EP3436737A2

EP3436737A2 - Pressure vessel and method for forming an outer layer of a pressure vessel

Info

Publication number: EP3436737A2
Application number: EP17713686.8A
Authority: EP
Inventors: Alice PERROT; Bjorn Criel
Original assignee: Plastic Omnium Advanced Innovation and Research SA
Current assignee: Plastic Omnium Advanced Innovation and Research SA
Priority date: 2016-03-30
Filing date: 2017-03-30
Publication date: 2019-02-06
Also published as: EP3225900A1; WO2017167858A3; WO2017167858A2

Abstract

The invention relates to a method for forming an outer layer around a liner having a cylindrical portion, in order to obtain a pressure vessel. The method comprises: forming one or more hoop wrapping layers by wrapping one or more first fibre bundles with a first fibre angle between 80 and 100 degrees with respect to the axial direction of the cylindrical portion; and forming one or more braided layers by braiding one or more second fibre bundles with a second fibre angle below 75 degrees with respect to the axial direction of the cylindrical portion. The one or more hoop wrapping and braided layers together form an outer layer around the cylindrical portion, wherein preferably the hoop wrapping layers comprise between 5 and 30 weight percent of the total fibre content of the outer layer; and the braided layers comprises between 70 and 95 weight percent thereof.

Description

Pressure vessel and method for forming an outer layer of a pressure vessel

Field of Invention

The field of the invention relates to the manufacturing of pressure vessels by wrapping an outer layer around a liner. Particular embodiments relate to a method for forming an outer layer to be arranged around a liner of a pressure vessel, to a pressure vessel manufactured according to the method, and to a machine used for manufacturing a pressure vessel.

Background

Existing methods for manufacturing pressure vessels, such as CNG (Compressed Natural Gas) tanks, CHG (Compressed Hydrogen Gas) tanks, LPG (Liquefied Petroleum Gas) tanks or the like, produce a relatively light weight vessel by forming a fibre reinforced plastics (FRP) layer on the periphery of a hollow cylindrical liner. A first prior art method lays a circumferential winding, also called a hoop winding or a helical winding around the liner. Two types may be distinguished: a FW (Filament Winding) method and a TW (Tape Winding) method. The FW method may be a method in which fibre bundles are impregnated with resin beforehand to prepare a tow shaped prepreg and an FRP layer is formed by winding the tow shaped prepreg on the liner, or a method in which fibre bundles which are fed in a predetermined direction are impregnated with resin to be wound around a liner. The TW method is a method in which a tape shaped prepreg is wound around the liner to form an FRP layer. In such embodiments, typically the liner or the mandrel is rotated to apply a filament or tape from a spool and the spool, optionally with resin bath, is moved in the axial direction of the liner. For a hoop winding, the winding angle is typically between 80 and 100 degrees, e.g. just below 90 degrees. For a helical winding the winding angle may be e.g. between 10 and 60 degrees.

A second prior art method is the so-called "braiding" method in which a braider is used to form a body on the periphery of the liner by braiding a plurality of fibre bundles, and the body is impregnated with resin to be cured to form the FRP layer. The braiding method shortens the manufacturing time and reduces the manufacturing cost of the pressure vessel compared with the case of applying the FW method or the TW method, because the entire braided layer can be laid in one pass. Further, vessels with a braided outer layer are better suited to resist explosion since it is avoided due to the fibre interlocking that small vessel parts can burst away when an explosion in the vessel takes place. In vessels with hoop windings and in vessels with a braided outer layer, typically the fibre cost is dominant. Therefor it is desirably to reduce the amount of fibres used for producing a vessel with a predetermined strength. Summary

Embodiments of the invention aim to provide a method allowing reducing the amount of fibres used for producing a pressure vessel with a predetermined strength.

According to a first aspect of the invention, there is provided a method for forming an outer layer around a cylindrical portion of liner in order to obtain a pressure vessel. The method comprises forming one or more hoop wrapping layers by wrapping one or more first fibre bundles with a first fibre angle between 80 and 100 degrees with respect to the axial direction of the cylindrical portion; and forming one or more braided layers by braiding one or more second fibre bundles with a second fibre angle below 75 degrees with respect to the axial direction of the cylindrical portion. The forming of the one or more hoop wrapping and braided layers is performed such that said one or more hoop wrapping and braided layers together form an outer layer around a liner, said outer layer containing a total fibre content. Further, the one or more hoop wrapping layers are formed such that they comprise between 5 and 30 weight percent of the total fibre content of the outer layer; and said one or more braided layers are formed such that they comprise between 70 and 95 weight percent of the total fibre content.

In the context of the present application the term "wrapping" refers to all types of wrapping, e.g. filament winding, braiding, etc. In other words the hoop wrapping layer may be a filament winding layer, a braided layer, etc.

Embodiments are based inter alia on the inventive insight that by combining one or more "hoop" wrapping layers, i.e. wrapping layers with a first fibre angle between 80 and 100 degrees, with one or more braided layers with a second fibre angle below 75 degrees, in accordance with a particular balance between the fibre content in the one or more hoop wrapping layers and the fibre content in the one or more braided layers, higher pressures can be better resisted with a lower amount of fibres. Further, the one or more hoop wrapping layers will be better suited to withstand radial forces while the one or more braided layers are suited to withstand axial forces.

It is noted that, according to the first aspect, a braided layer may be applied before and/or after a hoop wrapping layer or a braided layer. In other words, any sequence of hoop wrapping and braided layers is possible, e.g. liner - hoop wrapping layer - braided layer, liner - braided layer - hoop wrapping layer, liner - hoop wrapping layer - braided layer - hoop wrapping layer, liner - braided layer - hoop wrapping layer - braided layer, etc.

According to an exemplary embodiment, the first fibre angle is between 82 and 98 degrees, more preferably between 85 and 95 degrees.

According to an exemplary embodiment, the second fibre angle is below 70 degrees, more preferably below 65 degrees. In an exemplary embodiment, the second fibre angle is between 30 and 75 degrees, preferably between 30 and 70 degrees, more preferably between 30 and 65 degrees, e.g. between 40 and 60 degrees.

According to an exemplary embodiment, the forming of the one or more hoop wrapping layers and braided layers is such that a braided layer of the one or more braided layers is formed around a hoop wrapping layer of the one or more hoop wrapping layers. By applying a braided layer around a hoop wrapping layer, the burst resistance is improved since the braided layer avoids that small parts burst away in the event of an explosion.

According to an exemplary embodiment, a hoop wrapping layer of the one or more hoop wrapping layers is formed directly on top of the liner. In that way, the hoop wrapping layer will be able to absorb a larger portion of the radial forces, and the one or more braided layers can provide burst resistance.

According to a preferred embodiment, the one or more hoop wrapping layers are formed such that they comprise between 5 and 25 weight percent of the total fibre content of the outer layer; and the one or more braided layers are formed such that they comprise between 75 and 95 weight percent of the total fibre content. More preferably, the one or more hoop wrapping layers are formed such that they comprise between 5 and 20 weight percent of the total fibre content of the outer layer; and the one or more braided layers are formed such that they comprise between 80 and 95 weight percent of the total fibre content.

According to a preferred embodiment, a hoop wrapping layer of the one or more hoop wrapping layers is formed by arranging a hoop winding with a winding angle between 80 and 100 degrees with respect to the axial direction of the liner, more preferably between 85 and 95 degrees. Such winding angles will allow a good absorption of the radial forces. According to an exemplary embodiment, the one or more hoop wrapping layers are applied by a wrapping assembly whilst moving the liner in the axial direction. According to an exemplary embodiment, the one or more braided layers are applied by moving the liner through a braiding assembly. In a possible embodiment, the various layers are applied in consecutive movement passes, e.g. a first movement pass through a wrapping assembly followed by a second movement pass through a braiding assembly. However, in a preferred embodiment, a hoop wrapping layer of the one or more hoop wrapping layers is applied by moving the liner through the wrapping assembly, whilst moving the liner through a braiding assembly such that a braided layer of the one or more braided layers is applied after said hoop wrapping layer during the same movement pass of the liner. In another embodiment, a braided layer of the one or more braided layers is applied by moving the liner through a braiding assembly, whereupon a hoop wrapping layer is applied immediately after the application of said braided layer by the wrapping assembly, downstream of the braiding assembly, such that a hoop wrapping layer of the one or more hoop wrapping layers is applied after said braided layer during the same movement pass of the liner.

According to an exemplary embodiment, the wrapping assembly comprises at least one hoop winding head configured to apply a winding layer by rotating the at least one hoop winding head around the liner. According to another embodiment, the wrapping assembly may be a braiding assembly configured to apply the first fibre bundles with a fibre angle between 80 and 100 degrees. In a possible embodiment, the braiding assembly for applying the first fibres comprises weft and warp spools, wherein only the warp spools or only the weft spools may be used. For example, only one warp spool may be operated to apply one first fibre bundle (also called first yarn) with a first fibre angle between 80 and 100 degrees, or a plurality of warp spools may be operated to apply a plurality of first fibre bundles (also called a plurality of first yarns) simultaneously. In yet another possible embodiment, the braiding assembly for applying the first fibres comprises weft and warp spools, a stem yarn application means. Also, in such an embodiment only one or more warp spools or only one or more weft spools may be operated. For example, one or more warp spools may be operated to apply one or more first fibre bundles with a first fibre angle between 80 and 100 degrees, and the stem yarn application means may be operated to apply a further first fibre bundle extending in the axial direction of the liner (also called stem yarn), simultaneously. Optionally a controller may be added to control the spools to be used. However, it is also possible to use a standard braiding assembly and to provide only the spools that need to be used with yarn.

According to an exemplary embodiment, the forming of the one or more hoop wrapping layers and braided layers is such that a braided layer of the one or more braided layers is formed directly on top of a hoop wrapping layer of the one or more hoop wrapping layers. According to an exemplary embodiment, the forming of the one or more hoop wrapping layers and braided layers is such that a braided layer of the one or more braided layers is formed directly on top of a hoop wrapping layer of the one or more hoop wrapping layers, and that a further hoop wrapping layer of the one or more hoop wrapping layers is formed directly on top of said braided layer. By having the combination hoop wrapping layer - braided layer - further hoop wrapping layer, the further hoop wrapping layer may compress the braided layer, further improving the strength of the pressure vessel. According to an exemplary embodiment, the forming of the one or more hoop wrapping layers and braided layers is such that a hoop wrapping layer of the one or more hoop wrapping layers is formed directly on top of a braided layer of the one or more braided layers, and that a further braided layer of the one or more braided layers is formed directly on top of said hoop wrapping layer. By having the combination braided layer - hoop wrapping layer - further braided layer, the strength of the pressure vessel can be further improved, wherein e.g. a different fibre bundle material and/or a different angle may be used for the braided layer and the further braided layer.

According to an exemplary embodiment, the forming of the one or more hoop wrapping layers and braided layers is such that a braided layer of the one or more braided layers is formed directly on top of a hoop wrapping layer of the one or more hoop wrapping layers, and that a further hoop wrapping layer of the one or more hoop wrapping layers is formed directly on top of said braided layer. By having the combination hoop wrapping layer - braided layer - further hoop wrapping layer, the further hoop wrapping layer may be made of glass fibre, further improving the impact resistance of the pressure vessel.

According to an exemplary embodiment, the one or more first and/or the one or more second fibre bundles comprise any one or more of the following: dry fibres, fibres in a resin matrix, a commingled yarn comprising fibre filaments and thermoplastic filaments, a thermoplastic prepreg, a tape comprising fibre filaments and a thermoplastic prepreg, a towpreg. Depending on the type of first and/or second bundles that are being used, there may be performed a suitable post-processing of the liner with outer layer, e.g. heating the outer layer, or applying resin around the first and/or second bundles.

According to another aspect of the invention, there is provided a pressure vessel comprising a liner having a cylindrical portion and an outer layer around said cylindrical portion comprising a resin. The outer layer comprises one or more hoop wrapping layers of one or more first fibre bundles, said one or more hoop wrapping layers being wrapped with a first fibre angle between 80 and 100 degrees with respect to the axial direction of the cylindrical portion; and one or more braided layers of one or more second fibre bundles, said one or more braided layers being braided with a second fibre angle below 75 degrees with respect to the axial direction of the cylindrical portion. The one or more hoop wrapping layers and braided layers form together an outer layer around the liner. The outer layer contains a total fibre content. The one or more hoop wrapping layers comprise between 5 and 30 weight percent of the total fibre content of the outer layer, and the one or more braided layers comprise between 70 and 95 weight percent of the total fibre content. According to an exemplary embodiment, the first fibre angle is between 82 and 98 degrees, more preferably between 85 and 95 degrees. According to an exemplary embodiment, the second fibre angle is below 70 degrees, more preferably below 65 degrees. In an exemplary embodiment, the second fibre angle is between 30 and 75 degrees, preferably between 30 and 70 degrees, more preferably between 30 and 65 degrees.

Preferably, the one or more hoop wrapping layers comprise between 5 and 25 weight percent of the total fibre content of the outer layer, and the one or more braided layers comprise between 75 and 95 weight percent of the total fibre content. More preferably, the one or more hoop wrapping layers comprise between 5 and 20 weight percent of the total fibre content of the outer layer, and the one or more braided layers comprise between 80 and 95 weight percent of the total fibre content.

According to an exemplary embodiment, a braided layer of the one or more braided layers is arranged around a hoop wrapping layer of the one or more hoop wrapping layers. Preferably, a hoop wrapping layer of the one or more hoop wrapping layers is arranged directly around the liner.

According to a preferred embodiment, a hoop wrapping layer of the one or more hoop wrapping layers comprises a hoop winding, said hoop winding being arranged with a winding angle between 80 and 100 degrees, and more preferably between 85 and 95 degrees with respect to the axial direction of the liner.

According to an exemplary embodiment, a braided layer of the one or more braided layers is arranged directly on top of a hoop wrapping layer of the one or more hoop wrapping layers.

According to an exemplary embodiment, a further hoop wrapping layer of the one or more hoop wrapping layers is formed directly on top of the braided layer. According to an exemplary embodiment, a hoop wrapping layer of the one or more hoop wrapping layers is arranged directly on top of a braided layer of the one or more braided layers, and a further braided layer of the one or more braided layers is arranged directly on top of said hoop wrapping layer.

According to an exemplary embodiment, the one or more first and/or the one or more second fibre bundles comprise any one or more of the following: dry fibres, fibres in a resin matrix, a commingled yarn comprising fibre filaments and thermoplastic filaments, a thermoplastic prepreg, a tape comprising fibre filaments and a thermoplastic prepreg, a towpreg.

According to yet another aspect of the invention there is provided an apparatus for forming an outer layer around a liner in order to obtain a pressure vessel. The apparatus comprises a wrapping assembly configured to wrap a wrapping layer around a liner by wrapping one or more first fibre bundles, preferably with a first fibre angle between 80 and 100 degrees; and a braiding assembly configured to form a braided layer around a liner by braiding one or more second fibre bundles, preferably with a second fibre angle (also called braid angle) below 75 degrees. The wrapping assembly and the braiding assembly are arranged in-line such that the wrapping layer can be applied by moving the liner through the wrapping assembly in a first direction, whilst moving the liner through the braiding assembly in said first direction such that the braided layer is applied directly after or before the wrapping layer during a single first movement pass of the liner. The apparatus is further configured to move the liner through the wrapping assembly in a second direction opposite to the first direction, whilst moving the liner through the braiding assembly in said second direction such that such that at least one further layer is applied during a single second movement pass of the liner. The at least one further layer may be a further braided layer and/or a further wrapping layer. Preferably, the apparatus is configured such that a further braided layer is applied directly after or before a further wrapping layer during a single second movement pass of the liner.

According to an exemplary embodiment, the wrapping assembly comprises at least one hoop winding head configured to apply a winding layer by rotating the at least one hoop winding head around the liner. According to another embodiment, the wrapping assembly may be a braiding assembly configured to apply the first fibre bundles with a fibre angle between 80 and 100 degrees. In a possible embodiment, the braiding assembly for applying the first fibres comprises weft and warp spools and is operated to rotate only warp spools or only weft spools. For example, only one warp spool may be operated to apply one first fibre bundle (also called first yarn) with a first fibre angle between 80 and 110 degrees, or a plurality of warp spools may be operated to apply a plurality of first fibre bundles (also called a plurality of first yarns) simultaneously. In another possible embodiment, the braiding assembly for applying the first fibres comprises weft and warp spools, a stem yarn application means. For example, one or more warp spools may be operated to apply one or more first fibre bundles with a first fibre angle between 80 and 110 degrees, and the stem yarn application means may be operated to apply a further first fibre bundle extending in the axial direction of the liner (also called stem yarn), simultaneously.

In a preferred embodiment, the wrapping assembly, e.g. comprising the at least one winding head, is arranged upstream of the at least one braiding assembly, seen in the first direction, such that a braided layer can be applied on a wrapping layer. In such an embodiment the wrapping assembly is preferably surrounded at least partially by the braiding assembly, resulting in a compact apparatus which can apply a wrapping layer and a braided layer in one movement pass. More in particular, the wrapping assembly may be arranged at least partially in an area delimited by the yarns (i.e. the one or more second fibre bundles) used by the braiding assembly, as illustrated in the embodiment of figure 5A.

According to yet another aspect of the invention, there is provided a method for forming an outer layer around a liner in order to obtain a pressure vessel. The method comprises: applying a wrapping layer around a liner by moving the liner through a wrapping assembly in a first direction; moving the liner through a braiding assembly in said first direction such that a braided layer is applied directly after or before the wrapping layer during a single first movement pass of the liner;

moving the liner through the wrapping assembly in a second direction opposite to the first direction, whilst moving the liner through the braiding assembly in said second direction such that at least one further layer is applied during a single second movement pass of the liner. The at least one further layer may be a further braided layer and/or a further wrapping layer. In a preferred embodiment a further braided layer is applied directly after or before a further wrapping layer during the single second movement pass of the liner.

Such a method has the advantage that a plurality of wrapping layers and braided layers can be applied one after the other in a fast manner. Indeed, the liner can be reciprocated through the combination of the wrapping assembly and braiding assembly, such that during each movement pass a wrapping layer and/or a braiding layer can be applied.

It is noted that the second movement pass may be performed after or before the first movement pass.

In other words, there may be applied e.g. the following combinations:

a combination of a braided layer and hoop layer followed by a combination of a braided layer and hoop layer (e.g. hoop-braided-braided-hoop, hoop-braided-hoop-braided, etc.); a combination of a braided layer and hoop layer followed by a braided or hoop layer (e.g. hoop-braided-hoop; hoop-braided-braided, etc.);

a braided or hoop layer followed by the combination of a braided layer and a hoop layer (e.g. hoop-braided-hoop; hoop-braided-braided, etc.).

The skilled person understands that in further developed embodiments also one or more wrapping assemblies may be combined with one or more braiding assemblies, such that during each movement pass one or more wrapping layers and/or one or more braiding layers may be applied. Further, the liner may be reciprocated (in the first/second direction) a number of times depending in the required number of layers.

According to an exemplary embodiment of this method, the wrapping assembly comprises at least one winding head configured to wind a winding layer. According to another embodiment, the wrapping assembly may be a braiding assembly configured to apply the first fibre bundles with a fibre angle between 80 and 100 degrees, see also the explanation and advantages mentioned above for the corresponding apparatus feature.

According to an exemplary embodiment of this method, seen in the first direction, the braided layer is applied directly after the wrapping layer during the first single movement pass of the liner. By applying a braided layer around a hoop wrapping layer, the burst resistance is improved since the braided layer avoids that small parts burst away in the event of an explosion.

According to an exemplary embodiment of this method, the wrapping layer is formed by arranging a hoop winding around the liner, said hoop winding being arranged with a winding angle between 75 and 105 degrees with respect to the axial direction of the liner, preferably between 80 and 100 degrees. Such winding angles will allow a good absorption of the radial forces. According to an exemplary embodiment of this method, the braided layer is applied with a fibre angle (also called braid angle) below 70 degrees, preferably below 65 degrees, more preferably between 30 and 65 degrees.

According to an exemplary embodiment of this method, the wrapping layer is formed by wrapping a first fibre bundle as a dry fibre bundle and/or wherein braiding layer is formed by braiding a second fibre bundle as a dry fibre bundle, wherein a resin is applied after forming said wrapping layer and/or said braided layer. Alternatively, the first and/or the second fibre bundle may comprise any one of the following: a commingled yarn comprising fibre filaments and thermoplastic filaments, a thermoplastic prepreg, a tape comprising fibre filaments and a thermoplastic prepreg, a towpreg. According to another aspect of the invention, there is provided a method for forming an outer layer around a liner in order to obtain a pressure vessel, said method comprising: forming a winding layer around a liner by winding a first fibre bundle around the liner; forming a braided layer on said winding layer by braiding a second fibre bundle around the winding layer, wherein the winding layer is replaced with a "hoop" braided layer (i.e. a hoop layer arranged using a braiding assembly as explained before) having a first fibre angle between 80 and 100 degrees, and wherein the braided layer has a second fibre angle below 70 degrees, preferably below 65 degrees, more preferably between 30 and 65 degrees. Similarly there is provided a pressure vessel comprising a liner and an outer layer, said outer layer comprising: a winding layer comprising a winding of a first fibre bundle, a braided layer comprising a second fibre bundle, said braided layer being arranged on said winding layer, wherein the winding layer is replaced with a "hoop" braided layer having a first fibre angle between 80 and 100 degrees, and wherein the braided layer has a second fibre angle below 70 degrees, preferably below 65 degrees, more preferably between 30 and 65 degrees.

The skilled person understands that most preferred features disclosed above for other aspects of the invention also apply for this aspect of the invention.

According to an exemplary embodiment, the volume of the pressure vessel is between 4 and 150 litres. In an exemplary embodiment, the length of the pressure vessel is between 350 mm and 1500 mm, and the diameter of the vessel is between 100 and 600 mm. The thickness of the liner is typically between 1 and 3 mm. The thickness t of the outer layer is typically between 5 and 50 mm.

According to an exemplary embodiment, the pressure vessel is configured to store any one of the following: hydrogen gas, liquid petroleum gas (LPG), compressed natural gas (CNG), or ammonia.

According to an exemplary embodiment, the liner is moulded from a material having good gas barrier properties, e.g. blow moulded, injection moulded or rotation moulded. In an exemplary embodiment, the liner is moulded from any one or more of the following materials: polyamide, high-density polyethylene, a metallic material such as an aluminium base alloy or the like, a thermoplastic coextruded structure.

According to an exemplary embodiment, the liner comprises a cylindrical portion and two dome portions formed at both ends of the cylindrical portion. A metal mouth piece may be attached to the top of each dome portion. According to an exemplary embodiment, the first fibre bundles are prepared by bundling fibres, wherein the fibres may be covered with a (fibrous) thermoplastic or thermoset resin. Optionally fibre bundles with different diameters may be used. Alternatively the fibre bundles may be included in a tape material. Suitable reinforcing fibres included: carbon fibres, glass fibres, aramid fibres and the like.

According to an exemplary embodiment, the first fibre bundles are prepared as a so-called "towpreg". In this configuration the fibre bundles are prepared by bundling fibres and pre- impregnating the fibres by a thermoset resin. According to an exemplary embodiment, the second fibre bundles for the one or more braided layers may be bundled dry, i.e. not impregnated with resin, such as a dry carbon fibre or the like.

Brief description of the figures

The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

Figures 1A and IB illustrate schematically a cross section and a partially cut perspective view of a pressure vessel according to a first exemplary embodiment;

Figures 2A and 2B illustrate schematically two exemplary variants of the embodiment of figure 1 ; Figure 3 illustrates schematically a cross section of a pressure vessel according to a second exemplary embodiment;

Figures 4A and 4B illustrate schematically two exemplary variants of the embodiment of figure 3; Figures 5A-5C illustrate schematically three exemplary embodiments of the method where a hoop winding layer is formed in the same movement pass as a braided layer;

Figure 6 illustrates schematically another exemplary embodiment of the method; and

Figure 7 illustrates schematically another exemplary embodiment of the method where a braided hoop wrapping layer is formed in the same movement pass as another braided layer.

Description of embodiments

Figure 1 A illustrates schematically a cross section of an exemplary embodiment of a pressure vessel comprising a liner 1 and an outer layer 2, 3 comprising a resin. The outer layer comprises a wrapping layer 2, here a winding layer 2 wound around the liner 1 using a first fibre bundle, and a braided layer 3 braided around the winding layer 2 using a second fibre bundle. The winding layer 2 and braided layer 3 form together an outer layer around the liner 1. In this exemplary embodiment, the braided layer 3 is arranged directly on top of the winding layer 2, and the winding layer 2 is arranged directly around the liner 1. Preferably, the winding layer 2 comprises a hoop winding with a winding angle a between 75 and 105 degrees with respect to the axial direction of the liner, more preferably between 80 and 100 degrees, and most preferably between 85 and 95 degrees. The winding angle a, also called the first fibre angle, is shown in figure IB. In that way, the winding layer 2 allows a good absorption of the radial forces, and the braided layer 3 can provide burst resistance. Indeed, by applying the braided layer 3 around the winding layer 2, the burst resistance is improved since the braided layer 3 avoids that small parts burst away in the event of an explosion. Preferably, the braided layer 3 is applied with a braid angle β, also called the second fibre angle below 75 degrees with respect to the axial direction of the cylindrical portion, more preferably below 70 degrees, and most preferably below 65 degrees. In an exemplary embodiment, the second fibre angle β is between 30 and 75 degrees, preferably between 30 and 70 degrees, more preferably between 30 and 65 degrees.

Figures 2A and 2B illustrate schematically cross sections of two further exemplary embodiments of a pressure vessel comprising a liner 1 and an outer layer 3', 2, 3; 2, 3, 2' comprising a resin. In figure 2 A the outer layer comprises a winding layer 2 and two braided layers 3, 3'. One braided layer 3' is arranged directly around the liner 1. The winding layer 2 is wound around the braided layer 3' , and a further braided layer 3 is braided around the winding layer 2. The braided layer 3' , the winding layer 2, and the further braided layer 3 form together an outer layer around the liner 1. In this exemplary embodiment, the braided layer 3 is arranged directly on top of the winding layer 2. Preferably, the winding layer 2 comprises a hoop winding with a winding angle between 75 and 105 degrees with respect to the axial direction of the liner, more preferably between 80 and 100 degrees, and most preferably between 85 and 95 degrees. In that way, the winding layer 2 allows a good absorption of the radial forces, and the further braided layer 3 can provide burst resistance. Indeed, by applying the braided layer 3 around the winding layer 2, the burst resistance is improved since the braided layer 3 avoids that small parts burst away in the event of an explosion. By having a combination of two braided layers 3, 3' and a winding layer 2, the absorbing of the radial and axial forces can be improved with a reduced amount of fibres. In figure 2B the outer layer comprises two winding layers 2, 2' and a braided layer 3. One winding layer 2 is arranged directly around the liner 1. The braided layer 3 is wound around the winding layer 2, and a further winding layer 2' is wound around the braided layer 3. The winding layer 2, the braided layer 3, and the further winding layer 2' form together an outer layer around the liner 1. Preferably, the winding layer 2 and/or the further winding layer 2' comprises a hoop winding with a winding angle between 75 and 105 degrees with respect to the axial direction of the liner, more preferably between 80 and 100 degrees, and most preferably between 85 and 95 degrees. In that way, the winding layer 2 allows for a good absorption of the radial forces. Further, by having the combination winding layer 2 - braided layer 3 - further winding layer 2' , the further winding layer 2' may compress the braided layer 3, further improving the strength of the pressure vessel. Figure 3 illustrates schematically a cross section of a further exemplary embodiment of a pressure vessel comprising a liner 1 and an outer layer 2, 3 comprising a resin, similar to the embodiment of figure 1 , but with an indication of the fibre content in the various layers 2, 3 of the outer layer. The features that have been described for figure 1 also apply for figure 3. The outer layer comprises a winding layer 2 wound around the liner 1 using a first fibre bundle, and a braided layer 3 braided around the winding layer 2 using a second fibre bundle.

The winding layer 2 has a thickness dl which is preferably between 5 and 30 percent of the total thickness d of the outer layer. The braided layer 3 has a thickness d2 which is preferably between 70 and 95 percent of the total thickness d of the outer layer. The total thickness d of the outer layer is typically between 5 and 50 mm, depending on the diameter of the pressure vessel and the required strength. It is noted that other thickness percentages are also possible.

The winding layer 2 comprises preferably between 5 and 30 weight percent of the total fibre content in the outer layer, more preferably between 5 and 25 weight percent, and most preferably between 5 and 20 weight percent. The braided layer 3 comprises preferably between 70 and 95 weight percent of the total fibre content in the outer layer, more preferably between 75 and 95 weight percent, and most preferably between 80 and 95 weight percent. By combining a hoop winding layer 2 with a braided layer 3 in accordance with a particular balance between the fibre content in the winding layer 2 and the fibre content in the braided layer 3, higher pressures can be resisted with a lower amount of fibres. Further, the hoop winding layer 2 will be better suited to withstand radial forces while the braided layer 3 is suited to withstand axial forces. It is noted that the weight percentage values may be chosen independently of the thickness values and percentages mentioned in the previous paragraph. Figure 4A illustrates schematically a cross section of an exemplary embodiment of a pressure vessel comprising a liner 1 and an outer layer 2, 3 comprising a resin, similar to the embodiment of figure 3, but with the hoop winding layer 2 on top of the braided layer 3. Also in this embodiment, the winding layer 2 has a thickness dl which is preferably between 5 and 30 percent of the total thickness d of the outer layer, and the braided layer 3 has a thickness d2 which is preferably between 70 and 95 percent of the total thickness d of the outer layer. The winding layer 2 comprises preferably between 5 and 30 weight percent of the total fibre content in the outer layer, more preferably between 5 and 25 weight percent, and most preferably between 5 and 20 weight percent. The braided layer 3 comprises preferably between 70 and 95 weight percent of the total fibre content in the outer layer, more preferably between 75 and 95 weight percent, and most preferably between 80 and 95 weight percent. Compared to the embodiment of figure 3, the embodiment of figure 4A has the disadvantage that the burst resistance will be less, but the braided layer 3 will be compressed by the hoop winding layer 2 leading to an improved strength.

Figure 4B illustrates schematically a cross section of an exemplary embodiment of a pressure vessel comprising a liner 1 and an outer layer 2, 3, 2' comprising a resin, similar to the embodiment of figure 2B, but with an indication of the fibre content in the various layers 2, 3, 2' of the outer layer. The features that have been described for figure 2B also apply for figure 4B. The winding layer 2 has a thickness dl, and the second winding layer 2' has a thickness dl '. The sum of the thicknesses dl+dl ' is preferably between 5 and 30 percent of the total thickness d of the outer layer. The braided layer 3 has a thickness d2 which is preferably between 70 and 95 percent of the total thickness d of the outer layer. Preferably, the winding layer 2 and the further winding layer 2' comprise together between 5 and 30 weight percent of the total fibre content in the outer layer, more preferably between 5 and 25 weight percent, and most preferably between 5 and 20 weight percent. The braided layer 3 comprises preferably between 70 and 95 weight percent of the total fibre content in the outer layer, more preferably between 75 and 95 weight percent, and most preferably between 80 and 95 weight percent.

In the embodiments of figures 2A-2B, 3, 4A-4C, the winding angle of layers 2, 2' and the braid angle of layer 3 may be similar to the values disclosed above for figure IB for the winding angle a and the braid angle β, respectively. It is further noted that the winding angle of layer 2 and of layer 2' may be different. Also, it is noted that layers 2, 2' may be braided layers with a first fibre angle (braid angle) between 80 and 100 degrees.

According to an exemplary embodiment, the one or more first and/or the one or more second fibre bundles used for one or more winding layers 2, 2' and one or more braided layers 3, 3', respectively, comprise any one or more of the following: dry fibres, fibres in a resin matrix, a commingled yarn comprising fibre filaments and thermoplastic filaments, a thermoplastic prepreg, a tape comprising fibre filaments and a thermoplastic prepreg, a towpreg, etc.

In the exemplary embodiments above, the liner 1 may be moulded from a material having good gas barrier properties, e.g. blow moulded, injection moulded or rotation moulded. In an exemplary embodiment, the liner 1 is moulded by a blow moulding method using polyamide in order to obtain a liner with a good dimensional stability and chemical resistance as well as good gas barrier properties. The material to form the liner is not limited to polyamide. For example, any thermoplastic material having good gas barrier properties such as high-density polyethylene or the like, or metallic materials such as aluminium base alloys or the like may also be used to prepare the liner. The liner 1 may also consist of a multilayer structure.

The liner 1 comprises a cylindrical portion la and two dome portions lb, lc formed at both ends of the cylindrical portion, see also figure 6. A metal mouth piece Id, le may be attached to the top of each dome portion lb, lc.

Fibre bundles for a hoop winding 2, 2' may be prepared as follows. Carbon fibres are bundled to prepare a fibre bundle and may be covered with a (fibrous) thermoplastic or thermoset resin. In exemplary embodiments of the invention, fibre bundles with different diameters may be used. Alternatively, the fibre bundles may be included in a tape material. Also other reinforcing fibres such as glass fibres, aramid fibres or the like may be used. Optionally, the outer portion of carbon fibres may be protected by covering them with glass fibres or the like.

Fibre bundles for a braided layer 3, 3' may be prepared as follows. The fibre bundles may be dry bundles, i.e. not impregnated with resin, such as a dry carbon fibre or the like.

In exemplary embodiments, the length of the pressure vessel is between 350 mm and 1500 mm, and the diameter of the vessel is between 100 and 600 mm. The thickness of the liner is typically between 1 and 3 mm. The thickness d of the outer layer is typically between 5 and 50 mm. Figure 5A illustrates a first embodiment of the method. In this embodiment, there is used a machine which combines features of a ring winding machine with features of a braiding machine to combine both processes. The machine comprises a winding assembly with a winding ring 53 with multiple winding heads 51, 52 mounted for being rotated around a liner 1 while liner 1 moves forward in a direction V. The machine further comprises a braiding assembly with two guide rings 55 and a plurality of moveable weft and warp spools 56 mounted on carriers (not shown) that move in the spool plane. Weft and warp yarns are pulled from the weft and warp spools 56. The warp spools move clockwise while the weft spools move counter-clockwise, both with the same speed. The warp and weft yarns interlock, forming a closed biaxial fabric on the mandrel. Optionally, a stem yarn application means for applying stem yarns extending in an axial direction of the liner can be inserted to form a triaxial braid (not shown). The braiding assembly is provided downstream of the winding assembly such that first a winding layer is applied and then a braided layer. However, the set-up may be such that the yarns B and/or the guide ring 56 surround the winding assembly.

The liner 1 moves through the winding ring 53 while the hoop winding heads 51, 52 turn around the liner axis to arrange the hoop winding 2. For the first hoops H, the fibres may be held in a fixed position. Dry fibre(s) can be hold e.g. mechanically (e.g. a robot arm with an adapted tool), or by using a binder (blown on the fibres), or stapled, or glued, or welded (if a thermoplastic resin matrix is present). Next, the liner 1 moves through the guide rings 55 of the braiding assembly, and a braided layer 3 is applied with yarns B.

In a possible embodiment, the hoop winding fibres are cut at the end of the winding step, when arriving to the opposite section of the liner. Again, dry fibre(s) can be fixed by using a binder (blown on the fibres), or stapled, or glued, or welded (if a thermoplastic resin matrix is present). This will allow achieving an outer layer comprising a hoop layer 2, followed by a braided layer 3.

In a possible embodiment, the hoop winding fibres are positioned through the braided layer B in order to be able to restart the operation when the cylinder is moving in the opposite direction for the next layers during the process. Depending on the required number of layers the liner may be reciprocated a number of times. This will allow achieving an outer layer comprising e.g. a hoop layer, followed by a braided layer, followed by a hoop layer, followed by a braided layer, etc. ; or a hoop layer, followed by a braided layer, followed by a braided layer, followed by a hoop layer, etc. Note that it is possible to have a movement pass where only a braided layer or only a hoop layer is applied. The fibres from the hoop layer and/or the braided layer may be cut before reciprocating the movement of the mandrel, in function of the layers to be applied.

Figure 5B illustrates a second embodiment of the method, wherein a hoop layer 2 is arranged around a liner 1 in the same movement pass with a braided layer 3, and a further hoop layer 2'. The winding layer 2 is applied by rotating at least one hoop winding head 51, 52 around the liner 1 whilst moving the liner 1 in the axial direction V. Next, a braided layer 3 is applied by moving the liner 1 through a braiding assembly 55, 56, such that a braided layer 3 is applied after said winding layer 2 during the same movement pass of the liner 1. Downstream of the braiding assembly 55, 56, there is provided a further winding assembly 51 ', 52' , 53' for applying a further winding layer 2', in the same movement pass as the one used for the winding layer 2 and the braided layer 3. The skilled person understands that a further braiding assembly could be provided if it is desirable to apply a further braided layer on the further winding layer 2'. For the embodiment "hoop-braided-braided-hoop", the machine of figure 5A may be used as illustrated. Further, there is no need to cut fibres from the braiding ring after the first pass of the mandrel; the movement can be simply reciprocated to apply the further braided layer. The fibres of the hoop winding are cut each time it is desirable to change the direction of the mandrel: indeed, hoops are generally wound only on the cylindrical section of the vessel.

For the embodiment hoop-braided-hoop-braided the machine of figure 5B may be used. In that case also, the fibres from the hoop winding are cut each time it is desirable to change the direction of the mandrel.

Figure 5C illustrates a third embodiment of the method, wherein a braided layer 3 is arranged around a liner 1 in the same movement pass as a winding layer 2. In this embodiment, first a braided layer 3 is applied by moving the liner 1 through a braiding assembly 55, 56, whereupon a winding layer 2 is applied immediately after the application of said braided layer 3 by rotating at least one hoop winding head 51, 52 around the liner 1, downstream of the braiding assembly 55, 56, such that the winding layer 2 is applied after the braided layer 3 during the same movement pass of the liner 1.

The skilled person understands that any number of layers can be realized with such a combined machine, wherein for every movement pass one or more hoop winding assemblies and one or more braiding assemblies may be activated.

In other exemplary embodiments, a fibre reinforced tape may be used for the hoop winding. Such a tape may be welded and compressed using a roller on the mandrel to ensure a correct winding. After the dry winding process combining the braiding and hoop winding four options can be considered. Firstly, if a thermoplastic matrix is included in the yarn, e.g. if commingled yarns are used, then a bladder inflation moulding process may be used for the manufacturing and consolidation of the composite reinforcement. Secondly, if dry yarns are used, a resin transfer moulding (RTM) process or the like may be used for the manufacturing and consolidation of the composite reinforcement. Thirdly, if a towpreg based yarn is used, a consolidation process based on heating may be applied. Fourthly, if dry yarns are used, the consolidation can be based on reactive thermoplastic polymerization, RTM (Resin Transfer Molding), or infusion of a thermoset or thermoplastic resin matrix.

In an exemplary embodiment, the braiding assembly 55, 56 may be configured to braid the total surface of the liner while winding heads 51, 52 may be used to cover only the cylindrical area of the liner with hoops, preferably at 90° +/-10⁰. Figure 6 illustrates a second embodiment of the method. In this embodiment there is used a hoop winding station 61 followed by a braiding machine 62 to combine both processes. The hoop winding station 61 may be any suitable station configured for applying a hoop winding 2 on a liner 1. The braiding station 62 may be any suitable station configured for applying a braided layer 3 on a liner 1 on which a hoop winding 2 has been arranged. The skilled person understands that any number of layers can be realized with stations 61, 62, by passing the liner a number of times through these stations in a predetermined order. Figure 7 illustrates a further exemplary embodiment of the method and apparatus. In this embodiment there is used a machine which combines features of a first braiding machine operating with a braiding angle between 80 and 100 degrees, with features of a second braiding machine operating with a braiding angle below 75 degrees, to combine both processes. The machine comprises a first braiding assembly mounted for braiding a first "hoop" braided layer while liner 1 moves forward in a direction V. The first braiding assembly comprises a braiding ring 54' with a plurality of moveable weft and warp spools 56' and a guide ring 55' . For example, only one warp spool 56' may be operated to apply one first fibre bundle (also called first yarn) with a first fibre angle between 80 and 110 degrees, or a plurality of warp spools 56' may be operated to apply a plurality of first fibre bundles (also called a plurality of first yarns) simultaneously.

The apparatus of figure 7 further comprises a second braiding assembly with two guide rings 55 and a braiding ring 54 with a plurality of moveable weft and warp spools 56 mounted on carriers (not shown) that move in the spool plane. Weft and warp yarns B are pulled from the weft and warp spools 56. The second braiding assembly with spool 56 is provided downstream of the first braiding assembly with spools 56' such that first a "hoop" braided layer is applied and then a "normal" braided layer. The configuration may be such that the yarns B and/or the guide ring 56 surround the braiding ring 54 of the first braiding assembly.

It is noted that conventional braiding assemblies may be used in embodiments of the inventions. In such a braiding assembly the spools may be oriented parallel to the movement direction V, or may be oriented in a radial direction perpendicular to the movement direction V. In yet other embodiments the spools may be oriented under an angle with respect to the movement direction V.

EXAMPLE 1

Now an example of method for manufacturing a pressure vessel is described. In this example, a pressure vessel according to figure 3 is manufactured using the method of figure 5A. The liner 1 is blow moulded in a polyamide material. A first hoop winding layer 2 is applied, directly followed by a braided layer 3 using first and second fibre bundles with the properties specified in the table below.

From the table above it can be derived that the percentage of carbon fibres in the winding layer 2 with respect to the total weight of the fibres is 17 weight %, and that the percentage of carbon fibres in the braided layer 3 with respect to the total weight of the fibres is 83 weight %.

EXAMPLE 2

Now an example of a method for manufacturing a pressure vessel is described. In this example, a pressure vessel according to figure 2B or figure 4B is manufactured using the method of figure 5B. The liner 1 is blow moulded in a polyamide material. A first hoop winding layer 2 is applied, directly followed by a braided layer 3, and further followed by a second hoop winding layer 2' using fibre bundles with the properties specified in the table below.

Material fibres Weight % of Thickness of Type of fibre fibre layer bundle

Winding layer 2 carbon 20% 4,5mm Towpreg:

Impregnated carbon fibre bundle

Braided layer 3 carbon 75% 6mm Towpreg:

Impregnated carbon fibre bundle

Winding layer 2' glass 5% 1mm Towpreg:

Impregnated glass fibre bundle From the table above it can be derived that the percentage of carbon and glass fibres in the winding layers 2, 2' with respect to the total weight of the fibres is 25 weight , and that the percentage of carbon fibres in the braided layer 3 with respect to the total weight of the fibres is 75 weight . It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

Whilst the principles of the invention have been set out above in connection with specific embodiments, it is to be understood that this description is merely made by way of example and not as a limitation of the scope of protection which is determined by the appended claims.

Claims

1. A method for forming an outer layer around a liner having a cylindrical portion, in order to obtain a pressure vessel, said method comprising:

forming one or more hoop wrapping layers by wrapping one or more first fibre bundles with a first fibre angle between 80 and 100 degrees with respect to the axial direction of the cylindrical portion;

forming one or more braided layers by braiding one or more second fibre bundles with a second fibre angle below 75 degrees with respect to the axial direction of the cylindrical portion;

wherein said forming of the one or more winding and braided layers is performed such that said one or more hoop wrapping and braided layers together form an outer layer around the cylindrical portion of the liner, said outer layer containing a total fibre content;

wherein said one or more hoop wrapping layers are formed such that they comprise between 5 and 30 weight percent of the total fibre content of the outer layer; and wherein said one or more braided layers are formed such that they comprises between 70 and 95 weight percent of the total fibre content.

2. The method of claim 1 , wherein the forming of the one or more hoop wrapping layers and braided layers is such that a braided layer (3) of the one or more braided layers is formed around a hoop wrapping layer (2) of the one or more hoop wrapping layers.

3. The method of claim 1 or 2, wherein a hoop wrapping layer (2) of the one or more hoop wrapping layers is formed directly on top of the liner.

4. The method of any one of the previous claims, wherein a hoop wrapping layer of the one or more hoop wrapping layers is formed by winding a hoop winding, said hoop winding being arranged with a winding angle between 80 and 100 degrees with respect to the axial direction of the liner.

5. The method of any one of the previous claims, wherein a hoop wrapping layer of the one or more hoop wrapping layers is applied by moving the liner through a wrapping assembly, whilst moving the liner through a braiding assembly such that a braided layer of the one or more braided layers is applied after said hoop wrapping layer during the same movement pass of the liner.

6. The method of claim 5, wherein the wrapping assembly comprises at least one rotating hoop winding head; or wherein the wrapping assembly comprises a braiding assembly.

7. The method of any one of the previous claims, wherein the forming of the one or more hoop wrapping layers and braided layers is such that a braided layer (3) of the one or more braided layers is formed directly on top of a hoop wrapping layer (2) of the one or more hoop wrapping layers.

The method of any one of the previous claims, wherein the forming of the one or more hoop wrapping layers and braided layers is such that a braided layer (3) of the one or more braided layers is formed directly on top of a hoop wrapping layer (2) of the one or more hoop wrapping layers, and that a further hoop wrapping layer (2') of the one or more hoop wrapping layers is formed directly on top of said braided layer (3); or

wherein the forming of the one or more hoop wrapping and braided layers is such that a hoop wrapping layer (2) of the one or more hoop wrapping layers is formed directly on top of a braided layer (3) of the one or more braided layers, and that a further braided layer (3') of the one or more braided layers is formed directly on top of said hoop wrapping layer (2).

9. The method of any one of the previous claims, wherein the one or more first and/or the one or more second fibre bundles comprise any one or more of the following: dry fibres, fibres in a resin matrix, a commingled yarn comprising fibre filaments and thermoplastic filaments, a thermoplastic prepreg, a tape comprising fibre filaments and a thermoplastic prepreg, a towpreg.

10. A pressure vessel comprising a liner having a cylindrical portion and an outer layer around said cylindrical portion, said outer layer comprising a resin, said outer layer further comprising:

one or more hoop wrapping layers of one or more first fibre bundles wrapped with a first fibre angle between 80 and 100 degrees with respect to the axial direction of the cylindrical portion;

one or more braided layers of one or more second fibre bundles braided with a second fibre angle below 75 degrees with respect to the axial direction of the cylindrical portion;

said one or more hoop wrapping layers and braided layers together forming an outer layer around the cylindrical portion of the liner, said outer layer containing a total fibre content; wherein said one or more hoop wrapping layers comprise between 5 and 30 weight percent of the total fibre content of the outer layer; and wherein said one or more braided layers comprise between 70 and 95 weight percent of the total fibre content.

11. The pressure vessel of claim 10, wherein a braided layer (3) of the one or more braided layers is arranged around a hoop wrapping layer (2) of the one or more hoop wrapping layers.

12. The pressure vessel of claim 10 or 11, wherein a hoop wrapping layer (2) of the one or more hoop wrapping layers is arranged directly around the liner.

13. The pressure vessel of any one of the claims 10-12, wherein a hoop wrapping layer of the one or more hoop wrapping layers comprises a hoop winding, said hoop winding being arranged with a winding angle between 80 and 100 degrees with respect to the axial direction of the liner.

14. The pressure vessel of any one of the claims 10-13, wherein a braided layer (3) of the one or more braided layers is arranged directly on top of a hoop wrapping layer (2) of the one or more hoop wrapping layers.

15. The pressure vessel of claim 14, wherein a further hoop wrapping layer (2') of the one or more hoop wrapping layers is formed directly on top of the braided layer (3).

16. The pressure vessel of any one of the claims 10-13, wherein a hoop wrapping layer (2) of the one or more hoop wrapping layers is arranged directly on top of a braided layer (3') of the one or more braided layers, and a further braided layer (3) of the one or more braided layers is arranged directly on top of said hoop wrapping layer (2).

17. The pressure vessel of any one of the claims 10-16, wherein the one or more first and/or the one or more second fibre bundles comprise any one or more of the following: dry fibres, fibres in a resin matrix, a commingled yarn comprising fibre filaments and thermoplastic filaments, a thermoplastic prepreg, a tape comprising fibre filaments and a thermoplastic prepreg, a towpreg.

18. A apparatus for forming an outer layer around a liner in order to obtain a pressure vessel, said apparatus comprising:

a wrapping assembly configured to wrap a wrapping layer around a liner by wrapping one or more first fibre bundles;

a braiding assembly configured to form a braided layer around a liner by braiding one or more second fibre bundles;

wherein said wrapping assembly and said braiding assembly are arranged in-line such that the wrapping layer can be applied by moving the liner through the wrapping assembly in a first direction, whilst moving the liner through a braiding assembly in said first direction such that the braided layer is applied directly after or before the wrapping layer during a single first movement pass of the liner;

wherein the apparatus is further configured to move the liner through the wrapping assembly in a second direction opposite to the first direction, whilst moving the liner through the braiding assembly in said second direction such that at least one further layer is applied during a single second movement pass of the liner.

19. The apparatus of claim 18, wherein the apparatus is further configured such that a further braided layer is applied directly after or before a further wrapping layer during the single second movement pass of the liner.

20. The apparatus of claim 18 or 19, wherein the wrapping assembly comprises at least one winding head configured to wind a winding layer.

21. The apparatus of any one of the claims 18-20, wherein the wrapping assembly is arranged upstream of the at least one braiding assembly, seen in the first direction, such that the braided layer is applied directly after the wrapping layer during the first single movement pass of the liner.

22. A method for forming an outer layer around a liner in order to obtain a pressure vessel, said method comprising:

applying a wrapping layer around a liner by moving the liner through a wrapping assembly in a first direction;

moving the liner through a braiding assembly in said first direction such that a braided layer is applied directly after or before the wrapping layer during a single first movement pass of the liner;

moving the liner through the wrapping assembly in a second direction opposite to the first direction, whilst moving the liner through the braiding assembly in said second direction such that at least one further layer is applied during a single second movement pass of the liner.

23. The method of claim 22, wherein the applying of at least one further layer comprises applying a further braided layer directly after or before a further wrapping layer during the single second movement pass of the liner.

24. The method of claim 22 or 23, wherein the wrapping assembly comprises at least one winding head configured to wind a winding layer.

25. The method of any one of the claims 22-24, wherein, seen in the first direction, the braided layer is applied directly after the wrapping layer during the first single movement pass of the liner.

26. The method of any one of the claims 22-25, wherein the wrapping layer is formed by arranging a hoop winding around the liner, said hoop winding being arranged with a winding angle between 75 and 105 degrees with respect to the axial direction of the liner, preferably between 80 and 100 degrees.

27. The method of any one of the claims 22-26, wherein the wrapping layer is formed by wrapping a first fibre bundle as a dry fibre bundle and/or wherein braiding layer is formed by braiding a second fibre bundle as a dry fibre bundle, and wherein a resin is applied after forming said wrapping layer and/or said braided layer.

28. The method of any one of the claims 22-26, the wrapping layer is formed by wrapping a first fibre bundle and wherein braiding layer is formed by braiding a second fibre bundle; wherein the first and/or the second fibre bundle comprises any one of the following: dry fibres, fibres in a resin matrix, a commingled yarn comprising fibre filaments and thermoplastic filaments, a thermoplastic prepreg, a tape comprising fibre filaments and a thermoplastic prepreg, a towpreg.

29. The method of any one of the claims 22-28, wherein the braided layer is applied with a fibre angle (also called braid angle) below 70 degrees, preferably below 65 degrees, more preferably between 30 and 65 degrees.