Note: Descriptions are shown in the official language in which they were submitted.
Back no of the Invention
This invention relates to a bellows capsule. It
relates more particularly to a nesting metal bellows
capsule for use in applications where the pressure on the
outside of the bellows is sometimes substantially higher
than the pressure at the inside thereof.
Bellows capsules are used in a wide variety of
applications as pressure transducers linear actuators,
temperature and pressure responsive devices, etc. In
many cases, the bellows capsule is composed of a series
of annular rippled diaphragms whose alternate inner and
outer edges are welded, brazed or otherwise secured to
the corresponding edges of adjacent diaphragms to form a
series of bellows convolutions.
In the application of particular interest here the
bellows capsule is situated inside a pressure vessel.
One end of the capsule is closed while its other end is
connected to a header in the vessel to isolate the spaces
inside the pressure vessel at the inside and outside of
the bellows. Further, fluid communication is provided
through the header into the bellows and through the wall
; of the pressure vessel to the space inside the vessel but
outside the bellows. When fluid under high pressure is
injected into the pressure vessel, it tends to compress
or collapse the bellows capsule so that the rippled
diaphragms nest against one another, the fluid inside the
bellows then being expelled through the header.
Conversely, when the pressure in the vessel is reduced
relative to the pressure inside the capsule, the capsule
tends to extend, drawing fluid into the capsule.
It has been found that when a conventionally
fabricated, nesting welded bellows is subjected to
repeated high pressure stress upon assuming its fully
nested position diaphragm fatigue occurs within a
Jo
relatively few pressure cycles. It is believed that this
diaphragm fatigue stems from excessive strain of small
unsupported annular portions of the bellows diaphragms
forming each bellows convolution near the inner edges of
the diaphragms. These diaphragm portions are unsupported
because the widths of the joints, i.e. the weld beads or
spill over, between the bellows diaphragms at the inner
and outer diameters of the capsule are wider than twice
the diaphragm thickness. Consequently when the bellows
is compressed, adjacent beads contact one another
preventing the bellows diaphragms from nesting completely
at those portions and leaving a small space in each
convolution.
Since these diaphragm portions "see" high pressure
I on one side and low pressure on the other, they are bowed
or bent toward each other into the intervening space thus
producing pressure cycling fatigue. In actual practice,
this fatigue occurs within only a relatively few pressure
cycles on the capsule. Consequently, such capsules used
in high pressure applications have a relatively short
life. Many of the capsules with which We are
particularly concerned here are used in aircraft and
aerospace applications. Also, they are often made of
expensive metals, such as stainless steel, titanium, etc.
Thus it is important that they be made more reliable and
long-lived both for cost and safety reasons.
It is possible to avoid the spill over problem by
connecting the diaphragm edges together by brazing them.
However, this involves inserting a thin ring of different
metal between the diaphragms which melts forming the
bond. In many applications, the use of this different
brazing metal creates manufacturing problems. Also
corrosion occurs because of electrolytic action.
Consequently in such applications it has been found
necessary to weld the diaphragms together.
Also it is known that weld beads such as those found
on conventional bellows can be removed by coining. This
entails smashing the bead between a hammer and an anvil
to flatten eye bead. This can be accomplished relatively
easily at the joints between the diaphragm pairs at the
inside diameter of the bellows. This is because each
such diaphragm pair is a separate unit so that there is
ready access to both sides of the weld bead. however, it
is very difficult and not economically feasible to coin
the weld beads at the outside diameter of the bellows
because the bellows is already formed at this point and
the individual we'd beads cannot easily be segregated
from the adjacent beads for the coining operation.
Summary of the Invention
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Accordingly the present invention aims to provide a
bellows capsule which is particularly effective in high
pressure applications
Another object is to provide a bellows capsule whose
adjacent convolutions are able to nest completely.
A further object of the invention is to provide a
nesting rippled, welded diaphragm bellows which is able
to withstand repetitive high pressure stresses for a
prolonged period.
A further object of the invention is to provide a
method of making a metal bellows capsule having one or
more of the aforesaid advantages.
Other objects will in part, be obvious and will, in
part appear hereinafter.
The invention accordingly comprises the several
steps and the relation of one or more of such steps with
respect to each of the others, and the article possessing
the features, properties and relation of elements which
are exemplified in the following detailed disclosure, and
the scope of the invention will be indicated in the
claims
Briefly, the present bellows capsule is able to
withstand repeated cycling to a fully compressed
position in a high pressure environment because it is
fabricated so as to leave no unsupported diaphragm
portions that axe exposed to high pressure when the
capsule is fully nested. This is accomplished by
sandwiching a flat spacer ring between the inner edges of
the bellows diaphragms forming adjacent bellows
convolutions. For purposes of this disclosure, a
convolution is defined as a segment of the bellows
comprising a pair of annular diaphragms joined together
at their rims.
Each ring is TWIG welded in place at the time the
inner edges of the diaphragms of adjacent bellows
convolutions are joined. The thickness of the spacer
ring is selected to be substantially the same as the
added thickness of the weld beads or spill over at the
rims of the adjacent bellows convolutions. Consequently,
when the bellows is in its fully compressed position, the
diaphragms forming each bellows convolution are able to
nest against one another providing mutual support across
their entire widths. Furthermore, the inner margin of
the diaphragms and the spacer rings form a continuous
load bearing column that supports the stack of bellows
convolutions so that the weld beads at their rims barely
contact one another when the bellows is fully nested
With this arrangement there are no unsupported
portions of the bellows diaphragms subjected to a high
pressure differential that are not also fully supported
by an adjacent diaphragm portion when the bellows is in
its phyla compressed position. Resultantly the diaphragms suffer minimum
stress when the capsule is subjected to repeated pressure cycling and there-
fore the capsule should have a long, useful life. Yet the implementation of
the present improvement does not result in any material increase in the overall
cost of such bellows because the only added components are a plurality of
identical flat rings Lucia are easily formed by conventional stamping technic
quest
Thus, in accordance with one broad aspect of the invention, there
is provided a metal bellows capsule comprising: A. a. stack of annular metal
diaphragms, B. means connecting the rims of pairs of adjacent diaphragms
directly to one another so as to form a series of convolutions, the opposing
surfaces of the diaphragms of each convolution configured so as to ma tingly
contact one another over their en-tire areas, and C. means for joining the
idler edges of the diaphragms in adjacent convolutions, each said joining means
including: (1) a metal spacer ring sandwiched between said inner edges, and
: (2) means for connecting said inner edges to opposite surfaces of said spacer
ring to form continuous seams all around the ring, whereby the opposing sun-
; faces of the diaphragms in each convolution are able to contact one another
over their entire areas when the bellows is fully compressed thereby providing
mutual support over their entire areas enabling the capsule to withstand no-
natively high external pressure.
In accordance with another broad aspect of the invention there is
provided the method of forming a metal bellows capsule comprising the steps of:
A. forming a plurality of pairs of radically mating annular metal diaphragms,
B. forming a plurality of metal spacer rings whose inner edge has substantially
the same diameter as the inner edges of said diaphragms, C. securing the rings
between the inner edges of each pair of said diaphragms, and D. joining the
outer rims of the adjacent diaphragms of each pair flush to one another to form
a series o-E convolutions so that when the capsule is -fully compressed, the
diaphragms in each convolution contact one another over their entire areas to
provide mutual support over their entire areas whereby the capsule is able to
tolerate relatively high external pressures.
In accordance with another broad aspect of the invention there is
provided a metal bellows enclosure comprising: A. a stack of alternating
first and second anmllar metal diaphragms, each pair of said first and second
diaphragms having a generally sinuous cross-section, but being separately
dimensioned for intimate abutting contact along the entire radial length there-
of; B. means connecting the rims of pairs of adjacent diaphragms directly to
one another so as to form a series of convolutions, and C. means err joining
the inner edges of the diaphragms in adjacent convolutions, each said joining
means including: (1) a metal spacer ring sandwiched between said inner edges
and (2) means for connecting said inner edges to opposite surfaces of said
spacer ring to form continuous seams all around the ring.
In accordance with another broad aspect of the invention there is
provided a metal bellows comprising: A. a stacked set of pairs of annular
metal diaphragms, the diaphragms of each pair having a sinuous cross-section
intimately nonformal at their mutual interface; B. bead means for joining
the outer peripheries of the diaphragms in each pair so as to form a series
of convolutions; and C. a set of annular spacers, each spacer joining the inner
peripheral edge regions of the two diaphragms which face each other in adja-
cent pairs in said stack.
Brief Description of the Drawing
... .. _.
For a fuller understanding of the nature and objects owe the invent
-lion, reference should be had to the following detailed description, taken in
- 5b -
connection with the accompanying drawing, in which:
Figure I is a perspective view of a rippled diaphragm bellows capsule
made in accordance Wyeth this invention, shown in a high pressure environment;
Figure 2 so a perspective view of the spacer ring incorporated into
the Figure l capsule;
figure its a fragmentary sectional view of the Figure 1 capsule on
a larger scale showing the capsule in greater detail; and
Figure 4 is a similar view showing the conventional bellows capsule
construction.
Description of the Preferred Embodiments
Referring to Figure 1 of the drawing, the subject bellows capsule
shown generally at 10 is positioned inside a pressure vessel indicEl-ted in
dotted lines at 12. Ike winner end of the capsule is dosed by a circular disk
14. The outer end owe the capsule has a flange lob that is welded or otherwise
secured to an end wall or header aye of vessel 12. Thus the capsule 10
divides the volume
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of vessel 12 into two isolated spaces, namely, a space 16
inside the capsule and a space 18 outside the capsule.
In use, fluid communication from without is established
to the two spaces 16 and 18 via conduits extending
through the walls of vessel 12 as shown in dotted lines
at 22 and 24 respectively.
Referring now to FIGS. l and 3, the bellows capsule
lo comprises a series of identical convolutions shown
generally at 26. Each convolution comprises a female
lo diaphragm 28 and male diaphragm 32. Typically, bellows
diaphragms are made of stainless steel, titanium or other
rugged metal and they are rippled so that they Alex
readily with minimum stress as the capsule is cycled
between its fully extended and fully compressed
positions.
Fig 3 shows the relative positions of adjacent
bellows convolutions 26 when the capsule lo is in its
fully nested or compressed position. FIG. 4 illustrates
the comparable positions of adjacent convolutions aye of
a prior conventional capsule loan
Refer, for a moment to FIX. 4. In prior bellows of
this general type, each bellows convolution aye consists
of a pair of nesting, rippled female and male diaphragms
28 and 32. Each convolution is formed by joining the
outer edges or rims of diaphragms 28 and 32 usually by
TWIG welding those edges together. Invariably, this
process results in the formation of an annular bead 34
due to spill over of molten metal during the welding
process. In a typical case, each weld bead 34 has a
cross section which is roughly three times the width of
the diaphragm thickness. Thus, each weld bead 34 has a
portion aye that projects out beyond the surface of each
diaphragm at the joint in the direction of the bellows
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axis A, a distance roughly equal to one-half the
diaphragm thickness.
Similar weld beads 38 are formed at the inner
diameter of the bellows when the diaphragms of adjacent
bellows convolutions are joined together in the same
manner. These inner weld beads 38 also have portions aye
which project out beyond the surfaces of the diaphragms
as show. r
Still referring to FIG. 4, when assure is applied
to the outside of capsule 10, the bellows is prevented
from nesting completely because the adjacent weld beads
34 and the adjacent weld beads 38 contact one another at
the inner and outer diameters of the capsule. The
stacking of the weld beads 38 at the inner diameter of
the bellows leaves annular diaphragm portions aye and aye
adjacent those weld beads unsupported. Moreover, the
space between those diaphragm portions corresponds to the
space 16 FIG. 1) inside the capsule which is maintained
at relatively low pressure. On the other hand, the
opposite sides of those diaphragm portions aye and aye
are exposed to the relatively high pressure in the space
18 at the outside of the bellows capsule. Resultantly,
when the capsule lo is fully nested, the pressure
differential across those diaphragm portions causes those
portions to bulge toward one another into the gap between
them as shown in dotted lines at P in FIG. 4. As a
consequence, the diaphragms suffer fatigue distress at
those diaphragm portions aye and aye after the bellows
capsule lo has undergone only a relatively few pressure
cycles.
Turning now to FIGS. 2 and 3 of the drawing t the
present long lived bellows capsule 10 is somewhat similar
to the prior one in that it is composed of a stack of
bellows convolutions formed by connecting rippled female
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and male diaphragms 28 and 32 alternately at their inner
and outer edges. Actually, the joints at the outer rims
of the diaphragms are more or less the same as those
described above. That is, they are characterized by weld
beads 34, having portions aye projecting out from the
surfaces of the diaphragms along the bellows axis A.
The capsule 10 does differ substantially from the
prior one, however, in its joints or connections between
the inner edges of the diaphragms of adjacent
convolutions. In lieu of the usual inner connections
that form weld beads 38 (FIG. 4), the present capsule 10
has flat spacer rings 42 sandwiched between the
diaphragms 28 and 32 of adjacent convolutions 26. The
inner diameter of each ring 42 is substantially the same
as the diaphragm inner diameter. The ring outer diameter
is not particularly critical.
As best seen in FIG. 3, when forming the diaphragms
28 and 32, their inner edge margins 28b, 32b are
flattened so that when the rings 42 are in position, they
lie flush against those edge margins as shown. Each ring
42 is more or less coextensive with those edge margins
28b, 32b and the thickness of each ring is approximately
equal to twice the thickness of the weld bead portion
aye. Each pair of diaphragm margins 28b, 32b and the
intervening spacer ring 42 are joined by TWIG welding as
indicated at 46 in FIG. 3.
It should be understood that the process of welding
the inner joints 46 between the bellows convolutions does
itself result in some spill over. however, the extra
thickness provided by the ring 42 accommodates most of
the molten metal flow as the joint is formed.
Resultantly, there is no great flow of metal beyond the
edges of the sandwich comprising each inner joint so that
the resultant weld bead is relatively small. In any
event, the weld beads at the inner joints are easily
removed by coining as described above.
With this arrangement, the diaphragm portions aye
and 32_ of each convolution 26 inboard of the rings
support one another and there is no gap or void between
them. In other words the diaphragms 28~ 32 forming each
convolution 26 are able to nest completely along their
entire width. Consequently, when the space 18 between
the bellows convolutions 26 is exposed to high pressure
and the space 16 inside the bellows is exposed to a lower
pressure, those engaging diaphragm portions aye end aye
provide mutual support for one another. In fact there
era no portions of the bellows diaphragms that are
exposed to a pressure differential that are not also
supported by an adjacent diaphragm.
Further as shown in FIG. 3, the thickness of each
; ring 42 is such that when the bellows is fully
compressed, the diaphragm margins 28b, 32b and rings 42
form a load bearing column that permits the weld beads 34
at the rips of the convolutions to barely contact one
another so that there is little or no distortion at the
outer edge margins of the diaphragms. Resultantly, the
subject capsule 10 can undergo numerous pressure cycles
without suffering fatigue distress.
The spacer rings 42 being simple stamped metal parts
add little to the overall cost of the bellows capsule id.
Accordingly, a high pressure capsule of superior
performance and long life can be fabricated at a cost not
appreciably more than that of prior comparable capsules
having lesser performance characteristics.
It will thus be seen that the objects set forth
above among those made apparent from the preceding
description are efficiently attained, and, since certain
changes may be made in carrying out the above method and
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in the construction set forth without departing from the
scope of the invention, it is intended that all matter
contained in the above description or shown in the
accompanying drawing shall be interpreted as illustrative
and not in a limiting sense.
It is also to be understood that the following
claims are intended to cover all of the generic and
specific features of the invention herein described
