WO2011152733A1

WO2011152733A1 - Composite pressure container and method of manufacturing the same

Info

Publication number: WO2011152733A1
Application number: PCT/NO2010/000200
Authority: WO
Inventors: Rune Ulekleiv; Per Vidar Hamnvik
Original assignee: Ragasco As
Priority date: 2010-05-31
Filing date: 2010-05-31
Publication date: 2011-12-08

Abstract

The present invention concerns a light weight composite pressure container for fluids adapted to hold fluids under both high and low pressures, such as H₂, industrial gases, CNG (compressed natural gas) and LPG (liquefied petroleum gas), as well as a method of manufacturing the same.

Description

COMPOSITE PRESSURE CONTAINER AND METHOD OF MANUFACTURING THE SAME

Field of the invention

Pressure containers for fluids have been commonly known for many years, based on metal as construction material, in particular steel. These known containers, being to a large extent utilized by people during cabin and outdoor life, have the drawback of being heavy and accordingly difficult to handle. Moreover there is often a problem of knowing how much of the original contents which is still left in the bottle or container.

Because of the risk of explosion and accidents, many and strict requirements are imposed with respect to such pressure containers. Thus, the safety aspect is very essential in this connection.

In recent years there has been put on the market a pressure container of composite materials, as described in Norwegian Patent No. 306 226, and which is

manufactured according to the disclosure of Norwegian Patent No. 309 667. This known container is made in part of transparent or translucent materials, wherein these materials are of relatively light weight, such that some of the drawbacks mentioned above concerning pressure containers of steel, are eliminated. Another example of a solution wherein the pressure container has been

manufactured from composite materials is described in European patent No. 0 810 081 Al , including a method for manufacturing pressure containers, wherein an inner, gas impenetrable liner made of plastic first is blow moulded, and thereafter, an outer layer consisting of a fibre-reinforced plastic which has been soaked in a resin bath, is wound around the liner. However, the inner and the outer layers in this pressure container are not adhered in any other way, which leads to the formation of gas pockets between the layers. This involves a safety risk, as the gas pockets will expand, should under pressure occur inside the container, which may cause a collapse of the inner layer. Collapse of the inner liner layer may also occur due to service conditions, for example when evacuating the container, giving rise to under pressure inside the container, or when cooling, so that the temperature of the fluid becomes to low. The industry considers the generally low wetting and adhesive properties of plastic materials as a problem. Some of the reasons for this are that several plastic materials have chemical inert and non-porous surfaces, having low surface tensions. The wetting and adhesive properties of plastic materials may be increased for example by flame treatment or by corona discharge treatment. Flame treatment and corona discharge treatment are characterized in that plasma is generated, i.e., a very reactive gas comprising free electrons, positive ions and other chemical

components. The physical mechanisms are different, but their impact on the wetting and adhesive properties is similar. The free electrons, the positive ions, the meta- stabile components and the radicals, together with ultraviolet radiation (UV radiation) being generated in the plasma areas, may impact the surface with energies that are sufficient to break the molecule bonds on the surface of the polymer material. On the surface of the polymer material, very reactive free radicals are formed, which them selves may form chemical functional groups, cross-link to chemical functional groups, or rapidly react in the presence of oxygen so that functional groups are formed.

Polar functional groups which can increase the bonding property of the polymer material comprise among other carbonyl (-C=0), carboxyl (-COOH), hydroperoxide (-00H) and hydroxyl groups (-OH). US 5280084 discloses a similar method for increasing the surface energy and the hydrophilic properties of surfaces of polymer materials. Japanese patent No. JP 63215736 (abstract) and Japanese patent Nr. JP- 59093632 (abstract) relates to treatment methods for polymer materials for improvement of the surface properties of the material, but intended for completely different tasks than the present invention. WO 98/30646 describes a process for obtaining improved adhesion between the surfaces of two polymer compositions, and a product having several polymer layers. This object is manufactured according to the described process. Apparently, the term product is directed to films and sheets having several polymer layers, and not hollow objects as in the present invention. In claim 1 of the publication, three features of the process are indicated:

1) The polymer compositions are joined by means of corona discharge treatment,

2) the layers are in contact with each other during the plasma treatment, and

3) the electrical field passes through the adjacent surfaces of the polymer

compositions.

According to one embodiment of the present invention, corona discharge treatment may be part of the pre-treatment before joining of the inner liner layer and the outer, pressure supporting layer. In addition, the inner liner layer is not in contact with the outer fibre-reinforced, pressure supporting layer during the treatment step. US 4096013 describes a method for laminating two or more chemically different sheets using a method for laminating two or more chemically different sheets by alternating current electrical corona discharge in air, and an apparatus for laminating at least two chemically different sheets to form a laminate. Appearing from the specification, an object of the invention is that the joined sheets are free of adhesives or adhesive film layers. US 4415394 discloses an apparatus for adhering two or more layers by corona discharge treatment. The material is exposed to corona discharge treatment before products are manufactured, as opposed to the present invention, wherein the inner liner layer is a finished part before being treated so as to increase the wetting and adhesive properties.

According to WO 98/30646, US 4096013 and US 4415394, corona discharge treatment is utilised so as to increase the wetting and adhesive properties for the materials for adhering polymer layers. Manufacturing of films, foils and laminates of several polymer layers are described in these publications. None of these publications show that adhesives are employed between the polymer layers. Also, they do not show that an inner polymer layer / liner layer is rotated during the complete process. The present invention avoids the disadvantages mentioned above. By using a method for manufacturing a composite pressure container according to the present invention, a light weight, strong pressure container is possible to manufacture, appearing in one piece, and in addition being easy to handle, and being resistant to under-pressure inside the container.

The known pressure containers of composite materials, e.g., the container of the above-mentioned NO 306 226, can in contrast to traditional steel containers be manufactured in a rational and inexpensive way when the strict safety requirements are to be satisfied, while at the same time preventing damage and accidents as a result of mechanical stresses, such as shock and impact. In the manufacturing according to the above Norwegian patent specification, it is particularly

advantageous to produce the actual composite pressure container by first making an inner liner and then winding around it fibre -reinforced elements, for example glass fibre bands/ribbons or treads.

However, the prior art composite pressure containers are mainly adapted to hold fluids of relatively low pressures, and are adapted to hold gases like propane and butane.

Thus, there is an object of the present invention to provide a light weight composite pressure container for fluids adapted to hold fluids under both high and low pressures, and which container at the same time retains the advantages of the prior art composite pressure containers compared to traditional steel containers. This goal is achieved by the composite pressure container of the present invention. Summary of the invention

The present invention is related to a composite pressure container for fluids adapted to hold fluids under both high and low pressures, such as H₂, industrial gases, CNG and LNG, comprising an inner, fluid-tight liner layer (1) and a pressure supporting layer (2) formed by winding a continuous fibre ribbon onto the liner layer (1) after treatment of the outside of the inner layer (1), as well as an outer, protective casing (5,57,67),

wherein said layers (1,2) as known per se consist of transparent or translucent materials, wherein the overall thickness of the layers (1,2) is reduced by winding the fibre ribbon onto the liner layer (1) in a designed pattern to obtain maximum strength with the use of a minimum length of fibre ribbon, and that the casing (5,57,67) comprises a middle section (7,57,67) having surface portions

(7A,7B,7C,41-48, 51-53,61) being cut-away so that parts of the actual container (3), being located inside the casing (5,57,67), are visible from the outside, and that the casing has shock-absorbing properties.

The present invention also concerns a method for manufacturing a pressure container comprising an inner liner layer (1) of polymer material, such as

polyolefines or a similar material, and an outer, fibre-reinforced, pressure

supporting layer (2). The method is characterized in that, during rotation of the inner liner layer relative to treatment, employment, and/or winding equipment, treatment of the outer side of the inner liner layer so as to increase the wetting and adhesive properties of the polymer material, employment of adhesive onto the outer side of the inner liner layer and/or direct contact between the outer side of the inner liner layer and the inner side of the outer, fibre-reinforced, pressure supporting layer, for adhesion of the inner liner layer and the outer, fibre-reinforced, pressure supporting layer, and winding of the outer, fibre-reinforced, pressure supporting layer onto the inner liner layer, in designed pattern to obtain maximum strength with the use of a minimum length of fibre ribbon.

In a preferred embodiment, the treatment of outer side of the inner liner layer comprise flame treatment, but also corona discharge treatment, if desired, in combination with ozone treatment or a corresponding method for improvement of the wetting and adhesive properties of the polymer material may be used.

Detailed description of the invention In the following and above, the term "fluid" is meant to comprise a compound in both liquid form and in gas form. The term "in optical contact" is meant to describe the contact between two or more materials forming a layer, wherein the two or more materials are in optical contact when the layer formed by the two or more materials is transparent or translucent. The term "dome" with reference to the pressure container of the invention means the top and the bottom part of the inner liner layer (1) which is not cylindrical in shape, as compared to the middle section of the same.

The novel and specific features of the pressure container according to the invention is that it is adapted to not only hold fluids of relatively low pressures, such as propane and butane, but also fluids of high pressures, such as H₂, CNG and industrial gases. This is achieved by winding the continuous fibre ribbon onto the fluid-tight inner layer in a designed pattern to achieve maximum strength of the pressure container. The designed pattern winding also ensures that the overall thickness of the liner layer and the pressure supporting layer is kept at a minimum, giving an overall thickness which is reduced compared to the prior art pressure containers. This is achieved by winding the pressure supporting layer (2) onto the outside of the inner layer (1) in a different way compared to the prior art of

Norwegian Patent No. 309 667. In the prior art containers, the ribbon winded onto the inner layer was mainly focused on the cylindrical portion of the inner layer. In the present invention, the ribbon is winded onto the inner layer such that it also covers more of the dome shaped ends of the inner layer, ensuring that the overall strength of the pressure container is increased. This pattern of winding the pressure- supporting layer (2) onto the outside of the inner layer (1) ensures that liquids of higher pressures could be stored in the container of the present invention, compared to the prior art containers.

The liner or inner layer can be manufactured by methods known per se, in particular blow-moulding as one piece or injection moulding in two or more parts to be assembled. The particular form of casing comprised by the invention can also be produced by injection moulding, possibly in two or three separate parts being then assembled into an integral structure. In this connection it is essential that the casing structure has shock-absorbent properties, provided for by a suitable choice of materials and/or the actual configuration of the casing.

The pressure container according to the invention, having a casing as stated above, has substantial advantages, in particular in consideration of two important factors with respect to this type of pressure containers, where there is involved a filling of a fluid in liquid phase, such as propane, to be delivered to a consumer appliance or for industrial purposes and the like upon vaporization in the pressure container. In order that a desired capacity is obtained in a use situation, it is important that the required heat of vaporization can be supplied from the environment. On the other hand and as already mentioned above, it is of much interest to the users to be able to observe the liquid level in the container, which is possible when this consists of transparent or translucent materials. The cut-away portions of the casing make it possible to observe the liquid level. Besides, these portions will involve a 'Venetian blind" effect, which in strong sun radiation prevents a too intense heating of the actual pressure container. It is more important however, that the configuration of the casing with the cut-away portions enable an air flow from the outside and over the actual container surface, so that the required heat can be supplied thereto for the varorization mentioned above. This latter and highly desirable effect will be particularly enhanced when at least the preferably cylindrical middle section of the casing, according to a preferred embodiment of the invention, is designed with spacer elements so as to form air flow passages between the container surface and the casing in general. In this connection it is a particular advantage when the air flow passages are adapted to extend in a generally vertical direction when the pressure container has a normal, standing position resting on the bottom and with the axis of the cylindrical section oriented substantially vertically. The pressure container according to the invention will be explained more closely in the following description with reference to the drawings, which illustrate exemplary embodiments based on the invention.

Fig. 1 in axial section shows a pressure container according to the invention, Fig. 2 shows the actual container in the example of Fig.1,

Fig. 3 in exploded perspective view shows three sections of the casing for the container in Fig. I,

Fig. 4 shows a cylindrical middle section of a casing for a larger (higher) pressure container than the one found in Figs. 1 and 2,

Fig. 5 shows another form of protective casing in elevation,

Fig. 6 in partial view shows a further embodiment of the protective casing,

Fig. 7 in partial cut-away elevation shows an advantageous design of a bottom section for the pressure container,

Fig. 8 at a smaller scale shows the bottom section in Fig. 7 as seen from above,

Fig. 9 in a corresponding manner as Fig. 8, shows a first alternative bottom section to the one in Fig. 8, Fig. 10 shows a second alternative bottom section,

Fig. 11 shows a third alternative design of a bottom section for the pressure container, and

Fig. 12 is an isometric view of an untreated, inner liner layer.

Fig. 13 shows an example of how the liner layer may be treated.

Fig. 14 shows winding of an outer, fibre-reinforced, pressure supporting layer,

Fig. 15 shows another embodiment of a pressure container according to the invention.

The actual container, which is manufactured for a desired volume capacity, in Figs. 1 and 2, is indicated with reference numeral 3. As illustrated in Fig. 1 the container 3 comprises an inner layer or liner 1 , in the first place adapted to be a fluid-tight layer so that the contents can not escape from the container, even when being under comparatively high pressure. Outside the liner 1 there is shown a reinforcing or pressure-supporting layer 2 being here provided by means of winding fibre reinforced elements, such as glass fibres or fibre ribbons to which there has been applied a suitable adhesive or the like, for subsequent curing in the form of a number of winding layers on the liner 1. There is here the question of

manufacturing steps and a choice of materials being known per se and without any need for closer explanation. In this connection it is obvious that the selected materials and material compositions in the layers 1 and 2, in a way known per se can provide a container 3 having transparent or translucent walls. This property is particularly desired in the cylindrical wall portions being usually incorporated in such containers. This however, does not exclude the possibility that e.g. purely spherical containers with transparent walls can be of interest in connection with the invention. A main shape with rotational symmetry is clearly preferred. Quite in general in Fig. 2 at 4 there are shown parts incorporated in a mounting arrangement for a valve or the like, at an opening on top of container 3. See also Fig. 1 in this connection. These parts of the structure however, are only of subordinate interest in connection with the present invention, and will not be discussed further here. Of particular interest however, in this connection is the surrounding casing, which according to the above explanations, has a particular combination of functions.

As will appear from Figs. 1 and 3, the casing 5 shown, comprises a middle section 7 being preferably of a generally cylindrical shape, a top section 8 and a bottom section 9. As indicated in Fig. 3 these three sections can be produced separately and then be assembled into a more or less integrated, total structure constituting the casing 5. As an alternative sections 7 and 9 can be manufactured integrally as one piece, e.g. by injection moulding, and subsequently be joined to the top section 8 when the actual container 3 has been put into the middle section 7. Another alternative consists in producing sections 7 and 8 integrated as one piece, with subsequent joining to the bottom section 9. Taking into account, inter alia, a rational production, the casing can also as a whole in its basic shape deviate more or less from the basic shape of the container within it. The middle section 7 is built up by a number of ribbon like elements of which two are indicated at 7E and 7F, extending around the whole circumference of section 7 and having a spacing in axial direction, as indicated e.g. at 7A, 7B and 7C. These spaces form the cut-away surface portions mentioned above, that make it possible to observe parts of the actual container 3 inside the casing, in particular for the purpose of seeing the liquid level in the container. In this connection it can be an advantage when the cut-away portions or spaces 7A, 7B and 7C have a substantially larger dimension in the lateral direction than in the height direction.

This design is also favourable in view of the Venetian blind effect mentioned above, i.e. a shading effect against undesired solar heating. So as to form an integral and strong structure in the middle section 7, there is in addition to the ribbon elements around the circumference, also provided longitudinal elements as shown e.g. at 11 and 12, forming in this example a rectangular, cross- wise pattern of the ribbon elements. It is clear that the configuration of pattern or elements forming the middle section 7 of the casing can be varied within wide limits while maintaining the effect described, on the basis of cut-away surface portions. These can be more or less elongate and can extend in different directions, also at an inclination. Oval and circular open portions can also be contemplated. The proportion of the total surface of the middle section representing the cut-away surface portions can vary a good deal in relation to what is seen from the example of Fig. 1 and 3. It is preferred however, that the cut-away portions constitute a relatively significant proportion of the total surface. It has been found that the proportion of cut-away surface portions should be at least 20% of the total exterior surface of the casing. On the inside of middle section 7 there is provided a number of projections, ribs or webs adapted to form relatively wide air gaps between the outer surface of container 3 and the main parts of the adjacent casing. Such ribs or webs are shown at 14 and 15 in Fig. 1, and an additional example is illustrated at 16 in Fig. 3. As will appear from this figure there is a relatively high number of such projecting ribs around the whole

circumference interiorly of middle section 7. In this way there are formed air gaps that make possible air flows, in particular in vertical direction as indicated with arrow 20 in Fig. 1. This solution as also seen in association with the cut-away portions 7A, 7B and 7C in Fig. 1 , is highly advantageous in view of the desired vaporization effect, at the same time as the air through flow in the case of undesired intense solar heating, has the effect of maintaining a lower and acceptable surface temperature on container 3. It is obvious that spacer elements in the form of projections, ribs or webs as discussed above, can be provided for in different manners and at various locations interiorly of middle section 7.

In order that the spacer elements shall also have a resilient and shock-absorbing effect in relation to container 3, they can be adapted to be deformed preferably elastically when there is a tendency to small relative movements between the casing and the container, i.e. movements or stresses mainly normal to the major surfaces. Such a resilient structure can also be useful in the case of expansion of container 3, e.g. during filling to a certain overpressure, or in the case of different heat expansion of the container and the casing 7 during temperature changes. It is obvious that such resilient spacer elements can have their effect based on other mechanisms than bending as mentioned, e.g. in that the element material as such yields, or by some form of break mechanism, possibly with a resulting permanent deformation. Elastically resilient spacer elements as discussed above, can also serve to accommodate or even out dimension variations in containers 3 as produced, and besides they can have a useful effect for load distribution so that reaction forces between casing and container will be distributed over a larger surface area on the basis of contact or engagement that in principle can have a linear form. This latter effect will be present on condition that the spacer elements are provided and distributed at such a number and with such length that a regular distribution of the load or stresses as mentioned, will be attained.

When looking at the top section 8 in Figs. 1 and 3, it will be seen that at the lower portion thereof there is an edge 18 around the circumference, intended for cooperation with and joining to the top of section 7. At the upper part of top section 8 there is shown a relatively strong ring 8A which e.g. forms a practical and convenient handgrip for lifting and manipulating the pressure container as a whole. From handgrip 8A there is shown a deep cut-out portion 8B which permits a convenient leading out of e.g. a propane hose from a connector and valve device (not shown) on top of the actual container 3. This top area of container 3 with components 4 (Fig. 2) are freely accessible from above through a top opening 8D in top section 8.

Finally Fig. 3 also shows at the interior of top section 8, a number of radial ribs or webs 8C adapted to engage the upper side of container 3 when the whole pressure container is assembled. Ribs 8C like the spacer elements described above can have an effect both for the desired air flow as for shock-absorbing and compensation for expansion, as explained above. As far as bottom section 9 is concerned, this has also an upwardly directed edge or the like 19 for joining to the lower circumference of middle section 7. Bottom section 9 has a central opening 9A making possible inspection of the bottom of container 3 after assembly, whereby the profiled shape of the bottom portion of bottom section 9 brings opening 9A to be located somewhat elevated in relation to the downwardly facing supporting surface of bottom section 9. As known per se the underside of bottom section 9 and the top of top section 8, in particular handgrip 8A, are so mutually adapted and designed that pressure containers can be stacked on top of each other. The profiled form of the bottom as mentioned, has a wavy shape as shown at 9B and 9C in Figs. 1 and 3, forming rings in a bellows-like bottom portion or supporting member which has a certain degree of resiliency, and thus has a shock-absorbing effect in relation to the bottom of container 3. As will appear in particular from bottom section 9 in Fig. 3, this has a recess 9E being open laterally at a portion of the circumference, so that there is provided a suitable handgrip, obtained in particular in view of the spacer elements, which means that this circumferencial portion below edge 19 will lie at a certain distance from the adjacent container surface.

The above described sectional subdivision of the whole casing 5, enables a very rational production of the complete pressure container. In particular it is

advantageous that the cylindrical middle section 7 can be manufactured with different, selected height dimensions for corresponding pressure containers of various capacities. Whereas e.g. the embodiment of Fig. 1 , 2 and 3 can be suitable for gas bottles with contents of maximum 6 kg, there is in Fig. 4 shown a middle section 27 intended for a gas bottle of maximum capacity 11 kg. Section 27 in Fig. 4 is composed of quite corresponding elements as section 7 in Fig. 3, but the number of ribbon elements 31-38 is approximately doubled. The corresponding gaps or cut-away portions are denoted 41-48 in Fig. 4. Moreover in compliance with the embodiment described above, the example of Fig. 4 has longitudinal, bracing elements as shown at 21 and 22. Finally in the interior of section 27 there is shown a rib shaped spacer element 26, as one of several such elements around the internal circumference of section 27.

Fig. 5 in a simplified way shows another embodiment of a casing for the pressure container according to the invention, more specifically a middle section 57 for such a casing. There is here the question of a generally cylindrical middle section 57 being provided with a number of substantially axially extended cut-away surface portions, whereby three such portions 51, 52 and 53 are indicated in the figure. It is obvious that a larger number of such cutaway portions can be distributed around the whole circumference of middle section 57. Thus, portions 51, 52 and 53 here have a relatively slit-like shape, being distinguished from the surface pattern of Figs. 3 and 4 in that the slit or gap portions extend generally in the axial direction instead of the circumferencial direction. In both cases the Venetian blind effect referred to above will be obtained, and the same applies to the effect on the air flow between the casing and a container inside it.

A particular variant of cut-away surface portions is illustrated in Fig. 6, which shows only a partial segment of a middle section 67 in a corresponding perspective view as Fig. 5. At 63 in Fig. 6 there is indicated how an upper part of the actual container will be located in relation to the casing middle section 67. At 61 there is indicated a recess or opening that in itself alone has a relatively small extension, but with a quite high number of such openings or cut-away portions, being located at a quite small spacing, there is provided a total through- flow area that can have the same effect as the gaps or openings in Fig. 3 and Fig.5, respectively. With an arrangement or pattern of openings 61 as in Fig. 6, each of these or groups in combination can represent letters or other characters, or possibly a logo being a company symbol or a trademark. This may then indicate the manufacturer or distributor of the pressure container. Irrespective of the type of openings shown, it can be an advantage to employ a float device for clearly indicating a liquid level in the container.

A further modification, relating to the bottom section, is illustrated in Fig. 7. In contrast to the bellows-like bottom section in Figs. 1 and 3, the one in Fig. 7 has a number of rib-like spacer elements, three such elements 71, 72 and 73 being specifically indicated in the interior of bottom section 79 in Fig. 7. Like the spacer elements described above, also these elements 71, 72 and 73 and so forth, will have a favourable effect both on the air flow and with respect to shock-absorbing, heat expansion and dimensional tolerances in the actual container and the casing. In Fig. 7 it is to be noted specifically that spacer elements 71, 72, 73 and so forth, have a certain inclination so that they form an angle to adjacent surface portions of the actual container 77, this angle being different from 90°. Such an inclination implies that the elements so to speak are prepared for a deformation by flexing, namely to a more bent inclination upon presence of sufficiently high stress or forces from container 77. Of course a quite corresponding effect will be present with spacer elements extending further upwards along container 77, in a middle section of the casing, or also in a top section. Fig. 8 shows a complete arrangement of such elements 71, 72, 73 and so forth, in bottom section 79, being here seen from above. There is also seen a relatively large central opening 75 where the radially inner ends of the spacer elements are located. The bottom of container 77 will be accessible through such an opening 75, but it is obvious that this does not necessarily have to be provided, since a substantially complete, cover or bottom design can be incorporated in bottom section 79. Such a tight bottom will be able to protect the actual container 77 in a better way against damage from below, but nevertheless can be provided with smaller holes or perforations, e.g. for draining out water. An alternative embodiment of the bottom structure with associated spacer elements is shown in Fig. 9. From the

circumference of the bottom section 99 shown therein, plate shaped elements are extended to be tangent to a central opening 95 similar to opening 75 in Fig. 8. One such element is indicated at 91. With such an arrangement the spacer elements will have an inherent inclination in relation to the bottom itself, or possibly the top, of an inserted container, so that a corresponding effect as discussed above with reference to Figs. 7 and 8 will be obtained. In Fig. 9 there is also at 97 indicated an outer circumference of a more or less cylindrical part of the actual container, and at this part the elements 91 can be extended axially but with a relatively short length as shown at 91 A, from the inside of the casing corresponding to contour 99, for contacting the outside of the actual container 97. The inclination of the element length or piece 91 A is clearly shown in this figure of drawings. Figs. 10 and 1 1 are in particular directed to arrangements of spacer elements in the bottom section, in the principle by locating a number of such elements in an arcuate or circular form about the central axis of the associated container and casing. More definitely bottom section 100 i Fig. 10 has upwardly projecting, relatively long spacer elements 101 and 102 which in a polygonal pattern extend around the bottom section.

The somewhat related arrangement in Fig. 11 shows a higher number of spacer elements 11 1 and 112, respectively, being each shorter than the elements in Fig. 10, and forming together approximately circular patterns in bottom section 110.

Because of the curvature of the bottom of the associated container itself, the spacer elements both in Fig. 10 and in Fig. II will engage the container surfaces at the respective locations at an angle different from 90° between the container surface and the general plane of the spacer elements described. As already indicated above the arrangements of spacer elements as illustrated in Figs. 7-11 for the bottom section, in a corresponding manner could as well be employed in the top section of the casing. In addition to spacer elements as described and illustrated, there can also be provided shock-absorbing shapes or bodies at other desired locations in the casing structure, as will be obvious to an expert in the field. It is to be noted specifically in this connection that handgrip 8A on top section 8 and supporting or engagement members around the bottom of bottom section 9 (Figs. 1 and 3), can be formed as hollow structures as known per se, with e.g. an open or foam-like core, so as to sustain mechanical stresses that will occur during practical use of such pressure containers. The mounting device or boss 4 as generally shown in Fig. 2, advantageously can have a design at the top as illustrated in Fig. 12. As will appear from Fig. 12 there is provided a nut-like part 4A that can e.g. have a hexagonal shape, which by the strong anchoring of the boss structure at the top of the actual container 3, implies that this and nut-part 4A are rotationally securely interconnected. When mounting a valve or connecting device or the like to the boss 4 in Fig. 2, e.g. by means of a thread connection, the nut-part 4A thus can be favourably utilized. Thereby the users of such pressure containers will not be dependent on a secure rotational anchoring of the casing structure described, outside the actual pressure container.

Referring now to fig. 12, which is an isometric view of an inner liner layer 1 which has not been treated. The inner liner layer is made of a polymer material, such as polyethylene (polyethene) and may be manufactured in a per se known manner, for example by blow moulding, extruding, or a similar method. As previously

mentioned, polymer materials have low wetting and adhesive properties. By treatment of the surface of the polymer material, these can be increased. Fig. 13 shows an example of such a treatment, by flame treatment of the outer side la of the inner layer 1. Some treatment methods are interesting in this connection. In a preferred embodiment, flame treatment or corona discharge treatment, if desired, in combination with ozone treatment, is used. Surface treatment by flame treatment takes place by flaming of the surface with a burner. Adiabatic flame temperature is about 1800 °C. Flame treatment using excess air, i.e., that fuel/air-mixture has excess air in relation to fuel, gives the best surface treatment. The amount of air in relation to the amount of fuel can in other words be expressed as the excess air ratio X, which is defined as: m amount of air m stoechiometric amount of air m

( ^ )

f wherein

λ = 1 gives stoechiometric combustion, λ > 1 gives excess air (lean) ,

λ < 1 gives deficiency of air (fuel rich) and wherein (ma/mf) is the ratio between amount of the air and the amount of fuel as is present and (ma/mf) at is the ratio between the amount of air and the amount of fuel at stoechiometric combustion.

The amount of air in relation to the amount of fuel may also be expressed as the equivalence ratio φ: ( m_f/ _a )

Φ =

( m_f/m_a ) ,

wherein

Φ = 1 gives stoechiometric combustion,

Φ < 1 gives excess air (lean) ,

Φ > 1 gives deficiency of air (fuel rich) and wherein (mf /ma) is the ratio between the amount of fuel and the amount of air as present and (mf/ma)_st is the ratio between the amount of fuel and the amount of air at stoechiometric combustion.

The main components in a flame treatment apparatus may comprise:

• one or more burners

· unit for supplying air/fuel and control of the air/fuel ratio, including a cut off valve for fuel

Use of flame treatment is preferred before corona discharge treatment, as correct tolerances may be more difficult to obtain due to uneven treatment. When using inflammable materials, corona discharge treatment may be a solution of preference. Other alternatives may also be of interest, for example use of cold-gas-plasma treatment or other methods for increasing the wetting and adhesive properties of the polymer material. Moreover, adhesives which harden when exposed to ultraviolet radiation (UV-radiation) can be used because such a use also involves an alteration of the properties of the polymer material.

Fig. 14 shows winding of an outer, fibre-reinforced, pressure supporting layer 2 onto the inner liner layer 1 in a designed pattern. Having increased the wetting an adhesive properties of the surface of the polymer material, adhesion between the inner liner layer 1 and the outer, fibre-reinforced, pressure supporting layer 2 is possible to obtain. An epoxy-polymer (not shown) or a similar means may be used as adhesive. The adhesive can be employed onto the outer side la of the inner liner layer 1 before winding of the outer, fibre-reinforced, pressure supporting layer 2 onto the outer side la of the inner liner layer 1. Alternatively, the adhesive can at first be employed onto the inner side 2a of the outer, fibre-reinforced layer 2 before adhesion of the outer side la of the inner liner layer 1. The adhesive may also be employed at the same time as the outer, fibre-reinforced, pressure supporting layer 2 is wound onto the outer side la of the inner liner layer 1. In addition, direct contact between the inner liner layer 1 and the outer, fibre-reinforced, pressure supporting layer 2 is possible. Naturally, the outer, fibre-reinforced, pressure supporting layer 2 can also be employed in other appropriate ways. Alternatives of interest may, e.g., be hand lay-up, employment of pre-impregnated mats or tapes (tape laying), injection lamination, RTM-method (resin transfer moulding), filament winding or braiding. The outer, fibre-reinforced, pressure supporting layer 2 may possibly be made of a translucent material, so as to make it easier to see the level of fluid still remaining in the pressure container.

Thus, the present invention concerns a composite pressure container for fluids adapted to hold fluids under both high and low pressures, such as H₂, industrial gases, CNG and LPG, comprising an inner, fluid-tight liner layer (1) and a pressure supporting layer (2) as well as an outer, protective casing (5,57,67),

characterized in that said layers (1,2) as known per se consist of transparent or translucent materials, wherein the overall thickness of the layers (1,2) is reduced by the fibre ribbon constituting the pressure supporting layer (2) being winded onto the liner layer (1), after treatment of the outside of the inner layer (la), in a designed pattern to obtain maximum strength with the use of a minimum length of fibre ribbon, and that the casing (5,57,67) comprises a middle section (7,57,67) having surface portions (7A,7B,7C,41-48, 51-53,61) being cut-away so that parts of the actual container (3), being located inside the casing (5,57,67), are visible from the outside, and that the casing has shock-absorbing properties. In a more specific embodiment the container of the invention is one wherein the fibre ribbon constituting the pressure supporting layer (2) is winded onto the liner layer (1) such that the top and bottom domes of the liner layer (1) has a denser coverage of winded fibre material than the cylindrical middle section of the same.

In another more specific embodiment the container of the invention is one wherein the treatment of the outside of the inner layer (la) is the application of a resin in optical contact to the outside of the inner layer (la).

The invention also concerns a method of manufacturing a composite pressure container according to the present invention, wherein, during rotation of the inner liner layer (1) relative to treatment, employment, and/or winding equipment, the outer side (la) of the inner liner layer (1) is treated so as to increase the wetting and adhesive properties of the polymer material, an adhesive is employed at the outer side (la) of the inner liner layer (1) and/or in direct contact between the outer side (la) of the inner lining layer (1) and the inner side (2a) of the outer, fibre- reinforced, pressure supporting layer (2), for adhering the inner liner layer (1) and the outer, fibre-reinforced, pressure supporting layer (2), and the outer, fibre- reinforced, pressure supporting layer (2) is winded onto the inner liner layer (1) in designed pattern to obtain maximum strength with the use of a minimum length of fibre ribbon.

In amore specific embodiment of the method above, the winding of the outer, fibre- reinforced, pressure supporting layer (2) onto the inner liner layer (1) is performed such that the top and bottom domes of the liner layer (1) has a denser coverage of winded fibre material than the cylindrical middle section of the same.

Claims

PATENT CLAIMS

1. Composite pressure container for fluids adapted to hold fluids under both high and low pressures, such as H₂, industrial gases, CNG and LPG, comprising an inner, fluid-tight liner layer (1) and a pressure supporting layer (2) as well as an outer, protective casing (5,57,67),

characterized in that said layers (1,2) as known per se consist of transparent or translucent materials, wherein the overall thickness of the layers (1,2) is reduced by the fibre ribbon constituting the pressure supporting layer (2) being winded onto the liner layer (1), after treatment of the outside of the inner layer (la), in a designed pattern to obtain maximum strength with the use of a minimum length of fibre ribbon, and that the casing (5,57,67) comprises a middle section (7,57,67) having surface portions (7A,7B,7C,41-48, 51-53,61) being cut-away so that parts of the actual container (3), being located inside the casing (5,57,67), are visible from the outside, and that the casing has shock-absorbing properties.

2. The container of claim 1, wherein the fibre ribbon constituting the pressure supporting layer (2) is winded onto the liner layer (1) such that the top and bottom domes of the liner layer (1) has a denser coverage of winded fibre material than the cylindrical middle section of the same.

3. The container of claim 1, wherein the treatment of the outside of the inner layer (la) is the application of a resin in optical contact to the outside of the inner layer (la).

4. Method for manufacturing a composite pressure container according to any of the preceding claims,

characterized in, during rotation of the inner liner layer (1) relative to treatment, employment, and/or winding equipment,

- treatment of the outer side (la) of the inner liner layer (1) so as to increase the wetting and adhesive properties of the polymer material,

- employing an adhesive at the outer side (la) of the inner liner layer (1) and/or in direct contact between the outer side (la) of the inner lining layer (1) and the inner side (2a) of the outer, fibre-reinforced, pressure supporting layer (2), for adhering the inner liner layer (1) and the outer, fibre-reinforced, pressure supporting layer (2), and

- winding of the outer, fibre-reinforced, pressure supporting layer (2) onto the inner liner layer (1) in designed pattern to obtain maximum strength with the use of a minimum length of fibre ribbon.

5. The method of claim 4, wherein the winding of the outer, fibre-reinforced, pressure supporting layer (2) onto the inner liner layer (1) is performed such that the top and bottom domes of the liner layer (1) has a denser coverage of winded fibre material than the cylindrical middle section of the same.