TECHNICAL FIELD The present invention relates to membrane accumulators, such as, for example, used in hydraulic, pneumatic and hydro-pneumatic systems. In particular, the invention relates to a method for manufacturing membrane accumulators by means of Electro Magnetic Pulse (EMP) welding and/or crimping . PRIOR ART

A membrane accumulator is a gas and liquid tight container which is divided into compartments by a membrane. The membrane is hereby elastic so that the volumes or the volume ratio of the compartments can be changed under the influence of a pressure difference between the compartments. Membrane accumulators are used in many fluidic or hydro-pneumatic systems to store energy under the form of a compressed gas or liquid.

Membrane accumulators are particularly suitable to regulate the pressure in a fluid system of, for example, pipelines, wherein typically a first compartment is connected to the system and contains the fluid, while a second compartment is filled with a gas, e.g. nitrogen, under pressure. By using a membrane accumulator, it is possible to, among others,

- absorb pressure differences in the fluidic system ;

- regulate the flow rate;

- anticipate fluctuations in the demand for fluid;

- absorb pressure waves or pressure shocks, which, for example, originate from a pump with a non-constant flow rate. Membrane accumulators comprise a housing which is, in most cases, an assembly of two parts, wherein at least one connection is provided for connecting to a fluidic system. They are mostly applied in hydraulic systems to which they are able to return stored pressure when required. The connection serves therein as feed and/or discharge of the fluid of the hydraulic system . In the housing, a membrane is mounted which divides the housing into a fluid compartment and a gas compartment. Various embodiments of membrane accumulators and methods for manufacturing accumulators are already known from the prior art.

German patent DE 2 834 403 discloses a membrane accumulator wherein the top part is mounted on the bottom part by means of a groove and a ring-shaped tongue to the bottom part in which the top part is clamped by means of radial and axial tensions. German application DE 10 2009 021463 discloses an accumulator wherein an outer housing and an inner housing fit together at the edges and are attached to one another by deformation of the edges through the formation of a form-locking . These documents disclose examples of mechanical manufacture, wherein two parts of the housing are mounted to one another by means of a screw thread and/or pre- tensioned ring and/or mechanical deformation. The clamping of the membrane can be obtained in various ways. The technique is voluminous and expensive, and is only applied in case of extremely high pressure requirements.

German application DE 2 139 367 discloses a method for manufacturing an accumulator by welding the parts using an electron beam . This application provides an example of a technique wherein a membrane accumulator is built-up of typically two, mostly deep-drawn from sheet metal, pre-formed and processed halves, in which the membrane is mounted in advance. The halves are welded to one another by means of the electro-beam welding technique. This process is tolerance-sensitive and requires an expensive preparation (grinding out and boring) of both halves. The connection is attached to the housing in a separate process. Although this technique is relatively expensive and slow due to the required preparation, it is probably the most frequently applied technique.

Another known technique consist of the sealing, after mounting the membrane, of a cylindrical pot around a connection. When sealing the pot, sealing of the membrane in relation to the housing is also provided. Subsequently, the housing and the connection are connected to one another in a gas tight manner by means of a weld . In terms of costs, this is a technically advantageous technique, but it is only applicable at relatively low pressure requirements.

European patent EP 2 024 130 discloses a method for manufacturing a pressure vessel using EMP welding. A pressure vessel as referred to in this document does, however, need to meet higher pressure requirements, and has a simpler construction because of the absence of a membrane and an optional connection to a fluidic system . It should further be mentioned that the vessels as referred to in this document are filled with a gas other than N2 (nitrogen) and fulfil a different function, as a result of which they are loaded in a distinctive manner compared to hydraulic accumulators. Hydraulic accumulators undergo a pulsating load, as a result of which mentioned high stress concentration or notching constitutes a significant risk. For the type of pressure vessel as disclosed in EP 2 024 130, the quality of the welding image of EMP welding is, in addition, from a radial point of view, insufficiently constant in order to exclude this risk. Avoiding a welded joint may therefore be desired. Mounting the second sub-housing on the first sub-housing, or vice versa, in an overlap zone by any assembling technique, in particular by EMP welding and/or crimping, but also by other molding, forming, re-shaping, welding or other process, may and does require the application of considerable radial pressing forces and/or stresses. For EMP welding, the stress could e.g. be up to 100.000 MPa and even more.

These stresses and/or forces at the position of the overlap zone, need to be absorbed in the inner sub-housing. Taking into account the mechanical forces or loads to which the housing could be subjected during use of the accumulator, any undesired deformation and/or damage of one or both sub-housings is to be limited and eliminated if possible.

In assemblies of sub-housings wherein the edges of the overlap zone are disposed over each other in an axially opposite direction (e.g . as in WO 2010/130 332 Al), the inner sub-housing needs to be conceived sufficiently robust to absorb the above mentioned stresses or forces. This can be achieved e.g. by an increased wall thickness or by applying an internal support ring or a combination thereof. To ensure the stability of the mounting process, usually extra material (e.g. steel, stainless steel, aluminum) is provided, at least at the edges of the sub-housings in or near the overlap zone. This results in extra material being used, which does not provide extra functionality to the membrane accumulator, i.e. this extra material is to be considered pure loss from a functional point of view.

The present invention aims to find a solution for at least some of the above- mentioned problems.

There is a need for a membrane accumulator which meets high-pressure requirements, and can be manufactured in an efficient and relatively inexpensive way. There is therefore a need for an improved method for manufacturing a membrane accumulator.

SUMMARY OF THE INVENTION

The invention relates to a method for manufacturing a membrane accumulator, comprising the steps of:

- providing a first sub-housing, preferably a cylindrical sub-housing;

- providing a second sub-housing, preferably a cylindrical sub-housing;

- mounting a membrane in the first and/or the second sub-housing, preferably using a clamping ring;

- mounting the second sub-housing on the first sub-housing whereby a sealed housing is obtained which is divided into two compartments separated from one another by the membrane, wherein the second sub-housing is mounted on the first sub-housing by means of Electro Magnetic Pulse (EMP) crimping and/or Electro Magnetic Pulse (EMP) welding to ensure a gas and fluid tight assembly. Preferably, EMP crimping is used . Alternatively or additionally, EMP welding is used.

In a second aspect, the invention relates to a method for manufacturing a membrane accumulator, comprising the steps of:

providing a first sub-housing, preferably a cylindrical sub-housing;

providing a second sub-housing, preferably a cylindrical sub-housing;

mounting a membrane in the first and/or the second sub-housing;

mounting the second sub-housing on the first sub-housing whereby a sealed housing is obtained which is divided into two compartments separated from one another by the membrane, wherein the second sub-housing comprises an edge with a curled overlap profile.

In a third aspect, the invention relates to a method for manufacturing a membrane accumulator, comprising the steps of:

providing a first sub-housing, preferably a cylindrical sub-housing;

providing a second sub-housing, preferably a cylindrical sub-housing;

mounting a membrane in the first and/or the second sub-housing;

mounting the second sub-housing on the first sub-housing whereby a sealed housing is obtained which is divided into two compartments separated from one another by the membrane, wherein the second sub-housing is mounted on the first sub-housing by means of Electro Magnetic Pulse (EMP) welding and/or crimping in order to ensure a gas and fluid tight assembly and wherein the second sub-housing comprises an edge with a curled overlap profile.

In an embodiment, a clamping ring is provided for clamping the membrane in the first and/or second sub-housing. In a preferred embodiment, said clamping ring is integrated into said first and/or second sub-housing, e.g. by welding a clamping ring to said first and/or second sub-housing. Alternatively, no clamping ring is provided and/or said membrane is clamped or held by one or more grooves and/or protrusions provided in or on said first and/or said second sub-housing, e.g. by milling or casting, said grooves and/or protrusions suitable for, preferably arranged for, clamping said membrane. In a preferred embodiment, said grooves and/or protrusions are provided at or near the edge of the first and/or second sub-housing, more preferably in an overlap zone.

In a preferred embodiment, the methods of the present invention comprise the step of temporarily supporting a radially inwards surface of the edge with a curled overlap profile when mounting of the second sub-housing on the first sub-housing, preferably by a support tool which can be applied before and at least partially during said mounting of the second sub-housing on the first sub-housing and which can be removed after said mounting of the second sub-housing on the first sub-housing.

In a further aspect, the invention relates to a membrane accumulator provided with a first sub-housing, a second sub-housing, a membrane mounted in the first and/or second sub-housing, wherein the second sub-housing is mounted on the first sub- housing such that a sealed housing is obtained which is divided by the membrane into two compartments separated from one another, wherein the second sub- housing is mounted in a gas and liquid tight manner on the first sub-housing by means of Electro Magnetic Pulse (EMP) crimping and/or Electro Magnetic Pulse (EMP) welding. In yet a further aspect, the present invention relates to a membrane accumulator provided with a first sub-housing, a second sub-housing, a membrane mounted in the first and/or the second sub-housing, wherein the second sub-housing is mounted on the first sub-housing such that a sealed housing is obtained which is divided into two compartments separated from one another by the membrane, characterized in that the second sub-housing comprises an edge with a curled overlap profile. In a preferred embodiment, the second sub-housing is mounted in a gas and fluid tight manner on the first sub-housing by means of Electro Magnetic Pulse (EMP) crimping and/or Electro Magnetic Pulse (EMP) welding .

In a preferred embodiment, the first sub-housing comprises an edge with an overlap profile adapted to an edge of the second sub-housing and/or the second sub-housing comprises an edge with an overlap profile adapted to an edge of the first sub- housing .

In a preferred embodiment, the membrane is mounted with a clamping ring in the first or the second sub-housing. Said clamping ring preferably has an overlap profile which is adapted to the first sub-housing and/or to the second sub-housing, preferably adapted to the edge of the first sub-housing and/or the second sub- housing .

In a preferred embodiment, a sealing ring is mounted between the first and the second sub-housing to extra ensure the gas and fluid tight assembly.

In a preferred embodiment, a support ring is inserted into the first and/or second sub-housing. In a preferred embodiment, a retaining ring is arranged around the first and the second sub-housing in an overlap zone.

In a preferred embodiment, after the step of the EMP crimping and/or welding, a weld, preferably a conventional weld such as a MIG-weld, a Tig-weld or an electron beam weld, is arranged between the first and the second sub-housing to ensure the gas and fluid tight assembly even further. In this case, the sealing ring may be omitted.

Thus, when manufacturing the membrane accumulator, two, preferably preformed, parts are brought together by means of EMP crimping and/or welding as an alternative to the electron beam welding. Preferably, EMP crimping is used. Apart from some other mechanical advantages, this technology generates no or a negligible heat input and the technology causes no contamination, such as spatters, which could affect en/or damage the membrane. This technique also provides the advantage that the membrane, seen from the longitudinal direction of the accumulator, can be mounted optimally in the accumulator independent of the position of the welding zone, for example, in the middle of the housing, as a result of which the possible deformation in both directions is more or less identical. This provides an optimum operation of the membrane in the accumulator as a function of the application.

Alternatively or additionally, EMP welding is used to bring together the two parts.

A curled overlap profile, as according to one aspect of the present invention and in particular as illustrated in figs. 3 and 4, wherein the edges of the overlap zone are disposed over each other in an axially same direction provides in the possibility of a temporary, process-functional, support of the sub-housing at the position of the overlap zone, i.e. a robust, possibly over-dimensioned, support can be applied before the start of the mounting process, can remain in position during the mounting process, and can be removed after the mounting process.

In a preferred embodiment, said support can be provided by a support tool, preferably comprising a cylindrical axis, said cylindrical axis preferably comprising one or more sides with a profile which corresponds at least partially with the shape of the sub-housing it intends to support, e.g. the second sub-housing. In a more preferred embodiment, said support tool comprises a conical or conic-like shape at a position where it is intended to provide support to the second sub-housing, to ease withdrawal of the support tool after the mounting process.

In a preferred embodiment, and at least partially due to the curled overlap profile (9b) of the second sub-housing, the curled overlap profile (9b) of the edge (6a) of the second sub-housing comprises a radially inwards side surface (45) which is preferably substantially cylindrical. This radially inwards side surface (45) could serve as a contact surface for a support tool ( 12) which can be used to absorb the shock or force which accompanies the EMP welding and/or crimping processes for assembling the two sub-housings. DESCRIPTION OF THE FIGURES

Figure 1 is an illustration of a membrane accumulator before and after the assembly by means of EMP crimping and/or welding according to the present invention, wherein the second sub-housing is arranged over the first sub-housing.

Figure 2 is an illustration of a membrane accumulator before and after the assembly by means of EMP crimping and/or welding according to the present invention, wherein the second sub-housing is arranged in the first sub-housing. Figure 3 is an illustration of a membrane accumulator before and after the assembly by means of EMP welding according to the present invention, wherein the second sub-housing with an edge with curled overlap profile is arranged in the first sub- housing .

Figure 4 shows another embodiment of the present invention before and after assembly, wherein the first sub-housing comprises an edge with a curled overlap profile.

Figure 5 is an illustration of a membrane accumulator before and after the assembly by means of EMP crimping and/or welding according to the present invention, wherein the second sub-housing is arranged in the first sub-housing and wherein the membrane is clamped between the first sub-housing and a recess in the outer surface of the second sub-housing at the overlap zone.

DETAILLED DESCRIPTION

The invention relates to a method for manufacturing membrane accumulators using Electro Magnetic Pulse (EMP) welding and/or crimping, as well as a membrane accumulator which was manufactured by means of EMP welding and/or crimping. When applying Electro Magnetic Pulse welding and/or crimping, the two parts (6 & 7) are partially shifted over one another and connected in the overlap zone (9). Unless otherwise defined, all terms used in the description of the invention, including technical and scientific terms, have the meaning as commonly understood by those skilled in the art in the technical field of the invention. For a better assessment of the description of the invention, the following terms are explained explicitly.

"A", "an" and "the" in this document refer to both the singular and the plural form, unless the context clearly implies otherwise. For example, "a segment" means one or more than one segment. Where "about" or "around" are used in this document with a measurable quantity, a parameter, a time period or moment, and the like, variations are meant of +/- 20% or less, preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/-!% or less, and even more preferably +/-0.1% or less than and of the cited value, to the extent that such variations apply in the described invention. It should, however, be understood that the value of the quantity in which the term "about" or "around" is used, is itself specifically disclosed. The terms "comprise", "comprising", "consist of", "consisting of", "provided with", "include", "including", "contain", "containing" are synonyms and are inclusive or open terms which indicate the presence of what follows, and which do not preclude or prevent the presence of other components, features, elements, members, steps, as known from or described in the prior art.

The term "edge of the sub-housing" refers to the end of the sub-housing. This end is preferably substantially circular. Examples of what is meant by "edge" are indicated in the figures with the references (6a) and (7a). The term "overlap profile" refers to the shape of a sub-housing or of the edge of a sub-housing in the vicinity of the connection of the first sub-housing on the second sub-housing and where the first and the second sub-housing closely connect to one another, preferably where the first and second sub-housing touch one another. Preferably, the first and/or the second sub-housing comprises, prior to the assembly, an overlap profile which enhances the gas and fluid tightness after the assembly. The overlap profile of the sub- housings can be deformed due to the assembly process. Unless clearly implied otherwise, in this text, by the term "overlap profile" the profile is meant of a sub-housing prior to the assembly of the second sub-housing on the first sub-housing. Examples of what is understood by "overlap profile" are indicated in the figures with references (9a) and (9b).

The terms "first sub-housing" and "second sub-housing" refer to the two parts which are mounted on one another to form one sealed housing. Preferably, the first sub-housing is adapted to be in contact with a fluid and the second sub-housing is adapted to be in contact with a gas, preferably a gas under pressure.

The citing of numerical intervals by the endpoints comprises all integers, fractions, and/or real numbers between the endpoints, these endpoints included. In a first aspect, the invention relates to a method for manufacturing a membrane accumulator as described in claims 1 to 10. In a second aspect, the invention relates to a membrane accumulator as described in claims 11 to 20. As already indicated, the invention relates to a method wherein no or a negligible heat input is generated and wherein no contamination is caused, such as spatter, which may affect and/or damage the membrane. In addition, the method offers the advantage that the membrane, seen from the longitudinal direction of the accumulator, can be mounted optimally in the accumulator, independent of the position of the welding or crimping zone, for example, in the middle of the housing, as a result of which the deformation of the membrane which is possible in both directions, is more or less identical. Thus, the invention also relates to an improved membrane accumulator wherein the position of the membrane is chosen independent of the position of the welding or crimping zone.

The method offers some other mechanical benefits, including :

- Two different materials (e.g. chosen from steel, stainless steel, aluminum,...) can be combined, for example, first sub-housing out of stainless steel and second sub- housing out of aluminum.

- The material shows minimal "spring back" in the deformed and thus sealing zone. This is possibly the most important and distinctive feature compared to other applied, whether or not protected, mechanical sealing techniques such as roll or press forming.

- The thinning of the wall thickness for the purpose of positioning and/or mounting the membrane and/or the clamping ring has no adverse effects, since the thinning may be compensated by overlapping parts of the sub-housings.

- It is possible to laminate the least deformed part (6) with the aim of increasing the wall thickness and hence to reinforce the wall. The wall thickness that can maximally be deformed is estimated, for example, for steel, to be 3 to 4 mm in the current prior art.

- There is a possibility to crimp an additional retaining ring (8) at the position of the clamping zone.

- The mechanical properties of the material are not affected by high temperatures, e.g., high melting or welding temperatures.

There are also a number of other advantages associated with the method and the membrane accumulator as described in this document, including :

- It is an energy-friendly process without the addition of filling and/or melting materials.

- The cost of welding or crimping is a fraction of other, more conventional welding processes such as MIG/MAG/TIG welding, electron beam welding,...

- Considerably less preparation is required and the preparation of the deformed deep-drawn parts (6, 7) is simpler due to the limited tolerance requirements.

- As a consequence of the limited material loss in the overlap zone, there is no or only a minimal material compensation required to maintain a minimum wall thickness in the connection zone. This leads to material and weight saving . On the other hand, the overlap and the possible support ring ( 11) and/or retaining ring (8) may lead to an increase of the weight and the material used . Depending on the application and the requirements, it is possible to make a choice between the various embodiments which are described in this document. According to an embodiment, the second sub-housing is mounted on the first housing part by means of EMP crimping to circumvent some disadvantages of EMP welding. Advantages of EMP crimping over welding may be the following :

- There is a considerably reduced risk of stress concentration or notching from high pulse or shock loads.

- The quality control of the assembly is simpler and/or cheaper.

- There is no fusion at molecular level between the sub-housings.

In a preferred embodiment, the first sub-housing comprises an edge with an overlap profile adapted to an edge of the second sub-housing and/or the second sub-housing comprises an edge with an overlap profile adapted to an edge of the first sub- housing .

In a preferred embodiment, the first and/or the second sub-housing comprises an edge with an overlap profile adapted to hold and/or clamp said membrane. In a particularly preferred embodiment, said membrane comprises an edge with a membrane profile which is adapted to cooperate with the overlap profile of the edge of the first and/or second sub-housing to hold and/or clamp said membrane within said first and/or second sub-housing and/or within said housing. According to a preferred embodiment, the membrane is inserted into the first (7) or the second sub-housing (6) with a clamping ring ( 10), preferably in the first sub- housing (7) and preferably before the second sub-housing is mounted on the first sub-housing. Hereby the membrane is mounted in the first or the second sub- housing with a clamping ring. Said clamping ring preferably has an overlap profile which is adapted to the first sub-housing and/or to the second sub-housing, preferably adapted to the edge of the first sub-housing and/or the second sub- housing . Since no "fusing" takes place in the overlap zone when using EMP crimping, it may be necessary to provide both a gas seal as well as a mechanical connection. This may be achieved in various ways, as illustrated in Figures 1 to 5.

In a preferred embodiment, a support ring ( 11) is inserted to absorb unwanted deformation of the inner wall of the first and/or second sub-housing due to impact forces. In a preferred embodiment, a retaining ring (8) is arranged around the first and the second sub-housing in an overlap zone. This retaining ring can be arranged, for example, by first heating it up, for example via induction, as a result of which the retaining ring expands, by then placing the retaining ring over the sub-housings in the overlap zone, and by subsequently cooling off the retaining ring or letting it cool off so that the retaining ring is clamped over the sub-housings. The retaining ring can preferably be applied by means of the same EMP crimping and/or welding technology, which is used for mounting the second sub-housing on the first sub- housing . The retaining ring is arranged on the outside and at the position of the overlap zone. The retaining ring is intended to ensure the gas and/or liquid tightness of the housing, in particular when the membrane accumulator is used in a high-pressure application. The appliance of the retaining ring via EMP crimping and/or welding can be done at the same time as or after mounting the second sub-housing on the first sub-housing. Preferably, this is done at the same time, i.e. applying the retaining ring and mounting the second sub-housing on the first sub-housing takes place in a single assembly step.

In a preferred embodiment, the membrane accumulator is able to withstand maximum pressures of at least 20 bar, preferably at least 40 bar, more preferably at least 70 bar, even more preferably at least 100 bar, even more preferably at least 200 bar, even more preferably at least 300 bar.

In a preferred embodiment, the parameters of the components of the membrane accumulator and/or the parameters of the EMP crimping and/or welding are chosen as a function of the pressure requirements of the membrane accumulator. The various parameters that may play a role herein, are :

- The choice of the materials of the components, such as the first and second sub- housing, the membrane, the retaining ring, the clamping ring, the sealing ring;

- The thickness, shape, diameter or curvature of the components.

- The size, orientation, and the time-dependent profile of the magnetic field which is generated during the EMP crimping and/or welding.

In a preferred embodiment, the membrane accumulator is provided with a clamping ring in the first and/or second sub-housing which clamps the membrane.

In a preferred embodiment, the membrane accumulator is provided with a support ring in the first and the second sub-housing at the position of an overlap zone between the first and the second sub-housing.

In a preferred embodiment, the membrane accumulator is provided with a retaining ring over the first and second sub-housing at the position of the overlap zone between the first and the second sub-housing.

In a further aspect, the invention relates to a membrane accumulator comprising a first sub-housing, a second sub-housing and a membrane, wherein the second sub- housing is mounted on the first sub-housing in an overlap zone, thereby obtaining a housing which comprises a longitudinal direction, wherein the membrane is mounted in the housing and divides the housing into two compartments, wherein the position of the membrane in the longitudinal direction of the housing is set independently of the position of the welding zone. The described method using Electro Magnetic Pulse crimping and/or welding, and in particular EMP crimping, allows to obtain optimal technical results with relatively simple principles, and this at a lower cost than with known techniques.

In what follows, the invention is described on the basis of non-limiting examples which illustrate the invention, and which are not intended or should not be interpreted as to limit the scope of the invention.

In Figure 1, half of the cross-section of a membrane accumulator is illustrated before ( 100) and after ( 101) the assembly by means of EMP crimping and/or welding according to the present invention, wherein the second sub-housing (6) is arranged over the first sub-housing (7). The membrane accumulator is essentially cylindrically symmetrical around the axis (20). In Figure 2, half of the cross-section of a membrane accumulator is illustrated before (200) and after (201) the assembly by means of EMP crimping and/or welding according to the present invention, wherein the second sub-housing (6) is arranged in the first sub-housing (7) . The membrane accumulator is essentially cylindrically symmetrical around the axis (20).

In Figure 3, half of the cross-section of a membrane accumulator is illustrated before (300) and after (301) the assembly by means of EMP welding according to the present invention, wherein the second sub-housing (6) is arranged in the first sub-housing (7). The membrane accumulator is essentially cylindrically symmetrical around the axis (20). The edge (6a) of the second sub-housing (6) comprises a curled overlap profile (9b) .

The membrane accumulator comprises a housing ( 1), built-up of sub-housings (6, 7) with a connection (2) which is mounted here to the housing, e.g. with a weld, wherein a membrane (3) is mounted in a sub-housing (7), said membrane separating the fluid compartment (4) from the gas compartment (5). In an embodiment, the connection can be mounted to the housing by any attachment means, which may comprise a weld. The connection (2) may comprise a screw thread on its outer surface or other attachment means to fluidly connect, e.g. via a pipe, tube, pipeline, the fluid compartment (4) to a fluidic system, more preferably to fluidly connect the fluid compartment (4) to a fluidic system for holding and/or transporting liquids. The housing ( 1) is typically manufactured from metal, e.g. stainless steel, steel, aluminum or a combination thereof. The membrane needs to be mounted prior to sealing the housing. Examples of how the membrane can be mounted are illustrated in Figs. 1 to 5, both before (alternatives 102-105 and 110 in Fig. 1, alternatives 202-205, 210, 212 and 214 in Fig. 2, alternatives 302-303 in Fig .3, alternatives 402-404 in Fig. 4, alternative 500 in Fig. 5) the assembly of the second sub-housing (6) on the first sub-housing (7) and after (alternatives 106-109 and 111 in Fig . 1, alternatives 206-209, 211, 213 and 215 in Fig. 2, alternatives 306-307 in Fig. 3, alternatives 406-408 in Fig. 4, alternative 501 in Fig. 5). The various alternatives illustrate some of the different possibilities as regards the profile of the edges (6a, 7a) of the sub-housings (6, 7), the overlap profiles (9a, 9b) in the overlap zone (9) and the profile of the support ring ( 11), clamping ring ( 10), retaining ring (8) and sealing ring ( 14). Alternatives ( 110), ( 111), (212) and (213) show an example of an overlap profile (9a, 9b) of the first sub-housing (Fig. 1, reference 9a) or of the second sub-housing (Fig. 2, reference 9b) which comprises a recess ( 13). Because of the EMP welding or crimping, this recess is at least partially filled by, respectively, a part of the edge of the second sub-housing (Fig. 1) or the first sub-housing (Fig. 2), which is deformed by the EMP welding or crimping . The recess ( 13) can for example be made by injection molding, preferably when the sub-housing with the recess is made from aluminum. The recess ( 13) can also be made, for example, by milling or boring.

Alternatives (214) and (215) illustrate an overlap profile according to an embodiment of the present invention, wherein no sealing ring ( 14) is arranged, but where a weld ( 13) is applied between first and second sub-housing, at the position of the end of the edge of the sub-housing which is situated over the other sub- housing. In this case, the weld ( 13) is situated at the position of the end of the edge (7a) of the first sub-housing. The weld can be arranged via e.g. Mig or Tig welding. This weld, which is applied afterwards, when the sub-housings have already been mounted onto one another through the EMP crimping and/or welding, is easier to apply than a weld to mount two sub-housings onto one another as has been used in the prior art.

Figure 3 shows several alternative embodiments of the present invention, wherein the edges (6a) of the second sub-housing (6) comprise a, preferably outward directed, curled overlap profile (9b). Such overlap profile allows to externally, i.e. on the outside of the membrane accumulator, absorb the impact of the EMP welding on the sub-housing with the curled profile. Alternatives (303) and (307) illustrate an embodiment wherein the overlap profile (9b) of the edge (6a) of the second housing (6) comprises a shape which clamps the membrane (3) against the overlap profile (9a) of the edge (7a) of the first sub-housing (7). Figure 3 illustrates an embodiment of the present invention, wherein the sub-housings are mounted onto one another via EMP welding. This makes it possible to omit the sealing ring, as the weld itself already ensures a sufficient gas and fluid tight assembly.

As the curled overlap profile of the edge of the second sub-housing in fig. 3 allows to absorb the impact of the EMP welding, it also allows to absorb the impact of an EMP crimping process, which is usually smaller than an EMP welding process. Therefore, the sub-housing with an edge with a curled overlap profile can also be used in an accumulator whose sub-housings are mounted on one another by EMP crimping.

In a preferred embodiment, such as illustrated in alternatives 303 and 307 of fig. 3, the curled overlap profile (9b) of the edge (6a) of the second sub-housing comprises a radially outwards side surface (47) which is preferably substantially parallel to a radially inwards surface (46) of the overlap profile (9a) of the edge (7a) of the first sub-housing (7). These side surfaces (47, 46) are preferably substantially parallel before, during and/or after assembly of the two sub-housings. The radially outwards side surface (47) of the second sub-housing hereby serves as a surface against which the radially inwards side surface (46) of the first sub- housing can be held, supported, mounted, pressed, welded, shaped and/or formed during assembly, in particular during EMP welding and/or crimping.

In a preferred embodiment, and at least partially due to the curled overlap profile (9b) of the second sub-housing, the curled overlap profile (9b) of the edge (6a) of the second sub-housing comprises a radially inwards side surface (45) which is preferably substantially cylindrical. This radially inwards side surface (45) could serve as a contact surface for a support tool ( 12) which can be used to absorb the shock or force which accompanies the EMP welding and/or crimping processes for assembling the two sub-housings.

Figure 3 also shows a detail of the overlap profile (9a) of the edge (7a) of the first sub-housing (7). In a preferred embodiment, the overlap profile (9a) comprises a circumferential groove (50) which is suitable, and preferably arranged, for at least partially supporting a lower side (49) of the overlap profile (9b) of the edge (6a) of the second sub-housing (6). Such a circumferential groove allows to easily position the second sub-housing on the first sub-housing prior to assembly.

In a preferred embodiment, the overlap profile (9b) of the edge (6a) of the second sub-housing (6) comprises a radially outwards protrusion (48). Such a protrusion serves as an edge around which the edge (7a) of the first sub-housing may be bent by the EMP welding and/or crimping process.

Figure 4 shows another embodiment of the present invention before (400) and after (401) assembly, wherein the first sub-housing comprises a curled overlap profile. Different alternative of the overlap profiles are illustrated before (402-404) and after (406-408) assembly. Alternatives (402) and (406) are essentially similar to alternatives (302) and (306) of fig. 3. However, the present figure also illustrates how a support tool ( 12) in the form of a cylindrical axis with an edge profile (60) which at least partially corresponds to the outer surface of the second sub-housing and to the overlap profile of the edge of the second sub-housing, can be inserted into the curled overlap profile (9b) of the second sub-housing.

Figure 4 also shows a detail of the overlap profile (9a) of the edge (7a) of the first sub-housing (7).

In a preferred embodiment, the overlap profile (9a) comprises a slanted circumferential groove (53) which is suitable, and preferably arranged, for at least partially supporting a slanted lower side (55) of the overlap profile (9b) of the edge (6a) of the second sub-housing (6). Such a slanted circumferential groove allows to easily position the second sub-housing on the first sub-housing prior to assembly, and helps to ensure that the edges of the first and second sub-housings contact one another over the complete circumference. Furthermore, such a slanted engagement helps to prevent damage to the membrane during mounting of the two sub-housings on one another. Hereby, it should be noted that the groove (53) and lower side (55) are slanted, i.e. not parallel and not perpendicular but under an angle with respect to the longitudinal axis (20) of the accumulator and/or the sub-housings. In a preferred embodiment, said angle is between 1° and 89°, such as 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, 60°, 61°, 62°, 63°, 64°, 65°, 66°, 67°, 68°, 69°, 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, or any value there between, preferably between 5° and 30°, more preferably between 10° and 15°, even more preferably about 13°..

In a preferred embodiment, the overlap profile (9b) of the edge (6a) of the second sub-housing (6) comprises a radially outwards protrusion (54). Such a protrusion serves as an edge around which the edge (7a) of the first sub-housing may be bent by the EMP welding and/or crimping process as shown in alternative (407) .

Another alternative of the overlap profile before (404) and after (408) the mounting process, is shown in fig. 4. In a preferred embodiment, the overlap profile (9b) of the edge (6a) of the second sub-housing (6) comprises a first radially outwards protrusion (51a) and a second radially outwards protrusion (51b) with a recess (52) therebetween. In a preferred embodiment, more than two radially outwards protrusions are provided on the overlap profile (9b) of the edge (6a) of the second sub-housing (6). Said protrusions and recess may result in a connection with enhanced gas- and liquid-tight properties and enhanced pressure resistance as can be seen in alternative (408).

Figure 5 is an illustration of a membrane accumulator before and after the assembly by means of EMP crimping and/or welding according to the present invention, wherein the second sub-housing is arranged in the first sub-housing and wherein the membrane is clamped between the first sub-housing and a recess in the outer surface of the second sub-housing at the overlap zone. In Figure 5, half of the cross-section of a membrane accumulator is illustrated before (500) and after (501) the assembly by means of EMP crimping and/or welding according to the present invention, wherein the second sub-housing (6) is arranged in the first sub-housing (7). The membrane accumulator is essentially cylindrically symmetrical around the axis (20). In the embodiment of fig. 5, the membrane is clamped between the first sub-housing (7) and the second sub-housing (6) in the overlap zone (9). The overlap profile (9b) of the edge (6a) of the second sub-housing (6) comprises a recess (71) in the outer surface, in which a rim (72) of the membrane can be fitted before, during and after mounting the second sub-housing to the first sub-housing.

In a preferred embodiment, the first sub-housing (7) comprises an edge (7a) with an overlap profile (9a) in the overlap zone (9), which comprises a slanted circumferential groove (70) which is suitable, and preferably arranged, for at least partially supporting a corresponding slanted lower side of the overlap profile (9b) of the edge (6a) of the second sub-housing (6). Such a slanted circumferential groove allows to easily position the second sub-housing on the first sub-housing prior to assembly, and helps to ensure that the edges of the first and second sub-housings contact one another over the complete circumference. Furthermore, such a slanted engagement helps to prevent damage to the membrane during mounting of the two sub-housings on one another. Hereby, it should be noted that the groove (70) and lower side are slanted, i.e. not parallel and not perpendicular but under a n angle (a) with respect to the longitudinal axis (20) of the accumulator and/or the sub- housings., In a preferred embodiment, said angle is preferably of between 1° and 89°, such as 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, 60°, 61°, 62°, 63°, 64°, 65°, 66°, 67°, 68°, 69°, 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, or any value there between, preferably between 5° and 30°, more preferably between 10° and 15°, even more preferably about 13°.

In the embodiment shown in fig. 5, after mounting the first sub-housing to the second sub-housing, the first sub-housing (7) can be welded (73) at or near its edge to the second sub-housing, in order to ensure the gas and fluid tight assembly even further and/or to increase the overall strength of the assembly, using a conventional welding process.

The alternatives which are illustrated in the figures do not constitute an exhaustive list. Furthermore, it is also assumed that the present invention is not limited to the embodiments described above and that several modifications or changes can be added to the described examples without reappraisal of the appended claims. In this way, this text states that the second sub-housing is or is to be mounted on the first sub-housing, but it should be understood that, for example, the first sub- housing can also be mounted on the second sub-housing. In other words, the orientation of the sub-housings (e.g. the first sub-housing above, below or next to the second sub-housing) or the order of assembly (e.g. first providing the first sub- housing and then mounting the second sub-housing thereon) may vary depending on the embodiment.