U.S. patent application number 12/567065 was filed with the patent office on 2010-04-01 for method of machining an end portion of a long tubular member.
Invention is credited to Kazuhiro Ishii.
Application Number | 20100077819 12/567065 |
Document ID | / |
Family ID | 39830900 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100077819 |
Kind Code |
A1 |
Ishii; Kazuhiro |
April 1, 2010 |
METHOD OF MACHINING AN END PORTION OF A LONG TUBULAR MEMBER
Abstract
Thread cutting of the end portion of a long tubular member (1)
held by a chuck system (3) is carried out with high accuracy
without leaving mill scale on the complete thread portion of the
resulting threads. The protruding length L of the long tubular
member from the chuck system (3) to the end face of the tubular
member is controlled so that the ratio L/D of the protruding length
L to the outer diameter D of the long tubular member (1) is in a
range predetermined depending on the outer diameter D and the ratio
t/D of the wall thickness t to the outer diameter D of the tubular
member (1). When the chuck system is a floating chuck system having
a floating chuck and a positioning chuck, the protruding length L
of the tubular member from the floating chuck and the protruding
length L' thereof from the positioning chuck are controlled.
Inventors: |
Ishii; Kazuhiro; (Kyoto-shi,
JP) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW, SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
39830900 |
Appl. No.: |
12/567065 |
Filed: |
September 25, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/JP2008/056074 |
Mar 28, 2008 |
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12567065 |
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Current U.S.
Class: |
72/68 |
Current CPC
Class: |
B23B 31/16 20130101;
B23Q 3/183 20130101; B23G 1/52 20130101; B23B 2231/22 20130101;
B23B 2270/12 20130101; B23G 1/22 20130101 |
Class at
Publication: |
72/68 |
International
Class: |
B21B 23/00 20060101
B21B023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2007 |
JP |
2007-084670 |
Claims
1. A method of machining an end portion of a long tubular member
which has an outer diameter D and a wall thickness t and which is
held by a chuck system, characterized by carrying out machining
while holding the long tubular member with the chuck system in a
position such that the protruding length L of the end portion being
machined of the long tubular member from the chuck system
satisfying below-described (A) when the chuck system is of the
non-floating type and satisfying below-described (B) when it is of
the floating type: (A) the chuck system is a non-floating chuck
system having at least one chuck, and it holds the long tubular
member in a position such that the ratio L/D of the protruding
length L of the long tubular member, which is the distance from the
chuck closest to the end portion being machined to the end face of
the end portion being machined of the long tubular member, with
respect to the outer diameter D of the tubular member is in the
following range: (1) when the outer diameter D of the tubular
member is less than 88.9 mm: if the ratio t/D of the wall thickness
t to the outer diameter D of the long tubular member is at most
0.07, L/D is at least 3.0 and at most 4.5; and if t/D is greater
than 0.07, L/D is at least 2.5 and at most 3.5; (2) when the outer
diameter D of the tubular member is at least 88.9 mm and at most
139.7 mm: if t/D is at most 0.07, L/D is at least 2.0 and at most
3.5; and if t/D is greater than 0.07, L/D is at least 1.5 and at
most 3.5; and (3) when the outer diameter D of the tubular member
is greater than 139.7 mm: if t/D is at most 0.07, L/D is at least
1.5 and at most 2.5; and if t/D is greater than 0.07, L/D is at
least 1.0 and at most 2.5; (B) the chuck system is a floating chuck
system having a floating chuck and in front of it a positioning
chuck for centering, and it holds the long tubular member in a
position such that the ratios L/D and L'/D of the protruding length
L of the long tubular member, which is the distance from the
floating chuck to the end face of the end portion being machined of
the long tubular member, and the protruding length L from the
positioning chuck to the end face with respect to the outer
diameter D of the long tubular member are in the following ranges:
(1') when the outer diameter D of the tubular member is less than
88.9 mm: if the ratio t/D of the wall thickness t to the outer
diameter D of the long tubular member is at most 0.07, L/D is at
least 3.0 and L'/D is at most 3.0; and if t/D is greater than 0.07,
L/D is at least 2.5 and L'/D is at most 3.0; (2') when the outer
diameter D of the tubular member is at least 88.9 mm and at most
139.7 mm: if t/D is at most 0.07, L/D is at least 2.0 and L'/D is
at most 2.0; and if t/D is greater than 0.07, L/D is at least 1.5
and L'/D is at most 2.0; and (3') when the outer diameter D is
greater than 139.7 mm: if t/D is at most 0.07, L/D is at least 1.5
and L'/D is at most 1.5; and if t/D is greater than 0.07, L/D is at
least 1.0 and L'/D is at most 1.5.
2. A method of machining an end portion of a long tubular member
having an outer diameter D and a wall thickness t which is held by
a non-floating chuck system having at least one chuck,
characterized by carrying out machining while holding the long
tubular member with the chuck system in a position such that the
ratio L/D of the protruding length L of the long tubular member
from the chuck closest to the end portion being machined to the end
face of the end portion being machined of the long tubular member
with respect to the outer diameter D of the tubular member is in
the following ranges: (1) when the outer diameter D of the tubular
member is less than 88.9 mm: if the ratio t/D of the wall thickness
t to the outer diameter D of the long tubular member is at most
0.07, L/D is at least 3.0 and at most 4.5; and if t/D is greater
than 0.07, L/D is at least 2.5 and at most 3.5; (2) when the outer
diameter D of the tubular member is at least 88.9 mm and at most
139.7 mm: if t/D is at most 0.07, L/D is at least 2.0 and at most
3.5; and if t/D is greater than 0.07, L/D is at least 1.5 and at
most 3.5; and (3) when the outer diameter D of the tubular member
is greater than 139.7 mm: if t/D is at most 0.07, L/D is at least
1.5 and at most 2.5; and if t/D is greater than 0.07, L/D is at
least 1.0 and at most 2.5.
3. A method as set forth in claim 2 wherein machining is carried
out on a long tubular member having an outer diameter D of less
than 88.9 mm and t/D of at most 0.07 while holding it with the
chuck system in a position such that L/D is at least 3.0 and at
most 4.5.
4. A method as set forth in claim 2 wherein machining is carried
out on a long tubular member with an outer diameter D less than
88.9 mm and t/D greater than 0.07 while holding it with the chuck
system in a position at which L/D is at least 2.5 and at most
3.5.
5. A method as set forth in claim 2 wherein machining is carried
out on a long tubular member having an outer diameter D of at least
88.9 mm and at most 139.7 mm and t/D of at most 0.07 while holding
it with the chuck system in a position such that L/D is at least
2.0 and at most 3.5.
6. A method as set forth in claim 2 wherein machining is carried
out on a long tubular member having an outer diameter D of at least
88.9 mm and at most 139.7 mm and t/D greater than 0.07 while
holding it with the chuck system in a position such that L/D is at
least 1.5 and at most 3.5.
7. A method as set forth in claim 2 including carrying out
machining on a long tubular member having an outer diameter D
greater than 139.7 mm and t/D of at most 0.07 while holding it with
the chuck system in a position such that L/D is at least 1.5 and at
most 2.5.
8. A method as set forth in claim 2 wherein machining is carried
out on a long tubular member having an outer diameter D greater
than 139.7 mm and t/D greater than 0.07 while holding it with the
chuck system in a position such that L/D is at least 1.0 and at
most 2.5.
9. A method of machining an end portion of a long tubular member
held by a floating chuck system having a floating chuck and in
front of it a positioning chuck for centering, characterized by
carrying out machining while holding the long tubular member with
the floating chuck system in a position such that the ratios L/D
and L'/D of the protruding length L from the floating chuck to the
end face of the end portion being machined of the long tubular
member and the protruding length L' from the positioning chuck to
the end face with respect to the outer diameter D of the long
tubular member are within the following ranges: (1') when the outer
diameter D of the tubular member is less than 88.9 mm: if the ratio
t/D of the wall thickness t to the outer diameter D of the long
tubular member is at most 0.07, L/D is at least 3.0 and L'/D is at
most 3.0; and if t/D is greater than 0.07, L/D is at least 2.5 and
L'/D is at most 3.0; (2') when the outer diameter D of the tubular
member is at least 88.9 mm and at most 139.7 mm: if t/D is at most
0.07, L/D is at least 2.0 and L'/D is at most 2.0; and if t/D is
greater than 0.07, L/D is at least 1.5 and L'/D is at most 2.0; and
(3') when the outer diameter D is greater than 139.7 mm: if t/D is
at most 0.07, L/D is at least 1.5 and L'/D is at most 1.5; and if
t/D is greater than 0.07, L/D is at least 1.0 and L'/D is at most
1.5.
10. A method as set forth in claim 9 wherein machining is carried
out on a long tubular member having an outer diameter D of less
than 88.9 mm and t/D of at most 0.07 while holding it with the
chuck system in a position such that L/D is at least 3.0 and L'/D
is at most 3.0.
11. A method as set forth in claim 9 wherein machining is carried
out on a long tubular member having an outer diameter D of less
than 88.9 mm and t/D greater than 0.07 while holding it with the
chuck system in a position such that L/D is at least 2.5 and L'/D
is at most 3.0.
12. A method as set forth in claim 9 wherein machining is carried
out on a long tubular member having an outer diameter D of at least
88.9 mm and at most 1397 mm and t/D of at most 0.07 while holding
it with the chuck system in a position such that L/D is at least
2.0 and L'/D is at most 2.0.
13. A method as set forth in claim 9 wherein machining is carried
out on a long tubular member having an outer diameter D of at least
88.9 mm and at most 139.7 mm and L/D greater than 0.07 while
holding it with the chuck system in a position such that L/D is at
least 1.5 and L'/D is at most 2.0.
14. A method as set forth in claim 9 wherein machining is carried
out on a long tubular member having an outer diameter D greater
than 139.7 mm and t/D of at most 0.07 while holding it with the
chuck system in a position such that L/D is at least 1.5 and L'/D
is at most 1.5.
15. A method as set forth in claim 9 wherein machining is carried
out on a long tubular member having an outer diameter D greater
than 139.7 mm and t/D greater than 0.07 while holding it with the
chuck system in a position such that L/D is at least 1.0 and L'/D
is at most 1.5.
16. A method of machining an end portion of a long tubular member
as set forth in claim 9 wherein the centering position of the
positioning chuck is located at most 200 mm from the floating
chuck.
Description
TECHNICAL FIELD
[0001] This invention relates to a method of machining an end
portion of a long tubular member held by a chucking device, the
method being suitable for cutting with high accuracy of threads for
a joint on the end portion of an oil country tubular good with or
without a metal-to-metal sealing portion. The chuck system which is
employed in the method may be a normal chuck system of the
non-floating type or a floating chuck system having a floating
chuck mechanism.
BACKGROUND ART
[0002] Oil country tubular goods (OCTG) used for excavation of oil
wells or gas wells and for production of crude oil or natural gas
are connected to each other during use by couplings. To this end,
threads (typically tapered threads) for connection are formed on
the end portions of tubular members. These threads require a high
degree of gas tightness. Therefore, as shown in FIG. 3, when
cutting the threads on an end portion of an oil country tubular
good 1, a high degree of accuracy of machining is required, and it
is not permissible that mill scale 1b which indicates that no
cutting is performed thereon remains on a complete thread portion
1a. In FIG. 3, 1c indicates an incomplete thread portion, and 1d
indicates the border between the complete thread portion 1a and the
incomplete thread portion 1c.
[0003] Thread cutting on an end portion of a long tubular member
such as an oil country tubular good is carried out by holding the
tubular member in the vicinity of the end portion to be machined by
means of a chuck, which is a rotatable workpiece-holding tool, then
rotating the tubular member by rotating the chuck, and allowing the
end portion of the rotating tubular member to be contacted with a
cutting tool which can be adjusted in position relative to the
tubular member.
[0004] An oil country tubular good is often formed from a long
tubular member having a length of approximately 10 meters or more.
There are also small-diameter tubular members referred to as tubing
having an outer diameter of at most 114 mm. Such long tubular
members have a slight amount of bending in the lengthwise
direction. As the outer diameter and wall thickness of an oil
country tubular good increase, its weight also increases and it is
necessary for its joint to have a threaded portion with an
increased length. The accuracy of machining decreases if the oil
country tubular good is not accurately centered during thread
cutting.
[0005] When performing thread cutting of an end portion of a long
tubular member such as an oil country tubular good, a floating
chuck system as shown in FIG. 4, for example, is frequently used
which has a positioning chuck which can move in the axial direction
and in vertical (up and down) and horizontal (to the left and
right) directions and a floating chuck which can move in vertical
and horizontal directions. With the illustrated floating chuck
system 2, a tubular member is first centered while it is held by a
positioning chuck 2a in the position at the border 1d between the
complete thread portion 1a and the incomplete thread portion 1c
which are to be formed on the tubular member. The tubular member is
then held by the floating chuck 2b in a position closer to the
midpoint of the tubular member than the border 1d, and centering is
carried out again. The positioning chuck 2a is then released to
accomplish holding of the long tubular member in position (see JP
64-6886 B).
[0006] When using a floating chuck system of this type, centering
of a long tubular member is carried out at a position which
corresponds to the position where the positioning chuck is located
and which is closer to the tube end portion than when using a
conventional chuck. As a result, the accuracy of centering is
improved.
DISCLOSURE OF INVENTION
[0007] However, no matter how accurately centering is performed,
due to bending of the tubular member at the end portions, the
resulting complete thread portion may sometimes has mill scale
remaining thereon. Furthermore, due to rotation of the tubular
member during machining, a centrifugal force acts on the floating
chuck in such a direction that the chuck opens, and it is necessary
to increase the holding pressure of the chuck to a certain extent
to counteract the centrifugal force. An oil country tubular good
which is held with such an increased pressure is deformed to assume
an elliptical shape in the vicinity of the position where it is
held. If the elliptical shape extends to the complete thread
portion, mill scale remains on the complete thread portion.
[0008] The present invention provides a method which can perform
highly accurate machining on an end portion of a long tubular
member such as an oil country tubular good without leaving mill
scale on a complete thread portion formed by thread cutting even
when the end portion of the tubular member undergoes bending or
becomes elliptical due to the holding pressure, whether using a
floating chuck system or a conventional non-floating chuck
system.
[0009] In a method of machining an end portion of a long tubular
member according to the present invention, when machining an end
portion of a long tubular member having an outer diameter D and a
wall thickness t held by a chuck system, the position at which the
tubular member is held by the chuck system is controlled in the
following manner, thereby making it possible to perform machining
with high accuracy which does not leave mill scale on the complete
thread portion when machining threads on the end portion of the
tubular member:
[0010] (A) When using a conventional chuck system of the
non-floating type:
[0011] Machining is carried out while holding a long tubular member
with the chuck system in a position such that the ratio L/D of the
protruding length L of the long tubular member from the chuck
closest to the end portion being machined to the end face of the
end portion being machined with respect to the outer diameter D of
the tubular member is in the following ranges:
[0012] (1) When the outer diameter D of the tubular member is less
than 88.9 mm: when the ratio t/D of the wall thickness t to the
outer diameter D of the long tubular member is at most 0.07, L/D is
at least 3.0 and at most 4.5; and when t/D is greater than 0.07,
L/D is at least 2.5 and at most 3.5;
[0013] (2) When the outer diameter D of the tubular member is at
least 88.9 mm and at most 139.7 mm: when t/D is at most 0.07, L/D
is at least 2.0 and at most 3.5; and when t/D is greater than 0.07,
L/D is at least 1.5 and at most 3.5; and
[0014] (3) When the outer diameter D of the tubular member is
greater than 139.7 mm: when t/D is at most 0.07, L/D is at least
1.5 and at most 2.5; and when t/D is greater than 0.07, L/D is at
least 1.0 and at most 2.5.
[0015] (B) When using a floating chuck system having a floating
chuck and a positioning chuck for centering located ahead of the
floating chuck:
[0016] Machining is carried out while holding a long tubular member
with the floating chuck system in a position such that the ratios
L/D and L'/D of the protruding length L of the long tubular member
from the floating chuck to the end face of the end portion being
machined and the protruding length L' from the positioning chuck to
the end face with respect to the outer diameter D of the tubular
member are within the following ranges:
[0017] (1') When the outer diameter D of the tubular member is less
than 88.9 mm: when the ratio t/D of the wall thickness t to the
outer diameter D of the long tubular member is at most 0.07, L/D is
at least 3.0 and L'/D is at most 3.0; and when t/D is greater than
0.07, L/D is at least 2.5 and L'/D is at most 3.0;
[0018] (2') When the outer diameter D of the tubular member is at
least 88.9 mm and at most 139.7 mm: when t/D is at most 0.07, L/D
is at least 2.0 and L'/D is at most 2.0; and when t/D is greater
than 0.07, L/D is at least 1.5 and L'/D is at most 2.0; and
[0019] (3') When the outer diameter D is greater than 139.7 mm:
when t/D is at most 0.07, L/D is at least 1.5 and L'/D is at most
1.5; and when t/D is greater than 0.07, L/D is at least 1.0 and
L'/D is at most 1.5.
[0020] In above-described case (B) where a floating chuck system is
used, it is preferable to use a floating chuck system for which the
centering position of the positioning chuck is at most 200 mm from
the floating chuck.
[0021] The term "long tubular member" as used herein means a
tubular member with a length of at least 8 meters. A preferred
length of a long tubular member for which the effects of the
present invention are more pronounced is at least 10 meters.
[0022] The term "chuck", when used by itself, means a holding chuck
of the non-floating (rigid) type which cannot move vertically (up
and down) or horizontally (to the left and right). The term
"floating chuck" means a holding chuck which can move vertically
and horizontally. The term "positioning chuck" means a chuck which
is used for centering and released after centering and which has
its axis movable vertically and horizontally.
[0023] When machining an end portion of a long tubular member
according to the present invention, the projecting length of the
long tubular member from a chuck is controlled so as to be in an
optimal range. As a result, the end portion can be machined with
high accuracy, and mill scale does not remain on a complete thread
portion when thread cutting is carried out even when the end
portion undergoes bending or it is deformed into an elliptical
shape under a large holding pressure.
[0024] A machining method according to the present invention is
ideal for use in thread cutting on an end portion of an oil country
tubular good, but it is not limited to this use. The present
invention can be applied to any type of machining of an end portion
of a long tubular member. Namely, a long tubular member is not
limited to an oil country tubular good, and it may also be a line
pipe or similar tubular member. Machining of an end portion of a
tubular member is not limited to thread cutting, and it can also be
machining such as beveling or bevel cutting on an end face of a
tubular member.
BRIEF EXPLANATION OF THE DRAWINGS
[0025] FIG. 1 is an explanatory view of an embodiment in which an
end portion of a long tubular member held in the vicinity of the
end portion is machined using a conventional chuck system having a
rigid chuck.
[0026] FIG. 2 is an explanatory view of another embodiment in which
an end portion of a long tubular member held in the vicinity of the
end portion is machined by a floating chuck system.
[0027] FIG. 3 is an explanatory view of a mill scale defect which
occurred in thread cutting on an end portion of a long tubular
member.
[0028] FIG. 4 is an explanatory view of centering using a floating
chuck system.
LIST OF REFERENTIAL NUMBERS
[0029] 1: tubular member, 1a: complete thread portion, 1b: mill
scale, 1c: incomplete thread portion, 1d: border, 2: floating chuck
system, 2a: positioning chuck, 2b: floating chuck, 3: rigid chuck
system, 3a: front chuck
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] Below, the progress until the present invention has
completed and examples of the best mode of the invention will be
explained while referring to FIG. 1 which illustrates a normal
chuck of the non-floating type and to FIG. 2 which illustrates a
floating chuck.
[0031] The present inventors studied why mill scale sometimes
remains on the complete thread portion when carrying out thread
cutting on an end portion of a long tubular member and specifically
an oil country tubular good, even when centering is accurately
carried out using a floating chuck system.
[0032] The causes of mill scale remaining on a complete thread
portion are swinging about of an end portion of a long tubular
member due to bending of the end portion, and deformation of the
portion of the tubular member held by a chuck system into an
elliptical shape due to the holding pressure. Mill scale which
remains due to bending of a tube end portion is present on the side
of the complete thread portion closer to the tube end surface. In
contrast, mill scale which remains due to deformation caused by the
holding pressure of the chuck is present on the side of the
complete thread portion closer to the portion being held by the
chuck (the side closer to the midpoint of the tube longitudinal
axis) as shown in FIG. 3.
[0033] Of these causes, swinging about of an end portion of a long
tubular member can be suppressed by reducing the distance (the
protruding length) L from the end face of the tubular member to the
end face of the chuck system which is holding the tubular member.
As for the other cause, if the holding pressure exerted by the
chuck system is too small, the holding force decreases and chatter
develops at the time of machining. Therefore, a certain amount of
deformation of the tubular member in the vicinity of the holding
portion due to the holding pressure is unavoidable. The larger is
the diameter of a tubular member and the smaller is its wall
thickness, the greater is the deformation of the tubular member,
and the greater is the effect of the deformation on the portion
being machined.
[0034] Based on this knowledge, the present inventors carried out
experiments which varied machining conditions. As a result, they
found that when using a conventional chuck system of the
non-floating type, there is an optimal range for the ratio L/D of
the distance L from the end face of an end portion being machined
of a long tubular member to the end face of the chuck of the chuck
system closest to the end portion being machined (the distance by
which the tubular member protrudes from the portion of the long
tubular member held by a chuck at the time of machining) to the
outer diameter D of the long tubular member.
[0035] The present inventors also found that when using a floating
chuck system, there are optimal ranges for the ratios L/D and L'/D
of the distance L from the end face of the long tubular member to
the end face of a floating chuck and the distance L' from the end
face of the long tubular member to a positioning chuck with respect
to the outer diameter D.
[0036] FIG. 1 is an explanatory view of an example of a method of
machining an end portion of a long tubular member according to the
present invention when using a conventional chuck system of the
non-floating type. This figure shows cutting of prescribed threads
on one end peripheral portion of a long tubular member 1 by a
thread cutter.
[0037] 3 is a usual chuck system provided on a thread cutter. When
prescribed threads are cut on an end portion of the long tubular
member 1, the chuck system 3 holds the long tubular member 1 with a
front chuck 3a and a rear chuck (not shown) in a position away from
the end portion being machined and with a prescribed spacing
between these chucks, such as 2000-2500 mm. Both chucks are of the
rigid type, namely, the location of the axis of each chuck in the
vertical and horizontal directions cannot be adjusted. However, the
position of each chuck in the axial direction may be adjustable by
moving the chuck system or each chuck in the axial direction. The
front chuck 3a is the chuck closest to the end portion being
machined. The axial direction means the axial direction of the long
tubular member.
[0038] Needless to say, an unillustrated cutting tool which can be
adjusted in position relative to the long tubular member 1 is
disposed to one side of one end portion of the long tubular member
1 held by the chuck system 3 (namely, the end portion of the
tubular member protruding from the front chuck 3a).
[0039] In the present invention, when cutting threads on an end
portion of a long tubular member 1 which is held in the vicinity of
the end portion by this type of conventional chuck system 3, the
thread cutting is carried out while holding the long tubular member
1 with the chuck system 3 in a position such that the ratio L/D of
the above-mentioned protruding length L to the outer diameter D is
in the below-described ranges depending on the outer diameter D of
the long tubular member 1 and the ratio t/D of the wall thickness t
to the outer diameter D.
[0040] (1) For a long tubular member 1 having an outer diameter D
of less than 88.9 mm, [0041] (1-1) When t/D (wall thickness/outer
diameter ratio) is at most 0.07: L/D is at least 3.0 and at most
4.5; [0042] (1-2) When t/D is greater than 0.07: L/D is at least
2.5 and at most 3.5;
[0043] (2) For a long tubular member 1 having an outer diameter D
of at least 88.9 mm and at most 139.7 mm, [0044] (2-1) When t/D is
at most 0.07: L/D is at least 2.0 and at most 3.5; [0045] (2-2)
When t/D is greater than 0.07: L/D is at least 1.5 and at most
3.5;
[0046] (3) For a long tubular member 1 having an outer diameter D
greater than 139.7 mm: [0047] (3-1) When t/D is at most 0.07: L/D
is at least 1.5 and at most 2.5; [0048] (3-2) When t/D is greater
than 0.07: L/D is at least 1.0 and at most 2.5.
[0049] When a long tubular member is mounted on the chuck system 3
and is held by the front chuck 3a and the unillustrated rear chuck,
the protruding length L of the long tubular member 1 can be
adjusted such that L/D is in the above-described ranges by
adjusting the length by which the tubular member protrudes from the
front chuck 3a. Additionally or alternatively, if the chuck system
3 or the front chuck 3a is movable in the axial direction, the
protruding length L of the tubular member 1 can be adjusted by this
movement such that L/D is in the above-described ranges.
[0050] FIG. 2 shows an example of the use of a floating chuck
system 2. The floating chuck system 2 includes a positioning chuck
2a which is used for centering prior to machining and a floating
chuck 2b which can adjust the position at which it holds a long
tubular member during machining (the position of the chuck in the
tube axial direction) in both vertical and horizontal directions.
The floating chuck 2b may also be movable in the axial direction by
movement of the chuck system 2 or by movement of the floating chuck
2b itself in the axial direction. Although not shown in the
drawings, a rigid rear chuck is normally disposed to the rear of
the floating chuck 2b (towards the midpoint of the tubular member).
In the illustrated floating chuck system, in contrast to the
floating chuck system 2 shown in FIG. 4, the centering position of
the positioning chuck 2a can be adjusted in the axial direction of
the tubular member. This adjustment is carried out by extending or
retracting axially extending arms 2a' of the positioning chuck 2a
from the body of the chuck system 2 by hydraulic pressure, for
example.
[0051] During the use of a floating chuck system 2, a long tubular
member 1 is held in a position such that the ratios L/D and L'/D of
the distance L (the protruding length of the tubular member during
machining) from the end face of the end portion being machined of
the long tubular member 1 to the end face of the floating chuck 2b
and the distance L'(the protruding length of the tubular member at
the time of centering) from the end face of the long tubular member
1 to the centering position of the positioning chuck 2a (a location
at the center of the positioning chuck) with respect to the outer
diameter D of the tubular member 1 are in the following ranges.
[0052] (1') For a long tubular member 1 having an outer diameter D
of less than 88.9 mm, [0053] (1'-1) When t/D (thickness/outer
diameter ratio) is at most 0.07: L/D is at least 3.0 and L'/D is at
most 3.0; [0054] (1'-2) When t/D is greater than 0.07: L/D is at
least 2.5 and L'/D is at most 3.0;
[0055] (2') For a long tubular member 1 having an outer diameter D
of at least 88.9 mm and at most 139.7 mm, [0056] (2'-1) When t/D is
at most 0.07: L/D is at least 2.0 and L'/D is at most 2.0. [0057]
(2'-2) When t/D is greater than 0.07: L/D is at least 1.5 and L'/D
is at most 2.0;
[0058] (3') For a long tubular member 1 having an outer diameter D
greater than 139.7 mm: [0059] (3'-1) When t/D is at most 0.07: L/D
is at least 1.5 and L'/D is at most 1.5; [0060] (3'-2) When t/D is
greater than 0.07: L/D is at least 1.0 and L'/D is at most 1.5.
[0061] In the case of a floating chuck, the upper limit on the
protruding length of the tubular member 1 is prescribed by the
ratio L'/D, so there is no particular upper limit on L/D.
[0062] The protruding length L of a tubular member 1 from a
floating chuck 2b can be adjusted in the same manner as described
above with respect to a conventional chuck system. The protruding
length L'from the positioning chuck 2a (namely, the amount of
protrusion from the centering position of the chuck) can be
adjusted by changing the position of the positioning chuck 2a in
the axial direction.
[0063] In the present invention, the reason why the optimal ranges
for the ratios L/D and L'/D of the protruding lengths L and L' of
the tubular member to the outer diameter D are varied in accordance
with the outer diameter D and the wall thickness t of the long
tubular member 1 is because the larger is the outer diameter D and
the smaller is the wall thickness t, the greater is the amount of
deformation caused by the holding pressure of the chuck system 2 or
3, and the deformed portion may extend into the region being
machined.
[0064] The reasons why the ratios L/D and L'/D of the protruding
lengths L and L' of a tubular member to the outer diameter D are in
the above-described ranges in the present invention are as
follows.
[0065] If L/D is smaller than the lower limit, the projecting
length of the long tubular member 1 is insufficient, and when the
tubular member is held by a front chuck 3a or a floating chuck 2b,
deformation caused by the holding pressure reaches the complete
thread portion which undergoes thread cutting, and mill scale
remains on a portion of the complete thread portion and
particularly on the side closer to the midpoint of the tube. On the
other hand, if L/D is greater than the upper limit, the protruding
length of the tubular member 1 becomes too large, and due to
bending of the end portion, mill scale remains on part of the
complete thread portion which is formed and particularly toward the
end of the tube.
[0066] When using a floating chuck system 2, the centering position
of the positioning chuck 2a is preferably at most 200 mm from the
floating chuck 2b. Namely, in FIG. 2, the distance A from the
centering position of the positioning chuck 2b (the center of this
chuck) and the end face of the floating chuck 2a is preferably at
most 200 mm.
[0067] The present invention also provides a floating chuck system
2 in which the centering position of the positioning chuck 2a is at
most 200 mm from the floating chuck 2b. If the centering position
of the floating chuck 2a is greater than 200 mm from the floating
chuck 2b, when the end of the long tubular member 1 undergoes a
large amount of bending, the amount of swinging about of the
floating chuck 2b increases, and vibrations of the floating chuck
system 2 so increase that it becomes necessary to decrease the
maximum rotational speed of the tubular member 1.
[0068] The floating chuck system 2 may be of the type shown in FIG.
4 in which the position of the positioning chuck 2a cannot be moved
in the axial direction (and accordingly the centering position is
fixed). In this case as well, the chuck system is preferably
designed such that the centering position of the positioning chuck
2a is at most 200 mm from the floating chuck 2b, and the long
tubular member 1 can be held by the positioning chuck 2 such that
L/D and L'/D are within the ranges of the present invention by
adjusting the protruding length L of the long tubular member 1.
However, if the centering position is fixed, depending upon the
outer diameter D and the wall thickness t of a long tubular member,
it may not always be possible to carry out the method of the
present invention. Accordingly, it is preferable to use a floating
chuck system of the type as shown in FIG. 2 in which the position
of a positioning chuck 2a is movable in the axial direction such
that the centering position of an elongated member 1 can be
changed.
[0069] The manner how a long tubular member 1 is e held by a
floating chuck system 2, i.e., how the chuck system is operated may
be the same as described above with respect to the prior art. The
end to be machined of a long tubular member 1 is inserted into the
chuck system. At this time, the position of the positioning chuck
2a comes at the position of the border (1d in FIG. 3) between the
complete thread portion and the incomplete thread portion of the
threads which are to be formed on an end portion of the tubular
member, and the protruding length L of the tubular member 1 from
the floating chuck 2b and the protruding length L' of the tubular
member 1 from the positioning chuck 2a are made to satisfy L/D and
L'/D prescribed by the present invention. If necessary, the axial
positions of the positioning chuck 2a, the chuck system 2, and/or
the floating chuck 2b are adjusted.
[0070] The tubular member 1 is held by an unillustrated rigid rear
chuck and the positioning chuck 2a, and the positioning chuck 2a is
moved vertically and horizontally in order to perform centering of
the tubular member 1 at the border between the complete thread
portion and the incomplete thread portion. Subsequently, the
floating chuck 2b grips the tubular member 1, after it is moved
vertically and horizontally as required. Upon release of the
positioning chuck 2a, centering of the tubular member 1 is
achieved. Thread cutting is then performed on the peripheral
surface of the end portion of the tubular member 1 which is held by
the rear chuck and the floating chuck 2b such that the protruding
lengths L and L' have prescribed values.
Examples
[0071] In order to ascertain the effects of the present invention,
long tubular members having an outer diameter D (nominal outer
diameter) of 73.0 mm, 114.3 mm, or 177.8 min (each having a length
of 10 meters with bending of the end of the tubular member being at
most 3.0 mm per 300 mm) were held using the chuck system 2 or 3
shown in FIG. 1 or FIG. 2, and API threads were cut on one end
portion of each tubular member. For each outer diameter D, tubular
members having two different wall thicknesses t were prepared, and
machining was carried out while varying the protruding lengths L
and L'of the tubular members for different values of t/D.
[0072] An example of the results is shown in Table 1 and Table 2.
Table 1 shows the results using the conventional chuck system 3 of
FIG. 1 which does not have a floating chuck, and Table 2 shows the
results using the floating chuck system 2 of FIG. 2. The underlined
values for L/D and L'/D are values outside the ranges of the
present invention.
[0073] If the holding pressure of the front chuck 3a (FIG. 1) or
the floating chuck 2b (FIG. 2) in a machining test is too small,
the holding force decreases and chatter develops at the time of
machining. Therefore, the holding pressure was set in the range of
20-40 kgf/cm.sup.2 so that chatter would not develop and so that
the amount of deformation would not become large.
[0074] The results of the machining test were evaluated in terms of
mill scale defects and elliptical defects after machining.
[0075] Mill scale defects were evaluated by visually determining
the percentage of the area of a complete thread portion on which
mill scale was present. The case in which mill scale was present on
at least 5% of the area was given mark "X" (poor), and the case in
which mill scale was present on less than 5% of the area was given
mark "O" (good).
[0076] Elliptical defects were evaluated by measuring the maximum
diameter and the minimum diameter around the entire periphery of
the portion of the tubular member 1 held by the chuck and
calculating the value of ellipticity as [(maximum diameter-minimum
diameter).times.100]/nominal outer diameter. Elliptical defects
were evaluated as poor (X) when the value of ellipticity was 5% or
larger and as good (O) when it was less than 5%.
[0077] The overall evaluation of a tubular member was "O" (good)
when the evaluations for both mill scale defects and elliptical
defects were "O" and was "X" (poor) when at least one evaluation
was "X".
TABLE-US-00001 TABLE 1 Tube outer diameter D (mm) 73.0 114.3 Tube
wall thickness t (mm) 4.60 5.51 6.88 t/D (--) 0.06 0.08 0.06
Protruding length L (mm) 225 345 195 195 345 165 255 415 215 L/D
(--) 3.1 4.7 2.7 2.7 4.7 2.3 2.2 3.6 1.9 Elliptical defects
.largecircle. .largecircle. X .largecircle. .largecircle. X
.largecircle. .largecircle. X Mill scale defects .largecircle. X
.largecircle. .largecircle. X .largecircle. .largecircle. X
.largecircle. Overall evaluation .largecircle. X X .largecircle. X
X .largecircle. X X Tube outer diameter D (mm) 114.3 177.8 Tube
wall thickness t (mm) 9.65 9.19 14.99 t/D (--) 0.08 0.05 0.08
Protruding length L (mm) 215 415 165 335 475 255 255 475 165 L/D
(--) 1.9 3.6 1.4 1.9 2.7 1.4 1.4 2.7 0.9 Elliptical defects
.largecircle. .largecircle. X .largecircle. .largecircle. X
.largecircle. .largecircle. X Mill scale defects .largecircle. X
.largecircle. .largecircle. X .largecircle. .largecircle. X
.largecircle. Overall evaluation .largecircle. X X .largecircle. X
X .largecircle. X X
TABLE-US-00002 TABLE 2 Tube outer diameter D (mm) 73.0 114.3 Tube
wall thickness t (mm) 4.60 5.51 6.88 t/D (--) 0.06 0.08 0.06
Protruding length L (mm) 225 345 195 195 345 165 255 415 215
Protruding length L '(mm) 110 230 80 80 230 50 140 300 100 L/D (--)
3.1 4.7 2.7 2.7 4.7 2.3 2.2 3.6 1.9 L'/D (--) 1.5 3.2 1.1 1.1 3.2
0.7 1.2 2.6 0.9 Elliptical defects .largecircle. .largecircle. X
.largecircle. .largecircle. X .largecircle. .largecircle. X Mill
scale defects .largecircle. X .largecircle. .largecircle. X
.largecircle. .largecircle. X .largecircle. Overall evaluation
.largecircle. X X .largecircle. X X .largecircle. X X Tube outer
diameter D (mm) 114.3 177.8 Tube wall thickness t (mm) 9.65 9.19
14.99 t/D (--) 0.08 0.05 0.08 Protruding length L (mm) 215 415 165
335 475 255 255 475 165 Protruding length L '(mm) 100 300 50 180
320 100 100 320 10 L/D (--) 1.9 3.6 1.4 1.9 2.7 1.4 1.4 2.7 0.9
L'/D (--) 0.9 2.6 0.4 1.0 1.8 0.6 0.6 1.8 0.1 Elliptical defects
.largecircle. .largecircle. X .largecircle. .largecircle. X
.largecircle. .largecircle. X Mill scale defects .largecircle. X
.largecircle. .largecircle. X .largecircle. .largecircle. X
.largecircle. Overall evaluation .largecircle. X X .largecircle. X
X .largecircle. X X
[0078] From Table 1 and Table 2, it can be seen that by holding a
long tubular member by a chuck system and machining an end portion
of the tube according to the present invention, bending and
elliptical deformation are suppressed, and the occurrence of mill
scale or elliptical defects can be suppressed to less than 5%.
[0079] Embodiments of the present invention have been explained,
but the present invention is not limited to these embodiments, and
various modifications can be made within the scope of the technical
concept set forth in the appended claims.
* * * * *