JPS61264251A - Eddy current flaw inspecting method and its device - Google Patents

Abstract

PURPOSE:To perform eddy current flaw inspection effectively by allowing a material to be examined to pass the flaw detecting part of a rotating coil type eddy current flaw inspector to inspect flaws after giving an alternating magnetic field to the material to be examined, which passes through a degausser consisting of a through type coil, by this degausser to degauss it. CONSTITUTION:A material supply base 1 drops arranged and prepared bar materials to be examined onto a carrying device 2 horizontally at every specified time one by one. This device 2 has many rolls whose outside peripheral surfaces having V-shaped grooves are provided on, and dropped materials to be examined are carried in a uniform speed in the direction of an arrow. A degausser 4 consists of the through type coil and gives the alternating magnetic field to materials to be examined, which pass through the degausser 4, to degauss them. Materials to be examined after degaussing pass the inside of a flaw inspecting part 3 of the rotating coil type eddy current flaw inspector and flaws are inspected in this stage. Materials to be examined are dropped to a defective goods frame 5 or an indefectible goods frame 6 in accordance with the results.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rotating coil type eddy current flaw detection method and apparatus.

[Conventional technology]

In the eddy current flaw detection method, a magnetic field that changes over time, such as an alternating magnetic field, is applied to the test material, which is a conductor, to generate eddy currents in the test material.
This method takes advantage of the fact that this eddy current is affected by scratches or other defects on the material to be inspected, and usually a pair of coils are placed facing each other in two close locations on the material to be inspected, and each coil is placed oppositely in the opposite location. By detecting and comparing the eddy current in the part of the inspection material, or by using the excitation coil for inducing eddy current and the detection coil in common and comparing their impedances,
A method that detects non-uniformity, that is, defects, in the image area of the material to be inspected is generally adopted.

In addition, many eddy current flaw detection devices for test materials such as rods continuously run through the test material in the length direction thereof. Eddy current testing for bar materials is generally divided into two methods, each called a through-type method and a rotating coil-type method. The former is a pair of detection coils arranged coaxially and spaced apart from each other, and is passed through the material to be tested along its axis, while the latter is a sensor that is spaced apart in the circumferential direction of the material to be tested. Generally, a pair of detection coils, the axial direction of which is the radial direction of the specimen, are rotated at high speed around the outer peripheral surface of the specimen. The latter has recently become popular in place of the former because it is highly sensitive and has a small dead length at both ends of rod-shaped specimens.

[Problem that the invention seeks to solve]

Since the eddy current flaw detection method indirectly detects flaws in the material being tested, the same output (noise) as caused by flaws may be generated due to causes other than flaws.
They often make errors in judgment, so to speak. In particular, the rotating coil type is highly sensitive, and this error in judgment is common.

The present invention, by elucidating the cause of this judgment error,
It is an object of the present invention to provide a rotating coil type eddy current flaw detection method and device that eliminates this cause.

[Means to solve the problem]

The present invention provides a rotating coil type eddy current flaw detection method in which a material to be treated is demagnetized in advance prior to flaw detection, and a rotating coil type eddy current flaw detection device in which a demagnetizer is provided on the upstream side of the travel of the test material of a detection coil. .

[Effect]

The present inventor conducted various experiments to examine the causes of judgment errors in the rotating coil type eddy current flaw detection method. As a result, for bar materials made of ferromagnetic materials such as tool steel, approximately half of the cases that are determined to be defective due to causes other than scratches are due to weak magnetization that occurred during the previous process of the test material. I figured it out. The present invention is based on this elucidation result, and flaw detection is performed after demagnetization treatment.

In the conventional penetrating eddy current flaw detection method, magnetization of the test material does not cause judgment errors, and therefore there is no need to specifically demagnetize the test material. However, in the case of a rotating coil type, magnetization causes errors in judgment. The reason for this is unknown. However, it is thought that the bar to be tested probably vibrates due to bending during travel or due to the gap with the travel guide device, and also because the axis of the bar to be tested does not necessarily align with the rotation center axis of the detection coil due to assembly errors in the device. , etc. are possible. In other words, leakage magnetic flux is emitted from the test material due to magnetization, and if the detection coil rotates eccentrically around this at high speed, an electromotive force will be generated within the detection coil, and this electromotive force will cause the phase to be detected. Since it differs between coils, the comparison result is output. Incidentally, according to experiments conducted by the present inventors, if the test material is magnetized even when the test material stops running, noise is still generated. This phenomenon is not observed in the through-coil type.

〔Example〕

FIG. 1 shows the arrangement of an embodiment of the device of the present invention, and FIG. 2 shows an example of the arrangement of a conventional device. A material supply table 1 horizontally transports the lined and prepared test bars one by one at regular intervals to a conveying device 2.
drop it on top. The conveying device 2 has a large number of rollers having V-shaped grooves on the outer periphery, and conveys the dropped test material at a constant speed in the direction of the arrow.

The demagnetizer 4 is a penetrating coil, and applies an alternating magnetic field to the test material passing through it to demagnetize it. After demagnetization, the test material passes through the flaw detection section 3 of the rotating coil type eddy current flaw detection device, and is tested during this process. Depending on the results, the test material falls into the defective product frame 5 or the non-defective product frame 6, respectively? be given

The flaw detection section 3 is provided with guides with funnel-shaped openings at the front and rear.
In the middle, a pair of detection coils are arranged on each side of the cross, and the intersection of the cross is aligned with the axis of the material being tested and rotates at high speed. Signals are exchanged with the coils using a rotating transformer. It looks like this.

The conventional device was not provided with a demagnetizer 4, as shown in FIG. With conventional equipment, when testing a bar material that has been straight-stretched, straightened, and centerless ground from a coiled wire material such as annealed tool steel, about 36% of the material determined to be defective was found to be due to an unknown cause at the time. However, when the device shown in Figure 1 was used to demagnetize the materials, approximately 20 of the materials with unknown causes were discarded.
%. Therefore, about 16% of
This had the great effect of avoiding disposal. In addition, in the device of the present invention, the distance between the detection coil and the amount of demagnetization is 500 m due to the modification of the conventional device. At this distance, we are currently processing specimens with a length longer than the normal length of 1.5771, but the demagnetizer has no effect on the detection coil. It seems that the distance between these two coils can be further shortened.

〔Effect of the invention〕

As described above, the present invention is based on the discovery that, in the rotating coil type eddy current flaw detection method, about half of the causes of previously unknown flaws are due to magnetization of the test material. This has made it possible to salvage materials that were previously treated as defective products. Note that the present invention is also applicable to coil materials.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 show examples of the arrangement of rotating coil type eddy current flaw detection devices of the present invention and a conventional one, respectively. 1; material supply table, 2; conveyance device, 3; flaw detection section, 4; demagnetizer. Figure 1 Procedure amendment band (spontaneous) 1. Indication of the case 1985 Patent Application No. 105228 2. Name of the invention Eddy current flaw detection method and device 3. Person making the amendment Relationship with the case Patent applicant address Tokyo 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Name (508) Hitachi Metals Co., Ltd. Akira! Book II, page 2, line 13, ``excitation'' is corrected to ``excitation.''

Claims (1)

[Claims] 1. A test material, which is a long conductor with a circular cross section, is passed continuously in its length direction, and during the passage, the direction of the axis is set to the radius of the test material. A rotating coil type eddy current flaw detection method in which a detection coil with a direction is rotated around the outer peripheral surface of the test material, characterized in that the test material is demagnetized in advance prior to flaw detection. Eddy current flaw detection method. 2. A test material, which is a long conductive material with a circular cross section, is passed continuously in the length direction, and a detection coil whose axis is oriented in the radial direction of the test material is installed in the middle of the passage. , a rotating coil type eddy current flaw detection device that rotates around the outer peripheral surface of the test material, characterized in that a demagnetizer is provided on the upstream side of the movement of the test material of the detection coil. . 3. The eddy current flaw detection device according to claim 2, wherein the detection coil and the demagnetizer are separated by 550 mm or more.