CN102495129A - Adjustable magnetic pumping array detecting method for metal damage and adjustable magnetic actuated array detecting device for same - Google Patents

Abstract

The invention relates to a method and a device for rapidly, qualitatively and quantitatively testing and evaluating defects such as cracks, corrosion pits and the like of metal materials, which belong to the technical field of electromagnetic non-destructive testing for metal damage. The method uses an array receiving coil as a feedback element to test the magnetization state of the surface of a tested piece, and the exciting current of an exciting coil is adjusted according to testing results, so that the magnetization condition of a magnetic field of is improved, and flaw detection sensitivity of the tested piece in different directions is enhanced. By means of designing the orthogonal exciting magnetic field on the device, the amplitude and the direction of the exciting magnetic field can be changed. Compared with a traditional magnetic actuated mode, the method has the advantages that defect omission ratio can be reduced to a great degree, reliability of test results is improved, and the method has high practical application value for electromagnetic non-destructive testing of tested pieces in complicated shapes.

Description

An adjustable magnetic excitation array detection method and device for metal damage

technical field

The invention relates to a rapid qualitative and quantitative detection and evaluation method and device for defects such as cracks and corrosion pits of metal materials, and belongs to the technical field of electromagnetic nondestructive detection of metal damage. the

Background technique

Cracks and corrosion defects in metal components are widespread metal damage forms that affect the fatigue and service life of industrial equipment. The detection and evaluation of this type of metal damage is of great importance for ensuring the safe operation of equipment and prolonging the service life of equipment. value and significance. the

The magnetic field detection method is to apply an alternating magnetic field of a certain frequency in the metal material, and a uniform alternating current will be induced on the metal surface due to the skin effect, and an alternating magnetic field will be generated in the outer space of the metal surface. If there are defects such as cracks on the metal surface, Due to the change of resistivity, it is bound to affect the current distribution. The current line will deflect near the defect, and the magnetic field on the surface of the workpiece will be distorted. By measuring the change of this magnetic field, the length and depth of defects such as cracks can be determined. the

Most of the known methods of using alternating magnetic field to detect metal defects use a magnetic field excitation source with constant amplitude and direction; The patent "ACFM Defect Intelligent Visual Detection System" application number: CN101701934A) proposes and implements an orthogonal rotatable magnetic field generator, which has a significant effect on improving the detection sensitivity of randomly distributed cracks on the actual measured object; however, The above-mentioned patent mainly studies the effect of the change of the magnetic field direction on improving the detection sensitivity, but does not mention the change of the magnetic field strength value on the sensitivity of detecting randomly distributed cracks. the

The sensitivity of using the alternating magnetic field to detect defects is not only related to the direction of the magnetic field, but also related to the magnitude of the magnetic field strength and the uniformity of the magnetic field distribution; due to the difference in the strength of the alternating magnetic field, it will bring great errors to the detection results; and the actual The shape of the tested part is irregular. If the change of the magnetic field strength is not considered during the rotation excitation process, it is easy to affect the detection effect due to the uneven distribution of the magnetic field strength, which will affect the magnetization effect of the defect. the

Therefore, on the basis of the above work, a variable excitation magnetic field with variable magnetic field direction and adjustable amplitude is designed, and a nondestructive detection method using this excitation field and array sensors to detect metal damage is proposed. the

Contents of the invention

The purpose of the present invention is to use the basic principle of the magnetic field detection method to design a non-destructive detection and evaluation method and device for metal damage, which can quickly replace the tested piece, thereby providing technical feasibility for quickly and conveniently detecting the damage of the test piece . the

The present invention is achieved through the following technical solutions. the

The excitation magnetic field adopts a variable magnetic field excitation method in which the magnetization direction changes uniformly with time, and the amplitude can be adjusted according to the actual magnetization effect, so as to ensure sufficient detection sensitivity for defects randomly distributed along various directions in actual conditions; the change of the magnetic field direction It is realized by combining two excitation magnetic fields with a phase difference of 90 degrees, and the adjustment of the magnetic field amplitude is realized by an array detection coil. The array detection coil is used to detect metal damage on the test piece, and can also sense the change of the magnetization field strength. When the detection coil is located in the defect area, the amplitude of the output signal generally has a large jump; when the detection coil is in the non-defect area, the difference in the amplitude of the output signal reflects the difference in the strength of the magnetization field. According to the strength of the detection coil signal amplitude, the magnetization current of the excitation coil can be adjusted, so that the magnetization field on the test piece can be adjusted, the magnetization effect can be as uniform as possible, and the detection sensitivity to defects at different positions can be improved. The specific implementation method is as follows:

Take the 3×3 array sensor shown in Figure 1 as an example, as shown in Figure 2 . First take the difference in the readings of adjacent coils in horizontal and vertical order:

Transversely, u ₁₂ =u ₁ -u ₂ ; u ₂₃ =u ₂ -u ₃ ;

u ₄₅ =u ₄ -u ₅ ; u ₅₆ =u ₅ -u ₆ ;

u ₇₈ =u ₇ -u ₈ ; u ₈₉ =u ₈ -u ₉ ;

Longitudinal, u ₁₄ =u ₁ -u ₄ ; u ₄₇ =u ₄ -u ₇ ;

u ₂₅ =u ₂ -u ₅ ; u ₅₈ =u ₅ -u ₈ ;

u ₃₆ =u ₃ -u ₆ ; u ₆₉ =u ₆ -u ₉

Set defect discrimination threshold M and magnetic field inhomogeneity discrimination threshold m

(1) If a certain value in the above calculation result is greater than M, it is considered that the result is caused by the defect, not by the uneven magnetization field; at this time, the function of the array coil is to detect the defect, and the excitation magnetic field does not need to be adjusted, and the discrimination result is directly output ;

(2) If the above calculation result is less than M, do the following:

Horizontal: $u_h=\frac{u_{12}+u_{\mathrm{twenty\; three}}+u_{45}+u_{56}+u_{78}+u_{89}}{6}$

Vertical: $u_z=\frac{u_{14}+u_{47}{+u}_{25}+u_{58}+u_{36}+u_{69}}{6}$

If u _h >m, it indicates that the uniformity of transverse magnetization needs to be adjusted. At this time, increase the excitation current of the transverse coil to enhance the strength of the transverse magnetization field and improve the effect of the transverse magnetization field;

If u _z >m, it indicates that the uniformity of longitudinal magnetization needs to be adjusted. At this time, increase the excitation current of the longitudinal coil to enhance the strength of the longitudinal magnetization field and improve the effect of the longitudinal magnetization field;

If both u _h and u _z are smaller than m, it indicates that the current magnetization field is in good effect and no adjustment is required.

The array detection element is used as the feedback element, and the magnetization field strength on the test piece is used as the feedback signal to adjust the magnetization effect of the excitation field in time to ensure that the magnetic field is approximately uniform in all directions. The detection system adopts an array structure, which replaces the traditional scanning detection method, thereby greatly improving the detection speed. the

The basic method of the invention mainly adopts the excitation magnetization field whose amplitude and direction can be automatically adjusted and the array type receiving coil to realize the detection of metal damage. Due to the randomness of the direction and position distribution of metal damage such as cracks in actual working conditions, the magnetization excitation field with a fixed amplitude and direction only has a better magnetization effect on defects distributed along a certain direction, and the magnetization effect is also similar to that of The location of the damage is related, so some damages in insensitive directions may be missed. In this patent, a two-dimensional alternating magnetic field is designed in which the directions are perpendicular to each other, the phase difference is 90 degrees, and the amplitude can be adjusted in real time according to the magnetization field. The two-dimensional magnetic field synthesizes an elliptical magnetization field with variable amplitude and direction on the test piece, so that according to the shape characteristics of the test piece, the magnetic field intensity distribution in the weak direction of the magnetization effect can be enhanced, and the detection sensitivity can be improved; at the same time, due to the magnetization field The direction and intensity change with time, which effectively reduces the magnetization blind area of defects and reduces the missed detection rate. the

The above method is realized by the designed detection device, which is shown in Figure 1 and consists of a two-dimensional excitation magnetic field, an array receiving element, a test piece and a base plate. The two-dimensional excitation magnetic field is composed of signal excitation circuit, excitation coil, yoke, pole shoes, etc.; the signal excitation circuit is shown in Figure 3, which is composed of sine wave generation circuit, feedback link, program-controlled amplifier, phase shifter and power amplifier; The oscillating signal is divided into two paths, one of which passes through the phase shifter and forms a 90-degree phase difference with the other path, so that the direction of the magnetization field changes with time; the amplitude of the magnetization current is adjusted through the receiving elements of the array structure on the test piece, and the state of the magnetic field is adjusted. After sampling through A/D, it is sent to the computer. The computer judges the uniformity of the magnetic field through an algorithm. According to the result, the excitation current is changed through the program-controlled amplifier to form an adjustable mode of the magnetic excitation current amplitude. The excitation magnetic field amplitude can be adjusted according to the distribution of the magnetic field intensity. The value is adjusted to effectively enhance the excitation effect on the weak orientation of the magnetic field, so that the defects in all orientations on the specimen can be detected with high sensitivity. During testing, the test piece is placed on a rigid frame composed of four pole pieces, and the frame plays a positioning role; the test piece placed on the pole piece, the excitation coil, and the bottom plate of the device form a closed magnetic circuit, and the excitation coil passes through the magnetic field. The path will generate a gradient magnetic field with varying amplitude and direction on the test piece, so as to realize the magnetization of defects at various positions on the test piece. The number of array sensors and the adjacent distance of each sensor are determined according to the actual detection requirements. In order to ensure that the defect signal is not missed, it should be ensured that the effective range of the array detection coil has a certain overlapping area, so that the defect information generated is redundant and Superposition can be solved by algorithms such as blind source separation and discrimination strategies. the

Beneficial effect

In the present invention, the variable magnetic excitation field whose direction changes with time and whose amplitude is fed back and automatically adjusted according to the state of the magnetic field is used as the detection excitation source, and the arrayed electromagnetic coil is used as the receiving element, so that the metal damage in each direction on the test piece can be realized. Compared with the traditional magnetic excitation method, it can greatly reduce the missed detection rate of defects and improve the reliability of the detection results. It has strong practical application value for electromagnetic nondestructive testing of complex-shaped specimens.

Description of drawings

Below in conjunction with accompanying drawing and embodiment the present invention will be further described:

Figure 1 Metal damage adjustable magnetic field detection device. the

Figure 2 Schematic diagram of array sensor locations. the

Figure 3 Two-dimensional magnetic field signal excitation circuit. the

Detailed ways

In order to better illustrate the implementation and advantages of this patent, this patent will be further described below in conjunction with specific embodiments. the

The test piece is made of commonly used low-carbon steel Q235 steel, with a length of 100mm, a width of 40mm, and a thickness of 3mm. the

The receiving coil in this embodiment is wound by enameled wire with a wire diameter of 0.06 mm, the inner diameter of the coil is 2 mm, the outer diameter is 4 mm, the effective length of the coil is 2 mm, and the number of turns of the coil is 500. The coil bobbin has a maximum outer diameter of 5mm and a height of 5mm. the

The excitation devices in this embodiment are distributed in two perpendicular directions, the transverse direction and the longitudinal direction. There are two identical field coils in each direction. The coil is wound with enameled wire with a diameter of 0.6, the inner diameter of the coil is 32mm, the effective length of the coil is 24mm, and the number of turns of the coil is 250 turns. the

The sine generation circuit supplemented by RC and UA741CP integrated chip and the power amplifier circuit with TDA2030 as the core provide excitation power for this embodiment, and the peak value of the power supply is 6.8V. the

Implementation process: first follow the steps to connect various parts of the detection system and fix the array probe. Start the power supply of the signal receiving circuit and the subsequent processing circuit; start the power supply of the excitation device, adjust the feedback resistance in the sine wave generating circuit, and make the circuit start to vibrate, and the waveform is required to be good and not distorted. In order to ensure the uniformity of the magnetic field on the surface of the test piece, an array receiving coil is used as the feedback link to adjust the magnetic field strength of the test piece surface in the horizontal and vertical directions. By controlling the collection software of the industrial computer, the state information of the specimen in the area covered by the array probe can be collected, processed and judged. The detection results under single-direction excitation magnetic field and adjustable excitation magnetic field are compared. The test shows that using the array element as the excitation magnetic field detection method for feedback adjustment can effectively detect defects at various positions on the test piece, improve the uniformity of the magnetic field, and increase the detection sensitivity. the

In this embodiment, only a test piece of one material is tested. The invention can detect the results of various ferromagnetic materials, and the number and spacing of probes can be flexibly arranged according to needs. All equivalents or modifications that do not deviate from the spirit disclosed in the present invention are included in the protection scope of the present invention. the

Claims (2)

1. scalable exciting field array detection method that is applicable to the damage of metal material electromagnetic nondestructive comprises can changing magnetization current amplitude and direction and the magnetic field excitation mode that changes, thereby realizes the high-sensitivity detecting method of different azimuth damaged metal; And utilize the array detecting element, thereby the method for realization magnetic field uniform magnetization effect etc. as magnetic field detection and feedback element; It is characterized in that:

(1) adopted detection defective measurement and the signal feedback element of array coil as the magnetizes effect; Utilize relatively in time the magnetization effect of test specimen being adjusted of testing result and driving voltage, to guarantee on test specimen, obtaining magnetizing field comparatively uniformly;

(2) proposed a kind of self-adaptation method of discrimination that magnetic field is regulated that carries out, through defective discrimination threshold and magnetic field uniformization threshold value are set, can effectively distinguish the information that detecting element extracts, thereby realize the differentiation of defective and the adjusting in magnetic field.

2. the adjustable magnetic fields array detection device with feedback and adaptation function according to claim 1 is characterized in that:

(1) arrayed elements has defects detection simultaneously and is used for information measurement and the feedback function that magnetic field is regulated;

(2) adopt a kind of symmetrical expression magnetization configuration, this structure is made up of magnetic pole base plate, four field coils and frame-type pole shoe, and the frame-type pole shoe has the fixedly effect of test specimen again, and the while can be changed test specimen quickly and easily;

(3) adopt the array test coil as feedback element, through sample circuit with relatively differentiate algorithm, control programmable amplifier multiple is regulated the magnetic field excitation electric current, the adjusting of realization magnetic excitation field.

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