WO1994012396A1

WO1994012396A1 - Compressed gas container and method of manufacture

Info

Publication number: WO1994012396A1
Application number: PCT/US1993/011255
Authority: WO
Inventors: Audie L. Price
Original assignee: Ngv Systems, Inc.
Priority date: 1992-11-20
Filing date: 1993-11-19
Publication date: 1994-06-09

Abstract

A composite container (10) for gas under high pressure comprises a seamless polymeric liner (140) having a bore through one end (30) a metal fitting (120A and 120B) bonded to the liner and penetrating the bore (134) a plurality of metal foil layers wrapped over the liner and metal fitting, a plurality of non-metallic film layers (180) wrapped about the metal foil layer (160) and fitting, and an outermost layer selected from the group consisting of: a thermosetting resin matrix structure which includes a plurality of metallic fibers for reinforcement and an insulation shell. Process for manufacturing such containers include: winding the plurality of layers of non-metallic fibers (180) about the metal foil layer (160) to form a resin matrix structure; curing the resin matrix structure; and applying a thermal insulation shell about the resin matrix structure.

Description

COMPRESSED GAS CONTAINER AND METHOD OF MANUFACTURE

BACKGROUND OF THE INVENTION

1. Field of the invention - this inventio relates to the field of lightweight, gas storage tanks an their methods of manufacture. The invention furthe relates to the field of high pressure composite cylinder or containers.

2. Technology Review - compressed gas tank and manufacturing methods for the same are generally know in the art. In such tanks, air, oxygen, natural gas an propane are typically stored for end used ranging fro scuba tanks and firemen's breathing system (FBS) cylinder to fuel containers for aircraft and land vehicles (e.g carts and forklifts) . Depending on the compatibility o contacting materials, still other end uses may includ fluid holding tanks, storage vessels for chemicals an energy storage vessels for pneumatic-powered mechanica devices.

In recent years, interest has increased in usin compressed natural gas (CNG) as an alternative fuel sourc for automobiles, trucks and vans. Safety and the light weighing of compressed gas containers are critical to th success of this application. Major logistica difficulties have often risen when large volumes of ga were involved. All-metal containers are heavy, awkward t transport and store, and more susceptible to corrosio than their composite counterparts. The size, shape an weight of such containers have also complicated many en product designs. Conventional techniques fo manufacturing such containers from steel, and eve aluminum, include deep drawing, extrusion, swaging an spinning processes. The pressurized gas vessels of sensitive military applications may not tolerate the weight penalties associated with an all-metal tank construction. Design and fabrication techniques have been developed for making lightweight containers with a significant amount of composite components. Many such tanks stored gases at lower pressures and/or smaller quantities than those required above. In such applications, end users tended to focus on ballistic resistance as yet another design constraint.

One known means of manufacturing composite containers for the military commences with forming a pressure vessel liner about a mandrel made from water soluble salt or a sand composite held together with water soluble binders. Reinforced composite fibers are then filament wound onto this mandrel. After curing, the mandrel is "washed out" by flushing the dissolved salt or sand from the wound liner's interior. This approach is costly and rather labor intensive. Still other composite containers and manufacturing methods are set forth in U.S. Patent No.s 2,744,043, 2,848,133, 3,073,475, 3,132,761, 3,210,228, 3,282,757, 3,449,182, 4,123,307, 4,585,041, 4,699,288, and 4,927,038, all of which are incorporated by reference herein.

SUMMARY OF THE INVENTION

It is a principal objective of this invention to develop composite containers which overcome many of the disadvantages associated with storing high pressure gases in an all-metal or all-composite tank. It is another principal objective to provide uncomplicated, cost- effective means for making composite containers of a reduced weight. it is another objective to provide high pressure vessels with a one-piece, semi-rigid polymeric liner about which is wrapped at least one all-metal foil layer. Past methods which employed metallized resin film layers rather than a solid metal film have resulted in inferior vessels, at least with respect to gas containment and service temperature capability. It is still another objective to provide composite compressed gas containers which are capable of: withstanding temperatures of about 350^° (177^°C) or more; and storing gases for long terms at pressures in the range of about 4500 psi. It is still another objective to enhance container safety by substituting a molded inner liner for liners made from more fracture sensitive metals.

Yet another objective of this invention is to provide containers which may pass current U.S. Department of Transportation (DOT) standards for FRP-1 exemption qualifications, said standards including: a .30 caliber armor piercing gunfire test, bonfire test, thermal cycle burst test and pressure reversal cycle test, all of said DOT standards being fully incorporated by reference herein.

These and other objectives/advantages are met or exceeded by the invention described below, one embodiment of which pertains to a composite container for storing and transporting gas under high pressure. This container comprises a seamless polymeric liner having a bore through at least one end, a metal fitting penetrating into and adhesively bonded to said liner, a plurality of metal foil layers wrapped over said liner and fitting, a plurality of non-metallic film layers wrapped about the metal foil layer, an electrical non-conducting film layer and an outermost layer selected from the group consisting of: a fiber-reinforced resin matrix structure which fibers may be non-metallic (i.e. glass) or metallic (i.e. carbon) ; a metallic insulation shell; and combinations thereof.

Another aspect of this invention addresses means for manufacturing such composite containers. Said method comprises: providing a polymeric liner having a generally cylindrical shaped with opposed ends and a bore extending through at least one of said ends; penetrating a metal fitting into and adhesively bonding said fitting to each liner bore; laminating at least one metal foil layer about said liner and fitting assembly; winding a plurality of non-metallic fiber layers about the metal foil layer to form a resin matrix structure; curing said resin matrix structure; and preferably applying a thermal insulation shell about said resin matrix structure.

BRIEF DESCRIPTION OF THE DRAWINGS Further features, objectives and advantages of the present invention will be made clearer by reference to the accompanying drawings in which:

FIGURE 1 is a side view of one preferred embodiment of gas container according to the invention, said container having a bore through only one of its opposed ends;

FIGURE 2 is a side view depicting three representative end configurations for the containers of this invention;

FIGURE 3 is a side view showing a second preferred embodiment with bores through both opposed ends;

FIGURE 4 is a front view taken along lines IV-IV of FIGURE 3;

FIGURE 5 is a side sectional view taken along lines V-V of FIGURE 4 for detailing the metal fitting in one preferred embodiment; and FIGURE 6 is a sectional view of FIGURE 5 exploded to highlight the various component layers in one preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS When referring to any numerical range of values herein, such ranges are understood to include each and every number, and fraction, between the range minimum and maximum. For example, any reference to a total thickness of about 5-16 mils would further disclose all intermediate thicknesses of about 6, 6.25, 7, 7.5 and 8 mils, and so on...up to a metal foil layer 16 mils thick. The same applies to all temperature ranges set forth herein.

Referring now to the accompanying FIGURES, there are shown two representative embodiments of the present invention. The first embodiment of FIGURES 1 and 2 shows a compressed gas container, item 10, having a generally cylindrical shape with only one meal fitting 20 penetrating into and adhesively bonded to an end 30 of the container. End 30 may or may not be opposed to a similarly-shaped end at the other side of container 10 but, nevertheless, comprises an efficient shape for subsequently loading fibers in tension, one example of which is isotensoid in cross-section, said shape having no discrete radii. It is to be understood that still other cross-sectional configurations are available for use with either embodiment, however. In FIGURE 2, this isotensoid profile is shown as item 32 for comparison with other representative shapes 34 and 36, the first alternative cross-section 34 being ellipsoidal with two separate radii and the second, item 36, being substantially hemispherical.

The container 110 of FIGURE 3 has a pair of metal fittings 120A and 120B adhesively secured to the liner and penetrating the bores at opposed ends 130A and 13OB of this alternative embodiment. As better seen in FIGURES 4 and 5, each fitting is comprised of several integral parts, namely: a shaft 132, fitting bore 134, flange 136 and internal conductor 138. It is preferred that such fittings be made from a temperature conducting alloy, such as 6061-T6 aluminum, in order to provide adequate thermal heat transfer paths into the container. Such paths may be critical when containers of this sort are subjected to bonfire testing pursuant to DOT FRP-1 Exemption Standards. For those tests, metal fittings transfer bonfire heat from outside the container, through the conductor portion 138 of fitting 120 and into the region of the tank where compressed gas may be stored. This causes the tank's internal pressure to rise, thereby activating any pressure relief devices built into the tank. For ease of description, no pressure relief valves are shown or described in the accompanying drawings.

The fittings of this invention provide access to the polymeric liner where gases (or fluids) are stored. They allow for repeated filling and emptying of each tank or vessel. On a preferred basis, such fittings should be self-fixturing, by which it is meant that they will install in a liner bore in only one proper direction and angle. For the installation of said fittings, epoxy coatings or other adhesives are typically applied to one or both bonding surfaces.. In some cases, adhesion may be enhanced by first mechanically abrading, chemically treating and cleaning the surfaces to be bonded.

In FIGURES 5 and 6, detailed views of the various layers comprising the main body of this container are shown. An innermost polymeric liner 140 is first provided, said liner preferably being rotationally molded from one or more resins selected from the group consisting of: nylon, polypropylene, polyethylene, polyolefin, thermoplastic polyester, polycarbonate, polybutylterephthalate, vinyl and polyurethane. It is to be understood that still other known or subsequently developed resins or resin combinations may be adapted for use as a liner material according to this invention. Alternative liner formation processes may include blow molding, injection molding or subsequently developed processes. Preferable liner thicknesses range from a minimum of about 60 mils (1.52 mm), to the more preferred range of about 80-250 mils (2.03-6.35 mm). Maximum thickness levels for any particular layer of this invention are only limited by DOT standards, if any, and by the underlying goal of this program: to produce a gas impermeable container of reduced size and weight.

The liner of this invention has a generally cylindrical shape although alternative container configurations can still be constructed within the spirit of the invention. At each opposed end 130 of this embodiment, an aperture or bore 145 extends completely through liner 140 for penetration of a metal fitting therein. In still other embodiments, this bore may be fully or partially threaded, slotted, or abraded for better adhesion to the metal fittings 120 inserted therein.

On a preferred basis, a first adhesive coating 150 is applied to the entire outer surface of polymeric liner 140. Any suitable epoxy or other compatible resin will suffice. First coating 150 is intended to enhance adhesion between liner 140 and the plurality of metal foil/strip layers 160 applied thereover. On a preferred basis, thin strips of metal foil at least about 0.5 mils

(0.013 mm) thick, and preferably between about 5-16 mils

(0.013-0.41 mm) thick, impart a gas impervious layer over the liner and at least some portion of the metal fitting installed into bore 145. Such metal foil strips or sheet serve as significantly better gas barriers than their metallized resin film counterparts, the latter of which also provide inferior service temperature capabilities compared to the present invention. On a preferred basis, the edges to these metal foil layers overlap each other by at least about 0.75 inch (19 mm) to assure a complete surrounding of the liner and fitting assembly.

Any suitable metal may be used for layer 160 so long as it is compatible from corrosion (emf) standpoint with any other container layers that layer 160 contacts. For the present invention, commercially available aluminum alloy foil was used though it is to be understood that a number of other metal foil products may be substituted therefor.

A second epoxy coating layer 170 may next be applied to enhance adhesion between metal foil layer 160 and the non-metallic film layer 175 wrapped therearound.

This adhesive layer should be compatible with both layers that it contacts while also insulating materials of disparate electromotive force (emf) potentials to reduce the risk of galvanic or anodic corrosion forming between adjacent layers. Separation of these two layers becomes critical when an aluminum foil layer precedes the winding of a carbon-fiber reinforced, filament wound structure about the intermediate container forms of this invention. When fiberglass layers are to be applied, by contrast, there is less need for electrical insulation between layers, through the application of an outermost thermal insulation shell may become necessary.

Layer 175 is comprised of electrical insulative film and may be installed either in a single piece, in strips or in sections with a minimum 0.75 inch (19.1 mm) width overlap. Suitable materials for said film layer 175 include nylon, polyurethanes, various polyesters and a variety of elastomers. Layer 180 is preferably installed using known filament winding equipment and practices. Depending on end use expectations for the container so manufactured, the material comprising said layer may consist of various fiberglass strands, carbon, boron and/or silicon carbide strands, Kevlar®-type fibers or other synthetics, including but not limited to the Spectra® filaments manufactured by Union Carbide. Combinations of materials may also be wound near simultaneously, alternatively or as separate layers so as to form a resin matrix structure. Layer 180 is preferably wrapped around the container intermediate in multiple strands using multiple passes, although pre-woven sheets or strips of fibers may be used. In either event, fibers, sheets or strips are impregnated with, or run near simultaneously through a bath of, thermosetting resin for subsequent curing.

On a preferred basis, non-metallic layer 180 is filament wound about the intermediate container shell in a plurality of stages to form the resin matrix structure. It is to be understood, however, that other application means may also be employed. A first stage, having a minimum thickness of about 20 mils (0.51 mm), is applied, bi-directionally in a first winding stage before curing. All or a significant portion of this first stage may be scuffed, washed and dried before additional layers are applied thereover. Subsequent stages of the same, or different, fibrous layers may be applied over the first non-metallic stage, preferably at a slight angle relative to the first stage. In one representative container, a first non-metallic layer is applied circumferentially followed by a second layer applied at a minimum angle to the longitudinal axis of the cylinder. This series of circumferential and longitudinal layers may then be repeated, in alternating layers, to create a 4-ply, 6-ply, 8-ply, 10-ply or even thicker construction. Following completion of all resin matrix, fiber- reinforced layer windings, an optional third adhesive coating 190 may be applied over the intermediate product when a thermal insulation shell 200 is to be used. The latter two layers are especially critical when low thermal conductivity fiber/resin composites are situated about non-metallic layer 175, or where said composite layer is wound relatively thin. Thermal transfer shell 200 should then be bonded onto the latter layer, mostly for protection, using an adhesive coating loaded with insulative fillers. One representative third coating 190 consists essentially of bisphenol A epoxy, loaded with hollow, phenolic microspheres. To this coating is bonded an aluminum thermal transfer shell 200, though it is to be understood that still other metal or conductive plastic shells may be substituted therefor. When the latter shell is applied, it should be at least about 5 mils (0.13 mm) thick, with preferred shell thicknesses ranging between about 7-20 mils (0.18-0.51 mm). Shell 200 may function as an impact protector and also substitute for paint or other container coloring.

With the foregoing container, total pressures of up to about 6000 psi may be maintained for prolonged periods of time, up to about 10 years, at standard temperatures. The composite vessels of this invention may also exhibit burst strengths ranging from 15,000 to 40,000 psi. Another advantage of this invention is its overall resistance to temperature variation. Tanks with a metallized resin film layer exhibit temperature resistances of up to 275^°F (135^°C) . Some automobile manufacturers require temperature resistances of up to 350^°F (177^°C) if CNG tanks are to be included as an alternate fuel source. the present invention, with its use of an all-metal layer wrapped about a one-piece, polymeric liner, achieves continuous temperature resistances of up to about 350^°F (177^°C) , although tanks according to the present invention may exhibit one-time temperature resistances in excess of 500^°F (260^°C) .

A significant weight savings is also attributed to the practice of this invention. For a half-hour capacity manbreather tank, past aluminum containers have weighed as much as 20 pounds (9060 grams) . Hybrid glass fiber/aluminum tanks of an equivalent size, which have been replacing their all-metal counterparts for the last 15 years, weigh as little as 10 pounds (4530 grams) . Compressed gas containers of the present invention by comparison only weigh about 5 lbs. (2265 grams) , or half the weight of today's models, in an equivalent capacity/size.

EXAMPLE A polymeric liner was obtained from RMB

Products, said liner being rotationally molded from a nylon polyamide resin sold by Huels AG under the name "Vestamid L 1722". The bores at opposed ends of this cylindrical liner were scuff sanded, washed and dried before bonding to respective fittings machined from 6061- T6 aluminum using about 10 mils (0.25 mm) of an epoxy adhesive, sold commercially by 3M as ".2216". Excess epoxy was then removed from the outer surface of this liner. The outer surface was next coated with a resin mix consisting of 70 parts by weight "EPON 826", 30 parts by weight "EPON 815" and 40 parts by weight "V-40 Versamid", each of said resins and catalyst modifiers being sold commercially by Shell Chemical. A 2 mil (0.05 mm) thick section of aluminum foil was then wrapped over the liner and fittings, the joints between adjacent layers of said foil overlapping by a minimum of about 0.75 inch (19.1 mm) . Excess resin was then brushed into these overlapping foil layer joints. A first layer of nylon film, about 2 mils (0.05 mm) thick, was applied over this intermediate foil layer. The entire unit was then placed in a filament winding apparatus for applying first layers of fibers thereabout, said first layers consisting of 2 sublayers, one of which was circumferentially applied, the second of which was applied at a slight angle relative to the first layer. Upon completion of this first winding phase, the assembly was installed into a curing oven. Internal pressure of this assembly was regulated to about 15-20 psi for heating at 85-125^°F (29-52^°C) for a minimum of 16 hours.

After curing, resin glaze was removed from the winding surface of this assembly. Additional layers of carbon fibers were then installed as follows: 4 strands in 4 separate passes; another 4 strands in 4 passes using a different winding configuration; and a final layer of 2 strands in 2 passes. Internal pressure of the assembly was again regulated to about 25-35 psi before further curing for a minimum of 48 hours at 85-125^°F (29-52^°C) . The final assembly was then subjected to testing according to DOT FRP-1 standards.

Having described the presently preferred embodiments, it is to be understood that the invention may be otherwise embodied by the scope of the claims appended hereto.

Claims

What is claimed is:

1. A compressed gas container comprising:

(a) a seamless polymeric liner having a bore through at least one end;

(b) a metal fitting adhesively bonded to said liner;

(c) at least one metal foil layer laminated over said liner and metal fitting;

(d) at least one layer of non-metallic film wrapped over said metal foil layer; and (e) a fiber-reinforced, resin matrix composite layer.

2. The gas container of claim 1 which further includes:

(f) a thermal insulation shell applied about composite layer (e) .

3. The gas container of claim 1 wherein said polymeric liner is made from a material selected from the group consisting of: nylon, polypropylene, polyethylene, polyolefin, thermoplastic, polyester, polycarbonate, polybutylterephthalate, vinyl, , polyurethane and combinations thereof.

4. The gas container of claim 1 wherein said polymeric liner is rotationally molded.

5. The gas container of claim 1 wherein said polymeric liner is at least about 60 mils (1.52 mm) thick.

6. The gas container of claim 5 wherein said polymeric liner is between about 80-250 mils (2.03-6.35 mm) thick.

7. The gas container of claim 1 wherein said polymeric liner has a bore through each opposed end.

8. The gas container of claim 1 wherein said polymeric liner is generally cylindrically-shaped with opposed ends, each end having a cross-sectional shape selected from the group consisting of: an isotensoid, an ellipsoid and a hemisphere.

9. The gas container of claim 1 wherein said metal foil layer is at least about 0.5 mils (0.013 mm) thick.

10. The gas container of claim 9 wherein said metal foil layer is between about 5-16 mils (0.13-0.41 mm) thick.

11. The gas container of claim 1 wherein said non-metallic film layer is made from a material selected from the group consisting of: vinyl, nylon, polypropylene, polyethylene, polyolefin, polyester, polycarbonate, polybutylterephthalate, vinyl, polyurethane and combinations thereof.

12. A composite container for storing and transporting gas under high pressure, said container comprising:

(a) a seamless polymeric liner having a bore through at least one end;

(b) a metal fitting penetrating in and adhesively bonded to said polymeric liner;

(c) a plurality of metal foil layers wrapped over said liner and metal fitting; (d) a plurality of non-metallic film layers wrapped about said metal foil layer;

(e) a fiber-reinforced, resin matrix composite layer; and (f) a thermal insulation layer bonded to the composite layer.

13. The composite container of claim 12 wherein said polymeric liner is rotationally molded from one or more materials selected from the group consisting of: nylon, polypropylene, polyethylene, polyolefin, thermoplastic polyester, polycarbonate, polybutylterephthalate, vinyl and polyurethane; and said non-metallic film layer comprises filament strands made from one or more materials selected from the group consisting of: vinyl, nylon, polypropylene, polyethylene, polyolefin , polyester , polycarbonate , polybutylterephthalate, vinyl and polyurethane.

14. The composite container of claim 12 wherein said polymeric liner is at least about 60 mils (1.52 mm) thick and said metal foil layer is at least about 0.5 mils (0.013 mm) thick.

15. The composite container of claim 14 wherein said polymeric liner is between about 80-250 mils (2.03- 6.35 mm) thick; and said metal foil layer is between about 5-16 mils (0.13-0.41 mm) thick.

16. The composite container of claim 12 which is generally cylindrically-shaped with opposed ends, each end having a cross-sectional shape selected from the group consisting of: an isotensoid, an ellipsoid and a hemisphere.

17. The composite container of claim 16 wherein each opposed end has a bore extending therethrough.

18. A method of manufacturing a composite container for storing and transporting gas under high pressure, said method comprising:

(a) providing a generally cylindrically-shaped polymeric liner with opposed ends and a bore extending through at least one of said ends, said liner being at least about 60 mils (1.52 mm) thick;

(b) inserting a metal fitting into the bore of said polymeric liner; (c) wrapping a metal foil layer about the polymeric liner and at least a portion of said metal fitting, said metal foil layer being at least about 0.5 mils (0.013 mm) thick;

(d) wrapping the outermost metal foil layer in a plurality of non-metallic film layers;

(e) wrapping the film layers with a fiber- reinforced, resin matrix structural composite layer; and

(f) curing the structural composite layer.

19. The method of claim 18 which further includes:

(g) bonding a thermal insulation shell to the structural composite layer of step (e) .

20. The method of claim 19 wherein the insulation shell of step (g) is a metal shell.

21. The method of claim 20 wherein said metal shell is made from an aluminum-based alloy.

22. The method of claim 19 which further includes the step of priming an outermost surface of the container with an adhesive prior to one or more of steps (c) , (d) and (g) .

23. The method of claim 22 wherein the priming adhesive is nylon-based.

24. The method of claim 18 wherein step (a) includes rotationally molding the polymeric liner from one or more materials selected from the group consisting of: nylon, polypropylene, polyethylene, polyolefin, thermoplastic polyester, polycarbonate, polybutylterephthalate, vinyl and polyurethane.

25. The method of claim 18 wherein step (b) includes bonding said metal fitting to the liner bore.

26. The method of claim 25 wherein said metal fitting is bonded to the bore with a thermoset adhesive.

27. The method of claim 18 wherein step (d) is performed in a plurality of stages using a filament winding machine.

28. The method of claim 27 wherein the outermost surface of the container is abraded prior to application of the next adjacent non-metallic film layer.

29. The method of claim 18 wherein the structural composite layer of step (e) includes reinforcing fibers made from materials selected from the group consisting of: carbon, glass, boron, silicon carbide and combinations thereof.

30. The method of claim 18 wherein the structural composite layer of step (e) includes a resin selected from the group consisting of: an epoxy, polyester and combinations thereof.

31. A method of manufacturing a composite container for storing and transporting gas under high pressure, said method comprising:

(a) providing a polymeric liner having a generally cylindrical shape with opposed ends and a bore extending through at least one of said ends, said liner being made from one or more materials selected from the group consisting of: nylon, polypropylene, polyethylene, polyolefin, thermoplastic polyester, polycarbonate, polybutylterephthalate, vinyl and polyurethane;

(b) adhesively bonding a metal fitting to each liner bore;

(c) priming the exterior of said liner with a first adhesive coating; (d) laminating at least one metal foil layer onto said first adhesive coating, said metal foil layer being at least about 0.5 mils (0.013 mm) thick;

(e) priming the outermost layer of metal foil with a second adhesive coating; (f) filament winding a plurality of resin- impregnated fibers onto said second adhesive coating to form a resin matrix structure;

(g) curing the resin matrix structure; and (h) applying a thermal insulative shell to said resin matrix structure.

32. The method of claim 31 wherein step (f) includes:

(i) winding a first set, of fiers about the second adhesive coating in a first direction; (ϋ) abrading at least some portion of the outermost layer of said first set of fibers; and

(iii) winding a second set of fibers about the abraded first set in a second direction.

33. The method of claim 31 wherein the thermal insulative shell of step (h) is made from an aluminum- based alloy.