JPH09325132A - Device and method for eddy current flaw detection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the device and method for eddy current flaw detection which minimize the dead zones of edge parts on both sides of a steel belt even when a belt plate varies in width or travels zigzag, and precisely detect an internal defect. SOLUTION: A probe (p) having an LC parallel resonance circuit formed by connecting capacitors (c) to an exciting coil (a) and a detecting coil (b) respectively in parallel increases the detection sensitivity and conductivity to a rotary transformer, and the probe (p) is made small-sized to reduce the blind zones physically; and the detection of the edge parts by the detecting coil is controlled by making good use of the disorder of the detection signal of the edge parts by the detecting coil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detection apparatus and an eddy current flaw detection method. More specifically, the present invention relates to an eddy-current flaw detection device and an eddy-current flaw detection method capable of accurately detecting internal and surface defects by minimizing dead zones at both edge portions of a strip steel.

[0002]

2. Description of the Related Art Conventionally, for example, ultrasonic flaw detection or eddy current flaw detection has been carried out in order to detect internal defects in a strip steel manufactured by cold rolling, such as double cracking due to non-metallic inclusions. For example, in Japanese Patent Laid-Open No. 6-66772,
A rotating disk with a rotating transformer equipped with a gate-type mechanism provided on a running metal strip, and a tire probe that comes into contact with the strip and a probe that rotates in a contactless manner near both edges of the strip. Inside of a metal strip that is configured so that the rotation axis is located on or near the edge, and the ultrasonic and AC current inputs and outputs necessary for flaw detection and measurement and display means are added. An apparatus for inspecting defects has been proposed.

However, since the eddy current flaw detection apparatus according to the above proposal has a structure in which an ultrasonic probe and a rotary disk type eddy current flaw detection probe from both ends are simply provided together with a portal frame located above the strip steel. , Has the following problems.

(1) When the width of the steel strip changes, the dead zone of the eddy current flaw detection at the end portion becomes wider and narrower.

(2) Even when the strip plate runs while meandering, the dead zone in the eddy current flaw detection at the end portion is widened similarly to the above.

(3) When the strip thickness of the steel strip changes, it is difficult to maintain an appropriate gap.

(4) Since the detection signal regarding the internal defect is weak, the flaw detection accuracy is poor.

(5) Since the low frequency power supply is used to detect the internal defect, the transmissibility of the rotary transformer is low.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art. Even if the width of the strip changes or the strip runs meandering, the strips on both sides of the strip are An object of the present invention is to provide an eddy current flaw detection device and an eddy current flaw detection method capable of accurately detecting an internal defect by minimizing a dead zone at an edge portion.

[0010]

The eddy current flaw detection apparatus of the present invention is characterized in that, in the eddy current flaw detection apparatus, a capacitor is connected in parallel to each of the excitation coil and the detection coil.

More specifically, the eddy current flaw detector of the present invention is, for example, an eddy current flaw detector for a running steel strip, which is arranged above the running steel strip orthogonal to the running direction of the steel strip. A guide member provided, an elevating means for raising and lowering the guide member, and at least two flaw detecting means slidably arranged on the guide member and having a pair of rotary flaw detectors at the bottom thereof. And a capacitor connected in parallel to each of the exciting coil and the detecting coil of the rotary flaw detector.

In the eddy current flaw detection apparatus of the present invention, there is provided a moving means for sliding the flaw detection means along the guide member, the flaw detection means is a position sensor for measuring the edge position of the strip steel, and a reference. It is preferable to have a distance sensor for measuring the height from the surface.

Further, in the eddy current flaw detector of the present invention,
The flaw detection means is disposed between the front and rear pressing rollers that hold the strip steel, is arranged on the opposite side between the front and rear pressing rollers that holds the strip steel, and holds the strip steel. It may be arranged facing the presser roller.

Further, in the eddy current flaw detector of the present invention, the guide member is provided with a stopper for regulating the descending position, or the power supply frequency used for exciting the exciting coil is 1 when the penetration depth of the eddy current is the plate thickness. It is preferable that the frequency is set to be about / 1/1/2.

On the other hand, in the eddy current flaw detection method of the present invention, a guide member is disposed above the traveling strip steel and orthogonal to the traveling direction of the strip steel, and an elevating means for elevating the guide member. An eddy current flaw detection method for a traveling steel strip using an eddy current flaw detection device comprising at least two flaw detection means having a pair of rotary flaw detectors at the bottom, which are slidably arranged on the guide member. The detection signal is processed as a dead zone for a certain period of time after the disturbance of the detection signal from the detection coil due to the edge of the strip steel is detected by the rotary flaw detector.

In the eddy current flaw detection method of the present invention, for example, the detection signal is processed with the flaw detection zone being a fixed time after the dead zone.

[0017]

The flaw detecting means is slid along the guide member and positioned at a predetermined position above the strip steel, and then the raising and lowering means lowers the flaw detecting means together with the guide member.
The rotary flaw detector is adjusted to have a predetermined gap with the strip steel. In this state, the rotary flaw detector is rotated and excited to excite an eddy current in the steel strip. If a defect exists inside the strip steel, the excited eddy current is disturbed. This disorder
For example, an internal defect is detected by detecting and amplifying as an induced voltage in a rotary flaw detector having a probe formed of a coil in which a parallel resonance circuit is formed, and extracting this voltage by, for example, a rotary transformer. Here, since the probe coil and the rotary transformer coil are the LC parallel resonance circuit, the probe coil and the rotary transformer coil can obtain desired detection sensitivity with a small number of turns and the transmissibility with the rotary transformer is improved. Further, since the probe can be downsized because the number of turns of the coil can be small, the dead zone at the edge of the steel strip can be minimized.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described based on the embodiments with reference to the accompanying drawings, but the present invention is not limited to the embodiments.

FIG. 1 shows an equivalent circuit of a flaw detector having a probe p and a rotary transformer t of the eddy current flaw detector of the present invention. The probe p has an exciting coil a and a detecting coil b.
And a capacitor c is connected in parallel to each of them to form an LC parallel resonance circuit. With such a configuration of the probe p, a large detection signal can be obtained with a small number of turns, and the transmissibility with the rotary transformer t can be improved. For example, the transmissibility of the probe p consisting of a coil having 10 turns with the rotary transformer t is about 15%, but by connecting the capacitor c in parallel to form an LC parallel resonance circuit, the value is about 80%. To improve. In addition, since the number of coil turns is small, the probe p
Can be reduced. For example, a probe p having a desired detection sensitivity can be obtained by using a 2 mm square ferrite core.

When eddy-current flaw detection is performed using the probe p having such a structure, 1/1 to 1 of the strip steel plate thickness is used.
The detection sensitivity can be increased by selecting an AC power source having a frequency with a penetration depth of about ½, preferably about ½. For example, when flaw detection is performed on a strip steel having a plate thickness of 0.15 mm, the frequency at which the penetration depth is about 0.075 mm is 15
It is preferable to use an AC power source of 0 KHz.

[0021]

EXAMPLE Next, an eddy current flaw detector having such a probe will be described based on an example.

Example 1 An eddy current flaw detector for strip steel (hereinafter, simply referred to as eddy current flaw detector) according to Embodiment 1 of the present invention is shown in FIG.
The eddy current flaw detection apparatus A is a guide frame (guide member) 1 and a hydraulic cylinder (elevating means) 2 for raising and lowering the guide frame 1.
And the flaw detection units (flaw detection means) 3 and 3 which are slidably mounted on the guide frame 1.

The guide frame 1 presses the surface of the running steel strip W and applies a constant tension to the steel strip W to prevent vibration and the like above the pair of pressing rollers R, R. Is arranged, and its both ends are located outside both edges of the running steel strip W. Further, at the center of the upper surface of the guide frame 1, the tip portion 21 of the piston rod 21 of the hydraulic cylinder 2 fixed to the beam B provided at the upper portion.
a is engaged. Further, lifting guides 11 are provided on both ends 1a and 1b of the guide frame 1 on the downstream side (hereinafter, simply referred to as the downstream side) in the traveling direction of the steel strip W. The guide post P is attached to the lifting guide 11.
Is slidably inserted in parallel with the piston rod 21. With such a configuration, the guide frame 1 can be smoothly moved up and down as the piston rod 21 moves up and down.

Here, in order to adjust the elevation position of the guide frame 1 by the hydraulic cylinder 2, the elevation guide 1 is adjusted.
A stopper 4 having a stopper member 41 that can move up and down is provided in the vicinity of 1. This stopper member 4
Reference numeral 1 denotes a bolt 41 which is projectingly provided on the downstream side surface 1c of the guide frame 1 and is screwed vertically to the screw body 12. Although not clearly shown in the figure, the head of the bolt 41 is, for example, a knob for adjusting the position so that the advancing length can be easily adjusted.

Two flaw detection units 3 and 3 are slidably mounted on the guide frame 1. The flaw detection unit 3 includes a unit main body 31 slidably mounted on the guide frame 1 and a main body 31 below the unit main body 31.
A rotary head 32 rotatably provided with respect to
A drive motor 33 provided on the upper part of the unit main body 31, and a drive force transmission mechanism 34 (see FIG. 4) for transmitting the drive force of the drive motor 33 to the rotary shaft 32a of the rotary head 32, A lock mechanism 35 for fixing the unit main body 31 to the guide frame 1 at a predetermined position.
Further, in the rotary head 32, a pair of probes (scratches) 36, 36 are embedded with their flaw detection portions 36a facing the strip steel W (see FIG. 4).

This probe 36, as shown in FIG.
Exciting coil 5 and a pair of coils arranged in the exciting coil 5, that is, a first coil 61 and a second coil 6.
The detection coil 6 is composed of 2 and the turbulence of the eddy current excited in the steel strip W by the excitation coil 5 is detected by the detection coil 6. Although not shown in the drawings, the exciting coil 5 and the detecting coil 6 are connected in parallel with each other to form an LC parallel resonance circuit as described above. Then, the probe 36 having a desired sensitivity can be obtained by setting the capacitance of the capacitor to an appropriate value.

The detection of defects by the probe 36 will be described more specifically as follows. If there is no defect in the steel strip W, the eddy current is not disturbed. Therefore, the voltages excited in the first coil 61 and the second coil 62 by this eddy current are equal, and there is no potential difference across the detection coil 6. However, if there is a defect in the steel strip W, the eddy current is disturbed. Therefore, the voltages excited in the first coil 61 and the second coil 62 are different due to this eddy current, and a potential difference is generated across the detection coil 6. Defects in the steel strip W can be detected by detecting this potential difference.

Then, in order to take out the potential difference detected by the probe 36, a rotary transformer 7 is constructed in the unit main body 31, as shown in FIG. That is, the primary coil 7 is attached to the rotary shaft 32a of the rotary head 32.
1 is provided with a first disk 32b, and the first disk 3b
The second disk 31a, in which the secondary coil 72 is arranged on the unit body 31 side with respect to 2b, is arranged on the same axis line so as to be opposed to the second disk 31a via a slit. The conducting wire from the probe 36 is connected to the primary coil 71, and the secondary coil 7
The lead wire from 2 is connected to a processing unit (not shown) of the eddy current flaw detector A. Further, a driven gear 341 is mounted on the rear portion of the rotary shaft 32a of the rotary head 32. Further, one end of a timing belt 342 of an endless type is stretched around the driven gear 341. The other end of the timing belt 342 has the drive motor 33 provided on the upper surface 31b of the unit body 31.
It is suspended on a drive gear 343 mounted on a drive shaft 33a extending inside the unit body 31 of FIG. Thus, in this embodiment, the drive gear 343, the timing belt 342, and the driven gear 341 constitute the drive force transmission mechanism 34.

The lock mechanism 35 for fixing the unit main body 31 to the predetermined position of the guide frame 1 is, as shown in FIG.
For example, one end of the square tubular steel 18 that is integrated with the guide frame 1 by welding 182 is in contact with the guide frame 1 and the other end penetrates the guide frame 1 and the guide frame 1 of the square tubular steel 18 is formed. Of the guide pipe 351 fixedly protruding from the surface opposite to the joint surface, the male screw member 352 having a thread formed at the tip end inserted into the guide pipe 351, and the male screw. The lock handle 353 is fixed to the rear end of the member 352, and the lock member 354 is screwed to the male screw at the tip of the male screw member 352. Here, the large plate-shaped portion (first sliding portion) of the lock member 354 is slidably mounted in the groove portion 381 of the lip groove-shaped slide frame 38 provided on the rear surface 31d of the unit body 31, and The upper surface 354a and the lower surface 354b of the block body (second sliding portion) provided on the side surface of the large plate-shaped portion are slidable in the guide groove 13 formed on the downstream side surface 1c of the guide frame 1. In addition to being mounted, the end surface 354c is mounted with a slight clearance from the bottom surface 13a of the guide groove 13. And
This lock member 3 is rotated by rotating the lock handle 353.
54 is drawn toward the bottom surface 13a of the guide groove 13, whereby the slide frame 38 is drawn toward the guide frame 1 and the square tube steel 18 to lock the unit main body 31. here,
Since the guide pipes 351 are fixed to both side surfaces of the square tube steel 18 as described above, they serve to prevent the square tube steel 18 from being deformed during this locking. That is, the guide pipe 351 also has a function as a reinforcing material for the square tube steel 18.

Next, with reference to FIGS. 6 to 8, an example of a flaw detection procedure for the strip steel W by the eddy current flaw detector A having such a configuration will be described.

The position of the stopper 4 is adjusted. That is, the advancing length of the stopper member 41 is adjusted.

After the flaw detection unit 3 is positioned at a predetermined position, it is locked by the lock mechanism 35. Here, because the strip steel W meanders about 5 mm, the rotation center O of the rotary head 32 is, for example, 10 mm inside the edge Wa of the strip steel W at this predetermined position (see FIG. 7).

The hydraulic cylinder 2 is driven to lower the guide frame 1 until the lower end of the stopper member 41 contacts the lowering stop member 44.

The drive motor 33 is rotated to rotate the rotary head 32 at a predetermined rotation speed (see FIG. 6). The predetermined rotation speed is determined by the traveling speed of the steel strip W, the size of the defect to be detected, and the probe 36 embedded in the rotary head 32.
It is appropriately selected according to the interval (rotation diameter) of 36. In addition,
The relationship between the number of rotations and the size of a defect that can be detected, that is, the flaw detection rate will be described later.

The probes 36, 36 are excited. As described above, this excitation is performed with a strip steel plate thickness of 0.15 m, for example.
In the case of m, it is done using an AC power supply of 150 KHz.

The strip steel W is run to start flaw detection.

When the probe 36 approaches the edge Wa of the steel strip W, the detection signal from the detection coil 6 is disturbed as shown in FIG. 8 (b). At this time, when the detection signal first exceeds the negative threshold value, a negative detection pulse signal is generated as shown in FIG. 8C, and then the detection signal first exceeds the positive threshold value. A positive detection pulse signal is generated as shown in 8 (d). Therefore, at the same time when the plus detection pulse signal is generated, the edge signal removal pulse is generated in order to remove the disturbed edge signal to make a certain range of the edge dead zone as shown in FIG. 8 (e). Is generated. Thereby, for example, a predetermined range from the edge Wa becomes a dead zone (see FIG. 7). At the same time as the disappearance of the edge signal removal pulse, a flaw detection enable pulse indicating that flaw detection is possible is generated as shown in FIG. Further, this flaw detection enable pulse enables flaw detection in a predetermined range from the edge Wa, for example. At the same time that the flaw detection enable pulse disappears, the flaw detection impossible pulse is generated so as not to detect the flaw detection unnecessary area where the ultrasonic flaw detection is performed. The pulse width of the flaw-detection-disabled pulse is such that the disturbance of the detection signal from the detection coil 6 that occurs when the probe 36 is rotated to deviate from the edge Wa and go out of the strip steel W can be detected. Is adjusted to disappear before the occurrence of. Then, when the non-detectable pulse disappears and the probe 36 approaches the edge Wa, the detection signal from the detection coil 6 is disturbed again, and the positive detection pulse and the negative detection pulse are generated as before. Then, after this positive detection pulse, the probe 36 is located outside the strip W, and there is no need for flaw detection. Therefore, as shown in FIG. 8 (h), the probe 36 is outside the strip W. A non-flaw detection pulse that makes the flaw detection impossible is generated. The pulse width of this non-detectable pulse is adjusted so that it disappears before this disturbance occurs so that the disturbance of the detection signal from the detection coil 6 that occurs when the probe 36 makes a half turn and approaches the edge Wa again. Has been done.

Here, regarding the dead zone and the feasible flaw detection range, for example, if the rotation diameter of the probes 36, 36 is 120 mm, the dead zone is within 5 mm from the edge Wa of the strip steel W, and the range from 5 to 30 mm from the edge Wa. It becomes possible to detect flaws.

Next, the flaw detection rate used here will be briefly described.

Considering the case where two probes 36 each having a diameter of 2 mm are used and the rotary head 32 is rotated at 4000 rpm for flaw detection, the feasible flaw length is 16 m / min from the probe diameter × probe rotation number × probe number. Becomes Therefore, if the traveling speed of the steel strip W is 16 m / min, the flaw detection rate is 100%. In addition, the traveling speed of the strip steel W is 32 m /
If so, the flaw detection rate is 50%.

As described above, according to the first embodiment, the flaw detection unit 3 can be installed at a desired position, and even if the width dimension of the strip steel W is changed, it can be easily dealt with, and the desired detection sensitivity can be obtained with the minimum number of turns. Since the probe 36 is miniaturized because it is obtained, the dead zone can be minimized and eddy current flaw detection can be performed.

Embodiment 2 FIG. 9 shows the essential parts of an eddy current flaw detector according to Embodiment 2 of the present invention.
10 and FIG. 10, the eddy current flaw detector A1 of the second embodiment is a modification of the first embodiment, in which the flaw detection unit 3 is moved by the motor 14 and the position sensor 81 for detecting the edge of the steel strip W is used. When the strip steel W meanders by providing the above, the position of the flaw detection unit 3 can be adjusted according to the meandering. More specifically, the guide frame 1
A moving motor (moving means) 14 is arranged in the central portion of the lower surface 1f of the above, and male screw members 15 and 16 rotated by the motor 14 are arranged on both sides of the motor 14, and the male screw members 15 and 16 are Since it is provided in the unit main body 31, it is screwed into the threaded portion 31c, and a position sensor 81 is provided in a portion located on the upstream side of one unit main body 31. Here, one of the male screw members, for example, the male screw member 16 is a reverse screw. Here, the movement of the flaw detection unit 3 is performed by the control device C shown in a block diagram in FIG. Since the remaining structure is similar to that of the first embodiment, detailed description of the structure is omitted.

Next, an eddy current flaw detector A having such a configuration
An example of the flaw detection procedure for the strip steel W according to No. 1 will be described. The control of whether or not the flaw detection of the detection coil 6 is possible is performed in the same manner as in the first embodiment.

The position of the stopper 4 is adjusted.

The flaw detection unit 3 is positioned in accordance with the width of the strip steel W designated in advance by the controller C.

The hydraulic cylinder 2 is driven to lower the guide frame 1 until the stopper member 41 contacts the lowering stop member 44.

The drive motor 33 is rotated to rotate the rotary head 32 at a predetermined rotation speed. The selection of the predetermined rotation speed is performed in the same manner as in the first embodiment.

The probes 36, 36 are excited. This excitation is also performed in the same manner as in the first embodiment.

The strip steel W is run to start flaw detection.

The edge W of the steel strip W is detected by the position sensor 81.
The position a is measured, and the instrumentation result is input to the control device C.

When the controller C compares the input measurement result with the reference position and finds a deviation, the controller C operates the moving motor 14 to move the flaw detection unit 3 to the edge Wa of the steel strip W.
To move to a predetermined position.

As described above, in the second embodiment, the position sensor 81 measures the position of the edge Wa of the strip steel W, and the position of the flaw detection unit 3 is also adjusted accordingly, so that the strip steel W meanders. The dead zone can always be minimized and eddy current flaw detection can be performed.

Embodiment 3 FIG. 11 shows the essential parts of an eddy current flaw detector according to Embodiment 3 of the present invention.
As shown in FIG. 12 and FIG. 12, the eddy current flaw detector A2 of the third embodiment is a modification of the second embodiment, in which the stopper 4 is of an automatic lifting type, and the extension length of the stopper member 41 is one unit main body 31. It is configured to be controlled by the distance sensor 82 provided in the. Here, as the automatic lifting type stopper 4, there is a stopper by a hydraulic motor D as shown in FIG. Alternatively, a worm may be formed on the stopper member, and the worm may be moved forward and backward by a worm wheel mounted on the rotary shaft of the motor. Since the remaining structure is similar to that of the second embodiment, detailed description of the structure is omitted.

Next, an eddy current flaw detector A having such a structure
Regarding an example of the flaw detection procedure for the strip steel W according to No. 2, the part different from the second embodiment will be described.

The distance to the reference plane S is measured by the distance sensor 82, and the measurement result is input to the controller C. Here, as the reference surface S, for example, one of the both end edges of the strip steel W or the upper surface of the central portion is used.

The controller C calculates the amount of advance of the stopper member 41 based on the input measurement result.

The control device C operates the hydraulic motor D and the like by the operation amount corresponding to the calculated advance amount to advance the stopper member 41 by a predetermined amount.

The flaw detection unit 3 is positioned in accordance with the width of the steel strip W designated in advance by the controller C.

The hydraulic cylinder 2 is driven to lower the guide frame 1 until the stopper member 41 contacts the lowering stop member 44.

As described above, in the third embodiment, the edge Wa of the steel strip W is detected by the position sensor 81 as in the second embodiment.
Since the position of the flaw detection unit 3 is adjusted according to the measurement, even if the steel strip W meanders, the dead zone can always be minimized and eddy current flaw detection can be performed. In addition to this, the distance sensor 82 measures the distance to the reference plane S, and the advancing length of the stopper member 41 is adjusted accordingly. Therefore, the change in plate thickness affects the height adjustment of the flaw detection unit 3. Even in the case, no special work is required.

The present invention has been described above based on the embodiments and examples, but the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in Examples 1 to 3, the flaw detection unit 3 is installed between the pressing rollers R, R, but, for example, as shown in FIG. 14, the flaw detection unit 3 is installed on the opposite side between the pressing rollers R, R. Alternatively, as shown in FIG. 15, the rotary head 32 may be installed so as to face the pressing roller R. In the example shown in FIG. 14, the rollers R, R
Since the rotary head 32 does not exist between them, the space between the pressing rollers R, R can be narrowed, and the vibration of the strip steel W can be suppressed more effectively. Therefore, the effect that the flaw detection accuracy can be improved, which is not obtained in the first to third embodiments, is obtained. Further, in the example shown in FIG. 15, in order to detect a portion of the steel strip W pressed by the pressing roller R, the steel strip W is
Since the vibration of is reliably suppressed, it is possible to obtain the effect of further improving the flaw detection accuracy. Further, as a matter of course, the ultrasonic flaw detection may be used in combination with the ultrasonic eddy current flaw detector.

[0062]

As described in detail above, according to the eddy current flaw detector of the present invention, since the probe having the desired sensitivity is downsized, the edge of the strip steel can be accurately edged while minimizing the dead zone. It is possible to obtain an excellent effect that eddy current flaw detection of the portion can be performed.

Further, since the position of the rotary head can be adjusted and the advancing length of the stopper can be adjusted, even if the width dimension and the plate thickness of the strip steel change, the edge portion can be properly positioned. An excellent effect that eddy current flaw detection can be achieved is obtained.

Further, according to the preferred embodiment of the present invention in which the edge position of the strip steel is measured by the position sensor and the position of the unit main body is adjusted according to the measurement result, the dead zone even if the strip steel meanders. It is possible to obtain an excellent effect that eddy current flaw detection can be performed with a constant value.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of a flaw detection unit used in an eddy current flaw detector of the present invention.

FIG. 2 is a perspective view of an essential part of an eddy current flaw detector according to Embodiment 1 of the present invention.

FIG. 3 is an explanatory diagram of a principle of flaw detection by a probe.

FIG. 4 is a cross-sectional view of the flaw detection unit according to the first embodiment.

FIG. 5 is an exploded perspective view of a lock mechanism according to the first embodiment.

FIG. 6 is an explanatory diagram of eddy current flaw detection of the steel strip in Example 1.

FIG. 7 is an explanatory diagram showing a flaw detection possible range of the probe in the first embodiment.

FIG. 8 is an explanatory diagram of a control signal that controls detection by the detection coil in the first embodiment.

FIG. 9 is an explanatory view of a main part of an eddy current flaw detector according to a second embodiment of the present invention.

FIG. 10 is a side view of the flaw detection unit according to the second embodiment.

FIG. 11 is an explanatory diagram of a main part of an eddy current flaw detector according to a third embodiment of the present invention.

FIG. 12 is a side view of a flaw detection unit according to a third embodiment.

FIG. 13 is an explanatory diagram of a hydraulic motor operating stopper used in the third embodiment.

FIG. 14 is an explanatory diagram of an embodiment in which the flaw detection unit is installed on the opposite side between the front and rear pressing rollers.

FIG. 15 is an explanatory diagram of an embodiment in which the flaw detection unit is installed so as to face a pressing roller.

[Explanation of symbols]

 a excitation coil b detection coil c capacitor p probe t rotary transformer 1 guide frame (guide member) 11 lifting guide 12 female screw body 13 guide groove 14 moving motor (moving means) 15, 16 male screw member 18 square tube steel 2 Hydraulic cylinder (elevating means) 21 Piston rod 3 Flaw detection unit (flaw detection means) 31 Unit body 32 Rotary head 33 Drive motor 34 Drive force transmission mechanism 35 Lock mechanism 36 Probe (flaw detector) 38 Slide frame 4 Stopper 41 Stopper member, bolt 44 Fall prevention member 5 Excitation coil 6 Detection coil 61 First coil 62 Second coil 7 Rotation transformer 71 Primary coil 72 Secondary coil 81 Position sensor 82 Distance sensor A Eddy current flaw detection device B Beam C Control device D Hydraulic motor P Guide post R Presser roller The rotation center of the reference plane W steel strip O rotary head

Claims (13)

[Claims] 1. An eddy-current flaw detector according to claim 1, wherein a condenser is connected in parallel to each of an exciting coil and a detection coil of the flaw detector. 2. A eddy current flaw detector for a running steel strip, comprising:
A guide member arranged above the traveling steel strip orthogonal to the traveling direction of the steel strip, an elevating means for elevating the guide member, and a slidable arrangement on the guide member. , At least two having a pair of rotary flaw detectors at the bottom
An eddy current flaw detection device comprising: individual flaw detection means, wherein a condenser is connected in parallel to each of the exciting coil and the detection coil of the rotary flaw detector. 3. The eddy current flaw detection apparatus according to claim 2, further comprising moving means for sliding the flaw detection means along the guide member. 4. The flaw detection means comprises a position sensor for measuring the edge position of the strip steel.
Alternatively, the eddy current flaw detection apparatus described in 3. 5. The eddy current flaw detector according to claim 2, 3 or 4, wherein the flaw detector comprises a distance sensor for measuring a height from a reference plane. 6. The eddy current flaw detection apparatus according to claim 2, wherein the flaw detection means is disposed between the pressing rollers before and after pressing the strip steel. 7. The eddy current flaw detection apparatus according to claim 2, wherein the flaw detection means is disposed on the opposite side between the front and rear pressing rollers pressing the strip steel. 8. The eddy current flaw detection apparatus according to claim 2, wherein the flaw detection means is disposed so as to face a pressing roller that is pressing the strip steel. 9. The eddy current flaw detection apparatus according to claim 2, wherein the guide member is provided with a stopper that regulates a lowered position. 10. The power supply frequency used for exciting the exciting coil is set so that the penetration depth of the eddy current is about 1/1 to 1/2 of the plate thickness.
10. The eddy current flaw detection apparatus according to any one of 1 to 9. 11. A guide member, which is disposed above the running steel strip and is orthogonal to the running direction of the steel strip, an elevating means for moving the guide member up and down, and slidable on the guide member. A method for eddy current flaw detection of a running steel strip using an eddy current flaw detection device comprising at least two flaw detection means having a pair of rotary flaw detectors at the bottom thereof, the method comprising: An eddy current flaw detection method characterized in that the detection signal is processed by setting a certain period of time after detection of disturbance of the detection signal from the detection coil due to the edge of steel as a dead zone. 12. The eddy-current flaw detection method according to claim 11, wherein the detection signal is processed using a flaw detection zone for a certain period of time after the dead zone. 13. A flaw detector for an eddy current flaw detector, comprising a capacitor connected in parallel to each of an exciting coil and a detecting coil.