GB2113392A

GB2113392A - Magnetoacoustic converters for ultrasonic flaw detectors.

Info

Publication number: GB2113392A
Application number: GB08301123A
Authority: GB
Inventors: Mikhail Iosifovich Maizenberg; Vladimir Usherovich Moshkovich; Vladimir Timofeevich Bobrov; Mikhail Danilovich Kaplan; Jury Alexeevich Semenov
Original assignee: VNII RAZRABOTKE NERAZRUSCHA
Current assignee: VNII RAZRABOTKE NERAZRUSCHA
Priority date: 1982-01-15
Filing date: 1983-01-17
Publication date: 1983-08-03
Also published as: GB2113392B; FR2520120B1; FR2520120A1; DE3301118A1; GB8301123D0

Abstract

A magnetoacoustic converter for an ultrasonic flaw detector comprises a magnet (1) and an inductance coil (7). The magnet (1) sets up a normal magnetic field in a predetermined section of a magnetostrictive plate (8) located on an article (4) being tested. The inductance coil (7) constitutes a solenoid which is disposed relative to the magnetostrictive plate (8) so that it sets up a tangential variable magnetic field in a predetermined section of the magnetostrictive plate (8). The plate (8) is provided with means (9) for reflecting elastic vibrations propagating therein and caused by the presence of a defect (14) in article (4), the reflecting means being perpendicular to the solenoid axis along the path of propagation of elastic vibrations. <IMAGE>

Description

SPECIFICATION Improvements in or relating to magnetoacoustic converters for ultrasonic flaw detectors The present invention relates to ultrasonic flaw detectors and in particular to magnetoacoustic converters for ultrasonic flaw detectors, which may be used to reveal minor surface defects such as hardening and surface cracks, as well as stuck welds in parts and articles fabricated from ferromagnetic materials.

Stringent requirements are placed upon quality of articles and source materials, as regards ferromagnetic materials utilized in various instruments and facilitates, operation of which is characterised by the presence of corrosive media and a wide range oftemperatures, loads, and pressures. More specifically, a vital problem is to reveal minor surface defects occurring in articles or source materials and blanks during production of operation of parts and assemblies of various facilities.

According to the invention, there is provided a magnetoacoustic converter for an ultrasonic flaw detector, comprising: a magnet for establishing a normal constant magnetic field in a predetermined section of a magnetostrictive plate to be located on an article to be tested; an inductance coil forming a solenoid disposed relative to the magnetostrictive plate so as to set up a tangential variable magnetic field in a predetermined section of the magnetostrictive plate; and means for reflecting elastic vibrations propagating in the magnetostrictive plate, the reflecting means being provided directly in the plate and arranged perpendicularly to the solenoid axis along the path of propagation of the elastic vibrations.

The reflecting means may be arranged symmetrically to the solenoid.

The solenoid may be wound around the magnet.

The converter may further comprise a magnetic field concentrator and the solenoid may be wound around the concentrator.

The magnetostrictive plate may have a U-shaped structure accommodating the solenoid.

Preferably the converter incorporates a protector disposed between the magnetostrictive plate and the article being tested, the protector being shaped to suit the shape of the plate on the side of said plate and the shape of the article on the side of said article.

Such a magnetoacoustic converter for an ultrasonic flaw detector permits optimum excitation and reception of elastic vibrations in the magnetostrictive plate, a feature enhancing sensitivity in the case of surface defects having small geometric dimensions in ferromagnetic articles.

The invention will be further described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a schematic front view of a magnetoacoustic converter for an ultrasonic flaw detector constituting a preferred embodiment of the invention: Figure 2 is a view of the embodiment of Figure 1 along arrowA; Figure 3 is a schematic front view of another magnetoacoustic converter for an ultrasonic flaw detector constituting another preferred embodiment of the invention; Figure 4 is a view of the embodiment of Figure 3 along arrow B; Figure 5 is a schematic front view of a further magnetoacoustic converter for an ultrasonic flaw detector constituting a further embodiment of the invention; and Figure 6 is a view of the embodiment of Figure 5 along arrow C (rotated through 90 in the drawing plane).

A magnetoacoustic converter for an ultrasonic flaw detector comprises a magnet 1 (Figures 1 and 2), south and north poles) and an inductance coil 2 estabiished, respectively, a normal constant magnetic field and a variable magnetic field in a predetermined section of a disc-shaped magnetostrictive plate 3 located on a ferromagnetic article 4 being tested, the article representing an elongate strip.

The inductance coil 2 (hereinafter referred to as the solenoid 2) is a solenoid which is disposed relative to the magnetostrictive plate 3 so that it sets up a tangential magnetic field therein. In the preferred embodiment of the invention, the solenoid encompasses the magnet 1.

The magnetostrictive plate 3 (Figure 2) is provided with means 5 for reflecting elastic vibrations propagating within said plate, said reflecting means being perpendicular to the solenoid axis along the path of propagation of said elastic vibrations. The reflecting means 5 are arranged symmetrically to the solenoid. In the preferred embodiment of the invention, the reflecting means 5 are slots provided in the plate 3.

In another embodiment of the invention, the magnetoacoustic converter comprises a magnetic field concentrator 6 (Figure 3). Similarly to the embodiment of Figures 1 and 2, an inductance coil 7 (hereinafter referred to as the solenoid 7) is a solenoid encompassing the concentrator 6, as shown in Figure 3. A magnetostrictive plate 8 (Figure 4) is provided in the form of a rectangular strip whose opposite butt ends serve as means 9 for reflecting elastic vibrations within the plate 8.

The magnetoacoustic converter of Figures 5 and 6 is essentially similar to the embodiment of Figures 3 and 4, but differs in that a magnetostrictive plate 10 (Figure 5) is a U-shaped structure accommodating the concentrator 6 surrounded by the solenoid 7.

Butt ends of the plate 10 serve as means 11 (Figures 5 and 6) for reflecting elastic vibrations within said plate.

The magnetoacoustic converter further comprises a protector 12 (Figure 5) disposed between the magneto-strictive plate 10 and a ferromagnetic article 13 being tested, said article representing a cylindrical structure in the embodiment of Figure 6.

The protector 12 (Figure 5) is shaped to suit the shape of the plate 10 on the side of said plate and the shape of the article 13 on the side of said article.

Such a structure of the converter permits a substantial reduction in its dimensions and an increase in its service life.

The magnetoacoustic converter for an ultrasonic flaw detector operates in the following manner.

The inductance coil 2 (Figures 1 and 2) is connected to an ultrasonic flaw detector (not shown in the drawing since it forms no part of the invention).

The inductance coil 2 sets up a tangential variable magnetic field within the magnetostrictive plate 3.

After the magnetostrictive plate 3 is placed on the article 4 being tested, the magnet 1 establishes a normal constant magnetic field within the magnetostrictive plate 3. When the article 4 has a surface defect 14 (a dashed line in Figure 1) the original normal constant magnetic field is distorted due to the fact that magnetic lines of force are bent as a result of the defect 14. A tangential constant magnetic field is set up in the magnetostrictive plate 3. In the presence of said field, elastic vibrations are excited within the magnetostrictive plate 3. The elastic vibrations propagating within the plate 3 are repeatedly reflected by the reflecting means 5, added up underthe inductance coil 2, converted into a variable magnetic field, sensed by the inductance coil 2, and recorded by the flaw detector.

The magnetoacoustic converter of Figures 3 to 6 operates in much the same manner as the magnetoacoustic converter of Figures 1 and 2.

The magnetoacoustic converter for an ultrasonic flaw detector permits an appreciable increase in the capabilities of said flaw detector and reveals surface defects having small geometric dimensions without the utilization of contact liquids and lubricants, another advantage being an efficient rechecking of the resuits obtained by using magnetic testing methods.

Specific terms are used for clarity in the description of the preferred embodiments of the invention.

However, the invention shown and described herein is by no means limited to the exact terms used since each term is understood to embrace all equivalent elements functioning similarly and used for solving like problems.

While particular embodiments of the invention have been shown and described, various modifications thereof within the scope of the invention will be apparent to those skilled in the art.

Thus, the departures therefrom are understood to be covered by the appended claims.

Claims

1. A magnetoacoustic converter for an ultrasonic flaw detector, comprising: a magnet for establishing a normal constant magnetic field in a predetermined section of a magnetostrictive plate to be located on an article to be tested; an inductance coil forming a solenoid disposed relative to the magnetostrictive plate so as to set up a tangential variable magnetic field in a predetermined section of the magnetostrictive plate; and means for reflecting elastic vibrations propagating in the magnetostrictive plate, the reflecting means being provided directly in the plate and arranged perpendicularly to the solenoid axis along the path of propagation of the elastic vibrations.

2. A magnetoacoustic converter as claimed in Claim 1, wherein the reflecting means are arranged symmetrically to the solenoid.

3. A magnetoacoustic converter as claimed in claim 1 or 2, wherein the solenoid is wound around the magnet.

4. A magentoacoustic converter as claimed in claim 1 or 2, including a magnetic field concentrator around which the solenoid is wound.

5. A magnetoacoustic converter as claimed in any one of claims 1 to 4, wherein the magnetostrictive plate is a U-shaped structure accommodating the solenoid, butt ends of the plate serving as the means for reflecting elastic vibrations.

6. A magnetoacoustic converter as claimed in any one of claims 1 to 5, including a protector arranged to be disposed between the magnetostrictive plate and an article to be tested, the protector being shaped to suit the shape of the plate on the side of the plate and the shape of the article on the side of the article.

7. A magnetoacoustic converter substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. An ultrasonicflaw detector including a magnetoacoustic converter as claimed in any one of the preceding claims.