U.S. patent application number 11/274441 was filed with the patent office on 2006-03-30 for method and apparatus for polishing an internal surface of an aluminum extrusion hollow shape.
This patent application is currently assigned to NISSIN UNYU KOGYO CO., LTD.. Invention is credited to Tadashi Aiura, Kazuo Akagi, Katsuhiko Inoue, Toshihiko Sasaki, Koji Takahashi.
Application Number | 20060065518 11/274441 |
Document ID | / |
Family ID | 18174320 |
Filed Date | 2006-03-30 |
United States Patent
Application |
20060065518 |
Kind Code |
A1 |
Aiura; Tadashi ; et
al. |
March 30, 2006 |
Method and apparatus for polishing an internal surface of an
aluminum extrusion hollow shape
Abstract
There is provided an electrolytic integrated polishing apparatus
which enables high precision polishing of the internal surface of a
long sized cylindrical workpiece such as a metallic tube. The
apparatus includes a work supporting unit for disposing the
cylindrical workpiece, so that the axial center of the cylindrical
portion is aligned with the vertical direction, a rotation shaft
supported downward along the vertical direction and free-rotatably
supported in an external tube which is freely movable along the
vertical direction, a tool electrode including a grindstone
directed to radial directions, attached to the tip of the rotation
shaft, and a plastic tube wound around the external surface of the
external tube for pressurization.
Inventors: |
Aiura; Tadashi;
(Shimonoseki-shi, JP) ; Inoue; Katsuhiko;
(Shimonoseki-shi, JP) ; Sasaki; Toshihiko;
(Shimonoseki-shi, JP) ; Akagi; Kazuo;
(Shimonoseki-shi, JP) ; Takahashi; Koji;
(Shimonoseki-shi, JP) |
Correspondence
Address: |
WEINGARTEN, SCHURGIN, GAGNEBIN & LEBOVICI LLP
TEN POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Assignee: |
NISSIN UNYU KOGYO CO., LTD.
|
Family ID: |
18174320 |
Appl. No.: |
11/274441 |
Filed: |
November 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09341339 |
Aug 30, 1999 |
6994610 |
|
|
PCT/JP98/04494 |
Oct 5, 1998 |
|
|
|
11274441 |
Nov 14, 2005 |
|
|
|
Current U.S.
Class: |
204/212 ;
204/198 |
Current CPC
Class: |
B24B 5/40 20130101; B24B
5/08 20130101; B23H 5/04 20130101; B23H 5/08 20130101; B23H 9/005
20130101; C25F 7/00 20130101 |
Class at
Publication: |
204/212 ;
204/198 |
International
Class: |
C25D 17/00 20060101
C25D017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 1997 |
JP |
9-325215 |
Claims
1. An electrolytic integrated polishing apparatus for polishing an
internal surface of a cylindrical portion of a long sized
cylindrical workpiece by integrating elution by electrolyte and
abrasion by a grindstone attached to a tool electrode inserted into
the cylindrical portion, said apparatus comprising a work
supporting unit for disposing the long sized cylindrical workpiece
so that the axial center of its cylindrical portion is aligned with
the vertical direction, a rotation shaft inserted into the
cylindrical portion of said long sized cylindrical workpiece, a
coaxial external tube supported downward along the vertical
direction to free-rotatably support said rotation shaft and
inserted together with said rotation shaft into the cylindrical
portion of said long sized cylindrical workpiece, a tool electrode
attached to the tip of said rotation shaft, and a transportation
unit for moving said rotation shaft and/or the work supporting unit
along the axial direction.
2. The electrolytic integrated polishing apparatus for polishing
the internal surface of the cylindrical portion of a long sized
cylindrical workpiece according to claim 1, wherein a plastic tube,
inside of which can be pressurized, is spirally wound around the
periphery of said external tube.
3. The electrolytic integrated polishing apparatus for polishing
the internal surface of the cylindrical portion of a long sized
cylindrical workpiece according to claim 2, wherein a free ring,
having approximately the same bore as the finished bore of said
cylindrical portion, is free-rotatably disposed to the upper and
the lower positions of the cylindrical portion of the long sized
cylindrical workpiece, and a guide sleeve with a predetermined
length, having approximately the same bore as the bore of said free
ring, is disposed further above the free ring disposed at the upper
side.
4. An aluminum extrusion hollow shape finished by the electrolyte
integrated polishing apparatus according to claim 1, wherein a
length of a cylindrical portion thereof being ten times as large as
a diameter thereof, or more, and a roundness of an internal surface
of the cylindrical portion equal to or smaller than 10 .mu.m and a
surface roughness Rmax equal to or small than 1 .mu.m.
5. The electrolytic integrated polishing apparatus for polishing
the internal surface of the cylindrical portion of a long sized
cylindrical workpiece according to claim 1, wherein a free ring,
having approximately the same bore as a finished bore of said
cylindrical portion, is free-rotatably disposed to the upper and
the lower positions of the cylindrical portion of the long sized
cylindrical workpiece.
6. The electrolytic integrated polishing apparatus for polishing
the internal surface of the cylindrical portion of a long sized
cylindrical workpiece according to claim 2, wherein a free ring,
having approximately the same bore as a finished bore of said
cylindrical portion, is free-rotatably disposed to the upper and
the lower positions of the cylindrical portion of the long sized
cylindrical workpiece.
7. The electrolytic integrated polishing apparatus for polishing
the internal surface of the cylindrical portion of a long sized
cylindrical workpiece according to claim 1, wherein a hollow
portion is provided inside the tool electrode, and a plastic tube,
inside of which can be pressurized, is provided in said hollow
portion.
8. The electrolytic integrated polishing apparatus for polishing
the internal surface of the cylindrical portion of a long sized
cylindrical workpiece according to claim 2, wherein a hollow
portion is provided inside the tool electrode, and a plastic tube,
inside of which can be pressurized, is provided in said hollow
portion.
9. The internal surface of the cylindrical portion of a long sized
cylindrical workpiece according to claim 3, wherein a hollow
portion is provided inside the tool electrode, and a plastic tube,
inside of which can be pressurized, is provided in said hollow
portion.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application under
.sctn.1.53(b) of prior application Ser. No. 09/341,339 filed Aug.
30, 1999; which was a .sctn.371 filing of PCT/JP98/04494 filed Oct.
5, 1998, entitled: METHOD AND APPARATUS FOR POLISHING INNER SURFACE
OF CYLINDRICAL PORTION OF ELONGATED CYLINDRICAL WORK AND ELONGATED
CYLINDRICAL WORK; which claimed priority under 35 USC
.sctn.119(a)-(d) to Japanese Application No. 9/325215 filed Nov.
10, 1997.
FIELD OF THE INVENTION
[0002] The present invention relates to a polishing method and
apparatus for mirror processing of the internal surface of a long
sized cylindrical workpiece such as a metallic tube, shape or the
like, including an aluminum extrusion hollow shape with a
cylindrical portion, using electrolytic integrated polishing
technology, and to a long sized cylindrical workpiece such as an
aluminum extrusion hollow shape polished by electrolytic integrated
polishing according to the method.
BACKGROUND ART
[0003] Cylindrical portions of fluid pressure cylinders such as
hydraulic cylinders, air cylinders or the like are required to have
roundness of 25 .mu.m for hydraulic cylinders and 150 .mu.m for air
cylinders. For example, because aluminum extrusion hollow shapes
used for these cylinders have inadequate precision by normal
extrusion only, roundness or dimensional precision of cylindrical
portions of most products thereof are improved by machining such as
cutting or by post-machining burnishing. However, a material, the
cylindrical portion of which has a small bore or a longitudinal
size larger than the bore, can not be machined. Therefore, the
current situation has been such that, for example, yield is
declining for not achieving required roundness, or productivity is
staying low for having to machine the pieces, one by one, of a long
sized material which must be cut into product length
beforehand.
[0004] On the other hand, electrolytic integrated polishing
technology, a hybrid of elution by electrolyte and abrasion by
abrasives, is known as a method for polishing the surface of metal
with a high precision. The electrolytic integrated polishing
technology, applied to mirror finishing of the internal surface of
metallic tubes, generally inserts a rotation shaft, to the tip of
which a tool electrode is attached, into a metallic tube, rotates
the metallic tube about the rotation shaft, then supplies
electrolyte inside the metallic tube and passes current, and
polishes the internal surface of the metallic tube by a grindstone
attached to the tool electrode, withdrawing the rotation shaft
slowly.
[0005] With such electrolytic integrated polishing methods for the
internal surface of metallic tubes, abrasion of the grindstone
prevents high precision mirror finishing due to inappropriate
polishing of the internal surface. Therefore, apparatuses coping
with abrasion of the grindstone by applying pressing force onto the
grindstone via a leaf, a diaphragm or the like are conventionally
known. (See Japanese utility Model Laid-Open Publication No. Hei
4-130120, 5-86429 and so on.) The above mentioned conventional
method using a leaf cannot preserve the desired polishing
performance because pressing force decreases as the grindstone
abrades, especially in narrow places such as the internal surface
of a long sized metallic tube. Besides, there have been
shortcomings such as the necessity of a specific insertion guide
for inserting the polishing tool into the metallic tube because the
leaf generates force by being bent to a predetermined extent.
[0006] On the other hand, although a method using a diaphragm can
resolve the above mentioned problem caused by the leaf, a plurality
of diaphragms corresponding to a plurality of grindstones must be
individually disposed, which makes processing of the installation
sections, and installation work complicated. Besides pressing force
applied to individual grindstones is not uniform due to variations
in the plurality of diaphragms, which makes mirror finishing with a
high precision impossible.
[0007] The above mentioned method is mainly applied to processing
of the internal surface of pipes made from steel or stainless
steel. Most apparatuses are horizontal types that can easily
perform processing of long sized products, while there are few
vertical types. (See Japanese Patent Laid-Open Publication No. Hei
3-98758.) Furthermore, there is no concrete example of application
to aluminum extrusion shapes having a variety of external
shapes.
[0008] Machining (cutting, for example) of the internal surface of
the cylindrical portion of an aluminum extrusion hollow shape is
more difficult than processing of external surface. Besides, long
materials, with difficulties in processing due to problems with
rigidity of the tool, must be cut short for processing in order to
preserve a certain processing precision. Therefore, other than
increase in cost, ultra high precision mirror finishing of aluminum
alloy by cutting has been difficult because aluminum alloy, having
a low rigidity which is about one-third of steel and a coefficient
of thermal expansion twice as large as steel, is easy to be
deformed by cutting resistance or cutting heat.
[0009] On the other hand, electrolytic integrated polishing which
is an ultra high precision finishing technology with a roundness of
finished surface equal to or smaller than lO .mu.m and a surface
roughness equal to or smaller than 1 .mu.m, can be applied to long
sized pipes. However, a problem remains in that directly applying
electrolytic integrated polishing methods and apparatuses that have
been mainly used for polishing of the internal surface of steel or
stainless steel tubes to polishing of the internal surface of a
cylindrical portion of an aluminum extrusion hollow shape will not
result in processing with a high precision.
[0010] For example, the inventors of the present invention failed
to obtain the desired processing precision by electrolytic
integrated polishing of the internal surface of an aluminum
extrusion tube using a conventional electrolytic integrated
polishing apparatus (a type in which axial directions of a long
sized metallic tube and a tool electrode are horizontally oriented,
and the metallic tube and the tool electrode are rotated in
opposite directions with each other.) This is because processing
was performed with the pressing force of the grindstone controlled
at a low pressure due to softness and easiness to deformation of
aluminum, having a low strength and a low rigidity which are about
one-third of steel or stainless steel, and because precision of
processing degrades by deflection of the axial center due to
influence of weight of the tool electrode supported horizontally by
the rotation axis.
[0011] Besides, since rotating metallic shapes having a variety of
external shapes is virtually impossible, long sized cylindrical
workpieces to which the above mentioned electrolytic integrated
polishing apparatus can be applied are limited to cylinder
pipes.
[0012] It is an object of the present invention, having been made
considering the above mentioned problems in the prior art, to
provide an electrolytic integrated polishing method and apparatus
which enables high precision polishing of the internal surfaces of
the cylindrical portions of metallic shapes having a variety of
external shapes such as aluminum extrusion hollow shapes or the
like, and to provide long sized cylindrical workpieces such as
aluminum extrusion hollow shapes having internal surfaces of the
cylindrical portions polished with a high precision.
DISCLOSURE OF THE INVENTION
[0013] The method according to the present invention is an
electrolytic integrated polishing method for polishing the internal
surface of the cylindrical portion of a long sized cylindrical
workpiece such as an aluminum extrusion hollow shape by integrating
elution by electrolyte and abrasion by a grindstone attached to a
tool electrode inserted into the cylindrical portion, characterized
by disposing the long sized cylindrical workpiece so that the axial
center of its cylindrical portion is aligned with the vertical
direction, inserting the tool electrode attached to the tip of a
rotation shaft supported downward similarly along the vertical
direction into the cylindrical portion, and rotating as well as
relatively moving the tool electrode vertically.
[0014] Besides, the apparatus according to the present invention is
an electrolytic integrated polishing apparatus for polishing the
internal surface of the cylindrical portion of a long sized
cylindrical workpiece such as an aluminum extrusion hollow shape by
integrating elution by electrolyte and abrasion by a grindstone
attached to a tool electrode inserted into the cylindrical portion,
characterized by comprising a work supporting unit for disposing
the long sized cylindrical workpiece so that the axial center of
its cylindrical portion is aligned with the vertical direction, a
rotation shaft supported downward along the vertical direction and
inserted into the cylindrical portion of the above mentioned long
sized cylindrical workpiece, the tool electrode attached to the tip
of the rotation shaft, and a transportation unit for moving the
above mentioned shaft and/or the work supporting unit along the
axial direction.
[0015] In the present method and apparatus, because the rotation
shaft is supported downward along the vertical direction and the
tool electrode is attached to the tip thereof, influence of the
weight of the tool electrode and the rotation shaft themselves is
eliminated to suppress deflection of the tool electrode, which
improves the precision of processing. Besides, the present method
and apparatus can be similarly applied to a variety of metallic
shapes such as aluminum extrusion hollow shape or the like having a
variety of external shapes, because only the tool electrode is
rotated without rotating the long sized cylindrical workpiece.
[0016] Here, the above mentioned transportation unit may be
disposed at either one or both sides of the rotation shaft and the
work supporting unit. That is, any disposition will do if the long
sized cylindrical workpiece and the tool electrode move along the
axial direction relatively to each other.
[0017] Note that as an embodiment of the above mentioned polishing
apparatus, the above mentioned rotation shaft is free-rotatably
supported inside an external tube supported downward along the
vertical direction. The external tube does not rotate, preferably
covers almost throughout the whole length of the rotation shaft
except for the tool electrode at the tip thereof, and is moved
along the axial direction simultaneously with the rotation axis. In
this case, since the rotation shaft is free-rotatably supported at
the center of the external tube, deflection of the tool electrode
when rapidly rotating is suppressed to improve the precision of
processing.
[0018] Besides, when the above external tube is provided, it is
preferable to wind a plastic tube spirally around the periphery
thereof and to enable pressurization inside the plastic tube. When
the external tube is inserted, for example, into the cylindrical
portion of a long sized cylindrical workpiece, such as an aluminum
extrusion hollow shape, and pressure is applied onto the plastic
tube at the state, the plastic tube expands and is pressed against
the internal surface of the cylindrical portion. The effect,
preventing minute deflections caused by rotation of the rotation
axis and the tool electrode and maintaining the external tube
always at the center of the cylindrical portion, results in further
improvement of the precision of processing.
[0019] Furthermore, preferably a hollow portion is provided inside
the tool electrode, a pressure tube composed of silicon tube or the
like, inside of which can be pressurized, is provided in the above
mentioned hollow portion. By pressurizing inside the pressure tube,
elastic grindstones can be pressed with a constant pressure toward
radial directions. Besides, a constant pressing force is always
maintained when the grindstones are worn out.
[0020] Moreover, by the electrolytic integrated polishing method
and apparatus, it becomes possible to perform finish polishing,
without machining, of a long sized metallic shape such as an
aluminum extrusion hollow shape, the length of the cylindrical
portion of which is ten times as large as the diameter, or more,
with a roundness of the internal surface of the cylindrical portion
equal to or smaller than lO .mu.m and a surface roughness Rmax
along the axial and circular directions equal to or smaller than 1
.mu.m.
[0021] Other characteristics of the present invention will be
described in detail in the following sections about preferred
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a general view of an electrolytic integrated
polishing apparatus according to the present invention;
[0023] FIG. 2 is a view illustrating the major portion thereof;
[0024] FIG. 3 is a vertical cross sectional view of the tool
electrode;
[0025] FIG. 4 is a horizontal cross sectional view of the electrode
at plane A-A in FIG. 3; and
[0026] FIG. 5 is a cross sectional view of an aluminum extrusion
hollow shape used in the example.
BEST MODE FOR CARRYING OUT THE INVENTION
[0027] The electrolytic integrated polishing apparatus according to
the present invention will be described in detail hereinafter with
reference to FIGS. 1 to 5.
[0028] As shown in FIGS. 1 and 2, the electrolytic integrated
polishing apparatus includes a platform 1, a frame 2 disposed on
the platform, an external tube 3 vertically disposed, a rotation
shaft 4 vertically and free-rotatably disposed via a plurality of
bearings (not shown) inside the external tube 3, a tool electrode 5
attached to the tip of the rotation shaft 4 at the lower portion of
the external tube 3, a plastic tube 6, inside of which can be
pressurized by a mechanism (not shown), comprising a silicon tube
or the like and being spirally wound around the periphery of the
external tube 3, a guide 7 attached to the frame 2, a sliding
member 8 freely and vertically slidable along the guide 7, a
supporting member 9 fixed to the sliding member 8 for supporting
the upper end of the external tube 3, a bearing member 10 fixed to
the sliding member 8 for supporting nearby the upper portion of the
rotation shaft 4, a transportation motor 11 for sliding the sliding
member 8 vertically along the guide 7 thus moving the external tube
3 and the rotation shaft 4 upward and downward, a motor 12 attached
to the sliding member 8 for rotating the rotation shaft 4, and a
fixed chuck 13 (positive pole energizing chuck) for fixing a long
sized cylindrical workpiece, such as, for example, an aluminum
extrusion hollow shape.
[0029] In the electrolytic integrated polishing apparatus, the
rotation shaft 4 is a hollow shaft (see FIG. 3) the top of which
enabling introduction of air into a hollow bore 4a via a rotary
joint 15. Besides, the present apparatus also includes a free ring
mechanism 16, which is located above the fixed chuck 13, freely
slidable along the guide 7 and can be fixed to any appropriate
position, a guide sleeve 17 disposed on the free ring mechanism 16,
a liquid receiver 18 for receiving electrolyte flowing out from an
opening of the guide sleeve 17, a free ring mechanism 19 fixed at a
lower position of the fixed chuck 13, and a negative pole
energizing brush 20 contacting the rotation shaft 4.
[0030] The free ring mechanisms 16 and 19 have approximately the
same structure, wherein free rings 23, 24, 25 and 26 are
free-rotatably supported, in two layers within fixed sleeves 21 and
22, independent of each other, via a mechanical seal. Then, the
free ring mechanisms 16 and 19 are kept in contact, via seal
packings 27 and 28 with the upper and the lower openings of the
cylindrical portion of the aluminum extrusion hollow shape W
attached to the fixed chuck 13. The free rings 23 to 26 have the
same or slightly larger bore than the finished bore of the
cylindrical portion of the aluminum extrusion hollow shape W, and
approximately the same length as that of an elastic grindstone,
described hereafter, of the tool electrode 5. The free rings 23 to
26 are rotated freely and synchronously by the pressing force of
the elastic grindstone, and prevent the end surface of the
cylindrical portion of the aluminum extrusion hollow shape W from
deforming into a bell-mouth shape because of the polishing.
[0031] Besides, the guide sleeve 17, successively disposed on the
free ring mechanism 16, has approximately the same bore as those of
the free rings 23 and 24.
[0032] As shown in FIG. 3, the rotation shaft 4 is free-rotatably
supported in the external tube 3 by the bearing 30. Besides, a
felt-like seal 33 intermediates between a seal holder 31 screwed
into the lower end of the external tube 3 and a seal holder 32
fixed to the rotation shaft 4 to prevent electrolyte from flowing
in between the external tube 3 and the rotation shaft 4 which are
rotating relatively to each other.
[0033] The tool electrode 5 is attached, via a mounting member 34,
to the tip of the rotation shaft 4 projecting from the lower end of
the external tube 3. As also shown in FIG. 4, hollow electrodes 35
and 36 are attached to the upper and the lower sections of the tool
electrode 5, apart from each other by a predetermined interval.
Openings are provided to each of the electrodes 35 and 36, in a
radial manner, 180 degrees apart from each other. The openings of
each of the electrodes 35 and 36 are faced to directions 90 degrees
apart. In each opening, as abrasives, elastic grindstones 37 and 38
for coarse polishing and finishing, respectively, are supported as
well as a holder 39 along radial directions to be freely slidable.
Disposed in the hollow of the tool electrode 5 is a pressure tube
41, composed of a silicon tube or the like, one end of which
communicates with the hollow bore 4a of the rotation shaft 4 while
the other end thereof is sealed by a plug 40. The pressure tube 41
expands by air introduced into the hollow bore 4a via the rotary
joint 15, and presses the elastic grindstones 37 and 38, toward
radial directions, against the internal surface of the cylindrical
portion of the aluminum extrusion hollow shape W with a constant
pressure according to the air pressure. A hard glass 42 is attached
to the side walls of the openings of the electrodes 35 and 36 to
reduce the friction between the electrodes and the holder 39.
[0034] In order to prevent leakage current, insulation is provided
between the supporting member 9 and the external tube 3 and between
the bearing member 10 and the rotation shaft 4, and the external
surface of the external tube 3 is insulated by sheathing. Besides,
the metallic portions of the tool electrode 5 are insulated by
sheathing except that the sides of the external surface of the
electrode 35 sandwiching the elastic grindstone 37 are exposed. As
for the exposed surface, the front side of the direction of
rotation of the elastic grindstone 37 is an exposed surface 35a for
passivation coating generation, and the rear side thereof is an
exposed surface 35b for intensive elution.
[0035] The plastic tube 6 wound around the external tube 3 is, as
shown in FIG. 2, located between the external surface of the
external tube 3 and the internal surface of the cylindrical portion
of the aluminum extrusion hollow shape W, the free rings 23 and 24,
and the guide sleeve 17, respectively. Applying pressure inside of
the plastic tube 6 expands and presses the plastic tube 6 against
the internal surface of the above mentioned elements, which
prevents minute deflections of the external tube 3 caused by rapid
rotation of the rotation shaft 4 and the tool electrode 5.
[0036] The polishing process using the electrolytic integrated
polishing apparatus will be described next.
[0037] Firstly, the aluminum extrusion hollow shape W to be
processed is grasped by the fixed chuck 13 and fixed on the free
ring mechanism 19 via the seal packing 28, and the free ring
mechanism 16 is fixed on the aluminum extrusion hollow shape W via
the seal packing 27. Here, the axial center of the internal
surfaces of the cylindrical portion of the aluminum extrusion
hollow shape W, each of the free rings 23 to 26 and the guide
sleeve 17 must be aligned on the same axial line, and, at the same
time, they must be aligned on the same axial line of the external
tube 3, the rotation shaft 4 and the tool electrode 5. (see FIG. 1)
Under this situation the transportation motor 11 is driven to bring
down the sliding member 8 and to insert the tool electrode 5 from
the guide sleeve 17. Thus the bringing down is stopped at a
position shown in FIG. 2, that is, a position where the elastic
grindstone 37 for coarse polishing meets the lower position, for
example, being the location of the free ring mechanism 19, of the
cylindrical portion of the aluminum extrusion hollow shape W.
Because no air is introduced into the pressure tube 41 and the
inside of the plastic tube 6 is not pressurized, the tool electrode
5 and the external tube 3 can be smoothly inserted without
resistance.
[0038] Next, air is introduced into the plastic tube 6 and the
pressure tube 41 for pressurization, and electrolyte is introduced
from the electrolyte injection opening at the lower portion of the
free ring mechanism 19. Then the motor 12 is driven to rapidly
rotate the rotation shaft 4 and the tool electrode 5. The rotation
shaft 4 and the fixed chuck 13 are energized, setting the
electrodes 35 and 36 to be the negative pole and the aluminum
extrusion hollow shape W to be the positive pole and driving the
transportation motor 11 to bring up the tool electrode 5 at a
constant velocity.
[0039] Now, the electrolyte rises through the gap between the tool
electrode 5 and the internal surfaces of the free rings 25 and 26,
and passes through the gap between the internal surface of the
cylindrical portion of the aluminum extrusion hollow shape W and
the external surface of the external tube 3, the gap between the
internal surfaces of the free rings 24 and 23 and the external
surface of the external tube 3, and the gap between the internal
surface of the guide sleeve 17 and the external surface of the
external tube 3. Then the electrolyte is discharged to the liquid
receiver 18, recovered and, after having the polishing sludge
separated by precipitation and filtered, forcedly fed again to the
electrolyte injection opening.
[0040] At the beginning of the polishing process, the elastic
grindstones 37 and 38 are pressed against the internal surfaces of
the free rings 25 and 26, however the free rings 25 and 26 will not
be polished because they are rotating in synchronization with the
rotation of the elastic grindstones 37 and 38. Here, by disposing
the free rings 25 and 26 in two layers with approximately the same
length as the elastic grindstones 37 and 38, inertia weight of each
becomes small, which results in better response to the rotation of
the elastic grindstones 37 and 38.
[0041] As the tool electrode 5 rises and the elastic grindstone 37
comes into the cylindrical portion of the aluminum extrusion hollow
shape W, the elastic grindstone 37 is pressed against its internal
surface and polishing is performed based on the following
principle. That is, while the electrode 35 is rapidly rotating, a
thin passivation coating is generated on the internal surface of
the cylindrical portion via the exposed surface 35a for passivation
coating generation before the elastic grindstone 37 begins
polishing. Then the elastic grindstone 37 abrades the internal
surface of the cylindrical portion, which results in removing the
passivation coating which lacks viscosity and exposing the metallic
base. Immediately after that, electrolytic current concentrates on
the height of the metallic base via the exposed surface 35b for
intensive elution and performs selective electrolysis. Following
the above, the tool electrode 5 gradually rises and the
electrolytic integrated polishing is performed on the internal
surface of the cylindrical portion until the elastic grindstones 37
and 38 are withdrawn from the cylindrical portion of the aluminum
extrusion hollow shape W, smoothing the internal surface.
[0042] At the initial stage of the polishing process, the free
rings 25 and 26 prevent the end surface of the cylindrical portion
of the aluminum extrusion hollow shape W from being polished into a
bell-mouth shape. That is, with regard to the elastic grindstone 37
for example, on its way entering the cylindrical portion, a portion
of the elastic grindstone 37 is pressed against the internal
surface of the cylindrical portion while the rest of the portions
thereof are pressed against the free ring 25. However, because the
bores of the cylindrical portion and the free ring 25 are the same,
the pressed surface of the elastic grindstone 37 being pressed does
not tilt, therefore the end surface of the cylindrical portion will
not be polished into a bell-mouth shape.
[0043] When the elastic grindstones 37 or 38 are being withdrawn
from the cylindrical portion of the aluminum extrusion hollow shape
W at the final stage of the polishing process, the free ring 24
prevents the end surface of the cylindrical portion from being
polished into a bell-mouth shape.
[0044] While the polishing process is being performed, the plastic
tube 6 is pressurized and pressed against the internal surfaces of
the cylindrical portion of the aluminum extrusion hollow shape W,
the free rings 23 and 24, and the guide sleeve 17, respectively
preventing minute deflections of the external tube 3 caused by
rapid rotation of the rotation shaft 4 and the tool electrode 5,
which eventually prevents deflection of the tool electrode 5 in the
cylindrical portion. By disposing the guide sleeve 17 with a
constant length successively above the free ring mechanism 16, the
plastic tube 6 can provide a contacting internal surface until the
elastic grindstones 37 and 38 are completely withdrawn from the
cylindrical portion of the aluminum extrusion hollow shape W and
stopped rotating, which can prevent deflection of the external tube
3.
[0045] Here, metallic tubes or shapes made from steel, stainless
steel, aluminum, aluminum alloy or the like may be exemplified,
although not limited to them, for the long sized cylindrical
workpiece to which the method according to the present invention is
applied. Besides, the length of the cylindrical portion is ten
times as large as the diameter, or more. The long sized cylindrical
workpiece is finished to have a roundness of the internal surface
of the cylindrical portion thereof equal to or smaller than 10
.mu.m and a surface roughness Rmax equal to or smaller than 1
.mu.m, by the electrolytic integrated polishing.
EXAMPLE 1
[0046] A 600 mm long aluminum extrusion hollow shape, having a
cross section shown in FIG. 5 was disposed in a vertical type
electrolytic integrated polishing apparatus shown in FIG. 1 for
polishing its central cylindrical portion (32 mm of finishing
bore). Polishing was performed with the tool electrode having
two-layered electrodes and elastic grindstones for coarse polishing
and finishing, and under a condition that the electrolyte was
sodium nitrate aqueous solution (20%), applied voltage was 8V,
rotation speed of the tool electrode was 2.5 m, rising speed was 1
m per minute.
[0047] As a result, roundness of the shape at the central
cylindrical portion, which was 450 .mu.m before polishing, became
9.2 .mu.m after polishing, surface roughness (Rmax) along axial
direction, which was 0.8 .mu.m before polishing, became 0.5 .mu.m
after polishing, and surface roughness (Rmax) along circular
direction, which was 1.98 .mu.m before polishing, became 0.3 .mu.m
after polishing, all of which showed a largely improved
precision.
EXAMPLE 2
[0048] A 600 mm long stainless steel cold-finished tube was
disposed in a vertical type electrolytic integrated polishing
apparatus shown in FIG. 1 for polishing its internal surface (32 mm
of finishing bore). Polishing was performed with the tool electrode
having two-layered electrodes and elastic grindstones for coarse
polishing and finishing, and under a condition that the electrolyte
was sodium nitrate aqueous solution (20%), applied voltage was 8V,
rotation speed of the tool electrode was 3.0 m, rising speed was
0.4 m per minute.
[0049] As a result, surface roughness (Rmax) of the base tube,
which was 10 .mu.m before polishing, became after finishing, 0.2
.mu.m with a grain size #1500 and 0.08 .mu.m with a grain size
#6000, all of which provided an excellent mirror finishing.
APPLICABILITY TO INDUSTRY
[0050] According to the present invention, polishing of the
internal surface of the cylindrical portion of a long sized
cylindrical workpiece with a high precision in terms of roundness
and surface roughness becomes possible, without machining.
Therefore, for example, a process, wherein a workpiece still in the
form of a long sized material is polished and afterwards cut into
pieces with a length of a fluid pressure cylinder, can be
performed, improving the efficiency of the high-precision polishing
and the productivity. Additionally, the present invention can be
applied to high-precision polishing of the internal surfaces of the
cylindrical portions of metallic shapes having a variety of
external shapes.
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