Plate heat exchanger

Abstract

The invention relates to a plate heat exchanger with several heat exchanger plates (4) between which at least two channels are formed for the passage of a heat exchange medium, wherein the respective heat exchange medium can be introduced into and discharged from the respective channel via inlet and outlet openings, wherein at least one seal (6) runs between the individual heat exchanger plates (4) to seal the respective channels and / or the openings against an environment (U) and / or against each other, wherein the at least one seal (6) has a main body (9) made of an elastic sealing material (MD) and with a first permeability (P9).According to the invention, the at least one seal (6) further comprises at least one barrier layer (B) made of a barrier material (MB) and with a second permeability (PB), wherein the first permeability (P9) of the main body (9) is greater than the second permeability (PB) of the barrier layer (B) and wherein the barrier layer (B) has a barrier thickness (DB) of a maximum of 50µm, preferably a maximum of 25µm, in particular a maximum of 10µm.

Description

[0001] The invention relates to a plate heat exchanger according to the preamble of claim 1.

[0002] Known plate heat exchangers feature a multitude of embossed heat exchanger plates stacked on top of each other, enclosing several channels to transport two different heat exchange media between inlets and outlets in a known manner. Loop-shaped gaskets and / or ring seals are arranged between the heat exchanger plates, which are all or at least paired together by brazing or welding. These prevent the two heat exchange media from mixing or escaping into the environment. Examples of such plate heat exchangers are described, among others, in EP 2 017 562 A1, WO 2012041287 A2, EP 1 001 240 A1, and DE 699 19 540 T2.

[0003] The seals are made of an elastic sealing material such that, when the heat exchanger plates are compressed, each seal deforms, forming a flat, sealing contact with the two adjacent plates. This generally prevents leakage even at high pressures and temperatures of the heat exchanger medium. However, a disadvantage of such seals is that, depending on the type of heat exchanger medium, penetration of the elastic sealing material cannot always be prevented, as elastic materials inherently have increased permeability. Therefore, with conventional seals, the escape of potentially hazardous gases from the heat exchanger medium through the seal into the surrounding environment cannot be reliably prevented.

[0004] The object of the invention is therefore to provide a plate heat exchanger that can be operated reliably with a low hazard potential.

[0005] This problem is solved by a plate heat exchanger according to the independent claim. The dependent claims specify preferred embodiments.

[0006] According to the invention, a plate heat exchanger is provided with several adjacent heat exchanger plates, between which at least one seal runs, wherein the at least one seal has a main body made of an elastic sealing material, for example of an elastomer, preferably of rubber, in particular NBR, EPDM, FKM, CR, and with a first permeability, and (additionally) at least one barrier layer made of a barrier material that differs from the sealing material and with a second permeability, wherein the first permeability of the main body is greater than the second permeability of the barrier layer to reduce permeability or penetrability of the seal, wherein the barrier layer has a barrier thickness of at most 50µm, preferably at most 25µm, in particular at most 10µm.

[0007] The solution according to the invention already achieves the advantage that, due to the barrier layer extending completely in the longitudinal direction or expansion direction of the seal, penetration or permeation of the heat exchanger medium from the channels or openings through the seal and into the environment can be prevented or at least significantly reduced. The sealing material of the main body itself, which must be made of an elastic material to efficiently prevent leakage, therefore does not need to be modified or adapted and can continue to be specifically designed to prevent leakage.In contrast, the barrier material of the barrier layer can then be designed to prevent the heat exchanger medium from penetrating the seal, preferably in such a way that the elastic properties of the seal change only minimally, if at all, so that both effects (preventing leakage and reducing permeability) have only a minimal impact on each other. Preferably, both the seal material and the barrier material are designed to operate in the plate heat exchanger at a heat exchanger medium pressure of 25 bar or higher, particularly 30 bar or higher, and / or a heat exchanger medium temperature of 100°C or higher, particularly 140°C or higher. Appropriate temperature-resistant materials are therefore selected.

[0008] The permeability of the seal can be reduced particularly efficiently if the barrier layer runs at least partially, and preferably completely, between a first sealing surface and a second sealing surface of the seal, i.e., perpendicular to the direction of expansion or the longitudinal direction of the seal. The first sealing surface thus rests against a first heat exchanger plate of the multiple heat exchanger plates, for example, against a lower plate surface of the first heat exchanger plate, and the second sealing surface rests against a second heat exchanger plate of the multiple heat exchanger plates, for example, against an upper plate surface of the second heat exchanger plate. In this way, an efficient permeability barrier is provided.

[0009] According to one embodiment, the barrier layer is designed as a coating with a thickness of between 10 nm and 10 µm, preferably between 100 nm and 2 µm, for a metallic coating, and between 0.5 µm and 50 µm, preferably between 1 µm and 10 µm, for an organic coating. This allows for a well-controlled and easy-to-manufacture permeability barrier on the seal. Accordingly, it can be provided, for example, that the coating is applied to a surface of the main body of the seal, in particular to an inner sealing surface of the seal facing the channel and / or the opening, and / or an outer sealing surface of the seal facing the environment. The main body of the seal can therefore be applied to the sides or...The open, uncovered sealing surfaces, which also come into contact with the heat exchanger medium during operation, are coated with a thin layer. This coating then exhibits a lower secondary permeability, thus reducing the overall permeability of the seal.

[0010] In another embodiment, the coating can be applied to one or both sides of a substrate with a thickness between 5 µm and 300 µm, and the substrate is embedded in the main body of the seal. This allows the coating to be made thinner overall and, together with the substrate, inserted into the appropriate tool during the seal manufacturing process to embed the barrier layer in the main body and ensure an effective permeability barrier. The substrate can then be made of an elastic material to avoid significantly impairing the elastic properties of the main body.

[0011] To prevent the elastic properties of the main body, and thus of the seal itself, from deteriorating too much, the support can also be curved, in particular C-shaped or S-shaped. This allows the support, together with the coating, to deform more easily within the main body, or to adapt more readily to the deformation of the main body, without unduly impairing the pressure of the main body against the adjacent heat exchanger plates and thus a leak-free seal.

[0012] According to a further embodiment, the barrier layer is designed as an insert with a maximum thickness of 50 µm, preferably a maximum of 25 µm, and particularly a maximum of 10 µm, wherein the insert is embedded in the main body of the seal. In contrast to a coated substrate, an insert is also possible that is formed as a solid material from the barrier material. This insert can be placed in the appropriate tool during the manufacturing of the seal to embed the barrier layer in the main body and ensure an efficient permeability barrier. In this case, a coating can be omitted, and a correspondingly flexible insert can be selected, preferably with minimal impact on the elastic properties of the main body.In addition, it may be provided that the insert is curved, in particular C-shaped or S-shaped, in order to ensure that, even in this design, the pressure of the main body against the adjacent heat exchanger plates and thus a leak-free seal is not unduly impaired.

[0013] Preferably, the barrier material of the barrier layer is a metal, an organic material (e.g., PTFE-based), or a fluorine-like material. Such materials have densely packed atoms, resulting in low second permeability, and are also easy to incorporate into or attach to the main body.

[0014] Preferably, the at least one seal may also have several barrier layers arranged side by side or offset from each other on the seal. Depending on the design and configuration, the different configurations can therefore also be combined to achieve a more flexible structure and / or improved effectiveness.

[0015] Preferably, the multiple heat exchanger plates are assembled in pairs to form a cassette, with the first heat exchanger plate and the second heat exchanger plate, between which the at least one seal with the main body and the at least one barrier layer is arranged, each belonging to a different cassette. Advantageously, the seal with the barrier layer according to the invention is thus used in a semi-welded design of the plate heat exchanger, in which a leak-free and penetration-free or penetration-reduced seal between the cassettes is generally particularly important.

[0016] The invention is explained in more detail below with reference to exemplary embodiments. The figures shown are: Fig. 1: Perspective view of a plate heat exchanger with several heat exchanger plates within a frame; Fig. 2: A sectional view of two superimposed heat exchanger plates made of Fig. 1 Fig. 3 a sectional view of seals in grooves between overlapping heat exchanger plates; Fig. 4 a schematic cross-sectional view of a seal between two overlapping heat exchanger plates; and Figs. 5A, 5B, 5C different designs of the seal according to Fig. 4 in cross-section.

[0017] In Figur 1 An example of a plate heat exchanger 1 is shown, which has several heat exchanger plates 4 within a frame 2 between two frame end plates 3. In the finished plate heat exchanger 1, these plates form a composite plate pack. Within the plate pack, the individual heat exchanger plates 4 are stacked on top of each other. In a semi-welded configuration, the heat exchanger plates 4 are joined in pairs to form a cassette 5, and the cassettes 5 are then stacked on top of each other. Alternatively, in a fully welded configuration, all the plates are joined together. The welded joint can be formed, for example, by laser welding or similar processes.

[0018] The heat exchanger plates 4 typically each have non-planar, structured areas 4a (distribution area and heat transfer surface) and openings 4b for the inlet and outlet of the heat exchange medium. As shown from Figur 2 As can be seen, the non-planar, structured areas 4a of the heat exchanger plates 4 are each formed by protrusions 4e and depressions 4f, for example by embossing, whereby in the stacked state, a protrusion 4e of one heat exchanger plate 4 rests against a depression 4f of the immediately adjacent heat exchanger plate 4 in the usual manner. This creates channels 7 between adjacent heat exchanger plates 4 through which the heat exchange medium can flow.

[0019] Furthermore, seals 6 are provided on or between selected heat exchanger plates 4, which seal the channels 7 between two heat exchanger plates 4 (or within a cassette 5) and direct the heat exchange media into alternating channels 7. The respective heat exchange medium is supplied via inlet nozzles 10 (see figure). Fig. 1 The heat exchange medium is introduced into inlet passages 11 in the plate pack or heat exchanger plates 4 or cassettes 5 in one of the frame end plates 3, wherein the inlet passages 11 are formed by those superimposed openings 4b in the heat exchanger plates 4 that are located directly below the inlet nozzles 10. The inlet passages 11 are flow-connected to a portion of the channels 7 by a corresponding design of the non-planar, structured areas 4a and the openings 4b, in order to allow the heat exchange medium to enter.

[0020] Similarly, superimposed openings 4b in the heat exchanger plates 4, located below outlet nozzles 12 in the respective frame end plate 3, form outlet passages 13 that are flow-connected to the outlet nozzles 12. The outlet passages 13 are flow-connected to a portion of the channels 7 by means of a corresponding design of the non-planar, structured areas 4a and the openings 4b. The heat exchange medium can exit through these passages, thus enabling a continuous flow of the respective heat exchange medium during operation.

[0021] To keep the heat exchange medium contained within the system and prevent leaks, the gaskets 6 extend along the edges of the respective heat exchanger plates 4 around the non-planar, structured areas 4a, as well as around leakage chambers 4c and openings 4b. To hold each gasket 6 in its desired position, sealing grooves 4d are formed in the respective heat exchanger plates 4, into which the gaskets 6 are inserted in a correspondingly aligned manner, as shown in the example in Fig. 3 shown for several stacked heat exchanger plates 4.

[0022] Depending on the design, a (one-piece or segmented) loop-shaped or elongated seal 6a can be used as the seal 6, which is inserted into a sealing groove 4d that runs continuously around the non-planar, structured areas 4a, the leakage chambers 4c, and the openings 4b. Alternatively, an elongated seal 6a, which, for example, continuously surrounds at least the non-planar, structured areas 4a, can be combined with a separate ring seal 6b that surrounds and seals the openings 4b.

[0023] Such a seal 6 has the following functions in the relevant plate heat exchanger 1: to prevent an unwanted escape of the heat exchanger medium from the channels 7 and / or the openings 4b through gaps between the seal 6 and the heat exchanger plates 4 into an environment U even at higher pressures and higher temperatures, i.e. to enable continuous leak-free transport of the heat exchanger medium, and to provide a so-called permeability barrier so that the heat exchanger medium is prevented from penetrating the material of the seal 6.

[0024] An example of such a seal 6 (elongated seal 6a or ring seal 6b or the like) is shown in Fig. 4 The diagram is shown in a highly simplified cross-section. Leak-free transport can be achieved with such a seal 6 essentially by ensuring that the seal 6, even at higher pressures and temperatures of the heat exchanger medium, maintains continuous contact in the sealing groove 4d with a (top) first sealing surface 8a against a (bottom) first plate surface 15a of a (top) first heat exchanger plate 15 and with a (bottom) second sealing surface 8b against a (top) second plate surface 16a of a (bottom) second heat exchanger plate 16, thus preventing the formation of leakage gaps. To achieve this, the seal 6 is elastically deformed, at least at its edges, by the pressure of the adjacent (top and bottom) heat exchanger plates 4, 15, 16 against each other, and is thereby pressed against the material of the respective heat exchanger plates 4, 15, 16 over a large area in the sealing groove 4d.

[0025] The elastic deformability of the respective seal 6 is achieved by manufacturing a main body 9 of the seal 6 from an elastic sealing material MD, for example, NBR, EPDM, FKM, CR, or the like. The elasticity is generally achieved through the specific arrangement and chain-like or cross-linked connection of the atoms within such a sealing material MD of the seal 6. However, this arrangement of atoms in the main body 9 of the seal 6 also results in a certain permeability or penetrability of the main body 9, which can be quantified by a first permeability P9 of the sealing material MD. The heat exchanger medium can thus pass through the main body 9 from an inner sealing surface 8c, which corresponds to the channel 7 or the opening 4b, respectively.The fluids can penetrate the heat exchanger medium and, if no additional measures are taken, enter the environment U via an external sealing surface 8d facing the environment U. Depending on the type of heat exchanger medium, especially ammonia, this can lead to a hazard to the environment U.

[0026] To avoid this, i.e., to provide an effective permeability barrier, the seal 6 has, as in Fig. 4 and also in Fig. 3 In a highly schematic representation, a barrier layer B is added to the main body 9, having a barrier thickness DB of preferably a maximum of 50 µm. The barrier layer B preferably extends continuously in cross-section between the (upper) first sealing surface 8a and the (lower) second sealing surface 8b, which are pressed against the heat exchanger plates 4, 15, 16 and ensure leak-free transport. The barrier layer B has a second permeability PB that is lower than the first permeability P9 of the main body 9, preferably by at least one order of magnitude.

[0027] The barrier layer B contains a portion of barrier material MB or is made entirely of such barrier material MB, where, for example, a metal, an organic material (e.g., PTFE-based), or a fluorine-like material is used as barrier material MB. The barrier material MB is characterized by its dense packing, in particular by its higher density than the sealing material MD of the main body 9 of the seal 6. This dense material packing ensures that the heat exchanger medium can no longer penetrate the entire seal 6 from the inner sealing surface 8c to the outer sealing surface 8d, or at least that such transport is significantly reduced.

[0028] The barrier layer B preferably extends continuously, i.e., 100%, between the (upper) first sealing surface 8a and the (lower) second sealing surface 8b. In further embodiments, however, it is also possible for the barrier layer B to extend only partially, at least 80%, and in particular at least 90%, between the (upper) first sealing surface 8a and the (lower) second sealing surface 8b. It is also possible for more than one barrier layer B to be arranged in or on the seal 6, for example, one above the other, next to each other, or offset from each other, in which case all existing barrier layers B, in combination, preferably completely bridge (overlap) the (upper) first sealing surface 8a and the (lower) second sealing surface 8b.

[0029] In summary, the seal 6 is made of two different materials with different permeabilities P9 and PB, whereby the sealing material MD, through compression or deformation, ensures a leak-free seal, and the barrier material MB, through its densely packed atoms, reduces the overall permeability P6 of the seal 6. The barrier layer B can be, according to the Figuren 5A, 5B, 5C arranged in different ways on or in the seal 6 relative to the main body 9: As in Fig. 5A As shown, the barrier layer B can, for example, be designed as a coating 17 extending onto a surface 9a of the main body 9 in the area of ​​the inner sealing surface 8c and / or the outer sealing surface 8d between the (upper) first sealing surface 8a and the (lower) second sealing surface 8b. Such a coating 17 on one or both (inner and outer) sealing surfaces 8c, 8d can already prevent the heat exchanger medium from completely penetrating the seal 6 and thus from escaping into the environment U.

[0030] The coating 17 has a uniform coating thickness D17 of between 10 nm and 10 µm, preferably between 100 nm and 2 µm for metallic coatings, and between 0.5 µm and 50 µm, preferably between 1 µm and 10 µm for organic coatings. The coating 17 can be applied, for example, by any vapor deposition process. The coating thickness D17 can be selected depending on the barrier material MB, i.e., in particular, depending on the density of the atoms in the coating 17. Thus, for a barrier material MB with a denser atomic packing, a lower coating thickness D17 can generally be selected than for a barrier material MB with a less dense atomic packing. For example, in the case of a coating 17 made of a metal, a coating thickness D17 of less than 10µm can be chosen, since metallic materials usually have a very dense packing.

[0031] The coating thickness D17 and / or the density (in area) of the coating 17 can be selected such that the coating 17 only minimally affects the elastic properties of the main body 9. To this end, gaps or holes can be deliberately left in the coating 17 to avoid excessively impairing elasticity. Otherwise, reduced elasticity could prevent the first and second sealing surfaces 8a, 8b of the gasket 6 from being pressed firmly against the heat exchanger plates 4, even at high pressures and temperatures, potentially leading to leakage. Therefore, the reduction in permeability can be balanced with a reduction in the leakage capacity of the gasket 6.

[0032] According to another embodiment, which in Fig. 5B As shown, the barrier layer B can be formed by an insert 18, which has a maximum thickness D18 of 50 µm and is made entirely of the barrier material B. The insert 18 is embedded in the main body 9, thus extending (preferably completely) within the main body 9 of the seal 6 between the (upper) first sealing surface 8a and the (lower) second sealing surface 8b. The insert thickness D18, like the coating thickness D17 of the coating 17, can be selected depending on the barrier material MB, i.e., in particular depending on the dense packing of the atoms in the insert 18. For example, with an insert 18 made of a metal, insert thicknesses D18 of less than 10 µm can also be selected. Such an insert 18 can also prevent the heat exchanger medium from completely penetrating the seal 6 and thus escaping into the environment U.

[0033] The cross-sectional shape of the insert 18 is chosen such that, when the seal 6 is deformed by applying a force to the first and second sealing surfaces 8a, 8b during the compression of the two adjacent heat exchanger plates 4; 15, 16, the insert 18 yields or also deforms, so that the elasticity of the seal 6 is not negatively affected. For this purpose, the insert 18 is designed as shown in Fig. 5B The cross-section is shown as a C-shaped solid line or as an S-shaped dashed line. Other shapes are also conceivable that can achieve this level of flexibility.

[0034] Furthermore, such an insert 18 could also be applied to the surface 9a of the main body 9 in the area of ​​the inner sealing surface 8c and / or the outer sealing surface 8d, provided that a suitable durable bonding agent is used.

[0035] In the version in Fig. 5CThe two embodiments described above are essentially combined, i.e., a carrier 19 is provided which is coated on one or both sides with a coating 17. The coating 17 can have a coating thickness D17 of between 10 nm and 10 µm, preferably between 100 nm and 2 µm, in the case of a metallic coating, and between 0.5 µm and 50 µm, preferably between 1 µm and 10 µm, in the case of an organic coating. The carrier 19 has a thickness D19 of, for example, between 5 µm and 300 µm, preferably with a flexible C-shape or S-shape or the like. The carrier 19 can, for example, be made of an elastic material, so that only the coating 17 consists of the barrier material MB. Accordingly, only the coating 17 reduces the permeability of the seal 6 and the carrier 19 enables easier embedding of a very thin coating 17 in the main body 9.This allows the amount of barrier material MB to be saved, thereby improving elasticity properties and reducing costs. Reference symbol list

[0036] 1 Plate heat exchanger 2 Frame 3 Frame end plate 4 Heat exchanger plate 4a Structured area of ​​the heat exchanger plate 4 4b Openings in the heat exchanger plate 4 4c Leakage space in the heat exchanger plate 4 4d Sealing grooves in the heat exchanger plate 4 4e Raising in the respective structured area 4a 4f Recess in the respective structured area 4a 5 Cassette 6 Gasket 6a Elongated gasket 6b Ring gasket 7 Channel 8a First sealing surface of the gasket 6 8b Second sealing surface of the gasket 6 8c Inner sealing surface of the gasket 6 8d Outer sealing surface of the gasket 6 9 Main body of the gasket 6 9a Surface of the main body 9 10 Inlet nozzle 11 Inlet passage 12 Outlet nozzle 13 Outlet passage 15 First heat exchanger plate 15a First plate surface of the first heat exchanger plate 9 16 Second heat exchanger plate 16a Second plate surface of the second heat exchanger plate 10 17 Coating 18 Insert 19 Carrier B Barrier layer DB Barrier thickness D17 Coating thickness D18 Insert thickness D19 Carrier thickness MB Barrier material of barrier layer B of the seal 6 MD Sealing material of the main body 9 of the seal 6 PB Second permeability of barrier layer B P6 Total permeability of the seal 6 P9 First permeability of the main body 9 U Environment

Claims

1. Plate heat exchanger (1) with several adjacent heat exchanger plates (4) and a frame (2) in which the several heat exchanger plates (4) are clamped, wherein at least two channels (7) are formed between adjacent heat exchanger plates (4) for the passage of a heat exchange medium, wherein the respective heat exchange medium can be introduced into and discharged from the respective channel (7) via inlet openings (11) and outlet openings (13) formed by mutually aligned openings (4b) in the superimposed heat exchanger plates (4), wherein at least one seal (6) runs between the individual heat exchanger plates (4) to seal the respective channels (7) and / or the openings (4b) against an environment (U) and / or against each other, wherein the at least one seal (6) has a main body (9) made of an elastic sealing material (MD) and with a first permeability (P9), characterized by the fact thatthe at least one seal (6) further comprising at least one barrier layer (B) made of a barrier material (MB) and with a second permeability (PB), wherein the first permeability (P9) of the main body (9) is greater than the second permeability (PB) of the barrier layer (B) and wherein the barrier layer (B) has a barrier thickness (DB) of a maximum of 50µm, preferably a maximum of 25µm, in particular a maximum of 10µm.

2. Plate heat exchanger (1) according to claim 1, characterized by the fact that the barrier layer (B) is designed as a coating (17) with a coating thickness (D17) of between 10nm and 10µm, preferably between 100nm and 2µm, in the case of a metallic coating (17) and of between 0.5 µm and 50 µm, preferably between 1µm and 10 µm, in the case of an organic coating (17).

3. Plate heat exchanger (1) according to claim 2, characterized by the fact thatthe coating (17) is applied to a surface (9a) of the main body (9) of the seal (6), in particular to an inner sealing surface (8c) of the seal (6) which faces the channel (7) and / or the opening (4b), and / or an outer sealing surface (8d) of the seal (6) which faces the environment (U).

4. Plate heat exchanger (1) according to claim 2, characterized by the fact that the coating (17) is applied to one or both sides of a carrier (19) with a carrier thickness (D19) of between 5µm and 300µm, and the carrier (19) is embedded in the main body (9) of the seal (6).

5. Plate heat exchanger (1) according to claim 4, characterized by the fact that the support (19) is curved, in particular C-shaped or S-shaped.

6. Plate heat exchanger (1) according to any one of the preceding claims, characterized by the fact thatthe barrier layer (B) is designed as an insert (18) with an insert thickness (D18) of a maximum of 50µm, preferably a maximum of 25µm, in particular a maximum of 10µm, wherein the insert (18) is embedded in the main body (9) of the seal (6).

7. Plate heat exchanger (1) according to claim 6, characterized by the fact that the insert (18) is curved, in particular C-shaped or S-shaped.

8. Plate heat exchanger (1) according to any one of the preceding claims, characterized by the fact that the barrier material (MB) of the barrier layer (B) is or contains a metal or an organic material, for example PTFE-based, or a fluorine-like material.

9. Plate heat exchanger (1) according to any one of the preceding claims, characterized by the fact that the sealing material (MD) of the main body (9) is made of or comprises an elastomer, preferably of rubber, in particular of NBR, EPDM, FKM, CR.

10. Plate heat exchanger (1) according to any one of the preceding claims, characterized by the fact that the barrier layer (B) extends at least partially, preferably completely, between a first sealing surface (8a) of the seal (6), which abuts a first heat exchanger plate (15) of the several heat exchanger plates (4), and a second sealing surface (8b), which abuts a second heat exchanger plate (16) of the several heat exchanger plates (4).

11. Plate heat exchanger (1) according to one of the preceding claims, characterized by the fact that the at least one seal (6) has several barrier layers (B) which are arranged next to each other or offset from each other on the seal (6).

12. Plate heat exchanger (1) according to one of the preceding claims, characterized by the fact thatthe several heat exchanger plates (4) are joined together in pairs to form a cassette (5), wherein the first heat exchanger plate (15) and the second heat exchanger plate (16), between which the at least one seal (6) with the main body (9) and the at least one barrier layer (B) is arranged, each belong to a different cassette (5).

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