JPS62145162A - Split type rotary magnetic field eddy current flaw detector - Google Patents

Abstract

PURPOSE:To prevent a detection output from being deteriorated due to a gas variation, by executing an inspection by making a detecting part constituted of an exciting coil which is divided in the peripheral direction of a material to be inspected, and plural pieces of detecting coils, follow the material to be inspected. CONSTITUTION:In a slot of the inside periphery of an exciting iron core 2 which has been divided in the peripheral direction of a material to be inspected 1, an exciting coil 4 is provided so that a winding of each phase of three phases is placed at every two slots each. On the side of the material to be inspected 1 of this exciting coil 4, plural pieces of detecting coils 6a... are placed in the peripheral direction. ACs from a low frequency power source 7 and a high frequency power source 8 are superposed by a waveform synthesizer 9, converted to a three-phase AC by shifting a phase by 120 deg. each, amplified by a power amplifier 10, and applied to the energizing coil 4. An eddy current which is induced on the surface of the material to be inspected by a shifting magnetic field generated by the energizing coil 4 is detected by the detecting coils 6a..., and amplified by an amplifier 11. Subsequently, after a detection by a detector 13, a signal of the detecting coils 6a... is detected by synchronizing with a moving speed of a magnetic field by a switching circuit 14.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an eddy current flaw detection device for test materials such as magnetic materials such as steel products or non-magnetic materials such as aluminum products that are in a hot state above the cue point. In particular, it relates to a device that prevents a decrease in detection ability due to gap fluctuations due to changes in the size of the material to be inspected or vibrations of the material to be inspected, and improves the ability to detect flaws.

[Conventional technology]

Quality requirements for steel products and non-ferrous metal products have become increasingly sophisticated in recent years, and the quality level of surface flaws in steel products in particular can lead to serious defects such as product destruction during hot forging or cold forging during secondary processing. Because of the connection, the content has become stricter. For this reason, surface flaws have conventionally been checked by non-destructive inspection at the final product stage, as well as quality control at the build-up stage in the steel manufacturing process. Furthermore, recently, there has been an increasing demand for surface flaw inspection in the intermediate stage of manufacturing, that is, in the hot state of intermediate materials, for the purpose of process and cost savings.

Conventionally, surface flaw inspection in a hot state has generally been performed using an eddy current flaw detection method. The eddy current flaw detection method uses an excitation coil for magnetic field formation to generate eddy current loss, and eddy current changes due to cracks, as disclosed in Inspection Equipment News No. 579 (dated April 5, 1980) X, '7. It consists of a detection coil to detect induced voltage or impedance change, and is divided into three types depending on the method of excitation and detection.The self-induction type uses the same coil for excitation and detection, and the self-induction type uses separate coils. What is done is called a mutual induction type.

[Problem that the invention seeks to solve]

FIG. 7 shows a state of flaw detection using a mutual induction type probe type coil which is generally used for inspecting surface flaws on round bars, plate materials, parts, etc. The probe type coil 22 is composed of an excitation coil 4 and a detection coil 6. When the specimen 1 passes through the probe type coil 22 in the direction of an arrow 23, the specimen directly below the excitation coil 4 and the detection coil 6 If there are cracks on the surface of the material 1, the detection coil 6 can detect changes in eddy current caused by the cracks. FIG. 8 shows an example of the configuration of a flaw detection device using a probe type coil. The eddy current generated by the excitation coil 4 is detected by the detection coil 6, and the output signal from the balance circuit 24 is amplified by the amplifier 11, then periodically detected by the detector 13 at the excitation frequency of the oscillator 25, and amplified by the DC amplifier 26. After that, the flaw detection signal is recorded on the recorder 16.

This type of flaw detection method using a probe-type coil has good detection power because the detection coil is small, but in order to inspect the entire circumference of the test material, the probe must be rotated in the circumferential direction of the test material or the It is necessary to rotate the inspection material. The method of mechanically rotating the probe in the circumferential direction of the material to be inspected requires a complicated rotation mechanism, and the rotation speed of the probe decreases as the diameter of the material to be inspected increases, making it difficult to detect short cracks. In addition, the method of rotating the test material has problems such as increasing the cost of In transport equipment for the test material and low throughput.

In order to eliminate such drawbacks of probe-type coils, a rotating magnetic field eddy current flaw detection method shown in FIG. 9 has been considered. This method achieves the same effect electrically instead of mechanically rotating the probe, and the excitation coil 4 is wound in the circumferential direction of the specimen 1 in the same manner as the stator winding of a three-phase induction motor. Furthermore, a plurality of detection coils 6 are arranged inside the excitation coil 4, and a low frequency three-phase alternating current of several tens to hundreds of Hz is superimposed on a high frequency of several tens of KHz, which is the flaw detection frequency, to the excitation coil. 4 to rotate a magnetic field in the circumferential direction of the test material 1, and this rotating magnetic field induces an eddy current on the surface of the test material 1 by rotating the detection coil 6 arranged in the circumferential direction of the test material 1. It detects cracks by switching in synchronization with the magnetic field and inspects for cracks.

Since this method electrically rotates a magnetic field, the rotation speed can be increased and it has the advantage of being suitable for detecting short cracks. However, on the other hand, the excitation coil is similar to the stator winding of an induction motor. Due to the integrated structure, when changing the size of the specimen, the entire detection section consisting of the excitation coil and detection coil must be replaced.Furthermore, if the specimen being transferred through the excitation coil vibrates, This causes a gap variation between the excitation coil and the test material, leading to a problem of deterioration of detection power.

[Means for solving problems]

The present invention was devised to solve these problems, and in a rotating magnetic field flaw detection method in which an excitation magnetic field is electrically rotated, the excitation coil is divided into a plurality of pieces in the circumferential direction of the test material. The detection power due to gap fluctuations can be improved by mechanically tracking the surface flaws by mechanically following the exposed part, which consists of an excitation coil and multiple detection coils, to maintain a constant gap with the material to be inspected. In addition, two sets of divided detection sections are arranged in a staggered manner in the front and back to prevent the deterioration of the test material, and also to cope with changes in the size of the material to be inspected, so that there are no undetected areas.

[Effect]

Hereinafter, the split type rotating magnetic field eddy current flaw detection apparatus of the present invention will be explained in detail.

FIG. 2 shows a sectional view of the split type rotating magnetic field detection section of the present invention. As shown in FIG. 2(A), n slots 3 are inserted into the inner periphery of the excitation core 2 on the side of the test material 1, which is divided in the circumferential direction of the test material 1. As shown in Figure (b), excitation coils 4 are attached so that the windings of each of the three phases are separated by two slots. The manner in which the excitation coil I is attached to the excitation core 2 is exactly the same as the state in which a stator winding is attached to the stator core of a three-phase induction motor. When a low-frequency three-phase alternating current of several tens of Hz to several hundred Hz with a high frequency of several tens of KHz, which is the flaw detection frequency, superimposed on this excitation coil 4 is applied, a magnetic field with a flaw detection frequency component is generated as shown in Fig. 2 (a). It moves in the direction of slot #l to #n in the direction of arrow 5 at a period determined by the number of magnetic poles of exciting iron core 2 and the frequency of the low frequency three-phase alternating current.

That is, a moving magnetic field 5 is generated, which has the same effect as scanning the probe in the circumferential direction of the specimen 1. Therefore, by arranging a plurality of detection coils 6 inside the excitation coil 4 and operating the detection coils in synchronization with the moving magnetic field generated by the excitation coil 4, the probe can be moved to detect the specimen l. The same operation as surface flaw detection can be performed.

FIG. 1 shows an embodiment in which the detection section of the flaw detection apparatus of the present invention is divided into four parts. The flaw detection device is shown in Figure 1A.

Detection unit shown by <a> of 4 formulas shown by B, C, D, <1
)> and a receiving circuit shown as <c>. The detection unit <a> includes an exciting iron core 2 and an exciting coil 4.
The excitation coil 4 is attached to the excitation core 2 as shown in FIG. 2, and the excitation coil has a plurality of detection coils 6a, 6b, 6c, .
... are arranged in the circumferential direction. The entire circumference of the test material 1 is simultaneously covered by four detection units A, B, (), D, and D. The transmitting circuit <b> is composed of a low frequency AC power supply 7, a high frequency AC power supply 8, a waveform synthesizer 9, and a power amplifier 10.
An alternating current of several kilohertz to several tens of kilohertz, which is the flaw detection frequency of eddy current flaw detection, is produced with high frequency alternating current i1mB. The waveform synthesizer 9 superimposes both of these alternating currents by addition or multiplication, and shifts the phase by 120 degrees to create a three-phase alternating current.

The three-phase alternating current generated by this waveform synthesizer is amplified by a power amplifier device 0 for each phase, and is applied to the excitation coil 4. In this manner, in the detection unit <3>, the high frequency alternating current, which is the flaw detection frequency, moves at a speed determined by the number of magnetic poles determined by the winding method of the excitation coil 4 and the frequency of the low frequency three-phase alternating current.

Next, the receiving circuit <c> is composed of an amplifier 11, a phase shifter 12, a detector 13, a switching circuit 14, a differential amplifier 815, and a recorder 16. Excitation coil 4 of detection unit <a>
The eddy current induced on the surface of the test material 1 by the moving magnetic field created by the detection coil 6 arranged in the circumferential direction of the test material 1
a, 6b, 6C1... are detected. That is, the signals detected by the detection coils 6a, 6b, 6c, . , low frequency AC power supply 7 and phase shifter 12
By switching the switching circuit 14 according to the timing, signals from the detection coils 6a, 6b, 6c, . . . are detected in synchronization with the moving speed of the magnetic field.

The signals from the detection coils 6a, 6b, 6c, . 15, the level difference of the signals is compared, and the presence or absence of surface flaws is determined. It is also output to the recorder 16. Although the size of the detection coil 6 is within a few millimeters, two detection coils 6 are operated at the same time.
It is better to have two adjacent pieces.

FIG. 3 shows a cross-sectional view taken along line x-x'' in FIG. This is to avoid being influenced.

In addition, the excitation coil 4 is configured to be as long as 100 to 150 mm in the longitudinal direction in order to reduce changes in detection power due to gap fluctuations between the excitation coil 4 and the test material 1, and the detection coil 4 is configured to be as long as 100 to 150 mm in the longitudinal direction. Number 6 is small, with only a few fins. Signal lines from the plurality of sensing coils 6 are connected to the receiving circuit from the outlet 17.

Figures 4 and 5 (In the front view of Figure 4, (A) is on the left side,
(B) on the right) shows an example of the configuration of the follow-up mechanism when the detection section is divided into four parts in the circumferential direction. The follow-up mechanism is integrally constituted by V rollers 19 before and after the detection section 18 and an air cylinder 20. The detection unit 18 is brought into contact with and separated from the test material 1 by the operation of the air cylinder 20. Test material 1 and detection unit 1
The gap between the V roller 19 and the air cylinder 20 is set by the V rollers 19 before and after the detection unit 18, and even if there is vibration when the test material 1 is conveyed, the gap between the V roller 19 and the air cylinder 20 is maintained. The built-in follow-up function keeps the gap constant and prevents a drop in detection power due to gap fluctuations. Furthermore, FIG. 4 shows the arrangement of the two divided detection units on the left and right sides, and FIG. 5 shows the left and right front views of the same figure. Figure 5 on the right (b)
are shifted by 45 degrees from each other and overlapped to avoid undetected areas. This makes it possible not only to inspect the entire circumference of one size of the material to be inspected, but also to perform flaw detection when the size becomes larger.

Figure 6 shows an example of flaw detection using this flaw detection device. Figure 6 (a)
, the vertical axis indicates the detection coils 6a, 6b, 6, etc. arranged in the circumferential direction of the cross section of the test material shown in Fig. 1, the horizontal axis indicates the longitudinal direction of the test material, and the diagonal line 2 shows a detection coil that detects an eddy current induced on the surface of a test material by a moving magnetic field generated by an excitation coil. As mentioned above, the magnetic field generated by the excitation coil moves at a constant speed in the circumferential direction of the cross section of the material to be tested, so the eddy current induced on the surface of the material to be tested also moves due to this magnetic field, and therefore the detection coil detects this eddy current. Also, in the circumferential direction of the cross section, it operates in synchronization with the moving speed of the magnetic field, as shown by diagonal lines in FIG. 6 (a). Here, as shown in the same figure, if a crack 21 exists on the surface of the material to be inspected, the crack 21
A flaw signal shown in FIG. 6 (t2) is obtained every time the two detection coils located directly above the one where the number 1 is operated. This flaw signal is obtained more frequently as the speed of the moving magnetic field is increased, and the detection power can be improved.

〔Effect of the invention〕

As described above, according to the split type rotating magnetic field eddy current flaw detection apparatus of the present invention, the complexity of the rotation mechanism associated with the mechanical rotation of the conventional probe rotation method or test material rotation method shown in FIG. This not only solves problems such as difficulty and processing capacity, but also solves the size change and lift-off fluctuation problems of rotating magnetic field eddy current flaw detection shown in Figure 9. It is extremely effective industrially for inspecting surface defects on inspection materials. Furthermore, it goes without saying that the present flaw detection apparatus can be applied not only to test materials having a circular cross section, but also to test materials having a square cross section and plate-shaped test materials.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the split type rotating magnetic field eddy current flaw detection device of the present invention, Figs. 2 (a) and (b) are diagrams showing the principle of the split type rotating magnetic field of the present invention, and Fig. Figure 4 is a side view showing the tracking mechanism of the detection unit;
Figures (A) and (B) are front views of Figure 4, Figure 6 is a diagram showing an example of flaw detection, Figure 7 is a diagram showing a conventional flaw detection method using a probe type coil, and Figure 8 is a diagram showing the flaw detection method. A block diagram of the circuit, FIG. 9 is an explanatory diagram showing a flaw detection method using a rotating magnetic field eddy current method. ■...Test material, 2...Exciting core, 3...Slot, 4...Exciting coil, 5...Moving magnetic field,
6 (6a, 6b, 6c,...)...Detection coil, 7...Low frequency AC power supply, 8...High frequency AC power supply, 9...Waveform synthesizer, 10... power amplifier,
11...Amplifier, 12...Phase shifter, 13...
・Detector, 14...Switching circuit, 15...
・Differential amplifier, 16... Recorder, 17... Outlet, 18... Detection section, 19... V roller,
20...Air cylinder, 21...Crack, 2
2... Probe type coil, 23... Moving direction of the test material, 24... Balance circuit, 25... Oscillator,
26...DC amplifier. Applicant Minoru Aoyagi, Patent Attorney for Nippon Steel Corporation Figure 11 abc jiTZ diagram

Claims (1)

[Claims] An excitation coil and a detection coil are arranged in the circumferential direction of the cross section of the material to be inspected, and a low frequency three-phase AC superimposed with a high frequency alternating current at the flaw detection frequency is applied to the excitation coil to rotate the magnetic field in the circumferential direction of the cross section of the material to be inspected. In an eddy current flaw detection device that inspects surface flaws by detecting eddy currents induced by high-frequency alternating current in a rotating magnetic field using a detection coil, the detection section consisting of an excitation coil and a detection coil is divided into multiple pieces in the circumferential direction. A split rotating magnetic field eddy current flaw detection device that is characterized by: