JP2002126860A - Abnormal behavior detecting method for cast piece in continuously casting, and casting condition controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a flaw, breakout, and deterioration of the condition of the cut face of a cast piece, by enabling the cast piece to be cast into a complete round in its cross-sectional shape and preventing an abnormal behavior of the cast piece caused by billet's vertical oscillation. SOLUTION: The traveling amounts of the cast piece 5 in the casting direction and in the reverse casting direction in the continuous casting are measured with a resolving power of preferably 0.01-0.2 mm per pulse. When one pulse or several pulses in the reverse direction is detected after several-several ten pulses in the casting direction continue, the generation of the abnormality behavior of the cast piece 5 is decided. After the detection of the abnormal behavior, the frequency of the oscillation is made to increase in proportion to the amount of the abnormal behavior, and the amplitude is made to decrease, or the casting speed and the frequency of the oscillation are made to decrease, and the amplitude of the oscillation and the inputting amount of mold powder are made to increase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting an abnormal behavior of a slab, particularly in casting of a billet or the like in continuous casting, and a condition of oscillation and a mold based on the abnormal behavior detected by the method. The present invention relates to a method for controlling casting conditions such as the amount of powder (hereinafter simply referred to as "powder").

[0002]

2. Description of the Related Art An oscillation device is installed in a continuous casting facility, in which powder is poured between molten steel and a mold so that the molten steel in the mold does not fuse to the inner surface of the mold, and the mold is moved at a predetermined frequency and stroke. Have been.
The oscillation device alleviates the friction between the mold and the molten steel to prevent breakout and prevent the surface of the slab from burning. Tokuhei 3-568
No. 24 proposes a method for improving the surface properties of a continuous cast slab, in which breakout and seizure are more effectively prevented by vibrating the mold in a non-sine waveform.

However, when a round billet, a square billet, or a small-diameter bloom is continuously cast, vibration of the 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 mold inner surface and the solidifying molten steel in the mold. This is because it may be cast while shaking in 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 slab holding force, that is, the rolling force on the slab. However, when the rolling force by the pinch roll is increased more than necessary, it becomes a cause of deteriorating the cross-sectional shape of the slab. 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 performed at a higher speed from the viewpoint of improving productivity and preventing the temperature of molten steel in a ladle and molten steel in a tundish from being lowered. A slab cooled by a water spray for cooling the slab 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.

In this case, the surface temperature of the slab whose surface located downstream from the mold has solidified becomes higher than before, and
The entire slab is soft. Therefore, it is desirable that the pinch roll holding the soft slab is 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, which is the next step, the shape of the round slab has a large effect on the uneven wall thickness of the pipe and the drilling efficiency. This is because a round billet that is as close to a perfect circle as possible is required from the viewpoint of rolling properties. Therefore, in order to ensure roundness, it is necessary to slightly reduce the pressure with a pinch roll.

[0008]

However, when the rolling force of the pinch roll is reduced, the restraining force of the slab by the pinch roll is weakened, so that the shaking phenomenon of the slab is caused by the influence of the mold oscillation as described above. Appear. 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 body have abnormal behavior of the slab due to the shank of the slab. This is because they do not always move in tune with (Shakuri).

In other words, the vibration of the main body of the torch and the vibration of the blow tube do not coincide with the time period and the amount of vibration of the torch bogie due to the minute fine vibration of the slab due to the shank. As a result, the cutting surface is deviated, and the cutting properties of the cut surface are deteriorated. 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.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems that occur due to the shearing phenomenon, and is based on a method for detecting an abnormal behavior of a slab during continuous casting, and a method for detecting the abnormal behavior of the slab. It is an object of the present invention to provide a method of controlling casting conditions such as oscillation conditions and powder input amount.

[0012]

In order to achieve the above object, the method for detecting abnormal behavior of a slab during continuous casting according to the present invention comprises a method of moving a slab in a casting direction and a counter casting direction during continuous casting. The amount is measured, and after one to several tens of pulses in the anti-casting direction are detected after a few to several tens of pulses in the casting direction continue, it is determined that abnormal behavior of the slab has occurred. This makes it possible to accurately detect the abnormal behavior of the slab, that is, the occurrence of 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 abnormal behavior of a slab during continuous casting according to the present invention measures the amount of movement of the slab in the casting direction and the counter-casting direction during continuous casting. After one to several tens of pulses have been detected, when one or several pulses are detected in the anti-casting direction, it is determined that abnormal behavior of the slab 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. 0.01 to 0.2 mm per pulse
By measuring at a resolution of, any size of abnormal behavior can be measured.

That is, in a continuous casting facility comprising a tundish 1, a sliding gate 2, an immersion nozzle 3, a mold 4 and the like as shown in FIG. A cutting machine 6 (generally, a gas-type torch) is provided for cutting. This cutting machine 6 is used for casting a slab 5
Must be cut without stopping casting,
A torch truck 6a to which a torch blowing tube 6c is attached has a clamp device 6b for cutting to a predetermined length while moving in synchronization with a slab 5 coming out at a casting speed.

As a length measuring device for measuring the cutting length when cutting by the cutting device 6, a roll called a measuring roll 7 which is in direct contact with the slab 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 rotation amount is provided on the axis of the roll.

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. This pulse generator 8 has 1000
Thousands of pulses can be output from the pulse, and the detection resolution is selected according to the precision required for length measurement. Usually, the precision required for length measurement in continuous casting equipment is 0.5 to 1 mm per pulse.
A degree is enough.

Incidentally, since the slab 5 that is continuously cast and comes out of the mold 4 is drawn out only in the pouring direction, the measuring roll 7 always rotates in only one direction (hereinafter, this will be referred to as “positive direction”). Turning 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 only in the normal rotation direction counts in the normal rotation direction even in the case of reverse rotation.

Therefore, in general, a two-phase output type pulse generator 8 capable of discriminating the direction of the pulse is used. However, even when the two-phase output type pulse generator 8 is used, the purpose of use is to the last. 5 is a length measurement for cutting to a predetermined length, and since it is only necessary to have the necessary precision for measuring the cut length, as described above,
Normally, one pulse has a resolution of about 0.5 to 1 mm.

However, when the abnormal behavior of the slab, that is, the shearing phenomenon, occurs, the abnormal behavior of the slab, that is, the shaking phenomenon, is detected by the above-described normal use method, regardless of the pulse generator 8 of the two-phase output method. Can not do it. 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 into a predetermined length. Can not.

Therefore, in the method for detecting an abnormal behavior of a slab during continuous casting according to the present invention, for example, one pulse is set to 0.0.
A high-resolution two-phase output type pulse generator 8 having a resolution of 1 mm to 0.2 mm is used, and a fine shark amount is accurately detected as follows.

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 is operated. Then, the magnitude of the abnormal behavior amount (shaking amount) and its movement, that is,
As shown in FIG. 3B, when one or several pulses in the anti-casting direction are detected after the pulse in the casting direction continues for several pulses to several tens of pulses, that is, the detected two-phase pulse is It 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, it is determined that the shaking phenomenon has started and this is regarded as an abnormal behavior of the slab 5. According to such a method for detecting abnormal behavior of the slab 5 during continuous casting according to the present invention, the minimum 0.1 m
It becomes possible to detect the shearing behavior of a cast slab of about m with high accuracy.

In the method for controlling casting conditions during continuous casting according to the present invention, the abnormal behavior of a slab is detected by the above-described method for detecting abnormal behavior of a slab during continuous casting according to the present invention. In proportion to the amount of abnormal behavior, FIG.
As shown in FIG. 2A, the oscillation frequency (solid line) is increased, the amplitude (broken line) is reduced, and the amount of powder input (dashed line) is increased. ), The casting speed (two-dot chain line) and the oscillation frequency (solid line) are reduced, and the oscillation amplitude (dashed line) and the amount of powder input (single-dot chain line) are increased.

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 based on the analyzed abnormal behavior amount. In order to eliminate the abnormal behavior, that is, the shearing force, the oscillation frequency and the amplitude, the powder input amount and, if necessary, the pouring speed are calculated in proportion thereto.

Based on the data calculated and analyzed, a 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 analyzed. In addition, since the quality of the powder is deteriorated due to entrainment in the molten steel in the mold, the oscillation is normally controlled with a minimum amount of injection in order to prevent seizure.) And a control signal to the oscillation control device 10 and the powder supply control device 13 in order to correct the pouring speed, and, if necessary, the pouring rate from the powder supply device 12 and the pouring speed. To stop the shakuri phenomenon.

In FIG. 1, reference numeral 11a denotes an oscillation table; 11b, a stepping cylinder; 11c, a stepping motor; and 11d, a drive unit. Also, 1
4 is a pinch roll and 15 is a transport roller.

When an abnormal behavior (shearing phenomenon) as shown in FIG. 3B is detected by the method of the present invention, it is proportional to the amount of abnormal behavior by the method of the present invention as shown in FIG. When the oscillation frequency was increased and the amplitude was reduced from the steady state, and the amount of powder injected into the mold was increased from the steady state in proportion to the amount of abnormal behavior, FIG. The abnormal behavior has ceased as shown in FIG.

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 more effectively prevent breakout while preventing quality deterioration due to excessive powder input.

FIG. 3 (c) shows a thermocouple embedded in a mold in order to prevent a breakout and monitoring the temperature behavior of these thermocouples during casting. Is an abnormality determination signal by a breakout prediction device that predicts a breakout or issues an alarm when a failure occurs, and the position at which the abnormality determination signal is generated and the detection position of the abnormal behavior according to the present invention shown in FIG. It turns out that they match well.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 implementing 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 opening level of the sliding gate 2 of the immersion nozzle 3 so that the level of the molten metal in the mold 4 can be improved. Has been stabilized.

The oscillation device 11 is operated at a predetermined amplitude (stroke) and frequency at the same time as the casting speed in response to a signal from the oscillation control device 10 in conjunction with the casting speed. The start of pouring is guided by pulling out with a dummy bar (not shown).
After 4, it is removed, after which only the slab 5 is withdrawn.

A high-resolution pulse generator 8 is provided on a measuring roll 7 for counting a 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. Analyze abnormal behavior with. 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.

FIG. 3 shows that, as described above, when the abnormal behavior shown in (b) occurs, the frequency and amplitude of the oscillation are converted into the abnormal behavior amount obtained by the above-described analysis as shown in (a). The amplitude is made smaller in proportion to the normal value, the frequency is increased, and the amount of powder injected into the mold 4 is increased from the normal state in proportion to the amount of the abnormal behavior. This is an example of the loss.

In FIG. 3, the two-phase pulses which are detected by the high-resolution pulse generator 8 of the measuring roll 7 to determine normal rotation and reverse rotation are represented as A-phase and B-phase, respectively (see FIG. 3B). This is a two-pulse signal having a phase difference of 90 degrees, in which case the phase A appears earlier in time and the phase B
The phases are appearing 90 degrees late. 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 indicates that the slab 5 is abnormally behaving in a so-called shaky state.

FIG. 4 shows an example in which the casting speed is further 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, FIG.
As shown in FIG. 4C, the casting speed was rapidly reduced from 3 m / min to 0.5 m / min, and the oscillation amplitude was reduced from a stroke of 4 mm to 8 mm as shown in FIG. The frequency was increased from 200 (cycles / minute) to 25 (cycles / minute) as shown in FIG.
In this case, the casting speed is decreased rapidly as in the case of the casting speed, and this state is maintained for 10 seconds, and thereafter, during the return time, each is returned at a predetermined rate in conjunction with the original casting speed.

As described above, when the abnormal behavior of the slab, that is, the shaking phenomenon, occurs, the amplitude and frequency of the oscillation and, if necessary, the casting speed are changed from the steady state in proportion to the amount of the abnormal behavior that has occurred. Was eliminated. As described above, as a result of performing various casting tests, the abnormal behavior amount of the slab and the end 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]

As described above, according to the present invention,
If the shank of the slab occurs during casting and it is allowed, a flaw on the slab surface is generated, and the worst breakout occurs in the oscillating mold or directly below the mold, If the slab has a shearing action against the cutting torch of the cutting machine that is cutting to a predetermined length, the properties of the cut surface will deteriorate because the slab always performs a shearing action against the cutting flame of the torch, bad And when engraving or marking on the cut surface to identify the slab cut in the subsequent process, it can not be processed well,
By lightly reducing the problem described above, the cross-sectional shape of the slab can be cast to a more perfect circle, and when shank of the slab occurs, it can be promptly prevented, and It is possible to prevent the occurrence of flaws and breakout of the piece and the deterioration of the properties of the cut section of the cast piece.

[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 a 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. 7C is a diagram illustrating an example of (shake phenomenon), and FIG. 9C is a diagram illustrating an abnormality determination signal by the breakout prediction device.

FIG. 4A is a diagram showing an example in which the amplitude of oscillation is increased from the steady state in proportion to the abnormal behavior amount,
(B) is a diagram showing an example in which the frequency of the oscillation is reduced, and (c) is a diagram showing an example in which the casting speed is also reduced.

[Explanation of symbols]

 5 Slab 9 Abnormal behavior judgment circuit 10 Oscillation control device 13 Powder supply control device

Claims (4)

[Claims] An amount of movement of a slab in a casting direction and a counter casting direction during continuous casting is measured, and after a pulse in the casting direction continues for several pulses to several tens of pulses, a pulse in the counter casting direction is changed to one pulse or several pulses. A method for detecting abnormal behavior of a slab during continuous casting, wherein it is determined that abnormal behavior of the slab occurs when a pulse is detected. 2. The amount of movement of the slab in the casting direction and the counter-casting direction during continuous casting to be measured is 0.
2. The method for detecting abnormal behavior of a slab during continuous casting according to claim 1, wherein the method has a resolution of 01 to 0.2 mm. 3. After detecting an abnormal behavior of a slab by the method according to claim 1 or 2, increasing the oscillation frequency and decreasing the amplitude in proportion to the detected abnormal behavior amount; And a method for controlling casting conditions during continuous casting, characterized by increasing the injection amount of mold powder. 4. After detecting an abnormal behavior of a slab by the method according to claim 1 or 2, the casting speed and the oscillation frequency are reduced and the oscillation frequency is reduced in proportion to the detected abnormal behavior amount. A method for controlling casting conditions during continuous casting, characterized by increasing the amplitude and the amount of mold powder charged.