Manufacturing method and manufacturing apparatus for metallic bellows

Information

  • Patent Grant
  • 6564606
  • Patent Number
    6,564,606
  • Date Filed
    Friday, June 8, 2001
    23 years ago
  • Date Issued
    Tuesday, May 20, 2003
    21 years ago
Abstract
A manufacturing method for manufacturing a bellows having pleat walls with S-shaped profiles comprises a primary forming process for forming a formed bellows, a pressing process for compressing the formed bellows in the axial direction, and a stretching process for pulling the compressed bellows in the axial direction, thereby obtaining desired pitches and free length. After the stretching process is carried out, the bellows is subjected to an annealing and ageing heat-treatment process. An apparatus for manufacturing the bellows comprises a pair of molds that have their respective forming surfaces in shapes corresponding individually to the pleat walls. The die is slightly retreated away from the pleat walls just before the dies open in the diametrical direction after the pleat walls are formed.
Description




CROSS-REFERENCE TO RELATED APPLICATIONS




This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-181727, filed Jun. 16, 2000; and No. 2000-192802, filed Jun. 27, 2000, the entire contents of both of which are incorporated herein by reference.




BACKGROUND OF THE INVENTION




The present invention relates to a manufacturing method and a manufacturing apparatus for a metallic bellows incorporated in an accumulator, vacuum valve, or pump.




A metallic bellows has top portions and bottom portions that are formed alternately in its axial direction. The top and bottom portions constitute pleat walls. Conventionally, the top and bottom portions have V-, Ω-, or S-shaped profiles, besides U-shaped profiles. When a bellows that has pleat walls with S-shaped profiles is compressed in its axial direction, its length (compact-state length) is shorter enough than that of an ordinary bellows with U-shaped pleat walls. Thus, the S-profiled bellows can enjoy a long stroke for extension and contraction from its free length. The “free length” described herein is the axial length of the bellows that is not subjected to any external force. The “compact-state length” is the axial length of bellows obtained when the bellows is compressed so that pleat walls come into contact with one another.




In a known method for manufacturing an S-profiled metallic bellows, a plurality of disc-shaped bellows elements with S-shaped profiles that are formed by pressing, for example, are welded in succession to one another. In an alternative method, top portions and bottom portions are formed integrally with one another by bulging a metallic blank tube as a material of a bellows. The former is called a welded bellows, and the latter a formed bellows. The formed bellows has an advantage over the welded bellows in enjoying higher yield of material, small number of manufacturing steps and steadier quality.




As an example of bulging, hydraulic forming may be used integrally to form an S-profiled bellows. In the bellows formed by the hydraulic forming, the radius of curvature of the distal end of each bottom portion, in particular, is considerably greater than that of the distal end of each top portion. Accordingly, the hydraulic forming only cannot make the most of the advantage (shorter compact-state length) of the S-profiled bellows.




A bellows manufacturing apparatus for hydraulic forming comprises first and second dies that are arranged around a blank tube as a material of a bellows. Hydraulic pressure is applied from inside the tube to expand a part of the tube between the first and second dies. At the same time, these dies are moved toward each other so that the expanded part of the tube is held between them, whereupon pleat walls are formed.




The bellows manufacturing apparatus of this type has a problem that if the taper angles of the respective opposite forming surfaces of the paired dies are narrow, the pleat walls are scratched as the dies are opened in the diametrical direction of the tube after the walls are formed. The pleat walls can be prevented from being scratched by widening the taper angles of the forming surfaces of the dies. If the taper angles of the forming surfaces are wide, however, the distance between the respective distal end portions of the dies is so long that the pleat walls cannot be easily formed into desired corrugated configurations (S-shaped configurations).




BRIEF SUMMARY OF THE INVENTION




Accordingly, a first object of the present invention is to provide a manufacturing method for a metallic bellows, whereby the compact-state length of a metallic bellows having pleat walls with S-shaped profiles can be made short enough and the elastic stroke of the bellows can be adjusted to a desired value.




A second object of the invention is to provide a bellows manufacturing apparatus capable of forming pleat walls in accurate shapes without scratching a bellows with S-shaped profiles.




A manufacturing method for a metallic bellows of the present invention that achieves the first object comprises: a primary forming process for forming top portions and bottom portions, having pleat walls with S-shaped profiles, on a metallic blank tube as a material of the bellows so as to be arranged alternately in the axial direction of the tube, thereby obtaining a formed bellows; a pressing process for compressing the formed bellows in the axial direction; and a stretching process for pulling the bellows in the axial direction, thereby obtaining desired pitches and free length, after the pressing process.




According to the bellows manufacturing method of the invention, the compact-state length of the bellows having the S-profiled pleat walls can be made short enough, and a metallic bellows having a desired elastic stroke can be manufactured.




In this bellows manufacturing method, the stretching process may be followed by an annealing and ageing heat-treatment process (removal of distortion), which is carried out at a temperature of, for example, 400° C. to 600° C., in order to increase a spring limit value. According to this invention, the annealing and ageing heat-treatment process improves the elastic limit of the bellows as a spring that extends and contracts repeatedly, and therefore, the durability of the bellows.




In the manufacturing method of the invention, moreover, the heat-treatment process may be followed by a setting process to improve permanent set of the bellows and obtain desired pitches and free length. According to this invention, the pitches and length of the bellows can be adjusted, and the permanent set of the bellows can be improved.




In the manufacturing method of the invention, furthermore, the pressing process may include applying an axial load to the formed bellows and applying hydraulic pressure to the bellows from inside, thereby reducing the radius of curvature of a distal end of each bottom portion of the bellows. According to this invention, the compact-state length of the bellows can be reduced.




A bellows manufacturing apparatus of the invention that achieves the second object comprises: a first die provided around a blank tube; a second die located at a distance from the first die in the axial direction of the tube and dividable in the diametrical direction of the tube; first seal means provided on the inner surface of the tube so as to be located corresponding to the first die; second seal means provided on the inner surface of the tube so as to be located corresponding to the second die and defining a hydraulic chamber in conjunction with the first seal means; hydraulic supply means for supplying a compressed liquid to the hydraulic chamber, thereby causing a part of the tube to expand outward; a die drive mechanism for moving the second die toward the first die, thereby plastically deforming the expanded region of the tube to form pleat walls between the first die and the second die; fine-retreat means for slightly retreating the second die away from the pleat walls before the second die is opened in the diametrical direction of the tube after the pleat walls are formed; a die opening/closing mechanism for opening the second die in the diametrical direction after the second die is retreated by means of the fine-retreat means; and a tube feed mechanism for relatively moving the tube for a given distance in the axial direction of the tube with respect to the second die and the first die after the second die is opened in the diametrical direction.




In the bellows manufacturing apparatus of the invention, a part of the blank tube expands outward as the pressurized liquid is supplied to the hydraulic chamber between the first and second seal means. At the same time, the second die moves toward the first die. Thus, the expanded part of the tube is elastically deformed between the first and second dies, whereupon the pleat walls are formed. After the pleat walls are formed, the fine-retreat means slightly retreats the second die away from the pleat walls. Thereafter, the second die opens in the diametrical direction. After the second die is opened in the diametrical direction, the tube feed mechanism causes the tube to move for the given distance in the axial direction with respect to the second die and the first die. At the same time, the second die is retreated to its initial position.




According to the bellows manufacturing apparatus of the invention, the bellows can be formed having desired pleat walls with S-, V-, Ω-, or U-shaped profiles, depending on the shapes of forming surfaces of the dies. In the case where the pleat walls of bellows are formed by means of irregular forming surfaces with, for example, S-shaped profiles, in particular, they can be prevented from being scratched by the forming surfaces as the dies open in the diametrical direction even if the respective taper angles of the forming surfaces are narrow.




In the bellows manufacturing apparatus of the invention, the respective opposite surfaces of the first die and the second die are provided individually with forming surfaces for forming the pleat walls with S-shaped profiles, for example.




In the bellows manufacturing apparatus of the invention, the respective taper angles of the forming surfaces, with respect to segments perpendicular to the axis of the tube, should be narrow angles of 10° or less. According to this invention, the distance between the respective distal end portions of first die and the second die during forming operation can be made shorter. Thus, the shape of the pleat walls with the S-shaped profiles is stabilized, so that a high-durability metallic bellows can be manufactured.




Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.











BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING




The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.





FIG. 1

is a sectional view showing a part of a metallic bellows manufactured by a method according to an embodiment of the present invention;





FIG. 2

is a flowchart showing bellows manufacturing processes according to the embodiment;





FIG. 3

is a sectional view showing a part of a formed bellows;





FIG. 4

is an enlarged sectional view showing a part of the bellows shown in

FIG. 1

;





FIG. 5

is a sectional view showing a part of a bellows manufacturing apparatus according to a first embodiment of the invention;





FIG. 6

is a side view schematically showing an outline of the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 7

is a front view showing a part of a die opening/closing mechanism of the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 8

is a sectional view showing a blank tube set in dies in the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 9

is a sectional view showing the tube subjected to hydraulic pressure in the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 10

is a sectional view showing pleat walls formed in the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 11

is a sectional view showing the dies slightly retreated in the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 12

is a sectional view showing the dies opened in the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 13

is a sectional view showing one of the dies moved in the axial direction in the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 14

is a sectional view showing the dies closed in the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 15

is an enlarged partial sectional view showing the dies of the bellows manufacturing apparatus shown in

FIG. 5

;





FIG. 16

is an enlarged partial sectional view showing dies according to a comparative example;





FIG. 17

is a diagram showing results of durability tests on bellows formed by means of dies of two types with different taper angles;





FIG. 18

is a sectional view showing a part of a bellows manufacturing apparatus according to a second embodiment of the invention;





FIG. 19

is a sectional view showing pleat walls formed in the bellows manufacturing apparatus shown in

FIG. 18

;





FIG. 20

is a sectional view of an axial drive unit used in a pressing process;





FIG. 21

is an enlarged partial sectional view showing top and bottom forces of the axial drive unit shown in

FIG. 20

;





FIG. 22

is a diagram showing the relation between annealing and ageing conditions and endured frequency;





FIG. 23

is a sectional view of a compressing unit used in a setting process;





FIG. 24

is a partial sectional view showing top and bottom forces of an axial drive unit according to a third embodiment of the invention;





FIG. 25

is a sectional view of an axial drive unit according to a fourth embodiment of the invention; and





FIG. 26

is a sectional view of an axial drive unit according to a fifth embodiment of the invention.











DETAILED DESCRIPTION OF THE INVENTION




A first embodiment of the present invention will now be described with reference to

FIGS. 1

to


15


.




A metallic bellows


1


shown in

FIG. 1

has a plurality of top portions


2


and bottom portions


3


that are arranged alternately in the direction of its axis X. Pleat walls


4


and


5


that form the top portions


2


and bottom portions


3


have an S-shaped profile each. The “S-shaped” used herein describes a configuration such that indentations (curved surfaces) that are smoothly continuous in the diametrical direction of the bellows


1


are formed alternately like waves, and not exactly qualify the shape of an S. Possibly, therefore, each pleat wall may be formed having any other S-shaped profile than the one shown in FIG.


1


.





FIG. 2

shows manufacturing processes for manufacturing the metallic bellows


1


. First, in a primary forming process S


1


, bulging is carried out.

FIG. 3

shows a formed bellows


1


′ that is manufactured in the primary forming process S


1


. After the primary forming process S


1


is carried out, a pressing process S


2


and a stretching process S


3


are carried out in succession. If necessary, an annealing and ageing heat-treatment process S


4


and a setting process S


5


are executed. Although the heat-treatment process S


4


and the setting process S


5


are not essential, they are expected to be carried out in order to improve the durability and permanent set of the metallic bellows


1


, which will be mentioned later.




The primary forming process S


1


is carried out using a bellows manufacturing apparatus


10


shown in

FIGS. 5

to


15


.

FIG. 6

schematically shows the manufacturing apparatus


10


. The manufacturing apparatus


10


hydraulically bulges a thin-walled metallic blank tube


11


in the form of a straight pipe as the material of the metallic bellows.




The bellows manufacturing apparatus


10


comprises a base frame


12


, a die set


15


including a first die


13


and a second die


14


, a die drive mechanism


16


for moving the second die


14


in the axial direction of the tube


11


, and a chuck


17


for holding the tube


11


. The apparatus


10


further comprises a mandrel


18


inserted in the tube


11


, a mandrel drive mechanism


19


for moving the mandrel


18


in the axial direction of the tube


11


, a tube feed mechanism


20


for moving the chuck


17


in the axial direction of the tube


11


, and the like.




As shown in

FIG. 5

, the first die


13


is fixed to a first die holder


30


. The second die


14


is fixed to a second die holder


31


. The second die


14


and the die holder


31


can reciprocate relatively to the first die


13


and the die holder


30


in the axial direction of the tube


11


. In this embodiment, the second die holder


31


is moved integrally with the second die


14


in the axial direction of the tube


11


by means of the die drive mechanism


16


(shown in

FIG. 6

) that includes an actuator such as a servomotor.




The die drive mechanism


16


includes, for example, a servomotor


16




a


, a ball screw


16




b


rotated by means of the servomotor


16




a


, etc. As the servomotor


16




a


rotates in response to input pulses, the second die


14


moves in the axial direction of the tube


11


. The die drive mechanism


16


functions also as fine-retreat means according to the present invention.




In this embodiment, the first and second dies


13


and


14


serve as a cavity-side die and a force-side die, respectively, according to the present invention. Alternatively, however, the second die


14


and the die holder


31


may be fixed. In this case, the first die


13


and the die holder


30


are movable in the axial direction of the tube


11


.




As shown in FIG.


5


and other drawings, the dies


13


and


14


are formed having holes


34


and


35


in which the tube


11


is inserted. Corresponding to the pleat walls


4


and


5


of the bellows


1


to be formed, forming surfaces


36


and


37


having an S-shaped profile each are formed individually on the respective opposite surfaces of the first and second dies


13


and


14


.




As shown in

FIG. 15

, taper angles α1 and α2 of the respective forming surfaces


36


and


37


of the dies


13


and


14


are narrow angles of 10° or less. For example, α1 and α2 are 6.5° and 8.9°, respectively.

FIG. 16

shows dies


13


′ and


14


′ as comparative examples, of which taper angles β1 and β2 of forming surfaces


36


′, and


37


′ exceed 20°. For example, β1 and β2 are 20.6° and 20.4°, respectively. The taper angles α1, α2, β1 and β2 described herein are angles that are formed individually between segments A that extend at right angles to the respective axes of the dies (or the axis of the tube


11


) and segments D that connect proximal portions B and distal end portions C of the forming surfaces.




As shown in the partial view of

FIG. 7

, the dies


13


and


14


and the die holders


30


and


31


can be halved along a division surface


38


in the diametrical direction (direction indicated by arrow W in

FIG. 7

) by means of a die opening/closing mechanism


39


.




The mandrel


18


is provided with a cylindrical body


40


inserted in the tube


11


, a center rod


41


, a seal head


42


, etc. The center rod


41


, which penetrates the body


40


, can axially move with respect to the body


40


. The seal head


42


is in the form of a piston provided on the distal end portion of the center rod


41


. A first seal member


45


that is located on the inner peripheral side of the first die


13


is provided on the outer periphery of the seal head


42


.




A second seal member


46


that is located on the inner peripheral side of the second die


14


is provided on the outer periphery of the body


40


. Between the seal members


45


and


46


, a hydraulic chamber


47


is defined inside the tube


11


. The first and second seal members


45


and


46


function as first and second seal means, respectively, according to the present invention.




The center rod


41


is formed having a hydraulic inlet port


48


opening in the hydraulic chamber


47


and a liquid circulating portion


49


that communicates with the port


48


. The circulating portion


49


is connected with a hydraulic supplier


50


(shown in

FIG. 6

) that supplies a pressurized fluid (e.g., water) to the hydraulic chamber


47


.




The following is a description of bellows manufacturing processes carried out using the bellows manufacturing apparatus


10


.




As shown in

FIG. 5

, the first and second dies


13


and


14


are isolated from each other. The tube


11


is set in the dies


13


and


14


that are halved (or opened in the diametrical direction). The mandrel


18


is inserted into the tube


11


through its open end.




Thereafter, the dies


13


and


14


are closed in their diametrical direction, as shown in FIG.


8


. In

FIG. 8

, arrow M


1


indicates the direction in which the dies


13


and


14


are closed. In this state, the first seal member


45


is located on the inner peripheral side of the first die


13


, and the second seal member


46


on the inner peripheral side of the second die


14


.




As shown in

FIG. 9

, the pressurized fluid (e.g., water) from the hydraulic supplier


50


is fed into the hydraulic chamber


47


through the liquid circulating portion


49


and the hydraulic inlet port


48


. The pressure of the liquid supplied to the hydraulic chamber


47


causes a portion


11




a


of the tube


11


slightly to bulge outward in the diametrical direction between the seal members


45


and


46


.




With the hydraulic pressure in the hydraulic chamber


47


kept at a certain value, the second die


14


and the second die holder


31


, along with body


40


and the seal member


46


, are moved in synchronism with each other in the direction of arrow F


1


toward the first die


13


, as shown in FIG.


10


. As this is done, the portion


11




a


of the tube


11


is plastically deformed between the respective forming surfaces


36


and


37


of the dies


13


and


14


, whereupon the pleat walls


4


and


5


with the S-shaped profile are formed corresponding to the forming surfaces


36


and


37


, respectively.




After the pleat walls


4


and


5


for one pleat are formed in this manner, the second die


14


is returned for a very short distance Δd by means of the die drive mechanism


16


(shown in

FIG. 6

) in a fine-retreat process shown in FIG.


11


. More specifically, the second die


14


is moved away from the first die


13


(in the direction indicated by arrow R) for the short distance Δd. The distance Δd is set corresponding to the pitch (P shown in

FIG. 3

) of the pleat walls


4


and


5


. If the pitch P is 4.4 mm, Δd is about 2 mm. If the pitch P is 2.8 mm, Δd is about 1 mm. If the retreat distance Δd is too long, the second die


14


may possibly scratch the adjacent pleat wall


4


. Preferably, the retreat distance Δd should be a short distance not longer than half the pitch P.




After the second die


14


is slightly retreated in the fine-retreat process, the first and second dies


13


and


14


open in the diametrical direction (direction indicated by arrow M


2


), as shown in FIG.


12


. Since the die


14


is slightly retreated in the fine-retreat process before the dies


13


and


14


open, the respective forming surfaces


36


and


37


of the dies


13


and


14


can avoid heavily touching the pleat walls


4


and


5


. Thus, pleat walls


4


and


5


can be prevented from being scratched as the dies


13


and


14


open.




After the dies


13


and


14


are opened in the diametrical direction, the tube


11


is fed relatively to the dies


13


and


14


for a given distance in the direction (axial direction) indicated by arrow F


2


in

FIG. 13

by means of the tube feed mechanism


20


. Further, the second die


14


and the second die holder


31


retreat in the direction indicated by arrow F


3


and return to the position before the start of forming, and the body


40


and the seal member


46


also retreat synchronously.




When the forming surface


37


of the second die


14


is situated in front of the pleat wall


4


, the first die


13


, die holder


30


, second die


14


, and die holder


31


are closed in the direction of arrow M


1


, as shown in FIG.


14


. The pleat walls


4


and


5


for the next pleat are formed as the aforesaid series of processes shown in

FIGS. 9

to


14


is repeated. The formed bellows


1


′ shown in

FIG. 3

is completed by successively forming the pleat walls


4


and


5


for every pleat in this manner.




In the dies


13


and


14


of this embodiment, as shown in

FIG. 15

, the respective taper angles α1 and α2 of the forming surfaces


36


and


37


are narrow angles of 10° or less. Therefore, a distance L between the respective distal end portions C of the dies


13


and


14


is shorter enough as the pleat walls


4


and


5


are formed. Accordingly, the respective shapes of the forming surfaces


36


and


37


can be easily and accurately copied to the walls


4


and


5


of the tube


11


, so that the resulting formed bellows


1


′ can enjoy a shape similar to that of the bellows


1


, a final product, shown in FIG.


4


.




If the formed bellows


1


′ is compressed in the axial direction so that the pleat walls


4


and


5


are brought intimately into contact with one another, the respective radii of curvature of a distal end


2




a


of each top portion


2


and a distal end


3




a


of each bottom portion


3


can be further reduced, as shown in FIG.


4


.





FIG. 16

shows the dies


13


′ and


14


′ (comparative examples), of which the respective taper angles β1 and β2 of forming surfaces


36


′ and


37


′ exceed 20°.

FIG. 17

shows results of durability tests on S-profiled bellows (comparative examples) formed by means of the dies


13


′ and


14


′ and S-profiled bellows (embodiments) formed by means of the dies


13


and


14


shown in FIG.


15


.




As seen from

FIG. 17

, the durability of the bellows formed by means of the forming surfaces


36


and


37


with the taper angles α1 and α2 is much higher than that of the bellows formed by means of the forming surfaces


36


′ and


37


′ with the taper angles β1 and β2. The reason is that the distance L between the respective distal end portions C of the dies


13


and


14


can be made shorter in the case where the pleat walls


4


and


5


are formed by means of the forming surfaces


36


and


37


than in the case where the forming surfaces


36


′ and


37


′ are used, whereby the shapes of the pleat walls


4


and


5


can be stabilized.




In the case where the pleat walls


4


and


5


are formed by means of the forming surfaces


36


and


37


, however, the forming surfaces


36


and


37


partially heavily run against the just formed pleat walls


4


and


5


, thereby scratching the walls, if the dies


13


and


14


are directly opened in the diametrical direction after the walls


4


and


5


are formed.




Accordingly, the second die


14


of the bellows manufacturing apparatus


10


is slightly retreated in the fine-retreat process, as shown in

FIG. 11

, just before the dies


13


and


14


are opened in the diametrical direction after the pleat walls


4


and


5


are formed. Thus, the forming surfaces


36


and


37


can be prevented from scratching the pleat walls


4


and


5


as the dies


13


and


14


open in the diametrical direction.




In the foregoing embodiment, the die drive mechanism


16


itself doubles as the fine-retreat means. In carrying out the present invention, however, the fine-retreat means may be a hydraulic or mechanical drive mechanism that is independent of the die drive mechanism


16


and can slightly retreat the second die (force-side die).





FIGS. 18 and 19

show a bellows manufacturing apparatus


10


′ according to a second embodiment of the present invention. A mandrel


18


′ of the manufacturing apparatus


10


′ is composed of a body


40


′ and a member that integrally includes a seal head


42


′. For other configurations and functions, the second embodiment is similar to the first embodiment. When a second die


14


is moved toward a first die


13


, in this bellows manufacturing apparatus


10


′, the seal head


42


′ and a seal member


45


move in synchronism with the second die


14


. As this is done, the seal member


45


moves in the axial direction while sliding on the inner surface of the tube


11


. According to this arrangement, the mandrel


18


′ can enjoy a simple construction.




The following is a description of the pressing process S


2


shown in FIG.


2


.




The pressing process S


2


is carried out by means of an axial drive unit


60


shown in FIG.


20


. The axial drive unit


60


has a function to compress the formed bellows


1


′ manufactured in the primary forming process S


1


in the direction of the axis X. The unit


60


comprises a base member


61


, a ring-shaped support seat


62


on the base member


61


, a columnar core


63


, a ring-shaped bottom force


64


on the support seat


62


, a top force


65


opposite to the top of the bottom force


64


, a pressure member


66


overlying the top force


65


, etc. The pressure member


66


can be moved for a desired distance in the direction of the axis X of the formed bellows


1


′ (direction indicated by arrow X


1


in

FIG. 20

) by means of an actuator (not shown).




The bottom and top forces


64


and


65


can be opened and closed in the diametrical direction of the bellows


1


′ (direction indicated by arrow Y


1


in

FIG. 20

) by means of actuators (not shown), individually.




The core


63


, which are coaxial with the forces


64


and


65


, has a centering function to align the respective centers of the dies


64


and


65


and the formed bellows


1


′. Besides, the core


63


serves to prevent the formed bellows


1


′ from falling or bending outward as the bellows


1


′ is compressed in the axial direction.




As shown in

FIG. 21

, bearing surfaces


67


and


68


are formed on the respective opposite surfaces of the bottom and top forces


64


and


65


, respectively. The one bearing surface


68


has a shape corresponding to one pleat wall


4


. The other bearing surface


67


has a shape corresponding to the other pleat wall


5


. The formed bellows


1


′ to be set in the axial drive unit


60


is oriented so that the pleat walls


4


and


5


face the bearing surfaces


68


and


67


, respectively.




As shown in

FIG. 20

, one end portion


1




a


of the formed bellows


1


′ is interposed between the support seat


62


and the bottom force


64


. The other end portion


1




b


is interposed between the top force


65


and the pressure member


66


. The end portion


1




a


is held by means of the support seat


62


and the bottom force


64


, and the other end portion


1




b


by means of the top force


65


and the pressure member


66


. The bottom and top forces


64


and


65


can be halved in the diametrical direction so that they can be released from the opposite end portions


1




a


and


1




b


of the bellows


1


′.




The pressure member


66


presses the top force


65


toward the bottom force


64


. AS this is done, the formed bellows


1


′ is compressed in the direction of the axis X by means of the forces


64


and


65


so that the pleat walls


4


and


5


come intimately into contact with one another. By carrying out the pressing process S


2


, the respective radii of curvature of the distal end


2




a


of each top portion


2


and the distal end


3




a


of each bottom portion


3


can be reduced, as shown in

FIG. 4

, so that the bellows


1


of a desired product shape can be obtained. Since the radius of curvature of the distal end


3




a


of each bottom portion


3


can be made smaller enough than that of the formed bellows


1


′ (shown in FIG.


3


), in particular, the short compact-state length, a feature of an S-shaped bellows, can be utilized efficiently.




The bellows


1


having undergone the pressing process S


2


is substantially a rigid body without springiness because its pleat walls


4


and


5


are located very close to one another. In order to give the bellows


1


the function of a spring, therefore, the stretching process S


3


is carried out. The axial drive unit


60


shown in

FIG. 20

is also used for the stretching process S


3


. By pulling the bellows


1


in the direction of the axis X by means of the axial drive unit


60


, the length of the bellows


1


can be freely adjusted to ensure given pitches.




In this embodiment, the opposite end portions


1




a


and


1




b


of the bellows


1


are held by means of the bottom and top forces


64


and


65


, respectively. With use of the axial drive unit


60


, the stretching process S


3


can be carried out without interruption after the pressing process S


2


, and in the stretching process S


3


, the bellows


1


can be stretched by a desired length in the direction of the axis X. Thus, a series of processes including the pressing process S


2


and the stretching process S


3


can be continuously carried out with high efficiency.




In pulling the bellows


1


in the direction of the axis X in the stretching process S


3


, the whole bellows


1


may be pulled at a time to obtain a desired free length. Alternatively, the bellows


1


may be divided into a plurality of regions in the direction of the axis X so that the individual regions can be pulled separately. Alternatively, moreover, the whole bellows


1


may be pulled after individual regions of the bellows in the direction of the axis X are pulled separately.




The annealing and ageing heat-treatment process S


4


is carried out after the stretching process S


3


. The heat-treatment process S


4


is carried out in order to ease residual stress that is generated in the bellows


1


in the primary forming process S


1


, pressing process S


2


, stretching process S


3


, etc. In the heat-treatment process S


4


, annealing and ageing (removal of distortion) are carried out in a manner such that the bellows


1


is kept within the following temperature region for a given time. In the heat-treatment process S


4


, the residual stress of the bellows


1


is eased, and besides, the area of elasticity of the bellows


1


as a spring extends, so that the durability of the bellows


1


regarding to the repeated amplitude is improved.




The inventors hereof conducted durability tests for examining the durability of the bellows


1


of stainless steel for the case where the bellows


1


was subjected to the heat-treatment process S


4


.

FIG. 22

shows results of the tests. When the annealing and ageing temperature was 400° C., the durability was not improved much. However, the durability of the bellows was higher than in the case where annealing and ageing were not carried out. The durability of the bellows was considerably improved in the annealing and ageing temperature range higher than 400° C. and not lower than 600° C. It is to be desired, therefore, that the bellows


1


should be subjected to the heat-treatment process S


4


at 400° C. to 600° C. for about 60 minutes, and it is advisable, in particular, to carry out annealing and ageing at a temperature higher than 400° C.




After undergoing the heat-treatment process S


4


, the bellows


1


is subjected to the setting process S


5


by means of a compressing unit


70


. The compressing unit


70


comprises a base member


72


including a core


71


, a cylindrical compressing member


73


movable in the axial direction of the core


71


, an actuator (not shown) for moving the compressing member


73


for a given distance in the axial direction of the bellows


1


, and the like.




In the compressing unit


70


, the compressing member


73


applies an axial compressive load to the bellows


1


, thereby compressing the bellows more deeply than during use. In this setting process S


5


, the permanent set of the metallic bellows


1


can be improved. The setting process S


5


may alternatively be carried out by means of the axial drive unit


60


(

FIG. 20

) that is used in the pressing process S


2


and the stretching process S


3


.




In the formed bellows


1


′ that is compressed in the pressing process S


2


, the pleat walls


4


and


5


are formed into S-shaped configurations in advance in the primary forming process S


1


. In the pressing process S


2


, therefore, it is necessary only that the bellows


1


be able to be compressed in the direction so that the respective radii of curvature of the distal end


2




a


of each top portion and the distal end


3




a


of each bottom portion are shorter than those of the formed bellows


1


′.




As shown in

FIG. 24

, therefore, bottom and top forces


64


and


65


with bearing surfaces


67


and


68


in a common shape may be used in the pressing process S


2


. The bottom and top forces


64


and


65


having the common-shaped bearing surfaces


67


and


68


can be oriented without regard to the direction of the formed bellows


1


′. Thus, the formed bellows


1


′ can be easily set in the axial drive unit


60


, and there is no possibility of the bellows


1


′ being set in a wrong direction.




A formed bellows


1


′ shown in

FIG. 25

has opposite end portions


1




c


and


1




d


in the form of a straight pipe each. In this case, bottom and top forces


83


and


84


having annular slits


81


and


82


into which the end portions


1




c


and


1




d


can be inserted, respectively, should be used in the pressing process S


2


and the setting process S


5


. With use of an axial drive unit


80


including these forces


83


and


84


, the formed bellows


1


′ having the straight end portions


1




c


and


1




d


can be compressed in the axial direction along a guide member


85


.




Alternatively, an axial drive unit


91


including a hydraulic pressure applying mechanism


90


shown in

FIG. 26

may be used in the pressing process S


2


. The unit


91


comprises a hydraulic source


92


, a liquid channel


93


opening into the internal space of a bellows


1


′, a seal member


94


for hermetically sealing the internal space of the bellows


1


′, a pressure member


95


, a cylindrical guide member


96


, etc. The hydraulic source


92


feeds a pressurized liquid (e.g., water or oil) into the formed bellows


1


′.




With the formed bellows


1


′ compressed in the axial direction (direction indicated by arrow X


2


in

FIG. 26

) by means of the pressure member


95


, a liquid


97


compressed by means of the hydraulic source


92


is introduced into the bellows


1


′. The radius of curvature of the distal end


3




a


(shown in

FIG. 4

) of each bottom portion can be reduced by causing the pressure of the liquid


97


to act on pleat walls


4


and


5


.




Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.



Claims
  • 1. A manufacturing method for a metallic bellows, comprising:a primary forming process for forming top and bottom portions comprising pleat walls with S-shaped profiles on a metallic blank tube so as to be arranged alternately in the axial direction of the tube to thereby form the metallic bellows; a pressing process for compressing the formed metallic bellows in the axial direction, said pressing process includes applying an axial load to the formed metallic bellows and applying hydraulic pressure to the metallic bellows from inside thereby reducing the radius of curvature of a distal end of each bottom portion of the metallic bellows; and a stretching process for pulling the metallic bellows in the axial direction after the pressing process to thereby obtain desired pitches and free length.
  • 2. A manufacturing method for a metallic bellows according to claim 1, wherein said stretching process is followed by an annealing and ageing heat treatment process.
  • 3. A manufacturing method for a metallic bellows according to claim 2, wherein said heat-treatment process is followed by a setting process for compressing the bellows in the axial direction to obtain desired pitches and free length.
  • 4. A manufacturing apparatus for a metallic bellows formed from a metallic blank tube, comprising:a first die provided around the metallic blank tube; a second die located at a distance from the first die in the axial direction of the tube and dividable in a diametrical direction of the tube, respective opposite surfaces of said first die and said second die are provided individually with forming surfaces for forming the pleat walls with S-shaped profiles, respective taper angles of the forming surfaces of said first die and said second die, with respect to segments perpendicular to an axis of the tube, are narrow angles of 10° or less, first seal means provided on an inner surface of the tube so as to be located corresponding to the first die; second seal means provided in the inner surface of the tube so as to be located corresponding to the second die and defining a hydraulic chamber in conjunction with the first seal means; hydraulic supply means for supplying a pressurized liquid to the hydraulic chamber, thereby causing a part of the tube to expand outward; a die drive mechanism for moving the second die toward the first die, thereby plastically deforming the expanded part of the tube to form pleat walls between the first die and the second die; fine-retreat means for slightly retreating the second die away from the pleat walls before the second die is opened in the diametrical direction of the tube after the pleat walls are formed; a die opening/closing mechanism for opening the second die in the diametrical direction after the second die is retreated by means of the fine-retreat means; and a tube feed mechanism for relatively moving the tube for a given distance in the axial direction of the tube with respect to the second die and the first die after the second die is opened in the diametrical direction.
Priority Claims (2)
Number Date Country Kind
2000-181727 Jun 2000 JP
2000-192802 Jun 2000 JP
US Referenced Citations (12)
Number Name Date Kind
2773538 De Mers Dec 1956 A
3015354 Wood Jan 1962 A
3040426 Hamren Jun 1962 A
3105539 Johnson Oct 1963 A
3130771 Peyton Apr 1964 A
3247694 Homfeldt et al. Apr 1966 A
3326091 Allen Jun 1967 A
3699624 De Gain Oct 1972 A
3782156 Panfill Jan 1974 A
4364252 Koizumi Dec 1982 A
6202281 Semenov et al. Mar 2001 B1
6282939 Minamidate et al. Sep 2001 B1
Foreign Referenced Citations (3)
Number Date Country
0 395 042 Oct 1990 EP
0 395 042 Oct 1990 EP
1 053 800 Nov 2000 EP
Non-Patent Literature Citations (2)
Entry
Patent Abstracts of Japan, Publication No. 57146426, published Sep. 9, 1982.
Patent Abstracts of Japan, Publication No. 11-226658, published Aug. 24, 1999.