BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a forming method and forming stand for forming welded
pipes to accurate dimensions in a welded pipe manufacturing line on which a metallic
strip of a predetermined width is continuously formed by rolls and welded by the electric
resistance welding method or other welding methods.
2. Related Art
[0002] In general, in a manufacturing process in which welded pipes such as electric resistance
welded pipes are manufactured, a metallic strip of a predetermined width is continuously
supplied to a group of forming rolls including a plurality of breakdown rolls, side
rolls and fin-pass rolls, and then the formed metallic strip is subjected to welding
such as high frequency welding in which squeeze rolls are used.
[0003] According to this method, welded pipes are continuously manufactured. Therefore,
this method is greatly advantageous in that the manufacturing efficiency is improved
and the cost is reduced. Accordingly, this method is widely used when mechanical structure
pipes, boiler pipes, oil well pipes and other various pipes are manufactured. Recently,
there is a demand for applying this method to the manufacture of thin wall pipes,
thick wall pipes and high tensile strength pipes. Further, there is a strong demand
for manufacturing pipes of high quality and high accuracy.
[0004] However, when these thin wall pipes, thick wall pipes and high tensile strength pipes
are formed by the conventional pipe manufacturing method, the profiles of these pipes
are defective. To describe this in detail, in the initial process of edge forming
in which a pair of breakdown rolls composed of upper and lower rolls are used, the
edge portions of a work piece are lack of bending.
[0005] In order to solve the above problem, a "W-bend method", in which the middle portion
of a work piece is bent at a radius of curvature opposite to that of a product in
the edge forming process and both edge portions of the work piece are bent to the
same side as that of the product has come into pfactical use. The effect of this method
is introduced, for example, on page 519 of the proceedings of a plastic working lecture
meeting (held in spring of 1985) published by the Plastic Working Society.
[0006] According to the method disclosed in Japanese Unexamined Patent Publication (Kokai)
No. 1-44217, two rolls are constituted for the horizontal lower caliber roll applied
to the edge forming roll stand, and the inclination angles of the two rolls are capable
of being adjusted with respect to the metallic strip advancing direction, so that
the edge portions of both thick and thin wall metallic strips are sufficiently bent.
[0007] In the process for manufacturing metallic pipes by means of roll forming and welding,
it is desired to provide forming rolls capable of being applied for manufacturing
various sizes of pipes for the purpose of reducing the roll cost by reducing the number
of rolls, and also for the purpose of improving the operation rate of the manufacturing
line by reducing the frequency of roll change. In order to accomplish the above object,
a set of rolls are disclosed in Japanese Unexamined Patent Publication (Kokai) No.
62-166027, and these rolls have been put into practical use.
[0008] As described above, in the breakdown roll used for edge forming in the conventional
pipe forming method, the problem of defective profile is caused especially when thin
wall pipes, thick wall pipes and high tensile strength pipes are formed. In the case
where the work piece is additionally subjected to edge forming by the fin-pass rolls
disposed in the after-stage so as to solve the problem of defective profile, the thickness
of the edge portion is increased as shown by numeral 1 in Fig. 1. This increase of
thickness 1 is a factor to deteriorate the size accuracy.
[0009] In the case of a breakdown roll of the W-bend system, a sufficiently high bending
force can be applied to the edge portions compared with the conventional method. However,
in the forming process from the start of contact of a work piece with an upper roll,
to a position right below the roll, the upper roll locally comes into contact with
the work piece. Therefore, an indentation 2 tends to occur as illustrated in Fig.
2, which is a factor to deteriorate the accuracy of thickness. Even when this method
is applied, the problem of defective profile can not be essentially solved in the
case where thick wall and thin wall pipes exceeding the designed thickness of the
upper roll 3 are formed. Therefore, this method is not sufficient for extending the
range of wall thicknesses to which the same forming roll can be applied.
[0010] On the other hand, in the edge forming method disclosed in Japanese unexamined Patent
Publication (Kokai) No. 1-44217 described before, since a work piece continuously
comes into contact with the edge forming roll, the occurrence of indentations can
be avoided as compared with the conventional edge forming method. However, according
to this method, only the lower rolls are crossed and tilted. Accordingly, from the
viewpoint of construction, the range of wall thickness to which the same edge forming
roll can be applied is limited.
[0011] On the other hand, the edge forming rolls disclosed in Japanese unexamined Patent
Publication (Kokai) No. 62-166027 can be applied to a wide range of pipe diameters,
however, since the radius of curvature of the roll is continuously changed, the roll
locally comes into contact with a metallic strip, so that the problem of defective
profile tends to occur, and this method is not appropriate for forming thick wall
pipes.
SUMMARY OF THE INVENTION
[0013] The present invention has been achieved to solve the above problems in the prior
art. It is an object of the present invention to provide a forming method and forming
stand applied to a welded pipe manufacturing line by which welded pipes of high size
accuracy can be formed and especially edge portions of a metallic strip can be accurately
bent.
[0014] The summary of the invention will be described as follows.
(1) A welded steel pipe forming method comprising the step of bending the edges of
a metallic strip of a predetermined width in a manufacturing line for roll-forming
and welding the metallic strip, wherein each edge of the metallic strip is bent with
a pair of upper and lower horizontal rolls provided when a pair of horizontal rolls
is divided into two with respect to the width direction of the metallic strip, and
the upper and lower horizontal rolls are crossed to each other being turned on a vertical
turning axis.
(2) The welded steel pipe forming method according to item (1), wherein the upper
roll turning angle αu and lower roll turning angle αd of the pair of upper and lower horizontal forming rolls are determined to satisfy
the following inequalities, wherein the turning directions of the upper and lower
rolls are set to be opposite to each other.


where
αu : an angle formed between a line in the width direction of the metallic strip and
a roll axis of the upper horizontal roll
αd : an angle formed between a line in the width direction of the metallic strip and
a roll axis of the lower horizontal roll
(3) The welded steel pipe forming method according to item (1) or (2), wherein the
turning angles of the upper and lower horizontal rolls are determined so that the
upper roll is directed to the edge side of the metallic strip at an entry side of
the roll stand and directed to the center side of the metallic strip at a delivery
side of the roll stand.
(4) A welded steel pipe forming method comprising the step of bending the edges of
a metallic strip of a predetermined width in a manufacturing line for roll-forming
and welding the metallic strip, wherein each edge of the metallic strip is bent with
an upper horizontal roll provided when a horizontal roll is divided into two with
respect to the width direction of the metallic strip, and the upper horizontal roll
is turned and fixed on a vertical turning axis.
(5) The welded steel pipe forming method according to item (4), wherein the upper
horizontal roll turning angle αu is determined to satisfy the following inequality.

where
αu : an angle formed between a line in the width direction of the metallic strip and
a roll axis of the upper horizontal roll
(6) The welded steel pipe forming method according to item (4) or (5), wherein the
turning angle of the upper horizontal roll is determined so that the upper horizontal
roll is directed to the edge side of the metallic strip at an entry side of the roll
stand and to the center side of the metallic strip at a delivery side of the roll
stand.
(7) A welded steel pipe forming method comprising the step of bending the edges of
a metallic strip of a predetermined width in manufacturing line for roll-forming and
welding the metallic strip, wherein each edge of the metallic strip is bent with a
pair of upper and lower horizontal rolls provided when a pair of horizontal rolls
is divided into two with respect to the width direction of the metallic strip, and
the upper and lower horizontal rolls are disposed at different positions with respect
to the metallic strip forming direction and crossed to each other being turned on
a vertical turning axis.
(8) A forming stand for forming welded pipes used for a group of initial forming rolls
in a manufacturing line for forming and wedding a metallic strip of a predetermined
width, comprising: two pairs of upper and lower horizontal rolls for bending the edges
of the metallic strip, the upper and lower horizontal rolls being provided when the
upper and lower horizontal rolls are divided into two with respect to the width direction
of the metallic strip, wherein the positions of upper and lower rolls on both sides
can be adjusted being turned on a vertical turning axis, and the positions of upper
and lower rolls with respect to the width direction of the metallic strip can be also
adjusted.
(9) A forming stand for forming welded pipes used for a group of initial forming rolls
in a manufacturing line for forming and welding a metallic strip of a predetermined
width, comprising: two upper horizontal rolls for bending the edges of the metallic
strip, the two upper horizontal rolls being provided on both sides when an upper horizontal
roll is divided into two with respect to the width direction of the metallic strip,
wherein the positions of upper rolls on both sides can be adjusted being turned on
a vertical turning axis, and the positions of upper rolls with respect to the width
direction of the metallic strip can be also adjusted.
(10) The forming stand for forming welded pipes according to item (8) or (9), wherein
the divided horizontal rolls are disposed at different positions with respect to the
metallic strip forming direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Fig. 1 is a sectional view of a metallic strip, the edge thickness of which is increased,
which deteriorates the size accuracy.
[0016] Fig. 2 is a sectional view of a metallic strip on which a bend indentation is caused,
which deteriorates the size accuracy.
[0017] Fig. 3 is a view showing the progress of forming of a metallic strip right below
the forming roll.
[0018] Figs. 4(a), 4(b), 4(c) and 4(d) are views showing the example of the present invention
of a gap formed between the upper and lower rolls in accordance with the forming radius
of curvature and the thickness, wherein Fig. 4(a) shows a case of a thin wall, Fig.
4(b) shows a case of a small radius of curvature (large diameter), Fig. 4(c) shows
a case of a thick wall, and Fig. 4(d) shows a case of large radius of curvature (small
diameter).
[0019] Figs. 5(a) and 5(b) are schematic illustrations showing the direction of a roll,
wherein Fig. 5(a) shows a case of the forming roll of the invention directed inside,
and Fig. 5(b) shows a case of the forming roll of the invention directed outside.
[0020] Fig. 6 is a schematic illustration showing the direction of a thrust in the case
of the forming roll of the invention directed inside.
[0021] Fig. 7 is a schematic illustration showing a case in which the upper roll deviates
in the case of a forming roll of the invention directed outside.
[0022] Figs. 8(a) and 8(b) are plan views showing an example of the roll to which the present
invention is applied, wherein Fig. 8(a) is a front view and Fig. 8(b) is a plan view.
[0023] Fig. 9 is a view showing an example of the forming apparatus to which the present
invention is applied.
[0024] Figs. 10(a) and 10(b) are views showing the examples of the distributions in the
radius of curvature and wall thicknesses after a metallic strip has passed through
a single stand in the case where the present invention is applied and in the case
where the present invention is not applied.
[0025] Fig. 11 is a view showing an example of the distributions in the radius of curvature
and wall thicknesses expressing the properties of sharing a roll in the case where
the present invention is applied.
[0026] Figs. 12(a) and 12(b) are views showing an example of the roll to which the present
invention is applied, wherein Fig. 12(a) is a front view and Fig. 12(b) is a plan
view.
[0027] Fig. 13 is a view showing an example of the forming apparatus to which the present
invention is applied.
DESCRIPTION OF THE MOST PREFERRED EMBODIMENT
[0028] According to the present invention, as illustrated in Fig. 8, metallic strips can
be accurately formed into pipes with thin or thick walls with two pairs of upper and
lower horizontal edge forming rolls disposed on both sides of the metallic strip in
a breakdown stand for the purpose of edge forming, the two pairs of rolls being provided
when a pair of upper and lower rolls are divided into two with respect to the width
direction of the metallic strip, wherein the edge forming is performed under the condition
that the pair of upper and lower horizontal rolls are crossed by being turned on a
vertical axis. As illustrated in Fig. 3, a pair of upper and lower horizontal edge
forming rolls 3, 4 are crossed, and the upper and lower rolls are continuously contacted
with both sides of a metallic strip 5 to be formed right below the upper forming roll.
Therefore, in this forming process, a local contact of the forming roll and the metallic
strip can be avoided, which is different from the forming process of the prior art.
With reference to Figs. 4(a) to 4(c), Fig. 4(a) shows a case of a small wall thickness,
Fig. 4(b) shows a case of a small radius of curvature (large pipe diameter), and Fig.
4(c) shows a case of large wall thickness. As shown in the drawings, when the turning
angle of the upper roll 3 is changed, the radius of curvature right below the upper
forming roll, which is made by the hysteresis of the upper roll, is changed, so that
the hysteresis of the gap between the upper and lower rolls can be provided in accordance
with the thickness of the metallic strip to be formed. Therefore, edge forming can
be accurately performed with respect to a wall thickness range which includes thin
and thick walls.
[0029] Further, with reference to Fig. 4(d) in which a case of a large radius of curvature
(small pipe diameter) is shown, when the turning angle of the lower roll is changed,
the radius of curvature formed by the lower roll coming into contact with the outside
of the metallic strip is changed, and when two pairs of upper and lower rolls disposed
on both sides are moved so as to be adjusted in the width direction of the metallic
strip in accordance with the strip width. In this way, the edge forming rolls can
be shared by metallic strips of different sizes from which pipes of different sizes
are formed.
[0030] In general, the turning angle of the upper roll is determined by the profile of the
upper roll caliber, the outside diameter of the pipe to be formed from the metallic
strip, the wall thickness of the metallic strip, and the upper roll diameter. Also,
the turning angle of the lower roll is determined by the profile of the lower roll
caliber, the outside diameter of the pipe to be formed from the metallic strip, and
the lower roll diameter. In the second embodiment of the present invention, in order
to exhibit the effect of the invention at the maximum, the turning angle directions
of the upper and lower rolls are limited as follows.
[0031] It is necessary to increase the turning angle of the upper roll when the wall thickness
of the metallic strip is small. However, when the turning angle is increased too much,
an amount of slippage caused between the upper roll and the metallic strip is increased.
As a result, the strip surface is damaged, the forming rolls are seized, and the roll
life is reduced. For this reason, while consideration is given to the sharable range
of metallic strips to be formed, the upper limit of the turning angle is determined
to be 45°.
[0032] When the turning angle of the lower roll is increased, the sharable range of metallic
straps to be formed is extended. However, when the turning angle is extremely increased,
the same problems as those described above are caused, and further the sharable range
of metallic strips is limited due to the interference of the upper and lower rolls
disposed on both sides. Accordingly, consideration is given to the sharable range
of the metallic strips to be formed, and the upper limit of the turning angle is determined
to be 30°. Due to the foregoing, the sharable range of the diameter of the pipe to
be formed from the metallic strip can be extended by 1.5 to 2.0 times.
[0033] Further, according to the present invention, each pair of upper and lower rolls are
disposed at different positions with respect to the metallic strip forming direction.
Therefore, after the forming of one edge of the metallic strip has been started, the
forming of the other edge is started. Due to the foregoing, in the case where small
size pipes are formed, interference of the forming rolls on both sides caused when
the upper and lower rolls are turned can be avoided, so that the turning angles of
the forming rolls are not restricted. In this case, an interval with respect to the
metallic strip forming direction between the pairs of upper and lower rolls disposed
on both sides, is determined by the diameters of the upper and lower rolls and the
range of the designed turning angle.
[0034] Next, a case will be explained as follows in which the upper horizontal roll is divided
into two rolls.
[0035] The horizontal upper rolls divided with respect to the metallic strip width direction
are disposed on both sides for the purpose of edge forming. Then horizontal upper
rolls are turned on and fixed at a vertical axis. When the metallic strip is formed
under the above condition, pipes of various wall thickness, that is, pipes of thin
and thick walls can be formed with high accuracy. The reason why the pipes of various
wall thickness can be accurately formed in the above manner will be described as follows:
As illustrated in Fig. 3, when the upper horizontal forming roll is turned on a vertical
axis, the upper roll 3 continuously comes into contact with the edge of the metallic
strip to be formed right below the roll on both sides, so that both edge portions
of the metallic strip are subjected to forming. Therefore, the occurrence of local
contact, which tends to occur when the conventional method is applied, can be avoided
in the forming process. Also, as illustrated in Figs. 4(a) to 4(c), when the turning
angle of the upper roll 3 is changed, the radius of curvature, which is formed by
the hysteresis of a portion right below the upper roll, is changed. Accordingly, the
hysteresis of a gap can be constructed in accordance with the wall thickness of the
metallic strip to be formed. Therefore, pipes with thin or thick walls can be formed
with high accuracy.
[0036] The turning angle of the upper roll is determined by the profile of the upper roll
caliber, the outside diameter of the pipe to be formed from the metallic strip, the
wall thickness of the metallic strip, and the upper roll diameter. In the fifth embodiment
of the present invention, in order to exhibit the effect of the invention at the maximum,
the turning angle direction of the upper roll is limited as follows.
[0037] It is necessary to increase the turning angle of the upper roll when the wall thickness
of the metallic strip is small. However, when the turning angle is increased too much,
an amount of slippage caused between the upper roll and the metallic strip is increased.
As a result, the strip surface is damaged, the forming rolls are seized, and the roll
life is reduced. For this reason, while consideration is given to the sharable range
of metallic strips, the upper limit of the turning angle is determined to be 45°.
[0038] Next, the roll direction will be explained as follows. In the case where the upper
and lower rolls are divided into two, a slippage is caused between the rolls and the
metallic strip when the upper and lower rolls are turned. Therefore, a force is applied
to the rolls in the width direction of the metallic strip, and torsion is generated
in the rolls. For example, as illustrated in Fig. 5(a), the upper rolls are positioned
in such a manner that the rolls are directed to the edges of the metallic strip on
the entry side of the roll stand and also the rolls are directed to the center of
the metallic strip on the delivery side of the roll stand. The lower rolls are positioned
in the opposite direction to that of the upper roll. In the manner described above,
the upper and lower rolls are crossed with each other. In this case, since the contact
point between the upper roll and the metallic strip is shifted from the edge portion
to the center of the metallic strip, the above roll arrangement will be referred to
as "a forming roll arrangement directed inside", hereinafter. In this case, as illustrated
in Fig. 6, the upper roll is given a thrust directed inside, and the lower roll is
given a thrust directed outside. Also, a deviation directed outside with respect to
the width direction is caused in the upper roll, and a deviation directed inside with
respect to the width direction is caused in the lower roll. On the other hand, as
illustrated in Fig. 5(b), the upper rolls are positioned in such a manner that the
rolls are directed to the center of the metallic strip on the entry side of the roll
stand and also the rolls are directed to the edge of the metallic strip on the delivery
side of the roll stand. The lower rolls are positioned in the opposite direction to
that of the upper roll. In the manner described above, the upper and lower rolls are
crossed with each other. In this case, since the contact point between the upper roll
and the metallic strip is shifted from the center to the edges of the metallic strip,
the above roll arrangement will be referred to as "a forming roll arrangement directed
outside", hereinafter. As illustrated in Fig. 7, a deviation directed inside with
respect to the width direction is caused in the upper roll, and a deviation directed
outside with respect to the width direction is caused in the lower roll. In the case
of "the forming roll arrangement directed outside", the following problems are caused:
Since the upper roll is not contacted with an extreme edge portion, the edge portion
is not sufficiently bent. In the case where the present invention is applied to the
W-bend method, the gap becomes narrow due to the deviation, and the wall thickness
is locally reduced.
[0039] On the other hand, in the case of "the forming roll arrangement directed inside",
the above problems are not caused, and further the torsion forces applied to the upper
and lower rolls are advantageous for edge forming, and the reduction force of the
upper and lower rolls are advantageously reduced. Accordingly, in the case of a roll
stand in which torsion tends to occur due to insufficient rigidity, it is preferable
to employ "the forming roll arrangement directed inside".
[0040] The circumstances explained above are essentially the same as those in which only
upper rolls are turned, so that it is preferable to employ "the forming roll arrangement
directed inside" in the case where only upper rolls are turned.
[0041] With reference to the accompanying drawings, an embodiment of the present invention
will be explained as follows.
Example 1
[0042] Fig. 8(a) is a front view of the rolls to which the present invention is applied,
and Fig. 8(b) is a plan view. In this case, the turning angle α
d of the lower roll 4 is determined in accordance with the forming radius of curvature
of the edge portion 13 of the metallic strip 5. In accordance with the width of the
metallic strip and the length of a portion of the metallic strip to be bent, the positions
of upper and lower rolls on both sides are determined with respect to the width direction.
Further, in accordance with the wall thickness of the metallic strip 5, the turning
angle α
u of the upper roll 3 is determined.
[0043] In the case where the turning angle is determined in accordance with the wall thickness
of the metallic strip and the radius of curvature of the portion to be bent, the hysteresis
of a roll gap right below the upper roll is shown in Fig. 4. Also, the deformation
of the metallic strip according to the roll gap hysteresis is shown in Fig. 3. In
these drawings, numeral 3 is an upper roll, numeral 4 is a lower roll, numeral 5 is
a metallic strip, and numeral 7 is a center of the metallic strip.
[0044] Fig. 9 is a front view of an example of the edge bending roll stand to which the
present invention is applied. The roll support beam members 14, 15 vertically hold
the upper and lower roll bearing members 17, 18, and the upper roll support beam member
14 is vertically moved and fixed by the action of the reduction screw shaft 16. The
upper and lower roll support stands 19, 20 are moved and fixed in the width direction
by the rotation of a screw shaft not shown in the drawing or by the sliding motion
of a sliding bracket on a rail not shown in the drawing, wherein the screw shaft or
the sliding bracket is disposed in the beam members 14, 15. Further, the upper and
lower roll support stands 19, 20 are turned and fixed on a vertical shaft by means
of a gear drive unit not shown in the drawing.
[0045] In this connection, when necessary, bearing members for supporting the middle portions
of the upper and lower rolls, or a bearing member for supporting one of them may be
fixed to the roll support beam members 14, 15.
[0046] In this embodiment, two pairs of upper and lower horizontal rolls are disposed on
both sides of the same stands. However, as shown in the seventh embodiment of the
present invention, two pairs of upper and lower rolls are disposed at different positions,
and after one pair of rolls have completed edge forming of the edge on one side, the
other pair of roll start edge forming of the edge on the other side. In this case,
the two pairs of forming rolls may be disposed in different roll stands. Further,
it is possible to provide a guide roll at the side where edge forming is not conducted.
[0047] Figs. 10a and 10b shows the distributions of radius of curvature and wall thickness
after a steel strip of φ50.8 × t2.10 mm, the yield strength of which was 294 N/mm²,
was subjected to edge forming, wherein one is a case to which the present invention
was applied and the other is a case to which the present invention was not applied.
To this example, "the forming roll arrangement directed inside" was applied. According
to the conventional method, steel strips of small wall thickness were not sufficiently
bent, and indentations were caused on steel strips of large wall thickness. However,
in the case where the present invention was applied, excellent profiles were provided.
[0048] Further, Fig. 11 shows the distributions of radius of curvature and wall thickness
after a steel strip of φ34.0 × t5 mm was subjected to edge forming, wherein the same
forming rolls as those described above were used and the turning angle was adjusted.
The obtained radius of curvature was approximately the same as the radius of curvature
which was previously set, and further the provided profile was good. It can be seen
that the outer diameter of the forming roll can be shared when the present invention
is applied.
[0049] Table 1 shows the results on the radius of curvature and the reduced wall thickness
in the case where edge forming was conducted using the same rolls, wherein the turning
angles of the upper and lower rolls were changed with respect to various forming diameter
and wall thickness. It can be seen that the edge forming properties were improved,
the reduction of wall thickness was decreased, and the roll outer diameter was shared,
when the present invention was applied. Further, when the turning angle setting conditions
described in the second and third embodiments of the present invention were applied,
the effects of the present invention were exhibited to the maximum.
Example 2
[0050] Fig. 12(a) is a front view, and Fig. 12(b) is a plan view, of the rolls to which
the present invention is applied. The dimensions of the lower roll 4 are determined
in accordance with the width of the metallic strip 5 and the length of a portion of
the metallic strip 5 to be bent, and the positions of upper and lower roll on both
sides with respect to the width direction are also determined in accordance with the
width of the metallic strip 5 and the length of a portion of the metallic strip 5
to be bent. Further, in accordance with the wall thickness of the metallic strip 5,
the turning angle α
u of the upper roll 3 is determined, and numeral 7 is a central portion of the metallic
strip.
[0051] In the case where the turning angle of the forming roll is determined in accordance
with the wall thickness and the radius of curvature of edge forming, the hysteresis
of the upper roll gap right below the upper roll 3 is shown in Fig. 4, and the hysteresis
of the lower roll is the same as that of the conventional case. Circumstances of the
metallic strip deformed in accordance with the roll gap hysteresis are shown in Fig.
3, in which numeral 3 is an upper roll, numeral 4 is a lower roll, and numeral 5 is
a metallic strip.
[0052] Fig. 13 is a front view of the exemplary edge bend roll stand to which the present
invention is applied. The roll support beam member 14 vertically holds the upper roll
bearing member 17, and the upper roll support beam member 14 is vertically moved and
fixed by the action of the reduction screw shaft 16. The upper roll support stand
19 is moved and fixed in the width direction by the rotation of a screw shaft not
shown in the drawing or by the sliding motion of a sliding bracket on a rail not shown
in the drawing, wherein the screw shaft or the sliding bracket is disposed in the
beam member 14. Further, the upper roll support stand 19 is turned and fixed on a
vertical shaft by means of a gear drive unit not shown in the drawing. On the other
hand, the lower rolls 4 can be rotated by the lower roll shaft 20 through the lower
roll bearing members 18. Further, the positions of the lower rolls 4 can be changed
and fixed in the width direction by means of a screw means or hydraulic means not
shown in the drawing.
[0053] In this connection, when necessary, a bearing member for supporting the middle portion
of the upper roll may be fixed to the roll support beam member 14.
[0054] According to the results showing the distributions of radius of curvature and wall
thickness after a steel strip of φ50.8 × t2.10 mm, the yield strength of which was
294 N/mm², was subjected to edge forming though a single stand, wherein one was a
case to which the present invention was applied and the other was a case to which
the present invention was not applied, in the case where the conventional method was
applied, steel strips of small wall thickness were not sufficiently bent, and indentations
were caused on steel strips of large wall thickness. However, in the case where the
present invention was applied, excellent profiles were provided.
[0055] Table 2 shows the results of radius of curvature and reduced wall thickness in the
case where edge forming was conducted using the same rolls, wherein the turning angles
of the upper roll was changed with respect to various wall thickness. It can be seen
that the edge forming properties were improved and the reduction of wall thickness
was decreased when the present invention was applied. Further, when the turning angle
setting conditions described in the fifth and sixth embodiments of the present invention
were applied, the effects of the present invention were exhibited at the maximum.

[Industrial Availability]
[0056] As described above, according to the present invention, when a metallic strip is
continuously formed by rolls and then welded so as to manufacture a welded pipe, the
metallic strip is subjected to edge forming by the breakdown roll unit provided in
the initial edge forming process without the deterioration of accuracy of the wall
thickness of the metallic strip to be formed. Further, the forming roll can be shared
when metallic strips for various pipe diameters are formed.
Reference numerals shown in the drawings
[0057]
- 1
- Increase in the wall thickness
- 2
- Indentation
- 3
- Upper roll
- 4
- Lower roll
- 5
- Metallic strip
- 6
- Fin
- 7
- Central portion of the metallic strip
- 8
- Thrust
- 9
- Hysteresis of the upper roll
- 10
- Hysteresis of the lower roll
- 11
- Deviation of the roll
- 12
- Contact position
- 13
- Edge portion of the metallic band
- 14
- Upper roll support beam member
- 15
- Lower roll support beam member
- 16
- Reduction screw shaft
- 17
- Upper roll bearing member
- 18
- Lower roll bearing member
- 19
- Upper roll support stand
- 20
- Lower roll support stand
- 21
- Lower roll of the central portion
1. A welded steel pipe forming method comprising the step of bending the edges of a metallic
strip of a predetermined width in a manufacturing line for roll-forming and welding
the metallic strip, wherein each edge of the metallic strip is bent with a pair of
upper and lower horizontal rolls provided when a pair of horizontal rolls is divided
into two with respect to the width direction of the metallic strip, and the upper
and lower horizontal rolls are crossed to each other being turned on a vertical turning
axis.
2. The welded steel pipe forming method according to claim 1, wherein the upper roll
turning angle α
u and lower roll turning angle α
d of the pair of upper and lower horizontal forming rolls are determined to satisfy
the following inequalities, wherein the turning directions of the upper and lower
rolls are set to be opposite to each other.
where
α
u : an angle formed between a line in the width direction of the metallic strip and
a roll axis of the upper horizontal roll
α
d : an angle formed between a line in the width direction of the metallic strip and
a roll axis of the lower horizontal roll
3. The welded steel pipe forming method according to claim 1 or 2, wherein the turning
angles of the upper and lower horizontal rolls are determined so that the upper roll
is directed to the edge side of the metallic strip at an entry side of the roll stand
and directed to the center side of the metallic strip at a delivery side of the roll
stand.
4. A welded steel pipe forming method comprising the step of bending the edges of a metallic
strip of a predetermined width in a manufacturing line for roller-forming and welding
the metallic strip, wherein each edge of the metallic strip is bent with an upper
horizontal roll provided when a horizontal roll is divided into two with respect to
the width direction of the metallic strip, and the upper horizontal roll is turned
and fixed on a vertical turning axis.
5. The welded steel pipe forming method according to claim 4, wherein the upper horizontal
roll turning angle α
u is determined to satisfy the following inequality.
where
α
u : an angle formed between a line in the width direction of the metallic strip and
a roll axis of the upper horizontal roll
6. The welded steel pipe forming method according to claim 4 or 5, wherein the turning
angle of the upper horizontal roll is determined so that the upper horizontal roll
is directed to the edge side of the metallic strip at an entry side of the roll stand
and directed to the center side of the metallic strip at a delivery side of the roll
stand.
7. A welded steel pipe forming method comprising the step of bending the edges of a metallic
strip of a predetermined width in a manufacturing line for roll-forming and welding
the metallic strip, wherein each edge of the metallic strip is bent with a pair of
upper and lower horizontal rolls provided when a pair of horizontal rollers is divided
into two with respect to the width direction of the metallic strip, and the pair of
upper and lower horizontal rolls are disposed at different positions with respect
to the metallic strip forming direction and crossed to each other being turned on
a vertical turning axis.
8. A forming stand for forming welded pipes used for a group of initial forming rolls
in a manufacturing line for forming and welding a metallic strip of a predetermined
width, comprising: two pairs of upper and lower horizontal rolls for bending the edges
of the metallic strip, said upper and lower horizontal rolls being provided when the
upper and lower horizontal rolls are divided into two with respect to the width direction
of the metallic strip, wherein the positions of upper and lower rolls on both sides
can be adjusted being turned on a vertical turning axis, and the positions of upper
and lower rolls with respect to the width direction of the metallic strip can be also
adjusted.
9. A forming stand for forming welded pipes used for a group of initial forming rolls
in a manufacturing line for forming and welding a metallic strip of a predetermined
width, comprising: two upper horizontal rolls for bending the edges of the metallic
strip, said two upper horizontal rollers being provided on both sides when an upper
horizontal roll is divided into two with respect to the width direction of the metallic
strip, wherein the positions of upper rolls on both sides can be adjusted being turned
on a vertical turning axis, and the positions of upper rolls with respect to the width
direction of the metallic strip can be also adjusted.
10. The forming stand for forming welded pipes according to claim 8 or 9, wherein said
divided horizontal rolls are disposed at different positions with respect to the metallic
strip forming direction.