JP5128061B2 - Laser ultrasonic material measuring device - Google Patents

Description

  The present invention relates to a laser ultrasonic material measuring apparatus that measures the material of a rolled product in a rolling line.

Steel materials have strength and ductility called mechanical properties, and these properties are determined by the metal structure such as crystal grain size. For this reason, the mechanical properties can be calculated by grasping the metal structure such as the crystal grain size. However, the measurement of the particle diameter requires steps such as polishing and microscopic observation when a test piece is cut out and requires a lot of labor. For this reason, an apparatus using an ultrasonic pulse is disclosed as an apparatus for measuring the crystal grain size in a nondestructive manner (see, for example, Patent Document 1).
Japanese Patent No. 3184368

  However, the apparatus as described above is not intended for various conditions in a situation where a rolled product is manufactured, and is not suitable for installation in a rolling line for manufacturing a rolled product.

  Therefore, an object of the present invention is to provide a laser ultrasonic material measuring device that can cope with various conditions in a situation where a rolled product is manufactured in a rolling line for manufacturing the rolled product.

A laser ultrasonic material measuring device according to an aspect of the present invention is a measuring device using a laser ultrasonic wave that is installed in a rolling line for manufacturing a rolled product and measures a crystal grain size of the rolled product flowing through the rolling line. there are, by irradiating the transmission-side laser beam on the rolled product, the ultrasonic generator that generates a longitudinal wave of the ultrasonic wave in the rolled product, the ultrasonic generator to the rolled product to illuminate the transmission-side laser beam By irradiating the surface facing the surface with the receiving laser beam and inputting the receiving laser beam reflected from the rolled product to the receiving unit, the longitudinal wave of the ultrasonic wave generated in the rolled product is detected. transmitted the detection signal, the an extension of the optical path of the irradiated the sender laser beam from the ultrasonic oscillator and an ultrasonic detector the receiving unit is found provided not located, from the ultrasonic detector The sent inspection Based on the signal, and a said rolled product signal performs processing for measuring the crystal grain size processor, the ultrasonic oscillator as a reference axis perpendicular to the plane to be irradiated to the rolled product The center line of the irradiated transmission side laser light is provided at an angle inclined within 45 degrees not including 0 degrees, and the ultrasonic detector is formed on the extension line of the irradiated reception side laser light by the ultrasonic oscillator. It is the structure provided so that the sound source of the longitudinal wave of the said ultrasonic wave which generate | occur | produced in the rolled product may be located .

  ADVANTAGE OF THE INVENTION According to this invention, the laser ultrasonic material measuring apparatus corresponding to the various conditions in the condition which manufactures a rolling product can be provided in the rolling line which manufactures a rolling product.

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

  First, as a method for measuring a crystal grain size performed nondestructively according to the present embodiment, a method using attenuation due to scattering of an ultrasonic crystal particle (Rayleigh scattering) will be described.

The ultrasonic wave uses a longitudinal wave (bulk wave) in a particle size measurement method using Rayleigh scattering. The attenuation of the bulk wave is expressed by Equation (1) using the attenuation constant a, where x is the propagation distance in the steel sheet, p and p0 are the sound pressures, and a is the attenuation coefficient.

When the frequency of the bulk wave is in the Rayleigh region, a is approximated by a quartic function of the ultrasonic frequency f, where f is a bulk wave frequency and a1 and a4 are coefficient attenuation constants.
(Here, in Equation (2), the first term is the absorption attenuation term due to internal friction, and the second term is the Rayleigh scattering term.)

This Rayleigh region is a region in which the crystal grain size is sufficiently smaller than the wavelength of the bulk wave, where d is the crystal grain size and λ is the wavelength of the bulk wave, for example, the range of the formula (3). .

Further, it is known that the fourth-order coefficient a4 in the equation (2) is a coefficient proportional to the cube of the crystal grain size d. Therefore, a4 is expressed as in Equation (4).

  Here, S is a scattering constant.

Since the bulk wave transmitted by the transmitter includes frequency components having a certain distribution in the waveform, the attenuation rate of each frequency component can be obtained by frequency analysis of the received waveform. Furthermore, since the propagation distance in the steel plate can be determined from the transmission / reception time difference, each coefficient of the equation (2) can be identified based on the propagation distance and the attenuation rate of each frequency component. Furthermore, if the scattering constant S is determined in advance using a standard sample or the like, the crystal grain size d can be obtained from the equation (4).
(First embodiment)
FIG. 1 is a block diagram for explaining the configuration of the laser ultrasonic material measuring apparatus according to the present embodiment.

  This apparatus is provided in the rolling line in which a rolling product is manufactured from a rolling raw material (slab).

  This apparatus includes an ultrasonic oscillator 1 installed on the lower side of a rolling line through which a rolled product (including a state in the middle of being completed as a product from a slab) flows, and ultrasonic detection on the lower side of the rolling line. And a signal processing device 4 connected to receive a detection signal from the ultrasonic detector 2.

  The ultrasonic oscillator 1 irradiates the bottom surface of the material to be measured 3 (rolled product) with a strong pulsed laser beam to generate an ultrasonic pulse on the bottom surface of the material to be measured 3. The ultrasonic oscillator 1 is, for example, a YAG laser capable of Q switch operation. The ultrasonic oscillator 1 irradiates the measured material 3 with a target beam diameter by, for example, narrowing the laser beam with a lens.

  The ultrasonic detector 2 uses a CW (continuous wave) laser to detect a vibration displacement on the upper surface of the material 3 to be measured due to an ultrasonic pulse. The ultrasonic detector 2 is a Fabry-Perot method using a Fabry-Perot interferometer.

  With reference to FIG. 4, the structure which detects the vibration displacement (ultrasonic vibration) by a Fabry-Perot system is demonstrated.

  The Fabry-Perot ultrasonic detector 2 </ b> A includes a CW laser 21, a mirror 24, beam splitters 25 and 26, a Fabry-Perot interferometer 23, and a photodetector 22. The Fabry-Perot interferometer 23 includes a reflection mirror 27 that includes a pair of two mirrors configured as a resonator, and an actuator 28 that adjusts the distance between the two mirrors.

  The actuator 28 is, for example, a piezo element. The actuator 28 is sequentially operated by the control mechanism so as to keep the interval between the reflection mirrors 27 accurately.

  The laser light output from the CW laser 21 is reflected by the mirror 24 and is split by the beam splitter 25 into laser light that irradiates the material 3 to be measured and laser light that enters the Fabry-Perot interferometer 23. The laser light applied to the material to be measured 3 is reflected on the upper surface of the material to be measured 3 that is ultrasonically vibrated and enters the Fabry-Perot interferometer 23. The Fabry-Perot interferometer 23 resonates two incident laser beams by a reflection mirror 27 adjusted by an actuator 28. The two resonated laser beams become interference light and enter the photodetector 22 via the beam splitter 26.

  As described above, the ultrasonic vibration generated on the upper surface of the material to be measured 3 is utilized as a result of the change in the optical path generated between the reference light and the reflected light. Detection is performed when the intensity change of the interference light occurs according to the vibration displacement of the upper surface.

  With reference to FIG. 3, the installation positions of the ultrasonic oscillator 1 and the ultrasonic detector 2 will be described. The same parts as those in FIG. 1 are denoted by the same reference numerals and detailed description thereof is omitted, and different parts are mainly described here. In the following embodiments, the same description is omitted.

  The ultrasonic oscillator 1 is installed so that the optical path of the emitted laser light has an inclination within 45 degrees (angle θ in FIG. 3) not including 0 degrees with respect to an axis perpendicular to the bottom surface of the material 3 to be measured. ing. The laser from the ultrasonic oscillator 1 has this angle θ, so that the laser irradiated to the rolled product becomes elliptical. If the ratio of the elliptical vertical axis and horizontal axis is large, the detection accuracy of ultrasonic waves is deteriorated. For this reason, the angle θ of 45 degrees is a substantially limitable angle that can be detected. Therefore, in order to maintain high detection accuracy, the angle θ is preferably within 20 degrees.

  In the ultrasonic detector 2, the optical path of the emitted laser light is substantially perpendicular to the upper surface of the material to be measured 3, and the point on the bottom surface of the material to be measured 3 irradiated with the laser light from the ultrasonic oscillator 1 ( It is installed so as to pass through either one (or both) of the ultrasonic sound source) or the point on the upper surface of the measurement object 3 facing this point. Alternatively, the ultrasonic detector 2 is installed at a position where the emitted laser light is reflected by the material 3 to be measured and the reflected laser light can be incident. The ultrasonic detector 2 is installed on the extended line of the laser beam path of the ultrasonic oscillator 1 so that a light receiving unit (for example, a lens) that enters the laser beam is not located.

  As described above, the ultrasonic oscillator 1 and the ultrasonic detector 2 are installed.

  The signal processing device 4 obtains the material (crystal grain size) of the material 3 to be measured by processing the detection signal detected by the ultrasonic detector 2.

  With reference to FIG. 2, the processing method of the detection signal detected by the ultrasonic detector 2 by the signal processing device 4 will be described.

  The signal processing device 4 collects a plurality of dense wave echo signals using an ultrasonic detector (step S1).

  The signal processing device 4 analyzes the frequency of the plurality of coarse / fine wave echo signals, and calculates the attenuation amount for each frequency from the difference in the spectral intensity of the multiple echo signals from the surface of the material to be measured (step S2). If necessary, diffusion attenuation correction and transmission loss correction are performed, and the frequency characteristic of the attenuation constant is calculated.

  The signal processing device 4 calculates the propagation distance in the steel plate from the transmission / reception time difference, and identifies each coefficient of the equation (2) based on the propagation distance and the attenuation rate of each frequency component (step S3).

  The signal processing device 4 obtains a coefficient vector of the multi-order function by fitting a multi-order function such as a quartic curve by the least square method or the like from the frequency characteristic of the attenuation constant (step S4).

The signal processing device 4 uses a coefficient vector of a multi-order function obtained when fitting a quartic curve to an attenuation constant by the least square method or the like, and a scattering coefficient S obtained from a measured material for calibration. A crystal grain size measurement value d ₀ before correction by the volume ratio of the tissue is calculated (step S5).

  Specifically, these are as follows.

An ultrasonic pulse train such as a first ultrasonic pulse, a second ultrasonic pulse,... Is measured by the ultrasonic detector. At this time, the energy contained in each ultrasonic pulse is gradually reduced due to loss during reflection and attenuation due to propagation in the material. When only the part of the first ultrasonic pulse or the second ultrasonic pulse is taken out and frequency analysis is performed to obtain the respective energy (power spectrum), the second ultrasonic pulse has a material plate thickness t as compared with the first ultrasonic pulse. Since the propagation distance is long by two times, energy attenuation according to the equation (1) occurs. The amount of attenuation between the two is determined as the difference from the power spectrum of the first ultrasonic pulse. This curve corresponds to a value obtained by multiplying the attenuation constant a in the equation (2) by the propagation distance difference 2t. From this, each coefficient of the equation (2) at the unit propagation distance is obtained by the least square method or the like. Then, the crystal grain before correction by the volume ratio of each substructure is performed by calculating back the equation (3) from the scattering constant S obtained in advance by a standard sample and a ₄ of the obtained coefficients. A diameter measurement d ₀ can be determined.

  According to the present embodiment, the ultrasonic sound source (or the surface on the opposite side of the measured material 3 at the shortest distance from the sound source) generated by the laser beam of the ultrasonic oscillator 1 and the ultrasonic wave. Since the optical axis of the laser of the detector 2 overlaps, the ultrasonic detection by the ultrasonic detector 2 can be performed efficiently.

  Further, even if the measurement object 3 is not located at the position to be measured, the laser beam of the ultrasonic oscillator 1 does not directly enter the receiving portion of the ultrasonic detector 2, so that the ultrasonic detector 2 is damaged. I can be spared. In particular, the incident side laser (ultrasonic oscillator 1) is usually a pulse laser having an energy density high enough to cause ablation, so that it is effective in preventing the reception side laser (ultrasonic detector 2) from being damaged. It is. Ablation refers to explosive separation of a solid surface phase accompanied by plasma emission and impact sound that occurs when a high-intensity laser is irradiated. In addition, by tilting the ultrasonic oscillator 1, the ultrasonic detector 2 can be irradiated with laser light substantially perpendicularly to the upper surface of the material 3 to be measured. Can be performed efficiently. Therefore, it can be used safely even in an environment in which the material to be measured 3 moves, and ultrasonic detection can be performed efficiently.

  Furthermore, by installing the ultrasonic detector 2 for detecting ultrasonic waves on the upper side of the rolling line, it is possible to suppress the hindrance to detection due to water vapor and dust generated in the rolling line. In addition, by installing the inclined ultrasonic oscillator 1 on the lower side of the rolling line, an environment just below the rolling line where the rolled product flows, that is, a place avoiding an adverse environment such as falling objects such as vibration, water vapor, and dust. Can be installed.

  As a result, it is possible to provide a laser ultrasonic material measuring apparatus that can efficiently detect ultrasonic waves and can be used safely even in an environment in which a rolled product moves in a rolling line.

(Second Embodiment)
The laser ultrasonic material measuring apparatus according to the present embodiment is a photorefractive ultrasonic detection using a photorefractive element in place of the Fabry-Perot ultrasonic detector 2A in the apparatus according to the first embodiment. The apparatus is the same as the apparatus according to the first embodiment except that the apparatus 2B is used and the installation positions of the ultrasonic oscillator 1 and the ultrasonic detector 2 are not limited.

  A configuration for detecting vibration displacement (ultrasonic vibration) by a photorefractive method will be described with reference to FIG.

  In the photorefractive type ultrasonic detector 2B, the Fabry-Perot interferometer 23 of the Fabry-Perot type ultrasonic detector 2A is replaced by the photorefractive element 29, the splitter 26 is eliminated, and interference light from the photorefractive element 29 is directly received. It is the same except that it is incident on the photodetector 22.

  The photorefractive element 29 causes the reference light and the reflected light to interfere with each other in the crystal and makes the interference light enter the photodetector 22.

  Next, measurement of a thin plate in the laser ultrasonic material measuring apparatus as described above will be described.

  A photorefractive interferometer has a limitation that a surface displacement exceeding 1/8 of the wavelength of received light cannot be detected. That is, the displacement of the surface exceeds 66.5 nm (wavelength 532 nm = green) or 133 nm (wavelength 1064 nm = infrared).

  In particular, when measuring a thin plate (about 1 to 2 mm), the thin plate is likely to generate a large vibration (plate wave vibration) having a specific low frequency due to the laser light of the ultrasonic oscillator 1. Plate wave vibration is a phenomenon in which ultrasonic vibration vibrates the entire plate.

  This apparatus reduces the spot diameter without decreasing the output of the laser beam from the ultrasonic oscillator 1 in order to reduce the surface displacement itself. For example, when the output amount of the laser beam is X, when plate wave vibration is generated in a thin plate of 2 mm or less, the laser beam output amount X is output without changing and the spot diameter of the laser beam is reduced. Thus, plate wave vibration is suppressed. However, the laser beam from the ultrasonic oscillator 1 is made to have a small spot diameter before reaching the material 3 to be measured, with a lower limit that does not cause ablation in the space. Note that the output amount of the laser beam is a heat amount or work amount expressed in units such as J (joule) or W (watt).

  According to the present embodiment, by adopting the photorefractive method, a part that is easily affected by external disturbances such as the mirror 27 of the Fabry-Perot interferometer 23, and a precise mechanism such as the actuator 28 and the control mechanism. It becomes a measuring device with few parts. Therefore, it is possible to provide an apparatus that is not easily affected by disturbances such as vibrations and that is suitable for stable ultrasonic measurement over a long period of time even in a rolling environment with a poor environment.

  In particular, in the case of online measurement in a hot rolling line, the environment is poor, such as vibration caused by rolling mills and rolling material passing, water vapor generated from a cooling line for controlling the temperature of the rolling material to a desired temperature. . Further, the material to be rolled in the hot range is about 500 to about 900 degrees, and the temperature in the vicinity of the material to be rolled is very high. An apparatus suitable for these environments can be provided.

  Further, by reducing the spot diameter without lowering the output of the laser light from the ultrasonic oscillator 1, the amplitude of the low frequency vibration is reduced, and instead, the amplitude of the ultrasonic wave effective for the particle size measurement is increased. Thereby, it is possible to detect the ultrasonic vibration effective for material measurement while avoiding the plate wave vibration that causes a decrease in measurement accuracy.

  Accordingly, it is possible to detect an ultrasonic vibration effective for material measurement even in a rolling line having a poor effect environment, and it is possible to provide an apparatus suitable for performing stable ultrasonic measurement over a long period of time.

  Note that the first embodiment is not limited to the Fabry-Perot method. For example, a system using a Michelson interferometer may be used.

  In the first embodiment, the laser beam from the ultrasonic oscillator 1 is irradiated from the bottom surface, and the laser beam from the ultrasonic detector 2 is irradiated from the top surface to detect the vibration displacement. It is good also as a structure which irradiates the laser beam from a top surface, and irradiates the laser beam from an ultrasonic detector from a bottom surface. Accordingly, the ultrasonic oscillator 1 may be installed on the upper side of the rolling line 1 and the ultrasonic detector may be installed on the lower side of the rolling line, or other than these. It can be arbitrarily selected depending on the environmental conditions in which this apparatus is provided.

  1st Embodiment and 2nd Embodiment can be set as the structure satisfy | filled simultaneously. In this case, a laser ultrasonic material measuring apparatus having the effects of both the first embodiment and the second embodiment can be provided.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The block diagram for demonstrating the structure of the laser ultrasonic material measurement apparatus regarding the 1st Embodiment of this invention. The flowchart for demonstrating the process sequence of the signal processing apparatus regarding 1st Embodiment. The block diagram for demonstrating the installation position of the ultrasonic oscillator and ultrasonic detector regarding 1st Embodiment. The block diagram for demonstrating the structure of the Fabry-Perot system regarding 1st Embodiment. The block diagram for demonstrating the structure of the photorefractive system regarding 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ultrasonic oscillator, 2 ... Ultrasonic detector, 3 ... Material to be measured, 4 ... Signal processing apparatus.

Claims (3)

A measuring device using a laser ultrasonic wave that is installed in a rolling line for producing a rolled product and measures a crystal grain size of the rolled product flowing through the rolling line,
Irradiating the transmission-side laser beam on the rolled product, the ultrasonic generator that generates a longitudinal wave of the ultrasonic wave in the rolled product,
Irradiating the rolled product with a receiving laser beam on a surface facing the surface on which the ultrasonic oscillator emits the transmitting laser beam, and inputting the receiving laser beam reflected from the rolled product to a receiving unit. By detecting the longitudinal wave of the ultrasonic wave generated in the rolled product, a detection signal is transmitted, and the receiving unit is not positioned on the extension line of the optical path of the transmission side laser beam emitted from the ultrasonic oscillator and provided it ultrasound detector,
Based on the detection signal transmitted from the ultrasonic detector, a signal processing device that performs processing for measuring the crystal grain size of the rolled product ,
The ultrasonic oscillator is
With respect to an axis perpendicular to the surface irradiated to the rolled product, the center line of the irradiated laser beam on the transmitting side is provided at an angle inclined within 45 degrees not including 0 degrees,
The ultrasonic detector is
Provided so that the ultrasonic longitudinal wave sound source generated in the rolled product by the ultrasonic oscillator is positioned on the extended line of the irradiated laser beam on the receiving side.
The laser ultrasonic material measuring apparatus according to claim. A photorefractive method measuring device using laser ultrasonic waves that is installed in a rolling line for producing a rolled product and measures a crystal grain size of the rolled product flowing through the rolling line,
The output of the laser beam on the transmission side that irradiates the rolled product is X, and the spot diameter is set so that the rolled product does not generate plate wave vibration without making the output smaller than X. the said sender laser light irradiating the rolled product by reducing, the ultrasonic generator that generates a longitudinal wave of the ultrasonic wave in the rolled product,
Irradiating the rolled product with a receiving laser beam on a surface facing the surface on which the ultrasonic oscillator emits the transmitting laser beam, and inputting the receiving laser beam reflected from the rolled product to a receiving unit. By detecting the longitudinal wave of the ultrasonic wave generated in the rolled product, a detection signal is transmitted, and the receiving unit is not positioned on the extension line of the optical path of the transmission side laser beam emitted from the ultrasonic oscillator and provided it ultrasound detector,
Based on the detection signal transmitted from the ultrasonic detector, a signal processing device that performs processing for measuring the crystal grain size of the rolled product ,
The ultrasonic oscillator is
With respect to an axis perpendicular to the surface irradiated to the rolled product, the center line of the irradiated laser beam on the transmitting side is provided at an angle inclined within 45 degrees not including 0 degrees,
The ultrasonic detector is
Provided so that the ultrasonic longitudinal wave sound source generated in the rolled product by the ultrasonic oscillator is positioned on the extended line of the irradiated laser beam on the receiving side.
The laser ultrasonic material measuring apparatus according to claim. The said ultrasonic oscillator irradiates the said transmission side laser beam to the upper surface of the said rolling product, The laser ultrasonic material measuring apparatus of Claim 1 or Claim 2 characterized by the above-mentioned.

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