TECHNICAL FIELD
[0001] The present invention relates to a method suitable for producing a thick and large-diameter
steel pipe used for a line pipe or the like, wherein a plate material is formed into
a preformed body having a U-shaped cross-section by bending, the preformed body is
pressed into an open pipe with a gap at plate width end portions faced each other
in a longitudinal direction thereof, and the end surfaces of the gap portion are joined
to each other into a steel pipe, and a press die used for the method.
BACKGROUND ART
[0002] As a technique for producing a thick and large-diameter steel pipe used for a line
pipe or the like, a so-called UOE forming technique is widely used which presses a
steel plate having a predetermined length, width and plate thickness into a U-shape,
press-forms the steel plate into an O-shape to make an open pipe, thereafter its gap
portion is butt-jointed by welding, and enlarges its diameter (so-called pipe expansion)
to further improve the roundness.
[0003] In the above-described UOE forming technique, however, since there is a need for
a high pressing force in the process of pressing the steel plate to form the steel
plate into a U-shape and an O-shape, it cannot help using a large-scale press machine.
[0004] Therefore, recently, a technique for decreasing the pressing force has been considered
upon producing this kind of steel pipe.
[0005] As a prior art related to this point, Patent Document 1 discloses a method of preliminarily
forming a material in a C-shape forming process and a U-shape forming process, then
performing an O-shape forming process thereon, so that a deformation mode of the material
to be formed becomes fitting to dies at both top and bottom portion in the O-shape
forming process. Further, Patent Document 2 discloses a method of changing a position
of a butted part of a U-shaped steel plate to dies by performing a plurality of O-shape
presses on the U-shaped steel plate and also rotating the U-shaped steel plate during
the O-shape press, and Patent Document 3 discloses a method of performing the O-shape
press on a member formed into a U-shape by a U-shape press with an insert liner which
is applied for larger outer diameter pipe to an intermediate outer diameter.
[0006] As other prior arts, Patent Document 4 discloses a forming method in which a strain
detector capable of detecting the inclination or distortion of a bending member mounted
on a slide is disposed, the bending member is disposed in a tiltable or parallel-movable
manner corresponding to the detection of the inclination or distortion by the strain
detector, and the bending member is inclined or parallel moved to be subjected to
press-forming so that an amount of distortion is smaller than an amount of inclination
or an amount of distortion of the bending member when press-forming a material to
be formed into a pipe shape. Patent Document 5 discloses a method of forming a slit
pipe equipped with a non-circular preform by performing the slight forming compared
to other bending steps in at least one bending step of acting on the inner surface
of the plate material on left and right with respect to a center defined by a longitudinal
axis of an upper tool that enters a plate material to be progressively formed, and
thereafter, forming a finished slit pipe by appropriately applying a pressing force
acting on an area formed slightly in advance on both sides of the center from the
outside to the non-circular preform. Furthermore, Patent Document 6 discloses a method
of forming a pipe with a closed slit portion, by applying the plastic deformation
only to the flat portion of at least one location in the preformed body having a flat
portion between at least two bent portions bent to a predetermined pipe curvature.
PRIOR ART DOCUMENTS
PATENT DOCUMENTS
SUMMARY OF THE INVENTION
TASK TO BE SOLVED BY THE INVENTION
[0008] Meanwhile, the conventional press-forming techniques have problems as described below,
and hence there is still room for improvement.
[0009] That is, in Patent Documents 1 to 3, a circumferential length on a forming surface
of the die is set to be substantially equal to the width size of a plate material
(a raw plate), and the plate material is formed into a pipe shape by bringing a extending
portion of the material into contact with a forming surface of the die during deformation
of the O-shape press to adjust it into a shape of the forming surface of the die.
However, when a contact portion with the die is increased, the pressing force is gradually
increased, and there is a need for a large press machine.
[0010] In a technique particularly aimed at a thick and high-strength material, a large
pressing force is needed and thus the material is not completely pressed in the O-shape
press, whereby a degradation of the shape cannot be avoided.
[0011] Meanwhile, according to the methods described in Patent Documents 4, 5 and 6, although
they do not accompany an increase in pressing force as in Patent Documents 1 to 3,
since the material to be formed or the non-circular preform is separately formed on
each of left and right sides, when the amount of deformation differs on the left and
right sides, there is a risk of formation of a step difference (offset) in the gap
portion or the slit portion serving as a welded portion. Further, in these methods,
the deformation is locally concentrated when trying to deform a shape to a desired
shape at one time, and there is a fear of worsening the roundness. Accordingly, deformations
of several times are inevitable, and there is also a limit in efficient production.
[0012] The present invention is to provide a producing method of efficiently producing a
steel pipe having high roundness without requiring an excessive bending force (load),
and a press die used in the method.
SOLUTION FOR TASK
[0013] The present invention is a method of producing a steel pipe by subjecting a plate
material which is bent at width end portion to at least one bending along its widthwise
direction to provide a preformed body having a U-shaped cross-section, pressing the
preformed body by applying a bending force to thereby form an open pipe with a gap
portion in its longitudinal direction, and butt-joining end surfaces of the gap portion
of the open pipe to each other, characterized in that a lightly-bent portion to which
a very slight curvature is applied as compared to other regions or a non-bent portion
in which the bending is omitted is provided in at least a part of the plate material
in a process performing the bending on the plate material, and a bending-force is
applied to a part spaced apart from the center of the lightly-bent portion or the
non-bent portion in a direction to width end of the plate material by amount of W/4
(where W is a width size of the plate material) without constraining the lightly-bent
portion or the non-bent portion in a process pressing the preformed body into the
open pipe. Here, the open pipe refers to a pipe body of a state in which the plate
material is formed into a cylindrical shape and a gap portion is formed between plate
end portions facing each other.
[0014] In the method of producing a steel pipe having the above configuration, the following
specific means are preferable for solving the problem of the present invention:
- 1) The center of the lightly-bent portion or the non-bent portion is provided in a
part including a part spaced apart from the width end portion of the plate material
by amount of W/4;
- 2) The length of the lightly-bent portion or the non-bent portion along the widthwise
direction of the plate material is not more than 10% of the plate width;
- 3) When applying the bending force to press the preformed body, the preformed body
is supported at a part not on the line of action of the bending force, and when the
opening angle of the preformed body defined based on the part supporting the preformed
body is defined by θs and the angle of the line of action of the bending force applied
to the preformed body is defined by θf, the pressing of the preformed body is started
under a condition of θf > θs;
- 4) At the time of pressing of the preformed body, a press die provided with a forming
surface of not coming into contact with the lightly-bent portion or the non-bent portion
is used;
- 5) At the time of pressing of the preformed body, the bending force is simultaneously
applied to a part each spaced apart from the center of the lightly-bent portion or
the non-bent portion toward the width end of the plate material by amount of W/4;
further,
- 6) At the time of pressing of the preformed body, a forming center of the press die
used for pressing of the preformed body coincides with a center in the widthwise direction
of the preformed body; and
- 7) The preformed body is held in a U-shaped posture with its opening portion facing
upward, and is supported at the center in the widthwise direction located at its lowermost
end.
[0015] Further, according to the present invention, there is provided a press die preferably
used in the producing method having the above configuration, wherein the press die
includes a pair of the bending bodies configured to interpose the preformed body therebetween,
and the bending bodies have a forming surface having a cross-sectional shape that
does not come into contact with the lightly-bent portion or the non-bent portion during
pressing of the preformed body.
[0016] In the press die having the above configuration, the following specific means is
preferable for solving the problem of the present invention:
- 1) At least one of the bending bodies has a circular arc surface having a width center
that coincides with the forming center of the press die, and a forming surface having
an inclined surface which leads to each of both ends of the circular arc surface and
is directed toward the forming center of the press die.
[0017] Further, the circular arc surface has a central angle of not less than 28°, an angle
formed between the inclined surface and a straight line intersecting with the straight
line passing through a widthwise center of the circular arc forming surface is preferably
not less than 14°, and a surface having a radius of not more than 1.2 times the diameter
of a steel pipe to be produced may be applied as the circular arc surface.
EFFECTS OF THE INVENTION
[0018] According to the method of producing a steel pipe of the present invention, in a
case where a plate material having an end bending portion is subjected to at least
one bending along its widthwise direction to provide a preformed body having a U-shaped
cross-section, an open pipe with a gap portion in its longitudinal direction is formed
by applying a bending force to the preformed body to press the preformed body, and
end surfaces of the gap portion of the open pipe are butt-joined to each other to
form a steel pipe, a lightly-bent portion to which a very slight curvature is applied
as compared to other regions or a non-bent portion in which the bending is omitted
is provided in at least a part of the plate material in a process performing the bending
on the plate material, and the bending force is applied to a part spaced apart at
least from the center of the lightly-bent portion or the non-bent portion in a width
end portion direction of the plate material by amount of W/4 (where W is a width size
of the plate material) without constraining the lightly-bent portion or the non-bent
portion in a process of pressing the preformed body into the open pipe. Therefore,
it is possible to efficiently form a steel pipe having high roundness with a relatively
small bending force.
[0019] According to the method of producing a steel pipe having the above-described configuration,
since the lightly-bent portion or the non-bent portion is provided at a part spaced
apart from a width end portion of the plate material by amount of W/4, when the preformed
body having a U-shaped cross-section is pressed into an open pipe, the part is not
restricted by the press die, and thus, it is possible to suppress an increase in forming
reaction force.
[0020] According to the method of producing a steel pipe of the present invention, since
a length of the lightly-bent portion or the non-bent portion along the widthwise direction
of the plate material is not more than 10% of the plate width dimension, it is possible
to obtain an open pipe having a small open amount of the butted portion, while maintaining
the dimensional accuracy.
[0021] According to the method of producing a steel pipe of the present invention, at the
time of pressing of the formed boy by applying a bending force thereto, the preformed
body is supported at a part at least away from an extension line on which the bending
force acts, and the pressing of the preformed body is started under the condition
of θf > θs in which an opening angle of the preformed body defined based on the part
supporting the preformed body is defined by θs, and an angle of the bending force
is defined by θf, so that the lightly-bent portion or the non-bent portion is deformed
so as to extend outward.
[0022] According to the method of producing a steel pipe of the present invention, at the
time of pressing of the preformed body, since the press die provided with a forming
surface not coming into contact with the lightly-bent portion or the non-bent portion
is used, it is possible to press the preformed body while decreasing the bending force.
[0023] According to the method of producing a steel pipe of the present invention, since
the bending force is simultaneously applied to parts (two locations) spaced apart
from the center of the lightly-bent portion or the non-bent portion toward the width
end of the plate material by amount of W/4 at the time of pressing of the preformed
body, an offset in which the end surfaces greatly differ in the gap portion is not
formed.
[0024] According to the method of producing a steel pipe of the present invention, since
the forming center of the press die used in the pressing of the preformed body matches
with the width center of the preformed body at the time of pressing of the preformed
body, it is possible to evenly bend a portion corresponding to the width end of the
plate material in the gap portion of the open pipe on the left and right sides, and
a large offset is not formed in the gap portion.
[0025] According to the method of producing a steel pipe of the present invention, since
the preformed body is held in a U-shaped posture and is supported at its lowermost
end (the center in the widthwise direction of the preformed body), it is possible
to symmetrically deform the preformed body on the boundary of the center in the widthwise
direction, and it is possible to obtain an open pipe with high roundness.
[0026] According to the press die used in the method of producing a steel pipe of the present
invention, the press die is constituted by a pair of bending members interposing the
preformed body therebetween, and a forming surface having a cross-sectional shape
which does not come into contact with the lightly-bent portion or the non-bent portion
during pressing of the preformed body is formed in the bending member. Thus, the forming
reaction force is decreased, and it is possible to efficiently produce the steel pipe.
[0027] Further, according to the press die of the present invention, since at least one
of the bending members has a circular arc surface having a width center matching the
forming center of the press die, and a forming surface having a slope leading to each
of both ends of the circular arc surface and directed toward the forming center of
the press die, it is possible to obtain a steel pipe with high roundness without forming
a step in the gap portion.
[0028] In the press die of the present invention, when the central angle of the circular
arc surface is set to not less than 28°, and the angle between the inclined surface
and the straight line intersecting with a straight line passing through the widthwise
center of the circular arc forming surface is set to not less than 14°, at the time
of pressing of the preformed body, it is possible to reliably extend the lightly-bent
portion or the non-bent portion toward the outside.
[0029] Furthermore, according to the press die of the present invention, the lightly-bent
portion or the non-bent portion is not restricted by the forming surface of the press
die by setting the circular arc surface to have the diameter of not more than 1.2
times the diameter of the steel pipe to be produced at the time of pressing of the
preformed body, whereby the forming reaction force can be decreased.
BRIEF DISCRIPTION OF THE DRAWINGS
[0030]
FIG. 1 is a diagram schematically illustrating a preferred punch and die used to form
a preformed body having a U-shaped cross-section.
FIG. 2 is a diagram schematically illustrating a preferred press die used to form
an open pipe.
FIG. 3 is a diagram illustrating a specific forming condition when forming a plate
material into a preformed body having a U-shaped cross-section.
FIG. 4 is an enlarged diagram illustrating a cross-section of the preformed body having
the U-shaped cross-section.
FIG. 5 is a diagram illustrating a state in which the preformed body having the U-shaped
cross-section is pressed into an open pipe.
FIG. 6 is a graph showing a relation between an amount of roundness variation/an outer
diameter and (a length of lightly-bent portion or non-bent portion)/a plate width.
FIG. 7 is a graph showing a relation between an opening (mm) of a gap portion and
(a length of lightly-bent portion or the non-bent portion)/a plate width.
FIG. 8 is a graph showing a relation between an opening (mm) of the U-shaped cross-section
and (a length of lightly-bent portion or the non-bent portion)/a plate width.
FIG. 9 is an enlarged diagram illustrating essential portions of an upper die.
FIG. 10 is a graph showing a relation between an angle θd of a forming surface of
the upper die and a direction θf of force.
FIG. 11 is a diagram illustrating a biting situation of the upper die.
FIG. 12 is a diagram illustrating a state in which a gap is formed between the upper
die and the preformed body.
FIG. 13 is a graph showing a relation between (a radius of the circular arc surface
of the upper die / a radius of the steel pipe) and the residual index.
FIG. 14 is a graph showing a relation between (a radius of the circular arc surface
of the lower die / a radius of the steel pipe) and (forming load/load when the lightly-bent
portion or the non-bent portion is freely bent).
FIG. 15 is a diagram illustrating the contact situation between the upper die and
the lower die.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0031] Hereinafter, the present invention will be more specifically described with reference
to the drawings.
[0032] FIGs. 1 and 2 are diagrams schematically illustrating a preferred punch and die and
a preferred press die, respectively, that are used in the practice of the method of
producing a steel pipe according to the present invention.
[0033] The punch and die shown in FIG. 1 is used when forming a plate material into a preformed
body having a U-shaped cross-section by bending the plate material along its widthwise
direction, and the press die shown in FIG. 2 is used when forming the preformed body
into an open pipe having a gap in the longitudinal direction by applying a bending
force to the preformed body having the U-shaped cross-section.
[0034] Reference number 1 in FIG. 1 denotes a die disposed in a conveying path of the plate
material S. The die 1 is configured with a pair of left and right rod-like members
1a and 1b that supports the plate material S at two locations along its feeding direction
and enables a change in an interval e between the rod-like members 1a and 1b depending
on the size of the steel pipe to be produced.
[0035] Moreover, reference number 2 denotes a punch which is movable in a direction of moving
close to or away from the die 1. The punch 2 includes a punch tip 2a having a downward
convex forming surface that comes into direct contact with the plate material S to
bend the plate material S into a concave shape, and a punch support 2b that is connected
to the rear (upper end) of the punch tip 2a with the same width thereof to support
the punch tip 2a.
[0036] Although a specific structure of the punch support 2b is not illustrated, its upper
end portion is connected to a driving device such as hydraulic cylinder, and the punch
support 2b can apply a bending force to the punch tip 2a by the driving device. Further,
reference number 3 denotes a roller for forming the conveying path of the plate material
S.
[0037] Further, reference number 4 in FIG. 2 denotes an upper die (bending tool), and reference
number 5 denotes a lower die which mates with the upper die 4 (bending tool). The
preformed body (which has a U-shaped cross-section) formed by the die 1 and the punch
2 is located between the upper die 4 and the lower die 5, and a bending force is applied
to the preformed body to form an open pipe.
[0038] The upper die 4 may have a circular arc surface 4a having a width center that matches
the forming center thereof, and a forming surface (inclined surface) 4b connected
to each of both ends of the circular arc surface 4a and having a slope directed toward
the forming center side of the press die. The lower die 5 may have a forming surface
that does not come into contact with the lightly-bent portion or the non-bent portion
during pressing of the preformed body. Further, the upper die 4 may have a press die
having a forming surface that does not come into contact with the lightly-bent portion
or the non-bent portion during pressing of the preformed body. As the lower die 5,
it is possible to apply one that includes a circular arc surface having a width center
matching the forming center thereof, and an inclined surface which is connected to
each of both ends of the circular arc surface and is directed toward the forming center
side of the press die.
[0039] In order to form the plate material S as a starting material into a tubular shape,
first, end bending (also referred to as crimping) is performed on the width end portion
of the plate material S.
[0040] The end bending is performed on a plate width end portion that is harder to bend
as compared to the case of performing the bending using the die 1 and the punch 2,
and it is possible to obtain a steel pipe in which high roundness is secured by providing
an end bending portion by this forming.
[0041] Further, the roundness of the steel pipe is an indicator that indicates how much
the cross-sectional shape of the steel pipe is close to a circle. Specifically, for
example, when the produced steel pipe is equally divided into twelve sections or twenty-four
sections in the circumferential direction at any pipe length position to measure the
outer diameters at the opposite positions, and a maximum diameter and a minimum diameter
thereof is defined by D
max and D
min, respectively, the roundness = D
max - D
min is defined. This indicates that as the roundness comes closer to 0, the cross-sectional
shape of the steel pipe has a shape that is closer to a perfect circle.
[0042] The plate material S provided with the end bending portion is mounted on the die
1 as shown FIG. 1, and bending (3-point bending) is applied over the entire region
as illustrated in FIG. 3, while intermittently feeding the plate material S by a predetermined
feed amount, thereby forming the plate material into a preformed body which has a
U-shaped cross-section as a whole.
[0043] Around a portion of the preformed body S
1 obtained by the bending, especially, a part each spaced apart from the width end
portion by amount of W/4, a lightly-bent portion to which the slight curvature is
applied as compared to other regions or a non-bent portion P in which the bending
is omitted is provided as shown in Fig. 4 by enlarging its cross-section.
[0044] The lightly-bent portion P can be provided by pressing while decreasing the bending
amount applied by the punch 2, and the non-bent portion P can be provided by omitting
the bending of the punch 2 while increasing the feeding of the plate material S.
[0045] Further, FIG. 3 specifically illustrates an example of a case of performing the bending
and the feeding of the plate material S on the plate material S previously subjected
to edge bending, sequentially from the top to the bottom of the left column, from
the top to the bottom of the center column, and further from the top to the bottom
of the right column, and the arrow assigned to each of the punch 2 and the plate material
S in FIG. 3 illustrates the moving direction of the punch 2 and the plate material
S at each stage.
[0046] As the punch 2 which performs bending on the plate material S, it is possible to
use, for example, a punch having a substantially inverted T-shape in which the width
of the punch tip 2a is larger than the width (thickness) of the punch support 2b.
In this case, it is possible to bend a larger area with respect to the plate material
by single step bending as compared to the configuration in which the width of the
punch tip 2a is almost the same as the width (thickness) of the punch support 2b illustrated
in FIG. 1, whereby the bending times can be decreased.
[0047] After a preformed body S
1 having a U-shaped cross-section is obtained, in order to form the preformed body
S
1 into an open pipe, the preformed body S
1 is pressed using the upper die 4 and the lower die 5 illustrated in FIG. 2.
[0048] At the time of pressing of the preformed body S
1, the preformed body S
1 is held in a U-shaped posture so that an opening portion faces upward, and is located
on the lower die 5 so that its lowest end, that is, the center in the widthwise direction
becomes a support part. Thus, as illustrated in FIG. 5, the bending force is simultaneously
applied to two locations of the width end portions of the plate material S which are
parts spaced apart from the lightly-bent portion or the non-bent portion P toward
the width end by amount of W/4 by the upper die 4.
[0049] In such pressing, since the preformed body S
1 is supported on the lower die 5 at a part at least away from the line of action of
the bending force, and the lightly-bent portion or the non-bent portion P is not constrained
by the press die, the preformed body S
1 is formed into a tubular shape without requiring excessive bending force.
[0050] As the lower die 5, in the present invention, although one having a forming surface
that does not constrain the lightly-bent portion or the non-bent portion P is used,
when the forming surface is a circular arc surface having a concave shape, it can
be achieved by setting a larger diameter than the diameter of the steel pipe to be
produced. Further, the forming surface may be a flat surface with which the preformed
body S
1 linearly comes into contact.
[0051] In the stage of pressing the preformed body S
1 into an open pipe of the present invention, the bending force is applied at least
to a part away from the center of the lightly-bent portion or the non-bent portion
P by amount of W/4, the reason of which is as follows.
[0052] That is, the bending moment (M) when the whole preformed body S, has a circular shape
is F·r ·cos
φ (F: bending force, r: radius of circle) at a position of an angle
φ from the position applied with the bending force, and becomes maximum at the position
away from the position applied with the bending force by 90°, and the deformation
also becomes maximum. Therefore, by applying the bending force to the position away
from the center of the lightly-bent portion or the non-bent portion P by 90°, that
is, 1/4 of the entire circumference, the lightly-bent portion or the non-bent portion
P is effectively deformed. At this time, the bending moment is maximum at the position
away from the applying position of the bending force by 90° and it becomes smaller
as going away from this position. In order to allow the sufficient plastic deformation
to occur in the lightly-bent portion or the non-bent portion P, the bending force
is preferably applied by amount of W/4 ± 0.07 W.
[0053] Further, in the present invention, the center of the lightly-bent portion or the
non-bent portion P is provided in a part including a part away from the width end
portion of the plate material S by amount of W/4, the reason of which is as follows.
[0054] That is, as described above, although the bending force is preferably applied to
a position apart from the center of the lightly-bent portion or the non-bent portion
P in the width end direction of the plate material by amount of W/4, since its shape
is changed at the step of forming the preformed body S
1 into an open pipe, a contact position with the upper die 4 is changed, and the position
applied with the bending force is also changed. When the lightly-bent portion or the
non-bent portion P is provided at a position spaced apart from the width end portion
of the plate material S by amount of W/4, a position applied with the bending force
is always a width end portion of the plate material S, and the lightly-bent portion
or the non-bent portion P are most deformed. Thus, it is possible to give deformation
to the lightly-bent portion or the non-bent portion P by single bending without changing
the bending position. Further, in order to give a sufficient deformation to the lightly-bent
portion or the non-bent portion P, the lightly-bent portion or the non-bent portion
P is preferably provided in a range of W/4± 0.07W from the position applied with the
bending force, that is, the width end portion of the plate material.
[0055] In the present invention, when the lightly-bent portion is provided in a part of
the plate material S, particularly, in a part including the part away from the width
end portion of the plate material S by amount of W/4, or when the non-bent portion
P in which bending is omitted is provided in bending the plate material S , the length
L (see FIG. 4) along the widthwise direction of the plate material S of the lightly-bent
portion or the non-bent portion P is preferably set to not more than 10% of the plate
width. The reason is as follows.
[0056] That is, when applying the bending force to the preformed body S
1 of a U-shaped cross-section having the lightly-bent portion or the non-bent portion
P of the length L at the part spaced apart from the lightly-bent portion or the non-bent
portion P by amount of W/4, bending moment acts on the lightly-bent portion or the
non-bent portion P, and the portion is deformed.
[0057] The bending moment (M) when the whole preformed body S
1 becomes a circular shape is F ·r ·cos
φ (F: bending force, r: radius of circle) at the position of the angle
φ from the position applied with the bending force, and bending moment becomes maximum
at the position spaced apart from the position applied with the bending force by 90°,
and the amount of deformation is also the maximum. However, the amount of deformation
is not uniform in the lightly-bent portion and the non-bent portion P. Therefore,
the obtained open pipe has irregularities, rather than a uniform circular arc.
[0058] Here, as for a tubular material of an API standard Gr. X65 and a thickness of 38.1
mm, a relation between a value obtained by dividing the length L of the lightly-bent
portion or the non-bent portion P of the shaped body S
1 having the U-shaped cross-section by the plate width and a value obtained by dividing
an irregularity amount by the outer diameter of the tubular material is investigated.
As illustrated in FIG. 6, as the length of the lightly-bent portion or the non-bent
portion P is longer and the outer diameter is smaller, the irregularity amount is
also larger. In the tubular material having the outer diameter of 559 mm, when the
length of the lightly-bent portion or the non-bent portion P exceeds 10% of the plate
width, the irregularity amount exceeds 1.5% of the outer diameter.
[0059] In the API standard which is a general standard of the line pipe, although the shape
correction of a tube expansion ratio (rate for expanding the diameter) of about 1.5%
is observed in the tube expanding process after joining (welding) the gap portion,
when the irregularity amount exceeds 1.5% of the outer diameter, the dimensional accuracy
of the finished product may be impaired. Therefore, in the present invention, the
length L of the lightly-bent portion or the non-bent portion P along the widthwise
direction of the plate material S is preferably set to not more than 10% of the plate
width. Furthermore, in order to provide sufficient deformation to the lightly-bent
portion or the non-bent portion P, the length L is preferably in the range of W/4±
0.07 W from the position applied with the bending force.
[0060] Further, when the length L of the lightly-bent portion or the non-bent portion P
becomes longer, the difference in the gap portion of the open pipe increases by the
spring back when releasing the bending force as illustrated in FIG. 7 and the butt-joining
between the end surfaces may become difficult, which may cause restriction in some
cases.
[0061] FIG. 8 is a graph showing a relation between the interval (opening of U-shaped cross-section)
of the opening portion of the preformed body S
1 having a U-shaped cross-section and the length L of the lightly-bent portion or the
non-bent portion P. Although the dimensional accuracy is better as the length L of
the lightly-bent portion or the non-bent portion P becomes smaller, since the opening
interval of the preformed body S
1 also becomes smaller, when the opening interval is smaller than the width of the
punch 2, it is not possible to raise the punch 2 after the final bending (the last
state of FIG. 3), and it is difficult to detach the preformed body S
1 from the press machine. Therefore, the lower limit of the length L is set depending
on the size of the applied device or the steel pipe to be produced. For example, when
a pipe having an outer diameter of 559 mm is produced by a press machine having the
punch 2 having a width of 150 mm, L/W is required to be not less than 0.05.
[0062] In the present invention, when the opening angle defined based on the part on which
the preformed body S
1 is supported is defined as θs, and the angle of the bending force applied to the
preformed body S
1 is defined as θf, the pressing of the preformed body S
1 is started under a condition of θf > θs. However, the part in which the preformed
body S
1 is supported by satisfying this condition is not existent on the line of action of
the bending force, and the lightly-bent portion or the non-bent portion P can reliably
extend toward the outside with relatively small bending force.
[0063] Further, when the widthwise center of the preformed body is located at the lowermost
end (part on which the preformed body is supported) in the U-shaped posture in which
the opening portion of the preformed body is located upward, and the straight line
q which symmetrically bisects the preformed body through the widthwise center is defined
as a reference line, the opening angle θs of the preformed body S
1 is defined as an angle formed between the reference line and the straight line r
connecting the widthwise center (W/2) of the preformed body and the widthwise end
portion of the preformed body S
1 (see FIG. 5). Further, the angle (direction of the bending force) θf of the bending
force is determined by the press die shape and the friction coefficient, when the
angle (angle to the horizontal plane) of the forming surface of the press die is defined
as θd, and the friction coefficient of the press die surface is defined as µ, the
angle θf is determined as θf = θd - tan
-1 (µ) (see FIG. 9).
[0064] When the forming surface of the upper die 4 is configured to include a circular arc
surface 4a having a width center that matches the forming center O of the press die,
and a pair of forming surfaces 4b which is connected to each of both ends of the circular
arc surface 4a and is directed toward the forming center O side of the press die,
the forming surfaces 4b may be a straight inclined surface or a curved inclined surface.
[0065] The central angle θc of the circular arc surface 4a is set in the range of not less
than 28°, and the forming surface 4b is deformed so as to reliably extend the lightly-bent
portion or the non-bent portion P to the outside at the time of pressing of the preformed
body S
1. Therefore, it is possible to set the angle θd formed with the straight line intersecting
with the straight line passing through the widthwise center of the circular arc surface
4a in the range of not less than 14° (see FIG. 2).
[0066] The reason of desirably setting the central angle θc of the circular arc surface
4a of the upper die 4 to not less than 28° is as follows. FIG. 10 illustrates the
result of a relation between the angle θd of the forming surface 4b of the upper die
4 and the direction θf (angle of the bending force) of force obtained for a general
lubrication state (the case of the friction coefficient of 0.1).
[0067] As seen from FIG. 10, the larger the angle θd of the forming surface of the upper
die 4 is, the larger the direction θf of force is, and lightly-bent portion or the
non-bent portion P easily extends outward. For example, when a pipe having an outer
diameter of 559 mm is produced by a press machine having the width of the punch 2
of 150 mm (an example of a minimum dimension of paragraph (0055)), the minimum value
of L/W is 0.05, and the opening angle θs of the preformed body S
1 is 9°. At this time, if the press die angle θd is not less than 14°, the direction
θf of power is larger than the opening angle θs of the preformed body S
1. In addition, the opening angle θs of the preformed body S
1 is geometrically determined by the ratio of the length L and the plate width W of
the lightly-bent portion or the non-bent portion P, and when the L/W increases, the
opening angle θs of the preformed body S
1 also increases. Thus, in some cases, it may be necessary to further increase the
central angle θc of the circular arc surface 4a of the upper die 4.
[0068] Meanwhile, when the angle θd of the forming surface 4b of the upper die 4 is large,
the opening portion of the press die becomes smaller than the maximum width of the
preformed body S
1 having a U-shaped cross-section, and as illustrated in FIG. 11, since the upper die
4 may bite into the preformed body S
1 and scratch it, its upper limit is determined depending on a maximum width of the
preformed body S
1.
[0069] At the time of pressing of the preformed body S
1, when the bending force is simultaneously applied to each of the parts (two locations)
spaced apart from the lightly-bent portion or the non-bent portion P toward the width
end (width end of the preformed body S
1) of the plate material S by amount of W/4, it is effective to mate the forming center
O of the press die used for the pressing of the preformed body S
1 with the widthwise center W/2 of the preformed body S
1, whereby an occurrence of a step difference (offset) in the gap portion of the open
pipe S
2 can be avoided.
[0070] The circular arc surface 4a of the upper die 4 may be set to the radius of not more
than 1.2 times the diameter of the steel pipe to be produced. The reason is as follows.
[0071] When the radius of the circular arc surface 4a of the upper die 4 is small, as illustrated
in FIG. 12, a space is formed between the upper die 4 and the preformed body S
1 during forming, there is a risk of mis-alignment of the end surface in the gap portion,
and its lower limit is defined depending on the shape near the plate end defined by
the end bending so that the contact is possible in the range of about the plate thickness
from the plate end.
[0072] FIG. 13 shows a relation between (the radius of circular arc surface 4a of the upper
die 4/ the radius of the steel pipe) and the index (residual index) in which the lightly-bent
portion or the non-bent portion P is left (not bent to circular) as it is. When the
radius of the circular arc surface 4a of the upper die 4 increases, the restriction
is insufficient, and thus, the lightly-bent portion or the non-bent portion P remains
as it is. When the residual index 1.0 is defined as a reference value, in order not
to exceed the reference value, the radius of the circular arc surface 4a of the upper
die 4 is desirably suppressed to not more than 1.2 times the radius of the steel pipe
to be produced.
[0073] Next, when the lower die 5a has a circular arc surface 5a in which a forming surface
has a concave shape, as illustrated in Fig. 5, there is a need to use one larger than
the external diameter of the steel pipe to be produced so that the preformed body
S
1 having a U-shaped cross-section fits into the press die.
[0074] FIG. 14 is a graph showing a relation between (the radius of the circular arc surface
5a of the lower die 5/the radius of the steel pipe) and (the forming load/the load
when the lightly-bent portion or the non-bent portion P is freely bent). When the
radius of the circular arc surface 5a of the lower die 5 is small, since the lightly-bent
portion or the non-bent portion P is restricted by the press die during forming of
the preformed body S
1, the forming load increases. In particular, when the radius of the circular arc surface
5a of the lower die 5 is less than 1.05 times the diameter of the steel pipe to be
produced, the forming load rapidly increases. Therefore, the radius of the circular
arc surface 5a of the lower die 5 is desirably not less than 1.05 times the diameter
of the steel pipe to be produced. When the radius of the circular arc surface 5a of
the lower die 5 is set to not less than 1.07 times the diameter of the steel pipe
to be produced, it can be suppressed to not more than twice of the load applied when
forming the preformed body S
1 in a non-restriction state.
[0075] When the radius of the circular arc surface 5a of the lower die 5 is large, as illustrated
in FIG. 15, since the contact with the upper die 4 is unavoidable, a desired pressing
rate is not attained, the deformation of the lightly-bent portion or the non-bent
portion P may be insufficient or the opening amount of the gap portion may increase,
so that it is necessary to select the lower die 5 depending on the shape of the upper
die 4. When using the lower die 5 having the circular arc surface 5a having the concave
shape, it is possible to directly use the die used when producing the steel pipe by
the UO method without any change, and there is no need for producing the die. However,
as long as it is possible to avoid the restrictions of the lightly-bent portion or
the non-bent portion P, those having the same configuration as the upper die 4 may
be applied.
[0076] Further, although an example in which the forming surface (inclined surface) 4b is
made up of a circular arc surface 4a and the forming surface (inclined surface) 4b
is adopted as the upper die 4, as long as it is possible to satisfy the condition
θs > θf at the time of starting of pressing, a press die equipped with a forming surface
formed with the circular arc surface 5a such as the lower die 5 may be used, and is
not limited to the illustrated configuration.
[0077] As the lower die 5, it is possible to use one such as die 1 illustrated in FIG. 1
which supports the preformed body S
1 at two points or a roller-type die. Even when using the die, since the lightly-bent
portion or the non-bent portion P is not restricted by the forming surface of the
press die during pressing, the preformed body S
1 can be formed into a tubular shape with a relatively small bending force.
[0078] Thereafter, the open pipe S
2 obtained by pressing using the upper die 4 and the lower die 5 mutually abuts the
end surfaces of the gap portion, is welded by a welding machine (a joining means)
and is further formed into a steel pipe by being expanded as required.
[0079] As the welding machine (a joining means), for example, a welding machine made up
of three kinds of welding machines, such as a tack welding machine, an inner surface
welding machine and an outer surface welding machine, is applied. In the welding machine,
the tack welding machine continuously brings the butted surfaces into close contact
with each other at the appropriate positional relation by cage rolls, and welds the
close-contact portions over its entire length.
[0080] Next, the tack pipe is welded (submerged arc welding) from the inner surface of the
butted portion by the inner surface welding machine, and is further welded (submerged
arc welding) from the outer surface of the butted portion by the outer surface welding
machine.
[0081] The positional relation between the welding machine (the joining means) and the press
die (the upper die 4 and the lower die 5) for pressing the preformed body S
1 is not particularly limited, and can be arbitrarily changed.
EXAMPLE 1
[0082] In order to form the steel pipe with a diameter of 36 inches using a line pipe steel
plate(API grade X60) having a thickness of 38.1 mm and a width of 2711 mm, the material
is placed on a die in which an interval of a rod-like member is set to 450 mm, and
bending of the three-point bending is performed from the position of 1120 mm from
the width center of the plate material, with a plate material feeding pitch of 224
mm and 11 bending times (five times from the paper right end, and five times from
the left end) by a punch having a forming surface of a radius of 308 mm. At that time,
the bending amount is set to an amount in which the punch tip reaches a position of
15.8 mm from the line connecting the uppermost part of the rod-like member, and bending
is performed by 30° for a time. However, at the position of 672 mm from the width
center of the plate material (at the time of third feeding from the right end, and
third feeding from the left end), the bending is not performed, and the non-bent portion
is formed at the position of 571 to 795 mm. Next, while holding the preformed body
having the U-shaped cross-section obtained by bending in a U-shaped posture so that
the opening portion faces upward, when pressing the preformed body into an open pipe
until an inter-apex distance (the apex of the R part is an uppermost part of the circular
arc surface in the upper die, and a lowermost part of the circular arc surface in
the lower die) of a R part of the press die reaches 880 mm, using an upper die having
a circular arc surface of a radius R: 457.2 mm and a central angle θc: 60° and a flat
surface leading to the circular arc surface at the angle θd: 30° and a lower die having
a concave circular arc surface of a radius R: 502.9 mm, the degree of the decrease
of the bending force of the press die, the opening amount in the gap portion of the
open pipe, the amount of offset, and the roundness of the steel pipe after welding
are investigated.
[0083] As a result, after performing the U-shape press at a standard condition, by performing
the O-shape press at the compression ratio of 0.2% using a press die of the radius
R: 452.6 mm, as a result of being compared to the case (conventional method) of producing
the steel pipe of an outer diameter of 36 inches and a thickness (wall thickness)
of 38.1 mm, when producing the steel pipe according to the present invention, it is
confirmed that the bending force of the O-shape press is decreased to about 15% as
compared to the conventional method.
[0084] In addition, it becomes clear that the steel pipe can be obtained in which the opening
amount in the gap portion of the open pipe is 21 mm, the amount of offset after welding
(steel pipe) is 0.1 mm, the roundness is 5.2 mm and a difference to an outer diameter
of 36 inches is only 0.6%.
EXAMPLE 2
[0085] As in Example 1, in order to form a steel pipe with a diameter of 36 inches using
a line pipe steel plate(API grade X60) having a thickness of 38.1 mm and a width of
2711 mm, the material is placed on a die in which an interval of a rod-like member
is set to 450 mm, and bending of the three-point bending is performed by 30° for a
time, from the position of 1120 mm from the width center of the plate material, with
a plate material feeding pitch of 224 mm and 11 bending times (five times from the
paper right end, and five times from the left end) by a punch having a forming surface
of a radius of 308 mm. At that time, the bending amount is set to an amount in which
the punch tip reaches a position of 15.8 mm from the line connecting the uppermost
part of the rod-like member, and bending is performed by 30° for a time. However,
at the position of 672 mm from the width center of the plate material (at the time
of third feeding from the right end, and third feeding from the left end), the lightly-bent
portion is formed at the position of 571 to 795 mm, while decreasing the bending amount
to 8.8 mm and performing the bending of 10°.
[0086] Next, while holding the preformed body having the U-shaped cross-section obtained
by bending in a U-shaped posture so that the opening portion faces upward, when pressing
the preformed body into an open pipe until an inter-apex distance (the apex of the
R part is the uppermost part of the circular arc surface in the upper die, and the
lowermost part of the circular arc surface in the lower die) of the R part of the
press die reaches 880 mm, using the upper die having a circular arc surface of a radius
R: 457.2 mm and a central angle θc: 60° and a flat surface leading to the circular
arc surface at the angle θd: 30°, and the lower die having a concave circular arc
surface of a radius R: 502.9 mm, the degree of pressing of the bending force of the
press die, the opening amount in the gap portion of the open pipe, the amount of offset,
and the roundness of the steel pipe after welding are investigated.
[0087] As a result, after performing the U-shape press at a standard condition, by performing
the O-shape press at the compression ratio of 0.2% using a press die of the radius
R: 452.6 mm, as a result of being compared to the case (conventional method) of producing
the steel pipe of an outer diameter of 36 inches and a thickness (wall thickness)
of 38.1 mm, when producing the steel pipe according to the present invention, it is
confirmed that the bending force of the O-shape press is decreased to about 15% as
compared to the conventional method.
[0088] Further, it becomes clear that the steel pipe can be obtained in which the opening
amount in the gap portion of the open pipe is 16 mm, the amount of offset after welding
(in steel pipe) is 0.1 mm, the roundness is 8.2 mm, and a difference to an outer diameter
of 36 inches is only about 0.9%.
EXAMPLE 3
[0089] In order to form a steel pipe with a diameter of 42 inches using a line pipe steel
plate(API grade X80) having a thickness of 44.5 mm, a width of 3180 mm and a length
of 12.2 mm, the material is placed on the die in which the interval of the rod-like
members is set to 500 mm, and bending of the three-point bending is performed by a
punch having a forming surface with a radius of 360 mm, and a preformed body having
a U-shaped cross-section with different position and length of the non-bent portion
from the width end portion is prepared.
[0090] Next, the lower die having a concave circular arc surface having a radius R: 609.6
mm is installed on the rod-like member, and the preformed body having the U-shaped
cross-section obtained by bending is pressed from the outside into an open pipe until
an inter-apex distance (the apex of the R part is the uppermost part of the circular
arc surface in the upper die, and the lowermost part of the circular arc surface in
the lower die) of the R part of the press die reaches 1027 mm.
[0091] In the case of pressing the preformed body into the open pipe, the bending force
of the press die, the opening amount and the amount of offset in the gap portion of
the open pipe, and the roundness of the steel pipe after welding are investigated.
The results are shown in Table 1 together with the bent position and the shape of
the preformed body.
Table 1
No |
Press condition |
Shape of preformed body |
Index of press condition (ratio to plate width) |
Result |
Bending force addition position |
Center position of non-bent portion |
Length of non-bent portion |
Distance between bending force addition position and center of non-bent portion |
Center position of non-bent portion |
Length of non-bent portion |
Load |
Roundness |
Amount of offset |
Opening |
[mm] |
[mm] |
[mm] |
[MN] |
[mm] |
[mm] |
[mm] |
1 |
477 |
986 |
318 |
0.16 |
0.31 |
0.10 |
27 |
18.1 |
1.5 |
60 |
2 |
382 |
986 |
318 |
0.19 |
0.31 |
0.10 |
23 |
13.9 |
0.8 |
50 |
3 |
286 |
986 |
318 |
0.22 |
0.31 |
0.10 |
20 |
8.5 |
0.9 |
80 |
4 |
191 |
986 |
318 |
0.25 |
0.31 |
0.10 |
18 |
7.5 |
0.6 |
100 |
5 |
95 |
986 |
318 |
0.28 |
0.31 |
0.10 |
16 |
10.7 |
0.8 |
120 |
6 |
0 |
986 |
318 |
0.31 |
0.31 |
0.10 |
15 |
13.9 |
1.0 |
150 |
7 |
95 |
890 |
318 |
0.25 |
0.28 |
0.10 |
16 |
10.7 |
0.6 |
90 |
8 |
0 |
795 |
318 |
0.25 |
0.25 |
0.10 |
17 |
5.3 |
0.7 |
80 |
9 |
0 |
700 |
318 |
0.22 |
0.22 |
0.10 |
20 |
9.6 |
0.5 |
120 |
10 |
0 |
604 |
318 |
0.19 |
0.19 |
0.10 |
23 |
14.9 |
0.7 |
100 |
11 |
0 |
509 |
318 |
0.16 |
0.16 |
0.10 |
28 |
17.1 |
1.0 |
110 |
12 |
0 |
795 |
127 |
0.25 |
0.25 |
0.04 |
17 |
7.5 |
0.2 |
60 |
13 |
0 |
795 |
191 |
0.25 |
0.25 |
0.06 |
18 |
9.1 |
0.5 |
70 |
14 |
0 |
795 |
254 |
0.25 |
0.25 |
0.08 |
18 |
11.2 |
0.7 |
80 |
15 |
0 |
795 |
382 |
0.25 |
0.25 |
0.12 |
18 |
10.1 |
1.0 |
120 |
16 |
0 |
795 |
445 |
0.25 |
0.25 |
0.14 |
19 |
19.2 |
0.9 |
140 |
[0092] As in Nos. 2 to 6, when adding the bending force to a position spaced apart from
the center of the non-bent portion by 0.19 to 0.31 of the plate width, the roundness
and the amount of offset are good. However, in No. 1 of 0.16 which is close to the
non-bent portion, the roundness is 18.1 mm which exceeds 1.5 % of the product diameter,
and the amount of offset is also 1.5 mm which is larger than the other cases.
[0093] In addition, as the addition position of the bending force is away from the non-bent
portion, the bending force becomes smaller.
[0094] In addition, as in Nos. 7 to 10, when setting the non-bent portion from the plate
width end portion in the range of 0.28 to 0.19, the satisfactory roundness is obtained,
but in No. 11 in which the non-bent portion is close to the plate width end portion,
the roundness is 17.1 mm which exceeds 1.5% of the product diameter.
[0095] In addition, as in Nos. 12 to 15, when the length of the non-bent portion is not
more than 0.12 of the plate width, the satisfactory roundness is obtained, but in
No. 16 in which the length of the non-bent portion is large, the roundness is 19.2
mm which exceeds 1.5% of the product diameter.
EXAMPLE 4
[0096] In order to form a steel pipe with a diameter of 42 inches using a line pipe steel
plate(API grade X80) having a thickness of 44.5 mm, a width of 3180 mm and a length
of 12.2 mm, the material is placed on the die in which the interval of the rod-like
members is set to 500 mm, and bending of the three-point bending is performed by a
punch having a forming surface with a radius of 360 mm, and a preformed body having
a U-shaped cross-section with different position and length of the non-bent portion
from the width end portion is prepared.
[0097] Next, while holding the preformed body having the U-shaped cross-section obtained
by bending in a U-shaped posture so that the opening portion faces upward, when pressing
the preformed body into an open pipe, until an inter-apex distance (the apex of the
R part is the uppermost part of the circular arc surface in the upper die, and the
lowermost part of the circular arc surface in the lower die) of the R part of the
press die reaches 1027 mm, using the upper die having a circular arc surface of a
radius R: 533.4 mm and a central angle θc: 60° and a flat surface leading to the circular
arc surface at the angle θd: 30°, and the lower die having a concave circular arc
surface of a radius R: 609.6 mm, in the state that the upper die is in contact with
both plate width end portions, the degree of pressing of the bending force of the
press die, the opening amount in the gap portion of the open pipe, the amount of offset,
and the roundness of the steel pipe after welding are investigated. The results are
shown in Table 2 together with the bent position and the shape of the preformed body.
The same shapes as in Example 3 are denoted by the same No.
Table 2
No |
Press condition |
Shape of preformed body |
Index of press condition (ratio to plate width) |
Result |
Bending force addition position |
Center position of non-bent portion |
Length of non-bent portion |
Distance between bending force addition position and center of non-bent portion |
Center position of non-bent portion |
Length of non-bent portion |
Load |
Roundness |
Amount of offset |
Opening |
[mm] |
[mm] |
[mm] |
[MN] |
[mm] |
[mm] |
[mm] |
7 |
0 |
890 |
318 |
0.28 |
0.28 |
0.10 |
32 |
8.0 |
0.2 |
110 |
8 |
0 |
795 |
318 |
0.25 |
0.25 |
0.10 |
36 |
4.3 |
0.1 |
100 |
9 |
0 |
700 |
318 |
0.22 |
0.22 |
0.10 |
40 |
8.5 |
0.1 |
90 |
10 |
0 |
604 |
318 |
0.19 |
0.19 |
0.10 |
47 |
11.2 |
0.2 |
100 |
11 |
0 |
509 |
318 |
0.16 |
0.16 |
0.10 |
56 |
16.5 |
0.1 |
80 |
12 |
0 |
795 |
127 |
0.25 |
0.25 |
0.04 |
35 |
6.4 |
0.1 |
70 |
13 |
0 |
795 |
191 |
0.25 |
0.25 |
0.06 |
35 |
5.9 |
0.0 |
70 |
14 |
0 |
795 |
254 |
0.25 |
0.25 |
0.08 |
36 |
5.3 |
0.1 |
90 |
15 |
0 |
795 |
382 |
0.25 |
0.25 |
0.12 |
37 |
6.4 |
0.2 |
130 |
16 |
0 |
795 |
445 |
0.25 |
0.25 |
0.14 |
37 |
17.1 |
0.1 |
140 |
[0098] As in Nos. 7 to 10, when setting the non-bent portion from the plate width end portion
within the range of 0.28 to 0.19, the satisfactory roundness is obtained. However,
in No. 11 in which the non-bent portion is close to the plate width end portion, the
roundness is 16.5 mm which exceeds 1.5% of the product diameter.
[0099] In addition, as in No. 12 to 15, when the length of the non-bent portion is not more
than 0.12 of the plate width, the satisfactory roundness is obtained. However, in
No. 16 in which the length of the non-bent portion is large, the roundness is 17.1
mm which exceeds 1.5% of the product diameter. Furthermore, all the amount of offset
is not more than 0.2 mm which is smaller than in Example 3 performing the bending
one side by one side.
EXAMPLE 5
[0100] In order to form a steel pipe with a diameter of 22 inches using a line pipe steel
plate(API grade X80) having a thickness of 31.8 mm, a width of 1640 mm and a length
of 12.2 mm, the material is placed on the die in which the interval of the rod-like
members is set to 400 mm, and bending of the three-point bending is performed by a
punch having a forming surface with a radius of 188 mm, and a preformed body having
a U-shaped cross-section with different position and length of the non-bent portion
from the width end portion is prepared.
[0101] Next, a lower die having a concave circular arc surface having a radius R: 330.2
mm is installed on the rod-like member, and the preformed body having the U-shaped
cross-section obtained by bending is pressed from the outside into an open pipe, until
an inter-apex distance (the apex of the R part is the uppermost part of the circular
arc surface in the upper die, and the lowermost part of the circular arc surface in
the lower die) of the R part of the press die reaches 538 mm,
[0102] In the case of pressing the preformed body into the open pipe, the bending force
of the press die, the opening amount and the amount of offset in the gap portion of
the open pipe, and the roundness of the steel pipe after welding are investigated.
The results are described in Table 3 together with the bent position and the shape
of the preformed body.
Table 3
No |
Press condition |
Shape of preformed body |
Index of press condition (ratio to plate width) |
Result |
Bending force addition position |
Center position of non-bent portion |
Length of non-bent portion |
Distance between bending force addition position and center of non-bent portion |
Center position of non-bent portion |
Length of non-bent portion |
Load |
Roundness |
Amount of offset |
Opening |
[mm] |
[mm] |
[mm] |
[MN] |
[mm] |
[mm] |
[mm] |
1 |
246 |
508 |
164 |
0.16 |
0.31 |
0.10 |
37 |
10.1 |
1.4 |
60 |
2 |
197 |
508 |
164 |
0.19 |
0.31 |
0.10 |
32 |
7.8 |
0.7 |
50 |
3 |
148 |
508 |
164 |
0.22 |
0.31 |
0.10 |
28 |
5.0 |
0.9 |
80 |
4 |
98 |
508 |
164 |
0.25 |
0.31 |
0.10 |
25 |
4.6 |
0.7 |
100 |
5 |
49 |
508 |
164 |
0.28 |
0.31 |
0.10 |
22 |
6.7 |
0.6 |
120 |
6 |
0 |
508 |
164 |
0.31 |
0.31 |
0.10 |
21 |
7.8 |
0.9 |
150 |
7 |
49 |
459 |
164 |
0.25 |
0.28 |
0.10 |
23 |
5.6 |
0.5 |
90 |
8 |
0 |
410 |
164 |
0.25 |
0.25 |
0.10 |
24 |
3.9 |
0.4 |
80 |
9 |
0 |
361 |
164 |
0.22 |
0.22 |
0.10 |
28 |
5.0 |
0.6 |
120 |
10 |
0 |
311 |
164 |
0.19 |
0.19 |
0.10 |
32 |
7.8 |
0.6 |
100 |
11 |
0 |
262 |
164 |
0.16 |
0.16 |
0.10 |
40 |
10.6 |
1.0 |
110 |
12 |
0 |
410 |
98 |
0.25 |
0.25 |
0.06 |
25 |
5.0 |
0.5 |
70 |
13 |
0 |
410 |
131 |
0.25 |
0.25 |
0.08 |
26 |
5.6 |
0.9 |
80 |
14 |
0 |
410 |
197 |
0.25 |
0.25 |
0.12 |
26 |
5.3 |
0.9 |
120 |
15 |
0 |
410 |
229 |
0.25 |
0.25 |
0.14 |
26 |
11.2 |
1.1 |
140 |
[0103] As in Nos. 2 to 6, when adding the bending force to a position spaced apart from
the center of the non-bent portion by 0.19 to 0.31 of the plate width, both the roundness
and the amount of offset are good. However, in No. 1 of 0.16 which is close to the
non-bent portion, the roundness is 10.1 mm which exceeds 1.5 % of the product diameter,
and the amount of offset is 1.4 mm which is larger than the other cases.
[0104] Further, as the addition position of the bending force is away from the non-bent
portion, the bending force becomes smaller. Further, as in Nos. 7 to 10, when providing
the non-bent portion in the range of 0.28 to 0.19 from the plate width end portion,
the satisfactory roundness is obtained, but in No. 11 in which the non-bent portion
is close to the plate width end portion, the roundness is 10.6 mm which exceeds 1.5%
of the product diameter. Furthermore, as in Nos. 12 to 14, when the length of the
non-bent portion is not more than 0.12 of the plate width, the satisfactory roundness
is obtained, but in No. 15 in which the length of the non-bent portion is large, the
roundness is 11.2 mm which exceeds 1.5% of the product diameter.
EXAMPLE 6
[0105] In order to form a steel pipe with a diameter of 22 inches using a line pipe steel
plate(API grade X80) having a thickness of 31.8 mm, a width of 1640 mm and a length
of 12.2 mm, the material is placed on the die in which the interval of the rod-like
members is set to 400 mm, and bending of the three-point bending is performed by a
punch having a forming surface with a radius of 188 mm, and a preformed body having
a U-shaped cross-section with different position and length of the non-bent portion
from the width end portion is prepared.
[0106] Next, while holding the preformed body having the U-shaped cross-section obtained
by bending in a U-shaped posture so that the opening portion faces upward, when pressing
the preformed body into an open pipe, until an inter-apex distance (the apex of the
R part is the uppermost part of the circular arc surface in the upper die, and the
lowermost part of the circular arc surface in the lower die) of the R part of the
press die reaches 538 mm, using the upper die having a circular arc surface of a radius
R: 279.4 mm and a central angle θc: 60° and a flat surface leading to the circular
arc surface at the angle θd: 30°, and the lower die having a concave circular arc
surface of a radius R: 330.2 mm, in the state that the upper die is in contact with
both plate width end portions, the degree of pressing of the bending force of the
press die, the opening amount in the gap portion of the open pipe, the amount of offset,
and the roundness of the steel pipe after welding are investigated. The results are
described in Table 4 together with the bent position and the shape of the preformed
body. The same shapes as in Example 5 are denoted by the same No.
Table 4
No |
Press condition |
Shape of preformed body |
Index of press condition (ratio to plate width) |
Result |
Bending force addition position |
Center position of non-bent portion |
Length of non-bent portion |
Distance between bending force addition position and center of non-bent portion |
Center position of non-bent portion |
Length of non-bent portion |
Load |
Roundness |
Amount of offset |
Opening |
[mm] |
[mm] |
[mm] |
[MN] |
[mm] |
[mm] |
[mm] |
7 |
0 |
459 |
164 |
0.28 |
0.28 |
0.10 |
46 |
4.7 |
0.0 |
110 |
8 |
0 |
410 |
164 |
0.25 |
0.25 |
0.10 |
50 |
3.1 |
0.2 |
100 |
9 |
0 |
361 |
164 |
0.21 |
0.22 |
0.10 |
55 |
4.5 |
0.1 |
90 |
10 |
0 |
311 |
164 |
0.19 |
0.19 |
0.10 |
65 |
7.3 |
0.2 |
100 |
11 |
0 |
262 |
164 |
0.16 |
0.16 |
0.10 |
78 |
9.8 |
0.3 |
80 |
12 |
0 |
410 |
98 |
0.25 |
0.25 |
0.06 |
50 |
36 |
0.0 |
70 |
13 |
0 |
410 |
131 |
0.25 |
0.25 |
0.08 |
51 |
3.9 |
0.1 |
90 |
14 |
0 |
410 |
197 |
0.25 |
0.25 |
0.12 |
51 |
3.4 |
0.3 |
130 |
15 |
0 |
410 |
229 |
0.25 |
0.25 |
0.14 |
52 |
10.1 |
0.2 |
140 |
[0107] As in Nos. 7 to 10, when providing the non-bent portion within the range of 0.28
to 0.19 from the plate width end portion, the satisfactory roundness is obtained.
However, in No. 11 in which the non-bent portion is close to the plate width end portion,
the roundness is 9.8 mm which exceeds 1.5% of the product diameter.
[0108] In addition, as in Nos. 12 to 14, when the length of the non-bent portion is not
more than 0.12 of the plate width, the satisfactory roundness is obtained. However,
in No. 15 in which the length of the non-bent portion is large, the roundness is 10.1
mm which exceeds 1.5% of the product diameter. Furthermore, all the amount of offset
is not more than 0.3 mm which is smaller than in Example 3 performing bending one
side by one side.
EXAMPLE 7
[0109] In order to form a steel pipe with a diameter of 36 inches using a line pipe steel
plate(API grade X60) having a thickness of 38.1 mm, a width of 2711 mm and a length
of 12.2 mm, the material is placed on the die in which the interval of the rod-like
members is set to 450 mm, and bending of the three-point bending is performed by a
punch having a forming surface with a radius of 308 mm, and a preformed body having
a U-shaped cross section provided with non-bent portions of the length of 109 mm and
224 mm around the position of 683 mm from the plate width end portion is prepared.
[0110] Next, while holding the preformed body having the U-shaped cross-section obtained
by bending in a U-shaped posture so that the opening portion faces upward, when pressing
the preformed body into an open pipe, until an inter-apex distance (the apex of the
R part is the uppermost part of the circular arc surface in the upper die, and the
lowermost part of the circular arc surface in the lower die) of the R part of the
press die reaches 880 mm, using the upper die having a circular arc surface of a radius
R: 457.2 mm and various central angles and a flat surface leading to the circular
arc surface, and the lower die having a concave circular arc surface of a radius R:
502.9 mm, in the state that the upper die is in contact with both plate width end
portions, the degree of pressing of the bending force of the press die, the opening
amount in the gap portion of the open pipe, and the roundness of the steel pipe after
welding are investigated. Table 5 describes the results together with the length of
the non-bent portion, the opening angle θs of the preformed body having the U-shaped
cross-section, the central angle of the upper die and the angle θf of the bending
force.
Table 5
No |
Lengh of non-bent portion |
Opening angle θs |
Center angle of upper die θc |
Angle of bending force θf |
Opening |
Roundness |
[mm] |
[degree] |
[degree] |
[degree] |
[mm] |
[mm] |
1 |
109 |
7.2 |
5.0 |
2.1 |
240 |
- |
2 |
109 |
7.2 |
10.0 |
7.1 |
120 |
15.7 |
3 |
109 |
7.2 |
15.0 |
12.1 |
40 |
7.1 |
4 |
224 |
14.4 |
15.0 |
12.1 |
240 |
- |
5 |
224 |
14.4 |
20.0 |
17.1 |
31 |
6.2 |
6 |
224 |
14.4 |
30.0 |
27.1 |
21 |
5.2 |
[0111] As in Nos. 3, 5 and 6, under the condition of θf > θs, the opening amount is also
small and the roundness is also good. Meanwhile, in Nos. 1, 2 and 4 of θf < θs, the
opening amount is large, and in Nos. 1 and 4, the opening amount is too large to perform
the welding. In addition, although the welding can be performed in No. 2, the roundness
is 15.7 mm which exceeds 1.5% of the product diameter.
EXAMPLE 8
[0112] In order to form a steel pipe with various diameters of 28 to 38 inches using a line
pipe steel plate (API grade X60) having a thickness of 38.1 mm and a length of 12.2
mm, bending of the three-point bending is performed, and a preformed body having a
U-shaped cross section provided with a non-bent portion of 0.08 times the plate width
around the position of W/4 from the plate width end portion is prepared.
[0113] Next, while holding the preformed body having the U-shaped cross-section obtained
by bending in a U-shaped posture so that the opening portion faces upward, when pressing
the preformed body into an open pipe, until an inter-apex distance (the apex of the
R part is the uppermost part of the circular arc surface in the upper die, and the
lowermost part of the circular arc surface in the lower die) of the R part of the
press die reaches 0.96 times the outer diameter, using the upper die having a circular
arc surface of a radius R: 457.2 mm and a central angle θc: 60° and various radiuses
leading to the circular arc surface at the angle θd: 30°, and the lower die having
a concave circular arc surface of a radius larger than the outer diameter by 50.8
mm, in the state that the upper die is in contact with both plate width end portions,
the degree of pressing of the bending force of the press die, the amount of offset
in the gap portion of the open pipe, and the roundness of the steel pipe after welding
are investigated. Table 6 describes the results together with the outer diameter of
the steel pipe, and the ratio of the radius of the upper die to the outer radius of
the steel pipe.
Table 6
No |
Outer diameter of steel pipe |
Radius of upper die/ outer radius of steel pipe |
Roundness |
Amount of offset |
[mm] |
[mm] |
[mm] |
1 |
965.2 |
0.95 |
5.7 |
1.0 |
2 |
914.4 |
1.00 |
5.2 |
0.2 |
3 |
863.6 |
1.06 |
6.2 |
0.1 |
4 |
812.8 |
1.13 |
8.3 |
0.2 |
5 |
762.0 |
1.20 |
10.2 |
0.3 |
6 |
711.2 |
1.29 |
17.2 |
0.2 |
[0114] In Nos. 1 to 5 in which the ratio of the radius of the upper die to the outer radius
of the steel pipe is not more than 1.2, the roundness is good, and smaller the ratio
is, the better the roundness is. In addition, in No. 1 in which the radius of the
upper die is smaller than the outer radius of the steel pipe, the amount of offset
is larger than Nos. 2 to 5 in which the ratio is not less than 1.0. Meanwhile, in
No. 6 in which ratio of the radius of the upper die to the outer radius of the steel
pipe is large, the roundness is 17.2 mm which exceeds 1.5% of the product diameter.
EXAMPLE 9
[0115] In order to form a steel pipe with a diameter of 36 inches using a line pipe steel
plate(API grade X60) having a thickness of 38.1 mm, a width of 2711 mm and a length
of 12.2 mm, the material is placed on the die in which the interval of the rod-like
members is set to 450 mm, and bending of the three-point bending is performed by a
punch having a forming surface with a radius of 308 mm, and a preformed body having
a U-shaped cross section provided with a non-bent portion of the length of 224 mm
around the position of 683 mm from the plate width end portion is prepared.
[0116] Next, while holding the preformed body having the U-shaped cross-section obtained
by bending in a U-shaped posture so that the opening portion faces upward, when pressing
the preformed body into an open pipe, until an inter-apex distance (the apex of the
R part is the uppermost part of the circular arc surface in the upper die, and the
lowermost part of the circular arc surface in the lower die) of the R part of the
press die reaches 880 mm, using the upper die having a circular arc surface of a radius
R: 457.2 mm and a central angle θc: 60° and various radiuses R leading to the circular
arc surface at the angle θd: 30°, and the lower die having a concave circular arc
surface of various radiuses, in the state that the upper die is in contact with both
plate width end portions, the bending force (load) of the press die is investigated.
Table 7 describes a relation among deformation of the lower die, a ratio to the outer
radius of the steel pipe, and the bending force.
Table 7
No |
Radius of lower die |
Radius of lower die / outer radius of steel pipe |
Load |
[mm] |
[MN] |
1 |
482.6 |
1.06 |
75 |
2 |
508.0 |
1.11 |
50 |
3 |
533.4 |
1.17 |
35 |
4 |
558.8 |
1.22 |
35 |
[0117] As the radius of the lower die is increased, its load is decreased. In Nos. 3 and
4 in which the ratio is in excess of 1.15, there is no contact with the press die,
and the load is not more than half of No. 1.
INDUSTRIAL APPLICABILITY
[0118] According to the present invention, it is possible to efficiently produce a steel
pipe having a high roundness, without requiring excessive pressure.
DESCRIPTION OF REFERENCE SYMBOLS
[0119]
- 1
- die
- 1a
- rod-like member
- 1b
- rod-like member
- 2
- punch
- 2a
- punch tip
- 2b
- punch support
- 3
- roller
- 4
- upper die
- 4a
- circular arc surface
- 4b
- forming surface (inclined surface)
- 5
- lower die
- 5a
- circular arc surface
- S
- plate material
- S1
- preformed body
- S2
- open pipe