Magnetic flux leakage detection device and magnetic flux leakage detection method

Abstract

To provide a magnetic flux leakage flaw detection device that can suppress a decrease in defect detection accuracy even with a small and inexpensive handheld device. [Solution] The leakage flux flaw detection device 1 comprises a magnetizer 7 that is swept along the surface of the object to be inspected W and magnetizes the object to be inspected W in the sweeping direction, a magnetic sensor 9 that measures the horizontal magnetic flux φy in the sweeping direction and the vertical magnetic flux φz perpendicular to the surface of the leakage magnetic flux of the object to be inspected W, and a processing unit 10 that limits the measured data of the horizontal magnetic flux φy and the vertical magnetic flux φz to a frequency band corresponding to the sweeping operation. The processing unit 10 detects defects in the object to be inspected W by the cross-correlation waveform Corr of the interval integral data of the band-limited horizontal magnetic flux φy and the data of the band-limited vertical magnetic flux φz.

Description

Technical Field

[0001] The present invention relates to a leakage magnetic flux flaw detection device and a leakage magnetic flux flaw detection method.

Background Art

[0002] As a method for non-destructively inspecting the presence or absence of defects in an inspection object such as a steel material, typically, X-ray flaw detection, ultrasonic flaw detection, magnetic particle flaw detection, eddy current flaw detection, leakage magnetic flux flaw detection, etc. are known. In particular, leakage magnetic flux flaw detection can detect relatively small defects by acquiring the waveform of the magnetic flux leaking from the defective part while magnetizing the inspection object.

[0003] For example, Patent Document 1 discloses a leakage magnetic flux flaw detection device that mounts a device for acquiring the waveform of the magnetic flux leaking from the defective part while magnetizing the inspection object on a moving carriage that moves the upper surface of the inspection object at a constant speed. Such a leakage magnetic flux flaw detection device is often used for inspecting products before factory shipment by being incorporated into a steelmaking line in a steelmaking plant, and is used for detecting defects from relatively large steel plates.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, when it comes to easily determining whether or not there are defects in relatively small steel materials cut from large steel plates for product manufacturing, a handheld magnetic flux leakage detector is required. However, when configuring a magnetic flux leakage detector in a handheld type, the demands for cost reduction and miniaturization are strict, making it difficult to use analog elements with relatively high magnetic flux measurement accuracy. Furthermore, the performance of the processing unit is also limited, so there is a risk that the measured magnetic flux data cannot be processed with sufficient accuracy. In addition, since magnetic flux testing is performed manually, the sweep speed is not constant, which may further reduce the measurement accuracy of the magnetic flux data. As a result, there is a risk that the accuracy of detecting defects in steel materials will decrease with a handheld magnetic flux leakage detector.

[0006] This invention has been made in view of the above circumstances, and its objective is to provide a magnetic flux leakage flaw detection device and a magnetic flux leakage flaw detection method that can suppress a decrease in defect detection accuracy even with a small and inexpensive handheld device. [Means for solving the problem]

[0007] <First aspect of the present invention> A first aspect of the present invention is a magnetic flux leakage flaw detection device comprising: a magnetizer that sweeps along the surface of an object to be inspected and magnetizes the object in the sweeping direction; a magnetic sensor that measures the horizontal magnetic flux in the sweeping direction and the perpendicular magnetic flux perpendicular to the surface of the object to be inspected; and a processing unit that limits the measured data of the horizontal magnetic flux and the perpendicular magnetic flux to a frequency band corresponding to the sweeping operation, wherein the processing unit detects defects in the object to be inspected by the cross-correlation of the interval integral data of the band-limited horizontal magnetic flux and the band-limited data of the perpendicular magnetic flux.

[0008] The leakage flux flaw detection device according to the first aspect of the present invention measures the leakage flux while magnetizing the object to be inspected, and extracts the signal component by manual sweep while removing noise by performing a band-limiting process on the measurement data. Furthermore, the leakage flux flaw detection device performs interval integration on the band-limiting horizontal flux to align the phase of the peak with that of the band-limiting vertical flux. By calculating the cross-correlation of the horizontal and vertical fluxes whose peak phases are aligned, the magnitude of the flux when both the horizontal and vertical components of the leakage flux are present is emphasized. As a result, even if the measurement accuracy of the measurement data is low, the user can determine the presence or absence of defects in the object to be inspected based on this cross-correlation, which has a high signal-to-noise ratio. Therefore, according to the leakage flux flaw detection device according to the first aspect, even with a small and inexpensive handheld device, a decrease in the accuracy of defect detection can be suppressed.

[0009] <Second aspect of the present invention> A second aspect of the present invention is a leakage flux flaw detection device in which, in the first aspect of the present invention described above, the processing unit performs moving average processing on the bandwidth-limited measurement data.

[0010] According to the leakage flux flaw detection apparatus of the second aspect of the present invention, noise processing can be performed by moving average processing on band-limited horizontal and vertical magnetic flux, thereby further improving the signal-to-noise ratio of the calculated data.

[0011] <Third aspect of the present invention> A third aspect of the present invention is a leakage magnetic flux flaw detection device in which, in the first or second aspect of the present invention described above, the magnetic sensor outputs a digital signal of the measurement data to the processing unit.

[0012] According to the third aspect of the present invention, since both the magnetic sensor and the processing unit can be directly connected as digital components, there is no need to employ related equipment such as amplifiers and AD converters, which are analog components, making the device compact and inexpensive to configure.

[0013] <Fourth aspect of the present invention> A fourth aspect of the present invention is a magnetic flux leakage flaw detection device in which, in the first or second aspect of the present invention described above, the magnetizer includes a permanent magnet and is configured to allow manual disconnection and reconnection of a closed magnetic path between the permanent magnet and the object to be inspected.

[0014] According to the fourth aspect of the present invention, the magnetic flux leakage flaw detection device is configured with a manually operated permanent magnet, rather than a coil wound around a yoke that is energized, thereby suppressing power consumption for magnetization and its operation.

[0015] <Fifth aspect of the present invention> A fifth aspect of the present invention is a magnetic flux leakage flaw detection device that, in the first or second aspect of the present invention described above, is equipped with a display unit for displaying the maximum value of the cross-correlation.

[0016] According to the fifth aspect of the present invention, the leakage flux flaw detection device allows the user to intuitively grasp the magnitude of the leakage flux based on the maximum value of the cross-correlation, and since the measurement, processing, and display of the leakage flux can be completed within the device, a communication module and an external processing server are not required.

[0017] <Sixth aspect of the present invention> A sixth aspect of the present invention is a leakage flux flaw detection method comprising: a magnetization step of sweeping a magnetizer along the surface of an object to be inspected to magnetize the object in the sweeping direction; a measurement step of measuring the leakage flux of the object to be inspected, specifically the horizontal magnetic flux in the sweeping direction and the vertical magnetic flux perpendicular to the surface; a band limiting step of limiting the measurement data of the horizontal magnetic flux and the vertical magnetic flux to a frequency band corresponding to the sweeping operation; and a cross-correlation step of detecting defects in the object to be inspected by cross-correlation between the interval integral data of the band-limited horizontal magnetic flux and the data of the band-limited vertical magnetic flux.

[0018] The leakage magnetic flux flaw detection method according to the sixth aspect of the present invention measures the leakage magnetic flux while magnetizing the inspection object, and extracts the signal components by manual scanning while removing noise by performing band-limiting processing on the measurement data. Further, the leakage magnetic flux flaw detection method performs a process of aligning the phases of taking peaks with respect to the band-limited vertical magnetic flux by performing interval integration processing on the band-limited horizontal magnetic flux. Here, by calculating the cross-correlation between the horizontal magnetic flux and the vertical magnetic flux with aligned peak phases, the magnitude of the magnetic flux when both the horizontal component and the vertical component of the leakage magnetic flux occur is emphasized. As a result, even when the measurement accuracy of the measurement data is low, the user can determine the presence or absence of defects in the inspection object based on the cross-correlation with a high S / N ratio. Therefore, according to the leakage magnetic flux flaw detection method according to the sixth aspect, even a small and inexpensive handy-type device can suppress a decrease in defect detection accuracy.

[0019] <The seventh aspect of the present invention> The seventh aspect of the present invention is a leakage magnetic flux flaw detection method that performs a moving average process on the band-limited measurement data in the band-limiting step in the sixth aspect of the present invention described above.

[0020] According to the leakage magnetic flux flaw detection method according to the seventh aspect of the present invention, noise processing can be performed by performing a moving average process on the band-limited horizontal magnetic flux and vertical magnetic flux, and the S / N ratio of the calculated data can be further improved.

[0021] <The eighth aspect of the present invention> The eighth aspect of the present invention is a leakage magnetic flux flaw detection method that outputs the measured measurement data as a digital signal in the measurement step in the sixth or seventh aspect of the present invention described above.

[0022] According to the leakage magnetic flux flaw detection method according to the eighth aspect of the present invention, since both the magnetic sensor and the processing unit can be directly connected as digital components, there is no need to employ related devices such as an amplifier or an AD converter like analog components, and leakage magnetic flux flaw detection can be configured in a small and inexpensive device.

[0023] <The ninth aspect of the present invention> The ninth aspect of the present invention is a magnetic flux leakage flaw detection method in the sixth or seventh aspect of the present invention described above, in which in the magnetization step, the closed magnetic circuit between the permanent magnet and the inspection object is manually disconnected and connected.

[0024] According to the magnetic flux leakage flaw detection method according to the ninth aspect of the present invention, the mechanism for magnetizing the inspection object is constituted by a permanent magnet that is manually operated, rather than a configuration in which a coil wound around a yoke is energized, so that power consumption for magnetization and its operation can be suppressed.

[0025] <The tenth aspect of the present invention> The tenth aspect of the present invention is a magnetic flux leakage flaw detection method in the sixth or seventh aspect of the present invention described above, including a display step of displaying the maximum value of the cross-correlation.

[0026] According to the magnetic flux leakage flaw detection method according to the tenth aspect of the present invention, the user can intuitively grasp the magnitude of the magnetic flux leakage based on the maximum value of the cross-correlation, and the measurement, processing, and display of the magnetic flux leakage can be completed within the device, so that a communication module and an external processing server are not required.

Advantages of the Invention

[0027] According to the present invention, it is possible to provide a magnetic flux leakage flaw detection device and a magnetic flux leakage flaw detection method capable of suppressing a decrease in the accuracy of defect detection even in a small and inexpensive handy-type device.

Brief Description of the Drawings

[0028] [Figure 1] It is an external configuration diagram of a magnetic flux leakage flaw detection device according to the present invention. [Figure 2] It is a conceptual diagram showing a magnetizer when the magnetic force output is OFF. [Figure 3] It is a conceptual diagram showing a magnetizer when the magnetic force output is ON. [Figure 4]This is a block diagram representing the electronic circuit of a magnetic flux leakage flaw detection device. [Figure 5] This is a flowchart illustrating the procedure for magnetic flux leakage testing. [Figure 6] This is an example of measurement data for horizontal and vertical magnetic flux at the location of a defect. [Figure 7] This is an example of the results of digital signal processing on measurement data at the defect location. [Figure 8] This is an example of how leakage magnetic flux flaw detection results are displayed on the display unit. [Figure 9] This is an example of measurement data for horizontal and vertical magnetic flux when the sweep speed changes. [Figure 10] This is an example of the results of digital signal processing on measurement data when the sweep speed changes. [Figure 11] This is an example of measurement data for horizontal and vertical magnetic flux when there is a step in the object being inspected. [Figure 12] This is an example of the results of digital signal processing on measurement data when the object being inspected has steps or uneven surfaces. [Modes for carrying out the invention]

[0029] The embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to what is described below, and can be modified and implemented as long as the gist of the invention is not altered. Furthermore, the drawings used in describing the embodiments are schematic representations of the components, and may have been partially emphasized, enlarged, reduced, or omitted to enhance understanding, and may not accurately represent the scale or shape of the components.

[0030] Figure 1 is an external view diagram of the leakage magnetic flux flaw detection device 1 according to the present invention, with Figure 1(a) showing a front perspective view and Figure 1(b) showing a rear perspective view. The leakage magnetic flux flaw detection device 1 is a handheld device for performing leakage magnetic flux flaw detection mainly on iron-based steel plates, and detects defects in steel materials by manually sweeping along the surface of the object to be inspected. The leakage magnetic flux flaw detection device 1 is formed with dimensions of, for example, W69mm × D60mm × H145mm, and its external configuration includes a base part 2, a body part 3, a connecting part 4, a display part 5, and a magnetization operation part 6. In each figure, the depth direction of the leakage magnetic flux flaw detection device 1 is the X direction, the width direction is the Y direction, and the height direction is the Z direction.

[0031] The base unit 2 is equipped with four aluminum wheels and is configured to move smoothly in the Y direction on the surface of the object being inspected. The base unit 2 is not limited to the shape shown in the illustration, and has multiple variations to accommodate objects of different shapes, such as cylindrical steel pipes, and is designed as an attachment system that allows for replacement according to the object being inspected.

[0032] The body section 3 is a roughly rectangular prism-shaped main body extending in the height direction, and is the part that the user grips when sweeping during magnetic flux testing. The body section 3 is provided with a battery cover 3a on its rear side, and a battery for power supply is housed inside. Also on the rear side of the body section 3 is a power switch 3b for switching the power of the magnetic flux leakage device 1 ON / OFF.

[0033] The connecting section 4 is provided on both sides of the magnetic flux leakage flaw detection device 1 in the Y direction and is a connecting member that connects the base section 2 and the body section 3. The display section 5 is provided on the upper surface of the body section 3 and is a display capable of displaying the results of magnetic flux flaw detection, etc.

[0034] The magnetization control unit 6, as will be described in detail later, is a magnetic force switch that controls the ON / OFF state of the magnetic force output to the object being inspected, and is configured to rotate around the Z-direction as its axis of rotation between the base unit 2 and the body unit 3. The user can control the ON / OFF state of the magnetic force output by rotating the magnetization control unit 6 by 90° via a handle 6a that protrudes from the magnetization control unit 6. In Figure 1, the magnetic force output of the magnetization control unit 6 is in the OFF state.

[0035] Next, the structure of the magnetizer 7 operated by the magnetization operation unit 6 will be described. Figure 2 is a conceptual diagram showing the magnetizer 7 when the magnetic force output is OFF. More specifically, Figure 2(a) shows the YZ cross-section of the magnetizer 7, and Figure 2(b) is a top view of the magnetization operation unit 6 and the magnetizer 7 as seen through the top surface of the magnetization operation unit 6.

[0036] The magnetizer 7 is located inside the base 2 and magnetization operation section 6 described above, and comprises a permanent magnet 7a, a pair of vertical yokes 7b, and a horizontal yoke 7c. The permanent magnet 7a is made of, for example, a neodymium magnet, and is positioned so that both ends face in the Y-axis direction. The pair of vertical yokes 7b are made of iron material with high magnetic permeability, and form an H-shaped yoke structure by sandwiching both ends of the permanent magnet 7a with their longitudinal direction facing the Z-axis direction (vertical direction). The yoke structure is fixed so as not to be displaced inside the leakage magnetic flux flaw detection device 1.

[0037] The horizontal yoke 7c is made of the same iron material as the vertical yoke 7b and is mounted on the upper surface of the vertical yoke 7b so as to bridge the pair of vertical yokes 7b with its longitudinal direction in the Y-axis direction (horizontal direction). As a result, in the state of magnetic force output OFF as shown in Figure 2, the magnetizer 7 can turn off the external output of magnetic force by circulating the magnetic force of the permanent magnet 7a internally through a closed magnetic circuit Moff formed by a part of the pair of vertical yokes 7b and the horizontal yoke 7c.

[0038] Furthermore, the magnetization operation section 6 has a recess R formed on its bottom side that can accommodate the horizontal yoke 7c. The recess R is formed such that its horizontal cross-section is slightly wider than that of the horizontal yoke 7c, and its depth is greater than the height of the horizontal yoke 7c in the Z direction.

[0039] Furthermore, a yoke lifting section 8, as shown in Figure 2(b), is provided near the upper surface of the pair of vertical yokes 7b. The yoke lifting section 8 is made of a material with low magnetic permeability, such as resin, and includes a disc section 8L, a fan-shaped protrusion 8H, and an inclined section 8S. The disc section 8L has a rectangular hole for housing the yoke structure, and its upper surface is set at approximately the same height as the upper surface of the pair of vertical yokes 7b. The fan-shaped protrusion 8H is provided at both ends of the disc section 8L in the X direction and has its top surface at a higher position than the disc section 8L. The inclined section 8S is formed as an inclined surface that extends from the upper surface of the disc section 8L to the top surface of the fan-shaped protrusion 8H along the circumferential direction of the disc section 8L.

[0040] Figure 3 is a conceptual diagram representing the magnetizer 7 when the magnetic force output is ON. More specifically, Figure 3(a) shows the YZ cross-section of the magnetizer 7, and Figure 3(b) is a top view of the magnetization operation unit 6 and the magnetizer 7 as seen through the top surface of the magnetization operation unit 6.

[0041] As shown in Figure 3(b), when the user rotates the magnetization operation unit 6 by 90° in the XY plane, the horizontal yoke 7c inside the magnetization operation unit 6 also rotates accordingly so that both ends face the X direction. At this time, the horizontal yoke 7c rides up onto the top surface of the fan-shaped convex portion 8H via the inclined portion 8S, with both ends aligned with the circumferential direction of the disc portion 8L.

[0042] In this case, as shown in Figure 3(a), the magnetizer 7 has a horizontal yoke 7c separated from the pair of vertical yokes 7b, thus eliminating the closed magnetic path Moff described above. On the other hand, if there is an object to be inspected W such as steel material on the bottom side of the pair of vertical yokes 7b, a closed magnetic path Mon is formed by the permanent magnet 7a, a part of the pair of vertical yokes 7b, and the object to be inspected W, so the magnetizer 7 is in an ON state that outputs magnetic force to the object to be inspected W.

[0043] In other words, the user can output magnetic force from the magnetizer 7 to the object W by turning on the magnetization operation unit 6 while the leakage magnetic flux flaw detection device 1 is placed on the surface of the object W to be inspected. At this time, since the magnetizer 7 outputs magnetic force using a permanent magnet, power consumption can be reduced compared to a magnetizer of the type that energizes a coil wound around a yoke. Furthermore, since the magnetizer 7 is configured so that the closed magnetic path Mon between the permanent magnet and the object to be inspected can be manually disconnected and reconnected, power consumption associated with the ON / OFF operation of magnetization can be further reduced.

[0044] As a result, the leakage magnetic flux flaw detection device 1 can magnetize the object W to be inspected, and if there is a minute defect such as a scratch in the object W to be inspected, the defect can be detected by measuring the leakage magnetic flux leaking from the defect with the magnetic sensor 9.

[0045] Figure 4 is a block diagram showing the electronic circuit of the magnetic flux leakage flaw detection device 1. In addition to the display unit 5 described above, the magnetic flux leakage flaw detection device 1 includes a magnetic sensor 9, a processing unit 10, a battery 11, and a converter 12 as its electronic circuit configuration.

[0046] The magnetic sensor 9 is a known three-axis Hall element, an IC component capable of measuring magnetic flux up to ±160mT in 12 bits and outputting the measurement data as a digital signal. The magnetic sensor 9 is positioned in close proximity (separation distance = approximately 0.5 mm) to the object W being inspected at the midpoint of a pair of vertical yokes 7b. In this embodiment, the magnetic sensor 9 measures the horizontal magnetic flux φy, which is the component in the Y direction (sweep direction) of the leakage magnetic flux due to defects in the X direction of the object W being inspected, and the perpendicular magnetic flux φz, which is the component in the Z direction perpendicular to the surface of the object W being inspected.

[0047] The processing unit 10 is a known CPU (Central Processing Unit) operating at 240MHz and 32-bit. It receives measurement data from the magnetic sensor 9 via I2C communication, detects defects in the object W being inspected using digital signal processing described later, and transmits the results to the display unit 5 via SPI communication.

[0048] The battery 11 consists of two 1.5V alkaline batteries or two 1.8V nickel-zinc rechargeable batteries and supplies power to the leakage magnetic flux flaw detection device 1. The converter 12 is a voltage converter that converts the power from the battery 11 to a voltage suitable for the processing unit 10 (e.g., 5V) and supplies it to the processing unit 10.

[0049] Next, the procedure for magnetic flux leakage testing using the magnetic flux leakage testing device 1 will be described. Figure 5 is a flowchart showing the procedure for magnetic flux leakage testing. The user controls the power supply of the magnetic flux leakage testing device 1 to ON and starts magnetic flux leakage testing with the magnetic flux leakage testing device 1 placed on the surface of the object to be inspected W.

[0050] When leakage magnetic flux testing is initiated, the user operates the magnetization control unit 6 to ON while sweeping the leakage magnetic flux testing device 1 along the surface of the object W to be inspected, thereby magnetizing the object W in the sweeping direction (Step S1, magnetization process).

[0051] At this time, the processing unit 10 measures data of the horizontal magnetic flux φy and the vertical magnetic flux φz of the leakage magnetic flux via the magnetic sensor 9 (step S2, measurement process). The processing unit 10 also determines whether or not to terminate the data measurement (step S3), and continues the data measurement as long as it is determined not to terminate (No in step S3). Here, the termination of data measurement can be determined, for example, by whether or not a certain amount of time has elapsed since the start of measurement.

[0052] Figure 6 shows an example of measurement data for the horizontal magnetic flux φy and vertical magnetic flux φz at the defect location. The measurement is performed with a sampling period of 3 ms, the horizontal axis represents the sweep distance since the start of measurement, and the vertical axis represents the number of bits reflecting the magnitude of the magnetic flux. Theoretically, the horizontal magnetic flux φy is an even function waveform with a peak near the defect, and the vertical magnetic flux φz is theoretically an odd function waveform with peaks on both sides of the defect that have opposite polarities (directions of magnetic flux). The measurement data from the magnetic sensor 9 itself has a relatively low signal-to-noise ratio, as seen in Figure 6, due to the influence of magnetic flux and static magnetic fields leaking from locations other than the defect in the object W being inspected, and the low measurement accuracy associated with inexpensive measuring equipment. Therefore, the processing unit 10 performs the digital signal processing described below on this data.

[0053] When data measurement is complete (Yes in step S3), the processing unit 10 performs a bandpass filter process on each of the measured horizontal magnetic flux φy and vertical magnetic flux φz data to limit them to a frequency band corresponding to the sweep operation (step S4, bandpass limiting process). This extracts the signal component corresponding to the manual sweep from each measurement data, eliminating the effects of static magnetic fields and other noise-causing factors. The bandpass filter bandwidth can be arbitrarily set based on prior experiments. Alternatively, moving average processing may be performed on the band-limited horizontal magnetic flux φy and vertical magnetic flux φz data, in which case the effects of noise can be further reduced.

[0054] Figure 7 shows an example of the results of digital signal processing on measurement data at the defect location. More specifically, Figure 7 shows the banded horizontal magnetic flux BPFφy, which is band-limited with respect to the horizontal magnetic flux φy, and the banded vertical magnetic flux BPFφz, which is band-limited with respect to the vertical magnetic flux φz, as well as the integrated banded horizontal magnetic flux ∫BPFφy and the cross-correlation waveform Corr, which will be described later.

[0055] As shown in Figure 7, the band-transverse flux BPFφy and band-transverse flux BPFφz exhibit reduced noise compared to the horizontal flux φy and vertical flux φz mentioned above, and their waveform phases are each shifted by π / 2.

[0056] Next, the processing unit 10 calculates interval integral data for the horizontal magnetic flux φy from the bandwidth-limited measurement data (step S5). The integration interval is arbitrarily set based on prior experiments, etc. As shown in Figure 7, the calculated integrated bandwidth horizontal magnetic flux ∫BPFφy has a phase shift of π / 2, so it can be aligned with the peak position of the bandwidth vertical magnetic flux BPFφz. Then, the processing unit 10 calculates the cross-correlation waveform Corr between the interval integral data of the integrated bandwidth horizontal magnetic flux ∫BPFφy and the bandwidth vertical magnetic flux BPFφz (step S6, cross-correlation step). As a result, the processing unit 10 can calculate data with a high S / N ratio by multiplying and emphasizing the peaks of the signal components of the horizontal magnetic flux φy and the vertical magnetic flux φz, thereby improving the defect detection accuracy of the object W under inspection.

[0057] The processing unit 10 then displays the maximum value of the calculated cross-correlation waveform Corr on the display unit 5 as a result of detecting defects due to leakage flux (step S7, display step). Figure 8 shows an example of the display of leakage flux flaw detection results on the display unit 5. More specifically, Figure 8(a) is the display screen when a defect-free area is swept, and Figure 8(b) is the display screen when a defect-containing area is swept. Here, the display unit 5 displays the cross-correlation waveform Corr using triangles with heights corresponding to the magnitude of the maximum value. However, the display method is not limited to this, and the cross-correlation waveform Corr may be displayed directly on the display unit 5 as a liquid crystal panel, or a display method may be used in which a number of LEDs corresponding to the magnitude of the maximum value are lit.

[0058] Then, once the display process is completed, the processing unit 10 terminates the above series of steps. Alternatively, the processing unit 10 may continuously perform leakage flux testing and display of the results by repeatedly executing the above series of steps.

[0059] Next, we will explain the leakage flux flaw detection results when the sweep speed of the leakage flux flaw detection device 1 is changed. Figure 9 shows an example of measurement data for the horizontal magnetic flux φy and vertical magnetic flux φz when the sweep speed is changed. Here, we show the results when the device is manually swept on a defect-free object W, pausing at sweep distances of approximately 300 mm and approximately 600 mm. In this data as well, as can be seen in Figure 9, the signal-to-noise ratio is relatively low, and it can be confirmed that the waveform changes near the stopping position.

[0060] Figure 10 shows an example of digital signal processing results for measurement data when the sweep speed changes. More specifically, Figure 10 shows the banded horizontal flux BPFφy, banded vertical flux BPFφz, integrated banded horizontal flux ∫BPFφy, and cross-correlation waveform Corr calculated for the horizontal flux φy and vertical flux φz in Figure 9.

[0061] As described above, the horizontal magnetic flux φy and vertical magnetic flux φz measured by the magnetic sensor 9 showed the effect of changing the sweep speed, but it can be confirmed that this effect is mitigated in the cross-correlation waveform Corr shown in Figure 10. Therefore, even when the sweep speed is changed manually, the value of the cross-correlation waveform Corr does not increase, thus reducing the risk of falsely detecting waveform changes due to changes in sweep speed as defects.

[0062] Next, we will explain the results of leakage flux testing when there is a step in the object W being inspected. Figure 11 shows an example of measurement data for the horizontal magnetic flux φy and vertical magnetic flux φz when there is a step in the object W being inspected. Here, we show the results when a defect-free object W, in which a resin plate with a height of 0.2 mm is placed, is manually swept in a sweep distance range from approximately 200 [mm] to 600 [mm]. In this data as well, as can be seen in Figure 9, the S / N ratio is relatively low, and it can be confirmed that the waveform changes in the step section.

[0063] Figure 12 shows an example of digital signal processing results for measurement data when the object W under inspection has a step. More specifically, Figure 12 shows the banded horizontal magnetic flux BPFφy, banded vertical magnetic flux BPFφz, integrated banded horizontal magnetic flux ∫BPFφy, and cross-correlation waveform Corr calculated for the horizontal magnetic flux φy and vertical magnetic flux φz in Figure 11.

[0064] As described above, the horizontal magnetic flux φy and vertical magnetic flux φz measured by the magnetic sensor 9 showed the effect of the step in the object W being inspected, but it can be confirmed that this effect is mitigated in the cross-correlation waveform Corr shown in Figure 12. Therefore, the leakage flux flaw detection device 1 can reduce the risk of falsely detecting waveform changes caused by riding over the step in the object W being inspected as defects.

[0065] As described above, the leakage flux flaw detection device 1 according to the present invention measures the leakage flux while magnetizing the object W to be inspected, and extracts the signal component by manual sweep while removing noise by performing band-limiting processing on the measurement data. Furthermore, the leakage flux flaw detection device 1 performs interval integration processing on the band-limited horizontal flux φy to align the phase of the peak with that of the band-limited vertical flux φz. Here, by calculating the cross-correlation waveform Corr of the horizontal flux φy and vertical flux φz whose peak phases are aligned, the magnitude of the flux when both the horizontal and vertical components of the leakage flux are present is emphasized. As a result, even if the measurement accuracy of the measurement data is low, the user can determine the presence or absence of defects in the object W to be inspected based on the cross-correlation waveform Corr, which has a high S / N ratio.Therefore, the leakage flux flaw detection device 1 can suppress a decrease in the accuracy of defect detection even with a small and inexpensive handheld device. [Explanation of symbols]

[0066] 1. Leakage magnetic flux flaw detection device 5 Display section 6 Magnetization operation section 6a Handle 7 Magnetizer 7a permanent magnet 7b Vertical Yoke 7c horizontal yoke 8. Yoke lifting section 9 Magnetic Sensor 10 Processing Unit 11 batteries W: Items to be inspected φy Horizontal magnetic flux φz Normal magnetic flux

Claims

1. A magnetizer that sweeps along the surface of the object to be inspected and magnetizes the object in the sweeping direction, A magnetic sensor that measures the horizontal magnetic flux in the sweeping direction and the vertical magnetic flux perpendicular to the surface of the leakage magnetic flux of the object to be inspected, The system includes a processing unit that restricts the measurement data of the horizontal magnetic flux and the vertical magnetic flux to a frequency band corresponding to the sweep operation, The processing unit is a magnetic flux leakage flaw detection device that detects defects in the object under inspection by cross-correlation between the interval integral data of the band-limited horizontal magnetic flux and the band-limited data of the vertical magnetic flux.

2. The leakage flux flaw detection apparatus according to claim 1, wherein the processing unit performs moving average processing on the bandwidth-limited measurement data.

3. The magnetic sensor outputs a digital signal of the measurement data to the processing unit, as described in claim 1 or 2.

4. The magnetic flux leakage detection apparatus according to claim 1 or 2, wherein the magnetizer includes a permanent magnet and is configured to allow manual disconnection and reconnection of a closed magnetic path between the permanent magnet and the object to be inspected.

5. Leakage magnetic flux flaw detection apparatus according to claim 1 or 2, further comprising a display unit for displaying the maximum value of the cross-correlation.

6. A magnetization step in which a magnetizer is swept along the surface of the object to be inspected to magnetize the object in the sweeping direction, A measurement step of measuring the horizontal magnetic flux in the sweeping direction and the vertical magnetic flux perpendicular to the surface of the leakage magnetic flux of the object to be inspected, A band limiting step is performed to restrict the measurement data of the horizontal magnetic flux and the vertical magnetic flux to a frequency band corresponding to the sweep operation. A leakage flux flaw detection method comprising a cross-correlation step of detecting defects in an object under inspection by cross-correlation between band-limited interval integral data of the horizontal magnetic flux and band-limited data of the vertical magnetic flux.

7. The leakage magnetic flux flaw detection method according to claim 6, wherein in the bandwidth limiting step, moving average processing is performed on the bandwidth-limited measurement data.

8. The leakage magnetic flux flaw detection method according to claim 6 or 7, wherein the measurement step outputs the measured measurement data as a digital signal.

9. The leakage magnetic flux inspection method according to claim 6 or 7, wherein in the magnetization step, the closed magnetic path between the permanent magnet and the object to be inspected is manually disconnected and reconnected.

10. A leakage magnetic flux flaw detection method according to claim 6 or 7, comprising a display step of displaying the maximum value of the cross-correlation.

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