U.S. patent application number 16/331067 was filed with the patent office on 2019-07-04 for welding monitoring apparatus and welding monitoring method.
This patent application is currently assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION. The applicant listed for this patent is NIPPON STEEL & SUMIKIN PIPE CO., LTD., NIPPON STEEL & SUMITOMO METAL CORPORATION. Invention is credited to Noboru HASEGAWA, Michimasa MUKAI, Michitoshi TANIMOTO.
Application Number | 20190201957 16/331067 |
Document ID | / |
Family ID | 60156809 |
Filed Date | 2019-07-04 |
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United States Patent
Application |
20190201957 |
Kind Code |
A1 |
HASEGAWA; Noboru ; et
al. |
July 4, 2019 |
WELDING MONITORING APPARATUS AND WELDING MONITORING METHOD
Abstract
Provided is a welding monitoring apparatus that monitors a
welding state of a V-convergence region in which a strip-shaped
metal sheet is converged in a V-shape, when the metal sheet is
cylindrically formed while being conveyed, and both side edges of
the metal sheet are heated and melted in a manner of being butted
each other while being converged in the V-shape, such that an
electric resistance welded steel pipe is manufactured. This welding
monitoring apparatus includes an image capturing unit that captures
images of a region including the V-convergence region in time
series; and an image processing unit that extracts a welding point
based on the images captured in time series and detects the
presence or absence and a position of irregular arcing at the
welding point or on an upstream side of the welding point.
Inventors: |
HASEGAWA; Noboru; (Tokyo,
JP) ; TANIMOTO; Michitoshi; (Tokyo, JP) ;
MUKAI; Michimasa; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON STEEL & SUMITOMO METAL CORPORATION
NIPPON STEEL & SUMIKIN PIPE CO., LTD. |
Tokyo
Tokyo |
|
JP
JP |
|
|
Assignee: |
NIPPON STEEL & SUMITOMO METAL
CORPORATION
Tokyo
JP
NIPPON STEEL & SUMIKIN PIPE CO., LTD.
Tokyo
JP
|
Family ID: |
60156809 |
Appl. No.: |
16/331067 |
Filed: |
November 8, 2016 |
PCT Filed: |
November 8, 2016 |
PCT NO: |
PCT/JP2016/083135 |
371 Date: |
March 6, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 31/125 20130101;
B21C 37/0818 20130101; G01N 29/041 20130101; B21C 51/00 20130101;
B23K 13/08 20130101; B21C 37/08 20130101; B23K 11/0873 20130101;
G01N 2291/267 20130101; B23K 11/252 20130101; B23K 13/02 20130101;
G01N 21/952 20130101; G01N 29/043 20130101; B23K 31/003 20130101;
B23K 11/062 20130101; G01N 21/892 20130101 |
International
Class: |
B21C 51/00 20060101
B21C051/00; B21C 37/08 20060101 B21C037/08; B23K 13/02 20060101
B23K013/02; B23K 13/08 20060101 B23K013/08; B23K 31/00 20060101
B23K031/00; G01N 21/892 20060101 G01N021/892; G01N 21/952 20060101
G01N021/952; G01N 29/04 20060101 G01N029/04 |
Claims
1. A welding monitoring apparatus that monitors a welding state of
a V-convergence region in which a strip-shaped metal sheet is
converged in a V-shape, when the metal sheet is cylindrically
formed while being conveyed, and both side edges of the metal sheet
are heated and melted in a manner of being butted each other while
being converged in the V-shape, such that an electric resistance
welded steel pipe is manufactured, the apparatus comprising: an
image capturing unit that captures images of a region including the
V-convergence region in time series; and an image processing unit
that extracts a welding point based on the images captured in time
series and detects the presence or absence and a position of
irregular arcing at the welding point or on an upstream side of the
welding point.
2. The welding monitoring apparatus according to claim 1, wherein
the images captured by the image capturing unit are RGB images, and
wherein the image processing unit extracts at least one of a red
image and a blue image from the RGB images, performs inverted
binarization and labeling of the red image with respect to the red
image, and detects a high-luminance portion in the blue image with
respect to the blue image.
3. The welding monitoring apparatus according to claim 1, wherein
the image capturing unit is a camera capturing 200 frames or more
per second.
4. A welding monitoring method for monitoring a welding state of a
V-convergence region in which a strip-shaped metal sheet is
converged in a V-shape, when the metal sheet is cylindrically
formed while being conveyed, and both side edges of the metal sheet
are heated and melted in a manner of being butted each other while
being converged in the V-shape, such that an electric resistance
welded steel pipe is manufactured, the method comprising: an image
capturing step of capturing images of a region including the
V-convergence region in time series; and a detecting step of
extracting a welding point based on the images captured in time
series and detecting the presence or absence and a position of
irregular arcing at the welding point or on an upstream side of the
welding point.
5. The welding monitoring method according to claim 4, wherein RGB
images are used as the images, and wherein in the detecting step,
at least one of a red image and a blue image is extracted from the
RGB images, inverted binarization and labeling of the red image are
performed with respect to the red image, and a high-luminance
portion in the blue image is detected with respect to the blue
image.
6. The welding monitoring method according to claim 4, wherein in
the image capturing step, images are captured at a frame rate of
200 frames or more per second.
7. The welding monitoring method according to claim 4, further
comprising: a marking step of marking the position of the irregular
arcing in a longitudinal direction in the electric resistance
welded steel pipe.
8. The welding monitoring method according to claim 7, further
comprising: a defect presence-or-absence specifying step of
performing an ultrasonic test with respect to a region to which the
marking is applied.
9. The welding monitoring method according to claim 4, further
comprising: a tracking step of tracking the position of the
irregular arcing in a longitudinal direction in the electric
resistance welded steel pipe.
10. The welding monitoring apparatus according to claim 2, wherein
the image capturing unit is a camera capturing 200 frames or more
per second.
11. The welding monitoring method according to claim 5, wherein in
the image capturing step, images are captured at a frame rate of
200 frames or more per second.
12. The welding monitoring method according to claim 5, further
comprising: a marking step of marking the position of the irregular
arcing in a longitudinal direction in the electric resistance
welded steel pipe.
13. The welding monitoring method according to claim 6, further
comprising: a marking step of marking the position of the irregular
arcing in a longitudinal direction in the electric resistance
welded steel pipe.
14. The welding monitoring method according to claim 5, further
comprising: a tracking step of tracking the position of the
irregular arcing in a longitudinal direction in the electric
resistance welded steel pipe.
15. The welding monitoring method according to claim 6, further
comprising: a tracking step of tracking the position of the
irregular arcing in a longitudinal direction in the electric
resistance welded steel pipe.
16. The welding monitoring method according to claim 11, further
comprising: a marking step of marking the position of the irregular
arcing in a longitudinal direction in the electric resistance
welded steel pipe.
17. The welding monitoring method according to claim 16, further
comprising: a defect presence-or-absence specifying step of
performing an ultrasonic test with respect to a region to which the
marking is applied.
18. The welding monitoring method according to claim 11, further
comprising: a tracking step of tracking the position of the
irregular arcing in a longitudinal direction in the electric
resistance welded steel pipe.
19. The welding monitoring method according to claim 12, further
comprising: a defect presence-or-absence specifying step of
performing an ultrasonic test with respect to a region to which the
marking is applied.
20. The welding monitoring method according to claim 13, further
comprising: a defect presence-or-absence specifying step of
performing an ultrasonic test with respect to a region to which the
marking is applied.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a welding monitoring
apparatus and a welding monitoring method for an electric
resistance welded steel pipe.
RELATED ART
[0002] An electric resistance welded steel pipe is manufactured
through the following step. That is, first, a strip-shaped metal
sheet is continuously formed into a cylindrical shape by a roll
group while being conveyed along its longitudinal direction. Then,
while an upset is applied to the cylindrically formed metal sheet
from its side by a pair of squeeze rolls, and while heat-input is
controlled with respect to both side edges in a circumferential
direction of the metal sheet converged in a V-shape, both the side
edges are welded by being heated and melted through high-frequency
resistance welding or induction heating welding and being butted
each other. Since this step of welding an electric resistance
welded steel pipe is an important step which directly affects the
quality of an electric resistance welded steel pipe, various
examinations have been performed in the related art.
[0003] For example, Patent Document 1 discloses that the form of a
welding spot changes into "a first kind", "a second kind", "a
transition region", or "a subordinate second kind" depending on the
heat input amount applied at the time of welding (refer to FIG. 8).
This Patent Document 1 employs an electric resistance welding work
management apparatus including "an arc detecting region extraction
unit that extracts a narrow region including a welding slit
generated between a V-convergence point (VI) that is an abutment
point at which the steel sheet abuts and a welding point (W) in
which a molten steel starts to be discharged from the inside of the
steel sheet, as an arc detecting region; and an arc detecting unit
that detects an arc generated in the arc detecting region".
[0004] According to this constitution, it is possible to obtain a
frequency of generation of an arc regularly generated (which will
hereinafter be referred to as a steady state arc) on a downstream
side of the V-convergence point.
[0005] Moreover, this electric resistance welding work management
apparatus employs a constitution "including an arc generation
frequency measuring unit that measures a frequency of generation of
an arc, and a welding phenomenon determining unit that determines a
welding phenomenon thereof based on whether or not the frequency of
generation of an arc is equal to or greater than a predetermined
value".
[0006] According to this constitution, the form of a steady state
arc downstream of the V-convergence point is grasped based on the
frequency of generation of the steady state arc, and thus an
appropriate heat input amount is controlled.
PRIOR ART DOCUMENT
Patent Document
[0007] [Patent Document 1] Japanese Unexamined Patent Application,
First Publication No. 2016-78056
[0008] According to the technology disclosed in Patent Document 1,
it is possible to realize an appropriate welding state downstream
of the V-convergence point. However, from the viewpoint of
improving the quality of a welding spot, further amelioration is
demanded.
[0009] For example, high-frequency electric resistance welding is a
technology in which currents are concentrated on a welding surface
such that welding is efficiently performed by utilizing a proximity
effect and a skin effect of steel edges in a weld. However, when
high-frequency electric resistance welding is performed, a strong
electromagnetic field is formed around the steel edges due to
significant currents flowing in the steel edges. Since this
electromagnetic field is maximized at a welding point (V point), if
a magnetic substance is present around the steel edges, it is
likely to be incorporated into the welding point.
[0010] As a material of an electric resistance welded steel pipe,
sometimes a steel sheet to which scale generated at the time of hot
rolling adheres is adopted, and the scale is peeled off from a
surface layer through a forming process or by a fin pass roll.
Particularly, the fin pass roll can form a newly formed surface by
scraping a welding surface. On the other hand, scale or iron powder
may be generated. In addition, there is a possibility that iron
powder may be similarly generated even in a pickled material in
which scale seldom adheres to its surface layer. In this manner, a
phenomenon, in which scale that has been peeled off or scale
powder, iron powder, or the like that has been scraped is caught in
a weld as a foreign substance, occurs sometimes. In this case, if a
foreign substance has a large size to a certain degree, there is a
possibility that it will remain on the welding surface as a solid
without being melted until an upset is applied and it will become a
defect without being discharged. Although the frequency of
generation of a defect is not high, it degrades toughness of a weld
and causes a crack at the time of working. Therefore, it is
strongly demanded that a foreign substance is to be detected during
pipe-making regardless of its size.
[0011] However, in the technology disclosed in Patent Document 1,
the frequency of generation of a steady state arc on a downstream
side of the welding point (V point) is obtained and the heat input
state of welding is grasped, but countermeasures related to
generation of a defect caused by a caught-in foreign substance are
not provided.
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0012] The present invention has been made in consideration of the
foregoing circumstances, and an object thereof is to provide a
welding monitoring apparatus and a welding monitoring method, in
which a relatively light caught-in defect caused by an incorporated
foreign substance such as scale powder or iron powder can be
detected in real time in a welding step of an electric resistance
welded steel pipe.
Means for Solving the Problem
[0013] In order to gratify the foregoing object, first, the
inventors have analyzed a target defect. FIG. 1A and FIG. 1B show a
result obtained by installing an electric resistance welded steel
pipe such that a weld of a defect-generated portion is at a
90.degree. position in a vertical direction, and performing a
flattening test for reduction in the vertical direction. FIG. 1A
shows an external appearance photograph of a fracture surface
having a crack, and FIG. 1B shows a secondary electron image
captured by a scanning electron microscope (SEM). As shown in FIG.
1A, a defect to be regarded as a target is characterized by a
slender black streak pattern present in a central position of the
crack while extending in the through-thickness direction and having
a width of several millimeters or smaller present. In the secondary
electron image shown in FIG. 1B as well, a boundary between a black
streak part and the surrounding part is manifested, and a dimple
fracture surface which is characteristically formed in the
surrounding part at the time of a low heat input has been observed.
From the results of the flattening test described above, it is
speculated that the defect has been generated due to a caught-in
foreign substance which has a lower temperature than a welding
surface at the time of welding and causes a heat release of the
surrounding part.
[0014] Moreover, FIG. 2A and FIG. 2B show scanning electron
microscope (SEM) analysis results of the black streak part. As a
result of composition analysis of a portion 3 in FIG. 2A, in which
the black streak part is enlarged, using a scanning electron
microscope (SEM), the peaks of iron and oxygen are noticeable as
shown in FIG. 2B. On the other hand, compositions other than both
the elements are at a substantially noise level, and thus it is
ascertained that the composition of the black streak part is iron
oxide. When a plurality of places are analyzed, fine ingots of such
iron oxide are scattered inside the black streak part and are
highly concentrated in their entirety. Therefore, it is determined
that this defect is caused due to iron oxide (scale) which has been
caught in or the welding surface in which iron powder is caught in
and is oxidized.
[0015] The caught-in process through which such a defect is
generated has not been clarified until now. Therefore, an
experiment in which a defect at the time of welding was
artificially generated by using scale or iron powder was performed.
At this time, a weld was cyclically image-captured by a camera
installed above the weld, and comparison was performed with respect
to a crack (that is, a defect-generated portion) generated through
a flattening test. As a result, it has been found that there is a
possibility that a foreign substance will be carried from an
upstream side of a welding point while it adheres to the welding
surface and will be caught in. Moreover, it has been found that if
welding surfaces (edges) approach each other when a foreign
substance is caught in, both the edges are short-circuited, and
arcing (which will hereinafter be referred to as irregular arcing)
occurs. Therefore, the inventors have invented an image processing
method of automatically detecting irregular arcing by utilizing the
features that this irregular arcing occurs at a welding point or on
an upstream side thereof.
[0016] That is, the present invention provides the following
aspects.
[0017] (1) According to an aspect of the present invention, there
is provided a welding monitoring apparatus that monitors a welding
state of a V-convergence region in which a strip-shaped metal sheet
is converged in a V-shape, when the metal sheet is cylindrically
formed while being conveyed, and both side edges of the metal sheet
are heated and melted in a manner of being butted each other while
being converged in the V-shape, such that an electric resistance
welded steel pipe is manufactured. The welding monitoring apparatus
includes: an image capturing unit that captures images of a region
including the V-convergence region in time series; and an image
processing unit that extracts a welding point based on the images
captured in time series and detects the presence or absence and the
position of irregular arcing at a welding point or on an upstream
side of the welding point.
[0018] (2) The aspect according to (1) may be constituted as
follows. The images captured by the image capturing unit are RGB
images. The image processing unit extracts at least one of a red
image and a blue image from the RGB images, performs inverted
binarization and labeling of the red image with respect to the red
image, and detects a high-luminance portion in the blue image with
respect to the blue image.
[0019] (3) In the aspect according to (1) or (2), the image
capturing unit may be a camera capturing 200 frames or more per
second.
[0020] (4) In addition, according to another aspect of the present
invention, there is provided a welding monitoring method for
monitoring a welding state of a V-convergence region in which a
strip-shaped metal sheet is converged in a V-shape, when the metal
sheet is cylindrically formed while being conveyed, and both side
edges of the metal sheet are heated and melted in a manner of being
butted each other while being converged in the V-shape, such that
an electric resistance welded steel pipe is manufactured. The
welding monitoring method includes: an image capturing step of
capturing images of a region including the V-convergence region in
time series; and a detecting step of extracting a welding point
based on the images captured in time series and detecting the
presence or absence and a position of irregular arcing at the
welding point or on an upstream side of the welding point.
[0021] (5) The aspect according to (4) may be constituted as
follows. RGB images are used as the images. In the detecting step,
at least one of a red image and a blue image is extracted from the
RGB images, inverted binarization and labeling of the red image are
performed with respect to the red image, and a high-luminance
portion in the blue image is detected with respect to the blue
image.
[0022] (6) In the aspect according to (4) or (5), in the image
capturing step, images may be captured at a frame rate of 200
frames or more per second.
[0023] (7) The aspect according to any one of (4) to (6) may
further include a marking step of marking the position of the
irregular arcing in a longitudinal direction in the electric
resistance welded steel pipe.
[0024] (8) In the case of (7), the aspect may further include a
defect presence-or-absence specifying step of performing an
ultrasonic test with respect to a region to which the marking is
applied.
[0025] (9) The aspect according to any one of (4) to (6) may
further include a tracking step of tracking the position of the
irregular arcing in a longitudinal direction in the electric
resistance welded steel pipe.
[0026] As a camera to be used in the image capturing unit and the
image capturing step, any of a monochrome camera and a color camera
can be used. However, in a case where the aspects of (2) and (5)
are employed, it is preferable to use a color camera which can
perform color separation so as to distinguish light emission from a
molten steel and irregular arcing from each other with high
contrast.
Effects of the Invention
[0027] According to the welding monitoring apparatus and the
welding monitoring method of each of the aspects of the present
invention, it is possible to detect a defect which is generated due
to a foreign substance caught on a welding surface, including a
relatively light defect. Then, this detection information can be
tracked in a step of manufacturing an electric resistance welded
steel pipe, or marking can be performed on a steel pipe itself
immediately after a defect is detected. In this case, a defect
portion is unerringly eliminated from a product, so that only a
normal portion having no caught-in defect can be shipped as a
product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1A shows a photograph showing an external appearance of
a target defect.
[0029] FIG. 1B is a photograph showing a secondary electron image
of a target defect.
[0030] FIG. 2A is a view showing an example in which qualitative
analysis is performed with respect to a target defect by using a
scanning electron microscope (SEM), and it is a photograph of a
backscattered electron image of a scanning electron microscope
(SEM).
[0031] FIG. 2B is a view showing an example in which qualitative
analysis is performed with respect to a target defect by using a
scanning electron microscope (SEM), and it is a graph showing
results of composition analysis of a portion 3 in FIG. 2A performed
by using a scanning electron microscope (SEM).
[0032] FIG. 3 is a perspective view showing an electric resistance
welded steel pipe welding apparatus in which a welding monitoring
apparatus and a welding monitoring method according to an
embodiment of the present invention are applied.
[0033] FIG. 4 is a flowchart of an image processing algorithm for
detecting generation of a defect by using the same welding
monitoring apparatus and the same welding monitoring method.
[0034] FIG. 5 is a photograph showing an example of an image of an
image processing process for detecting generation of a defect. FIG.
5(a) shows a captured image, FIG. 5(b) shows a detected welding
point, FIG. 5(c) shows a detected blue component, and FIG. 5(d)
shows a detected high-luminance portion.
[0035] FIG. 6 is a photograph in which a state of a weld at the
time of generation of a defect is image-captured.
[0036] FIG. 7 is a view showing an example in which a
defect-generated position and a portion where a crack is generated
through a flattening test are butted each other. FIG. 7(a) is a
photograph showing an actual defect portion checked after the
flattening test and the external appearance thereof, and FIG. 7(b)
shows comparison between a portion where irregular arcing has
occurred and an image.
[0037] FIG. 8 is a view describing an example of a welding
monitoring method in the related art, and it is a view showing each
of welding phenomena of "a first kind", "a second kind", "a
transition region", and "a subordinate second kind" in a welding
spot.
EMBODIMENT OF THE INVENTION
[0038] An embodiment of a welding monitoring apparatus and a
welding monitoring method for an electric resistance welded steel
pipe according to the present invention will be described below
with reference to the drawings.
[0039] FIG. 3 shows a perspective view of an electric resistance
welded steel pipe welding apparatus in which the same welding
monitoring apparatus and the same welding monitoring method are
applied. The same electric resistance welded steel pipe welding
apparatus is an apparatus which manufactures an electric resistance
welded steel pipe by cylindrically forming a strip-shaped metal
sheet 1 while the strip-shaped metal sheet 1 is conveyed along its
longitudinal direction, and heating and melting both side edges
(edges) 1a and 1b of the metal sheet 1 in a manner of being butted
each other while the side edges are converged in a V-shape in a
plan view. The reference sign 3 indicated in FIG. 3 is a
V-convergence point at which both the side edges 1a and 1b
converged in the V-shape are butted each other and are heated and
melted. In this FIG. 3, the metal sheet (steel sheet) 1 proceeds
from the front side on the paper toward the deep side on the paper
along its longitudinal direction. Therefore, in a case where the
V-convergence point 3 is taken as a reference, the front side on
the paper becomes an upstream side, and the deep side on the paper
becomes a downstream side.
[0040] The welding monitoring apparatus of the present embodiment
monitors a welding state of a V-convergence region in which the
metal sheet 1 is converged in a V-shape, when an electric
resistance welded steel pipe is manufactured.
[0041] The reference signs 4a and 4b in FIG. 3 indicate a pair of
contact tips disposed to come into contact with spots near both the
side edges 1a and 1b of the metal sheet 1 in the circumferential
direction, which travels toward the V-convergence point 3. In
addition, the reference sign 5 in FIG. 3 indicates an impeder which
is disposed in a central part of the cylindrically formed metal
sheet 1, and the reference sign 6 indicates a high-frequency power
supply which is connected to each of the contact tips 4a and 4b.
High-frequency currents supplied through the contact tips 4a and 4b
flow as indicated with arrows along the extending direction of both
the side edges 1a and 1b in the circumferential direction of the
metal sheet 1, so that both the side edges 1a and 1b of the metal
sheet 1 are heated and melted due to high-frequency resistance.
Similar to that in the related art, a heat input is controlled by
means of these high-frequency currents. A pair of squeeze rolls 2
and 2 near the V-convergence point 3 apply an upset to both the
side edges 1a and 1b of the metal sheet 1 which have been heated
and melted such that both the side edges 1a and 1b are subjected to
electric resistance welding. Instead of high-frequency resistance
welding using the contact tips 4a and 4b, an induction heating-type
welding in which heating is performed by using an induction coil
can also be employed.
[0042] The squeeze rolls 2 and 2 apply an upset to both the side
edges 1a and 1b of the metal sheet 1 which have been heated and
melted in this manner, so that oxide on a surface of the metal
sheet 1 is extruded and discharged from a welding surface, and
thereby excellent welding quality is achieved. However, as
described above, if a foreign substance is caught on the welding
surface, strength of the welding surface is degraded, and a
possibility of a crack at the time of working of a steel pipe or
when an internal pressure is applied to a steel pipe increases.
[0043] The welding monitoring apparatus of the present embodiment
includes an image capturing unit 7 and an image processing unit 8
in order to monitor a caught-in defect in real time including a
light defect which have not been able to be monitored in the
related art. According to this welding monitoring apparatus,
irregular arcing (arcing into which a foreign substance is
incorporated) which has occurred in a weld or on an upstream side
of the weld is detected, and thus a defect portion in an electric
resistance welded steel pipe can be specified. Irregular arcing
differs from the steady state arcing described above in regard to
the following points. That is, steady state arcing occurs on a
downstream side of a weld (V-convergence point 3). On the other
hand, irregular arcing occurs in a weld (V-convergence point 3) and
on an upstream side of a weld (V-convergence point 3). In addition,
steady state arcing occurs between a pair of end edges (edges) when
an electric resistance welded steel pipe is formed. Therefore, the
material of a welded portion generated as a result thereof is
equivalent to the base material of the metal sheet 1. In contrast,
in a case of irregular arcing, it occurs due to a foreign substance
such as iron oxide (scale) or iron powder. Therefore, the material
of a welded portion differs from the base material of the metal
sheet 1.
[0044] The image capturing unit 7 captures an image of a surface of
a region including the V-convergence region in which both the side
edges 1a and 1b of the metal sheet 1 are converged in a V-shape.
For example, a CCD camera is used. The image capturing apparatus is
disposed above a weld (V-convergence point 3) such that a range
including a weld (V-convergence point 3) and the upstream side of
the weld (V-convergence point 3) can be captured from above
thereof. Since such a way of disposing the image capturing
apparatus above is employed, for example, even in a case of being
applied to a small-diameter line, the image capturing apparatus can
be installed without hardship and without interfering with other
equipments (a nitrogen purge nozzle, a cooling water piping, and
the like).
[0045] In the metal sheet 1, since both the side edges 1a and 1b
thereof are intensively heated and melted, radiant light is emitted
from both the side edges 1a and 1b and places in the vicinity
thereof. From this radiant light, the image capturing unit 7
captures an image on a surface of the metal sheet 1 including red
light.
[0046] FIG. 4 shows an image processing algorithm for automatically
performing detection using the image capturing unit 7 and the image
processing unit 8. In addition, (a) to (d) of FIG. 5 show examples
of processed images.
[0047] At least one of a red component and a blue component is
extracted from an RGB image (refer to (a) of FIG. 5) captured in
Step S1 of FIG. 4 (FIG. 4 shows an example of a case where both are
extracted).
[0048] When a red component shown in Step S2 is extracted, inverted
binarization (Step S3) and labeling (Step S4) are performed to
obtain a welding point in a red image, and a downstream end point
in a wedge-type region interposed between steel edges (both the
side edges 1a and 1b) is set as the welding point (Step S5, also
refer to (b) of FIG. 5).
[0049] On the other hand, when a blue component shown in Step S6 is
extracted, a blue image is subjected to binarization (Step S7, also
refer to (c) of FIG. 5) and labeling (Step S8), and a
high-luminance portion is detected (Step S9, also refer to (d) of
FIG. 5). In the present image in which a radiant pattern of a
molten steel is captured, in a case where irregular arcing is
present in spite of the low level of the blue component, the blue
component exhibits high luminance and can be detected. Here, high
luminance indicates a level of 200 or higher in 255 gradations, for
example. This high-luminance portion is subjected to labeling (the
foregoing Step S8), and positional information is derived out.
Labeling indicates processing in which the same label number is
attached to one lump (blob) in a binary image, a particular blob is
extracted, and the position (the maximum point and the minimum
point of the X-coordinate, and the maximum point and the minimum
point of the Y-coordinate), the width, the length, the area, and
the like of the blob within the image are extracted. Even if a
plurality of irregular arcing portions are present, the positional
information of each thereof can be derived out.
[0050] The position of the welding point and the high-luminance
portion obtained in this manner are compared to each other in Step
S10. If the position of the high-luminance portion is not on a
downstream side of the welding point (Step S10: YES), generation of
an irregular arcing portion is determined as generation of a defect
(Step S11), and the processing returns to Step S1. On the other
hand, if the position of the high-luminance portion is on a
downstream side of the welding point (Step S10: NO), it is
determined as normal (Step S12), and the processing subsequently
returns to Step S1.
[0051] As described above, a defect can be determined at all times.
Here, a blue component image is extracted and processed in order to
detect an irregular arcing portion with high contrast. However,
since an irregular arcing portion is also saturated (Level 255 in
255 gradations) even in a red component image with high
probability, only a red component can also be detected.
[0052] If a camera capturing 200 frames or more per second is used
when an image is captured, it is experimentally ascertained that
there is no leakage in detection of an irregular arcing portion.
Therefore, it is preferable to use a camera capturing 200 frames or
more per second when an image is captured in Step S1.
[0053] Hereinafter, Examples of the present invention will be
described.
EXAMPLES
[0054] In an actual manufacturing line, the positions of a welding
point were measured while continuously capturing images of a weld
and performing image processing. The pipe adopted as a welding
monitoring target was an actual pipe of .phi.100 mm.times.4 mmt. In
the camera used for capturing images, the frame rate was set to 200
frames/second, and the exposure time was set to 1/10,000
seconds.
[0055] FIG. 6 shows an example of welding monitoring. In the image
of FIG. 6 captured at the time of generation of a defect, when a
pair of welding surfaces (edges) approached each other, the welding
surfaces were short-circuited due to a foreign substance such as
scale or iron powder having conductivity, and thus irregular arcing
occurred. In places where no foreign substance adhered, no
irregular arcing occurred even when the welding surfaces approached
each other, and it could be checked that no defect was
generated.
[0056] An example in which this phenomenon and generation of a
defect are butted is shown in (a) and (b) of FIG. 7.
[0057] In (a) of FIG. 7, actual defect portions in which a crack
has been generated after a flattening test, and photographs of the
external appearance respectively corresponding to these actual
defect portions are shown. It is ascertained that a crack has been
generated in three places of 0.24 m, 1.93 m, and 2.51 m from a
steel pipe head. A "notch" at a position of 1.17 m indicates a
portion in which a notch has been made in the edge in advance as a
marker for tracking. This marker was used as a reference position
for specifying the position along the longitudinal direction of the
actual pipe.
[0058] In (b) of FIG. 7, among captured images, images of the
portion in which irregular arcing has occurred in the welding point
or on an upstream side thereof and the corresponding portions are
butted each other are shown. An image of the marker was also able
to be checked (not shown). Therefore, it is ascertained that each
generation portion corresponds extremely well to the flat crack
portion. Since images other than the corresponding portions did not
have irregular arcing and any other abnormality, thereby being
normal, it was actually verified that generation of a defect was
accompanied by irregular arcing.
[0059] The main points of the welding monitoring apparatus and the
welding monitoring method according to the embodiment described
above will be summarized below.
[0060] (1) The welding monitoring apparatus of the present
embodiment monitors the welding state of the V-convergence region
in which the strip-shaped metal sheet 1 is converged in a V-shape,
when the metal sheet 1 is cylindrically formed while being conveyed
along its longitudinal direction, and both the side edges 1a and 1b
of the metal sheet 1 are heated and melted in a manner of being
butted each other while being converged in the V-shape, such that
an electric resistance welded steel pipe is manufactured. Then,
this welding monitoring apparatus includes: the image capturing
unit 7 that captures images of a region including the V-convergence
region in time series; and the image processing unit 8 that
extracts a welding point based on the images captured in time
series and detects the presence or absence and the position of
irregular arcing at the welding point or on an upstream side of the
welding point.
[0061] (2) The welding monitoring apparatus according to (1) is
constituted as follows. The images captured by the image capturing
unit 7 are RGB images. The image processing unit 8 extracts at
least one of a red image and a blue image from the RGB images,
performs inverted binarization and labeling of the red image with
respect to the red image, and detects a high-luminance portion in
the blue image with respect to the blue image.
[0062] (3) In the aspect according to (1) or (2), the image
capturing unit is a camera capturing 200 frames or more per
second.
[0063] (4) In addition, the welding monitoring method of the
present embodiment is used for monitoring the welding state of the
V-convergence region in which the strip-shaped metal sheet 1 is
converged in a V-shape, when the metal sheet 1 is cylindrically
formed while being conveyed along its longitudinal direction, and
both the side edges 1a and 1b of the metal sheet 1 are heated and
melted in a manner of being butted each other while being converged
in the V-shape, such that an electric resistance welded steel pipe
is manufactured. This welding monitoring method includes: an image
capturing step of capturing images of a region including the
V-convergence region in time series; and a detecting step of
extracting a welding point based on the images captured in time
series and detecting the presence or absence and the position of
irregular arcing at the welding point or on an upstream side of the
welding point.
[0064] (5) In the welding monitoring method according to (4), the
followings are performed. RGB images are used as the images. In the
detecting step, at least one of a red image and a blue image is
extracted from the RGB images, inverted binarization and labeling
of the red image are performed with respect to the red image, and a
high-luminance portion in the blue image is detected with respect
to the blue image.
[0065] (6) In the welding monitoring method according to (4) or
(5), in the image capturing step, images are captured at a frame
rate of 200 frames or more per second.
[0066] Moreover, the following steps in (7) and (8), or (9) can be
performed.
[0067] (7) The welding monitoring method according to any one of
(4) to (6) further includes a marking step of marking the position
of the irregular arcing in the longitudinal direction in the
electric resistance welded steel pipe.
[0068] (8) The welding monitoring method according to (7) further
includes a defect presence-or-absence specifying step of performing
an ultrasonic test with respect to a region to which the marking is
applied.
[0069] (9) The aspect according to any one of (4) to (6) further
includes a tracking step of tracking the position of the irregular
arcing in the longitudinal direction in the electric resistance
welded steel pipe.
[0070] According to the welding monitoring apparatus and the
welding monitoring method described above, the presence or absence
of a caught-in defect can be easily detected in real time by
extracting a welding point and automatically determining the
presence or absence of generation of irregular arcing in the
vicinity of the welding point or on an upstream side of the welding
point. Then, product-tracking is performed or a steel pipe is
subjected to marking in the vicinity of the squeeze rolls 2
immediately after irregular arcing is detected, based on the
information of the presence or absence of generation of irregular
arcing, so that the position of a defect-generated portion is
clarified, and thus the defect-generated portion can be easily
eliminated in a refining step. Therefore, only a normal portion
including no defect can be shipped as a product.
INDUSTRIAL APPLICABILITY
[0071] According to the present invention, it is possible to
provide a welding monitoring apparatus and a welding monitoring
method, in which a relatively light caught-in defect caused by an
incorporated foreign substance such as scale powder or iron powder
can be detected in real time in a welding step of an electric
resistance welded steel pipe.
BRIEF DESCRIPTION OF THE REFERENCE SYMBOLS
[0072] 1: metal sheet [0073] 1a, 1b: both side edges of metal sheet
[0074] 2: squeeze roll [0075] 3: welding point [0076] 4a, 4b:
contact tip [0077] 5: impeder [0078] 6: high-frequency power supply
[0079] 7: image capturing unit [0080] 8: image processing unit
* * * * *