JPS58135449A - Eddy current flaw detecting probe - Google Patents

Abstract

PURPOSE:To obtain a sufficient current for detection of flaws and to improve both sensitivity and S/N, by providing ferrite core electrodes to generate 2 pairs of magnetic fluxes to the surface of a material to be checked. CONSTITUTION:A knife edge is formed at the area where ferrite core electrodes 1 and 1' wound with coil windings 2 and 2' face a material 3 to be checked, and the distance between a pair of knife edges is set equal to the minimum distance between a pair of electrodes. As a result, the magnetic fluxes are easily concentrated between knife edges to increase the efficiency. Therefore two units of electrodes are used to generate 2 pairs of magnetic fluxes, and a differential connection is given between the coils 2 and 2'. Then a current is flowed to the coils, and the material 3 is shifted toward an arrow mark. Thus the balance of coil impedance is lost when surface flaws 6 orthogonal to an eddy current 5 pass through. As a result, flaw signals are detected. In such a constitution, the sensitivity is increased, and at the same time the S/N is improved since the magnetic fields are concentrated at the knife edge part.

Description

[Detailed description of the invention] Akira Mokuzuko is concerned with glove-type eddy current flaw detection gloves.

As is well known, eddy current deep field detects flaws on the metal surface by generating eddy currents on the metal surface through the magnetic flux induced from the flaw detection probe.
Surface flaws are detected from the change in impedance caused by flaws on the metal surface, and it is clear from this (〉× principle) that the form of magnetic flux generation in the lobe has an extremely important meaning. It is no exaggeration to say that the characteristics and performance of the two-rope are determined by the form of occurrence of the defects.
It is necessary to configure the plow so that the magnetic flux generated from the plow 1 is approximately parallel to the flaw, or so that the eddy current generated through the magnetic flux is approximately perpendicular to the flaw.

Therefore, in the conventional method, the coil is made into a rectangular or circular shape, and one side of the coil is arranged parallel to the surface of the material to be inspected. In this case, even if the number of coil turns is increased, the efficiency of the magnetic flux effective on the surface of the material to be tested will not improve because the distance from the surface of the material to be tested will equivalently increase as the coil winding layer thickness increases. Only the coil impedance becomes large, and as a result, sufficient current necessary for flaw detection does not flow, and sufficient flaw detection cannot be performed.

In order to solve these problems and develop a highly efficient method, the inventors conducted various studies and came up with a method that actively uses ferrite cores. It is a well-known fact that there was already an idea of applying 6C1 to ferrite cores, but the previous idea was to simply increase the magnetic flux density of the coil, and 6C1 was not able to produce sufficient effects and was not put into practical use. Not quite yet. The present invention aims to provide a prong that uses a ferrite core and has improved both electric shock and S/N. Hereinafter, the present invention will be explained in detail with reference to a specific example LC.

First, before explaining the present invention, an example of a conventional system will be explained with reference to FIG. Figure 1(a) shows a circular eddy current probe.
Figure 1 6) is a rectangular linear eddy current probe.
As shown in Figure (a'), a circular eddy current 5 is generated. When the side 3 to be inspected moves with respect to such an eddy current coil, the flaw 6 enters the eddy current region, and the coil impedance changes, so that the flaw is not detected. However, in the case of this coil V), there are quite a few components of eddy current that are perpendicular to the inner court, and ir? '+ The effect of using current is poor, and the S/N ratio is generally not good.

Father, Figure 1 (b) In the globe coil shown in K, the material to be tested:
The state of the eddy current 5 and magnetic flux 4 occurring in the magnetic flux 3 is shown in Fig. 1(b). In FIG. 1(b'), when the side to be inspected 3 moves, the flaw 6 crosses the eddy current 5 by 1:1, causing an impedance change and detecting the flaw. In the case of this method, the eddy current component perpendicular to the flaw () is larger than that of the circular coil described above, and the eddy current usage efficiency is high (S/N is also good for the circular coil. The conventional method is 1,1
A part of the core uses a bobbin made of general pepoxy resin.

In contrast to the conventional method described above, the inventors proposed the method shown in FIG. 1(a).

When 1 and 1' of (b) were used as ferrite cores, the absolute sensitivity was improved by about 5 to 7 times compared to epoxy resin, as expected, by increasing the magnetic flux density.

Conventionally, the idea of using a ferrite core was more effective than expected in the configuration shown in Figure 1(a), although it is a well-known fact, and the example of using ferrite in the configuration shown in Figure 1(b) was , the inventors were the first to do so, and it cannot be found anywhere else.

The coil windings 2 and 2' are normally coupled differentially, but there are cases where the coil is directly differentially coupled, and where the differentially coupled is carried out within a bridge or amplifier that detects the coil impedance. As mentioned above, we were able to obtain more effects than expected, but the inventors continued various studies to improve not only the absolute sensitivity but also the S/N ratio, as shown in Figure 2.
When a flaw detection probe with the configuration shown in Fig. 3 was manufactured and a crane experiment was conducted, it was possible to see a significant improvement in both sensitivity and S/N compared to the conventional method.

1: The present invention will be explained in detail. Figure 2<a
> , (b) In VC, 1.1' is a ferrite core, 2°2' is a coil winding, and 3 is a flat plate-shaped specimen. Fig. 2(b) is a view of the flaw detection glove seen from the bottom.
1.1' is a ferrite core, 6D, and 2, 2' are coil windings. In addition, the dotted line 4 shows the state of magnetic flux generation.As shown in the figure, the ferrite core electrode facing the surface to be measured is a knife edge, and the distance between the pair of knife edges is equal to the distance between the pair of electrodes. Since it is configured so that the distance between the blades is the minimum, magnetic flux is easily concentrated between the knife gills/parts, and efficiency can be increased. This glove uses two of these pair of electrodes to generate two pairs of magnetic flux, and the coils 2 and 2' are generally differentially coupled or / differentially coupled within the bridge circuit for bias detection or signal detection amplifier. FIG. 2(c) shows the distribution form of the magnetic flux 4 and eddy current 5 generated on the surface of the test material when the probe is placed. 6 is a surface flaw, and the eddy current 5 is perpendicular to the surface flaw 6. When the specimen 1 moves in the direction of the arrow, the flaw 6 passes under the probe, and as it passes through the flaw. This causes the coil impedance to become unbalanced, which is detected as a flaw signal.

Figure 3 shows a method for creating two pairs of differential magnetic fields with one coil. The magnetic poles are configured so that the part facing the surface of the material to be tested is a knife (6'), and the distance between the two pairs of magnetic poles centered on the central magnetic pole is minimized in that part, so that the part facing the surface of the material being tested is the knife. This is an extremely efficient configuration since no magnetic flux is generated. FIG. 3(,) shows a probe of the type in which a coil winding 2 is wound around the central ball of a three-pole ferrite core l, and is placed on a flat plate-shaped specimen 3. FIG. 3(b) is a view of the probe when viewed from the back side, 6D, 1 is a three-pole ferrite core, 2 is a coil winding, and the 40-dot line shows the distribution of magnetic flux between poles. As explained above, by using the configurations shown in Figures 2 and 3, the inventors conducted experiments and found that the absolute λ and J sensitivities were improved by about 5 to 7 times compared to the conventional case. Since the magnetic field is concentrated on the knife edge, the S/N ratio can be improved by about 3 to 5 times compared to the conventional one.

[Brief explanation of the drawing]

FIG. 1 shows an example of a conventional method, and (a) and (a') are diagrams showing the relationship between a circular eddy current globe, magnetic flux, eddy current, and flaws,
(b) and (b') are diagrams showing the relationship between a rectangular linear eddy current probe and its magnetic flux, eddy current, and flaws. Figure 2 shows an embodiment of the glove of the present invention, (,) is an overall perspective view, and (b)
(C) is a diagram showing the relationship between magnetic flux, eddy current and flaws, and Figure 3 is a diagram showing a small example of the pond of the present invention.
(a) is an overall perspective view, and (b) is a view of the probe viewed from the first side. 1. Ferrite core, 2, 2'... Coil winding, 3... Nuclear inspection, 4, 4'... Magnetic flux,
5,5'...Eddy current, fi, li'--Patent attorney representing the patent applicant for clothing defects Tomoyuki Yafuki (and one other person)

Claims (1)

[Claims] An eddy current deep field globe characterized by 4 ferrite core electrodes arranged so as to generate magnetic flux of 1@(=4sjO) to the surface of the material to be tested in the At probe.