JP4286980B2 - Electromagnetic ultrasonic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of an electromagnetic ultrasonic sensor used for nondestructive inspection of metals using ultrasonic waves, and is mainly used for detection of defects in metal, material deterioration due to thermal aging and mechanical stress, and the like. It is.
[0002]
In recent years, an inspection method using ultrasonic waves has been developed in various fields as a method for detecting defects or material deterioration in a metal such as stainless steel.
However, since the ultrasonic beam passing through the metal is remarkably scattered by the metal crystal grains, the beam is attenuated and echoes as background noise are generated, and the S / N ratio is greatly reduced.
In addition, the traveling direction of the ultrasonic beam passing through the metal is distorted (skew) due to the acoustic anisotropy caused by the anisotropy of the metal crystal, and the sound speed greatly varies depending on the passing direction.
As a result, an ultrasonic sensor with a relatively low resolution such as a conventional piezoelectric microprobe has a coarse crystal grain such as austenitic stainless cast steel and a non-uniform distribution, and has crystal anisotropy. In such a case, there has been a problem that it is impossible to efficiently detect the position and magnitude of the defect inside the material and the material deterioration with high accuracy.
[0003]
In order to solve the problems related to the conventional ultrasonic sensor as described above, the inventors of the present application have previously developed a magnetic microprobe (electromagnetic ultrasonic sensor) having a structure as shown in FIG. This is disclosed as No. 363453 and Japanese Patent Application No. 10-363454.
That is, the electromagnetic ultrasonic sensor A has substantially the same configuration as a known magnetic reading head used for reading a floppy disk or a hard disk, and specifically, a detection gap G of 0.5 μm or less. A magnetic microprobe provided with a core body 20a having a coil and a detection coil 20b wound around the core body 20a is used.
[0004]
In FIG. 7, 20c is a slider, and 21 and 22 are magnetic poles provided in the vicinity of the gap G. The slider 20c is moved at an appropriate speed along the outer surface of the object to be inspected in a state where the contact surface is in contact with the outer surface of the object to be inspected.
[0005]
The permanent magnets 21 and 22 are for forming a non-uniform magnetic field on the surface layer of the object to be inspected. Specifically, as shown in FIG. 7, the permanent magnets 21 and 22 are inclined in the vicinity of both sides of the gap G of the core body 20a. N magnetic pole 21 and S magnetic pole 22 are provided, and a non-uniform magnetic field having a predetermined strength is formed on the outer surface layer of the object to be inspected near the core body 20a.
[0006]
In FIG. 7, the pair of N · S magnetic poles 21 and 22 are arranged to face each other. However, the magnetic poles may be arranged as shown in FIGS. 8 and 9, and the magnetic poles easily form a non-uniform magnetic field. Any magnetic pole arrangement may be used as long as it is an arrangement.
[0007]
The electromagnetic ultrasonic sensor A is brought into contact with the outer surface of the object to be inspected. When the ultrasonic wave (surface SH wave or surface SV wave) incident from the transmitting ultrasonic probe (not shown) reaches the surface layer portion of the inspection object, the surface layer of the inspection object is generated by the energy of the ultrasonic wave. Vibrates.
As a result, the magnetic field formed on the surface layer of the object to be inspected by the N / S magnetic poles 21 and 22 also fluctuates oscillatingly, and the fluctuation of the magnetic field on the surface of the object to be inspected is read by the electromagnetic ultrasonic sensor A and passes through the amplifier. It is displayed on a display (not shown).
For example, when the object to be inspected is austenitic stainless cast steel, when the surface layer is vibrated by the energy of ultrasonic waves (surface SH waves), the α phase (ferrite phase, about 10 to 10 μm) distributed in the material with a width of about 10 μm forming the structure. Randomly mixed at a rate of 20%). As a result, the magnetic field in the vicinity of the α-phase grain boundary is disturbed by the magnetic field generated by the induced current generated by the vibration of the α-phase in the magnetic field, and becomes a strong and inhomogeneous magnetic field.
[0008]
The electromagnetic ultrasonic sensor A having the structure shown in FIG. 7 detects a material deterioration range due to thermal aging by processing a detection signal while scanning a predetermined range of the surface of the inspection object at an appropriate speed, By detecting the arrival point of the ultrasonic wave from the detected magnetic field fluctuation state, it is possible to detect the size and position of the defective portion inside the object to be inspected, and has excellent practical utility.
[0009]
However, many problems to be solved still remain in the electromagnetic ultrasonic sensor A of FIG. Among them, the problems that are particularly problematic are: (1) The structure of the magnetic poles 21 and 22 is provided, so that the structure of the sensor is remarkably complicated, and (2) the detection sensitivity is high because the ring-type core body is used. It is low, and (3) the detection sensitivity is likely to fluctuate due to changes in the magnetic characteristics of the magnetic poles 21 and 22. (4) Increasing the strength of the magnetic poles 21 and 22 inevitably increases the detection sensitivity. The point is that it becomes large in size.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-described problems in the electromagnetic ultrasonic sensor having the configuration shown in FIG. 7, and the use of the magnetic poles 21 and 22 eliminates the use of the bias coil. In addition to utilizing a DC magnetic field, only the alternating magnetic field generated by magnetic field fluctuations is detected by the regenerative coil using a center core type core body, thereby simplifying the sensor structure and reducing the size and greatly improving the detection sensitivity. Is the subject of the invention.
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, the ultrasonic wave from the transmitting ultrasonic probe is propagated inside the object to be inspected, and the surface layer of the object to be inspected is vibrated using the energy of the ultrasonic wave propagated through the inside. In an electromagnetic ultrasonic sensor that detects the propagation of ultrasonic waves by changing the magnetic field of the surface layer of the object to be inspected and detecting the fluctuation of the magnetic field by a detection coil that is movably disposed on the surface of the object to be inspected. In addition, the electromagnetic ultrasonic sensor includes a center core 1a and foot cores 1b and 1b disposed on both sides thereof, and a center core type in which a gap G between the center core 1a and both foot cores 1b is 0.01 to 0.05 mm. The core body 1, the bias coils 2 and 2 wound around the foot cores 1b and 1b, respectively, and generating a magnetic field in the opposite direction with the same strength, are respectively formed on the foot cores 1b and 1b. A reproducing coil 4 wound around the Koa 1a is for a basic configuration of the invention.
[0012]
According to the invention of claim 2, in the invention of claim 1, the core body 1 is formed using Mn-Zn ferrite, and the thickness t of the core body 1 is set to 0.1 to 0.2 mm. It is a thing.
[0013]
The invention according to claim 3, in the invention of claim 1, the in shape viewed from the front of the front end portion of the center core 1a, with the width W ₂ is a rectangular 0.02 to 0.05 mm, the center The shape of the front ends of the foot cores 1b and 1b facing the core 1a in a front view is a triangle having an inclination angle θ of the hypotenuse of 30 ° to 60 °.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing a first embodiment of an electromagnetic ultrasonic sensor according to the present invention, and FIG. 2 is a front view showing a second embodiment of the electromagnetic ultrasonic sensor according to the present invention. In Figures 1 and 2, 1 is Sentakoa type core body, 1a the center core, 1b is Futokoa, 2 bias coil, 3 reproducing coil, a gap W ₁ for detecting G ₁ · G ₂ · W ₂ is the width of the center core, t ₁ · t ₂ is the thickness of the core.
[0015]
The core body 1 is made of Mn—Zn ferrite and is selected so as not to cause magnetic saturation at a magnetic flux density of 0.5 to 2 (T) or less. In addition, the outer dimensions of the core body 1 are selected as t ₁ = 0.1 mm, H ₁ = 1.1 mm, L ₁ = 0.65 mm, G ₁ = 0.05 mm, and W ₁ = 0.1 mm, respectively. (In the case of the first embodiment in FIG. 1).
[0016]
Further, in the second embodiment of FIG. 2, the outer dimensions of the core body 1 are t ₂ (thickness) = 0.2 mm, H ₂ = 2.1 mm, H ₃ = 0.3 mm, H ₄ = 0. 0.01 mm, L ₂ = 0.7 mm, L ₃ = 0.3 mm, G ₂ = 0.01 mm, W ₂ = 0.02 mm, W ₃ = 0.2 mm, bias coil 2 AT = 100T × 0.025A, The number of turns of the reproduction coil 3 is selected to be 200T.
[0017]
That is, at the second embodiment, the shape of the tip portion 1a of the center core 1a 'is formed in a rectangular shape narrow, the width W ₂ is selected to be 0.02 mm. The width W ₂ is optimally in the range of 0.02 mm to 0.05 mm from the viewpoint of processability, magnetic field fluctuation detection sensitivity, and the like.
[0018]
Further, in the second embodiment, the shape of the tip portions 1b 'of both foot cores 1b facing the center core tip portion 1a' is formed into a triangle having a hypotenuse inclination angle θ of 45. It has been experimentally confirmed that the inclination angle θ is optimally set in the range of 30 ° to 60 ° from the viewpoint of processability, magnetic field fluctuation detection sensitivity, and the like.
[0019]
Further, the height H ₄ of the vertical surface of the foot core tip 1b ′ facing in parallel with the center core 1a is selected to be 0.01 mm, which is the same as the gap G, and the size of the H ₄ is 0.01˜ The range of 0.05 mm is optimal.
[0020]
Each of the bias coils 2 and 2 is supplied with a direct current of 0.025 A in the opposite direction as an exciting current, so that the magnetic field Hy in the center core 1 a at the normal time is zero.
FIG. 3 shows a magnetic field distribution Hy in the height direction of the sensor A inside the inspection object B in a steady state, and the magnetic field Hy in the center core 1a is zero.
[0021]
As will be described later, an ultrasonic wave is applied to the inspection object B from the transmitting ultrasonic probe, and this ultrasonic wave propagates through the inside (or the outer surface layer) of the inspection object B to a position below the sensor A. Suppose that it has reached. If it does so, the surface layer part of to-be-inspected object B will vibrate with the energy of the ultrasonic wave which has propagated.
[0022]
As shown in FIG. 4, when the surface layer portion of the inspection object B moves in the direction of arrow U due to vibration, eddy currents in the a and b directions are induced in the surface layer portion of the inspection object B facing the sensor A, As a result, a magnetic field hy is generated in the center core 1a.
The magnetic field hy in the center core 1a becomes an alternating magnetic field having the same frequency as the vibration frequency of the surface layer of the object to be inspected (that is, the vibration frequency of ultrasonic waves), and is linked to the reproduction coil 3 wound around the center core 1a. As a result, a detection signal indicating the propagation of ultrasonic waves having the same frequency as the alternating magnetic field hy is induced in the reproduction coil 3.
[0023]
FIG. 5 shows an example of the use of the electromagnetic ultrasonic sensor A according to the present invention, and shows a case where the sensor A is used to detect material deterioration of stainless cast steel. In FIG. 5, A is an electromagnetic ultrasonic sensor, 5 is a preamplifier, 4 is a transmission ultrasonic probe, 6 is an amplifier, 7 is a display, L is an incident point of the transmission probe and the center of the sensor A. An interval B from the core 1a, B is an object to be inspected (metal body).
[0024]
First, the surface (inspection surface) of the object to be inspected B is a clean surface, and then the object to be inspected is separated from the transmitting ultrasonic probe 4 and the electromagnetic ultrasonic sensor A by an appropriate distance, for example, L = 20 mm to 300 mm. Set on B.
When the setting of each device is completed, the transmitting ultrasonic probe 4 is operated. Thereby, ultrasonic waves (wavelength λ = about 6 mm to 0.6 mm) having a frequency of about 0.5 MHZ to 5 MHZ are transmitted from the transmitting ultrasonic probe 4 along the surface of the inspection object B. The transmission ultrasonic wave may be a longitudinal wave (SV wave) or a transverse wave (SH wave), and any type of transmission ultrasonic probe 4 may be used. A piezoelectric or electromagnetic type is most suitable.
The transmitted ultrasonic surface SV wave (or surface SH wave) penetrates from the surface of the inspected object B to a depth of about ½ of the wavelength λ (that is, about 2 to 3 mm). The surface layer of the test object B is advanced.
[0025]
When the ultrasonic surface SV wave (or surface SH wave) travels in the surface layer of the inspection object B, the surface layer of the inspection object B vibrates by the energy of the ultrasonic wave. As a result, the magnetic field formed on the surface layer of the inspection object B by the electromagnetic ultrasonic sensor A also fluctuates in vibration, and the fluctuation of the magnetic field on the surface layer of the inspection object B is caused by the reproducing coil 3 of the electromagnetic ultrasonic sensor A. Detected and displayed on the display 7.
[0026]
In addition, in FIG. 5, although the case where the electromagnetic ultrasonic sensor A which concerns on this invention was used for the material deterioration test | inspection of stainless steel material was demonstrated, it is the same also when using it for the inspection of the internal defect of stainless steel material, In this case, the ultrasonic wave is incident on the inside of the inspection object B from the transmitting ultrasonic probe 4 at a predetermined incident angle, and the ultrasonic wave reflected from the defective part is detected, thereby detecting the defective part. Will be detected.
Of course, as the inspection object B, not only stainless steel but also any kind of metal can be used as the inspection object B.
[0027]
【Example】
Stainless steel (thickness 25 mm, outer dimensions 100 mm × 200 mm) as the inspected object B, and a piezoelectric probe that transmits a surface SV wave with a frequency of 5 MHz as the transmitting ultrasonic probe 4, As the electromagnetic ultrasonic sensor A, the electromagnetic ultrasonic sensor A having a resolution (gap G) shown in FIG. 2 of about 0.01 mm is used, and the distance L between the electromagnetic ultrasonic sensor A and the transmitting ultrasonic probe 4 is L. Was set to 30 mm, 40 mm, and 50 mm, the state of change in the magnetic field on the surface of the test object B was detected by the electromagnetic ultrasonic sensor A.
[0028]
Note that the surface of the used object B to be inspected is machine-finished, and the object to be inspected B is not subjected to any special treatment such as thermal aging.
[0029]
FIG. 6 shows the measurement signal of the electromagnetic ultrasonic sensor A measured by an oscillator. The curve A is L = 30 mm, the curve B is L = 40 mm, and the curve C is L = 50 mm. Each one is shown.
In each of the curves A, B, and C, as clearly seen from the portions marked with the arrows A ′, B ′, and the arrow C ′, the fluctuation of the magnetic field due to the vibration near the surface of the inspection object B is clearly seen. It can be seen that the propagation of ultrasonic waves can be detected with high accuracy.
[0030]
【The invention's effect】
In the present invention, the core body of the electromagnetic ultrasonic sensor is a center core type core body, a reproduction coil is formed on the center core forming the core body, and a reverse magnetic field with the same intensity is applied to each foot core. Since the generated bias coils are wound respectively, alternating fluctuations in the magnetic field on the outer surface of the metal object to be inspected due to the propagation of ultrasonic waves can be detected with high sensitivity, and high accuracy detection of ultrasonic waves is possible. Become.
Further, since the detection gap G of the core body is set to 0.01 to 0.05 mm, the resolution as a sensor becomes higher and the detection accuracy of ultrasonic waves can be improved.
As described above, the present invention has an excellent practical utility as a sensor for electromagnetically detecting ultrasonic waves propagating in a metal.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a first embodiment of an electromagnetic ultrasonic sensor according to the present invention.
FIG. 2 is a front view showing a second embodiment of the electromagnetic ultrasonic sensor according to the present invention.
FIG. 3 is a diagram showing a magnetic field distribution in the height direction inside an object to be inspected in a steady state.
FIG. 4 is a diagram showing a state of a magnetic field in a surface layer portion of an inspection object B when detecting an ultrasonic wave.
FIG. 5 is an explanatory diagram showing an example of use of the electromagnetic ultrasonic sensor according to the present invention.
FIG. 6 shows an example of an ultrasonic detection waveform by an electromagnetic ultrasonic sensor.
FIG. 7 is a perspective view showing an outline of the electromagnetic ultrasonic sensor developed earlier.
FIG. 8 shows another example of the magnetic pole arrangement of the previously developed electromagnetic ultrasonic sensor.
FIG. 9 shows still another example of the magnetic pole arrangement of the electromagnetic ultrasonic sensor developed earlier.
[Explanation of symbols]
A is an electromagnetic ultrasonic sensor, B is an object to be inspected, L is a gap, G ₁ and G ₂ are gaps, W ₁ and W ₂ are widths of the center core, t ₁ and t ₂ are thicknesses of the core body, and θ is a foot core. Inclination angle of the hypotenuse of the tip 1 is a core body, 1a is a center core, 1b is a foot core, 2 is a bias coil, 3 is a reproduction coil, 4 is an ultrasonic probe for transmission, 5 is a preamplifier, 6 is an amplifier , 7 is a display.

Claims (3)

A magnetic field on the surface of the object to be inspected by propagating the ultrasonic wave from the transmitting ultrasonic probe through the inside of the object to be inspected and vibrating the surface layer of the object to be inspected using the energy of the ultrasonic wave that has propagated inside. In the electromagnetic ultrasonic sensor that detects the propagation of the ultrasonic wave by detecting the fluctuation of the magnetic field by a detection coil arranged movably on the surface of the object to be inspected, the electromagnetic ultrasonic sensor is And a center core (1a) and foot cores (1b) and (1b) disposed on both sides thereof, and a gap G between the center core (1a) and both foot cores (1b) is set to 0.01 to 0.05 mm. A bias core that is wound around a center core type core body (1) and both the foot cores (1b) and (1b) to generate a magnetic field in the same strength and in the opposite direction on each of the foot cores (1b) and (1b). Le (2) (2) and the electromagnetic ultrasonic wave sensor, characterized by being configured from said center core reproducing coil wound on (1a) (4). The electromagnetic ultrasonic wave according to claim 1, wherein the core body (1) is formed using Mn-Zn ferrite and the thickness (t) of the core body (1) is 0.1 to 0.2 mm. sensor. The in shape viewed from the front of the front end portion of the center core (1a), with the width W ₂ is a rectangular 0.02 to 0.05 mm, both Futokoa (1b) · facing the center core (1a) ( 2. The electromagnetic ultrasonic sensor according to claim 1, wherein a shape of the front end portion of 1 b) in a front view is a triangle having an inclination angle θ of a hypotenuse of 30 ° to 60 °.

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