Magnetic flux leakage probe based on wrapped yoke

Abstract

According to a leakage flux excitation U-shaped structure constructed by the wrapped yoke, a complete magnetic loop is formed by a magnet-yoke-magnet and a test piece according to the principle of mutual attraction of different-pole magnetic fields, and meanwhile, the magnetic flux leakage excitation U-shaped structure is formed in the contact areas of the two ends of the yoke and the magnet. Because a part of structure extending downwards from the yoke wraps the outer side parts of the two magnets, a magnetic field leaked into the air by the magnets is absorbed back to the yoke, the magnetic flux intensity is increased, the capacity of the whole magnetic flux magnetization test piece is further improved, a magnetic sensor array is arranged in a magnetic leakage center area to directly capture the change of a magnetic leakage field at the magnetic leakage center area, and the detection accuracy is improved. The wrapping type magnetic leakage excitation U-shaped structure overcomes the problem that the magnetizing capacity of traditional magnetic leakage has an overlarge requirement for the size of a magnet. Meanwhile, the magnetic flux leakage probe based on the wrapped yoke optimizes a magnetic flux leakage circuit, more magnetic flux flows into the yoke by reducing the magnetic flux leaked into the air from the magnet, the magnetization capability of the test piece is further improved, and a magnetic sensor array is adopted, so that the surface and external defect detection and discrimination capability is improved, and technical support is provided for effective defect evaluation.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic flux leakage detection, and more specifically, relates to a magnetic flux leakage probe based on a wrapped yoke, which is used for detecting surface and external defects of ferromagnetic materials. Background Art

[0002] In view of the huge demand for the application of ferromagnetic materials in aerospace and other fields, the structural integrity and safety detection of ferromagnetic materials pose a huge challenge to the safe service of equipment. Multi-physics non-destructive testing technologies such as electromagnetic acoustics have different detection advantages in the structural integrity detection of ferromagnetic material specimens of equipment.

[0003] At present, there are three relatively mature technologies for non-destructive testing of ferromagnetic material specimens: magnetic flux leakage (MFL), ultrasonic testing (UT), and eddy current testing (ECT). In addition to the need for surface and external defect detection, high-resolution imaging of defects is also crucial. At present, magnetic flux leakage detection can achieve simultaneous detection of surface and external defects. The main disadvantages of the current excitation structure are: the magnet of the excitation structure is large: it is a high-magnetic energy magnet. In order to detect external defects with a large burial depth, a large magnet is used to ensure effective magnetization of the ferromagnetic material specimen being tested, resulting in a large and bulky overall internal detection structure, which is not conducive to the detection of small specimens and is not easy to carry. Ultrasonic testing must have a coupling agent to ensure that the ultrasonic probe fits better with the ferromagnetic material specimen being tested, and there are certain restrictions on the testing environment. Eddy current testing is mainly based on the principle of electromagnetic induction. It analyzes defect characteristics according to the changes in eddy current field disturbance on the surface of the ferromagnetic material specimen being tested. However, due to the skin effect, it can only detect surface and near-surface defects, and cannot detect deeply buried defects. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a magnetic flux leakage probe based on a wrapped yoke to form a complete magnetic circuit, improve the ability of the overall magnetic flux to magnetize the test piece, and thus improve the ability to detect external defects. At the same time, it overcomes the problem that the magnetization capacity of traditional magnetic flux leakage requires too large a magnet volume.

[0005] To achieve the above-mentioned purpose, the magnetic flux leakage probe based on the wrapped yoke of the present invention is characterized by comprising:

[0006] Two magnets with opposite polarities placed horizontally at both ends are a NS magnet and a SN magnet. The NS magnet is magnetized vertically downward, with an S pole on the upper surface and an N pole on the lower surface. The SN magnet is magnetized vertically upward, with an N pole on the upper surface and an S pole on the lower surface.

[0007] It is characterized by further comprising:

[0008] A wrapped yoke is located on the upper surface of the two magnets and extends downward at both ends to wrap the outer parts of the two magnets, so that the wrapped yoke and the two magnets form a U-shaped leakage magnetic excitation structure;

[0009] A sensor array arranged in the middle area of ​​two magnets with opposite polarities serves as a signal acquisition module;

[0010] The leakage magnetic field excitation structure and the signal acquisition module are fixed by non-magnetic materials to form a leakage magnetic field probe based on a wrapped yoke.

[0011] The object of the present invention is achieved in this way.

[0012] The present invention is based on the leakage magnetic field probe of the wrapped yoke, and the leakage magnetic field excitation U-shaped structure constructed by the wrapped yoke. According to the principle of mutual attraction of magnetic fields of different levels, the magnet-yoke-magnet and the test piece form a complete magnetic circuit. At the same time, in the contact area between the two ends of the yoke and the magnet, due to the part of the structure extending downward from the yoke, the outer parts of the two magnets are wrapped, so that the magnetic field leaked into the air by the magnet is absorbed back into the yoke, the magnetic flux intensity is increased, and the ability of the overall magnetic flux magnetization test piece is further improved. The magnetic sensor array is arranged in the leakage magnetic center area to directly capture the leakage magnetic field changes there. This detection method can ensure the detection and classification of surface and external defects. In this way, the wrapped leakage magnetic field excitation U-shaped structure overcomes the problem that the magnetization capacity of the traditional leakage magnetic field requires too large a magnet volume. At the same time, the present invention optimizes the leakage magnetic field circuit based on the leakage magnetic field probe of the wrapped yoke, and by reducing the magnetic flux leaked from the magnet to the air, more magnetic flux flows into the yoke, further improving the magnetization capacity of the test piece, and adopts a magnetic sensor array to improve the detection and identification capabilities of surface and external defects, providing technical support for effective defect evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of a specific implementation mode of a magnetic flux leakage probe based on a wrapped yoke of the present invention;

[0014] Figure 2 yes Figure 1 The figure shows a schematic diagram of the magnetic flux leakage probe detection principle based on a wrapped yoke.

[0015] Figure 3 yes Figure 1 The schematic diagram of the structure of the wrapped yoke shown, wherein (a) is a front view and (b) is a bottom view;

[0016] Figure 4 yes Figure 1 The relationship curve between the wrapped yoke size (height and width) and the magnetic field strength is shown;

[0017] Figure 5 It is a structural schematic diagram of another specific embodiment of the wrapped yoke in the present invention;

[0018] Figure 6 It is a structural schematic diagram of another specific embodiment of the wrapped yoke in the present invention;

[0019] Figure 7 A magnetic flux leakage detection system based on the present invention;

[0020] Figure 8 1 is a comparison diagram of magnetic field distribution of a conventional magnetic flux leakage probe and a magnetic flux leakage probe based on a wrapped yoke of the present invention, wherein (a) is a magnetic field distribution diagram of a conventional magnetic flux leakage probe, and (b) is a magnetic field distribution diagram of a magnetic flux leakage probe based on a wrapped yoke of the present invention;

[0021] Fig. 9 It is a schematic diagram of test pieces with different types of defects;

[0022] Fig.10 These are the detection results of different types of defects. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0024] Figure 1 It is a structural schematic diagram of a specific implementation of the magnetic flux leakage probe based on the wrapped yoke of the present invention.

[0025] In this embodiment, if Figure 1 As shown, the magnetic flux leakage probe based on the wrapped yoke of the present invention includes: two magnets, namely, an NS magnet 1 and an SN magnet 2, a support plate 3 between the magnets, a wrapped yoke 4 and a sensor array 5.

[0026] The two magnets are placed horizontally at both ends with opposite polarities, wherein the NS magnet 1 is magnetized vertically downward, with its upper surface being an S pole and its lower surface being an N pole, and the SN magnet 2 is magnetized vertically upward, with its upper surface being an N pole and its lower surface being an S pole. In this embodiment, the NS magnet 1 is located at the left end, the SN magnet 2 is located at the right end, and a magnet support plate 3 made of non-magnetic material is used in the middle to connect and fix.

[0027] The wrapped yoke 3 is located on the upper surface of the two magnets, namely the NS magnet 1 and the SN magnet 2, and extends downward at both ends to wrap the outer parts of the two magnets, namely the NS magnet 1 and the SN magnet 2. In this way, the wrapped yoke 4 and the two magnets, namely the NS magnet 1 and the SN magnet 2, form a U-shaped leakage magnetic excitation structure.

[0028] A magnetic sensor array 5 is arranged in the middle area of ​​two magnets with opposite polarities as a signal acquisition module. The leakage magnetic excitation structure and the signal acquisition module are fixed by non-magnetic materials to form a leakage magnetic probe based on a wrapped yoke.

[0029] Figure 2 yes Figure 1 The figure shows a schematic diagram of the magnetic flux leakage probe detection principle based on a wrapped yoke.

[0030] In this embodiment, if Figure 2 As shown, in the leakage magnetic field probe based on the wrapped yoke of the present invention, the U-shaped leakage magnetic field excitation structure formed by the NS magnet 1, the wrapped yoke 4, and the SN magnet 2 will form an excitation (Magnetic flux) loop inside the ferromagnetic material specimen, and the magnetic sensor array 5 in the central magnetized region (leakage region) of the two magnets can obtain the leakage magnetic field changes of the ferromagnetic material specimen caused by external defects, thereby detecting the external defects.

[0031] In the present invention, the defect detection method is as follows: a leakage magnetic field probe based on a wrapped yoke is horizontally placed on the surface of a ferromagnetic material specimen to be tested; the wrapped yoke and the magnet are combined in a wrapped structure to form a U-shaped leakage magnetic field excitation structure, and the magnetic flux leaked into the air by the magnet is absorbed back into the wrapped yoke, thereby increasing the magnetic flux of the magnetic circuit between the wrapped yoke, the magnet and the ferromagnetic material specimen, and forming a stable local magnetization area, so that the magnetization area reaches a certain magnetization intensity; the magnetic sensor array detects the leakage magnetic field state change caused by the buried defect part located on the ferromagnetic material specimen to be tested; the signal change corresponding to the defect of the ferromagnetic material specimen to be tested is analyzed through the collected data, and the defect part is displayed.

[0032] Preferably, the magnetic sensor array 5 is located at the center of the two magnets 1 and 2, and the vertical position of the magnetic sensor array 5 in space is consistent with the level of the bottom of the magnets.

[0033] Preferably, the number of the magnetic sensor arrays 5 perpendicular to the magnets 1 and 2 is several, wherein: the sensors of the multiple magnetic sensor arrays 5 can be arranged along a single-axis linear array / along a two-axis linear array, and arranged in a staggered manner.

[0034] Preferably, the leakage magnetic excitation structure and the signal acquisition module are fixed by non-magnetic materials and then mounted on rollers to form a leakage magnetic probe based on a wrapped yoke.

[0035] Figure 3 yes Figure 1 Schematic diagram of the structure of the wrapped yoke shown.

[0036] In this embodiment, the wrapped yoke is a rectangular plate-shaped structure, with a portion extending downward to the left and right to wrap the NS magnet 1 and the SN magnet 2.

[0037] In this embodiment, the height and width parameters of the extended portion of the wrapped yoke are optimized, and the variation law of the magnetic field strength under different parameter changes such as height and width of 0mm-1mm, 1mm-1mm, 2mm-1mm, 4mm-1mm, 1mm-2mm and 3mm-2mm are analyzed respectively, so as to further verify the magnetization ability of the magnetic flux leakage probe based on the wrapped yoke of the present invention. The relationship curve between the size (height and width) of the wrapped yoke and the magnetic field strength is shown in the figure. Figure 4 shown.

[0038] pass Figure 4 We can find that when the wrapped yoke is 2-3 mm high and 1-2 mm wide, the magnetic field intensity is the largest.

[0039] Figure 5 It is a structural schematic diagram of another specific implementation method of the wrapped yoke in the present invention.

[0040] In this embodiment, the wrapped yoke is a circular plate-shaped structure, with a portion extending downward to the left and right to wrap the NS magnet 1 and the SN magnet 2. The corresponding NS magnet 1 and the SN magnet 2 are cylindrical structures.

[0041] Figure 6 It is a structural schematic diagram of another specific implementation method of the wrapped yoke in the present invention.

[0042] In this embodiment, the wrapped yoke is a hexagonal plate structure, with a portion extending downward to the left and right to wrap the NS magnet 1 and the SN magnet 2. The corresponding NS magnet 1 and the SN magnet 2 are quadrilateral columnar structures.

[0043] Therefore, the wrapped yoke is a polygonal plate structure or a circular plate structure.

[0044] The FPGA development board can be used to collect the digital signals output by the internal and external array magnetic sensors, store them and upload them to the data processing terminal; the host computer is used to analyze and process the digital signals collected by the development board to obtain the defect information in the tested piece;

[0045] Through Figure 4 and Figure 5 The height and width parameters of the extended area of ​​the wrapped yoke are optimized, and the variation of magnetic field intensity under different parameter changes such as 0mm-1mm, 1mm-1mm, 2mm-1mm, 4mm-1mm, 1mm-2mm and 3mm-2mm are analyzed to further verify the magnetization ability of the wrapped magnetic flux leakage probe.

[0046] pass Figure 6 It can be found that the magnetic field intensity is maximum when the height of the downwardly extending portion of the wrapped yoke is 2 to 3 mm and the width is 1 to 2 mm.

[0047] Figure 7 The invention relates to a magnetic flux leakage detection system.

[0048] like Figure 7 As shown in the figure, an FPGA data storage and processing module is built based on the FPGA development board, which can be used to collect the digital signals output by the sensor array, store, process and upload them to the data processing terminal (computer). The host computer analyzes and processes the digital signals collected by the development board to obtain the defect information in the ferromagnetic material specimen under test.

[0049] The invention is based on a wrapped yoke-based magnetic flux leakage probe which is horizontally placed on the surface of a ferromagnetic material specimen and moved. The probe lift-off, i.e., the distance between the probe and the specimen surface, is increased or decreased by adjusting the roller size, and the specimen is scanned by controlling the moving rate.

[0050] Figure 8 It is a comparison diagram of magnetic field distribution of a conventional magnetic flux leakage probe and a magnetic flux leakage probe based on a wrapped yoke of the present invention.

[0051] pass Figure 8 Finite element simulation analysis of conventional magnetic flux leakage probes and the magnetic flux leakage probe based on a wrapped yoke of the present invention found that, under the condition of the same magnet excitation intensity, the magnetic flux leakage probe based on the wrapped yoke of the present invention can achieve a magnetization intensity of 3.98T for the ferromagnetic material specimen under test based on the design of the sensing structure and the optimization of the magnetic circuit, and the magnetic field forms an obvious leakage magnetic field at the external defects, thereby improving the detection capability of external defects.

[0052] The defect detection capability of the magnetic flux leakage probe based on the wrapped yoke of the present invention is tested in a laboratory environment. The specific experimental implementation is as follows:

[0053] When the magnetic flux leakage probe based on the wrapped yoke of the present invention is controlled to scan the defects of the ferromagnetic material to be detected, the magnetic flux leakage probe is first placed on the test piece, and then the magnetic flux leakage probe is controlled to move on the surface of the test piece. At this time, the detection principle of the magnetic flux leakage probe based on the wrapped yoke of the present invention, the magnetic levels of the SN magnet and the NS magnet are different, and a complete magnetic circuit can be formed with the ferromagnetic material to be detected. When passing through the defect area, part of the magnetic field leaks into the air due to the increase of magnetic resistance in the defect area. When encountering external defects, the magnetic field inside the test piece reaches an oversaturated state due to the reduction of the magnetic conductive area. The magnetic field in the defect area will leak into the air due to oversaturation, and magnetic diffusion is formed at the same time. The magnetic sensor array in the middle area between the SN magnet and the NS magnet is used to capture the magnetic flux leakage information, and finally the magnetic field change is converted into a digital signal and sent to the FPGA module through serial communication; the detection method and data storage method are the same as those of zero magnetic disturbance. After data analysis and processing, the data processing terminal determines the position, size and category information of the defect.

[0054] Fig. 9 Schematic diagram of different types of defect specimens. In this embodiment, the specimen thickness is 10 mm and the material is 45# steel. Fig. 9 The test piece has surface and external defects, and the defect type is seven artificial cracks. There are 3 external defects with different buried depths and 4 surface defects with different depths. The buried depths of the 3 external defects are 4mm, 6mm and 8mm, the widths are all 1mm, and the lengths are 20mm; the 4 surface defects are 8mm, 6mm, 4mm and 2mm, the widths are all 1mm, and the lengths are 20mm. The relative positions of the defects are Fig. 9 Marked in. Fig. 9 It also gives the changes of external defects of different lengths at 30° inclination. The defect type is a rectangular defect. The length of the three rectangular buried defects is 20mm, the width is 2mm, and the depth is 2mm, 4mm, and 6mm respectively. The leakage magnetic probe based on the wrapped yoke of the present invention is placed on the flat-type ferromagnetic test piece and moves at a constant speed. When moving to the defect area, the FPGA module will record the output signal of the array magnetic sensor in real time. The vertical distance (lift-off) between the bottom of the leakage magnetic probe based on the wrapped yoke of the present invention and the flat-type upper surface is 5mm.

[0055] Fig.10 This is a diagram showing the defect detection results of a ferromagnetic material specimen being tested using a magnetic leakage probe based on a wrapped yoke iron according to the present invention.

[0056] like Fig.10As shown, when passing through defects with varying depths of the exterior and surface, the magnetic sensor array captures the leakage magnetic information of the defect area of ​​the leakage magnetic probe based on the wrapped yoke of the present invention. Seven defects at different angles can be detected, and the defect information is imaged and processed through the xyz three-axis magnetic field information. The x-axis defect feature presents a single valley feature, and the signal chromaticity value of each defect becomes deeper and deeper with increasing depth; the y-axis defect feature is different from the other two-axis signals and can be used as compensation for defect contour information. The z-axis signal feature presents a valley-peak feature, which is more sensitive to the defect angle contour information and conforms to the defect detection characteristics of the leakage magnetic technology. When passing through the back defect, the magnetic sensor array captures the leakage magnetic field at the defect. According to the detection results, the smaller the burial depth of the defect, the greater the signal strength. The leakage magnetic probe based on the wrapped yoke of the present invention can effectively detect external defects with a burial depth of 8 mm. Defect detection at different depths at a certain angle increases with the greater the defect depth, and the xyz three-axis signals have good consistency, which conforms to the actual defect detection law.

[0057] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A magnetic flux leakage probe based on a wrapped yoke, characterized in that: include: Two magnets with opposite polarities placed horizontally at both ends are a NS magnet and a SN magnet. The NS magnet is magnetized vertically downward, with an S pole on the upper surface and an N pole on the lower surface. The SN magnet is magnetized vertically upward, with an N pole on the upper surface and an S pole on the lower surface. It is characterized by further comprising: A wrapped yoke is located on the upper surface of the two magnets and extends downward at both ends to wrap the outer parts of the two magnets, so that the wrapped yoke and the two magnets form a U-shaped leakage magnetic excitation structure; A sensor array arranged in the middle area of ​​two magnets with opposite polarities serves as a signal acquisition module; The leakage magnetic field excitation structure and the signal acquisition module are fixed by non-magnetic materials to form a leakage magnetic field probe based on a wrapped yoke.

2. The magnetic flux leakage probe based on the wrapped yoke according to claim 1, characterized in that: The wrapped yoke is a polygonal plate structure or a circular plate structure.

3. The magnetic flux leakage probe based on the wrapped yoke according to claim 1, characterized in that: The downwardly extending portion of the wrapped yoke has a height of 2 to 3 mm and a width of 1 to 2 mm.

4. The magnetic flux leakage probe based on the wrapped yoke according to claim 1, characterized in that: The magnetic sensor array is located at the center of the two magnets, and the vertical position of the magnetic sensor array in space is consistent with the level of the bottom of the magnets.

5. The magnetic flux leakage probe based on the wrapped yoke according to claim 4, characterized in that: The number of the magnetic sensor arrays perpendicular to the magnets is several, wherein: the sensors of the plurality of magnetic sensor arrays are arranged along a single-axis linear array, or along two-axis linear arrays and arranged in a staggered manner.

6. The magnetic flux leakage probe based on the wrapped yoke according to claim 1, characterized in that: The leakage magnetic field excitation structure and the signal acquisition module are fixed by non-magnetic materials and then mounted on rollers to form a leakage magnetic field probe based on a wrapped yoke.

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