RU2566416C1 - Device for eddy-current magnetic examination of ferromagnetic objects - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention represents a device for eddy-current examination and may be used to detect and determine parameters of subsurface defects in ferromagnetic objects. The device comprises a source of DC magnetic field, a line of eddy-current converters between its poles, parallel to poles, and a unit to adjust intensity of magnetising DC magnetic field. The adjustment unit is arranged in the form of a frame and a subframe connected as capable of rotation relative to the axis of rotation, directed along one of the frame sides and perpendicular to the line of converters, and also a fixator of the subframe relative to the frame with the specified angle between their planes. The system provides for development of a permanent magnetic field, which monotonously varies along the line of converters.

EFFECT: increased sensitivity and information value of control.

4 dwg

Description

The invention relates to non-destructive testing and can be used for inspection of objects from electrically conductive ferromagnetic materials.

A device [1] for defectoscopy of ferromagnetic objects, containing a magnetization system formed by a U-shaped magnetic circuit with permanent magnets, a eddy current transducer, the exciting coil of which is connected to a harmonic voltage generator, and measuring and compensation windings to an electronic unit for processing and displaying information, is known. The change in the level of magnetic field in the sample is carried out by changing the gap z between the magnetization system and the controlled object. To change the clearance z, thrust adjusting screws associated with support rollers can be used to enable scanning.

By changing the gap z in the known device provides the strength of a constant magnetizing magnetic field, optimal for detecting subsurface defects occurring at an appropriate depth.

A disadvantage of the known device is the inability to detect defects with a potentially achievable sensitivity when varying the depth of their occurrence.

Closest to the proposed technical essence, the device adopted for the prototype [2], containing a magnetizing system consisting of a U-shaped magnetic circuit, a permanent magnet and a magnetic flux control unit, a line of eddy current transducers and a magnetically sensitive element located in the interpolar space. The magnetic flux control unit consists of a bar magnet located in the gap between the parts of the upper bridge of the U-shaped magnetic circuit. The ends of the mating parts of the upper bridge of the magnetic circuit are cylindrical, and the rod magnet is rotatable, thereby changing the magnitude of the magnetic flux coming from the permanent magnet to the magnetic circuit. The intensity of the magnetizing constant magnetic field in the zone of electromagnetic interaction of eddy current transducers with the monitored area is set before monitoring and is monitored during scanning by the signal of the magnetically sensitive element. When the set value of the constant magnetic field is deviated, it is corrected by rotation of the bar permanent magnet. Through the use of a line of eddy current transducers, greater control performance is ensured, for which scanning is performed in a direction perpendicular to the orientation of the line.

However, in this device, the potentially achievable sensitivity to defects when varying the depth of their occurrence is not provided, since in the zones of electromagnetic interaction of all eddy current transducers the same magnitude of the magnetizing constant magnetic field is established. In this case, as is known [3], a loss of sensitivity to even rather gross defects is possible.

The purpose of the invention is the provision of optimal sensitivity and information control.

The goal is a device for eddy-magnetic magnetic flaw detection of ferromagnetic objects, containing a magnetic system configured to adjust the strength of the magnetizing constant magnetic field in the control zone and consisting of a U-shaped magnetic circuit, a source of constant magnetic field and a node for adjusting the strength of the magnetizing magnetic field, a line of eddy current converters located in the interpolar space of the magnetic circuit, a switch and an electronic unit connected via a mutator with eddy-current transducers is achieved due to the fact that the magnetizing constant magnetic field intensity adjustment unit is made in the form of a frame and a subframe connected with the possibility of rotation relative to the axis of rotation directed along one side of the frame, as well as a subframe retainer relative to the frame with a given angle between them by planes and supporting elements fixed on the frame, designed to move along the surface of the controlled object, the U-shaped magnetic circuit is mounted with its own torus by means of a subframe so that the axis of rotation of the frame relative to the subframe is directed from one end of the magnetic circuit to the other, and the line of eddy current transducers is placed perpendicular to the axis of rotation and symmetrically between the poles of the magnetic system.

The design and operation of the inventive device are illustrated in FIG. 1-4.

, вносимого в измерительную обмотку вихретокового преобразователя дефектами с различной глубиной залегания, при вариации напряженности намагничивающего постоянного магнитного поля.In FIG. 1-2 shows a device with a magnetic circuit located above the defective sample. In FIG. 1 shows a side view of a U-shaped magnetic circuit, and FIG. 2 - in a perspective view. In FIG. Figure 3 shows the design of the unit for adjusting the strength of the magnetizing magnetic field. In FIG. Figure 4 shows the dependences of the amplitude normalized to the initial voltage at the output of the eddy current voltage converter $$U_{\mathrm{at}n}^{*}$$

introduced into the measuring winding of the eddy current transducer by defects with different depths, when the intensity of the magnetizing constant magnetic field is varied.

A device for detecting subsurface defects in ferromagnetic objects consists of a magnetic system 1, including a U-shaped magnetic circuit 2 and pole magnets 3 and 4, line 5 eddy current transducers 6.1-6.5, switch 7 and electronic unit 8 connected through switch 7 to eddy current transducers 6.1 -6.5. The device also comprises a magnetizing magnetic field intensity adjustment unit, consisting of a frame 9 and a subframe 10 connected along the axis of rotation by the rod 11, a retainer 12 of the subframe 10 relative to the frame 9 with a predetermined angle between their planes. The frame 9 is equipped with support elements made in the form of wheels 13.1-13.4, which allow the device to be moved along the surface of the controlled object 14 in the direction perpendicular to the rod 11, with a constant gap between the surface of the controlled object 14 and eddy current transducers 6.1-6.5. Line 5 consists of several, for example 5, eddy-current transducers 6.1-6.5 and is mounted on the frame 9 parallel to its plane, symmetrically between the poles of the magnetic circuit 2 perpendicular to the rod 11. The orientation of the line 5 eddy-current transducers coincides with the scanning direction of the surface of the controlled object 14.

The inventive device operates as follows.

Preliminarily, the subframe 5 is deflected relative to the frame 6 by a predetermined angle α and is retained in this position by the latch 12. The angle α determines the change in the constant magnetic field strength H along the line 5 of eddy-current transducers 6.1-6.2. From FIG. 4 it follows that as the defects developing on the back side of the object 14 have depth h of defects h and the depth δ of their occurrence associated with it, the optimal intensity H of the magnetizing magnetic field also changes. By varying the angle α, a range of variation H is established between the extreme eddy current transducers 6.1 and 6.5 of line 5. The specific value of the angle α is selected in accordance with the parameters of the controlled object 14, in particular with its thickness, magnetic properties, and the most likely range of changes in the parameters of detected defects 15.

(Н) определяют параметры дефекта с помощью предварительно полученных на образцах зависимостей.The device is mounted on the scanning surface of a controlled object 14 from a conductive ferromagnetic material with possible defects 15 with a previously unknown depth h and depth δ. The magnetic system 1 creates in the controlled object 14 in the zone of operation of eddy current transducers 6.1-6.5 a constant magnetic field directed perpendicular to the scanning direction and having a gradient in this direction defined by the angle α between the planes of the frame 9 and the subframe 10. A harmonic current is generated in the electronic unit 8 frequency f supply eddy current transducers 6.1-6.5. The frequency f is selected based on the depth of penetration of the magnetic field into the thin surface layer of the test object. In this case, “magnetic spots” are read out, arising due to the redistribution of the constant magnetic flux under the influence of defect 15. To obtain a contrast of the magnetic properties of the spot over the defect and the rest of the metal, it is necessary to coordinate the defect depth and the magnetizing field, which explains the curve in FIG. 4. With a small value of H, the change in the magnetic properties in the spot is weak, and with an excess, the contrast decreases due to a change in the magnetic properties of the metal not only over the defect, but also in the neighboring region. The switch 7 alternately connects the eddy current transducers 6.1-6.5 to the electronic unit 8. During the scanning process, the electromagnetic interaction of the eddy current transducers 6.1-6.5 with possible defects occurs at various monotonically varying levels of the constant magnetic field strength H. This ensures the interaction of one of the eddy-current transducers 6.1-6.5 with defect 15 at a value of H close to optimal. By registering the signals U _W from the eddy current transducers 6.1-6.5 normalized by the initial voltage U _o , from the totality of the obtained values $$U_{\mathrm{at}n}^{*}=U_{\mathrm{at}n}^{*}$$

(H) determine the defect parameters using previously obtained dependencies on the samples.

(Н), по которым можно судить о параметрах дефекта.The inventive device, in comparison with the known, provides greater sensitivity and information control. Great sensitivity is achieved due to the fact that the eddy current signal is read at different, monotonically changing values of the magnetizing constant magnetic field. Greater informational content is achieved due to the fact that in the process of scanning receive a set of values $$U_{\mathrm{at}n}^{*}$$

(N) by which it is possible to judge the parameters of the defect.

Information sources

1. RF patent No. 2442151 A method for detecting subsurface defects in ferromagnetic objects G01N 27/90. Publ. 02/10/2012, priority 02/10/2010

2. British patent GB 2475315-A. Apparatus and method for inspection of components made of electrically conductive material by partial saturation eddy current testing. G01N 27/90, G01B 7/06 and others. Priority from 11/16/2009 (prototype).

3. RF patent for the invention No. 2493561 Eddy-current-magnetic method of defectoscopy of ferromagnetic objects G01N 27/90 // - Publ. 09/20/2013, priority from 05/04/2012.

Claims (1)

A device for eddy-magnetic flaw detection of ferromagnetic objects, containing a magnetic system configured to adjust the strength of the magnetizing constant magnetic field in the control zone and consisting of a U-shaped magnetic circuit, a source of constant magnetic field and a node for adjusting the strength of the magnetizing magnetic field, a line of eddy current transducers, placed in the inter-polar space of the magnetic circuit, the switch and the electronic unit connected through the switch to the eddy current transducers, characterized in that the site for adjusting the magnetizing constant magnetic field strength is made in the form of a frame and a subframe connected to rotate about an axis of rotation directed along one of the sides of the frame, as well as a subframe retainer relative to the frame with a given angle between their planes and fixed on the frame of supporting elements designed to move along the surface of the controlled object, the U-shaped magnetic circuit is mounted with its ends on a subframe so that the axis rashchenija frame relative to the subframe is directed from one end of the magnetic circuit to another, eddy current probes ruler placed perpendicular to the rotation axis and symmetrically between the poles of the magnetic system.

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