PRESSURE RELIEF DEVICE AND HOUSING COMPRISING SUCH A DEVICE

Description

[0001] The invention relates to a pressure relief device and a housing with such a pressure relief device. In particular, the invention relates to explosion-proof housings with the "flameproof enclosure" protection type, referred to as ex-d protection type.

[0002] Flameproof enclosures often feature a so-called pressure relief device, through which excess pressure within the enclosure can escape to the atmosphere. Such pressure relief devices typically comprise a porous body that is permeable to gases but prevents the penetration of flames or glowing particles due to the narrowness and length of the pores.

[0003] DE 10 2010 016 782 A1 discloses a pressure relief device with such a porous body, which has a first side facing the housing interior and a second side facing the environment. The pressure relief device also has a membrane arranged between the environment and the second side of the pressure relief body to keep dust and moisture away from the pressure relief body. This is intended to prevent the pores of the pressure relief body from filling with dust, moisture leading to degradation, mold growth, or other damage, or the formation of biodeposits that could impair function or at least be unsightly. If an explosion is ignited in the housing and a gas flow passes through the pressure relief body, the membrane ruptures, opening the way to the environment.The diaphragm is provided with a cuff at its edge, which connects it to a connection point on the pressure relief device. If the diaphragm is damaged, it must be replaced, which is why the cuff must be detachably connected to the pressure relief device. This can also lead to the diaphragm being accidentally removed from the pressure relief device. Furthermore, the diaphragm can tear or be damaged by external influences, such as if an object presses against it.

[0004] WO 2010 / 031336 A1 discloses an annular pressure valve that is particularly suitable for compressors and engines, for example, as a pressure relief valve on the crankcase. The valve has a spring-loaded valve plate that, in the event of excess pressure, opens a valve path that then leads radially through a flame-arresting body. The annular flame-arresting body, which may be made of wire mesh, for example, can be covered with plastic material.

[0005] WO 2017 / 106204 A1 further describes a flame-resistant ventilation system with a metal mesh flame screen provided with a cover. This cover protects the filter and other components of the flame-resistant ventilation system from damage or dust accumulation. The cover can be rigid or semi-rigid to provide impact protection for the filter. Furthermore, the cover can be designed to rupture in the event of an explosion, allowing gas to escape through the filter.

[0006] It is an object of the invention to provide a simplified pressure sensing device.

[0007] This object is achieved with the pressure relief device according to claim 1 and a housing according to claim 12.

[0008] The pressure relief device comprises a porous, gas-permeable body arranged at a gas passage point through which gas can escape from a volume expanding, for example, due to an explosion, into the atmosphere or into a containment volume. On the downstream side of the porous, gas-permeable body, facing the environment or the containment volume, a membrane is attached and rests against the porous body. This membrane covers the pores of the gas-permeable body, keeping external contamination and moisture away from the porous body. The membrane's contact with the porous body supports the membrane, protecting it from impact and similar external stresses.

[0009] Preferably, the membrane is adhesively attached to the porous body, with the adhesion preferably being at least sufficiently strong that the membrane does not detach from the porous body under differential pressures such as those encountered during proper operation. This ensures that the protection of the membrane, which is provided by its support on the porous body, is maintained over time.

[0010] The membrane can preferably adhere to the porous body, at least in places, and at least so firmly that it cannot be lost uncontrollably or detach from the porous body during the intended period of use of the pressure relief device. On the other hand, however, the adhesion is preferably so low that it detaches from the porous body if a pressure difference exists across the porous body that exceeds negligible pressure differences present during normal operation. During normal operation, small pressure differences can arise if operational heating or cooling occurs in a housing to which the pressure relief device is attached.

[0011] A pressure difference leading to detachment of the membrane from the porous body is preferably lower than the pressure difference leading to damage, deformation, or rupture of the connected housing. For example, the pressure difference can be less than 5 bar, 3 bar, 1 bar, a few hundred mbar, or even less than 100 mbar. The adhesion of the membrane to the porous body can be based on adhesion and / or on a positive interlocking of the membrane with the surface roughness or with the pores of the porous body.

[0012] Preferably, the adhesive strength of the membrane to the porous body is lower than its tensile strength. In this way, a gas flow passing through the porous body can cause a large-area detachment of the membrane from the porous body, so that in the event of an explosion, the membrane is blown away in its entirety, exposing the entire cross-section of the porous body to the gas flow.

[0013] The membrane is preferably a moisture-impermeable film that is attached to the porous body in a removable, adhesive manner. The membrane can be produced on the porous body by primary shaping. However, it can also be provided in prefabricated form, e.g. as a cut film, and attached to the porous body and, if appropriate, to a component connected to it. For this purpose, the film can be provided with an adhesive on the side facing the porous body. The film can also be a flexible, self-adhesive film. The porous body is preferably flat or only simply curved, such as cylindrically curved. It can also have several parallel edges. The film can also be a shrink film. In this case, it is particularly suitable for attachment to a porous body that has a three-dimensional shape, e.g. spherically curved.

[0014] In principle, all elastomers and polymers or other plastics, as well as mixtures thereof, are suitable as film materials that can be applied to the porous body in an uncured or incompletely cured form, and thus as a pasty or liquid preform, without the uncured material penetrating and clogging the pores of the porous body. To ensure this, the porous body can be provided with a wetting-inhibiting substance before the membrane is applied. For example, by spraying or otherwise applying a release agent, e.g., oil, an oil suspension, silicone, a silicone suspension, or the like, onto the surface of the porous body to be coated before spraying on the membrane.

[0015] After the membrane material has been applied to the porous body and, if applicable, to areas of a supporting or surrounding component, the membrane material is dried. Drying can occur by evaporating volatile solvents and / or by crosslinking and thus curing the precursor material. Crosslinking can occur spontaneously over time or by influences that cause crosslinking. Such influences can include exposure of the membrane material to air, moisture, heat, radiation, light, or the influence of chemical substances contained in the membrane material or applied to the membrane.

[0016] The membrane can be single-layer or multi-layered. In the simplest case, the membrane is a rubber or elastomer membrane sprayed onto the porous body, made of a material that is commercially used, for example, as a spray film in the automotive body sector. Such material is sprayed onto the porous body from the outside and "dried," with the sprayed material forming the desired membrane.

[0017] The membrane can be constructed in one or more layers. According to the invention, the membrane includes a film that is partially or fully in contact with the porous body. During membrane production, for example, this film is applied to the porous body, and the arrangement is then sprayed with the still-liquid membrane material.

[0018] The film can be paper, a plastic film, a metal foil, a fabric, a plastic-metal composite material, or another flexible sheet material. This arrangement facilitates the detachment of the membrane from the porous body and allows the application of the inventive concept when even particularly low pressure differences are required to lead to membrane detachment or when particularly low diffusion permeabilities are desired.

[0019] The inventive concept can be applied to pressure relief bodies of virtually any shape. These can be designed as three-dimensional bodies, such as cylinders, spheres, pyramids, polyhedra, or, if necessary, as flat bodies. Thus, the inventive concept opens up a wide field of applications that could not previously be solved economically or structurally.

[0020] The membrane can extend in sections over a body-supporting component and can also be attached to it. Such a component can e.g. a housing wall to which the porous body is attached. Particularly large pressure relief bodies, which are located behind a flow-dividing grid when viewed from the outside, can also be provided with a membrane by spraying it with membrane material.

[0021] The membrane can contain functional elements that monitor, for example, membrane integrity or other factors. This can be achieved, for example, by incorporating conductive pathways, temperature sensors, pressure sensors, or the like into the membrane. For example, a multilayer membrane structure can be used for this purpose. For example, a first layer of hardening material is sprayed onto the porous body, then functional elements are applied, and then a further layer of hardening and / or drying material is sprayed on. Such multilayer structures can be used to detect the detachment and tearing of a membrane and generate a signal from this, for example, to be transmitted to a central monitoring station.

[0022] Further modifications of the invention are possible. Embodiments of the invention will become apparent from the drawings, claims, and description. They show: Figure 1a housing with a pressure relief device according to the invention, in a schematic perspective view, Figure 2 the pressure relief device of the housing according to Figure 1 , in vertical section, Figure 3 a section of the pressure relief device according to Figure 2 , Figure 4 a modified embodiment of a pressure relief device on a housing, in vertical section, Figure 5 a modified embodiment of a pressure relief body with a membrane and additional functional element, Figure 6 the pressure relief device, in a greatly enlarged section, Figure 7 an embodiment of the pressure relief device according to the invention, in a sectional view similar Figure 6 .

[0023] In Figure 1A housing 10 is illustrated in perspective, partially cut away, enclosing an interior 11 in which symbolically illustrated components 12, 13 can be mounted, which can act as ignition sources during operation, for example, due to heat development, sparking, radiation, or other influences. The housing 10 separates these ignition sources 12, 13 from the environment 14 in order to prevent the propagation of flames or explosions that occur in the interior 11 into the environment 12. The housing 10 is preferably a housing of the protection type "flameproof enclosure" (ex-d). However, in order to enable rapid pressure equalization and thus rapid reduction of the excess pressure that has developed in the housing 10, particularly in the event of an explosion in the interior 11, a pressure relief device 15 is provided, which Figure 1is shown purely by way of example attached to the side of the housing 10. However, the pressure relief device 15 can also be arranged on any other surface of the housing 10. The housing 10 can also have several such pressure relief devices 15 of the same or different sizes.

[0024] In the example, the pressure relief device 15 is effective between the interior 11 and the environment 14. However, it is equally possible to arrange the pressure relief device 15 between the interior 11 and a pressure relief volume closed to the outside, which is temporarily or permanently separated from the environment 14. The pressure relief volume can itself be provided with a pressure relief device.

[0025] The structure of the pressure relief device is described in more detail in the Figures 2 and 3According to this, the wall of the housing forms a component 16, to which a pressure relief body 17 is attached directly or indirectly. In the present exemplary embodiment, the pressure relief body 17 is welded to the component 16 by an annular weld seam 18 extending around the circumference of the porous body 17. However, all other possibilities for connecting the housing wall forming the component 16 to the pressure relief body 17 are contemplated within the scope of the invention. For example, the pressure relief body 17 can be arranged in a socket, which in turn is connected to the component 16, for example, screwed, welded, glued or otherwise fixed to it. If the housing 10 is produced by casting or another primary forming process, for example, by additive manufacturing, the pressure relief body 17 can also be integrated into the component 16 at the edge, iebe embedded in the housing wall.

[0026] In the present embodiment, the pressure relief body 17 is attached to a pressure relief opening 19, via which the interior 11 is connected to the environment 14. This pressure relief opening 19 can have any suitable shape, for example, a rectangular or square shape with sharp or rounded corners, an oval shape, a circular shape, or any other suitable shape. The porous body 17 itself can also occupy the entire relevant wall surface of the housing 10, i.e., form the wall itself, or extend over several walls.

[0027] In the exemplary embodiment, the pressure relief opening is divided into several partial openings by a grid 20, as shown in Figure 1is shown in dashed lines. The grid 20 can serve to divide the gas flow passing through the porous body 17 into several partial flows and thus to even out the flow and also to support the porous body 17. In other embodiments, the grid 20 can also be omitted.

[0028] The porous body 17 can be any suitable flame-extinguishing, gas-permeable pressure relief body, such as an open-pore metal foam, a sintered metal body, or a body sintered from metal wires, where the wires can be arranged, for example, in a random manner like a fleece or felt or in stacked woven or knitted fabrics. The porous body 17 can also be formed by a ceramic body, a metallized ceramic body, a body sintered from ceramic fibers or other ceramic particles, or bonded with organic binders, or the like.

[0029] The pressure relief body 17 is, like the Figures 2 and 3 can be seen, provided with a preferably moisture-impermeable membrane 21, which surrounds the body 17 on its side 22 facing the environment 14 (see Figure 3 ) is preferably covered over its entire surface. The membrane 21 can also extend over the edge of the component 16 and overlap it at an edge surrounding the pressure relief opening 19. The membrane 21 thus seals the pressure relief opening 19, in particular against the ingress of moisture.

[0030] The membrane 21 is preferably produced on the housing 10 and thus on the pressure relief device 15 by primary forming. The body 17 and, if applicable, the component supporting it thus form a basis, a mold, so to speak, on which the membrane 21 is formed and thus primary formed. In the simplest case, the membrane 21 is produced by applying a precursor composition to the pressure relief body 17 and the edge of the pressure relief opening 19, e.g., by spraying, printing, rolling, brushing, or similar methods. Depending on the process, the membrane 21 can be produced with a substantially constant layer thickness or with varying layer thicknesses. The material is applied to the side of the porous body 17 on which the lower pressure prevails in the event of a required pressure reduction.

[0031] The formless, pasty or liquid precursor composition can, for example, be a partially crosslinked or uncrosslinked elastomer or polymer, or the like, such as is commercially available as sprayable "liquid rubber." Any other applicable, particularly sprayable, film can also be used, provided it forms a film that can be removed from the porous body 17.

[0032] The housing 10 with the pressure relief device 15 according to the invention operates as follows: When the housing 10 is provided, the membrane 21 is sprayed onto the pressure relief opening 19 and the body 17 arranged on it from the outside, covering the opening edge, so that the pressure relief opening 19 is closed to the outside by the resulting membrane 21. This prevents contamination and, if necessary, the ingress of dust or moisture into the body 17, which may result in the blockage of the pores of the body 17. For this purpose, Figure 6, which shows a cross-sectional view of the body 17 on its side facing the membrane 21. The material of the membrane 21 covers the pores 23, 24, 25, 26 without penetrating deeply into them. The membrane 21 adheres to the porous body 17 at least so firmly that an unintentional detachment of the membrane 21 from the porous body 17 and the housing 10 is excluded.

[0033] If the housing 10 has absorbed an explosive gas mixture, for example through existing cracks or other openings, and this is ignited, or if one of the components 12, 13 explodes or burns, an excess pressure builds up in the interior 11 compared to the ambient pressure 14, leading to a pressure difference across the pressure relief body 17. This causes the membrane 21 to detach from the body 17, so that the membrane 21 can detach from it, expand away from it, and tear open. The now destroyed membrane 21 thus clears the way for gas flowing out of the interior 11. However, the body 17 prevents flame penetration to the outside due to the length and narrowness of the pores 23 to 26.

[0034] After such an event, the membrane 21 must be replaced. In the simplest case, this is done by re-spraying membrane material, such as liquid rubber, onto the pressure relief opening 19 and the underlying porous body 17.

[0035] According to the invention, Figure 7 with a multi-layer membrane 21. In the example according to Figure 7 a film 27 and a layer 21a sprayed onto it, consisting, for example, of liquid rubber and subsequently cured. The film 27 adheres to the porous body 17 with low adhesion, and possibly very low adhesion, and covers it partially or completely. The sprayed-on layer 21a can adhere to the film 27 or merely lie loosely against it. The layer 21a can have a uniform thickness or varying thicknesses. In particular, it can be thinner in the central region of the film 27 or, in some places, particularly in the central area, be completely absent.

[0036] This design is particularly suitable for applications in which the diaphragm 21 must release the flow path through the pressure relief body 17 at very low pressure differences.

[0037] In a further modification of this embodiment, the layer 21a can also be limited to an edge region of the film 27, so that the layer 21 creates a moisture-tight connection between the film 27 and the component 16.

[0038] Figure 4 illustrates an embodiment with a three-dimensionally shaped body 17 serving for pressure relief, which is illustrated merely as an example as a hemispherical dome. However, cylindrical shapes with flat or rounded ends, polyhedral shapes, conical or truncated cone shapes, and the like are also possible. The outer side of the body 17 facing the environment 14 is again provided with a sprayed-on membrane 21, which forms a removable film. Otherwise, the previous description of the embodiments according to Figures 1 to 3 as well as Figures 6 and 7 accordingly.

[0039] A further modification, which is also applicable to all the above-mentioned embodiments, is illustrated Figure 5. There, a membrane 21 is sprayed onto the porous body 17, which contains a further functional element 28. Such a conductive element can be a conductor strip, as shown, applied to the membrane 21 or embedded in it. For example, a conductor track made of conductive paint, a metal foil strip, or the like can serve as the conductive strip. If the membrane 21 is detached from the pressure relief body 17 and the membrane 21 tears, this can be detected by the functional element 28. For example, a corresponding conductor strip can tear, and this can be detected and reported by a monitoring circuit.

[0040] Functional elements can also be integrated into the membrane structure according to Figure 7 be integrated. For example, the film 27 can carry functional elements, such as electronic components, conductor tracks, electronic circuits, and the like, which are then covered by the layer 21a.

[0041] It should be noted that the membrane 21 can also be provided in its entirety in the form of a prefabricated flexible film cut and attached to the body 17 of the pressure relief device 15 in contact with it. For this purpose, the film can be coated on one side with an adhesive that provides adhesion to the porous body 17. Alternatively, the film can be self-adhesive. The film can be designed as a thermally deformable film, e.g., as a shrink film or as a film that softens when heated and adheres to the body 17.

[0042] The pressure relief device 15 according to the invention comprises a gas-permeable body 17 to which a membrane 21 is adhered, which is preferably designed to be moisture-impermeable. The membrane 21 can be a single- or multi-layer rubber membrane, which is produced, for example, by applying liquid rubber to the pressure relief body 17 and, if appropriate, a component 16 supporting the pressure relief body and enclosing it. Reference symbol:

[0043] 10Housing 11Interior 12, 13Components 14Environment 15Pressure relief device 16Component 17Porous body / pressure relief body 18Weld seam 19Pressure relief opening 20Grid 21, 21aMembrane 22Side of the body facing the environment 17 23 - 26Pores 27Foil 28Functional element

Claims

1. Pressure relief device (15), in particular for explosion-protected housings (10), having a porous, gas-permeable body (17) that comprises a first side, which, in use, faces a volume that contains at least one potential ignition source (12, 13), and a second side which, in use, faces away from the volume, having a membrane (21) that is attached to the porous body (17) in such a manner that it is in abutment against the porous body (17), characterized in that the membrane (21a) includes a foil (27) that abuts against the porous body (17).

2. Pressure relief device according to claim 1, characterized in that the membrane (21) is attached to the porous body (17) in such a manner that it is in abutment thereagainst over its entire surface.

3. Pressure relief device according to any of the preceding claims, characterized in that the membrane (21) is adhered to the porous body (17).

4. Pressure relief device according to any of the preceding claims, characterized in that the membrane (21) is a moisture-impermeable foil.

5. Pressure relief device according to any of the preceding claims, characterized in that the membrane (21) is adhered to the porous body (17) in a detachable manner.

6. Pressure relief device according to claim 1, characterized in that the foil (27) is a piece of paper, a plastic foil, a metal foil, a composite material foil, a plastic / metal composite foil, a woven fabric or another flexible sheet-like structure.

7. Pressure relief device according to any of the preceding claims, characterized in that the body (17) is a planar pressure relief body.

8. Pressure relief device according to any of the claims 1 to 5, characterized in that the body (17) has a non-planar second side.

9. Pressure relief device according to any of the preceding claims, characterized in that the membrane (21) extends in sections over a component (16) supporting the body (21) and is adhered thereto.

10. Pressure relief device according to any of the preceding claims, characterized in that the membrane (21) extends over a grid (20) arranged on the second side of the body (17).

11. Pressure relief device according to any of the preceding claims, characterized in that the membrane (21) has been created on the porous body (17) using a primary forming method.

12. Housing (10) having a pressure relief device (15) according to any of the preceding claims.