional shape of the slab can be cast to a more perfect circle, and when the slab of the slab is generated, it can be promptly prevented. Scratching or blurring of slab It is possible to prevent the prevention and properties deterioration of the slab cut surface of the checkout.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a continuous casting machine for implementing a method of the present invention.
FIGS. 2 (a) and 2 (b) are graphs showing the relationship between the abnormal behavior amount of the slab and the casting speed, mold powder amount, oscillation frequency, and oscillation amplitude that terminate the abnormal behavior amount.
3A is a diagram showing an example in which the frequency of the oscillation is increased and the amplitude is decreased from the steady state in proportion to the amount of abnormal behavior shown in FIG. 3B, and FIG. FIG. 4C is a diagram illustrating an example of (shake phenomenon), and FIG. 4C is a diagram illustrating an abnormality determination signal by a breakout prediction device.
FIG. 4A shows an example in which the amplitude of the oscillation is increased from the steady state in proportion to the abnormal behavior amount, and FIG. 4B shows an example in which the frequency of the oscillation is similarly decreased. FIG. 3C is a diagram showing an example in which the casting speed is similarly reduced.
[Explanation of symbols]
5 Slab 9 Abnormal behavior determination circuit 10 Oscillation control device 13 Powder supply control device

Claims (4)

The amount of movement of the slab in the casting direction and the counter casting direction during continuous casting performed while performing mold oscillation is measured, and after the pulse in the casting direction continues for several pulses to several tens of pulses, the pulse in the counter casting direction is changed to 1 pulse. A method for detecting abnormal behavior of a slab during continuous casting, wherein it is determined that abnormal behavior, which is vibration of the slab caused by oscillation, has occurred when a pulse or a few pulses are detected. 2. The slab according to claim 1, wherein the amount of movement of the slab in the casting direction and the counter casting direction during the continuous casting to be measured has a resolution of 0.01 to 0.2 mm per pulse. Abnormal behavior detection method. After detecting the abnormal behavior of the slab by the method according to claim 1 or 2, the oscillation frequency is increased and the amplitude is decreased in proportion to the detected abnormal behavior amount, based on the constant casting speed. And a method for controlling casting conditions during continuous casting, wherein the amount of mold powder charged is increased. After detecting an abnormal behavior of the slab by the method according to claim 1 or 2, the casting speed is reduced in proportion to the detected abnormal behavior amount to reduce the oscillation frequency and the oscillation amplitude. And a method of controlling casting conditions during continuous casting, characterized by increasing the amount of mold powder charged.

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