U.S. patent application number 10/541999 was filed with the patent office on 2006-10-05 for tube with high dimensional accuracy, and method and device for manufacturing the tube.
Invention is credited to Kazuhito Kenmochi, Takuya Nagahama, Toshio Ohnishi, Kei Sakata, Koji Sugano, Takaaki Toyooka, Akira Yorifuji.
Application Number | 20060218985 10/541999 |
Document ID | / |
Family ID | 37068737 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060218985 |
Kind Code |
A1 |
Kenmochi; Kazuhito ; et
al. |
October 5, 2006 |
Tube with high dimensional accuracy, and method and device for
manufacturing the tube
Abstract
There are provided a high dimensional accuracy pipe and a
manufacturing method thereof, the pipe being in response to wide
requirements of sizes, being manufactured at inexpensive cost, and
having a sufficient fatigue strength. The detailed structure
thereof is as follows. A push-to-pass process is performed in
which, while a plug 1 is being charged in a metal pipe 5, the metal
pipe is pushed in a hole provided in a die 2 and is then allowed to
pass therethrough. As a result, a high dimensional accuracy pipe
can be obtained in which at least one of the deviation of the outer
diameter, the deviation of the inner diameter, and the deviation of
the thickness in the circumferential direction is 3.0% or less as
processed.
Inventors: |
Kenmochi; Kazuhito; (Tokyo,
JP) ; Nagahama; Takuya; (Tokyo, JP) ; Sakata;
Kei; (Tokyo, JP) ; Sugano; Koji; (Tokyo,
JP) ; Ohnishi; Toshio; (Tokyo, JP) ; Yorifuji;
Akira; (Tokyo, JP) ; Toyooka; Takaaki; (Tokyo,
JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
220 Fifth Avenue
16TH Floor
NEW YORK
NY
10001-7708
US
|
Family ID: |
37068737 |
Appl. No.: |
10/541999 |
Filed: |
April 8, 2004 |
PCT Filed: |
April 8, 2004 |
PCT NO: |
PCT/JP04/05091 |
371 Date: |
February 28, 2006 |
Current U.S.
Class: |
72/284 |
Current CPC
Class: |
B21C 3/12 20130101; B21J
7/145 20130101; B21C 3/06 20130101; B21C 1/26 20130101; B21C 1/30
20130101 |
Class at
Publication: |
072/284 |
International
Class: |
B21C 1/26 20060101
B21C001/26 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2003 |
JP |
2003-107364 |
Apr 28, 2003 |
JP |
2003-123064 |
May 16, 2003 |
JP |
2003-139264 |
Jun 17, 2003 |
JP |
2003-171819 |
Claims
1. A high dimensional accuracy pipe manufactured by a push-to-pass
process comprising the steps of pushing at least one metal pipe in
a hole provided in a die while a plug is being charged in the metal
pipe, and allowing the metal pipe to pass through the hole, wherein
at least one of a deviation of the outside diameter, a deviation of
the inside diameter, and a deviation of the thickness in the
circumferential direction of the pipe as processed is 3% or
less.
2. The high dimensional accuracy pipe according to claim 1, which
is manufactured by a push-to-pass process comprising the steps of
pushing at least one metal pipe in a hole provided in a die while a
plug is being charged in the pipe, and allowing the metal pipe to
pass through the hole so that the thickness of the metal pipe at an
outlet side of the die is not more than that at an inlet side,
wherein at least one of the deviation of the outside diameter, the
deviation of the inside diameter, and the deviation of the
thickness in the circumferential direction of the pipe as processed
is 3% or less.
3. (canceled)
4. The high dimensional accuracy pipe according to claim 1, wherein
the die is at least one of an all-in-one type and a fixed type
die.
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. A highly efficient method for manufacturing a high dimensional
accuracy pipe, comprising a push-to-pass process which includes:
pushing at least one metal pipe in a hole provided in a die while a
plug is being charged in the metal pipe; and allowing the metal
pipe to pass through the hole; wherein when at least one of a
deviation of the outside diameter, a deviation of the inside
diameter, and a deviation of the thickness in the circumferential
direction of each of the pipes is improved by the push-to-pass
process, the pipes are continuously fed in the die using a pipe
feeding mechanism provided at an inlet side of the die while the
plug is being charged in each of the pipes and is being
floated.
11. The highly efficient method for manufacturing a high
dimensional accuracy pipe, according to claim 10, wherein the pipe
feeding mechanism comprises at least one caterpillar device which
holds the pipes before they are processed.
12. The highly efficient method for manufacturing a high
dimensional accuracy pipe, according to claim 10, wherein the pipe
feeding mechanism comprises at least one endless belt which holds
the pipes before they are processed.
13. The highly efficient method for manufacturing a high
dimensional accuracy pipe, according to claim 10, wherein the pipe
feeding mechanism comprises at least one intermittent feeding
device which alternately holds and intermittently feeds the pipes
before they are processed.
14. The highly efficient method for manufacturing a high
dimensional accuracy pipe, according to claim 10, wherein the pipe
feeding mechanism comprises a press which sequentially pushes the
pipes before they are processed.
15. The highly efficient method for manufacturing a high
dimensional accuracy pipe, according to claim 10, wherein the pipe
feeding mechanism comprises at least one grooved roll which holds
the pipes before they are processed.
16. (canceled)
17. (canceled)
18. A method for manufacturing a high dimensional accuracy pipe
having superior surface quality, comprising a push-to-pass process
which includes: pushing at least one metal pipe in a hole provided
in a die while a plug is being charged in the metal pipe; allowing
the metal pipe to pass through the hole; and applying a lubricant
film to at least one of an interior and an exterior surface of the
pine; and wherein after at least one of the interior and exterior
surface of the pipe is provided with a lubricant film, the plug is
charged in the pipe, and the push-to-pass process is performed
using the die.
19. The method for manufacturing a high dimensional accuracy pipe
having superior surface quality, according to claim 18, wherein the
pipe on which the lubricant film is formed is a steel pipe to which
oxide scales still adhere.
20. (canceled)
21. (canceled)
22. The method for manufacturing a high dimensional accuracy pipe
having superior surface quality, according to claim 18, wherein the
lubricant film is formed by using a drying resin.
23. (canceled)
24. (canceled)
25. (canceled)
26. (canceled)
27. (canceled)
28. A stable method for manufacturing a high dimensional accuracy
pipe, comprising a push-to-pass process which includes: pushing at
least one metal pipe in a hole provided in a die while a plug is
being charged in the metal pipe; and allowing the metal pipe to
pass through the hole; wherein: while the plug is being charged in
the pipe, the pipe is pushed in the hole provided in the die and is
then allowed to pass therethrough, the plug has an angle of 5 to
40.degree. which is formed between the surface of a diameter
reducing portion and a processing central axis and a length of 5 to
100 mm of the diameter reducing portion, and the die has an angle
of 5 to 40.degree. which is formed between the interior surface of
the hole at an inlet side and the processing central axis.
29. The stable method for manufacturing a high dimensional accuracy
pipe, according to claim 28, wherein the length of a bearing
portion of the plug is 5 to 200 mm.
30. (canceled)
31. (canceled)
32. (canceled)
33. (canceled)
34. (canceled)
35. (canceled)
36. (canceled)
37. A manufacturing apparatus for manufacturing a high dimensional
accuracy pipe, comprising: a plug capable of being in contact with
an entire inner circumference of at least one metal pipe, at least
one die having a hole capable of being in contact with an entire
outer circumference of the metal pipe, and a pipe pushing device
which pushes the metal pipe, wherein while the plug is being
charged in the metal pipe, the metal pipe is pushed in the hole in
the die and is then allowed to pass therethrough, whereby a
push-to-pass process is performed.
38. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 37, wherein the die
is at least one of an all-in-one type and a fixed type die.
39. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 38, wherein the plug
is a floating type plug.
40. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 37, wherein the pipe
pushing device comprises a device which continuously pushes the
metal pipes.
41. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 37, wherein the pipe
pushing device comprises a device which intermittently pushes the
metal pipes.
42. (canceled)
43. (canceled)
44. (canceled)
45. (canceled)
46. (canceled)
47. (canceled)
48. (canceled)
49. (canceled)
50. A manufacturing apparatus for manufacturing a high dimensional
accuracy pipe, wherein, in claim 37, in a manufacturing apparatus
having the die through which the pipe is allowed to pass, and the
pushing device pushing the pipe in the die, fine adjustment means
for adjusting pipe bending is provided at a position very close to
an outlet side of the die, the fine adjustment means having: a hole
body through which the pipe is allowed to pass, a support substrate
which supports the hole body movably in a plane perpendicular to a
pipe traveling direction, and a hole body-moving mechanism which is
supported by the support substrate and which moves the hole
body.
51. (canceled)
52. (canceled)
53. (canceled)
54. (canceled)
55. (canceled)
56. (canceled)
57. (canceled)
58. (canceled)
59. A manufacturing line for manufacturing a high dimensional
accuracy pipe, comprising the push-to-pass process device as
described in claim 37, wherein a pipe-end grinding device which
grinds an end surface of a pipe in the direction perpendicular to a
pipe axis, a lubricant immersion coating bath in which the pipe is
coated with a lubricant by immersion, a drying device which dries
the pipe coated with the lubricant, and the push-to-pass process
device are provided in that order.
60. (canceled)
61. (canceled)
62. (canceled)
63. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 63, wherein the plug
is a floating type plug.
64. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 39, wherein the pipe
pushing device comprises a device which continuously pushes the
metal pipes.
65. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 39, wherein the pipe
pushing device comprises a device which continuously pushes the
metal pipes.
66. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 39, wherein the pipe
pushing device comprises a device which continuously pushes the
metal pipes.
67. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 63, wherein the pipe
pushing device comprises a device which intermittently pushes the
metal pipes.
68. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 38, wherein the pipe
pushing device comprises a device which intermittently pushes the
metal pipes.
69. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, according to claim 39, wherein the pipe
pushing device comprises a device which intermittently pushes the
metal pipes.
70. A manufacturing line for manufacturing a high dimensional
accuracy pipe, comprising the push-to-pass process device as
described in claim 37, further comprising: a pipe-end grinding
device which grinds an end surface of the pipe in a direction
perpendicular to a pipe axis, and a lubricant spray coating device
which coats the pipe with a lubricant by spraying, the lubricant
spray coating device provided at an inlet side of the die of the
push-to-pass process device.
71. A manufacturing line for manufacturing a high dimensional
accuracy pipe, comprising the push-to-pass process device as
described in claim 37, further comprising: a pipe-end grinding
device which grinds an end surface of the pipe in a direction
perpendicular to a pipe axis, and a lubricant spray coating and
drying device which coats the pipe with a lubricant by spraying and
which thereafter dries the lubricant coating, the lubricant spray
coating device provided at an inlet side of the die of the
push-to-pass process device.
Description
TECHNICAL FIELD
[0001] The present invention relates to high dimensional accuracy
pipes, manufacturing methods thereof, and manufacturing
apparatuses. The present invention relates to a high dimensional
accuracy pipe applicable to components, such as drive train parts
for automobile, which require high dimensional accuracy, a
manufacturing method thereof, a manufacturing apparatus, and a
manufacturing line.
BACKGROUND ART
[0002] In general, a metal pipe such as a steel pipe is roughly
classified into a welded pipe and a seamless pipe. As is an
electric-resistance welded pipe, the welded pipe is manufactured in
a manner in which a band plate is roundly bent in the width
direction, and two ends of the rounded band plate are brought into
contact with each other and are then welded together. On the other
hand, the seamless pipe is manufactured by piercing a billet at a
high temperature, followed by rolling using a mandrel mill or the
like. In the case of the welded pipe, the dimensional accuracy is
improved by grinding a protrusion at a welded portion after
welding; however, the deviation of the thickness exceeds 3.0%. In
addition, in the case of the seamless pipe, it is very likely that
an eccentricity is introduced in a piercing step, and thereby the
thickness is liable to be more largely deviated. Although efforts
have been made in order to reduce the deviation of the thickness, a
sufficient reduction thereof has not been obtained as of today, and
as a result, the deviation is still 8.0% or more as the finished
product.
[0003] Recently, as measures for environment-related issues, weight
reduction of automobiles has been seriously desired. As for drive
train parts such as a drive shaft, hollow metal pipes have been
progressively increased instead of solid metal bars. The metal
pipes used, for example, for the drive train parts for automobile
are required to have high dimensional accuracy so that the
deviations of the thickness, inner diameter, and outer diameter are
each 3.0% or less and more strictly 1.0% or less.
[0004] The drive train parts must withstand fatigue caused by
long-run driving of automobile. When the accuracy of the thickness,
inner diameter, and outer diameter of a metal pipe is inferior, the
fatigue failure is inevitably liable to progress from
irregularities present on the interior and exterior surfaces of the
pipe, and as a result, the fatigue strength is extremely decreased.
For maintaining a sufficient fatigue strength, the accuracy of the
thickness, inner diameter, and outer diameter of the metal pipe
must be improved.
[0005] Hereinafter, the high dimensional accuracy pipe of the
present invention indicate a pipe in which at least one of the
deviations of the outer diameter, inner diameter, and thickness in
the circumferential direction is 3.0% or less, and the deviations
are each obtained by the following equations. Deviation=Amount of
fluctuation/(target value or average value).times.100% Amount of
fluctuation=maximum value-minimum value
[0006] As means for improving the accuracy of the thickness, inner
diameter, and outer diameter of a metal pipe, in general, two
methods have been known. Hereinafter, a welded steel pipe and a
seamless pipe (hereinafter referred to as a steel pipe or a pipe)
will be described. One of the above two is a method (so-called cold
drawing method) in which a steel pipe is cold-drawn using a die and
a plug (see Patent Document 5). The other one is a method
(so-called rotary press forging method) in which a steel pipe is
pressed in a die hole using a rotary forging device incorporating a
segmented die which is segmented in the circumferential direction
(see Patent Documents 1, 2, and 3).
[0007] Patent Document 1: Japanese Unexamined Patent Application
Publication No. 9-262637
[0008] Patent Document 2: Japanese Unexamined Patent Application
Publication No. 9-262619
[0009] Patent Document 3: Japanese Unexamined Patent Application
Publication No. 10-15612
[0010] Patent Document 4: Japanese Patent No. 2858446
[0011] Patent Document 5: Japanese Patent No. 2812151
[0012] However, in the cold drawing method, when production
capacity is insufficient, or when a diameter reduction rate must be
decreased since a sufficient drawing stress cannot be obtained due
to excessively large thickness and diameter of a pipe, the contact
between a die and the pipe and that between a drawing plug and the
pipe in a processing tool (a space between the plug and the
interior surface of the die hole) become insufficient. The reason
for this is that the stress of the pipe in the cold drawing method
is a tensile force. In this case, the smoothness of the interior
surface and the exterior surface of the pipe are not satisfactory,
and as a result, irregularities are liable to remain thereon. As
measures therefor, the diameter reduction rate of the pipe by the
cold drawing method is increased so as to increase the contact of
the interior and exterior surfaces of the pipe with the plug and
die in the processing tool. However, when a pipe is cold-drawn
using a die, as the diameter reduction rate thereof is increased,
the roughness is increased due to the irregularities of the
interior surface of the pipe. As a result, it is difficult to
obtain a high dimensional accuracy pipe by the cold drawing method.
Hence, the fatigue strength of the pipe is not satisfactory, and a
pipe having superior dimensional accuracy has been more strongly
desired. In the cold drawing method, since being held for
application of a tensile force, the front end of a pipe must be
made narrower. As a result, since drawing must be performed for one
pipe at a time, a problem has occurred in that the process
efficiency is extremely poor.
[0013] In addition, even when the production capacity is high, and
the diameter reduction rate can be increased, processing strain
caused by the diameter reduction is increased, and as a result,
work hardening of a pipe is liable to occur. After the drawing, the
pipe is further processed by bending or swaging. There has been a
problem in that cracking is liable to occur in a subsequent bending
step due to work hardening in the drawing described above. In order
to avoid the problem described above, heat treatment must be
performed for a sufficiently long time at a high temperature after
the drawing, and as a result, the production cost is very much
increased. Hence, a method for manufacturing a high dimensional
accuracy pipe, which is inexpensive and has superior workability,
with a high efficiency has been eagerly desired.
[0014] A pressure device for a metal pipe described in patent
Document 4 is an auxiliary device having functions in which, while
the metal pipe is being drawn by a different device, the pipe is
prevented from being broken caused by the above drawing and in
which a tensile force required for forming a groove in the interior
surface of the pipe is decreased. Hence, the pressure device
described above is not a device for smoothing the interior and the
exterior surfaces of the pipe.
[0015] In the rotary press forging method described in Patent
Documents 1 to 3, since a die of a rotary forging device is
segmented and is rocked, steps are easily formed at the segmented
portions, and the smoothness of the exterior surface may become
insufficient, or due to the difference in rigidity of the die in
the circumferential direction, non-uniform deformation may occurs
in some cases. As a result, the thickness accuracy also becomes
unsatisfactory, a targeted finish dimensional accuracy cannot be
sufficiently obtained, and the fatigue strength of the steel pipe
is also not enough; hence, the improvement has been desired.
[0016] In the rotary press forging method, the thickness of a pipe
after being pressed is larger than that before being pressed. This
is because of the restriction caused by the use of a rotary forging
device in which it is difficult to apply a force due to a
complicated structure thereof. In order to increase the thickness,
the space at the side close to an outlet of the processing tool is
increased so that the pipe is easily deformed; however, when the
space is provided, and the deformation easily occurs,
irregularities are generated on the interior surface of the pipe.
When the thickness is further increased, the space is increased,
and as a result, the pipe is not sufficiently brought into contact
with a die surface and/or a plug surface. As a result, the
smoothing of the pipe surface is not improved, and hence a problem
is encountered in that a high dimensional accuracy pipe is unlikely
to be obtained.
[0017] In addition, in manufacturing a high dimensional accuracy
pipe, when a friction force between the exterior surface of the
plug and the interior surface of the pipe and that between the
interior surface of the die and the exterior surface of the pipe
are not decreased as small as possible, faults such as burn marks
are generated on the surface of the pipe in processing, and the
surface quality of the pipe after processing is degraded, so that
the pipe thus obtained cannot be formed into a product. In addition
to that described above, a load in processing is extremely
increased, and it may become impossible to continue the process
itself in some cases, resulting in extreme decrease in production
efficiency.
[0018] Accordingly, in order to obtain a desired thickness after a
pipe is pressed, the thickness thereof before it is pressed must be
inevitably decreased. Hence, in order to prepare pipes having
various product sizes and to improve properties thereof such as the
fatigue strength, many raw pipe sizes must be prepared. However,
many sizes cannot be prepared due to the restriction by raw-pipe
production facilities, and hence it has been difficult to obtain
pipes having superior dimensions which can respond to all the
required sizes. In addition, also for automobile parts, pipes
having different degrees of processing are used. For example, for a
certain part, it has been considered in some cases to omit heat
treatment after processing by decreasing the degree of processing,
and for another part, the strength is increased by significantly
increasing the degree of processing.
[0019] However, according to a conventional cold drawing method and
rotary press forging method, since only a diameter reduction
process has been performed, the outer diameter of a processed pipe
is primarily determined by a die diameter, and the thickness is
also primarily determined by a die and a plug. Hence, from
identical pipes, only one particular degree of processing is
obtained, and it has been almost impossible to manufacture pipes
having the same size and different degrees of processing from
identical raw pipes. Accordingly, in order to manufacture pipes
having the same size and different degrees of processing, raw pipes
having plural sizes must be inevitably prepared so as to change the
diameter reduction rate thereof, and as a result, manufacturing of
raw pipes requires lots of time and effort.
[0020] As described above, a high dimensional accuracy pipe is
difficult to obtain by conventional techniques, and in addition, a
problem has occurred in that when pipes having the same size and
different degrees of processing are manufactured, many raw pipes
having different sizes must be prepared.
[0021] In order to solve the above problems, research was carried
out by the inventors of the present invention on methods for
forming a pipe having a higher dimensional accuracy than that
obtained by drawing, and finally, it was found that a push-to-pass
process is a potential candidate. In the case of the push-to-pass
process, as shown in FIG. 10, since a plug 1 is charged in a pipe
4, and the pipe 4 is pushed in a die 2 by a pipe pushing device 3
while the plug 1 is being floated, a compressive force works in the
entire processing tool. As a result, regardless of an inlet side
and an outlet side of the processing tool, the pipe can be
sufficiently brought into contact with the plug and the die.
Furthermore, even when the diameter reduction rate is small, since
the inside of the processing tool is placed in a compressed stress
state, compared to the case of drawing, the pipe are likely to be
sufficiently brought into contact with the plug and the die, and
hence the pipe is likely to be smoothed, thereby obtaining a high
dimensional accuracy pipe.
[0022] However, in performing the push-to-pass process, the
following case occurred. That is, the plug clogged the pipe to
increase a load, the raw pipe which was pushed was buckled, and
hence the process could not be further continued. As the reasons
for this, for example, there may be mentioned an insufficient
amount of lubricant applied onto the raw pipe, the change in
surface condition of the raw pipe, and deformation of the plug or
die due to frictional heat or process heat generated in the
push-to-pass process. However, in order to continue a stable
push-to-pass process for pipes, whether the process can be continue
or not must be first determined in situ during the process.
[0023] Heretofore, after the above determination was sensuously
made by an operator in consideration of noise of a pipe pushing
device, fluctuation shown by oil-pressure meters, and the like, or
the process was stopped due to die cracking caused by a process
which was forcedly continued, push-to-pass conditions were
reviewed, and the process was then restarted. That is, even when
the process was performed under conditions much milder than the
upper limit of the push-to-pass process standard, the conditions
were changed, or when the die was cracked under extremely severe
process conditions, the conditions were then first changed. Hence,
an unnecessary process time was increased, or a time for exchanging
the die was extremely increased, and as a result, a low
productivity has not been improved as of today.
[0024] In conventional drawing, in order to improve the dimensional
accuracy of a pipe, after bonderizing treatment was performed for a
pipe before drawing, it was necessary that metal soap be applied
thereto so as to form a sufficient lubricant film. Accordingly, a
sufficient time was required for forming the lubricant film, and in
addition, pretreatment of the pipe, such as pickling, was also
required; hence, in a manufacturing line for drawing, a plurality
of baths for pretreatment such as pickling and a plurality of baths
for lubricant treatment were required. In addition, for performing
the drawing process, metal pointing was necessarily performed for
the front end of the pipe by using a rotary forging device or the
like. However, when the above manufacturing line is allowed to go
online and is arranged at an inlet side of a drawing process
device, the productivity is decreased, thereby causing a serious
problem. Hence, the lubrication treatment was performed in a
separate process, and the pipes thus treated were then introduced
in the online manufacturing line of drawing for processing.
[0025] That is, in a conventional manufacturing line for a high
dimensional accuracy pipe, since the drawing which requires a long
pretreatment process must be performed, it has been difficult to
improve the production efficiency.
[0026] As described above, according to the conventional cold
drawing method and rotary press forging method, a high dimensional
accuracy pipe is difficult to obtain, and in addition, the problem
has not still been solved in that the surface quality of a pipe may
be degraded in some cases. In consideration of the problems of the
conventional techniques described above, an object of the present
invention is to provide high dimensional accuracy pipes, a
manufacturing method thereof, and a manufacturing line for
performing manufacturing with high efficiency, the high dimensional
accuracy pipes capable of meeting wide requirements of sizes, being
manufactured at inexpensive cost, and having a sufficient fatigue
strength.
DISCLOSURE OF INVENTION
[0027] The present invention which achieved the above objects is as
follows.
[0028] 1. A high dimensional accuracy pipe manufactured by a
push-to-pass process comprising the steps of pushing at least one
metal pipe in a hole provided in a die while a plug is being
charged in the metal pipe, and allowing the metal pipe to pass
through the hole, wherein at least one of the deviation of the
outside diameter, the deviation of the inside diameter, and the
deviation of the thickness in the circumferential direction of the
pipe as processed is 3.0% or less.
[0029] 2. The high dimensional accuracy pipe described in 1. above,
which is manufactured by a push-to-pass process comprising the
steps of pushing at least one metal pipe in a hole provided in a
die while a plug is being charged in the pipe, and allowing the
metal pipe to pass through the hole so that the thickness of the
metal pipe at an outlet side of the die is not more than that at an
inlet side, wherein at least one of the deviation of the outside
diameter, the deviation of the inside diameter, and the deviation
of the thickness in the circumferential direction of the pipe as
processed is 3.0% or less.
[0030] 3. The high dimensional accuracy pipe described in 1 or 2
above, wherein the push-to-pass process is performed while the
metal pipe is being in contact with the entire outer circumference
of the plug and with the entire inner circumference of the die in
the same cross-section of the metal pipe.
[0031] 4. The high dimensional accuracy pipe described in one of 1.
to 3. above, wherein the die is an all-in-one type and/or a fixed
type die.
[0032] 5. A method for manufacturing a high dimensional accuracy
pipe, comprising a push-to-pass process which comprises the step of
pushing at least one metal pipe in a hole provided in a die while a
plug is being charged in the metal pipe, and allowing the metal
pipe to pass through the hole.
[0033] 6. The method for manufacturing a high dimensional accuracy
pipe, described in 5 above, wherein the thickness of the pipe at an
outlet side of the die is set not more than that at an inlet side
thereof.
[0034] 7. The method for manufacturing a high dimensional accuracy
pipe, described in 5. or 6. above, wherein the push-to-pass process
is performed while the metal pipe is being in contact with the
entire outer circumference of the plug and with the entire inner
circumference of the die in the same cross-section of the metal
pipe.
[0035] 8. The method for manufacturing a high dimensional accuracy
pipe, described in one of 5 to 7 above, wherein the die is an
all-in-one type and/or a fixed type die.
[0036] 9. The method for manufacturing a high dimensional accuracy
pipe, described in one of 5. to 8. above, wherein the plug is a
floating plug.
[0037] 10. A highly efficient method for manufacturing a high
dimensional accuracy pipe, wherein, in 5. above, when at least one
of the deviation of the outside diameter, the deviation of the
inside diameter, and the deviation of the thickness in the
circumferential direction of each of the pipes is improved by the
push-to-pass process, the pipes are continuously fed in the die
using pipe-feeding means provided at an inlet side of the die while
the plug is being charged in each of the pipes and is being
floated.
[0038] 11. The highly efficient method for manufacturing a high
dimensional accuracy pipe, described in 10. above, wherein the pipe
feeding means is at least one caterpillar holding the pipes before
they are processed.
[0039] 12. The highly efficient method for manufacturing a high
dimensional accuracy pipe, described in 10. above, wherein the pipe
feeding means is at least one endless belt holding the pipes before
they are processed.
[0040] 13. The highly efficient method for manufacturing a high
dimensional accuracy pipe, described in 10. above, wherein the pipe
feeding means is at least one intermittent feeding device which
alternately holds and intermittently feeds the pipes before they
are processed.
[0041] 14. The highly efficient method for manufacturing a high
dimensional accuracy pipe, described in 10. above, wherein the pipe
feeding means is a press which sequentially pushing the pipes
before they are processed.
[0042] 15. The highly efficient method for manufacturing a high
dimensional accuracy pipe, described in 10. above, wherein the pipe
feeding means is at least one grooved roll holding the pipes before
they are processed.
[0043] 16. The highly efficient method for manufacturing a high
dimensional accuracy pipe, described in 15 above, wherein the
number of said at least one grooved roll is at least two.
[0044] 17. The highly efficient method for manufacturing a high
dimensional accuracy pipe, described in 15 or 16 above, wherein at
least two stands each having the grooved roll are provided.
[0045] 18. A method for manufacturing a high dimensional accuracy
pipe having superior surface quality, wherein, in 5. above, after
an interior and/or an exterior surface of the pipe is provided with
a lubricant film, the plug is charged in the pipe, and the
push-to-pass process is performed using the die.
[0046] 19. The method for manufacturing a high dimensional accuracy
pipe having superior surface quality, described in 18. above,
wherein the pipe on which the lubricant film is formed is a steel
pipe to which oxide scales still adhere.
[0047] 20. The method for manufacturing a high dimensional accuracy
pipe having superior surface quality, described in 18. or 19.
above, wherein the lubricant film is formed by using a liquid
lubricant.
[0048] 21. The method for manufacturing a high dimensional accuracy
pipe having superior surface quality, described in 18. or 19.
above, wherein the lubricant film is formed by using a grease-based
lubricant.
[0049] 22. The method for manufacturing a high dimensional accuracy
pipe having superior surface quality, described in 18. or 19.
above, wherein the lubricant film is formed by using a drying
resin.
[0050] 23. The method for manufacturing a high dimensional accuracy
pipe having superior surface quality, described in 22 above,
wherein the lubricant film is formed by the steps of applying the
drying resin, a liquid containing the drying resin diluted with a
solvent, or an emulsion of the drying resin, and then supplying a
hot wind or performing air drying.
[0051] 24. A method for manufacturing a high dimensional accuracy
pipe, wherein, in 5. above, in a high dimensional accuracy pipe
manufacturing method for manufacturing pipes having a predetermined
size and different degrees of processing with high dimensional
accuracy from raw pipes having the same size, a plug capable of
expanding the pipes and reducing the diameters thereof is charged
in the pipes, and the push-to-pass process is performed for the
pipes using the die.
[0052] 25. The method for manufacturing a high dimensional accuracy
pipe, described in 24. above, wherein the plug is floated in the
pipes, and the pipes are continuously supplied to the die.
[0053] 26. The method for manufacturing a high dimensional accuracy
pipe, described in 24. or 25. above, wherein the plug is a plug in
which a corn angle at a pipe expanding portion is set to be smaller
than a corn angle at a diameter reducing portion.
[0054] 27. The method for manufacturing a high dimensional accuracy
pipe, described in one of 24. to 26. above, wherein a target
outside diameter of the pipe at an outlet side of the die is set to
be smaller than the outside diameter of the pipe at an inlet side
of the die.
[0055] 28. A stable method for manufacturing a high dimensional
accuracy pipe, wherein, in 5. above, in manufacturing a high
dimensional accuracy pipe by the push-to-pass process in which,
while the plug is being charged in the pipe, the pipe is pushed in
the hole provided in the die and is then allowed to pass
therethrough, a plug having an angle of 5 to 40.degree. which is
formed between the surface of a diameter reducing portion and a
processing central axis and a length of 5 to 100 mm of the diameter
reducing portion is used as the plug, and as the die, a die is used
having an angle of 5 to 40.degree. which is formed between the
interior surface of the hole at an inlet side and the processing
central axis.
[0056] 29. The stable method for manufacturing a high dimensional
accuracy pipe, described in 28. above, wherein the length of a
bearing portion of the plug is set to 5 to 200 mm.
[0057] 30. The stable method for manufacturing a high dimensional
accuracy pipe, described in 28. or 29. above, wherein the thickness
of the pipe at an outlet side of the die is set to be not more than
that at an inlet side thereof.
[0058] 31. The stable method for manufacturing a high dimensional
accuracy pipe, described in one of 28. to 30. above, wherein as the
die, an all-in-one fixed type die is used.
[0059] 32. The stable method for manufacturing a high dimensional
accuracy pipe, described in 28 or 31 above, wherein the plug is
being floated in the pipe.
[0060] 33. A stable method for manufacturing a high dimensional
accuracy pipe, wherein, in 5. above, in manufacturing a high
dimensional accuracy pipe by the push-to-pass process in which,
while the plug is being charged in the pipe and is being floated,
the pipe is pushed in the hole provided in the die and is then
allowed to pass therethrough, during the push-to-pass process, a
load in a push-to-pass direction is measured, the measured load is
compared with a calculated load calculated using one of the
following [equation 1] to [equation 3] obtained from material
properties of a raw pipe, which is a pipe before processing, and
the continuation of the push-to-pass process is determined based on
the result of the comparison;
Note .sigma..sub.k.times.the cross-section of a raw pipe [Equation
1]
[0061] In the above equation,
.sigma..sub.k=YS.times.(1-a.times..lamda.), .lamda.=(L/ n)/k,
a=0.00185 to 0.0155, L represents the length of the raw pipe, k
represents the secondary radius of the cross-section,
k.sup.2=(d.sub.1.sup.2+d.sub.2.sup.2)/16, n represents pipe end
conditions (n=0.25 to 4), d.sub.1 represents the outer diameter of
the raw pipe, d.sub.2 represents the inner diameter of the raw
pipe, and YS represents a yield strength of the raw pipe; yield
strength YS of the raw pipe.times.the cross-section of the raw
pipe; and [Equation 2] tensile strength TS of the raw
pipe.times.the cross-section of the raw pipe. [Equation 3]
[0062] 34. The stable method for manufacturing a high dimensional
accuracy pipe, described in 33. above, wherein, when the measured
load is not more than the calculated load, it is determined that
the continuation can be performed, so that the process is continued
as it has been, and when the measured load is more than the
calculated load, after it is determined that the continuation
cannot be performed, and the process is then interrupted so that
the die and/or the plug is exchanged with a new one which has a
different shape in conformity with the same pipe product
dimensions, the process is restarted.
[0063] 35. The stable method for manufacturing a high dimensional
accuracy pipe, described in 34. above, wherein the die and the plug
to be used after the exchange have angles smaller than those of the
die and the plug used before the exchange.
[0064] 36. The stable method for manufacturing a high dimensional
accuracy pipe, described in one of 33. to 35. above, wherein a
lubricant is applied onto the raw pipe before the push-to-pass
process, and only when the measured load exceeds the calculated
load, the type of lubricant is changed.
[0065] 37. A manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, comprising: a plug capable of being in
contact with the entire inner circumference of at least one metal
pipe, at least one die having a hole capable of being in contact
with the entire outer circumference of the metal pipe, and a pipe
pushing device pushing the metal pipe, wherein while the plug is
being charged in the metal pipe, the metal pipe is pushed in the
hole in the die and is then allowed to pass therethrough, whereby
the push-to-pass process is performed.
[0066] 38. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in 37. above, wherein the die
is an all-in-one type and/or a fixed type die.
[0067] 39. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in 37 or 38. above, wherein
the plug is a floating type plug.
[0068] 40. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in one of 37. to 39., wherein
the pipe pushing device is a device continuously pushing the metal
pipes.
[0069] 41. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in one of 37. to 39. above,
wherein the pipe pushing device is a device intermittently pushing
the metal pipes.
[0070] 42. A highly efficient manufacturing method for
manufacturing a high dimensional accuracy pipe, wherein, in 37.
above, in a manufacturing method for manufacturing a high
dimensional accuracy pipe, in which a plug is charged in pipes and
is floated, and the pipes are continuously or intermittently pushed
in a die and are then allowed to pass therethrough so as to perform
a push-to-pass process, a plurality of dies having different hole
shapes is arranged along the same circumference, and one of the
dies in conformity with product dimensions is moved in the
circumference direction of the arrangement and is disposed in a
pass line so that the push-to-pass process is performed.
[0071] 43. A highly efficient manufacturing method for
manufacturing a high dimensional accuracy pipe, wherein, in 37.
above, in a manufacturing method for manufacturing a high
dimensional accuracy pipe, in which a plug is charged in pipes and
is floated, and the pipes are continuously or intermittently pushed
in a die and are then allowed to pass therethrough so as to perform
a push-to-pass process, a plurality of dies having different hole
shapes is arranged on the same linear line, and one of the dies in
conformity with product dimensions is moved in the linear line
direction of the arrangement and is disposed in a pass line so that
the push-to-pass process is performed.
[0072] 44. The highly efficient manufacturing method for
manufacturing a high dimensional accuracy pipe, described in 42. or
43. above, wherein when production dimensions for the following
pipe are changed from those for the preceding pipe, after the
push-to-pass process for the preceding pipe is performed, the
following pipe is allowed to stay at an inlet side of the die, and
before or after a die in conformity with the production dimensions
for the following pipe is moved or while the die is being moved, a
plug in conformity with the same production dimensions is charged
in the following pipe.
[0073] 45. A highly efficient manufacturing apparatus for
manufacturing a high dimensional accuracy pipe, wherein, in 37.
above, the dies through which the pipes are allowed to pass, the
pushing device pushing the pipes in a die placed in a pass line,
and a die rotating platform are provided, the die rotating platform
supporting the dies arranged in the same circumference and moving
one of the dies in a circumference direction to dispose it in the
pass line.
[0074] 46. A highly efficient manufacturing apparatus for
manufacturing a high dimensional accuracy pipe, wherein, in 37.
above, above, the dies through which the pipes are allowed to pass,
the pushing device pushing the pipes in a die placed in a pass
line, and a die linear-driving platform are provided, the die
linear-driving platform supporting the dies arranged on the same
linear line and moving one of the dies in a linear line direction
to dispose it in the pass line.
[0075] 47. A manufacturing method for manufacturing a high
dimensional accuracy pipe, wherein, in 5. above, in a manufacturing
method for manufacturing a high dimensional accuracy pipe by the
push-to-pass process in which, while the plug is charged in the
pipe and is floated, the pipe is pushed in the die and is then
allowed to pass therethrough, the pipe at an outlet side of the die
is allowed to pass through a hole body provided at a position which
is very close to the outlet side of the die and which is adjusted
beforehand in the plane perpendicular to a pipe traveling
direction, whereby pipe bending is prevented.
[0076] 48. The manufacturing method for manufacturing a high
dimensional accuracy pipe, described in 47 above, wherein the pipe
at an inlet side of the die and/or an outlet side of the hole body
is allowed to pass through a guide tube.
[0077] 49. The manufacturing method for manufacturing a high
dimensional accuracy pipe, described in 47. or 48. above, wherein
the pipes are continuously pushed in the die.
[0078] 50. A manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, wherein, in 37. above, in a
manufacturing apparatus having the die through which the pipe is
allowed to pass, and the pushing device pushing the pipe in the
die, fine adjustment means for adjusting pipe bending is provided
at a position very close to an outlet side of the die, the means
having a hole body through which the pipe is allowed to pass, a
support substrate supporting the hole body movably in the plane
perpendicular to a pipe traveling direction, and a hole body-moving
mechanism which is supported by the support substrate and which
moves the hole body.
[0079] 51. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in 50. above, wherein the hole
body-moving mechanism is a mechanism in which at least one place of
a peripheral portion of the hole body is pushed in the direction
perpendicular to the pipe traveling direction by a tapered surface
of a wedge-shaped mold which is moved in the pipe traveling
direction.
[0080] 52. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in 51 above, wherein the
movement of the wedge-shaped mold is biased by a screw.
[0081] 53. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in 50. above, wherein the hole
body-moving mechanism is in accordance with a pushing or a pulling
method in which at least one place of a peripheral portion of the
hole body is directly pushed or pulled in the direction
perpendicular to the pipe traveling direction.
[0082] 54. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in 53. above, wherein the
pushing or pulling of the pushing or pulling method is biased by a
fluid pressure cylinder.
[0083] 55. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in one of 50. to 54. above,
wherein the diameter of a hole provided in the hole body is not
less than the diameter of the hole in the die at the outlet
side.
[0084] 56. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in one of 50. to 55. above,
wherein the hole in the hole body is a straight hole or a tapered
hole.
[0085] 57. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in one of 50. to 56. above,
wherein at least one guide tube is further provided, through which
the pipe at an inlet side of the die and/or an outlet side of the
fine adjustment means for adjusting pipe bending is allowed to
pass.
[0086] 58. The manufacturing apparatus for manufacturing a high
dimensional accuracy pipe, described in one of 50. to 57. above,
wherein the pushing device is a continuous pushing device capable
of continuously pushing the pipes.
[0087] 59. A manufacturing line for manufacturing a high
dimensional accuracy pipe, comprising the push-to-pass process
device described in 37. above, wherein a pipe-end grinding device
grinding the end surface of the pipe in the direction perpendicular
to a pipe axis, a lubricant immersion coating bath in which the
pipe is coated with a lubricant by immersion, a drying device
drying the pipe coated with the lubricant, and the push-to-pass
process device are provided in that order.
[0088] 60. The manufacturing line for manufacturing a high
dimensional accuracy pipe, described in 59. above, wherein a
cutting device cutting the pipe into short pipes is further
provided at an inlet side of the pipe-end grinding device.
[0089] 61. The manufacturing line for manufacturing a high
dimensional accuracy pipe, described in 59. or 60. above, wherein,
instead of the lubricant immersion coating bath and the drying
device, at an inlet side of the die of the push-to-pass process
device, a lubricant spray coating device for coating the pipe with
a lubricant by spraying or a lubricant spray coating and drying
device in which the pipe is coated with a lubricant by spraying and
is then dried is provided.
[0090] 62. The manufacturing line for manufacturing a high
dimensional accuracy pipe, described in one of 59. to 61, wherein,
in addition to the push-to-pass process device, at least one of a
die exchange device exchanging the die, a plug exchange device
exchanging the plug, and a bending prevention device preventing
pipe bending at an outlet side of the die is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0091] FIG. 1 is a view for illustrating an embodiment of a
push-to-pass process of the present invention.
[0092] FIG. 2 is a view for illustrating an embodiment of a
conventional drawing process.
[0093] FIG. 3A is a view for illustrating an embodiment of a
pressing process by a rotary forging device in which a conventional
segmented die is provided and is rocked, the view being a
cross-sectional view including a pipe central axis.
[0094] FIG. 3B is a cross-sectional view taken along the line A-A
for illustrating an embodiment of a pressing process by a rotary
forging device in which a conventional segmented die is provided
and is rocked.
[0095] FIG. 4 is a characteristic graph showing the relationship
between the stress and endurance cycles in a fatigue test.
[0096] FIG. 5 is a vertical cross-sectional view showing an example
of the present invention using caterpillars as pipe feeding
means.
[0097] FIG. 6 is a vertical cross-sectional view showing an example
of the present invention using endless belts as pipe feeding
means.
[0098] FIG. 7 is a vertical cross-sectional view showing an example
of the present invention using intermittent feeding devices as pipe
feeding means.
[0099] FIG. 8 is a vertical cross-sectional view showing an example
of the present invention using grooved rolls as pipe feeding
means.
[0100] FIG. 9 is a view illustrating corn angles of parts of a
plug.
[0101] FIG. 10 is a cross-sectional view showing the outline of a
push-to-pass process.
[0102] FIG. 11 is a schematic view showing an embodiment of a
method according to the present invention using a first example of
an apparatus of the present invention.
[0103] FIG. 12 is a schematic view showing an embodiment of a
method according to the present invention using a second example of
an apparatus of the present invention.
[0104] FIG. 13 is a view for illustrating a comparative example
(die is exchanged by hand).
[0105] FIG. 14 is a perspective view showing one of examples of the
present invention.
[0106] FIG. 15 is a plan view showing one example of fine
adjustment means for adjusting pipe bending, according to the
present invention.
[0107] FIG. 16 is a cross-sectional view showing one example of a
hole body-moving mechanism according to the present invention.
[0108] FIG. 17 is a perspective view showing one of examples
according to the present invention.
[0109] FIG. 18 is a plan view showing one example of fine
adjustment means for adjusting pipe bending, according to the
present invention.
[0110] FIG. 19 is a perspective view showing one of comparative
examples.
[0111] FIG. 20 is a perspective view showing one of comparative
examples.
[0112] FIG. 21 is a perspective view showing one of comparative
examples.
[0113] FIG. 22 is a schematic view showing the arrangement of a
manufacturing line which is one example of the present
invention.
[0114] FIG. 23 is a schematic view showing the arrangement of a
manufacturing line and pre-treatment processes required for a
drawing process, according to one comparative example.
BEST MODE FOR CARRYING OUT THE INVENTION
[0115] In a conventional cold drawing method, when a metal pipe is
drawn out using a die and a plug, it has been difficult to improve
the dimensional accuracy of the pipe. The reason for this is that
since a drawing force works as a tensile force, the contact between
the die and the exterior surface of the pipe and that between the
plug and the interior surface of the pipe in a processing tool
become insufficient. As shown in FIG. 2, when a plug 1 is charged
in a pipe 5, and the pipe 5 is drawn out through a hole provided in
a die 2, by a drawing force 9 applied at an outlet side of the die
2, a tensile stress is generated inside the processing tool, and as
a result, irregularities are generated and increased on the
interior and the exterior surfaces of the pipe from an inlet side
to an outlet side of the processing tool. In addition, at the inlet
side of the processing tool, since the interior surface of the pipe
is deformed along the plug 1, contact of the exterior surface of
the pipe is not substantially made or is only slightly made. At the
outlet side of the processing tool, since the exterior surface of
the pipe is in contact with the die 2 and is deformed, the contact
of the interior surface of the pipe is not substantially made or is
only slightly made. Hence, on both the interior and the exterior
surfaces of the pipe, since portions which can be freely deformed
are present, irregularities cannot be sufficiently smoothed, and as
a result, the dimensional accuracy of the pipe obtained by drawing
was inferior.
[0116] Compared to the method described above, according to the
push-to-pass method of the present invention, as shown in FIG. 1,
the plug 1 is charged in the pipe 5, and the pipe 5 is pushed in
the hole provided in the die 2 and is then allowed to pass
therethrough. By a pushing force 8 applied at an inlet side of the
die 2, a compressive force works entirely in the processing tool.
As a result, even at the inlet and outlet sides of the processing
tool, the pipe 5 can be sufficiently brought into contact with the
plug 1 and die 2 along the entire circumferential direction in the
same cross-section. In addition, even at a small diameter reduction
rate, since a compressive strength is generated inside the
processing tool, compared to the drawing, the contact between the
pipe and the plug and that between the pipe and the die are made
along the entire circumferential direction in the same
cross-section. Hence, the pipe is likely to be smoothed, and as a
result, a high dimensional accuracy pipe can be obtained.
[0117] As a result, when the fatigue strengths of these pipes are
compared with each other, the pipe manufactured by the push-to-pass
can obtain a targeted sufficient fatigue strength as compared to
that of the pipe manufactured by the conventional drawing. In
addition, in the case of the push-to-pass, even at a small diameter
reduction rate, since smoothing of the interior and exterior
surfaces of the pipe can be performed, strain caused by the
push-to-pass is not increased as compared to that of the drawing;
hence, a heat treatment load after the diameter reduction is small,
and the manufacturing cost can also be decreased.
[0118] In a pressing process performed by using a conventional
rotary forging device 8 shown in FIG. 3, since the process is
performed by rocking 12 a die which is a segmented die 9 formed by
dividing an all-in-one type die in the circumferential direction,
steps are formed, and as a result, the accuracy in thickness cannot
be satisfactorily improved. On the contrary, according to the
present invention, the steps described above are not generated at
all, and as a result, the interior and the exterior surfaces of the
pipe can be smoothed, thereby obtaining a sufficient fatigue
strength. In the present invention, for example, the steps may be
eliminated by using an all-in-one type die, or alternatively, the
formation of the steps caused by rocking rotation may be prevented
by using a fixed die. Of course, an all-in-one fixed type die may
be used for preventing the formation of the steps.
[0119] Furthermore, compared to the method in which a die is rocked
by using a conventional rotary forging device, since the device
structure can be simplified in the present invention, a sufficient
load required for processing can be applied, and in addition,
sufficient processing can be performed even when a load is
increased in the case in which the thickness at the outlet side of
the die is formed equivalent to or less than that at the inlet side
thereof. Hence, in response to wide requirements of sizes, high
dimensional accuracy pipes having a sufficient fatigue strength can
be obtained.
[0120] In the past, as a method for decreasing the deviations of
the outer diameter, inner diameter, and thickness in the
circumferential direction to 3% or less, a method by machining
(process including removal of parts of materials) has been known;
however, the process cost was considerably increased, the process
efficiency was inferior, and a long metal pipe having a small
diameter was difficult to be processed. Hence, it has been
difficult to apply the method described above to automobile parts
such as a drive shaft.
[0121] As a method for discriminating the above metal pipe
processed by machining from this metal pipe (as-processed metal
pipe obtained by the push-to-pass of the present invention), a
method for observing the surface of the pipe may be mentioned by
way of example, and by this method, the discrimination can be made.
The reason for this is that a black skin adheres to the surface of
this metal pipe, which skin is generated in pre-steps, such as
heating and rolling, for the manufacturing, and on the contrary, on
the surface of the pipe formed by machining, a black skin is not
present since it was removed thereby.
[0122] Furthermore, in terms of thickness deviation, this metal
pipe is outstandingly superior to that manufactured by the
conventional method (for example, see Patent Documents 1, 2, and 3)
by a process of pressing a pipe in a die using a rotary forging
device. That is, in the past, a metal pipe as processed by
push-to-pass has not been obtained in which at least one of the
deviations of the outer diameter, inner diameter, and thickness in
the circumferential direction is 3% or less.
[0123] In the present invention, the deviations of the outer
diameter, inner diameter, and thickness in the circumferential
direction are obtained as follows.
[0124] The deviation of the outer diameter (or inner diameter) is
calculated as the maximum deviation with respect to a target outer
diameter (or target inner diameter) from the distribution data of
the outer diameter (or inner diameter) in the circumferential
direction measured by rotating a pipe while a micrometer is being
in contact with the exterior surface (or interior surface) thereof.
Alternatively, from the distribution data in the circumferential
direction of the distance between a laser generator and a measured
pipe, the exterior surface (or interior surface) of which is
irradiated with laser light, the deviation is calculated as the
maximum deviation with respect to the target outer diameter (or
target inner diameter). In addition, by performing image analysis
of a cross-section of the pipe in the circumferential direction,
the deviation from a perfect circle is calculated in the
circumferential direction, so that the deviation of the outer
diameter (inner diameter) may be obtained.
[0125] The deviation of the thickness in the circumferential
direction is calculated as the difference between the distribution
data of the outer diameter in the circumferential direction and
that of the inner diameter in the circumferential direction, or is
directly measured as the maximum deviation with respect to the
target thickness from an image of the cross-section of the
thickness obtained by an image analysis of the cross-section of the
pipe in the circumferential direction.
[0126] In addition, the measurement is performed at optional places
with intervals of 10 mm or less except for areas 150 mm from the
front and back ends of the pipe, and the deviation is obtained from
values measured at 10 places or more.
[0127] That is, the deviations of the outer diameter, inner
diameter, and thickness (=deviation of the thickness in the
circumferential direction) are defined as follows. Deviation of
outer diameter: (maximum outer diameter-minimum outer
diameter)/target outer diameter (or average outer
diameter).times.100 (%) Deviation of inner diameter: (maximum inner
diameter-minimum inner diameter)/target inner diameter (or average
inner diameter).times.100 (%) Deviation of thickness: (maximum
thickness-minimum thickness)/target thickness (or average
thickness).times.100 (%)
[0128] Since being a metal pipe in which at least one of the three
dimensional accuracy indexes is 3.0% or less, the high dimensional
accuracy pipe of the present invention can be used as a metal pipe
for drive train parts for automobile required to have a high
dimensional accuracy of 3.0% or less.
[0129] In addition, in the conventional rotary press forging method
shown in FIGS. 3A and 3B, since a die 4 is composed of segmented
parts and is rocked 12 while it is being used, due to steps formed
by the die segmentation, or non-uniform deformation under high
stress conditions caused by difference in rigidity of the die in
the circumferential direction, the deviation of the thickness in
the circumferential direction cannot be satisfactorily
improved.
[0130] Compared to the case described above, according to the
push-to-pass of the present invention, since the die is an
all-in-one type die and is not necessary to be rocked, non-uniform
deformation is not generated, and as a result, the interior and the
exterior surfaces of the pipe can be smoothed.
[0131] Furthermore, in the conventional rotary press forging
method, since the pipe 5 must be fed cooperatively with the rock 12
of the die 4, a rocking speed cannot be increased more than a
predetermined value due to an impact load limit of the die, and
hence the process efficiency is low. In addition, in the
conventional drawing, since it has been necessary to strongly hold
the front end of the pipe and to apply a tensile force thereto, the
pipe must be drawn after the front end of the pipe is narrowed;
hence, the processing must be performed for one pipe at a time, and
as a result, the process efficiency has bee extremely low.
[0132] On the other hand, in the present invention, since the
push-to-pass is used, and the plug is being floated, by using pipe
feeding means 3, a pushing force 15 is applied to the pipe from the
inlet side of the die, and pipes can be continuously fed in the
die. Hence, compared to the case in the past, a highly
efficient-process can be performed. In this case, the "continuous
feeding" indicates the case in which one pipe 5 and the following
pipe 5 are continuously fed without any interval interposed
therebetween as shown in FIG. 1, and a method for moving a pipe
member in a pipe traveling direction may be performed in a
continuous movement manner or in an intermittent movement manner in
which a stop time is decreased as small as possible.
[0133] As preferable pipe feeding means 3, for example, there may
be mentioned caterpillars 13 (small pieces holding the pipe
connected to each other to form an endless track; see FIG. 5)
holding the pipe 5 before processing, endless belts 14 (see FIG. 6)
holding the pipe 5 before processing, intermittent feeders 15 (see
FIG. 7) holding and alternately and intermittently feeding pipes
before processing, a press (not shown in the figure) sequentially
pushing pipes before processing, and grooved rolls 16 (see FIG. 8)
holding the pipe before processing. The pipe feeding means 3 may be
formed in combination of at least one of those described above.
[0134] The pipe feeding means is most appropriately selected in
consideration of the size (diameter, length, and thickness) of the
pipe, a force required for performing the push-to-pass of the pipe,
a length required for the pipe after the push-to-pass process, and
the like, and in addition, it is also important to ensure a
necessary push-to-pass force while faults are being prevented which
are caused when the pipe is sandwiched and/or held.
[0135] When the pipe before processing is held between grooved
rolls, since the push-to-pass force is easily ensured while faults
are prevented from being generated on the pipe, it is preferable to
use the structure in which two or more grooved rolls are used,
and/or the structure in which at least two stands each having a
grooved roll are provided.
[0136] In addition, when the plug is being floated, although the
push-to-pass conditions are varied which complicatedly relate to
angles of the die and plug, lubrication conditions of the surfaces
of the die and plug, and the like, the plug is always stably
present at a position to which a compressive stress is applied, and
hence superior dimensional accuracy can be obtained.
[0137] In addition, in manufacturing a high dimensional accuracy
pipe, when lubrication occurs between the exterior surface of the
plug and the interior surface of the pipe and between the interior
surface of the die and the exterior surface of the pipe, since
faults such as burn marks are not generated on the surface of the
pipe in processing, a pipe having superior surface quality can be
manufactured. Furthermore, sine the friction force is decreased by
the lubrication, a load required for processing can be decreased,
process energy can also be decreased, and in addition, the
production efficiency is also improved.
[0138] Through research on various lubrication methods carried out
by the inventors of the present invention, the following method was
discovered and was defined as an essential method of the present
invention. That is, on one of the interior surface and the exterior
surface of the pipe or both of them, lubricant films are formed
beforehand, and the push-to-pass is then performed. As a lubricant
used for the lubricant film, any one of liquid lubricants,
grease-based lubricants, and drying lubricants is preferably used.
As the liquid lubricants, for example, there may be mentioned a
mineral oil, a synthetic ester, a plant and animal oil, and a
mixture containing at least one of the aforementioned lubricants
and an additive. As the grease-based lubricants, for example, there
may be mentioned a Li-based grease lubricant, a Na-based grease
lubricant, and a mixture containing at least one of the
aforementioned lubricants and an additive such as molybdenum
disulfide. As the drying lubricants, for example, there may be
mentioned a polyacrylic resin, epoxy resin, polyvinyl resin, and
polyester resin.
[0139] In a method for forming a lubricant film using the resin
mentioned above, the resin, a liquid containing the resin diluted
with a solvent, or an emulsion of the resin is applied to the pipe.
Subsequently, drying is preferably performed using a hot wind or by
air-drying. As the solvent for diluting the resin mentioned above,
for example, ethers, ketones, aromatic hydrocarbons, linear and
branched hydrocarbons may be mentioned. As a dispersion medium for
forming the emulsion of the above resin, for example, water,
alcohols, and the mixtures thereof may be mentioned.
[0140] As a method for more efficiently manufacturing a high
dimensional accuracy pipe, an electric-resistance welded steel pipe
formed by performing electric welding of an as-hot rolled steel
sheet or a seamless steel pipe as heated in a furnace may be
processed without removing oxide scales, and by the method
described above, the process cost can be decreased.
[0141] In the conventional cold drawing method and rotary press
forging method, only the diameter reduction is performed. From raw
pipes having the same size, only a specific one degree of
processing can be obtained, and pipes having the same outer
diameter and different degrees of processing can be hardly
manufactured. On the other hand, according to the present
invention, as shown in FIG. 1, the plug 1 is formed so as to have a
pipe expanding portion 1A expanding the pipe 4 and a diameter
reducing portion 1B reducing the diameter of the expanded pipe 4 in
cooperation with the die 2. Accordingly, by the use of the raw
pipes having the same size, pipes having a predetermined size and
different degrees of processing can be manufactured. The reason for
this is as follows. Even when the sizes of the raw pipe and the
pipe after the push-to-pass process are individually set to
predetermined levels, by adjusting the pipe expansion rate at the
expanding portion of the plug, the diameter reduction rate by the
diameter reducing portion of the plug is inevitably increased or
decreased, and as a result, the degrees of processing of the pipes
to be obtained are different from each other. Pipe expansion
rate=1-D0/D1 Diameter reduction rate=1-D2/D1
[0142] In the above equations,
[0143] D0 indicates the outer diameter of the raw pipe,
[0144] D1 indicates the target outer diameter after pipe expansion,
and
[0145] D2 indicates the target outer diameter after diameter
reduction.
[0146] In addition, according to the present invention, in order to
increase the production efficiency, sequential and continuous feed
of pipes is preferably performed. In this case, when the plug is
supported from the inlet side or the outlet side of the die, means
such as a bar or a wire used for the above support may become an
obstruction, and as a result, it becomes difficult to continuously
supply pipes. Hence, the plug is preferably floated in the
pipe.
[0147] In addition, in order to stably perform the push-to-pass
process of the present invention, the plug must be stabilized in
processing. That is, the plug must be stabilized not to be deviated
from an appropriate position with respect to the die. Research has
been made on this point. The plug receives a surface pressure from
the pipe by the pipe expansion and the diameter reduction. When the
surface pressure at the diameter reduction side is set larger than
that at the pipe expansion side, it was found that the stability of
the plug can be obtained. As one of methods for increasing the
surface pressure at the diameter reduction side than that at the
pipe expansion side, as shown in FIG. 9, a corn angle .theta.A of
the pipe expanding portion 1A of the plug 1 is effectively set
smaller than a corn angle .theta.B of the diameter reducing portion
1B. In this case, the corn angle of the portion of the plug
indicates an angle formed between the surface of the plug at that
portion and a linear line 17 parallel to the plug central axis set
along the pipe traveling direction. In addition, preferably,
.theta.A=0.3 to 35.degree. and .theta.B=3 to 45.degree. hold. As
another method, the diameter reduction rate is preferably set
larger than the pipe expansion rate, and for this purpose, the
outside diameter of the pipe at the outlet side of the die is
effectively set smaller than the outside diameter of the pipe at
the inlet side.
[0148] In the present invention, since an all-in-one type fixed die
can be used, steps caused by die segmentation and non-uniform
deformation in the circumferential direction do not occur at all.
As a result, the interior surface and the exterior surface of the
pipe can be smoothed. In addition, by the use of the all-in-one
fixed type die, a sufficient load can be applied in processing.
Although the load is increased when the thickness at the outlet
side of the die is set to equal to or smaller than that at the
inlet side, processing can be sufficiently performed. As a result,
a superior high dimensional accuracy pipe can be obtained. By using
raw pipes having the same size, the range of sizes of product pipes
which can be manufactured is increased. However, in order to stably
perform the push-to-pass process, plugs and dies must be used which
satisfy requirements discovered by the inventors of the present
invention. The requirements mentioned above are that the angle (:
angle of plug diameter-reducing portion) formed between the surface
of the diameter reducing portion of the plug and the processing
central axis is set to 5 to 400, the length (:length of plug
diameter-reducing portion) of the same portion is set to 5 to 100
mm, and the angle (:angle of die) formed between the interior
surface of the hole in the die at the inlet side and the processing
central axis is set to 5 to 40.degree.. In addition, more
preferably, the length (: plug bearing portion length) of a bearing
portion of the plug is set to 5 to 200 mm. In the case of the plug,
the processing central axis is the axis which is perpendicular to
the cross-section in the diameter direction of the plug and is
allowed to pass through the center of the cross-section described
above, and in the case of the die, the processing central axis is
the axis which is perpendicular to the cross-section in the
diameter direction of the die hole and is allowed to pass through
the center of the cross-section described above. In addition, the
bearing portion is a cylindrical portion ranging to the minimum
diameter part of the diameter reducing portion.
[0149] The reasons the plug and the die are defined as described
above are as follows.
(Angle of Plug Diameter-Reducing Portion: 5 to 40.degree.)
[0150] When the angle of the plug diameter-reducing portion is set
to less than 5.degree., the plug may pass through with the material
(: pipe) in some cases, and on the other hand, when the angle of
the plug diameter-reducing portion is set to more than 40.degree.,
the plug and the material clog the die, so that the push-to-pass
process may not be carried out in some cases.
(Length of Plug Diameter-Reducing Portion: 5 to 100 mm)
[0151] When the length of the plug diameter-reducing portion is set
to less than 5 mm, the plug may pass through with the material in
some cases. On the other hand, when the length of the plug
diameter-reducing portion is set to more than 100 mm, since the
friction force between the plug and the material is increased, both
of them clog the die, so that the push-to-pass process may not be
carried out in some cases.
(Angle of die: 5 to 40.degree.)
[0152] When the angle of the die is set to less than 5.degree., the
plug charged in the material may pass through together therewith in
some cases, and on the other hand, when the angle of the die is set
to more than 40.degree., the plug and the material clog the die, so
that the push-to-pass process may not be carried out in some
cases.
(Length of Plug Bearing Portion: 5 to 200 mm)
[0153] By a reaction force of the material and the die applied to
the diameter reducing portion of the plug, a force is applied to
the plug so as to pass it to the inlet side of the die; hence, a
force which pushes the plug to the outlet side of the die and which
is balanced with the reaction force described above must be applied
so as to place the plug in a stable state. For this purposes, the
bearing potion is preferably provided for the plug so that a
friction force working on the surface thereof is used. According to
research by the inventors of the present invention, in order to use
this friction force for sufficient stabilization of the plug, the
length of the plug bearing portion is preferably set to 5 to 200
mm. When the length of the plug bearing portion is less than 5 mm,
the friction force pushing the plug is insufficient, and by the
reaction force of the material and the die, the plug is liable to
be pushed back toward the inlet side of the die. On the contrary,
when the length of the plug bearing portion is more than 200 mm,
since the friction force is excessively large, the plug is liable
to be pushed to the outlet side of the die. Hence, in both cases,
the position of the plug becomes unstable.
[0154] In addition, in the present invention, since the plug is
being floated, even when the push-to-pass conditions are varied
which complicatedly relate to the angles of the die and plug, the
lubrication conditions of the surfaces of the die and plug, and the
like, the plug can be placed at a position at which a stable
compressive stress state can be obtained. In addition, since the
stability of the push-to-pass process can be further improved, it
is preferable that the thickness at the outlet side of the die be
set to equal to or less than the thickness at the inlet side.
[0155] When the push-to-pass process is performed, it may occur in
some cases that the pipe is clogged with the plug, and that the
load is increased. In the case described above, a raw pipe pushed
in may be buckled, and as a result, the process may not be carried
out in some cases. Accordingly, in order to stably perform the
push-to-pass process, the buckling of the raw pipe must be
prevented beforehand. Hence, the inventors of the present invention
focused on the load during the push-to-pass process. That is, when
the plug clogs the pipe, the load in the push-to-pass process
direction is extremely increased; hence, when this load is not more
than a specific value, the push-to-pass process can be performed.
When the load is more than the specific value, it is determined
that this push-to-pass process cannot be further continued, and in
this case, the push-to-pass conditions may be changed to optimum
conditions. This specific value is called a push-to-pass load
limit.
[0156] In the case in which the push-to-pass process cannot be
performed, since the raw pipe pushed in the die is buckled, when
the push-to-pass load limit is obtained from an equation
representing the buckling of the pipe, the stable push-to-pass
process can be performed at a load not more than the load limit. As
the equation representing the buckling of the pipe, Euler's
equation obtained from the elastic modulus of materials has been
well known. However, according to the investigation by the
inventors of the present invention, values apparently different
from those of the actual phenomenon were obtained, and hence, the
equation described above cannot be used at all. Accordingly,
through research on various equations relating to the buckling, it
was found that the following equation 4 most appropriately
represents the actual phenomenon.
.sigma..sub.k.times.cross-sectional area of raw pipe [Equation
1]
[0157] In the above equation, the following equations hold, and
reference labels indicate as follows.
.sigma..sub.k=YS.times.(1-.alpha..times..lamda.), .lamda.=(L/ n)/k,
a=0.00185 to 0.0155,
[0158] L: Length of raw pipe,
[0159] k: Secondary diameter of cross-section
[0160] k.sup.2=(d.sub.1.sup.2+d.sub.2.sup.2)/16,
[0161] n: Pipe end conditions (n=0.25 to 4),
[0162] d.sub.1: Outer diameter of raw pipe,
[0163] d.sub.2: Inner diameter of raw pipe, and
[0164] YS: Yield strength of raw pipe
[0165] In order to stably perform the push-to-pass process, when a
load (measured load) measured in the push-to-pass direction is not
more than the value (calculated value) of the equation 4, the
push-to-pass process may be continued. When the measured load
exceeds the above value, after the process is once stopped, the
conditions are changed, and the process may be again started.
[0166] However, since the equation 4 is relatively complicated,
when it is desired that the determination be more easily made, the
following equation 5 which is obtained by simplifying the equation
4 may be used. Yield strength YS of raw pipe.times.cross-sectional
area of raw pipe [Equation 5]
[0167] By the equation 5, although the push-to-pass load limit is
increased by up to approximately 10 percent as compared to that by
the equation 4, the inventors of the present invention understood
that sufficient determination can be simply made by the value thus
obtained.
[0168] In addition, when a raw pipe having an extremely short
length (such as a length of approximately 0.2 m or less) is
processed by the push-to-pass, or when the process is forcedly
performed in a very short period of time in which even when the
pipe is buckled to a certain extent, the load is increased by
increasing the processing speed to a level at which the die may not
be cracked, the following equation 6 may also be used. Tensile
strength TS of raw pipe.times.cross-sectional area of raw pipe
[Equation 6]
[0169] In the case described above, as a measurement method of the
measured load (actual load in the push-to-pass direction), for
example, a method using a load cell provided at a punch of the
push-to-pass, or a method using a load cell integrated with a die
which is floated from a platform is preferably used.
[0170] When the measured load exceeds the calculated load obtained
by using one of the equations 4 to 6, that is, when the execution
of the process is regarded as impossible, the push-to-pass process
is temporarily stopped, and after the die and/or the plug is
exchanged to that having a different shape and being in conformity
with the same product pipe dimension, the process may be restarted.
In the case described above, since the die and/or the plug having a
different shape in conformity with the same product pipe dimension
is used for processing raw pipes identical to that used before,
selection may be performed from that having the same diameter
reduction rate.
[0171] In addition, in order to obtain more stable process
conditions, according to research carried out by the inventors of
the present invention, it was found that the angles (see FIG. 10)
of the plug and die to be used after the exchange are preferably
smaller that that of those used before the exchange.
[0172] In order to obtain even more stable process conditions, the
type of lubricant applied to the raw pipe may be changed. However,
when a method is performed in view of convenience in which a
lubricant is applied by immersing a raw pipe into a coating bath
containing a lubricant, for example, since the exchange of the
lubricant may take a lot of time, it is difficult to frequently
change the type of lubricant. Hence, as for the lubricant, it is
important that, by experiments performed beforehand, a material be
selected which has properties capable of significantly decreasing
the load in the push-to-pass direction.
[0173] Compared to the case described above, in the case of the
push-to-pass of the present invention, as shown in FIG. 1, the plug
1 is charged in the pipe 4, and the pipe 4 is pushed in the hole
provided in the die 2 and is then allowed to pass therethrough. In
this step, the plug can be in contact with the entire circumference
of the interior surface of the pipe in the processing tool and the
hole can be in contact with the entire circumference of the
exterior surface of the pipe in the processing tool. By a pushing
force 11 applied at the inlet side of the die 2, a compressive
force works entirely inside the processing tool. As a result, at
both the inlet and outlet sides of the processing tool, the pipe 4
can be sufficiently brought into contact with the plug 1 and die 2.
In addition, even at a small diameter reduction rate, since the
compressive strength is generated inside the processing tool,
compared to the drawing, the contact between the pipe and the plug
and that between the pipe and the die are likely to be sufficiently
made. Hence, the pipe is likely to be smoothed, and as a result, a
high dimensional accuracy pipe can be obtained. In addition, in the
case of the push-to-pass, smoothing of the interior and the
exterior surfaces of the pipe can be performed even at a small
diameter reduction rate, and the processing strain is small as
compared to that of the drawing; hence, a load of heat treatment
performed after the diameter reduction is small, or the heat
treatment may be omitted, and as a result, the manufacturing cost
is decreased.
[0174] Hence, the structure of the apparatus of the present
invention has the plug 1 contactable with the entire circumference
of the interior surface of the metal pipe 4, the die 2 having the
hole contactable with the entire circumference of the exterior
surface of the metal pipe 4, and a pipe pushing device 3 pushing
the metal pipe 4, and the push-to-pass can be performed in which,
while the plug 1 is being charged in the pipe, the metal pipe 4 is
pushed in the hole provided in the die 2 by the pipe pushing device
3 and is then allowed to pass therethrough.
[0175] In addition, in a pressing process using the conventional
rotary forging device 8 shown in FIG. 3, since the segmented die 9
formed by dividing an all-in-one type die in the circumferential
direction is used, and in addition, the segmented die 9 is rocked
12, steps are formed due to the segmentation, or non-uniform
deformation is generated under high stress conditions due to the
difference in rigidity of the die in the circumferential direction,
the accuracy of the thickness cannot be satisfactorily improved. On
the contrary, according to the apparatus formed to be capable of
performing the push-to-pass of the present invention, since the
metal pipe is allowed to pass through the hole provided in the die,
which hole can be in contact with the entire circumference of the
exterior surface of the pipe in the same cross-section, the steps
formed by the use of the segmented die are not generated at all,
and as a result, smoothing of the interior and the exterior
surfaces of the pipe can be performed.
[0176] Furthermore, in the present invention, as the die, an
all-in-one type die is used. Compared to the conventional method
using a segmented die fitted to a rotary forging device, the
structure of the apparatus can be simplified. A sufficient load
required for processing can be applied, and even when the load is
increased since the thickness at the outlet side of the die is
formed equivalent to or less than that at the inlet side,
sufficient processing can be performed. Hence, in response to wide
requirements of sizes, pipes having significantly superior
dimensional accuracy can be obtained.
[0177] In addition, according to the present invention, the plug is
being floated. Even when the push-to-pass conditions, such as
angles of the die and plug, lubrication of the surfaces of the die
and plug, and the like, are complicatedly varied, the plug is
always stably located at a position at which the compressive stress
is applied. Hence, superior dimensional accuracy can be stably
obtained.
[0178] Furthermore, in the conventional drawing, since the front
end of the pipe must be narrowed so as to be drawn, the process
must be performed for one pipe at a time. On the other hand,
according to the present invention, it is not necessary to narrow
the front end of the pipe, and pipes themselves can be sequentially
pushed. When the plug is being floated, the push-to-pass can be
continuously performed, and hence the productivity is significantly
improved. In addition, when the length of the pipe is small, by
using a device performing intermittent pushing operation as the
pipe pushing device, high dimensional accuracy pipes can be
manufactured while a high productivity is being maintained. In this
case, the pipe pushing device may hold a body portion of the pipe
and push it or may push one end of the pipe.
[0179] Pipes which must be processed by the push-to-pass have
widely diverse product dimensions. In the push-to-pass, in order to
change the outer diameters of products, dies having different hole
sizes are prepare and must be exchanged whenever the outer diameter
of a product is changed. In addition, the hole dimension of the die
is generally represented by the diameter, angle, and length of a
tapered portion.
[0180] Since the dimensions of the outer diameters among products
are finely different from lot to lot by a several-ton unit at
minimum, at each change in dimension, a die which has been used
must be removed, and a die to be used must be fitted; however, the
die-fitting accuracy is very severe, such as .+-.0.1 mm units, and
hence considerable time and labor have been required.
[0181] For reducing the time and labor required for the die
exchange, the inventors of the present invention found the
solution. That is, the solution is that dies having various hole
sizes in conformity with the outer diameters of products are
prepared, are arranged in a predetermined manner, and are then
exchanged sequentially.
[0182] In a method for manufacturing a high dimensional accuracy
pipe by the push-to-pass in which a plug is charged in pipes and is
being floated, and the pipes are continuously or intermittently
pushed in a die, a plurality of dies having different hole sizes is
arranged in the same circumference. A die having a hole size in
conformity with a target product dimension is only rotated in the
circumferential direction of the arrangement to be disposed in a
pass line for performing the push-to-pass. When the product
dimension of the following pipe is different from that of the
preceding pipe, in the same manner as described above, a die having
a hole size in conformity with the outer diameter dimension of the
following pipe may also be rotated so as to be disposed in the pass
line for performing the push-to-pass.
[0183] As one example, as shown in FIG. 11, the die 2 through which
the pipe 4 is allowed to pass, a pushing device 2 pushing the pipe
4 in the die 2 placed in the pass line, and a plurality of dies 2,
20, - - - , 20 disposed in the same circumference are supported and
moved in the circumferential direction. When an apparatus having a
die rotating platform 19 which disposes one of the dies 2 in the
pass line is used, the process can be easily performed.
[0184] In addition, as another example, a plurality of dies having
different hole sizes is arranged on the same liner line, one of the
dies in conformity with the product dimension may be moved in the
linear line direction of the arrangement so as to be disposed in
the pass line for performing the push-to-pass.
[0185] In the case described above, for example, as shown in FIG.
12, the die 2 through which the pipe is allowed to pass, the
pushing device 2 pushing the pipe 4 in a die 3 placed in the pass
line, and a plurality of dies 2, 20, - - - , 20 disposed on the
same linear line are supported and moved in the linear line
direction. When an apparatus having a die linear-driving platform
23 which disposes one of the dies 2 in the pass line is used, the
process can be easily performed.
[0186] Furthermore, the charge of the plug must also be efficiently
performed. When the plug can be easily exchanged while the die is
being exchanged, the efficiency is further improved. Since
remaining in the die, the plug 1 used for the preceding process is
removed at the same time when the die is exchanged. A plug 22
necessary for the following step is preferably charged in the pipe
during the exchange of the die.
[0187] For the purpose described above, in one of the first and the
second methods of the present invention, when the production
dimension for the preceding pipe is changed to that for the
following pipe, after the push-to-pass is completed for the
preceding pipe, the following pipe is stopped at the inlet side of
the die. Before or after a die in conformity with the production
dimension for the following pipe is moved or during the movement
thereof, the plug 22 in conformity with the above production
dimension is preferably charged in the following pipe. Accordingly,
in addition to the die, the plug can also be efficiently
exchanged.
[0188] When the push-to-pass process is performed, the pipe at the
outlet side of the die is liable to be bent. When being bent, the
pipe cannot be formed into a product, and hence a technique for
performing the process without bending pipes is required. In the
conventional drawing, since the process is performed while a
tension is applied to each pipe by holding the front end thereof at
the outlet side of the die, although the process efficiency is low,
the pipe is unlikely to be bent since being guided in the drawing
direction. However, in the push-to-pass, the movement of the pipe
at the outlet side of the die is free, and depending on the forming
accuracy of the die, thickness accuracy and surface conditions of a
pipe before processing, and non-uniform lubrication states of the
die and plug, the pipe is liable to be bent. Hence, a technique
preventing the pipe from being bent at the outlet side of the die
has been seriously desired.
[0189] Accordingly, the inventors of the present invention carried
out experiments on bending of the pipe after the push-to-pass. In
the experiments, the pipe is guided through guide tubes provided at
the inlet and the outlet sides of the die. When the guide tube is
provided at one of the inlet and the outlet sides of the die, the
pipe becomes unlikely to be bent, when the tubes are provided at
both sides, the pipe becomes more unlikely to be bent, and when the
position of the guide tube is provided closer to the outlet of the
die, the pipe becomes more unlikely to be bent.
[0190] Accordingly, the guide tubes may be provided at the inlet
side of the die and at a position very close to the outlet side of
the die. That is, the guide tube is preferably provided at the
outlet side of the die and at a position very close thereto.
However, it was found that, depending on the bending direction of
the pipe, the bending cannot be sufficiently prevented in some
cases. In order to prevent the bending regardless of the bending
direction of the pipe, the space between the exterior surface of
the pipe and the interior surface of the guide tube must be
decreased to substantially zero. However, in the case described
above, it was found that since the pipe and the guide tube are too
much brought into contact, with each other, problems occur in that
faults are generated, a push-to-pass force is extremely increased,
and the like.
[0191] The inventors of the present invention understood that
bending of the pipe starts even at a position which is very close
to the outlet side of the die. That is, depending on the forming
accuracy of the die, thickness accuracy and surface conditions of a
pipe before processing, and non-uniform lubrication states of the
die and plug, a residual stress is generated in the pipe, and since
this residual stress is rapidly released at a position which is
very close to the outlet side of the die, the bending is liable to
occur. Hence, when fine adjustment means for adjusting the bending
direction of the pipe is provided at a position which is very close
to the outlet side of the die, the bending of the pipe can be
sufficiently prevented.
[0192] Through intensive research carried out by the inventors of
the present invention, at a position which is very close to the
outlet side of the die, fine adjustment means for adjusting pipe
bending is provided which has a hole body allowing the pipe to pass
therethrough, a support substrate supporting the hole body so as to
enable it to move in the plane perpendicular to the pipe traveling
direction, and a hole body-moving mechanism which is supported by
the support substrate and which moves the hole body. It was
understood that when the pipe at the outlet side of the die is
allowed to pass through the hole body, which is finely moved
beforehand in the plane of the support substrate by fine adjustment
of the hole body-moving mechanism so as to be placed at a position
in the plane perpendicular to the pipe traveling direction, pipe
bending can be sufficiently prevented.
[0193] For finely adjusting the position of the hole body, for
example, by using a plurality of dummy pipes is used before actual
production is performed, a push-to-pass process experiment is
performed in which the hole body position is changed several times
so that the pipe bending is measured, and the relationship between
the change amount of the position of the hole body and that of the
pipe bending after the push-to-pass is obtained. A method is
preferably used in which when the pipe bending in actual production
is about to exceed a predetermined threshold, the hole body is
moved to the direction so as to decrease the bending based on the
relationship described above.
[0194] As the hole body-moving mechanism, for example, a method is
preferably used in which at least one place of the peripheral
portion of the hole body is pushed in the direction perpendicular
to the pipe traveling direction through a tapered surface of a
wedge-shaped mold, the tapered surface being designed to be moved
in the pipe traveling direction by using a screw. Alternatively,
for example, a method is preferably used in which at least one
place of the peripheral portion of the hole body is directly pushed
or pulled in the direction perpendicular to the pipe traveling
direction using a fluid pressure cylinder (such as hydraulic
cylinder or air cylinder).
[0195] When the hole size of the hole body is formed larger than
the hole size of the outlet of the die, it is preferable since the
pipe is not blocked at the outlet side of the die, and the process
can be smoothly performed. In particular, when the hole size is
larger than that of the outlet of the die by +0 to +3 mm, it is
more preferable since fine adjustment can be easily performed. In
this case, the hole provided in the hole body may be either a
straight hole or a tapered hole.
[0196] Of course, in the support substrate, a hollow portion
through which the pipe is allowed to pass with a sufficient space
therebetween is provided at a position intersecting a path of the
pipe passing through the die.
[0197] In addition, at the inlet side of the die and/or an outlet
side of the fine adjustment means for adjusting pipe bending, when
a guide tube through which the pipe about to enter the die is
allowed to pass and/or a guide tube through which the pipe passing
through the fine adjustment means for adjusting pipe bending is
allowed to pass is provided, the pipe enters the die approximately
perpendicularly thereto and/or passes through the fine adjustment
means for adjusting pipe bending approximately perpendicularly
thereto, and it is preferable since the bending of the pipe can be
more easily prevented.
[0198] In addition, in the present invention, it is preferable that
pipes be continuously fed and pushed in the die. By continuously
feeding the pipes, compared to the case in which processing is
performed for one pipe at a time, heat generated by friction and
that generated by processing, which are applied to the die and
plug, are stabilized, and hence the bending can be more easily
prevented. In the push-to-pass, unlike the drawing, since a metal
pointing process is not required which enables a drawing device
provided at the outlet side of the die to hold the front end of the
pipe, pipes can be continuously fed by pushing the back end of the
preceding pipe with the front end of the following pipe, and hence
the production efficiency can be improved.
[0199] In the conventional drawing, a sufficient lubricant film is
necessary in order to obtain high dimensional accuracy, and hence
bonderizing treatment having superior lubrication has been
performed. A method therefor is performed by the steps of removing
oxide scales from a pipe by pickling, performing alkaline washing
for neutralization of an acid used in the above treatment, and then
performing water washing. Subsequently, the pipe is immersed in a
bath in which the bonderizing treatment is performed to form a
lubricant film, and is then immersed in a bath containing metal
soap to form a film, followed by drying of the pipe with a hot
wind. Accordingly, the steps described above take several hours or
more, and when the steps are incorporated in a manufacturing line
which performs drawing of pipes, the productivity is extremely
decreased; hence, the treatment has been performed in a different
process.
[0200] Compared to the case described above, according to the
push-to-pass process, even when the diameter reduction rate is
small, since high dimensional accuracy can be easily obtained, the
lubrication treatment of the pipe may be simply performed. That is,
the pipe may not be processed by pickling and may be simply dried
with a hot wind after coating of a lubricant is performed by
immersion. However, when the push-to-pass is continuously
performed, since the perpendicularity of the end surface of the
pipe is important, a grinding device for obtaining this
perpendicularity must be provided.
[0201] These treatment performed before the push-to-pass process
are most efficiently carried out when the steps of obtaining the
perpendicularly of the end surface of the pipe, applying the
lubricant thereto by immersion, and drying are performed in that
order. In the present invention, from the above point of view,
since a manufacturing line is formed in which a pipe end-grinding
device grinding the end surface of the pipe perpendicularly with
respect to the pipe axis direction, a lubricant immersion coating
bath for applying a lubricant to pipes by immersion, and a drying
device drying the pipes coated with the lubricant are provided in
that order at an inlet side of the push-to-pass device, high
dimensional accuracy pipes can be efficiently manufactured.
[0202] In addition, since the step of obtaining the perpendicularly
of the end surface of the pipe is more efficiently performed right
after the pipe is cut into short ones, in the manufacturing line of
the present invention, a cutting device cutting the pipe into short
ones is preferably provided at the inlet side of the pipe
end-grinding device.
[0203] In addition, as the lubricant, when a material which easily
forms a film by drying is used, instead of performing coating by
immersion at the inlet side of the push-to-pass device, followed by
drying, spray coating may be performed at a position very close to
the inlet side of the die in the push-to-pass process device,
followed by drying, or when lubricant properties are more superior,
by omitting the drying, the push-to-pass process may be performed
for a pipe coated with a lubricant which is still being in a wet
state. Hence, in the manufacturing line of the present invention,
instead of the lubricant immersion coating bath and the drying
device, there may be provided, at the inlet side of the die of the
push-to-pass device, a spray coating device spraying a lubricant to
the pipe or a lubricant spray coating and drying device for coating
the pipe with a lubricant, followed by drying.
[0204] In addition, in order to further improve the efficiently of
the push-to-pass process, it is preferable that the die and plug be
easily exchanged on-line, and that the pipe be controlled so as not
be bent at the outlet side of the die. In consideration of the
points described above, in the manufacturing line of the present
invention, in addition to the push-to-pass device, there is
preferably provided at least one of a die exchange device for
exchanging the die, a plug exchange device for exchanging the plug,
a bending prevention device for preventing the bending of the pipe
at the outlet side of the de.
[0205] The die (or plug) exchange device preferably has the
structure in that dies (or plugs) having different dimensions
(and/or shapes) are arranged in the order in which they are to be
used and are then sequentially moved to a predetermined place in a
pipe traveling line. The bending prevention device preferably has
the structure in that, for example, by using a movable disc or the
like having a hole through which the pipe is allowed to pass, a
force may be applied to a pipe at a place very close to the outlet
side of the die in the direction opposite to that in which the pipe
is about to be bent.
[0206] In addition, in both the drawing conventionally used and the
push-to-pass of the present invention, since pipes having a surface
processed by pickling may be frequently required after the above
process is completed, shipment is preferably carried out after
pickling is performed in a different process. In the drawing, when
the bonderizing treatment is performed before the process is
carried out, in order to form a strong film of a lubricant, raw
pipes must be processed by pickling, and after the drawing,
pickling must again be performed for removing the lubricant; hence,
pickling must be performed twice. Compared to the case described
above, in the push-to-pass process, simple lubrication treatment
may be performed before processing, and oxide scales may still
adhere to raw pipes. Hence, after being designed to be operated
on-line, the lubrication treatment can be incorporated in the
manufacturing line, and as a result, an efficient manufacturing
line can be realized at a reasonable cost.
EXAMPLE 1
[0207] Hereinafter, the present invention will be described in
detail with reference to examples.
[0208] In Example 1.1, a push-to-pass process having the structure
shown in FIG. 1 was performed for a steel pipe having an outer
diameter of 40 mm and a thickness of 6 mm. In this case, a plug
having a mirror surface which was to be brought into contact with
the interior surface of the pipe and a die which was an all-one-in
fixed die and has a mirror surface to be brought into contact with
the exterior surface of the pipe were used. The plug was fixed at
one end and was charged in the pipe. The process conditions were
set so that the thickness at the outlet side was made equal to that
at the inlet side, and the diameter reduction rate was set to
10%.
[0209] In Example 1.2, the process was performed in the same manner
as that in Example 1.1 except that the diameter reduction rate was
set to 5%.
[0210] In Example 1.3, the process was performed in the same manner
as that in Example 1.2 except that the plug was being floated.
[0211] In addition, as Comparative Example 1.1, the process was
performed in the same manner as that in Example 1.2 except that the
drawing was performed having the structure shown in FIG. 2 instead
of the push-to-pass having the structure shown in FIG. 1, and that
the thickness at the outlet side was set smaller than that at the
inlet side.
[0212] In addition, as 1.2, the process was performed in the same
manner as that in Example 1.2 except that instead of the all-in-one
fixed type die, a segmented die was incorporated in a rotary
forging device having the structure shown in FIG. 3 and was rocked,
and that instead of the push-to-pass process, a pressing process
was performed.
[0213] In addition, as Comparative Example 1.3, the process was
performed in the same manner as that in Comparative Example 1.2
except that the process conditions were changed so that the
thickness at the outlet side was set to equal to the thickness at
the inlet side +1 mm (=7 mm).
[0214] The three dimensional accuracy indexes of the above steel
pipes processed by diameter reduction were obtained, and the steel
pipes were subjected to a fatigue test. The results are shown in
Table 1.
[0215] In this case, the deviations of the outer and the inner
diameters shown in Table 1 were obtained by the measurement using
laser light described above, and from the difference in
distribution of the measured data in the circumferential direction,
the deviation of the thickness in the circumferential direction was
obtained, which is also shown in the same table as described
above.
[0216] In addition, a test for obtaining the number of repeated
cycles (that is, endurance cycles) until cracking is generated at a
constant stress is performed, and in FIG. 4, the relationship
between the number of endurance cycles and stress levels which are
variously changed is shown. In this figure, the number of cycles
until an endurance limit shown in Table 1 represent the number of
endurance cycles at an elbow point at which the stress in a
decreasing state is about to reach an approximately constant value
as the number of the endurance cycles is increased, and the fatigue
strength is more superior as the value described above is
increased. That is, in this example, the number of the endurance
cycles was at a stress of approximately 150 MPa.
[0217] As can be seen from Table 1, the pipe products of Examples
1.1 to 1.3 had significantly superior dimensional accuracy and the
most superior fatigue strength, and when the plug was being
floated, the dimensional accuracy was further improved (Example
1.3). On the other hand, in the conventional drawing, the
dimensional accuracy of the pipe product was degraded, and as a
result, the fatigue strength was also extremely decreased
(Comparative Example 1.1). In the pressing process by using the
rotary forging device, the dimensional accuracy of the pipe product
was degraded (Comparative Example 1.2), and when the thickness is
increased, the dimensional accuracy was further degraded
(Comparative Example 1.3); hence, a sufficient fatigue strength
could not be obtained.
EXAMPLE 2
[0218] As one example of the present invention, the push-to-pass
process was carried out in which a steel pipe 40 mm in diameter, 6
mm thick, and 5.5 m long was used as a raw material, a plug having
a mirror surface and an all-in-one fixed type die were used, the
plug was floated and charged in the steel pipe, the steel pipe was
pushed from the inlet side of the die at a diameter reduction rate
of 5%, and the thickness of the steel pipe at the outlet side of
the die was set to 6 mm which was equivalent to that at the inlet
side of the die. In this example, as pipe feeding means,
intermittent feeding device having the structure shown in FIG. 7
was used so that the pipes were continuously fed in the die.
[0219] In addition, as Comparative Example 2.1, drawing having the
structure shown in FIG. 2 was performed. In this example, the same
steel pipe as described above was used a raw material, the same
plug and die were used as above, the plug was charged in the steel
pipe, the steel pipe was drawn from the outlet side of the die at
the same diameter reduction rate as above, and the thickness of the
steel pipe at the outlet side of the die was decreased to 5.5
mm.
[0220] In addition, as Comparative Example 2.2, a rotary press
forging method having the structure shown in FIGS. 3A and 3B was
performed. In this example, the same steel pipe as described above
was used as a raw material, a rotary forging device was employed
which used a segmented die instead of the above all-in-one fixed
type die, the same plug as above was charged in the steel pipe, the
rotary press forging was performed at the same diameter reduction
rate as above, and the thickness of the steel pipe at the outlet
side of the forging device was increased to 7 mm.
[0221] The dimensional accuracy (deviation of the outer diameter,
deviation of the inner diameter, and deviation of the thickness in
the circumferential direction) of the steel pipes manufactured by
the methods of the above individual examples was measured, and the
process efficiency was also investigated. The results are shown in
Table 2. The deviation of the outer diameter and that of the inner
diameter were obtained by performing image analysis of the
cross-section of the pipe in the circumferential direction,
followed by calculation of the deviation from a perfect circle in
the circumferential direction. In addition, image analysis of the
cross-section of the pipe in the circumferential direction was
performed, and the deviation of the thickness in the
circumferential direction was directly measured as the maximum
deviation with respect to the average thickness from the image of
the cross-section of the thickness.
[0222] As can be seen from Table 2, the steel pipes manufactured by
the push-to-pass of the examples of the present invention had
significantly superior dimensional accuracy and also had superior
process efficiency. On the other hand, the steel pipe manufactured
by the drawing of Comparative Example 2.1 had degraded dimensional
accuracy. In addition, the steel pipe manufactured by the rotary
press forging of Comparative Example 2.2 also had degraded
dimensional accuracy. In addition, in both the drawing and the
rotary press forging, the process efficiency was very low.
EXAMPLE 3
Comparative Example 3.1
[0223] An electric-resistance welded pipe 40 mm in diameter, 6.0 mm
thick, and 5.5 m long having scales on the surface thereof caused
by hot rolling was processed by the push-to-pass shown in FIG. 1
under the following conditions A.
(Conditions A)
[0224] Plug: a plug having a mirror surface being charged in the
pipe and being floated. [0225] Die: an all-in-one fixed type die
[0226] Diameter reduction rate: 5% [0227] Thickness of the pipe at
the outlet side of the die: 6.0 mm (=the thickness at the inlet
side)
Example of Present Invention 3.1
[0228] Lubricant films were formed by applying a liquid lubricant
(mineral oil) onto the interior and exterior surfaces of the same
pipe as described above, and subsequently, the process was
performed in the same manner as that in Comparative Example
3.1.
Example of Present Invention 3.2
[0229] Lubricant films were formed by applying a grease-based
lubricant (lubricant composed of a Li-based grease lubricant and
molybdenum disulfide added thereto) onto the interior and exterior
surfaces of the same pipe as described above, and subsequently, the
process was performed in the same manner as that in Comparative
Example 3.1.
Example of Present Invention 3.3
[0230] Lubricant films were formed by applying a drying lubricant
(polyalkyl-based lubricant) onto the interior and exterior surfaces
of the same pipe as described above, followed by drying with a hot
wind (approximately 200.degree. C.), and subsequently, the process
was performed in the same manner as that in Comparative Example
3.1.
Example of Present Invention 3.4
[0231] Lubricant films were formed by applying a liquid obtained by
diluting a drying lubricant (polyalkyl-based lubricant) with a
solvent (acetone) onto the interior and exterior surfaces of the
same pipe as described above, followed by drying with a hot wind
(approximately 50.degree. C.), and subsequently, the process was
performed in the same manner as that in Comparative Example
3.1.
Example of Present Invention 3.5
[0232] Lubricant films were formed by applying an emulsion obtained
by dispersing a drying lubricant (polyalkyl-based lubricant) in a
dispersion medium (water) onto the interior and exterior surfaces
of the same pipe as described above, followed by drying with a hot
wind (approximately 70.degree. C.), and subsequently, the process
was performed in the same manner as that in Comparative Example
3.1.
Comparative Example 3.2
[0233] Lubricant films were formed by applying the same liquid
lubricant as that of Example 1 of the present invention onto the
interior and exterior surfaces of the same pipe as described above,
and subsequently, the process was performed by the cold drawing
method shown in FIG. 2 under the following conditions B.
(Conditions B)
[0234] Plug, die, diameter reduction rate: the same as those of the
conditions A [0235] Thickness of the pipe at the outlet side of the
die: 5.5 mm (<the thickness at the inlet side)
Comparative Example 3.3
[0236] Lubricant films were formed by applying the same liquid
lubricant as that of Example 1 of the present invention onto the
interior and exterior surfaces of the same pipe as described above,
and subsequently, the process was performed using the rotary press
forging method shown in FIG. 3 under the following conditions
C.
(Conditions C)
[0237] Plug: the same as that of the conditions A [0238] Die: a
segmented die [0239] Diameter reduction rate: the same as that of
the conditions A [0240] Thickness of the pipe at the outlet side of
the die: 7.0 mm (>the thickness at the inlet side)
[0241] Surface fault conditions and dimensional accuracy (deviation
of the outer diameter, deviation of the inner diameter, and
deviation of the thickness) were measured for the steel pipes
manufactured by the methods of the above individual examples, and
the results are shown in Table 3. The deviation of the outer
diameter and that of the inner diameter were obtained by performing
image analysis of the cross-section of the pipe in the
circumferential direction, and then calculating the maximum
deviation (that is, (maximum diameter-minimum diameter)/diameter of
the perfect circle.times.100%)) deviated from the perfect circle in
the circumferential direction. In addition, the deviation of the
thickness in the circumferential direction was obtained by
performing image analysis of the cross-section of the pipe in the
circumferential direction, and directly measuring the maximum
deviation (that is, (maximum thickness-minimum thickness)/average
thickness.times.100%)) with respect to the average thickness from
the image of the cross-section of the thickness.
[0242] As can be seen from Table 3, in all the examples of the
present invention in which the push-to-pass was performed under the
lubrication conditions, faults were not generated at all on the
surface of the steel pipe after the process, superior surface
quality was obtained, and the dimensional accuracy was also
significantly superior. On the contrary, in Comparative Example 3.1
in which the push-to-pass was performed under non-lubrication
conditions, faults were generated on the surface of the steel pipe
after the process. In Comparative Example 3.2 in which the process
was performed by the cold drawing method under the lubrication
conditions, the dimensional accuracy was degraded. In Comparative
Example 3.3 in which the rotary press forging was performed under
the lubrication conditions, the dimensional accuracy was further
degraded.
[0243] In the examples of the present invention described above,
the case of so-called double-sided lubrication was shown in which
the lubrication films were formed on the interior and the exterior
surfaces of the pipe; however, the present invention is not limited
thereto, and the case in which a lubricant film is formed on one of
the interior and the exterior surfaces of the pipe may also be
included. In the case of this one-sided lubrication, it is apparent
that the generation of faults on the surface on which the
lubrication film is formed can be effectively prevented.
EXAMPLE 4
Example of Present Invention
[0244] After steel pipes 40 mm in diameter, 6 mm thick, and 5.5 m
long was prepared as raw pipes, pipe expansion and diameter
reduction of this raw pipe were sequentially performed by the
process (push-to-pass using a plug capable of performing pipe
expansion and diameter reduction) of the present invention, the
brief structure of the process being shown in FIG. 1. A target
thickness at the outlet side. of the die was set to 6.0 mm which
was the same as that at the inlet side. A plug having a mirror
surface was floated in the pipe. An all-in-one fixed type die was
used as the die in which the interior surface of the die hole was
mirror finished. The pipe expansion rate, diameter reduction rate,
corn angles .theta.A and .theta.B of the pipe expanding portion and
the diameter reducing portion, respectively, and a target outer
diameter D2 of the pipe at the outer side (after diameter
reduction) of the die of each example were set to the values shown
in Table 4. The pipes were continuously fed to the die.
Comparative Example A
[0245] By the cold drawing method (: only diameter reduction could
be performed) shown in FIG. 2, the diameter reduction of the same
raw pipe as described above was performed. The target thickness at
the outlet side of the die was set to 6.0 mm which was the same as
that at the inlet side. A mirror finished plug was floated in the
pipe. An all-in-one fixed type die was used as the die in which the
interior surface of the die hole was mirror finished. The diameter
reduction rate and the target outer diameter of the pipe at the
outer side of the die of each example were set to the values shown
in Table 4. The pipes were continuously fed to the die.
Comparative Example B
[0246] By the rotary press forging method (: only diameter
reduction could be performed) shown in FIG. 3, the diameter
reduction of the same raw pipe as described above was performed.
The target thickness at the outlet side of the die was set to 6.0
mm which was the same as that at the inlet side. A mirror finished
plug was floated in the pipe. A segmented die was used as the die
in which the interior surface of the die hole was mirror finished.
The reduction rate and the target outer diameter of the pipe at the
outer side of the die of each example were set to the values shown
in Table 4. The pipes were continuously fed to the die.
[0247] The dimensional accuracy (deviation of the outer diameter,
deviation of the inner diameter, and deviation of the thickness) of
the steel pipes manufactured by the methods of the above individual
examples was measured. The deviation of the outer diameter and that
of the inner diameter were obtained by performing image analysis of
the cross-section of the pipe in the circumferential direction, and
then calculating the maximum deviation (that is, (maximum
diameter-minimum diameter)/diameter of the perfect
circle.times.1100%)) deviated from the perfect circle in the
circumferential direction. In addition, the deviation of the
thickness in the circumferential direction was obtained by
performing image analysis of the cross-section of the pipe in the
circumferential direction, and directly measuring the maximum
deviation (that is, (maximum thickness-minimum thickness)/average
thickness.times.100%)) with respect to the average thickness from
the image of the cross-section of the thickness. In addition, as
the index of the degree of processing, cross-sectional hardness was
measured. In addition, as the index for determining whether a pipe
having a predetermined size is obtained after processing or not,
the average outer diameter and the average thickness of the pipe
after processing were used, which were simultaneously obtained when
the measurement of the above dimensional accuracy was performed.
The results are shown in Table 4.
[0248] As can be seen from Table 4, all the examples according to
the present invention had significantly superior dimensional
accuracy after processing, and when the combination of the plug and
the die was changed, from raw pipes having the same size, pipes
having a predetermined size and having different degrees of
processing could be obtained. On the contrary, in the comparative
examples, the dimensional accuracy was degraded, and, in order to
obtain pipes having different degrees of processing from raw pipes
having the same size, pipes having a predetermined outer diameter
or thicknesses could not be obtained. In the example of the present
invention in which at least one of .theta.A<.theta.B and
D2<D0 was satisfied, the floating state of the plug in the pipe
was further stabilized.
[0249] In addition, the individual rates are defined as follows.
Pipe expansion rate a(%)=(D1-D0)/D1.times.100 Diameter reduction
rate b(%)=(D1-D2)/D1.times.100
EXAMPLE 5
Examples 5.1 to 5.4
[0250] After electric-resistance welded steel pipes 40 mm in outer
diameter and 6 mm thick were prepared as raw pipes, the raw pipe
was experimentally processed by the push-to-pass process shown in
FIG. 1 using a plug having a mirror surface and an all-in-one fixed
type die. Shape conditions (angle of plug diameter-reducing
portion, length of plug diameter-reducing portion, length of plug
bearing portion, and angle of die) of the plugs and the dies used
in these examples are shown in Table 5. The plug was floated in the
pipe. The thickness of the pipe at the outlet side of the die was
set to 5 mm.
Comparative Examples 5.1 to 5.4
[0251] By using steel pipes of the same lot as that of the example
of the present invention as raw pipes, the push-to-pass process was
experimentally performed in the same manner as that of the example
of the present invention except that the shape conditions of the
plug and die used in this example were changed as shown in Table
5.
Conventional Example 5.1
[0252] By using steel pipes of the same lot as that of the example
of the present invention as raw pipes, a process by the cold
drawing method shown in FIG. 2 was experimentally performed with a
plug having a mirror surface and an all-in-one fixed type die. The
shape conditions of the plug and the die used in this example are
shown in Table 5. The plug was floated in the pipe. The thickness
of the pipe at the outlet side of the die was set to 5 mm.
Conventional Example 5.2
[0253] By using steel pipes of the same lot as that of the example
of the present invention as raw pipes, a process by the rotary
forging press method shown in FIGS. 3A and 3B was experimentally
performed using a plug having a mirror surface and a rotary forming
device provided with a segmented die. The shape conditions of the
plug and the die used in this example are shown in Table 5. The
plug was floated in the pipe. The thickness of the pipe at the
outlet side of the die was increased to 7 mm.
[0254] Whether the productions by the methods of the above
individual examples can be executed or not were evaluated, and the
results are shown in Table 5. In addition, measured dimensional
accuracy (deviation of the outer diameter, deviation of the inner
diameter, and deviation of thickness) of product pipes produced by
the method evaluated as a method used for production are also shown
in Table 5. The deviation of the outer diameter and that of the
inner diameter were obtained by performing image analysis of the
cross-section of the pipe in the circumferential direction, and
then calculating the maximum deviation (that is, (maximum
diameter-minimum diameter)/diameter of the perfect
circle.times.100%)) deviated from the perfect circle in the
circumferential direction. In addition, the deviation of the
thickness in the circumferential direction was obtained by
performing image analysis of the cross-section of the pipe in the
circumferential direction, and directly measuring the maximum
deviation (that is, (maximum thickness-minimum thickness)/average
thickness.times.100%)) with respect to the average thickness from
the image of the cross-section of the thickness.
[0255] As can be seen from Table 5, in all the examples according
to the present invention, the push-to-pass process could be stably
performed, and the dimensional accuracy of the product pipes was
significantly superior. On the contrary, in the comparative
examples, the push-to-pass process could not be performed, and no
product pipes could be obtained. In addition, in the conventional
examples, although the process could be performed, the dimensional
accuracy of the product pipes was degraded.
EXAMPLE 6
Example 6.1
[0256] By using steel pipes of YS400MPa as raw pipes, which had an
outer diameter of 40 mm, a thickness of 6 mm, and a length of 5.5
m, manufacturing of a high dimensional accuracy pipe was
experimentally performed by the push-to-pass process having the
structure shown in FIG. 10 at a diameter reduction rate of 13%. At
the initial stage of the manufacturing, a die having an angle of
21.degree., and a plug having an angle of 21.degree. and a tapered
length of 11 mm were used. The plug was floated in the pipe. Onto
the raw pipes before processing, a lubricant was applied by
immersing the raw pipes in the lubricant in a coating bath. As the
lubricant, a solvent solution containing a quick drying polymer
lubricant was used.
[0257] In processing, the load in the push-to-pass direction was
always measured by the measurement method described above, and the
push-to-pass was performed while the measured load and the
calculated load obtained by using the equation 4 were being
compared with each other. In the equation 4 of this example, as the
values of a and n, 0.00185 and 1 (corresponding to the case in
which the pipe end condition is in free rotation) were used,
respectively, which were the optimum values obtained beforehand by
experiments.
[0258] When a second or later raw pipe was processed, since the
measured load exceeded the calculated load, the process was
determined not to be continued, and after the process was stopped,
the process conditions were changed as follows. That is, the die
and the plug were changed to a die having an angle of 11.degree.,
and a plug having an angle of 11.degree. and a tapered length of 20
mm, respectively. The process was then restarted after this
exchange, and the process for remaining raw pipes could be
performed without any difficulty.
[0259] When the above exchange and restart of the process were
performed, a part of the pipe in process at the inlet side of the
die and that at the outlet side were cut away, the pipe being
placed in the die used before the exchange. In addition, the die
used before the exchange was then removed from a predetermined
fitting place, in which a part of the pipe was still in the die
together with the plug used before the exchange. Subsequently, a
die to be used was fitted to the same predetermined fitting place
as above, and a plug to be used was charged in a raw pipe of the
same YS which was to be processed and which had the same size as
that used before, and the process was then restarted. In addition,
the part of the pipe which was located at the outlet side of the
die and was separated could be used as the product. The part of the
pipe at the inlet side of the die was scraped.
Comparative Example 6.1
[0260] By using the same steel pipes as that in Example 6.1 as raw
pipes, manufacturing of a high dimensional accuracy pipe was
experimentally performed by the push-to-pass process having the
structure shown in FIG. 10 at a diameter reduction rate of 13%. At
the initial stage of the manufacturing, a die having an angle of
21.degree., and a plug having an angle of 21.degree. and a tapered
length of 20 mm were used. The plug was floated in the pipe. Onto
the individual raw pipes before processing, a lubricant was applied
by immersing the raw pipes in the lubricant in a coating bath. As
the lubricant, a solvent solution containing a quick drying polymer
lubricant was used.
[0261] In processing, the measurement of the load in the
push-to-pass direction was not performed, and an operator was
delegated to judge whether the conditions were to be changed or not
in an abnormal situation.
[0262] In processing a second or later raw pipe, since the die was
cracked, after the process was interrupted, the die and the plug
were exchanged with the same as those used at the initial stage,
and the lubricant in the lubricant coating bath was totally changed
to a solvent solution containing a quick drying polymer lubricant
having a higher molecular weight. Subsequently, when the process
was restarted, in processing a second or later raw pipe from the
restart, the die was again cracked. Hence, the process was stopped,
and the process conditions were changed as follows. That is, the
die and the plug were changed to a die having an angle of
11.degree., and a plug having an angle of 11.degree. and a tapered
length of 20 mm, respectively. The process was restarted after this
exchange, and the process for remaining raw pipes could be
performed without any difficulty.
Comparative Example 6.2
[0263] By using the same steel pipes as that in Example 6.1 as raw
pipes, manufacturing of a high dimensional accuracy pipe was
experimentally performed by a drawing process at a diameter
reduction rate of 13%. At the initial stage of the manufacturing, a
die having an angle of 21.degree., and a plug having an angle of
21.degree. and a tapered length of 20 mm were used. The plug was
floated in the pipe. For the individual raw pipes before
processing, bonderizing treatment and application of metal soap
were performed, and in addition, a meal pointing process (this
metal pointing process was not necessary for the push-to-pass
process) was performed for the front end of the pipe was performed,
the process being essential for the drawing.
[0264] In processing, the measurement of the load in the
push-to-pass direction was not performed, and an operator was
delegated to judge whether the conditions were to be changed to not
in an abnormal situation.
[0265] In processing a second or later raw pipe, since the die was
cracked, after the process was interrupted, the process conditions
were changed as follows. That is, the die and the plug were changed
to a die having an angle of 11.degree., and a plug having an angle
of 11.degree. and a tapered length of 20 mm. The process was
restarted after this exchange, and the process for remaining raw
pipes could be performed without any difficulty.
[0266] The conditions changed in processing, the relative process
times, and losses in processing in the examples and comparative
examples are shown in Table 6 in addition to the results of the
dimensional accuracy of the products. The relative process time is
shown by the value obtained by dividing the time (total process
time/total number of processed pipes) required for processing in
each example by that in Comparative Example 6.1. The dimensional
accuracy is shown by the deviation of the thickness and the
deviation of the outer diameter. From the data obtained by image
analysis of the cross-section of the pipe in the circumferential
direction, the deviation of the thickness was obtained as the value
with respect to the average thickness, and the deviation of the
outer diameter was obtained as the value with respect to the
perfect circle (target outer diameter).
[0267] As can be seen from Table 6, according to the present
invention, a high dimensional accuracy pipe could be stably and
efficiently manufactured.
EXAMPLE 7
[0268] Hereinafter, the present invention will be further described
in detail with reference to examples.
[0269] An apparatus of Example 7.1 was formed in combination of the
plug 1, the die 2, and the pipe pushing device 3 as shown in FIG.
1, the plug 1 having a mirror surface to be brought into contact
with the interior surface of a pipe, and having a diameter of 28 mm
at the inlet side, a diameter of 30 mm at the central portion, and
a diameter of 28 mm at the outlet side, the die 2 being an
all-in-one fixed type die in which the interior surface of the hole
was mirror finished and the diameter thereof at the outlet side was
40 mm, the pipe pushing device 3 being formed of a hydraulic
cylinder and being operated by either one of two operation modes,
"continuous pushing" and "intermittent pushing". The plug 1 was
used as a fixed plug which was fixed at one end thereof and which
was charged in the pipe, and the operation mode of the pipe pushing
device 3 was set to the "intermittent pushing". By the use of the
apparatus described above, the push-to-pass of a carbon steel pipe
having an outer diameter of 40 mm and a thickness of 6 mm was
performed, thereby obtaining a pipe product having an outer
diameter of 38 mm and a thickness of 6 mm.
[0270] In Example 7.2, except that the plug 1 was changed to a
floating plug instead of the fixed plug, the push-to-pass process
of a carbon steel pipe having an outer diameter of 40 mm and a
thickness of 6 mm was performed in the same manner as that in
Example 7.1, thereby obtaining a product pipe having an outer
diameter of 38 mm and a thickness of 6 mm.
[0271] In Example 7.3, except that the operation mode of the pipe
pushing device 3 was changed from the "intermittent pushing" to the
"continuous pushing", the push-to-pass process of a carbon steel
pipe having an outer diameter of 40 mm and a thickness of 6 mm was
performed in the same manner as that in Example 7.2, thereby
obtaining a product pipe having an outer diameter of 38 mm and a
thickness of 6 mm.
[0272] In addition, as Comparative Example 7.1, an apparatus having
the structure as shown in FIG. 2 was formed in combination of a
plug 5 which had a mirror surface to be brought into contact with
the interior surface of a pipe, and which had a diameter of 28 mm
at the inlet side, a diameter of 28 mm at the central portion, and
a diameter of 26 mm at the outlet side, a die 6 which was an
all-in-one fixed type die in which the interior surface of the hole
was mirror finished and the diameter thereof at the outlet side was
38 mm, and a pipe drawing device 7 which was formed of a hydraulic
cylinder, was operable in an "intermittent drawing" mode, and was
able to apply a drawing force to the pipe in a predetermined
operation mode. The plug 5 was a fixed plug which was fixed at one
end thereof and which was charged in the pipe. By the use of the
apparatus described above, the drawing of a carbon steel pipe
having an outer diameter of 40 mm and a thickness of 7 mm was
performed, thereby obtaining a product pipe having an outer
diameter of 38 mm and a thickness of 6 mm. In Comparative Example
7.1, time and labor were required for making the steel pipe pass
through the die hole after the front end thereof was narrowed.
[0273] In addition, as Comparative Example 7.2, except that the
same plug 5 as that in Comparative Example 7.1 was used instead of
the plug 1, and that instead of the die 2, a segmented die 9 (the
inner diameter at the outlet side was equal to the diameter of the
hole provided in the die 2 at the outlet side) incorporated in the
rotary forging device 8 was used so as to form the structure shown
in FIG. 3, a carbon steel pipe having an outer diameter of 40 mm
and a thickness of 5 mm was pressed in the same manner as that in
Example 7.1, thereby obtaining a product pipe having an outer
diameter of 38 mm and a thickness of 6 mm.
[0274] The measurement results of the dimensional accuracy of these
product pipes are shown in Table 7. The measurement methods for
measuring the deviations of the thickness in the circumferential
direction, the inner diameter, and the outer diameter shown in
Table 7 are as follows.
[0275] The deviation of the outer diameter (or the inner diameter)
was calculated as the maximum deviation with respect to the perfect
circle from the distribution data of the outer diameter (or the
inner diameter) measured by the steps of permitting a micrometer to
be brought into contact with the outer diameter (or the inner
diameter) of the pipe, and then rotating the pipe. The deviation of
the thickness in the circumferential direction was directly
measured as the maximum deviation with respect to the target
thickness from an image of the cross-section of the thickness.
Instead of using the micrometer which was brought into contact the
outer diameter or the like, the deviation of the outer diameter and
the deviation of the inner diameter may be calculated from the
distribution data in the circumferential direction of the distance
between a laser generator and a pipe, which distance was measured
by radiating laser light thereto. In addition, the deviation of the
thickness in the circumferential direction may be calculated as the
difference between the distribution data of the outer diameter in
the circumferential direction and the distribution data of the
inner diameter in the circumferential direction.
[0276] In addition, the deviation of the thickness (=deviation of
the thickness in the circumferential direction), the deviation of
the inner diameter, and the deviation of the outer diameter are
defined as follows. Deviation of thickness=(maximum
thickness-minimum thickness)/target thickness (or average
thickness).times.100 (%) Deviation of inner diameter=(maximum inner
diameter-minimum inner diameter)/target inner diameter (or average
inner diameter).times.100 (%) Deviation of outer diameter=(maximum
outer diameter-minimum outer diameter)/target outer diameter (or
average outer diameter).times.100 (%)
[0277] As can be seen from Table 7, according to the product pipes
formed by using the apparatuses of Examples 7.1 to 7.3,
significantly superior dimensional accuracy was obtained, and in
particular, when floating was performed, the dimensional accuracy
was further improved (Example 7.2). In addition, even when
continuous push-to-pass was performed, a product pipe having a high
dimensional accuracy was obtained (Example 7.3). On the contrary,
by the conventional drawing, the dimensional accuracy of the
product pipe was degraded (Comparative Example 7.1). By the
pressing using the rotary forging device, the dimensional accuracy
of the product pipe was also degraded (Comparative Example
7.2).
EXAMPLE 8
Example of Present Invention 8.1
[0278] By using steel pipes having a diameter of 40 mm, a thickness
of 6 mm, and a length of 5.5 m as a raw material, as shown in FIG.
11, the push-to-pass process was performed. That is, a plurality of
dies 2, 20, - - - , 20 in conformity with dimensions of product
pipes was set beforehand in a die rotating platform 19 in
accordance with the order of pipes to be processed, the die 2 in
conformity with the dimensions of the product of the preceding pipe
4 was then disposed in the pass line, the preceding pipe 4 was
pushed in the die 2 by the pushing device 2 so as to complete the
push-to-pass process, the plurality of dies was then sequentially
moved by rotating the die rotating platform 19, and the die 20 in
conformity with the outside dimension of a product of the following
pipe 7 was disposed in the pass line instead of the die 2. In the
case described above, before the die 20 was disposed in the pass
line, the plug 22 was charged in the following pipe 5, followed by
the push-to-pass process performed by pushing the following pipe 7
in the die 20 by the pushing device 2. By repeating the steps
described above, high dimensional accuracy pipes having various
product dimensions were manufactured.
Example of Present Invention 8.2
[0279] By using steel pipes having a diameter of 40 mm, a thickness
of 6 mm, and a length of 5.5 m as a raw material, as shown in FIG.
12, the push-to-pass process was performed. That is, a plurality of
dies 2, 20, - - - , 20 in conformity with dimensions of product
pipes was set beforehand in a die linear-driving platform 23 in
accordance with the order of pipes to be processed, the die 2 in
conformity with the dimensions of the product of the preceding pipe
4 was then disposed in the pass line, the preceding pipe 4 was
pushed in the die 2 by the pushing device 2 so as to complete the
push-to-pass process, the plurality of dies was then sequentially
moved by linearly driving the die linear-driving platform 23, and
the die 20 in conformity with the outside dimension of a product of
the following pipe 7 was disposed in the pass line instead of the
die 2. In the case described above, before the die 20 was disposed
in the pass line, the plug 22 was charged in the following pipe 5,
followed by the push-to-pass process performed by pushing the
following pipe 7 in the die 20 by the pushing device 2. By
repeating the steps described above, high dimensional accuracy
pipes having various product dimensions were manufactured.
Comparative Example 8.1
[0280] Steel pipes having a diameter of 40 mm, a thickness of 6 mm,
and a length of 5.5 m were as a raw material, a plurality of dies
having different hole sizes was prepared, and the push-to-pass
process was performed as shown in FIG. 13. The die 2 to be first
used was disposed in the pass line, and the preceding pipe 4 was
pushed in the die 2 by the pushing device 3 so as to complete the
push-to-pass process. Next, by hand, the die 20 in conformity with
the outside dimension of a product of the following pipe 7 was
disposed in the pass line instead of the die 2. In this step,
before the die 20 was disposed in the pass line, the plug 22 was
charged in the following pipe 7. Subsequently, the push-to-pass
process was performed by pushing the following pipe 7 in the die 20
by the pushing device 2. The process was repeatedly performed, and
hence high dimensional accuracy pipes having various product
dimensions were manufactured.
Comparative Example 8.2
[0281] Steel pipes having a diameter of 40 mm, a thickness of 6 mm,
and a length of 5.5 m were used as a raw material, a plurality of
dies having different hole sizes was prepared, and the push-to-pass
process was performed as shown in FIG. 13. The die 2 to be first
used was disposed in the pass line, and the preceding pipe 4 was
pushed in the die 2 by the pushing device 2 so as to complete the
push-to-pass process. Next, by hand, the die 20 in conformity with
the outside dimension of a product of the following pipe 7 was
disposed in the pass line instead of the die 2. In this step, the
following pipe 7 was once moved outside the pass line, and after
the plug 22 was charged therein, the pipe 7 was returned in the
pass line. Subsequently, the push-to-pass process was performed by
pushing the following pipe 7 in the die 20 by the pushing device 2.
The process was repeatedly performed, and hence high dimensional
accuracy pipes having various product dimensions were
manufactured.
[0282] The process efficiency and the dimensional accuracy of the
products according to the examples of the present invention and the
comparative examples are shown in Table 8. The process efficiency
was evaluated by the number of steel pipes processed by the
push-to-pass per working hour, and in Table 8, the relative values
thereof are shown which are obtained when the process efficiency of
Comparative Example 8.2 is set to 1. The dimensional accuracy was
shown by the deviation of the thickness and the deviation of the
outer diameter. These deviations were calculated from data obtained
by image analysis of the cross-section of the pipe in the
circumferential direction, the deviation of the thickness was the
value with respect to the average thickness, and the deviation of
the outer diameter was the value with respect to the perfect circle
(target diameter).
[0283] As can be seen from Table 8, according to the present
invention, the process efficiency was significantly improved.
EXAMPLE 9
[0284] Hereinafter, the present invention will be further described
in detail with reference to examples.
Example 9.1
[0285] As shown in FIG. 14, fine adjustment means 24 for adjusting
pipe bending was provided at a position very close to the outlet
side of the die 2. Although not shown in the figure, a continuous
pushing device, which held the pipes 4 by endless tracks and
continuously pushed them in the die 2, was provided at the inlet
side of the die 2.
[0286] As shown in FIG. 15, the fine adjustment means 24 for
adjusting pipe bending was formed so that a hole body 26 having a
hole 27 through which a pipe was allowed to pass was movably
supported by a support substrate 28 in the plane perpendicular to
the pipe traveling direction and so that at least one of four
places of the periphery of the hole body 26 was pushed by a hole
body-moving mechanism 29 supported by the support substrate 28 in
the direction (hole body-moving direction 33) perpendicular to the
pipe traveling direction. This pushing force was to be obtained by
moving a wedge-shaped mold 30 having a tapered surface which was in
contact with the periphery of the hole body in the pipe traveling
direction by using an adjustment screw 31 which was engaged with
the wedge-shaped mold 30. In FIG. 16, when the adjustment screw was
turned clockwise, the wedge-shaped mold 30 was lifted, and the hole
body 26 in contact with the tapered surface was moved to the left.
In addition, after the fine adjustment of the hole body position
was performed, fixing screws 32 were driven home, so that the hole
body 26 was fixed to the support substrate 28.
[0287] By using this apparatus and steel pipes having a diameter of
40 mm, a thickness of 6 mm, and a length of 5.5 m as a raw
material, manufacturing of a high dimensional accuracy pipe was
experimentally performed by the push-to-pass process in which this
raw material was continuously fed in the die 2 while the plug 1 was
being charged in the pipe and was being floated. The steel pipe
after the push-to-pass process was allowed to pass through the hole
27 in the hole body 26 provided at a position very close to the
outlet side of the die 2. The hole 27 provided in the hole body 26
was a straight hole, and the diameter thereof was formed larger
than that (in this example, the diameter was 35 mm) of the hole
provided in the die 2 at the outlet side by 0.5 mm.
[0288] By using a plurality of dummy pipes before the actual
manufacturing trial, push-to-pass process experiments were
performed by changing the position of the hole body several times
so as to measure the bending of the pipe, and the relationship
between the change amount of the position of the hole body and that
of the pipe bending after the push-to-pass was obtained. During the
actual manufacturing trial, when the pipe bending was about to
exceed a predetermined threshold, based on the above relationship,
the hole body was moved in the direction so as to decrease the
bending, that is, the fine adjustment of the hole body position was
performed.
Example 9.2
[0289] As shown in FIG. 17, the fine adjustment means 24 for
adjusting pipe bending was provided at a position very close to the
outlet side of the die 2, a guide tube 35 was provided at a
position very close to the inlet side of the die 2, and a guide
tube 36 was provided at a position very close to the outlet side of
the fine adjustment means 24 for adjusting pipe bending. Although
not shown in the figure, a continuous pushing device, which held
the pipes 4 and continuously pushed them in the die 2 by endless
tracks, was provided at an inlet side of the inlet-side guide tube
35.
[0290] As shown in FIG. 18, the fine adjustment means 24 for
adjusting pipe bending was formed so that the hole body 26 having
the hole 27 through which a pipe was allowed to pass was movably
supported by the support substrate 28 in the plane perpendicular to
the pipe traveling direction and so that at least one of four
places of the periphery of the hole body 26 was pushed or pulled by
the hole body-moving mechanism 29 supported by the support
substrate 28 in the direction (hole body-moving direction 33)
perpendicular to the pipe traveling direction. This pushing or
pulling force was imparted by compact hydraulic cylinders 34 each
of which was in contact with the periphery of the hole body 26. In
FIG. 18, by adjusting the difference in pressure between the two
opposing hydraulic cylinders 34, the hole body 26 was moved in the
opposing direction between the above two hydraulic cylinders 34.
After the fine adjustment of the hole body position, the difference
in pressure between the two opposing hydraulic cylinders 34 was set
to zero, so that the hole body 26 was fixed to the support
substrate 28.
[0291] By using this apparatus and steel pipes having a diameter of
40 mm, a thickness of 6 mm, and a length of 5.5 m as a raw
material, manufacturing of a high dimensional accuracy pipe was
experimentally performed by the push-to-pass process in which this
raw material was continuously fed in the die 2 while the plug 1 was
being charged in the pipe and was being floated. The steel pipe
before the push-to-pass process was allowed to pass through the
inlet-side guide tube 35, and the steel pipe after the push-to-pass
process was allowed to sequentially pass through the hole 27 in the
hole body 26 provided at a position very close to the outlet side
of the die 2 and the outlet-side guide tube 36. The hole 27
provided in the hole body 26 was a tapered hole, and the diameter
thereof at the maximum inner diameter portion (located at the inlet
side) was formed larger than the diameter (in this example, the
diameter was 33 mm) of the hole provided in the die 2 at the outlet
side by 2.5 mm. The diameter of the hole provided in the hole body
26 at the minimum inner diameter portion (located at the outlet
side) was formed equal to that of the hole provided in the die 2 at
the outlet side. In addition, in order to prevent the generation of
faults on the pipe, the inlet-side and the outlet-side guide tubes
35 and 36 were formed so that the inner diameters thereof were
larger than the outer diameters of the pipe at the respective sides
by 0.5 mm.
[0292] By using a plurality of dummy pipes before the actual
manufacturing trial, push-to-pass process experiments were
performed by changing the position of the hole body several times
so as to measure the bending of the pipe, and the relationship
between the change amount of the position of the hole body and that
of the pipe bending after the push-to-pass was obtained. During the
actual manufacturing trial, when the pipe bending was about to
exceed a predetermined threshold, based on the above relationship,
the hole body was moved in the direction so as to decrease the
bending, that is, the fine adjustment of the hole body position was
performed.
Comparative Example 9.1
[0293] As shown in FIG. 19, the guide tube 35 was provided at a
position very close to the inlet side of the die 2, and the guide
tube 36 was provided at a position very close to the outlet side of
the die 2. In addition, although not shown in the figure, a
continuous pushing device, which held the pipes 4 and continuously
pushed them in the die 2 by endless tracks, was provided at the
inlet side of the inlet-side guide tube 35.
[0294] By using this apparatus and steel pipes having a diameter of
40 mm, a thickness of 6 mm, and a length of 5.5 m as a raw
material, manufacturing of a high dimensional accuracy pipe was
experimentally performed by the push-to-pass process in which this
raw material was continuously fed in the die 2 (in this example,
the hole diameter at the outlet was 33 mm) while the plug 1 was
being charged in the pipe and was being floated. The steel pipe
before the push-to-pass process was allowed to pass through the
inlet-side guide tube 35, and the steel pipe after the push-to-pass
process was allowed to pass through the outlet-side guide tube
36.
Comparative Example 9.2
[0295] As shown in FIG. 20, nothing was provided at positions very
close to the inlet side and the outlet side of the die 2. Although
not shown in the figure, a continuous pushing device, which held
the pipes 4 and continuously pushed them in the die 2 by endless
tracks, was provided at the inlet side of the die 2.
[0296] By using this apparatus and steel pipes having a diameter of
40 mm, a thickness of 6 mm, and a length of 5.5 m as a raw
material, manufacturing of a high dimensional accuracy pipe was
experimentally performed by the push-to-pass process in which this
raw material was continuously fed in the die 2 (in this example,
the hole diameter at the outlet was 35 mm) while the plug 1 was
being charged in the pipe and was being floated.
Comparative Example 9.3
[0297] As shown in FIG. 21, nothing was provided at positions very
close to the inlet side and the outlet side of the die 2. At the
inlet side of the die 2, a pushing device was not provided, and at
the outlet side of the die 2, a drawing device 37 was provided.
[0298] By using this apparatus and steel pipes having a diameter of
40 mm, a thickness of 6 mm, and a length of 5.5 m as a raw
material, manufacturing of a high dimensional accuracy pipe was
experimentally performed by a drawing process in which the drawing
device 37 held the front end of the pipe and drew it through the
die 2 (in this example, the hole diameter at the outlet was 35 mm)
in a drawing direction 38 while the plug 1 was being charged in the
pipe and was being floated.
[0299] The pipe bending and the dimensional accuracy of the pipes
manufactured by the methods of the examples and comparative
examples described above were measured, and the results are shown
in Table 9. For the measurement of the pipe bending, a linear ruler
was placed along the pipe, and the evaluation was made by the
maximum gap between the linear ruler and the central portion of the
pipe per length of 500 mm thereof. The dimensional accuracy of the
pipe was shown by the deviation of the thickness and the deviation
of the outer diameter (in each example, the maximum value of the
data of the manufactured pipes). These deviations were calculated
from data obtained by image analysis of the cross-section of the
pipe in the circumferential direction, the deviation of the
thickness was the value with respect to the average thickness, and
the deviation of the outer diameter was the value with respect to
the perfect circle (target diameter).
[0300] As can be seen from Table 9, according to the present
invention, significantly superior dimensional accuracy was
obtained, and in addition, the pipe bending after the push-to-pass
could be sufficiently prevented.
EXAMPLE 10
[0301] As an example of the present invention, a manufacturing line
as shown in FIG. 22 was formed. Reference numeral 39 indicates a
push-to-pass process device, and this device performs the
push-to-pass process in which while the plug 1 is being charged in
pipes and is being floated, the pipes are continuously fed in the
die 2. This push-to-pass process device 39 was provided with a die
exchange device 45, a plug exchange device 44, and a bending
prevention device 46 which were formed as the preferable
embodiments described above.
[0302] At the inlet side of the push-to-pass process device 39,
from the upstream side, a pipe end-surface grinding device 40, a
lubricant immersion coating bath 41, and a drying device 42 were
disposed in that order. The pipe end-surface grinding device 40 was
formed so that the end surfaces of pipes arranged on a table were
cut using a grinding tool to make the end surface perpendicular to
the pipe axis direction. The lubricant immersion coating bath 41
stored an emulsion containing a drying liquid lubricant, and by
immersing the pipe in the above emulsion bath, application of the
lubricant to the pipe was performed. The drying device 42 was
formed so that the pipes processed by lubricant application and
then arranged on a table were dried by supplying a hot wind. In
addition, at an inlet side of this manufacturing line, a pipe
receiving table 47 was provided receiving raw pipes fed from the
preceding step and sending them to the pipe end-surface grinding
device 40, and at an outlet side, a pipe sending table 48 was
provided sending pipes, which were formed into product pipes by the
push-to-pass process, to the following step.
[0303] In this manufacturing line, the formation of the
perpendicular angle of a pipe end-surface, lubricant immersion
coating, drying, and push-to-pass process were performed in that
order for raw pipes to which oxide scales still adhered and which
had various sized, such as an outer diameter of 25 to 120 mm, a
thickness of 2 to 8 mm, and a length of 5 to 13 m, thereby forming
product pipes.
[0304] On the contrary, in FIG. 23, as a comparative example, a
manufacturing line of a conventional drawing process is shown. In
this manufacturing line, the pipe receiving table 47 was provided
at an inlet side of a drawing process device 50 and the pipe
sending table 48 was provided at an outlet side thereof, and the
drawing process device 50 was a device in which while the plug 1
was being charged in a pipe and was being floated, this pipe was
drawn through the die 2. In addition, the drawing process device 50
was provided with the plug exchange device 44 and the die exchange
device 45 which were formed as described in the example. In this
manufacturing line, a raw pipe to which oxide scales still adhered
as that of the example could not be drawn, and hence a pipe
processed by a first pre-treatment process and the following second
pre-treatment process must be used as the raw pipe.
[0305] The first pre-treatment process was essential as means for
forming a strong lubricant film for the drawing process, and have
many steps of cutting a raw pipe having scales thereon into short
ones, removing scales by pickling, neutralizing an acid with
alkali, washing with water, performing bonderizing treatment,
applying metal soap, and drying, which were performed in that
order. When a plurality of immersion baths or devices used for this
first pre-treatment process was provided in the same line as that
for the drawing process device 50, the productivity is decreased;
hence, they were provided in a different line. In addition, the
second pre-treatment process was essential as means for performing
metal pointing of the front end of the pipe by a rotary forging
device or the like so that the pipe was to be held by the drawing
process device 50. When this rotary forging device was provided in
the same line as that for the drawing process device 50, the
productivity is also decreased; hence, the rotary forging device
was provided in a different line.
[0306] By using this manufacturing line of the comparative example,
the drawing process was performed for pipes obtained by
sequentially processing the same raw pipes having scales thereon as
that in the example by the first and the second pre-treatment
processes, thereby obtaining product pipes.
[0307] Times required for manufacturing and the dimensional
accuracy of the product pipes of the example and the comparative
example were measured, and the results are shown in Table 10. The
time required for manufacturing was evaluated by the total
treatment time/the total number of processed pipes, the total
treatment time being a time required for obtaining product pipes
from one lot of raw pipes, the lot containing a predetermined
number of raw pipes. The relative values obtained when the
evaluation value in the comparative example is set to 1 are shown
in Table 10. The dimensional accuracy was shown by the deviation of
the thickness and the deviation of the outer diameter. These
deviations were obtained from data of image analysis of the
cross-section of the pipe in the circumferential direction, the
deviation of the thickness was the value with respect to the
average thickness, and the deviation of the outer diameter was the
value with respect to the perfect circle (target diameter).
[0308] As can be seen from Table 10, according to the present
invention, high dimensional accuracy pipes can be efficiently
manufactured.
INDUSTRIAL APPLICABILITY
[0309] A high dimensional accuracy pipe of the present invention
has a significantly superior dimensional accuracy and hence also
has a superior fatigue strength. In addition, since manufacturing
can be performed at inexpensive cost, a superior advantage of
greatly contributing to the reduction in weight of drive train
parts of automobile and the like can be obtained. Furthermore,
according to a manufacturing method of the present invention, a
superior advantage can be obtained in which high dimensional
accuracy metal pipes in response to wide requirements of sizes can
be manufactured at inexpensive cost. TABLE-US-00001 TABLE 1
DIAMETER THICKNESS PROCESSING REDUCTION AT OUTLET MODE DIE PLUG
RATE (%) SIDE EXAMPLE 1.1 PUSH-TO-PASS ALL-IN-ONE FIXED 10
EQUIVALENT TO FIXED THICKNESS AT INLET SIDE EXAMPLE 1.2
PUSH-TO-PASS ALL-IN-ONE FIXED 5 EQUIVALENT TO FIXED THICKNESS AT
INLET SIDE EXAMPLE 1.3 PUSH-TO-PASS ALL-IN-ONE FLOATING 5
EQUIVALENT TO FIXED THICKNESS AT INLET SIDE COMPARATIVE DRAWING
ALL-IN-ONE FIXED 5 DECREASED EXAMPLE 1.1 FIXED THICKNESS
COMPARATIVE PRESSING SEGMENTED FIXED 5 EQUIVALENT TO EXAMPLE 1.2
ROTARY THICKNESS AT INLET SIDE COMPARATIVE PRESSING SEGMENTED FIXED
5 INCREASED EXAMPLE 1.3 ROTARY THICKNESS DEVIATION OF THICK- CYCLES
NESS IN UNTIL DEVIATION DEVIATION CIRCUMFER- ENDURANCE OF OUTER OF
INNER ENTIAL LIMIT IN DIAMETER* DIAMETER* DIRECTION* FATIGUE (%)
(%) (%) TEST EXAMPLE 1.1 0.5 0.5 0.5 500 .times. 10.sup.3 EXAMPLE
1.2 0.7 2.5 0.7 500 .times. 10.sup.3 EXAMPLE 1.3 0.3 0.5 0.5 500
.times. 10.sup.3 COMPARATIVE 4.0 4.0 5.0 100 .times. 10.sup.3
EXAMPLE 1.1 COMPARATIVE 3.3 3.5 4.2 200 .times. 10.sup.3 EXAMPLE
1.2 COMPARATIVE 3.5 4.0 4.5 200 .times. 10.sup.3 EXAMPLE 1.3
*DEVIATION FROM TARGET VALUE
[0310] TABLE-US-00002 TABLE 2 DEVIATION OF THICK- PROCESS NESS IN
EFFICIENCY: DEVIATION DEVIATION CIRCUMFER- PROCESSABLE THICKNESS OF
OUTER OF INNER ENTIAL NUMBER PER PROCESSING AT OUTLET DIAMETER
DIAMETER DIRECTION ONE HOUR METHOD SIDE (%) (%) (%) (PIPES) EXAMPLE
OF PUSH-TO- EQUIVALENT TO 0.5 0.5 0.5 130 PRESENT PASS THICKNESS AT
INVENTION INLET SIDE COMPARATIVE DRAWING DECREASED 4.0 4.6 5.0 40
EXAMPLE 2.1 THICKNESS COMPARATIVE ROTARY INCREASED 3.8 4.0 4.5 60
EXAMPLE 2.2 PRESS THICKNESS FORGING
[0311] TABLE-US-00003 TABLE 3 PRESENCE DEVIATION DEVIATION OF
GENERA- DEVIATION OF INNER OF OUTER PROCESSING LUBRICANT TION OF OF
THICK- DIAMETER DIAMETER METHOD FILM LUBRICANT FAULTS NESS (%) (%)
(%) COMPARATIVE PUSH-TO- NO LIQUID YES 2.0 2.0 1.0 EXAMPLE 3.1 PASS
LUBRICANT EXAMPLE OF PUSH-TO- YES LIQUID NO 0.5 0.5 0.5 PRESENT
PASS LUBRICANT INVENTION 3.1 EXAMPLE OF PUSH-TO- YES GREASE- NO 0.5
0.5 0.5 PRESENT PASS BASED INVENTION 3.2 LUBRICANT EXAMPLE OF
PUSH-TO- YES DRYING NO 0.3 0.3 0.3 PRESENT PASS LUBRICANT INVENTION
3.3 EXAMPLE OF PUSH-TO- YES SOLVENT NO 0.3 0.3 0.3 PRESENT PASS
SOLUTION OF INVENTION 3.4 DRYING RESIN EXAMPLE OF PUSH-TO- YES
EMULSION NO 0.3 0.3 0.3 PRESENT PASS OF DRYING INVENTION 3.5 RESIN
COMPARATIVE DRAWING YES LIQUID NO 4.5 3.5 3.5 EXAMPLE 3.2 LUBRICANT
COMPARATIVE PRESSING YES LIQUID NO 4.5 4.0 3.5 EXAMPLE 3.3
LUBRICANT *ROTARY PRESS FORGING METHOD
[0312] TABLE-US-00004 TABLE 4 PIPE DIAMETER TARGET OUTER DEVIATION
PROCESSING EXPANSION REDUCTION .theta.A .theta.B DIAMETER*.sup.2 OF
METHOD RATE % RATE % .cndot. .cndot. mm THICKNESS % 1 PUSH-TO-PASS
8 8 4.95 4.97 40 0.3 2 PUSH-TO-PASS 6 8 3.64 4.85 39 0.25 3
PUSH-TO-PASS 1 17 0.59 9.88 34 0.15 4 DRAWING -- 8 0 4.85 39 5.0 5
DRAWING -- 16 0 9.20 34 4.5 6 PRESSING -- 8 0 4.85 39 4.5 OUTER
DEVIATION DEVIATION CROSS- DIAMETER THICKNESS OF INNER OF OUTER
SECTIONAL AFTER AFTER DIAMETER DIAMETER HARDNESS PROCESSING
PROCESSING % % Hv mm mm REMARKS 1 0.3 0.3 320 40 6.0 EXAMPLE OF
PRESENT INVENTION 2 0.3 0.3 320 39 6.0 EXAMPLE OF PRESENT INVENTION
3 0.2 0.2 320 34 6.0 EXAMPLE OF PRESENT INVENTION 4 4.0 4.0 200 39
5.8 COMPARATIVE EXAMPLE A 5 3.5 3.5 320 34 5.1 COMPARATIVE EXAMPLE
B 6 4.0 3.5 200 39 6.2 COMPARATIVE EXAMPLE C *1: ROTARY PRESS
FORGING METHOD *.sup.2TARGET OUTER DIAMETER OF PIPE AT OUTLET SIDE
OF DIE
[0313] TABLE-US-00005 TABLE 5 SHAPE CONDITIONS OF PLUG AND DIE
ANGLE LENGTH DIMENSIONAL ACCURACY OF PLUG OF PLUG LENGTH DEVIA-
DEVIA- DIAMETER- DIAMETER- OF PLUG EXECU- DEVIA- TION OF TION OF
PROCESS- REDUCING REDUCING BEARING ANGLE TION OF TION OF INNER
OUTER ING PORTION PORTION PORTION OF DIE MANUFAC- THICKNESS
DIAMETER DIAMETER METHOD (.degree.) (mm) (mm) (.degree.) TURING (%)
(%) (%) EXAMPLE OF PUSH-TO- 21 11 20 21 YES 0.5 0.5 0.5 PRESENT
PASS INVENTION 5.1 EXAMPLE OF PUSH-TO- 11 20 15 13 YES 0.5 0.5 0.5
PRESENT PASS INVENTION 5.2 EXAMPLE OF PUSH-TO- 5 90 4 5 YES 0.8 0.8
0.7 PRESENT PASS INVENTION 5.3 EXAMPLE OF PUSH-TO- 40 5 35 40 YES
0.3 0.4 0.3 PRESENT PASS INVENTION 5.4 COMPAR- PUSH-TO- 4 11 4 4.5
NO -- -- -- ATIVE PASS EXAMPLE 5.1 COMPAR- PUSH-TO- 45 11 210 45 NO
-- -- -- ATIVE PASS EXAMPLE 5.2 COMPAR- PUSH-TO- 21 4 4.5 21 NO --
-- -- ATIVE PASS EXAMPLE 5.3 COMPAR- PUSH-TO- 5 105 210 5 NO -- --
-- ATIVE PASS EXAMPLE 5.4 CONVEN- DRAWING 21 11 20 21 YES 4.5 3.5
3.5 TIONAL EXAMPLE 5.1 CONVEN- ROTARY 21 11 20 21 YES 4.5 4.0 3.5
TIONAL PRESS EXAMPLE FORGING 5.2
[0314] TABLE-US-00006 TABLE 6 DEVIATION OF CONDITIONS RELATIVE
DEVIATION OUTER PROCESSING CHANGED IN PROCESS LOSS IN OF THICK-
DIAMETER METHOD PROCESSING TIME PROCESSING NESS (%) (%) EXAMPLE 6.1
PUSH-TO- SHAPES OF 0.2 NO 0.5 0.6 PASS DIE AND PLUG COMPARATIVE
PUSH-TO- TYPE OF 1 BREAKAGE 0.5 0.6 EXAMPLE 6.1 PASS LUBRICANT, OF
DIE SHAPES OF DIE AND PLUG COMPARATIVE DRAWING SHAPES OF 2 BREAKAGE
3.5 3.2 EXAMPLE 6.2 DIE AND OF DIE PLUG
[0315] TABLE-US-00007 TABLE 7 DEVIATION OF THICKNESS IN CIRCUMFER-
DEVIATION DEVIATION ENTIAL OF INNER OF OUTER PROCESSING THICKNESS
AT DIRECTION DIAMETER DIAMETER MODE DIE PLUG OUTLET SIDE (%) (%)
(%) EXAMPLE 7.1 PUSH-TO-PASS ALL-IN-ONE FIXED EQUIVALENT TO 0.5 0.5
0.5 (INTERMITTENT) FIXED THICKNESS AT INLET SIDE EXAMPLE 7.2
PUSH-TO-PASS ALL-IN-ONE FLOATING EQUIVALENT TO 0.4 0.5 0.3
(INTERMITTENT) FIXED THICKNESS AT INLET SIDE EXAMPLE 7.3
PUSH-TO-PASS ALL-IN-ONE FLOATING EQUIVALENT TO 0.3 0.3 0.3
(CONTINUOUS) FIXED THICKNESS AT INLET SIDE COMPARATIVE DRAWING
ALL-IN-ONE FIXED DECREASED 5.0 4.0 4.0 EXAMPLE 7.1 (CONTINUOUS)
FIXED THICKNESS COMPARATIVE PRESSING SEGMENTED FIXED INCREASED 4.5
4.0 3.5 EXAMPLE 7.2 (INTERMITTENT) ROTARY THICKNESS
[0316] TABLE-US-00008 TABLE 8 DEVIATION DEVIATION OF OUTER PROCESS
OF THICK- DIAMETER EFFICIENCY NESS (%) (%) EXAMPLE OF 10 0.5 0.5
PRESENT INVENTION 8.1 EXAMPLE OF 10 0.5 0.5 PRESENT INVENTION 8.2
COMPARATIVE 1.2 0.8 0.7 EXAMPLE 8.1 COMPARATIVE 1 0.8 0.7 EXAMPLE
8.2
[0317] TABLE-US-00009 TABLE 9 DEVIATION OF PROCESSING BENDING
DEVIATION OF OUTER METHOD BENDING PREVENTION MEANS (mm) THICKNESS
(%) DIAMETER (%) EXAMPLE 9.1 PUSH-TO- FINE ADJUSTMENT MEANS 0.1 0.5
0.6 PASS FOR ADJUSTING PIPE BENDING AT POSITION VERY CLOSE TO
OUTLET SIDE OF DIE EXAMPLE 9.2 PUSH-TO- FINE ADJUSTMENT MEANS FOR
0.2 0.5 0.6 PASS ADJUSTING PIPE BENDING AT POSITION VERY CLOSE TO
OUTLET SIDE OF DIE + INLET SIDE AND OUTLET SIDE GUIDE TUBES
COMPARATIVE PUSH-TO- INLET SIDE AND OUTLET SIDE 0.7 0.5 0.6 EXAMPLE
9.1 PASS GUIDE TUBES COMPARATIVE PUSH-TO- MO MEANS 1.8 0.5 0.6
EXAMPLE 9.2 PASS COMPARATIVE DRAWING TENSION AT OUTLET SIDE IN 0.3
3.5 3.0 EXAMPLE 9.3 DRAWING DIRECTION
[0318] TABLE-US-00010 TABLE 10 TIME REQUIRED FOR DEVIA- DEVIA-
MANUFAC- TION OF TION OF PROCESS- TURING THICK- OUTER ING (RELATIVE
NESS DIAME- METHOD VALUE) (%) TER (%) EXAMPLE PUSH-TO- 0.1 0.5 0.6
PASS COMPAR- DRAWING 1 3.5 3.2 ATIVE EXAMPLE
* * * * *