GB2639973A

GB2639973A - Gas tank and manufacturing method thereof

Info

Publication number: GB2639973A
Application number: GB2404609.6A
Authority: GB
Inventors: Pichon Vincent; Paul Bernard; Grioche Olivier; Carneau Stéphane
Original assignee: Phinia Delphi Luxembourg SARL
Current assignee: Phinia Delphi Luxembourg SARL
Priority date: 2024-03-29
Filing date: 2024-03-29
Publication date: 2025-10-08
Also published as: GB202404609D0; WO2025202435A1

Abstract

A method for manufacturing a gas tank for storage of pressurised fuel gas, comprises providing a liner 12 defining a chamber, the liner being cylindrical with rounded ends 14. A composite shell is then formed by winding resin-coated filaments around the liner, the winding including applying circumferential windings 20 having a winding angle between 80-90° and applying polar windings 18 with at least 80% of the polar windings having a winding angle between 0-3°. The resin-coated filaments have a friction coefficient between 0.5-0.9. The composite shell can be formed with a first set of circumferential windings, polar windings and then finishing with a second set of circumferential windings, or alternatively there can be three sets of each of the circumferential and polar windings, with the outer windings being circumferential. When applied to the liner, the filaments can be at ambient temperature or higher. The circumferential windings can have a friction coefficient below 0.5.

Description

GAS TANK AND MANUFACTURING METHOD THEREOF Technical field [0001] The present invention generally relates to gas tanks, more particularly to type III and type IV tanks for hydrogen storage having an optimized composite shell thickness.

Background Art

[0002] Pressure vessels are used in a wide variety of technical fields to store fluids under pressures significantly higher than atmospheric, typically between 350 and 700 bar. Many applications, such as hydrogen tanks for the automotive industry, require pressure vessels to be as light as possible whilst being strong enough to ensure reliable and durable sealing of the fluid within.

[0003] Modern hydrogen tanks are typically cylindrical and can generally be categorized in five types: Type I tanks are simple metallic tanks, generally formed by a relatively thick cylinder of aluminum or steel. Type II tanks are similar to type I tanks and additionally comprise windings of glass or carbon fibers around the metallic cylinder. Type III tanks are made from a composite shell closely surrounding a relatively thin metallic liner. The metallic liner mainly ensures sealing of the fluid within the tank, whilst the composite shell bears most of the mechanical load generated by the pressure within. Type IV tanks are similar to Type III tanks but have a polymer liner instead of a metallic one. Finally Type V tanks are liner-less, fully composite tanks.

[0004] The composite shell of type III and type IV tanks is typically made by filament winding technique. A continuous bundle/tape comprising a plurality of glass or carbon filaments is tensioned, submersed in a resin bath and wound around the liner to enclose it. Once the desired number of filaments has been wound around the liner, the resin is cured. The mechanical properties of the final composite shell largely depend on its winding configuration, which is defined by its number of windings, their winding angle (i.e. the angle between the longitudinal axis of the gas tank and the projection of the filaments onto the longitudinal plane), the width of the filament tape, the order in which windings are layered around each other, etc...

[0005] Windings may be sorted in three patterns based on their winding direction. Polar windings have a winding angle comprised between about 13 and 30° and improve the mechanical strength of the composite shell in the longitudinal direction. Circumferential windings (a.k.a. hoop windings) have a winding angle between 80 and 90° and improve the mechanical strength of the composite shell in the radial direction. Finally, helical windings have a winding angle between 30 and 80°, slightly improve the mechanical strength of the composite shell in all directions, and mainly serve to maintain the polar windings in place, thereby preventing the latter from slipping.

[0006] While the overall weight and production cost of the tank have been significantly reduced by producing composite shell, the current windings patterns may still be improved to further reduce the thickness and thus weight of the composite shell.

Technical problem [0007] It is an object of the present invention to provide a method of manufacturing a gas tank which is as light as possible whilst being strong enough to ensure reliable and durable sealing of the fluid within.

General Description of the Invention

[0008] According to a first aspect, the invention provides a method of manufacturing a gas tank for the storage of pressurized fuel, particularly gaseous fuel such as hydrogen. The method comprises the steps of a) providing a liner defining a chamber, said liner having a cylindrical portion and two rounded portions at bases thereof; b) forming a composite shell by winding a plurality of resin-coated filaments around the liner, said winding including applying circumferential windings having a winding angle comprised between 80 and 90° and polar windings; characterized in that a majority of the polar windings, i.e. more than 80% or even more than 90% of the polar windings, are formed with a winding angle (apt) comprised between 0° and 3° using pre-impregnated filaments having a friction coefficient between 0.5 and 0.9.

[0009] The present method thus allows manufacturing a type III or IV gas tank with a composite shell where the majority of the polar windings are laid with a winding angle (api) comprised between 0° and 3°, i.e. much lower than conventional polar winding angles (typically between 13° and 30°). The use of such polar windings with a winding angle between 0° and 3°, as opposed to conventional winding angles, already leads to a strength increase, in particular a greater mechanical strength in the longitudinal direction, for a given weight of the composite shell. In fact, using more of such polar windings further improves these advantages; it is thus desirable that the majority of polar windings, e.g. above 80% (and more) in the composite shell, have a winding angle comprised between 0° and 3°.

[0010] It will be appreciated that the inventive method relies on the use of high friction resin-coated filaments. As will be discussed in more detail, the high friction coefficient allows to avoid filament slipping issues when applying the polar windings at the very small angles of 0 to 3°. It may be noted that, considering industrialization of filament winding techniques, resin-coated filaments having a too high friction coefficient (also referred to as tack or tackiness level) would too strongly adhere to each other and would thus be difficult to unwind from the spool during a manufacturing process of a composite gas tank, thereby preventing homogeneous winding thereof. However, resin-coated filaments conventionally used in the industry have a too low friction coefficient to be applicable at low winding angles. Indeed, filaments with conventional friction coefficient would insufficiently adhere to the liner or underlying windings, to prevent slipping/sliding and thus would not remained in place around the liner, thereby inducing local defects.

[0011] The inventors surprisingly found that such a small winding angle of polar windings as per the present invention is possible with the friction coefficient of the resin-coated filaments being between 0.5 and 0.9, as opposed to conventional winding with an angle of between about 13 and 30° wherein the friction coefficient is often as low as 0.02. In other words, the high friction coefficient of the resin-coated filaments / polar windings allows for the small winding angle.

[0012] It may be noted that whereas the composite shell can be generally manufactured using filament winding technique, the polar windings with winding angle of 0 to 3° are herein applied using pre-impregnated filaments.

[0013] As will be known to those skilled in the art, and as used herein, the term pre-impregnated filaments designate a specific type of resin-coated filaments, where the bundle of filaments is impregnated with a matrix material in a preliminary process, forming a semi-finished product. In general, the matrix material may be a thermoplastic material or a partially cured (B-staged) thermoset resin. The pre-impregnated filaments are thus pre-coated with resin and are usually stored at low temperature to stop the polymerization process of matrix material. The winding process, when carried out using pre-impregnated filaments is thus referred to as dry winding, as compared to wet winding or direct impregnation, where the filaments are coated with liquid resin just before application, i.e. within the component production process. For the polar rovings formed with the narrow angle 0 to 3°, the use of partially cured thermoset resin is preferred for its higher tack.

[0014] Accordingly, the term resin-coated filaments herein covers both wet coated filaments (coated with liquid matrix during component production process) and dry coated filaments, i.e. pre-impregnated filaments.

[0015] As used herein, the term filaments, or also filament roving, refers to a long (or endless, continuous) and narrow bundle of filaments used in the filament winding technique. In the context of the present disclosure, the filaments (or filament rovings) are thus understood as any appropriate type of long / endless / continuous strand of filament, fibers or wire, e.g. in the form of roving or yarns.

[0016] The term "winding a plurality of resin-coated filaments" should be understood applying filament roving by the technique of filament winding (either via wet or dry process-as the case may be) to form windings. As is known, in practice, the processing apparatus can be configured to work with one or several filament bundles at a time. In such case, the filament bundles are laid contiguous to one another, forming a tape of increased width, and hence reducing the production time.

[0017] As used herein, the term "winding" conventionally refers to a single turn of filament, i.e. of reinforcing tape or filament tape, around the liner.

[0018] The term "set" of windings is used to designate a plurality of windings made with a same winding pattern/angle.

[0019] The term "winding angle" defines the angle between the longitudinal axis of the gas tank and the projection of the filaments/tape onto the longitudinal plane.

[0020] In practice, a set of circumferential windings or polar windings comprises a multitude of windings, which are arranged in several layers or plies. A layer is typically defined as a single thickness of windings arranged next to one another so as to cover the layer underneath it. The windings may be formed by wrapping contiguous windings (adjacent windings touch each-other or overlap) or allowing some spacing between them. The entire surface of the gas tank may be covered by a plurality of layers of resin-coated filaments. In particular, circumferential windings are generally applied to cover the entire surface of the cylindrical portion of the liner, and may optionally cover the base of the rounded portions.

[0021] In practice, one winding may be consist of a single filament roving, or a plurality of filament rovings. In the latter case the filaments rovings are laid flat next to one another, and thus the term tape refers to this group of filament rovings.

[0022] In embodiments, the individual filament rovings may have a with between 2 and 10 mm. A given winding may be formed by applying / winding one roving at a time, or a plurality of filaments roving at a time, forming a tape where the filaments are arranged adjacent to one another to increase the width of the winding. For example the winding may comprise/consist of 3 or 4 filament rovings. If the tank is manufactured with, e.g. three filament rovings of 5 mm, then the resulting tape has a width of 3*5 = 15 mm.

[0023] The polar windings extend from one axial end to another over the cylindrical portion, and covering the rounded end portions. They are generally applied to cover the entire surfaces of the rounded end portions.

[0024] In embodiments, a first set of polar windings is applied with a winding angle comprised between 10° and 20°. Most preferably, the first set is the only set of polar windings having a winding angle greater than 3°. In the present text, the first set of polar windings is to be understood as the first set of polar windings applied in manufacturing order, hence closest to the liner. This first set of polar windings is applied with a larger winding angle than the other polar windings, to cover the outer surface of the liner which is conventionally smoother and provides less adherence than resin-coated filaments. In other words, the first set of polar windings is realized at greater winding angle, which is easier and safer, and provides an underlying surface of enhanced adhesion for the windings that will be laid thereon. A second set of polar windings with a winding angle of 0 to 3° is then preferably directly applied onto this first set of polar windings.

[0025] According to the same or other embodiments, a first set of circumferential windings is directly applied to the liner (i.e. before any other filament roving). In preferred embodiments, winding of the first set of polar windings starts from the middle of the cylindrical portion of the liner, so as to ensure a sufficient contact between resin-coated filaments of the first set of circumferential windings and first set of polar windings, thereby preventing sliding/slipping of the polar windings on the rounded portions of the liner.

[0026] Preferably, the outermost layer of the shell is a set of circumferential windings radially surrounds all previous polar and circumferential windings along the cylindrical liner portion. Such a set of circumferential windings advantageously compress the polar windings around the cylindrical portion of the liner.

[0027] In embodiments, the shell comprises the above first set of circumferential windings followed by the first and second sets of polar windings, and finishes with an outermost layer of circumferential windings. In between, there may be an alternance of sets of circumferential windings with winding angle 80 to 90° and polar windings with angle 0 to 3°. The number of such sets and their respective thickness can be adjusted depending on the application by those skilled in the ad.

[0028] In embodiments, wherein the forming step b) comprises: applying (S2) a first set of circumferential windings onto the liner, said circumferential windings having a winding angle comprised between 80° and 90°; applying (S3) a first plurality of polar windings around the liner onto the first set of circumferential windings, the polar windings having a winding angle comprised between 10 and 20°; applying (S4) a second plurality of polar windings with a winding angle comprised between 0 and 3° around the liner onto the first plurality of the polar windings; applying (S5) a second set of circumferential windings with a winding angle comprised between 80° and 90° around the liner onto the second plurality of polar windings; applying (S6) a third plurality of polar windings with a winding angle comprised between 0 and 3°around the liner onto the second set of circumferential windings; and applying (S7) a third set of circumferential windings with a winding angle comprised between 80° and 90° around the liner onto the third plurality of polar windings.

[0029] Generally, the composite shell may be devoid of filament windings having a winding angle comprised between 21 and 79°. In other words, the composite shell is exclusively formed from polar windings, wherein a majority (i.e. 80% or more) of the polar windings have a winding angle comprised between 0 and 3°, while a minority (i.e. less than 20%) of the polar windings have a winding angle greater than 3°, and from circumferential windings with a winding angle comprised between 80 and 90°. It has indeed been found that by using the herein prescribed circumferential and polar windings, a composite reinforcement of sufficient strength can be obtained, without the need for windings in complimentary directions, such as conventional helicoidal windings with a winding angle between 30 and 79°, and also without the need for windings with a winding angle between 21 and 30°. This provides a significant reduction in terms of cost and production time. For an identical liner, using the winding configuration according to the invention enables a reduction of thickness for the composite shell of at least 20% and possibly up to 40%, drastically reducing its weight, when compared to conventional gas tanks for a given mechanical strength.

[0030] The filaments may be made from any continuous fiber like material, for example from carbon, glass, basalt, aramid, polyethylene or any other reinforcement fiber. The reinforcing fibers add strength and stiffness to a part along the direction of the fiber length. The fibers are preferably continuous or near continuous in length and are preferably aligned substantially parallel to one another.

[0031] In embodiments, the fibers are carbon fibers of the High-Modulus (HM) or High-Resistance (HR) type, with a tensile modulus comprised between 200 and 600 GPa and a tensile strength between 3000 and 5000 or 6000 MPa.

[0032] The thermoset resin may be an epoxy or unsaturated polyester or polyurethane.

[0033] As with most polymer composite applications, the specific resin and fibers used and their composition may be selected by the skilled person depending on the application and properties of the composite shell to be manufactured.

[0034] In embodiments, the pre-impregnated filaments have a filament/fiber content between 60 and 70 wt.%, including all values within the range, in particular integer values between 60 and 70 wt.%.

[0035] The filament rovings can be of almost any shape, for example band shape or wave shape. Preferably, the rovings are in a band or tape shape. In particular, the tape may be formed by as a continuous or nearly continuous bundle of untwisted fibers.

[0036] Generally, the liner is formed as an elongate vessel, having a cylindrical middle portion closed at both ends by a rounded end portion. The liner may be metallic or plastic. An opening is provided to allow gas to flow into/from the chamber defined by the liner, typically in one of the end portions. In embodiments each end portion comprises an opening fitted with a boss. Since the composite is applied directly onto the liner, it will have a similar shape. The liner can be manufactured using conventional techniques (e.g. by extrusion), where the end portion are fixed in a gas-tight manner (e.g. by wielding) to the middle cylindrical portion. Alternatively, the liner may be manufactured by additive manufacturing.

[0037] In embodiments, the gas tank further comprises at least one boss configured to define a gas passage through the liner and the composite shell, said boss being arranged on a rounded portion, preferably at an apex thereof. The width of the polar windings may then be selected in accordance with the dimensions of the rounded portion and the boss.

[0038] The present invention has been particularly developed for the manufacture of gas tanks for compressed fuel gas, in particular hydrogen, but also CNG or other fuel gas, with nominal pressures of up to 700 bar.

[0039] In general, the tank may comprise a liner with an outer diameter between 150 and 600 mm. The overall length of the gas tank may range from 0.5 to 3.0 m.

[0040] In the context of the invention, the friction coefficient of a given pre-impregnated filament roving represents the friction between two such pre-impregnated filaments. The friction coefficient is advantageously determined as follows: preparing a test sample by arranging two samples of pre-impregnated filament roving of predetermined length L=200 mm and width W=6 mm, one above the other such that they overlap over a predetermined distance of 100 mm (over the entire width), and applying a load with a mass of 2 kg, preferably uniformly, over the overlapping region, for a period of 30 s. Then submitting the test sample to a tensile test and determining a tangential force Fr as the maximum of the resulting force-displacement plot. The friction coefficient is then calculated as the ratio of the tangential force Fr over normal load (here 19.62 N). The test is a carried out with the pre-impregnated filament roving being at ambient temperature, preferably at 20°C, but can be in the range 20 to 25°C as this temperature range is considered to give similar results.

[0041] These and other embodiments of the present method are also recited in the appended dependents claims 2 to 9. The invention also concerns a gas tank as claimed in claim 10, with embodiments thereof recited in claims 11 to 20. Features and related advantages described in relation to the method are likewise applicable to the corresponding gas tank, and vice versa.

Brief Description of the Drawings

[0042] A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic diagram representing a cross section of a typical type III or type IV gas tank; Fig. 2 is a schematic diagram representing a side view of the type III or type IV gas tank of fig 1; Fig. 3 is a schematic diagram representing a side view of a type III or type IV gas tank according to the invention; Fig. 4 is a flowchart of the method for manufacturing a type III or type IV gas tank according to the invention; and Fig. 5 is a schematic diagram representing the method for measuring a frictional coefficient of filament bundles pre-impregnated with resin; Fig.6 is a traction test Force-Displacement performed to determine the tangential force FT of a test sample.

Description of Preferred Embodiments

[0043] The schematic diagrams of figures 1 and 2 illustrate a type III or type IV hydrogen tank 1 of conventional design, having a spherocylindrical shape and comprising a spherocylindrical liner 3 surrounded by a spherocylindrical composite shell 5. The composite shell 5 is applied directly on the liner 3. The liner 3 is hollow and defines a chamber 7 in its inner volume.

[0044] The liner 3 is relatively thin with a thickness ti and can be made from any appropriate metal for a type III tank, e.g. aluminum, aluminum alloys, steel, stainless steel, titanium and/or titanium alloys, nickel-based alloys, etc., or from any appropriate polymer for a type IV tank. The liner is typically formed as a spherocylinder, i.e. a cylinder with domes sealingly attached at the ends thereof. At least one of the domes is provided with an opening in which a boss is fixed, here both domes as shown on figure 2. Such a spherocylinder can be manufactured by deep extrusion. Alternately the liner may be manufactured in one piece (cylinder + end domes) by additive manufacturing. These are only examples of liner construction and shall not be construed as limiting.

[0045] As is known, the function of the liner 3 is mainly to fluidly seal the volume of the chamber 7 from the atmosphere, i.e. it defines a fluid-tight volume. The liner 3, due to its low thickness t1, is by itself not meant to bear the load generated by the high pressures within the chamber 7. Instead, the liner 3 is closely surrounded by the composite shell 5 of comparatively larger thickness t2, which bears the vast majority of the mechanical load generated by the pressure inside the chamber 7.

[0046] The composite shell is best seen on the schematic diagram of figure 2, which illustrates a side view of the tank of figure 1. As it can be seen, the gas tank comprises a cylindrical portion 12 and two rounded portions 14 at the bases thereof. Here the rounded portions 14 have a quasi-hemispherical shape (e.g. elliptical or isotensoid), at least for the outer surface. The overall shape of the gas tank is thus similar to that of a capsule. The composite shell 5 is typically formed by winding/wrapping filament rovings around the liner. Conventionally, the fiber rovings are coated in situ with a liquid matrix material (wet winding), before the fiber rovings are wound onto the liner, resp. layers of fiber rovings.

[0047] As previously mentioned, the mechanical strength of the composite shell 5 largely depends on the configuration of its windings, in particular on the winding angle (i.e. the angle between the longitudinal axis of the gas tank and the projection of the filaments onto the longitudinal plane) of each winding. A winding is generally defined as a single turn of a wound material (here the filament tape) around an object (here the liner). According to typical prior art designs, the shell includes three types of windings (shown on figure 2): polar windings 18 with winding angle op and width wp, circumferential windings 20 with winding angle cc and width wc, and helical windings 22 with winding angle OH and width wH. For the sake of clarity, only a single winding of each type is shown on figure 2, but composite shells normally comprise a multitude of such windings. Polar windings 18 conventionally follow a geodesic path having a single winding angle op around the liner. In other words, the winding angle op of polar windings is typically constant along their length.

[0048] Generally, in conventional processes, the winding process follows a sequence, whereby a set of polar windings is wound around the liner, followed by a set of helicoidal windings which maintain the polar windings in place, itself followed by a set of circumferential windings. This sequence is then repeated until the desired number of filaments has been wound around the liner, at which point the resin is cured.

<Invention> [0049] The present invention proposes a new design approach, wherein the composite shell comprises polar windings having a winding angle api comprised between 0 and 3°.

[0050] The winding angle api is shown in Fig.3 and by definition represents the angle between the longitudinal axis X of the gas tank and the projection of the polar filaments/tape 18 onto the longitudinal plane (in Fig. 3, the plane containing axis X and parallel to the plane of the Figure).

[0051] The inventive gas tank 10 is show in Fig.3, comprising a composite shell 5 with polar and circumferential windings 18, 20. The liner design is similar to that described in reference to Figs.1 and 2, comprising a cylindrical portion 12 closed by two rounded portions 14. The liner may be metallic or plastic.

[0052] As shown on figure 3, in the present design, the polar windings 18 follow a geodesic path having a single winding angle api, ap2 on the entire surface of the gas tank. A majority (i.e. at least 80% or at least 90%, in terms of number of polar windings/turns) of the polar windings have a winding angle api comprised between 0 and 3°. A minority of polar windings (preferably only the windings of the first set of polar windings) may have a winding angle ap2 greater than 3°, such as e.g. between 10 and 20°. The winding angle ap2 of the first set of polar windings is selected to prevent/limit filament slipping upon direct contact with the outer surface of the liner. So, considering the total number of polar windings within shell, more than 80% of the polar windings are applied with winding angle api.

[0053] As will be appreciated by those skilled in the art, a main difficulty of manufacturing a composite shell with polar windings having such a small winding angle is that, during component manufacturing, the filaments tend to slip, more particularly on the rounded ends, making the wiring impossible or improper due to local defects and deformities that lower the overall mechanical strength of the composite shell.

[0054] In this context, the inventors have found that by using pre-impregnated filaments having a friction coefficient of between 0.5 and 0.9 for polar windings 18, it is possible to decrease the winding angle api for a majority of polar windings, thereby improving the mechanical strength of the composite shell whilst reducing its overall weight. More specifically, the inventors have found that, by increasing the friction coefficient of the filament bundle of resin-coated fibers, it is possible to prevent slipping of the windings on the liner during manufacturing. In particular, the inventors have found that using polar windings with the prescribed winding angle and friction coefficient, it is possible to achieve a given mechanical strength with a composite shell thickness reduction of at least 20% when compared to the traditional winding configuration of figure 2.

[0055] It may be noted that the polar and circumferential windings can use same/similar or different filaments. The filaments may be made of e.g. glass (type E, S or other), carbon, polymeric material (polyamide such as aramid, polyethylene, or other), natural materials etc. In embodiments, the fibers are carbon fibers of the High-Modulus (HM) or High-Resistance (HR) type, with a tensile modulus comprised between 200 and 600 GPa and a tensile strength between 3000 and 6000 MPa. Filaments are typically arranged parallel to each other as a continuous, untwisted bundle/tape.

[0056] Figure 4 is a flowchart representing an embodiment of the method for manufacturing a gas tank according to the present disclosure.

[0057] In an initial step S1, a thin liner defining a chamber for pressurized hydrogen is provided. A plurality of circumferential windings 20 is then performed S2 by winding a resin-coated filament roving(s) around the liner, thereby forming a first set of circumferential windings, each circumferential winding having a winding angle ac comprised between 80 and 90°.

[0058] Subsequently, a first plurality of polar windings 18 is performed S3 by winding resin-coated filament roving(s) around the first set of circumferential windings, thereby forming a first set of polar windings, each polar winding having a winding angle ap2 comprised between 10 and 20°.

[0059] A second plurality of polar windings 18 is then formed S4 by winding a resin-coated filament roving(s) around said first set of polar windings, thereby forming a second set of polar windings, each polar winding having a winding angle api comprised between 0 and 3°.

[0060] Next, a second plurality of circumferential windings 20 is formed S5 by winding a resin-coated filament roving(s)around the set of polar windings formed in S4, thereby forming a second set of circumferential windings, each circumferential winding having a winding angle ac comprised between 80 and 90°.

[0061] A third plurality of polar windings 18 is then formed S6 by winding filament roving(s) around the second set of circumferential windings (S5), thereby forming a third set of polar windings, each polar winding having a winding angle am comprised between 0 and 3°.

[0062] A further plurality of circumferential windings 20 is then formed S7 by winding a filament roving(s) around the set of polar windings formed in S6, thereby forming a third set of circumferential windings, each circumferential winding having a winding angle ac comprised between 80 and 90°.

[0063] Once all windings performed, the component is subject to hardening or curing, i.e. to allow full polymerization of the resin, S8.

[0064] As indicated above, the polar windings 18 with the winding angle api (step S4) are realized using pre-impregnated filaments having a friction coefficient p between 0.5 and 0.9.

[0065] As discussed herein above, so-called pre-impregnated filaments are filament bundles impregnated with a matrix material (e.g. thermoplastic material or a partially cured (B-staged) thermoset resin) in a preliminary process, forming a semi-finished product. Such pre-impregnated filaments are usually known as TowPreg. Accordingly, the manufacture of such TowPregs will not be further discussed herein. Those skilled in the art will know how to select the matrix material in view of adjusting the friction coefficient (tack).

[0066] In the following, the term pre-impregnated filaments and TowPreg are used interchangeably / synonymously.

[0067] Referring to the filament winding, any appropriate machines and techniques may be employed. As understood, the polar windings with narrow angle are (0 to 3°) are formed using TowPreg with the prescribed friction coefficient.

[0068] As is understood, TowPreg with the prescribed friction coefficient is desired to form the polar windings with winding angle api comprised between 0 and 3°. The other windings could be by wet winding to reduce manufacturing costs. However, for ease of implementation, all windings may advantageously be formed using pre-impregnated filament rovings. For the polar windings, TowPreg having the prescribed friction coefficient between 0.5 and 0.9 is used. For the circumferential windings, the same can be used, but TowPreg with lower friction coefficient can also be used, in particular lower than 0.4, which may be as low as between 0.05 and 0.10.

[0069] That is, steps S3, S4 and S6 are formed with TowPreg having the prescribed friction coefficient between 0.5 and 0.9. Steps S2, S5 and S7 are performed with same TowPreg or rather Towpreg having lower friction coefficient.

[0070] In embodiments, the outermost circumferential winding (step S7) may be formed using TowPreg comprising a thermoplastic matrix rather than thermosetting resin, to facilitate component recycling.

[0071] For improved adherence, during winding of the TowPreg to form the polar windings with winding angle comprised between 0 and 3°, a radial force is applied onto the pre-impregnated filaments as the TowPreg is laid onto the liner over underlying windings. This radial force is of about 20 N, or could be greater [0072] The number of polar and circumferential windings is typically determined by design, depending on the desired mechanical properties.

Accordingly, the respective thickness of the polar and circumferential windings depends on the application, mainly governed by mechanical strength.

[0073] Preferably, the TowPreg is subject to heating during the shell manufacturing, in order to bring the TowPreg to ambient temperature and exhibit the prescribed (tack). Indeed, in practice TowPreg is typically stored cool, to avoid matrix polymerization. Such pre-heating is conveniently achieved by means of a laser source or other heat source, or by allowing the spools to heat up at ambient T° before winding. In some embodiments, the TowPreg may be heated above ambient temperature. Such heating, preheating or warning is conventional in dry winding with towpreg.

Measure of the friction coefficient [0074] A method for measuring the friction coefficient pre-impreganted filaments/TowPreg will now be disclosed. Two samples of TowPreg 111, 112 having a width Wr of 6 mm and a length LT of 20 cm are cut from the TowPreg spool 100 and are arranged in an overlaying manner with an overlap length OL of 10 cm over their whole width WT so as to obtain a test sample. This assembly or overlaying of the two TowPreg samples is done with the TowPreg samples being at ambient temperature, i.e. 20°C. The entire test is carried out at ambient temperature (in the range 20 to 25°C).

[0075] The test sample is laid on a horizontal surface and a normal load, noted LoadN, of 19.62 N is applied during 30 seconds to the overlapping section using a 2 kg weight 114. A plastic plate 116 or any other covering having the dimensions of the overlapping section may be provided between the overlapping section and the weight so as distribute the load i.e. exert a homogeneous force over the overlapping section between the two samples 111, 112 of tape.

[0076] After 30 s, the weight 114 is then removed and the test sample is placed in a tensile test machine to perform a tensile test, wherein the corresponding force-displacement plot (graph) is recorded. A tangential force is determined from the force-displacement plot as being the force FT just before separation of the two samples: this is the maximum force reached during the test. An exemplary force-displacement plot obtained from such test sample is shown in Fig.6, where FT is indicated.

[0077] The tensile tests were carried out in a tensile test machine model where the test sample was placed between grips, which were moved apart at a displacement speed of 5 mm/min. The tensile test machine was equipped with a force sensor having a sensitivity of up to 25 N (i.e. max. force).

[0078] The friction coefficient, noted p, is then calculated as follows:

FT

k LoadN [0079] As previously mentioned, traditional composite shell manufacturing typically repeats an ordered sequence of polar, helicoidal, and radial windings. Such methods require reorienting the filament tape about the liner each time a different winding pattern is performed. In contrast, the inventive method provides a manufacturing process for a gas tank, whereby all polar windings are consecutively performed before all circumferential windings, and whereby no helicoidal winding is performed. The inventive method therefore requires far fewer reorientation of the filament tape about the liner, thereby reducing manufacturing time.

[0080] <Exemplary application> [0081] The conventional design is here compared to the present design for a type III or type IV tank with a nominal working pressure of 700 bar.

Prior art Invention

Liner outer diameter 500 mm 500 mm Circumferential winding 17 mm 14.5 mm total thickness Polar winding total 18 mm 14.5 mm thickness [0082] The tank according to the inventive design has thinner polar and circumferential windings but is able to operate at the same working pressure and burst pressure, hence meeting homologation test requirements. As can be seen, for a same liner, using the winding configuration according to the invention enables a reduction in thickness for the composite shell of about 20%, drastically reducing its weight.

Claims

Claims 1. Method for manufacturing a gas tank for the storage of pressurized fuel gas, the method comprising the steps of: a) providing a liner defining a chamber, said liner having a cylindrical portion s and two rounded portions at bases thereof; b) forming a composite shell by winding a plurality of resin-coated filaments around the liner, said winding including applying circumferential windings having a winding angle comprised between 80 and 90° and polar windings; characterized in that at least 80% of the polar windings are formed with a winding angle (apt) comprised between 0° and 3° using pre-impregnated filaments having a friction coefficient between 0.5 and 0.9.
2. Method according to claim 1, wherein the forming step b) comprises: b1) applying a first set of circumferential windings onto the liner, said circumferential windings having a winding angle comprised between 80° and 90°; b2) applying a plurality of polar windings around the liner onto the first set of circumferential windings, wherein at least 80% of the polar windings have a winding angle comprised between 0 and 3°; b3) finishing with a further set of circumferential windings around the previous polar and circumferential windings, said circumferential windings having a winding angle comprised between 80 and 90°; c) hardening the composite shell.
3. Method for manufacturing a gas tank according to claim 2, wherein step b2) involves applying a first set of polar windings having a winding angle (aP2) comprised between 10° and 20° onto the first set of circumferential windings and then applying at least one set of polar windings having a winding angle (cm) comprised between 0° and 3°.
4. Method for manufacturing a gas tank according to claim 1, wherein the forming step b) comprises: applying (S2) a first set of circumferential windings onto the liner, said circumferential windings having a winding angle comprised between 80° and 90°; applying (S3) a first plurality of polar windings around the liner onto the first set of circumferential windings, the polar windings having a winding angle comprised between 10 and 20°; applying (S4) a second plurality of polar windings with a winding angle comprised between 0 and 3° around the liner onto the first plurality of the polar windings; applying (S5) a second set of circumferential windings with a winding angle comprised between 80° and 90° around the liner onto the second plurality of polar windings; applying (S6) a third plurality of polar windings with a winding angle comprised between 0 and 3°around the liner onto the second set of circumferential windings; and applying (S7) a third set of circumferential windings with a winding angle comprised between 80° and 90° around the liner onto the third plurality of polar windings.
5. Method according to any of the preceding claims, wherein the circumferential windings are formed using pre-impregnated filaments, in particular having a friction coefficient below 0.5.
6. Method according to any of the preceding claims, wherein said pre-impregnated filaments are pre-heated before winding, such that when applied onto the liner, the pre-impregnated filaments are at ambient temperature or higher.
7. Method according to any of the preceding claims, wherein during winding of pre-impregnated filament to form the polar windings with winding angle comprised between 0 and 3°, a radial force is applied onto the pre-impregnated filaments as it is applied around the liner over underlying windings, said radial force being of 20 N or greater.
8. Method according to any of the preceding claims, wherein the filaments are coated, respectively impregnated with thermosetting resin, optionally excepted for the outermost circumferential winding that is coated/ impregnated with a thermoplastic matrix.
9. Method for manufacturing a gas tank according to any of the preceding claims, wherein the polar windings comprise filament rovings having a width comprised between 2 and 10 mm, and wherein the polar windings include of one or more filament rovings, in particular four filament rovings.
10.A gas tank for storage of pressurized fuel, comprising a liner defining a chamber for containing pressurized gas and a composite shell surrounding said liner; wherein the liner has a cylindrical portion and two rounded portions at bases thereof; wherein the composite shell is formed by a plurality of resin-coated filament windings, the plurality of filament windings including circumferential windings having a winding angle comprised between 80 and 90° and polar windings; characterized in that at least 80%, preferably at least 90%, of the polar windings have a winding angle (owl) comprised between 0° and 3°.
11. The gas tank according to claim 10, wherein the polar windings with a winding angle (am) comprised between 0° and 3° are formed using pre-impregnated filaments having a friction coefficient between 0.5 and 0.9.
12. The gas tank according to claim 10 or 11, wherein the polar windings include a plurality of sets of polar windings and wherein a first set of polar windings has a winding angle (ap2) comprised between 10° and 20°.
13. The gas tank according to claim 12, wherein the first set of polar windings is the only set of polar windings having a winding angle greater than 3°.
14. The gas tank according to any of claims 10 to 13, wherein the circumferential windings include a plurality of sets of circumferential windings and wherein a first set of circumferential windings is directly applied to the liner.
15. The gas tank according to any of claims 10 to 14, wherein said shell includes an outermost winding set that consists of circumferential windings.
16. The gas tank according to claim 10 or 11, wherein the shell comprises or consists of: a first set of circumferential windings onto the liner, said circumferential windings having a winding angle comprised between 80° and 90°; a first plurality of polar windings having a winding angle comprised between 10 and 20° having a winding angle comprised between 10 and 20 around the liner onto the first set of circumferential windings, a second plurality of polar windings with a winding angle comprised between 0 and 3° around the liner onto the first plurality of the polar windings; a second set of circumferential windings with a winding angle comprised between 80° and 90° around the liner onto the second plurality of polar windings; a third plurality of polar windings with a winding angle comprised between 0 and 3°around the liner onto the second set of circumferential windings; and a third set of circumferential windings with a winding angle comprised between 80° and 90° around the liner onto the third plurality of polar windings.
17. The gas tank according to any of claims 10 to 16, wherein the composite shell is devoid of filament windings having a winding angle comprised between 21° and 790.
18. The gas tank according to any of claims 10 to 17, further comprising at least one boss configured to define a gas passage through the liner and the composite shell, said boss being arranged on a rounded portion, preferably an apex thereof.
19. The gas tank according to any of claims 10 to 18, wherein the polar and/or circumferential windings include filament rovings having a width comprised between 2 and 10 mm.
20. The gas tank according to claim 19, wherein the polar and/or circumferential windings are formed by applying two or more filament rovings, whereby the polar or circumferential windings have a width of up to 30 to 40 mm.