JPS63271157A - Eddy current flaw detector for external surface deformed metallic material - Google Patents

Abstract

PURPOSE:To detect a true defect of an external surface deformed metallic material with high sensitivity by placing plural detecting coils at the same gap as the external surface of a metallic material to be inspected, and also, by inclining them in the longitudinal direction of the metallic material to be inspected. CONSTITUTION:In case when a metallic material to be inspected is, for instance, a hexagonal steel bar 1, hexagonal annular coils 2A, 2B are placed in an inclined state in the longitudinal direction. As for the detecting coils 2A, 2B, its ground position is invariable, and the steel bar 1 is moved by a carrying roll group being a moving means. At the time of detecting a flow, in a signal processor 3, a short flaw is detected by a level discrimination by which a level exceeding some level is regarded as a defect, based on a difference of the impedance of the detecting coils 2A, 2B. A long flaw is detected by detecting a difference of the impedance of the oil to all keys and executing a level discrimination, while catching a variation of a signal of the detecting coil 2A.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an eddy current flaw detection device for metal materials with irregular outer surfaces, such as hexagonal steel bars.

[Conventional technology]

For example, the surface of a steel bar has short flaws such as sagging, handling, and roughness; long flaws such as cracks, folds, and processing cracks.

This type of surface defect can be detected by rotating probe eddy current testing when the steel bar is a round steel bar.

[Problem that the invention seeks to solve]

However, in the case of irregularly shaped steel bars such as hexagonal steel bars, it is difficult to apply rotary eddy current testing due to their shape, and satisfactory detection performance cannot be achieved even with through-type eddy current testing in which the metal material passes through a detection coil. I can't get it.

That is, as shown in FIGS. 5 and 6, through-type eddy current flaw detection is carried out with circular detection coils 2OA and 20B arranged with a gap between them along a plane orthogonal to the axis of the deformed steel bar 1. When doing this, relatively large scratches X, X, as shown in Fig. 3 (δ).

and short flaws due to small sagging flaws Xc, and crack flaws Y
When there are long defects due to
Unable to detect Y, sagging defect X11. Xb is beak P,,P
In addition, as shown in Fig. 4, when the deformed steel bar 1 is pulled out during manufacturing, it is grabbed and pulled out at a certain pitch, so a stepped part 1a with a length of 2 to 3 wm, twisting, and stress strain parts are generated. , this is detected as a pseudo defect peak P8.

Therefore, in order to increase the detection sensitivity by shortening the distance between the outer surface of the deformed steel bar 1 and the detection coil, the shape of the detection coil was changed to a hexagonal detection coil 20G parallel to the outer surface shape of the deformed steel bar 1ijll.
It is conceivable to use a circular detection coil 2OA, but the detection sensitivity can certainly be increased, as shown in Fig. 3(C).
Although small scratches TiEXc and cracks Y, which could not be detected with 20B, could be detected as a peak PCrP, the false defect peak P2 was still picked up, and the desired correct defect detection could not be performed.

Therefore, traditionally, we mainly rely exclusively on visual inspection;
This not only burdens the inspector but also tends to lead to incorrect judgments, which is an important problem in terms of quality assurance.

Therefore, the main object of the present invention is to provide a flaw detection device that can detect true defects with high accuracy.

[Means for solving problems]

The present invention for solving the above-mentioned problems provides a structure in which, around a metal material whose outer surface is irregularly shaped when viewed in cross section, a longitudinal part having substantially the same gap as the outer surface of the metal material and which is inclined in the longitudinal direction of the metal material is provided. a plurality of annular detection coils arranged in a plurality of directions; a moving means for relatively moving a metal material in the longitudinal direction within the annular detection coil; based on a difference in output signals from one and the other of the annular detection coils; The present invention is characterized by comprising: a signal processing device for determining whether a short flaw in the longitudinal direction is a long flaw based on a change in an output signal of a certain annular detection coil; and;

[Effect]

In the present invention, since the detection coil is arranged with the same gap as the outer surface of the metal material, the filling rate is high and the detection sensitivity is high.

In addition, since the annular detection coil is arranged obliquely in the longitudinal direction so as to be oblique to the axis of the irregularly shaped metal material to be inspected, the through-type coil can detect eddy currents in the circumferential direction well. When the pseudo defect relatively passes through the detection coil,
Since only a portion of the pseudo defects in the circumferential direction face the detection coil simultaneously in the circumferential direction, the signal level of the pseudo defects is suppressed, and as a result, only the true defect signal can be exposed. can.

[Specific structure of the invention]

The present invention will be explained in more detail below.

Figures 1 and 2 show an embodiment of the method of the present invention, in which hexagonal annular detection coils 2A and 2B are arranged inclined in the longitudinal direction when testing a hexagonal steel bar 1 as a metal material with an irregular outer surface. At the same time, the detection coils 2A and 2B remain in position relative to the ground, while the steel bar 1 is moved in the direction of the arrow on the white board by riding on a group of conveying rollers (not shown) as a moving means. .

A well-known eddy current flaw detection is performed using these detection coils 2A and 2B, but in the present invention, the signal processing device 3 uses level discrimination to determine defects above a certain level based on the difference in impedance between the detection coils 2A and 2B. Detect flaws.

In addition, in the case of a long defect, since the detection coils 2A and 2B are crossed, the difference in signal cannot be corrected. Detects the difference in impedance between the coils and performs level discrimination to detect long defects.

According to this method, as shown in FIG.
, x, and cracks Y can be detected with high accuracy.

By the way, in the present invention, since it is only necessary that the metal material and the detection coil move relative to each other, it is sufficient to fix the metal material and
The detection coil may be moved. Of course, both may move in opposite directions.

Further, for long flaw determination, the detection coil 2B may be used, or detection may be performed from a detection coil arranged other than the detection coils 2A and 2B.

Further, the irregularly shaped metal material may be a cylindrical shape other than a steel bar, and the outer shape is not limited to a hexagonal shape.

When the material to be inspected is a magnetic material, a commonly used magnetic saturation coil is used in combination, since a pseudo defect signal is generated even by a minute change in magnetic permeability.

〔Effect of the invention〕

As described above, according to the present invention, a target true defect can be detected with high accuracy.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the method of the present invention, Fig. 2 is a left side view thereof, and Figs. and a waveform diagram of the detection output signal based on the example of the present invention, FIG. 4 is a perspective view of a hexagonal steel bar with a stepped portion, and FIG. 5 is a front view of the detection coil arrangement of the conventional example.
FIG. 6 is a left side view thereof. 1...Hexagonal steel bar (externally deformed metal material), 2A, 2B
...Annular detection coil, 3...Signal processing device Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6

Claims (1)

[Claims] (1) A plurality of annular detection coils arranged around a metal material whose outer surface has an irregular shape in cross section, having substantially the same gap as the outer surface of the metal material, and slanting in the longitudinal direction of the metal material. and; A moving means for relatively moving a metal material in the longitudinal direction within the annular detection coil; An eddy current flaw detection device for externally deformed metal materials, comprising: a signal processing device that determines major flaws based on changes in the output signal of an annular detection coil; and;