Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
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This in~ention relates to an improvement in techniques
for the manufacture of nollow, fiber-reinforced articles, and
more particularly it pertains to a process for forming a resin-
¦ rich inner coating in a pressure vessel to eliminate possible
wicking of che~icals through the wall of the vessel. ~his
in~ention is an improvement in the type of molding technique
described in U. S. Patent No. 2,977,269 to Nerwick and U. S.
Patent No. Reissue 25,241 to Randolph. According to the technique
described in those patents, hollow, cylindrical, fiber-reinforced
plastic tanks have been successfully and economically pressure-
i molded. Generally, those techniques include the steps of laying
up a fiber form within a rigid mold casing in the approximate
form of the desired article. A complete fiber for~ may include
preformed, matted fiber end wall caps which telescope into a laid
up cylindrical sidewall portion. More desirably, the fiber form
comprises a preformed tube having a closed end, as described ~n-
U. S. Patent No, 3,911,965 and a single preformed end ap closi~g
¦ the open end of the preform.
¦ An eY.pandable bag or envelope, which will define the
I interior shape of the finished article, is positioned within the -
¦ fiber form in the mold. Rigid casing caps, which shape the end
¦ walls of the final article, are clamped to the ends of the mold
I ¦ casin~ to enclose the laid-up form. With the fiber form and mold
thus assembled, the fiber form is placed under a suitable moderate
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pressure by e panding ehe bag to hold it in pllce against the
mold. The fiber form is then permeated with a thermosetting resi
or the like. The bag, besides defining the interior surface oi
the molded ~ank and determining the proper fiber-to-resin ratio,
compresses the fiber form in such a manner as to avoid migration
of fibers with resin~flow and resulting destruction of the lay-up.
The bag is further expanded to compress the lay-up and to evenly
distribute the resin throughout the lay-up. The mold is then
heated to cure the resin, the bag is removed from the interiox
of the molded tank, and the finished molded tank is remoYed from
the mold. -
Tanks produced in accordance with the aforementionedprior art techniques have been widely employed as water softener
tanks, swimming pool filter tanks, and the like. One problem
exists, however, which is not serious when the tanks are employed i~
to hold water, bu~ which is serious when the tanks are employed
to hold corrosive chemicals. That problem involves a phenomenon
known as "wicking," wherein fibers may communicate with the inner
surface of the tank and the outer surface of the tank. In such
an inscance, the fluid contained in ~he tank may be draw~ along
the fiber by capillary action so that the fluid migrates through : _
the sidewall of the eank and forms a finely beaded liquid coating ,
on the exterior surface.
In view of this problem, attempts have been made to
line the interior of the tank with a resin-rich or gel coat.
This involves a separate step in the process, since the operation
is performed after the tank is cured and removed from the mold.
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Furthermore, such an operation results in a secondary bond
between the molded sidewal] oE the tank and the coating,
which creates the possibility of delamination of the coa-ting
during use.
SUMMARY OF THE INVEN~['ION
According to this invention, a resin-rich coating is
provided on the inner surface of a fiber-reinforced pressure
vessel during the molding opera-tion. This resin-rich coa-ting
is induced by providing a polyes~er fiber surfacing ~abric
on the inner sidewall of the vessel during the molding operation.
The fabric becomes permeated with the resin to thereby provide
a barrier between the fahrous reinforcing material and the
interior of the tank.
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~ More specifically, the pressure vessel is produced
-` by positioning a hollow lay-up of loosely felted reinforcing
fibers against the inner surface of a rigid mold having a
cylindrical wall portion and domed end portions. A str~tchable
polyester surfacing *abric is positioned against the inner surfaces
of the reinforcing fibers. The mold is vented and the lay-up
-~ 20 and surfacing fabric are compressed by an internally pressurized,
inflatable core
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to hold the surfacing fabric in place against the hollow lay-up
and to hold the hollow lay-up in place against the inner surface
o the mold. A metered amount of thermosetting resin is in~ected
into the ~old and the pressure of the core is increased to com-
presx the lay-up and to evenly distribute the resin throughout
the lay-up and form a resin-rich coating with the surfacing
fabric. The resin is then cured and the molded article is ~ ~`
removed from the mold.
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~ BRIEF DESCRIPTION OF THE DRA~?ING
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Fig. 1 is a cross sectional view of a mold assembly
having disposed therein fiber matting co~pressed between the
outer mold casing and the inner inflatable core;
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- Fig, 2 is a view on an enlarged scale of a portion
of Fig. 1 taken at an end of the cylindrical wall section of the
asse~bly;
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Fig. 3 is a perspective view of a surfacing fabric
sleeve employed in the molding process of this invention; and
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;~ Fig. 4 is a perspective view, similar to Fig. 3, showing
a bag encased in the sleeve of Fig. 3.
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I I DETAILED DESCRIPrION OF THE INVENTION
¦ Referring now to the figures, a molding assembly 9
I includes a rigid cylindrical mold casing 10 surrounding a cylin-
¦ drical sidewall portion 11 of a molded article or tank 12 of
I fiber-reinforced resin. The inner surface 13 of the cylindrical
¦ mold casing 10 de~ines the outer surface of the cylindrical
-I ¦ portion 11 of the tank 12. A rigid, domed mold casing end wall
¦ cap 18 is secured ~o the lower end of the cylindrical casing
10. This domed end cap 18 forms an outwardly convex bottom end
¦ wall 19 of the tank. At the upper end of the cylindrical mold
¦ casing 10 a rigid mold casing end wall cap 21, similar to the
lower end cap 18, is provided to form a tQR end wall 22 of the
I I fiber-reinforced tank 12.
¦ Fiber-reinforcing material for ~he end wall 22 of the
~ I tank is provided in the form of a cup-shaped fiber preform whose
I ¦ production is familiar to those skilled in the art. The cylin-
drical sidewall portion 11 and the end wall 19 are integrally
formed by the techniques set forth in U. S. Patent No. 3,654l002.
¦ With the rigid mold casing end wall cap 21 removed, the preform,
¦ which includes the sidewall portion 11 and the end wall portion
¦ 19, is inserted in the mold. ,-
The end wall 22 is provided with an aperture 28 at its
¦ center or apex. Ultimately, this aperture may become a port in
the finished tank. An inflation tube assembly 29 is inserted
through this aperture 28 and a corresponding opening or hole 31
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in the upper mold end wall cap 21. The inflation tube assembly
29 is adapted to sealingly clamp a mouth of an inElatable envelop
or ba~ 32 of a rubber or similar elastomeric material. The rubbe~
ba~ 32 comprises an inflatable mold core. As may be seen in
Figs. 3 and 4, a sleeve, consisting of a polyester fiber surfacin
fabric 33, is slipped over the bag 32, and one end thereof is
cupped around the tube assembly 29. The other end of the sle~ve
is folded over the end of the bag.
Desirably, the polyester fiber surfacing fabric comprise
a binder-free material having its fibers intertangled so that the
fabric has both vertical and horizontal fiber orientation. Pref-
erably, the fabric is a polyester fabric produced by Burlington ¦~
Glass Fabrics Company under the trademark "NEXUS.!' According to ~ e
manufacturer, this fabric is 1.5 denier Dacro~ type 106 homopolyme
staple. The fiber elongation at break is approximately 25 percent¦
and contains small amounts of titanium d:ioxide and an optical
brightener to improve fabric whiteness. Neither additive adversel
affects corrosion resistance. These fabrics conform rPadily to
contoured surfaces and are quickly wet by polyester, vinyl ester,
and epoxy laminating resins. The dry and wet tensile strengths
of these fabrics are superior to both C-glass mat and commonly
used adhesive bonded polyester and modacrylic fiber surfacing ~ ;
veils. It is also desirable to employ an apertured fabric desig-
nated as "Style 1012" by the manufacturer. The material i6
formed into a sleeve by an ultrasonically -~ormed seam 47, as
shown ln Fig. 3.
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The mold is completely assembled by clamping the upper
cap 21 on the cylindrical casing lO to enclose the fiber form. ~.
The rubber bag 32 is in its deflated state, indica~ed generally
by the phantom lines 36. As the upper cap ïs being assembled,
~he preform for ~he end wall 22 is positioned inside the edges
26 of the sidewall 11. It should be noted that mating edges
26 and 27 of the fiber matting of ~he sidewall 11 and the preform
for ~he top end wall 22, respectively, are tapered to form a
uniform wall joint.
The fibers reinforcing the sidewalls may be looselyfelted glass fibers held together with a suitable high solubility
binder in a reLatively compressible a~d porous orm. After the
rubber bag 32 and the surrounding sleeve 33 are infla~ed to hold
the fiber form against the rigid mold casing, a conventional
liquid resin, such as a polyes~er or vinyl ester settable by
heat, a catalyst, or the like, is introduced to a supply llne 40.
The amount of resin`introduced into the mold is sufficient to
permea~e the entire fiber body and provide a slight excess to
ensure that all of the ~ir will be driven out of the mold through
a set of vents 41. The compression of the fiber body lay-up by t~ e ,
rubber bag 32 is effective in preventing migration of the indi-
vidual fibers of the lay-up with the flow of impregn ting resin. .
~o accelerate the permeation of the lay-up the pressure in the
ba~ i9 lncre sed.
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The presence of the surfacing fabric against the fiber
lay-up promotes a resin-rich coa~ing on the inside of the ~ank,
I which is substantially free of fibers and which yrovides a pro-
¦ tective barrier between li.quids in the tank and the fibers, which
¦ might tend to draw the liquid through the sidewall of the tsnk.
¦ The rubber~bag 32 may be encased in a protective sheath
¦ of polyvinyl acetate film or nylon film, or similar material,
I which will protect the folding resin against the chemical action
¦ of vulcanizing agents or residues thereof associated ~ith the bag.
¦ Although a preferred embodimen~ of this invention i8
illustrated, it is to be understood tha~ various modifications
¦ and rearrangements of parts may be resorted to without departing
I from the scope of the inventlon.
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