JP2001272220A - Hot ultrasonic thickness game and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot ultrasonic thickness gage, which enables non contact and highly sensitive transmission or reception of ultrasonic waves having an inexpensive structure of the apparatus and a thickness measuring method, which enables cold measurement of the thickness of an object to be measured simply and at a high accuracy from the hot propagation time of the ultrasonic waves. SOLUTION: The hot ultrasonic thickness gage includes a pulse laser 2 for generating an ultrasonic wave 4 in an object 1 to be inspected, an electromagnetic ultrasonic sensor 3a for receiving the ultrasonic wave 4 and a radiation thermometer 7 which estimates the temperature of a measuring part of the object 1 to be inspected. The propagation time of the ultrasonic wave 4 is calculated from the waveform of the ultrasonic wave 4, received by the electromagnetic ultrasonic sensor 3a and the sound velocity of the object 1 is calculated from the temperature estimated by the radiation thermometer 7. The thickness of the object 1 is calculated by using the propagation time and the sound velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hot ultrasonic thickness gauge using a pulse laser and an electromagnetic ultrasonic sensor, and a thickness measuring method.

[0002]

2. Description of the Related Art In recent years, as the quality of steel products has increased, there has been a demand for a steel sheet having a high assurance accuracy in the thickness of an iron plate and the thickness of an iron tube. Therefore, in the manufacturing process, it is desired to measure the thickness immediately after rolling and reflect the measurement result on the manufacturing line. In response to such demands, a gamma ray thickness meter and the like have been invented, and the gamma ray thickness gauge has been installed on a production line for thick plates and the like. However, since the γ-ray thickness gauge is very expensive, it is not widely used in a line for manufacturing a small value-added product. Further, in order to measure the thickness of the iron tube, an advanced measuring method as disclosed in Japanese Patent Application Laid-Open No. Hei 6-160068 is required. Therefore, γ-ray thickness gauges are used only in limited production lines.

Therefore, as a method for measuring the thickness at low cost by hot, as disclosed in JP-A-60-53806,
A method for measuring the thickness of an object to be inspected by ultrasonic waves has been invented.
The measurement method using ultrasonic waves can be applied to the measurement of the thickness of a steel pipe, and has the advantage that equipment is not expensive as in a γ-ray thickness gauge.

However, the method for measuring the thickness of an object to be inspected using ultrasonic waves as described above has the following problems.

First, as a first problem, an electromagnetic ultrasonic sensor is used as a means for transmitting and receiving ultrasonic waves, and the sensitivity is extremely low. Generally, transmission of ultrasonic waves by electromagnetic ultrasonic waves
1/100 to 1/1 compared to the method using a piezoelectric element
The sensitivity is poor about 000. Further, in the transmission and reception of ultrasonic waves by electromagnetic ultrasonic waves, the sensitivity is lowered by the square of the poor sensitivity described above. Therefore, the distance between the object and the sensor (hereinafter referred to as “lift-off”) needs to be 2 mm or less.
Electromagnetic ultrasonic sensors are very difficult to handle. On the other hand, in a steel product rolling line, a pass line fluctuation of about 5 mm is inevitable, so that the electromagnetic ultrasonic sensor cannot be used in a non-contact ultrasonic transmission / reception technology with a lift-off of about 2 mm. Therefore, in order to avoid the problem of the sensitivity of the electromagnetic ultrasonic sensor, attempts have been made to improve the transmission output of the electromagnetic ultrasonic wave by using a transmission voltage of several kilovolts. Further, attempts have been made to improve the transmission / reception sensitivity of electromagnetic ultrasonic waves by using a magnetizer that generates a DC magnetic field of 1T. However, improvement of sensitivity by these attempts was not sufficient. For this reason, the thickness gauge using electromagnetic ultrasonic waves is not actually operated unless it is used in a state close to contact in a part of cold state.

As a second problem, when measuring the thickness of an object to be inspected using ultrasonic waves, the speed of sound changes depending on the temperature. In the method of measuring the thickness of a test object by propagating ultrasonic waves hot, the thickness of the test object is measured from the ultrasonic propagation time of heat. For this reason, it is naturally necessary to measure the hot sound speed of the test object in advance, but the thickness of the test object calculated using the hot sound speed is The thickness of the body. Therefore, JP-A-60-53
In the method disclosed in 806, the thickness of the test object in the cold state is calculated from the thickness of the test object in the hot state using the linear expansion coefficient α of the material. However, since the linear expansion coefficient α changes depending on the temperature, it is necessary to previously measure the linear expansion coefficient α hot. That is, in the conventional method, the sonic velocity V (T) and the coefficient of thermal expansion α (T) at each temperature T between heat are obtained.
Is required to be measured in advance, and it takes time to measure the thickness of the test object. Further, in the actual measurement, the thickness of the test object in the cold state must be calculated from the thickness of the test object in the hot state. Therefore, the cold thickness is calculated in two steps. Therefore, there is a problem that an error is included in calculating the thickness of the test object in the cold state from the thickness of the test object in the hot state.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an inexpensive apparatus configuration for transmitting and receiving ultrasonic waves without contact and with high sensitivity. It is to provide a hot ultrasonic thickness gauge that is capable of. Another object of the present invention is to provide a thickness measuring method capable of easily and accurately measuring the thickness of a test object in a cold state from the ultrasonic propagation time in a hot state.

[0008]

The present invention uses the following means to achieve the above object.

The hot ultrasonic thickness gage according to the present invention is a hot ultrasonic thickness gage for measuring the thickness of a test object by transmitting ultrasonic waves into a hot test object. Ultrasonic wave generating means for generating ultrasonic waves on the body, ultrasonic wave receiving means for receiving the ultrasonic waves, propagation time calculating means for calculating the ultrasonic wave propagation time from the received ultrasonic waves, and Temperature estimating means for estimating the temperature of the measuring part of the test object; sound speed calculating means for calculating the sound speed of the test object from the estimated temperature; thickness of the test object based on the propagation time and the sound speed. Thickness calculating means for calculating the thickness, the ultrasonic wave generating means is a pulse laser, and the ultrasonic wave receiving means is an electromagnetic ultrasonic sensor.

[0010] In the above-described hot ultrasonic thickness gauge according to the present invention, the electromagnetic ultrasonic sensor may have a through hole through which a pulsed laser beam passes.

[0011] The thickness measuring method of the present invention uses ultrasonic waves to
The first propagation time in the test object during the heat at the temperature T is measured, the cold thickness of the test piece of the same material as the test object is measured, and the ultrasonic wave is applied to the test piece at each temperature. After measuring the second propagation time, the sound velocity is calculated from the cold thickness and the second propagation time to determine the relationship between the sound velocity and the temperature, and the sound velocity at the temperature T is derived from the relationship between the sound velocity and the temperature. The cold thickness of the test object is determined from the sound speed and the first propagation time.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] In a first embodiment of the present invention, the thickness of a test object in a hot state is measured with an ultrasonic wave using a transmission type hot ultrasonic thickness gauge, and the heat is measured. It is characterized in that the thickness of the test object in the cold state is calculated without using the expansion coefficient.

First, the principle by which the thickness of a test object in a cold state can be measured without using the linear expansion coefficient will be described.

A specimen having a cold temperature T ₀ and a thickness L (T ₀ )
At the hot temperature T, the length becomes L (T).
It is represented by Here, α is a coefficient of linear expansion, and the coefficient of linear expansion α is represented by Expression (2).

L (T) = L (T ₀ ) + L (T ₀ ) × α × (T−T ₀ ) (1) α = 1 / L × dL / dT (2) On the other hand, if the temperature T exceeds When the propagation time of the sound wave is Δt (T),
The sound speed V (T) is defined by (thickness / propagation time). For this reason, the sound speed V (T) is represented by Expression (3).

V (T) = L (T) / Δt (T) (3) However, ignoring the thermal expansion of the test specimen during hot, the thickness L (T ₀ ) at the cold temperature T ₀ The sound velocity V '(T) using
It is represented by equation (4).

V ′ (T) = L (T ₀ ) / Δt (T) (4) Therefore, according to equations (1), (3) and (4), the sound velocity V (T)
And the speed of sound V ′ (T) are represented by equation (5).

V (T) = V ′ (T) × {1 + α × (T−T ₀ )} (5) When an object to be inspected is measured, the temperature is T and the propagation time of one-way ultrasonic wave Is Δt ′. Therefore,
The thickness WT (T) of the object to be inspected is expressed by Expression (6) using the sound speed of Expression (3).

WT (T) = V (T) × Δt ′ (6) Since the thickness WT (T) is the thickness at the temperature T, the thickness WT (T) at the cold temperature T _{0 0} ) needs to be calculated using the linear expansion coefficient α. Therefore, the thickness W at the cold temperature T ₀
T (T ₀ ) is represented by equation (7).

WT (T ₀ ) = WT (T) / {1 + α × (T−T ₀ )} (7) By rewriting equation (7), equation (8) is obtained.

WT (T ₀ ) = V (T) × Δt ′ / {1 + α × (T−T ₀ )} = V ′ (T) × {1 + α × (T−T ₀ )} × Δt ′ / ｛1 + α × (T−T ₀ )｝ = V ′ (T) × Δt ′ (8) That is, the apparent sound velocity V ′ at the temperature T necessary for measurement in advance.
By examining (T) and the propagation time Δt ′ of the ultrasonic wave, the cold thickness WT (T ₀ ) can be measured without using the linear expansion coefficient.

Next, a description will be given of a hot ultrasonic thickness gauge for measuring the thickness of an object to be inspected by ultrasonic waves.

FIG. 1A shows a configuration diagram of a hot ultrasonic thickness gauge. FIG. 1B shows a configuration diagram in which the radiation thermometer 7 is applied to the temperature estimating unit 13 in FIG. Note that the method of estimating the temperature is not limited to using the radiation thermometer 7, and any method may be used for heat transfer calculation or measurement using a contact-type thermometer as long as the temperature of the test object can be estimated.

In FIGS. 1A and 1B, reference numeral 1 denotes an object to be inspected, 2 denotes a pulse laser, and 3a denotes an electromagnetic ultrasonic sensor. In the first embodiment, in order to receive ultrasonic waves by the transmission method, the electromagnetic ultrasonic sensor 3a is disposed on the opposite side of the pulse laser 2 with the inspection object 1 interposed therebetween. The radiation thermometer 7 shown in FIG. 1B is connected to the test object 1 by a fiber 6.

When such a hot ultrasonic thickness gauge is used, the thickness of the test object is measured by a laser ultrasonic method. In the laser ultrasonic method, a pulse laser beam or modulated light is applied to an object to be inspected, so that the surface of the object to be inspected receives a reaction of thermal ablation or thermal stress to generate an ultrasonic wave. The intensity of generation of this ultrasonic wave can be arbitrarily changed depending on the conditions of the pulsed laser beam to be irradiated. Therefore,
The intensity of the generated ultrasonic waves can be about 10 times the normal intensity that can be generated by the piezoelectric element. When such an intense ultrasonic wave is received by the electromagnetic ultrasonic sensor, it is 1000 to 10000 in comparison with a conventional transmitting and receiving method using electromagnetic ultrasonic waves.
Ultrasonic waves can be received with twice the sensitivity.

Hereinafter, a method for measuring the thickness of an object to be inspected by the above-described laser ultrasonic method will be described in detail.

First, an optical density of 10 MW from the pulse laser 2
/ Cm ² or more pulse laser light 5 is emitted. Here, the pulse laser beam 5 has a pulse energy of, for example, 2
00 mJ and the pulse width is 5 ns, for example. The pulse laser beam 5 is condensed to, for example, 2 mm, and is irradiated on the inspection object 1 such as a steel plate. As a result, the surface 1 of the test object 1
b causes ablation, and ultrasonic waves 4 are generated by the reaction of the ablation. The ultrasonic wave 4 is reflected by the back surface 1a or the front surface 1b of the device 1 and reciprocates in the device 1 a plurality of times. Here, an electromagnetic ultrasonic sensor 3a is arranged on the back surface 1a of the test object 1. Therefore, the ultrasonic wave 4 is applied to the back surface 1 of the test object 1 on the side of the electromagnetic ultrasonic sensor 3a.
Each time it reaches a, the ultrasonic wave 4 is detected from the electromagnetic ultrasonic sensor 3a. The electromagnetic ultrasonic sensor 3a includes a magnet having a magnetic flux density of, for example, 3500 gauss and a coil having, for example, 10 turns.

Next, the signal of the ultrasonic wave 4 detected by the electromagnetic ultrasonic sensor 3a is sent to the
It is amplified to 0 dB. Of the amplified signal, only the frequency band of the ultrasonic wave transmitted through the material is passed by the band-pass filter 9. Then, the A / D converter 10
As a result, a multiple reflection waveform of the ultrasonic wave as shown in FIG. 2 is obtained. At this time, the lift-off of the electromagnetic ultrasonic sensor 3a is, for example, 8 mm, and the gain of the broadband amplifier 8 is, for example, 80d.
B, the band of the band-pass filter 9 is, for example, 1 to 5 MHz.
z.

Since the multiple reflection waveform shown in FIG. 2 is obtained by the arrangement of the transmission method, the first echo peak P1 in the figure is determined when the ultrasonic wave 4 first arrives at the electromagnetic ultrasonic sensor 3a. Is the peak. Second echo peak P2
Is one reciprocation from the first echo peak P1. The third echo peak P3 is one more round trip from the second echo peak P2. Here, when measuring the time interval Δt between the second echo peak P2 and the third echo peak P3, Δt = 7.744 μs. When the multiple reflection waveform shown in FIG. 2 was obtained, the indicated value of the radiation thermometer 7 (shown in FIG. 1B) used as the temperature estimating unit 13 was 872 ° C.

FIG. 3 shows the relationship between the speed of sound and the temperature of the test object made of the same material as the test object 1. According to FIG. 3, it can be seen that the sound speed depends on the temperature, as the sound speed decreases as the temperature increases. The detailed description of FIG. 3 will be described later. When the sound speed is obtained using the graph of FIG. 3, the sound speed at a temperature of 872 ° C. is 4970 m /
s.

Therefore, from equation (9), Δt = 7.744
When μs and sound velocity V = 4970 m / s, the thickness WT of the test object in a cold state is 19.24 mm.

WT = Δt × V ÷ 2 (9) In this manner, the thickness WT of the test object in the cold state is calculated by the thickness calculating section 11, and the result is displayed on the display section 12.
Is displayed.

The same experiment was carried out many times and compared with the measurement by a micrometer. As a result, the difference between the thickness measured by the micrometer and the thickness WT calculated by the above method was all less than 10 μm.

By the way, when the propagation time of the ultrasonic wave is originally measured hot and the thickness of the test object is calculated using the hot sound velocity, the thickness of the test object in the hot state, that is, the thermal expansion is obtained. The thickness of the test object will be known. However, in the present invention, the thickness of the test object at normal temperature is directly calculated. This is because the sound speed shown in FIG. 3 is not the true sound speed.

The relationship between temperature and sound speed as shown in FIG.
I led as follows. First, the thickness WT ₀ of the material whose sound speed is to be determined at room temperature T ₀ ° C is measured using a micrometer. Next, the propagation time Δt _{0 of the} ultrasonic wave is measured by a hot ultrasonic transmission / reception method. This thickness WT ₀ and the propagation time Δ
From t ₀ , the sound velocity V ₀ at normal temperature T ₀ ° C is determined. Next, while sequentially heating the material, the propagation times Δt ₁ , Δt ₂ , Δt ₃ ,... Are measured at the respective temperatures T ₁ , T ₂ , T ₃ ,. Here, the thickness used for the calculation of the sound velocity is not the thickness that has undergone hot expansion but the thickness WT ₀ at the normal temperature T ₀ ° C. Thus, the relationship between the speed of sound and the temperature as shown in FIG. 3 is derived. Therefore, if the sound speed and the propagation time between heat shown in FIG. 3 are used, the thickness at room temperature can be immediately calculated.

In the first embodiment, the speed of sound is directly calculated using the graph of FIG. 3 to measure the thickness at room temperature, but the present invention is not limited to this. If the relationship between sound speed and temperature is derived using the above method using the thickness at an arbitrary temperature, the thickness at any temperature can be calculated from the measurement of the propagation time of the material in different temperature ranges without correcting for thermal expansion. can do.

In the first embodiment, the speed of sound is determined from the surface temperature of the device under test 1. This is because the temperature difference between the surface temperature and the internal temperature when the test object 1 is allowed to cool is about 1
Since the temperature is lower than 0 ° C., the thickness calculation error due to the temperature distribution cannot be 0.2% or more. Therefore, the surface temperature of the test object 1 is represented as the temperature of the material.

Although the surface 1b of the inspection object 1 is ablated by the pulsed laser beam 5, the amount of the surface melted by one ablation is about 1 μm in depth, which is not a degree that deteriorates the quality of the product. .

According to the hot ultrasonic thickness gauge according to the first embodiment, the ultrasonic wave is used as a means for measuring the thickness of the test object. For this reason, rather than using gamma rays,
A safe and inexpensive hot ultrasonic thickness gauge can be provided.

Also, since the thickness is measured using ultrasonic waves, the thickness is measured 10 times less than the conventional transmission / reception method using electromagnetic ultrasonic waves.
The ultrasonic wave 4 can be received with a sensitivity of 00 to 10000 times.
Therefore, since ultrasonic waves can be transmitted and received with high sensitivity, even if the lift-off of the electromagnetic ultrasonic sensor 3a is separated by 10 mm or more, S
The signal can be received when the / N ratio is 2 or more. As described above, if the lift-off is large, it is easy to provide the electromagnetic ultrasonic sensor 3a with a cooling mechanism, so that the influence of radiant heat can be reduced. Furthermore, if the lift-off can be made large, there is also room for following the line fluctuation of the inspection object, and it is not necessary to always maintain a constant lift-off. Therefore, it is possible to easily and stably transmit and receive the ultrasonic wave to and from the hot inspection object.

According to the thickness measuring method of the first embodiment, the thickness of the test object at normal temperature can be known from the propagation time between heat without using the thermal expansion coefficient.
Therefore, the thickness of the test object can be measured simply and accurately.

[Second Embodiment] In a second embodiment of the present invention, the thickness of a test object in a hot state is measured by an ultrasonic wave using a reflection type hot ultrasonic thickness gauge, and the heat is measured. It is characterized in that the thickness of the test object in the cold state is calculated without using the expansion coefficient. In the second embodiment, the description of the same structure as in the first embodiment will be omitted, and only different structures will be described.

FIG. 4A shows a configuration diagram of a hot ultrasonic thickness gauge. FIG. 4B is a configuration diagram in which the radiation thermometer 7 is applied to the temperature estimating unit 13 in FIG.

4A and 4B, reference numeral 1 denotes an object to be inspected, 2 denotes a pulse laser, and 3b denotes an electromagnetic ultrasonic sensor. In the second embodiment, since the ultrasonic wave is received by the reflection method, the electromagnetic ultrasonic sensor 3b is arranged on the same side as the pulse laser 2 with respect to the test object 1. Also,
A through hole 14 is provided at the center of the electromagnetic ultrasonic sensor 3b so that the pulse laser beam 5 can pass through the center of the electromagnetic ultrasonic sensor 3b. The radiation thermometer 7 shown in FIG.
Are connected to the test object 1 by a fiber 6.

Hereinafter, a method for measuring the thickness of an object to be inspected using the above-described hot ultrasonic thickness gauge will be described.

First, similarly to the first embodiment, a pulse laser beam 5 having a light density of 10 MW / cm ² or more is emitted from the pulse laser ² . This pulse laser beam 5 is, for example, 2 m
Then, the light is converged on the test object 1 such as a steel plate through the through hole 14. Thereby, the surface 1 of the test object 1
b causes ablation, and ultrasonic waves 4 are generated by the reaction of the ablation. The ultrasonic wave 4 is reflected by the back surface 1a or the front surface 1b of the device 1 and reciprocates in the device 1 a plurality of times. Here, the electromagnetic ultrasonic sensor 3b is arranged on the surface 1b of the test object 1. Therefore, the ultrasonic wave 4 is applied to the surface 1 of the inspection object 1 on the side of the electromagnetic ultrasonic sensor 3b.
Each time it reaches b, the ultrasonic wave 4 is detected from the electromagnetic ultrasonic sensor 3b. The following is the same as in the first embodiment, and a description thereof will not be repeated.

According to the second embodiment, the same effects as in the first embodiment can be obtained. Further, in the second embodiment, a through hole 14 is provided at the center of the electromagnetic ultrasonic sensor 3b so that the pulse laser beam 5 can pass therethrough. For this reason, it is possible to transmit and receive ultrasonic waves not only by the transmission method such as γ-rays but also by the reflection method. Therefore, the second
The hot ultrasonic thickness gauge according to the embodiment of the present invention can also be applied to a test object such as a steel pipe.

In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0050]

As described above, according to the present invention, it is possible to provide a hot ultrasonic thickness gage having an inexpensive apparatus configuration and capable of transmitting and receiving ultrasonic waves with high sensitivity without contact. Further, it is possible to provide a thickness measuring method capable of simply and accurately measuring the thickness of the test object in the cold state from the ultrasonic propagation time in the hot state.

[Brief description of the drawings]

FIG. 1 shows a configuration diagram of a hot ultrasonic thickness gauge using a transmission method according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a multiple reflection waveform obtained by a hot ultrasonic thickness gauge according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the speed of sound and the temperature of the test object used in the first embodiment of the present invention.

FIG. 4 shows a configuration diagram of a hot ultrasonic thickness gauge using a reflection method according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inspection object, 1a ... Back surface of an inspection object, 1b ... Front surface of an inspection object, 2 ... Pulse laser, 3a, 3b ... Electromagnetic ultrasonic sensor, 4 ... Ultrasonic wave, 5 ... Laser beam, 6 ... Fiber, 7: radiation thermometer, 8: broadband amplifier, 9: bandpass filter, 10: A / D converter, 11: thickness calculator, 12: display, 13: temperature estimator, 14: through hole.

Claims (3)

[Claims] 1. A hot ultrasonic thickness gage for measuring the thickness of a test object by transmitting ultrasonic waves into a hot test object, wherein an ultrasonic wave is generated in the test object. Means, an ultrasonic wave receiving means for receiving the ultrasonic wave, a propagation time calculating means for calculating a propagation time of the ultrasonic wave from the waveform of the received ultrasonic wave, and estimating a temperature of the measuring unit of the inspection object. Temperature estimating means, sound speed calculating means for calculating the sound speed of the test object from the estimated temperature, and thickness calculating means for calculating the thickness of the test object from the propagation time and the sound speed. Wherein the ultrasonic wave generating means is a pulse laser, and the ultrasonic wave receiving means is an electromagnetic ultrasonic sensor. 2. The hot ultrasonic thickness gauge according to claim 1, wherein said electromagnetic ultrasonic sensor has a through hole through which a pulse laser beam passes. 3. A method of measuring a first propagation time in a test object between heat at a temperature T by using an ultrasonic wave, measuring a cold thickness of a test piece of the same material as the test object, After measuring the second propagation time in the test piece at each temperature by calculating the sound speed from the cold thickness and the second propagation time to determine the relationship between sound speed and temperature, the sound speed and temperature A thickness measuring method, wherein a sound speed at a temperature T is derived from the relationship, and a cold thickness of the test object is obtained from the sound speed and the first propagation time.