JPH1183814A - Solidification state detecting method for cast piece device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately find a solidification state, for example, a central solid phase rate. SOLUTION: A transverse ultrasonic wave is made incident on a cast piece S from an electromagnetic ultrasonc transmitting element 1a of a transmitting probe 1, a received signal from an electromagnetic ultrasonic receiving element 2a of a receiving probe 2 is fed to a transmitted signal measuring circuit 7, and the circuit 7 computes the intensity of the transverse ultrasonic wave. A lift-off data obtained from eddy current type range finders 1b/2b is taken in an operation circuit 8 to correct intensity of the transverse ultrasonic wave. A central solid phase rate is calculated from the corrected intensity of the transmitted transverse ultrasonic wave to be output to a measured result outputting device 9. The device 9 finds a pressure data corresponding to a computed result from the operation circuit 8 based on a preliminarily given relation between a central solid phase rate and a drafting rate to be output to rolling rolls 32, 32.

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 the solidification state of a continuously cast slab by obtaining information such as the ratio of the solid phase in the center, and an apparatus used for implementing the method.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 3, a molten metal 23 is poured from a tundish 21 into a mold 22 having a predetermined sectional shape, and a molten portion 24 and a solidified portion 25 are mixed. This is performed by continuously drawing the cast slab S from below the mold 22. Immediately after being drawn from the mold 22, the slab S has a large portion of the unsolidified molten portion 24 occupying the inside, but as the solidification progresses due to the subsequent cooling, the ratio of the solidified portion 25 increases. And the whole solidifies.

[0003] In this cooling process, it is necessary to prevent a breakout accident in which the molten portion 24 inside breaks the solidified portion 25 outside and leaks to the outside, and to reduce center segregation to improve quality. Is important, and it is necessary to extract at the maximum drawing speed in order to improve productivity.

Therefore, conventionally, as shown in FIG.
A method of actually driving a stud 31 in the thickness direction and then cutting the cast piece S at the position of the stud 31 to determine the internal melting state is performed. Fused portion 24 inside slab S
A trace of melting is seen at the portion of the stud 31 that has come into contact with, so that the presence or absence of the fused portion 24 can be determined.

As shown in FIG. 5, there is a method in which a slab S is sandwiched between rolling rolls 32, 32 from both sides, and a load change applied to the rolling roll 32 is detected by a load load meter 33 to estimate the internal condition. . This method utilizes the fact that the expansion force of the slab S changes when the melting state inside the slab S changes. However, it has not yet been put to practical use because it can only detect abnormalities without directly measuring the melting state.

Further, in Japanese Patent Application Laid-Open No. 62-148852, a transverse ultrasonic wave is applied from the transmitter 35 in the thickness direction of the slab S,
A method of estimating the internal solidification state from the intensity of the shear wave ultrasonic wave transmitted through the slab S and received by the receiver 36 (FIG. 6) is disclosed. This method utilizes the property that the transverse wave does not propagate in the liquid, and when the liquid, that is, the molten portion 24 is present, the transverse wave ultrasonic wave is not received by the receiver 36, and the inside is completely coagulated. In this case, the transmitted transverse ultrasonic waves are received by the receiver 36.

[0007]

In a continuous cast slab, a center segregation, called a W-shaped crater end, as shown in FIG. 7 is apt to occur. Worsen. Therefore, as described above, it is necessary to reduce the center segregation in order to improve the product quality. For this reason, the control of applying light pressure by the rolling rolls 32, 32 (FIG. 5) is performed. As shown in FIG. 8, it has been found that the slab S must be strictly controlled by the solidification state (central solid fraction).

[0008] However, it is difficult to obtain the central solid fraction by the conventional method. In the method using the studs 31 as shown in FIG. 4, only the situation at the position where the studs 31 are driven can be obtained, and information cannot be obtained in real time.

Although the method shown in FIG. 6 can theoretically estimate the center solid fraction, the actual distance (lift-off) between the transmitter 35 and the receiver 36 and the slab S fluctuates. Therefore, the output fluctuates, and it is difficult to obtain accurate information.

The present invention has been made in view of the above circumstances, and measures the intensity of transmitted transverse ultrasonic waves in a slab, simultaneously detects lift-off, and corrects the measured intensity to obtain a solidified state. For example, it is an object of the present invention to provide a method for detecting a solidification state capable of accurately determining a center solid fraction and an apparatus used for carrying out the method.

[0011]

[Means for Solving the Problems] FIG.
It is a graph which shows the lift-off characteristic of the received signal intensity in a thick Pb cast piece. For the 50 mm thick Pb slab, the lift-off decreased at a rate of about -17% / mm in the range of 10 to 26 mm. In the case of the Pb slab having a thickness of 100 mm, the lift-off was reduced at a rate of about -16.5% / mm in the range of 5 to 16 mm. From this graph, it can be seen that the received signal strength fluctuates greatly due to lift-off regardless of the difference in thickness.

Table 1 shows the results of investigating the effects of various conditions on the received signal strength. 'Lift off'
It is obtained by changing the lift-off between the sensor and the sample using a cold sample and measuring the sensor output at that time. The effects of the 'slab (slab) thickness' and the 'sensor temperature' indicate the maximum value of the width that fluctuates in the operation line, and the measured values are much smaller. The 'solid phase ratio evaluation error' is a relation between the sensor output and the central solid phase ratio in advance (for example, when the central solid phase ratio is between 0.7 and 1.0, the received signal intensity changes to an average of 2 to 6 V). ) Was calculated, and the output error when various conditions were changed was converted into the central solid phase ratio.

The influence value (1) was similarly obtained by assuming the current operation as shown in the table. That is, the lift-off change is 0.3 mm or less, the slab thickness change is 3 mm or less, and the temperature change in the sensor is 20 mm or less.
℃ or below. The influence value (2) is a result of similarly examining the influence when a distance meter is installed in the sensor.

[0014]

[Table 1]

In the influence value (1), the influence of the slab thickness is large, but since this information can be obtained through the process computer in the operation line, it can be corrected relatively easily. When a distance meter is installed in the sensor, the temperature in the sensor may increase. However, the influence of the temperature on the measurement accuracy (solid-state-ratio evaluation error) is so small that it can be neglected.

Therefore, according to the first aspect of the present invention, a transverse wave ultrasonic wave is transmitted from a transmitter in a thickness direction of a continuously cast slab, and a transmitted transverse wave ultrasonic wave transmitted through the slab is received. In the method for detecting the solidification state of the slab, by receiving the transmitted transverse wave ultrasonic wave, the distance between the transmitter and the slab when transmitting the transverse wave ultrasonic wave is measured, and the transmitted transverse wave ultrasonic wave is received. And measuring the distance between the receiver and the slab at the time of performing the correction and correcting the intensity of the transmitted transverse ultrasonic wave received using the distance.

According to a third aspect of the present invention, a transverse wave ultrasonic wave is transmitted from a transmitter in a thickness direction of a cast piece to be continuously cast, and a transmitted transverse ultrasonic wave transmitted through the cast piece is received by a receiver. In the apparatus for detecting the solidification state of the cast slab, the distance measuring means for measuring the distance between the transmitter and the cast slab when the shear wave ultrasonic wave is transmitted; and Distance measuring means for measuring the distance between the receiver and the slab when receiving a sound wave, and means for correcting the intensity of the transmitted transverse ultrasonic wave received using these distances, I do.

Since the intensity of the transmitted transverse ultrasonic wave which fluctuates greatly due to the lift-off is corrected by the measured value of the lift-off, it is possible to obtain a reception signal which is free from the influence and accurately indicates the solidification state in the slab. it can.

According to a second aspect of the present invention, in the first aspect, the central solid phase ratio is calculated from the corrected intensity using a predetermined arithmetic expression.

The invention according to a fourth aspect is characterized in that, in the third aspect, there is provided means for calculating the central solid phase ratio from the corrected intensity using a predetermined arithmetic expression.

By rolling the slab with a pressing force corresponding to the obtained center solid fraction, center segregation is effectively suppressed,
For example, it is possible to manufacture a high-quality cast piece having no W-shaped crater end.

According to a fifth aspect of the present invention, in the third or fourth aspect, the distance measuring means is an eddy current type distance meter,
It is characterized in that it is built in the transmitter and the receiver.

The hot distance measurement can be performed without contact, and even when a protective plate such as a metal plate is interposed between the object and the object to be measured.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. Embodiment 1 FIG. FIG. 1 is a block diagram showing a configuration of a device for detecting a solidification state of a slab according to the present invention. The transmitting probe 1 is equipped with an electromagnetic ultrasonic transmitter 1a and an eddy current type distance meter 1b, and the receiving probe 2 is equipped with an electromagnetic ultrasonic receiver 2a and an eddy current type distance meter. 2b is installed. The electromagnetic ultrasonic transmitter 1a and the electromagnetic ultrasonic receiver 2a are connected to an excitation power source 3 for driving these electromagnets, and the pulsar 4 for driving the electromagnetic ultrasonic transmitter 1a is connected to the electromagnetic ultrasonic transmitter 1a. Have been. An amplifier 5 for amplifying a signal output from the electromagnetic ultrasonic receiver 2a is connected to the electromagnetic ultrasonic receiver 2a, and the output signal is supplied to a transmission signal measuring circuit 7.

The excitation power supply 3, pulser 4, amplifier 5, and transmission signal measuring circuit 7 are connected to a synchronizing circuit 6 for synchronizing the operation timing. Transmission signal measurement circuit 7,
The output signals of the eddy current rangefinders 1b and 2b are supplied to a calculation circuit 8, and the calculation results are appropriately processed by a measurement result output device 9 and output.

The operation when the transmitting probe 1 and the receiving probe 2 are mounted on the front side and the back side of the slab S at appropriate intervals as shown in FIG. 1 will be described. Excitation power supply 3
The transverse ultrasonic waves generated by the electromagnets excited by the
At the output timing of the electromagnetic probe of the transmitting probe 1
It is made to enter the slab S from 1a. The electromagnetic ultrasonic receiver 2a of the receiving probe 2 driven in synchronization with this timing
Is amplified by the amplifier 5 and supplied to the transmission signal measuring circuit 7. The transmission signal measuring circuit 7 reads the maximum amplitude value of this signal and calculates it as the intensity of the shear wave ultrasonic wave.

On the other hand, data on the distance between the transmitting probe 1 and the surface of the casting S at the time of ultrasonic transmission, which is obtained from the eddy current type distance meter 1b, and the distance data obtained from the eddy current type distance meter 2b. The arithmetic circuit 8 fetches data on the distance between the receiving probe 2 and the back surface of the slab S at the time of sound wave reception, and corrects the intensity of the shear wave ultrasonic wave based on the lift-off data. Then, from the corrected intensity V of the transmitted transverse ultrasonic wave, the central solid phase ratio P is calculated by, for example, equation (1) and output to the measurement result output device 9. Here, the lift-off measurement data is L, and C1, C2, C
Let 3 be a constant. P = C1 * (V−C3 * L) + C2 (1) The measurement result output device 9 calculates an arithmetic circuit based on a predetermined relationship between the center solid phase ratio and the reduction amount as shown in FIG. 8 is obtained and output to the rolling rolls 32, 32... The rolling rolls 32 press the slab S with the supported pressure.

The precision of the lift-off measurement in the apparatus of the present invention shown in FIG. 1 was 0.05 mm. Further, the center solid phase ratio was actually obtained using the conventional apparatus shown in FIG. 6 and the apparatus shown in FIG. As a result, the accuracy of evaluation of the center solid fraction was improved from 0.27 to 0.11. Further, continuous casting was performed while rolling by the roll 32 using the obtained center solid phase ratio. As a result, the non-defective product rate was greatly improved.

Embodiment 2 FIG. 2 is a block diagram showing a configuration of a device for detecting a solidified state of a slab according to a second embodiment. The transmitting probe 1 and the receiving probe 2 are not provided with an eddy current type distance meter.
a, impedance meters 11 and 21 for measuring the impedance change of the electromagnetic ultrasonic receiver 2a, and the electromagnetic ultrasonic transmitter 1
a, when the electromagnetic ultrasonic receiver 2a is used as a distance meter, these impedances are
Switchers 12 and 22 for inputting the signals to 1 and 21 are provided. Distance data obtained from the impedance meters 11 and 21 is input to the arithmetic circuit 8. Other configurations are the same as those of the first embodiment, and the same reference numerals are given and the description is omitted.

The operation when the transmitting probe 1 and the receiving probe 2 are mounted on the front side and the back side of the slab S at appropriate intervals as shown in FIG. 2 will be described. Excitation power supply 3
The transverse ultrasonic waves generated by the electromagnets excited by the
At the output timing described above, the beam is made to enter the slab S from the transmission probe 1. The reception signal from the reception probe 2 driven in synchronization with this timing is amplified by the amplifier 5 and supplied to the transmission signal measurement circuit 7. The transmission signal measuring circuit 7 reads the maximum amplitude value of this signal and calculates it as the intensity of the shear wave ultrasonic wave.

On the other hand, each time the switches 12 and 22 measure the intensity of the shear wave ultrasonic wave, the switching is performed, and the electromagnetic ultrasonic wave transmitter 1a,
The impedance of the electromagnetic ultrasonic receiver 2a is input to the impedance meters 11 and 21. Then, the impedance meter 11 measures a change in impedance, obtains data on the distance between the transmitting probe 1 and the surface of the slab S during ultrasonic transmission, and supplies the data to the arithmetic circuit 8. The impedance meter 12 measures the change in impedance, obtains data on the distance between the transmission probe 2 and the back surface of the slab S during ultrasonic transmission, and supplies the data to the arithmetic circuit 8. The arithmetic circuit 8 uses the distance data (lift-off data) to correct the intensity of the shear wave ultrasonic wave from the transmission signal measuring circuit 7. Then, the central solid fraction is calculated from the corrected intensity of the transmitted transverse ultrasonic wave,
Output to the measurement result output device 9. Measurement result output device 9
Calculates pressure data corresponding to the calculation result from the calculation circuit 8 based on the relationship between the center solid phase ratio and the reduction amount as shown in FIG. Output. The rolling rolls 32 press the slab S with the supported pressure.

The precision of the lift-off measurement in the apparatus of the present invention shown in FIG. 2 was 0.1 mm. Further, the center solid phase ratio was actually obtained using the conventional apparatus shown in FIG. 6 and the apparatus shown in FIG. As a result, the evaluation accuracy of the center solid phase ratio was improved from 0.27 to 0.1. Further, when the continuous casting was carried out while rolling with the rolling roll 32 using the obtained center solid phase ratio, the yield rate was slightly lower than that of the first embodiment, but far higher than the conventional one.

[0033]

As described above, the method for detecting the solidification state of a slab according to the present invention and the apparatus used for carrying out the method measure the intensity of transmitted transverse ultrasonic waves in the slab and simultaneously detect lift-off to obtain the intensity. By correcting the measured values, the effect of lift-off has been removed, it is possible to obtain a reception signal that accurately indicates the solidification state in the slab, and it is possible to accurately determine the solidification state, for example, the center solid fraction. For example, the present invention has excellent effects.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an apparatus for detecting a solidified state of a slab according to a first embodiment.

FIG. 2 is a block diagram showing an apparatus for detecting a solidified state of a slab according to a second embodiment.

FIG. 3 is a schematic sectional view showing a configuration of a continuous casting machine.

FIG. 4 is a schematic view showing a conventional method for detecting a solidification state of a slab.

FIG. 5 is a schematic view showing a conventional method for detecting a solidification state of a slab.

FIG. 6 is a schematic view showing a conventional method for detecting a solidification state of a slab.

FIG. 7 is a schematic diagram showing a state of occurrence of a W-shaped crater end.

FIG. 8 is a conceptual diagram of rolling control using a center solid fraction.

FIG. 9 is a graph showing a lift-off characteristic of a received signal intensity of transmitted transverse ultrasonic waves.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmitting probe 1a Electromagnetic ultrasonic transmitter 1b, 2b Eddy current type distance meter 2 Receiving probe 2a Electromagnetic ultrasonic receiver 7 Transmission signal measuring circuit 8 Arithmetic circuit S Cast piece

Claims (5)

[Claims] 1. A transverse wave ultrasonic wave is transmitted from a transmitter in a thickness direction of a slab to be continuously cast, and a transmitted transverse wave ultrasonic wave transmitted through the slab is received by a receiver. In the method for detecting the solidification state of the slab, the distance between the transmitter and the slab when transmitting the shear wave ultrasonic wave is measured, and the receiver when the transmitted transverse wave ultrasonic wave is received. A method for detecting a solidification state of a slab, comprising measuring a distance from the slab and correcting the intensity of the transmitted transverse ultrasonic wave received using the distance. 2. The method for detecting a solidified state of a slab according to claim 1, wherein the central solid phase ratio is calculated from the corrected intensity using a predetermined arithmetic expression. 3. A transverse wave ultrasonic wave is transmitted from a transmitter in a thickness direction of a cast piece to be continuously cast, and a transmitted transverse wave ultrasonic wave transmitted through the cast piece is received by a receiver. In a device for detecting the solidification state of the slab, a distance measuring means for measuring the distance between the transmitter and the slab when transmitting the shear wave ultrasonic wave, and when receiving the transmitted shear wave ultrasonic wave A solidification state of the slab, comprising: a distance measuring unit that measures a distance between the receiver and the slab; and a unit that corrects the intensity of the transmitted transverse ultrasonic wave received using these distances. Detection device. 4. The apparatus for detecting a solidified state of a slab according to claim 3, further comprising means for calculating a central solid fraction from the corrected intensity using a predetermined arithmetic expression. 5. The apparatus according to claim 3, wherein the distance measuring means is an eddy current type distance meter, and is incorporated in the transmitter and the receiver. .