JPH01314961A - Low frequency eddy current flaw detection method - Google Patents

Abstract

PURPOSE:To detect the flaw of a non-magnetic material through a magnetic material by inserting a magnetically permeable rod composed of a magnetic body in the piercing hole at the central part of a probe and surrounding the outer periphery of the probe by other magnet. CONSTITUTION:A magnetically permeable rod 20 composed of a magnetic body is inserted in the piercing hole 15 at the central part of a probe and the outer periphery of the probe is surrounded by a magnet 21. The lower end surface of the detection coil of the probe is brought into contact with a magnetic material 13 to generate an eddy current by the line of magnetic force of the coil 2. When a line 12 of magnetic force is generated toward the coil 2, the magnetic material 13 is magnetically saturated by the line 22 of magnetic force generated by the magnet 21 and, therefore, the presence of the material 13 effectively becomes same to the presence of a non-magnetic body. By this method, the line 12 of magnetic force of the coil 12 penetrates even in a non-magnetic material 14 being a back plate in this case. Therefore, if a flaw 14a is present, the state of an eddy current is changed from that when there is no flaw and the equilibrium state of the bridge circuit of the probe is collapsed and the flaw 14a present in the non-magnetic material 14 being the back plate can be detected.

Description

[Detailed Description of the Invention] <Industrial Application> The present invention relates to a low-frequency eddy current flaw detection method, and is useful as a non-destructive flaw detection method for non-magnetic materials of a test object in which a magnetic material and a non-magnetic material are combined. It is.

<Prior Art> A low frequency eddy current flaw detection method has been known as a non-destructive flaw detection method for a test object.

FIG. 3 is a longitudinal sectional view showing a conventional probe used in this type of low frequency eddy current flaw detection method. As shown in the figure, this probe (2) has a standard coil 1 and a detection coil 2 arranged vertically, which is the axial direction. These standard and detection coils 2 are inner coils la, 2a and outer coils lb, 2b housed in a space formed by inner cylinders 3, 4 and outer cylinders m5, 6.
have. These inner and outer carp 7L, Ia, lb,
A total of 4 wires at the beginning and end of winding 2a and 2b are slit 7.
8 into a cap 9 and connected within this cap 9 to form a bridge circuit. In addition, the inner cylinders 3, 4 and the outer cylinder @5.6 each have one connecting screw 10, 11.
The two blocks thus connected are joined together to form a probe.

When performing flaw detection using such a probe (2), the lower end surface of the probe (I) on the detection coil 2 side is brought into contact with the object to be inspected, and eddy currents are generated by magnetic lines of force generated from the detection coil 2. Then, lines of magnetic force are generated from this eddy current toward the detection coil 2. At this time, the bridge circuit constituted by the standard coil 1 and the detection coil 2 is kept in equilibrium with no defects such as scratches on the subject. Therefore, if there is a defect in the object to be inspected, the eddy current changes, and as a result, the strength of the magnetic lines of force due to the eddy current acting on the detection coil 2 also changes.

As a result, the equilibrium condition of the bridge circuit is disrupted and defects can be detected.

<Problems to be Solved by the Invention> In the above-mentioned prior art, defects in the non-magnetic material of a test object in which a magnetic material and a non-magnetic material are laminated are detected by a probe I that comes into contact with the magnetic material. In other words, it has been impossible to detect flaws in a non-magnetic material when a magnetic material is used as a top plate and a non-magnetic material is used as a back plate.

To further comment, in the above case, as shown in FIG. 4, the lines of magnetic force 12 generated by the detection coil 2 are
This is because it cannot enter the magnetic material 14 and is not affected by the state of the non-magnetic material 14.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, an object of the present invention is to provide a low frequency eddy current flaw detection method capable of detecting defects in a non-magnetic material through a magnetic material.

Means for Solving the Problems> The configuration of the present invention that achieves the above object includes standard coils and detection coils that are arranged in the axial direction, that is, the vertical direction, and are connected to form an electrical bridge circuit. In a low-frequency eddy current flaw detection method, in which eddy currents are generated in a test object by magnetic lines of force generated from a detection coil, and defects such as scratches on the test object are detected based on the state of the lines of magnetic force generated by the eddy currents. , When detecting scratches in the non-magnetic material of a test object in which a magnetic material and a non-magnetic material are laminated using a probe that comes into contact with the magnetic material, it is necessary to insert a magnetic material into the through hole in the center of the probe. Inserting a magnetic bar and surrounding the outer periphery of the probe with other magnets, the lines of magnetic force generated by these magnets magnetically saturate the magnetic material, and the lines of magnetic force generated by the detection coil of the probe turn into non-magnetic material. It is characterized by being transparent.

Effect> According to the present invention having the above configuration, the magnetic material is magnetically saturated by the magnet, so the presence of the magnetic material is effectively the same as the presence of a non-magnetic material, and therefore, the magnetic material and the laminated layer are The magnetic field lines of the detection coil penetrate into the non-magnetic material that is the back plate, and if there is a defect in this non-magnetic material, the equilibrium state of the bridge circuit in the probe will be disrupted. Therefore, the presence of defects in the non-magnetic material can be detected.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings. Note that parts that are the same as those in the prior art are given the same numbers and redundant explanations will be omitted.

FIG. 1 (al, (bl +) is a vertical cross-sectional view showing a probe used in the embodiment method of the present invention and its A-A!s cross-sectional view. As shown in both figures, the probe ■ is It has a through hole 17 that passes through the center part in the vertical direction, and the inner cylinders 3, 4
The structure is the same as that of the probe (2) shown in FIG. be.

When using such a probe (2) to deep-pot a non-magnetic material in a test object in which a magnetic material and a non-magnetic material are laminated from the magnetic material side, as shown in FIG.
The lower end surface, which is the end surface on the detection coil 2 side, is brought into contact with the magnetic material 13 to generate an eddy current by the magnetic lines of force generated from the detection coil 2, and from this eddy current, lines of magnetic force are generated in the opposite direction toward the detection coil 2. . At this time, at the same time, a magnetic conductive rod 20 is inserted into the through hole 15, and the outer periphery of the probe (2) is surrounded by another magnet 21. saturate to. Therefore, the presence of the magnetic material 13 is effectively the same as the presence of a non-magnetic material. As a result, the magnetic lines of force 12 of the detection coil 2 penetrate into the non-magnetic material 14, which is the back plate in this case. Thus, if the defect 14a exists in the non-magnetic material 14, the state of the eddy current changes compared to when there is no defect 14, and the equilibrium state of the bridge circuit of the probe (2) is disrupted, which causes the non-magnetic material that is the back plate to 14 can be detected.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, defects existing in the non-magnetic material on the back side of the magnetic material can be easily detected.

[Brief explanation of the drawing]

Fig. 1 (al is a longitudinal sectional view showing a probe implementing an embodiment of the present invention, Fig. 1 fb) is a sectional view taken along the line A-A, and Fig. 2 shows a flaw detection method according to an embodiment of the present invention. FIG. 3 is a longitudinal sectional view showing a probe according to the prior art, and FIG. 4 is an explanatory diagram showing a flaw detection method according to the prior art. In the drawing, ■ is a probe, 1 is a standard coil, 2 is a detection coil, 12.22 is a line of magnetic force, 13 is a magnetic material, 14 is a non-magnetic material, 15 is a through hole, 20 is a magnetic guide bar, 21 is It's a magnet.

Claims (1)

[Claims] Using a probe that has a standard coil and a detection coil that are arranged in the axial direction (vertical direction) and connected to form an electrical bridge circuit, eddy currents are applied to the subject by magnetic lines of force generated from the detection coil. In the low-frequency eddy current flaw detection method, which detects defects such as scratches on the specimen based on the state of magnetic lines of force generated by this eddy current, When detecting scratches, etc. with a probe that comes into contact with a magnetic material, insert a magnetic conductive rod into the through hole in the center of the probe, and surround the outer periphery of the probe with other magnets. A low frequency eddy current flaw detection method characterized in that the magnetic material is magnetically saturated by the magnetic lines of force generated by the magnet, and the lines of magnetic force generated by the detection coil of the probe are transmitted to the non-magnetic material.