JPS60247157A - Flaw detecting method and apparatus thereof - Google Patents

Abstract

PURPOSE:To detect a surface or internal flaw with high sensitivity, by providing an inspection coil to the surface of a material to be inspected in a separable manner to form a high static magnetic field to the material to be inspected and vibrating the inspection coil by the change in the static magnetic field when there is a flaw in the material to be inspected. CONSTITUTION:A slab 1 being a material to be inspected is fed to the longitudinal direction and N and S poles 2 are provided to both sides of said slab 1 in the lateral direction thereof to form a static magnetic field. An inspection coil 3 is suspended from a support material 5 by a coil spring 6 so as to be capable of being contacted with and separated from the slab 1. Then, a flaw is inspected by the inspection coil 3 while the slab 1 is fed. When the slab 1 has the flaw 14 at this time, disturbance is generated in the static magnetic field and an induction current is flowed to the inspection coil 3 which is, in turn, vibrated in the up-and-down direction by the Fleming's rule and the moving distance thereof is detected by a distance sensor 4. Because the static magnetic field of the material to be inspected is made high to detect the movement of the inspection coil, flaw detection can be performed with high sensitivity and lift-off can be made large.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a flaw detection method and apparatus for detecting flaws existing on the surface and under the skin of a magnetic material to be inspected. A completely new flaw detection method in which flaws are detected by forming a static magnetic field along this surface, and measuring the distance traveled by an inspection coil so that the static magnetic field changes when a flaw exists on the surface. This paper proposes a device to be used for its implementation. .

[Prior art]

A number of methods have been used to detect flaws on the surface and under the skin of inspected materials such as slabs and steel pipes, including the eddy current flaw detection method and the leakage magnetic flux flaw detection method. In all of these methods, flaws are detected by using a magnetic sensor to detect eddy currents and fluctuations in magnetic fields when flaws exist on the surface or under the skin of a material to be inspected.

In such conventional methods, in order to improve the detection sensitivity of the magnetic sensor, it is necessary to place the magnetic sensor as close to the material to be inspected as possible. However, since the material to be inspected vibrates during transportation, if the vibration is large, there is a risk that the material to be inspected will collide with the magnetic sensor and damage it. For this reason, there is a limit to how close the magnetic sensor can be to the material to be inspected, which has been a constraint on improving flaw detection sensitivity.

Therefore, as a method to prevent damage to the magnetic sensor and improve the detection sensitivity of the magnetic sensor, for example, the air gap distance (hereinafter referred to as lift-off) between the magnetic sensor and the material to be inspected is
There is a method in which a circuit for sensitivity compensation is provided in the signal processing system connected to the magnetic sensor in order to increase the detection sensitivity of the magnetic sensor and compensate for the decrease in detection sensitivity of the magnetic sensor.

However, when using such a method, there are restrictions in compensating for the decrease in detection sensitivity of the magnetic sensor due to reasons such as the complexity of the signal processing system, and there is a limit to increasing the lift-off.

[Purpose] The present invention has been made in view of the above circumstances, and includes an inspection coil that is movable towards and away from the surface of a material to be inspected,
In addition, a magnetizing means installed on the surface of the material to be inspected forms a static magnetic field along the surface of the material to be inspected at a portion of the surface facing the inspection coil, thereby causing defects on the surface and under the skin of the material to be inspected. This method detects defects by measuring the travel distance of the inspection coil caused by disturbances in the static magnetic field when a The purpose of the present invention is to provide a flaw detection method that is free from the risk of damage and equipment used to carry out the method.

[Structure of the invention]

In the flaw detection method according to the present invention, an inspection coil is provided so as to be movable toward and away from the surface of a material to be inspected, and a static magnetic field is formed along the surface of the surface of the material to be inspected at a portion facing the inspection coil. The present invention is characterized in that a flaw is detected by providing a magnetizing means to detect a flaw on the surface of a material to be inspected, and measuring the distance of movement of the inspection coil caused by disturbance of the static magnetic field when a flaw exists on the surface of a material to be inspected.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof.

FIG. 1 is a schematic front view of an apparatus used to carry out the flaw detection method according to the present invention.

In the drawing, numeral 1 indicates a slab, which is transported in the front and back directions of the drawing by a transport device (not shown). At a predetermined position in the transfer area of the slab 1, an electromagnet 2 is provided with a magnetic north pole and a south pole facing each other in the width direction of the slab 1, with the slab 1 passing between them. The electromagnet 2 is connected to a DC power supply 11, and when a DC current is passed from the DC power supply 11, a static magnetic field is formed in the surface layer of the slab 1 located directly below the electromagnet 2 in the direction of the width of the slab. Note that a permanent magnet may be provided instead of the electromagnet 2.

A support member 5 is provided above the electromagnet 2.

The support member 5 is moved in the width direction of the slab 1 by a drive means (not shown) for scanning in the width direction of the slab 1. The test coil 3 is suspended from the support member 5 so as to be vertically movable via a coil spring 6.6 with its axis perpendicular to the surface of the slab 1 and separated from the surface by an appropriate length.

A distance sensor 4 for measuring the distance to the test coil 3, such as an optical sensor, a microwave sensor, or an ultrasonic sensor, is provided on the lower surface of the support member 5 directly above the test coil 3. The measurement result of the distance sensor 4 is input to a comparator 13, which will be described later.

Now, in such a configuration, if a flaw 14 exists on the surface of the slab 1, magnetic flux leaks from the flaw 14 as shown by the broken line in the figure, and this leakage occurs before and after the flaw 14 passes directly under the inspection coil 3. The static magnetic field changes due to magnetic flux. An induced current flows in the test coil 3 due to the change in the horizontal component of the static magnetic field, and therefore, an electromagnetic force acts in the vertical direction according to Fleming's left hand rule. As a result, the test coil 3 vibrates in the vertical direction before and after that, as shown in FIG.

Therefore, the amplitude ΔL of this vibration (the gap distance LQ between the distance sensor 4 and the inspection coil 3 when there is no flaw 14 and the flaw 1
4) is measured by the distance sensor 4 and input to the comparator 13.

The comparator 13 has a threshold value ΔL that serves as a criterion for determining the presence or absence of a flaw 14.
If the opening is set and ΔL>ΔLo, it is assumed that a flaw 14 exists, and the alarm 15 is activated, and a predetermined signal is issued to a marking device (not shown).

In the case of the present invention as described above, the distance between the surface of the slab 1 and the inspection coil 3 becomes a lift-off, and the detection sensitivity can be increased by increasing the current flowing to the electromagnet 2, so it is possible to increase the lift-off. can. Also,
With this configuration, flaw detection can be performed with a simple configuration without requiring a circuit configuration for sensitivity compensation. Furthermore, if the vertical fluctuation of the slab 1 during transportation is detected by some means and this fluctuation is added to the measurement result of the distance sensor 4 as a correction amount, not only the presence or absence of a flaw but also its depth must be detected. I can do it.

In the above-described embodiments, the method of the present invention is applied to flaw detection of slabs, but it is of course applicable to flaw detection of other magnetic materials such as steel pipes.

〔effect〕

As described in detail above, the flaw detection method according to the present invention includes a test coil that is movable toward and away from the surface of the material to be inspected, and
A magnetizing means installed on the surface of the material to be inspected forms a static magnetic field along the surface of the material to be inspected at a portion facing the inspection coil, and detects the presence of flaws on the surface and under the skin of the material to be inspected. Since flaws are detected by measuring the distance traveled by the inspection coil due to disturbances in the static magnetic field when
By increasing the magnitude of the static magnetic field, detection sensitivity can be increased, which can increase lift-off.
The present invention has excellent effects such as stable flaw detection without the risk of accidents and no need for a complicated signal processing system.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a schematic front view of an apparatus used to carry out the method of the present invention, and FIG. 2 is a vibration waveform diagram of a test coil. ■... Slab 2... Electromagnet 3... Inspection coil 4... Distance sensor 6, 6... Coil spring patent
Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Noboru Kono $1 Figure 2

Claims (1)

[Claims] 1. An inspection coil is provided so as to be movable toward and away from the surface of the material to be inspected, and a static magnetic field is formed along the surface of the surface of the material to be inspected at a portion facing the inspection coil. and detects a flaw by measuring the distance of movement of the inspection coil caused by disturbance of the static magnetic field when a flaw exists on the surface or under the skin of the material to be inspected. flaw detection method. 2. An inspection coil that is movable toward and away from the surface of the material to be inspected; a magnetizing means that forms a static magnetic field along the surface of the material to be inspected; A flaw detection device comprising: a distance meter for measuring the separation dimension of the flaw detection device.