Measuring apparatus, piercing and rolling equipment, hole processing method, and steel pipe manufacturing method

Abstract

To provide a measuring apparatus that can be installed in a limited space and that can measure the end face dimensions of a heated cylindrical steel piece having a recess formed in the end face of the cylindrical steel piece.SOLUTION: There is provided a measuring apparatus for measuring end face dimensions of a heated cylindrical steel piece in which a recess is formed in an end face by punch to form the recess. The measuring apparatus comprises an imaging device and an image processing device. The imaging device captures an image of the end face of the cylindrical steel piece in which the recess is formed. The image processing device detects, from brightness information of the image, an outer circle being an outline of the end face and an inner circle being an outline of the recess.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a measuring device, and more particularly to a measuring device that measures the end face dimensions of a heated cylindrical steel billet having a recess formed on the end face thereof by hole processing to form the recess. [Background technology]

[0002] In the manufacturing process of seamless steel pipes, a cylindrical billet (hereinafter also referred to as a round billet) is heated in a heating furnace, and then the heated cylindrical billet is pierced in a piercing mill (piercer) to form a cylindrical hollow blank, a process known as Mannesmann piercing. In this process, to assist the Mannesmann piercing, a hole may be formed as preliminary processing on the end surface of the round billet heated in the heating furnace to form a recess.

[0003] This hole drilling affects the amount of wall thickness deviation at the tip end of the blank pipe during piercing and Mannesmann cracking, and it is desirable that the center position of the recess formed by the hole drilling be close to the center position of the end face of the round billet. It is also desirable that the diameter of the recess formed by the hole drilling be a predetermined target value.

[0004] One technique for measuring the dimensions of an item involves workers manually measuring parts of the product offline using calipers or micrometers.

[0005] As a technique for measuring dimensions of an article online, for example, Patent Document 1 proposes a technique for measuring dimensions of a slab by using images of the slab photographed from the side and above in a continuous casting facility and processing the images. Also, Patent Document 2 proposes a technique for measuring the radial wall thickness of a hollow cylindrical object such as a perforated round billet using a CCD camera. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-260551 [Patent Document 2] Japanese Patent Application Publication No. 7-260435 Summary of the Invention [Problem to be solved by the invention]

[0007] When measuring manually, there are problems such as the need to remove the product to be measured from the production line, which reduces measurement efficiency, and there is also the problem that measurement results are subject to measurement error by the worker, making it difficult to obtain sufficient accuracy.

[0008] Furthermore, in the method of Patent Document 1, for example, in a steel pipe piercing and rolling facility, the surrounding space is not as generous as in a continuous casting facility, and the installation space for measuring equipment is restricted. In the method of Patent Document 1, the cameras used to take photographs from the side and above must be installed close to the subject, which poses a problem of unavoidable equipment trouble due to radiant heat. Furthermore, the method of Patent Document 2 also has the problem of limited installation space for the measuring equipment.

[0009] Furthermore, the method of Patent Document 2 is a measurement technique for steel pipes that are already hollow. Patent Document 2 does not consider the possibility of application to the measurement of depressions formed in red-hot objects, nor the measurement accuracy.

[0010] The present invention has been made in consideration of the above circumstances, and has an object to provide a measuring device that can be installed in a limited space and can measure the end face dimensions of a heated cylindrical steel billet having a recess formed on the end face of the cylindrical steel billet. [Means for solving the problem]

[0011] The inventors came up with the idea of ​​utilizing the difference in brightness between the drilled and un-drilled areas that occurs after drilling when the scale layer that forms during heating in a heating furnace peels off during drilling, exposing the new surface.

[0012] Specifically, in the present invention, the measurement target is an end face of a heated round billet on which a recess is formed. In this case, the outer circle that defines the outline of the end face of the heated round billet has a large difference in brightness between the end face and the surrounding background due to the self-luminescence of the end face caused by heating (red heat), making it easy to detect. However, the inner circle that defines the outline of the recess formed on the end face is formed on the end face of the heated round billet and is therefore a heated portion, so there is little difference in brightness between the recess and the other areas of the end face.

[0013] Therefore, the inventors came up with the idea that when drilling to form a recess in the end face, scale peels off in the drilled area, exposing a new surface, and the area where the new surface is exposed has a higher temperature and brightness, making it possible to extract the brightness difference between the drilled area (recess) and the other area of ​​the end face (unprocessed area).

[0014] The present invention has been made based on the above idea, and the gist and configuration thereof are as follows. [1] A measuring device for measuring the end face dimensions of a heated cylindrical steel billet having a recess formed on the end face thereof by hole processing to form a recess, comprising: An imaging device and an image processing device are included, the imaging device captures an image of the end face of the cylindrical steel billet on which the recessed portion is formed, The image processing device detects an outer circle that defines the outline of the end face and an inner circle that defines the outline of the recessed portion from brightness information of the image. [2] The image processing device detects the outer circle from the brightness difference of brightness information acquired in the image from the outside to the inside, and detects the inner circle from the brightness difference of brightness information acquired in the image from the center of the outer circle in the outward direction. [1] The measuring device described in [1]. [3] The measuring device according to [1] or [2], wherein the image processing device calculates the amount of eccentricity between the center of the outer circle and the center of the inner circle from the center coordinates of the outer circle and the center coordinates of the inner circle. [4] The measuring device according to [1] or [2], further comprising a detection device that detects that the cylindrical steel billet on which the recessed portion is formed has been transported. [5] The measuring device according to [3], further comprising a detection device that detects that the cylindrical steel billet on which the recessed portion is formed has been transported. [6] Piercing-rolling equipment comprising: the measuring device according to any one of [1] to [5] above; a hole processing machine that forms a recess in an end surface of a heated cylindrical steel billet; and a piercing-rolling mill that pierces and rolls the cylindrical steel billet having a recess formed in the end surface by the hole processing machine. [7] A hole processing method for forming a recess in an end surface of a heated cylindrical steel billet by a hole processing machine, A hole processing method, which determines the center coordinates of the outer circle and the center coordinates of the inner circle by the measuring device described in [1], [2] or [4], and adjusts the hole processing position of the next processed material so that the difference between the center coordinates of the outer circle and the center coordinates of the inner circle becomes small. [8] A hole processing method for forming a recess in an end surface of a heated cylindrical steel billet by a hole processing machine, A hole processing method, which calculates the eccentricity between the center of the outer circle and the center of the inner circle using the measuring device described in [3] or [5], and adjusts the hole processing position of the next processed material so that the eccentricity becomes small. [9] A method for manufacturing a steel pipe, comprising manufacturing a steel pipe using the hole processing method according to [7] or [8] above. [Effects of the Invention]

[0015] According to the present invention, a measuring device can be provided that can be installed in a limited space and can measure the end face dimensions of a heated cylindrical steel billet having a recess formed on the end face of the cylindrical steel billet.

[0016] According to the present invention, it is possible to measure with high accuracy the end face dimensions of a heated (red-hot) cylindrical billet having a recess formed on its end face. According to the present invention, it is possible to detect the outer circle that defines the outline of the end face of a heated round billet, and the inner circle that defines the outline of the recess formed on the end face. Furthermore, it is possible to detect the center of the outer circle (outer circle center), the center of the inner circle (inner circle center), the amount of eccentricity thereof, the diameter of the outer circle, the diameter of the inner circle, etc. Furthermore, it is possible to detect these with high accuracy, for example, a measurement error of within ±0.5 mm.

[0017] Furthermore, by using this information, it is possible to predict the wear state of the hole-making tool (punch) and the positional deviation of the hole-making. By using this information to make holes, it is possible to improve the processing accuracy of the hole-making of the subsequent processed material. By making holes using the measuring device of the present invention, it is possible to improve the eccentricity of the hole-making. This also has the effect of improving the uneven thickness of the steel pipe (product). [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram showing a general configuration of a piercing-rolling facility 50 having a measuring device 1 according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the drilling process for forming a recess in the end surface of a heated round steel billet by the drilling machine 10. As shown in FIG. [Figure 3] FIG. 3 is a diagram showing an example of a procedure of image processing performed by the image processing device. [Figure 4] FIG. 4 is a diagram showing two circles, an outer circle and an inner circle, and the relationship between the eccentricity of the center of the outer circle (outer circle core) and the center of the inner circle (inner circle core). [Figure 5] FIG. 5 is a diagram showing the relationship between the amount of eccentricity in hole drilling, which is preliminary processing when manufacturing a steel pipe with a product outer diameter equivalent to 190 mm, and the wall thickness deviation of the hollow blank after piercing and rolling. [Figure 6] FIG. 6 is a diagram showing the results of verifying the measurement accuracy of the measuring device of the present invention using a cold machined workpiece. [Figure 7] FIG. 7 shows the results of verifying the effect of improving the positional accuracy of hole processing on the improvement of thickness deviation in actual steel pipe manufacturing equipment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiment shown below.

[0020] (piercing and rolling equipment) Fig. 1 is a schematic diagram showing the overall configuration of a piercing-rolling facility 50 having a measuring device 1 according to one embodiment of the present invention. The piercing-rolling facility 50 shown in Fig. 1 has the measuring device 1, a hole processing machine 10, and a piercing-rolling mill 20. Furthermore, a heating furnace (a rotary heating furnace in this embodiment) for heating cylindrical steel billets (round steel billets) is disposed upstream of the piercing-rolling facility 50. The piercing-rolling facility 50 has, from the upstream side to the downstream side of a conveying line for round steel billets, the hole processing machine 10, the measuring device 1, and the piercing-rolling mill 20, in that order.

[0021] Cylindrical steel billets (round steel billets) that are used as raw materials for steel pipes are not particularly limited, and can be obtained by, for example, a known method. Specifically, molten steel having a predetermined chemical composition is produced by a melting method such as a converter, and then round steel billets can be obtained by a method such as a continuous casting method or an ingot-making and blooming rolling method.

[0022] A round billet is charged into a heating furnace and heated to a temperature of, for example, 1200°C or higher, and then removed from the heating furnace. The heated round billet (also referred to as round billet B in this specification) is transported to a hole-making machine 10, which performs hole-making to form recesses in the end faces. The end face dimensions of the hole-made round billet (also referred to as round billet HB in this specification) are measured by a measuring device 1, and then the billet is transported to a piercing-rolling mill 20, where it is pierced and rolled into a hollow blank. Each component of the piercing-rolling equipment will be described below.

[0023] (Measuring equipment) As shown in FIG. 1, a measuring device 1 according to one embodiment of the present invention has an imaging device (a camera 2 in this embodiment) and an image processing device 3. In this embodiment, the measuring device 1 also has a detection device (a temperature sensor 4 in this embodiment) and a display device (a monitor 5). The imaging device, image processing device, detection device, and display device are connected by wire or wirelessly. The measuring device 1 is disposed downstream of the hole processing machine 10 on the round billet conveying line, and measures the end face dimensions of the round billet HB after hole processing. A method for measuring the end face dimensions of the round billet HB using the measuring device 1 will be described later.

[0024] <Imaging device> In this embodiment, a camera 2 is used as the imaging device. The camera 2 captures an image of the end face of the round steel billet HB on which a recess is formed by the hole processing machine 10. The camera 2 is not particularly limited, and for example, a digital camera or the like can be used. The camera 2 can be selected taking into consideration, for example, the number of pixels, resolution, etc. of the camera.

[0025] It is desirable to adjust the position of camera 2 so that the center of the HB end face of the round billet, which is the material being measured, is captured in the center of its field of view. To achieve this, as shown in Figure 1, camera 2 is generally installed directly in front of the material being measured (the HB end face of the round billet). That is, camera 2 is installed at the same height as the material being measured. More specifically, camera 2 is installed parallel to the conveying line for the round billet, and its position is adjusted so that the center height of camera 2 (the optical axis of camera 2) coincides with the center height of the HB of the round billet (the axis of the HB). By installing camera 2 in this manner, it is possible to prevent areas other than the end face of the round billet (the side surface of the round billet) from being captured in the image captured by camera 2. When installing camera 2, it is desirable to calibrate the camera 2 in advance by comparing the results of an image captured using a highly precisely machined hollow cylinder or the like that allows the actual dimensions to be confirmed, in order to determine whether the installation position of camera 2 is appropriate.

[0026] For example, if the measurement field of view of camera 2 is 600mm x 450mm, it can capture an image of a workpiece with an outer diameter of 350mm. If a general-purpose camera with about 2 million pixels is used as camera 2, the distance of 1 dot will be about 0.38mm. These conditions are determined by the relationship between the dimensions of the workpiece and the distance between camera 2 and the workpiece, so it is desirable to determine the relationship between their relative positions and the resolution of camera 2 in advance.

[0027] It is desirable to place any imaging device, such as camera 2, at least 1 m away from the material being measured. This is to avoid the effects of radiant heat from the rolled material; by keeping the distance between the imaging device and the material being measured at 1 m or more, the effects of radiant heat can be reduced to less than 1 / 10. It is also desirable to keep the distance between the imaging device and the material being measured at 3 m or less. This is because if the imaging device is placed at a greater distance, it becomes difficult to obtain accurate measurement of the end face dimensions of the round billet being measured. However, this distance can be changed by adding or modifying equipment to provide heat resistance. It is also desirable to keep the distance between the imaging device and the material being measured constant, but if the distance between them changes, actual measurements can be taken using a laser distance meter or similar, and numerical correction can be performed when converting the number of pixels into a numerical value.

[0028] <Image processing device> The image captured by the camera 2 is sent to the image processing device 3, where it is processed. The image processing device 3 is not particularly limited, but may be a computer such as a personal computer. The image processing device 3 outputs the detection results to a monitor 5.

[0029] <Detection device> The measuring device 1 according to this embodiment further includes a detection device that detects the material to be measured. The detection device detects that the material to be measured has been transported to the measuring device 1. The detection device is not particularly limited as long as it can detect the material to be measured, and examples include a temperature sensor and a laser sensor. A temperature sensor is desirable as the detection device. In this embodiment, the heated round steel billet HB is the object to be detected, and good detection accuracy can be achieved by using a temperature sensor as the detection device. Furthermore, dust and other particles may be present in the atmosphere of the transport line in this embodiment. For example, if a laser sensor is used as the detection device, the detection accuracy may be reduced due to the influence of dust and other particles. By using a temperature sensor as the detection device, the detection device is less susceptible to the influence of dust and other particles.

[0030] In this embodiment, the temperature sensor 4 may be, for example, a radiation thermometer. This is because the round steel billet HB, which is the material to be measured, is usually heated to 1200°C or higher in a heating furnace, and is usually still at a high temperature of 500°C or higher even after the hole drilling is completed. There are no particular restrictions on the radiation thermometer, as long as it can measure the temperature range of the expected material to be measured.

[0031] It is desirable that the position of the temperature sensor 4 is also adjusted in the same way as the camera 2. As shown in Fig. 1, the temperature sensor 4 is installed in front of the material to be measured (the HB end face of the round steel billet). That is, the temperature sensor 4 is installed at the same height as the material to be measured, just like the camera 2. It is also desirable that the distance between the temperature sensor 4 and the material to be measured is adjusted in the same way as the distance between the above-mentioned imaging device and the material to be measured.

[0032] In this embodiment, the temperature sensor 4 detects the material to be measured (round billet HB) transported to the measuring device 1, and a timer is adjusted to capture an image of the end face of the round billet HB when the round billet HB is transported in front of the camera 2. This allows adjustments to be made so that the center of the end face of the round billet HB is captured near the center of the field of view of the camera 2, and adjustments can be made so that areas other than the end face of the round billet (the side surface of the round billet) are not captured in the image captured by the camera 2, thereby improving detection accuracy during image processing. Furthermore, images may be captured continuously, and specific images may be extracted from multiple captured images based on information from a temperature sensor. For example, information from a temperature sensor may be used to extract images with a large temperature difference (brightness difference) between the scale-adhered portion and the newly exposed surface of the drilled portion on the end face after drilling. The measuring device of the present invention does not necessarily have to include a detection device. In this case, the timing of capturing images may be adjusted based on the transport speed of the round billet HB, or the timing may be adjusted visually by an operator.

[0033] By adopting the above configuration, the measuring device 1 can be installed in a limited space. For example, by installing a box (H 150 mm x W 150 mm x D 300 mm) that can store the camera 2 and storing the camera 2 inside the box, the measuring device 1 can be installed on a conveyance line. Furthermore, by utilizing detection devices such as temperature sensors, automatic online measurement becomes possible.

[0034] The round steel billet HB, whose end face dimensions have been measured by the measuring device 1, is transported to the piercing-rolling mill 20, where it is pierced and rolled into a hollow blank. In this embodiment, the measurement results by the measuring device 1 are fed back to the hole-making machine 10, so that the hole-making position of the next processed material (the heated round steel billet to be subsequently subjected to hole-making) can be adjusted.

[0035] (Steel pipe manufacturing method) Next, a method for manufacturing a steel pipe using the piercing and rolling equipment 50 will be described. As shown in Fig. 1, first, a round billet, which is the raw material for the steel pipe, is charged into a heating furnace. The round billet is inserted into the heating furnace and heated to a temperature of, for example, 1200°C or higher.

[0036] Next, the round billet (round billet B) heated in the heating furnace is removed from the heating furnace and transported to a hole processing machine 10. The hole processing machine 10 has a punch 11 at its tip, and performs hole processing to form a recess in the end surface of the round billet B by pressing the punch 11 against the end surface of the round billet B. This hole processing (hole processing step) corresponds to preprocessing for the next step (piercing and rolling step).

[0037] (Hole drilling method) Here, the hole processing method will be described. FIG. 2 is a schematic diagram illustrating hole processing in which a recess is formed in the end surface of a heated round billet (round billet B) using a hole processing machine 10. The round billet B heated in a heating furnace is placed on a holding means (trough T in this embodiment) provided on a conveying line (FIG. 2(a)). Next, the round billet B is gripped by dies (upper die D1, lower die D2) and fixed in a predetermined position (FIG. 2(b)). Then, a punch 11 of the hole processing machine 10 is pressed against the end surface of the round billet B fixed in the predetermined position, thereby forming a recess in the end surface of the round billet B (FIG. 2(c)).

[0038] Fig. 2(d) is a schematic diagram showing the end face of a round billet (round billet HB) after hole drilling has been performed. As shown in Fig. 2(d), a recess is formed on the end face of the round billet HB by a punch 11 of a hole drilling machine 10. In this specification, the outline of the end face of the round billet HB is referred to as the "outer circle," and the outline of the recess formed on the end face of the round billet HB is referred to as the "inner circle" (see Fig. 2(d)).

[0039] The position of the recess formed on the end face of the round billet B can be adjusted, for example, by adjusting the horizontal position of the trough T on which the round billet B is placed or the vertical fixing position of the round billet B by the dies (upper die D1, lower die D2). In this embodiment, the horizontal and vertical positions can each be adjusted in 1 mm increments, for example. In FIG. 2(d), the shape of the recess is circular when viewed from the front of the end face of the round billet HB, but is not limited to this. The shape of the recess can be any shape depending on the shape of the punch 11 of the hole processing machine 10, and may be, for example, a polygon such as a regular polygon when viewed from the front of the end face of the round billet HB.

[0040] (Method for measuring the end face dimensions of round steel billets HB) Next, a description will be given of a method for measuring the end face dimensions of the round steel billet HB using the measuring device 1. As described above, the round steel billet HB has holes drilled on its end face by the drilling machine 10, and has recesses on its end face. The measuring device 1 measures the shape of the end face of the round steel billet HB after drilling.

[0041] First, the camera 2 of the measuring device 1 captures an image of the end face of the round billet HB. The camera 2 preferably captures an image of the end face of the round billet HB immediately after drilling, for example, within 5 seconds after drilling is completed. As described above, in this embodiment, the temperature sensor 4 detects the material to be measured (the round billet HB) and adjusts the timer so that areas other than the end face of the round billet (the side surface of the round billet) do not appear in the image captured by the camera 2. This improves detection accuracy during image processing and enables automatic online measurement. The image data captured by the camera 2 is sent to the image processing device 3.

[0042] <Image processing method> FIG. 3 shows the image processing procedure by the image processing device 3. As part of the image processing procedure, first, the image processing device 3 grayscales the image of the captured end face of the round billet HB (FIG. 3(a)). Next, the image processing device 3 detects the boundary between the self-luminous region of the round billet HB and the background region outside it as an outer circle. To do this, the image processing device 3 calculates the brightness difference from brightness information acquired from the outside to the inside of the captured image, and detects positions where the brightness difference exceeds a specified value as edge points (outer circle edge points). Then, a virtual circle passing through the detected outer circle edge points is detected as the outer circle (FIG. 3(b)). Furthermore, the image processing device 3 calculates the center (outer circle core) of the outer circle.

[0043] Next, the image processing device 3 detects the boundary between the hole-machined portion (recessed portion) and the other area (unmachined portion) on the end face of the round steel billet HB as the inner circle. To do this, the image processing device 3 calculates the brightness difference from the brightness information acquired in the outward direction from the outer circle center calculated above, and detects the position where the brightness difference exceeds a specified value as an edge point (inner circle edge point). Then, the image processing device 3 detects a virtual circle passing through the detected inner circle edge point as the inner circle (Figure 3(c)). Furthermore, the image processing device 3 calculates the center of the inner circle (inner circle center).

[0044] In this case, as described above, the hole-machined portion on the end face of the HB of the round steel billet has a high temperature and brightness because the scale has peeled off and the new surface is exposed. Therefore, the inner circle edge points can be extracted from the brightness difference between the hole-machined portion (recessed portion) and the other area of ​​the end face (unmachined portion).

[0045] Furthermore, areas (unmachined areas) other than the hole-machined areas (recessed areas) may also have areas where the scale peels off due to the impact of drilling, etc. As described above, by determining the brightness difference from brightness information acquired in the outward direction from the outer circle core, the influence of such areas can be avoided, and the detection accuracy of the inner circle edge points can be improved.

[0046] Furthermore, the image processing device 3 can determine the outer diameter (diameter of the outer circle). The method for detecting the outer diameter is not particularly limited. For example, the image processing device 3 can calculate the sum of the distance between the detected outer circle edge point and the outer circle core and the distance between the outer circle edge point at a position opposite to the outer circle edge point and the outer circle core, and detect the maximum value of the sum as the maximum outer circle diameter, the minimum value of the sum as the minimum outer circle diameter, and the average of the maximum and minimum outer circle diameters as the average outer circle diameter (FIG. 3(d)).

[0047] Similarly, the image processing device 3 can determine the inner circle diameter (diameter of the inner circle). The method for detecting the inner circle diameter is not particularly limited. For example, the sum of the distance between the detected inner circle edge point and the inner circle core and the distance between the inner circle edge point at a position opposite the inner circle edge point and the inner circle core is calculated, and the maximum value of the sum is detected as the maximum inner circle diameter, the minimum value of the sum is detected as the minimum inner circle diameter, and the average of the maximum and minimum inner circle diameters is detected as the average inner circle diameter (FIG. 3(e)).

[0048] Furthermore, the image processing device 3 can obtain the amount of eccentricity from the center coordinates of the outer circle and the center coordinates of the inner circle. FIG. 4 is a diagram showing the relationship between two circles, the outer circle and the inner circle, and the amount of eccentricity between the center of the outer circle (outer circle core) and the center of the inner circle (inner circle core). As shown in FIG. 4, the image processing device 3 obtains the composite value [√(x 2 +y 2)) is calculated as the amount of eccentricity. The amount of eccentricity can be converted into a numerical value, for example, from the number of pixels and resolution of the imaging device. If the shape of the recess is polygonal when viewed from the front of the end face of the round billet, the amount of eccentricity may be calculated from the coordinates of the center of the outer circle and the coordinates of the area center of gravity of the polygon.

[0049] In this embodiment, the end face dimensions of the round steel billet HB can be measured as described above using the measuring device 1. That is, in this embodiment, the outer circle that defines the outline of the end face and the inner circle that defines the outline of the recess formed on the end face can be detected. Furthermore, the diameter of the outer circle (outer circle diameter), the diameter of the inner circle (inner circle diameter), and the amount of eccentricity between the center of the outer circle (outer circle core) and the center of the inner circle (inner circle core) can be determined.

[0050] The image processing device 3 of this embodiment may have a calculation unit having an image conversion means and an end face dimension detection means. The image conversion means performs a process of converting the image acquired by the camera 2 into a grayscale image. The end face dimension detection means performs a process of detecting end face dimensions such as the outer circle, inner circle, outer circle core, inner circle core, outer circle diameter, inner circle diameter, and eccentricity amount from the image converted into a grayscale image as described above.

[0051] It should be noted that the image processing method by the image processing device 3 is not limited to this. For example, in detecting the contour (arc shape) of a recessed portion, it is possible to use a method in which known shapes are learned using machine learning to extract features, or to detect the contour (arc shape) of a recessed portion by detecting brightness differences in a captured image and performing a Hough transform on the point coordinates.

[0052] The measurement data obtained by the measuring device 1 is fed back to the hole drilling machine 10, which adjusts the hole drilling position of the next workpiece. Specifically, the hole drilling position of the next workpiece is adjusted so that the difference between the position (coordinates) of the outer circle core and the position (coordinates) of the inner circle core determined by the image processing device 3 becomes small, preferably so that the positions of the outer circle core and the inner circle core coincide. The adjustment of the hole drilling position may also be performed by adjusting the hole drilling position of the next workpiece so that the amount of eccentricity determined by the image processing device 3 becomes small, preferably so that the amount of eccentricity becomes minimum. As described above, the hole drilling position can be adjusted, for example, by adjusting the horizontal position of the trough T installed on the conveying line or the vertical fixing positions of the dies (upper die D1, lower die D2).

[0053] This allows for small eccentricity between the outer and inner cores, resulting in hole machining with excellent machining accuracy.

[0054] Next, the round billet (round billet HB) having a recess on its end surface is conveyed to a piercing mill (piercer) 20. The piercing mill 20 has main rolls 21a, 21b and a plug 22 disposed between the main rolls 21a, 21b. The round billet HB fed between the main rolls 21a, 21b is pierced at its center by the plug 22, and formed into a hollow blank. The hollow blank is then conveyed to a drawing mill such as a plug mill or a mandrel mill, where it is subjected to diameter and wall reduction processing to form a product pipe (steel pipe) of predetermined dimensions.

[0055] In this case, in this embodiment, since the holes are drilled with excellent machining accuracy as described above, the amount of wall thickness deviation of the hollow shell after piercing by the piercing-rolling mill can be made small (uniform).

[0056] FIG. 5 is a diagram showing the relationship between the amount of eccentricity in hole drilling, which is a preliminary process when manufacturing a steel pipe with a product outer diameter equivalent to 190 mm, and the wall thickness deviation of the hollow blank after piercing and rolling. The horizontal axis shows the amount of eccentricity at the hole drilling position, and the vertical axis shows the wall thickness deviation rate of the hollow blank. The wall thickness deviation rate indicates the percentage (%) at which the value of the wall thickness deviation rate % of the hollow blank [((maximum wall thickness - minimum wall thickness) / average wall thickness) × 100] exceeds 10.0%. A wall thickness deviation rate of 10.0% indicates the manufacturing conditions under which the manufacturing length variation and the trim thickness of the flawed portion can be ensured when the wall thickness tolerance is ±10%. In other words, it is preferable that the wall thickness deviation rate of the hollow blank is within 10.0%.

[0057] As shown in Fig. 5, when the amount of eccentricity in the hole drilling was large and the drilling accuracy was low, the wall thickness deviation of the hollow blank increased significantly. This tendency was not dependent on the outer diameter of the steel pipe, but was common to all diameters. In this way, the wall thickness deviation of the hollow blank can be improved by aligning the center position of the hole drilling, which is a preliminary drilling process, closer to the center position of the end face of the material to be rolled (round steel billet B). [Example]

[0058] In order to verify the measurement accuracy of the measuring device of the present invention, measurements of the end face dimensions were carried out using cold machined pieces, and the results are shown in Figure 6.

[0059] (1) A cylindrical workpiece (steel billet) with an outer diameter of 170 mm was obtained by machining. A hole was machined on the end face of this workpiece to form a circular recess with a diameter of 70 mm. Using the same method, (2) a cylindrical workpiece with an outer diameter of 350 mm was obtained, and a circular recess with a diameter of 110 mm was machined on the end face of this workpiece. In both (1) and (2), the eccentricity between the center of the outline (outer circle) of the end face of the workpiece and the center of the outline (inner circle) of the recess was set to 15 mm.

[0060] A test piece was prepared that was painted with paint so that the self-luminescence of the hole-machined and unmachined parts of the end face of the heated round steel piece in the above embodiment, and the brightness information of the outside (background) of the end face, would be equivalent to that of the hole-machined and unmachined parts of the machined piece to the above dimensions.

[0061] The end face dimensions of the test piece were then measured using the measuring device of the above-described embodiment (however, no detection device was used in this example). The camera of the measuring device was installed in front of the end face of the test piece, and was positioned so that the optical axis of the camera coincided with the height of the outer center of the end face of the test piece. The horizontal distance between the camera and the end face of the test piece was 3 m. The image captured by the camera was then processed using the image processing device as described above to determine the outer diameter, inner diameter, and eccentricity. This measurement was performed 50 times consecutively, and repeatability was evaluated.

[0062] The evaluation results are shown in Figure 6. Figure 6(a) shows the evaluation results for a test piece (machined piece) with an outer diameter of 170 mm, and Figure 6(b) shows the measurement results for a test piece (machined piece) with an outer diameter of 350 mm. The average, maximum, and minimum outer diameter values, inner diameter (hole diameter), and eccentricity obtained through the measurement all achieved an accuracy of ±0.5 mm compared to the actual values ​​measured separately.

[0063] Next, the effect of introducing the measuring device on improving the accuracy of hole processing on the end face of a round steel billet was verified in an actual steel pipe manufacturing facility.

[0064] The results are shown in Figure 7. The upper part of Figure 7 shows the change in the amount of eccentricity before the measurement device was introduced, and the lower part of Figure 7 shows the change in the amount of eccentricity after the measurement device was introduced. These results show that the introduction of the measurement device of the present invention can improve the hole drilling accuracy of round steel billets. [Explanation of symbols]

[0065] 1. Measuring equipment 2 Cameras 3. Image processing device 4 Temperature Sensors 5 monitors 10 hole drilling machine 20 Piercing and rolling mill 50 Piercing and rolling equipment B Heated round steel billet Round steel billet with HB holes

Claims

1. A measuring device for measuring an end face dimension of a heated cylindrical steel billet having a recess formed on the end face thereof by hole processing, the measuring device comprising: An imaging device and an image processing device are included, the imaging device captures an image of the end face of the cylindrical steel billet on which the recessed portion is formed, The image processing device detects an outer circle that defines the outline of the end face and an inner circle that defines the outline of the recessed portion from brightness information of the image.

2. 2. The measurement device according to claim 1, wherein the image processing device detects the outer circle from a luminance difference of luminance information acquired in a direction from the outside to the inside of the image, and detects the inner circle from a luminance difference of luminance information acquired in a direction from the center of the outer circle to the outside.

3. 3. The measuring device according to claim 1, wherein the image processing device determines the amount of eccentricity between the center of the outer circle and the center of the inner circle from the coordinates of the center of the outer circle and the coordinates of the center of the inner circle.

4. 3. The measuring device according to claim 1, further comprising a detection device that detects that the cylindrical steel billet on which the recessed portion is formed has been conveyed.

5. 4. The measuring device according to claim 3, further comprising a detection device that detects that the cylindrical steel billet on which the recessed portion is formed has been conveyed.

6. 3. A piercing-rolling facility comprising: the measuring device according to claim 1; a hole processing machine that forms a recess in an end surface of a heated cylindrical steel billet; and a piercing-rolling mill that pierces and rolls the cylindrical steel billet having the recess formed in the end surface by the hole processing machine.

7. 4. A piercing-rolling facility comprising: the measuring device according to claim 3; a hole processing machine that forms a recess in an end surface of a heated cylindrical steel billet; and a piercing-rolling mill that pierces and rolls the cylindrical steel billet having the recess in the end surface formed by the hole processing machine.

8. 5. A piercing-rolling facility comprising: the measuring device according to claim 4; a hole processing machine that forms a recess in an end surface of a heated cylindrical steel billet; and a piercing-rolling mill that pierces and rolls the cylindrical steel billet having the recess formed in the end surface by the hole processing machine.

9. 6. A piercing-rolling facility comprising: the measuring device according to claim 5; a hole processing machine that forms a recess in an end surface of a heated cylindrical steel billet; and a piercing-rolling mill that pierces and rolls the cylindrical steel billet having a recess in the end surface formed by the hole processing machine.

10. A hole processing method for forming a recess in an end surface of a heated cylindrical steel billet by a hole processing machine, 3. A hole processing method, comprising: determining the center coordinates of the outer circle and the center coordinates of the inner circle by the measuring device according to claim 1 or 2; and adjusting the hole processing position of the next processed material so that the difference between the center coordinates of the outer circle and the center coordinates of the inner circle becomes small.

11. A hole processing method for forming a recess in an end surface of a heated cylindrical steel billet by a hole processing machine, 4. A hole drilling method, comprising: determining an amount of eccentricity between the center of the outer circle and the center of the inner circle by the measuring device according to claim 3; and adjusting a hole drilling position of a subsequent workpiece so as to reduce the amount of eccentricity.

12. A hole processing method for forming a recess in an end surface of a heated cylindrical steel billet by a hole processing machine, 5. A hole processing method, comprising: determining the center coordinates of the outer circle and the center coordinates of the inner circle by the measuring device according to claim 4; and adjusting the hole processing position of the next workpiece so that the difference between the center coordinates of the outer circle and the center coordinates of the inner circle becomes small.

13. A hole processing method for forming a recess in an end surface of a heated cylindrical steel billet by a hole processing machine, 6. A hole drilling method, comprising: determining an amount of eccentricity between the center of the outer circle and the center of the inner circle by the measuring device according to claim 5; and adjusting a hole drilling position of a next workpiece so that the amount of eccentricity becomes small.

14. A method for manufacturing a steel pipe, comprising manufacturing a steel pipe using the hole drilling method according to claim 10.

15. A method for manufacturing a steel pipe, comprising manufacturing a steel pipe using the hole drilling method according to claim 11.

16. A method for manufacturing a steel pipe, comprising manufacturing a steel pipe using the hole drilling method according to claim 12.

17. A method for manufacturing a steel pipe, comprising manufacturing a steel pipe using the hole drilling method according to claim 13.

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