JPH0815227A - Magnetizing device for steel plate - Google Patents

Abstract

PURPOSE:To provide a magnetizing device for a steel plate, by which an unnecessary floating magnetic field can be restrained without installing a special magnetizing device for restraining a floating magnetic field so as to magnetic-saturate a steel plate uniformly in the cross direction thereof. CONSTITUTION:Two magnetic poles 12 are erected in the cross direction of a steel plate 11 at a designated space between them. The upper ends of the magnetic poles 12 are connected to each other by a yoke 13. A magnetizing coil 14 for magnetizing two magnetic poles 12 to be N-pole and S-pole and magnetizing the steel plate 11 in the cross direction is wound round the yoke 13. A ferromagnetic plate 15 is disposed close to the steel plate 11 between two magnetic poles 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetizing device used in a leakage magnetic flux flaw detection method for detecting defects in a steel sheet.

[0002]

2. Description of the Related Art There is a leakage magnetic flux flaw detection method as a method for detecting defects in a steel sheet continuously produced at a speed of several meters per second such as a steel sheet used for an automobile body. In this method, a steel sheet is magnetized until it is magnetically saturated, and a magnetic flux leaking due to the presence of defects is detected by a magnetic sensor.

By the way, as shown in FIG. 5, the magnetizing device used in the conventional leakage magnetic flux flaw detection method has a magnetizing coil 1 as shown in FIG.
The two magnetic poles 2 wound around are installed opposite to each other on the same line, the two magnetic poles 2 are magnetized to the N pole and the S pole, respectively, and the lower ends of these two magnetic poles 2 are connected by the yoke 3. It is generally configured to apply a magnetic field in the width direction of the steel plate 4.

In such a magnetizing device, a magnetic closed circuit is formed by the two magnetic poles 2 around which the magnetizing coil 1 is wound, the yoke 3 and the steel plate 4. However, in this case, since it is necessary to maintain a certain distance between the magnetic pole 2 and the steel plate 4, the magnetic resistance becomes large, and the magnetic force line distribution flowing from the magnetic pole 2 to the steel plate 4 or in the opposite direction is as shown in FIG. ,
Since the magnetic field has a spread near the magnetic pole 2, as shown in FIG. 7, the magnetic field has a vertical component or a horizontal component along the magnetization direction (hereinafter, this magnetic field is referred to as a “stray magnetic field”).
That).

In the leakage magnetic flux flaw detection, a magnetic sensor generally detects a vertical component or a horizontal component of a defect leakage magnetic field, but each magnetic sensor has a detection characteristic and the detectable magnetic field range is, for example, ± 100 (Gauss). Since there is a limit, for example, in the case of FIG. 7, it is impossible to detect a leakage magnetic field when a stray magnetic field exceeding the detectable magnetic field range (0 to 100 Gauss) near the magnetic field is generated.

Therefore, in Japanese Patent Laid-Open No. 50-138399, a roller 5 rolling on one surface of a steel plate 4 to be inspected is used.
A pair of magnetic poles 2 connected to each other by a yoke 3 on its axis, and these magnetic poles 2 contact the steel plate 4 via a thin-walled cylindrical non-magnetic body 6 constituting a roller 5. An apparatus for magnetizing the steel plate 4 by forming a magnetic closed circuit including the steel plate 4 in part is disclosed (see FIG. 8).

However, JP-A-50-138399
In the magnetizing device disclosed in the publication, it is impossible to suppress unnecessary stray magnetic fields other than the stray magnetic field due to defects that occur in the steel plate, so the stray magnetic field adversely affects the flaw detection signal, and There is a problem that the detection characteristic is saturated and a defect signal cannot be obtained.

A device that solves the drawbacks of the magnetizing device disclosed in Japanese Patent Laid-Open No. 50-138399 and can suppress an unnecessary stray magnetic field in a state where the steel sheet is magnetically saturated is, for example, 1
It is shown on pages 57 to 62 of "Iron Making Research No. 339" issued in 990. FIG. 9 is a front view schematically showing this device, and the magnetic pole 2 of the stray magnetic field suppressing magnetizing device is spaced above the tip of the magnetic pole 2 of the magnetizing device similar to the device shown in FIG. It is installed such that the lower ends of the are opposed to each other. In FIG. 9, the same parts as those in FIG. 5 are designated by the same reference numerals.

That is, in the apparatus shown in FIG. 9, a stray magnetic field suppressing magnetizing device having a magnetizing force equivalent to that of the magnetizing device is installed so as to face each other in the vertical direction to magnetically saturate the steel plate 4, and The stray magnetic field from the magnetic device is canceled by the stray magnetic field suppressing magnetizing device to suppress an unnecessary stray magnetic field.

[0010]

However, in the case where the stray magnetic field suppressing magnetizing device having the same magnetizing force as that of the magnetizing device as shown in FIG. 9 is installed so as to face each other in the vertical direction, two magnetizers are used. Therefore, the equipment cost becomes high, and a large space for installing the stray magnetic field suppressing magnetizing device is required above the steel plate.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to suppress an unnecessary stray magnetic field without the need for a separate stray magnetic field suppressing magnetizing device, and moreover, in the width direction of the steel sheet. It is an object of the present invention to provide a magnetizing device for a steel sheet that can be uniformly magnetically saturated.

[0012]

In order to achieve the above-mentioned object, a magnetizing device for a steel sheet according to the present invention comprises two magnetic poles standing upright in the width direction of the steel sheet with a predetermined space therebetween.
A yoke that connects these magnetic poles, a magnetizing coil that magnetizes the two magnetic poles to N and S poles to magnetize the steel sheet in the width direction, and a strong coil that is arranged between the two magnetic poles and is close to the steel sheet. It is equipped with a magnetic plate.

[0013]

The magnetizing device for a steel sheet according to the present invention comprises two magnetic poles standing upright in the width direction of the steel sheet with a predetermined space between them.
A yoke that connects these magnetic poles, a magnetizing coil that magnetizes the two magnetic poles to N and S poles to magnetize the steel sheet in the width direction, and a strong coil that is arranged between the two magnetic poles and is close to the steel sheet. The magnetic circuit includes two magnetic poles, a yoke and a steel plate, and a magnetic circuit including two magnetic poles, a yoke and a ferromagnetic plate. Two magnetic circuits will be formed, and the stray magnetic field that was flowing from one magnetic pole to the steel plate with a spread will flow to the other magnetic pole through the magnetic circuit that partially contains the ferromagnetic plate. Therefore, unnecessary stray magnetic field generated in the space above the steel plate can be suppressed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A steel plate magnetizing apparatus according to the present invention will be described below with reference to one embodiment shown in FIGS. FIG. 1 is a front view showing a schematic configuration of a magnetizing apparatus for a steel sheet of the present invention, and FIG. 2 is a perspective view showing a schematic configuration of a magnetizing apparatus for a steel sheet of the present invention.

In FIGS. 1 and 2, reference numeral 11 denotes a steel plate which is a target of the defect inspection, and in FIG. 12 stands upright at a predetermined interval in the width direction of the steel plate 11, for example 50 to 150 mm.
There are two magnetic poles, and the upper ends of these magnetic poles 12 are connected by a yoke 13. Reference numeral 14 is a magnetizing coil wound around the yoke 13. By passing a current through the magnetizing coil 14, one magnetic pole 12 is magnetized to the N pole and the other magnetic pole is magnetized to the S pole, and the steel plate 11 is magnetized. It is magnetized in the width direction.

Reference numeral 15 denotes a steel plate 11 between the two magnetic poles 12.
Is a ferromagnetic plate closely arranged at a distance of, for example, 5 to 40 mm, for example, iron having a thickness of 0.5 to 10 mm,
Plates of nickel and cobalt are used. This ferromagnetic plate 1
5 has a width substantially the same as the distance between the two magnetic poles 12,
The length in the magnetization direction varies depending on the magnetized range, but it is set to be substantially the same as the magnetized range. In addition, this ferromagnetic plate 1
As a method of holding the steel sheet 5, for example, as shown in FIG. 2, the steel plate 11 can be formed on the sensor holding device 17 that holds the magnetic sensor group 16 or by incorporating it in the sensor holding device 17.
It is possible to appropriately change the distance between the and the ferromagnetic plate 15.

As described above, in the steel plate magnetizing apparatus of the present invention in which the ferromagnetic plate 15 is disposed, one of the magnetic poles including the two magnetic poles 12, the yoke 13 and the steel plate 11 is included in the magnetic circuit. The stray magnetic field flowing from the magnetic pole 12 to the steel plate 11 in a spread state is generated by the two magnetic poles 12, the yoke 13 and the ferromagnetic plate 1.
The other magnetic pole 12 passes through a magnetic circuit including 5 as a part.
And the unwanted stray magnetic field can be suppressed.

For example, in FIG. 3, when magnetizing a range of 150 mm, the thickness is 1.2 mm and the length in the magnetizing direction is 15 mm.
In a device of the present invention in which a 0 mm ferromagnetic plate (made of iron) is installed in a sensor holding device and installed at a position of 10 mm on a steel plate, and in a conventional device in which no ferromagnetic plate is installed, a stray magnetic field generated on the steel plate is measured by a Gauss meter. It is a figure which shows the result of having measured and compared the distribution state.

The horizontal axis of FIG. 3 is the distance from the center of the two magnetic poles, and the vertical axis is the vertical component (Oe) of the stray magnetic field generated at the position of 0.5 mm on the steel plate at each position. 3 shows the result when the device of the present invention was used, and ● shows the result when the conventional device was used. It can be seen from FIG. 3 that in the device of the present invention, the stray magnetic field can be generally suppressed from the center between the two magnetic poles to the magnetic poles, and can be greatly suppressed particularly in the portion close to the magnetic poles.

FIG. 4 shows the distribution state of the stray magnetic field when the thickness of the steel sheet to be inspected is changed by the Gauss meter as in the case of FIG. 3 when the apparatus of the present invention same as that of FIG. 3 is used. It is a figure which shows the result of having compared. FIG.
From this, it can be seen that the distribution of the stray magnetic field hardly changes even if the thickness of the steel sheet changes. From this, it is clear that the stray magnetic field can be suppressed regardless of the thickness of the steel sheet.

[0021]

As described above, the magnetizing apparatus for a steel sheet according to the present invention disposes the two magnetic poles, the yoke and the steel sheet in part by disposing the ferromagnetic plate between the two magnetic poles in the vicinity of the steel sheet. A magnetic circuit including two magnetic poles and a magnetic circuit including two magnetic poles and a yoke and a ferromagnetic plate as a part, and the stray magnetic field flowing from one magnetic pole to the steel sheet with a spread, Since it passes through a magnetic circuit that includes a ferromagnetic plate in one part and flows to the other magnetic pole, it is possible to suppress unnecessary stray magnetic fields generated in the space above the steel plate without separately installing a magnetizing device for suppressing stray magnetic fields. The defect of the steel sheet can be detected with high sensitivity.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of a magnetizing device for a steel sheet of the present invention.

FIG. 2 is a perspective view showing a schematic configuration of a magnetizing device for a steel sheet of the present invention.

FIG. 3 is a diagram showing the results of comparing stray magnetic fields generated on a steel sheet with a Gauss meter and comparing their distributions when the device of the present invention and a conventional device are used.

FIG. 4 is a graph showing a stray magnetic field when a thickness of a steel sheet is changed, measured by a Gauss meter, when the device of the present invention is used,
It is a figure which shows the result of having compared the distribution state.

FIG. 5 is a front view showing a schematic configuration of a conventional device.

FIG. 6 is a diagram showing lines of magnetic force flowing from a magnetic pole to a steel plate when a conventional device is used.

FIG. 7 is a diagram showing a distribution of a stray magnetic field when a conventional device is used.

FIG. 8 is an explanatory diagram of an apparatus disclosed in Japanese Patent Laid-Open No. 50-138399.

[Fig. 9] No. 5 "Ironmaking Research No. 339" issued in 1990
FIG. 6 is an illustration of the device disclosed on pages 7-62.

[Explanation of symbols]

 11 Steel Plate 12 Magnetic Pole 13 Yoke 14 Magnetizing Coil 15 Ferromagnetic Plate

Claims (1)

[Claims] 1. A pair of magnetic poles standing upright in the width direction of a steel sheet with a predetermined space therebetween, a yoke connecting these magnetic poles, and the two magnetic poles being magnetized into N poles and S poles. A magnetizing device for a steel sheet, comprising: a magnetizing coil for magnetizing the steel sheet in the width direction; and a ferromagnetic plate disposed between the two magnetic poles and close to the steel sheet.