U.S. patent application number 11/187038 was filed with the patent office on 2007-01-25 for metal pipe straightening method, straightening roller, and manufacturing device.
This patent application is currently assigned to Nakata Manufacturing Co., Ltd.. Invention is credited to Manabu Kiuchi, Tomoyasu Nakano, Feizhou Wang.
Application Number | 20070017268 11/187038 |
Document ID | / |
Family ID | 37677826 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070017268 |
Kind Code |
A1 |
Wang; Feizhou ; et
al. |
January 25, 2007 |
Metal pipe straightening method, straightening roller, and
manufacturing device
Abstract
A straightening method is presented where a concave roller,
which has a roller caliber and in which the projection of the roll
caliber forms an arc with respect to the cross section of a pipe.
The projection arc radius can freely be changed by adjusting the
angle between the roller axis and the axis line of the pipe. A
plurality of concave rollers are arranged on the outer surface of
the metal pipe in the circumferential direction, and rolling is
applied on the outer diameter of the pipe while revolving these
rollers about the pipe axis.
Inventors: |
Wang; Feizhou; (Osaka-shi,
JP) ; Nakano; Tomoyasu; (Osaka-shi, JP) ;
Kiuchi; Manabu; (Zushi-shi, JP) |
Correspondence
Address: |
DARBY & DARBY P.C.
P. O. BOX 5257
NEW YORK
NY
10150-5257
US
|
Assignee: |
Nakata Manufacturing Co.,
Ltd.
Osaka-shi
JP
|
Family ID: |
37677826 |
Appl. No.: |
11/187038 |
Filed: |
July 20, 2005 |
Current U.S.
Class: |
72/78 |
Current CPC
Class: |
B21D 3/06 20130101 |
Class at
Publication: |
072/078 |
International
Class: |
B21D 3/06 20060101
B21D003/06 |
Claims
1. A metal pipe straightening method comprising: revolving a
straightening roller group about the axis of a metal pipe to apply
pressure to the metal pipe to straighten the outer circumference of
the metal pipe, wherein said straightening roller group includes: a
plurality of concave rollers with a roller caliber to be arranged
in the circumferential direction of the outer surface of the metal
pipe, the roller caliber of the concave roller, which is made to
contact the metal pipe, having a structure in which parts of the
projection of the roller surfaces on the cross-section surface of
the metal pipe are on the same circumference of the metal pipe, and
the radius of the projection arc can be adjusted according to the
angle of inclination of the roller with respect to the axial line
of the pipe and the position in the radial direction of the
pipe.
2. A metal pipe straightening method comprising: revolving about
the axis of a metal pipe a plurality of straightening roller groups
arranged in a axial direction of the metal pipe to apply pressure
to the metal pipe to straighten the outer circumference of the pipe
wherein each of the straightening roller groups include: a
plurality of concave rollers with a roller caliber, which are
arranged in the circumferential direction of the outer surface of
the metal pipe, the roller caliber of the concave roller, which
contacts the metal pipe, having a structure in which parts of the
projection of the roller surfaces on the cross-section surface of
the metal pipe are on the same circumference of the metal pipe, and
the radius of the projection arc can be adjusted according to the
angle of inclination of the roller with respect to the axial line
of the pipe and the position in the radial direction of the
pipe.
3. The metal pipe straightening method according to claim 2,
wherein a pipe axial pass line of the whole metal pipe, which
passes through the plurality of straightening roller groups, has an
eccentric relationship to the axis of the metal pipe in the
position which is the geometrical center of the arrangement of the
rollers, which form any of the straightening roller groups and
which are the center of revolution thereof, and deformation by
bending occurs in the longitudinal direction of the metal pipe,
which passes through the roller groups in order to increase the
straightness of the pipe in the axial direction.
4. The metal pipe straightening method according to claim 2,
wherein the geometrical center of the arrangement of the rollers,
which form any of the straightening roller groups, has an eccentric
relationship with the center of revolution of that roller group,
and deformation by bending occurs in the longitudinal direction of
the metal pipe, which passes through the roller groups in order to
increase the straightness of the pipe in the axial direction.
5. A metal pipe straightening roller, which is used in the metal
pipe straightening method according to claim 1, wherein the roller
caliber of concave rollers contacting the metal pipe is constructed
such that parts of the projection of the surfaces of the rollers on
the cross-section surface of the metal pipe are on the same
circumference of the metal pipe, and the radius of the projection
arc can be adjusted according to the angle of inclination of the
roller with respect to the axial line of the pipe and the position
of the rollers in the radial direction of the pipe.
6. A manufacturing apparatus for a metal pipe comprising: an
apparatus which continuously produces a metal pipe from metal
strapping in a forming process which uses a forming roller, forming
shoe, or both, and an apparatus which straightens the metal pipe
after production in a sizing process, wherein the metal pipe
straightening method according to claim 1 is used in the sizing
process.
7. A manufacturing apparatus for a metal pipe comprising: an
apparatus which continuously produces a metal pipe from metal
strapping in a forming process which uses a forming roller, forming
shoe, or both, and an apparatus which straightens the metal pipe
after production in a sizing process, wherein the metal pipe
straightening method according to claim 2 is used in the sizing
process.
8. A metal pipe straightening roller which is used in the metal
pipe straightening method according to claim 2, wherein the roller
caliber of concave rollers contacting the metal pipe is constructed
such that parts of the projection of the surfaces of the rollers on
the cross-section surface of the metal pipe are on the same
circumference of the metal pipe, and the radius of the projection
arc can be adjusted according to the angle of inclination of the
roller with respect to the axial line of the pipe and the position
of the rollers in the radial direction of the pipe.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is a technology which can provide a
metal pipe with a high level of circularity and a high level of
straightness at a low-cost because of high productivity, and
relates to a metal pipe straightening method and straightening
roller and manufacturing device which straightens a metal pipe
using a plurality of concave rollers without causing the metal pipe
to rotate on its axis, and for instance, can perform a continuous
sizing process in the manufacturing process of electrically welded
pipe for instance.
[0002] Conventionally, as shown in FIG. 1, the continuous welding
process of metal pipe represented by electrically welded pipe is
generally comprising the steps of a preliminary process 2 wherein
coil material 1 is uncoiled and prepared in a looper, a roll
forming process 3 performed by a break down roller, cluster roller,
and fin pass roller, a welding process 4, followed by a sizing
process 5, which is immediately prior to a final cutting process 7
where the metal pipe is cut to the desired length, and in the
sizing process 5, the circularity and straightness of the pipe is
corrected by a straightening roller 6.
[0003] As shown in FIG. 2, the sizing process uses a double roller
6 (FIG. 2A) where the center axes are arranged orthogonal to the
axis line of the pipe in the same plane, a triple roller 8 (FIG.
2B) or a quadruple quadruple roller 9 (FIG. 2C), and in any of
these combinations, these rollers cover nearly the whole
circumference of the outer surface of a pipe 10 to form a grooved
pass.
[0004] When straightening is performed in the sizing process of a
pipe production line as shown in FIG. 1, the sizing is efficiently
and continuously performed, which is an advantage, but there are
also the following problems. First, a grooved roll with dimensions
nearly identical to the desired outer dimension is necessary, so
when the outer dimension of the manufactured pipe is to be changed,
a changeover operation is necessary where the sizing roll is
rearranged and the roll positions adjusted, so high productivity
cannot be obtained particularly for small lot diversified
production.
[0005] Next, the mechanism of the straightening method which uses
this grooved pass roll is to press and deform the pipe in the
circumferential direction, but pipe which is manufactured by normal
roll forming has widely varying deformation history received in the
different regions in the circumferential direction, and therefore
obtaining a high level of circularity is extremely difficult
because of the effects of elastic recovery and residual stress or
the like.
[0006] Furthermore, warping of the manufactured pipe is
straightened by arranging a plurality of roller stands in the
longitudinal direction of the pipe, but this straightening effect
is limited to only certain regions in the circumferential direction
of the pipe, so obtaining a high level of straightness is
difficult.
[0007] In order to obtain finished product with a higher level of
circularity and straightness than the precision of the metal pipe
obtained by the manufacturing process shown in FIG. 1, the cut
product normally must be resized and straightened in specialized
straightening equipment such as a straightener or a draw dice.
[0008] For instance, when a straightener is used as shown in FIG.
3, three sets of rollers are arranged, and while rotating, the
metal pipe 10 is passed between a pair of concave rollers 11, 11 in
each set, and thereby each region of the pipe is repeatedly bent in
the cross-sectional plane and in the longitudinal direction, thus
making the shape dimensions and the internal stress uniform, and
greatly improving both the circularity and the straightness.
[0009] If specialized straightening apparatus and equipment is
used, a higher level of circularity and straightness can be
obtained, but an additional process separate from the pipe
manufacturing line is required, so the process must be performed on
each individual pipe after cutting, and therefore productivity is
poor, and additional equipment and stockyard are required, so the
pipe manufacturing costs are also increased.
SUMMARY OF THE INVENTION
[0010] Therefore, as apparatus for continuous straightening in the
pipe manufacturing process, a so called planetary type
straightening method and apparatus is disclosed in Japanese Patent
Application Laid-open Nos. H2-41706, H5-220507, and H7-246403
wherein a plurality of convex rollers are arranged concentric to
the outer surface of the metal pipe, and while revolving about the
axis of the pipe, these roller groups apply pressure on the outer
diameter of the pipe.
[0011] The target of the planetary type straightening apparatus is
to greatly improve productivity by both including the straightening
process into the pipe forming process, and at the same time,
providing a straightening roller. In other words, the rollers
arranged about the outer surface of the pipe in the planetary
system are aligned at an angle to the axis of the pipe, and this
angle can be adjusted, so the degree of freedom to expand and
contract in the radial direction of the pipe is relatively large
and the rollers can be used for a certain outer dimension range of
product.
[0012] However, with the planetary type straightening apparatus,
the convex roller cannot restrain the whole circumference of the
pipe cross-section with almost no gaps as good the conventional
grooved pass roller, and therefore it is extremely difficult to
effectively press and deform the pipe in both directions. However,
this type of technology disclosed in the aforementioned literature
uses the same basic straightening mechanism to press on the
circumferential direction of the pipe as the conventional
method.
[0013] In actuality, as shown in FIG. 4A-C, when pressure is
applied without restraining the whole circumference of the
cross-section of the pipe 10, a plurality of convex rollers 12 are
used, so the form and strength of the retention received by the
cross-section of the pipe will vary along the axial direction of
the pipe more than when the whole circumference of the pipe 10 is
restrained and deformed. Furthermore, because rotation about the
axis of the pipe by the rollers 12 proceeds at the same time as the
metal pipe 10 proceeds, the way that each section of the pipe will
deform is not fixed, so obtaining the desired circularity and
straightness cannot be guaranteed.
[0014] In other words, from the aspect of commonizing rollers and
productivity, the planetary type straightening apparatus has great
advantages which other straightening apparatus do not have, but as
described above, there are technical problems with the basic
straightening mechanism of the pressing process in the
circumferential direction of the pipe, so the advantages have not
been sufficiently achieved to date.
[0015] An object of the present invention is to propose a metal
pipe straightening method and straightening roller and metal pipe
production apparatus which can be implemented continuously in the
sizing process of the electrically welded pipe manufacturing
process, and which can inexpensively provide metal pipe with a high
level of circularity and a high level of straightness while
maintaining high productivity and commonizing the rollers.
[0016] In order to perform continuous sizing in the pipe
manufacturing process and to commonize rollers, the present
inventors thought it was necessary to escape the thinking of
conventional pressing processes, and implement a more accurate
straightening mechanism, and as a result of various investigations,
have focused on the fact that repeatedly bending the pipe was easy
when considering the restraining form of the metal pipe in a
conventional planetary type straightening apparatus.
[0017] As a result of diligent investigations concerning the roller
caliber of the straightening roller, the present inventors have
discovered that a continuous repetitive bend can be applied to all
regions in the circumferential direction of the cross-section of
the pipe utilizing revolution of the roller group if the roller
caliber is such that the shortest distance from the roller surface
to the pipe axis is a certain value in any cross-section in the
axial direction of the pipe, and the present inventors have
confirmed that an objective of the present invention can be
achieved if a concave roller with this specific roller caliber is
used, a straightening roller group is constructed of a plurality of
these concave rollers arranged in the circumferential direction of
the outer surface of the metal pipe, and pressure is applied to the
pipe to straighten the outer circumference of the pipe while the
roller group is revolving about the axis of the pipe.
[0018] In other words, the present invention is a method to
straighten the outer circumference of a pipe by arranging a
plurality of concave rollers in the circumferential direction of
the outer surface of a metal pipe, and applying pressure to the
pipe while revolving the roller group about the axis of the pipe,
wherein the roller calibers of each of the rollers which contact
the metal pipe has a structure where parts of the projection of the
roller surfaces with respect to the cross-section of the pipe are
on an identical circumference, and the radius of the projected
circumference can be changed by determining the angle of
inclination of the roller to the axis of the pipe and the position
in the radial direction of the pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a process explanatory diagram showing the
continuous manufacturing process for metallic pipe;
[0020] FIG. 2A-C are explanatory diagrams showing the structure of
various conventional groove pass rollers;
[0021] FIG. 3 is a perspective view explanatory diagram showing the
structure of a conventional straightener;
[0022] FIG. 4A is a perspective view explanatory diagram showing
the operating principle of a conventional planetary type
straightening apparatus;
[0023] FIG. 4B is a schematic diagram showing the restraint
condition of the pipe;
[0024] FIG. 4C is an explanatory diagram showing the roller pressed
condition;
[0025] FIG. 5 is an explanatory diagram showing the relationship
between the metal pipe and concave type straightening rollers
according to the present invention, wherein A is the view from the
top surface and B is the view in the axial direction of the
pipe;
[0026] FIG. 6 is an explanatory diagram showing the relationship
between the metal pipe and a straightening roller group of concave
straightening rollers according to the present invention, wherein A
is the case of a small diameter pipe and B is the case of a large
diameter pipe;
[0027] FIG. 7 is a graph showing the relationship between the
distance from the roller width center and the distance from the
rotational axis of the roller for a preferred embodiment of the
present invention; and
[0028] FIG. 8A-B are explanatory diagrams showing the eccentric
relationship between the straightening roller group according to
the present invention and the metal pipe.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present inventors have considered the characteristics of
the restraining form of a metal pipe in a planetary type
straightening apparatus, have focused on the fact that repeatedly
bending a pipe is easy, and have conceived a structure which can
introduce the same straightening mechanism as the aforementioned
straightener. In other words, the ability to achieve this type of
mechanism is directly related to the design of the roller
caliber.
[0030] Only the fact that each region in the circumferential
direction of the pipe is randomly bent and deformed by a standard
convex roller caliber is as previously described, and the present
inventors have discovered that a continuous repetitive bend can be
applied to all regions in the circumferential direction of the
cross-section of the pipe utilizing revolution of the roller group
if the roller caliber is such that the shortest distance from the
roller surface to the pipe axis is a certain value in any
cross-section in the axial direction of the pipe.
[0031] As shown in FIG. 5, the straightening roller according to
the present invention is concave rather than convex, and this
roller form is required to meet the aforementioned conditions. In
detail, as shown in FIG. 5A, the trail on the surface of the pipe
by the roller 20 which is the shortest distance is shown by curved
line A-B-O-C-D, but as shown in FIG. 5B when looking at the pipe 10
from the axial direction, the projection A'-B'-O'-C'-D' forms an
arc 21.
[0032] Therefore, as shown in FIG. 6, according to the present
invention, if a straightening roller group 22 is constructed using
three straightening rollers 20, and all of the rollers 20 are
concentric and arranged at the same angle of inclination (.alpha.)
to the axis of the metal pipe 10, a part of the projection of the
surface of each roller 20 on the cross-section of the metal pipe 10
will be on the same circumference (Hereinafter this circumference
is referred to as the projection circumference).
[0033] In other words, the straightening method according to the
present invention is comprising the step of applying pressure to a
pipe and straightening the outer circumference of the pipe while
revolving about the axis of the pipe a correction roller group
wherein a plurality of concave rollers having a roll caliber are
arranged in the circumferential direction of the outer surface of
the metal pipe wherein the roller caliber of the concave rollers
which contact the metal pipe is structured such that part of the
projection of the roller surfaces on the cross-section of the metal
plate are all on the same circumference and the radius of the
projection arc can be adjusted according to the position of the
rollers in the radial direction of the pipe and the angle of
inclination of the rollers to the axial line of the pipe.
[0034] With the present invention, the sum of the angles of the
projections of the concave straightening rollers 20 will not
necessarily be 360 degrees in the circumferential direction of the
pipe 10, but the straightening roller group 22 is revolving, so
while any arbitrary cross-section of the metal pipe 10 passes
through the restraining region of the roller group 22, each region
in the circumferential direction of the pipe 10 can be pressed at
least one time in the radial direction.
[0035] Furthermore, as the relative speed of the revolution of the
roller group 22 increases in regards to the flow speed of the metal
pipe 10, the number of times that each region in the same direction
of the pipe 10 is pressed by the rollers 20 will increase, so the
target straightness can be achieved by increasing the number of
repeated bending deformations which occur when the region is
pressed. With the present invention, roller caliber designs which
have the aforementioned characteristics which meet a specific
product outer diameter are of course possible, but in actuality,
one of the strongest characteristics of the present invention is
that the outer diameter of various products can be met by changing
the angle of inclination of the rollers which have the same roll
caliber.
[0036] For example, as shown in FIG. 7, if the roller calibers
which can form projection circumferences with a radius of 25
millimeters, 50 millimeters, and 75 millimeters are designed at
different respective angles of inclination and compared, the
geometrical difference can be seen to be extremely small within a
certain range of roll width. Furthermore, with the present
invention, there is no practical problem with using a roll caliber
for any straightening roller as a common caliber by restricting the
roller width such that the difference is a value clearly smaller
than the required circularity tolerance.
[0037] Therefore, the straightening roller according to the present
invention is comprising a concave roller caliber with a structure
wherein a part of the projection of the roll surface with respect
to the cross-section of the metal pipe is on the same
circumference, and the radius of the projection arc can be adjusted
according to the position of the roller in the radial direction of
the pipe and the angle of inclination of the roller with respect to
the axis of the pipe.
[0038] With the planetary type and straightening methods disclosed
to date, roller communization was primarily performed by adjusting
the position of the rollers in the radial direction of the pipe,
and the inclination of the roller was primarily to generate a
propulsive force component in the direction of progression of the
metal pipe.
[0039] In contrast, with the present invention, the inclination of
the straightening roller is proactively utilized to achieve roller
commonization. Incidentally, when rollers are commonized, there is
a restriction to the roller width which can actually be utilized,
and there is a possibility that repetitive bending will not be
performed a sufficient number of times on an area of the
cross-section of the metal pipe particularly in the communized
range for large diameter products.
[0040] However, with the present invention, this problem can be
resolved by arranging a plurality of straightening roller groups in
tandem in the progressive direction of the pipe. Furthermore, using
a plurality of straightening roller groups of the present
invention, not only improves the circularity, but is also very
effective for improving the straightness.
[0041] In other words, the metal pipe straightening method arranges
in the axial direction of the pipe a plurality of straightening
roller groups wherein a plurality of concave rollers having the
aforementioned roller caliber are arranged in the circumferential
direction of the outer surface of the metal pipe, and each roller
group applies pressure to the pipe while revolving about the axis
of the pipe in order to straighten the metal pipe.
[0042] Normally, the geometric center of the arrangements of
rollers which make a roller group matches the center of revolution,
or in other words, the projection circumference center and the
roller group center of revolution are the same, and if the center
of revolution for each roller group is arranged on the same
straight-line (pass line), the metal pipe will not be repeatedly
bent and deformed in the longitudinal direction when passing
through these roller groups. In Japanese Patent Application
Laid-open No. H7-246403, a method is disclosed where the bending of
the pipe can be controlled by setting the center of revolution of
part of the roller groups away from the pass line. However, unlike
the case of the aforementioned straightener shown in FIG. 3, the
metal pipe 10 does not rotate, so with this method, bending can
only be controlled in the designated direction which are the same
as that of the conventional sizing process.
[0043] With the present invention, in order for repetitive bending
to the performed in the longitudinal direction without rotating the
metal pipe, the projection circumference of the roller group and
the center of rotation must beset to be different. In this case,
the projection circumference will eccentrically rotate with respect
to the center of revolution, so the regions in the circumferential
direction of the metal pipe which are restrained in the projection
circumference will successively be bent and deformed in the
longitudinal direction. There are two methods to provide that the
center of revolution of at least one straightening roller group
will eccentrically revolve with respect to the center of revolution
of the other straightening roller groups in order to improve the
straightness of the pipe. The first method is to eccentrically
rotate the center of rotation of part of the roller groups with
respect to the pass line. In this case, as shown in FIG. 8A, the
axis 30 of the region of the metal pipe 10 which is restrained by a
straightening roller group comprising 3 straightening rollers 20 is
constructed to eccentrically rotate with respect to the roller
group and to rotate about the pass line 31. Note, in the figure,
the center of revolution and the geometrical center of the roller
positions match the axis of the pipe 30, and the single point
broken line shows the course of travel for the revolution of the
straightening roller, and the broken line shows the course of
travel for the center of revolution.
[0044] In the aforementioned straightening method, a plurality of
groups of straightening rollers are arranged in the axial direction
of the pipe, the axis pass line of the whole metal pipe which
passes through the plurality of straightening roller groups has an
eccentric relationship to the metal pipe axis in the position which
is the geometrical center of the arrangement of the rollers which
form any one of the straightening roller groups, and which is the
center of revolution thereof, and bending deformation is created in
the longitudinal direction of the metal pipe which passes through,
to increase the straightness in the axial direction of the pipe.
The second method is to set the geometrical center of the roller
arrangement of a straightening roller group and the corresponding
center of revolution to be different. In this case, as shown in
FIG. 8B, the geometrical center of the roller arrangement and the
overlaying axis of the pipe 30 will eccentrically rotate with
respect to the pass line 31 even though the center of revolution of
the straightening roll group does not differ from the pass line 31.
Note, in the figure, the axis of the pipe 30 matches the
geometrical center of the arrangement of the rollers, and the
center of revolution of the straightening roller group matches the
pass line 31, the single point broken line shows the course of
travel for the straightening roller revolution, and the broken line
shows the course of travel of the geometrical center of the roller
arrangement. Furthermore, if there is a need to apply relatively
stronger straightening effects on a specific region (for instance a
welded region of a welded pipe) as opposed to other regions of the
pipe 10, the center of revolution of the roller group can be
shifted from the pass line toward this specific region, and
additional bending and deformation will be applied only in this
region.
[0045] The aforementioned straightening method arranges a plurality
of straightening roller groups in the axial direction of the pipe,
and the geometrical center of the arrangement of the rollers which
form any of the straightening roller groups and the center of
revolution of that roller group have an eccentric relationship, and
therefore bending and deformation can occur in the longitudinal
direction of the metal pipe which passes through, and the
straightness in the longitudinal direction of the pipe can be
increased.
[0046] When the aforementioned straightening method according to
the present invention is applied to the sizing process of welded
pipe as described in FIG. 1, the complicated operation of
exchanging rollers will not be necessary and productivity can be
dramatically improved. Furthermore, because a positive
straightening mechanism is incorporated, a product with a higher
level of circularity and straightness can be obtained as compared
to conventional sizing processes.
[0047] Furthermore, the present invention can show a similar effect
if the aforementioned straightening method is used in the resizing
process in a pipe mill which continuously produces metal pipe from
metal straps in a forming process which has a form roller, a form
shoe, or both.
[0048] Using the straightening method of the present invention as
shown in FIG. 5 and FIG. 6, straightening the circularity and
straightness of various outer diameters of pipe was attempted in
the sizing process for welded steel pipe. The commonization range
of the straightening apparatus which uses straightening rollers
with the characteristics shown in FIG. 5 was compared to the
various inclination angles of a roller caliber which can form
projection circumferences corresponding to the dimensions of
various metal pipes with diameters from 25 mm to 75 mm and was
expressed in FIG. 7 as the relationship between the distance from
the roller width center and the distance from the roller rotational
axis.
[0049] As shown in FIG. 7, the roller calibers which could form a
projection arc with a radius of 12.5 millimeters, 25.0 millimeters,
and 27.5 millimeters had different respective inclination angles
.alpha., or in other words, when an inclination angle of
approximately 27.5.degree. was used for a metal pipe with a
diameter of 25 millimeters, and an inclination angle of
approximately 32.5.degree. was used for a metal pipe with a
diameter of 75 millimeters, in the range where there was a roll
width, there was clearly very little geometrical difference. In
other words, if the roll width is restricted so that the
geometrical difference is clearly smaller than the value of the
circular tolerance required, there will be no problem using any
roll caliber as a common roll caliber, and in actuality, the
circularity and straightness can be increased in pipes with a wide
range of outer diameters.
[0050] The present invention is a new straightening method wherein
a plurality of concave rollers which have a specific shape of
roller caliber are arranged in the circumferential direction of the
outer surface of a metal pipe to form straightening roller groups
which apply pressure on the pipe while revolving about the axis of
the pipe in order to straighten the pipe, and if this straightening
method is applied to the sizing process of welded pipe, the
productivity can be dramatically improved and complicated roller
changeover operations will not be necessary.
[0051] The present invention implements a sure straightening
mechanism, so compared to conventional sizing processes, a product
with a higher level of circularity and straightness can be
obtained, the sizing process can be continuously performed in the
pipe forming process, high productivity and roller communization
can be achieved, and a metal pipe with a high level of circularity
and high level of straightness can be provided inexpensively.
* * * * *