Track key part crack detection method based on electromagnetic thermal coupling eddy current

Abstract

The invention belongs to the technical field of defect detection, and discloses a track key part crack detection method based on electromagnetic thermal coupling eddy current, which comprises the following steps of: loading low-frequency alternating current in a detection coil to enable the detection coil to be close to the surfaces of track key parts such as a steel rail and a turnout; induction eddy current is generated in the induction part, and a secondary magnetic field is induced; the change of the comprehensive magnetic induction intensity B is detected through a detection module, and the position, suspected to have the crack defect, in the part is judged; high-frequency alternating current is loaded in the induction heating coil, so that the induction heating coil is close to the position, suspected to have the crack defect, in the part, the position is induced to generate large induction eddy current, a high-temperature area within a certain range is formed, and the shape and size of the crack are changed; the change of the comprehensive magnetic induction intensity B and the temperature distribution is detected through the detection module and the thermal infrared imager, so that the position and the size of the crack are judged, and the accurate detection of the crack defect in the part is realized.

Description

Technical Field

[0001] The present invention relates to a method for detecting cracks in key components of tracks based on electromagnetic-thermal coupled eddy currents, belonging to the technical field of defect detection. Background Art

[0002] In recent years, eddy current detection technology has been increasingly widely used in fields such as rail transit, aerospace, petrochemical, etc. With the advantages of fast detection speed, low cost, non-contact, etc., it can effectively solve the problems existing in conventional detection technologies, such as low efficiency, poor safety, cumbersome operation, etc., and realize large-area and rapid detection of key components of tracks such as rails and turnouts, saving labor and material costs. As a detection technology widely used in the detection of crack defects in components at present, eddy current detection uses an alternating current as the excitation signal, collects the changes in the electromagnetic field on the surface of the component and transmits them to a computer for analysis and processing, so as to judge the position and size of the crack and achieve the purpose of defect detection. However, in engineering applications, in the face of defects such as fine micro-cracks and dense cracks, the accuracy of eddy current detection technology is difficult to meet the detection requirements, and it is easy to cause misjudgment and missed detection of crack defects, resulting in a decrease in the repair quality of components and seriously affecting their safety performance. Therefore, there is an urgent need to propose a method for detecting defects in key components of tracks that can achieve accurate crack judgment. Summary of the Invention

[0003] In order to solve the above problems, the present invention proposes a method for detecting cracks in key components of tracks based on electromagnetic-thermal coupled eddy currents, including the following steps:

[0004] (1) Load a low-frequency alternating current in the detection coil, make the detection coil close to the surface of key components of tracks such as rails and turnouts, and the low-frequency alternating magnetic field generated by the detection coil will induce an induced eddy current in the component and induce a secondary magnetic field;

[0005] (2) Detect the change in the comprehensive magnetic induction intensity B through the detection module, and judge the position where a crack defect is suspected to exist in the component;

[0006] (3) Load a high-frequency alternating current in the induction heating coil, make the induction heating coil close to the position where a crack defect is suspected to exist in the component, and the high-frequency alternating magnetic field generated by the induction heating coil will induce a large induced eddy current in the position where a crack defect is suspected to exist in the component. The Joule heat generated by the induced eddy current forms a high-temperature area within a certain range in the component, resulting in changes in the shape and size of the crack and affecting the induced eddy current density inside the component, amplifying the difference in the comprehensive magnetic induction intensity B between the position where a crack defect exists and other positions in the component;

[0007] (4) Detect the changes in the comprehensive magnetic induction intensity B and the temperature distribution through the detection module and the infrared thermal imager, so as to judge the position and size of the crack, and achieve the precise detection of crack defects in the parts.

[0008] Further, in step (2), the comprehensive magnetic induction intensity B detected by the detection module includes the magnetic induction intensity B1 generated by the detection coil and the magnetic induction intensity B2 of the secondary magnetic field induced by the induced eddy current in the part; the existence of crack defects will directly affect the magnitude of the magnetic induction intensity B2 of the secondary magnetic field. Compare the magnitudes of the comprehensive magnetic induction intensity B at different positions of the part. When the change amplitude of the comprehensive magnetic induction intensity B at a certain position exceeds a certain threshold, it is judged that there may be a crack defect at this position of the part.

[0009] Further, in step (3), under the influence of the high-frequency alternating magnetic field, due to the skin effect, the induced eddy current generated at the position where the crack defect is suspected to exist in the part is mainly concentrated within the skin depth δ of the part surface. The calculation formula for the skin depth δ is:

[0010]

[0011] where σ is the electrical conductivity of the material, μ is the relative magnetic permeability of the material, μ0 is the magnetic permeability of vacuum, and f a is the magnetic field frequency;

[0012] According to the position information of the part where the crack defect is suspected to exist detected by the detection module, predict the crack depth through the change amplitude of the comprehensive magnetic induction intensity B. If the crack depth is greater than the skin depth δ, reduce the frequency of the high-frequency alternating current applied to the induction heating coil, so that the induced eddy current in the part can reach the crack depth, avoiding the misjudgment of the crack depth in the part caused by the skin effect. If the crack depth is less than the skin depth δ, there is no need to adjust the frequency of the high-frequency alternating current applied to the induction heating coil.

[0013] Further, in step (3), according to Joule's law, the induced eddy current in the part will generate Joule heat, resulting in a local temperature rise of the part. The calculation formula for the heat power density Q generated by the induced eddy current is:

[0014]

[0015] where J is the induced eddy current density;

[0016] The parts material in the high-temperature area expands due to heat, and the linear expansion amount ΔL calculation formula is:

[0017] ΔL = α × L × ΔT

[0018] where α is the coefficient of thermal expansion of the material, L is the linear original dimension, and ΔT is the temperature change;

[0019] During the expansion of the component material, if there are crack defects in the high-temperature area, it will cause changes in the shape and size of the cracks, increasing the influence of the crack defects on the magnetic induction intensity B2 of the secondary magnetic field induced by the induction eddy current in the component, and improving the accuracy of crack defect detection.

[0020] Furthermore, in step (4), the comprehensive magnetic induction intensity B detected by the detection module after induction heating includes the magnetic induction intensity B1 generated by the detection coil, the magnetic induction intensity B2 of the secondary magnetic field induced by the induction eddy current in the component, and the magnetic induction intensity B3 generated by the induction heating coil. An appropriate detection range is set. Within this detection range, if the detection result of the comprehensive magnetic induction intensity B presents a complete defect waveform, it is judged as a single crack; if the detection result of the comprehensive magnetic induction intensity B has two or more defect waveforms with obvious intervals, it is judged as a dense crack. At the same time, the infrared thermal imager records the thermal field information on the surface of the component in real time. The linear expansion amount ΔL of the component material can be calculated through the obtained temperature change amount ΔT. If the linear expansion amount ΔL is less than a certain threshold, the change in the shape and size of the crack is not obvious, and it is impossible to judge whether there are crack defects. Then, the intensity of the high-frequency alternating current loaded in the induction heating coil is increased, so that the local temperature of the component further increases, the linear expansion amount ΔL of the component material increases, the change in the shape and size of the crack is more obvious, and the accuracy of crack defect detection by the detection module and the infrared thermal imager is improved. By comprehensively comparing and analyzing the comprehensive magnetic induction intensity B at different positions of the component detected by the detection module, the computer is used to realize the conversion of the fluctuation amplitude of the defect waveform and the crack depth within the detection range. The thermal image sequence representing the thermal field distribution information detected by the infrared thermal imager is input into the computer for analysis and processing to obtain the contour information of the crack, so as to accurately judge the position and size of the crack in the component.

[0021] The beneficial effects of the present invention are as follows:

[0022] A method for detecting cracks in key components of tracks based on electromagnetic-thermal coupled eddy currents according to the present invention adopts a combined coil design with multi-physical field coupling, couples two technologies of electromagnetic induction heating and eddy current detection. The high-frequency alternating magnetic field generated by the induction heating coil causes a large induction eddy current to be generated at the position suspected of having crack defects in the component and forms a high-temperature area within a certain range, resulting in changes in the shape and size of the cracks, increasing the difference in the comprehensive magnetic induction intensity B and temperature distribution in the detection, making up for the disadvantage that it is difficult to accurately judge fine cracks in eddy current detection, improving the accuracy of eddy current detection, and effectively reducing the misjudgment and missed detection of crack defects in components. Description of the Drawings

[0023] Figure 1Overall schematic diagram of a method for detecting cracks in key components of a track based on electromagnetic-thermal coupled eddy currents according to the present invention;

[0024] Figure 2 Schematic diagram of the crack change process;

[0025] Figure 3 Schematic diagram of the comprehensive magnetic induction intensity B at different positions before and after heating;

[0026] In the figure: 1 - rail, 2 - induction heating coil, 3 - detection coil, 4 - detection module, 5 - infrared thermal imager, 6 - computer, 7 - excitation power supply, 8 - crack, 9 - high-temperature area. Specific implementation manner

[0027] In order to make the purpose, technical solution and advantages of the method for detecting cracks in key components of a track based on electromagnetic-thermal coupled eddy currents according to the present invention clearer, the following will be described in detail with reference to the drawings and specific embodiments. The following embodiments are only used to illustrate the present invention, and the scope of the rights protected by the present invention includes but is not limited to the following embodiments.

[0028] In the following embodiments, the key component of the track is selected as the rail 1, and the specific implementation manner of this method will be described.

[0029] As Figure 1 shown, a method for detecting cracks in key components of a track based on electromagnetic-thermal coupled eddy currents provided in this embodiment is characterized by including the following steps:

[0030] Step 1: Load a low-frequency alternating current generated by an excitation power supply 7 controlled by a computer 6 into the detection coil 3. A low-frequency alternating magnetic field is generated in the space near the detection coil 3. Keep the detection coil 3 close to the tread of the rail 1 and parallel. During the detection process, the distance between the two is always about 5 mm; the low-frequency alternating magnetic field generated by the detection coil 3 will cause the magnetic flux in the rail 1 to change continuously, inducing an induced eddy current in the rail 1 and generating a secondary magnetic field. In this embodiment, the intensity of the low-frequency alternating current is 20 A and the frequency is 20 kHz.

[0031] Step 2: When there is a crack 8 defect in the rail 1, it will affect the flow path of the induced eddy current at this position and change the density of the induced eddy current at this position, thereby causing a change in the magnetic induction intensity B2 of the secondary magnetic field. If there is a small crack 8 with a depth of about 1 mm, it is difficult to directly judge the crack 8 defect information; use the detection module 4 to detect the comprehensive magnetic induction intensity B, transmit it to the computer 6 for analysis and processing, and judge the position where there is a suspected crack 8 defect in the rail 1 by observing the change curve of the comprehensive magnetic induction intensity B; the comprehensive magnetic induction intensity B detected by the detection module 4 includes the magnetic induction intensity B1 generated by the detection coil 3 and the magnetic induction intensity B2 of the secondary magnetic field induced by the induced eddy current in the rail 1.

[0032] Step 3: Load a high-frequency alternating current generated by an excitation power supply 7 controlled by a computer 6 into the induction heating coil 2. A high-frequency alternating magnetic field is generated in the space near the induction heating coil 2, making the induction heating coil 2 approach the suspected crack 8 defect position in the rail 1 and keep parallel to the tread of the rail 1. During the heating process, the distance between the two is always about 2 mm. The high-frequency alternating magnetic field generated by the induction heating coil 2 will cause the magnetic flux in the rail 1 to change continuously, inducing a large induction eddy current at the suspected crack 8 defect position in the rail 1. In this embodiment, the intensity of the high-frequency alternating current is 100 A and the frequency is 180 kHz.

[0033] Under the influence of the high-frequency alternating magnetic field, due to the skin effect, the induction eddy current generated at the suspected crack 8 defect position in the rail 1 is mainly concentrated within the skin depth δ of the rail 1 tread. The calculation formula for the skin depth δ is:

[0034]

[0035] where σ is the electrical conductivity of the material, μ is the relative magnetic permeability of the material, μ0 is the magnetic permeability of vacuum, and f a is the magnetic field frequency.

[0036] According to the position information of the suspected crack 8 defect in the rail 1 detected by the detection module 4, predict the crack 8 depth by comprehensively considering the change amplitude of the magnetic induction intensity B. If the crack 8 depth is greater than the skin depth δ, reduce the frequency of the high-frequency alternating current loaded in the induction heating coil 2 so that the induction eddy current in the rail 1 can reach the crack 8 depth, avoiding misjudgment of the crack 8 depth in the rail 1 caused by the skin effect. If the crack 8 depth is less than the skin depth δ, there is no need to adjust the frequency of the high-frequency alternating current loaded in the induction heating coil 2.

[0037] A certain range of high-temperature region 9 is formed in the rail 1 by the Joule heat generated by the induction eddy current. The calculation formula for the heat power density Q generated by the induction eddy current is:

[0038]

[0039] where J is the induction eddy current density.

[0040] The material of the rail 1 in the high-temperature region 9 expands due to heat. The calculation formula for the linear expansion amount ΔL is:

[0041] ΔL = α × L × ΔT

[0042] where α is the coefficient of thermal expansion of the material, L is the linear original dimension, and ΔT is the temperature change.

[0043] If there is a crack 8 defect in the high-temperature region 9, it will cause changes in the shape and size of the crack 8 during the expansion process and affect the induced eddy current density inside the rail 1. As Figure 2 shown.

[0044] Step 4: Use the detection module 4 to detect the comprehensive magnetic induction intensity B and transmit it to the computer 6 for analysis and processing. Accurately judge the position and depth of the crack 8 in the rail 1 by observing the change curve of the comprehensive magnetic induction intensity B; the comprehensive magnetic induction intensity B detected by the detection module 4 after induction heating includes the magnetic induction intensity B1 generated by the detection coil 3, the magnetic induction intensity B2 of the secondary magnetic field induced by the induced eddy current in the rail 1, and the magnetic induction intensity B3 generated by the induction heating coil 2.

[0045] Figure 3 It reflects the comprehensive magnetic induction intensity B at different positions before and after heating. The difference between the comprehensive magnetic induction intensity B at the crack 8 after heating and the comprehensive magnetic induction intensity B at other positions is more obvious. In this detection range, if the detection result of the comprehensive magnetic induction intensity B presents a complete defect waveform, it is judged as a single crack 8. If the detection result of the comprehensive magnetic induction intensity B has two or more defect waveforms with obvious intervals, it is judged as a dense crack 8.

[0046] At the same time, the crack 8 defect will affect the heat diffusion at this position, resulting in abnormal temperature field distribution at this position; use the infrared thermal imager 5 to record the change of the temperature distribution of the rail 1 in real time. The linear expansion amount ΔL of the rail 1 material can be calculated through the obtained temperature change amount ΔT; if the linear expansion amount ΔL is less than a certain threshold value, the change in the shape and size of the crack 8 is not obvious, and it is impossible to judge whether there is a crack 8 defect. Then increase the intensity of the high-frequency alternating current applied in the induction heating coil 2 to further increase the local temperature of the rail 1, increase the linear expansion amount ΔL, make the change in the shape and size of the crack 8 more obvious, and improve the detection accuracy of the crack 8 defect by the detection module 4 and the infrared thermal imager 5.

[0047] Through comprehensive comparative analysis of the comprehensive magnetic induction intensity B at different positions of the rail 1 detected by the detection module 4, use the computer 6 to realize the conversion of the fluctuation amplitude of the defect waveform and the depth of the crack 8 within the detection range. Transmit the thermal image sequence representing the thermal field distribution information detected by the infrared thermal imager 5 to the computer 6 for analysis and processing, compare the temperature distribution changes before, during, and after heating, and obtain the contour information of the crack 8 in the rail 1, so as to accurately judge the position and size of the crack 8 in the rail 1.

[0048] Through the above embodiments, the object, method, and content of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. The present invention can be appropriately modified to be applied to other suitable scenarios in the welding field. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A crack detection method for key components of tracks based on electromagnetic-thermal coupled eddy current, characterized in that, It includes the following steps: (1) Load a low-frequency alternating current in the detection coil, bring the detection coil close to the surfaces of key track components such as rails and switches. The low-frequency alternating magnetic field generated by the detection coil will induce eddy currents in the components and generate a secondary magnetic field; (2) Detect the change in the comprehensive magnetic induction intensity B through the detection module to judge the position where a crack defect is suspected to exist in the component; (3) Load a high-frequency alternating current in the induction heating coil, bring the induction heating coil close to the position where a crack defect is suspected to exist in the component. The high-frequency alternating magnetic field generated by the induction heating coil will induce a large eddy current in the position where a crack defect is suspected to exist in the component. The Joule heat generated by the eddy current forms a high-temperature area within a certain range in the component, causing changes in the shape and size of the crack and affecting the eddy current density inside the component, amplifying the difference in the comprehensive magnetic induction intensity B between the position with a crack defect and other positions in the component; (4) Detect the changes in the comprehensive magnetic induction intensity B and the temperature distribution through the detection module and the infrared thermal imager, so as to judge the position and size of the crack and achieve precise detection of crack defects in the component.

2. A crack detection method for key components of an orbit based on electromagnetic thermal coupling eddy current according to claim 1, characterized in that, In step (2), the comprehensive magnetic induction intensity B detected by the detection module includes the magnetic induction intensity B1 generated by the detection coil and the magnetic induction intensity B2 of the secondary magnetic field induced by the eddy current in the component; The existence of a crack defect will directly affect the magnitude of the magnetic induction intensity B2 of the secondary magnetic field. Compare the magnitudes of the comprehensive magnetic induction intensity B at different positions of the component. When the change amplitude of the comprehensive magnetic induction intensity B at a certain position exceeds a certain threshold, it is judged that a crack defect is suspected to exist in the component at this position.

3. A crack detection method for key components of an orbit based on electromagnetic thermal coupling eddy current according to claim 1, characterized in that In step (3), under the influence of the high-frequency alternating magnetic field, due to the skin effect, the eddy current induced in the position where a crack defect is suspected to exist in the component is mainly concentrated within the skin depth δ on the surface of the component. The calculation formula for the skin depth δ is: where σ is the conductivity of the material, μ is the relative magnetic permeability of the material, μ0 is the magnetic permeability of vacuum, and f a is the magnetic field frequency; According to the position information of the component where a crack defect is suspected to exist detected by the detection module, predict the crack depth through the change amplitude of the comprehensive magnetic induction intensity B. If the crack depth is greater than the skin depth δ, reduce the frequency of the high-frequency alternating current loaded in the induction heating coil so that the eddy current in the component can reach the crack depth, avoiding misjudgment of the crack depth in the component caused by the skin effect. If the crack depth is less than the skin depth δ, there is no need to adjust the frequency of the high-frequency alternating current loaded in the induction heating coil.

4. A crack detection method for key components of tracks based on electromagnetic thermal coupling eddy current according to claim 1, characterized in that In step (3), according to Joule's law, the eddy current in the component will generate Joule heat, resulting in a local temperature rise of the component. The calculation formula for the heat power density Q generated by the eddy current is: where J is the eddy current density; The component material in the high-temperature area expands due to heat, and the linear expansion amount ΔL calculation formula is: ΔL = α × L × ΔT where α is the coefficient of thermal expansion of the material, L is the linear original dimension, and ΔT is the temperature change; During the process of the expansion of the component material, if there are crack defects in the high-temperature area, it will cause changes in the shape and size of the cracks, increasing the influence of the crack defects on the magnetic induction intensity B2 of the secondary magnetic field induced by the induction vortex in the component, and improving the accuracy of crack defect detection.

5. A crack detection method for key components of a track based on electromagnetic thermal coupling eddy current according to claim 1, characterized in that In step (4), the comprehensive magnetic induction intensity B detected by the detection module after induction heating includes the magnetic induction intensity B1 generated by the detection coil, the magnetic induction intensity B2 of the secondary magnetic field induced by the induction vortex in the component, and the magnetic induction intensity B3 generated by the induction heating coil. Set an appropriate detection range. Within this detection range, if the detection result of the comprehensive magnetic induction intensity B presents a complete defect waveform, it is judged as a single crack; if there are two or more defect waveforms with obvious intervals in the detection result of the comprehensive magnetic induction intensity B, it is judged as a dense crack. At the same time, the infrared thermal imager records the thermal field information on the surface of the component in real time. The linear expansion amount ΔL of the component material can be calculated through the obtained temperature change amount ΔT. If the linear expansion amount ΔL is less than a certain threshold, the shape and size of the crack do not change significantly, and it is impossible to judge whether there are crack defects. Then, increase the intensity of the high-frequency alternating current applied to the induction heating coil, so that the local temperature of the component further increases, the linear expansion amount ΔL of the component material increases, the shape and size of the crack change more significantly, and the accuracy of crack defect detection by the detection module and the infrared thermal imager is improved. Through comprehensive comparative analysis of the comprehensive magnetic induction intensity B at different positions of the component detected by the detection module, the computer is used to realize the conversion of the fluctuation amplitude and crack depth of the defect waveform within the detection range. The thermal image sequence representing the thermal field distribution information detected by the infrared thermal imager is input into the computer for analysis and processing to obtain the contour information of the crack, so as to accurately judge the position and size of the crack in the component.

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