JPH0628690Y2 - Metal plate defect detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a defect detection device for magnetically leaking surface defects and internal defects of a metal plate, for example, a thin steel plate, and highly accurate defect detection is performed online. Regarding the device.

(Prior Art) As an apparatus for detecting defects in a thin steel sheet online, particularly internal defects, a magnetizer for magnetizing the steel sheet is installed on the bottom surface of the steel sheet as disclosed in JP-A-56-61645. A sensor group that detects the leakage magnetic flux from the internal defect is provided on the upper surface,
There is a device for inspecting a steel plate at a constant width by intermittently moving the steel plate and scanning the sensor in the width direction.

However, in this case, it is difficult to continuously perform the defect inspection because the sensor is scanned, and if it is performed, the sheet passing speed of the steel sheet is limited by the sensor scanning speed and the scanning width, and the steel sheet is only slowed down. Not be able to spend time, and impair operating ability.

As another device, as disclosed in, for example, Japanese Patent Application Laid-Open No. 61-147158, a magnetizing device sandwiching a strip and a detecting coil facing the magnetizing device are provided to detect a leakage magnetic flux passing through the strip. There is a method in which a coil defect is detected and a strip defect is detected from a change in the detected value.

According to this, there is an effect that the defect is detected even when the strip is continuously passed or at high speed.

(Problems to be solved by the invention) By the way, in the defect detection of the strip in the actual operation line, even if the defect actually exists, it is not detected, or it is detected as a defect smaller than the actual product. There is a case. In addition, a defect that can be ignored may be detected as a serious defect. The problem of such defect detection can be solved by the sensitivity calibration of the detector. As a method of calibrating the sensitivity of the defect detector, there is a method of scanning the standard flaw sample or a certain magnetic transmitting element in the plate width direction or detecting all channels at the same time to adjust the sensitivity of all channels. Will be resolved. However, it is necessary to eliminate erroneous detection that sufficiently ensures strict quality assurance, because the sensitivity adjustment is performed under a fixed condition of offline or online or within a limited range.

SUMMARY OF THE INVENTION The present invention is directed to an apparatus having higher detection accuracy in detecting defects by magnetic leakage flaw detection on-line of a metal plate such as a strip.

(Means for Solving Problems) Hereinafter, the present invention will be described in detail with reference to the drawings.

The inventors of the present invention have conducted tests and examinations to solve erroneous detection. Change of the magnetic flux intensity of the defective portion and the magnetic flux intensity of the portion of the metal plate to be inspected, that is, the portion having no defect, changes between the magnetic flux intensity of the defective portion and the magnetic flux intensity of the metal sheet to be inspected. It has been found that there is a certain correlation between. From this knowledge, the surface roughness of the metal plate to be tested, the plate passing speed,
The magnetic field strength and the gap are detected.
The detection is performed by changing the leak component level value.

Specific description will be made with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a metal plate to be inspected, which is, for example, a thin steel plate and is passed in the direction of the arrow.

A magnetizer 2 is provided inside the non-magnetic roll 3, and contacts the roll 3 to magnetize the plate 1 to be detected.

Reference numeral 4 denotes a detector, which is provided so as to face the magnetizer 2 and detects a leakage magnetic flux from the metal plate 1 to be tested. Reference numeral 5 denotes a gap interval adjusting device, which adjusts the interval between the metal plate 1 to be detected and the detector 4, for example, by ejecting gas from the bottom of the detector.

Reference numeral 6 denotes a gap sensor, which is provided at both ends of the detector 4 in this embodiment and detects a gap.

Reference numeral 7 denotes a bandpass filter, which passes the defect component and the leakage component of the metal plate to be inspected from the leakage magnetic flux detection signal from the detector 4, and the band to pass is compared with the velocity signal from the plate passing velocity detector 8 Change. Reference numeral 9 is an amplifier, which amplifies the signal from the bandpass filter 7. This amplifier preferably has a digital gain setting function.

A converter 10 converts a signal from the amplifier 9 into a digital signal and separates it into a defect signal 11 and a leak signal 12 of the metal plate to be tested itself. The defect signal 11 is input to the signal processing device 13, where it is edited and output.

The leak signal 12 of the metal plate itself is compared with the leak component level value 14 set in the present invention by the comparator 15, and the difference is output to the digital gain setter 16.

In the present invention, the leakage component level value 14 is determined by the surface roughness of the metal plate to be tested, the plate passing speed, the magnetic field strength of the magnetizer, and the gap.
Change with the preset device 17. This point will be described in detail.
When the surface roughness of the metal plate 1 to be tested changes, the leakage signal becomes the second
We have found that it changes as shown in the figure. That is, as the roughness increases, the leak signal (B) increases almost in proportion.

Further, when the passing speed changes, the defect signal A and the leak signal B of the metal plate to be inspected change substantially in proportion to the speed as shown in FIG. This test was conducted with a magnetic field strength of 400 gauss, a gap of 80 μm, and a strip running speed of 30 to 600 m / min. The test material was a tin plate having a surface roughness of 1 μmRa, and defects in the plate were preliminarily measured by inclusions and found to be 8
It was × 10 ^-4 mm ³ . When the magnetic field strength and the gap change, as shown in FIGS. 4 and 5, the defect signal A and the leak signal B of the metal plate to be tested are almost proportional to the magnetic field strength, while the gap signal is almost equal to the gap signal. It was found that it changed in inverse proportion. In the case of magnetic field strength,
Magnetic field strength of 250 to 400 with 600m / min, gap of 80μm
I went as Gauss. As the test material, the same kind as the above-mentioned one in which the passing speed was changed was used. In the case of a gap, the strip running speed was 600 m / min, the magnetic field strength was 400 gauss, and the gap was 80 to 120 μm.

As described above, the output signal changes due to the change in the condition at the time of flaw detection, and erroneous detection occurs. Therefore, the present invention solves this by the following.

That is, the speed signal from the strip speed detector 8 and the ammeter 19
The current detection signal of the magnetizer 2 detected in 1 and the gap signal from the gap sensor 6 are input to the presetter 17. Further, since the surface roughness of the metal plate 1 to be tested is known separately before passing through the plate, the setting device 20 inputs it to the presetting device 17. The presetter 17 determines the leakage component level value f and outputs the magnetic field intensity signal Φ based on the input speed signal V, the current detection signal, the gap signal G and the surface roughness signal S by the following equation.

f = K ₁ V + K ₂ Φ + K ₃ G + K ₄ S (1) However, K ₁ , K ₂ , K ₃ , and K ₄ are all constants. In this way, the leak component level value f that is set and the leak signal 12 of the test metal plate itself are sometimes compared by the comparator 15, and the gain of the digital gain setting device 16 is changed by the difference signal so that the difference is eliminated. To do.

(Effects of the Invention) Since leakage magnetic flaw detection is carried out as described above, even if the surface roughness of the metal plate to be tested, the stripping speed magnetic field strength, the gap, etc. are changed, over-detection and over-detection are prevented, and high detection is possible. It is possible to detect flaws continuously with accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a graph showing an example in which the leakage magnetic flux component signal changes depending on the surface roughness of the test metal plate. FIG. 3: A graph showing an example in which the leakage magnetic flux detection signal changes depending on the passage speed of the test metal plate. FIG. 4 is a graph showing an example in which the leakage magnetic flux detection signal changes depending on the magnetic field strength. FIG. 5: A graph showing an example in which the leakage magnetic flux detection signal changes depending on the gap. 1: Metal plate to be inspected 2: Magnetizer 3: Roll, 4: Detector 5: Gap interval adjusting device 6: Gap sensor, 7: Band filter 8: Plate speed detector, 9: Amplifier 10: Converter, 11: Defect signal 12: Leakage signal of the metal plate to be inspected 13: Signal processing device, 14: Level value 15: Comparator, 16: Setting device 17: Preset device, 18: Magnetizer power supply 19: Ammeter, 20: Setting device

Claims (1)

[Scope of utility model registration request] 1. A device for detecting flaws by detecting a magnetic flux leaking from a magnetizer by a magnetizer with a detector and passing through a defect component in a signal from the detector and a leak component of the metal plate itself. Bandpass filter, an amplifier that widens the signal from the bandpass filter, a converter that inputs the signal from the amplifier and separates and detects the defect signal and the leak signal of the metal plate to be detected, and a separately input target. The surface roughness signal of the metal inspection plate, the plate speed signal, the magnetic field strength signal of the magnetizer, and the gap signal of the metal to be detected and the preset signal that outputs the leakage component level value and the leakage component level value are input. And a comparator that outputs a difference signal by comparing the leak signal of the test plate itself from the converter, and a digital gain setting device that inputs the difference signal and changes the gain of the amplifier so that the difference is eliminated. Characterized by Defect detecting apparatus of a metal plate.