JPH05288733A - Electromagnetic ultrasonic transducer - Google Patents

Abstract

PURPOSE:To reduce noise caused when a defect of metal is detected and thickness, stress and deep drawing moldability is detected by utilizing an electromagnetic ultrasonic transducer in a non-contact state. CONSTITUTION:By placing a metallic foil 4 set at the same potential as a coil 3 between metal 5 to be measured and a transmitting/receiving coil 3 of an electromagnetic ultrasonic transducer, the metallic foil absorbs external noise from the metal to be measured or the like. Ultrasonic waves can be stably generated in the meal 5 to be measured and the ultrasonic waves in the metal 5 can be stably detected, so that noise during measurement using electromagnetic ultrasonic waves can be reduced.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to nondestructive and noncontact detection of metal defects using electromagnetic ultrasonic waves, measurement of thickness, speed of sound, thickness resonance frequency, stress, etc., and deep drawing of metal sheets. The present invention relates to an electromagnetic ultrasonic transducer for measuring sex and the like.

[0002]

2. Description of the Related Art An electromagnetic ultrasonic transducer is a device which can generate an ultrasonic wave in a metal to be measured in a non-contact manner or detect an ultrasonic wave in a metal to be measured by utilizing electromagnetic force. Yes, longitudinal and transverse waves, plate waves, surface waves, etc. can be generated and detected by the type of magnets and coils that make up the transducer, and are used to measure various physical properties of metals (Kawashima, "Electromagnetic Ultrasonic Transducers and Applications," Applied Physics, 52-12 (1983), etc.).

Generally, in the measurement using such an electromagnetic ultrasonic transducer, if the electromagnetic ultrasonic transducer is arranged in a non-contact manner with the metal to be measured, a lot of noise is generated, which hinders the measurement. Most of this noise can be removed by short-circuiting the measured metal and the transmission and reception coils of the electromagnetic ultrasonic transducer to make them conductive. By the way, when measuring a metal to be measured with respect to an electromagnetic ultrasonic transducer in a stationary state, it is not possible to short-circuit the transmitting and receiving coils of the electromagnetic ultrasonic transducer and the metal to bring them into a conductive state as described above. Although easy, if the metal to be measured is moving relative to the electromagnetic ultrasonic transducer, it is appropriate to short-circuit between the metal to be measured and the transmitting and receiving coils of the electromagnetic ultrasonic transducer. There was no way. For example, as a method thereof, a conductive roll is brought into contact with a metal to be measured, and the roll surface, a roll bearing and a shaft, and the coil are electrically connected to each other to transmit and receive the metal to be measured and the electromagnetic ultrasonic transducer. A method of short-circuiting between the coil and the coil can be considered, but there are problems such as wear of the roll and scratches on the metal surface to be measured. Therefore, in this way, when the metal to be measured is moving relative to the electromagnetic ultrasonic transducer, measurement in a noisy state is forced.

[0004]

In the measurement using the conventional electromagnetic ultrasonic transducer, when the metal to be measured and the electromagnetic ultrasonic transducer are arranged in a completely non-contact state, the metal to be measured is However, there is a problem in that a large amount of electromagnetic ultrasonic noise is generated due to the fact that the same potential is not generated between the transmitting and receiving coils of the electromagnetic ultrasonic transducer, which hinders measurement. It is an object of the present invention to provide an electromagnetic ultrasonic transducer capable of reducing noise generated during measurement of a metal in a non-contact state.

[0005]

In order to achieve the above object, the present invention provides an electromagnetic ultrasonic transducer for measuring a metal in a non-contact manner, the metal being electrically connected to the coil of the transducer with the metal to be measured. The gist is an electromagnetic ultrasonic transducer characterized by arranging a foil.

[0006]

By placing a metal foil having the same potential as the coil between the metal to be measured and the transmitting and receiving coils of the electromagnetic ultrasonic transducer, the metal foil prevents noise from the outside such as the metal to be measured. It is possible to absorb, stably generate ultrasonic waves in the metal to be measured, and to stably detect ultrasonic waves in the metal, and reduce noise in measurement using electromagnetic ultrasonic waves. The metal foil is preferably a non-magnetic material having a low magnetic permeability and a material having a relatively low conductivity. This is because the magnetic field from the transducer is prevented from being blocked by the metal foil as much as possible, and the eddy current is generated in the metal foil, and the power exchanged between the transducer and the metal under measurement is generated during transmission / reception. This is to prevent it from being robbed as much as possible.

Further, if the metal foil is provided with radial cuts or the like, eddy currents are less likely to be generated in the metal foil, and during transmission and reception, the metal foil exchanges between the transducer and the metal to be measured. This eliminates the loss of a portion of the power that is consumed, enabling more efficient measurement.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to FIG. Electromagnetic ultrasonic transducer 1 to be measured metal 5
On the other hand, in the electromagnetic ultrasonic measurement system which is arranged in an electrically non-contact state and generates and detects electromagnetic ultrasonic waves inside and on the surface of the metal 5 to be measured, the surface of the metal 5 to be measured and the electromagnetic ultrasonic transducer 1 are A metal foil 4 is arranged between the transmitter / receiver coil 3 in parallel with the surface of the metal 5 to be measured, and the metal foil and the transmitter / receiver coil are at the same potential.

The electromagnetic ultrasonic transducer 1 comprises a magnet 2 for generating a magnetic field in the metal 5 to be measured and a transmitting coil / receiving coil 3 for generating / detecting an eddy current. Electromagnetic ultrasonic transducers include
There are one that is equipped with only one of this coil and the receiving coil and is used only for transmission and reception, and one that is equipped with one coil for both transmission and reception to perform both transmission and reception. There are types that generate waves of various modes such as plate waves and surface waves.

Further, electromagnetic ultrasonic transducers have operating frequencies of about several 100 kHz to 100 MHz, and those using pulsed ultrasonic waves, those using continuous waves, and those generating standing waves in the metal to be measured are also available. Yes, it is used for the purpose of detecting defects on the metal to be measured, sound velocity measurement, thickness measurement, resonance frequency measurement, material measurement, stress measurement and the like. Among them, the one that generates a standing wave is used when the metal to be measured has a plate shape of about 0.1 to 10 mm, and generates ultrasonic waves of each frequency traveling in the thickness direction of the plate as a continuous wave,
This is used by catching the phenomenon that resonance occurs in the thickness direction when ultrasonic waves of a specific frequency are generated. The electromagnetic ultrasonic transducer 1 may be brought into contact with the metal to be measured 5 for measurement, but it is also possible to dispose it in a non-contact manner, and the gap between them is usually about 10 mm or less.

As the metal 5 to be measured, iron, stainless steel,
Whether aluminum, titanium, copper, etc., iron or non-ferrous metal,
In addition, various alloys and those with plating, coating, rust, etc. on the surface can be used.

For the metal foil 4, a non-magnetic material having a relatively low conductivity is suitable. For example, austenitic stainless steel, titanium, manganin, constantan, evanome, invar, platinum, etc. can be used. The same effect can be obtained by using a conductive film instead of the foil. The thickness of the metal foil 4 is about 1 to 100 μm,
For example, 30 μm austenitic stainless steel has an effect of reducing noise at a frequency of about 100 kHz to 50 MHz. The metal foil 4 is arranged between the transmitter coil / receiver coil and the measured metal 5 in parallel with the surface of the measured metal 5, but the distance between the metal foil 4 and the transmitter coil / receiver coil 3 is arbitrary. The metal foil 4 may be arranged so as to be in contact with the transmitting / receiving coil 3. Further, the size thereof may be the same as or larger than that of the transmitting coil / receiving coil 3.

Furthermore, when an eddy current is generated in the metal foil 4, the transducer and the metal to be measured 5 are transmitted and received.
Since a part of the power exchanged between them is lost and the signal sensitivity is lowered, it is desirable to reduce the eddy current generated in the metal foil 4 as much as possible. For that purpose, if the metal foil 4 is provided with radial cuts as shown in FIG. 2 or a large number of parallel cuts as shown in FIG. 3, eddy currents are generated in the metal foil 4. It is less likely to occur, and more efficient measurement becomes possible. Further, in the embodiments, the present invention is effective even if the metal surface to be measured is not a flat surface but a curved surface.

Finally, the measurement result of the ultrasonic spectrum in the case of measuring the frequency at which the longitudinal wave of the ultrasonic wave propagating in the thickness direction of the cold-rolled steel plate resonates in the thickness direction will be shown.
First, FIG. 4 shows the result when the noise reduction measure of the present invention was not measured, and the result was measured by the conventional method, and FIG. 5 is the result when the noise reduction measure using the metal foil of the present invention was carried out. Indicates. In the graphs of FIGS. 4 and 5, the horizontal axis represents frequency and the vertical axis represents power spectrum. In this measurement example, the measurement result in the case of implementing the present invention has a noise level from −66 dB to −84 dB as compared with the conventional measurement result.
It is about 18 dB lower. Further, since the peak level of the resonance frequency is -45 dB and both are the same, the implementation of the present invention improves the signal noise ratio by 18 dB.

[0015]

INDUSTRIAL APPLICABILITY The present invention uses electromagnetic ultrasonic waves to non-destructively
Significantly reduces noise in electromagnetic ultrasonic signals when non-contact metal defects are detected, thickness, sound velocity, thickness resonance frequency, stress, etc., and deep drawing formability of thin metal sheets are measured. To be able to do.

[Brief description of drawings]

FIG. 1 shows an electromagnetic ultrasonic transducer in which a metal foil is arranged.

[FIG. 2] A metal foil with radial cuts.

FIG. 3 is a metal foil in which slits are made in parallel.

FIG. 4 shows a measurement example when the present invention is not carried out.

FIG. 5 shows a measurement example when the present invention is carried out.

[Explanation of symbols]

 1 Electromagnetic Ultrasonic Transducer 2 Magnet Coil 3 Transmission / Reception Coil 4 Metal Foil 5 Metal to be Measured 6 Magnet Power Supply 7 Signal Processing Device

Claims (3)

[Claims] 1. An electromagnetic ultrasonic transducer for measuring a metal in a non-contact manner, characterized in that a metal foil electrically connected to the coil of the transducer is arranged between the metal to be measured. 2. The electromagnetic ultrasonic transducer according to claim 1, wherein the electromagnetic ultrasonic transducer is of a type that generates and detects a standing wave of ultrasonic waves in the metal to be measured. 3. The electromagnetic ultrasonic transducer according to claim 1 or 2, wherein the metal foil is a slit.