Ferromagnetic material defect rapid chromatography system based on alternating current magnetic flux leakage

Abstract

The invention discloses a ferromagnetic material defect rapid chromatography system based on alternating current magnetic flux leakage, comprising: a magnetizer for magnetizing a to-be-detected sample by introducing alternating current to generate an excitation magnetic field; the sensor is used for detecting a leakage magnetic field signal generated at the defect of the to-be-detected sample piece; and the upper computer is electrically connected with the sensor and is used for receiving and processing an output signal of the sensor and outputting a characteristic pattern. A result shows that the rising time point and the defect burial depth are in a linear relationship; research is carried out on the relationship between the defect width, the defect depth, the defect burial depth, the defect shape and the rising time point through a simulation model, it is found that the position of the rising time point is only related to the defect burial depth and is irrelevant to the defect depth or the defect shape, and a linear model of the defect burial depth and the rising time point obtained through simulation is y = 0.1392 x + 1.19326, R2 = 0.99819; wherein x is the defect burial depth, and y is the rising time point. In addition, the cushion blocks are used for fixing the front end and the rear end of the magnetizer, and the lift-off effect is eliminated.

Description

Technical Field

[0001] The present application relates to the field of non-destructive testing systems, and in particular to a ferromagnetic material defect rapid tomography system based on AC magnetic flux leakage. Background Art

[0002] Ferromagnetic materials possess excellent elasticity and plasticity, are economical, practical, and inexpensive, and have broad industrial applications, particularly in construction, instrumentation, transportation, and aerospace. However, during use, ferromagnetic materials often develop tiny cracks, ranging from a few microns to a few millimeters, due to extrusion or corrosion. These cracks are difficult to see with the naked eye and often lead to equipment failure, resulting in incalculable losses.

[0003] Currently, the primary detection devices used are ultrasonic, X-ray, and pulsed eddy current (PEC). Ultrasonic devices require a coupling agent, making them cumbersome to use and challenging to operate. They are also impractical for testing in confined spaces. X-ray devices are bulky and immobile, and the radiation they produce can be harmful to humans. While PEC devices don't require a coupling agent and don't generate radiation, they suffer from a lift-off effect, resulting in low detection accuracy and an inability to pinpoint the exact location of defects. Summary of the Invention

[0004] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a rapid tomography system for ferromagnetic material defects based on AC magnetic leakage, which can accurately locate the defect position while overcoming the lift-off effect and improving the detection accuracy.

[0005] According to an embodiment of the first aspect of the present application, a rapid tomography system for ferromagnetic material defects based on AC magnetic flux leakage comprises: The magnetizer is used to generate an excitation magnetic field by passing alternating current to magnetize the sample to be tested; A sensor is used to detect leakage magnetic field signals generated at defects of the sample to be tested; The host computer is electrically connected to the sensor and is used to receive and process the output signal of the sensor and output a characteristic signal. Furthermore, the magnetizer consists of a shell and a magnetizing coil arranged in the shell. The shell is a hollow opening structure on the side for the sample to be tested to pass through the side opening and is fixed by pads located at the front and rear ends of the magnetizer.

[0006] Furthermore, the sensor is a differential probe, which is composed of two Hall sensors arranged at intervals. The differential probe is moved along the surface of the sample to be detected to detect the change of the leakage magnetic field signal over time.

[0007] Furthermore, after obtaining the curve of the leakage magnetic field signal changing with time, the rising time point of the leakage magnetic field is determined. The specific process includes: obtaining the amplitude change curve of the leakage magnetic field signal, dividing the leakage magnetic field signal characteristics into three stages according to the amplitude change curve, the first stage is the low amplitude stage when the magnetic shielding layer is shielding, the second stage is the linear increase stage when the magnetic shielding layer moves over the defect, and the third stage is the drastic increase stage after the magnetic shielding layer is removed. The transition point from the first stage to the second stage is determined as the rising time point, and the transition point from the second stage to the third stage is determined as the mutation time point.

[0008] Furthermore, the change of the leakage magnetic field signal is detected by a sensor, including: setting a measurement point above the sample to be detected, the measurement point is located at the central axis of the magnetizer, obtaining a change curve of the leakage magnetic field signal through the measurement point, and analyzing the mutation characteristics of the leakage magnetic field signal according to the change curve.

[0009] Furthermore, the host computer also uses simulation software to simulate the relationship between the defect burial depth, defect depth, defect shape and rising time point.

[0010] Furthermore, a simulation model was used to study the defect width and rise time point. The widths were set to 0.2mm, 0.5mm, 0.8mm, 1.2mm, and 1.5mm, respectively, and the rise time points were the same. The simulation results showed that changes in defect width did not affect the rise time point.

[0011] Furthermore, a simulation model was used to study the relationship between the defect burial depth and the rise time point. The burial depths were set to 2mm, 2.5mm, 3mm, 3.5mm, 4mm, and 4.5mm, respectively. The rise time point was gradually pushed back from 0ms to 2ms. The simulation results showed that the defect burial depth and the rise time point were linearly related, and the linear equation was y=0.1392x+1.19326, R 2 =0.99819, y is the rising time point, and x is the defect depth.

[0012] Furthermore, a simulation model was used to study the defect depth and the rising time point. The defect depths were set to 0.6mm, 0.9mm, 1.5mm, 2.0mm, and 2.5mm, respectively, and the projection length of the rising time period corresponding to the second stage on the X-axis was obtained. The simulation results show that at the same burial depth, the defect depth and the projection length of the rising time period on the X-axis are linearly related.

[0013] Furthermore, simulations were conducted for a spherical defect with a diameter of 0.5 mm and a sawtooth defect with an equivalent length of 0.65 mm. The defect depth was increased from 0.5 mm to 4.0 mm in 0.5 mm steps. The results showed that different defect types exhibited the same three-segment signal characteristics of a rectangular defect, demonstrating that defect shape is independent of the rise time.

[0014] According to the rapid tomography system for ferromagnetic material defects based on AC leakage magnetic field in the embodiment of the present application, the defect leakage magnetic field signal is detected by a differential Hall sensor and output to the host computer to obtain the relationship between the defect signal and the rise time point, and it is found that the rise time point is linearly related to the defect burial depth; through simulation of different defect widths and rise time points at the same burial depth, it is found that the change in defect width does not affect the position of the rise time point; through simulation of different burial depths and rise time points of the same defect, it is found that the defect burial depth and the rise time point are linearly related, thereby the defect burial depth can be accurately located; through simulation of defect depth (referring to the longitudinal height of the defect) and rise time point, it is found that at the same burial depth, the defect depth is linearly related to the projection length of the rise time period on the X-axis; through simulation of defects of different shapes and rise time points, it is found that different types of defects also show the three-segment signal characteristics of rectangular defects, and the defect shape is independent of the rise time point.

[0015] According to some embodiments of the present application, by using spacers to fix the front and rear ends of the magnetizer, the stability of the magnetizer is ensured during the measurement process, and vibration of the magnetizer or sensor due to human jitter during the measurement process is avoided, which causes the differential probe to change the measurement signal due to the change in the lifting distance, thereby eliminating the lifting effect and improving the detection accuracy.

[0016] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 This is a schematic structural diagram of a magnetizer in an embodiment of the present application; Figure 2 This is a cloud diagram of the magnetic permeability distribution of the sample to be tested at different times in the embodiment of the present application; Figure 3 The magnetic field intensity variation curve of defects of the same buried depth and different widths of the sample to be detected in the embodiment of the present application is shown; Figure 4 : is a linear relationship diagram between the depth of the defect buried in the sample to be tested and the rising time point in the embodiment of the present application; Figure 5: is a linear relationship diagram between the depth of the defect of the sample to be detected and the length of the rising time period in the embodiment of the present application; Figure 6 is a curve showing the change in magnetic field intensity of circular defects with different buried depths in the embodiment of the present application; Figure 7 3 is a curve showing the change in magnetic field intensity of sawtooth defects with different buried depths in the embodiment of the present application.

[0019] Description of reference numerals: 1. Housing; 2. Magnetizing coil; 3. Sample to be tested; 4. Pad. DETAILED DESCRIPTION

[0020] The embodiments of the present application are described in detail below. The embodiments described with reference to the accompanying drawings are exemplary. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0022] like Figure 1 As shown, the present application provides a rapid tomography system for ferromagnetic material defects based on AC magnetic flux leakage. The system includes a magnetizer, which consists of a housing and a magnetizing coil 2 disposed within the housing 1. The housing 1 is a hollow structure with openings on the side, through which the sample 3 to be tested passes and is secured by pads 4 located at the front and rear ends of the magnetizer. A sensor, such as a differential probe, is used to detect the leakage magnetic field signal generated at the defect of the sample 3 to be tested. The differential probe is composed of two Hall sensors spaced apart. The differential probe is moved along the surface of the sample to be tested to detect the change in the leakage magnetic field signal over time. A host computer is electrically connected to the sensor and is used to receive and process the sensor's output signal and output a characteristic signal. Specifically, the signal is received by the differential sensor, and the signal is input into the host computer through a signal amplifier and a digital converter. The host computer processes the obtained data and then outputs a signal result graph. AC power is passed through the magnetizer to magnetize the sample to be tested, stimulating the leakage magnetic field at the defect location. The differential probe is moved across the surface of the sample to be tested to obtain leakage magnetic field change data. The host computer receives the leakage magnetic field change data and generates a data graph showing the relationship between the defect parameters and the rising time point.

[0023] After obtaining the curve of the leakage magnetic field signal changing with time, the rising time point of the leakage magnetic field is determined. The specific process includes: obtaining the amplitude change curve of the leakage magnetic field signal, and dividing the leakage magnetic field signal characteristics into three stages according to the amplitude change curve. The first stage is the low amplitude stage when the magnetic shielding layer is shielding, the second stage is the linear increase stage when the magnetic shielding layer moves over the defect, and the third stage is the drastic increase stage after the magnetic shielding layer is removed. The transition point from the first stage to the second stage is determined as the rising time point, and the transition point from the second stage to the third stage is determined as the mutation time point.

[0024] Specifically, a differential Hall effect sensor was used to collect magnetic field leakage signals from the surface of the test sample at a sampling frequency of 100kHz, recording complete waveform data (two cycles) within the time range of 0-40ms. A sliding window difference algorithm was used to analyze the waveform data. Rise times were marked when the amplitude difference between adjacent sampling points exceeded 5mV. Signal values ​​corresponding to rise times t1 = 2ms and t2 = 5ms within the first cycle were extracted. Three stages were identified based on the amplitude characteristics of the sudden change points. The first stage of magnetic shielding was determined when the signal amplitude remained within ±2mV in the 0-2ms interval. A linear regression algorithm was used to calculate the signal slope in the 2-5ms interval. When the slope stabilized at 0.15mV / ms and R² > 0.98, the second stage of linear growth was determined. The second-order derivative method was used to measure the signal change rate after 5ms. When the rate of change exceeded 1.2mV / ms², the third stage was identified. The rise time of the signal in the 5-8ms interval was calculated to be 3ms, coinciding with the end of the second stage. Establish a linear model between the rising time point t1 and the defect depth , ; Where x is the defect depth and t1 is the rising time point.

[0025] like Figure 2 As shown in the figure, after the alternating current passes through the magnetizer, a magnetic permeability distribution is formed inside the sample to be tested. The X-axis represents the distance along the length of the sample to be tested, and the Y-axis represents the distance along the wall thickness of the sample to be tested. As can be seen from the figure, there is a region in the wall thickness direction of the sample to be tested that is opposite to the magnetic field distribution. In this region, because the magnetic field is close to 0, the magnetic permeability is consistent with theoretical analysis and is the initial magnetic permeability of the ferromagnetic material. It can be inferred that a magnetic shielding layer exists in the wall thickness direction of the sample to be tested, which will shield the leakage magnetic field generated by the defect below. Moreover, this area with higher magnetic permeability moves along the thickness direction over time. When the magnetic shielding layer moves to the defect location, a detectable leakage magnetic field signal is generated.

[0026] In order to further verify the accuracy of the experiment, the embodiment of the present application also uses simulation software (such as COMSOL Multiphysics 6.1 simulation software, JMAG simulation software) to study the relationship between the defect signal and the rise time point, mainly simulating the relationship between the defect burial depth, defect width, defect depth, defect shape and the rise time point.

[0027] like Figure 3 As shown in the figure, without changing the defect burial depth, only the defect width is changed. The defect widths are 0.2mm, 0.5mm, 0.8mm, 1.2mm, and 1.5mm, respectively. The rise time points are the same. The simulation results show that the change in defect width does not affect the rise time point.

[0028] like Figure 4 As shown in the figure, the relationship between defects with different burial depths and the rise time point is simulated. The defect burial depths are selected as 0.2mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm, 3.0mm, 3.5mm, 4.0mm, and 4.5mm, and the corresponding rise time points are obtained. The results show that the defect burial depth and the rise time point are linearly related, and the linear equation is y=0.1392x+1.19326, R 2 =0.99819, y is the rising time point, x is the defect depth, the simulation results are consistent with the actual measurement results; Figure 5 As shown in the figure, the relationship between the projection length of the rising time period on the X-axis (i.e., the difference between the rising time point t1 and the mutation time point t2) is simulated at different defect depths (referring to the longitudinal height of the defect) at the same time. The defect depths are selected as 0.6mm, 0.9mm, 1.5mm, 2.0mm, and 2.5mm, and the projection length of the rising time period on the X-axis corresponding to the second stage is obtained. The results show that the defect depth at the same burial depth is linearly related to the projection length of the rising time period on the X-axis. The depth change of the defect at the same burial depth is linearly related to the projection length of the length from the rising time point to the mutation time point on the X-axis (i.e., the difference between the rising time point t1 and the mutation time point t2): Y=-1.4x+6.4, with a correlation coefficient R 2 =0.99323; where x is the defect depth in millimeters, and Y is the difference between the first rising time point and the second rising time point.

[0029] like Figure 6 and Figure 7As shown in the figure, a spherical defect with a diameter of 0.5mm and a sawtooth defect with an equivalent length of 0.65mm were simulated. The burial depth increased from 0.5mm to 4.0mm with a step size of 0.5mm. The leakage magnetic field of the two defects is shown in the figure. The results show that the different types of defects also display the three-segment signal characteristics of rectangular defects. The magnetic permeability distribution of the two defects is similar to that of the rectangular defect. When the magnetic shielding layer moves to the top of the defect, the leakage magnetic field begins to rise. The mathematical model of the rise time point and defect burial depth of the two defects is the same as that of the rectangular defect. The results show that the shape of the defect does not affect the rise time point.

[0030] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation to the invention.

[0031] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "example," "specific example," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment or example of the present application. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0032] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and intent of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A ferromagnetic material defect rapid tomography system based on AC magnetic flux leakage, characterized in that: include: The magnetizer is used to generate an excitation magnetic field by passing alternating current to magnetize the sample to be tested; A sensor is used to detect leakage magnetic field signals generated at defects of the sample to be tested; The host computer is electrically connected to the sensor and is used to receive and process the output signal of the sensor and output a characteristic map.

2. The AC magnetic flux leakage based rapid tomography system for ferromagnetic material defects according to claim 1, characterized in that: The magnetizer consists of a shell and a magnetizing coil arranged in the shell. The shell is a hollow opening structure on the side for the sample to be tested to pass through the side opening and is fixed by pads located at the front and rear ends of the magnetizer.

3. The AC magnetic flux leakage based rapid tomography system for ferromagnetic material defects according to claim 1, characterized in that: The sensor is a differential probe, which is composed of two Hall sensors arranged at intervals. The differential probe is moved along the surface of the sample to be detected to detect the change of the leakage magnetic field signal over time.

4. The AC magnetic flux leakage based rapid tomography system for ferromagnetic material defects according to claim 3, characterized in that: After obtaining the curve of the leakage magnetic field signal changing with time, the rising time point of the leakage magnetic field is determined. The specific process includes: obtaining the amplitude change curve of the leakage magnetic field signal, and dividing the leakage magnetic field signal characteristics into three stages according to the amplitude change curve. The first stage is the low amplitude stage when the magnetic shielding layer is shielding, the second stage is the linear increase stage when the magnetic shielding layer moves over the defect, and the third stage is the drastic increase stage after the magnetic shielding layer is removed. The transition point from the first stage to the second stage is determined as the rising time point, and the transition point from the second stage to the third stage is determined as the mutation time point.

5. The AC magnetic flux leakage based rapid tomography system for ferromagnetic material defects according to claim 1, characterized in that: Detecting changes in the leakage magnetic field signal through a sensor includes: setting a measurement point above the sample to be detected, the measurement point being located at the central axis of the magnetizer, obtaining a change curve of the leakage magnetic field signal through the measurement point, and analyzing the mutation characteristics of the leakage magnetic field signal based on the change curve.

6. The AC magnetic flux leakage based rapid tomography system for ferromagnetic material defects according to claim 1, characterized in that: The host computer also uses simulation software to simulate the relationship between the defect burial depth, defect width, defect depth, defect shape and rising time point.

7. The AC magnetic flux leakage based rapid tomography system for ferromagnetic material defects according to claim 6, characterized in that: The simulation model was used to study the defect width and rise time point, and the width was set to 0.2mm, 0.5mm, 0.8mm, 1.2mm, and 1.5mm respectively.

8. The AC magnetic flux leakage based rapid tomography system for ferromagnetic material defects according to claim 6, characterized in that: The simulation model is used to study the defect burial depth and rising time point. The defect burial depth is set to 2mm, 2.5mm, 3mm, 3.5mm, 4mm, and 4.5mm respectively. The linear equation is y=0.1392x+1.19326, R 2 =0.99819, y is the rising time point, and x is the defect depth.

9. The AC magnetic flux leakage based rapid tomography system for ferromagnetic material defects according to claim 6, characterized in that: A simulation model was used to study the defect depth and rise time point, and the defect depths were set to 0.6mm, 0.9mm, 1.5mm, 2.0mm, and 2.5mm respectively.

10. The AC magnetic flux leakage based rapid tomography system for ferromagnetic material defects according to claim 6, characterized in that: A spherical defect with a diameter of 0.5 mm and a sawtooth defect with an equivalent length of 0.65 mm were simulated respectively. The burial depth increased from 0.5 mm to 4.0 mm with a step size of 0.5 mm.

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