JP2011196768A - Method and device for detecting flaw of wire material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the inspection of the surface damage of a wire material formed by hot rolling in a rolling line without using an external light source when the surface damage of the wire material is optically inspected.SOLUTION: A flaw detection device 10 is installed between a cooling part 3 and a take-up part 4 on the rolling line 1 and the wire material (w) red-heated through a rolling roller group 2 and the cooling part 3 is directly imaged by a CCD camera 11. An image processor 12 inspects the presence of the damage of the wire material (w) on the basis of a contrast difference between an adjacent bright part region and a dark part region of the obtained image. Since the wire material (w) is red-heated to emit light, an image clear in contrast can be obtained even if the external light source is not used. Equipment cost is suppressed because no external light source is used. Since inspection is performed in the rolling line 1, it is unnecessary to separately provide an inspection line and labor for transferring the inspection line and a space for the inspection line can be omitted.

Description

  The present invention relates to a flaw detection method and a flaw detection apparatus for inspecting surface flaws of a wire rod during rolling.

  As a general inspection method for inspecting a surface flaw of a steel material such as a wire rod, there are an eddy current flaw detection method and an optical flaw detection method.

  As an eddy current flaw detection method, as in Patent Document 1, a method is used in which magnetism is applied to a wire being hot-worked to be inspected, and a change in magnetism associated with a flaw on the surface of the wire is detected to detect a flaw. Are known.

  Further, as an optical flaw detection method, as in Patent Document 2, a square steel material before the wire rod rolling process is mainly transferred to an inspection line and imaged with a camera while illuminating the surface with an external light source (light). There is known a method for detecting a flaw based on the contrast between a bright area and a dark area that appear in a captured image.

Japanese Patent No. 2760166 JP 2003-75358 A

In the method of Patent Document 1, in order to detect a change in magnetism, a coil as a flaw detection device must be disposed close to the entire circumference of a red-hot wire during hot rolling.
However, when a part of the flaw detection apparatus is brought close to the high-temperature wire as described above, it is necessary to take measures against heat, and there is a problem that equipment costs required for the entire flaw detection apparatus, running costs required for maintenance, and the like increase. In addition, there is a problem that it is not possible to reconfirm the location where the scratch is detected.

On the other hand, the method of Patent Document 2 requires an external light source for illuminating the square steel material. However, in the optical flaw detection method, it is preferable that such an external light source can be omitted because the cost can be reduced.
The method of Patent Document 2 is suitable for inspecting a relatively short square steel material because it is easy to transport and does not take up space, but is suitable for inspecting a relatively long object such as a wire. Is not suitable because it takes a lot of time to move to another line and requires a large space for another line. For this reason, in the optical flaw detection method, it is desirable that the surface flaw of the steel material can be inspected in the rolling line.

  Therefore, the problem to be solved by the present invention is to realize the inspection in the rolling line without using an external light source when optically inspecting the surface flaw of the wire formed by hot rolling. .

  In order to solve the above-described problems, a method for flaw detection of a wire rod according to the invention includes a step of preparing a wire rod rolling line in which a group of rolling rollers performing hot rolling on the upstream side and a camera on the downstream side are arranged, and the rolling roller A step of imaging a non-illuminated wire rod hot-rolled by a group with the camera, and a contrast difference (light intensity difference) between adjacent bright area and dark area of the wire image obtained by the imaging And determining the presence or absence of surface flaws on the wire.

  When the wire rod that has undergone the hot rolling process is imaged with a camera immediately after that, the wire rod glows red and emits light, so that a wire rod image with clear contrast between the scratched area and the intact area can be obtained without using an external light source. be able to. Therefore, an external light source can be omitted and cost reduction can be achieved.

Since the camera used for flaw detection is installed on the rolling line and inspection is carried out continuously during rolling, it is not necessary to provide a separate inspection line for flaw detection. Space and equipment costs can be saved.
The determined portion can be reconfirmed by recording the wire image.

The perspective view which shows the outline | summary of the rolling line incorporating the flaw detection apparatus of the wire rod concerning embodiment Front view of wire flaw detector according to an embodiment Diagram showing the surface of the wire with scratches The figure which shows typically the image processing of the location shown in FIG. Flow chart showing criteria for determining the presence or absence of scratches

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  A wire flaw detector 10 according to the embodiment shown in FIG. 1 and FIG. 2 is used by being incorporated in a rolling line 1 that performs hot rolling of the wire w, and the surface flaw of the wire w by an optical method using a camera 11. This is to check for the presence or absence.

As shown in FIG. 1, the general rolling line 1 which forms the wire w by hot rolling is provided with the rolling roller group 2, the cooling part 3, and the winding part 4 in order from the upstream side to the downstream side.
The wire w that has been hot-rolled by the rolling roller group 2 and has a high heat is cooled by the cooling unit 3 and is finally wound by the winding unit 4.

As illustrated, the flaw detection apparatus 10 according to the embodiment is disposed between the cooling unit 3 and the winding unit 4 on the rolling line 1. Here, the wire w is cooled by the cooling unit 3, but also flows at a place where the flaw detection apparatus 10 on the rolling line 1 is red-heated by residual heat and emits light.
The flaw detection apparatus 10 according to the embodiment includes a plurality of CCD (Charge Coupled Device) cameras 11 and an image processor 12 that is electrically connected to the CCD camera 11 and that can process an image captured by the camera 11.

As shown in FIG. 2, four CCD cameras 11 are arranged in parallel at substantially equal intervals (90 degrees) in the circumferential direction of the wire rod w, and the red-hot wire rods flowing through the rolling line 1 by these cameras 11. Can be imaged all around.
As the CCD camera 11, for example, a general camera having a number of pixels of about several million pixels is used, and the wavelength of detectable light is about 300 to 1000 nm including light (infrared rays) having a wavelength longer than visible light. ing.

On the other hand, the image processor 12 can input image data of the wire w obtained by imaging with the CCD camera 11.
The image processor 12 includes a processing unit, a storage unit, and a comparison unit.
The processing means can calculate the contrast difference (light intensity difference) between the adjacent dark area and bright area on the surface of the wire w from the image data of the wire w. In addition, the area (number of pixels of the camera) of the continuous dark area can be calculated from the image data of the wire rod w.
The storage means stores a light / dark threshold and an area threshold (converted from the number of pixels of the camera), and the comparison means can compare these thresholds with the numerical values calculated by the processing means described above.

Here, the light and dark thresholds and the area threshold are obtained based on a master image obtained by imaging a wire with a surface flaw with the CCD camera 11 in advance.
For example, the light / dark threshold value is obtained based on an average value of contrast differences between a scratch area and an intact area of a plurality of master images.
For example, the area threshold value is obtained based on the minimum value of the area of the scratch area of the plurality of master images.

  The configuration of the flaw detection apparatus 10 according to the embodiment is as described above. Next, the flaw detection method of the embodiment using the flaw detection apparatus 10 will be described with reference to the flowchart of FIG.

First, in step S1 of FIG. 5, the outer circumference of the wire w flowing through the rolling roller group 2 and the cooling unit 3 to the installation location of the flaw detection apparatus 10 on the rolling line 1 having a flaw region f as shown in FIG. Are directly imaged by the CCD camera 11 without being illuminated by a light or the like.
Since the wire w emits red heat and emits light, an image in which contrast between light and dark appears clearly in the scratched region f and the intact region can be obtained without illumination. Here, since the flaw area f is recessed from the surface of the wire w, it becomes a dark area when imaged.

The thus obtained image of the wire rod w as shown in FIG. 4 is input to the image processor 12 in step S2 of FIG. 5, and the contrast difference between the adjacent bright area b and the dark areas d1 and d2 is calculated by the processing means. Is done.
Here, FIG. 4 schematically represents an image of the wire w, and it goes without saying that the actual pixel p of the CCD camera 11 is much smaller than this figure.

Next, in step S3 of FIG. 5, the comparison means of the image processor 12 compares each contrast difference with the contrast threshold stored in the storage means.
When the contrast difference is smaller than the light / dark threshold value, that is, when there is not much light / dark difference between the dark area d1, d2 and the bright area b, it is determined that the wire is not damaged.
When the contrast difference is larger than the brightness threshold, that is, when the brightness difference between the dark area d1, d2 and the bright area b is clear, the process proceeds to the next step.

  In step S4 of FIG. 5, the areas (pixels p) of the dark part regions d1 and d2 where the contrast difference between the adjacent bright part region b in step S3 is determined to be larger than the light / dark threshold value by the processing unit of the image processor 12. Number of).

In step S5 of FIG. 5, the comparison unit of the image processor 12 compares the areas of the dark part regions d1 and d2 obtained in step S4 with the area threshold value stored in the storage unit.
When the dark part area is smaller than the area threshold, that is, when the dark part area is very small as shown by d2 in FIG. 4, it is determined that the wire w is not damaged.
When the dark part area is larger than the area threshold, that is, when the dark part area is so large that it cannot be ignored as shown by d1 in FIG. 4, it is determined that the wire w has a flaw such as a flaw area f.

If it is determined that the wire w has scratches, for example, if the elapsed time from the start of the flaw detection is stored in the storage means of the image processor 12, the time and the feed of the wire w on the rolling line 1 are stored. It becomes possible to calculate the distance from the end of the wire rod in the flaw region f from the speed.
Further, if the image of the determination location is stored in the storage means of the image processor 12, the presence or absence of a flaw can be reconfirmed later by other methods such as visual observation, so that the flaw detection accuracy is further improved.

According to the wire flaw detection method of such an embodiment, since a light source such as a light for illuminating the wire w is unnecessary, the equipment cost can be suppressed.
Further, since flaw detection is also performed in the rolling line, there is no need to transfer the wire w to another inspection line, and the space for the inspection line and equipment costs can be saved.
Since the CCD camera 11 can also detect infrared rays, it can detect flaws that are weak in red heat and cannot be visually recognized by human eyes. Further, since the entire circumference of the wire rod w is imaged by the plurality of CCD cameras 11, it is possible to prevent an inspection omission.

In addition, the concept of the area in terms of the area of the dark area and the area threshold in the embodiment includes the length of the dark area and the length of the scratch area in the length direction of the wire rod w.
That is, since the wire w flowing on the rolling line 1 is likely to have a long and narrow scratch extending in the length direction of the wire w, the width of the dark part region and the scratch region (the length in the circumferential direction of the wire w) is ignored. If only this is observed, the flaw area f can be detected.
In FIG. 4, an example is given in which the areas of the dark part regions d1 and d2 (number of pixels p) are equal to the lengths of the dark part regions d1 and d2 in the length direction (number of pixels p). .

Further, the flaw detection method of the embodiment may be simplified, and the presence or absence of a flaw may be determined based on only the contrast difference between the dark area and the bright area of the wire material image.
That is, only the contrast threshold value is stored in the storage means of the image processor 12, and the contrast difference between the adjacent bright area b and the dark area d1 and d2 calculated by the processing means is compared by the comparison means. When the contrast difference is larger than the light / dark threshold, it is determined that there is a scratch, and when it is small, it is determined that there is no scratch.
In this way, calculation of the area of the dark area and comparison with the area threshold can be omitted, so that the processing is simplified. However, the flaw detection method of the embodiment is more reliable in order not to erroneously detect a minute dark area that is not actually a flaw as a flaw.

The camera of the flaw detection apparatus is preferably the CCD camera 11 of the embodiment, but is not limited thereto. Furthermore, the number of cameras is not limited to four in the embodiment, but a number that can capture the entire circumference of the wire is preferable.
Further, as the image processor 12, a device dedicated to image processing may be used, or a general-purpose device such as a personal computer may be used.

Moreover, the flaw detection apparatus 10 and the flaw detection method shown in the embodiments are merely examples, and the scope of the present invention is not limited thereby.
The scope of the present invention is defined based on the description of the scope of claims, and all modifications can be made to the embodiments within the scope of the contents shown in the scope of claims. It is intended to be included in the invention.

DESCRIPTION OF SYMBOLS 1 Rolling line 2 Rolling roller group 3 Cooling part 4 Winding part 10 Wire flaw detection apparatus 11 CCD camera 12 Image processor w Wire material f Wound area p Pixels d1, d2 Dark area b Bright area

Claims (5)

A step of preparing a rolling roller group for performing hot rolling on the upstream side, a camera on the downstream side, and a rolling line for the arranged wire rods;
Imaging the red-hot wire rod hot-rolled by the rolling roller group under non-illumination by the camera;
Determining the presence or absence of surface flaws on the wire based on the contrast difference between adjacent bright and dark regions of the wire image obtained by the imaging. The step of determining the presence or absence of surface flaws on the wire based on the contrast difference between the adjacent bright area and dark area of the wire image,
A contrast difference between adjacent dark area and bright area in the wire image obtained by the imaging, and a contrast threshold determined in advance based on a contrast difference at the time of imaging of the wound area and the intact area of the wire with surface flaws. A substep to compare;
And a sub-step of determining that the wire has a flaw when the contrast difference is larger than the light and dark threshold, and determining that the wire has no flaw when the contrast difference is smaller than the light and dark threshold. The flaw detection method for a wire described in 1. The step of determining the presence or absence of surface flaws on the wire based on the contrast difference between the adjacent bright area and dark area of the wire image,
A contrast difference between adjacent dark area and bright area in the wire image obtained by the imaging, and a contrast threshold determined in advance based on a contrast difference at the time of imaging of the wound area and the intact area of the wire with surface flaws. A substep to compare;
When the contrast difference is smaller than the light and dark threshold, it is determined that there is no scratch on the wire, and when the contrast difference is larger than the light and dark threshold, the dark part region area of the wire material image obtained by the imaging, and A sub-step of comparing a predetermined area threshold based on the area of the scratch area of the wire with surface flaws;
And a sub-step of determining that there is no damage to the wire when the dark area area is smaller than the area threshold, and determining that the wire is damaged when the dark area is larger than the area threshold. The flaw detection method for a wire described in 1. The step of imaging the red-hot wire with a camera includes:
The flaw detection method for a wire according to any one of claims 1 to 3, wherein the entire periphery of the outer periphery of the wire is performed by a plurality of cameras arranged in parallel in the outer peripheral direction of the wire. A wire flaw detector arranged on the downstream side of a rolling roller group that performs hot rolling on a wire rolling line,
A plurality of CCD cameras arranged in parallel in the circumferential direction of the rolling line, capable of imaging the entire circumference of the red-hot wire rod rolled hot by the rolling roller group under non-illumination;
An image processing machine capable of inputting wire rod image data obtained by imaging of the plurality of CCD cameras,
The image processor is
A processing unit capable of calculating a contrast difference between adjacent bright area and dark area of the wire material image, and an area of the dark area;
A storage means capable of storing a light / dark threshold predetermined based on a contrast difference at the time of imaging of a wound area and an intact area of a wire with surface flaws, and an area threshold predetermined based on the area of the scratch area,
A comparison means capable of comparing the contrast difference calculated by the processing means with the contrast threshold stored in the storage means, and the area of the dark area calculated by the processing means and the area threshold stored in the storage means, respectively. And a wire flaw detection apparatus.

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