JP4696895B2 - Water column type ultrasonic flaw detector and water column type ultrasonic flaw detection method - Google Patents

Description

  The present invention relates to a water column type ultrasonic flaw detection apparatus and a water column type ultrasonic flaw detection method that can detect an internal defect having a diameter of 50 μm or more and 100 μm or less with a traveling metal band as an inspection target.

  Inclusions in metal strips such as steel strip products are said to cause cracking and necking during press working, and it is required to detect even very fine ones. For example, steel strip products processed into automobile parts are required to detect internal defects with a diameter of 50 μm or more. For this reason, an ultrasonic flaw detector is installed in the production line, internal defects of the steel strip are detected, and product quality assurance is performed based on defect information such as the number, position, type, and form of the internal defects.

There are various types of metal strip products manufactured according to the customer's use, and metal strips of various thicknesses are passed through the pickling line of hot-rolled steel sheets. Therefore, it is necessary to install an ultrasonic flaw detector capable of accurately detecting internal defects of the traveling metal band even when the thickness of the metal band changes, in such a metal band production line.
In addition, as a water column type ultrasonic flaw detector installed in a production line, an ultrasonic probe (hereinafter referred to as a probe) housed in a nozzle is disposed on one side of a metal band, and the probe is used as a transmission / reception probe. One side sensor type (Patent Documents 1 to 3) and a transmission type sensor type in which probes housed in nozzles are arranged on both sides of a metal band are known.

Patent Document 1 discloses a thin steel strip that detects an inclusion in a steel by performing signal processing from an attenuation amount of a predetermined bottom surface reflected wave among reflected waves received by a transmitter / receiver probe with respect to a one-side sensor type device. The inclusion continuous exploration method is disclosed.
Patent Document 2 discloses an invention in which the shape of a water column nozzle is devised with respect to a one-side sensor type device, and Patent Document 3 relates to a device with the same as above, and a poorly conductive vapor film generated at the interface between water and a high-temperature steel sheet. Has been disclosed to restore the acoustic coupling function.
JP 61-271448 A Japanese Patent Application Laid-Open No. 7-113795 Japanese Patent Publication No.55-28015

However, the thin steel strip inclusion continuous exploration method described in Patent Document 1 detects scattered echoes, but the detectable inclusion is limited to a thickness of 20 μm × width of 100 μm × length of 200 μm. The defect detection ability is insufficient.
Moreover, since the water column type ultrasonic flaw detection apparatus described in Patent Documents 1 to 3 is a one-side sensor type apparatus, the defect echo is easily affected by the pass line fluctuation and the inclination of the steel strip, and further in the thickness direction. It is extremely difficult to detect an inclusion defect having a sensitivity distribution and having a diameter in the traveling metal strip of 50 μm or more and 100 μm or less.

Moreover, the conventional water column type ultrasonic flaw detector does not have the function of moving the sensor in the thickness direction of the metal band, so that when the thickness of the metal band changes over a wide range, the detectability of internal defects is dependent on the thickness. There is a problem that it appears prominently.
Therefore, in view of the above-described conventional technology, the present invention can be applied to a traveling metal strip, even when the thickness of the metal strip changes over a wide range, and the diameter in the metal strip is 50 μm to 100 μm. An object of the present invention is to provide a water column type ultrasonic flaw detection apparatus and a water column type ultrasonic flaw detection method capable of accurately detecting the following internal defects.

The inventors of the present invention diligently studied the water column type ultrasonic flaw detector and found that the above-mentioned problems can be solved by adopting a transmission type sensor system, and made the present invention.
The present invention is as follows.
1. A pair of sensors that separately inject a probe for transmitting ultrasonic waves and a probe for receiving ultrasonic waves inside the lower nozzle are jetted of water toward the surface of the traveling metal band. In a water column type ultrasonic flaw detector configured to be opposed to both upper and lower sides and configured to detect an internal defect, the nozzle nozzle has an oval nozzle and the area of the nozzle is ultrasonic transmission of the probe in the nozzle. The area of the surface or the receiving surface is 2.5 times or more, and the aperture ratio expressed by the ratio of the flow path area on the inlet side to the area of the injection port is 3.0 or more, and the upper nozzle is injected. The long axis to short axis ratio of the port is 3.0 to 3.4, the long axis to short axis ratio of the lower nozzle is 1.5 or less, and a porous rectifying plate is installed in the flow path of the nozzle is, and in accordance with the plate thickness of the metal strip, the sensor elevating means for elevating said sensor Water column type ultrasonic flaw detection apparatus characterized by comprising.

2 . 1. The amount of water sprayed from the nozzle outlet can be adjusted by a flow rate control valve . Water column type ultrasonic flaw detection apparatus according to.
3 . A thickness gauge for measuring the thickness of the metal strip is provided on the upstream side of the sensor, and the sensor is lifted and lowered via the sensor lifting means based on the measured value of the thickness gauge. Characteristic 1. Or 2. The water column type ultrasonic flaw detector described in 1.

4 . 1. A marker for marking the metal strip is provided on the downstream side of the sensor, and the internal defect position in the metal strip is marked. ~ 3 . The water column type ultrasonic flaw detector according to any one of the above.
5 . Above 1. ~ 4 . In the method for detecting an internal defect of a traveling metal strip using the water column type ultrasonic flaw detector according to any one of the above, the sensor is moved up and down through the sensor lifting means according to the thickness of the metal strip, A water column type ultrasonic flaw detection method characterized in that an internal defect is detected after setting an interval between probes to a predetermined value.

  The water column type ultrasonic flaw detector according to the present invention employs a transmission type sensor system that is not easily affected by disturbances, and has a sensor elevating means for elevating the sensor in accordance with the thickness of the metal band. Correspondingly, even if the plate thickness of the metal plate changes over a wide range, the defect detection ability of the transmission type sensor system can be fully exerted, and the internal defect whose diameter in the traveling metal strip is 50 μm or more and 100 μm or less can be accurately detected. Can be detected.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall view showing a configuration of a water column type ultrasonic flaw detector according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a main part of the water column type ultrasonic flaw detector of FIG.
The water column type ultrasonic flaw detector according to the embodiment of the present invention shown in FIG. 1 is a transmission type sensor system. That is, the probe 1 for transmitting the ultrasonic beam 3 to the upper and lower nozzles 2 and the probe 1 for receiving the ultrasonic beam 3 are separately accommodated and arranged oppositely on the upper and lower sides of the metal band to detect internal defects. It is configured to be possible. The nozzle 2 has an injection port for injecting water to form a water column 4 between the surface of the metal strip.

As shown in FIGS. 1 and 2, the upper probe 1 transmits the ultrasonic beam 3 vertically toward the surface of the metal band, and the lower probe 1 transmits the ultrasonic beam 3 from the metal band. The reception probe 1B will be described. In FIG. 2, t indicates the thickness of the metal strip S to be inspected.
As the probe 1, a line focus type probe as shown in FIG. It is known that the line focus type probe is formed by laminating a plurality of elements, and there is an interval of the probe 1 at which the height of the defect echo from the internal defect is maximized (Japanese Patent No. 3629913).

Here, reference numeral 5 in FIG. 1 denotes sensor lifting / lowering means for lifting / lowering the sensor in accordance with the thickness t of the metal strip S, and includes a drive motor M and the like. For example, the rotation of the drive motor M is transmitted to a rack member having teeth at one end, and the sensor elevating means 5 having a structure in which the interval L of the probe 1 is changed by the vertical movement of the rack member.
According to such a water column type ultrasonic flaw detector, when the thickness t of the metal strip S changes, the sensor is lifted and lowered by the sensor lifting means 5 in accordance with the thickness t of the metal strip S. The interval L can be changed. In FIG. 1, reference numeral 6 denotes a thickness gauge provided on the upstream side of the sensor, and is connected to the computer 10. It is preferable that the sensor is moved up and down via the sensor lifting and lowering means 5 based on the measured value of the thickness gauge 6 to change the interval L between the probes 1. According to such a water column type ultrasonic flaw detector, the interval L between the probes 1 can be quickly and accurately set to a predetermined value that maximizes the height of the defect echo from the internal defect.

  Reference numeral 7 denotes a marker provided on the downstream side of the sensor, which is preferably connected to the computer 10 and is configured to mark the position of the internal defect with the marker 7 by a signal from the computer 10. According to such a water column type ultrasonic flaw detector, when an internal defect is detected in the metal band S, the position of the internal defect can be quickly and accurately marked with the marker 7. The computer 10 includes signal processing means for detecting an internal defect based on a transmission wave emitted from the transmission probe 1A and a reception wave received by the reception probe 1B. Further, as the porous rectifying plate 8 installed in the nozzle 2, for example, as shown in FIG. 4, a plate having through holes with a pitch p to hole diameter d ratio (p / d) = 1.28 is preferably formed. Can be used.

Here, the injection port shape of the nozzle 2 to accommodate the probe 1, as shown in FIG. 3 (b), ing as oval to fit the probe profile. This was obtained from the water column stabilization experiment described below.
FIG. 3B is a schematic plan view when the nozzle 2 shown in FIG. 1 is viewed from the metal band side, and the nozzle 2 accommodates a line focus type probe. As shown in FIG. 3A, the line focus type probe has a rectangular shape as seen from the focal direction of the ultrasonic beam 3 on the ultrasonic wave transmission surface or reception surface. α indicates the area of the ultrasonic transmission surface or reception surface of the probe 1, x is the long side dimension of the ultrasonic transmission surface or reception surface, and y is the short side dimension of the ultrasonic transmission surface or reception surface. . Moreover, a is the major axis dimension of the injection port formed in the nozzle 2, and b is the minor axis dimension of the injection port. The relationship of a> x and a> y is satisfied.

Next, a result of a water column stabilization experiment in the case where the nozzle 2 is formed in an oval shape according to the shape of the line focus type probe will be described.
In this water column stabilization experiment, various nozzles with different oval nozzle areas were used, the amount of water sprayed was changed, a sufficient cross-sectional area of the water column could be secured, and there was no generation of bubbles that would interfere with ultrasonic transmission. The water column formation conditions were examined (see FIG. 5).

  The length of the water column exceeds the minimum required 30 mm (corresponding to the interval L of the probe 1 with respect to the plate thickness of 1.2 to 6.5 mm = 46 to 78 mm), and the area of the injection port is the ultrasonic transmission surface Alternatively, it was changed in a range of 1 to 14 times the area α of the receiving surface, the aperture ratio was constant at 3.0, and the amount of water jetted from the nozzle 2 was 300 liters / min at the maximum. In this case, a line focus type probe having a focal length of 38 mm, a long side dimension x = 60 mm of the ultrasonic transmission surface or the reception surface, and a short side dimension y = 11 mm of the ultrasonic transmission surface or the reception surface was used as the probe 1. .

As a result, by setting the nozzle 2 that accommodates the probe 1 to the following (a) to (e), a water column that does not include bubbles, has a minimum length of 30 mm, and has a sufficient cross-sectional area is effective. The result that it can form automatically was obtained.
(A) Using a nozzle whose area of the injection port is 2.5 times or more the area α of the ultrasonic transmission surface or reception surface of the probe 1 in the nozzle, and then the amount of water to be injected is 300 liters / minute or more on the upper side. The water column type ultrasonic flaw detector which can be made 160 liters / min or more on the lower side (range of hatched portion in FIG. 5).
(B) A water column type ultrasonic flaw detector in which the aperture ratio represented by the ratio of the flow path area on the inlet side of the nozzle 2 to the area of the nozzle is 3.0 or more.
(C) The shape of the nozzle 2 is an oval, the ratio of the major axis to the minor axis of the upper nozzle is 3.0 to 3.4, and the ratio of the major axis to the minor axis of the lower nozzle is 1. Water column type ultrasonic flaw detector which is 5 or less.
(D) A water column type ultrasonic flaw detector in which the amount of water ejected from the ejection port of the nozzle 2 can be adjusted by the flow rate control valve 9.
(E) A water column type ultrasonic flaw detector in which a porous rectifying plate 8 is installed in the flow path of the nozzle 2.

By accommodating separately the probe 1 which transmits an ultrasonic wave to such a nozzle 2, and the probe 1 to receive, since a transmissive | pervious sensor with favorable S / N can be comprised, it is preferable.
Here, the reason (d) is that the greater the aperture ratio, the higher the water pressure in the water supply system. Therefore, when a nozzle having a predetermined value exceeding the aperture ratio of 3.0 is used, Compared to the case of using a nozzle having a diameter of 3.0 (result of FIG. 5), the amount of jet water for effectively forming a water column having a sufficient cross-sectional area exceeding 30 mm in length is 300 liter / This is because it can be less than a minute and can be less than 160 liters / minute on the lower side. Further, the reason (e) is useful for forming a stable water column 4.

  However, when the shape of the nozzle 2 is circular, the area of the nozzle is changed within a range of up to 14 times the area of the ultrasonic wave transmitting surface or the receiving surface, and the amount of water sprayed from the nozzle 2 Even if the maximum is 300 liters / minute, the cross-sectional area exceeding 30 mm on the upper side cannot stably form a sufficient water column, resulting in an insufficient acoustic coupling function. On the other hand, on the lower side, when the nozzle 2 has a circular shape with a diameter of 110 mm and the amount of water sprayed from the nozzle 2 is 160 liters / minute or more, the cross-sectional area does not include bubbles and exceeds 30 mm in length. Sufficient water column could be formed stably.

A method for detecting an internal defect of a traveling metal strip using the water column type ultrasonic flaw detector according to the embodiment of the present invention described above will be described. 6 and 7 schematically show the internal defect detection principle of a water column type ultrasonic flaw detector employing a transmission type sensor system.
In the case of the transmission type sensor system, the ultrasonic beam 3 transmitted from the transmission probe 1A is transmitted to the surface of the metal band through the water column 4, propagates through the metal band S, and is then received by the reception probe 1B through the water column 4. Is done. The received waves (transmitted waves T1, T2 and reflected waves F1, F2) received by the reception probe 1B are signal-treated by the defect detection gate signal, and when a defect echo (reflected wave F2) of a predetermined value or more is extracted, It is detected that there is an internal defect in the metal band S. If the defect echo is weak, it is difficult to extract the defect echo from the noise, and even if an internal defect having a diameter of 50 μm or more and 100 μm or less exists in the metal band S, it cannot be detected.

  According to the method for detecting an internal defect of a traveling metal strip using the water column type ultrasonic flaw detector shown in FIG. 1, when the thickness of the metal strip changes, the sensor goes up and down according to the thickness of the metal strip. After the sensor is moved up and down via the means 5 and the interval between the probes 1 is set to a predetermined value at which the height of the defect echo from the internal defect is maximized, the internal defect can be detected. When the line focus type probe is used, it is found that there is an interval between the probes 1 that is separated from the metal band S by a predetermined amount and the height of the defect echo from the internal defect is maximized according to the thickness t of the metal band. ing.

  Therefore, according to the water column type ultrasonic flaw detector according to the embodiment of the present invention, the sensor lifting / lowering that adopts a transmission type sensor system that is not easily affected by disturbance and moves the sensor up and down according to the thickness of the metal strip. Therefore, even if the thickness of the metal strip changes over a wide range, the defect detection ability of the transmission type sensor system can be sufficiently exhibited, and the diameter of the traveling metal strip S is 50 μm. When there is an internal defect of 100 μm or less, it can be detected with high accuracy.

  A water column type ultrasonic flaw detector as shown in FIG. 1 was constructed and installed in a pickling line of a hot-rolled steel plate through which a steel plate having a thickness of 1.2 to 6.5 mm was passed. At that time, a line focus type probe capable of detecting an internal defect having a focal length of 38 mm and a defect detection capability of 50 μm or more and 100 μm or less is separately housed in the nozzle 2 and arranged oppositely on both upper and lower sides of the steel strip. The sensor elevating means 5 for elevating the sensor in accordance with the thickness t of the steel strip is provided.

  Using the water column type ultrasonic flaw detector provided with the sensor lifting / lowering means 5, when the thickness of the steel strip changes, the sensor is lifted / lowered via the sensor lifting / lowering means 5 in accordance with the thickness of the steel strip. After the interval was set to a predetermined value, an internal defect was detected. As a result, even when the thickness of the steel strip to be inspected changed over a wide range, inclusion defects having a diameter of 50 μm or more and 100 μm or less could be accurately detected.

  On the other hand, since the conventional water column type ultrasonic flaw detector is a one-side sensor type device, it can detect an inclusion defect having a diameter of 100 μm or more and 200 μm or less when the plate thickness is constant. Therefore, even when there is an inclusion defect having a diameter of 50 μm or more and 100 μm or less in the steel plate when the thickness t of the steel strip is changed, it cannot be detected.

1 is an overall view showing a configuration of a water column type ultrasonic flaw detector according to an embodiment of the present invention. It is a schematic side view which shows the principal part of the water column type ultrasonic flaw detector of FIG. (A) is a schematic perspective view which shows a suitable probe used for a sensor, (b) is a schematic plan view at the time of seeing the sensor which accommodated it from the metal strip side. FIG. 2 is a schematic plan view of a porous rectifying plate suitable for being provided in the water column type ultrasonic flaw detector of FIG. It is a characteristic view which shows the water column stabilization experiment result of the nozzle used for the water column type ultrasonic flaw detector of FIG. It is explanatory drawing explaining the internal defect detection principle by a transmissive | pervious sensor system. It is a characteristic view explaining the signal processing with the water column type ultrasonic flaw detector which employ | adopted the transmission type sensor system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Probe 2 Nozzle 3 Ultrasonic beam 4 Water column 5 Sensor raising / lowering means 6 Thickness gauge 7 Marker 8 Porous rectifying plate 9 Flow control valve 10 Computer 11 Internal defect S Metal strip t Metal strip thickness L Probe interval x Ultrasonic transmission surface Or long side dimension of receiving surface y short side dimension of ultrasonic transmitting surface or receiving surface α area of ultrasonic transmitting surface or receiving surface a long axis size of injection port b short axis size of injection port p hole pitch d hole diameter

Claims (5)

A pair of sensors that separately inject a probe for transmitting ultrasonic waves and a probe for receiving ultrasonic waves inside the lower nozzle are jetted of water toward the surface of the traveling metal band. In a water column type ultrasonic flaw detector configured to be opposed to both upper and lower sides and configured to detect an internal defect, the nozzle nozzle has an oval nozzle and the area of the nozzle is ultrasonic transmission of the probe in the nozzle. The area of the surface or the receiving surface is 2.5 times or more, and the aperture ratio expressed by the ratio of the flow path area on the inlet side to the area of the injection port is 3.0 or more, and the upper nozzle is injected. The long axis to short axis ratio of the port is 3.0 to 3.4, the long axis to short axis ratio of the lower nozzle is 1.5 or less, and a porous rectifying plate is installed in the flow path of the nozzle is, and in accordance with the plate thickness of the metal strip, the sensor elevating means for elevating said sensor Water column type ultrasonic flaw detection apparatus characterized by comprising. The water column type ultrasonic flaw detector according to claim 1, wherein an amount of water ejected from an ejection port of the nozzle is adjustable by a flow rate control valve. A thickness gauge for measuring the thickness of the metal strip is provided on the upstream side of the sensor, and the sensor is lifted and lowered via the sensor lifting means based on the measured value of the thickness gauge. The water column type ultrasonic flaw detector according to claim 1 or 2 . The marker according to any one of claims 1 to 3 , wherein a marker for marking the metal strip is provided on the downstream side of the sensor, and an internal defect position in the metal strip is marked. Water column type ultrasonic flaw detector. The method for detecting an internal defect of a traveling metal strip using the water column type ultrasonic flaw detector according to any one of claims 1 to 4 , wherein the sensor elevating means is used in accordance with the plate thickness of the metal strip. A water column type ultrasonic flaw detection method, wherein an internal defect is detected after raising and lowering a sensor to set a distance between probes to a predetermined value.

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