JPS6027361B2 - How to measure the thickness of conductive materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the thickness of a conductive material using ultrasound.

For products such as steel, thickness measurement is an essential inspection item for quality assurance, and various thickness measurement devices are used.

Among these, ultrasonic thickness gauges can measure thickness simply by touching the surface of the material to be measured with an ultrasonic transmitter/receiver, and since the ultrasonic transmitter/receiver is small, it is possible to measure the thickness of a material in a narrow range. It has the characteristics of being able to measure thickness with relatively simple electrical signal processing and being able to measure thickness with high precision, and has been widely applied in recent years and plays an important role in thickness measurement. on the other hand,
In addition to measuring the thickness of the product, we also measure the thickness during the manufacturing process. For example, we measure the thickness during or immediately after rolling to discover problems such as poor rolling early and provide feedback to the rolling operation. This allows quality control in the manufacturing process.

To this end, there is a need for a thickness gauge that can accurately measure thickness during manufacturing processes, particularly during hot treatment processes such as casting and rolling, and high-speed processing processes such as continuous rolling. However, ultrasonic thickness gauges using conventional piezoelectric ultrasonic transmitters and receivers require contact substances such as water and oil as the ultrasonic transmission medium to the material being measured, and are also difficult to measure the thickness of high-temperature materials. This requires a special high-temperature ultrasonic transceiver with a heat-resistant material attached to the front of the transducer.

However, even if this high-temperature ultrasonic transceiver is used, the applicable temperature is limited to approximately 500° C., and long-term measurement is not possible. Furthermore, since the sound velocity of the heat-resistant material changes significantly depending on the temperature, there is a drawback that the accuracy of thickness measurement is low. Furthermore, even in the case of thickness measurement of cold materials, it is extremely difficult to apply the method to processes where the material to be measured moves at high speed, such as continuous rolling processes. Another object of the present invention is to provide a thickness measurement method that solves the drawbacks of thickness measurement using an ultrasonic thickness gauge using the above-mentioned follower-type piezoelectric ultrasonic transmitter/receiver.

The first aspect of the present invention to achieve this object is to provide a thickness measurement method using ultrasonic waves that measures the thickness of a material by measuring the propagation time of ultrasonic waves in the material. Using an electromagnetic ultrasonic transmitter/receiver consisting of a coil, the propagation time of transverse mode ultrasonic waves and the propagation time of longitudinal wave mode ultrasonic waves in the material to be measured are determined, and the two modes are determined from the ratio of the two propagation times. On the other hand, the relationship between the sound speed of each mode and the sound speed ratio of both modes at different temperatures for a material of the same quality as the material to be measured is determined in advance, and the sound speed ratio obtained for the material to be measured and From the relationship between the previously determined sound speed and the sound speed ratio, the sound speed of the ultrasonic wave in transverse wave mode or longitudinal wave mode corresponding to the temperature of the material to be measured is determined, and from the sound speed and the measured propagation time, the sound speed of the ultrasonic wave to be measured is determined. This is a method for measuring the thickness of a conductive material, which is characterized by determining the thickness of the material. below,
The present invention will be explained in detail based on illustrated embodiments.

FIG. 1 is a diagram showing a device configuration in a first embodiment of the present invention, FIG. 2 is a diagram showing a time chart of signals of each part of the device in FIG. 1, and FIG. 3 is a diagram showing longitudinal wave modes and transverse waves in steel materials. FIG. 3 is a diagram showing the relationship between the sound speed of ultrasonic waves in a mode and the sound speed ratio. As shown in FIG. 1, an electromagnetic ultrasonic transceiver A that transmits and receives longitudinal wave mode ultrasonic waves is constructed by disposing a transmitting/receiving coil 3 on an electromagnet consisting of a magnetic core 1 and an excitation coil 2 as shown in the figure, and a magnetic core. An electromagnetic ultrasonic transmitter/receiver B, which transmits and receives transverse mode ultrasonic waves, is connected to the surface of the conductive material to be measured 10 by disposing a transmitting/receiving coil 3' on an electromagnet 1' and an excitation coil 2' as shown in the figure. be placed close to.

Then, a DC or intermittent current is caused to flow from the excitation power source 200 of the excitation coils 2 and 2' of the respective ultrasonic transceivers A and B to generate a magnetic flux. In this case, the same effect can be obtained even if a permanent magnet is used instead of an electromagnet to generate magnetic flux 0, ◇'. Further, the transmitting/receiving coils 3, 3' may be one coil for both transmitting and receiving purposes, or may be composed of two coils for transmitting and receiving. When high-frequency pulses a, a' are applied from pulse generators 101, 101' driven by the synchronous circuit 10 to the transmitting/receiving coils 3, 3' of the ultrasonic transmitting/receiving devices A, B, they cause damage to the surface of the material to be measured 10. A current 1,r is generated. At this time, ultrasonic vibrations F and F' are generated on the surface of the material to be measured due to the interaction between the magnetic fluxes ◇ and G' and the eddy currents 1 and 1'. This means that the vibration F is a longitudinal wave mode.
The vibration F' becomes an ultrasonic wave in a transverse wave mode, and the material to be measured 10
Propagates inside in the thickness direction. The ultrasonic vibrations that propagated inside the material to be measured 10, reflected at the bottom surface, and propagated to the surface again are transmitted to the transmitting and receiving coils 3 and 3 by interaction with the magnetic flux ◇,
′. In this way, the transmitter/receiver coil 3
, 3', the received pulse signal ,b' is obtained. Transmission pulse a,
a' and the received pulses b, b' are transmitted through the intensifier 102,
102', the waveform shaping circuit 103, 103', and the second
The signal shown in the figure c. The waveforms are shaped into c', d, and d'.
Signals c, c' and d. d' is the gate circuit 104, 104'
gate waveforms such as signals e and e' having intermediate values between signals c and d and c' and d' above the threshold level S are obtained. During the gates of these signals e and e', t,
t' has information proportional to twice the thickness of the material 10 to be measured. By ANDing these signals e, e' and the clock signal f from the clock source 105, the AND circuit 10
Pulse signals g, g' are obtained at 6, 106', these pulse signals g, g' are counted by counter circuits 107, 107', and digital signals T, T' are output. In this way, signals T and T' are obtained which are proportional to the propagation time of the ultrasonic waves in the longitudinal wave mode and transverse wave mode in the material to be measured. Next, these signals T and T' are input to the divider 108 and divided by T/T' to obtain a signal proportional to the ratio of the sound velocity V of the transverse wave mode ultrasonic wave and the sound velocity V2 of the longitudinal wave mode ultrasonic wave. obtain. Signal T/T
' is input to the calculator 109, and is converted into a signal Vs proportional to the sound speed of the ultrasonic wave in the transverse wave mode in accordance with the temperature of the material to be measured using the known relationship between sound speed and sound speed ratio as shown in FIG. Ru. On the other hand, the signal T' is divided by T'/2 by the divider 112. Next, a signal T'/2 proportional to half the propagation time of the transverse wave mode ultrasonic wave in the village to be measured and a signal Vs proportional to the sound speed of the transverse wave mode ultrasonic wave are input to the multiplier 110 and multiplied. A signal proportional to the thickness of the material to be measured is obtained. This thickness signal is recorded and displayed in the recording and display circuit 111. Here, the meaning of determining the sound speed of an ultrasonic wave using the relationship between the sound speed and the sound speed ratio in FIG. 3 will be explained.

Generally, in the case of a turtle-conducting material, as the temperature increases, the sound speed of the ultrasonic wave becomes smaller, and the ratio of the sound speed of the longitudinal wave mode ultrasonic wave to the sound speed of the transverse wave mode ultrasonic wave also becomes smaller. That is,
The sound speed and sound speed ratio of ultrasonic waves are both functions of the temperature of the material being measured. Since the sound speed ratio can be easily determined from the propagation time ratio even when the thickness of the material to be measured is unknown, the sound speed and sound speed ratio at each temperature were measured in advance for the same material as the material to be measured, and as shown in Figure 3. If you obtain the relationship shown in Figure 1, you can calculate the sound speed of the ultrasonic waves in the longitudinal and transverse modes corresponding to the temperature of the material to be measured from the sound speed ratio described above, without having to measure the temperature of the material to be measured each time. can be determined accurately. Next, a second embodiment of the present invention will be described.

4 and 5 are diagrams explaining the reflection behavior of ultrasonic waves, FIG. 6 is a diagram showing the device configuration in the second embodiment of the present invention, and FIG. 7 is a diagram showing signals of various parts of the device in FIG. 6. FIG. 2 is a diagram showing a time chart of FIG. In Figures 4 and 5, 10
' is the bottom surface of the material to be measured, D is the traveling direction of the ultrasonic wave in the longitudinal wave mode, D' is the traveling direction of the ultrasonic wave in the transverse wave mode, F is the vibration direction of the ultrasonic wave in the longitudinal wave mode, and F' is the traveling direction of the ultrasonic wave in the shear wave mode. Each shows the vibration direction of the ultrasonic wave. From Fig. 4 and Fig. 5, when the ultrasonic wave is reflected from the bottom surface 10' of the material to be measured, the bottom surface 1
0' is not a perfect plane but a curved surface as shown in the figure. In this state, the ultrasonic vibration direction at point P and point P2 is F
and has a component indicated by F'. That is, a portion of the longitudinal wave mode ultrasonic wave is converted to a transverse wave mode ultrasonic wave, and a portion of the transverse wave mode ultrasonic wave is converted to a longitudinal wave mode ultrasonic wave, and each of the ultrasonic waves is reflected. Therefore, signals received using a longitudinal wave mode or transverse wave mode ultrasonic transmitter include both longitudinal wave mode ultrasonic waves and transverse wave mode ultrasonic waves. Therefore, in the second embodiment, a transverse wave mode or longitudinal wave mode ultrasonic wave is transmitted from one ultrasonic transceiver, and the transverse wave mode ultrasonic wave and the longitudinal wave mode ultrasonic wave reflected from the bottom surface are simultaneously transmitted. The system receives and processes the signals to determine the thickness of the material to be measured. That is, as shown in FIG. 6, an electromagnetic ultrasonic transceiver B for transverse wave mode, which has a transmitter/receiver coil 3' arranged as shown in an electromagnet consisting of a magnetic core 1' and an excitation coil 2', is connected to a conductive object to be measured. It is placed close to the surface of the material 10. Then, as described with reference to FIG. 1, ultrasonic waves in transverse wave mode are transmitted to the material to be measured 10. As explained in FIG. 5, a portion of the transverse wave mode ultrasonic waves that propagate inside the material to be measured 10 and are reflected by the bottom surface 10' is converted into longitudinal wave mode ultrasonic waves and returns to the surface to boil. . The vibrations of the ultrasonic waves in the structured wave mode and the longitudinal wave mode that have propagated to the surface of the material to be measured 10 and returned in this way are magnetic flux? ′ induces a current in the transmitting/receiving coil 3′. That is, the transmitting/receiving coil 3' obtains a transverse mode ultrasonic reception pulse b' and a longitudinal wave mode ultrasonic reception pulse b''.The transmission pulse a' and the reception pulses b' and b'' are Middle vessel 102', 10
2'' and waveform shaping circuits 103' and 103'', the signal jumps to the signal shown in FIG. 7 and is waveform-shaped to d''. Signal c
', d', d'' are input to gate circuits 104', 104'', and gate waveforms such as signals e', e are obtained from these and the threshold level S. The gate t' of this signal e' has information proportional to the propagation time of the transverse mode ultrasonic wave through the thickness of the material to be measured, and the gate t' of the signal e'' has information about the thickness of the material to be measured. It has information proportional to the propagation time of ultrasonic waves propagated in transverse wave mode on the outward path and in longitudinal wave mode on the return path. By ANDing these signals e', e'' and the clock signal f from the clock 105, AND circuits 106', 106'' obtain pulse signals g, g'',
These pulse signals g', g'' are sent to the counter circuit 1 07'
, 107'', and outputs digital signals T', T''. On the other hand, the signal T' is input to the divider 112 and T'
/2 is calculated. Next, the signals T'' and T'/2 are input to the subtracter 113 and subtracted, resulting in a signal (T''-T'/2
) is obtained, and then the signals (T''-T'/2) and T'/2 are input to the divider 1o8 to perform division of m't'/2),
A signal corresponding to the sound speed ratio of ultrasonic waves in transverse wave mode and longitudinal wave mode is obtained. The signal] Koe Miyoshi/2 is input to the calculator 109, and using the relationship between the sound speed and the sound speed ratio as shown in FIG. converted.

On the other hand, by inputting and multiplying the signal T'/2, which is proportional to the half value of the propagation time of the ultrasonic wave in the transverse wave mode in the material being measured, and the signal Vs, which is proportional to the sound speed of the ultrasonic wave in the transverse wave mode, to the multiplier 1101, Obtain a signal proportional to the thickness of the material being measured. This thickness signal is recorded and displayed in the recording and display circuit 111.
Here, in the embodiment shown in FIG. 6, the case where an electromagnetic ultrasonic transceiver for transverse wave mode is used has been explained, but even if an electromagnetic ultrasonic transceiver for longitudinal wave mode is used, the material to be measured can be measured by the same means. It is possible to measure the thickness of In actual measurement, for example, on a steel rolling line, especially a hot rolling line, the temperature of the material to be measured varies from room temperature to 1000 m depending on the size and type of the rolled material, as well as the time and place of measurement.
Furthermore, even when measuring under the same conditions, the temperature is not constant for each individual steel material, so when measuring thickness on such a line, the sound velocity corresponding to the temperature of the material to be measured must be determined. If not used, sufficient thickness measurement accuracy cannot be obtained.

For example, in the case of steel, when the temperature changes by about 100 degrees, the ultrasonic sound speed changes by about 2%, resulting in an error of about 2% in the thickness measurement value. For this reason, we proposed a method to easily determine the sound speed using the sound speed ratio of ultrasonic waves in Fujinami mode and longitudinal wave mode. This method requires a simpler device than the method of measuring the surface temperature of the material to be measured and correcting the speed of sound. As described above, the present invention uses an electromagnetic ultrasonic transmitter/receiver that can be installed in a non-contact manner in measuring the thickness of a material to be measured, and the propagation time of the two ultrasonic waves in the longitudinal wave mode and the transverse wave mode. The same level of thickness measurement accuracy as measuring the temperature of the material to be measured and performing temperature correction can be easily obtained by simply using the sound velocity ratio and the temperature range applicable to the conventional ultrasonic thickness gauge. The range has been expanded, and its industrial value is high.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a diagram showing a device configuration in a first embodiment of the present invention, Fig. 2 is a diagram showing a time chart of signals of each part of the device in Fig. 1, and Fig. 3 is a diagram showing a steel material FIG. 3 is a diagram showing the relationship between the sound speed and sound speed ratio of ultrasonic waves in longitudinal wave mode and Fuji wave mode in the middle. Figure 4 is a diagram explaining the reflection behavior of ultrasonic waves in longitudinal wave mode.
Figure 5 is a diagram explaining the reflection behavior of ultrasonic waves in transverse wave mode.
FIG. 6 is a diagram showing a device configuration in a second embodiment of the present invention, and FIG. 7 is a diagram showing a time chart of signals of various parts of the device in FIG. 1, 1': Magnetic core, 2, 2': Excitation coil, 3, 3': Transmitting/receiving coil, 10: Material to be measured, 10'
: Bottom surface of the material to be measured, 100: Synchronous circuit, 101, 101'
: Pulse generator, 102, 102', 102'': Multiplier, 103, 103', 103'': Waveform shaping circuit, 104
, 104', 104'': Gate circuit, 105: Clock, 106, 106', 106'': AND circuit, 107,
107', 107'': Counter circuit, 108: Divider, 109: Arithmetic unit, 110: Multiplier, 111: Record display circuit, 1121: Divider, 113: Subtractor, 200: Excitation power supply. ShigeruFigure 2Figure 3Figure 4Figure 5Figure 7

Claims (1)

[Claims] 1. In a thickness measurement method using ultrasonic waves that measures the thickness of a material by measuring the propagation time of ultrasonic waves in the material, an electromagnetic ultrasonic transceiver consisting of a magnet and a transmitting/receiving coil is used. The propagation time of the ultrasonic wave in the transverse wave mode and the propagation time of the ultrasonic wave in the longitudinal wave mode in the material to be measured are determined, and the sound speed ratio of the two modes is determined from the ratio of both propagation times. The relationship between the sound speed of each mode and the sound speed ratio of both modes at different temperatures for the material is determined, and the sound speed ratio determined for the material to be measured and the relationship between the sound speed and the sound speed ratio determined in advance are used to determine the sound speed of the material. Conductivity characterized by determining the sound velocity of ultrasonic waves in transverse wave mode or longitudinal wave mode in accordance with the temperature of the material to be measured at the time of measurement, and determining the thickness of the material to be measured from the sound velocity and the measured propagation time. How to measure material thickness.