JP6922516B2 - How to visualize melting defects on the surface of steel slabs - Google Patents

Description

The present application discloses a method for visualizing edging defects existing on the surface of a high-temperature steel slab after thawing.

Steel slabs (particularly slabs) manufactured in a casting facility are hot-melted (hot scarf) for surface maintenance depending on the steel type and application. Specifically, in a scarf facility, the surface of the steel slab is oxidized and melted by the heat of combustion of the fuel and oxygen while the fuel and oxygen are sprayed from the scarf unit onto the surface of the steel slab to generate a molten iron pool (preheating process). After that, while adjusting the amount and ratio of fuel and oxygen, the surface of the steel slab is continuously melted and scraped by the heat of oxidation reaction between molten iron and oxygen while transporting the steel slab (melting process). As a result, defects such as flaws and inclusions on the surface of the steel slab can be removed.

When the surface of a steel slab is melted, poor melting may occur on the surface of the steel slab. Examples of the types of poor milling include the following four types.
(1) Molten iron may adhere to the surface of the leading portion of the steel slab in a convex shape. It is considered that this is because the molten iron generated in the preheating process flowed to the leading portion of the steel slab due to the gas flow and adhered. In the present application, this is referred to as "return of molten iron".
(2) The slab surface may not be sufficiently melted. It is considered that this is caused by the shortage of molten iron due to the lack of combustion heat in the preheating process. In the present application, this is referred to as "remaining".
(3) A streak-like convex portion extending in the longitudinal direction may be formed on the surface of the steel slab. This is because the surface of the steel slab is locally insufficiently preheated due to clogging of the injection holes of the scarf unit, etc., which causes the surrounding molten iron to flow in the longitudinal direction and is cooled over the entire length by oxygen. It is thought that it occurs in. In the present application, this is referred to as "welded bullion".
(4) There may be streaky recesses extending in the longitudinal direction on the surface of the steel slab. It is considered that this is caused by excessive scraping of the surface of the steel slab due to oxygen leaking from the gap of the scarf unit. In the present application, this is referred to as "linear deep digging".

Poor melting of the surface of a steel slab may cause a decrease in product yield, such as causing a flaw on the surface of the thin plate when the steel slab is subsequently rolled into a thin plate. Therefore, after thawing, it is important to properly determine the presence or absence of blunting defects on the surface of the steel slab, and if there are blunting defects, identify the cause and improve the operation of the thawing equipment. Is. In order to determine the presence or absence of a melting defect, for example, it is conceivable to visualize the melting defect in the captured image by diverting the methods disclosed in Patent Documents 1 to 3 below.

Patent Document 1 discloses a problem of accurately and surely detecting hot water dripping and an unmelted portion remaining on the surface of a steel material whose surface has been melted, and as a means for solving the problem, it is heated to 1200 ° C. or higher. The surface of the steel material whose surface has been melted is continuously imaged by an image pickup device (CCD camera), the brightness signal of the obtained image is converted into temperature, and based on the temperature difference from the healthy part, dripping or dripping A method for detecting a suspected uncut portion is disclosed.

Patent Document 2 discloses a problem of easily detecting preheating unevenness in the width direction of a steel material during preheating of hot melting, and as a means for solving the problem, faces a crater provided in the melting device. A method of detecting preheating unevenness of a steel material through a predetermined step after deploying an imaging means (CCD camera) for imaging the surface of the steel material is disclosed.

Patent Document 3 discloses a problem of hotly inspecting the entire surface of a slab in a high temperature state, and as a means for solving the problem, the surface of the hot slab is irradiated with light from a one-dimensional line light source. A method of generating a two-dimensional image by continuously imaging the reflected light reflected from the surface with a one-dimensional imaging device and detecting a surface defect of the slab based on the two-dimensional image is disclosed.

Japanese Unexamined Patent Publication No. 2012-236215 Japanese Unexamined Patent Publication No. 2015-167977 Japanese Unexamined Patent Publication No. 2014-10004

As shown in FIG. 1, on the surface of the steel slab, the poorly melted portion and the healthy portion have a predetermined temperature difference (luminance difference) according to the elapsed time after the completion of the welding. For example, since the recess such as "linear deep digging" exists in the center of the slab as compared with the healthy part, the temperature is higher and the brightness is higher than that of the healthy part. On the other hand, convex portions such as "welded iron return" and "welded bullion" have a large specific surface area, are easily cooled, and have lower brightness than healthy portions. In addition, the temperature of the "remaining part" is lower than that of the healthy part due to insufficient combustion heat, and the brightness is also lower. Here, when the elapsed time after the completion of welding is short, there is almost no temperature difference (luminance difference) between the poorly melted portion and the healthy portion on the surface of the steel slab, and even if an image is taken with an imaging device, the welding is performed. It can be difficult to identify defects. Further, when the surface of the steel slab is imaged using a CCD camera as disclosed in Patent Documents 1 and 2, if the temperature (luminance) on the surface of the steel slab is too high, the upper limit of the brightness identification range of the camera is exceeded. There is a risk that halation will occur and it will not be possible to properly determine the welding defects on the surface of the steel slab. On the other hand, if the elapsed time after the completion of welding is long, the temperature difference (luminance difference) between the poorly melted portion and the healthy portion on the surface of the steel slab becomes too large and exceeds the brightness identification range of the imaging device. It may be difficult to identify poor melting. In addition, when a low-temperature steel slab whose temperature has dropped completely is imaged with an imaging device, there is no difference in brightness between the poorly melted part and the healthy part on the surface of the steel slab, and the poorly melted steel slab surface is appropriate. It may not be possible to distinguish between. Furthermore, when the surface temperature of the steel slab is low, there is almost no difference in brightness between the steel slab and the background, making it difficult to distinguish between the steel slab and the background in the captured image, and in particular, the outer edge of the steel slab. In some cases, it may not be possible to properly determine the welding defects in the vicinity. In the methods disclosed in Patent Documents 1 and 2, no studies are made on the problems caused by the surface temperature of such steel slabs and the brightness discrimination range of the image pickup apparatus, and naturally, solutions are also shown. Not.

On the other hand, the method disclosed in Patent Document 3 requires a device for a line light source in addition to the imaging device, so that the device as a whole becomes large and difficult to install in the casting line of the casting facility. It lacks convenience, such as the possibility of becoming a problem. In addition, no studies have been made on the problems caused by the surface temperature of the steel slab and the brightness identification range of the image pickup apparatus, and no solution has been shown as a matter of course.

According to the findings of the present inventor, a commonly used CCD camera as disclosed in Patent Documents 1 and 2 has sufficient brightness identification as an imaging device for determining the presence or absence of wrought defects in steel slabs. Has no range. The reason for this is not clear, but it is thought to be related to smear and blooming, which are known as characteristics of CCD sensors. That is, when observing a high-temperature object such as a steel slab after welding, it is considered that the brightness discrimination range is narrowed because the light exudes from the portion having a large amount of light to the periphery.

In order to solve this problem, the present inventor has come up with the idea of applying an image pickup device using a CMOS sensor as an image pickup element instead of a CCD sensor. In principle, the CMOS sensor does not have the problems such as smear and blooming described above. Therefore, it is considered that the image pickup device using the CMOS sensor has a wider luminance identification range than the image pickup device using the CCD sensor.

However, even in an imaging device using a CMOS sensor, the brightness identification range is limited to a specific range. Therefore, the present inventor has proceeded with the study on the relationship between the brightness identification range of the image pickup apparatus using the CMOS sensor and the surface temperature (brightness) of the steel slab after welding. As a result, in the case of a steel slab having a surface temperature of 400 ° C. or higher and 900 ° C. or lower, the temperature (luminance) of the poorly welded portion has a sufficient temperature difference (luminance difference) between the poorly welded portion and the healthy portion. It was found that both the temperature (brightness) of the healthy part and the temperature (brightness) of the healthy part are within the brightness discrimination range of the image pickup apparatus using the CMOS sensor.

In view of the above, the present application provides one of the means for solving the above problems.
A method for visualizing wrought defects on the surface of a steel slab, which is an image pickup device using a CMOS sensor as an image pickup device on the surface of the steel slab whose surface temperature is 400 ° C. or higher and 900 ° C. or lower after the slab. Disclose a method characterized by imaging by.

"Surface temperature" means the average temperature of the surface of a steel slab. The average temperature of the surface of the steel slab can be measured by using thermography or the like. That is, in the method of the present disclosure, even if the field of view of the image pickup apparatus includes a steel slab surface that is not within the range of 400 ° C. or higher and 900 ° C. or lower, the steel slab included in the visual field of the image pickup apparatus. The average temperature of the entire surface of the steel may be 400 ° C. or higher and 900 ° C. or lower.

"Steel slabs having a surface temperature of 400 ° C. or higher and 900 ° C. or lower after thawing" means steel slabs whose surface temperature decreases with the passage of time after melting, and the surface temperature of which is 400 ° C. or higher and 900 ° C. or higher. It means a steel slab that has been kept at the following temperature. Although it is obvious to those skilled in the art, even if the surface temperature of the slab that has been heat-treated after the heat treatment is 400 ° C. or higher and 900 ° C. or lower, the "after-melting" referred to in the present application. It does not correspond to "steel slabs having a surface temperature of 400 ° C. or higher and 900 ° C. or lower". For example, a steel slab whose surface temperature is raised to a range of 400 ° C. or higher and 900 ° C. or lower by heating or the like after the surface temperature of the steel slab becomes less than 400 ° C after welding is referred to in the present application. It is excluded from "steel slabs whose surface temperature is 400 ° C or higher and 900 ° C or lower after welding".

In the method of the present disclosure, the operating conditions of the casting equipment and the installation position of the imaging device in the casting equipment so that the surface temperature of the steel slab imaged by the imaging device is within the range of 400 ° C. or higher and 900 ° C. or lower. It is preferable to adjust at least one of them.

The "operating conditions of the casting equipment" are, for example, the temperature condition when the steel slab is melted and the transport speed condition of the steel slab after the slab (from the completion of the slab to the transfer to the imaging device). At least one of the operating conditions in which the surface temperature of the steel slab can be adjusted before the image is taken by the imaging device in the casting equipment, such as the condition of the time) and the presence or absence of the cooling process of the steel slab after welding. Say one.

In the method of the present disclosure, by using a CMOS sensor as an image pickup device of an image pickup device, halation or the like at the time of image pickup can be prevented. In addition, since the surface temperature of the steel slab to be imaged is 400 ° C. or higher and 900 ° C. or lower, a sufficient temperature difference (luminance difference) between the poorly melted portion and the healthy portion on the surface of the steel slab after welding. And, both the temperature (luminance) of the poorly melted portion and the temperature (luminance) of the healthy portion can be kept within the brightness identification range of the CMOS sensor. Further, it is not necessary to separately prepare a line light source for irradiating the surface of the steel slab with light. As described above, according to the method of the present disclosure, it is possible to appropriately visualize the wrought defects on the surface of the steel slab by a simple method.

It is a conceptual diagram for demonstrating the relationship between the elapsed time after smelting and the surface temperature of a steel slab (the temperature of a poorly smelted portion and the temperature of a healthy smelting portion). It is a conceptual diagram for demonstrating the relationship between the surface temperature of a steel slab (the temperature of a poor slab and the temperature of a healthy slab) and brightness. The brightness identification range of the conventional image pickup device (CCD camera) and the brightness discrimination range of the image pickup device (CMOS camera) used in the method of the present disclosure are also conceptually described. It is a conceptual diagram showing the relationship between the elapsed time after edging and the surface temperature of the steel slab (the temperature of the defective edging part and the temperature of the healthy edging part), and it is understood that the above-mentioned problems can be solved by the method of the present disclosure. It is a conceptual diagram for demonstrating. The four curves (one solid line and three broken lines) in the graph correspond to the four curves (one solid line and three broken lines) in the graph of FIG. 1, respectively. It is the schematic for demonstrating the installation angle of the camera in an Example. This is an image that attempts to visualize the "welded bullion". (A) is an image taken by a CMOS camera, and (B) is an image taken by a CCD camera. This is an image that attempts to visualize the "remaining". (A) is an image taken by a CMOS camera, and (B) is an image taken by a CCD camera.

The method disclosed in the present application is a method of visualizing a welding defect on the surface of a steel slab, and the surface of the steel slab whose surface temperature is 400 ° C. or higher and 900 ° C. or lower after the slab is CMOS. It is characterized in that an image is taken by an image pickup apparatus using a sensor as an image pickup element.

1. 1. Steel slab The steel slab to be imaged may be a slab cast by a casting apparatus and is made of steel, and its steel type and application (shape) are not particularly limited. This is because the relationship between the surface temperature and the brightness of a slab made of steel is almost the same regardless of the steel type and application (shape). Therefore, any of the steel slabs that have been welded can be the subject of imaging by the method of the present disclosure.

2. Melting The method disclosed in this disclosure targets steel slabs after melting. The smelting may be a general one carried out using a scarf unit. Generally, welding has a preheating process and a welding process. The preheating conditions and melt cutting conditions may be appropriately adjusted according to the steel type and application of the steel slab. It is self-evident that the preheating temperature and the welding temperature are more than 900 ° C. because they are "temperatures at which the steel melts". For example, preheating and welding can be performed at a temperature of about 1500 ° C. or higher, preferably about 1580 ° C. or higher. That is, the temperature of the steel slab immediately after the completion of welding can be, for example, about 1500 ° C. or higher, preferably about 1580 ° C. or higher.

3. 3. Image pickup device By imaging the surface of a steel slab with an image pickup device, an image capture image in which welding defects are visualized is obtained. Here, in the method of the present disclosure, it is important to use an image pickup device using a CMOS sensor (CMOS image sensor) as an image pickup element. As conceptually shown in FIG. 2, the image pickup apparatus using the CMOS sensor has a wider luminance identification range than the image pickup apparatus using the CCD sensor. As described above, it is considered that the CMOS sensor does not have problems such as smear and blooming peculiar to the CCD sensor. An image pickup device itself using a CMOS sensor as an image pickup device is known and is obvious to those skilled in the art, and thus the description thereof will be omitted here.

When imaging with an imaging device using a CMOS sensor, it is important that the surface temperature of the steel slab after welding is 400 ° C. or higher and 900 ° C. or lower. Here, the "surface temperature" means the "average temperature of the surface" of the steel slab. The average temperature of the surface of the steel slab can be measured by using thermography or the like. That is, in the method of the present disclosure, even if the field of view of the image pickup apparatus includes a steel slab surface that is not within the range of 400 ° C. or higher and 900 ° C. or lower, the steel slab included in the visual field of the image pickup apparatus. The average temperature of the entire surface of the steel may be 400 ° C. or higher and 900 ° C. or lower. However, since the welding defects on the surface of the steel slab can be visualized more appropriately, the difference between the minimum temperature and the maximum temperature of the surface of the steel slab included in the field of view of the imaging device is 100 ° C or more and 300 ° C or less. Is preferable. The surface of the steel slab has a minimum temperature of preferably 300 ° C. or higher, and a maximum temperature of preferably 1100 ° C. or lower. In particular, it is preferable that the entire surface of the steel slab included in the field of view of the image pickup apparatus is within the range of 400 ° C. or higher and 900 ° C. or lower.

If the surface temperature of the steel slab is 400 ° C or higher, it does not fall below the lower limit of the brightness identification range of the CMOS sensor, and if the surface temperature of the steel slab is 900 ° C or lower, the brightness discrimination range of the CMOS sensor Never exceed the upper limit of. Further, if the surface temperature of the steel slab is 400 ° C. or higher, the difference in brightness between the steel slab and the background is sufficient, so that it is easy to determine the boundary between the steel slab and the background in the captured image. , It is possible to appropriately discriminate the welding defects near the outer edge of the steel slab. Further, as conceptually shown in FIG. 3, when the surface temperature of the steel slab is 400 ° C. or higher and 900 ° C. or lower (in FIG. 3, the elapsed time after welding is A or higher and B or lower), the steel slab A sufficient temperature difference (luminance difference) occurs between the poorly melted part and the healthy part on the surface. From the above, when the surface temperature of the steel slab becomes 400 ° C or higher and 900 ° C or lower after thawing, the surface of the steel slab is imaged with an imaging device using a CMOS sensor, and the slab defect is appropriate. It is possible to obtain a visualized image.

4. Positional relationship between steel slabs and image pickup device The installation location of the image pickup device in the casting equipment is not particularly limited. However, as described above, it is necessary to take an image of the surface of the steel slab having a surface temperature of 400 ° C. or higher and 900 ° C. or lower after welding with an imaging device. In other words, it is preferable to adjust the installation position of the image pickup device so that the surface temperature of the steel slab imaged by the image pickup device after welding is within the range of 400 ° C. or higher and 900 ° C. or lower. Although it depends on the operating conditions of the casting equipment described later, for example, an imaging device is installed at a place where the surface of the steel slab can be imaged after a time of 5 seconds or more and 180 seconds or less has passed after the completion of the welding of the steel slab. It is preferable to do so.

5. Operating conditions of casting equipment The operating conditions of casting equipment are not particularly limited. However, as described above, it is necessary to take an image of the surface of the steel slab whose surface temperature is 400 ° C. or higher and 900 ° C. or lower after the welding with an imaging device. In other words, it is preferable to adjust the operating conditions of the casting equipment so that the surface temperature of the steel slab imaged by the image pickup apparatus after the welding is within the range of 400 ° C. or higher and 900 ° C. or lower. Alternatively, it is also preferable to adjust both the installation location of the imaging device and the operating conditions of the casting equipment described above. Although it depends on the installation location of the above-mentioned imaging device, for example, when a time of 5 seconds or more and 180 seconds or less elapses after the completion of melting of the steel slab, the surface of the slab to be imaged is imaged by the above-mentioned imaging device. It is preferable to adjust at least one of the temperature condition when the steel slab is melted, the transport speed condition of the steel slab after the slab, and the like so as to reach the range. Alternatively, when the surface temperature of the steel slab that reaches the imaging range of the imaging device becomes high, cooling may be promoted by using a cooling device or the like.

The upper surface, lower surface and side surface of the slab obtained by continuous casting were subjected to a preheating step and a welding step while spraying fuel gas and oxygen gas from the scarf unit under the conditions shown in Table 1 below.

On the other hand, an imaging device was installed at a point 10 m downstream from the scarf unit to image the surface of the slab after melting. At this time, as shown in FIG. 4, the imaging direction by the imaging device was set to an angle of 25 ° with respect to the lower surface of the slab. As the image pickup device, both a CCD camera and a CMOS camera were used, and the captured images were compared.

The shape of the slab that has been smelted, the temperature of the slab before smelting, the amount of slab, the transport speed of the slab during smelting, the surface temperature of the slab immediately after the end of smelting, the time required from the end of smelting to the imaging location, and imaging. The slab transport speed at the location and the surface temperature of the slab at the imaging location are shown in Table 2 below. The surface temperature of the slab was measured using thermography.

The captured image ((A) CMOS image, (B) CCD image) of the slab 1 is shown in FIG. 5, and the captured image ((A) CMOS image, (B) CCD image) of the slab 2 is shown in FIG.

As shown in FIG. 5A, the slab 1 was able to visualize the “welded bullion” which is poorly welded by taking an image with a CMOS camera. On the other hand, as shown in FIG. 5 (B), when a CCD camera was used, halation occurred in the captured image, and the welding defect could not be properly visualized. In the CCD camera, the brightness identification range is narrow as shown in FIG. 2, and the moment the front part of the slab enters the field of view of the camera, the amount of received light is adjusted so as to be within the brightness identification range, thereby performing halation. It is probable that it was caused.

As for the slab 2, as shown in FIG. 6 (A), by taking an image with a CMOS camera, it was possible to visualize the “remaining” that is poorly melted at the end of the slab. On the other hand, as shown in FIG. 6B, when the CCD camera was used, the slab end portion was crushed black in the captured image, and the welding defect could not be properly visualized. In the CCD camera, as shown in FIG. 2, it is considered that the luminance identification range is narrow and the temperature (luminance) at the end of the slab, which is easily cooled, is below the lower limit of the luminance identification range.

As described above, using an image pickup device using a CMOS sensor as an image pickup device, the surface temperature (brightness) of the steel slab to be imaged is within the brightness identification range of the image pickup device (surface temperature 400 ° C. or higher and 900 ° C. or lower). By adjusting so that it fits, a captured image in which welding defects were visualized was obtained.

From the mechanism shown in FIGS. 1 and 2 and the results of FIGS. The surface temperature (brightness) of the steel slab to be imaged is within the brightness identification range of the image pickup device (surface temperature 400 ° C. or higher and 900 or lower) using an image pickup device that uses a CMOS sensor as an image pickup device. It is self-evident that a visualized image can be obtained by adjusting it so that it fits.

Poor melting of the surface of a steel slab may cause a decrease in product yield, such as causing a flaw on the surface of the thin plate when the steel slab is subsequently rolled into a thin plate. By appropriately determining the presence or absence of melting defects on the surface of the steel slab by the method of the present disclosure, if there is a melting defects, the cause can be identified and the operation of the melting equipment can be improved. .. As a result, when the steel slab is subsequently rolled into a thin plate, the occurrence of defects on the surface of the thin plate can be suppressed, and the product yield can be improved.

Claims (2)

It is a method to visualize the melting defects on the surface of steel slabs.
The surface of the steel slab whose surface temperature has become 400 ° C. or higher and 900 ° C. or lower after edging is imaged by an image pickup device using a CMOS sensor as an image pickup element.
Method. At least one of the operating conditions of the casting facility and the installation position of the image pickup device in the continuous casting facility so that the surface temperature of the steel slab imaged by the image pickup device is within the range of 400 ° C. or higher and 900 ° C. or lower. Adjust one,
The method according to claim 1.

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