Magnetic gathering type eddy current probe

Abstract

An excitation coil adopts a semi-ellipsoidal structure, the thicknesses of an upper coil and a lower coil of the structure are consistent, and the bottom surface of the excitation coil is in contact with the upper surface of the bottom of a shell and is arranged at the upper part of the shell; the magnetic core is formed by processing permalloy with high magnetic conductivity and comprises a top circular truncated cone structure, a semi-ellipsoidal structure matched with the inner surface of the middle exciting coil and a tip structure located at the bottom, the size of the top circular truncated cone is matched with the upper side of the interior of the shell, and the tip of the bottom is matched with a notch groove in the upper portion of the center position of the bottom of the shell; the upper part of the central position of the outer bottom is provided with a notch groove conformal to the tip of the magnetic core, and the lower part of the central position of the bottom is provided with a circular notch groove conformal to the cylindrical detection coil; the detection coil is of a cylindrical structure and located under the excitation coil and the magnetic core and in a notch groove in the bottom of the cylindrical shell, the bottom of the excitation coil and the bottom face of the cylindrical shell are located on the same plane, the excitation magnetic field intensity on the metal test piece is improved, and the small defect detection sensitivity and accuracy are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic nondestructive testing, and further belongs to the technical field of eddy current testing, and specifically relates to a magnetic field focusing eddy current probe for metal component defect detection, and more particularly to an eddy current probe with a high magnetic permeability magnetic core structure and a magnetic field focusing effect. Background Art

[0002] Eddy current nondestructive testing technology is a detection method based on the principle of electromagnetic induction. It can evaluate the performance of conductive materials or find potential defects without damaging the surface of the material. This technology is widely used in many fields, including aviation, aerospace, metallurgy, machinery, chemical industry and nuclear power, and is essential to ensure the safe operation of equipment. Eddy current testing technology has many advantages, such as fast detection speed and sensitivity to defects on the surface or near the surface of the workpiece.

[0003] Most existing conventional eddy current probes use a cylindrical single-coil excitation form, which has shortcomings such as severe magnetic leakage and weak detection signals. Although the team has previously applied for a magnetic-gathering eddy current sensor (202110182154.7), which has a magnetic-gathering effect and enhances the sensitivity of the detection signal, the excitation coil used in this patent is a conical coil, and is equipped with a cylindrical ferrite core and a shielding cover, which increases the defect detection efficiency to a certain extent and reduces the impact of background noise. However, the magnetic permeability of the magnetic core of this structure is relatively low, the magnetic core is not conformal to the excitation coil, and it does not have a cutting-edge structure, so the magnetic-gathering effect has certain shortcomings.

[0004] The present invention adopts a semi-ellipsoidal excitation coil and is configured with a Permalloy core with a relative magnetic permeability of more than 30,000. The core structure is conformal to the excitation coil and has a sharp tip. This structure has a better magnetic concentration effect and improves the defect detection sensitivity and signal amplitude. Summary of the invention

[0005] The purpose of the present invention is to propose a high-sensitivity eddy current probe for defects with a magnetic focusing effect, which has the following characteristics: the excitation coil is a semi-ellipsoidal structure, which itself has a magnetic focusing effect; it is equipped with a magnetic core structure and conforms to the excitation coil, and the lower part of the magnetic core has a pointed structure, which can further improve the focusing effect of electromagnetic energy in the metal test piece to be tested under the probe, thereby improving the defect detection sensitivity.

[0006] The technical solution adopted by the present invention to solve the technical problem is: comprising modules such as a semi-ellipsoidal excitation coil, a Permalloy core with a tip conforming to the excitation coil, a detection coil, a shell, and a switching circuit board; the characteristics are as follows: the excitation coil adopts a semi-ellipsoidal structure, the thickness of the upper and lower coils of the structure is consistent, and the bottom surface of the excitation coil contacts and is at the upper part of the bottom upper surface of the shell; the magnetic core is made of Permalloy with high magnetic permeability, and the magnetic core comprises three parts: a top truncated cone structure, a semi-ellipsoidal structure conforming to the inner surface of the middle excitation coil, and a tip structure located at the bottom, the size of the top truncated cone is adapted to the inner upper side of the shell, and the bottom tip is adapted to the groove at the upper part of the center position of the bottom of the shell; the shell has a cylindrical structure, the upper part of the center position of the bottom has a groove conforming to the tip of the magnetic core, and the lower part of the center position of the bottom has a circular groove conforming to the cylindrical detection coil; the detection coil adopts a cylindrical structure, is located directly below the excitation coil and the magnetic core and in the groove at the bottom of the cylindrical shell, and the bottom of the excitation coil and the bottom surface of the cylindrical shell are in the same plane.

[0007] In order to achieve the above object, the present invention adopts the following design scheme: The magnetic field focusing eddy current probe is characterized in that the thickness of the excitation coil is consistent from bottom to top, and its cross-section is a curved trapezoidal structure, which focuses the magnetic field on the area to be tested, generating a gradient distribution and a high-energy magnetic field.

[0008] The magnetic field-concentrating eddy current probe is characterized in that: the high magnetic permeability Permalloy core consists of a top truncated cone structure, a middle semi-ellipsoidal structure that conforms to the inside of the excitation coil, and a pointed structure at the bottom, which binds the spatial magnetic lines of force to enhance the strength of the detection coil signal below and obtain rich magnetic field frequency components, playing the role of magnetic conduction and magnetic concentration; the top truncated cone structure is provided with mounting screw holes and wiring holes, and is exactly installed inside the cylindrical shell, flush with the upper surface of the cylindrical shell.

[0009] The magnetic field-concentrating eddy current probe is characterized in that the cylindrical shell is made of non-metallic material, such as resin, etc., the upper part of the bottom center has a groove that conforms to the tip of the magnetic core, and the lower part of the bottom center has a circular groove that conforms to the cylindrical detection coil.

[0010] The magnetic field-concentrating eddy current probe is characterized in that the top of the probe is a switching circuit board, which has switching circuits, mounting holes and routing holes, and its lower surface is in close contact with the cylindrical shell and the upper surface of the magnetic core, and is fastened to the cylindrical shell by fixing bolts.

[0011] The described magnetic-concentrating eddy current probe is characterized in that the detection coil is a cylindrical hollow coil and is located directly below the excitation coil and the magnetic core. It is used to measure the total magnetic field in the longitudinal direction after the coil excitation magnetic field and the magnetic field of the test piece are superimposed. The magnetic field intensity is the largest at this position and the received signal magnetic field intensity is the strongest.

[0012] The described magnetic field-concentrating eddy current probe is characterized in that the eddy current sensor can increase the magnetic field strength from the aspects of coil excitation of the magnetic field and the transfer of magnetic energy, reduce the influence of the background magnetic field, and at the same time improve the recognition rate of tiny defects within the effective skin depth range and improve the detection sensitivity.

[0013] The present invention can achieve the following beneficial effects: 1. Compared with the cylindrical excitation coil used in conventional eddy current sensors, the hemispherical excitation coil generates a larger and more concentrated magnetic field and a more concentrated eddy current distribution at the detection signal receiving position and near the object being measured.

[0014] 2. The high magnetic permeability core enhances the internal magnetic flux density of the metal material being tested, thereby increasing the amplitude of the defect signal.

[0015] 3. A high magnetic permeability magnetic core conforming to the excitation coil is placed above the detection coil and has a pointed structure that allows more magnetic lines of force to pass through the detection coil, thus achieving multiple magnetic concentration effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : A front view of the assembly of the excitation coil, magnetic core and detection coil of a magnetic concentrating eddy current probe; Figure 2 : A top view of the assembly of the excitation coil, magnetic core and detection coil of a magnetic concentrating eddy current probe; Figure 3 : A cross-sectional view of the assembly of an excitation coil, a magnetic core and a detection coil of a magnetic concentrating eddy current probe; Figure 4 : A perspective view of the left and right isometric angles of a magnetic field-concentrating eddy current probe housing; Figure 5 : A circuit adapter board diagram of a magnetic field-concentrating eddy current probe; Figure 6 : Schematic diagram of the magnetic field density of the semi-ellipsoidal line excitation coil and the cylindrical excitation coil changing with distance; Figure 7 : Magnetic field focusing effect diagram of two-dimensional axisymmetric models with different tip structures. Figure 1 Among them, 1. Permalloy core, 2. Semi-ellipsoidal excitation coil, 3. Cylindrical detection coil; Figure 2 In the middle, 1. Permalloy core, 4. Mounting screw hole, 5. Wire hole; Figure 3 In the figure, 101, the truncated cone structure at the top of the magnetic core, 102, the semi-ellipsoid structure in the middle of the magnetic core, 103, the tip structure at the bottom of the magnetic core; Figure 4 In the middle, 6, housing, 7, housing fixing screw hole, 601, housing bottom tip groove, 602, housing bottom cylindrical groove; Figure 5 In the middle, 8, transfer circuit board, 9, circuit board fixing screw hole, 10, soldering pad, 11, wire slot, 12, circuit board installation screw hole; Figure 7 In the figure, (a) is a diagram of the magnetic focusing effect of a parabolic tip structure, (b) is a diagram of the magnetic focusing effect of an acoustic black hole tip structure, and (c) is a diagram of the magnetic focusing effect of a conical tip structure. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0018] The front view, top view and cross-sectional view of the exciting coil, magnetic core and detection coil assembly designed by the present invention are respectively as follows: Figure 1 , 2 As shown in and 3. It comprises a magnetic core 1, an excitation coil 2 and a detection coil 3. The magnetic core 1 comprises a truncated cone structure 101 at the top of the magnetic core, a semi-ellipsoidal structure 102 in the middle and a tip structure 103 at the bottom. The truncated cone structure 101 is slightly larger than the largest part at the top of the excitation coil, the semi-ellipsoidal structure 102 in the middle is conformal to the inside of the excitation coil 2 and the inside of the excitation coil, and the tip structure 103 at the bottom is an acoustic black hole structure and protrudes from the bottom of the excitation coil 2; the bottom tip 103 can be a parabolic structure, an acoustic black hole structure, a conical structure, etc.; the detection coil 3 is located directly below the magnetic core 1 and the detection coil 2. There are M3 mounting screw holes on the truncated cone structure 101 of the magnetic core 1, and they are connected to the magnetic core 1. Figure 5 The mounting screw holes 12 on the adapter circuit board 8 are aligned and fixed on the scanning device during defect detection; there is a Φ1.5 wire hole 5 on the truncated cone structure 101 for passing the wires of the excitation coil 2 and the detection coil 3.

[0019] The left and right isometric perspective views of the probe housing designed by the present invention are as follows: Figure 4As shown, the shell wall of the shell 6 is provided with M1.6 bolt holes 7 for fixed connection with the adapter circuit board 8; the upper surface of the lower bottom of the shell 6 is provided with a groove 601 conforming to the tip 103 of the magnetic core 1; the lower surface of the lower bottom of the shell 6 is provided with a cylindrical groove 602 conforming to the detection coil 3; when the probe is assembled, the ellipsoidal structure 102 in the middle of the magnetic core 1 is inserted into the inside of the excitation coil 2, and the upper surface of the excitation coil 2 is flush with the bottom of the truncated cone structure 101 on the upper part of the magnetic core 1; the acoustic black hole tip structure 102 at the bottom of the magnetic core 1 contacts the inner wall of the tip groove 601 on the upper surface of the lower bottom of the shell 6; the detection coil 3 is placed in the cylindrical groove 602 on the lower surface of the lower bottom of the shell 6, and the lower surface of the detection coil 3 is flush with the lower surface of the lower bottom of the shell 6.

[0020] Figure 5 The diagram shows a probe circuit adapter board 8, wherein the fixing screw hole 9 has the same aperture and distribution as the bolt hole 7 on the outer shell 6, and is used for fixing the connection with the outer shell 6; the circuit board mounting screw hole 12 has the same aperture as the magnetic core mounting screw hole, and the two are aligned during installation; during installation, the wire groove 11 is located directly above the wire hole 5 to facilitate the passage of the wire; there are solder pads 10 on the circuit adapter board 8 for soldering the excitation coil 2, the detection coil 3 and the external excitation and receiving circuits.

[0021] Figure 6 This is a schematic diagram of the variation of magnetic flux density with distance on the cross-section of the specimen surface for the two-dimensional axisymmetric model of the semi-ellipsoidal wire excitation coil and the cylindrical excitation coil in finite element simulation. The semi-ellipsoidal excitation coil has a better magnetic field focusing effect.

[0022] Figure 7 The figures are the magnetic focusing effect diagrams of two-dimensional axisymmetric models with different tip structures, where (a) is the magnetic focusing effect diagram of the shaped tip structure, (b) is the magnetic focusing effect diagram of the acoustic black hole tip structure, and (c) is the magnetic focusing effect diagram of the tip structure; different tip structures have different magnetic focusing effects, among which the acoustic black hole tip structure has the best magnetic focusing effect.

Claims

1. A magnetic field-concentrating eddy current probe, characterized in that: It includes a semi-ellipsoidal excitation coil, a Permalloy core conforming to the semi-ellipsoidal excitation coil and having a pointed end, a detection coil, a housing and a switching circuit board; The thickness of the semi-ellipsoidal excitation coil is consistent from the bottom to the top, and its longitudinal section is a curved trapezoidal structure; the semi-ellipsoidal excitation coil focuses the magnetic field on the area to be measured and generates a gradient distribution and a high-energy magnetic field; The Permalloy core has a high relative magnetic permeability, i.e., more than 30,000, and is composed of a top truncated cone structure, a middle semi-ellipsoidal structure, and a bottom tip structure; the diameter of the top truncated cone structure is larger than the maximum opening diameter of the top of the semi-ellipsoidal excitation coil, and is provided with mounting screw holes and wiring holes, and is just installed inside the shell and flush with the upper surface of the shell; the middle semi-ellipsoidal structure conforms to the inside of the semi-ellipsoidal excitation coil; the top of the bottom tip structure is the same size as the bottom of the middle semi-ellipsoidal structure, and its bottom surface is circular, presenting a conical structure as a whole; the Permalloy core structure can further bind the spatial magnetic lines of force to enhance the strength of the detection coil signal below and obtain the magnetic field frequency component, playing the role of magnetic conduction and magnetic concentration.

2. The magnetic field-concentrating eddy current probe according to claim 1, characterized in that: The shell is made of non-metallic resin, and the upper part of the bottom center position has a groove conforming to the tip structure of the Permalloy core, and the lower part of the bottom center position has a circular groove conforming to the cylindrical detection coil.

3. The magnetic field-concentrating eddy current probe according to claim 1, characterized in that: The top of the probe is a switching circuit board, which has switching circuits, mounting holes and wiring holes. The lower surface of the switching circuit board is in close contact with the cylindrical shell and the upper surface of the magnetic core, and is fastened to the cylindrical shell by fixing bolts.

4. The magnetic field-concentrating eddy current probe according to claim 1, characterized in that: The detection coil is a cylindrical hollow coil and is located directly below the excitation coil and the magnetic core. It is used to measure the total magnetic field in the longitudinal direction after the coil excitation magnetic field and the magnetic field of the test piece are superimposed. The magnetic field strength is the largest at this position and the received signal magnetic field strength is the strongest.

5. The magnetic field-concentrating eddy current probe according to claim 1, characterized in that: The eddy current probe can improve the magnetic field strength from the aspects of magnetic field coil excitation and magnetic energy transfer, reduce the influence of the background magnetic field, and at the same time improve the recognition rate of small defects within the effective skin depth range and improve the detection sensitivity; the semi-ellipsoidal excitation coil and the Permalloy core of the probe both have the function of converging magnetic flux lines, and the conical tip of the Permalloy core further enhances the effect of converging magnetic flux lines, enhances the magnetic induction intensity directly below the core, and also enhances the intensity of the effective magnetic field on the test piece. Correspondingly, the induced eddy current in the test piece increases, and the secondary magnetic field intensity generated by the induced eddy current increases, so that the secondary magnetic field through the detection coil also increases, thereby improving the detection sensitivity.

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