JP6741044B2 - Method and equipment for detecting slab surface defects and equipment abnormalities in continuous casting machines - Google Patents

Description

The present invention relates to a slab surface defect and equipment abnormality detection method and detection equipment in a continuous casting machine, specifically, a surface defect of a slab based on the shape of a cut surface of a continuously cast slab of steel, and/or The present invention relates to a method and equipment for detecting an equipment abnormality in at least one of a water-cooled mold and a secondary cooling zone of a continuous casting equipment.

In continuous casting of steel, the molten steel injected into the mold is cooled by a water-cooled mold (referred to as "primary cooling"), and the molten steel solidifies at the contact surface with the mold and solidifies the shell (also called "solidified layer"). Is generated. The slab that uses this solidified shell as the outer shell and the inside as an unsolidified layer is cooled by a water spray or steam spray while being supported by a slab support roll installed on the downstream side of the mold (referred to as "secondary cooling"). ) And continuously pulled out below the mold. The slab is solidified to a thickness center by cooling with a water spray or a steam spray, and then cut with a slab cutting machine such as a gas cutting machine to manufacture a slab with a predetermined length. The range in which the slab is secondarily cooled is called a "secondary cooling zone".

When the cooling in the mold becomes uneven, or the cooling by water spray or steam spray becomes uneven, various defects such as vertical cracks, lateral cracks, and corner key cracks occur on the surface of the slab.

Further, if the cooling in the mold becomes non-uniform, the amount of heat shrinkage between the thick portion and the thin portion of the solidified shell may differ, and the cross-sectional shape of the slab may become non-uniform. Similarly, when the cooling water is no longer sprayed on the slab due to an abnormality in the secondary cooling zone, the surface temperature of the solidified shell becomes high due to insufficient heat removal at the part where the cooling water is not sprayed or insufficient, and the molten steel Static pressure may cause the solidified shell to bulge outward (expanding outward is referred to as "bulging"), and the cross-sectional shape of the slab may become uneven.

When the cross-sectional shape of the slab becomes uneven, internal cracks occur in the solidified shell at the corner of the slab, and when this internal crack propagates from the solidification interface to the surface of the solidified shell, the unsolidified layer inside the slab There is a risk that so-called bleeding will occur, which means that water will flow out. Here, "bleeding" is a phenomenon in which a crack from the solidification interface to the surface of the solidified shell occurs in the solidified shell, and a small amount of the unsolidified layer inside the slab leaks out from the crack. If the bleed expands, it will lead to a breakout. In the slab portion where bleeding occurs, the surface of the slab usually has double skin-like surface defects.

Since defects existing on the surface of the slab become surface defects of the steel product in the next hot rolling step, at the stage of the slab after casting, the surface of the slab should be maintained to remove the surface defects. Is required.

Basically, it is important to eliminate the cause of such surface defects, but a slab that has unexpected surface defects due to an unpredictable cause is separated from other sound slabs. Appropriate treatment separately is also an important item in actual operation. In other words, regarding the surface defects of the slab that become defects in the steel product after hot rolling, the slab with the surface defect is identified and separated, and the surface defects are removed by scarfing or grinder grinding. After that, it is important to subject it to hot rolling.

Therefore, many techniques have been proposed for detecting or predicting the surface defect of the slab during casting or immediately after casting online by using an optical imaging device or a radiation thermometer.

For example, in Patent Document 1, the surface temperature of the slab generated by the in-machine stop in the continuous casting machine is measured by an infrared camera, the surface temperature of the slab to be measured is lower than a preset target temperature, and, A secondary cooling zone that determines that a defect has occurred on the surface of the slab when the part with a low surface temperature reaches a predetermined length in the casting direction, and that the slab has a part with a low surface temperature. An abnormality detection method has been proposed in which the location is identified and an equipment abnormality is determined to have occurred in the identified area of the secondary cooling zone.

In Patent Document 2, a thermal image of the surface of the slab is photographed by an infrared camera, and based on the temperature profile in the thermal image, the slab is referenced with reference to the correspondence between the temperature profile in the past thermal image and the defect on the surface of the slab. Defect detection methods for detecting surface defects have been proposed.

In Patent Document 3, a cast piece being discharged from a machine end of a continuous casting facility is photographed by imaging devices provided on the side and the upper side, and a cast piece image photographed from the side is subjected to image processing to obtain a cast piece. Has been proposed, in which the thickness of the slab is measured, and the slab image photographed from above is image-processed to measure the width of the slab.

In Patent Document 4, from a diagonally lower side of a cast piece cut by a gas cutting machine, a cross-shaped slit laser beam is irradiated from a cut surface of the cast piece to a lower surface of the cast piece, and the cast piece irradiated with the cross-shaped slit laser light Cutting of the slab, which captures the cut surface and the bottom surface with a camera, processes the obtained images, and detects the presence of steps on the slab cutting surface and the presence of fusing chips (burrs) on the bottom surface of the slab A surface shape detection method has been proposed.

In addition, although it is not a technique for detecting surface defects of a cast piece, Patent Document 5 discloses a two-dimensional radiation thermometer for measuring the cross-sectional temperature of a cast piece cut by a cast piece cutting machine provided on the outlet side of a continuous casting facility. The method for estimating the final solidification position of the slab based on the measured cross-section temperature is proposed.

JP, 2014-217849, A JP, 2009-66602, A JP, 2003-260551, A JP, 11-291008, A JP, 2014-233734, A

According to Patent Document 1 and Patent Document 2, it is possible to detect surface defects mainly due to surface cracks in the slab, and the surface defects in the steel product caused by the surface cracks in the slab are greatly reduced. Further, according to Patent Document 3, it is possible to measure the change with time of the bulging amount of the slab, it is possible to quickly detect the equipment abnormality in the secondary cooling zone, and the surface defects caused by the abnormality in the secondary cooling zone are also reduced. There is. Further, according to Patent Document 4 and the like, surface defects of the steel product due to fusing chips adhering to the cut surface of the slab are significantly reduced.

However, the slab surface defect caused by the bleeding is difficult to detect from the captured images of the long side surface and the short side surface of the slab to be inspected in Patent Document 1 or Patent Document 2, and the like When the steel product is transported to the hot rolling process of the process, surface defects may occur in the steel product. This is because the bleed mainly occurs in the water-cooled mold or in the secondary cooling zone immediately below the mold.At the time of the inspection by the optical imaging device, the temperature of the bleed occurrence point becomes the same temperature as the sound point. This is because the bleed cannot be detected.

Patent Document 3 is a technique for measuring the bulging of a slab, and bleeding may occur even if the occurrence of bulging in an amount exceeding the threshold value is not observed in the slab. Therefore, in Patent Document 3, the bleeding occurs. There is a possibility of overlooking the slab surface defect caused by it.

As described later, the present invention detects a slab surface defect based on the slab cut surface (cross section), and Patent Documents 4 and 5 also inspect the slab cut surface (cross section). Intended. However, Patent Document 4 is a technique for detecting the presence/absence of a step on the cut surface of the slab, and Patent Document 5 is a technique for estimating the final solidification position of the slab based on the cross-sectional temperature. No mention is made of the cast slab surface defects.

The present invention has been made in view of the above circumstances, and an object thereof is to continuously detect a slab surface defect caused mainly by bleed with high accuracy in a continuous casting process of steel, and/or Detecting method and equipment for detecting slab surface defects and equipment abnormalities in continuous casting machines capable of detecting equipment abnormalities in the mold or secondary cooling zone of continuous casting equipment that causes slab surface defects due to bleeding Is to provide.

The present inventors have earnestly conducted experiments and researches to solve the above problems. As a result, bleeding occurs due to uneven bulging or heat removal of the solidification shell in the secondary cooling zone in the mold or immediately below the mold, and as the bulging amount increases, it occurs during continuous casting. We considered that it is possible to detect the slab surface defect caused by bleeding by monitoring the amount of deformation of the slab's cross-sectional shape, and focused on the temporal change of the slab's cross-sectional shape.

As a result of observing the temporal change of the cross-sectional shape of the slab, the cross-sectional shapes of each slab are compared in time series, and the bulging of the long side surface of the slab and the short side surface of the slab and the depression of the short side surface of the slab are promptly confirmed. By recognizing, it has been found that the slab surface defect caused by the bleed can be detected, and the equipment abnormality of the mold or the secondary cooling zone that causes the bleed can be detected.

The present invention has been made based on the above findings, and the summary thereof is as follows.
[1] A cross section of a cast piece cut by a cast piece cutting machine provided on the exit side of the continuous casting machine is photographed by an optical photographing device, and a cross-sectional shape of the cross section of the billet is obtained from the photographed image, Based on the obtained cross-sectional shape, surface defects of the slab, and/or the equipment abnormality of at least one of the mold and the secondary cooling zone of the continuous casting machine is detected, casting in the continuous casting machine One-side surface defect and equipment abnormality detection method.
[2] The slab surface defect and equipment abnormality in the continuous casting machine according to the above [1], wherein the cross-sectional shape is obtained by the bulging amount of the slab long side surface or the dent amount of the slab short side surface. Detection method.
[3] A surface defect of the slab and/or an equipment abnormality of at least one of a mold of a continuous casting machine and a secondary cooling zone is detected based on a change with time of the cross-sectional shape. A method for detecting a slab surface defect and equipment abnormality in the continuous casting machine according to [1] or [2] above.
[4] In the cross-sectional shape, when the occurrence of bulging in an amount exceeding a threshold value is confirmed on the long side surface of the cast slab, the position of the mold that cools the bulging occurrence position exceeding the threshold value and the two immediately below the mold. Casting in the continuous casting machine according to any one of the above [1] to [3], characterized in that it is determined that an equipment abnormality has occurred in at least one of the parts of the next cooling zone. One-side surface defect and equipment abnormality detection method.
[5] In the cross-sectional shape, when it is confirmed that the amount of dents exceeding the threshold value is generated on the short side surface of the cast slab, the position of the dents exceeding the threshold value is being cooled, and two parts are directly under the mold. Casting in the continuous casting machine according to any one of the above [1] to [3], characterized in that it is determined that an equipment abnormality has occurred in at least one of the parts of the next cooling zone. One-side surface defect and equipment abnormality detection method.
[6] An optical photographing device for photographing a cross section of a slab cut by a slab cutting machine provided on the exit side of the continuous casting machine, and a storage device for storing an image photographed by the optical photographing device And a cross-sectional shape of the cross-section of the slab from the image stored in the storage device, and based on the obtained cross-sectional shape, surface defects of the slab and/or equipment of the secondary cooling zone of the continuous casting machine A facility for detecting a slab surface defect and a facility abnormality in a continuous casting machine, comprising: a calculation display device for determining a malfunction.

According to the present invention, the slab surface defect caused by the bleeding caused by the nonuniformity of bulging and heat removal is detected based on the cross-sectional shape of the slab transverse cross section, so the bulging amount leading to the occurrence of bleeding. Is large, or when the amount of dent on the short side surface of the slab that causes bleeding is large, the amount of deformation of the cross section of the slab after completion of solidification is large, and therefore the slab resulting from bleeding is large. It becomes possible to detect surface defects with high accuracy. In addition, since it is possible to accurately detect the slab surface defect caused by bleeding, the equipment abnormality of the mold or the secondary cooling zone immediately below the mold that causes bulging that causes bleeding and uneven heat removal in the slab. Can also be detected.

1 is a schematic side view of a vertical bending type continuous casting machine equipped with a slab surface defect and equipment abnormality detection equipment according to the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic side view of a vertical bending type continuous casting machine equipped with a slab surface defect and equipment abnormality detection equipment according to the present invention.

As shown in FIG. 1, a continuous casting machine 1 for casting a slab 15 (a slab slab) is provided with a water-cooled mold 5 for injecting and solidifying the molten steel 14, and this mold is used. A tundish 2 that receives the molten steel 14 from a ladle (not shown) and supplies the received molten steel 14 to the mold 5 through the immersion nozzle 4 is arranged above the reference numeral 5. A sliding nozzle 3 for controlling a molten steel injection flow rate from the tundish 2 to the mold 5 is installed between the tundish 2 and the immersion nozzle 4.

On the other hand, below the mold 5, a plurality of sets of slab support rolls 6 each including a pair of facing rolls are installed, and the slab 15 pulled out from the mold 5 has slabs on its upper and lower surfaces. It is adapted to be pulled out below the mold 5 while being supported by the support roll 6. On the downstream side of the slab support roll 6, that is, on the delivery side of the continuous casting machine 1, a plurality of transport rolls 7 for delivering the cast slab 15 are installed. Then, the casting slab 15 being cast is moved above the transport roll 7 in synchronism with the slab withdrawing speed to form a slab casting 15a (hereinafter, cut slab casting of a predetermined length). A cast piece cutting machine 19 for cutting the piece into "cut pieces 15a" is installed. Generally, as the slab cutting machine 19, a gas cutting machine having two gas torches is used which melts and cuts the slab 15 while moving in the opposite direction toward the width center of the slab 15 in the width direction of the slab 15. Has been done.

In the range where the slab support roll 6 is installed, the first cooling zones 8 and 8, the second cooling zones 9 and 9, the third cooling zones 10 and 10, and the fourth cooling zone are provided from directly below the mold 5 toward the downstream side. A secondary cooling zone composed of a secondary cooling zone divided into a total of 12 places of the cooling zones 11, 11, the fifth cooling zones 12, 12, and the sixth cooling zones 13, 13 is installed. In each secondary cooling zone of the secondary cooling zone, a spray nozzle (not shown) such as a water spray nozzle or a water mist spray nozzle is provided between the slab support rolls 6 adjacent in the casting direction. The secondary cooling water is sprayed toward the surface of the slab 15, or the secondary cooling water is sprayed together with air. In FIG. 1, the total number of the secondary cooling zones of the secondary cooling zone is 12, but it may be divided into any number depending on the equipment length of the continuous casting machine 1.

An optical imaging device 20, such as a CCD camera or an infrared camera, is installed at a position facing the cutting surface 15s of the cutting slab 15a cut by the slab cutting machine 19, and the cutting surface 15s of the cutting slab 15a ( The slab 15 is configured to be photographed by the optical photographing device 20. There is no problem with the surface temperature of the cut surface 15s at the time of photographing by the optical photographing device 20. In this case, the optical imaging device 20 is configured so that the entire cut surface 15s of the cut slab 15a can be imaged.

The optical imaging device 20 is cooled with cooling water or cold air as needed. Further, the optical imaging device 20 faces the cutting surface 15s of the cutting slab 15a, and if the cutting slab 15a after photographing the cutting surface 15s is moved in the direction of the optical imaging device 20, the cutting slab is cut. 15a and the optical imaging device 20 collide, but by changing the conveying direction of the cutting slab 15a to a direction orthogonal to the casting direction of the slab 15 immediately before the installation position of the optical imaging device 20. The collision between the cutting slab 15a and the optical imaging device 20 can be avoided. Further, the collision between the cutting slab 15a and the optical photographic device 20 can be avoided by setting the optical photographic device 20 obliquely above or below the conveying direction of the cutting slab 15a. However, the optical photographing device 20 is a device for accurately photographing the shape (transverse cross-sectional shape) of the cutting surface 15s of the cutting slab 15a, and for that purpose, the optical photographing device 20 is It is preferable to install it at a position facing the cutting surface 15s, that is, at a position vertically facing the cutting surface 15s.

The image captured by the optical imaging device 20 is digitally processed, and the digitally processed image data is transmitted from the optical imaging device 20 to the storage device 21 and stored in the storage device 21. The stored image data also stores data such as charge number of molten steel 14, steel type, slab size, strand number, casting date and time.

Further, the image data stored in the storage device 21 is transmitted to the calculation display device 22. The calculation display device 22 obtains the cross-sectional shape of the cut surface 15s of the cut slab 15a from the input image data, and based on the obtained cross-sectional shape, the surface defect of the slab 15 and/or the continuous casting machine 1 The equipment abnormality of the mold 5 or the secondary cooling zone immediately below the mold is determined.

Based on the obtained cross-sectional shape, in determining the surface defect of the cast piece 15 and/or the equipment abnormality of the mold 5 of the continuous casting machine 1 or the secondary cooling zone immediately below the mold, a threshold value of the cross-sectional shape set in advance , It is possible to determine that a surface defect and/or equipment abnormality has occurred when the obtained cross-sectional shape exceeds the threshold value by comparing it with the cross-sectional shape obtained at that time. It is also possible to determine that a surface defect and/or equipment abnormality has occurred based on the above.

In the slab slab having a cross section of 150 to 350 mm in thickness and 950 to 3000 mm in width, which is the object of the present invention, is the slab 15 in which the operation abnormality does not occur usually have a rectangular cross section? Alternatively, the long side surface of the slab has a shape in which the upper surface and the lower surface are substantially parallel to each other and the short side surface of the slab is recessed in an arc shape (the depth of the recess; 2 to 4 mm). In contrast to this cross-sectional shape, for example, the cross-sectional shape is not rectangular, the long side of the slab is bulging, and the slab thickness on the left and right of the slab width direction is different (for example, the slab thickness difference on the left and right is 4 mm or more). Or, when the dent amount in the central portion of the short side surface of the slab is different between the left and right and one dent amount is large (for example, 5 mm or more), it is considered that the slab 15 is bleeded because the threshold value is exceeded. It is determined that a slab surface defect has occurred.

The mechanism by which the amount of dents in the center of the short side of the slab is related to the presence or absence of bleeding is not clear, but the dent in the center of the short side of the slab does not occur when the long side of the slab bulges between slab support rolls. It is considered that this is caused by the strain of the slab and the size of the dent reflects the degree of bulging on the long side surface of the slab. That is, it is considered that the larger the bulging amount on the long side surface of the slab, the larger the dent amount at the central portion of the short side surface of the slab. Therefore, it can be understood that the bleeding that tends to occur when the bulging amount of the long side of the slab is large is similarly related to the amount of depression of the central portion of the short side of the slab. The bulging on the long side of the slab is corrected by a plurality of pairs of the slab supporting rolls 6 on the downstream side of the position where the bulging occurs, and the bulging on the long side of the slab is observed on the cut surface 15s of the cut slab 15a. Some things are not done.

On the other hand, the temporal change of the image data can be compared by electronically comparing the contours of the cross-sectional images of the ingots 15 continuously cast in the same mold 5 for each time series. The comparison method is not particularly limited to this method, but there is, for example, a method of comparing the distance between the center positions of both short sides of both slabs and the distance between the center positions of both long sides of the slabs. If the distance between the slab short side center positions decreases with the passage of time, it can be determined that the slab short side surface has a concave shape, and the amount of the recess gradually increases, while If the distance between the central positions of the long sides of the slab is large, it can be determined that bulging has started to occur on the long side surface of the slab. That is, for example, the bulging speed of the slab 15 or the dent speed of the short side surface is obtained over time, and when the obtained bulging speed or dent speed exceeds a certain value, a surface defect and/or equipment abnormality occurs. It is judged that it did.

Then, when the photographed cross-sectional shape exceeds the range of the preset predetermined shape, or when it is determined that an abnormality has occurred due to the temporal change of the photographed cross-sectional shape, the calculation display device 22 causes the cutting slab 15a to be cut. It is determined that a surface defect has occurred in the, and equipment abnormality such that the cross-sectional shape of the cast piece 15 is abnormal, it is determined that at least one of the mold 5 and the secondary cooling zone immediately below the mold has occurred, The abnormality display is displayed on the arithmetic and display unit 22, and at the same time, the occurrence of the abnormality is reported via the alarm device 23.

The continuous casting machine 1 including the slab surface defect and equipment abnormality detection equipment according to the present invention is configured in this manner. In the continuous casting machine 1 having such a configuration, the detection method according to the present invention is carried out as follows.

Molten steel 14 is poured into the mold 5 from the tundish 2 through the immersion nozzle 4. The molten steel 14 poured into the mold 5 is cooled by the mold 5 to form a solidified shell 16 on the contact surface with the mold 5, and is supported by the slab support roll 6 as a slab 15 having an unsolidified layer 17 inside. Meanwhile, it is continuously drawn downward by a pinch roll (a plurality of rolls in the slab supporting roll 6). The slab 15 is cooled in each of the secondary cooling zones of the secondary cooling zone while passing through the installation range of the slab support roll 6, and the thickness of the solidification shell 16 is increased. Complete coagulation until. Then, the cast slab 15 is cut by the slab cutting machine 19 to obtain a cut slab 15a.

The cross-sectional shape of the cut surface 15 s (cross section of the slab) of the slab 15 a is photographed by the optical photographing device 20 every time the slab 15 is cut, and the image data is stored in the storage device 21. The arithmetic and display unit 22 obtains the cross-sectional shape of the transverse section of the slab 15 from the image data input from the storage unit 21, and based on the obtained cross-sectional shape, the surface defects of the slab 15 and/or the continuous casting machine 1 The equipment abnormality of the mold 5 or the secondary cooling zone immediately below the mold is determined.

If the cross-sectional shape of the slab 15 obtained from the image data is not rectangular and the slab thicknesses on the left and right in the slab width direction are different, bulging occurs in the slab 15 and even after the solidification is completed. It means that it remains. Therefore, when it is confirmed from the cross-sectional shape of the slab 15 that bulging exceeding the preset threshold value is generated in the slab 15, the bulging occurrence position of the slab 15 and the portion of the mold 5 that is cooling It can be determined that at least one of the sites of the secondary cooling zone immediately below has an equipment abnormality that causes a slab surface defect due to bleeding.

Since bulging of the slab 15 is unlikely to occur at the time when the thickness of the solidified shell 16 is increased, that is, at a position away from directly below the mold, it is a secondary cooling zone immediately below the mold and corresponds to the bulging occurrence position. It can be determined that an equipment abnormality has occurred in the next cooling zone. Here, the secondary cooling zone immediately below the mold may be a secondary cooling zone in the range from the lower end of the mold 5 to the downstream by about 3 m to 4 m. In the continuous casting machine 1 for slab cast, there is also a continuous casting machine having a facility length of more than 40 m, and the position of the facility abnormality in the secondary cooling zone that causes bulging is located about 3 to 4 m downstream from the lower end of the mold 5. By specifying the range up to, it becomes possible to easily find the location of the equipment abnormality in the secondary cooling zone.

Similarly, in the transverse cross-sectional shape of the slab 15, if it is confirmed that the short side surface of the slab 15 has an amount of dents exceeding the threshold value, the mold 5 that cools the position where the dents exceeding the threshold value are generated. It can be determined that an equipment abnormality that causes a slab surface defect due to bleeding has occurred in at least one of the site 2) and the site of the secondary cooling zone immediately below the mold.

When it is detected that the slab surface defect due to the bleeding is generated in the slab 15, the injection of the molten steel 14 into the mold 5 of the strand is stopped, and the slab 15 in the strand is transferred to the continuous casting machine 1 And then inspect for slab surface defects and other surface cracks caused by bleed. If surface defects are found, they are removed by scarfing or grinder grinding. When it is detected that the slab surface defect caused by the bleed is generated in the slab 15, it is determined that the slab surface defect caused by the bleed is not generated, and the cut casting before the strand of the strand having the same casting chance is determined. It is preferable that the piece 15a also be subjected to a detailed surface defect check. It is more preferable to feed back the obtained result to the threshold value of the judgment.

The present invention is mainly a technique for detecting a slab surface defect caused by bleeding. However, when bulging or non-uniform heat removal that causes bleeding occurs in the slab 15, secondary cooling is performed. Non-uniform cooling of the long side surface of the slab in the strip and supercooling of the corner portion of the slab are likely to occur, which may cause vertical cracks, lateral cracks, and corner key cracks in the slab 15. Therefore, although the present invention monitors the cross section of the slab 15, vertical cracks, lateral cracks, and corner key cracks on the surface of the slab can also be detected.

After the end of continuous casting, the presence or absence of equipment abnormality is inspected in the part of the mold 5 that cools the bulging occurrence position of the slab 15 or the dent occurrence position of the short side surface of the slab and the part of the secondary cooling zone immediately below the mold. .. First, the mold 5 is inspected, then the secondary cooling zone in the range of 3 m to 4 m downstream from the lower end of the mold 5 is inspected, and if no facility abnormality is found in that range, secondary cooling of the downstream side is performed. Continue to check the belt.

As described above, according to the present invention, a slab surface defect caused by bleeding due to bulging of the slab 15 and uneven heat removal is detected based on the cross-sectional shape of the slab cross section. Thus, it is possible to accurately detect the slab surface defect caused by the bleeding. Further, since the slab surface defect caused by the bleed can be detected with high precision, the mold 5 or the secondary cooling zone immediately below the mold 5 which causes the bulge or the short side surface indentation in the slab 15 to cause the bleed. It is also possible to detect equipment abnormalities. In addition, it goes without saying that the cut slab 15a having the slab surface defect caused by the bleeding is prevented from being carried out to the next step.

The present invention was carried out in a vertical bending type two-strand continuous casting machine for continuously casting a slab cast of a low carbon aluminum killed steel having a thickness of 220 mm and a width of 1900 mm at a cast drawing speed of 2.0 m/min. The cut slab slab is conveyed in the casting direction in the center position of the strand of the continuous casting machine, and then, in a continuous casting machine configured to be discharged in a direction orthogonal to the casting direction of the strand of the continuous casting machine. is there.

An air-cooled CCD camera is used as an optical photographing device, and a position where the transport direction of the slab slab is orthogonal to the casting direction, a position corresponding to the center position of the two strands and a thickness center position of the slab slab On the other hand, one CCD camera was arranged so as to face the cut surface of the slab slab.

Based on the image data taken by the CCD camera, the time-dependent change in the cross-sectional shape of the slab slab cross-section was monitored by the arithmetic display device. In the image data, as the threshold value of the cross-sectional shape, it was determined that the thickness of the slab slab was locally increased by 4 mm or more as compared with the normal case, or the dent of the short side surface of the slab slab was 5 mm or more. .. Then, when the monitored image data exceeded the threshold value, it was determined that a slab surface defect due to bleeding occurred in the slab slab, and a continuous steel casting operation was performed.

In the process of continuing the continuous casting operation, in one strand, the continuous casting operation in which the dent of the short side surface of the slab slab became 5 mm or more occurred. In this case, the amount of increase in local thickness of the slab slab was 2 mm or less as compared with the usual case. In the continuous casting operation, the continuous casting of the strand in which the short side surface of the slab slab has a recess of 5 mm or more is immediately stopped when it is determined that a slab surface defect has occurred, and the molten steel remaining in the ladle is removed. Continuous casting was performed on the other strands, and then the planned continuous casting of charges was stopped.

After the continuous casting of the charge was completed, the part of the mold on the side where the dent on the short side of the slab slab was enlarged and the part of the secondary cooling zone in the range of 3 m from directly below the mold were inspected. As a result, it was confirmed that the steam spray nozzle on the lower surface side of the slab slab in the secondary cooling zone was blocked, and the slab slab was not sprayed with the secondary cooling water. When the clogged water spray nozzle was replaced, in the subsequent continuous casting, the dent of the short side surface of the slab slab did not become 5 mm or more.

Further, all the slab slabs continuously cast by the strand having the dent of the short side surface of the slab slab of 5 mm or more were removed from the process operation, and the surface inspection of the slab slab was carried out. As a result of this surface inspection, the slab cast at the time when it was determined that the cast slab surface defects were generated, the cast slab surface defects caused by bleeding were observed. Further, a slab slab continuously cast after the slab surface defect was determined to have occurred (at the time when the continuous casting was stopped, that is, when the molten steel injection into the mold was stopped, the slab was present in the continuous casting machine. In the slab), slab surface defects due to bleeding were also recognized. On the other hand, in the slab slab continuously cast before the time when it was determined that a slab surface defect occurred, some bulging was observed on the long side of the slab, but a slab surface defect due to bleeding was observed. There wasn't.

For the slab slab in which the slab surface defect caused by the bleed was recognized, the slab surface defect caused by the bleed was removed by the scarfing and the process operation was performed.

DESCRIPTION OF SYMBOLS 1 Continuous casting machine 2 Tundish 3 Sliding nozzle 4 Immersion nozzle 5 Mold 6 Cast strip support roll 7 Conveying roll 8 1st cooling zone 9 2nd cooling zone 10 3rd cooling zone 11 4th cooling zone 12 5th cooling zone 13th 6 Cooling Zone 14 Molten Steel 15 Slab 15a Cutting Slab 15s Cutting Surface 16 Solidified Shell 17 Unsolidified Layer 18 Solidification Completed Position 19 Slab Cutting Machine 20 Optical Imaging Device 21 Storage Device 22 Arithmetic Display Device 23 Alarm

Claims (5)

The cross section of the cast piece cut by the cast piece cutting machine provided on the exit side of the continuous casting machine is photographed by an optical photographing device, and the cross-sectional shape of the cross section of the cast piece is taken from the photographed image , the long side of the cast piece. The amount of bulging of the cast slab or the amount of dent on the short side of the slab, and based on the obtained cross-sectional shape, surface defects caused by bleeding of the long side of the slab and short side of the slab , and/or A method of detecting a cast slab surface defect and a facility abnormality in a continuous casting machine, which comprises detecting a facility abnormality causing the surface defect in at least one of the mold and the secondary cooling zone. Based on the change with time of the cross-sectional shape, surface defects caused by bleeding of the slab, and / or, the equipment abnormality that causes the surface defects of at least one of the mold and the secondary cooling zone of the continuous casting machine. The method for detecting a slab surface defect and equipment abnormality in the continuous casting machine according to claim 1, wherein the method is for detecting. In the cross-sectional shape, if the occurrence of bulging in an amount exceeding the threshold on the long side surface of the slab is confirmed, the site of the mold that is cooling the occurrence position of bulging exceeding the threshold and the secondary cooling zone immediately below the mold. The cast piece in the continuous casting machine according to claim 1 or 2 , wherein it is determined that an equipment abnormality causing the surface defect has occurred in at least one of the above parts. Surface defect and equipment abnormality detection method. In the cross-sectional shape, if the occurrence of dents in an amount exceeding the threshold on the short side surface of the slab is confirmed, the site of the mold that is cooling the occurrence position of the dents exceeding the threshold and the secondary cooling zone immediately below the mold. The cast piece in the continuous casting machine according to claim 1 or 2 , wherein it is determined that an equipment abnormality causing the surface defect has occurred in at least one of the above parts. Surface defect and equipment abnormality detection method. An optical photographing device for photographing a cross section of a cast piece cut by a cast piece cutting machine provided on the exit side of the continuous casting machine,
A storage device for storing an image taken by the optical imaging device,
The cross-sectional shape of the slab transverse section from the image stored in the storage device is obtained by the amount of bulging of the slab long side surface or the amount of depression of the slab short side surface, and based on the obtained cross-sectional shape, the slab long side Display device for determining an equipment defect that causes surface defects caused by bleeding of the slab surface and the short side surface of the slab , and/or the surface defects of at least one of the mold and the secondary cooling zone of the continuous casting machine When,
A facility for detecting a slab surface defect and a facility abnormality in a continuous casting machine, which comprises:

Images