JPS61245056A - Plate wave trasducer - Google Patents

Abstract

PURPOSE:To execute stably a flaw inspection without being influenced by the vibration of a material to be inspected by placing the material to be inspected between a generating coil and a detecting coil opposed to each other. CONSTITUTION:A trasducer 7 is provided with an electromagnet 6 consisting of a core 5 and a coil 4, a generating coil 13 placed in one end face of a gap part of the core 5 and a detecting coil 14 placed in the other end face. Also, the coils 13, 14 are opposed to each by holding an interval L and a material to be inspected 1 is placed between them. In this state, when an exciting power source 8 and a pulser 9 are controlled by a flaw detector 11 and a vertical magnetic field B is applied to the material to be inspected from the electromagnet 6 and also an impulsive AC current is supplied to the coil 13, a plate wave 2 is generated in the material to be inspected 1. In this case, the plate wave 2 is generated by the same form on the surface and the reverse side of the material to be inspected 1, therefore, a plate wave echo from a defect is also generated on the surface and the reverse side of the material to be inspected 1 and the plate wave 2 containing an echo by the defect can be detected by the coil 14 placed in the lower face side of the material to be inspected 1.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is used as a transducer for flaw detection of conductive thin plates, pipes, rods, etc. Regarding transducers.

[Conventional technology]

FIG. 4 shows a typical conventional configuration of a plate wave transducer using a transverse wave generation method using electromagnetic ultrasonic waves.

In Fig. 4, (7) is a plate wave transducer, (1
) indicates a material to be tested consisting of a conductive thin plate such as a rolled steel plate.

The plate wave transducer (7) includes an electromagnet (6) consisting of a C-shaped core (5) and an excitation coil (4), and a C-shaped core (5).
) and a generating/detecting coil (12) disposed at one end face of the gap section. The material to be tested (1) is placed in the gap of the C-shaped core (5), and is indicated by the arrow (IL).
It is transferred in the direction of the plate surface like this.

DC current is supplied from the excitation power source (8) to the excitation coil (4), which excites the stain magnet (6) and causes the specimen to be inspected (
1) A unidirectional magnetic field perpendicular to the surface is applied.

Four specific configuration examples of the generation/detection coil (12) are shown in FIGS. 5(a) to 5(d). Figure 5 (IL) is 1
Two coils are used together as the generating coil and the detecting coil. In the other three examples, the generating coil (13) and the detecting coil (14) are used together.
) and are separated.

The generation/detection coil (12) is a coil that generates an eddy current in the material to be inspected (1) and detects the eddy current. In Figures 4 and 5, (9) is a pulsar for supplying pulsed alternating current to the generation/detection coil (12), and (10) is amplification of the detection signal of the generation/detection coil (12). (11) is the transmission timing of the pulser (9) and the ON/OIF of the excitation power supply (8).
This is a flaw detector that controls F and determines the presence, location, size, etc. of defects in the material to be inspected (1) from the output signal of the amplifier (10).

FIG. 6 shows the principle of plate wave generation and defect detection using this conventional transducer (7). What is the generation/detection coil (12) in Figure 6? It is of the format shown in Figure 5 (Jl).

The flaw detector (11) controls the excitation power source (8) and the pulser (9), applies a magnetic field B perpendicular to the test material (1) from the electromagnet (6), and also ) is supplied with a pulsed alternating current 1 as shown in FIG.

Then, the generation/detection coil (
12) Eddy currents J, at intervals equal to the pitch D.

J,, J,, J, are induced. This eddy current: r,
, :r,.

, T3.4T, and the interaction with DC magnetic field B (Fleming's left-hand rule) causes Lorentz force? ,, ? ,.

? ,, IF4 is generated, and this force causes the specimen material (1) to
causes an expansion and contraction movement in the mode shown by the broken line in the figure, and the arrow T
It propagates in both directions indicated by Lp TR. This is the plate wave (2).

The illustrated plate wave (2) vibrates (displaces) in opposite directions on the front and back sides of the H1 test material (1), and this is called S mode. Depending on the thickness of the test material (1) and the output frequency of the pulser (9), a plate wave called A mode in which the front and back sides of the test material (1) vibrate (displace) in the same direction is generated.

The detection operation is the opposite of the above, with the DC magnetic field B applied to the material to be inspected (1), the plate wave (2) propagates directly below the generation/detection coil (12), and the material to be inspected (1). When oscillates, a plate wave (2) is generated due to the interaction according to Fleming's right-hand rule.
Eddy currents are generated at a pitch equal to the vibration wavelength of
K'' is induced in the detection coil (12). This induced signal is amplified by the amplifier (lO) and input to the flaw detector (11). In the flaw detector (11), the reception signal is detected from the transmission timing of the pulser (9). The presence, size, location, etc. of a defect is determined based on the reception time and amplitude of (the above-mentioned induced signal).

[Problem that the invention seeks to solve]

The electromagnetic ultrasonic plate wave transducer described above utilizes electromagnetic induction and is therefore characterized in that it can generate and detect plate waves (ultrasonic waves) without contact. However, it has the drawback of low plate wave generation and detection ability (efficiency) (40 to 50 clB lower than piezoelectric transducers).

In order to compensate for this drawback even a little, the output voltage of the pulser (9) is set to an extremely high level of 10 to 20 KV, and a large current is passed through the generation/detection coil (12) to increase the amount of eddy current introduced. The amount of ultrasonic waves generated is increased.

However, in the case of a configuration in which one coil is used both as a generation coil and a detection coil as shown in FIG. 5(a), the pulsar (9
) is directly input to the amplifier (10). There is a limit to the withstand voltage characteristics of the input of the amplifier (10), and if this limit is exceeded, the output potential of the amplifier (10) will rise to the power supply voltage for a short period of time (the time it takes to detect the reflected ultrasound wave, for example 1
After 0 to 100 μm), the potential does not recover to normal. In this case, normal flaw detection cannot be performed during the saturated time period.

This time period is called a dead zone, and the smaller it is, the better.

In the case of a configuration in which the generating coil (13) and the detecting coil (14) are installed overlapping each other as shown in Fig. 5(b), the magnetic flux generated from the generating coil (13) interlinks with the detecting coil (14). , a high voltage is induced in the detection coil (14) by direct mutual induction between both coils, which in turn induces a high voltage in the detection coil (14).
) is input with excessive voltage. This results in a large dead zone, just as in the case above.

When the generating coil (13) and the detecting coil (14) are placed side by side apart from each other as shown in Fig. 5(C), direct mutual induction between the two coils is almost eliminated, but the This creates a large blind area in front of you.

When the generating coil (13) and the detecting coil (14) are arranged side by side and separated vertically as shown in Fig. 5(d), the dead area is also large because both coils are far apart in the propagation direction of the plate wave. Become.

Also, the second drawback of conventional transducers is that
As shown in the figure, the test material (1) and the generation/detection coil (1)
2) The amplitude of the plate wave echo may vary greatly due to variations in the distance (lift-off) L between the two. For example, 4
In the case of a 00 KHz So mode plate wave, the amplitude changes at a rate of 6 dB/m.

Such fluctuations cause deterioration in defect detection performance and ability to evaluate defect size and position based on amplitude.

In order to compensate for this drawback, it is necessary to reduce the vibration of the test material (1), that is, the change in lift-off. For example, it is necessary to take measures such as applying tension to the material to be inspected (1) with rollers or suppressing vibrations with rollers. However, anti-vibration measures are costly, and it is extremely difficult to provide sufficient anti-vibration in high-speed rolling lines.

This invention was made in view of the above-mentioned problems.The purpose of this invention is to have a small dead zone and dead area, to prevent excessive voltage from being input to the detection signal amplification system, and to prevent changes in lift-off from increasing the amplitude of the plate wave echo. An object of the present invention is to provide a plate wave transducer that does not affect

[Means for solving problems]

In the plate wave transducer according to the present invention, a separate generation coil and a detection coil are arranged so as to face each other while sandwiching the specimen material, and the surface of the specimen material is It is configured to apply a horizontal or vertical magnetic field to the

[Effect]

In this invention, the test material placed between the generating coil and the detecting coil serves as an electromagnetic shield, and even if a high voltage is applied to the generating coil, no excessive voltage is induced in the detecting coil. Therefore, the temporal dead zone should be short.
In addition, the coils are arranged in a plane with almost no dead area. Moreover, even if the specimen material vibrates, the sum of the distance between the upper surface of the specimen material and the generating coil and the distance between the lower surface of the specimen material and the detection coil remains constant, which improves ultrasonic echo detection performance and flaw detection. No impact on performance.

〔Example〕

FIG. 1 shows a first embodiment of the present invention, and parts that are the same as or correspond to those of the conventional device shown in FIG. 4 are given the same reference numerals.

This plate wave transducer (7) includes an electromagnet (6) consisting of a C-shaped core (5) and an excitation coil (4), and a generating coil ( 13) and a detection coil (14) disposed on the other end surface of the gap portion. The generating coil (13) and the detecting coil (14) face each other with a distance maintained between them, and the material to be inspected (1) is placed between the coils and transported in the direction of arrow (a).

The excitation power source (8), pulser (9), amplifier (IO), and flaw detector (11) are the same as those of the conventional one. Flaw detector (]1)
controls the excitation power source (8) and the balsa (9),
A perpendicular magnetic field B is applied from the electromagnet (6) to the specimen (1), and a pulsed alternating current is supplied to the generating coil (13). Then, a plate wave (2) is generated in the test material (1). The illustrated plate waves (2) are eight modes out of the nine S modes and A modes described above.

Since plate waves (2) are generated in the same manner on the front and back sides of the test material (1), plate wave echoes from defects are also generated on the front and back sides of the test material (1), and on the bottom side of the test material (1). The arranged detection coil (14
), plate waves (2) containing echoes due to defects can be detected.

When the material to be tested (1) vibrates up and down, the distance Ld between the generating coil (13) and the top surface of the material to be tested (1), and the distance Ld between the generating coil (13) and the top surface of the material to be tested, as shown in FIG. (1) Since the distance Lr from the lower surface increases or decreases in a complementary manner, the sum of L(l and Lr is always constant).

As shown in Fig. 2(b), as L(l increases, the plate wave generation performance decreases, and as Lr decreases, the plate wave detection performance improves.The amplitude of the finally detected flaw detection echo (
The amount of attenuation) is a combination of these two characteristics, and as shown in FIG. 2(C), it remains constant without being affected by the vibration of the test material (1). As a result, the flaw detector (11) can obtain flaw detection echoes that are unaffected by changes in lift-off, making it possible to accurately evaluate defects (defect position, size, etc.).

Moreover, the test material (1) serves as an electromagnetic shield plate for the generating coil (13) and the detecting coil (14), so even if a high voltage is applied to the generating coil (13), the detecting coil (1)
The induced electromotive force to 4) is very small.

Therefore, problems caused by overvoltage being input to the amplifier (10) can be eliminated.

Also, since the generating coil (13) and the detecting coil (14) are facing each other, the characteristics of the dead area around them are shown in Figure 5 (
JL) Same as (b), the range is very small.

FIG. 3 shows another example of the structure of the present invention.

In this example, the electromagnet is divided into two parts (6a) and (6b). Both electromagnets (6a) (sb) have the same configuration, with U-shaped cores (5a) (5b) and excitation coils (4a).
(4b) and the cores (sa) and (sb) are arranged opposite to each other with both end surfaces being spaced apart from each other. The material to be tested (1) is placed between these opposing parts.

When direct current is supplied to the excitation coil (4a) (41) so that the opposing surfaces of both cores (5a) (5b) have different polarities, a magnetic field B perpendicular to the test material (1) is generated. In this case, a generation coil (13) and a detection coil (14) are arranged on opposing surfaces of the excitation coil (4jL) (4b), and the specimen (1) is sandwiched between both coils. This is a transducer using the same transverse wave generation method as in FIG.

Furthermore, when direct current is supplied to the excitation coil (4k) (4m) so that the opposing surfaces of both cores (sa) and (sb) have the same polarity, a horizontal magnetic field BH is generated on the surface of the test material (1). Occur. In this case, a generating coil (13a) and a detecting coil (X4a) are arranged to sandwich the test material (1) in the center of the two opposing parts of both cores (sa) and (sb). This is a transducer using the longitudinal wave generation method.

Incidentally, surface waves can also be generated and detected by changing the frequency of the alternating current applied to the generation coil and the coil pitch of the generation coil and detection coil.

If the thickness of the material being tested is smaller than the wavelength of the surface waves, the surface of the material being tested opposite to the surface where the surface waves are generated will also vibrate at the same time.
With the configuration of the present invention, it is also possible to detect surface waves. Therefore, it can also be used as a surface wave transducer.

In addition, the electromagnet (6) may be replaced with a permanent magnet. [Effects of the Invention] As described in detail above, according to the plate wave transducer of the present invention, the generating coils in which the test materials face each other Since it is sandwiched between the test material and the detection coil, stable flaw detection can be performed without being affected by the vibration of the test material, improving flaw detection performance, accuracy, and reliability. In addition, since the material to be tested acts as an electromagnetic shield between the two coils, harmful high voltages are not induced in the detection coil, the dead zone is shortened, and a simple amplifier is required. play.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a plate wave transducer according to a first embodiment of the present invention, and FIG. 2 is an explanatory diagram of the operation of the first embodiment.
FIG. 3 is a block diagram of a plate wave transducer including two other embodiments of the present invention, FIG. 4 is a block diagram of a conventional plate wave transducer, and FIG. 5 is a block diagram of a conventional plate wave transducer. FIG. 6 is an explanatory diagram of the operation of the conventional one, and FIG. 7 is an explanatory diagram showing the problems of the conventional one. In the figure, (1) is the material to be tested, (2) is the plate wave, (6) is the electromagnet, (12) is the generation/detection coil, (13) is the generation coil, and (14) is the detection coil. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Patent Attorney Masuo Oiwa (and 2 others) 6 Sea (Spontaneous) Showa year, month, sun exposure

Claims (1)

[Claims] (1) A generating coil and a detecting coil are arranged on the front and back sides of the test material so as to sandwich and face each other, and the surface of the test material is horizontally or A plate wave transducer comprising a magnetic field generating means for applying a perpendicular magnetic field.