JP3950372B2 - Method and apparatus for detecting cracks in steel strip - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for detecting cracks in a steel strip, and is particularly suitable for use in order to enlarge a gap between a eddy current detection sensor and a steel plate.
[0002]
[Prior art]
Defects such as edge cracks and drilling that occur in steel strips are caused by non-metallic inclusions during slab casting, which is the previous process, scale biting during hot rolling, or rolling in an inappropriate temperature range. Various measures have been taken to eliminate these defects. However, it is difficult to completely eliminate these defects. For this reason, these defects are found, and processing such as deletion of defective portions or suspension of charging is performed. As devices for detecting the defect, an eddy current flaw detector, an optical flaw detector, and the like are known.
[0003]
In the case of the above optical flaw detection apparatus, for example, as disclosed in Japanese Patent Application Laid-Open No. H5-232045, light irradiated from the lower part of the steel sheet is received by a detector provided at the upper part of the steel sheet. Then, if even a slight amount of light is received or a larger amount of light received than usual is detected, it is determined that there is a defect.
[0004]
However, the above optical flaw detector can detect wrinkles in the case where the edge of the steel plate has a dead zone of about 10 mm due to the property of reflection or diffraction of light, or a linear crack with no opening. There were problems such as being unable to do so.
[0005]
On the other hand, in the case of the eddy current flaw detector, there is no problem as described above. As the eddy current flaw detector, for example, as disclosed in Japanese Patent Laid-Open No. 63-180850, an AC voltage is applied to the probe coil in order to non-destructively detect wrinkles in a magnetic metal object to be measured. Is applied to generate a magnetic field to generate an eddy current in the object to be measured, and a change in the eddy current generated by the soot or the like is detected as a change in voltage induced in the probe coil.
[0006]
[Problems to be solved by the invention]
However, in order to detect small wrinkles on the steel sheet using the eddy current flaw detector, it is necessary to reduce the sensor diameter to a wrinkle size level. As described above, when the sensor diameter is reduced to the heel size level, it is not possible to ensure a sufficient gap between the steel plate and the sensor.
[0007]
If a predetermined gap cannot be secured with respect to the steel plate that performs the wrinkle detection, there is a problem in that the sensor and the steel plate may come into contact if the shape of the steel plate is bad due to an ear wave or the like. .
[0008]
In other words, in the soot detection using the eddy current flaw detector, there is a problem that only a small gap of about 1/3 to 1/5 of the soot size can be secured as shown in FIG.
The present invention has been made in view of the above-described problems, and can detect the gap between a steel plate and a sensor in the detection of a wrinkle of a steel plate using an eddy current flaw detector so that the gap between the steel plate and the sensor can be expanded to 1/2 or more. The purpose is to.
[0009]
[Means for Solving the Problems]
The method for detecting cracks in the steel strip according to the present invention is provided by winding each of the two probe coils around each main body portion made of a non-magnetic material and arranging the main body portions in parallel. The magnetic fields of the two steel coils are repelled from each other to generate a magnetic field on the steel plate, the range of the magnetic field acting on the steel plate is expanded, and the winding directions of the two probe coils around the main body portions are the same. By applying a voltage, the magnetic fields of the two probe coils repel each other, and the power supply frequency of the AC voltage applied to the two probe coils is the same frequency and 1 MHz or more. .
[0010]
The steel strip ear crack detection apparatus according to the present invention includes two probe coils wound around the probe coils so that the probe coils are in the same direction with respect to the main parts made of a non-magnetic material, and the two probes. AC power supply means for applying an AC voltage to each probe coil of the coil, and the AC power supply means applies an AC voltage having the same frequency and a frequency of 1 MHz or more to each probe coil of the two probe coils. It is characterized by that.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the method and apparatus for detecting the cracks in the steel strip of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing a main configuration of an eddy current detection sensor showing an embodiment of a steel strip ear crack detection device according to the present invention. As shown in FIG. 1, the eddy current detection sensor 1 of the present embodiment includes a first eddy current detection sensor 1a and a second eddy current detection sensor 1b.
[0012]
The first and second eddy current detection sensors 1a and 1b are configured so that the width W of the main body portion is 6 mm and the length L is 10 mm, and are arranged at a predetermined gap G with respect to the steel plate 3. Installed and used. The main body of the sensor is made of a nonmagnetic material such as glass epoxy resin.
[0013]
The probe coil 2 is wound around the peripheral surface of the sensor body configured as described above. In the present embodiment, an example is shown in which the probe coil 2 is configured by winding the conductor around the circumferential surface of the sensor body 50 times.
[0014]
In the present embodiment, as shown in FIG. 2, the direction in which the coil is wound by the first eddy current detection sensor 1a and the second eddy current detection sensor 1b is the same direction. A high-frequency current i is supplied to each probe coil 2 from an AC power source 5 to generate magnetic fields from the first eddy current detection sensor 1a and the second eddy current detection sensor 1b.
[0015]
As shown in FIG. 3, the eddy current detection sensor 1 of the present embodiment configured as described above is installed above a roll push-up mechanism 36 provided in the steel plate production line. In FIG. 3, 31 is a steel sheet feed roller, 32 is a transport roller, 33 is a γ-ray thickness gauge, 34 is a leveler, 35 is an end plate shear, 37 is a welder, 38 is a bridle, 39 is a transport roller, and 40 is a winding. It is a take-off roller.
[0016]
FIG. 4 shows a gap when installing the eddy current detection sensor 1 of the steel strip ear crack detection device of the present embodiment and a gap when installing the eddy current detection sensor of the conventional steel strip ear crack detection device. It is a characteristic view to compare and explain. As shown in FIG. 4, when the sensor diameter (the heel size) is 10 mm, the conventional steel strip ear crack detecting device must have a gap of about 2 mm, that is, a gap length as small as about 1/5 of the heel size. did not become. On the other hand, in the case of the steel strip ear crack detection device of the present embodiment, the gap length can be expanded to about 5 to 8 mm.
[0017]
In the present embodiment, the first eddy current detection sensor 1a and the second eddy current detection sensor 1b are provided, and the two eddy current detection sensors 1a and 1b are arranged in a direction in which a magnetic field repels at the same frequency (coil winding). This is because, by applying an alternating voltage (with the same direction), the magnetic fields of the two eddy current detection sensors are repelled so that the magnetic field on the steel plate 3 is expanded.
[0018]
In addition, the power supply frequency of the alternating voltage applied to each eddy current detection sensor 1a, 1b shall be 1 MHz or more. The higher power supply frequency is desirable because the higher the power supply frequency, the easier the eddy current flows on the steel sheet surface, and the more the eddy current flows on the steel sheet surface, the higher the soot detection sensitivity can be.
[0019]
Penetration depth of eddy current with respect to power supply frequency f (63% of total eddy current): t is t = 503 × √ (ρ / μ · f) (ρ: conductor specific resistance × 10 (Ωm), μ: conductor The higher the power supply frequency, the easier the eddy current flows on the surface of the steel sheet and the more easily the edge is concentrated.
In the present embodiment, the two eddy current detection sensors 1a and the second eddy current detection sensor are set to have the same power supply frequency of the AC voltage applied to the two eddy current detection sensors 1a and the second eddy current detection sensor 1b. 1b 疵 detection sensitivity is available.
[0020]
In FIG. 5, the structural example of the detection system in the ear crack detection apparatus of the steel strip of this Embodiment is shown. As shown in FIG. 5, the detection output of the first eddy current detection sensor 1a is given to the first preamplifier 41, and the detection output of the second eddy current detection sensor 1b is given to the second preamplifier 42. The output of the first preamplifier 41 is supplied to the first amplifier and linearizer 43, and the output of the second preamplifier 42 is supplied to the second amplifier and linearizer 44. Then, the difference between the output of the first amplifier and linearizer 43 and the second amplifier and linearizer 44 is calculated by a subtractor 45 to detect wrinkles. In FIG. 5, reference numeral 46 denotes a gap range that can be used as a sensor. In this embodiment, the output saturation point is set to 100%, and 90% of the output is set to a gap range in which the sensor can be used.
[0021]
FIG. 6 is a diagram illustrating distance characteristics (data of the preamplifier output 41) for each sensor, different polarity parallel method, and same polarity parallel method. In FIG. 6, when compared with a gap of sensor output 90% (corresponding to reference numeral 46 in FIG. 5) which is a standard of a usable range as a sensor, the sensor alone has a gap of 4.5 mm. Further, the heteropolar parallel system has a gap of 5 mm, the homopolar parallel system has a gap of 8 mm, and it can be seen that the homopolar parallel system has the best distance characteristics.
[0022]
FIG. 7 is a diagram for explaining the relationship between the soot signal and the position of the eddy current detection sensor. Sensors 1a and 1b are arranged in parallel at a position 2 mm from the steel plate edge to detect an edge flaw of the moving steel plate. FIG. 7 shows a case where the sensor of this embodiment is used.
[0023]
FIG. 8 is a characteristic diagram showing the result of measuring the S / N ratio in the positional relationship of FIG. 7 using the steel band ear crack detection device of the present embodiment. When performing this measurement, as shown in FIG. 10, a wave eliminating roll 100 was disposed at a position of a distance l = 150 mm in front of the eddy current detection sensor 1. The wave eliminating roll 100 suppresses the ear wave by pressing the steel plate 3 from the upper surface, and is for reducing a noise component.
[0024]
In addition, the same-polarity parallel method (the winding direction of the two probe coils is the same) is used as measurement conditions, the sensor size is 6 mm × 10 mm, the sensor power supply frequency is 1 MHz, and the gap between the eddy current detection sensor 1 and the steel plate 3 is 5 mm. The line speed is 50 mpm, and the measurement scissor condition is a simulated scissors (artificial) with a depth of 10 mm. For comparison, a single sensor (same size) and a different polarity parallel method (the winding directions of the two probe coils are reversed) were used.
[0025]
As is clear from FIG. 8, in the case of the sensor single body and the heteropolar parallel system, the distance characteristic is inferior to that of the homopolar parallel system, and the S / N ratio is reduced because the saddle signal is reduced. I understand. In the present embodiment, an S / N ratio of 3 or more was able to be achieved for a gap of 10 mm with a gap of 5 mm. In general, it is said that an S / N ratio of 3 or more between the soot signal (S) and the noise signal (N) is required for stable soot measurement. In the case of a steel strip ear crack detection device, this condition is cleared.
[0026]
FIG. 9 shows magnetic field analysis results for each of the sensor unit (a), the heteropolar parallel system (b), and the homopolar parallel system (c). It can be seen that the spread of the magnetic field is larger in the parallel systems (b) and (c) due to repulsion of the mutual magnetic field than in the sensor alone (a). In addition, the homopolar parallel method (c) has better distance characteristics than the heteropolar parallel method (b) because the rate of change of the magnetic field in the gap direction including the sensor center is uniform with respect to the gap. ing. In addition, the contour line in a figure shows magnetic field distribution. In the heteropolar parallel method, the distance characteristic is inferior particularly because the rate of change of the magnetic field in the gap direction at the center of the sensor is coarser than that of the homopolar parallel method.
[0027]
In the case of the eddy current detection sensor, an eddy current that cancels the magnetic flux generated from the eddy current detection sensor 1 to the steel plate 3 flows through the steel plate 3. The magnitude of the eddy current can be detected by measuring the inductance of the probe coil 2. And if there is a flaw in the steel plate 3, the eddy current hardly flows, so the output of the probe coil 2 changes. The eddy current detection sensor 1 uses such a phenomenon to detect wrinkles on a steel sheet.
[0028]
Therefore, in the steel strip ear crack detection device of the present embodiment, the two eddy current detection sensors 1a and 1b are provided, and the magnetic fields of the two eddy current detection sensors 1a and 1b are repelled from each other. Since the magnetic field acting on the steel plate is expanded by generating the magnetic flux for 3, a long detection distance can be ensured, for example, about twice the detection as compared with the case of a single eddy current detection sensor. A distance can be secured.
[0029]
In the embodiment of the present invention, it is not always necessary to prepare power supplies for the number of probe coils. For example, as shown in FIG. 11 (a), as shown in FIG. 11b, even one AC power supply 5 for supplying a high-frequency current i to each probe coil 2 of the semicircular eddy current detection sensors 1a and 1b is provided. Good.
[0030]
FIG. 11 (c) is a diagram showing the circuit configuration. By connecting the probe coils 2 in series, a high frequency current i can be supplied from one AC power source 5, and even in this case, a long detection distance can be obtained. Can be secured.
[0031]
【The invention's effect】
As described above, according to the present invention, the two eddy current detection sensors are arranged in parallel and the magnetic field between the two eddy current detection sensors is repelled to generate a magnetic flux for the steel sheet. Since it did in this way, the range of the magnetic field which acts on the said steel plate can be expanded, and the gap between the said steel plate and a vortex | eddy_current detection sensor can be expanded to the length of 1/2 or more of ridge size. Furthermore, since the frequency of the AC voltage applied to the two probe coils is set to the same frequency and 1 MHz or more, the range of the magnetic field acting on the steel plate to be detected can be expanded, and eddy currents are applied to the steel plate surface. The wrinkle detection sensitivity of the steel sheet can be increased.
[Brief description of the drawings]
FIG. 1 shows an embodiment of the present invention and is a diagram showing a schematic configuration of an eddy current detection sensor.
FIG. 2 is a diagram showing a winding state of a probe coil.
FIG. 3 is a diagram illustrating an example in which an eddy current detection sensor is used.
FIG. 4 is a characteristic diagram showing a relationship between a sensor diameter and a measurement gap.
FIG. 5 is a diagram illustrating a configuration example of a detection system of an eddy current detection sensor.
FIG. 6 is a characteristic diagram showing distance characteristics of the eddy current detection sensor according to the embodiment.
FIG. 7 is a characteristic diagram showing a positional relationship between a sensor and a steel plate.
FIG. 8 is a characteristic diagram showing an example of a wrinkle detection experiment.
FIG. 9 is a diagram illustrating an example of a magnetic field analysis result of an eddy current detection sensor using the same polarity method.
FIG. 10 is a view showing an example in which wave-breaking rolls are installed.
FIG. 11 is a diagram showing an example of an eddy current sensor according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Eddy current detection sensor 1a 1st eddy current detection sensor 1b 2nd eddy current detection sensor 2 Probe coil 3 Steel plate 5 AC power supply G Gap W eddy current detection sensor width L L Eddy current detection sensor body length

Claims (2)

Each of the two probe coils is wound around each main body made of a non-magnetic material, and each main body is arranged in parallel, and the magnetic fields of the two probe coils are repelled from each other. Generate a magnetic field and expand the range of the magnetic field acting on the steel sheet,
By applying an alternating voltage with the same winding direction of the two probe coils with respect to the body portions, the magnetic fields of the two probe coils are repelled from each other,
A method of detecting an ear crack in a steel strip, wherein the power source frequency of the AC voltage applied to the two probe coils is the same frequency and 1 MHz or more. Two probe coils wound so that each probe coil is in the same direction with respect to each main body made of a non-magnetic material,
AC power supply means for applying an AC voltage to each probe coil of the two probe coils,
The above-mentioned AC power supply means applies an AC voltage having the same frequency and a frequency of 1 MHz or more to each of the probe coils of the two probe coils.

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