JPH1038854A - Non-destructive inspection method and device of conductive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable fine flaw to be detected with high sensitivity by providing a loop-back electric circuit closely contacted in parallel to an object inspected and insulated from the object inspected, feeding a current with its same strength in reverse direction to the object inspected and the electric circuit, and measuring a distribution of an external magnet field. SOLUTION: An object inspected 16 that wave carried is pressed on a loading base 11, respective end portions thereof are pressure-contacted with an electrode 14 and a contact 15, is opposed to a core body surface of the loading base 11 via an insulation layer 12, and a closely contacted with the surface of the loading base 11 by a vacuum pumping facility. A current is supplied from a power unit to electrodes 13 and 14, the loading base 11 is driven in X- and Y-axis directions under a magnetic flux sensor 18, a full area of a measured portion of the object inspected 16 is scanned, and a magnet field is measured, an internal defect is detected based on that pattern. The current flows from the electrode 13 the core body of the loading base 11, to a contact 15, the object inspected 16, and the electrode 14 in order, and the currents of the object inspected 16 and of the loading base 11 core body are in the reverse direction. Consequently, if there is a defect in the object inspected 16, the result is a magnetic flux pattern reflecting that defect, and that defect can be detected with high sensitivity by the magnetic flux sensor 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the field of nondestructive inspection methods for conductive materials, and in particular, detects surface and internal defects based on a magnetic field generated by an electric current flowing through the material, and generates defects. The present invention belongs to the field of nondestructive inspection methods using a magnetometer, particularly preferably using SQUID, for detecting material damage based on a change in magnetic characteristics before performing.

[0002]

2. Description of the Related Art Non-destructive inspections have been conducted for a long time to find defects such as scratches and cracks existing in materials and to select and use only non-defective products. By the way, in recent years, LN
With the increasing number of structures that cause serious accidents such as G tanks, nuclear power equipment, bridges, and airplanes, there has been an increasing demand for detecting minute defects and small scratches in materials before they are damaged or destroyed. In order to make these expensive structures usable for a long period of time, techniques for assessing the remaining life of the structures are attracting attention. For this reason, techniques for non-destructively inspecting minute scratches and defects in materials are required. You. In this way, in order to respond to demands for ensuring safety and improving reliability in various fields such as the durability diagnosis of nuclear facilities and structures, the manufacture and maintenance of aircraft and ships, and the diagnosis of material deterioration, etc. A highly accurate nondestructive inspection technique capable of detecting flaws is desired. Further, it is preferable to perform the nondestructive inspection automatically from the necessity from the measurement environment and the demand for the reliability of the measurement accuracy.

[0003] Conventional non-destructive inspection techniques include:
There are a radiation transmission test, an ultrasonic test, a magnetic particle test, a penetrant test using a fluorescent dye, and an eddy current test. Each of these has a limitation in flaw detection capability. For example, in the ultrasonic flaw detection technique, it is necessary to make a measurement by bringing a probe into contact with the surface of a material, and it is difficult to detect a shallow flaw from the surface because of a dead zone due to the influence of surface reflection. The eddy current flaw detection technique uses a current induced in the surface layer when a high-frequency magnetic field is applied, so that only surface flaws can be detected and the size of the flaw and the state of extension in the depth direction cannot be accurately known.
The magnetic particle flaw detection test cannot detect internal defects and flaws, and requires a pretreatment for applying magnetic powder to the surface of the material. In a radiographic test, not only is it difficult to detect surface flaws, but it is not possible to perform a continuous test. As described above, these nondestructive inspection techniques have respective limitations, and in actual nondestructive inspection, several techniques have been used complementarily to make up for the shortfall. For example, ultrasonic inspection and radiation transmission tests are mainly used to detect defects and scratches inside materials, and magnetic particle inspection tests, penetrant inspection tests, eddy current inspection tests, etc. are used to detect defects and scratches on the surface layer of materials. Has been used.

[0004] As a method having a principle different from these inspection methods, there is a method of detecting a defect portion in a conductive material by measuring a magnetic field generated when an electric current is applied to the material.
That is, when a current flows through the conductive material, a magnetic field is induced around the current in accordance with the strength and direction of the current. When there are no scratches or defects inside the material, the current flowing through the material is homogeneous, and the state of the magnetic field induced around the material is also homogeneous. However, if there is a defect or the like in the material, the current flows bypassing that portion or the current passing through the defect or the like decreases. As described above, the direction and the intensity of the current in the defective portion change. At this time, the fluctuation of the magnetic field distribution generated by the current deviated from the normal state exhibits a specific pattern depending on the size and shape of the defect or the scratch. Therefore, by supplying a predetermined current to the conductive material and measuring the magnetic field distribution outside the material, it is possible to detect a defect or the like on the material surface or inside.

In recent years, SQUIDs (superconducting quantum interference devices)
As a result, a magnetometer capable of detecting a magnetic field with high sensitivity has been obtained, and a material testing method using a magnetometer utilizing the above principle has attracted attention. SQUID is highly sensitive to conventional magnetic sensors,
It has a feature that the detection sensitivity does not depend on the frequency in a wide frequency range between Hz. Also, SQUID
Can be made into a very small element by being composed of a thin film element, so that the spatial resolution is high. Due to these characteristics, it has already been widely used for biomagnetic measurement such as brain waves and magnetocardiograms, and for geophysical measurements such as ground magnetic exploration. Such a small and highly sensitive SQUID has a sensitivity of 1
Although it is said to be 0fT, the magnetic field generated by the above principle is approximately several tens of pT levels depending on the conditions,
By measuring an abnormal magnetic field generated by applying a current to the material using the SQUID, it becomes possible to non-destructively detect a defect or a scratch inside the material.

[0006] Biomagnetic measurement can be performed in a high-performance magnetically shielded room, but nondestructive inspection is usually performed in a place where the magnetically shielded room cannot be relied upon. You will be subject to loud magnetic noise. The influence of terrestrial magnetism, which is usually about 50 μT, is extremely large as compared with the magnetic signal from the detection target. Also, in order to minimize environmental magnetic noise, for example, a circuit for conducting a current to a subject is placed as far away as possible to avoid influence on the measurement magnetic field or used as a component of a refrigerator for cooling a magnetic flux sensor. Ingenuity is taken, such as placing the ferromagnetic material in isolation or magnetically shielding itself.

However, in the nondestructive inspection based on this principle,
It detects where the surrounding magnetic field changes partially due to a portion of the current that changes direction, bypassing locally existing scratches and defects, so the entire current flowing through the material is generated Magnetic field fluctuation due to a bypass current around the defect or the like is small with respect to the generated magnetic field. As described above, the magnetic field existing in the surrounding environment was large, and the measurement signal was buried, making it difficult to detect. Therefore, in the measurement, it is necessary to extract a fluctuating magnetic flux component added to a large magnetic flux induced by the entire current to determine a defect or the like. As described above, in order to increase the detection sensitivity and make it practical for practical use, the magnetic field based on the environmental magnetic level and the current flowing through the material is canceled out, and only the magnetic field caused by the defective portion of the measurement target is extracted. Advanced signal processing technology is needed.

[0008]

Accordingly, an object of the present invention is to provide a magnetic flux detection type nondestructive inspection method and apparatus capable of detecting minute scratches in a conductive material with high sensitivity. Is to do. Another object of the present invention is to provide a nondestructive inspection method capable of detecting a defect in a material whether it is in a surface layer or a deep layer. It is still another object of the present invention to provide a non-destructive inspection method and apparatus of a magnetic flux detection type capable of detecting regardless of the presence of magnetic noise at an inspection site.

[0009]

According to a non-destructive inspection method for a conductive material of the present invention, which solves the above-mentioned problems, a return electric circuit is provided in close contact with a subject in parallel, and a return circuit is provided between the subject and the return circuit. It is characterized in that a current having the same strength is applied in the opposite direction to the subject and the return circuit in the opposite direction and the distribution of a magnetic field generated outside is measured, thereby detecting a current path abnormality of the subject.
Further, in the nondestructive inspection method of the present invention, it is preferable that an alternating current in which two or more different frequencies are superimposed flows to the subject and the return circuit. Further, it is preferable that the shape of the return circuit is formed to be substantially the same as that of the test object, and the test and the return circuit are insulated by a thin insulating layer. It is preferable to measure the magnetic field distribution while moving the magnetic flux sensor relatively to the surface of the subject. Furthermore, it is preferable to calculate the magnetic field distribution by extracting the signal of the abnormal magnetic part by locking in with the current signal to which the measurement signal of the magnetic field distribution is applied. Further, the measurement of the magnetic field distribution can be performed by a SQUID (superconducting quantum interference device).

A nondestructive inspection apparatus for a conductive material according to the present invention, which solves the above-mentioned problems, comprises a mounting table composed of a conductor having one end connected to a first electrode and having a contact at the other end, and a connection to a subject. A second electrode, a power supply device connected to the first and second electrodes for supplying a direct current or an alternating current having one or more frequencies, and detecting a magnetic flux generated at a position close to the mounting table. A magnetic flux sensor and a scanning device that relatively moves the magnetic flux sensor and the mounting table are provided.The test object is closely mounted on the mounting table via an insulator, and one end of the test object is connected to the contact point of the mounting table. , The other end is connected to the second electrode, and the first electrode and the second
It is characterized in that a defect or a flaw of the subject is detected by flowing a current between the electrodes and measuring the distribution of a magnetic field induced outside by a magnetic flux sensor. Further, the nondestructive inspection device of the present invention further includes a current sensor for detecting an output current of the power supply device, a lock-in detector, and a waveform analysis device, wherein the lock-in detector outputs the output of the magnetic flux sensor to the current sensor. It may lock in at the output, extract the magnetic detection output of the same frequency as the applied current including the phase, and analyze the waveform based on the magnetic flux detection output of the same periodic component as the applied current. . Further, it is more preferable to use the SQUID as a magnetic flux sensor. The magnetic flux sensor is composed of a plurality of SQUIDs in a one-dimensional or two-dimensional array.
D may be arranged.

According to the nondestructive inspection method for a conductive material of the present invention, a conductive return electric circuit is provided in close contact with a conductive material to be inspected in parallel, and an electric current is applied to the object to return electric current. Since the same amount of current flows in the circuit in the opposite direction,
The magnetic field induced externally due to the current flowing through the subject has almost the same strength in the opposite direction to the magnetic field induced by the current flowing through the close return circuit, and is almost offset by the superposition of the two magnetic fields Is done. Therefore, if a defect or the like exists in the subject, the current flowing in the subject avoids the defect or the like and locally takes a flow path different from the normal, so that the induced magnetic field is biased. The magnetic field resulting from the current flowing through the entire specimen is canceled by the magnetic field based on the current flowing through the return circuit, and only the deviation based on the current in the abnormal portion remains. Since the magnetic flux pattern for such a deviation has a specific form based on the shape and size of the defect, the shape and size of the defect can be estimated based on the measurement result of the deviation.

In the prior art, the magnetic flux sensor is required to have a range ability to detect a slight deviation in the magnetic field induced by the entire current, and it is necessary to extract only the deviation by signal processing. According to the method of the present invention, since the offset is performed by the return circuit and the magnetic flux sensor can directly measure this deviation, even if the defect is small and the deviation is minute, the magnetic flux sensor does not have high rangeability. The detection can be performed with high sensitivity by the sensor, and advanced signal processing is not required. As described above, according to the present invention, a measurement signal from which unnecessary bias has been eliminated is directly obtained with a very simple configuration, so that a very small defect can be detected with high sensitivity. In addition, there is no need to use advanced signal processing technology, and the economics of manufacturing the device have been improved. By using the non-destructive inspection method of the present invention, extremely small defects can be accurately measured, so that the state of material damage caused by high temperature, corrosive environment, load, vibration, etc. can be quantitatively and temporally. This has made it possible to grasp, and it has become easier to accumulate data for predicting the life of metallic materials used in aircraft, chemical plants, nuclear power plants, and the like.

In the nondestructive inspection method described above, an alternating current in which two or more different frequencies are superimposed is caused to flow to a subject and a return circuit. The distribution can be detected. That is, the depth at which the current flows due to the skin effect of the current varies depending on the frequency. Therefore, if a high-frequency current flows only through the surface layer, it can be detected only in a defect in the surface layer. However, if a low-frequency current is used, a defect in the deep layer can be detected. Therefore, it is possible to define the measurement range by adjusting the frequency of the applied current, and to combine the measurement results at each frequency using an alternating current in which a plurality of frequencies are superimposed, to reduce defects such as defects. It becomes possible to grasp the shape in the depth direction. Furthermore, by using an alternating current with two or more different frequencies superimposed, it is possible to clarify the measurement at one frequency when it is mixed with environmental noise when measured at one frequency. Becomes Here, superimposing a plurality of frequencies refers to a case in which an alternating current including a plurality of frequency components is used at the same time, a case in which alternating currents of different frequencies are alternately used in time and time-series mixing, and a combination of these. Including

Further, if the shape of the return circuit is formed to be substantially the same as that of the object, the distribution of the current flowing through the object and the distribution of the current flowing through the return circuit become almost the same. Then, the external magnetic fields induced by the two currents are almost exactly canceled, and there is an effect that the detection when the subject has a defect or the like becomes easier. With such a configuration, it is also possible to detect at once a defect or the like of a circuit board having a complicated pattern. For example, when a good printed circuit board is used as a return circuit, a printed circuit board as a test object is placed on the return circuit via a thin insulating film, and an external magnetic field is measured by flowing currents in opposite directions to the lead pattern of the same shape. If there is a defect in the subject, there is a difference between the corresponding upper and lower currents, and an abnormal magnetic field pattern appears in that portion, so that the defect can be easily detected.

If the magnetic field distribution is measured while moving the magnetic flux sensor relative to the surface of the subject, the inspection apparatus can be configured with a small number of magnetic flux sensors. Since the signal processing circuits are provided corresponding to the magnetic sensors, the number of magnetic sensors affects the cost as a whole. The magnetic flux sensors are not limited to one, and may be those arranged in a linear array or arranged in a two-dimensional matrix. By doing so, the area that can be measured by one scan is widened, and the measurement time can be shortened. Furthermore, if the magnetic field distribution is calculated by extracting the signal of the abnormal magnetic portion by locking in with the signal of the current applying the measurement signal of the magnetic field distribution, the magnetic flux caused by the current actively applied from the current power supply can be obtained. Only the extraction is performed, so that the influence of the environmental magnetic noise is cut off and accurate measurement can be performed.

If the magnetic field distribution is measured by using a SQUID (superconducting quantum interference device) as a magnetic flux sensor, a flux gate type magnetic flux sensor, a semiconductor magnetic sensor, or a magnetic flux sensor using a Hall element or the like can be used. Extremely sensitive measurement is possible. It should be noted that environmental magnetic noise can be further reduced by using a gradiometer as the structure of the detection coil in the SQUID. The order of the gradiometer can be selected from a first-order differential type, a second-order differential type, and the like according to the complexity of the spatial gradient of the environmental magnetic noise.

A nondestructive inspection device for a conductor material according to the present invention comprises:
When a test object is disposed on the mounting table in close proximity via an insulating layer and a current is supplied from the power supply device, the current flows through the first electrode, one end of the mounting table, the mounting table, a contact at the other end of the mounting table, , Flows in a circuit connected in series with the second electrode. Therefore, the currents flowing through the mounting table and the subject are the same in magnitude and opposite in direction, and since the two current paths are close to each other, the magnetic field induced by both currents and generated outside the subject or the mounting table is almost canceled. Stay at a low level. Therefore, if a defect or the like exists in the subject and the current flowing through the subject takes a locally biased flow path, only the deviation of the magnetic field based on the current disturbed by the defect or the like is applied to the external magnetic field. appear. If one of the magnetic flux sensor and the mounting table is fixed and the external magnetic field distribution is measured while moving the other, the shape and size of the defect can be estimated based on the obtained magnetic flux pattern corresponding to the deviation. In addition, since the depth of the current that can be reached can be adjusted by selecting the frequency of the applied current, the position of the defect in the material in the depth direction can be sensed. As described above, the nondestructive inspection apparatus for a conductor material according to the present invention can be used for performing the above-described nondestructive inspection method according to the present invention.

Further, the non-destructive inspection device including the current sensor for detecting the applied current and the lock-in detector locks in the output of the magnetic flux sensor based on the periodic waveform of the applied current. Among them, only the component caused by the applied current can be extracted. Therefore, it is possible to obtain a signal having a high information density with little influence of environmental magnetic noise, and it becomes easy to analyze a magnetic flux pattern. When the moving speed of a defect or the like in the object and the frequency of the applied current are almost synchronized because the magnetic flux sensor and the object relatively move, it is difficult to detect a small defect. If the lock-in is performed accurately in the period, the oversight of the defective signal is reduced. Further, if the frequency is changed or a current including two or more frequency components is applied to lock-in and analyze each frequency, the defect can be detected without oversight.

Furthermore, if a SQUID having extremely high magnetic flux detection sensitivity and high spatial resolution is used as a magnetic flux sensor, extremely small defects and scratches can be reliably detected. Note that the entire measurement target area is measured by scanning the magnetic flux sensor relative to the subject.However, in order to quickly scan the entire subject having a wide surface because the magnetic flux sensor is extremely small, It is necessary to make the moving speed of the magnetic flux sensor or the subject sufficiently high. Therefore, a plurality of SQs are arranged in a one-dimensional or two-dimensional array
If UIDs are arranged, a single SKU
Since the measurement range is larger than in the case where an ID element is used, the scanning speed of the object portion is improved, and the measurement can be completed in a short time.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the nondestructive inspection method for a conductive material according to the present invention, when an electric current is applied to a conductor, the electric field is disturbed by a defect or the like present therein. By observing the distribution of the magnetic field outside the body, a defect or a scratch existing in the conductor is detected. If there are no defects in the conductor, the current flowing through the conductor has a certain distribution determined by the shape of the conductor, and the magnetic field induced outside this conductor is a constant distribution corresponding to the current distribution Indicates a state. However, if a defect exists in the conductor, the current causes disturbance at the defect portion corresponding to the shape and size of the defect. This current disturbance is
Affects the distribution of the magnetic field induced outside the conductor,
Disturbance reflecting the position, shape and size of the defect is given.

For example, as schematically shown in FIG. 1, if a slit-shaped notch 3 exists in the conductive material 1 in a direction crossing the current 2, the current flows around the notch 3, so that the current flows. In the magnetic field distribution near the surface of the conductive material induced by the magnetic field, local disturbance occurs. The measurement output when this is measured by a magnetometer exhibits a pattern having a peak 5 at the right end of the notch 3 and a valley 6 at the left end as viewed from the upstream of the current, as represented by the contour line 4 in the figure. . Such a disturbance of the magnetic field has a specific pattern corresponding to the state such as the shape and orientation of the defect. Therefore, a defect state in the material can be detected nondestructively by applying a current to the conductive material, measuring the magnetic field distribution near the surface thereof, extracting and analyzing the disturbed portion.

However, the change in the magnetic field due to the disturbance of the current is small as compared with the strength of the magnetic field induced by the current flowing through the entire cross section of the material. It is not easy to detect it. For this reason, advanced signal processing is required to cancel out the magnetic field intensity caused by the total current flowing through the material and to extract only the disturbance of the magnetic field caused by defects. The magnetic flux sensor for measuring the magnetic field includes a semiconductor magnetic sensor, a fluxgate sensor, and a SQUID.
Because high-sensitivity sensors such as ID (superconducting quantum interference device) sensors are used, the effects of the ferromagnetic parts of the device itself, the current flowing in the device, and the devices located in the surroundings A magnetic field that generates, and environmental magnetic noise such as terrestrial magnetism cannot be ignored.

Therefore, the nondestructive inspection method of the present invention uses a magnetic field distribution information measured by a magnetic flux sensor to perform signal processing to detect relatively small turbulence. The magnetic flux distribution near the surface of the object is directly reflected by the defects in the object, offset by the magnetic field generated by the current of the same magnitude flowing through the object. According to the configuration of the present invention, a magnetic sensor directly measures a magnetic field reflected by a defect, so that the defect can be detected with high sensitivity without performing advanced signal processing. In the nondestructive inspection method of the present invention, the current applied to the subject may be direct current, but alternating current may be used. When an alternating current is used, the signal can be easily separated from environmental magnetic noise by locking in the measurement output of the magnetic flux sensor using the cycle information. Also,
When two or more frequencies are used, the magnetic field caused by a defect or the like can be more easily separated from the environmental magnetism. Hereinafter, a method and an apparatus for nondestructively inspecting a conductive material according to the present invention will be described in detail using examples.

[0024]

FIG. 2 is a partial cross-sectional view showing a detection portion during a main inspection step in an embodiment of a nondestructive inspection apparatus for a conductive material according to the present invention, and FIG. 3 is a block diagram showing a main portion thereof.
FIG. 2A shows a step of supplying the subject to the mounting table, and FIG.
FIG. 3C illustrates a step of fixing the subject to the mounting table, FIG. 3C illustrates a step of measuring an external magnetic field while scanning the magnetic flux sensor, and FIG. 3D illustrates a step of ejecting the subject after inspection.

As shown in FIG. 2A, the nondestructive inspection apparatus of the present invention inspects a flat conductive material, and automatically supplies and fixes a subject 16 to a mounting table 11 for measurement. Then, after the measurement, the subject 16 is automatically discharged and the next subject 16 is supplied, so that a continuous inspection can be performed. The core of the mounting table 11 is made of a conductive material,
A return circuit for a current flowing through the subject 16 is configured. The core body is preferably configured so that there are no defects in the inside and on the surface that may obstruct the flow of current, and the current distribution is the same as the current in the non-defective test object. The core is connected to the first electrode 13 on the back side of one end, and the contact 15 is disposed on the front side of the other end and is exposed on the surface. Mounting table 11
Is covered with a thin insulator 12 except for the ends.
A second electrode 14 is provided on one side of the mounting table 11 where the first electrode 13 is located, and is exposed on the surface of the insulator 12 of the mounting table 11. The second electrode 14 is electrically insulated from the core of the mounting table 11. The subject 16 is conveyed to the mounting table 11 by the rollers 17 and is set on the mounting table 11.

As shown in FIG. 2 (b), the transferred subject 16 is pressed by the mounting table 11, and its ends are pressed against the second electrode 14 and the contact 15, respectively, via the thin insulating layer 12. Facing the surface of the core. The subject 16 is placed on the mounting table 11
A vacuum suction device is provided on the surface of the mounting table 11 so as to be in close contact with the surface of the mounting table 11. Since the surface of the core of the mounting table 11 needs to be finished as flat as the surface of the subject 16, the vacuum circuit is disposed inside the insulator 12 or at both ends of the mounting table 11. I have.

Next, as shown in FIG. 2C, a direct current or an alternating current is supplied from a power supply device (not shown) to the first electrode 13 and the second electrode 14 while the mounting table is placed under the magnetic flux sensor 18. 11 is driven in the X-axis direction and the Y-axis direction, scans the entire region of the subject 16 to be measured, measures the magnetic field, and detects an internal defect based on the pattern. The current is applied to the first electrode 1
3, an electric circuit configured by connecting the mounting body 11 core, the contact 15, the subject 16, and the second electrode 14 in this order. Therefore, the direction of the current flowing through the subject 16 and the direction of the current flowing through the core of the mounting table 11 are reversed, and the core forms a return circuit for the subject. If the current distribution in the core is the same as that of the test object when there is no defect, the magnetic field generated outside is canceled out to zero level, and the magnetic flux pattern reflecting the defect only when there is a defect in the test object Represents

The power supply can adjust the frequency of the current. Since this inspection device detects a defect in the portion where current flows, by adjusting the frequency based on the skin effect and adjusting the skin thickness where the current flows,
Defects and the like existing up to a predetermined depth can be detected. Further, by analyzing the detection results at a plurality of frequencies in a complex manner, it is possible to measure the state of extension of a defect or the like in the depth direction and to grasp the state of the defect at a desired depth. In addition, even when the frequency of the magnetic noise is close to the frequency of the measurement current, confusion can be avoided by using a plurality of frequencies. In order to use a plurality of frequencies for the measurement current, an alternating current including a plurality of frequency components may be generated simultaneously by the power supply device, or alternating currents of different frequencies may be used alternately in time.

The magnetic sensor 18 is a SQUID (superconducting quantum interference device) composed of a thin film element using semiconductor technology.
And a detection coil formed by winding a superconducting wire such as niobium around a bobbin, and immersed in a liquid helium container to be used so as to maintain the superconducting state during the measurement. The mounting table 11 is driven by a fluid-driven actuator to avoid environmental magnetic noise, avoiding electric equipment. When the frequency of the applied current is lower, the current reaches the deeper portion, so that it is easier to detect defects in the subject. However, since the defect detection resolution is reduced, if the moving speed of the mounting table 11 is high, The probability of overlooking a defect increases. Therefore, there is an appropriate balance between the frequency of the current and the moving speed of the mounting table. Further, FIG.
When the measurement is completed, the vacuum suction is released and the subject 16 is released from the mounting table 11 and pushed out onto the discharge roller 19 installed on the opposite side of the supply roller 17 to be discharged. Is ready to receive the next subject 16.

FIG. 3 is a block diagram of the measuring system in this embodiment. The first electrode 13 and the second electrode 14 are connected to the power supply 2
1 is connected to the output terminal, and a low-frequency measurement current is applied to an electric circuit composed of the subject 16 and the core of the mounting table 11. Current is supplied by twisted pair wires to reduce magnetic noise. The detection coil 23 and the SQUID 24 are housed in a cryostat 25 to constitute a high-sensitivity magnetic flux sensor 18, and are arranged so as not to come into close contact with the surface of the subject 16. The magnetic flux sensor 18 is controlled by the SQUID drive circuit 26 to measure a magnetic flux density near the surface of the subject. The magnetic flux density detection signal output from the SQUID drive circuit 26 is input to the lock-in detector 27. In order to supply a reference signal required for lock-in detection, the lock-in detector 27 further includes a current converter 22 connected to the output terminal of the power supply 21 and a phase having a predetermined amplitude and the same frequency as the output current. A signal is input. The lock-in detector 27 extracts a signal component having the same frequency as the output current from the magnetic flux detection signal, and detects a phase difference based on the phase of the reference signal. The magnetic flux signal extracted in this way is
This eliminates environmental magnetic noise such as a magnetic field and geomagnetism caused by the inspection apparatus and peripheral devices, and reflects only defects in the subject. The mounting table 11 on which the subject 16 is mounted is moved in the directions of the X axis and the Y axis by a scanning device (not shown) so that the magnetic sensor 18 can scan the entire surface of the measurement area.

The output from the lock-in detector 27 is input to a waveform analysis / image processing device 28. The waveform analysis / image processing device 28 generates a distribution diagram representing the state of the magnetic field near the surface of the subject 16 based on the position information of the magnetic sensor obtained from the scanning device and the magnetic flux information input from the waveform analysis / image processing device 28. Generates, analyzes the distribution map based on the correspondence relationship between defects and the magnetic flux distribution obtained in advance, detects flaws and defects, evaluates the shape, converts the image into a flaw image that can be grasped by humans, and displays it It is displayed on the device 29. In this embodiment,
A magnetic flux sensor using a magnetometer type coil was used, but a second derivative type detection coil and SQUI were used.
D, a coil obtained by integrally forming these with a thin film, or a coil of a first-order differential type is not limited to this, and a fluxgate sensor or a semiconductor magnetic sensor can be used as a magnetic flux sensor. Can also be used. Since a semiconductor magnetic sensor or the like does not require a cryostat and does not have any restrictions on its posture, it can be configured to scan from the lower surface of the inspection apparatus, which has the advantage of increasing the degree of freedom in design.

Since the magnetic field induced by the measurement currents in both the forward and reverse directions appears on the subject side and the mounting table side in the same manner, no matter which surface is scanned by the magnetic flux sensor, the defect in the subject side can be detected. Etc. can be detected. Further, as described above, a thin film element formed by a pair of the detection coil and the SQUID can be used, but not only a pair but also a linear array in which these are arranged in a line or a matrix on a surface. A two-dimensional array can also be used. The use of a large number of sensors arranged side by side increases the area that can be covered by one scan and improves the spatial resolution of measurement. Various insulators such as ceramic, synthetic resin, and paper can be used as an insulator to insulate the subject from the return circuit of the mounting table. However, good quality can also be obtained by forming a vacuum space or an air layer. Insulation can be obtained. Various methods other than vacuum suction can be used for the close contact between the subject and the mounting table. For example, a chuck may be provided above the mounting table, and the subject mounted on the mounting table may be pressed from above and mechanically fixed. A jaw-type grip may be provided at the end of the mounting table, and the mounting table and the subject may be interposed and fixed.

FIG. 4 is a sectional view showing a detection portion in another embodiment of the nondestructive inspection apparatus for conductive material of the present invention.
This embodiment has a detection unit that is more convenient when the subject is not a flat plate but has an arbitrary shape, as compared with the above. In FIG. 4, reference numeral 31 denotes a subject having conductivity. Since the surface of the subject 31 is curved, it is not appropriate to use a flat mounting table. Therefore, an insulating layer 32 is formed of an insulator on the surface of the subject 31 and a cover 33 made of a conductive material is placed thereon. The insulator may be a film-shaped insulator made of synthetic resin or a film that is deformed according to the surface shape, and may be a highly insulating coating film or the like. . The subject 31 and one end of the cover 33 are electrically connected by a conducting wire 34, and a current is applied between the first electrode 13 connected to the cover and the second electrode 14 connected to the subject 31 at the other end. If a magnetic field formed outside is measured while flowing the magnetic flux sensor 18 while scanning, a defect in the subject can be detected from the pattern of the magnetic field.

FIG. 5 is a perspective view showing a detection portion in a mode in which the non-destructive inspection apparatus for a conductive material according to the present invention is used for detecting a defect in a pipe wall thickness. In FIG. 5, reference numeral 41 denotes a pipe made of a conductive material such as cast iron as a subject. A thick film 42 having a high insulating property is wound around the outside of the pipe 41, and a cylindrical cover 43 made of a material similar to the pipe 41 is placed thereon. Instead of using an insulating film, an insulating coating film may be formed. Cover 43
Is split in two in the axial direction, and one side end is connected by a hinge so that it can be opened and closed. Further, a fastener 44 is provided on the other side end, and is wound around the pipe 41 so as to be locked in a state where the ends are abutted with each other. A conductive band made of a good conductor such as copper is wound around the both ends of the cover 43 in the circumferential direction, so that the current is dispersed over the entire width of the cover 43 to prevent the current in the cover from drifting. . A first jaw-shaped bracket 46 for supplying a current with the pipe 41 interposed therebetween is connected to the conductive band 45 at one end. An electric wire connected to one pole of a power supply device (not shown) is connected from the conductive band 45 at the other end.

On the other hand, the second power supply device is connected to the other pole.
The jaw-shaped fitting 47 holds the pipe 41 in front of the portion where the cover 43 is hung. The magnetic field near the outer surface of the cover 43 is measured while scanning the magnetic flux sensor 48. The magnetic flux sensor is of the second derivative type,
If there is a change in the magnetic field, the change is expanded and detected. The current from the power supply is supplied to the second jaw-shaped bracket 47, the pipe 41, the first
It flows through the circuit of the jaw fitting 46 and the cover 43. When there is no defect inside the meat of the pipe 41, the magnetic field generated by the current in the pipe 41 and the magnetic field generated by the current in the cover 43 cancel each other, and a large change is observed in the measurement signal of the magnetic flux sensor 48. However, when there is a defect in the pipe 41, the current changes its direction there and the magnetic field appearing outside changes, so that the magnetic flux sensor 48 detects with high sensitivity.

FIG. 6 is a sectional view showing a detection portion in an embodiment in which the non-destructive inspection apparatus for conductive material of the present invention is used to inspect a circuit on a printed circuit board. In FIG. 6, reference numeral 51 denotes a printed circuit board to be a subject. A desired printed pattern 52 is formed on the printed board 51 by a conductor such as copper or aluminum. On the other hand,
Reference numeral 53 denotes a reference printed circuit board serving as a comparison reference in the inspection. Print pattern 54 formed on reference substrate 53
Is the same as the print pattern of the subject, and it has been confirmed that there is no defect in the pattern. The reference substrate 53 can be used by selecting from non-defective products among the test objects. The subject 51 is stacked under the reference substrate 53 in the same direction with the insulating sheet 55 interposed therebetween. Therefore, the print patterns of the subject 51 and the reference substrate 53 face each other with the insulating layer interposed therebetween. It is also possible to use an insulating layer made of air surrounded by a frame 55 with a frame interposed therebetween instead of the insulating sheet. By doing so, there is an advantage that there is no fear of soiling the surface of the subject 51. Further, the insulating layer of the printed circuit board can be used as it is as the insulating layer between the subject and the reference substrate.

An appropriate number of through holes 56 at corresponding positions on one end are electrically connected to each other by electrodes 57,
The corresponding appropriate through-holes 58, 59 on the other end side are connected to a power source via electrodes 60, 61, respectively, to flow current.
Then, the current flowing in the printed pattern 54 of the reference substrate 53 flows in the opposite direction to the same circuit as the circuit in which the current flows in the printed pattern 52 of the subject 51. If a defect exists in the subject 51, an abnormal pattern appears in a magnetic field formed outside, and this is detected by the magnetic flux sensor plate 62 disposed on the reference substrate 53. The magnetic flux sensor plate 62 has a large number of semiconductor magnetic flux sensors formed in a two-dimensional array on a plane. By electrically scanning the magnetic flux sensors, a magnetic field state of a large area can be measured at once. When the magnetic flux sensor plate 62 is smaller than the reference substrate 53, the surface of the reference substrate is
The magnetic field may be measured while scanning two-dimensionally or two-dimensionally. In this way, the nondestructive inspection apparatus of the present embodiment uses a non-defective product as it is without manufacturing a specific reference circuit, quickly detects defects present in the print pattern 52 with high sensitivity, and performs product inspection. It can be performed.

[0038]

As described above, the nondestructive inspection method and apparatus for a conductive material according to the present invention returns the external magnetic field induced by the current in the sample by forming the detection portion using the return circuit. By almost canceling out the current flowing through the circuit, the magnetic flux sensor can detect minute scratches in the conductive material with high sensitivity. Further, the method and apparatus for nondestructively inspecting a conductive material according to the present invention can detect a defect in a material whether it is in a surface layer or a deep layer, and can clarify its position. Further, it is possible to provide a highly practical non-destructive inspection device capable of detecting regardless of the presence of environmental magnetic noise at the inspection site.

[Brief description of the drawings]

FIG. 1 is a drawing for explaining a detection principle in the present invention.

FIG. 2 is a partial cross-sectional view illustrating a configuration of a detection part in an embodiment of the nondestructive inspection apparatus for a conductive material according to the present invention.

FIG. 3 is a block diagram illustrating a main part of the present embodiment.

FIG. 4 is a cross-sectional view illustrating a configuration of a detection portion according to another aspect of the present embodiment.

FIG. 5 is a perspective view illustrating a configuration of a detection portion according to still another embodiment of the present embodiment.

FIG. 6 is a cross-sectional view illustrating a configuration of a detection portion according to another aspect of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conductive material 2 Current 3 Notch 4 Contour line 5 Magnetic field peak 6 Magnetic field valley 11 Mounting table 12 Insulator 13, 14 Electrode 15 Contact 16 Subject 17 Supply roller 18 Magnetic flux sensor 19 Discharge roller 21 Power supply device 22 Current converter Reference Signs List 23 Detection coil 24 SQUID 25 Cryostat 26 SQUID drive circuit 27 Lock-in detector 28 Waveform analysis / image processing device 29 Display device 31 Subject 32 Insulating layer 33 Cover 34 Conductor 41 Subject pipe 42 Insulating film 43 Cylindrical cover 44 Fastening Fixture 45 Conductive band 46, 47 Jaw-shaped fitting 48 Magnetic flux sensor 51 Printed circuit board 52, 54 Printed pattern 53 Reference printed circuit board 55 Insulating sheet 56, 58, 59 Through hole 57, 60, 61 Electrode 62 Magnetic flux sensor plate

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masaru Onishi 118 Futatsuka Noda City, Chiba Prefecture Kawasaki Heavy Industries Noda Factory (72) Inventor Kenjiro Haraguchi 118 Futatsuka Noda City Chiba Prefecture Kawasaki Heavy Industries Noda Factory (72) Inventor Shoji Kamiya 118 Nobutsuka, Noda City, Chiba Prefecture Kawasaki Heavy Industries Noda Factory

Claims (10)

[Claims] 1. An electric circuit is provided in close contact with a subject in parallel to insulate the subject from the electric circuit, and the same current is applied to the subject and the electric circuit in opposite directions so that the subject and the electric circuit are supplied to the outside. A nondestructive inspection method for a conductive material, comprising detecting a current path abnormality of a subject by measuring a distribution of a generated magnetic field. 2. The nondestructive inspection method for a conductor material according to claim 1, wherein the current is an alternating current in which two or more different frequencies are superimposed. 3. The insulation between the subject and the electric circuit is provided by a thin insulating layer sandwiched between the two, and the electric circuit has substantially the same shape as the opposing subject. 3. The nondestructive inspection method for a conductor material according to 1 or 2. 4. The nondestructive inspection method of a conductive material according to claim 1, wherein the measurement of the magnetic field distribution is performed by a magnetic flux detection end that moves relatively to the subject. 5. The method according to claim 1, wherein the measurement signal of the magnetic field distribution is locked in with the current to extract a signal of an abnormal portion, and the magnetic field distribution is calculated based on the extracted signal.
5. The non-destructive inspection method for a conductor material according to any one of items 1 to 4. 6. The method according to claim 1, wherein the magnetic field distribution is measured by a SQUID (superconducting quantum interference device).
6. The non-destructive inspection method for a conductor material according to any one of claims 1 to 5. 7. A mounting table made of a conductor having one end connected to the first electrode and having a contact at the other end, a second electrode connected to the subject, and a first electrode and a second electrode. A power supply device connected to supply a direct current or an alternating current having one or more frequencies, a magnetic flux sensor for detecting a magnetic flux, and a scanning device for moving the magnetic flux sensor relative to the mounting table. The subject is placed on the mounting table in close contact with an insulator, the contact is connected to one end of the subject, the second electrode is connected to the other end, and the first electrode and the second electrode are connected. A non-destructive inspection apparatus for a conductive material, wherein a current or a current flows between the magnetic flux sensors and a distribution of a magnetic field generated externally is measured by the magnetic flux sensor to detect a defect or a flaw of the subject. 8. A current sensor for detecting an output current of the power supply device, a lock-in detector, and a waveform analyzer, wherein the lock-in detector outputs an output of the magnetic sensor by an output of the current sensor. 8. The method according to claim 7, further comprising: extracting a magnetic detection output having the same frequency as the applied current together with the phase by performing lock-in, and analyzing the waveform based on the magnetic detection output having the same cycle. Non-destructive inspection equipment for conductive materials. 9. The nondestructive inspection apparatus for a conductor material according to claim 7, wherein the magnetic flux sensor is a SQUID. 10. The non-destructive inspection apparatus for a conductive material according to claim 9, wherein said magnetic flux sensor has a plurality of SQUIDs arranged in a one-dimensional or two-dimensional array.