JP2897283B2 - Calibration method and apparatus for magnetic flaw detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic flaw detector which detects a defect existing in a steel sheet by generating a magnetic field in the steel sheet and detecting a leakage magnetic flux with a linear magnetic sensor. And a calibration device for the same.

[Prior Art] A magnetic flaw detector that detects defects such as flaws and bubbles existing inside or on the surface of a steel sheet by using magnetism is performed by a magnetic flaw detector while a steel sheet as a body to be flawed is stationary. It was necessary to detect the presence or absence of a defect at each position by moving the steel sheet over the entire surface. However, a magnetic flaw detection device that can continuously detect defects existing in the entire width of a thin steel strip running at a constant speed is built into a linear magnetic sensor that has a magnetically sensitive element that detects magnetic flux arranged linearly. It has been proposed (Japanese Utility Model Application Laid-Open No. 63-107849).

FIG. 3 is a diagram showing a magnetic flaw detector for continuously detecting the above-described defect of the running thin steel strip, and FIGS.
Are schematic cross-sectional views as seen from different directions.

In the figure, reference numeral 1 denotes a hollow roll formed of a non-magnetic material,
One end of a fixed shaft 2 penetrates the center shaft of the hollow roll 1. The other end of the fixed shaft 2 is fixed to a frame of a building (not shown). And the fixed shaft 2 is the hollow roll 1
The hollow roll 1 is supported on the inner peripheral surfaces at both ends by a pair of rolling bearings 3a and 3b so as to be positioned at the center axis of the hollow roll 1.
Therefore, the hollow roll 1 freely rotates about the fixed shaft 2 as a rotation center axis.

In this hollow roll 1, a magnetized iron core 4 a having a substantially U-shaped cross section is fixed to a fixed shaft 2 via a support member 5 with each free end approaching the inner peripheral surface of the hollow roll 1. ing. A magnetization coil 4b is wound around the magnetization core 4a. Therefore, the magnetizer 4 is constituted by the magnetized iron core 4a and the magnetized coil 4b. A linear magnetic sensor 7 in which a plurality of magnetically sensitive elements are linearly arranged in the axial direction between the free ends of the magnetized iron core 4a is also fixed to the fixed shaft 2.

A power supply cable 8 for supplying an exciting current to the magnetizing coil 4b and a signal cable 9 for extracting a detection signal output from the linear magnetic sensor 7 are led out through the fixed shaft 2 to the outside. Therefore, the positions of the magnetizer 4 and the linear magnetic sensor 7 are fixed, and the hollow roll 1 rotates around the outer periphery of the magnetizer 4 and the linear magnetic sensor 7 with a small gap.

When the outer peripheral surface of the hollow roll 1 of the magnetic flaw detector having such a configuration is pressed with a predetermined pressure against one surface of the thin steel strip 10 running in the direction of arrow A, for example, the fixed shaft 2 is fixed to the frame. Therefore, the hollow roll 1 rotates in the direction of the arrow.

FIG. 4 is a diagram showing a state where the magnetic flaw detector 11 having the above-described configuration is incorporated in an actual production line. Supply reel 12
The wide thin steel strip 10 fed from the
a, 13b, via the upper surface of the hollow roll 1 of the magnetic flaw detector 11, and via the rear pressing rolls 14a, 14b, the take-up reel 15
At a constant speed.

The power supply cable 8 derived from the magnetic flaw detector 11 is connected to a magnetization power supply 16, and the signal cable 9 is connected to a signal processing circuit 17. A data processing device 18 and a display 19 are connected to the signal processing circuit 17.

In such a magnetic flaw detector 11, when an exciting current is supplied to the magnetized coil 4b, the magnetized iron core 4a and the running thin steel strip 10
Thus, a closed magnetic path is formed. If the above-mentioned defect exists inside or on the surface of the thin steel strip 10, the magnetic path in the thin steel strip 10 is disturbed, and leakage magnetic flux is generated. The leakage magnetic flux is detected by the magnetically sensitive element facing the corresponding defect position constituting the linear magnetic sensor 7, and is detected from the linear magnetic sensor 7 as a defect signal corresponding to the relevant defect.

Since the detected defect signal has a signal level corresponding to the size (magnitude) of the defect inside or on the surface of the steel strip 10, by detecting the defect signal, the defect existing inside or on the surface of the steel strip 10 is detected. The occurrence position in the width direction and its scale can be grasped.

As described above, the size of the defect existing inside or on the surface of the steel sheet is determined based on the intensity of the leakage magnetic flux detected by each magnetically sensitive element constituting the linear magnetic sensor 7. Therefore, it is necessary to adjust the sensitivity of each magnetically sensitive element so as to be uniform over all the magnetically sensitive elements. It is also necessary to match the sensitivity of the linear magnetic sensor 7 as a whole with other magnetic flaw detectors. It is necessary to periodically adjust for changes in sensitivity over time. Further, it is necessary to understand the correspondence between the detected amount and the absolute value of the defect size.

For this reason, conventionally, a plurality of standard defect samples each having an artificial defect serving as a standard having a different scale are prepared from the same material as the material to be inspected, and the created standard defect samples constitute the linear magnetic sensor 7. The sensitivity was calibrated one by one on each magnetic sensitive element.

[Problems to be Solved by the Invention] However, in the case of calibrating each magnetic response inhibition of the linear magnetic sensor 7 using a standard defect sample, a change with time of the standard defect sample becomes a problem. Damage or deterioration due to corrosion or careless handling is a major factor in the change with time, but there is another case where deterioration of the material of the standard defect sample becomes a problem. Therefore, it took a lot of time and effort to store the standard defect sample and to remanufacture it when it was damaged.

In addition, a lot of time and labor was required for the calibration work.
That is, it is necessary to set the relative position between the standard defect sample and the reference magnetically sensitive element to the same condition over all the magnetically sensitive elements. Therefore, it takes a lot of time to calibrate the sensitivity of one magnetically sensitive element, and when the linear magnetic sensor 7 is composed of many magnetically sensitive elements,
Since these times are accumulated, there is a problem that work efficiency in calibrating one magnetic flaw detector is greatly reduced.

Furthermore, since the relative position adjustment between the standard defect sample and each magnetically sensitive element is performed by a manual operation by the operator, there is a problem that the alignment accuracy varies among the magnetically sensitive elements, and the calibration accuracy is inevitably reduced. is there.

The present invention has been made in view of such circumstances, and by applying a uniform magnetic field serving as a pseudo-leakage magnetic flux to the entire linear magnetic sensor from the outside, it is possible to eliminate the use of a standard defect sample, and in a short time. Calibration work can be performed easily,
Further, it is another object of the present invention to provide a method and an apparatus for calibrating a magnetic flaw detector which can greatly improve the calibration accuracy.

[Means for Solving the Problems] In order to solve the above problems, a method for calibrating a magnetic flaw detector according to the present invention generates a magnetic field on a steel plate, and linearly arranges a leakage magnetic flux generated due to a defect. In a magnetic flaw detector that detects defects inside or on the surface of a steel sheet by detecting with a linear magnetic sensor composed of multiple magnetically sensitive elements, a uniform leakage flux that is simulated in a wider area than the magnetic detection area of the linear magnetic sensor A magnetic field is generated by a magnetizer composed of a plate-shaped yoke and a magnetized coil wound on the outer peripheral surface of the plate-shaped yoke. In a state where one end surface of the plate-shaped yoke faces the linear magnetic sensor, the relative position between the linear magnetic sensor and the magnetizer is fixed, and the intensity of the uniform magnetic field is reduced due to a defect of a known scale. Strong corresponding to So that by controlling the excitation current, to adjust the sensitivity of the linear magnetic sensor in this state to the exciting coil of the magnetizer to be.

The calibration device for a magnetic flaw detector according to the present invention, in the magnetic flaw detector described above, comprises a plate-shaped yoke and a magnetized coil wound on an outer peripheral surface of the plate-shaped yoke, and a magnetic detection area of the linear magnetic sensor. A magnetizer that generates a uniform magnetic field that becomes a simulated leakage magnetic flux over a wider area, and one end surface of a plate-like yoke of the magnetizer is connected to the linear magnetic sensor so that the uniform magnetic field is detected uniformly by the linear magnetic sensor. A mounting jig for fixing the relative position between the linear magnetic sensor and the magnetizer in a state where the linear magnetic sensor and the magnetizer are opposed to each other, so that the intensity of the uniform magnetic field becomes the intensity corresponding to the leakage magnetic flux intensity caused by a defect of a known scale. And a power supply device for variably controlling the exciting current to the exciting coil of the magnetizer.

[Operation] With the calibration method and the calibration apparatus of the magnetic flaw detector configured as described above, a uniform magnetic field that becomes a simulated leakage magnetic flux in a region wider than the magnetic detection region of the linear magnetic sensor is used instead of the standard defect sample. A magnetizer comprising a plate-like yoke to be generated and a magnetizing coil wound on the outer peripheral surface of the plate-like yoke is used. Therefore, each magnetically sensitive element constituting the linear magnetic sensor detects the uniform magnetic field as a leakage magnetic flux due to a defect. Therefore, the sensitivity may be calibrated so that the sensitivity of the detected magnetic field intensity matches the defect size determined corresponding to the uniform magnetic field.

Therefore, since there is no need to use a standard defect sample, there is no need to manufacture and store the standard defect sample. Further, since the intensity of the uniform magnetic field generated by the power supply device can be arbitrarily set, detailed sensitivity calibration can be performed for each defect scale.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing a calibrating device using a method for calibrating a magnetic flaw detector according to an embodiment. This calibrating device is roughly divided into a mounting fixture 21 for mounting to the magnetic flaw detector 11 shown in FIG. 3, and a calibrating magnetizer 22 for generating a uniform magnetic field.
And a power supply device for supplying an exciting current to the magnetizing device 22 for calibration.
It consists of 23.

In the mounting fixture 21, as shown in FIG.
Fixing members 25a and 25b for fixing the fixed shaft 2 of the magnetic flaw detector 11 are attached to both ends of the magnetic flaw detector 11, and a rectangular window 26 is formed in the center of the mounting plate 24.
27b is installed.

The calibration magnetizer 22 has a magnetized coil 22b wound around an outer periphery of a plate-shaped yoke 22a.
Is inserted into the window 26 of the mounting plate 24, and is fixed to the mounting plate 24 by a support member (not shown) so that the position of the upper surface 22c coincides with the upper surface of the mounting plate 24. The length of the yoke 22a is set sufficiently longer than the length of the linear magnetic sensor 7 of the magnetic flaw detector 11. The reason for this is that when the magnetic flaw detector 11 is mounted on the mounting plate 24, the magnetic field generated by the magnetizing device 22 for calibration needs to cover all the magnetically sensitive elements constituting the linear magnetic sensor 7 uniformly. Because there is.

The power supply device 23 supplies an exciting current I to a magnetizing coil 22b of the calibration magnetizer 22 via a power cable 23a. The value of the exciting current I is detected by the ammeter 23b. The exciting current I can be set to an arbitrary value by operating the operation panel 23c.

If the detection circuit of the linear magnetic sensor 7 on the side of the magnetic flaw detector 11 is a DC circuit, the exciting current I output from the power supply device 23 is a DC current, and the detection circuit of the linear magnetic sensor 7 is an AC circuit. If there is, use AC current.

Next, the operation of the calibration device of the magnetic flaw detector configured as described above will be described with reference to FIG.

First, the fixing member 25 of the mounting plate 24 in the mounting fixture 21 is used.
The fixed shafts 2 of the magnetic flaw detector 11 are attached to a and 25b. Then, as shown, the mounting angle is set such that the linear magnetic sensor 7 in the hollow roll 1 faces the upper surface 22c of the yoke 22a.

In addition, as shown in FIG. 4, in a state where the magnetic flaw detector 11 is installed on the production line, the thin steel strip 10 is removed, the mounting fixture 21 is turned upside down, and the magnetic flaw detector 11 is mounted on the magnetic flaw detector 11. Is also good.

Next, the power of the magnetization power supply 16, the signal processing circuit 17, the data processing device 18, and the display 19 in the magnetic flaw detector 11 is turned on. Further, the power supply device 23 on the calibration device side is activated. In addition,
The magnetization power supply 16 can be calibrated without necessarily being activated.

When the power supply device 23 is operated to supply the exciting current I to the exciting coil 22b of the calibration magnetizer 22, a magnetic field is generated around the yoke 22a. In this case, in a certain region near the upper surface 22c of the yoke 22a, the magnetic field can be regarded as having a substantially constant strength. Therefore, the same magnetism is applied to each magnetically sensitive element constituting the linear magnetic sensor 7 in the magnetic flaw detector 11 facing the upper surface 22c of the yoke 22a.

Therefore, each magnetic sensing element detects this uniform magnetic field as a leakage magnetic flux caused by a defect, and sends a defect signal corresponding to the magnetic field strength to the signal processing circuit 17. The signal processing circuit 17 shapes the waveform of the input defect signal from each magnetically sensitive element, and then sends it to the data processing device 18. The data processing device 18 converts each defect signal of each magnetically sensitive element into size data such as a dimension indicating the size of the defect and displays the data on the display 19.

In this case, the exciting current I supplied from the power supply unit 23 to the calibration magnetizer 22 corresponds to the intensity of the uniform magnetic field as a pseudo leakage magnetic flux generated one-to-one. And the magnitude of the defect corresponds to the excitation current I and the magnitude of the defect. Therefore, if the intensity of the leakage magnetic flux caused by a defect of a known scale is measured in advance, and the exciting current I when a pseudo leakage magnetic flux corresponding to the measured leakage magnetic flux intensity is generated is measured, it is possible to correspond to each defect size. Is obtained.

Therefore, in a state where the excitation current I corresponding to the known scale defect is supplied to the magnetizing device 22 for calibration, the magnitude of each defect detected by the defect signal obtained from each magnetic sensitive element matches the known defect magnitude. What is necessary is just to adjust the sensitivity of the element.

If this adjustment operation is performed while changing the value of the exciting current I to a plurality of types, the sensitivity calibration of each magnetically sensitive element can be performed more precisely.

As described above, the pseudo leakage magnetic flux can be applied to the magnetic inspection device 11 only by controlling the excitation current I supplied from the power supply device 23 to the calibration magnetizer 22, so that the conventional calibration method has been described. There is no need to use such a standard defect sample. Therefore, there is no need to prepare and manage standard defect samples.

In addition, by using the calibration magnetizer 22 that generates a uniform magnetic field in a region wider than the magnetic detection region of the linear magnetic sensor 7, each magnetically sensitive element constituting the linear magnetic sensor 7 has completely the same magnetic field intensity. To detect. Therefore, unlike the conventional method, it is not necessary to align the standard defect sample for each magnetically sensitive element under constant conditions, so that the efficiency of the calibration operation can be greatly improved. Further, since it is not necessary for the operator to perform the alignment, it is possible to prevent the calibration accuracy from being lowered due to the alignment error.

Further, by changing the value of the exciting current I, the pseudo defect scale can be easily set in a plurality of stages, so that the sensitivity of each magnetically sensitive element can be calibrated more finely and more accurately.

As described above, the working efficiency of the calibration work can be greatly improved, and the calibration accuracy can be greatly improved. In addition, since a standard defect sample is not used, even a person unfamiliar with the calibration work can easily carry out the calibration work.

[Effect of the Invention] As described above, according to the method and the apparatus for calibrating a magnetic flaw detector of the present invention, a uniform magnetic field serving as a pseudo-leakage magnetic flux is applied from the outside to the entire linear magnetic sensor, thereby obtaining a linear magnetic sensor. Are made to perform pseudo defect detection. Therefore, since the sample of the standard defect sample can be eliminated, there is no need to perform a positioning operation or the like at the time of manufacturing, managing and configuring the standard defect sample when the standard defect sample is used. Therefore, the calibration operation can be performed easily and in a short time, and the efficiency of the calibration operation is greatly increased. Furthermore, since the positioning operation of the operator is not required,
Positioning errors are eliminated, and calibration accuracy can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of a calibration device using a method for calibrating a magnetic flaw detector according to one embodiment of the present invention, and FIG. 2 is a schematic diagram for explaining the operation of the method and the device in the embodiment. FIG. 3A is a schematic cross-sectional view taken along a plane parallel to the running direction of a thin steel strip in a general magnetic flaw detector, and FIG. FIG. 4 is a schematic view showing a general production line in which a magnetic flaw detector is incorporated, which is cut along a perpendicular plane. DESCRIPTION OF SYMBOLS 1 ... Hollow roll, 4 ... Magnetizer, 7 ... Linear magnetic sensor, 10 ... Thin steel strip, 11 ... Magnetic flaw detector, 17 ... Signal processing circuit, 18 ... Data processor, 21 ... … Mounting fixture,
22: Calibrator magnet, 22a: Yoke, 22b: Magnetizing coil, 23: Power supply unit, 24: Mounting plate.

Continuation of front page (72) Inventor Morihiro Masutani 1-4-1, Sakuragi, Tokuyama-shi, Yamaguchi Pref. System Measurement Co., Ltd. (56) References JP-A-58-182547 (JP, A) JP-A-52-75488 (JP, A) JP-A-54-128989 (JP, A) JP-A-63-107849 (JP, U) JP-A-58-2717 (JP, U) JP-A-60-11492 (JP, Y2) Kohei 6-28691 (JP, Y2) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 27/72-27/90

Claims (2)

(57) [Claims] A magnetic field is generated in a steel sheet, and a leakage magnetic flux generated due to a defect is detected by a linear magnetic sensor including a plurality of magnetically sensitive elements arranged linearly, thereby detecting the inside or the inside of the steel sheet. In the method for calibrating a magnetic flaw detector for detecting a defect on a surface, a uniform magnetic field serving as a simulated leakage magnetic flux in a region wider than the magnetic detection region of the linear magnetic sensor is wound around a plate-shaped yoke and an outer peripheral surface of the plate-shaped yoke. One end surface of a plate-like yoke of the magnetizer is opposed to the linear magnetic sensor so that the uniform magnetic field is detected uniformly by the linear magnetic sensor. In this state, the relative position between the linear magnetic sensor and the magnetizer is fixed, and the magnetizer is excited so that the intensity of the uniform magnetic field becomes an intensity corresponding to the leakage magnetic flux intensity caused by a defect of a known scale. For coil That controls the excitation current, the calibration method of the magnetic flaw detection apparatus and adjusting the sensitivity of the linear magnetic sensor in that state. 2. A magnetic field generated in a steel sheet, and a leakage magnetic flux generated due to a defect is detected by a linear magnetic sensor including a plurality of magnetically sensitive elements arranged linearly, thereby detecting the inside or the inside of the steel sheet. A calibration device for a magnetic flaw detector for detecting a surface defect, comprising: a plate-shaped yoke and a magnetized coil wound around an outer peripheral surface of the plate-shaped yoke, simulating a region wider than a magnetic detection region of the linear magnetic sensor. A magnetizer for generating a uniform magnetic field serving as a leakage magnetic flux; and one end surface of a plate-like yoke of the magnetizer faces the linear magnetic sensor so that the uniform magnetic field is uniformly detected by the linear magnetic sensor. A mounting jig for fixing a relative position between the linear magnetic sensor and the magnetizer in a state where the linear magnetic sensor and the magnetizer are arranged; and a strength of the uniform magnetic field corresponding to a leakage magnetic flux strength caused by a defect of a known scale. So before Calibration device in the magnetic flaw detection apparatus is characterized in that and a power supply unit for variably controlling an excitation current to the exciting coil of the magnetizer.