JP2890364B2 - Online magnetic diagnostic head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic head used for online non-destructive inspection of materials and stresses such as mechanical properties of an object to be measured from its magnetic properties.

[0002]

2. Description of the Related Art It has been attempted to nondestructively inspect the material and stress of an object to be measured by utilizing the fact that the magnetic properties of a material depend on the structure and strain such as crystal grain size and precipitates. ing. For example, there are a method of estimating the tensile strength of a steel material by measuring magnetic permeability, and a method of estimating quenching hardness by a coercive force. Recently, attention has been paid to a method using Barkhausen noise caused by discontinuous change in magnetization, and the fatigue strength of mild steel (LPKarjalainen et al., IEEE Trans.
Mag. MAG16, 514 (1980)) and a method for estimating the toughness of tool steels (Nakai et al., Iron and Steel, 75, 833 (1989)). Also, the correlation between the α-Fe grain size of carbon steel, the precipitated cementite grain size, and Barkhausen noise has been theoretically considered (H. Sakamoto et al., IEEE Trans.
Mag. MAG23, 2236 (1987)).

In general, there are a current penetration method, an energizing method, a coil method, and a yoke method as a method of exciting an object to be measured.
Among these, the yoke method has an advantage that it can be easily excited simply by applying it to a part of a relatively large product such as a steel product or an existing structure manufactured on an actual line. Used for excitation of measurement. As a method for detecting the magnetization of the DUT, there are a yoke method, a Hall element method, a magnetoresistive element method, and the like. The yoke method, which is less affected by the temperature of the DUT, is simple. However, the latter two methods can also be used if there is no temperature effect.

[0006] The excitation head and the detection head by the yoke method are usually arranged on the object to be measured as shown in FIG. As a material of the excitation head core 9 and the detection head core 3, a soft magnetic material such as a silicon steel, permalloy, or soft ferrite is used. By setting the waveform of the current flowing through the exciting coil 10 to be a triangular wave or a sine wave, an exciting magnetic field corresponding to each waveform can be obtained. The magnetic flux 6 generated by the excitation head flows through the DUT 5 as shown in FIG. 4, but a part of the magnetic flux 6 passes through the detection head. Voltage is induced. After this voltage is detected, signal processing is performed to obtain Barkhausen noise and a BH loop. From these magnetic properties, the material and stress of the object to be measured can be destructively evaluated. .

However, the structure of the conventional excitation head shown in FIG. 4 is not simple because it is composed of a soft magnetic material as a core material and an excitation coil for exciting it. In addition, devices such as a waveform generator and a power amplifier for generating an alternating current flowing through the excitation coil are required, and these devices must be managed with high accuracy, and the diagnostic device as a whole becomes large. As well,
Its management also becomes complicated. Further, in order to improve the diagnostic accuracy online, it is necessary to measure the same area of the object to be measured many times. For this purpose, it is necessary to arrange a large number of magnetic heads shown in FIG. Is complicated.

[0006]

As described above, in the conventional method, the structure of the excitation head is complicated when exciting and detecting the magnetization of the object to be measured by the magnetic head including the excitation head and the detection head. In addition, a device for generating an exciting current is required, and the management of the device is complicated, and a simple magnetic diagnostic device is not provided.

The present invention provides a magnetic diagnostic head in which, when an object to be measured is excited by a magnetic head, the exciting head is a magnetic pole composed of a permanent magnet in which N poles and S poles are alternately arranged and a yoke material. In addition to reducing the size and power consumption of the diagnostic device as a whole and facilitating their maintenance and management,
It is still another object of the present invention to provide an online magnetic diagnostic head that facilitates multiple measurements of the same area of a device under test and improves diagnostic accuracy.

[0008]

The gist of the present invention is as follows. In order to excite a local region of a magnetic material and detect a change in magnetization in the region, in a magnetic head including an excitation head and a detection head, the excitation head is configured by a permanent magnet and a yoke material, and the excitation head is An on-line magnetic diagnostic head comprising magnetic poles in which N poles and S poles are alternately arranged with respect to a moving direction of an object to be measured, wherein the detection head is located between magnetic poles of the excitation head.

In order to excite a local area of a magnetic material and detect a change in magnetization in the area, in a magnetic head including an excitation head and a detection head, the excitation head includes a permanent magnet and a yoke material. The excitation head is composed of magnetic poles in which N poles and S poles are alternately arranged with respect to the moving direction of the object to be measured,
An on-line magnetic diagnostic head, wherein the detection head is located on the opposite side of the excitation head across the object to be measured.

3. The on-line magnetic diagnostic head according to claim 1, wherein the excitation head and the detection head are two-dimensionally arranged with respect to the surface to be measured. It consists of three items. Here, when the excitation head composed of the permanent magnet and the yoke material has the permanent magnet as the magnetic pole, the permanent magnet is bonded to the plate-like yoke material so that the N pole and the S pole are alternately arranged. The excitation head can be configured. When the yoke material is a magnetic pole, the excitation head can be configured by laminating permanent magnets between the yoke materials so that the magnetic poles alternate between N and S poles.

[0011]

The present invention will be described below in detail with reference to the accompanying drawings. FIGS. 1 and 2 show schematic diagrams of an online magnetic diagnostic head including an excitation head and a detection head according to the present invention. A feature of the present invention resides in that the excitation head is constituted by a permanent magnet and a yoke material.

First, the case where the permanent magnets shown in FIGS. 1A and 1B are used as the magnetic poles of the excitation head will be described in detail. The excitation head includes a permanent magnet 1 and a yoke plate 2. As the permanent magnet, an Nd-Fe-B-based, Sm-Co-based rare earth magnet, an alnico magnet, or the like can be used. After magnetizing these permanent magnets 1 machined in the shape of the magnetic poles of the head, the permanent magnets 1 are bonded to the yoke plate 2 so that the N poles and the S poles are alternately arranged in the moving direction of the object to be measured. The exciting head of the invention can be constituted. By alternating the polarities of the magnetic poles, the DUT can be magnetized in the direction of the magnetic flux flow 6 in the DUT. The yoke plate 2 can be made of a soft magnetic material such as silicon steel, permalloy, or the like. An ordinary iron plate can also be used as a low-cost yoke material. Here, the number of magnetic poles in the moving direction of the DUT is shown in FIG.
In the case of averaging the same area of the device under test n times, it is sufficient that (n + 2) is used. The excitation head of the present invention can be constituted by at least three or more alternately arranged magnetic poles in total. If the number of magnetic poles is less than 3, both the excitation of the object to be measured and the detection of the magnetization cannot be performed online. The number of magnetic poles is desirably 50 or less. 5
If the number is larger than 0, the magnetic head becomes large, and the handling becomes complicated.

The detection head is made of permalloy, ferrite,
A detection coil 4 is attached to a U-shaped detection core 3 made of silicon steel, etc.
Is wound. The number of detection heads is n if the number of magnetic poles of the excitation head is (n + 2). As shown in FIGS. 1A and 1B, the detection head is placed on the same side (a) as the excitation head with respect to the DUT 5 as shown in FIGS.
There are two types on the opposite side (b). Which one to select is determined by the size, shape, and state of the object to be measured. When the thickness of the object to be measured is large, the method (a) is preferable because the amount of the detected magnetic flux increases. Also,
When the thickness of the object to be measured is small and the magnetic flux sufficiently penetrates in the thickness direction, either of (a) and (b) may be used. In online measurement, these magnetic heads are maintained in a state where a certain distance (lift-off distance 7) is maintained from the surface to be measured. As the shape of the core of the detection head,
In addition to the U type, an I type can also be used.

The magnetic flux can be detected by using a Hall element or a magnetoresistive element in addition to the yoke method. But,
Since they are easily affected by temperature, they are limited to use in a room where temperature is controlled. For detection, the yoke method is simple and versatile.

FIGS. 2A and 2B are schematic diagrams showing a case where the yoke material is used as the magnetic pole of the excitation head. In this excitation head, the two are adhered so that the permanent magnet 1 is sandwiched between the yoke members 2 processed into the shape of the magnetic poles. In this case, the permanent magnets 1 are bonded so that the polarities of the magnetic poles are alternated with the moving direction of the device under test. The materials of the permanent magnet and the yoke material, the detection head, and the like are the same as those described with reference to FIG.

Next, FIG. 3 shows the principle of measurement when the magnetic head according to the present invention is used. However, here, FIG.
Only the excitation and detection head shown in (a) will be described, but the principle is exactly the same in other cases. As shown in FIG. 3A, attention is paid to one area A of the measured object. At time t = 0 in FIG.
Is a state before excitation. The object to be measured moves at a constant speed from right to left in the drawing, and at time t ₁ in FIG. Time t in (c)
_When it reaches ₂ , it reaches the next position and is magnetized rightward in the opposite direction. The magnetization reversal of the region A when the time t ₁ becomes the time t ₂ occurs, the induced voltage due to the magnetization reversal is induced in the detection coil of the first detector head. further,
At time t ₃ of (d), the area A is magnetized again left, the induced voltage in the detection coil similarly detecting head at this time is induced. Hereinafter, similarly, until the time t _n−1 , n induced voltages due to the magnetization reversal of the region A are detected. Here, when the first detection coil and the second detection coil are wound in the same direction, the signs of the induced voltages are opposite as shown in the figure. If every other detection coil is wound in the opposite direction, an induced voltage having the same sign can be obtained. Thus, n voltage signals can be easily obtained from one region A. By taking these waveforms into a waveform calculator or the like in sequence, signals from the same area can be measured many times, and their averaging process can be easily performed. Thereby, detection accuracy can be improved. Although the case where the object to be measured moves is shown here, the same applies to the case where the object to be measured is fixed and the magnetic head moves at a constant speed.

By subjecting the induced voltage waveform induced in the detection coil to filtering, amplification, or integration, Barkhausen noise and BH loop can be obtained. Can be evaluated non-destructively. In addition, by arranging the magnetic head including the excitation and detection head of the present invention two-dimensionally on the measurement surface of the object to be measured, it is possible to easily inspect a large area.

By using such a magnetic diagnostic head, when the material and stress of an object to be measured are non-destructively inspected on-line, unlike a conventional excitation head, its structure is simplified and an excitation current is required. Therefore, the power supply device can be simplified. Therefore, the magnetic head and the diagnostic device as a whole can be reduced in size and power consumption, and their maintenance and management can be facilitated. Further, it is possible to easily perform multiple measurements of the same region of the object to be measured, thereby improving the diagnostic accuracy.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. Example 1 A magnetic head including the excitation head and the detection head according to the present invention shown in FIG. 1A was manufactured, and the excitation of the sample and the detection of the magnetic flux were actually performed. N for the permanent magnet of the excitation head
A silicon steel plate was used for the d- Fe-B sintered magnet and the yoke material. The number of magnetic poles of the excitation head is seven, and the distance between the magnetic poles is 40 mm. The detection head used was a U-shaped permalloy core wound with a detection coil. The number of detection heads is five. With this magnetic head, five voltage signals can be obtained from the same area. Medium carbon steel having a thickness of 2 mm was used as a measurement sample. The moving speed of the sample relative to the magnetic head was 200 mm / sec, and the lift-off distance of the head was 0.1 mm.

Comparative Example 1 As a comparison, five conventional magnetic heads shown in FIG. 4 were manufactured and arranged side by side in the moving direction of a measurement sample. The number of magnetic poles for excitation is ten in total. A silicon steel plate was used for the excitation core, and permalloy was used for the detection core. Here, the distance between the magnetic poles of the excitation core was set to 40 mm. The excitation method was DC excitation, and the excitation current was adjusted so that the magnitude of the excitation magnetic field was the same as the magnitude of the excitation magnetic field obtained in the case of Example 1. Further, the polarity of the excitation head was reversed every other direction. The moving speed of the sample relative to the magnetic head is 200 m
m / sec, and the lift-off distance of the head is 0.1 mm.

Results 1 Table 1 shows the results of a comparison between the magnetic heads manufactured in Example 1 and Comparative Example 1 and ancillary devices such as excitation power supplies.

[0022]

[Table 1]

As can be seen from the above comparison, the head of the present invention and the diagnostic apparatus using the same are smaller in size and power consumption than conventional ones, and their maintenance and management are easy. You can see that.

Result 2 In Example 1, the voltage waveforms induced in the five detection coils all had almost the same shape. The same applies to the case of Comparative Example 1. Table 2 shows the maximum detection voltage as one parameter of these voltage waveforms.

[0025]

[Table 2]

In both the present invention and the comparative example, it can be seen that the maximum voltage value induced in each detection coil has little variation. By increasing the number of excitation heads and detection heads, the accuracy of diagnosis of materials and stress can be improved. However, the head of the present invention can perform this much more easily than the conventional head.

Actually, a magnetic head composed of an excitation head having 12 magnetic poles and 10 detection coils according to the present invention was manufactured, and the induced voltage was detected 10 times from the same area of the sample as in the first embodiment. After that, signal processing was performed to measure Barkhausen noise. As a result, the diagnostic accuracy of the material and the stress was further improved.

Embodiment 2 The same magnetic head (the number of magnetic poles of the excitation head is 7 and the number of detection heads is 5) according to the present invention manufactured in the embodiment 1 is as follows.
3 parallel to the moving direction of the measurement sample at 100 mm intervals
The voltage waveforms induced in the respective detection heads were measured under the same conditions as in Example 1 by arranging them two-dimensionally in rows.
Table 3 shows the maximum detection voltages of these voltage waveforms.

[0029]

[Table 3]

As described above, the reliability of inspection is improved by arranging the magnetic head according to the present invention two-dimensionally and measuring a wider area of the sample.

[0031]

According to the present invention, the use of the magnetic head according to the present invention can reduce the size and power consumption of the magnetic head and the diagnostic apparatus using the same in online non-destructive inspection of steel and other materials and stress. As well as maintaining and managing them easily, the diagnostic accuracy can be easily improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram comprising (a) and (b), each showing two embodiments of a magnetic head according to the present invention.

FIGS. 2A and 2B are schematic diagrams showing two embodiments of a magnetic head according to the present invention, each of which comprises FIGS.

FIGS. 3A to 3E are schematic diagrams illustrating the principle of measurement by the magnetic head of the present invention.

FIG. 4 is a schematic diagram of a conventional magnetic head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Permanent magnet 2 Yoke material 3 Detector core 4 Detector coil 5 Object under test 5 'Object under test (when thin) 6 Flow of magnetic flux in object under test 7 Lift-off distance 8 Direction of magnetization in object under test 9 Excitation core 10 Excitation coil

Claims (3)

(57) [Claims] 1. A magnetic head comprising an excitation head and a detection head for exciting a local region of a magnetic body to detect a change in magnetization in the region, wherein the excitation head comprises a permanent magnet and a yoke material. Wherein the excitation head comprises magnetic poles in which N poles and S poles are alternately arranged with respect to the moving direction of the object to be measured, and the detection head is located between the magnetic poles of the excitation head. Magnetic diagnostic head. 2. A magnetic head comprising an excitation head and a detection head for exciting a local area of a magnetic body and detecting a change in magnetization in the area, wherein the excitation head comprises a permanent magnet and a yoke material. The excitation head is composed of magnetic poles in which N poles and S poles are alternately arranged with respect to the moving direction of the object to be measured, and the detection head is located on the opposite side of the excitation head across the object to be measured. An online magnetic diagnostic head characterized by the following. 3. The on-line magnetic diagnostic head according to claim 1, wherein the excitation head and the detection head are two-dimensionally arranged with respect to a surface to be measured.