Note: Descriptions are shown in the official language in which they were submitted.
CA 02270097 1999-09-21
METHOD FOR ROLL FORMING STEEL PIPES,
AND EQUIPMENT FOR SAME
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a roll forming method for welded steel pipes;
with said method the common-utilization of rolls can be realized regardless of
the wide
variation in dimensions of materials to be formed. The present invention, more
specially,
relates directly to a novel roll forming method for welded steel pipes by
setting the pinch-
point (which is a specified location for holding the material to be formed
with upper and
lower rolls) at the boundary area between the target forming zone and formed
or un-
formed zone along the width direction of the material, and by making said
target forming
zone in contact with the pre-determined caliber of the upper roll which is
placed on the
bend-inner side but not making the bend-outer side of the target forming zone
in contact
with the lower roll to perform the bend forming process, so that the bend-
formability can
be remarkably improved, roll-flaws or roll-scratches can be avoided, and
accordingly the
common-utilization of rolls can be realized at the break-down forming portion
for the
edge-bend method.
D ription of the prior arts'
In roll forming of welded steel pipes, a required cross sectional profile will
be
made by bending the band steel subsequently in the material's width direction
using
forming rolls. At the breakdown forming portion which indicates the early
stage of roll-
forming process, the material to be formed (which is the band steel plate) is,
in advance,
formed into a semi-circular shape. The thus pre-formed material is then
processed
CA 02270097 2004-11-O1
through the cluster forming and the fin-pass portion, where the material is
formed into an
open-shape circular cross-sectional profile.
At the aforementioned breakdown forming portion, mainly two types of forming
methods are employed such as the roll-flowers as seen in Figure 1. With the
edge-bend
method, the material to be formed is divided into several portions along the
width
direction and is formed portion by portion to approach the final circular
shape. (In the
followings, the bend-inner side is referred to the position above the steel
plate; while the
bend-outer side is referred to the position below the steel plate.) On the
other hand, in the
circular-bend method, the curvature of the total width of the material is
increased
stepwise.
In each of the methods described in the above, one pair of upper and lower
contour
rolls is normally used in the conventional breakdown forming stand, as seen in
Figure 2A.
For example, the pair of rolls consists of a lower roll 2 with concave roll
surface(caliber) and an upper roll 3 with convex caliber. The target forming
zone of the
material 1 to be formed(in other words, both sides of bend-inner and bend-
outer sides of
the material) is pressed in the pre-set roll gap.
When using such conventional forming methods, it is required to pre-set the
uniform roll-gap which is equivalent to the wall thickness of the band steel
plate in order to
provide the pre-determined radius of curvature to the material (which is the
band steel
plate). This forming method possesses following practical drawbacks.
As there are unavoidable variations in the plate thickness, and the material
is also
subjected to the variation in thickness during the deformation, even if the
uniform roll gaps
being equivalent to the plate thickness are pre-set, the roll surface and
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the band steel plate surface will not be perfectly in contact. They will
rather be in contact
in a discontinuous manner. Furthermore, the contacting zone as well as the
contacting
forces changes with time, and it is impossible to predict these variations.
As a result of the aforementioned technical problems associated with the
conventional type of bending methods, it is difficult to set the reference
diameter of the
roll (which is a diameter corresponding to the roll surface portion having an
equivalent
rotational speed to the moving speed of the material in the longitudinal
direction).
Consequently, it is very difficult to synchronize the rotational speeds of
rolls within each
stand, and there could be more loss in driving forces as well as their
energies. Also, the
surface of the final roll-formed product will suffer frorn~ surface scratches
and flaws.
Furthermore, since the forming load and driving force are asymmetric along the
width
direction of the material, the band steel plate is apt to twist in the forming
process.
Because both lower and upper rolls are used to form a desired roll gap, there
is no
flexibility to accommodate to the forming of the steel pipe with various
sizes. For example
in the edge-band method, when either the outer diameter or the wall thickness
of the
product changes all forming rolls need to be exchanged. On the other hand, in
the
circular-bend method, if the outer diameter of the products remains the same
value, rolls
can be commonly-employed in forming pipes with various wall thicknesses (if
they are
within a certain limit) by adjusting the roll-gaps.
As a result, the circular-bend method is considered to be more practical than
the
edge-bend method. However, when forming material with relatively thin wall
thickness, the roll-gaps will become uneven and constraint on the material is
not
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sufficient, so that the expected formability can not be achieved. In other
words, such
common-utilizing of rolls might negatively impact the resultant formability.
In order to solve the technical problems of the operational performance
and productivity associated with the exchanging operation of rolls,
technologies have
been developed with regard to the common-utilization of rolls. One
example of such advanced methods is the so-called cage-forming mill.
In cage-forming mills, the common-utilization of rolls has been proposed by
arranging a plurality of small-size rolls (cage rolls) instead of the
conventional type of
cluster rolls. At the breakdown forming portion, as in the case for the
conventional type
of mills, the common-utilization of rolls is not realized. In order to reduce
the number of
rolls which have to be exchanged, not only the forming load at the cluster
forming
portion but also a part of the forming load which is originally carried out at
the
breakdown forming portion are shifted to the cage-forming portion, so that the
number of
breakdown forming stands can be reduced.
However, the forming function of the cage rolls is extremely limited. Namely,
since the contact area between the cage rolls and the material to be formed is
very small,
each cross-sectional portion of the material is formed under the non-uniform
bending
moment. The formability of such a free-bending method depends strongly upon
the size
and material properties of the products. Accordingly, it is extremely
difficult to obtain the
desired curvature distribution as has been designed.
Particularly, there are many occasions when the over-bending phenomenon is
exhibited at the central portion of the steel plate, on which the largest
bending moment
4.
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usually acts. Even if the inner roll (which is the convex roll) is employed,
it is impossible
to make the bending moment uniform.
Because the excess forming work is allotted to the cage forming portion,
adverse
effects impinge on the forming function and stability of the entire mill
system.
Accordingly, there are many problems recognized with these types of roll
common-
utilizing mill system.
In order to overcome the aforementioned drawbacks associated with the cage-
type
mill system, a roll-forming method has been proposed(which is, hereafter,
referred as to
an FF - flexible forming - method), see U.S.P. No. 4770019. In the FF forming
method,
the common-utilization of rolls can be achieved not only at the cluster
forming portion but
also at the breakdown forming portion by using a special roll whose caliber is
an involute
(which changes its radius curvature either continuously or step-wisely) and
employing a
position-controlling mechanism for transferring and rotating such rolls.
In order to bend the edge portion of the material which is the most difficult
portion
to form, the roll arrangement as seen in Figure 2B is normally used for the so-
called No.
1 breakdown stand. According to the roll arrangement for the FF forming
method,
suitable involute curves are provided to the upper roll 3 (convex roll) and
the lower roll 2
(concave roll) respectively, corresponding to the limits of inner and outer
diameters of
products to be formed.
Although the roll gaps formed with these rolls are normally not uniform, the
upper
and lower roll positions are determined so as to form the favorable roll-gaps
at the
edge portion of the material 1, corresponding to the size of the product to be
formed. By
CA 02270097 2004-11-O1
employing this forming method, it is possible to perform edge-bending without
any roll
exchange, so that the overall mill formability is improved.
However, even with the FF forming method, the circular-bend type forming
method is used for stands other than the No. 1 breakdown stand. As a result,
most
of the forming work is still carried out at the cluster forming portion.
In order to overcome the problems found in the above described art, it
is, therefore, an object of the present invention to provide a novel roll
forming method
and equipment for same, in which, without mitigating any advantages of
the common-utilization of rolls in the FF forming method which uses the
circular-bend
method, the formability can be enhanced at the breakdown forming portion and
the overall
formability can be improved.
A novel forming method (Japan Patent Application Laid-Open No. HeilO-255319,
PCT/JP98/04962) has been proposed by the present inventors in which the edge-
bend
method is introduced to the FF forming method and a plurality of edge-bending
stands are
used at the breakdown forming portion in order to enhance the forming function
and
a zone approximately half of the plate's width is formed, portion by portion,
from its edges
(sides).
In the aforementioned method (which is now called FF/X forming method), the
overall formability and stability of the mill system are improved. However,
the bending
method as seen in Figure 2B of the FF forming method is conventionally used
only for
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forming the material's edge portions and it is difficult to set the suitable
roll-gaps for the
case-when the target forming zone is relatively wide.
In these advanced FF or FF/X methods, the basic system concept does not differ
from the conventional method in that the inner and outer surfaces of the
material are sandwiched between a pair of concave and convex rolls and pressed
in the
roll gap. Moreover, this forming method has a technical concept such that
although the
target forming zone is not expected to be in contact with both concave and
convex rolls
when the involute calibers are used, the appropriate roll surface portions of
convex and
concave rolls are selected in order to bend the material in the roll gap into
a shape similar
to that of roll gap as possible.
Experiments and analyses have been conducted to investigate the
relationships between roll arrangement/orientation and forming functions in
order to
enhance the forming function at the breakdown forming portion while
effectively achieving
all advantages of the FF, FF/X forming methods which make it possible to
common-utilize
the rolls at the pipe mill system. As a result of extensive investigations,
it has been concluded that, in order to bend the material into a desired
shape, it is not essentially necessary to employ a pair of concave and convex
contour rolls.
It has been found that, by winding a portion of the cross-
section of the material to be formed (which is hereafter referred merely as to
a target
forming zone) around either an entire or a portion of the surface of the
convex roll having
a roll caliber with a certain curvature distribution, the approximately same
curvature distribution
can be printed onto the target forming zone of the material without
constraining the
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opposing surface by using the concave roll. This new bending method is
referred to as
'embrace-bending'.
For examf le, the same forming can be achieved by employing a roll arrangement
wherein instead of providing a pair of convex and concave rolls as seen in
Figure 2A the control of the curvature distribution is mainly
conducted by an upper convex roll . Although a pair of left and right lower
rolls is
used, the principle function of these rolls is to provide a supporting force
in order to wind
the target forming zone around the convex roll surface , so that the embrace-
bending
can be performed. In other words, the target forming zone of the material can
be
controlled and supported in such a way that it can be in contact with the
convex roll
caliber portion whose curvature distribution is expected to be printed.
There are several important points associated with the aforementioned embrace-
bending method. Firstly, the pinch-point defined by a minimum distance between
the convex
and concave rolls is set at a specific location so as to control the position
of material along its
width axis. Secondly, the target forming zone of the material is wound around
a
caliber portion of the convex roll on its bend-inner side to print the
expected curvature
distribution to the target forming zone without constraining it from the bend-
outer side.
When a driving force needs to be generated, the minimum distance between
the convex and concave rolls at the pinch-point should be set to be equal to
the wall
thiclmess in order to obtain a sufficient amount of pressure or frictional
force. Both
surfaces of the material are simultaneously constrained only at the pinch-
point.
Normally, such a pinch-point is designed and set in a boundary area between
the
target forming zone and other portions of the material; which is, in turn, the
portion being
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formed previously including the bending non-sensitive zone of the material's
edge portion
or un-formed portion of the material.
On the other hand, when the driving force is not required, it is not essential
to
constrain the inner and outer surfaces of the material simultaneously at the
pinch-point.
Instead, it is simply required to set the position for the concave roll in
order to wind the
target forming zone around the convex roll surface.
In summarizing the above, the present novel bending method is characterized in
that (1) a zone along the width axis of the material to be formed at a certain
stand is a
target forming zone, (2) the pinch-point is set at the boundary between the
target forming
zone and other portions of the material in order to print the desired
curvature distribution
by winding the target forming zone around the surface of the convex roll
mounted on a
bend-inner side, and (3) the lower roll caliber is set in such a way that this
roll will not
contact the target forming zone from the bend-outer side (in other words, the
target
forming zone except the area at or near the pinch-point is not constrained by
the lower
roll). Consequently, it is not necessary to provide the conventional type of
roll caliber
since the concave roll is not directly involved in controlling the curvature
distribution of
the target forming zone.
In accordance with one aspect of the present invention there is provided a
method
of roll forming a material for welded steel pipe, the material having a bend-
inner side, a
bend-outer side opposite the bend-inner side, a target forming zone defined
along a width
axis of the material and boundary areas defined between the target forming
zone and one
of a previously formed zone and an unformed zone of the material, the method
comprising
the steps of: forming the target forming zone by winding the material around a
roll surface
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on the bend-inner side of the material; and pushing on the material proximate
the boundary
areas on the bend-outer side using a contact roll; wherein the contact roll
does not
constrain the target forming zone on the bend-outer side of the material.
In accordance with another aspect of the present invention there is provided a
roll
forming apparatus for forming a material for welded steel pipe, the material
having a bend-
inner side, a bend-outer side opposite the bend-inner side, a target forming
zone defined
along a width axis of the material and boundary areas defined between the
target forming
zone and one of a previously formed zone and an unformed zone of the material,
the
apparatus comprising: a lower roll, being one of a one-piece and a separate
type, for
pushing on the material proximate the boundary areas on the bend-outer side; a
pair of
upper rolls arranged along the width axis of the material for forming the
target forming
zone by winding the material on the bend-inner side of the material around the
pair of
upper rolls; and a pair of side rolls oriented horizontally proximate the
edges of the
material.
In accordance with yet another aspect of the present invention there is
provided a
roll forming apparatus for forming a material for welded steel pipe, the
material having a
bend-inner side, a bend-outer side opposite the bend-inner side, a target
foaming zone
defined along a width axis of the material and boundary areas defined between
the target
forming zone and one of a previously formed zone and an unformed zone of the
material,
the apparatus comprising: a lower roll, being one of a one-piece and a
separate type, for
pushing on the material proximate the boundary areas on the bend-outer side; a
pair of
upper rolls arranged along the width axis of the material for forming the
target forming
zone by winding the material on the bend-inner side of the material around the
pair of
9a
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upper rolls; and a plurality of side rolls arranged longitudinally to contact
the bend-outer
side proximate edges of the material.
In accordance with still yet another aspect of the present invention there is
provided
A method of roll forming a material, the material having a bend-inner side, a
bend-outer
side opposite the bend-inner side, a target forming zone defined along a width
axis of the
material and a boundary area defined between the target forming zone and one
of a
previously formed zone and an unformed zone of the material, the method
comprising the
steps of: positioning a pinch-point, formed by a pair of upper and lower
rolls, at the
boundary area; and forming the target forming zone by winding the material
around a roll
surface on the bend-inner side of the material; wherein the target forming
zone is not
constrained on the bend-outer side of the material.
According to the present novel roll-forming method, because the target forming
zone of the material is constrained by only the convex roll, severe
deformation is
mitigated. Moreover, occurrence of the excess deformation strain is minimized,
resulting
in that steel pipes with excellent secondary-formability can be produced.
'this is the first
advantage of the present novel roll-forming method.
9b
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Furthermore, when the rolls are driven, the roll diameter at the pinch-point
can be
considered as the reference roll diameter. Since the position of the pinch-
point is very
clearly identified and does not vary, it is very easy to synchronize the
driving speeds
within each stand. This is the second advantage of the roll-forming method
according to
the present invention.
Moreover, even if the surface pressure at the pinch-point is varied within a
certain
limited range due to the variation of the wall thickness, the symmetry with
respect to left
and right sides can be maintained, and twisting of the material is not caused
because the
contacting condition between the material and rolls is not altered. This is
another
advantage of the present novel roll-forming method.
As a result, it becomes possible to greatly improve the formability and
stability of the mill system by introducing the embrace-bending concept of the
present
invention to the conventional breakdown forming portion. Moreover, according
to the
present invention, since it is not required that both concave and convex rolls
have the
exclusive calibers corresponding to the size of product to be formed, it is
possible to
achieve the Gammon-utilization of rolls. This is a . further advantage of the
present novel roll-forming method.
According to the present novel roll-forming method for welded steel pipes, the
whole area of the target forming zone along the width axis of the material is
formed
mainly by winding it around the surface of the convex roll located at the bend-
inner side
without constraining the target forming zone from the bend-outer side.
Furthermore, the
pinch-point formed by at least one pair of upper and lower rolls is positioned
at the
boundary area between the target forming zone and previously-formed material
(which
might include the bending non-sensitive zone of the material's edge portian)
or un-
CA 02270097 2004-11-O1
formed portion, so that the target forming zone can be bent along the roll
surface at the
bend-inner side without constraining the whole target forming zone from the
bend-outer
side.
BRIEF DESCRIPTION OF DRAWINGS
The above and many other objectives, features and advantages of the present
invention will be fully understood from the ensuing detailed description of
the
embodiments of the present invention whose description should be read in
conjunction
with the accompanying drawings.
Figure 1 is a drawing to explain the roll-flower at the breakdown forming
portion;
A is for the edge-bend method and B is for the circular-bend method.
Figure 2 is an explaining figure of the roll arrangement of the conventional
type of
breakdown forming stands; A is for a pair of upper and lower rolls, and B is
of the rolls
for the FF forming method.
Figure 3 is a figure of the roll arrangement to explain the "embrace-bending"
concept of the present invention:
Figure 4A and 4B show the roll arrangements in which the "embrace-bending"
concept of the present invention is applied to the breakdown forming stands.
Figure 5 shows a breakdown forming stand where the "embrace-bending" concept
of the present invention is applied to welded steel pipe forming with common-
utilizing of
rolls; A is for the case of forming large diameter pipe, whereas B is for the
case of
forming the small diameter pipe.
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Figure 6A, 6B, and 6C show the roll forming method and roll arrangements of
the
roll stands for the breakdown forming portion as one of the embodiment of the
present
invention.
Figure 7A shows a perspective view of roll arrangement of the pipe mill when
the
roll forming method and its equipment of the present invention are applied;
while 7B is a
figure to explain the roll arrangement of the reverse-bend forming portion;
and 7C is a
figure to explain the roll arrangement of the cluster forming portion.
Figure 8A, 8B, and 8C show the roll arrangement of the roll stand for the
break-
down forming portion as another embodiment when the roll forming method and
equipment of the present invention are applied.
Figure 9A is a perspective view of the roll arrangement of the another pipe
mill
when the roll forming method and equipment of the present invention are
applied; while
9B is a figure to explain the roll arrangement of the reverse-bend forming
portion and 9C
is a figure to explain the roll arrangement for the cluster forming portion.
Figure 10 shows a case when the auxiliary rolls are mounted to the breakdown
forming stand; A is a front view and B is a side view.
Figure 11 shows the loci of the edge portion of the material at the breakdown
forming portion; A and B are side view and upper view when the pass-line is
set in order
to have the bottom of the roll flower to be a straight line; while C is a side
view when the
pass-line is arranged in order to have the edge locus to be a straight line.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
According to the present invention, the embrace-bending method is
applicable to all types of forming mills and forming methods and it is
possible to
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rationalize the existing forming processes. However, when it is employed as a
portion of
the common-utilization technology of rolls, the superior function which can
not be
realized with the. conventional forming methods can be achieved.
The bending method according to the present invention is indispensable in
order to
establish the advanced common-utilization technology of rolls based on the
edge-bend
forming method having a strong forming function similar to that of the
aforementioned
FF/X forming method. The following describes the roll arrangements and roll
forming
method by which the "embrace-bending" concept can be practiced and the common-
utilization of rolls can be realized.
As seen in Figure 4, the roll arrangements at the breakdown forming stand of
Figure 2B is modified in order to perform the "embrace-bending" method of the
present
invention. First, as seen in Figure 4A, the pinch-point, pp, is provided at a.
location spaced apart
from the plate edge with a certain distance. The area from the pinch-point,
pp, to the plate
edge is called the bending non-sensitive portion la since the sufficient
bending
moment is not normally obtained.
Although the range of the bending non-sensitive portion 1a depends upon the
product's dimensions and material type, it can be defined as to be almost the
same as the
plate thickness. The bending non-sensitive portion 1a being located on the
outer side of
the pinch-point, pp, is supported by the lower roll 20, and the target forming
zone 1b
located on its inner side is wound around the upper roll surface 21 in order
to be bent.
Therefore, the pinch-point, pp, is set between the bending non-sensitive
portion la
and the target forming zone lb. The contacting surface of the lower roll 20
has a flat
surface in order to avoid constraining the target forming zone from the bend-
outer side.
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In order to correspond to various diameters, it is necessary to adjust the
positions of
upper and lower rolls. A portion of the upper roll surface must be selected
with an appropriate curvature distribution to contact the target forming zone,
since the
degree of forming is mainly controlled by the roll caliber of the upper roll
21.
When the range of the common-utilization of rolls for products' outer diameter
is
relatively wide, similarly to the FF forming method, it is preferable to
provide an involute
caliber at the upper roll 21 and use the supporting mechanism with which the
supporting
axial direction of the roll can be freely changeable in order to not only
parallel-move but
also rotate the roll, so that an appropriate portion of caliber can be
selected to contact the
target forming zone.
It is not necessary to provide the involute caliber to the lower roll 20, as
has been
described previously. If the roller flower is properly designed, it is
possible to correspond
to forming operation of various pipe sizes even with the linear caliber, as
seen in Figure
4A.
If the occurrences of roll-marks or roll-flaws are suspected to be related to
the type
of material or wall thickness-diameter ratio, t/D, the involute caliber may
also be provided
to the lower roll 20, so that the material edge portion can be supported by
the roll surface
portion having the curvature close to that of the product.
On the other hand; although the embrace-bending does not necessarily need to
provide the central roll 22 and to form the W-shape cross-section of the
material, it
possesses a beneficial effect to widen the range of the target forming zone.
The shape of
the central roll 22 and its position can be set in such a manner that, for
forming all
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CA 02270097 2004-11-O1
different sizes of products, the expected target forming zone should be
certainly wound
around the upper roll 21.
The roll arrangement seen in Figure 4A is very effective to bend the edge
portion,
and is also applicable to bend other portions of material. However, when the
range of the
common-utilization of rolls is wide, while providing the pre-determined
curvature
distribution to the target forming zone, it is also necessary to support the
previously-
formed zone to prevent the bending-back phenomena.
Hence, the roll arrangement as seen in Figure 5A is extremely effective to
form
target forming zones other than the formed edge portion. With this roll
arrangement,
although the central roll 30 is similar to that in Figure 4A, it is used not
only to improve the embrace-bending efficiency, but also to form the pinch-
points, pp, by
combining with a pair of upper rolls 31,32 to generate the driving force.
Furthermore, in the roll arrangements seen in Figures 5A and 4B, compared with
that in Figure 4A, side rolls 33,34 are provided. The side rolls 33,34 are in
contact with
the above mentioned previously-formed zone in order to prevent the bending-
back
phenomenon. At the same time, by using the~bending moment caused by the
forming
force from the side rolls 33,34, the target forming zone 1c located at the
outer side of the
pinch-point, pp is wound around the upper rolls 31,32 efficiently.
Referring to Figure 4B, the bending moment acting on the
previously-formed zone 1b is small; namely the arm for the bending moment is
short
because the operating point of the side rolls is within the previously-formed
zone; so that
this zone is not subjected to a large deformation.
CA 02270097 2004-11-O1
Small size of rolls can be employed instead of side rolls 33,34 to
prevent the previously-formed zone from bending-back, so that it is possible
to arrange a
plurality of small rolls along the longitudinal direction of the material in
the above roll
arrangement.
Since the control of the curvature distribution of the target forming zone is
achieved by the upper rolls 31,32 even with the above mentioned roll
arrangements, it is
preferable to use the involute caliber to these rolls 31,32 and rotate and/or
parallel-move
these rolls 31,32 along the width direction of the material to select the
caliber portion to
contact the target forming zone of the material.
The side rolls 33,34, similarly to the lower rolls 10,11 in Figure 3, are
required to
provide parallel-movement in order to correspond to the forming of various
product sizes.
Moreover, it is preferable to provide an appropriate type of involute
caliber in order to prevent the occurrences of roll-flaws or roll-marks to the
utmost.
Figure SA shows the roll arrangement for the case when pipes with relatively
large
diameter are formed; while Figure SB shows the roll arrangement for the case
when the
pipes with relatively small diameter are formed.
A similar description can be made for the central rolls. It is preferable to
employ
the separate-type rolls such as two-part-type or three-part-type rolls, which
is preferred
to having a single roll as seen in the figure. It is easier to make the target
forming zone of the material attach to a certain portion of the caliber of the
upper roll by
appropriately selecting the position of central roll in width or vertical
direction.
On the other hand, at the breakdown forming stands, especially at the forming
stand where edge-bending is performed, the forming rolls suffer from the wear
damage
16
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due to large forming load. Moreover, it is known that edge stretch, which is
the main
cause of the edge wave, is apt to take place at these stands.
Roll wear and edge wave mentioned above may occur even when using the
embrace-bending method of the present invention. However, it has been found
that,
small-size auxiliary rolls being in contact to the edge of the material can
be mounted at vicinity of the upper and/or lower stream of the breakdown
forming stands,
so that some of the forming load will be allotted to the auxiliary roll,
resulting in that the
forming load and surface pressure which are acting on the lower roll will be
reduced.
With reference to the drawings, the auxiliary roll will be described in detail
below.
As seen clearly from Figures 6A and 6B, the edge portion of the material 1
will be
gradually rising while approaching to the center of the upper roll 40 or lower
roll 41 at
the breakdown forming stand. At an early stage of the contacting process, only
the sharp
outer edge corner of the material will be in contact to the lower roll surface
40.
At this stage, since the contact is almost the point contact, roll wear could
take
place easily due to the abnormally high surface pressure. In order to avoid
this abnormal
roll wear, as seen in Figure 7A, a pair of small-size non-driven type second
auxiliary rolls
53,55 is mounted at a vicinity of the upper and lower stream close to the
lower rolls 50,51
to attach to the outer edge corner of the material 1, so that the edge portion
of the material
1 can be supported.
When the auxiliary rolls 53,54 are provided at the upper stream as described
in the
above, the outer edge corner of the material will become in contact to the
auxiliary rolls
53,54 before contacting to the forming rolls 50,51. In such a case, when the
material is
moving towards forming rolls 50,51, the edge portion of the material has
already been
17
CA 02270097 2004-11-O1
raised to some extent. After contacting to the lower rolls 50,51, the contact
area increases
rapidly, so that the abnormally high surface pressure can be prevented.
Moreover; the contact with the auxiliary rolls 53,54 dulls the outer edge
corner of
the material and reduces the possibility of occurrence of the abnormally high
surface
pressure. Furthermore, by mounting the second auxiliary rolls 53,54, some of
the forming
load will be allotted to the auxiliary rolls 53,54 and the forming load and
surface pressure
acting on the lower rolls 50,51 can be reduced.
When the auxiliary roll 53 is provided at only the upper stream, it is
preferable to
constrain firmly the material along the longitudinal direction by mounting the
auxiliary
roll 55 at the lower stream side of the forming stand since the steel band
will rotate along
the longitudinal direction around the upper roll 52 as a supporting point and
the effect of
the auxiliary roll 53 will be reduced if there is no auxiliary roll mounted at
the lower
stream side of the forming stand.
In the present invention, the wear problem of the auxiliary roll can not be
avoided.
However, since the auxiliary roll according to the present invention is a
small-size non-
driven type, the roll per se as well as its supporting mechanism can be very
simply compared
with the forming rolls, so that the equipment and maintenance cost will be low
and
exchanging operation for polishing these roll surfaces will also be easier and
simpler.
Moreover, since the essential function of the second auxiliary roll is to
support the
edge of the material and it only contacts the edge comer of the material,
formability and
product quality will not adversely been affected even if they are worn. For
such a case, it
is not required to exchange and polish these auxiliary rolls.
18
CA 02270097 2004-11-O1
The above mentioned auxiliary roll not only controls the wear phenomenon of
the
forming roll, but also exhibits a great effect to prevent the so-called edge
wave of the
material caused by the excessive edge stretch during the forming process. The
occurrence
of the edge stretch is most noticeable at the breakdown forming area.
It is believed that a spatial transferring distance at the width edge portion
of the
material that is longer than that at other portions due to the spring-back
between the
stands is a main cause of the edge stretch. Through extensive experiments and
analyses,
it has been found that the effect of the spring-back on the differences in the
spatial locus
is not large, rather the edge wave takes place mainly due to the fact that the
edge portion
is locally stretched when it rises along the roll surface.
As seen in Figure l OB, when the material 1 is entering the roll gap, the edge
portion
winds around the surface of lower roll 40 and rises. Since, during this short
period of time,
the S-shaped spatial locus 42 created by the edge portion is much longer than
nearly-liner
loci created by,other portions, a large amount of edge stretch will take
place. Moreover,
due to such an edge stretch, downward-warp will occur on the longitudinal
direction of
the material after the material passes through the roll gap, causing the same
rising
problem at the subsequent stand.
In order to solve the problem, the height of the edge portion can be set prior
to
entering the roll gap to the same level as the edge portion in the roll gap or
slightly
higher than that in order to make the locus of the edge portion to close to be
linear as
possible.
19
CA 02270097 2004-11-O1
However, even if the pass-line 44 is set as described in the above, since the
height
of other portions of the material goes down due to the constraint of rolls
40,41, the edge
portion will leave from the pre-set pass-line 44 and continuously goes down
until the
position where it balances with the locus 46 of other portions. Then, the
locus 45 of the
edge portion will rise along the lower roll surface 40. As a result, the
effect of reducing
the rising of the edge portion by setting the pass-line 44 is very small.
As will be clearly understood from the aforementioned analyses, it is found
that,
before entering the roll gap, the rigidity itself of the material's edge
portion can not keep
the pre-set pass-line. However, the mounting of the second auxiliary roll as
seen in
Figure 11 can solve this problem.
According to the present invention, since the auxiliary roll does not
contribute
directly to the forming of the products, it is not required to design the roll
caliber with
respect to the products' dimension as done for the forming rolls. The flat
rolls can be
used if the edge corner of the material can be supported at the desired
position.
Furthermore, the auxiliary roll requires only a simple supporting device being
mounted
before and after the forming stand, so that the exclusive stand just for the
auxiliary roll is
not needed.
In the present invention, the shorter the distance (pitch) from the supporting
point of the material's edge corner to center of the lower roll, the larger
various effects
obtained from the auxiliary rolls. The shorter distance (pitch) can be
obtained if the
auxiliary roll is placed at the same stand as the Iower roll. Moreover, in
order to obtain
the short pitch, as seen in Figure 11B, it is extremely effective to decline
the axis of the
auxiliary roll toward the center of the lower roll along the longitudinal
direction.
CA 02270097 2004-11-O1
When the size of the product changes and the same auxiliary roll does not
correspond to this change, it is necessary to exchange rolls. However the
common-utilization of the auxiliary rolls can be achieved if the roll flowers
are designed
in such a way that the positions of the edge corners are on a certain curve.
With reference to Figures 8 and 9, an embodiment of applying the roll forming
method
and equipment of the present invention to the roll arrangements No.1 through 3
in the
break-down forming portion in the pipe mill system of FF/X forming method,
which the
present inventors have previously proposed, will be described. In such a pipe
mill system,
as clearly seen in Figure 9A, roll stands BDl,BD2,BD3 'at the breakdown
forming portion
are arranged, followed by roll stand RB at the reverse-bend portion, cluster
roll C1
through C6 in the cluster forming portion, and roll stands FP1,FP2 at the fin-
pass forming
portion.
At the roll stand BDl of the break-down forming portion, as seen in Figure 8A,
a
rotation-type pair of left and right upper rolls which is changeable to the
contacting
direction against the material and a pair of left and right lower roll
together with the
central roll having a narrow width are mounted. Between such upper and lower
rolls, the
pinch-point is set at the boundary area between the target forming zone along
the
material's width direction which is ready to form at the BD1 stand and the
bending non-
sensitive material's edge portion. Such a pinch-point possesses the same
mechanism and
function as described in Figure 4A to perform a certain edge-bending
operation.
21
CA 02270097 2004-11-O1
The roll stand BD2 seen in Figure 8B consists of a rotation-type pair of left
and
right upper rolls, a wide lower central roll, and a pair of horizontal rolls
to support the
edge potion of the material which was previously formed at the BD1 roll stand.
Between
the upper roll and shoulder portion of the central roll, the pinch-point is
provided at the
boundary area between the target forming zone which is planned to be formed at
the
stand BDZ and the un-formed zone of the material's central portion, to exhibit
the same
mechanism and function as described in Figure 4B to perform the bending
operation.
The roll stand BD3 has the same mechanism and function as the previous roll
stand
BD2 does, and is used to bend a target forming zone which is closer to the
center of the
material. The portion of material at the outer side of the target forming
zone, which has
already been formed at previous roll stands BD1 and BD2 is supported by the
horizontal
roll with an involute caliber, so that the bending-back of the formed portion
at the outer
side of the target forming zone is prevented.
In the next step, the central portion of material which is pushed upwardly by
the
central rolls at BDl, BD2 and BD3 is reversed at roll stand RB as seen in
Figure 9B.
Hence, introducing the material into the cluster forming portion will be much
easy.
Furthermore, the cross-section of the material will be formed into a profile
near an open
circle by subsequent fin pass forming portions FP1,FP2.
By employing the pipe mill system as seen in Figure 9A of the present
invention,
the edge-bend forming method without exchanging rolls can be realized at the
breakdown forming portion, so that formability is extremely improved and the
common-
utilization of rolls in a range of about three-fold in terms of diameter ratio
can be
achieved.
22
CA 02270097 2004-11-O1
In the conventional type of the FF forming method, another embodiment of
applying the roll forming method and equipment of the present invention to the
roll
arrangements No.l through 3 of the breakdown forming portion will be described
by
referring to Figures 6 and 7. The pipe mill, as seen in Figure 7A, comprises
of roll
stands BD1, BD2, BD3 at the breakdown forming portion, roll stand RB of the
reverse
forming portion, cluster roll stands C1,C2,C3, and roll stands FP1,FP2 in the
fin-pass
forming portion.
In the roll stand BD1 in the breakdown forming portion, as seen in Figure 6A,
a
rotation-type pair of left and right upper rolls which are changeable in the
contacting
direction with the material, a narrow central roll, and a pair of left and
right lower rolls
with involute calibers are mounted. Between the upper and lower pairs of
rolls, the pinch-
point is provided at the boundary area between the target forming zone which
is ready to
be formed at the roll stand BD1 and the bending non-sensitive zone of the
material's edge
portion. Such a pinch-point possesses the same mechanism and function as
described in
the Figure 4A to perform the edge-bending operation. The target forming zone
is not in
contact with the roll caliber of the lower roll except its boundary at the
pinch-point (not
seen in Figure).
At the roll stand BD2 as seen in Figure 6B, a rotation-type left and right
pair of
upper rolls and a pair of left and right lower rolls are provided. Between the
upper rolls
and lower rolls having involute calibers, the pinch-point is provided at the
boundary area
between the target forming zone which is ready to be formed at the roll stand
BD2 and
the previously-formed zone formed at the roll stand BD1. Such a pinch-point
exhibits
23
CA 02270097 2004-11-O1
same mechanism and function as described in Figure 4B. Here again, the target
forming
zone is not in contact with the roll caliber of the lower roll except its
boundary at the
pinch-point. On'the contrary, the material's edge portion which was previously
formed at
the roll stand BD1 is in contact and supported with the involute caliber of
the lower roll
to maintain the expected formability.
The roll stand BD3, as seen in Figure 6C, possesses the same mechanism and
function as previous roll stand BD2 does. At this stand, a target forming zone
which is
closer to the central of the material is bent. The material's edge portion
which was
already formed by previous roll stands BD1 and BD2 is supported along the
involute
caliber of the lower roll, sa that the bending-back of the formed portion is
avoided.
In the next step, the central portion pushed upwardly by central rolls at BD1,
BD2
and BD3 is reversed at the roll stand RB as seen in Figure 7B. Hence,
introducing the
material into the cluster forming portion will be much easier, as seen clearly
in Figure 7C.
Furthermore, the cross-section of the material will be formed into a profile
near an open
circle by subsequent fin pass forming portions FP1,FP2.
By employing the pipe mill system as seen in Figure 7A of the present
invention,
the edge-bend method without exchanging rolls can be realized at the breakdown
forming portion, so that formability is extremely improved and the common-use
of rolls
in a range of about 2.5-fold in terms of diameter ratio can be achieved.
Using the pipe mill system for the welded steel pipes which employs three
units of
forming stands to the break-down forming portion according to the FF/X forming
method,
the auxiliary rolls are provided with an attachable manner before and after
the breakdown
24
CA 02270097 2004-11-O1
forming portion. The edge stretch of the steel plate was measured at each
stand at the
breakdown forming portion. Table 1 shows the results for three cases; namely
they
include (1) without any auxiliary roll, (2) auxiliary rolls before and after
the roll stand
BDl, and (3) auxiliary rolls before and after roll stands BDl and BD2.
Tn the case when the auxiliary roll is not mounted, a large edge stretching
was
observed at roll stands BD1 and BD 2. On the other hand, in the case when the
auxiliary
rolls were mounted before and after the roll stand BD1, although the edge
stretching can
not be eliminated completely, the value of the edge stretching recorded was
less than half
at the BD1 and about one quarter at BD2.
Moreover, when the auxiliary rolls were also provided before and after the
roll
stand BD2 to support the edge portion of the steel plate, the edge stretching
at stand BD2
was furthermore reduced down to another half. From this result, it is clearly
understood
that the auxiliary roll possesses very effective function to prevent the edge
stretch.
Furthermore, Table 2 shows the results of effects of the auxiliary roll on the
thrust
and forming load at the roll stand BD2. From results presented in Table 2, it
is obvious
that the thrust on the BD2 roll stand and forming load acting on the lower
roll are clearly
different between the case when the auxiliary roll is not provided before and
after the roll
stand BD1 and the case when the auxiliary roll is provided before and after
the roll stand
BD1.
Introduction of the material into roll gap can be greatly improved due
to the fact that the edge rising is remarkably reduced due to the effects of
the auxiliary
roll. Moreover, the effect on the thrust and forming load is very significant.
CA 02270097 2004-11-O1
Table 1
without auxiliary roll auxiliary roll
auxiliary roll before & after before & after
BD1 BD1,2
BD1 stand 2.25% 1.1% 1.1%
BD2 stand 1.8% 0.48% 0.25%
BD3 stand 0.5% 0.48% 0.48%
Table 2
when the auxiliary when the auxiliary
roll is not roll is provided
provided
before and after before and after
BDl stand BD1 stand
forming load thrust at BD2 forming load thrust at BD2
acting stand acting stand
on the lower on the lower
roll of roll of
BD2 stand BD2 stand
6,530kg -lOkg 2,750kg 180kg
According to the present invention, the pinch-point formed by the upper and
lower
rolls is set at the boundary area between the target forming zone along the
material's
width direction and previously-formed zone or un-formed zone. The target
forming zone
is wound around a certain caliber of the upper roll being positioned at the
bend-inner side,
and bend-formed in such a manner that the lower roll is in almost no-contact
condition
with the target forming zone. As a result, the bending formability can be
greatly
improved, and roll flaws and roll-marks can be prevented.
26
CA 02270097 2004-11-O1
According to the roll forming method of the present invention, the concave
roll
does not contribute directly to control of the curvature distribution of the
target forming
zone. On the other hand, the target forming zone is constrained only by the
convex roll,
so that the excess deformation is reduced and the occurrence of the
superfluous
deformation strain can be prevented.
Moreover, when the roll is driven, the maximum surface pressure is generated
at
the pinch-point. Since the roll diameter corresponding to this pinch-point is
used as a roll
reference diameter and the position of the pinch-point is clearly identified
and not
changed, the driving force within each roll stand can be synchronized easy.
Furthermore, in the roll forming method of the present invention, the
contacting
condition between the material and rolls is stable regardless of variations in
wall
thickness of the material, so that the twist phenomena is not induced.
According to the roll forming method of the present invention, since it is not
necessary that both concave and convex rolls are rolls with exclusive roll
caliber
corresponding to the product to be formed, the common-utilization roll is easy
to realize.
Also, the forming function and operativity of mill can be greatly improved by
introducing
it to the breakdown forming portion.
Furthermore, by providing the auxiliary roll in the vicinity of up stream and
down stream of the lower roll of the breakdown forming stand to support the
edge of
the material to the pre-set height, the forming load and surface pressure
acting on the
lower roll can be reduced. As a result, the local wear on the roll can be
reduced. Also
forming defects such as the edge wave caused by the localized stretching of
the edge
portion can be eliminated.
27
CA 02270097 1999-09-21
While this invention has been described with respect to preferred embodiments
and
examples, it should be understood that the present invention is not limited to
those
embodiments and examples; rather many modifications and variations would
present
themselves to those of skill in the art without departing from the scope and
spirit of the
present invention, as defined in the appended claims.
28
