CA1111222A - Lined pressure vessels - Google Patents

Abstract

LINED PRESSURE VESSELS

ABSTRACT OF THE DISCLOSURE

A method of making hollow, fiber-reinforced resin articles having a resin-rich interior coating is disclosed. The interior coating provides a chemically resistant surface and inhibits wicking of fluids through the sidewall of the tank. The coating is formed 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 polyester fiber surfacing fabric is placed against the inner surface of the lay-up. The surfacing fabric and lay-up are com-pressed against the mold wall by a pressurized, inflatable core to hold the fabric and lay-up in place. A metered amount of a thermosetting resin is injected into the mold, and the pressure of the inflatable core is increased to compress the lay-up, to evenly distribute the resin throughout the lay-up, and to form a resin-rich coating with said surfacing fabric.

Description

~l ' 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.

_3_ 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;
:' Fig. 3 is a perspective view of a surfacing fabric sleeve employed in the molding process of this invention; and ~,' : :
;~ 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.

'' ' ; ' ! ' 8 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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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of making hollow fiber-reinforced resin articles having a resin-rich interior coating, comprising the steps of positioning a hollow lay-up of loosely felted rein-forcing fibers against the inner surface of a rigid mold having a cylindrical wall portion and domed end portions, positioning a stretchable polyester fiber surfacing fabric against the inner surfaces of the reinforcing fibers, venting said mold, compressing said lay-up and said surfacing fabric with an internally pressurized, inflatable core 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 of the mold, injecting a metered amount of a liquid thermosetting resin in said mold, increasing the pressure in said inflatable core to compress the lay-up and to evenly dis-tribute the resin throughout the lay-up and form a resin-rich coating with said surfacing fabric, curing said resin, and remov-ing the molded article from the mold.

2. A method according to claim 1, wherein said surfacing fabric comprises intertangled nonoriented polyester fibers.

3. A method according to claim 2, wherein said surfacing fabric is apertured.

4. A method of making hollow fiber-reinforced resin articles having a resin-rich interior coating, comprising the steps of positioning a hollow lay-up of loosely felted rein-forcing fibers against the inner surface of a rigid mold having a cylindrical wall portion and domed end portions, providing a stretchable tubular polyester fiber surfacing fabric having a diameter substantially corresponding to the inside diameter of the hollow article to be molded, slipping said fabric over an inflatable core, positioning the inflatable core and the fiber surfacing fabric within the hollow lay-up, venting said mold, inflating said inflatable core 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 of the mold, injecting a metered amount of a liquid thermosetting resin in said mold, increasing the pressure in said inflatable. core to compress the lay-up and to evenly distribute the resin throughout the lay-up and form a resin-rich coating with said surfacing fabric, curing said resin, and removing the molded article from the mold.

5. A method according to claim 4, wherein said surfacing fabric comprises intertangled nonoriented polyester fibers.

6. A method according to claim 5, wherein said surfacing fabric is apertured.