CN1131429C - Method for inspecting surface defects of ferromagnetic material by geomagnetic field - Google Patents
Method for inspecting surface defects of ferromagnetic material by geomagnetic field Download PDFInfo
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- CN1131429C CN1131429C CN 01123977 CN01123977A CN1131429C CN 1131429 C CN1131429 C CN 1131429C CN 01123977 CN01123977 CN 01123977 CN 01123977 A CN01123977 A CN 01123977A CN 1131429 C CN1131429 C CN 1131429C
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Abstract
The present invention relates to a method for inspecting the surface defects of ferromagnetic materials by a geomagnetic field, which comprises the steps that ferromagnetic materials to be inspected are horizontally put into a geomagnetic field first; the intensity of the magnetic field of each point in the same horizontal plane near the surfaces of the ferromagnetic materials is measured; under the same inspection condition, artificial defect thresholds of the known materials which are the same to the ferromagnetic materials to be inspected are set; the intensity signals of the obtained magnetic fields are amplified and filtered and then compared with the artificial defect thresholds set in advance to judge whether a defect exists or not. The present invention utilizes the geomagnetic field as a magnetic excitation source and can inspect various defects on the surfaces of the ferromagnetic materials, including surface cracks, etch pits, internal residues and pores near the surfaces of the ferromagnetic materials, stress concentration, etc.
Description
Technical field:
The present invention relates to a kind of method of utilizing the terrestrial magnetic field to detect surface defects of ferromagnetic material, belong to the technical field of nondestructive testing of ferrimagnet.
Background technology:
In the prior art, application number is 95212309 patented product steel pipe magnetic flux leakage testing device, adopt the dc magnetization mode, set upright clamp system, circumferential defect testing agency and axial flaw testing agency, and devices such as control desk, testing circuit and warning, demonstration, marking are formed by front and back two.Set upright before the steel pipe of advancing passes the rotating magnetic field of the fixed magnetic field of V-arrangement up and down wheel, circumferential defect testing agency of clamp system and probe, axial flaw testing agency and probe, after set upright the wheel of V-arrangement up and down of clamp system.Upwards distribute in detected week or axially go up promptly report to the police after the defective that distributes, demonstration, marking.
Summary of the invention:
The objective of the invention is to propose a kind of method of utilizing the terrestrial magnetic field to detect surface defects of ferromagnetic material, in the environment of terrestrial magnetic field, ferromagnetic material is magnetized, the changes of magnetic field that the test material surface produces, judge according to this variation whether material surface exists defective, comprise the nearly surface of surface crack, etch pit, material internal folder caye and pore, and stress is concentrated etc.
The method of surface defects of ferromagnetic material is detected in the terrestrial magnetic field that utilizes that the present invention proposes, and may further comprise the steps:
(1) ferrimagnet to be detected is placed horizontally in the environment of magnetic field of the earth, measures the magnetic field intensity of each point on the interior same surface level of the nearly surperficial 0.01mm～10mm of material, the distance between each measuring point is 0.01mm～0.2mm;
(2) under same testing conditions, the known materials identical with ferrimagnet to be detected is provided with the simulated defect threshold value;
(3) magnetic field intensity signal that the above-mentioned first step is obtained is carried out the amplification filtering processing, then itself and the above-mentioned prior defective threshold value that is provided with of second step is compared, and can judge has zero defect.
In the method for the present invention, also can carry out the A/D conversion to the signal after above-mentioned the 3rd step amplification filtering, obtain digital signal corresponding, then the digital defects detection threshold value of this digital signal with the known materials that is provided with in advance compared, to judge whether to exist defective.
Can also be with method of the present invention by following step, adopt digital signal processing method to improve detection sensitivity, promptly carry out difference processing, obtain a series of magnetic field intensity gradient signals on the nearly surperficial a certain plane of material with each value of vicinity of above-mentioned magnetic field intensity digital signal; Then each value of vicinity of this magnetic field gradient signal is carried out difference processing, obtain the magnetic field gradient rate of change of each check point; The ferrimagnet that be processed with Artificial discontinuity identical, draw the Artificial discontinuity as stated above and locate the magnetic field gradient rate of change, and this value is set at the threshold value that detects defective with the method with tested material; At last the magnetic field gradient rate of change of detected material and the threshold value of preset standard artificial defect are compared,, just think that there is defective in tested material surface when magnetic field gradient rate of change during greater than threshold value.
The detection method that the present invention proposes can be avoided requiring checking matter is carried out active magnetization in the traditional flux-leakage detection method, and the loaded down with trivial details operation of after detection is finished checking matter being demagnetized.And saved and be used to magnetize required electrical source consumption and magnetizable body, and then can reduce the volume of pick-up unit, be beneficial to the development portable detector.
The method utilizes the terrestrial magnetic field as the magnetization driving source, utilizes the method can detect the various defectives on ferrimagnet surface, comprise surface crack, etch pit, the nearly surface of material internal folder caye and pore, and stress is concentrated etc.
Description of drawings:
Fig. 1 is the detection schematic diagram of the inventive method, and 1 is detected material among the figure, the 2nd, and detection faces, the 3rd, artificial rectangular channel defective, h is a lift-off value.
Embodiment:
The 20# steel steel plate that 15mm to be detected is thick is placed horizontally in the environment of magnetic field of the earth, then, with fixing lift-off value h (h equals 2mm) the nearly surperficial detection faces of measured material (number in the figure is 1) (number in the figure is 2) being gone up spacing is that each measuring point magnetic field intensity of 0.01mm is measured, obtain the magnetic field intensity of each point on the detection faces, and it is carried out the A/D conversion, obtain digital value f (i with the magnetic field intensity of each point position correspondence, j), i, j is the coordinate of each measuring point, and the i span is the integer from 0 to n, and the j span is the integer from 0 to m, n, m depend on the size of measured material area.
Press following formula to f (i, j) carry out difference processing: g (i, j)=4f (i, j)-f (i-1, j)-f (i, j-1)-f (i, j+1)-f (i+1, j)
As 0＜i＜n, during and 0＜j＜m; G (0, j)=g (1, j), g (n, j)=(n-1 is j) as i=0 or n, during 0＜j＜m for g; G (i, 0)=g (i, 1), and g (i, m)=(i is m-1) as j=0 or m, during 0＜i＜n for g; And g (0,0)=g (1,1), g (n, 0)=g (n-1,1),
g(0，m)＝g(1，m-1)，g(n，m)＝g(n-1，m-1)
The g that calculates (i j) is the magnetic field intensity gradient signal of each measuring point, to g (i j) carries out difference processing by following formula again, obtain each measuring point magnetic field gradient rate of change e (i, j).
Being processed with Artificial discontinuity (the groove width 0.1mm of defective, dark 0.5mm) the thick 20# steel steel plate of 15mm, draw the gradient change rate k that the Artificial discontinuity locates magnetic field intensity as stated above, and this k value is set at the threshold value that detects this kind fault in material with the method.Relatively e (i, j) with the size of k value, when e (i, j)＞during k, just think that (i j) locates to exist surface imperfection to tested material at point.
Recording the fault location maximum magnetic field strength is 0.82Gs, and magnetic field gradient is 0.02Gs herein, and the magnetic field gradient rate of change is 0.015Gs herein, and corresponding crack detection threshold value k is 0.01Gs, and testing result shows can find this type of defective.
Claims (2)
1, a kind of method of utilizing the terrestrial magnetic field to detect surface defects of ferromagnetic material is characterized in that this method may further comprise the steps:
(1) ferrimagnet to be detected is placed horizontally in the environment of magnetic field of the earth, measures the magnetic field intensity of each point on the interior same surface level of the nearly surperficial 0.01mm～10mm of material, the distance between each measuring point is 0.01mm～0.2mm;
(2) under same testing conditions, the known materials identical with ferrimagnet to be detected is provided with the simulated defect threshold value;
(3) magnetic field intensity signal that the above-mentioned first step is obtained is carried out amplification filtering, then itself and the above-mentioned prior defective threshold value that is provided with of second step is compared, and can judge has zero defect.
2, a kind of method of utilizing the terrestrial magnetic field to detect surface defects of ferromagnetic material is characterized in that this method may further comprise the steps:
(1) ferrimagnet to be detected is placed horizontally in the environment of magnetic field of the earth, measures the magnetic field intensity of each point on the interior same surface level of the nearly surperficial 0.01mm～10mm of material, the distance between each measuring point is 0.01mm～0.2mm;
(2) under same testing conditions, the known materials identical with ferrimagnet to be detected is provided with digital defective threshold value;
(3) magnetic field intensity signal that the above-mentioned first step is obtained is carried out amplification filtering, and the A/D conversion compares itself and the above-mentioned prior digital defective threshold value that is provided with of second step then, and can judge has zero defect.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 01123977 CN1131429C (en) | 2001-08-10 | 2001-08-10 | Method for inspecting surface defects of ferromagnetic material by geomagnetic field |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 01123977 CN1131429C (en) | 2001-08-10 | 2001-08-10 | Method for inspecting surface defects of ferromagnetic material by geomagnetic field |
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| Publication Number | Publication Date |
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| CN1334462A CN1334462A (en) | 2002-02-06 |
| CN1131429C true CN1131429C (en) | 2003-12-17 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN 01123977 Expired - Fee Related CN1131429C (en) | 2001-08-10 | 2001-08-10 | Method for inspecting surface defects of ferromagnetic material by geomagnetic field |
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Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102012397A (en) * | 2010-10-27 | 2011-04-13 | 南昌航空大学 | Nondestructive testing method for nonferromagnetic material |
| CN102590326A (en) * | 2011-10-31 | 2012-07-18 | 北京理工大学 | Magnetic memory/magnetic leakage integrated multi-probe detection device for tube and shaft type parts |
| JP6241120B2 (en) | 2012-09-14 | 2017-12-06 | 株式会社リコー | Image inspection apparatus, image inspection method, and control program for image inspection apparatus |
| CN105181786A (en) * | 2015-07-16 | 2015-12-23 | 宁波市鄞州磁泰电子科技有限公司 | Weld defect magnetic detection method |
| CN105467000B (en) * | 2015-12-21 | 2019-05-21 | 中国石油大学(北京) | Buried pipeline tube body defect Indirect testing method and device |
| CN108051763A (en) * | 2017-11-30 | 2018-05-18 | 宁波市鄞州磁泰电子科技有限公司 | A kind of weak magnetic detection method of composite material |
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Granted publication date: 20031217 Termination date: 20130810 |