JPH06123730A - Continuous demagnetization / magnetic flaw detection method and device - Google Patents

Abstract

(57) [Summary] [Purpose] Demagnetization of magnetic materials and magnetic flaw detection are performed continuously. [Composition] Demagnetization by a polarity reversal magnetic field is started from a magnetic field strength higher than the magnetic field strength capable of performing the magnetization necessary for magnetic flaw detection, and the magnetic field strength at which the magnetization necessary for magnetic flaw detection can be performed is reduced during demagnetization. Magnetic flaw detection is performed, and after completion of magnetic flaw detection, demagnetization is performed by a polarity reversal magnetic field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel continuous demagnetization / magnetic flaw detection method and apparatus capable of demagnetizing a magnetic material and performing magnetic flaw detection substantially at the same time.

[0002]

2. Description of the Related Art A magnetic material, such as steel, is magnetized by a magnetic force such as a lifting magnet, an electric current flows, or a magnetic material passing near the magnetization due to a large current in the manufacturing process or the conveying process. In many cases, residual magnetism remains due to contact with something. If this residual magnetism is strong, problems such as magnetic blow due to subsequent arc welding and adhesion of cutting chips due to processing are harmful, which is harmful. Therefore, the harmful magnetic field is reduced in the degaussing process.

Specifically, the strength of the magnetic field is made higher than that of the remanent magnetism or the normal saturation magnetic field, and the polarity thereof is reversed and attenuated to remove unnecessary magnetism remaining in the magnetic material.
For magnetic field polarity reversal attenuation, reverse the polarity of the current,
The current value may be lowered or the material to be treated may be gradually moved away from the reversed magnetic field. When alternating current is used, the material to be processed is kept away from the magnetic field, and when direct current is used, the current value is lowered while reversing the polarity. In the case of degaussing a long material to be processed with a direct current, demagnetization is performed by combining the above operation and the gradual processing of the material to be processed.

This degaussing technique is disclosed in, for example, Japanese Patent Laid-Open No. 59-6.
3708, the residual magnetic polarity of the steel sheet is detected at a plurality of arbitrary positions in advance, and the direction of the first current flowing through the demagnetizing (degaussing) coil for the steel sheet is determined according to the result, and the induction voltage regulator is driven. Demagnetizing method of a steel plate in which the magnitude of demagnetizing current and demagnetizing time are controlled by changing the speed of the motor for motor, and the method of controlling the thickness or the radial direction of the steel material described in JP-A-48-61317. As described above, there is a continuous degaussing method for steel materials in which alternating magnetic poles are provided relative to each other and the steel material is demagnetized while being moved between the paired installations.

On the other hand, as one of the methods of nondestructively evaluating the quality of the surface of a steel material and the surface immediately below the surface, magnetic flaw detection methods including eddy current flaw detection and magnetic particle flaw detection (hereinafter, magnetic flaw detection includes magnetic particle flaw detection). is there.

This magnetic flaw detection is generally performed in a magnetic material having a high residual magnetism by once magnetizing to a saturation magnetic field and then performing flaw detection by the residual magnetism. A magnetic steel material having a weak residual magnetism is subjected to flaw detection while applying a magnetic field of about 80% of the saturation magnetic field. Here, the reason why the 80% magnetic field is widely applied is that the magnetic field strength is sufficient to detect the target defect in the magnetic flaw detection. When a saturation magnetic field is applied, a magnetic discontinuity that is not a defect appears as an image and becomes noise, which makes it difficult to detect a defect. Therefore, depending on the condition of the material to be processed, the level of the target defect, and the combination of the detection means, for example, 5
Other values such as 0% may be used.

A technique for automatically performing this magnetic flaw detection is disclosed in Japanese Patent Laid-Open No. 3246464/1993, in which a coil wound around a ferromagnetic core and a fixed frequency and a constant voltage are applied to the coil through a fixed impedance. AC power supply means for supplying the AC power, DC voltage detection means for detecting the positive voltage and negative voltage of the voltage output from both ends of the coil, and the positive voltage detected by the DC voltage detection means. A flaw detection device for a steel plate having a plurality of magnetic sensors including a magnetic detection means for calculating the difference between negative side voltages and detecting the strength of a magnetic field, and a flaw detection material disclosed in JP-A-51-131685. The timing generator that detects the transfer position detects the transfer length of the material to be inspected, and transmits the operation timing signal to the displacement detector, the side edge flaw detector, and the intermediate flaw detector, which are provided subsequently, and Displacement detectors divided in the width direction of the flaw detection material constantly detect the separated displacement state of the flaw detection material, and the detected amount is compared with the set allowable displacement amount determined by the characteristics of the flaw detection device. If within displacement,
There is a flaw detection device for a moving object in which a flaw detector is placed at a flaw detection position for flaw detection, and when the flaw detection is outside the allowable displacement, the moving object is retracted from the flaw detection position.

[0008]

However, in the past, degaussing and magnetic flaw detection were conventionally performed in different facilities or at different times. Therefore, although demagnetization and magnetic flaw detection are the same operation in which a magnetic field is applied to the material to be processed, the work itself is performed in two steps, resulting in a large economical loss.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to provide a continuous demagnetization / magnetic flaw detection method and apparatus capable of continuously performing demagnetization and magnetic flaw detection. And

[0010]

According to the present invention, when degaussing a magnetic material and performing magnetic flaw detection, a polarity reversal magnetic field of a direct current or an alternating current is applied from a magnetic field having a magnetic field strength higher than the magnetic field strength required for magnetization required for magnetic flaw detection. Degaussing is started, and in the middle of degaussing, the magnetic field is gradually reduced to the strength of the magnetic field capable of performing the magnetization required for magnetic flaw detection, and then magnetic flaw detection is performed.After the magnetic flaw detection is completed, demagnetization is performed with a DC or AC polarity reversal magnetic field. Thus, the above-mentioned object is achieved.

Further, when the magnetic field becomes a magnetic field suitable for magnetic flaw detection, the reversal of the magnetic field is stopped, and the DC or AC magnetic field at that time is maintained for the time required for magnetic flaw detection.

Further, the demagnetization is started from the strength of the magnetic field of the saturation magnetization, and the magnetic flaw detection is carried out with the strength of the magnetic field giving the magnetization of about 80% thereof.

According to the present invention, when demagnetizing a magnetic material and performing magnetic flaw detection, a magnetic field is cut off after applying a saturation magnetic field to the material to be processed, magnetic flaw detection is performed by residual magnetism, and after completion of magnetic flaw detection, the magnetic flaw detection is performed again. The object is achieved by applying a saturation magnetic field to the material to be processed and demagnetizing it while reversing the polarity of the magnetic field.

The present invention is also an apparatus for demagnetizing a magnetic material and for magnetic flaw detection, wherein the magnetic field forming means for forming a DC or AC polarity reversal magnetic field having a constant strength and the material to be treated are the magnetic field forming means. The above object is achieved by providing a transporting unit that gradually moves away from a location through a location of a magnetic flaw detection compatible magnetic field that gives magnetization necessary for magnetic flaw detection, and a unit that performs magnetic flaw detection at the location of the magnetic flaw detection compatible magnetic field. It was done.

The present invention also provides a through-type magnetizing coil for forming a DC or AC polarity reversal magnetic field having a constant strength, its magnetizing power source, and a material to be treated in an apparatus for demagnetizing a magnetic material and magnetic flaw detection. A transporting device that transports on a transport path that passes through the through-type magnetizing coil, and a position that is separated from the through-type magnetizing coil by a predetermined distance across the transport path.
Leakage magnetic flux detection means for magnetic flaw detection, a conveyance amount sensor that detects the conveyance amount of the material to be processed, and the widthwise flaw detection result of the material to be processed by the leakage magnetic flux detection means are recorded in synchronization with the output of the conveyance amount sensor. The above-described object is achieved by including a recording device that controls the above-described components and a control device that controls each of the components.

Further, the leakage magnetic flux detecting means is an array type in which a large number of elements are arranged in parallel over the entire width of the material to be processed, and magnetic flaw detection is performed without interrupting the degaussing work by the through type magnetizing coil. It was possible.

[0017]

The present invention achieves degaussing and magnetic flaw detection continuously by utilizing the initial magnetization common to degaussing and magnetic flaw detection to perform magnetic flaw detection in the initial stage of degaussing or in the middle of degaussing and then degaussing. That is, by applying a magnetic field up to the saturation magnetization value of a magnetic material, for example, a steel material, and then reversing the polarity, using a magnetizing device having a degaussing function capable of attenuating the strength of the magnetic field, Causes magnetic flaw detection after a saturated magnetic field is applied. In general ordinary materials, the magnetic field strength is maintained during magnetic flaw detection at about 80% of the saturation magnetization, and after magnetic flaw detection is completed, polarity inversion continues. While achieving demagnetization.

These concepts will be described with reference to the drawings.

FIG. 1 shows the magnetic hysteresis curve of steel material, and FIG. 2 shows the demagnetization curve. FIG. 3A shows an example of attenuation of the degaussing current by an alternating current, and FIG. 3B shows an example of attenuation of the degaussing current by a direct current. 3 (A) and (B)
It can be achieved by either decreasing the current while reversing the polarity or gradually moving the material to be processed away from the magnetic field having a constant value of the polarity reversal current.

FIG. 4 and FIG. 5 show a combination of magnetic flaw detection and demagnetization by a direct current by continuous magnetization according to the present invention. In demagnetization, the polarity is reversed from the saturation magnetic field to reduce the current value, or the material to be treated is demagnetized. This is achieved by keeping the field away from the magnetic field. At this time, the current is kept constant at about 80% of the saturation magnetic field for the time T1 required for magnetic flaw detection. If an array-type sensor that can simultaneously detect the leakage flux in the width direction of the material to be processed is used as the leakage flux sensor for magnetic flaw detection, the magnetic field retention time in the normal degaussing process
During the time t, the magnetic flux flaw detection can be completed and the magnetic flaw detection can be performed without interrupting the degaussing work. The same applies when an alternating current is used.

Further, in the case of demagnetization in which the material to be processed is moved away from the magnetic field, magnetic flaw detection is performed at a location of about 80% of the saturation magnetic field.

FIGS. 6 and 7 show a method in which magnetic flaw detection by the residual method and demagnetization are combined. After applying a saturation magnetic field, the current is cut off for a time T2 at that position to perform magnetic flaw detection. This is a method of returning to the saturation current again, reversing the polarity, and demagnetizing. The material to be processed is subjected to magnetic flaw detection and pitch feeding by the demagnetization width.

FIG. 8 shows the measurement result of the DC polarity reversal decay magnetic field for carrying out the present invention. According to this measurement result, when the central magnetic field of the penetrating magnetization coil 20 which is the magnetic field forming means is set to 100, the magnetic field is located at the position L of the magnetic field required for continuous magnetization (about 80% of the saturation magnetic field) suitable for magnetic flaw detection. A magnetic flaw detection sensor may be provided. In FIG. 8, 10 is a material to be treated, and 12 is a conveying roller for the material to be treated.

[0024]

Embodiments of the present invention will now be described in detail with reference to the drawings.

In the first embodiment of the present invention, as shown in FIGS. 9 and 10, a degaussing through-type magnetizing coil 20 for forming a DC polarity reversal magnetic field having a constant strength, a DC power source for magnetizing the magnetizing power source (hereinafter, magnetizing power source). 22) and its controller 23, and the thick plate 14 that is the material to be processed on the conveying path that passes through the inside of the through-type magnetizing coil 20, the driving roller 24, and for driving the driving roller 24. Of the motor 25, its controller (transport controller) 26 and an idle roller 28, and an array type leak disposed across the transport path at a position separated from the feed-through magnetizing coil 20 by a predetermined distance. A magnetic flux sensor 30 and an encoder (not shown) incorporated in the drive motor 25 for detecting the amount X of conveyance of the thick plate 14 from the amount of rotation of the conveyance roller drive motor 25,
The leakage magnetic flux sensor 30 is synchronized with the encoder output.
A recording device 32 for recording the flaw detection result in the width direction (Y direction) of the thick plate 14 and a control device 3 for controlling the above-mentioned respective components.
4 and.

In the leakage magnetic flux sensor 30, a large number of Hall elements are arranged side by side over the entire width of the plate thickness 14.

The operation of the embodiment will be described below.

The thick plate 14 is passed by a driving roller 24 and an idle roller 28 made of stainless steel, which is a non-magnetic material, for example. When the thick plate 14 passes through the degaussing place where the magnetizing coil 20 is arranged, by reversing the polarity, degaussing is performed while moving away from the degaussing place.

The magnetic flux flaw detection is performed by detecting the leakage magnetic flux from the defective portion of the thick plate 14 by the leakage magnetic flux sensor 30 at the magnetic flaw detection position of the thick plate 14 provided at a position of about 80% of the saturation magnetic field. .

Furthermore, when the degaussing portion of the thick plate 14 reaches a sufficient distance, the degaussing effect can be confirmed by, for example, a Gauss meter (not shown).

These results are recorded in the storage device 32.

In this embodiment, the leakage magnetic flux sensor 30 is used.
Since the array type sensor is used as
The widthwise leakage flux of the thick plate 14 can be detected during the polarity inversion period of 0 (t in FIG. 4). Therefore, the magnetic flaw detection can be performed in accordance with the normal degaussing operation without specially controlling the magnetizing coil 20 for the magnetic flaw detection.

In the first embodiment, the magnetizing coil 20 for degaussing has 60 turns and the initial energizing current is 560A. For magnetic flaw detection, SMD elements of about 2 mm were arranged vertically in the width direction. The thick plate 14 was passed at 4 m / min, and the direct current was passed while the polarity was reversed at the above current value. As a result, 1
The initial remanence of the 8 × 4000 × 10000 mm thick plate 14 was 80 gauss, but decreased to 35 gauss, and the leakage magnetic flux sensor 30 was used to extend the width direction from the front and back surfaces of the thick plate to a surface having a length of 3 mm or more. And, the defect just below the surface could be detected.

The type of the leakage magnetic flux sensor is not limited to the array type, and, for example, as in the second embodiment shown in FIG.
The mechanical scanning mechanism 40 allows a single leakage flux sensor 42.
A width-direction scanning type leakage magnetic flux sensor that scans in the width direction of the thick plate 14 may be used.

In the second embodiment, if necessary, as shown in FIG. 4, the conveyance of the thick plate 14 is stopped until the widthwise scanning is completed (T in FIG. 4), and the magnetizing coil is stopped. Two
It is necessary to stop the reversal of the 0 magnetic field.

In each of the above embodiments,
Although the leakage magnetic flux sensor was used as the magnetic flaw detection sensor, the type of the magnetic flaw detection sensor is not limited to this. For example, when magnetic powder is used, an imaging sensor that captures a magnetic powder indication pattern due to a defect can be used. .

In each of the above embodiments, the present invention was applied to the treatment of thick plates, but the scope of application of the present invention is not limited to this, and other steel materials and general magnetic materials are also applicable. Clearly, the same applies.

[0038]

As described above, according to the present invention, magnetic flaw detection including demagnetization and magnetic particle flaw detection can be performed by a single passage of the material to be treated, and the effects of both can be sufficiently achieved. Effect is immeasurable.

Further, according to the apparatus of the present invention, degaussing or magnetic flaw detection can be performed independently.

[Brief description of drawings]

FIG. 1 is a diagram showing a magnetic hysteresis curve of a steel material.

FIG. 2 is a diagram showing the same degaussing curve.

FIG. 3 is a diagram showing a comparison example of attenuation of degaussing current in the case of AC degaussing and the case of DC degaussing.

FIG. 4 is a diagram showing an example of decay of a degaussing current in the case of combining magnetic flaw detection by continuous magnetization and degaussing for explaining the principle of the present invention.

FIG. 5 is a diagram showing the same degaussing pattern.

FIG. 6 is a diagram showing an example of attenuation of the degaussing current when the magnetic flaw detection by the residual method and the degaussing are combined according to the present invention.

FIG. 7 is a diagram showing the same degaussing pattern.

FIG. 8 is a diagram showing an example of the relationship between the position of the magnetizing coil and the magnetic field suitable for magnetic flaw detection according to the present invention.

FIG. 9 is a plan view, including a partial block diagram, showing the configuration of a first embodiment of a continuous degaussing / magnetic flaw detector according to the present invention.

FIG. 10 is a front view of the same.

FIG. 11 is a plan view showing a widthwise scanning type leakage magnetic flux sensor used in a second embodiment of the present invention.

[Explanation of symbols]

 14 ... Thick plate (material to be processed) 20 ... Penetrating magnetizing coil 22 ... Magnetizing power supply 24 ... Driving roller 26 ... Conveyance control device 30 ... Array type leakage magnetic flux sensor X ... Conveyance amount Y ... Width direction position 32 ... Recording device 34 ... Controller 40 ... Mechanical scanning mechanism 42 ... Leakage magnetic flux sensor

Claims (7)

[Claims] 1. A method for continuously performing degaussing of a magnetic material and magnetic flaw detection, wherein degaussing is initiated by a polarity reversal magnetic field from a magnetic field having a magnetic field strength equal to or higher than a magnetic field capable of performing magnetization necessary for magnetic flaw detection. A continuous demagnetization / magnetic flaw detection method characterized by performing magnetic flaw detection at a point where the magnetic field strength is reduced to a level capable of performing the magnetization required for magnetic flaw detection, and then performing demagnetization by a polarity reversal magnetic field after the magnetic flaw detection is completed. 2. The magnetic field according to claim 1, wherein when the magnetic field becomes a magnetic flaw-adapted magnetic field, the reversal of the magnetic field is stopped, and the magnetic field at that time is maintained only for the time required for the magnetic flaw detection. Continuous demagnetization / magnetic flaw detection method. 3. The continuous method according to claim 1 or 2, wherein the demagnetization is started from the strength of the magnetic field of saturation magnetization, and the magnetic flaw detection is performed with the strength of the magnetic field that gives a magnetization of about 80% thereof. Degaussing and magnetic flaw detection methods. 4. A method for continuously performing demagnetization of a magnetic material and magnetic flaw detection, which comprises applying a saturation magnetic field to a material to be treated, turning off the magnetic field, and performing magnetic flaw detection by residual magnetism, after completion of magnetic flaw detection. The continuous demagnetization / magnetic flaw detection method is characterized in that a saturation magnetic field is applied to the material to be treated again, and then the polarity of the magnetic field is reversed to demagnetize the material. 5. A device for continuously demagnetizing a magnetic material and magnetic flaw detection, comprising: a magnetic field forming means for forming a polarity reversal magnetic field having a constant strength; and a material to be treated from a location of the magnetic field forming means. Continuous degaussing characterized by comprising: a transporting unit that gradually moves away from a magnetic flaw detection compatible magnetic field that gives magnetization necessary for magnetic flaw detection, and a unit that performs magnetic flaw detection at the magnetic flaw compatible magnetic field location. Magnetic flaw detector. 6. An apparatus for continuously performing demagnetization of a magnetic material and magnetic flaw detection, comprising: a through-type magnetizing coil for forming a polarity reversal magnetic field having a constant strength, a magnetizing power source thereof, and a material to be treated, A conveying device that conveys on a conveying path that passes through the magnetizing coil, a leakage magnetic flux detecting means for magnetic flaw detection, which is arranged at a position separated from the penetrating magnetizing coil by a predetermined distance and across the conveying path, and a material to be processed. A conveyance amount sensor that detects the conveyance amount of the workpiece, a recording device that records the flaw detection result in the width direction of the material to be processed by the leakage magnetic flux detection unit in synchronization with the output of the conveyance amount sensor, and a control that controls each of the components A continuous degaussing / magnetic flaw detector equipped with a device. 7. The leakage magnetic flux detecting means according to claim 6, wherein the leakage magnetic flux detecting means is an array type in which a large number of elements are arranged in parallel over the entire width of the material to be processed, and the degaussing work by the through type magnetizing coil is interrupted. A continuous degaussing / magnetic flaw detector that is capable of magnetic flaw detection without any damage.