JPH0737963B2 - Eddy current flaw detection coil device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detection coil device, and is particularly suitable for being applied to an eddy current flaw detection inspection device used in the intermediate and final steps of a steel hot rolling process. And a coil device.

Conventional technology Hot eddy current flaw detection is used to reliably detect external surface flaws in the hot rolling manufacturing process of steel materials, especially steel bars.Most of the conventional technology for cold metal pipes also uses it. Has adopted the eddy current flaw detection method using a through coil in which an electric wire is wound around a bobbin concentric with the material to be inspected. In such an eddy current flaw detection method, in order to detect a small flaw existing in a material to be inspected with high sensitivity, a combination of a through excitation coil and a plurality of inspection coils is performed.
JP-A-58-34357 discloses a method of signal processing from the plurality of inspection coils, and in this conventional method,
A multiplexer is used to perform scanning so as to extract a differential signal between the inspection coils arranged adjacent to each other on the circumference and between the quasi-adjacent inspection coils arranged shifted in the axial direction, and Japanese Unexamined Patent Publication No. 63-40850 discloses an eddy current flaw detector for in-pipe inspection to which a technique similar to this is applied.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention By the way, in eddy current flaw detection, in order to detect a smaller and shallower flaw with high sensitivity, it is necessary to appropriately set the ratio between the flaw size and the inspection coil size. When the size of the inspection coil is made smaller in order to detect a flaw, the following problems arise.

(1) Since the number of channels for arranging the inspection coil increases, it is necessary to consider the overlap of the effective sensing areas of the inspection coil and devise to ensure a substantially uniform flaw detection sensitivity over the entire circumference of the inspected material. Becomes

(2) It is necessary to improve the lift-off characteristic of the inspection coil (that is, the distance sensitivity characteristic of the inspection coil) as the inspection coil becomes smaller.

(3) What is important with the miniaturization of the inspection coil is that it is necessary to reduce the mechanical vibration pseudo-interference noise signal generated due to the distance variation between the material to be inspected and the inspection coil to improve the flaw detection accuracy. That is, the S / N ratio for small scratches is improved by the miniaturized inspection coil, but the relative sensitivity is reduced due to the fact that the relative sensitivity is proportional to the size of the probe. However, it is an essential condition in the rolling process that the mechanical distance from the inspection coil to the material to be inspected should be as large as possible in the case of eddy current flaw detection of hot bar steel or the like. However, if the distance from the inspection coil to the material to be inspected is increased, the magnetic field lines that mediate flaw detection will be attenuated, resulting in insufficient flaw detection sensitivity. In order to compensate for this, it is sufficient to expand and amplify the electric signal, but the mechanical vibration of the material to be inspected as described above becomes a large interfering signal and normal flaw detection becomes difficult.

(4) As the size of the inspection coil is reduced, the magnetic field line distance of the inspection coil is shortened, so that the flaw detection sensitivity is deteriorated, as described above. It is necessary to devise a mechanism for heat shield and cooling for protection. That is, when a small inspection coil is used, the sensitivity is lowered due to the shortening of the space magnetic path length due to the small inspection coil itself, and in addition, stainless steel as a heat shield / heat shield structure is used as a conventional means during hot material flaw detection. There is a problem that sensitivity is lowered due to overcurrent loss that occurs when a cylinder is used together.

As described above, although there are various problems to be considered in downsizing the inspection coil in eddy current flaw detection,
It cannot be said that the conventional eddy current flaw detection coil device as described above has been devised so as to sufficiently solve all of these problems.

An object of the present invention is to provide an eddy current flaw detection coil device which can solve the above-mentioned conventional problems.

Means for Solving the Problems According to the present invention, a through excitation coil mounted around a through hole for passing a material to be inspected of an eddy current flaw detection device, and an inspection coil mounting bobbin inserted in the through excitation coil. In a coil device for eddy current flaw detection, comprising: a plurality of inspection coils arranged on the circumference of the through coil, the through excitation coil includes a main coil portion extending over a predetermined width in the axial direction of the through hole, and the through excitation coil. An additional coil wound around both end portions of the coil portion so as to expand a vertical component magnetic field line distribution reduction region of an axial center inner wall portion of the plurality of inspection coils, and the plurality of inspection coils are excited by the through excitation coil. At least two of which are separated by a predetermined distance in the axial direction of the inspection coil mounting bobbin so as to be orthogonal to the penetrating excitation coil so as to be insensitive to the lines of magnetic force. The inspection coils arranged in two rows along one circumference are arranged such that adjacent inspection coils are differentially connected to each other to form a pair and output a flaw signal. Between the two rows, each test coil pair is arranged in a staggered arrangement.

EXAMPLES Next, the present invention will be described in more detail with reference to the accompanying drawings with reference to the examples of the present invention.

FIG. 1 is a partially cutaway side view schematically showing a hot eddy current flaw detection end to which an eddy current flaw detection coil device according to an embodiment of the present invention is applied, and FIG. 2 is the hot eddy current flaw detection detection. It is a front view of an end. As schematically shown in FIGS. 1 and 2, the hot eddy current flaw detection end has a side plate having a through hole 11 for passing a material to be inspected from the direction of arrow P.
The side plate 10 is provided with a jet device 20 for jetting cooling water. This jet device 20
Is connected to the water supply port 22 through the water supply pipe 21, and the cooling water supplied through the water supply port 22 is ejected along the inner peripheral surface of the through hole 11 of the side plate 10 to form a water film. ,
The heat shield cooling of the through excitation coil and the inspection coil described later is performed.

Further, around the through hole 11 in the side plate 10, the excitation frame 30
, Inspection coil mounting bobbin 40, excitation coil bobbin 60
And are attached. The detection coil mounting bobbin 40 is provided with a plurality of inspection coils 51 and 52, and the exciting coil bobbin 60 is wound with a main coil portion 70 and additional coil portions 71 and 72 that form a through exciting coil. Further, a magnetic shield member 73 is provided around the through excitation coil.

On the upper part of the side plate 10, a terminal cover 100 for attaching the plant tube 110 including a power supply connection line, a flaw signal lead-out line, etc. is attached, and the terminal cover 100 is attached to the excitation frame 30.
The terminal plate 80 fixed via the terminal plate collar 90 is covered. The terminal plate 80 has a through excitation coil 70, 7
Power connection terminal and test coil 5 for energizing 1, 72
A scratch signal output / deriving force terminal for deriving a scratch signal from 1, 52 or the like is provided.

In FIG. 1, reference numerals 120 and 121 indicate O-rings, and reference numeral 122 indicates packing.

Next, FIG. 3 is a perspective view showing only the exciting bobbin 60 in which the through exciting coil including the main coil portion 70 and the additional coil portions 71 and 72 is wound and the outer periphery is provided with the magnetic shield 73, as described above. Is shown. As well shown in FIG. 3, lead wires 74 and 75 for connecting to a power source are drawn out from both ends of the through excitation coil, and these lead wires 74 and 75 are corresponding terminals provided on the terminal board 80. Is connected to.

FIG. 4 shows only the inspection coil mounting bobbin 40 in a perspective view. As well shown in FIG. 4, the inspection coil mounting bobbin 40 has a circumferential groove formed in the middle portion thereof, and the bottom portion of the circumferential groove is, for example, 11 mm in the axial direction.
For example, 30 inspection coil insertion grooves 41 and 42 are formed along the two spaced apart circles at a pitch of 12 °, for example. Further, lead wire drawing grooves 43 and 44 for drawing out the inspection coil (scratch signal) leading lead are formed on both sides of the circumferential groove of the inspection coil mounting bobbin 40.

FIG. 5 is a perspective view showing one of the inspection coils 51 and 52. The inspection coil shown in FIG. 5 is a printed coil, and a printed conductor portion 53 that constitutes a winding portion of the coil and an output. The terminals 54 and 55 are provided on the substrate 56.

FIG. 6 is a partial perspective view showing a state in which the inspection coils 51 and 52 of FIG. 5 are inserted into the inspection coil mounting grooves 41 and 42 of the inspection coil bobbin 40 of FIG. 4, respectively.
Although FIG. 6 does not show the connecting line between the inspection coils 51 and 52 and the output lead wire, these line wires are connected between the output terminal portions of the inspection coils,
It will be easily understood that the test coil mounting bobbin 40 is drawn out through the corresponding lead wire lead-out grooves 43 and 44 and connected to the corresponding terminals of the terminal plate 80, respectively.

When the inspection coil mounting bobbin 40 in which the inspection coils 51 and 52 are arranged in this way is inserted into the exciting coil bobbin 60, the inspection coils 51 and 52 are the through exciting coils 70,
The magnetic field lines 71 and 72 are insensitive to the exciting magnetic field lines so that they intersect at right angles with the through exciting coil.

In the present invention, in order to ensure substantially uniform flaw detection sensitivity over the entire circumference of the material to be inspected, and to be able to detect leaks regardless of where on the outer surface of the material to be inspected scratches are scattered. To
A large number of small inspection coils are arranged, and the inspection coils are connected in a staggered arrangement so as to ensure a substantially uniform detection force in the directivity combination state of the inspection coils. That is, a first annular inspection coil group in which 30 inspection coils 51 are arranged at equal intervals so as to surround the material to be inspected on the same circle, and the circle around the circle in the axial direction of the inspection coil mounting bobbin 40. 30 on the same circumference at a position shifted by 1 pitch from the position (11 mm apart in the above example)
A second annular inspection coil group in which individual inspection coils 52 are arranged at equal intervals is provided. Then, as schematically and partially shown in FIG. 7, the first annular inspection coil group is an odd-numbered channel A, the second annular inspection coil group is an even-numbered channel B, and the odd-numbered channel A is In the above, a test coil pair that outputs a flaw signal by differentially connecting the test coil 51-1 having an odd coil number and the test coil 51-2 adjacent thereto is used, that is, the test coil 51 having the coil number 1 and the coil number. The test coil 51 of No. 2 and the test coil of No. 4 are differentially adjacent to each other
51 is differentially connected, and the inspection coil 51 having the coil number 5 and the inspection coil 51 having the coil number 6 are differentially connected, and the coil number 7 is connected.
The inspection coil 51 and the inspection coil 51 of the coil number 8 are differentially connected, and the adjacent adjacent inspection coils 51 are differentially connected. On the other hand, in the even-numbered channel B, the inspection coil 52 having an even coil number and the adjacent inspection coil 52 are differentially connected to form a pair of inspection coils for outputting a flaw signal, that is, the inspection coil 52 of the coil number 2. -2 and the inspection coil 52-3 of the coil number 3 are differentially connected, and the inspection coil 52-4 of the coil number 4 and the inspection coil of the coil number 5 are connected.
52-5 is differentially connected, the inspection coil 52 of the coil number 6 and the inspection coil 52 of the coil number 7 are differentially connected, and the inspection coil 52 of the coil number 8 and the inspection coil 52 of the coil number 9 are connected to each other. Then, the adjacent inspection coils 52 are made into a differentially connected pair.

Next, the present inventor, in the case of arranging a large number of such small inspection coils 51 and 52, examines how large the inspection coil should be in order to obtain various sizes. An experiment for obtaining a scratch signal by using test coils of various sizes for a scratch was repeated. The results are shown in the graph of FIG. In the graph of FIG. 8, the abscissa axis represents a value obtained by normalizing the size 1 of the used inspection coil by the length of the detected flaw with L, and the ordinate axis represents the S / N ratio. The results shown in FIG. 8 are obtained by differentially connecting the inspection coils and performing flaw detection across the flaw. As can be seen from the graph of FIG. 8, in order to obtain a flaw detection result with a good S / N ratio, it is preferable to set 1 / L <2, that is, the size of the inspection coil depends on the flaw to be flaw-detected. It is preferably less than twice the maximum length.

Further, the present inventor has found that the lift-off characteristics of the inspection coil, that is, the arrangement of the inspection coils such that the rate of change in sensitivity when the distance between the inspection coil and the material to be inspected changes as the inspection coil becomes smaller. In order to study the mode, when the distance between the probe and the inspected material (lift-off) is changed in the case where the pancake type probe is positioned parallel to the inspection target surface and the case where it is positioned vertically. I examined the degree of signal attenuation. As a result, it was found that when it was positioned vertically, the relative sensitivity was poor, but the attenuation due to lift-off was small.

Furthermore, the present inventor has examined a fundamental solution to this noise signal generation factor in order to reduce the size of the inspection coil and to reduce the mechanical vibration pseudo-interference noise signal that occurs with important distance variation. . There are various conceivable factors for generating an interfering noise signal generated due to a relative distance change between the inspection coil and the material to be inspected, but the noise signal can be substantially suppressed by considering the following two points. I thought. That is, (A) The alternating magnetic field generated due to the distance variation is a factor of noise signal generation, and the occurrence of interference may be achieved by arranging the inspection coil so that the change of the magnetic field line across the inspection coil is reduced.

(B) Eliminate other magnetic field distributions that contribute to the interference noise signal as much as possible.

First, the above item (A) was solved by making the sensitive axis of the inspection coil and the direction of the magnetic force lines substantially orthogonal. That is, the magnetic force lines generated by the exciting coil in the flaw detection test coil travel in the axial direction of the inner cylinder of the coil and then largely detour around the outer circumference of the coil to form a magnetic path. The sensitive axis of the inspection coil is made orthogonal to the magnetic field lines of excitation, and is made insensitive to the constant magnetic field lines of excitation in the normal state.
As in the above-described embodiment, this can be achieved by arranging the sensing shafts of the plurality of inspection coils in a skewer-like shape on the provisional empty circular ring that is annular along the inner circumference of the exciting coil.

Regarding the item (B), a positive measure is taken to reduce the vertical component of the magnetic force line distribution of the exciting coil. To describe this point in detail, for example, in a hot-rolled steel manufacturing facility, in order to perform a normal and smooth rolling operation, in general, the distance between the rolling roll and the rolling roll of the next stage is set to a certain value. Install as narrowly as possible. Immediately after the final rolling stand (roll), trumpet-shaped guides are provided everywhere. In such a layout, it is most feared that the steel bar runs meandering eggs outside the rolling facility, which is called a "miss roll" between the rolling roll stands or between the roll stands and another trumpet-shaped guide device. Under such circumstances, when installing non-destructive inspection equipment in rolling equipment, the hole (inner) diameter of the tunnel-hole-shaped flaw test coil should be as large as possible compared to the outer diameter of the rolled steel material. It is large, and it is compelled to shorten the axial length as much as possible. Therefore, also in the coil device for eddy current flaw detection, it is necessary to make the inner diameter of the through excitation coil as large as possible and the axial length as short as possible.

Therefore, when we examined the general characteristics of the magnetic field distribution of the magnetic field in the flaw test coil equipped with the cylindrical long-winding excitation coil, we found that it was as shown in FIGS. 9 and 10. It was The characteristics shown in FIG. 9 and FIG. 10 show the magnetic flux distribution of a simple solenoid air-core excitation coil. In FIG. 9, the horizontal axis indicates the distance in the coil length direction,
The vertical axis is the magnitude of the horizontal component of the exciting magnetic force line, and in FIG. 10, the horizontal axis is the distance in the longitudinal direction of the coil,
The vertical axis represents the magnitude of the vertical component of the exciting magnetic force line. Here, as is clear from the distribution characteristic of the vertical component of the exciting magnetic force line in FIG. 10, the inspection coil is preferably provided in the middle portion of the exciting coil, which is an area where the vertical component is small. If you try to make the axis as large as possible and make the axial length as short as possible, the reduction area of the vertical component of the magnetic field lines of the excitation in the middle part of the excitation coil will be narrowed by that much, and there will be restrictions on the placement position of the inspection coil. I found out that The present inventor considers a method in which even if the inner diameter of the exciting coil is increased and the axial length is shortened, a region in which the vertical component is reduced is sufficiently obtained in the middle portion of the exciting coil to arrange the inspection coil. Therefore, as shown in FIG. 11, it is necessary that the structure of the feedthrough excitation coil in which the additional coil portions 71 and 72 are wound around the outer periphery of the both ends of the main coil portion 70 can sufficiently meet the demand. I found it.

That is, in FIG. 11, reference numeral W _T indicates a winding width (mm) of the main foil portion 70, and reference numeral W ₀ indicates both end sides of the main coil portion 70 in order to reduce the vertical component of the exciting magnetic force line distribution. Winding width (m
m), and the reference number Dφ is the average diameter of the exciting coil (m
m) is shown. Various values of through excitation coils having various configurations as shown in FIG. 11 were produced, and W _0.1 φv / D value was obtained. Here, W _0.1 φv / D is 1 / of the maximum value of the vertical component of the magnetic force lines on both end faces of the exciting coil, where 1 /
A value obtained by dividing a region (mm) having a V-shaped characteristic having a strength of 10 by the average diameter D of the exciting coil is shown. The results are shown in Fig. 12. The graph shown in Fig. 12 shows W ₀ / W _{T on the} horizontal axis.
Is taken and the vertical axis is the value of W _0.1 φv / D. The curve A shows the characteristics when W _T /D=1.85, and the curve B shows the characteristics when W _T /D=0.81.
As can be seen from the curve in Fig. 12, the vertical component on the inner wall of the coil can be significantly reduced in the case of the exciting coil provided with the additional coil portion, compared with the case of the simple solenoid exciting coil. For example, as shown by the curve B, W _0.1 φ / D can be increased from 15% to 65%, that is, the vertical component reduction region can be expanded by about 4 times.

In order to confirm the effect of the additional coil according to the present invention as described above, a flaw detection apparatus using a simple solenoid coil without an additional coil as an exciting coil as in the prior art, and the same additional solenoid coil as described above are provided. The same flaw was inspected with the same flaw detector using the coil as an exciting coil. The graph of FIG. 14 shows a phase characteristic which is a flaw detection result when there is no conventional additional coil, and FIG. 13 shows a phase characteristic which is a flaw detection result when an additional coil is provided according to the present invention. There is. In these graphs, the upper two curves show the wound signals obtained for the two different types of wounds, respectively, and the lower two curves show the wound signals obtained for the two different types of wounds, respectively. 7 shows a captured noise (noise) signal. As is clear from these graphs, in the case of using the conventional exciting coil, the S / N ratio was about 5.9, whereas in the case of the exciting coil provided with the additional coil according to the present invention, , Its S / N ratio was confirmed to be about 11.8, which is a two-fold improvement.

In the embodiment shown in FIG. 1, the magnetic shield 73 is provided on the outer periphery of the exciting coil because the exciting magnetic circuit is formed by providing such a magnetic shield, which is used when high power excitation is performed. This is because the hysteresis loss of the outer peripheral case of the flaw detection test coil is prevented in advance, heat generation is suppressed, and the drift due to the rise in the ambient temperature of the inspection coil is reduced.

EFFECTS OF THE INVENTION Since the coil device for eddy current flaw detection according to the present invention has the above-described configuration, even if the inspection coil is downsized, uniform flaw detection sensitivity can be secured over the entire circumference of the material to be inspected, and the inspection coil Lift-off characteristics are improved, and even if the inner diameter of the exciting coil is increased and the axial length is shortened, mechanical vibration pseudo-interference noise signals can be reduced and flaw detection accuracy can be improved. Obtainable.

[Brief description of drawings]

FIG. 1 is a partially cutaway side view schematically showing a detection end for hot eddy current deep flaw to which a coil device for eddy current flaw detection as an embodiment of the present invention is applied, and FIG. 2 is a detection view for hot eddy current flaw detection. FIG. 3 is a front view of the end, FIG. 3 is a perspective view showing an exciting coil portion of the coil device for eddy current flaw detection at the detection end for hot eddy current flaw detection in FIG. 1, and FIG. 4 is a hot eddy current flaw detection in FIG. 5 is a perspective view showing only the inspection coil mounting bobbin at the detection end for use in
1 of the inspection coil at the detection end for hot eddy current flaw detection in FIG.
6 is a partial perspective view showing a state in which the inspection coil of FIG. 5 is inserted into the inspection coil mounting groove of the inspection coil bobbin of FIG. 4, and FIG. 7 is a partial perspective view of FIG. FIG. 8 is a schematic view for illustrating the mode of differential connection of the inspection coils of the eddy current flaw detection coil device at the hot eddy current flaw detection end, FIG. 8 shows the size of the inspection coil, the flaw size, and the obtained flaw signal S The figure which shows the graph which illustrates the relationship with / N ratio, 9th
FIG. 10 is a diagram illustrating a distribution of horizontal components of exciting magnetic flux by a simple solenoid air-core exciting coil. FIG. 10 is a diagram illustrating distribution of vertical components of exciting magnetic flux by a simple solenoid air-core exciting coil. FIG. 12 is a diagram schematically showing the basic structure of an exciting coil according to the present invention, and FIG. 12 is a graph for illustrating the reduction of the vertical component of the exciting magnetic field line distribution by the exciting coil having the configuration shown in FIG. FIG. 13 is a diagram showing a flaw signal when the coil device for eddy current flaw detection according to the present invention is used.
FIG. 14 shows a graph for illustrating the S / N ratio, and FIG. 14 shows the S / N of the scratch signal when the conventional eddy current flaw detection coil device is used.
It is a figure which shows the graph for illustrating a ratio. 10 ... Side plate, 11 ... Through hole, 20 ... Jet device, 21 ... Water supply pipe, 22 ... Water supply port, 30 ... Excitation frame, 40 ... Inspection coil mounting bobbin, 41, 42 ... Inspection coil Insertion groove, 43,44 …… Lead wire drawing groove, 51,52 …… Inspection coil, 53 …… Printed conductor section, 54,55 …… Output terminal section, 56 …… Board, 60 …… Excitation coil bobbin 60, 70 …… Main coil part, 71,72 …… Additional coil part, 73 …… Magnetic shield member, 74,75 …… Lead wire.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Akira Saeki 1-5-7 Sakuragawa, Itabashi-ku, Tokyo Hara Denshi Sokki Co., Ltd. (72) Inventor Shoji Hayashibe 1-5-7 Sakuragawa, Itabashi-ku, Tokyo Hara Denshi Sokki Co., Ltd. (72) Inventor Katsumi Taguchi 1-5-7 Sakuragawa, Itabashi-ku, Tokyo Hara Denki Sokki Co., Ltd. (56) Reference JP-A-58-34357 (JP, A) Kai 63-40850 (JP, A) JP 62-123352 (JP, A) Actually developed 62-167161 (JP, U)

Claims (3)

[Claims] 1. A through excitation coil mounted around a through hole for passing a material to be inspected of an eddy current flaw detection device, and a plurality of arrangements on the circumference of an inspection coil mounting bobbin inserted in the through excitation coil. In the coil device for eddy current flaw detection, the through excitation coil has a main coil portion extending over a predetermined width in the axial direction of the through hole, and a vertical center inner wall portion of the through excitation coil. And an additional coil portion wound around both ends of the main coil portion so as to extend the component magnetic field line distribution reduction region, and the plurality of inspection coils are insensitive to the exciting magnetic field lines generated from the through exciting coil. As described above, at least two of them are separated by a predetermined distance in the axial direction of the through hole of the inspection coil mounting bobbin so as to intersect the through excitation coil at right angles.
The inspection coils arranged in two rows along one circumference are arranged such that adjacent inspection coils are differentially connected to each other to form a pair and output a flaw signal. The coil device for eddy current flaw detection is characterized in that the inspection coil pairs are arranged in a staggered arrangement between the two rows. 2. The coil device for eddy current flaw detection according to claim 1, wherein the size of the inspection coil is smaller than twice the maximum length of the flaw to be flaw-detected. 3. The coil device for eddy current flaw detection according to claim 1, wherein the inspection coil is a printed coil.