Note: Descriptions are shown in the official language in which they were submitted.
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SPECIFICATION
Il'dPROVED BOSS FOR A FILAMENT WOUND PRESSURE VESSEL
BACKGROUND OF TFTE IrTVENTION
Technical Field
The present invention is an improved boss for
reinforcing the structural interface between a filament
wound outer shell and a non-metallic internal liner in a
rounded~high pressure vessel.
Background Art
In many circumstances, the qualities of lightweight
construction and high resistance to fragmentation and
corrosion damage are highly desia-able characteristics for
a pressure vessel. These design criteria have been met for
many years by the developanent of high pressure comp~site
containers fabricated of laminated ~:ayers of wound
fiberglass filaments or various types of synthetic
filaments which are bonded together by a thermal-setting
epoxy resin. An elastomeric or other non-metal resilient
liner or bladder is suspended within the filament wound
2U shell to seal the vessel and prevent internal fluids from
contacting the composite material.
Filament wound vessels often are constructed in a
spherical shape or a cylindrical shape with generally
spherical ends far use in high pressure applications. A
boss is used to reliably join the internal linex" with the
outer composite shell at pressurization ports in the outer
shell such that fluid is prevented from penetrating between
the liner and the shell. In many applications, such as in
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the aerospace industry, composite pressure vessels are required
to contain extremely high pressures, operating at 25,000 p.s.i.
with design burst values in the range of 50,000 p.s.i.
Consequently, as internal pressure increases, the interface of
the boss, the liner and the outer shell is subjected to extreme
structural loading.
More particularly, as pressure within the vessel is
increased, bearing stress is generated between the boss and the
composite shell, resulting in a steep strain gradient through the
shell, with the inner strains being much higher than those at the
outer surface. Shearing stress develops between the boss and the
internal liner due to relative displacement discontinuities
resulting from nonuniform loading during internal pressurization.
In addition, radially extending support members on the boss are
subjected to unacceptable levels of bending stress which can
result in fracture of the boss.
Moreover, it is critical that during the pressurization of
the vessel the liner and outer shell remain firmly engaged with
the boss, despite the adverse loading to which the liner and
shell are subjected. The present invention is directed toward
overcoming the above mentioned loading and sealing problems by
providing a unique construction in a boss for a filament wound
pressure vessel of the character described.
SUMMARY OF THE INVENTION
Accordingly the present invention, seeks to provide a new
and improved boss for reinforcing the structural interface
between a filament wound reinforcement shell and a non-metallic
internal liner in a rounded section of a high pressure vessel.
The invention in one broad aspect provides a boss for
pressure vessel having a filament wound outer shell and a non-
metallic internal liner, the shell having a circular section and
defining a rounded vessel end. The boss comprises a tubular neck
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projecting outwardly through an opening in the rounded vessel end
with an annular flange extending radially from an end of the neck
within the vessel, the annular flange having an outer surface for
reinforcing the perimeter of the opening in the rounded vessel
end. A shear stress relieving layer is at the rounded end and
is interposed between the inner surface of the outer shell and
the internal liner to accommodate relative slip therebetween
during pressurization of the vessel.
Another aspect of the invention provides a boss for a
pressure vessel having a filament wound outer shell and a non-
metallic internal liner, the boss comprising a tubular neck
projecting axially through an opening in the outer shell, and an
annular flange extending radially from the neck within the
vessel, the annular flange having an outer surface for
reinforcing the perimeter of the opening in the shell and an
inner surface for mounting the liner. An interface member is
interposed between the liner and the inner surface of the annular
flange and defines a site for attachment of the liner, and means
secures the interface member to at least one of the annular
flange and the neck.
A further aspect of the invention provides a pressure vessel
comprising a filament wound outer shell, a non-metallic internal
liner disposed within the shell and a boss having a tubular neck
projecting outwardly through an opening in the outer shell and
an annular flange extending radially from an end of the neck
within the vessel, the annular flange having an outer surface for
reinforcing the perimeter of the opening the shell.
Complementary inter-engaging locking means are between the
annular flange and the liner, and a shear stress relieving layer
is interposed between an outer surface of the annular flange and
an inner surface of the outer shell to accommodate relative slip
therebetween during pressurization of the vessel.
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Tn the exemplary embodiment of one form of the
invention, a boss is disposed in an opening in a spherical
section of a pressure vessel which has a filament wound
outer shell and a non-metallic internal liner. The boss
has a tubular neck which proj ects outwardly from the vessel
interior and an annular support flange which extends
radially from the internal end of the neck and supports the
perimeter of the interface of the shell and liner about the
opening. An offset attachment flange extends radially from
the support flange and has an annular locking groove
engaged with a complementary tab on the liner.
In'the disclosed embodiment of the invention, locking
grooves are provided on each of two axially opposite offset
surfaces of the attachment flange. The locking groove in
the outer surface of the attachment flange opens outwardly
and the locking groove in the inner surface of the '
attachment flange opens inwardly, with each of the locking
grooves having a bottom wall intermediate a pair of
mutually skewed sidewalls for maintaining positive
engagement with the liner. The offset characteristic of
the attachment flange reduces the risk that the liner will
extrude out of engagement kith the boss and cause leakage
between the outer shell and the liner.
In order to reduce shear stress between the boss and
the liner during internal pressurization of the vessel, a
non--metallic shear stress relieving layer is interposed
between the outer surface of the annular flange and the
inner surface of the outer shell. The interposed layer may
be made of any plastic, elastomeric, or other non-metallic
material, and may be manufactured by a molding process or
cut from sheet stock.
Pressurization damage is also reduced by the unique
construction of the boss. Tn a preferred form, the support
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flange has a diameter sufficient to prevent damage to the
outer shell when the vessel is pressurized and is
sufficiently thick to avoid unacceptable levels of bending
stress in the support flange and attachment flange. The
boss may be made from alloys of aluminum, steel, nickel,
titanium, or other metals.
In another form of the invention, the liner is
made of blow molded high density polyethylene, or HDPE. An
axisyznmetric interface member is secured to the boss
adjacen~: the pressurization port to provide a site for
attaching the liner. The interface member preferably is
made of injection molded HDPE which, when solidified,
shrinks into conformity with the boss and is thereby
securely molded ~o the boss. The liner is bonded, as by
plastic melding, directly to tkie inaerface member. A
threaded retainer nut is advanced through the neck of the
boss to lock the interface member in place.
Other abjects, features and advantages of the
invention will be ,apparent from the followizlg detailed
description taken in connection with the accompanying draw
ings.
BRIEF DESCRTPTION OF THE DRAWINGS
The features of this invention which are believed
to be novel are set forth with particularity in the append
ed claims. The invention, together with its objects and
advantages, may be understood from the following descrip-
tion taken in conjunction with the accompanying drawings,
in which like reference numerals identify like elements in
the figures and in which:
FIGURE ~. is fragmentary sectional view of the
rounded end of an axisymmetric pressure vessel having a
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boss which incorporates the features of the present
inventiono
FIGURE 2 is a fragmentary sectional view similar
to FIGURE 1 in which the boss is j oined to the pressure
vessel along only one side thereof, and wherein the
internal liner engages only one of the locking grooves in
the radial flanges and
FIGURE 3 is fragmentary sectional view of the
rounded end of an axisymmetric pressure vessel having a
further embodiment of a boss construction.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1'illustrates in fragmented section the
rounded, preferably substantially spherical, end of an
axisymmetric pressure vessel, generally designated 10. The
pressure vessel l0 is comprised of a fiber reinforced outer
shell 12 and a non-metallic internal liner 14. A boss 16
according to the present invention extends outwardly
through a polar opening 18 formed in the outer shell l2 and
defines a pressurization port 20 through which fluid at
high pressure may be communicated with the interior of the
pressure vessel 10. It is to be noted, however, that the
invention may be used in connection with non-polar openzngs
in vessels, as, for example, an opening in a purely
spherical vessel. A thin shear accommodating layer 22 is
interposed between the outer shell 12, the boss 16 and the
liner 14 to prevent damage to the shell or liner during
pressurisation of the vessel, as will be described
hereafter.
The outer shell 12 comprises a generally known
composite reinforcement made of fiber reinforcing material
in a resin matrix. The fiber may be fiberglass, ARAMID,
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carban, graphite, or any other generally known fibrous
reinforcing material. The resin matrix used may be epoxy,
polyester, vinylester, thermoplastic or any other suitable
resinous material capable of providing the fragmentation
resistance required for the particular application in which
the vessel is to be used.
The internal liner 14 may be made of plastic or
other elastomers and can be manufactured by compression
molding, blow molding, injection molding or any other
generally known technique. The boss 16 preferably is
composed of an alloy of aluminum, steel, nickel, or
titanium, although it is understoad that other metal and
non-metal materials, such as composite materials, are
suitable. The thin layer 22 may be made of plastic, or
other non-metallic material and may be manufactured by a
molding process or, al'cernatively, cut from sheet stock.
As shown in Figure 1, 'the subject boss 16 has an
outwardly projecting neck 24 with a tapered throat 26
extending through the polar opening 18 in the outer shell
12. The throat 26 is tapered so as to form a concave
peripheral groove for receipt of the fiber and resin matrix
which make up the shell so that the latter captures the
boss 16 to prevent movement of the boss into or out of the
vessel 10.
Immediately within the pressure vessel l0, an
annular support flange 28 radiates from the neck 24 and
defines an outer surface 30 of the support flange 28 by
which pressurization loads are distributed about the
perimeter of the polar opening 18 in the composite shell
12. The support flange 28 has a width W~ such that the
overall diameter of the support flange 28 is sufficient to
prevent damage to the outer shell 12 when the pressure
vessel 10 is pressurized.
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In addition, a portion of the thin layer 22 is
interposed between the support flange 28, the liner 14 and
the outer shell 12 to further minimize damage as the vessel
is pressurized. Specifically, pressurization of the vessel
interior results in expansive distortion of the rounded
vessel end, such that relative slip between the inner
surface of the outer shell 12 and the mating portions of
the liner 14 and the support flange 28 may occur. In order
to accommodate the relative slip and relieve shear stresses
otherwise occurring at this interface, the interposed layer
22 extends across the rounded vessel end a distance
substantially equal to the diameter D1 of the circular
section of the pressure vessel 10.
An annular attachment flange 32 projects radially
outward from the support flange 28 a distance W2. The
attachment flange 32 has an oui~er surface 34 which is
inwardly offset from the outer surface 30 of the support
flange 28 by a distance Tz, and the attachment 32 has an
inner surface 36 which ~.s outwardly offset from an inner
surface 38 of the support flange 28 by a distance TZ.
Thus, support flange 28 has a thickness T3 which is
sufficient to limit bending stresses in the boss to wn
acceptable level when the vessel is pressurized.
A pair of annular locking grooves 40 and 42,
respectively, are located one in outer surface 34 of the
attachment flange 32 and the other in the inner surface 36
of the support flange 38. Each groove receives a
complementary tab 44,46, respectively, on the internal
liner 12.
The locking groove 40 is an outwardly opening
groove having a bottom wall 48 intermediate a pair of
mutually skewed sidewalls 50, which is to say the groove 40
is a dove-tailed groove. It is understood that other
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undercut features effective to mechanically lock the liner
to the boss are contemplated by the present invention.
The looking groove 42 is formed in the inner
surface 36 of the attachment flange 32 and has a bottom
wall 52 intermediate a pair of mutually skewed sidewalls 54
to again define a dove-tail groove. The complementary
geometry of the skewed sidewalls 50 and 54 and respective
liner tabs 44 and 46 ensure positive engagement and
retention of the internal liner 14 on the bass 16 such that
to pressurized fluid is prevented from leaking between the
liner and the outer shell 12.
The offset characteristic of the attachment
flange 32 as defined by the inward offset Ti of the outer
surface 34 and the outward offset TZ of the inner .surface
36 reduces the risk that the liner 14 will extrude out of
engagement with t$e boss 16 when under pressure by
providing a sufficient surface area for the liner to seal
with the attachment flange and prevent leakage.
Figure 2 illustrates an alternative embodiment of
the invention in which the internal liner 14 only engages
the annular locking groove 40 formed in the outer surface
34 of the attachment flange 32. Tn the embodiment
illustrated in Figure 2, the internal liner 14 has only a
singular annular tab 44 engaged with the boss 16.
Figure 3 illustrates a further embodiment of a
boss 56 used in conjunction with a filament wound pressure
vessel, generally designated 58. Pressure vessel 58 has a
fiber reinforced outer shell 60 and a non-metallic internal
liner 62. In a preferred form, the internal liner is
formed of blow molded high density polyethylene (~IDPE).
Boss 56 has a tubular neck 64 which extends axially outward
through a polar opening 66 formed in the outer shell 60 and
defines a stepped pressurization port 68 through which
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fluid at high pressure may be communicated with the
interior of pressure vessel 58.
An annular support flange 70 radiates outwardly
from neck 64 immediately within the pressure vessel and has
a sloped outer surface 72 and an oppositely sloped inner
surface 74. In other words, surfaces 72 and 74 converge
toward the periphery of flange 70. cuter surface 72
distributes pressurization loads about the perimeter of the
polar opening 66 in the composite shell 60 to prevent
damage to the outer shell when pressure vessel 58 is
pressurized. Inner surface 74 has a recessed portion 75
adjacent pressurization port 68 and an axially inward
opening groove 77 for purposes to be described hereafter.
A thin shear accommodating layer 76 is interposed
between outer shell 60, boss 56 and internal liner 62 to
prevent damage to the shell or liner during pressurization
of the vessel. More specifically, shear accommodating
layer 76 has a pair of divergent leaves 78 and 80. Leaf 78
is interposed between outer surface 72 of support flange 70
and the inner surface of outer shell 60, and leaf 80 is
interposed between inner surface 74 of support flange 70
and the outer side of internal liner 62. S h a a r
accommodating layex 76 preferably is formed of a material
suitabxe for relieving slip-induced shear stresses
otherwise occurring at the interface of support flange 70,
internal liner 62, anc~ outer shell 60 when vessel 58 is
pressurized. Injection molded thermoplastic elastomers,
such as thermoplastic rubber, have been found to provide
suitable performance characteristics in a shear
accommodating layer.
Internal liner 62 is attached to boss 56 by means
of an axisymmetric interface member 82. The interface
member preferably is formed of injection molded high
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density polyethylene (HDPE) which, when cooled, shrinks
into conformity with boss 56 as shown in Figure 3. More
specifically, the HDPE solidifies to form an elongated hub
84 disposed in pressurization port 68 and a radially
extending collar 86 seated in the recessed portion 75 of
inner surface 74 on support flange 70, The HDPE flaws into
groove 77 and thereby forms a complementary tab 88 for
inter-locking the interface member and polar boss 56. In
applications where it is desired to more securely bond
interface member 82 to the polar boss, an adhesive coating
is applied to the boss prior to injection of the HDPE.
Once interface member 82 is firmly secured to boss 56,
liner s2 is bonded tn the interface member along a common
seam 90. Conventional plastic welding techniques, such as
hot plate welding, are effective to reliably bond the HDPE
liner 62 and interface member 82.
Securement of interface: member 82 is enhanced by
a threaded retainer nut 92 which is advanced through
pressurization port 68 in the boss to lock a distal end of
elongated hub 84 against the stepped inner side wall 93 of
neck 64, An 0-ring seal 94 is captured between retainer
nut 92 and interface member 82.
The boss construction illustrated in Figure 3
advantageously reduces the risk of leakage from liner 62 by
moving the principal leakage path, that is the junction at
which the distal end of hub 84 on interface member 82 meets
boss 56, into the neck of the pressure vessel and upstream
of retainer nut 92. Consequently, the junction is not
subjected to the pressure cantained within the vessel and
the likelihood of leakage thereby is reduced, In additian,
the embodiment of Figure 3 isolates bass 56 from fluids
contained within vessel 58 and thus prevents 1)
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contamination of the fluid contents of the pressure vessel,
and 2) corrasion of the boss.
It will be understood that the invention may' be
embodied in other specific forms without departing from the
spirit or central characteristics thereof, The present
examples and embodiments, therefore, are to be considered
in all respects as illustrative and not restrictive, and
the invention is not to be limited to the details given
herein.
