WO2011144232A1

WO2011144232A1 - Method for producing a leak-tight vessel, and a leak tight vessel as produced by that method

Info

Publication number: WO2011144232A1
Application number: PCT/EP2010/056695
Authority: WO
Inventors: Tony Vanswijgenhoven; Dieter Vanswijgenhoven; Axel D. Seifert
Original assignee: Covess
Priority date: 2010-05-17
Filing date: 2010-05-17
Publication date: 2011-11-24

Abstract

Present application describes a method for producing a leak- tight vessel (14) for holding a gas and/or liquid, comprising the steps of winding a barrier strip (60) around a removable mandrel (1) in such a way that each strip fragment overlaps with a substantially parallel strip fragment (62) over at least a lateral overlapping distance, consolidating the overlapping strip fragments so as to form a gas and/or liquid tight layer, winding a fibrous material (12) around the gas and/or liquid tight layer, thereby leaving an opening (4) large enough for removing the mandrel (1). Also described is a leak- tight vessel produced in this way.

Description

METHOD FOR PRODUCING A LEAK-TIGHT VESSEL, AND LEAK-TIGHT VESSEL AS

PRODUCED BY THAT METHOD

TECHNICAL FIELD

The invention relates to a method for producing a leak-tight vessel having a predetermined permeability for holding a gas and/or liquid, in particular a fibrous reinforced leak-tight vessel, and to a leak-tight vessel produced in this way.

BACKGROUND ART

Leak tight vessels comprising a fiber reinforced material as their wall structure and methods for producing them are known in the art.

With "leak-tight vessel" is meant a substantially liquid-tight vessel or a substantially gas-tight vessel or both, wherein the permeability of the vessel for the liquid and/or gas to be stored inside the vessel is below a maximum prescribed limit for the given application the vessel is intended for. For example, in case the application is a hot water boiler application, the relevant permeability is the permeability of hot water under the intended storage conditions (e.g. temperature, pressure).

A known method for making leak-tight vessels, in particular pressure vessels, uses filament winding of continuous fibers impregnated with a thermoset resin over an inner bottle (also called "liner") that will remain in the vessel after the filament winding step. The inner bottle is sufficiently rigid to be tightly overwrapped with continuous fibers, and is quite thick (e.g. 1 - 4 cm) to act as the gas and/or liquid barrier. A disadvantage of such a method is that the bottle (liner) is heavy and expensive.

US 4,760,949 describes a composite container for storage of products at non-atmospheric conditions. The composite container has a high barrier liner layer including a metal layer of vacuum deposited aluminum parallel with and spaced from the longitudinal edge of a synthetic plastic base thereby to define a first web that is helically wound around a cylinder in edge overlapping relation such that one longitudinal edge of the metal strip overlaps the other longitudinal edge of the metal strip by a given constant distance (d). The overlapping edges of the first web are hermetically joined by a heat-sealable bond between an adhesive layer covering the metal strip and the adjacent face of the first web, and a compatible heat sealable layer on the opposite face of the web. The method applies filament winding around a cylinder. After the fibrous cylindrical wall is removed from the mandrel, metal end parts are added to form a leak-tight vessel, and an end sealing compound is provided between the composite wall and the metal end part so as to obtain a hermetical connection.

A disadvantage of this method is that such a leak-tight vessel is not suitable to withstand high pressure (e.g. 2 bar or more).

With "gas and/or liquid tight" is meant that it can be gas tight, or liquid tight, or both, depending on the intended application.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a method for producing a leak-tight vessel able to resist a pressure higher than 2 bar, without using a liner bottle.

This is achieved according to the present invention with the method of the first claim. As will become clear further, the disclosed method and the disclosed leak-tight vessel thus obtained are also very well suited for producing leak-tight vessels or containers used for storage of liquids under atmospheric conditions.

Thereto the method for producing a leak-tight vessel according to the present invention, the vessel having a predetermined permeability for holding a gas and/or liquid, comprises the steps of: - assembling a removable mandrel having a rounded outer surface suitable for filament winding, the mandrel having a rotation symmetrical shape with a varying outer diameter D around a symmetry-axis; - winding a barrier strip around the mandrel so as to form a wound strip layer, thereby completely covering a predefined area of the rounded outer surface while leaving a first opening large enough for removing the mandrel after being disassembled, whereby the winding of the barrier strip is applied in such a way that the predefined area is completely covered with strip fragments of the barrier strip and that each strip fragment shows a first local overlap over at least a lateral overlapping distance with a first substantially parallel strip fragment and shows a second local overlap with a second crossing strip fragment the barrier strip comprising a first layer and a second layer located at opposite sides of the barrier strip and an inner layer located between the first and the second layer, the first resp. second layer comprising a first resp. second plastic material, the inner layer comprising a third material, whereby the first resp. second plastic material of strip fragments can be consolidated with the second resp. first plastic material of overlapping strip fragments, and the first and second plastic material show a leak- tight cohesion with the third material; - forming a shell layer by filament winding a fibrous material over the wound strip layer, thereby leaving the first opening for removing the mandrel, thereby exerting pressure upon the wound strip layer so that the strip fragments of the barrier strip are pressed tightly against the mandrel and against each other so that the materials of the overlapping strip fragments can be consolidated at their contacting surfaces; - consolidating the first resp. second plastic material of strip fragments with the second resp. first plastic material of overlapping strip fragments thereby forming a gas and/or liquid tight layer comprising a strip of the third material, the gas and/or liquid tight layer having said predetermined permeability; - disassembling and removing the mandrel through the first opening; - applying a first end fitting and hermetically connecting it with the gas and/or liquid tight layer.

As used herein, with "consolidation" of two or more materials is meant unification; in the context of thermoplastic materials consolidation means uniting by heating or local melting, in the context of thermoset plastic materials consolidation means polymerization also known as curing.

By providing a removable mandrel it is possible to apply filament winding without the need for a bottle (or "liner") with a strong (thus thick and heavy and expensive) wall to enable filament winding thereto. By winding a barrier strip around the mandrel, the thickness of the gas and/or liquid tight layer can be chosen independently of the size of the vessel, in contrast to the traditional approach, where the thickness of the bottle wall needs to increase for larger vessels in order to maintain sufficient stability for the winding process.

Further, thanks to the use of the mandrel, the filament wound material can be a thermoplastic material, which was not possible when using a thermoplastic bottle (liner), because it would weaken. This allows more materials to be used for the leak-tight vessel.

Due to the fact that the mandrel can be disassembled, the parts of the mandrel can be removed through the first opening after disassembly, irrespective of the shape the mandrel had during the winding step. This allows a mandrel with a shape different from a cylindrical shape while still being able to separate the vessel from the mandrel.

By providing a mandrel with a varying outer diameter the top and bottom parts can have a diameter smaller than the maximum outer diameter of the vessel, and can be overwrapped by the fibrous material thereby so as to be able to resist high pressure (e.g. more than 2 bar, or even 10 bar, or even 25 bar, or even 50 bar).

The inventor has surprisingly found that by winding a barrier strip of width W in an overlapping way as described above, a gas and/or liquid tight layer can be provided having similar barrier properties as an inner bottle ("liner") with a solid wall thickness of approximately W. By choosing proper materials for the barrier strip and by choosing the lateral overlapping distance large enough (e.g. 50% of the width of the strip), the permeability obtained can be determined mainly by the width W of the strip and not by its thickness. In this way a strip with a thickness of e.g. 800 μηη and a width of 4 cm using an overlap of 50% can achieve a similar barrier effect as an inner bottle of 4 cm thickness made of the same material as the first and/or second layer of the barrier strip!

Even though winding of protection strips is well known in relation to cylindrical tubes, no prior art of this technology has been found in the domain of producing fibrous vessels by filament winding continuous fibers over a non-cylindrical shape, in particular for producing pressure vessels, where the common belief is that a thick wall of solid material is required to achieve a high barrier effect. When applying the barrier strip to the non-cylindrical rounded outer surface of the mandrel of the current invention, the strip fragments are not overlapping in the same predictable way as illustrated in Fig 9 or Fig 10 of US 4,760,949, (also shown as Fig 1 of the present application), where the strip fragments run perfectly parallel to each other with a constant overlapping distance "d", and fit nicely and tightly to the cylindrical surface. This is not the case when winding the barrier strip around a non-cylindrical mandrel. The inventor has surprisingly found that nevertheless a high barrier effect can also be achieved even when the strip fragments are inter-woven in a way that substantially parallel strip fragments are separated by crossing strip fragments, sometimes only several windings later. Experiments have shown that the high barrier effect is still achieved by providing the above mentioned minimum overlapping distance, even though the overlapping distance is not constant on a non-cylindrical mandrel, provided that the strip fragments are consolidated to each other, which the inventor has observed can be achieved by exerting pressure upon the barrier strip fragments by filament winding the fibrous material at a larger tension than usual (in case the filament winding would be applied directly around a mandrel), so that the strip fragments are tightly pressed against the mandrel and to each other. This is important when using a non-cylindrical mandrel because the strip fragments do not in themselves show perfect contact with the rounded outer surface area, especially at their longitudinal edges.

As an additional advantage, the method of winding the barrier strip as described above can be fully automated, using the same equipment as used for the filament winding of fibrous material, thereby avoiding extra investment costs and factory space.

Another advantage of winding a barrier strip instead of using a bottle (liner) is that a barrier strip of a given width W can be used for vessels of different sizes, which is not the case when using "bottles", which have a fixed size. This offers a great advantage in logistics, stock and flexibility in production.

In addition, vessels with a higher barrier (also called impermeability) can be produced in a very fast and economical way by simply repeating the winding process so as to cover the predefined area multiple times, without noticeably increasing the weight of the vessel. In this way the useful lifetime of the product (e.g. a hot water boiler before leakage takes place) can be largely increased at only a minor additional cost.

In a preferred embodiment the end fitting is applied in the form of a dome shaped end fitting having an outer peripheral larger than the first opening and having a second opening large enough for removing the mandrel therethrough after being disassembled, and positioning the second opening in alignment with the first opening, and whereby the fibrous material is applied in such as way as to overlap at least the outer peripheral of the first end fitting.

By winding the fibrous material in such as way as to overlap at least the outer peripheral of the first end fitting, an excellent mechanical hold is provided of the first end fitting against internal pressure from inside the leak- tight vessel. In this way a pressure vessel can be produced that can withstand an elevated internal pressure (e.g. 2, 10, 25 or even 50 bar).

By providing a large overlapping area, preferably the entire first end fitting except for the opening, the force exerted upon the first end fitting to counteract the internal pressure can be distributed over a larger area, thereby reducing the stress exerted upon the first end fitting.

By applying the first end fitting before the filament winding of the fibrous material, the first end fitting is integrated into the wall structure during the construction of the wall, and an extra processing step for adding a top and/or bottom part afterwards can be omitted, thus reducing the risk of leakage, but also saving considerable time, production space and energy.

Preferably the barrier strip is applied as a single continuous strip, as this saves time in production, and avoids leakage at the location where the inner barrier layer would otherwise be interrupted.

Preferably the barrier strip has a predefined width W, and is applied in such a way that the lateral overlapping distance measured at the equatorial of the mandrel is 10% - 90% of the width of the barrier strip, preferably 20%-80%, more preferably 30%-70%, even more preferably 40%-60%, even more preferably 45%-55%, most preferably about 50%. The inventor has found that the value of 50% is an optimal overlapping distance in terms of barrier effect versus the amount of strip-material required to achieve that effect. With equatorial is meant the ring-shaped outer boundary of the cross-section of the rotation symmetric three dimensional mandrel, perpendicular to its symmetry axis, at the mandrel's midpoint or point of greatest radius (as in the equator of the Earth).

Preferably the first end fitting is applied to the mandrel before winding the barrier strip, and the barrier strip is applied in such a way as to overlap the entire outer peripheral of the first end fitting, and the method further comprises a step of consolidating the second plastic material with the material of the first end fitting so as to form the hermetical connection.

In this way the first end fitting is mounted on the inside of gas and/or liquid tight layer, and is hermetically joined thereto by consolidation.

Alternatively the first end fitting is applied on top of the wound barrier strip but before the step of winding the fibrous material, and the method further comprises a step of consolidating the first plastic material with the material of the first end fitting so as to form the hermetical connection.

In this way the first end fitting is mounted partially between the fibrous layer and the gas and/or liquid tight layer, and is hermetically joined to the latter by consolidation.

Preferably the fibrous material is applied by filament winding of continuous fibers impregnated with the fourth plastic material. By winding continuous fibers, the obtained endless filament structure will allow the vessel to withstand higher hydrostatic pressures. In this way a leak-tight vessel can be produced able to withstand very high internal pressure, e.g. up to 100 bar or even 200 bar or more.

Preferably the method further comprises a step of consolidating the first and the fourth plastic material, so as to create a consolidated wall structure. By consolidating the plastic material of the gas and/or liquid tight layer to the plastic material of the fibrous wall, good fastening of the gas and/or liquid tight layer to the fibrous outer wall is obtained, which prevents it from coming loose e.g. in case of under-pressure or even vacuum inside the vessel.

Preferably the method further comprises a step of consolidating the fourth plastic material and the material of the first end fitting, so as to obtain a consolidated leak-tight vessel. By choosing compatible materials, e.g. all thermoplastic materials or e.g. all thermoset materials, preferably also for the first and second material, the gas and/or liquid tight layer and the first end fitting and the fibrous wall can all be consolidated together, resulting in a consolidated leak-tight vessel with excellent mechanical properties.

It is also an object of the present invention to provide such a leak tight vessel.

Preferably the varying outer diameter D has a maximum outer diameter Dmax, and the width W of the barrier strip is 4% - 20% of the maximum outer diameter, preferably 6% - 15%, more preferably 8% - 12%, most preferably about 10%. By choosing a strip with such a width a good compromise is reached between low production time and quality of the vessel. A wider strip would require less time to wind, but would require more strip-deformation resulting in an increased risk of air inclusion, resulting in a lower barrier effect, and an increased risk of leakage.

Various materials can be used for the first and second and inner layer of the barrier strip.

In one very interesting combination using only plastic materials the barrier strip is a multi-layer strip and the first resp. second plastic material is a first resp. second thermoplastic material with a first resp. second melting temperature, and the third material is a third thermoplastic material having a melting temperature higher than the first melting temperature and higher than the second melting temperature. A vessel having only thermoplastic materials has a higher impact resistance, and is better recyclable. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further elucidated in the appending figures and figure description explaining preferred embodiments of the invention. Note that the figures are not drawn to the scale. The figures are intended to describe the principles of the invention. Embodiments of the invention can use combinations of the different features and elements of different drawings.

Fig 1A shows a cylindrical mandrel being wound with a barrier strip, as known in the art. Fig 2A shows a removable mandrel with a rounded outer surface suitable for filament winding, as can be used for producing a leak-tight vessel according to the invention.

Fig 2B shows the mandrel of Fig 2A whereto a first and a second end fitting is applied.

Fig 2C shows a practical implementation of the removable mandrel shown in Fig 2B, whereby only one segment is shown for clarity. The elongated segments are held in position by pulling two spindle parts away from each other. A first and a second end fitting are applied to the mandrel in this figure.

Fig 2D shows the releasable connection of the segments of the mandrel of Fig 2C in more detail.

Fig 2E shows a detailed view of a dome shaped end fitting that can be used in combination with the mandrel of Fig 2A.

Fig 2F shows a detailed view of another dome shaped end fitting that can be used in combination with the mandrel of Fig 2A, this end fitting having a flange for connection to external tubing.

Fig 3A shows the mandrel of Fig 2A at an early stage of production of a leak-tight vessel according to the invention, during the winding of a barrier strip around the mandrel.

Fig 3B shows the structure of Fig 3A at a later stage of production, still during the winding of the barrier strip around the mandrel, (only the strip is shown, the mandrel itself is hidden)

Fig 3C shows in more detail two substantially parallel strip fragments of the barrier strip of Fig 3B.

Fig 3D shows in more detail two substantially parallel strip fragments inter-woven with a crossing strip fragment.

Fig 3E shows the structure of Fig 3B after the barrier strip is completely wound around the mandrel, (only the strip is shown, the mandrel itself is hidden)

Fig 3F shows the position of the center-lines of the strip fragments of Fig 3E.

Fig 3G shows a top view on the structure of Fig 3E. Fig 3H shows in more detail two substantially parallel strip fragments of the barrier strip of Fig 3G.

Fig 3I shows the position of the center-lines of the strip fragments of Fig 3G.

Fig 4A shows a first preferred embodiment of a leak-tight vessel according to the invention, comprising an end fitting partially located between the gas and/or liquid tight layer and the fibrous material layer.

Fig 4B shows a second preferred embodiment of a leak- tight vessel according to the invention, whereby the end fitting is located on the inside of both the gas and/or liquid tight layer and the fibrous material layer.

Fig 5A shows a cross section of an embodiment of a barrier strip that can be used for the production of a leak-tight vessel according to the invention. It has an inner layer located between a first layer and a second layer.

Fig 5B illustrates the permeability through the inner layer and the permeability over the lateral overlapping distance through the consolidated first and second layers of overlapping barrier strips.

Fig 6A shows a wall structure of a leak-tight vessel according to the present invention.

Fig 6B shows a detailed cross section of a part of the wall structure of Fig 6A.

Fig 6C shows in more detail an example of a stack-up of strip fragments forming the gas and/or liquid tight layer of Fig 6B, showing substantially parallel and crossing strip fragments.

Fig 6D shows essentially the same picture as Fig 6C, but rotated and an additional strip fragment is shown.

Fig 6E shows an alternative stack-up of strip fragments, with an indication of the shortest path an amount of gas or liquid can take for escaping from the leak-tight vessel through the gas and/or liquid tight layer.

Fig 7A shows another (spherical) mandrel being wound by a continuous strip for producing a leak-tight vessel according to the present invention, at an intermediate stage of the production thereof, during the winding of a barrier strip around the mandrel. Fig 7B shows the mandrel of Fig 7A at a later stage of production, still during the winding of the barrier strip around the mandrel.

Fig 7C shows in detail two substantially parallel strip fragments and a crossing strip fragment.

Fig 8A shows a first embodiment of an end fitting comprising a metal material partly surrounded by a plastic material.

Fig 8B shows a second embodiment of an end fitting comprising a metal material partly surrounded by a plastic material.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the invention. The drawings are intended to describe the principles of the invention. Embodiments of the invention can use combinations of the different features and elements with the same reference number of different drawings.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the invention can operate in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the invention described herein can operate in other orientations than described or illustrated herein. The term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting of only components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Various methods for producing leak-tight vessels are known in the art. In one of these methods continuous fibers impregnated with a thermoset resin are filament wound over a plastic inner bottle (also called "liner") that will remain in the leak-tight vessel after the production. Because during filament winding of continuous fibers a large pressure is exerted upon the object being wound, the plastic bottle needs to be sufficiently thick (e.g. >1 cm thick for a diameter of about 50 cm). At the same time, such a bottle also acts as the gas and/or liquid barrier for the leak-tight vessel, while the fibers wound around the bottle act as a protection layer. When producing pressure vessels, the bottle is usually made of a thermoplastic material, in order to avoid cracks due to the internal pressure. While such a bottle can provide a high barrier for the gas and/or liquid, it is heavy and expensive.

It is an object of the present invention to find a method for producing a leak-tight vessel 14 that can resist a pressure of more than 2 bar, and that has a similar barrier effect as the bottle, but without requiring the bottle (liner). After years of experimenting the inventor has found such a method. Without going into all the details already, such a leak-tight vessel 14 can be produced by making use of a removable mandrel 1 as shown in Figures 2A-2E, and by winding a barrier strip 60 of e.g. 800 μηη thick and having several layers (as shown in Fig 5A) in a particular way around the mandrel 1 (as shown e.g. in 3E), whereby strip fragments 61 of the barrier strip 60 are wound in an overlapping and crossing manner as shown in Fig 3B-3D. After consolidation of the overlapping strip fragments 61 , 62, 63 a gas and/or liquid tight layer 49 is formed, which will be located on the inside of the leak-tight vessel 14. Around this gas and/or liquid tight layer 49 a shell layer 12 comprising a fibrous material, preferably comprising continuous fibers impregnated with a fourth plastic material, is wound. Furthermore at least one end fitting 8 (e.g. as shown in Fig 2F or 2G) is applied to the mandrel 1 before or after winding the barrier strip 60, which end fitting 8 has an opening 74 for removing the parts of the mandrel 1 after disassembly thereof. The result of this method is shown in Figures 4A and 4B, showing two preferred embodiments of leak-tight vessels 14 according to the invention. Even though these leak-tight vessels 14 can have a very thin wall (typically less than 8 mm thick at their equatorial), if proper materials are chosen, they can resist pressure higher than 2 bar (e.g. 10 or 25 or 50 bar or even more) and have similar barrier characteristics (impermeability for the gas and/or liquid to be contained inside the leak-tight vessel) as a prior art vessel with a bottle (liner), or even more.

The method according to the invention will now be described in more detail.

Fig 2A shows a removable mandrel 1 as can be used in the method of the present invention. The mandrel comprises fourteen elongated segments 6 that are placed side by side to form a rounded outer surface. The mandrel 1 has a rotation symmetrical shape with a varying outer diameter D around a symmetry axis 10, and is suitable for filament winding. Because the mandrel can be disassembled and removed, the mandrel is allowed to have a varying diameter D, while still being able to separate the structure wound around the mandrel from the mandrel itself after the winding process. This provides for flexibility in the choice of shapes of the leak-tight vessels 14 to be produced, not just cylindrical, but e.g. also spherical or ellopsoidal, or other shapes.

Fig 2B shows the removable mandrel 1 of Fig 2A after a first and a second end fitting 8, 28 are applied to it. According to the invention, a barrier strip 60 can be wound around the mandrel 1 before applying such an end fitting 8 (as shown in Fig 2A) or after applying such an end fitting 8 (as shown in Fig 2B).

Fig 2C shows a practical implementation of such a removable mandrel 1 in detail. It comprises a plurality of elongated segments 6 held in position by pulling two spindle parts 42, 43 away from each other, whereby segment holders 7 are mounted to the spindle parts 42, 43 for engaging with opposite ends of the segments 6.

The mandrel 1 is shown together with a first and a second end fitting 8, 28, but as already mentioned before, the end fittings 8, 28 can also be placed on the mandrel 1 after the winding of the barrier strip 60.

Preferably the elongated segments 6 of the mandrel 1 are made of metal, preferably a lightweight metal such as aluminium or an aluminum alloy, as this is easier to manipulate during assembly and disassembly of the mandrel 1 , but other metals can also be used, such as e.g. steel or stainless steel.

In an embodiment the first end fitting 8 consists of a plastic material. Such an end fitting 8 might be well suited for producing a small size and lightweight leak-tight vessel 14 (e.g. 6, 8, 10 kg for a leak-tight vessel 14 with an inner volume of 100, 150, 300 litre respectively), to be subjected to moderate pressure (e.g. < 5 bar). In another embodiment the first end fitting 8 consists of metal, e.g. stainless steel. In another embodiment the first end fitting 8 comprises a metal material at least partly covered by a plastic material, e.g. a metal inner core completely or partly surrounded by the plastic material, whereby the metal serves primarily as a mechanical reinforcement to the end fitting 8. Such an end fitting is especially suited for producing leak tight vessels 14 that need to resist high pressure (e.g. > 50 bar), and/or have a relatively large diameter (e.g. Dmin > 80 cm), and/or need a strong connection with external pipes. In yet another embodiment the first end fitting 8 comprises a plastic material and reinforcing fibers, e.g. chopped glass fibers. Such a fiber reinforced first end fitting whereby the plastic material acts as matrix material is considerably stronger than a pure plastic end fitting, and is suited for a wide range of applications where a pure plastic end fitting is not strong enough but an end fitting comprising metal is not required.

In Fig 2C only one (out of fourteen) segments 6 and only two (out of eight) segment holders 7, four on each side, are shown for clarity reasons. The person skilled in the art can choose another number of segments 6 or segment holders 7 using the same principle.

The invention would also work with another kind of removable mandrel 1 , e.g. a non-reusable mandrel made of plaster, but the mandrel shown in Fig 2C is preferred, because it can be re-used, and is fast and easy to assemble and disassemble. Fig 2D gives an enlarged view on the releasable connection of the first spindle part 42, the segment holder 7 and the segment 6. As shown, the first spindle part 42 has a circumferential groove 44, and the segment holder 7 has a circular protrusion 46 that fits in the groove 44. The segment 6 preferably has a curved or bended edge 47 that engages in a groove 45 of the segment holder 7. Preferably the first and second spindle parts 42, 43 are hollow tubes, so that the segment holders 7 can be manually placed on or removed from the first spindle part 42 e.g. by inserting a hand in the tube. After all segments 6 and segment holders 7 are placed on the first and second spindle parts 42, 43, the first and second end fittings 8, 28 each having an opening 74 (see Fig 2F), can then be shifted over the first resp. second spindle part 42, 43. The pulling of the first and second spindle parts 42, 43 in opposite directions can be implemented e.g. on the filament winding machine (not shown).

Disassembly of the mandrel after a leak-tight vessel 14 (not shown) is produced can be done as follows: pushing the spindle parts 42, 43 slightly inside the vessel 14, removing the segment holders 7 from the spindle parts 42, 43 (e.g. by inserting a hand inside the hollow spindle part), extracting the spindle parts 42, 43 out of the vessel 14, removing the segment holders 7 and the segments 6 out of the vessel 14 through the opening 74, while leaving the end fittings 8, 28 inside the vessel 14.

Fig 2E shows an embodiment of the first end fitting 8 or second end fitting 28 that can be used in conjunction with the mandrel of Fig 2A. The first and second end fittings 8, 28 can have the same size and geometry or a different size and geometry. Preferably the end fittings 8, 28 are applied before the filament winding step of the fibrous material 12. When mounted to the mandrel 1 before winding the fibrous material, at least one of the end fittings 8, 28 needs to have an opening 74 large enough to allow passage of the elements of the mandrel 1 , e.g. in case of the mandrel shown in Fig 2C : the segments 6, the segment holders 7, the first spindle part 41 and the second spindle part 43.

Fig 2F shows another embodiment of an end fitting 8, 28 having a flange 83 with holes 19 for connection to the outside world, e.g. to connect external piping (not shown). The exact shape of the first end fitting 8 can however be further modified by the person skilled in the art. It can for example have a flange with provisions for O-rings, or a hole with internal screw thread, or a V-clamp, or other fastening means.

Fig 3A shows the mandrel 1 of Fig 2A at an early stage of production of a leak-tight vessel 14 according to the invention, during the winding of a barrier strip 60 around the mandrel 1. This mandrel has a monotonically decreasing diameter D, ranging from Dmax at its equatorial 72 down to Dmin at its opposite ends. This is not absolutely required however for filament winding, although it is recommended for pressure vessels to avoid pressure concentrations. Preferably the barrier strip 60 is applied a single continuous strip, but in order to describe the barrier effect, the barrier strip 60 can be seen as composed of strip fragments, an arbitrary one being indicated by reference 61 .

Fig 3B shows the mandrel of Fig 3A at a later stage of production of a leak-tight vessel 14, but still during the step of winding the barrier strip 60 around the mandrel 1. (only the barrier strip 60 is shown, the mandrel itself is hidden) This figure shows a screenshot taken of the barrier strip 60 being wound around the mandrel at a selected moment for better illustrating the overlapping and crossing of strip fragments 61. When comparing Fig 3B with Fig 3A it can be seen that the strip fragment 61 shown in Fig 3A has a parallel overlapping strip fragment 62 in Fig 3B. It can also be seen however, that meanwhile multiple crossing strip fragments 63 have been wound between strip fragments 61 and 62, which is called inter-weaving.

Fig 3C shows in more detail the two substantially parallel strip fragments 61 , 62 of Fig 3B. The figure also shows the width W of the barrier strip 60, the predefined minimum overlapping distance 66 of the two strip fragments 61 , 62, the center-lines 69 of the strip fragments, and the distance 67 between the center-lines 69. When the distance between the center-lines 67 approaches zero, the lateral overlapping distance 66 approaches the complete width W of the barrier strip 60.

Fig 3D shows in more detail two substantially parallel strip fragments 61 , 62 inter-woven with a crossing strip fragment 63. The crossing strip fragments 63 help to bend the strip edges of the strip fragments underneath towards the rounded outer surface of the mandrel 1 . Fig 3E shows the structure of Fig 3B after the barrier strip 60 is completely wound around the mandrel 1 . (again only the barrier strip 60 is shown, the mandrel 1 itself is hidden). Note that the barrier strip 60 is wound around the mandrel while leaving an opening 4. According to the invention this opening 4 is chosen large enough to enable removal of the (parts of the) mandrel 1 after disassembly. When using the mandrel of Fig 2C, this means the segments 6 and the segment holders 7, and the first and second spindle parts 42, 43. As can be seen from Fig 3A the opening 4 can e.g. be a circle with a diameter Dmin.

Fig 3F shows the position of the center-lines 69 of the strip fragments 61 of the barrier strip 60 of Fig 3E. This figure illustrates that (for this shape of the mandrel) the lateral overlapping distance 66 is smallest at the equator 72, chosen to be approximately 50% of the strip width W in this case, where the distance between the center lines 69 is largest. And the overlapping distance 66 is largest (close to W) near the opening 4, where the distance 67 between the center lines 69 is smallest (close to zero).

Fig 3G shows a top view on the structure of Fig 3E, and Fig 3H shows in more detail two substantially parallel strip fragments 61 , 62 of the barrier strip of Fig 3G. As can be seen from this figure, the lateral overlapping distance 66 of substantially parallel strip fragments 61 , 62 close to the opening 4 is higher than the lateral overlapping distance 66 of substantially parallel strip segments near the equator 72.

This is also clearly visible in Fig 3I showing that the distance between the center-lines 69 of the strip fragments is very close to zero near the opening 4, meaning that the overlapping distance 66 is very close to W, as explained before.

The figures 2A-3I have shown the winding of the barrier strip 60. In a next step of the method according to the invention, a shell layer 12 is formed by filament winding a fibrous material over the wound strip layer (formed by the strip fragments), whereby the first opening 4 is left open for removal of the mandrel 1 . The area covered by the fibrous material can be larger or smaller than the area covered by the barrier strip 60, but preferably is the same. During the winding of the fibrous material pressure is exerted upon the wound strip layer in order to press all strip fragments 61 , 62, 63 to the mandrel 1 and to each other, so that contacting layers 51 , 53 of overlapping strip fragments 61 , 62, 63 can be consolidated together (at a later stage). The method further comprises a step of consolidating the first resp. second plastic material of strip fragments 61 with the second resp. first plastic material of overlapping strip fragments 62, 63 thereby forming a gas and/or liquid tight layer 49 comprising a strip of the third material, the gas and/or liquid tight layer 49 having said predetermined permeability. After consolidation of the materials the mandrel 1 is disassembled and removed through the opening 4. The result is a leak-tight vessel 14 according to the invention, as shown in Figure 4A or Figure 4B.

Fig 4A shows a first preferred embodiment of a leak-tight vessel 14 according to the invention, comprising a first end fitting 8 located between the gas and/or liquid tight layer 49 and the fibrous material layer 12. Preferably in this case the material of first and second end fittings 8, 28 are consolidated with the fourth plastic material and with the first plastic material of the barrier strip 60, so that the gas and/or liquid tight layer 49 and the first end fitting 8 and the fibrous material 12 are interconnected to each other.

To increase the impermeability (barrier effect) through the material of the first end fitting 8, several techniques are possible: such as e.g. using a first end fitting 8 made of a metal material, or using an end fitting 8 comprising a metal inner core as shown in Fig 8A, or using a first end fitting 8 made of any material having a sufficient thickness, or using a first end fitting 8 made of a plastic material coated with an aluminum layer, or any other way known by the person skilled in the art.

Fig 4B shows a second preferred embodiment of a leak- tight vessel 14 according to the invention, whereby the first end fitting 8 is located on the inside of the gas and/or liquid tight layer 49. In this case the gas and/or liquid tight layer 49 forms a first shell layer around the inner volume 73, and another shell layer comprising fibrous material 12 is wrapped around the gas and/or liquid tight layer 49, and is preferably consolidated thereto. In a preferred embodiment the outer shell layer 12 consists of longitudinal fibers (e.g. glass fibers) surrounded by a fourth thermoplastic material (e.g. polypropylene).

Fig 5A shows an example of a barrier strip 60 that can be used in the method of the present invention. The vertical dimensions of this figure are largely exaggerated with respect to the horizontal dimensions. It shows a three- layer barrier-strip 60 having a first layer 51 made of a heat-sealable thermoplastic material (such as e.g. polypropylene), an inner layer 52 made of a high barrier material (such as e.g. aluminum), and a second layer 53 also made of polypropylene. The first and second layer can e.g. each be 100 μηη thick, while the inner layer can e.g. be 40 μηη thick (75), thus the total thickness T of the strip would be 240 μηη in this example, but other materials and other dimensions can also be used. The strip can e.g. have a width W of 5 cm, but another width W can also be used, e.g. 2 cm, or 3 cm, or 4 cm; or 6 cm, or 8 cm or 10 cm, or 12 cm or 14 cm or 16 cm or 18 cm or 20 cm, or even higher. It should be noted that the invention would also work if the material of the inner layer 52 would not extend over the complete width W of the strip 60, provided the overlapping distance 66 is measured as the overlap of the inner layers 52 of the substantially parallel strip fragments. Preferably the materials of the first and second outer layer 51 , 53 of the barrier strip 60 are the same, but this is not absolutely required, as long as they are compatible materials that can be consolidated (e.g. heat sealed or cured).

Fig 5B illustrates the barrier effect of the gas and/or liquid tight layer 49, by considering two substantially parallel overlapping strip fragments. This figure illustrates the permeability through the inner layer 52 and the permeability across the lateral overlapping distance 66 through the consolidated layer 81 after consolidation of the first and second layers 51 , 53 of the overlapping strip fragments. According to the invention, the materials and the dimensions of the barrier strip 60 are chosen such that the amount of gas and/or liquid penetrating through the inner layer 52 in the Z-direction as indicated by arrow 70, combined with the amount of gas and/or liquid penetrating through the consolidated layer 81 as indicated by arrow 71 is less than a predetermined permeability, which predetermined permeability depends on the application. When a material such as aluminum is chosen for the inner layer 52, the permeability indicated by arrow 70 through the inner layer 52 is negligible (e.g. < 5%) as compared to the permeability in the transversal direction, indicated by arrow 71 , thus the permeability is practically only determined by the penetration through the consolidated first and second layer 81 of the barrier strip over the overlapping distance 66. Note that the same barrier effect would be obtained by a solid bottle (liner) having the same material as the consolidated first and/or second layer and a thickness equal to the overlapping distance 66. Even though only two overlapping strips are shown, the same principle applies for the entire gas and/or liquid tight layer 49, as will be described next.

Fig 6A shows a transversal cross section of the leak-tight vessel of Fig 4A.

When zooming into Fig 6A, Fig 6B shows a detailed cross section of the wall structure of Fig 6A. It comprising a fibrous material 12 obtained by filament winding, preferably comprising longitudinal fibers such as e.g. glass fibers on the outside of the leak-tight vessel 14, and a gas and/or liquid tight layer 49 on the inside of the vessel 14.

Fig 6C shows an enlarged view of a section of the gas and/or liquid tight layer 49 shown in Fig 6B, as obtained by winding a barrier strip

60 around the mandrel 1 according to the method of the present invention. The figure shows a snapshot of some inter-woven substantially parallel and crossing strip fragments 61 , 62, 63. The regular stack-up of strip fragments shown is only an example illustrating the overlapping and inter-weaving effect that can occur by the winding of the barrier strip 60. In practice however, the stack-up of strip fragments can be more complicated, but the principle remains the same.

Fig 6D shows almost the same picture as Fig 6C, but rotated and an additional strip fragment 62c is shown to illustrate that strip fragment

61 has two overlapping strip fragments 62a and 62c, one on each side. Assuming an overlap of 50%, the total barrier provided by this inter-woven structure is twice the barrier through the consolidated layer 81 over the lateral overlapping distance 66 shown in Fig 5B, once in each direction, thus over a total distance of W.

Fig 6E shows an alternative arrangement of strip fragments, with an indication of the shortest path an amount of gas or liquid 68 can follow for escaping from the leak-tight vessel 14 through the gas and/or liquid tight layer 49, assuming that the permeability through the inner layer 52 of the barrier strip fragments is negligible as compared to the permeability through the first and second layers 51 , 53, as in the example above. An amount of gas and/or liquid 68 present at the left edge of strip fragment 61 (as shown) would penetrate through the consolidated layer of the strip fragments 61 and 62b as indicated by the arrow 71 a, not being able to pass in an upwards direction through the inner layer 52b of the strip fragment 62b. When reaching the right edge of strip fragment 62b it can enter the consolidated layer of strip fragment 63a and 63b, not being able to pass through the inner layer of strip fragment 63b. Assuming a strip width W of 4 cm and an overlapping distance of 2 cm (50%), the barrier effect of this structure is about the same as would be provided by a solid bottle ("liner") of 4 cm thickness! However this effect is only obtained if the first and second layers 51 , 53 of the strip fragments (see Fig 5B) are consolidated to each other, in such a way as to exclude any air bubbles. The inventor has observed that this is reached by exerting an increased pressure upon the barrier strip 60 during the step of filament winding the fibrous material 12 thereto. It should be noted that in this figure schematically two separate sets of strip fragments are shown: a lower set indicated by references 61 and 62, and a higher set indicated by references 63. In reality however the upper set of strip fragments 63 is pressed tightly to the lower set of strip fragments 61 , 62, and the second layers 53 of the strip fragments 63 of the upper set are consolidated with contacting first layers 51 of the strip fragments 61 , 62 of the lower set.

Fig 7A shows another (spherical) rounded outer surface area of a mandrel 1 suitable for the method for producing a leak-tight vessel 14 according to the invention. The figure shows again an intermediate stage of the production of a leak-tight vessel, during the winding of a barrier strip 60 around the mandrel 1 . This figure was obtained by choosing the minimal lateral overlapping distance 66 to be 50% the width W of the barrier strip 60. As can be seen, the actual overlapping distance 66 is smallest at the equator 72 where the variable diameter of the mandrel is Dmax, and is largest near the opening 4 where the variable diameter of the mandrel is Dmin.

Fig 7B shows the structure of Fig 7A at a later stage of production, still during the winding of the barrier strip 60 around the mandrel 1. When comparing Fig 7B with Fig 3E, the stack-up of the overlapping strip fragments is quite different, but the obtained barrier effect is quite the same, assuming the same barrier strip 60 is used, as well as the same minimum overlapping distance 66. Fig 7C shows in detail two substantially parallel strip fragments 61 , 62 and a crossing strip fragment 63 for the location indicated by the dashed circle on Fig 7B. Fig 7C resembles the stack-up shown in Fig 6E, while the winding of Fig 3E resembles the stack-up shown in Fig 6D, but as explained above, they both have a similar barrier effect.

Figures 8A and 8B show a first end fitting 8 having a metal inner core partly surrounded by the third plastic material 88. As shown in Fig 8A, the metal core can e.g. have a plurality of blind holes 89 with internal screw thread wherein the third plastic material is applied so that there is a good mechanical connection of the third plastic material and the metal core, together forming the first end fitting 8. These holes 89 can be applied on the convex and/or on the concave side of the metal core, or on both sides. Instead of blind holes, also grooves or other mechanical provisions can be used for the same purpose. In Fig 8B the metal inner core has a bowl shape comprising through holes 90 so that the plastic material 88 on the convex side is connected to the plastic material on the concave side of the metal inner core. In another embodiment (not shown), the metal inner core is completely surrounded by the third plastic material. An advantage of an end fitting 8 comprising metal is that it is easy to provide through mounting holes 19 (as shown in Fig 2F) or holes 19, 89 with internal screw threat, which can be used for the connection of the plastic, but also for the connection of external pipes (not shown) during actual use of the leak-tight vessel 14.

Preferably the strip is a flat strip.

Preferably the inner layer 52 comprises a third material of a predefined thickness 75 such that a permeability 70 through the inner layer 52 is lower than a lateral permeability 71 through the consolidated first and second outer layers 51 , 53 across the lateral overlapping distance 66, but this is not absolutely required. What is important is not the permeability of the individual layers of the barrier strip 60, but the permeability of the gas and/or liquid tight layer 49 as a whole.

Preferably the barrier strip 60 is applied in the form of a single continuous strip, so that winding thereof can be achieved in a fast and easy way, with minimal human interference, e.g. on a standard filament winding machine traditionally used for filament winding of continuous fibers. Note that even when the surface is overwrapped multiple times, the strip can still be continuous.

Preferably the barrier strip 60 has a predefined width W, and the barrier strip 60 is applied in such a way that the lateral overlapping distance 66 measured at the equatorial 72 of the mandrel 1 is 10% - 90% of the width W of the barrier strip 60, preferably 20%-80%, more preferably 30%-70%, even more preferably 40%-60%, even more preferably 45%-55%, most preferably about 50%. The inventor has found that for a strip of a given width W, the value of 50% overlap is geometrically the optimum value in terms of barrier achieved versus the amount of strip material used (read: cost), but the value of 50% overlap is not absolutely required for the invention. For example, for storage of cold water an overlap lower than 50% can be used. In fact, to achieve a particular impermeability (or barrier effect) for the leak-tight vessel 14, the person skilled in the art can e.g. make a trade-off between the following parameters: 1 ) the width W of the strip (the broader, the higher the impermeability or barrier effect), 2) the amount of overlapping distance 66 (the more overlap, the higher the impermeability), 3) the number of times the vessel is completely covered, 4) the permeability of the first, second and third material of the barrier strip 60, 5) the dimensions of the first, second and inner layer of the barrier strip 60.

Preferably the fibrous material comprises continuous fibers impregnated with the fourth thermoplastic material. By winding continuous fibers, the obtained endless filament structure will allow the leak-tight vessel 14 to withstand higher hydrostatic pressures. In this way a leak-tight vessel 14 can be produced able to withstand very high pressure e.g. up to 100 bar or even 200 bar or even more.

The material of the continuous fibers is not essential for the invention. They can e.g. be selected from the group of fibers consisting of: glass fibers, carbon fibers, metal fibers, mineral fibers, wool, cotton, flax, polyester, polypropylene, polyethylene, polyamide, basalt, Kevlar®, aramide or a mix of two or more of these fibers, but the invention is not limited thereto, and other fibers can also be used. When using particularly strong fibers such as carbon fibers, a leak- tight vessel 14 can be provided that can possibly withstand a pressure of up to 500 bar. Preferably the method according to the present invention further comprises a step of consolidating the first plastic material, the second plastic material, the fourth plastic material and the material of the first end fitting 8, so as to obtain a unified leak-tight vessel 14. This would result in a leak-tight vessel with excellent mechanical properties. A unified wall structure has better mechanical strength and is less susceptible to damage, impact or wear. Such a vessel can also better resist external forces exerted upon the first end fitting 8 for connecting external tubing (not shown).

Preferably the barrier strip 60 has a thickness T in the range of 25 μηη - 2000 μηη, preferably in the range of 50 μηη - 500 μηη, more preferably in the range of 100 μπ 500 μηη.

The inventor has found that a multi-layer barrier strip 60 consisting of three layers: polypropylene (100 μηη) - aluminum (40 μηη) - polypropylene (100 μηη) can be wound without problems, however strips with other dimensions can also be used. For an equal amount of iterations of completely covering the outer surface as described above, a larger strip thickness T provides more strength to the gas and/or liquid tight layer 49, but is more expensive.

Preferably the variable outer diameter D has a maximum outer diameter Dmax, and the width W of the barrier strip is 4% - 20% of the maximum outer diameter Dmax, preferably 6% - 15%, more preferably 8% - 12%, most preferably about 10%.

The optimal value for the width W of the strip depends not only on the desired barrier effect, as described above, but also on the shape and size of the mandrel 1 , in order to get a gas and/or liquid tight layer 49. The optimal width can be determined by experiments, but for a mandrel 1 with a slowly changing diameter, the 10%-rule is a good rule-of-thumb. In a real-life example a barrier strip 60 was used having a width W of 50 mm, to wind a vessel with a shape as shown in Fig 4A, having a maximum diameter of 450 mm (and a minimum diameter of 220 mm), which is 9% of 450 mm.

In an embodiment the filament winding of the fibrous material is applied in such a way, and the materials of the barrier strip 60 and of the first end fitting 8 and of the fibrous material are selected so as to obtain a pressure vessel 14 able to withstand internal pressure up to 10 bar, preferably up to 25 bar, more preferably up to 50 bar, even more preferably up to 100 bar, or even 200 bar. Although the method according to the invention is ideally suited for making leak- tight pressure vessels 14, the invention is not limited thereto. In fact, the method disclosed is also very well suited for making leak-tight vessels 14 for low pressure applications (e.g. < 5 bar), such as water tanks or fuel tanks. The main advantages of the leak-tight vessel according to the present invention are: its high strength, low weight, and good or excellent barrier.

Preferably the leak-tight vessel 14 has an internal volume in the range of 5 - 1000 litre, preferably in the range of 10 - 500 litre, more preferably in the range of 20 - 250 litre, but the invention is not limited thereto. The invention is also very well suited for producing leak-tight vessels with an internal volume smaller than 5 litre, or larger than 1000 litre.

Several materials can be chosen for the barrier strip 60. It is important that the material of the first and second layers 51 , 53 show good cohesion with the inner layer 52, and that contacting first and second layers 51 , 53 of overlapping strips 61 , 62, 63 can be consolidated to each other, but this still leaves many options for the choice of the materials, as shown in table 1 , listing some examples. The invention is however not limited hereto, but only by the claims.

Table 1 . In one embodiment the first and second outer layers 51 , 53 comprise a heat-sealable material, in which case the consolidation is done by heat- sealing at a predefined temperature, depending on the chosen materials.

In an embodiment the heat-sealable material is a thermoplastic materials selected from the group consisting of : polypropylene (PP) and Polybutene-1 (PB-1 - and polyethylene (PE). Polypropylene can e.g. be used for low temperature applications up to about 55°C. Polybutene-1 is more expensive, but can be used in applications up to about 90°C. Other heat-sealable thermoplastic materials are however also possible.

In an embodiment the first and second outer layers 51 , 53 comprise a thermoset resin which is applied to the inner layer 52 of the barrier strip 60 during the step of winding the barrier strip 60 around the mandrel 1. The consolidation in this case is done by polymerisation of the resin at a predefined temperature and during a predefined time period, depending on the materials used.

In an embodiment the inner layer 52 of the barrier strip 60 comprises a metal. Some metal materials have excellent barrier properties for certain gasses or liquids.

In a preferred embodiment the inner layer 52 of the barrier strip 60 comprises aluminum. Aluminum is very well suited as a barrier against cold water, hot water or gasses such as oxygen or air. When using aluminum, the permeability of the inner layer 52 is negligibly small as compared to the permeability of the first and second layers 51 , 53, meaning that the leakage through the gas and/or liquid tight layer 49 is practically fully determined by the material and dimensions of the first and second outer layers 51 , 53 of the barrier strip 60, and by the minimum overlapping distance 66, typically encountered near the equatorial 72 of the vessel.

In another embodiment the inner layer 52 of the barrier strip 60 comprises a third material selected from the group consisting of : polyurethane (PUR), acrylonitrile (AN), polyacrylonitrile (PAN), polyamide (PA), polytheentereftalate (PET). These materials are all high barrier materials for specific gasses or liquids or vapours. Depending on the substance to be stored in the vessel, and the physical conditions of the storage (temperature, pressure) one of these materials can be used. For example, Polyurethane is very well suited for hot water applications. But other high barrier materials known to the person skilled in the art can also be used as the inner layer 52 of the barrier strip 60.

In another embodiment the first resp. second plastic material is a first resp. second thermoplastic material with a first resp. second melting temperature, and the third material is a third thermoplastic material having a melting temperature higher than the first melting temperature and higher than the second melting temperature. Preferably the third thermoplastic material of the inner layer 52 of the barrier strip 60, comprises a third material selected from the group consisting of High-Temperature-Polypropylene, Polyethylene (PE), Ethylene Vinyl Alcohol (EVOH). When such a barrier strip 60 is used, the consolidation is done at a temperature at which the first and second layers 51 , 53 weaken or melt, while the inner layer 52 does not and remains intact. High-Temperature polypropylene is very well suited for cold water applications, and is relatively cheap. EVOH provides an excellent barrier to gasses such as oxygen or air, but is relatively expensive. Thermoplastic barrier materials are generally cheaper than aluminum and easier to recycle.

EXAMPLES

As a first example of a method for producing a leak-tight vessel 14 according to the invention, a mandrel as shown in 2A is assembled, and two end fittings 8, 28 are placed on the spindle parts 42, 43, whereby the first end fitting 8 comprises polypropylene (= thermoplastic) reinforced with 40 weight % glass fibers, then optionally a mould release is applied to the segments 6 of mandrel 1 , then a three-layer barrier strip 60 having a first and a second layer 51 , 53 consisting of polypropylene and an inner layer 52 consisting of aluminum is wound around the mandrel 1 as explained above. Such a strip is e.g. available from the company Amcor Flexibles ®. Then the mandrel 1 is filament wound using continuous glass fibers pre-impregnated with polypropylene as the fourth plastic material (e.g. 60 weight % glass fibers, 40 weight % polypropylene, available as Twintex® from the company Vetrotex®), then the matrix material of the first end fitting (polypropylene) and the plastic material (polypropylene) of the outer layers 51 , 53 of the barrier strip 60 and the fourth plastic material (polypropylene) of the fiber impregnation are consolidated at a temperature of approximately 160°C for approximately 30 minutes, then after cooling down to room temperature, the mandrel 1 is disassembled by removing the elongated segments 6, the segment holders 7, and the first and second spindle parts 42, 43, while leaving the first and second end fittings 8, 28 behind in the vessel 14, and the leak-tight vessel 14 is ready for use, and the mandrel is ready for reuse. In this case a leak-tight vessel as shown in Fig 4A is obtained.

A second example is very similar to the first example, except that the first end fitting 8 comprises an aluminum core coated with polypropylene (thermoplastic), which polypropylene will be consolidated in further steps with the fourth thermoplastic material (polypropylene) surrounding the continuous fibers. In this example the end fittings 8, 28 are applied after winding the barrier strip 60 to the mandrel 1 , and before winding the continuous fibers, so as to obtain a leak-tight vessel as shown in Fig 4B.

In a third example of a method for producing a leak-tight vessel 14 according to the invention, a mandrel 1 is assembled and two end fittings 8, 28 are placed on the spindle parts 42, 43, but not yet shifted against the mandrel. Next a strip of aluminum with a thickness of e.g. 40 μηη is impregnated with a thermoset resin, e.g. Polysulfone (PSU) and wound around the mandrel 1 . Then the two end fittings 8, 28 are shifted over the spindle parts 42, 43 and pushed against the wound strip layer. Then the mandrel 1 is filament wound using continuous glass fibers pre-impregnated with Polysulfone (PSU). Next the first, second and fourth plastics materials are consolidated at for example 80°C temperature for approximately 2 hours, but the temperatures and duration can vary depending on the specific resin being used. After disassembly and removal of the mandrel, the leak-tight vessel 14 is ready for use.

It is clear to the person skilled in the art that many more combinations and alterations are possible, and that the materials and process can be optimized for specific applications.

SUMMARY

By the above description and figures it can be understood that a leak-tight vessel 14 with a fibrous wall 12 can be produced by winding a barrier strip 60 around a mandrel 1 , thereby avoiding the need for a heavy and expensive inner bottle ("liner"). By using compatible thermoplastic or thermoset materials as described above, a leak-tight vessel 14 with a very thin (e.g. < 1 cm) yet very strong structure (e.g. up to 25 bar) can be obtained, thereby saving material, cost and weight. By choosing proper materials for the barrier strip 60, the effective barrier of the gas and/or liquid tight layer 49 caused by winding the barrier strip 60 can be as high or even higher than the barrier of the traditional plastic bottle (or "liner").

The invention can be used to produce a wide variety of vessels for different applications, such as e.g. containers for storing potable water, milk, soft drinks, beer, wine, or other liquids, hot water boilers, fuel tanks, gas tanks, hydrogen tanks, oxygen tanks, chemical tanks, etc. Dimensions can range from about 20 cm in height H and/or diameter Dmax for portable containers such as e.g. oxygen bottles, up to several meters, e.g. 2 m in height and/or diameter for large leak-tight vessels such as e.g. storage tanks, and all sizes in between. The height can e.g. be 20 cm, 35 cm, 50 cm, 75 cm, 1 m, 1.25 m, 1 .50 m, 1.75 m, 2.0 m or higher. The maximum diameter Dmax can e.g. be 20 cm, 35 cm, 50 cm, 75 cm, 1 m, 1 .25 m, 1 .50 m, 1 .75 m, 2.0 m or higher. The height H can be the same as the diameter Dmax, or the height H can be larger than the diameter, or vice versa.

The described method for producing a leak-tight vessel 14 basically only requires a filament winding machine. A lot of factory space can be saved with respect to traditional approaches where additional processing steps and machinery are required. This is advantageous for the price of the leak-tight vessel 14 and for the environment. Another advantage of this method is that it causes essentially no material waste during the production. An additional advantage when using only thermoplastic materials is that a 100% recyclable leak-tight vessel can be produced. When carbon fibers are used, leak-tight vessels 14 for extremely high pressure (e.g. >200 bar) can be produced. The leak-tight vessel 14 can be produced in a fast and easy and highly economical way that can be highly automated.

Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader scope of the invention as set forth in the claims. Accordingly, the description and drawings are to be regarded in an illustrative sense rather than a restrictive sense.

Claims

1 . Method for producing a leak-tight vessel (14) having a predetermined permeability for holding a gas and/or liquid, comprising the steps of:

- assembling a removable mandrel (1 ) having a rounded outer surface suitable for filament winding, the mandrel (1 ) having a rotation symmetrical shape with a varying outer diameter (D) around a symmetry-axis (10);

- winding a barrier strip (60) around the mandrel (1 ) so as to form a wound strip layer, thereby completely covering a predefined area of the rounded outer surface while leaving a first opening (4) large enough for removing the mandrel (1 ) after being disassembled, whereby the winding of the barrier strip (60) is applied in such a way that the predefined area is completely covered with strip fragments (61 ) of the barrier strip (60) and that each strip fragment (61 ) shows a first local overlap over at least a lateral overlapping distance (66) with a first substantially parallel strip fragment (62) and shows a second local overlap with a second crossing strip fragment (63), the barrier strip (60) comprising a first layer (51 ) and a second layer (53) located at opposite sides of the barrier strip (60) and an inner layer (52) located between the first and the second layer (51 , 53), the first resp. second layer (51 , 53) comprising a first resp. second plastic material, the inner layer (52) comprising a third material, whereby the first resp. second plastic material of strip fragments (61 ) can be consolidated with the second resp. first plastic material of overlapping strip fragments (62, 63), and the first and second plastic material show a leak-tight cohesion with the third material;

- forming a shell layer (41 ) by filament winding a fibrous material (12) over the wound strip layer, thereby leaving the first opening (4) for removing the mandrel (1 ), thereby exerting pressure upon the wound strip layer so that the strip fragments (61 ) of the barrier strip (60) are pressed tightly against the mandrel (1 ) and against each other so that the materials of the overlapping strip fragments (61 , 62, 63) can be consolidated at their contacting surfaces; - consolidating the first resp. second plastic material of strip fragments (61 ) with the second resp. first plastic material of overlapping strip fragments (62, 63) thereby forming a gas and/or liquid tight layer (49) comprising a strip of the third material, the gas and/or liquid tight layer having said predetermined permeability;

- disassembling and removing the mandrel (1 ) through the first opening (4);

- applying a first end fitting (8) and hermetically connecting it with the gas and/or liquid tight layer (49).

2. Method according to claim 1 , wherein the first end fitting (8) is applied in the form of a dome shaped end fitting having an outer peripheral (82) larger than the first opening (4) and having a second opening (74) large enough for removing the mandrel (1 ) therethrough after being disassembled, and positioning the second opening (74) in alignment with the first opening (4), and whereby the fibrous material is applied in such as way as to overlap at least the outer peripheral (82) of the first end fitting (8).

3. Method according to claim 1 or 2, wherein the barrier strip (60) is applied in the form of a single continuous strip.

4. Method according to any one of the previous claims, wherein the barrier strip (60) has a predefined width (W), and wherein the barrier strip (60) is applied in such a way that the lateral overlapping distance (66) measured at the equatorial (72) of the mandrel (1 ) is 10% - 90% of the width (W) of the barrier strip (60), preferably 20%-80%, more preferably 30%-70%, even more preferably 40%-60%, even more preferably 45%-55%, most preferably about 50%.

5. Method according to any one of the previous claims, wherein the first end fitting (8) is applied to the mandrel (1 ) before winding the barrier strip (60) and the barrier strip (60) is applied in such a way as to overlap the entire outer peripheral (82) of the first end fitting (8), and the method further comprises a step of consolidating the second plastic material with the material of the first end fitting (8) so as to form the hermetical connection.

6. Method according to any one of the previous claims, wherein the first end fitting (8) is applied on top of the wound barrier strip (60) but before the step of winding the fibrous material (12), and the method further comprises a step of consolidating the first plastic material with the material of the first end fitting (8) so as to form the hermetical connection.

7. Method according to any one of the previous claims, wherein the fibrous material (12) is applied by filament winding of continuous fibers impregnated with a fourth plastic material.

8. Method according to claim 7, whereby the method further comprises a step of consolidating the first and the fourth plastic material, so as to create a consolidated wall structure.

9. Method according to claim 7 or 8, wherein the method further comprises a step of consolidating the fourth plastic material with the material of the first end fitting (8), so as to obtain a consolidated leak- tight vessel (14).

10. Method according to any one of the previous claims, wherein the filament winding of the fibrous material is applied in such a way that, and wherein the materials of the barrier strip (60) and the material of the first end fitting (8) and the fibrous material are selected so as to obtain a pressure vessel (14) able to resist an internal pressure up to 10 bar, preferably up to 25 bar, more preferably up to 50 bar, even more preferably up to 100 bar, or even 200 bar.

1 1. Method according to any one of the previous claims, wherein the first and second layer (51 , 53) comprise a thermoset resin which is applied to the inner layer (52) of the barrier strip (60) during the step of winding the barrier strip (60) around the mandrel (1 ).

12. A leak-tight vessel (14) having a predetermined permeability for holding a gas and/or liquid, produced in a way according to any one of claims 1 -1 1 .

13. The leak-tight vessel (14) according to claim

12, wherein the barrier strip (60) has a thickness (T) in the range of 25 μηη - 2000 μηι, preferably 50 μηη - 1000 μηι, more preferably in the range of 100 μηη - 500 μπι.

14. The leak-tight vessel (14) according to claim 12 or 13, wherein the varying outer diameter (D) has a maximum outer diameter (Dmax), and the width (W) of the barrier strip is 4% - 20% of the maximum outer diameter, preferably 6% - 15%, more preferably 8% - 12%, most preferably about 10%.

15. The leak-tight vessel (14) according to any one of the claims 12-14, wherein the leak-tight vessel (14) has an inner volume (73) in the range of 5 - 1000 litre, preferably in the range of 10 - 500 litre, more preferably in the range of 20 - 250 litre.

16. The leak-tight vessel (14) according to any one of claims 12-15, wherein each of the first and second layers (51 , 53) comprises a heat-sealable material.

17. The leak-tight vessel (14) according to claim 16, wherein the heat-sealable material is a thermoplastic material selected from the group consisting of : polypropylene and Polybutene-1 and polyethylene.

18. The leak-tight vessel (14) according to any one of the claims 12-17, wherein the inner layer (52) of the barrier strip (60) comprises a metal.

19. The leak-tight vessel (14) according to claim 18, wherein the metal is aluminum.

20. The leak-tight vessel (14) according to any one of the claims 12-17, wherein the third material is selected from the group consisting of : polyurethane, acrylonitrile (AN), polyacrylonitrile (PAN), polyamide (PA), polytheentereftalate (PET).

21 . The leak-tight vessel (14) according to any one of claims 12-17, wherein the first resp. second plastic material is a first resp. second thermoplastic material with a first resp. second melting temperature, and the third material is a third thermoplastic material having a melting temperature higher than the first melting temperature and higher than the second melting temperature.

22. The leak-tight vessel (14) according to claim 21 , wherein the third thermoplastic material is selected from the group consisting of High-Temperature-Polypropylene, HD-Polyethylene, Ethylene Vinyl Alcohol (EVOH).