JPH02310462A - Non-destructive inspecting device - Google Patents

Abstract

PURPOSE:To allow the detection of the defect in a ferromagnetic material by using a Barkhausen effect by detecting the Barkhausen signal when current falls. CONSTITUTION:The DC current is applied to an exciting electromagnet 5 by a trapezoidal wave generator 14 and a DC power source device 15 controlled by a computer 13 to generate a magnetic field in the sample 2. The Barkhausen signal by the Barkhausen effect is detected by a signal detector at the time of the rise and fall of the current at this time. The detected signal is amplified in a preamplifier 7, is passed through a high-pass filter 8 and is amplified in a main amplifier 9. Since the Barkhausen signal is an impulsive signal, the number of the pulse signals per unit time is counted by a counter 10 and is converted to an analog signal by a D/A converter 11. The analog signal is taken together with the signal from the device 15 into an A/D converter 12 and is sent to the computer 13 as the information to elucidate the correlativeness between the current change and the time when the signal is generated to the computer 13 where the information is processed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a non-destructive testing device, and more particularly to a non-destructive testing device that utilizes the Barkhausen effect that occurs in ferromagnetic materials.

(Prior art) Fig. 7 is a side view of a magnetic particle flaw detection device, which is one of the conventional non-destructive inspection devices. A pair of electrodes 1.1 are brought into contact with the front and back surfaces. And this electrode 1.
A power supply device (not shown) is connected to each of the test specimens 1 through conducting wires 3.3, and by supplying current from the power supply device, the sample 2 is magnetized and generates magnetic flux.

At this time, if there is a defective part 4 in the sample 2 that blocks the magnetic flux,
Magnetic flux leaks at that portion, magnetic poles are generated on both sides of this defective portion 4, and a local magnetic field is generated.

Therefore, when magnetic particles are scattered on the surface of the sample 2, the dispersed magnetic particles are magnetized by this local magnetic field of the defective portion 4, and the magnetic particles are attracted thereto. The magnetic particle pattern created at this time is several to several tens of times larger than the width of the defective portion 4, so that the presence of the defective portion 4 can be easily recognized visually.

(Problems to be Solved) However, in this conventional magnetic particle flaw detection device, it was not possible to obtain leakage magnetic flux of the required strength from the defective portion unless a strong magnetic field of a certain strength or more was applied.

On the other hand, when a magnetic field larger than necessary is applied, leakage magnetic flux is generated from parts other than the defective part, so it is not easy to obtain an optimum value. In addition, since magnetic powder is scattered to detect defective parts, the sample is contaminated, and it takes time and effort to remove it.

Furthermore, to generate magnetic flux, a current must be passed through the sample, which requires a pair of electrodes to be in contact with the sample, making it mechanically impossible to inspect a moving sample. Ta.

The present invention aims to solve the above conventional problems and provides a simple and easy-to-handle non-destructive inspection device that can detect defects in ferromagnetic bodies using the Barkhausen effect. It is.

(Means for Solving the Problems) This invention includes an excitation electromagnet that applies a static magnetic field that descends at a constant rate in proportion to time to a sample, and a Barkhausen electromagnet that is located near the sample in a non-contact manner. The present invention attempts to solve the above problem by configuring a non-destructive inspection device from a detector that detects a signal and a signal processing section that processes the signal detected by the signal detector.

(Operation) A current that decreases at a constant rate in proportion to time is supplied to an excitation electromagnet placed near a ferromagnetic sample to generate a static magnetic field in the sample. At this time, if a defect exists in the sample, a Barkhausen signal is generated due to the Barkhausen effect, so this Barkhausen signal is detected by a signal detector placed in a non-contact manner near the sample, and the signal processing section This process is used to determine the presence or absence of defects in the sample, as well as their shape and location. Note that the Barkhausen effect refers to a phenomenon in which discontinuous changes in magnetization occur continuously when the magnetizing force acting on a ferromagnetic material is changed.

(Embodiment) Fig. 1 is a block diagram of an embodiment of the non-destructive testing apparatus according to the present invention, in which 2 is a ferromagnetic sample, and 22 is positioned at a constant distance from the sample 1. This is a special detection section.

FIG. 2 is a detailed view of the detection unit 22, in which the end faces of a pair of legs of the gate-shaped excitation electromagnet 5 are in contact with the aluminum plate 21.
A gate-shaped iron case 19 is located within the inner space of the excitation electromagnet 5, and within this iron case 19, a small signal detector 6, which is also gate-shaped, is located at its pair of legs. It is positioned so that the end surface is in contact with the aluminum plate 21.The iron case 19 is provided to prevent the signal detector 6 from being exposed to external noise.

As a result, the signal detector 6 is electrostatically and electromagnetically shielded.

Note that 20 in the figure is an acrylic plate. Also, aluminum plate 21
is grounded, and a constant gap (two gaps in this example) is maintained between it and the sample 2.

In FIG. 1, 7 is a preamplifier connected to the signal detector 6, 8 is a bypass filter 4, 9 is a main amplifier, 10 is a counter, 11 is a D/A converter 1112 is an A/D converter. ,1
3 is a computer, these are connected in series, and the signal obtained by the signal detector 6 is sent to the computer 13 through each of these circuits.

Further, in the figure, 14 is a trapezoidal wave generator controlled by the computer 13, 15 is a DC power supply, 16 is a slider, 17 is a power plug, and 23 is a selection switch. By switching this selection switch 22, the exciting electromagnet 5
Direct current or alternating current is selectively supplied to. In addition, a preamplifier 7, a bypass filter 8, a main amplifier 9, a counter 10, a D/A converter 11, an A/D
The converter 12 is collectively referred to as a signal processing section.

This non-destructive inspection device applies a DC current that rises and falls at a constant rate in proportion to time to an exciting electromagnet 5 using a trapezoidal wave transmitter 14 and a DC power supply 15 controlled by a computer 13, and detects defects in a sample 2. A static magnetic field is generated in the section 4, and a Barkhausen signal is received from the defect section 4 to inspect the sample 2 for defects.

In this example, the strength of the magnetic field was, for example, a static magnetic field strength of 0.42 T when the distance between the sample 2 and the excitation electromagnet 5 was 21 m and a direct current of 4 A was passed.

In addition, in order to maintain normal operation, residual magnetism in the sample 2, signal detector 6, and excitation electromagnet 5 can be erased by using an alternating current (AC) from a commercial power source (100V) that passes through the power plug 17 and is set to an appropriate value by the slider 16. is applied to the exciting electromagnet 5 by switching the selection switch 23.

Next, its operation will be explained. A trapezoidal wave generator 14 and a DC power supply 15 controlled by a computer 13 apply a DC current having a waveform as shown in FIG. 3 to the exciting electromagnet 5 to generate a magnetic field in the sample 2.

At this time, as shown in FIG. 3, a Barkhausen signal due to the Barkhausen effect is detected by the signal detector 6 when the current rises and falls. This detected Barkhausen signal is amplified by a preamplifier 7, passes through a bypass filter 8, and is amplified by a main amplifier 9. Since this Barkhausen signal is a pulse signal, a counter 10 counts the number of pulse signals per unit time, and a D/A converter 11
Convert to analog signal. Next, the signal is input into the A/D converter 12 together with the signal from the DC power supply device 15, and sent to the computer 13 as information for elucidating the correlation between the current change and the time of signal generation, where it is processed. FIG. 4, FIG. 5, and FIG. 6 show the results processed by the computer 13. FIG. 4 shows the count value of the signal when the current increases.

Note that the horizontal axis indicates the position moved near the defective part 4. Fifth
The figure shows the waveform when the current falls, and FIG. 6 shows the waveform when the current falls when the shape of the defective part is changed.

From the above results, it can be seen that the Barkhausen signal appears prominently when the current drops, and that it is also possible to determine the shape of the defective portion 4.

Furthermore, by rotating the signal detector 6, it is also possible to determine in which direction the defective portion 4 continues.

(Name of the Invention) As mentioned above, this invention enables non-destructive detection of the shape position of a defective part in a ferromagnetic sample by detecting the Barkhausen signal when the current drops, and can also be used to inspect moving samples. It has practical effects.

Furthermore, since it does not require scattering of magnetic particles, there is no risk of contaminating the sample, and there is no need for the effort of removing magnetic particles, which has the excellent effect of allowing non-destructive testing to be performed simply and quickly.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the non-destructive testing device according to the present invention, FIG. 2 is a front view of the main parts thereof, and FIG.
The figure is a waveform diagram of the DC current supplied to the exciting electromagnet, and FIGS. 4, 5, and 6 are waveform diagrams of the measurement results. Moreover, FIG. 7 is a front view of a conventional magnetic particle flaw detection device. 2...Sample, 3...Conducting wire, 4...Defect part, 5...
・Exciting electromagnet, 6...detector, 7...preamplifier,
8... Bypass filter, 9... Main amplifier, 10.
...Counter, 11...D/A converter, 12...
A/D converter, 13... Computer, 14... Trapezoidal wave generator, 15... DC power supply device, 16... Slide duck, 17... Power plug, 19... Iron case, 20 ... Acrylic board, 21 ... Aluminum board, 22
...Detection section, 23...Selection switch 1 Figure 2 Time 閤 (,58C) Figure 3 Figure 4 Section 5

Claims (1)

[Claims] An excitation electromagnet that applies a static magnetic field that decreases at a constant rate in proportion to time to the sample, a signal detector that is located near the sample in a non-contact manner and detects the Barkhausen signal generated from the sample, and a signal detector. a signal processing unit that processes the detected signal;
A non-destructive inspection device comprising: