METHOD FOR PRODUCING A PRESSURE VESSEL AND PRESSURE VESSEL

Description

[0001] The invention relates to a method for producing a pressure vessel. Background of the invention

[0002] The market for pressure vessels, particularly those reinforced with fiber composite materials, is growing continuously. The increasing production of natural gas and fracking gas makes storage in pressure vessels necessary, especially in countries without a corresponding pipeline network. In addition, the automotive sector is working hard on the development of fuel cell vehicles, in which the fuel in the form of gaseous hydrogen is to be stored under high pressure in pressure vessels. This is not only intended for automobiles, but also for rail, aircraft, and watercraft. Applications are even conceivable in spacecraft. Lightweight pressure vessels are desired for transporting pressure vessels because transporting heavy pressure vessels consumes unnecessary amounts of energy and therefore results in excessive transport costs.

[0003] Currently used cylindrical fiber-reinforced pressure vessels have a reinforcement layer made of fiber composite material embedded in a matrix material, which is wound as an outer layer onto an inner container (the so-called liner) of the pressure vessel, which acts as the winding core. A winding process is the preferred process for the time- and cost-effective production of fiber composite layers. While the inner container, for example, guarantees the gas-tightness of the pressure vessel, the reinforcement layer made of fiber composite material gives the pressure vessel the necessary mechanical stability. Type 3 pressure vessels use a metallic inner container (metallic liner), e.g. made of aluminum or steel; Type 4 pressure vessels have a non-load-bearing inner container (liner) made of plastic.The plastic liners are usually manufactured by blow molding, rotomolding, or welding individual components. Materials that have good permeation properties towards hydrogen, such as polyamides or polyethylene, especially high-density polyethylene, can be used in this case. The pressure vessels must withstand very high internal pressure. Currently, for example, automobile hydrogen tanks are refueled at a pressure of approximately 700 bar. In particular, the pressure vessels must not deteriorate in the event of a crash. Therefore, such pressure vessels are constructed with a cylindrical center section that is sealed on both sides with so-called pole caps. The reinforcement layers are oversized accordingly to compensate for manufacturing tolerances. For example, the reinforcement layer is produced using the filament winding process, which winds the pressure vessels in a single operation.In other words, the fibers are wound onto the plastic liner in circumferential and cross layers or helical layers in a single operation. The production of such pressure vessels is therefore complex and expensive.

[0004] US Patent Application Publication US 2018 / 299067 A1 discloses a pressure vessel comprising a tubular body constructed of a composite material. A pair of end caps are adhesively attached to opposite ends of the body. A flexible, liquid-impermeable lining is provided inside the body. The flexible, liquid-impermeable lining is formed from a thin coating applied to the body.

[0005] German patent application DE 10 2011 105 627 A1 discloses an assembly method for a composite pressure vessel, wherein an end portion of a tubular member is fitted into an annular slot formed in an end cap. A sealing means may be located in the annular slot. The end cap includes an annular groove in an outer surface of the end cap body portion. A first material layer is formed on an outer surface of the tubular member. The first material layer comprises a first composite material having fibers oriented circumferentially to the tubular member. A second material layer is formed on the first material layer, wherein a portion of the second material layer is disposed into the annular groove comprising a second composite material having fibers oriented axially to the tubular member.A third material layer is formed adjacent to the second material layer and in the annular groove. This third material layer comprises a third composite material with fibers oriented circumferentially relative to the tubular element. A prefabricated cylindrical tube forms part of the liner, thus located inside the pressure vessel.

[0006] German patent application DE 31 03 646 A1 discloses a pressure vessel for storing and transporting gaseous fluids. The pressure vessel comprises a tubular metal body that is deformed at least at one end into a dome-shaped end cap. The wall thickness of the tubular section of the metal body, made of aluminum or an aluminum alloy, is reduced compared to the wall thickness of the dome-shaped cap and is surrounded by a jacket made of fiber-reinforced plastic, particularly one reinforced with glass, carbon, aramid, or boron fibers.

[0007] German patent application DE 10 2016 222 674 A1 discloses a method for producing a pressure vessel, a pressure vessel, and a pipe extrusion system. The method comprises the steps of: providing a central part of the pressure vessel, wherein the central part comprises an extruded liner pipe that is at least partially surrounded by at least one fiber-reinforced layer; joining the central part to at least one end piece; and applying at least one fiber-reinforced outer layer, wherein the fiber-reinforced outer layer extends at least partially over the at least one end piece and over the central part. The cylindrical pipe is part of the liner and is therefore located inside the pressure vessel.

[0008] German patent application DE 10 156 377 A1 discloses a composite compressed gas container, a method for its production, and its use. The compressed gas container consists of a composite of a cylindrical metal container and a prefabricated casing tube. The casing tube is preferably made of fiber material such as GRP or CFRP and serves as reinforcement.

[0009] There is a desire to make the production of fiber-reinforced pressure vessels more efficient. Summary of the invention

[0010] The object of the invention is to provide a manufacturing method for fiber-reinforced pressure vessels which can be carried out more efficiently and cost-effectively than the methods known in the prior art, whereby at least the same requirements are met for the pressure vessel.

[0011] The object is achieved by the manufacturing method according to claim 1.

[0012] The term "pressure vessel" encompasses all types and shapes of pressure vessels that comprise an inner container, also called a liner, made, for example, of a thermoplastic material, and are mechanically reinforced on the outside with a fiber composite material so that the pressure vessel meets the requirements for its pressure resistance. These pressure vessels are usually cylindrical with outwardly curved ends on both sides of the cylindrical center section. These connections are called pole caps and serve to seal the center section pressure-tight. To reinforce the pressure vessel, the outer surface of the inner container is wrapped with an outer layer of fiber composite material, which can also form the outer surface of the pressure vessel. The inner container can be manufactured using various techniques, for example, by welding, injection molding, or blow molding.The pole caps can also be subsequently attached to the center section, for example, by welding. The separate pole caps can be manufactured, for example, by injection molding. Pressure vessels with a thermoplastic inner container are, on the one hand, very lightweight, which is important for applications in transportation, for example. On the other hand, fillings such as hydrogen can be stored under high pressure with minimal loss, since suitable thermoplastic materials have sufficiently low hydrogen permeability, and the required strength is provided by the outer layer of fiber composite material.

[0013] A fiber composite material for the fiber composite layer generally consists of two main components: fibers embedded in a matrix material that creates the strong bond between the fibers. The fiber composite material can be wound from a single fiber or from multiple fibers, with the fiber(s) wound closely next to one another in contact with one another. In this case, the wound fibers are already impregnated with matrix material. This creates a fiber layer onto which the fibers are wound in further fiber layers until the fiber composite material has the desired thickness and represents a corresponding fiber layer of this thickness. The outer layer is wound in multiple layers of fiber composite material, with different layers having fibers at different fiber angles to the cylinder axis of the pressure vessel.In one embodiment, the fiber layers made of first and / or further fibers, for example second fibers, each comprise multiple layers of fibers. The composite gives the fiber composite material superior properties, such as greater strength than either of the two individual components could provide. The reinforcing effect of the fibers in the fiber direction occurs when the elastic modulus of the fiber in the longitudinal direction is greater than the elastic modulus of the matrix material, when the elongation at break of the matrix material is greater than the elongation at break of the fibers, and when the breaking strength of the fibers is greater than the breaking strength of the matrix material. All types of fibers can be used, for example glass fibers, carbon fibers, ceramic fibers, steel fibers, natural fibers, or synthetic fibers. Thermosets are generally used as matrix materials for the fiber composite layer.The material properties of the fibers and matrix materials are known to those skilled in the art, allowing them to select a suitable combination of fibers and matrix materials for producing the fiber composite material for the respective application. Individual fiber layers in the fiber composite area can comprise a single fiber or several identical or different fibers.

[0014] The term "thermoplastic material" refers to plastics that can be deformed (thermoplastically) within a specific temperature range. This process is reversible, meaning it can be repeated as often as required by cooling and reheating to a molten state, as long as overheating does not cause thermal decomposition of the material. This is what distinguishes thermoplastics from thermosets (or duromers) and elastomers. Another unique feature is the weldability of thermoplastics, unlike, for example, duromers.

[0015] The invention proposes first producing a pressure vessel blank. This separates the production of the pressure vessel blank from that of the entire pressure vessel. The pressure vessel blank is thus manufactured separately. "Separate production" is understood here and below to mean production separate from, in particular upstream of, the actual production of the pressure vessel. During the actual production of the pressure vessel, it is manufactured by overwrapping the pressure vessel blank, for example, with a fiber composite material. By manufacturing the pressure vessel blank separately, it can be manufactured under optimal conditions, which increases the efficiency and quality of this component and thus of the entire pressure vessel. Furthermore, the geometry of the pressure vessel is determined only by the prefabricated cylindrical tubes and no longer by the liner, thus increasing the manufacturing accuracy with regard tothe length and diameter of the pressure vessel is increased.

[0016] In detail, the manufacturing process can include the steps of manufacturing and machining a pole cap reinforcement, manufacturing and machining the cylindrical tube, mounting a connecting piece (boss) in the liner, joining the cylindrical tube and the pole caps with the liner, fixing the positions of the cylindrical tube and pole cap reinforcements, for example by spot bonding, wrapping the blank thus produced with helical and circumferential layers of a fiber composite material and curing the entire system.

[0017] According to the invention, the cylindrical tube is manufactured separately. This makes it possible to produce the tube from different materials using a manufacturing process optimally tailored to the respective material. Furthermore, the production of the cylindrical tube can be easily automated, further increasing production efficiency.

[0018] In a further advantageous embodiment, the cylindrical tube is wound from a fiber composite material. The fiber composite material can be, for example, carbon-reinforced plastic (CFRP). Components made of CFRP are lightweight, but also very strong. If the cylindrical tube is made from a material from the same group as that used later to wrap the pressure vessel blank, this offers advantages when bonding the pressure vessel blank to the wrapped layer, thereby increasing the overall strength of the pressure vessel. By manufacturing the cylindrical tube as a fiber composite component on a separate winding machine, the winding speed and the number of simultaneously wound threads can be increased. This also allows the cylindrical tube to be manufactured using a different fiber type than the rest of the pressure vessel. This can be advantageous for certain applications.Furthermore, the cycle time of the actual container winding machine, on which the pressure vessel is created in a later operation by overwinding the pressure vessel blank, is significantly reduced. This is particularly advantageous because the cylindrical tube, due to its simple, cylindrical geometry, can be manufactured on a simpler and therefore more cost-effective winding machine than the pressure vessel. The pressure vessel has pole caps that must be wrapped with helical layers, whereas the cylindrical tube, in one embodiment, can only be wound with circumferential layers. Furthermore, the separate production of the cylindrical tube makes it easier to incorporate different fiber angles in the circumferential layers or different fiber types with different stiffnesses into the product than with conventional manufacturing.

[0019] In addition, the cylindrical tube can be manufactured with a thinner wall than the entire container, which reduces the risk of fiber waviness and thus increases the utilization potential of the fibers.

[0020] In a further advantageous embodiment, the cylindrical tube is wound on a metallic winding core. The deposition of the threads is more precise on a metallic winding core than on a plastic liner. This can increase fiber utilization. Furthermore, a metallic winding core can be manufactured very precisely, allowing the inner diameter of the cylindrical tube or cylindrical semi-finished tube wound on it to be manufactured very precisely. This reduces manufacturing tolerances, which can lead to an increase in the filling volume of the pressure vessel within a given installation space.

[0021] In a further advantageous embodiment, the cylindrical tube is manufactured on a long winding core, so that several uses are achieved with a single winding. In other words, a cylindrical semi-finished tube is first wound, from which the cylindrical tube is cut to length. In particular, when using metallic winding cores, the strength of these cores makes it possible to wind very long cylindrical semi-finished tubes. By winding the longest possible cylindrical semi-finished tube and then cutting it to length to produce metallic tubes, production efficiency can be further increased. It is also possible, however, to manufacture the cylindrical tube to its final size on the winding core, for example using so-called flange disks, so that no cutting or other reworking is necessary.

[0022] According to the invention, the cylindrical tube is only partially cured. This makes it tradable and machineable, and can still form a material bond with the overwrap upon final curing after the overwrap.

[0023] In another embodiment, the cylindrical tube is extruded. Extrusion is a very economical manufacturing process. In particular, very long semi-finished tubes can be produced by extrusion, from which cylindrical tubes can be cut to length. However, long-fiber-reinforced materials and thermosetting materials, in particular, cannot be extruded, so short-fiber-reinforced thermoplastics such as fiber-reinforced polyamides can be used for extrusion. However, these materials may have disadvantages compared to wound tubes in terms of strength.

[0024] In another embodiment, the cylindrical tube is pultruded. The pultrusion process allows for processing materials with longer fibers, including so-called continuous fibers, than materials that can be processed by the extrusion process. The longer fibers increase the strength of tubes produced this way compared to extruded tubes.

[0025] In a further advantageous embodiment, the liner has an outer geometry for receiving the cylindrical tube, such that the cylindrical tube can form a positive connection with the liner. In particular, if this positive connection is at the transition from the cylindrical part of the pressure vessel to the pole caps, in particular if the pole caps have pole cap reinforcements, problems during so-called cold refueling can be avoided. If the positive connection is only on one side of the pressure vessel, the cylindrical tube can be pushed onto the liner from the other side. If the outer geometry of the liner has a recess into which the cylindrical tube can nestle, i.e. if the positive connection is on both sides of the liner, the cylindrical tube can be joined to the liner using a shrink-fitting process.

[0026] Typically, the boss, liner, and cylindrical tube form a single surface. The three components are then overwound together. In one embodiment, the cylindrical tube can be in direct contact with the metallic boss. The plastic liner then no longer has direct contact with the reinforcement winding. In an alternative advantageous embodiment, a pole cap reinforcement is applied to at least one pole area of the liner before the pressure vessel blank is overwound. The pole cap reinforcement can be manufactured separately, like the pressure vessel blank, which simplifies the manufacture of the pole cap reinforcement and allows the pole cap reinforcement to be manufactured in such a way that an optimal reinforcement effect is achieved. In this case, the cylindrical tube generally has no direct contact with the metallic boss.

[0027] In a further advantageous embodiment, the cylindrical pipe is pressed onto the liner. This pressing process allows a separately manufactured cylindrical pipe to be joined to a liner with undercuts that can form a positive connection with the cylindrical pipe. Furthermore, the pressing process makes it possible to create a prestressed connection between the liner and the cylindrical pipe, which can have advantages with regard to the possible formation of a gap between the liner and the cylindrical pipe during operation of the pressure vessel. The pressing process can be carried out mechanically, for example, by applying negative pressure to the interior of the liner. This temporarily shrinks the diameter of the liner. The pipe can then be pushed over the liner. After the negative pressure is removed, the liner grows against the inner surface of the pipe.

[0028] In a further advantageous embodiment, the cylindrical tube is thermally joined to the liner. For this purpose, the liner can be cooled significantly before joining and / or the cylindrical tube can be heated. Cooling causes the liner to shrink, meaning its diameter decreases. Conversely, heating causes the diameter of the cylindrical tube to increase. When the temperatures equalize after the joining process, the shrink connection is created.

[0029] In a further advantageous embodiment, the cylindrical tube is glued to the liner. This creates a solid connection in addition to the shrink connection, which can minimize or even completely prevent any gap formation between the liner and the cylindrical tube during operation of the pressure vessel.

[0030] For bonding, it has proven advantageous if the inner circumference of the cylindrical tube is at least partially pretreated, i.e., machined, prior to bonding. This can be, for example, a chemical pretreatment or a mechanical pretreatment. For example, the inner circumference of the cylindrical tube can be roughened using an abrasive process. This increases the surface area of the inner circumference of the cylindrical tube, allowing for a stronger bond. Another example of such processing is laser processing.

[0031] In addition, the surface of the inner circumference can be textured. This measure can lead to the removal of any gas that might penetrate between the liner and the cylindrical tube, which can help prevent liner buckling.

[0032] Machining the inner circumference of the cylindrical tube is only possible by manufacturing it separately.

[0033] The embodiments listed above may be used individually or in any combination without departing from the scope of the claims. Short description of the figures

[0034] These and other aspects of the invention are shown in detail in the figures as follows. Fig.1: a side section through a section of a pressure vessel Fig.2: a side section through a section of another pressure vessel Detailed description of the implementation examples

[0035] Fig.1 shows a lateral section through a section of a pressure vessel. In particular, Fig. 1A section through the wall structure of an inventive pressure vessel. The pressure vessel wall has an overwrap 1 made of a fiber composite material on its outer side. This overwrap 1 is applied to a pressure vessel blank comprising a cylindrical tube 2 and a liner 3 as the inner layer. The cylindrical tube 2 is located in the region of the cylindrical middle section 6 of the pressure vessel. The liner 3 has an outer geometry for receiving the cylindrical tube 2, such that the cylindrical tube 2 forms a positive connection with the liner 3. This positive connection is located at the transition from the cylindrical middle section 6 of the pressure vessel to the pole cap region 7. The outer geometry of the liner 3 has a recess into which the cylindrical tube 2 nestles. The positive connection can be designed so that it acts in the axial and / or radial direction.

[0036] Fig.2shows a lateral section through a section of another pressure vessel. The pressure vessel has a pole cap reinforcement 4 in the pole cap area 7, which is applied to the pole cap area 7 before the overwinding of the pressure vessel blank. The pole cap reinforcement 4, like the pressure vessel blank, can be manufactured separately, which facilitates the manufacture of the pole cap reinforcement 4 and allows the pole cap reinforcement 4 to be manufactured in such a way that an optimal reinforcement effect is achieved. A connecting piece 5, also called a boss, is inserted into the pole cap reinforcement 4 and the overwinding 1. This connecting piece is used for filling the pressure vessel and for removing the filler, for example a gas. The boss 5 is inserted into the pressure vessel in such a way that the liner fits snugly around it. In the Fig. 2In the embodiment shown, the liner 2 does not have a special outer geometry for receiving the cylindrical pipe 2, but is a standard liner with a cylindrical outer geometry without undercuts.

[0037] The embodiments shown here represent only examples of the present invention and are therefore not to be construed as limiting. Alternative embodiments contemplated by one skilled in the art are equally within the scope of the present claims. List of reference symbols

[0038] 1Overwrap 2Cylindrical tube 3Liner 4Pole cap reinforcement 5Boss 6Cylindrical middle section 7Pole cap area

Claims

1. A method for producing a fiber-reinforced pressure container, characterized by the steps of 1) producing a pressure container blank, wherein the pressure container blank has at least one liner made of plastic (3) and a cylindrical pipe (2) operatively connected thereto, wherein the cylindrical pipe (2) is produced separately, wherein the cylindrical pipe (2) is at most partially cured; 2) overwrapping the pressure container blank.

2. The method according to claim 1, characterized in that the cylindrical pipe (2) is wound from fiber composite material.

3. The method according to claim 2, characterized in that the cylindrical pipe (2) is wound on a metallic winding core.

4. The method according to any one of claims 1 to 3, characterized in that the cylindrical pipe (2) is cut to length from a cylindrical semi-finished pipe.

5. The method according to any one of claims 1 to 3, characterized in that the cylindrical pipe (2) is wound to its final dimension.

6. The method according to claim 1, characterized in that the cylindrical pipe (2) is extruded.

7. The method according to claim 1, characterized in that the cylindrical pipe (2) is pultruded.

8. The method according to any one of the preceding claims, characterized in that the liner made of plastic (3) has an outer geometry for receiving the cylindrical pipe (2) so that the cylindrical pipe (2) has a positive connection to the liner made of plastic (3).

9. The method according to any one of the preceding claims, characterized in that a boss (5) is in direct contact with the cylindrical pipe (2).

10. The method according to any one of the preceding claims, characterized in that prior to the overwrapping of the pressure container blank, a pole cap reinforcement (4) is applied to at least one pole region of the liner made of plastic (3).

11. The method according to any one of the preceding claims, characterized in that the cylindrical pipe (2) is pressed onto the liner made of plastic (3).

12. The method according to claim 10, characterized in that the cylindrical pipe (2) is thermally joined to the liner made of plastic (3).

13. The method according to any one of the preceding claims, characterized in that the cylindrical pipe (2) is adhesively bonded to the liner made of plastic (3).

14. The method according to any one of the preceding claims, characterized in that the cylindrical pipe (2) is at least partially processed at least on its inner circumference, before it is operatively connected to the liner made of plastic (3).