EP0829309A2 - Ultrasound generating method for non-destructive testing and test apparatus - Google Patents

Ultrasound generating method for non-destructive testing and test apparatus Download PDF

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Publication number
EP0829309A2
EP0829309A2 EP97115124A EP97115124A EP0829309A2 EP 0829309 A2 EP0829309 A2 EP 0829309A2 EP 97115124 A EP97115124 A EP 97115124A EP 97115124 A EP97115124 A EP 97115124A EP 0829309 A2 EP0829309 A2 EP 0829309A2
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Prior art keywords
workpiece
frequency
magnets
test device
magnetic field
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German (de)
French (fr)
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EP0829309A3 (en
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Dieter Lingenberg
Rainer Dipl.-Ing. Meier
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Siemens AG
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Siemens AG
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/04—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with electromagnetism

Definitions

  • the invention relates to a method for generating ultrasonic waves for non-destructive material testing and to a test device.
  • Ultrasonic testing is a method of non-destructive material testing to find cracks, inclusions, inhomogeneities and other defects.
  • the ultrasound is generated, for example, piezoelectrically or electrodynamically.
  • the ultrasound is generated directly in the test object, so that a coupling medium is not required.
  • the generation of ultrasonic vibrations is due to the interaction of high-frequency eddy currents with a magnetic field.
  • the eddy currents are generated, for example, by a high-frequency coil, which is brought close to the surface of the workpiece.
  • a magnetic field that acts at the same time creates Lorentz forces that generate the sound waves in the workpiece.
  • longitudinal waves and any polarized transverse waves can be excited.
  • the direction of propagation and oscillation are identical in the longitudinal wave, whereas the direction of oscillation in the transverse wave is perpendicular to the direction of propagation.
  • the transverse wave is also known as the shear or shear wave and only spreads in solid media.
  • the direction of polarization lies in the direction normal and propagation direction of the ultrasound through the workpiece surface spanned plane, one speaks of vertically polarized transverse waves. However, if the direction of polarization is perpendicular to this plane, one speaks of horizontally polarized transverse waves. Horizontal polarized transverse waves can only be generated for use in test practice by electrodynamic excitation.
  • test device with vertically oriented permanent magnets is known, the orientation of which changes like a chessboard.
  • the direction between the north and south poles of the permanent magnet is defined as an orientation.
  • the conductor tracks of the high-frequency coil are arranged in a meandering manner between a surface of the workpiece and the permanent magnets.
  • This test device is very complex to manufacture, since the transmitting or receiving coil must be wound very thinly in a flat form. With the usual test frequencies of approx. 0.7 MHz, this can only be done with great effort. Frequencies between 1 and 2 MHz are common for testing thin-walled components and pipes. In order to achieve this, permanent magnet and high-frequency coil arrangements must be reduced in accordance with the frequency. The reproducible production of such test devices is very expensive.
  • test device is known from patent specification EP 0 579 255, in which the eddy currents required for sound excitation are induced via a magnetic yoke enclosing the permanent magnets.
  • the distance between the two pole pieces of the magnetic yoke is therefore undesirably large.
  • This test device is therefore suitable for sound excitation and sound reception their efficiency is strongly dependent on the material to be tested, for example, no satisfactory results have been achieved with non-magnetic components. But especially in the case of non-magnetic weld seams and mixed seams, the use of horizontally polarized waves, which can practically only be generated electrodynamically, is particularly suitable due to the stem crystals to be passed through.
  • test devices known from the prior art using horizontally polarized transverse ultrasonic waves have in common that one or more high-frequency coils for exciting the ultrasonic waves are arranged in magnetic fields which are arranged with alternating polarity and are generated by a multiplicity of permanent magnets.
  • a problem turns out to be that in order to change the insonification angle ⁇ , the excitation frequency of the ultrasonic waves must also be changed in addition to a time control of the individual high-frequency coils. Different excitation frequencies must be used to generate different insonification angles ⁇ .
  • An incidence angle of 0 ° cannot be achieved.
  • the angle of incidence ⁇ is the angle between the direction of propagation of the ultrasonic waves in the workpiece and the surface normal of the workpiece.
  • the invention has for its object to provide a method for generating horizontally polarized transverse ultrasonic waves for non-destructive material testing, which ensures easy generation of the ultrasonic waves.
  • a test device for carrying out the method is to be specified, which ensures efficient generation and reception of ultrasonic waves and is inexpensive to manufacture.
  • the angle of incidence of the ultrasonic waves should be easily predefined in a non-destructive material test without having to change the frequency.
  • the first-mentioned object is achieved according to the invention by a method for generating ultrasonic waves for the non-destructive material testing of a workpiece with at least one high-frequency coil arranged in an essentially homogeneous magnetic field, the longitudinal axis of which is arranged approximately parallel to the surface of the workpiece, due to the interaction of the Magnetic field with the eddy currents generated by the high-frequency coil in the workpiece horizontally polarized transverse ultrasonic waves are generated in this.
  • a corresponding test device for non-destructive material testing of a workpiece with horizontally polarized transverse ultrasonic waves comprises according to the invention at least one high-frequency coil and at least three magnets, the high-frequency coil between the magnets is arranged and its longitudinal axis is aligned parallel to the surface of the workpiece.
  • the invention provides for a practically homogeneous magnetic field to be generated and for several high-frequency coils to be fed with a high-frequency alternating current, the frequency of which is the same in all coils.
  • the high-frequency coils are arranged next to one another in a homogeneous magnetic field in such a way that their longitudinal axes are aligned approximately parallel to one another and to the surface of the workpiece.
  • a corresponding test device contains a magnet arrangement for generating a practically homogeneous magnetic field and a plurality of high-frequency coils which are arranged next to one another in the homogeneous magnetic field and have longitudinal axes which are oriented practically parallel to one another and to the workpiece surface.
  • Each high-frequency coil is preferably assigned its own power supply, the power supplies of adjacent coils generating alternating currents with a predefinable time delay.
  • the high-frequency coils are arranged in one and the same magnetic field. By superimposing several sound waves from several neighboring high-frequency coils, a sufficiently strong signal is obtained for the material test under the angle of incidence ⁇ .
  • the magnet arrangement preferably comprises three magnets.
  • the magnetic field is preferably oriented perpendicular to the surface of the workpiece, ie also perpendicular to the high-frequency coils.
  • an oblique alignment is also possible, e.g. if the spatial conditions so require.
  • the first two magnets are arranged in the plane of the high-frequency coil and their orientations are aligned parallel to the surface of the workpiece.
  • the third magnet is arranged above the high-frequency coil, with its orientation is perpendicular to the surface. With this arrangement of the magnets, an essentially homogeneous magnetic field is generated in which the high-frequency coil is arranged.
  • the longitudinal axis of the high-frequency coil is preferably arranged parallel to the surface of the workpiece.
  • the distance between the high-frequency coils is as small as possible.
  • the diameter of the high-frequency coils is preferably approximately half the wavelength ⁇ of the ultrasound waves to be generated. With this measure, a sound wave bundle that is wide with respect to the insonation angle ⁇ is generated with each high-frequency coil, which in turn enables a large swiveling angle range of the test device.
  • a testing device 2 for material testing a workpiece 24 with horizontally polarized transverse ultrasonic waves 4 comprises three magnets 6, 8, 10 and the high-frequency coils 12 to 18, these being arranged between the magnets 6, 8, 10.
  • the high-frequency coils 12 to 18 each have their own power supply (only the power supplies are shown 13, 15 for the coils 12, 14) lying next to one another.
  • pulse inverters are used as power supplies, which apply a pulse-width-modulated, high-frequency AC voltage to the coils.
  • a pulse-controlled inverter By specifying a (for example sinusoidal) nominal curve, such a pulse-controlled inverter not only allows the frequency, but also the time of the zero crossings of current or voltage to be specified.
  • the symbols of the power supply can be seen that the current in the coil 14 has a phase shift with respect to the current in the coil 12, which is predetermined by a time delay ⁇ t for the power supply.
  • the longitudinal axes 20 of the high-frequency coils 12 to 18 are arranged parallel to a surface 22 of the workpiece 24 to be tested and parallel to one another.
  • the distance between the high-frequency coils 12 to 18 is as small as possible.
  • the high-frequency coils 12 to 18 are coupled to the surface 22 of the workpiece 24 via a protective layer (not shown further).
  • the first and second magnets 6 and 8 are arranged in the plane of the high-frequency coils 12 to 18, their orientations being parallel to the surface 22.
  • the third magnet 10 is arranged above the high-frequency coils 12 to 18, its orientation being perpendicular to the surface 22.
  • This arrangement of the magnets 6, 8, 10 generates an essentially homogeneous magnetic field 26 which is oriented perpendicular to the surface 22 of the workpiece 24 and is located between the magnets 6, 8, 10.
  • the coils 12 to 18 are thus arranged in this magnetic field 26. Alternating magnetic fields, as are known from the prior art, are no longer used.
  • the time-varying magnetic field of the high-frequency coils 12 to 18 is parallel to the outside of the workpiece 24 runs to the workpiece surface 22, the eddy currents in the workpiece generate transverse waves.
  • the angle of incidence ⁇ is only dependent on the delay time ⁇ t.
  • the frequency ⁇ of the ultrasonic waves 4 to be generated no longer has to be changed. It is only necessary to change the delay time ⁇ t of the control between two adjacent high-frequency coils 12, 14 or 14, 16 or 16, 18.
  • the diameter of the high-frequency coils 12 to 18 is approximately half the wavelength ⁇ of the ultrasonic waves 4 to be generated.
  • the magnets 6, 8, 10 are permanent magnets made of a soft magnetic material. In an embodiment not shown, however, they can also be designed as electromagnets.

Abstract

The method uses a tester (2) which generates the ultrasound waves (4) when applied to the material (24) under test. The four HF coils (12,14,16,18) are arranged in an essentially homogeneous magnetic field (26) produced by the three permanent magnets (6,8,10). The waves are generated due to the interaction between the eddy currents produced by the coils and the homogeneous magnetic field produced by the magnets, at right angles to the surface. The coils are arranged between the magnets. The irradiation angle alpha is dependent only on the delay time DELTA t of the drive between neighbouring coils.

Description

Die Erfindung bezieht sich auf ein Verfahren zum Erzeugen von Ultraschallwellen zur zerstörungsfreien Werkstoffprüfung und auf eine Prüfvorrichtung.The invention relates to a method for generating ultrasonic waves for non-destructive material testing and to a test device.

Die Ultraschallprüfung ist ein Verfahren der zerstörungsfreien Werkstoffprüfung zum Auffinden von Rissen, Einschlüssen, Inhomogenitäten und anderen Fehlern. Der Ultraschall wird dabei beispielsweise piezoelektrisch oder elektrodynamisch erzeugt.Ultrasonic testing is a method of non-destructive material testing to find cracks, inclusions, inhomogeneities and other defects. The ultrasound is generated, for example, piezoelectrically or electrodynamically.

Bei der elektrodynamischen Ultraschallerzeugung wird der Ultraschall direkt im Prüfling erzeugt, so daß ein Koppelmedium entfällt. Die Entstehung der Ultraschallschwingungen ist auf die Wechselwirkung von hochfrequenten Wirbelströmen mit einem Magnetfeld zurückzuführen. Die Wirbelströme werden beispielsweise durch eine Hochfrequenz-Spule erzeugt, die in die Nähe der Oberfläche des Werkstückes gebracht wird. Durch ein zugleich wirkendes Magnetfeld entstehen Lorentzkräfte, die die Schallwellen im Werkstück erzeugen. Je nach Orientierung von Magnetfeld und wirbelstromerzeugender Spule zueinander können Longitudinalwellen und beliebig polarisierte Transversalwellen angeregt werden. Bei der Longitudinalwelle sind Ausbreitungs- und Schwingungsrichtung identisch, wo hingegen bei der Transversalwelle die Schwingungsrichtung senkrecht zur Ausbreitungsrichtung ist. Die Transversalwelle wird auch als Schub- oder Scherwelle bezeichnet und breitet sich nur in festen Medien aus.In the case of electrodynamic ultrasound generation, the ultrasound is generated directly in the test object, so that a coupling medium is not required. The generation of ultrasonic vibrations is due to the interaction of high-frequency eddy currents with a magnetic field. The eddy currents are generated, for example, by a high-frequency coil, which is brought close to the surface of the workpiece. A magnetic field that acts at the same time creates Lorentz forces that generate the sound waves in the workpiece. Depending on the orientation of the magnetic field and the eddy current generating coil to one another, longitudinal waves and any polarized transverse waves can be excited. The direction of propagation and oscillation are identical in the longitudinal wave, whereas the direction of oscillation in the transverse wave is perpendicular to the direction of propagation. The transverse wave is also known as the shear or shear wave and only spreads in solid media.

Liegt die Polarisierungsrichtung in der durch die Werkstücksoberflächennormale und Ausbreitungsrichtung des Ultraschalls aufgespannten Ebene, spricht man von vertikal polarisierten Transversalwellen. Liegt die Polarisierungsrichtung hingegen senkrecht zu dieser Ebene, spricht man von horizontal polarisierten Transversalwellen. Horizontal polarisierte Transversalwellen lassen sich für die Anwendung in der Prüfpraxis nur durch elektrodynamische Anregung erzeugen.The direction of polarization lies in the direction normal and propagation direction of the ultrasound through the workpiece surface spanned plane, one speaks of vertically polarized transverse waves. However, if the direction of polarization is perpendicular to this plane, one speaks of horizontally polarized transverse waves. Horizontal polarized transverse waves can only be generated for use in test practice by electrodynamic excitation.

Mit der elektrodynamischen Ultraschallerzeugung ist eine Prüfung des Werkstückes bei Temperaturen bis etwa 1000 K möglich.With the electrodynamic ultrasound generation it is possible to test the workpiece at temperatures up to about 1000 K.

Aus der Patentschrift DE 42 04 643 ist eine Prüfvorrichtung mit senkrecht orientierten Permanentmagneten bekannt, deren Orientierung schachbrettartig wechselt. Als Orientierung wird dabei die Richtung zwischen Nord- und Südpol des Permanentmagneten definiert. Bei dieser Vorrichtung sind die Leiterbahnen der Hochfrequenz-Spule zwischen einer Oberfläche des Werkstückes und den Permanentmagneten mäanderförmig angeordnet. Diese Prüfvorrichtung ist sehr aufwendig herzustellen, da die Sende- bzw. Empfangsspule in ebener Form sehr dünn gewickelt werden muß. Bei den bisher üblichen Prüffrequenzen von ca. 0,7 MHz kann dies nur mit großem Aufwand erfolgen. Für eine Prüfung von dünnwandigen Komponenten und Rohrleitungen sind allerdings Frequenzen zwischen 1 und 2 MHz üblich. Um dies zu erreichen, müssen Permanentmagnet- und Hochfrequenz-Spulenanordnungen entsprechend der Frequenz verkleinert werden. Die reproduzierbare Herstellung solcher Prüfvorrichtungen wird damit sehr aufwendig.From the patent DE 42 04 643 a test device with vertically oriented permanent magnets is known, the orientation of which changes like a chessboard. The direction between the north and south poles of the permanent magnet is defined as an orientation. In this device, the conductor tracks of the high-frequency coil are arranged in a meandering manner between a surface of the workpiece and the permanent magnets. This test device is very complex to manufacture, since the transmitting or receiving coil must be wound very thinly in a flat form. With the usual test frequencies of approx. 0.7 MHz, this can only be done with great effort. Frequencies between 1 and 2 MHz are common for testing thin-walled components and pipes. In order to achieve this, permanent magnet and high-frequency coil arrangements must be reduced in accordance with the frequency. The reproducible production of such test devices is very expensive.

Aus der Patentschrift EP 0 579 255 ist eine weitere Prüfvorrichtung bekannt, bei der die zur Schallanregung erforderlichen Wirbelströme über ein die Permanentmagnete einschließendes Magnetjoch induziert werden. Der Abstand der beiden Polschuhe des Magnetjochs ist damit unerwünscht groß. Damit ist diese Prüfvorrichtung bezgl. Schallanregung und Schallempfang in ihrer Effizienz stark abhängig vom zu prüfenden Material, z.B. wurden bei nichtmagnetischen Komponenten bisher keine befriedigenden Ergebnisse erzielt. Aber gerade bei nichtmagnetischen Schweißnähten und Mischnähten ist aufgrund der zu durchschallenden Stengelkristalle die Anwendung horizontal polarisierter Wellen, die praktisch nur elektrodynamisch erzeugbar sind, besonders geeignet.Another test device is known from patent specification EP 0 579 255, in which the eddy currents required for sound excitation are induced via a magnetic yoke enclosing the permanent magnets. The distance between the two pole pieces of the magnetic yoke is therefore undesirably large. This test device is therefore suitable for sound excitation and sound reception their efficiency is strongly dependent on the material to be tested, for example, no satisfactory results have been achieved with non-magnetic components. But especially in the case of non-magnetic weld seams and mixed seams, the use of horizontally polarized waves, which can practically only be generated electrodynamically, is particularly suitable due to the stem crystals to be passed through.

Den aus dem Stand der Technik bekannten Prüfvorrichtungen unter Verwendung horizontal polarisierter transversaler Ultraschallwellen ist gemeinsam, daß eine oder mehrere Hochfrequenz-Spulen zum Anregen der Ultraschallwellen in Magnetfeldern angeordnet sind, die mit alternierender Polarität angeordnet sind und von einer Vielzahl von Permanentmagneten erzeugt werden. Als Problem erweist sich dabei, daß zum Verändern des Einschallwinkels α neben einer zeitlichen Ansteuerung der einzelnen Hochfrequenz-Spulen auch die Erregerfrequenz der Ultraschallwellen verändert werden muß. Dabei müssen zur Erzeugung unterschiedlicher Einschallwinkeln α unterschiedliche Erregerfrequenzen verwendet werden. Ein Einschallwinkel von 0° läßt sich dabei nicht erreichen. Als Einschallwinkel α wird der Winkel zwischen der Ausbreitungsrichtung der Ultraschallwellen im Werkstück und der Oberflächennormalen des Werkstückes definiert. Der Einschallwinkel α hat die funktionelle Abhängigkeit sin α = λ λ s ,

Figure imgb0001
wobei λ die Wellenlänge der Ultraschallwelle und λs die Spurwellenlänge ist, die durch die Priodizität des statischen Magnetfeldes bestimmt wird. Da die Wellenlänge λ von der Frequenz ν abhängt, ist somit auch der Einschallwinkel α von der Frequenz ν abhängig.The test devices known from the prior art using horizontally polarized transverse ultrasonic waves have in common that one or more high-frequency coils for exciting the ultrasonic waves are arranged in magnetic fields which are arranged with alternating polarity and are generated by a multiplicity of permanent magnets. A problem turns out to be that in order to change the insonification angle α, the excitation frequency of the ultrasonic waves must also be changed in addition to a time control of the individual high-frequency coils. Different excitation frequencies must be used to generate different insonification angles α. An incidence angle of 0 ° cannot be achieved. The angle of incidence α is the angle between the direction of propagation of the ultrasonic waves in the workpiece and the surface normal of the workpiece. The angle of incidence α has the functional dependency sin α = λ λ s ,
Figure imgb0001
 where λ is the wavelength of the ultrasonic wave and λ s is the track wavelength, which is determined by the priodicity of the static magnetic field. Because the wavelength λ depends on the frequency ν depends, the insonation angle α is also dependent on the frequency ν.

Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren zum Erzeugen horizontal polarisierter transversaler Ultraschallwellen zur zerstörungsfreien Werkstoffsprüfung anzugeben, das ein einfaches Erzeugen der Ultraschallwellen gewährleistet. Außerdem soll eine Prüfvorrichtung zum Durchführen des Verfahrens angegeben werden, die ein effizientes Erzeugen und Empfangen von Ultraschallwellen gewährleistet und dabei kostengünstig herzustellen ist.The invention has for its object to provide a method for generating horizontally polarized transverse ultrasonic waves for non-destructive material testing, which ensures easy generation of the ultrasonic waves. In addition, a test device for carrying out the method is to be specified, which ensures efficient generation and reception of ultrasonic waves and is inexpensive to manufacture.

Nach einer anderen Aufgabe soll der Einschallwinkel der Ultraschallwellen bei einer zerstörungsfreien Werkstoffprüfung einfach vorgegeben werden können, ohne die Frequenz ändern zu müssen.According to another task, the angle of incidence of the ultrasonic waves should be easily predefined in a non-destructive material test without having to change the frequency.

Die erstgenannte Aufgabe wird gemäß der Erfindung gelöst durch ein Verfahren zum Erzeugen von Ultraschallwellen zur zerstörungsfreien Werkstoffprüfung eines Werkstückes mit wenigstens einer in einem im wesentlichen homogenen Magnetfeld angeordneten Hochfrequenz-Spule, deren Längsachse ungefähr parallel zur Oberfläche des Werkstückes angeordnet ist, wobei aufgrund der Wechselwirkung des Magnetfeldes mit den von der Hochfrequenz-Spule im Werkstück erzeugten Wirbelströmen horizontal polarisierte transversale Ultraschallwellen in diesem erzeugt werden.The first-mentioned object is achieved according to the invention by a method for generating ultrasonic waves for the non-destructive material testing of a workpiece with at least one high-frequency coil arranged in an essentially homogeneous magnetic field, the longitudinal axis of which is arranged approximately parallel to the surface of the workpiece, due to the interaction of the Magnetic field with the eddy currents generated by the high-frequency coil in the workpiece horizontally polarized transverse ultrasonic waves are generated in this.

Eine entsprechende Prüfvorrichtung zur zerstörungsfreien Werkstoffprüfung eines Werkstückes mit horizontal polarisierten transversalen Ultraschallwellen umfaßt gemäß der Erfindung wenigstens eine Hochfrequenz-Spule und wenigstens drei Magnete, wobei die Hochfrequenz-Spule zwischen den Magneten angeordnet ist und ihre Längsachse parallel zur Oberfläche des Werkstückes ausgerichtet ist.A corresponding test device for non-destructive material testing of a workpiece with horizontally polarized transverse ultrasonic waves comprises according to the invention at least one high-frequency coil and at least three magnets, the high-frequency coil between the magnets is arranged and its longitudinal axis is aligned parallel to the surface of the workpiece.

Um den Einschallwinkel von Ultraschallwellen in einem Werkstück bei der zerstörungsfreien Werkstoffprüfung einfach vorzugeben, sieht die Erfindung vor, ein praktisch homogenes Magnetfeld zu erzeugen und mehrere Hochfrequenz-Spulen jeweils mit einem hochfrequenten Wechselstrom zu speisen, dessen Frequenz in allen Spulen gleich ist. Dabei werden die Hochfrequenz-Spulen nebeneinander derart im homogenen Magnetfeld angeordnet, daß ihre Längsachsen ungefähr parallel zueinander und zur Oberfläche des Werkstücks ausgerichtet sind.In order to easily specify the angle of incidence of ultrasonic waves in a workpiece during non-destructive material testing, the invention provides for a practically homogeneous magnetic field to be generated and for several high-frequency coils to be fed with a high-frequency alternating current, the frequency of which is the same in all coils. The high-frequency coils are arranged next to one another in a homogeneous magnetic field in such a way that their longitudinal axes are aligned approximately parallel to one another and to the surface of the workpiece.

Eine entsprechende Prüfvorrichtung enthält eine Magnetanordnung zur Erzeugung eines praktisch homogenen Magnetfeldes und mehrere Hochfrequenz-Spulen, die nebeneinander im homogenen Magnetfeld angeordnet sind und Längsachsen besitzen, die praktisch parallel zueinander und zur Werkstück-Oberfläche ausgerichtet sind. Vorzugsweise ist jeder Hochfrequenz-Spule eine eigene Stromversorgung zugeordnet, wobei die Stromversorgungen benachbarter Spulen Wechselströme mit einer vorgebbaren Zeitverzögerung erzeugen.A corresponding test device contains a magnet arrangement for generating a practically homogeneous magnetic field and a plurality of high-frequency coils which are arranged next to one another in the homogeneous magnetic field and have longitudinal axes which are oriented practically parallel to one another and to the workpiece surface. Each high-frequency coil is preferably assigned its own power supply, the power supplies of adjacent coils generating alternating currents with a predefinable time delay.

Dabei sind die Hochfrequenz-Spulen in ein und demselben Magnetfeld angeordnet. Durch die Überlagerung mehrerer Schallwellen aus mehreren benachbarten Hochfrequenz-Spulen erhält man ein ausreichend starkes Signal für die Werkstoffprüfung unter dem Einschallwinkel α.The high-frequency coils are arranged in one and the same magnetic field. By superimposing several sound waves from several neighboring high-frequency coils, a sufficiently strong signal is obtained for the material test under the angle of incidence α.

Im Gegensatz zu den aus dem Stand der Technik bekannten Prüfvorrichtungen werden die Hochfrequenz-Spulen also in einem im wesentlichen homogenen Magnetfeld angeordnet und nicht mehr in alternierenden Magnetfeldern. Dagegen wird ein Wechsel-Magnetfeld hoher Frequenz erzeugt, das senkrecht oder zumindest schräg zu dem homogenen Magnetfeld, aber parallel zur Werkstück-Oberfläche ausgerichtet ist. Für den Einschallwinkel α ergibt sich nunmehr der funktionelle Zusammenhang sin α = v t ·Δt d ,

Figure imgb0002
wobei

  • vt die Geschwindigkeit der Ultraschallwellen im Werkstück,
  • Δt die Verzögerungszeit der Ansteuerung zwischen zwei benachbarten Hochfrequenz-Spulen und
  • d der Abstand zwischen den Hochfrequenz-Spulen ist.
In contrast to the test devices known from the prior art, the high-frequency coils are thus arranged in an essentially homogeneous magnetic field and no longer in alternating magnetic fields. In contrast, an alternating magnetic field of high frequency is generated that is perpendicular or at least oblique to the homogeneous magnetic field, but parallel to the Workpiece surface is aligned. The functional relationship now arises for the incidence angle α sin α = v t · Δt d ,
Figure imgb0002
 in which
  • v t the speed of the ultrasonic waves in the workpiece,
  • Δt the delay time of the control between two adjacent high-frequency coils and
  • d is the distance between the high frequency coils.

Da die Geschwindigkeit vt der Ultraschallwellen und der Abstand d der Hochfrequenz-Spulen voneinander konstante Größen in dem funktionellen Zusammenhang sind, ist der Einschallwinkel α nur noch von der Verzögerungszeit Δt abhängig. Das heißt mit anderen Worten, um den Einschallwinkel α zu verändern muß nicht mehr die Frequenz ν der zu erzeugenden Ultraschallwellen verändert werden. Mit diesem Verfahren ist somit ein einfaches und effizientes Erzeugen von Ultraschallwellen im Werkstück unter einem vorgegebenen Einschallwinkeln α möglich. Die Magnetanordnung umfaßt bevorzugt drei Magnete.Since the speed v t of the ultrasonic waves and the distance d between the high-frequency coils are constant variables in the functional relationship, the insonification angle α is only dependent on the delay time Δt. In other words, in order to change the insonification angle α, the frequency ν of the ultrasound waves to be generated no longer has to be changed. With this method, a simple and efficient generation of ultrasonic waves in the workpiece at a given insonification angle α is possible. The magnet arrangement preferably comprises three magnets.

Vorzugsweise ist das Magnetfeld senkrecht zu der Oberfläche des Werkstückes ausgerichtet, also auch senkrecht zu den Hochfrequenz-Spulen. Es ist aber auch eine schräge Ausrichtung möglich, z.B. wenn die räumlichen Verhältnisse dies erfordern.The magnetic field is preferably oriented perpendicular to the surface of the workpiece, ie also perpendicular to the high-frequency coils. However, an oblique alignment is also possible, e.g. if the spatial conditions so require.

Insbesondere sind die ersten beiden Magnete in der Ebene der Hochfrequenz-Spule angeordnet und ihre Orientierungen parallel zur Oberfläche des Werkstückes ausgerichtet.In particular, the first two magnets are arranged in the plane of the high-frequency coil and their orientations are aligned parallel to the surface of the workpiece.

In einer weiteren Ausgestaltung ist der dritte Magnet oberhalb der Hochfrequenz-Spule angeordnet, wobei seine Orientierung senkrecht zur Oberfläche ist. Mit dieser Anordnung der Magnete wird ein im wesentlichen homogenes Magnetfeld erzeugt, in welchem die Hochfrequenz-Spule angeordnet ist.In a further embodiment, the third magnet is arranged above the high-frequency coil, with its orientation is perpendicular to the surface. With this arrangement of the magnets, an essentially homogeneous magnetic field is generated in which the high-frequency coil is arranged.

Vorzugsweise ist die Längsachse der Hochfrequenz-Spule parallel zu der Oberfläche des Werkstückes angeordnet.The longitudinal axis of the high-frequency coil is preferably arranged parallel to the surface of the workpiece.

In einer weiteren Ausgestaltung ist der Abstand zwischen den Hochfrequenz-Spulen möglichst klein.In a further embodiment, the distance between the high-frequency coils is as small as possible.

Vorzugsweise beträgt der Durchmesser der Hochfrequenz-Spulen jeweils ungefähr die Hälfte der Wellenlänge λ der zu erzeugenden Ultraschallwellen. Durch diese Maßnahme wird mit jeder Hochfrequenz-Spule ein bzgl. des Einschallwinkels α breites Schallwellenbündel erzeugt, wodurch wiederum ein großer Schwenkwinkelbereich der Prüfvorrichtung ermöglicht wird.The diameter of the high-frequency coils is preferably approximately half the wavelength λ of the ultrasound waves to be generated. With this measure, a sound wave bundle that is wide with respect to the insonation angle α is generated with each high-frequency coil, which in turn enables a large swiveling angle range of the test device.

Weitere vorteilhafte Ausgestaltungen sind in den Unteransprüchen beschrieben.Further advantageous configurations are described in the subclaims.

Zur weiteren Erläuterung der Erfindung wird auf das Ausführungsbeispiel der Zeichnung verwiesen, in deren einziger Figur eine Prüfungsvorrichtung zur zerstörungsfreien Werkstoffprüfung eines Werkstückes mit horizontal polarisierten transversalen Ultraschallwellen schematisch dargestellt ist.To further explain the invention, reference is made to the exemplary embodiment of the drawing, in the single figure of which a testing device for the non-destructive material testing of a workpiece with horizontally polarized transverse ultrasonic waves is shown schematically.

Im Ausführungsbeispiel nach dieser Figur umfaßt eine Prüfvorrichtung 2 zur Werkstoffprüfung eines Werkstückes 24 mit horizontal polarisierten transversalen Ultraschallwellen 4 drei Magnete 6, 8, 10 und die Hochfrequenz-Spulen 12 bis 18, wobei diese zwischen den Magneten 6, 8, 10 angeordnet sind.In the exemplary embodiment according to this figure, a testing device 2 for material testing a workpiece 24 with horizontally polarized transverse ultrasonic waves 4 comprises three magnets 6, 8, 10 and the high-frequency coils 12 to 18, these being arranged between the magnets 6, 8, 10.

Die Hochfrequenz-Spulen 12 bis 18 sind jeweils von einer eigenen Stromversorgung (dargestellt sind nur die Stromversorgungen 13,15 für die nebeneinander liegenden Spulen 12,14) gespeist. Dabei sind als Stromversorgungen Pulswechselrichter verwendet, die an die Spulen eine pulsbreiten-modulierte, hochfrequente Wechselspannung legen. Ein derartiger Pulswechselrichter gestattet durch Vorgeben einer (z.B. sinusförmigen) Sollkurve nicht nur die Frequenz, sondern auch den Zeitpunkt der Nulldurchgänge von Strom oder Spannung vorzugeben. An den Symbolen der Stromversorgung ist erkennbar, daß der Strom in der Spule 14 gegenüber dem Strom in der Spule 12 eine Phasenverschiebung aufweist, die durch eine Zeitverzögerung Δt für die Stromversorgung vorgegeben ist.The high-frequency coils 12 to 18 each have their own power supply (only the power supplies are shown 13, 15 for the coils 12, 14) lying next to one another. In this case, pulse inverters are used as power supplies, which apply a pulse-width-modulated, high-frequency AC voltage to the coils. By specifying a (for example sinusoidal) nominal curve, such a pulse-controlled inverter not only allows the frequency, but also the time of the zero crossings of current or voltage to be specified. The symbols of the power supply can be seen that the current in the coil 14 has a phase shift with respect to the current in the coil 12, which is predetermined by a time delay Δt for the power supply.

Die Längsachsen 20 der Hochfrequenz-Spulen 12 bis 18 sind dabei parallel zu einer Oberfläche 22 des zu prüfenden Werkstückes 24 und parallel zueinander angeordnet. Der Abstand zwischen den Hochfrequenz-Spulen 12 bis 18 ist dabei möglichst klein. Die Hochfrequenz-Spulen 12 bis 18 sind über eine nicht weiter dargestellte Schutzschicht an die Oberfläche 22 des Werkstückes 24 gekoppelt.The longitudinal axes 20 of the high-frequency coils 12 to 18 are arranged parallel to a surface 22 of the workpiece 24 to be tested and parallel to one another. The distance between the high-frequency coils 12 to 18 is as small as possible. The high-frequency coils 12 to 18 are coupled to the surface 22 of the workpiece 24 via a protective layer (not shown further).

Der erste und der zweite Magnet 6 bzw. 8 sind in der Ebene der Hochfrequenz-Spulen 12 bis 18 angeordnet, wobei ihre Orientierungen parallel zu der Oberfläche 22 sind. Der dritte Magnet 10 ist oberhalb der Hochfrequenz-Spulen 12 bis 18 angeordnet, wobei seine Orientierung senkrecht zur Oberfläche 22 ist. Diese Anordnung der Magnete 6, 8, 10 erzeugt ein im wesentlichen homogenes Magnetfeld 26, das senkrecht zur Oberfläche 22 des Werkstückes 24 ausgerichtet ist und sich zwischen den Magneten 6, 8, 10 befindet. Die Spulen 12 bis 18 sind somit in diesem Magnetfeld 26 angeordnet. Es werden keine alternierenden Magnetfeldern mehr verwendet, wie sie aus dem Stand der Technik bekannt sind.The first and second magnets 6 and 8 are arranged in the plane of the high-frequency coils 12 to 18, their orientations being parallel to the surface 22. The third magnet 10 is arranged above the high-frequency coils 12 to 18, its orientation being perpendicular to the surface 22. This arrangement of the magnets 6, 8, 10 generates an essentially homogeneous magnetic field 26 which is oriented perpendicular to the surface 22 of the workpiece 24 and is located between the magnets 6, 8, 10. The coils 12 to 18 are thus arranged in this magnetic field 26. Alternating magnetic fields, as are known from the prior art, are no longer used.

Da das zeitlich veränderliche Magnetfeld der Hochfrequenz-Spulen 12 bis 18 in den Außenbereich des Werkstücks 24 parallel zur Werkstück-Oberfläche 22 verläuft, erzeugen die Wirbelströme im Werkstück Transversalwellen.Since the time-varying magnetic field of the high-frequency coils 12 to 18 is parallel to the outside of the workpiece 24 runs to the workpiece surface 22, the eddy currents in the workpiece generate transverse waves.

Für den Einschallwinkel α ergibt sich nunmehr der funktionelle Zusammenhang sin α = v t ·Δt d ,

Figure imgb0003
wobei

  • vt die Geschwindigkeit der Ultraschallwellen 4 im Werkstück 24,
  • Δt die Verzögerungszeit zwischen den Ansteuerungen der Stromversorgungen für zwei benachbarte Hochfrequenz-Spulen 12, 14 bzw. 14, 16, bzw. 16, 18 und
  • d der Abstand zwischen den Hochfrequenz-Spulen 12 bis 18 ist.
The functional relationship now arises for the incidence angle α sin α = v t · Δt d ,
Figure imgb0003
 in which
  • v t the speed of the ultrasonic waves 4 in the workpiece 24,
  • Δt is the delay time between the actuations of the power supplies for two adjacent high-frequency coils 12, 14 or 14, 16 or 16, 18 and
  • d is the distance between the high-frequency coils 12 to 18.

Da die Geschwindigkeit vt der horizental polarisierten transversalen Ultraschallwellen 4 und der Abstand d der Hochfrequenz-Spulen 12 bis 18 voneinander konstante Größen in dem funktionellen Zusammenhang sind, ist der Einschallwinkel α nur noch von der Verzögerungszeit Δt abhängig. Das heißt mit anderen Worten, um den Einschallwinkel α zu verändern, muß nicht mehr die Frequenz ν der zu erzeugenden Ultraschallwellen 4 verändert werden. Es muß lediglich die Verzögerungszeit Δt der Ansteuerung zwischen zwei benachbarten Hochfrequenz-Spulen 12, 14 bzw. 14, 16, bzw. 16, 18 verändert werden. Mit diesem Verfahren ist somit ein einfaches und effizientes Erzeugen von Ultraschallwellen 4 im Werkstück 22 unter einem vorgegebenen Einschallwinkeln α möglich.Since the speed v t of the horizontally polarized transverse ultrasonic waves 4 and the distance d between the high-frequency coils 12 to 18 are constant variables in the functional relationship, the angle of incidence α is only dependent on the delay time Δt. In other words, in order to change the insonification angle α, the frequency ν of the ultrasonic waves 4 to be generated no longer has to be changed. It is only necessary to change the delay time Δt of the control between two adjacent high-frequency coils 12, 14 or 14, 16 or 16, 18. With this method, a simple and efficient generation of ultrasonic waves 4 in the workpiece 22 is thus possible at a predetermined insonification angle α.

Der Durchmesser der Hochfrequenz-Spulen 12 bis 18 beträgt jeweils ungefähr die Hälfte der Wellenlänge λ der zu erzeugenden Ultraschallwellen 4.The diameter of the high-frequency coils 12 to 18 is approximately half the wavelength λ of the ultrasonic waves 4 to be generated.

Die Magnete 6, 8, 10 sind Permanentmagnete aus einem weichmagnetischen Material. In einer nicht weiter dargestellten Ausführungsform können sie jedoch auch als Elektromagnete ausgeführt sein.The magnets 6, 8, 10 are permanent magnets made of a soft magnetic material. In an embodiment not shown, however, they can also be designed as electromagnets.

Claims (14)

Verfahren zum Erzeugen von Ultraschallwellen (4) zur zerstörungsfreien Werkstoffprüfung eines Werkstücks (24), mit wenigstens einer in einem im wesentlichen homogenen Magnetfeld (26) angeordneten Hochfrequenz-Spule (12 bis 18), deren Längsachse (20) parallel zu der Oberfläche (22) des Werkstückes (24) angeordnet ist, wobei aufgrund der Wechselwirkung des Magnetfeldes (26) mit den von der Hochfrequenz-Spule (12 bis 18) im Werkstück (24) erzeugten Wirbelströmen horizontal polarisierte transversale Ultraschallwellen (4) in diesem erzeugt werden.Method for generating ultrasonic waves (4) for non-destructive material testing of a workpiece (24), with at least one high-frequency coil (12 to 18) arranged in an essentially homogeneous magnetic field (26), the longitudinal axis (20) of which is parallel to the surface (22 ) of the workpiece (24) is arranged, wherein due to the interaction of the magnetic field (26) with the eddy currents generated by the high-frequency coil (12 to 18) in the workpiece (24), horizontally polarized transverse ultrasonic waves (4) are generated therein. Verfahren zum Erzeugen von Ultraschallwellen (4) zur zerstörungsfreien Werkstoffprüfung eines Werkstücks (24), wobei ein praktisch homogenes Magnetfeld (26) erzeugt wird und mehrere Hochfrequenz-Spulen (12 bis 18) mit Längsachsen (20), die nebeneinander und praktisch parallel zueinander und zur Oberfläche (22) des Werkstücks (24) ausgerichtet sind, jeweils mit einem hochfrequenten Wechselstrom gespeist werden, dessen Frequenz in allen Hochfrequenz-Spulen (12 bis 18) gleich ist.Method for generating ultrasonic waves (4) for non-destructive material testing of a workpiece (24), whereby a practically homogeneous magnetic field (26) is generated and several high-frequency coils (12 to 18) with longitudinal axes (20), which are next to each other and practically parallel to each other and are aligned with the surface (22) of the workpiece (24), are each fed with a high-frequency alternating current, the frequency of which is the same in all high-frequency coils (12 to 18). Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß die Wechselströme jeweils benachbarter Hochfrequenz-Spulen (12 bis 24) mit einer vorgegebenen Zeitverzögerung eingespeist werden und die Ausbreitungsrichtung der Ultraschallwellen (4) im Werkstück (24) durch die Zeitverzögerung vorgegeben wird.Method according to claim 2, characterized in that the alternating currents of respectively adjacent high-frequency coils (12 to 24) are fed in with a predetermined time delay and the direction of propagation of the ultrasonic waves (4) in the workpiece (24) is predetermined by the time delay. Verfahren nach einem der Ansprüche 1 bis 3,
dadurch gekennzeichnet, daß das Magnetfeld (26) ungefähr senkrecht zur Oberfläche (22) des Werkstücks (24) ausgerichtet wird.Method according to one of claims 1 to 3,
characterized in that the magnetic field (26) is aligned approximately perpendicular to the surface (22) of the workpiece (24). Prüfvorrichtung (2) zur zerstörungsfreien Werkstoffprüfung eines Werkstücks (24) mit horizontal polarisierten transversalen Ultraschallwellen (4), die wenigstens eine Hochfrequenz-Spule (12 bis 18) und wenigstens drei Magnete (6 bis 10) umfaßt, wobei die Hochfrequenz-Spule (12 bis 18), mit ihrer Längsachse (20) parallel zur Oberfläche (22) des Werkstücks (24), zwischen den Magneten (6 bis 10) angeordnet ist.Test device (2) for non-destructive material testing of a workpiece (24) with horizontally polarized transverse ultrasonic waves (4), which comprises at least one high-frequency coil (12 to 18) and at least three magnets (6 to 10), the high-frequency coil (12 to 18), with its longitudinal axis (20) parallel to the surface (22) of the workpiece (24), between the magnets (6 to 10). Prüfvorrichtung (2) nach Anspruch 5,
dadurch gekennzeichnet, daß die ersten beiden Magnete (6, 8) in der Ebene der Hochfrequenz-Spule (12 bis 18) angeordnet sind und ihre Orientierungen parallel zu der Oberfläche (22) des Werkstückes (24) ausgerichtet sind.Test device (2) according to claim 5,
characterized in that the first two magnets (6, 8) are arranged in the plane of the high-frequency coil (12 to 18) and their orientations are aligned parallel to the surface (22) of the workpiece (24). Prüfvorrichtung (2) nach Anspruch 5 oder 6,
dadurch gekennzeichnet, daß der dritte Magnet (10) oberhalb der Hochfrequenz-Spule (12 bis 18) angeordnet ist, wobei seine Orientierung senkrecht zur Oberfläche (22) ist.Test device (2) according to claim 5 or 6,
characterized in that the third magnet (10) is arranged above the high-frequency coil (12 to 18), its orientation being perpendicular to the surface (22). Prüfvorrichtung (2) nach einem der Ansprüche 5 bis 7,
dadurch gekennzeichnet, daß die Magnete (6 bis 10) Permanentmagnete sind.Test device (2) according to one of Claims 5 to 7,
characterized in that the magnets (6 to 10) are permanent magnets. Prüfvorrichtung (2) nach Anspruch 8,
dadurch gekennzeichnet, daß die Magnete (6 bis 10) aus einem weichmagnetischen Material bestehen.Test device (2) according to claim 8,
characterized in that the magnets (6 to 10) consist of a soft magnetic material. Prüfvorrichtung (2) nach einem der Ansprüche 5 bis 9,
dadurch gekennzeichnet, daß die Magnete (6 bis 10) Elektromagnete sind.Test device (2) according to one of Claims 5 to 9,
characterized in that the magnets (6 to 10) are electromagnets. Prüfvorrichtung (2) zur zerstörungsfreien Werkstoffprüfung eines Werkstücks (24) mittels Ultraschallwellen (4), mit einer Magnetanordnung (6 bis 10) zum Erzeugen eines praktisch homogenen Magnetfelds (26) und mehreren Hochfrequenz-Spulen (12 bis 18), die nebeneinander im homogenen Magnetfeld (26) angeordnet sind und Längsachsen (20) besitzen, die praktisch parallel zueinander und zur Oberfläche (22) des Werkstücks (24) ausgerichtet sind.Test device (2) for non-destructive material testing of a workpiece (24) by means of ultrasonic waves (4), with a magnet arrangement (6 to 10) for generating a practical homogeneous magnetic field (26) and a plurality of high-frequency coils (12 to 18) which are arranged next to one another in the homogeneous magnetic field (26) and have longitudinal axes (20) which are oriented practically parallel to one another and to the surface (22) of the workpiece (24) . Prüfvorrichtung (2) nach Anspruch 11,
dadurch gekennzeichnet, daß jeweils eine eigene Stromversorgung für jede Hochfrequenz-Spule (12 bis 18) vorgesehen ist, wobei die Stromversorgungen (13,15) benachbarter Hochfrequenz-Spulen (12 bis 18) hochfrequente Wechselströme mit einer vorgebbaren Zeitverzögerung erzeugen.Test device (2) according to claim 11,
characterized in that a separate power supply is provided for each high-frequency coil (12 to 18), the power supplies (13, 15) of adjacent high-frequency coils (12 to 18) generating high-frequency alternating currents with a predefinable time delay. Prüfvorrichtung (2) nach Anspruch 11 oder 12,
dadurch gekennzeichnet, daß das praktisch homogene Magnetfeld (26) ungefähr senkrecht zur Oberfläche (22) des Werkstücks (24) ausgerichtet ist.Test device (2) according to claim 11 or 12,
characterized in that the practically homogeneous magnetic field (26) is oriented approximately perpendicular to the surface (22) of the workpiece (24). Prüfvorrichtung (2) nach einem der Ansprüche 11 bis 13,
dadurch gekennzeichnet, daß die Magnetanordnung mehrere Magnete (6 bis 10) enthält, zwischen denen die Hochfrequenz-Spulen (12 bis 18) angeordnet sind.Test device (2) according to one of Claims 11 to 13,
characterized in that the magnet arrangement contains a plurality of magnets (6 to 10), between which the high-frequency coils (12 to 18) are arranged.
EP97115124A 1996-09-13 1997-09-01 Ultrasound generating method for non-destructive testing and test apparatus Withdrawn EP0829309A3 (en)

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