KR860000965B1 - The measuring method for magnetic property by measuring barkhausen noise - Google Patents

Abstract

This is the method of measuring magnetic characteristics by the average amplitude of barkhausen noise and ringdown count. Since this need not frame, it is a completely nondestructive measuring method that is not restricted by the size and shape of tested segment. In production line, it can display directly the locally variant magnetic characteristics due to impurity, remaining force and crevice and can discriminate only the bad portion. This contributes to increased productivity and can be applied to measure the static and dynamic force of the steel construction or welded portion.

Description

Method of measuring magnetic characteristics by measuring the Barkhausen noise

1 is a block diagram illustrating a measuring method of the present invention.

2 is an installation state diagram for explaining the measuring method of the present invention.

3 is a structural diagram of a yoke magnet of the present invention.

4 is a change in average amplitude according to the mother-of-pearl intensity measured by the measuring method of the present invention.

5 is a variation of the ringdown count according to the number of magnetization magnetic waves measured by the measuring method of the present invention.

6 is an explanatory diagram of a magnetic circuit formed between a test piece and a magnet of the present invention.

7 is a metallograph of a magnetic domain inside a specimen.

8 is an amplifier circuit diagram of FIG.

9 is a typical Baeckhausen noise measurement of 78% Ni-Fe.

* Explanation of symbols for main parts of the drawings

1: signal generator 2: power amplifier

3: Search unit 3a: Psalms

4: amplifier and filter 5: signal processor

6: display screen 7: yoke magnet

7a: coil winding 8: specimen

9: search coil 10: coil

The present invention relates to a method for measuring the magnetic properties of a magnetic body by using an average amplitude and a ringdown count of the Barkhausen Noise without limiting the size and shape of the test subject.

Variables for evaluating the magnetic properties of the magnetic body include coercive force, differential permeability, and iron loss. The conventional methods for measuring such magnetic properties are the Epstein frame method and the single method depending on the shape and size of the frame into which the specimen is inserted. It is classified into electric steel plate method and large electric steel plate method, and these are commonly used to cut and use the specimens for each standardized frame, so it is impossible to inspect the whole product and use the randomly collected specimens. Therefore, in addition to the loss of the product due to specimen collection, waste of material, time, expense, etc. caused by judging the local defect of the specimen as the defect of the entire batch is severe. In addition, there is a problem in that heat treatment is inevitably required to remove deformation and stress generated at the cutting portion when cutting the specimen, and a change in magnetic properties caused by the heat treatment is considered.

The conventional magnetic property measurement method is described in detail as follows.

Epstein frame measuring method is currently adopted as a standard measuring method in KS (KS C 4006, 1978) and AST (ASTM A 343-69, 1974) and widely used in industry. However, this method requires the production of a standardized Epstein frame, specimens of 3x28-30.5cm that fit the frame, and the measurement of the average magnetic properties by placing more than 20 specimens in one frame. Therefore, this method is difficult to determine the effective magnetic path because it overlaps the magnetic paths at the overlapping joints when 20 or more specimens are put into the frame, in addition to the above-mentioned drawbacks, and it is difficult to eliminate the leakage fluxes between the overlapping specimens. . In addition, it takes a lot of time to prepare and insert more than 20 specimens to be measured in the frame, there is a defect that can measure only the average magnetic properties for more than 20 specimens.

In the single steel sheet measuring method, the strength of the magnetic field is measured by the H-search coil and the magnetic induction by the B-search coil, but this also reduces the leakage flux and magnetically. Two "U" yokes must be used to reduce the path, the frame must be constructed out of the specimen in the order of H-coil, B-coil, and magnetization coil, and these coils should be in close contact with the specimen for accurate measurement. There is a drawback to this.

In addition, the measuring method of large electrical steel sheet is the same as the measuring method of single steel sheet, but the size of the specimen (50 × 50cm) is larger than that of the Epstein frame measuring method and the measuring method of single steel sheet. Do. However, this method also requires a large yoke to eliminate the leakage flux and measures the magnetic properties of the entire specimen. Therefore, the local magnetic characteristics change due to material defects cannot be known. Is measured. In addition, since it is not easy to completely eliminate the leakage magnetic flux, a measurement error becomes large and a large test piece needs to be cut | disconnected, and there exists a fault which wastes a lot of steel sheets.

In view of these considerations, the present invention is not limited to the size and shape of the test piece, and signal-processing the Barkhausen noise of the magnetic material to measure its average amplitude and ringdown count, thereby measuring impurities, residual stresses and cracks on the entire surface of the magnetic test piece. The invention is invented so that local magnetic property change due to the measurement can be measured.

The Bachhausen noise refers to the discontinuity in the magnetization of magnetic domains within a magnetic body when a constantly changing magnetic field or stress is applied to the magnetic body. As a result of discontinuity, abruptness, and randomness caused by displacement or rotation, the magnetic induction on the magnetic hysteresis trunk line of the specimen is observed to be abrupt, arbitrary, and discontinuous. Therefore, in the present invention, as shown in FIG. 1, when the AC signal generated by the signal generator 1 is amplified by the power amplifier 2 and applied to the magnet of the Barkhausen noise search unit 3, the specimen 3a is accordingly applied. Barkhausen noise is generated in the c), which is measured using a search coil (9 or 9a). When the Bachhausen noise measured at the search coil is amplified by the amplifier and filter 4 into a signal of appropriate magnitude and applied to the signal processor 5, the signal processor 5 processes the average amplitude and the ringdown count accordingly. On the display screen 6, the display screen 6 can measure and display local magnetic properties due to impurities, residual stresses, cracks, and the like on the entire surface. By scanning, the magnetic characteristic distribution of the entire surface of the specimen under test can be displayed on the display screen 6.

This will be described in more detail as follows.

As shown in Fig. 3, the "U" shaped yoke-shaped magnet 7 has a length (s) of 95 mm and a width (d) of 27 mm, and a height (h) of 50 mm and a thickness (t) of 15 mm on both sides. The in-coil winding part 7a is protruded, the coil 10 is wound 200 times by this coil winding part 7a, and the yoke-type magnet 7 is comprised. As shown in FIG. 2, the yoke-shaped magnet 7 configured as described above is contacted with an arbitrary specimen 8, and then an AC signal having a constant frequency generated by the signal generator 1, for example, 0.1 Hz, Hz, or the like. When the AC signal is amplified by the power amplifier 2 and applied to the coil 10 wound on the yoke-type magnet 7, the magnetic field induced by the yoke-type magnet 7 causes the displacement of magnetic domains on any specimen 8 or Barkhausen noise is generated by the rotation. This Barkhausen noise is detected by the search coil 9 or 9a at the opposite or trending position of the yoke-type magnet 7 in contact with an arbitrary position on the specimen 8, and applied to the amplifier and the filter 4, The amplifier and filter 4 amplify and filter the Barkhausen noise detected by the search coils 9 or 9a and apply it to the signal processor 5 so that the signal processor 5 obtains the average amplitude of the Barkhausen noise accordingly. The ringdown count can be measured to quantitatively measure the magnetic properties of the magnetic material. This operation process will be described in more detail as follows.

S로 변화하게 된다. 이와같은 상태에서 자성체 시험편(8)을 요크형 마그네트(7) 위에 밀착위치시키면 시험편(8)과 요크형 마그네트(7)사이에는 제6(a)도, 제6(b)도에 도시한 바와 같이 자기회로가 형성된다. 여기서, 제6(a)도는 코일(10)에 +3A가 흐를 때의 자기회로이고, 제6(b)도는 코일(10)에 -3A가 흐를 때의 자기회로이다.The signal generated by the signal generator 1 is amplified by the power amplifier 2 to about ± 3 A, and the amplified signal current is transferred to the coil 10 wound on the yoke magnet 7 as shown in FIG. Since it is applied, an alternating magnetic field is formed in the yoke type magnet 7. For example, if a 1 Hz alternating current signal is generated by the signal generator 1, an alternating magnetic field of 1 Hz is also formed in the yoke magnet 7, so that the magnetic pole of the yoke magnet 7 continues to be N.

It will change to S. In such a state, when the magnetic body specimen 8 is placed in close contact with the yoke magnet 7, the sixth (a) and sixth (b) are shown between the specimen 8 and the yoke magnet 7. Magnetic circuits are formed together. 6 (a) is a magnetic circuit when + 3A flows through the coil 10, and FIG. 6 (b) is a magnetic circuit when -3A flows through the coil 10. FIG.

In this way, since the magnetic field in which the intensity and direction change with time is formed in the test piece 8, the test piece 8 is repeatedly magnetized, and accordingly, the magnetic domains (11 in FIG. 7) constituting the test piece 8 suddenly undergo magnetic domain motion. To generate Barkhausen noise. By the way, the Barkhausen noise has different characteristics depending on the material, heat treatment state, residual stress, etc. of the specimen 8, and the voltage level of the noise. When this signal is properly processed, the magnetic characteristics of the specimen 8 can be measured. . Therefore, the Barkhausen noise generated in the test piece 8 is detected by the search coil 9 or 9a using magnetic induction, and then applied to the amplifier and the filter 4 to be amplified and filtered. An example of an amplifier circuit of this amplifier and filter 4 is shown in FIG.

In this way, the signal amplified and filtered by the amplifier and filter 4 is applied to the signal processor 5 to measure the average amplitude and ring down count of the Barkhausen noise to quantitatively measure the magnetic properties of the magnetic material.

FIG. 9 is a typical Barkhausen noise waveform photograph of a 78% Ni-Fe test piece detected by the above measuring method, wherein the X axis represents time and the Y axis represents voltage. The average amplitude measured by the signal processor 5 denotes V _rms , which is the voltage average amplitude of the Barkhausen noise, and the ring-down count means the number that is greater than a certain threshold voltage of the Barkhausen noise.

For example, according to the present invention, the variation in the average amplitude of the Baujkhausen noise with the magnetic field strength is shown in FIG. 4 in a 50% cold worked 78% permalloy specimen. The average amplitude of the Bachhausen noise is the maximum near the coercive force (Hc, -Hc), and as the magnetization frequency increases, the average amplitude of the Bachhausen noise decreases, which is in agreement with the results obtained by the conventional magnetic characteristics method. have. However, in FIG. 4, ○ indicates that the magnetization frequency is 0.01 Hz, and × and Δ indicates that the magnetization frequency is 0.05 Hz and 0.1 Hz, respectively.

Table 1 below shows the average amplitude of the Barkhausen noise at the coercive point when the Permalloy specimen was measured with varying angles in the magnetization direction with respect to the rolling direction, and when the structure was removed by heat treatment. have.

TABLE 1

As shown here, the coercivity changes from 1.4 (Oe) to 1.8 (Oe) (about 30%) when the angle of the magnetization direction with respect to the rolling direction of the cold worked specimen changes from 0 ° to 90 °. It can be seen that the average amplitude of the Akhausen noise varies from 0.17 (V) to 0.01 (V) (about 1,700%), indicating that the amplitude change of the Bachhausen noise is very large and sensitive to the dependence on the tissue. Can be. Therefore, by measuring the average amplitude of the Bachhausen noise of the magnetic body, the magnetic characteristic change of the magnetic body could be accurately measured.

In addition, FIG. 5 shows the threshold voltage of the signal processor 5 after amplifying the Barkhausen noise detected by the search coil 9 or 9a to an appropriate magnitude (49 dB in this experiment) in the amplifier and filter 4. The ring down count, which counts the number of abnormal Barkhausen noises per cycle, shows that the ring down count has changed significantly with the change of the magnetization frequency. That is, as shown in FIG. 5, when the hysteresis curve is drawn while the magnetization frequency is changed to 0.01, 0.05, 0.1, 0.5, and 1.0 Hz, the hysteresis curve is hardly changed. The ringdown count changes to 37000, 10500, 5500, 1000, and 130 counts / cycle, indicating that the sensitivity is extremely high, and even minute magnetic property changes can be measured.

As described above, since the method of the present invention does not require a frame that is essentially used in the conventional magnetic property measurement method, it is not limited to the size and shape of the test piece, and can be called a complete non-destructive test capable of measuring the magnetic property of the magnetic material. have. Accordingly, even in the production line, it is possible to directly inspect and show the change of local magnetic properties due to impurities, residual stresses, cracks, etc. of the entire steel sheet, and to identify only defective parts, thereby improving productivity. In addition, the present invention can be applied to a device capable of inspecting and showing static and dynamic stress magnitudes and distributions of steel structures and welded portions.

Claims (1)

(Correct) The yoke of the Barkhausen noise generated from the magnetization change of the specimen 8 by the yoke-type magnet 7 whose magnetic field strength is adjusted in proportion to the current generated by the signal generator 1 and the power amplifier 2 The detection magnets 9 and 9a are detected at the magnet type 7 and the trend or the opposite position, and the signals are processed by the amplifier and the filter 4 and the signal processor 5 to obtain an average amplitude and ring down of the Barkhausen noise. A magnetic characteristic measurement method by Barkhausen noise measurement in which a count is displayed on a display screen (6) to measure magnetic characteristics of a magnetic substance.

Images