Patent Publication Number: US-2022233989-A1

Title: Flame trap filter

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The application is a National Stage application of PCT/EP2020/062468, filed on May 5, 2020, which claims the benefit of German Application No. 10 2019 112 618.5, filed on May 14, 2019, the contents each of which are incorporated herein by reference thereto. 
    
    
     TECHNICAL FIELD 
     The invention refers to a flame trap filter for explosion protection. 
     BACKGROUND 
     A flame trap arrangement is known from EP 2 260 906 A1 that comprises an intermediate layer between two flame trap inserts allowing a radial distribution of gas escaping from one flame trap insert in principle in direction toward the second flame trap insert. 
     DE 10 2014 116 149 A1 describes a flame trap filter having an arrangement of subsequent woven filter layers. The opening width of the openings of a filter layer distinguishes from the opening width of openings of the subsequent filter layer. 
     DE 10 2017 112 162 A1 describes a flame trap filter having a number of woven layers having an intermediate layer with meshes comprising a mesh width of the intermediate layer openings that is larger than the size of meshes of the woven layers. 
     It can be considered as object of the present invention to provide an improved concept for flame trap filters. Particularly a need for pressure relief bodies exists in which the thermal input into the pressure relief body is distributed on a large surface and thus the effectiveness of the pressure relief body for pressure relief is increased. 
     BRIEF SUMMARY 
     Disclosed is a flame trap filter having at least one grid structure, wherein the at least one grid structure defines grid openings that are limited by web sections intersecting one another and/or wherein the at least one grid structure is formed by a laid scrim. 
     Also disclosed is a pressure relief device having a flame trap filter having at least one grid structure, wherein the at least one grid structure defines grid openings that are limited by web sections intersecting one another and/or wherein the at least one grid structure is formed by a laid scrim. 
     A method for manufacturing a grid structure of a flame trap filter having at least one grid structure, wherein the at least one grid structure defines grid openings that are limited by web sections intersecting one another and/or wherein the at least one grid structure is formed by a laid scrim, wherein a substance is solidified on a substrate, and/or wherein a material for the flame trap filter or a semi-finished product of the flame trap filter is compressed at locations. 
     The flame trap filter according to the invention comprises a grid structure. The grid structure according to the invention defines grid openings that are limited by intersecting web sections that are preferably arranged transverse, e.g. orthogonal, to a flooding direction of the pressure relief body and/or the grid structure according to the invention is formed by a laid scrim. 
     The web sections can be straight or curved. Web sections are preferably strip and/or rod shaped. The grid openings limited by intersecting web sections can be polygonal, preferably rectangular, particularly square. It is alternatively also possible that intersecting web sections limit circular or elliptical grid opening. The intersecting web sections can form a perforated grid, e.g. perforated metal sheet, that comprises, for example, circular and/or elliptical grid openings. Alternatively, a perforated foil can comprise intersecting web sections that limit, for example, circular and/or elliptical grid openings. 
     The laid scrim formed as an alternative or in addition is a two-dimensional structure of at least two layers having webs extending in one direction in a straight or curved manner in each case. Webs can be particularly strip and/or rod shaped. The laid fabric can be bidirectional or multi-directional. The directions are orientated transverse to each other, e.g. orthogonal, and extend transverse and particularly orthogonal to the flooding direction of the flame trap filter. 
     By means of the grid structure of the inventive flame trap filter, flooding channels or screens are formed. The flow through the filter is divided into partial flows. This may result in a distribution of the thermal input into the flame trap filter on a larger area. In doing so, the effectiveness of the flame trap filter can be improved. 
     In embodiments the flame trap filter can be formed from an arrangement of at least two layers that are not directly connected with each other. They form a flame trap filter arrangement. One or more of the layers can consist of one single layer or can be combined of at least two sub-layers that are directly connected with each other. 
     Two more layers of the flame trap filter can be arranged to adjoin one another or to abut one another, wherein these layers may be directly attached with one another or may not be directly attached with one another. The grid structure can form a layer that directly adjoins a layer or is arranged to abut against a layer that individually or guarantees a flameproof condition of the flame trap filter arrangement, if applicable together with additional layers. As an alternative, the grid structure can be arranged with distance to the layer that guarantees the flameproof condition. 
     Layers of the flame trap filter can form a flame trap filter body. For this purpose the layers can be connected with each other. For example, the layers can be sintered, glued, welded with each other or can be connected with each other in another manner, particularly by substance bond. For example, the grid structure can form a layer or can be part of a layer that is connected with an additional layer. In other embodiments the grid structure can form a layer or can be part of a layer that is separate from the adjacent layer. Particularly such a layer that is not connected with the adjacent layer can also be denoted as plane of the flame trap filter arrangement. 
     The flame trap filter individually or together with additional elements can form a pressure relief body for an explosion-protected housing for electrical operating means, particularly in the explosion protection type flameproof enclosure. By means of the grid structure, a pressure relief flow can be divided in partial flows, whereby the thermal input in the pressure relief body is distributed on a larger area and thus the effectiveness of the pressure relief body for pressure relief is increased. Another advantage of the flame trap filter according to the invention forming a pressure relief body for an explosion-protected housing is that an additional cumbersome processing of the housing may be avoided. This is because the grid structure is part of the flame trap filter and thus the pressure relief body. It is therefore not required to introduce part openings or grid webs in the wall of the explosion-protected housing. 
     The grid structure forms at least one layer of the flame trap filter. The flame trap filter can comprise at least one additional layer. At least one or all of the additional layers can be formed by a grid structure according to the invention as described herein. Accordingly, one or each additional layer can comprise a grid structure that defines grid openings that are limited by intersecting web sections from one another and/or wherein the grid structure is formed by a laid scrim. As an alternative or in addition, the flame trap filter according to the invention can comprise a number of woven layers. 
     A grid structure according to the invention can form an additional layer between two additional layers. As an alternative or in addition, the grid structure according to the invention can form a terminal layer at the side of the arrangement of additional layers orientated opposite to the flow direction or can form a terminal layer at the side of the arrangement of additional layers facing in flow direction. If the flame trap filter forms a pressure relief body of a pressure-resistant housing, the flow direction is preferably from the interior of the housing outwardly. 
     Embodiments of the flame trap filter according to the invention having grid openings that are limited from one another by intersecting web sections comprise, for example, at least one layer of sheet metal or foil with a plurality of openings that form grid openings. These openings can be manufactured by cutting sections out of the sheet metal or foil material. The grid structure can be formed by one or multiple of such layers. If multiple layers are present, the openings are preferably arranged on top of each other, such that the layers that are connected or not connected with each other form channels or screen openings as grid openings that extend through the arrangement of layers in an orthogonal orientation. 
     Independent from the embodiment of the grid structure with intersecting web sections limiting an opening, the web sections themselves are preferably free from openings. 
     The grid structure can be particularly manufactured by shearing (stamping) and/or laser cutting of the grid structure from foil or sheet metal. In doing so, the grid opening area is respectively cut out of the foil or sheet metal under material losses. Thereby one or more cutting lines are introduced into the material and the cutting or stamping remnant—that preferably foil or sheet metal shaped and/or comprises a shape different from a chip shape—is removed within the one or more stamping or cutting lines in order to form the grid opening in the sheet metal or foil. The grid structure is preferably not manufactured by perforating, wherein the foil of sheet metal is drilled by means of a laser, an electron beam or a mechanical drill. The grid structure can be formed by an expanded grid. This can consist of metal—in this case also denoted as expanded metal—or plastic. For manufacturing of expanded grids or expanded metals, the meshes (grid openings) are created by offset cuts, preferably substantially without material loss, under expanding deformation. 
     As an alternative or in addition an inventive grid structure can be manufactured by laying strips, particularly foil or cheap metal strips. 
     If the grid structure is formed by a laid scrim, each layer is preferably exclusively formed by webs extending in one direction. Webs of a first direction extend preferably either on top of or below (in case of respective potentially virtual orientation of the flame trap filter) the arrangement of webs of the second direction. A change does preferably not occur. 
     In relation to a woven fabric in which grid openings are formed by meshes, wherein between two adjacent meshes one single longitudinal warp element or longitudinal weft element is arranged in a grid structure with intersecting web sections or a grid structure that is formed by a laid scrim, the length of the webs can be shorter than in a woven fabric in which each “thread” comprises a kind of wavy structure in order to alternatingly extend on top of or below transverse extending webs or threads, provided equal dimensions of the grid structure. In doing so, the thermal conductivity of the web structure is improved compared with a woven fabric. 
     Additional layers that can be provided in addition to the grid structure in embodiments can comprise openings, the opening area of which is defined in an opening area range. The opening area of the grid openings of the grid structure is preferably multiple times, preferably at least ten times or at least thirty times or even at least one hundred times larger than the largest opening area within the opening area range. 
     In embodiments the grid structure can be at least in sections a woven fabric comprising meshes, the mesh width of which is in a first mesh width range and comprising meshes, the mesh width of which is in a second mesh width range, wherein each mesh width in the second mesh width range is larger than the largest mesh width in the first mesh width range. The meshes having mesh widths in the second mesh width range form the grid openings. The grid openings can have a uniform mesh width. Arrangements of multiple longitudinal warp elements or weft elements extend between adjacent grid openings. They are woven with weft elements or warp elements extending transverse thereto. Preferably in a manner such that the longitudinal weft elements or warp elements within the arrangement between two grid openings are individually or in groups alternatingly located above or below single or groups of warp elements or weft elements extending transverse thereto. 
     The mesh widths in the second mesh width range are preferably at least five times larger or even at least ten times larger than the largest mesh widths in the first mesh width range. Accordingly, a grid structure can be woven, wherein in regular or irregular distances between adjacent warp threads or adjacent weft threads a distance is selected from the second mesh width range, wherein the webs of the grid structure are formed by longitudinal warp elements or longitudinal weft elements that limit meshes between each other having mesh widths in the first mesh width range. The webs are preferably strip-shaped structures woven with one another on the level of warp and weft elements comprising multiple warp elements or multiple weft elements respectively. The warp elements and weft elements can be particularly wires or strips of metal or plastic. The mesh width zero can be particularly part of the first mesh width range. The warp elements and weft elements that form meshes having a mesh width in the first mesh width range can thus form zero meshes. For example, the warp elements and/or weft elements can be wire, thread and/or strip-shaped. 
     In embodiments the grid structure can be created by compressing a material for the flame trap filter or a semi-finished product of the flame trap filter, wherein the webs of the grid structure are formed by locations at which the material or the semi-finished product is compressed. 
     Compressing may have been carried out by mechanical deformation. Alternatively, compressing may have been carried out by introducing a substance in one or more layers of the material or the semi-finished product of the flame trap filter. Compressing may have been carried out on a single side of the material or the semi-finished product of the flame trap filter facing the flow or the side of the material of the flame trap filter or the semi-finished product of the flame trap filter facing in flow direction. 
     By compressing and/or mechanical deformation, a structure of the flame trap filter can be created in which the thickness of the flame trap filter measured at a web section is less than the thickness measured in a grid opening of the grid structure. 
     The side facing the flow and/or the side facing away from the flow can have a wavy structure having a period corresponding to the opening width of the grid structure. Due to compressing, cushion-like areas can be formed in which the layers are less compressed between compressed locations that form the web sections. 
     As an alternative or in addition, web sections of the grid structure can be manufactured by solidifying a substance on a substrate. The substrate can be a material of the filter body, a semi-finished product of the filter body or an aid substrate that is removed for manufacturing the flame trap filter in a later process step. For example, the substance can be silicone glue or metal. For example, the solidified substance can be a weld bead. The web sections can be formed by an additive manufacturing process. In embodiments the web sections can be created by welding and/or by laser deposit welding. 
     The web sections can block the direct passage of gas through openings of a layer of the flame trap filter. The substance can close openings of a layer of a flame trap filter. 
     In embodiments it is possible that the layers are free of connection locations for connection of the layers within the projection of each grid opening area of the grid structure in flooding direction. In other words the space past or followed by virtual shift of the grid opening area in flooding direction is preferably free of connection locations for connection of layers. 
     With the method for manufacturing a grid structure according to the invention, an inventive flame trap filter can be manufactured, for example, as described herein. According to the invention, a substance can be solidified on a substrate, particularly on a material or semi-finished product of the flame trap filter. Alternatively or in addition, a material for the flame trap filter or a semi-finished product of the flame trap filter can be compressed at locations that all together define a grid in order to create the grid structure, e.g. by mechanical deformation of the material or the semi-finished product. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional exemplary features and embodiments of the inventive flame trap filter, the pressure relief body as well as the method are derived from the dependent claims, the subsequent description as well as the figures. The drawings show: 
         FIG. 1 —a perspective view of an embodiment of an opened and apart therefrom, explosion-protected housing having two pressure relief devices with one inventive flame trap filter in each case, 
         FIG. 2 a   —a perspective view of an embodiment of the inventive flame trap filter, 
         FIG. 2 b   —a top view of a part of the flame trap filter according to  FIG. 2   a,    
         FIG. 2 c   —a top view of a part of the flame trap filter according to a further embodiment, 
         FIG. 2 d   —a top view of a part of a flame trap filter according to yet another embodiment, 
         FIG. 3 —a perspective view of another embodiment of an inventive flame trap filter, 
         FIG. 4 a   —a sectional view through a yet additional embodiment of an inventive flame trap filter, wherein the flooding direction is within the sectional plane, 
         FIG. 4 b   —a top view of a part of the flame trap filter according to  FIG. 4   a,    
         FIG. 5 —a perspective view of a semi-finished product of an example of a fourth embodiment of the inventive flame trap filter. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of explosion-protected housings are explosion protected according to the explosion protection category “flameproof enclosure”. Inventive housings can comprise one or more pressure relief devices having at least one inventive flame trap filter in each case. 
       FIG. 1  shows an embodiment of such an explosion-protected housing  10  with removed cover. The housing  10  defines an interior  11 . The housing  10  comprises two pressure relief openings  12   a ,  12   b . These are closed in a flameproof manner by pressure relief bodies  13   a ,  13   b  having at least one inventive flame trap filter  14   a ,  14   b  in each case. A gas exchange through the flame trap filter  14   a ,  14   b  is in principle possible, e.g. in order to achieve pressure compensation between the interior  11  of housing  10  and its environment. In case of an explosion in interior  11  of housing  10 , however, gases or particles can escape from housing  10  through flame trap filters  14   a  or  14   b  only cooled down, such that a gas or particles cannot ignite the atmosphere outside housing  10 . In the illustrated embodiment the flame trap filter  14   a  is arranged in a first pressure relief body  13   a  such that the inventive grid structure  15   a  for dividing the pressure relief opening  12   a  in multiple partial openings  16  is facing the interior  11  of the explosion-protected housing  10 . In the case of the first pressure relief body  13   a  the grid structure  15   a  is accordingly passed by a flow prior to at least one additional layer of the flame trap filter  14   a . The same also applies to the flame trap filter  14   b  of the second pressure relief body  13   b , the grid structure of which is covered by at least one additional layer of the flame trap filter  14   b  in the view shown in  FIG. 1 . Alternatively, the at least one flame trap filter  14   a ,  14   b  can be orientated such that the inventive grid structure faces outwardly, such that the grid structure is passed by flow after gas has flown through the at least one additional layer of the flame trap filter of the second pressure relief device. In yet further embodiments the grid structure can form an intermediate layer between at least two additional layers of the flame protection filter (not illustrated). 
     In each case each pressure relief body  13   a ,  13   b  divides the pressure relief opening  12   a ,  12   b  in the housing  10  into partial openings  16 . 
     The sub-division of the pressure relief opening  12   a ,  12   b  in partial openings  16  is carried out by the web sections  17  (compare e.g.  FIG. 2 a   ) of grid structure  15   a . Because the web sections are not monolithic parts of wall  18  of housing  10  that limits the pressure relief opening  12   a  or  12   b , a cumbersome processing of the housing wall  18  for manufacturing of grid structure  15   a  for spreading the thermal input and/or the gas flow is not required. It is rather sufficient to form a pressure relief opening  12   a ,  12   b  with continuous opening surface in the wall  18  of housing  10  that is only subdivided in partial openings  16  by a flameproof closing of the pressure relief opening  12   a  or  12   b  by means of the pressure relief bodies  13   a ,  13   b.    
     With the grid structure  15   a  created by web sections  17  a pressure relief flow outwardly out of interior  11  of housing  10  is subdivided in partial flows, whereby the thermal input in the pressure relief body  13   a  (the same applies for the pressure relief body  13   b ) is distributed over a larger area and thus the effectiveness of the pressure relief body  13   a  for pressure relief is increased. 
     In an embodiment the grid openings of the grid structure  15  can be limited by intersecting web sections  17   i ,  17   ii . Web section  17   i ,  17   ii  are arranged transverse, preferably orthogonal to a flooding direction D of the pressure relief body  13   a ,  13   b . Web sections  17   i ,  17   ii  can be straight or curved. Web sections  17   i ,  17   ii  can be rod-shaped. Web sections  17   i ,  17   ii  can form a perforated grid. Preferably web sections  17   i ,  17   ii  extend in a common plane. The grid structure  15   a  is preferably planar and/or the intersecting web sections  17   i ,  17   ii  are arranged in one plane. 
     A regular grid structure  15   a  that is formed by intersecting web sections  17   i ,  17   ii  is exemplarily shown in a perspective view in  FIG. 2 . Index a or b is omitted in the following, because the first flame trap filter  14   a  and/or the second flame trap filter can be carried out according to one of the subsequently described embodiments, for example. The grid structure  15   a  shown in  FIG. 2  comprises rectangular, here square, grid openings  19  that form the partial openings  16  of the pressure relief opening  12 . The grid openings  19 , apart from the grid openings at the edge of the grid structure  15 , comprise preferably the same area. The grid structure  15  is illustrated in  FIG. 2  as a terminal layer that either faces a gas flow direction D from the interior  11  of housing  10  or faces in gas flow direction D out of the interior  11  outwardly. It is, however, alternatively or in addition also possible that a grid structure  15  having grid openings  19  that are formed by web sections  17   i ,  17   ii  intersecting one another, forms an intermediate layer. 
     In the illustrated embodiment the outer contour of the grid structure  15  is round. The grid structure  15  can, however, also be polygonal or angular, e.g. rectangular or square. Preferably the shape of the outer contour is geometrically similar to the shape of the outer contour of the pressure relief body  13  and/or the pressure relief opening  12 . 
     For example, the grid structure  15  can be manufactured from a sheet metal or foil. Intersecting web sections  17   i ,  17   ii  can be formed, for example, in that grid openings  19  are cut off the foil or sheet metal, e.g. by laser cutting and/or stamping. The web sections  17   i ,  17   ii  can be made of metal or plastic. The grid structure  15  according to  FIG. 2  can be cut or stamped out of a sheet metal part or a metal foil, for example. In doing so, the grid opening areas  19  are manufactured under material losses. 
     In a modification the grid structure  15  can be formed by an expanded grid, particularly expanded metal (not shown). For manufacturing of an expanded grid, meshes are created by offset cuts without material loss under concurrent expanding deformation. These meshes are at least limited at two sides by web sections intersecting one another. Without additional measures, however, pairs of web sections intersecting one another do not extend parallel to a common plane, but even if the grid structure as a whole extends in a grid plane, the pairs of intersecting web sections are extending obliquely to this grid plane. By mechanical deformation transverse to the grid plane, all pairs can be deformed such that they extend parallel to the grid plane. 
     Due to intersecting web sections  17   i ,  17   ii , heat introduced at one point in the grid structure  15  cannot only be conducted substantially by the web in which the heat is introduced, as in case of a woven fabric, but the heat conduction can be partly taken by the intersecting web section at the intersections of two web sections  17   i ,  17   ii . If the webs or web sections  17   i ,  17   ii  are straight, short webs are obtained and as a result a remarkably good heat conductivity can be obtained. Contrary thereto, a web has to have a wavy shape in a woven fabric in order to alternatingly extend above or below of crossing rods. This elongates the web compared with a straight web in case of equal area of the flame trap filter. 
     Due to the intersecting web sections  17   i ,  17   ii , the grid opening limited by the intersecting web sections  17   i ,  17   ii  is delimited from an adjacent grid opening. A cross flow from one grid opening in the plane of the grid structure is thus impeded or blocked. The intersecting web sections  17   i ,  17   ii  thus form flooding screen openings or channels for a separation of the gas flow in partial flows at least within the plane of the grid structure  15 . This is contrary to a woven layer in which the webs cross, but not intersect such that less flow resistance encounters a cross flow in the woven layer. 
     The flame trap filter  14  comprises additional layers or sub-layers  20 . 2  to  20 . 8  that can form grids respectively. These additional layers  20 . 2  to  20 . 8  can be woven layers. Alternatively, one or more additional layers  20 . 2  to  20 . 8  can be formed from a laid scrim and/or intersecting web sections. It is alternatively or additionally also possible that at least one or all additional layers  20 . 2  to  20 . 8  are manufactured from entangled fiber material or felt material. The flame trap filter  14  can be formed by an arrangement of planes  20 . 1  to  20 . 8  that are not connected with one another. Preferably the grid structure  15  (layer  20 . 1 ) and the additional layers  20 . 2  to  20 . 8  are, however, connected with one another. For example, the layers  20 . 1  to  20 . 8  can be glued with one another, can be connected with one another by sintering, can be connected with one another by mechanical deformation, by screwing or the like. In other embodiments the grid structure  15  is not connected with the finer grids of layers  20 . 2  to  20 . 8 , wherein the finer grids of layers  20 . 2  to  20 . 8  are connected with one another or not connected with one another. Embodiments are possible in which more or less than eight layers  20 . 1  to  20 . 8  are arranged adjacent or on top of each other and namely in contact with one another or not in contact with one another. 
     Grid layers  20 . 2  to  20 . 8  present in addition to the grid structure  15  comprise a plurality of openings  21 , the opening area of which is defined within an opening area range. The opening area of the grid openings  19  of the grid structure  15  is preferably multiple times larger, preferably at least five times or even at least ten times or even at least thirty times or even at least one hundred times larger than the largest opening area within the opening area range. An example for this is shown in  FIG. 2 b   . It illustrates a top view of a part of the inventive flame trap filter  14  according to  FIG. 2 a   . The section A shown in  FIG. 2 b    is illustrated in dashed lines in  FIG. 2 a   . As illustrated, layer  20 . 2  arranged below the grid structure  15  forms openings  21  having an opening area that is multiple times smaller, in the present embodiment far more than ten times smaller than the opening area of a grid opening of the grid structure  15 . In doing so, a coarse division of the pressure relief flow in partial flows is achieved by grid structure  15 . The flame trap filter  14  can be configured such that the grid structure  15  furthermore does not contribute to the flameproof condition. Rather remaining layers  20 . 2  to  20 . 8  can together already provide flameproof condition. The grid structure  15  serves only for distribution of the gas flow over the entire area of the flame trap filter  14 . 
     While seven layers  20 . 2  to  20 . 8  are illustrated in the illustrated embodiment that together guarantee the flameproof condition, it could also be more or less layers (e.g. only one). 
     Alternatively or additionally and different to the illustrated embodiment, more than only one layer  20 . 1  can form the inventive grid structure  15 . For example, a flame trap filter  14  can have at least two layers (not illustrated) that respectively form inventive grid structures  15 . The multiple, at least two grid structures provided exemplarily subdivide the flow through the flame trap filter subsequently in coarse partial flows. Between at least two grid structures one or more finer grids can be arranged. With the at least two grid structures the gas flow can be controlled or guided. 
     The opening width (e.g. mesh width) of the multiplicity of openings  21  provided in the additional layers  20 . 2  to  20 . 8  are preferably defined within an opening width range. Preferably the width of the web sections  17   i ,  17   ii  of grid structure  15 , as apparent from  FIG. 2 b   , is larger than the largest opening width within the opening width range. Preferably the width of each web section  17   i ,  17   ii  covers at least one or at least two openings  21  of layer  20 . 2  arranged below the web sections  17   i ,  17   ii . “Below” refers to a respective—potentially virtual—orientation of flame trap filter  14 . 
       FIG. 2 c    shows a section A of another embodiment of the inventive flame trap filter  14 .  FIG. 2 c    illustrates a top view of the embodiment in part. Different to the embodiment illustrated in  FIG. 2 a    in which a perforated grid with square openings is shown, the grid structure of the embodiment illustrated in  FIG. 2 c    is a perforated grid, e.g. perforated sheet metal or perforated foil, having circular grid openings  19 . Apart therefrom the description referring to the embodiment according to  FIGS. 2 a  and 2 b    can be used for the explanation of the embodiment according to  FIG. 2   c.    
       FIG. 2 d    shows a section A of a further embodiment of an inventive flame trap filter  14 .  FIG. 2 c    illustrates a top view of the embodiment in part. The grid structure  15  can comprise grid openings  19  arranged in regular (as e.g. illustrated in  FIG. 2 a   ) or irregular distances that are formed in the embodiment according to  FIG. 2 d    by meshes  19  between two longitudinal warp elements  29  and two longitudinal weft elements  30 , wherein the meshes  19  have a mesh width in a second mesh width range. Between the meshes  19  webs  17   i ,  17   ii  extend that are formed of an arrangement of multiple longitudinal warp elements extending adjacent to one another or an arrangement of multiple longitudinal weft elements  30  extending adjacent to one another. The warp elements  29  and/or weft elements  30  can be particularly wire-, thread- or strip-shaped. Within the arrangement meshes  31  are formed between adjacent weft elements  30  and warp elements  29  having a mesh width in a first mesh width range. The mesh width in the second mesh width range is larger than each mesh width in the first mesh width range. The mesh widths in the second mesh width range are preferably at least five times larger or even at least ten times larger than the larges mesh width in the first mesh width range. The first mesh width range can particularly comprise the mesh width zero. Accordingly, zero meshes can form meshes  31  in the arrangements. 
     The grid structure according to  FIG. 2 d    comprises intersecting web sections  17   i ,  17   ii  that limit a grid opening  19 . The webs  17   i  are formed of an arrangement of multiple longitudinal warp elements  29  in each case, wherein distant thereto multiple transverse, preferably orthogonal, extending longitudinal weft elements  30  are woven—preferably in plain weave—forming a further web  17   ii , wherein the web  17   i ,  17   ii  limit a mesh  19  (grid opening) having a mesh width in the second mesh width range and the weft and warp elements limit meshes in the intersection ranges of the arrangement have a mesh width less than the mesh width of mesh  19 , for example mesh width zero, between intersecting arrangements. As illustrated, longitudinal weft elements  30  or longitudinal warp elements  29  within the arrangement are alternatingly arranged above or below singular warp elements  29  or weft elements  30  extending transverse thereto between two grid openings  19 . 
     The mesh width of the grid opening  19  is preferably and as apparent from  FIG. 2 d    larger than the width b of each web section  17   i ,  17   ii  that limit the grid opening  19 , e.g. at least five times larger or at least ten times larger. This applies accordingly for other inventive embodiments, e.g. for the embodiments that are illustrated in the further figures. 
     In the view according to  FIG. 2 d   , a layer  20 . 2  having openings  21  that are smaller than the grid opening  19  is schematically illustrated below the grid structure  15 . For this and for additional optional features reference can be made to the description referring to the further embodiments. 
       FIG. 3  shows an example of another embodiment of an inventive pressure relief body  13 . The pressure relief body can have the inventive flame trap filter  14  or can consist thereof. For the flame trap filter  14  reference can be made to the above description as long as it is not described otherwise in the following. The grid structure  15  is formed of a laid scrim in the embodiment illustrated in  FIG. 3 . The laid scrim comprises a layer of webs  17   i  orientated in a first direction R 1  and a second layer of webs  17   ii  orientated in a second direction R 2  transverse to the first direction R 1 , e.g. orthogonal. In doing so, rectangular, particularly square, or other polygonal grid openings  19  can be created. For example, the laid scrim can be formed by arranging of sheet strips, e.g. sheet metal strips, in the first direction R 1  and the arrangement of additional sheet strips in the second direction R 2 . As illustrated, preferably no web  17   i ,  17   ii  changes the layer, but all webs  17   i  or  17   ii  are arranged on one side over the entire length of the arrangement of webs  17   ii  or  17   i  orientated transverse thereto. The sheet strips of different orientation are preferably connected with one another at the crossing locations, e.g. glued, sintered, welded or the like. The webs  17   i  and/or  17   ii  of one or both layers are preferably straight in order to provide a connection to the edge of the flame trap filter  14  that is as short as possible in order to distribute heat in the pressure relief body  13  and/or discharge heat in the housing wall  18 . 
     Another possibility for configuration of the inventive grid structure is to compress a material for the flame trap filter  14  or a semi-finished product of the flame trap filter  14  by mechanical deformation at locations  22  that together form a grid structure  15 . The locations  22  at which the material or semi-finished product is compressed by mechanical deformation form the web sections  17   i ,  17   ii  of the grid structure  15 . The web sections  17   i ,  17   ii  thus intersect. Preferably the web sections  17   i ,  17   ii  are arranged in one plane. A wave structure is obtained having a period that corresponds to the opening width of the grid structure  15 . A respectively manufactured embodiment is shown in part cross-sectional illustration in  FIG. 4 a   . The flow or flooding direction D is within the cross-section plane.  FIG. 4 b    shows a section of a top view on the side of the flame trap filter  14  structured by compression. 
     Between the webs  17   i ,  17   ii  less compressed cushion-shaped areas  23  are formed such that as a whole a quilt structure results. These areas  23  form the grid openings  19 , because the permeability of the flame trap filter  14  through the webs  17   i ,  17   ii  is compared with the permeability through the areas  23  at least remarkably reduced. The locations  22  can be compressed so intensively that the webs  17   i ,  17   ii  are gas impermeable. As illustrated in the embodiment according to  FIG. 4 , side  24  of flame trap filter  14  having the quilt structure is opposed to flow direction D. The opposite side  25  is flat. In alternative embodiments the quilt-like three-dimensionally structured side  24  is orientated in flooding direction D. In again other embodiments the material for the flame trap filter  14  and/or the semi-finished product is compressed from both sides  24 ,  25  such that two opposite orientated sides  24 ,  25  result that can be three-dimensionally structured, e.g. quilt-like. 
     The material can comprise one or multiple layers, particularly woven layers. The material can comprise exclusively woven layers, for example. By mechanical deformation, however, a flame trap grid is created in total having a grid structure of web sections  17   i ,  17   ii  intersecting one another. 
     In embodiments as shown in  FIG. 4 , the thickness dl of flame trap filter  14  measured at web sections  17   i ,  17   ii  is less than thickness d 2  measured in a grid opening  19  of grid structure  15 . Measuring at a web section  17   i ,  17   ii  means that the web section  17   i ,  17   ii  is measured in straight line (parallel to flooding direction) between the two reference points, the distance of which is determined. The same applies for the grid opening  19 . 
       FIG. 5  shows an example of a still further embodiment. For explanation the description above can be applied as long as it is not otherwise indicated in the following description. In the further embodiment the grid structure  15  is at least partly manufactured by solidifying a substance on a substrate  26 . The substrate  26  can be an aid that has to be removed again for providing the flame trap filter  14 . As an alternative—and as illustrated—a substrate  26  can form at least one layer of the flame trap filter  14 . 
     In the embodiment illustrated in  FIG. 5  webs  17   ii  of one layer of one direction R 1  are already manufactured. A web  17   ii  extending in a direction orientated transverse thereto, preferably orthogonal is manufactured by means of an instrument I in that material  27  is applied on the flame trap filter semi-finished product  28  and is solidified there to form a web  17   i . The material  27  can be, e.g. silicone or adhesive. It is also possible to solidify at least partly liquid or soft material on the substrate  26 . For example, the web sections  17   i ,  17   ii  can be formed by weld beads. A possibility is to apply metal powder on substrate  26  and to at least partly melt them, e.g. by means of a laser, such that the metal particles connect during solidification. The web sections  17   i ,  17   ii  can be particularly manufactured by laser deposit welding or by another manufacturing method suitable for additive manufacturing of webs. Thereby, besides metal, also plastic or materials based on natural substances can be introduced or applied. If webs  17   i ,  17   ii  are created, a laid scrim of webs  17   i ,  17   ii  is obtained. 
     Independent from the configuration in particularly preferred embodiments, some layers or all layers  20 . 2  to  20 . 8  that can be present in addition to the grid structure  15  in the flame trap filter  14  are free from connection locations within the projection of each area of grid openings  19  of grid structure  15  in flooding direction D. In other words, the space that is passed by the virtual shift of an area of grid opening  19  in flooding direction D is preferably free of connection locations. From this a highly increased flow resistance results at the web sections  17   i ,  17   ii , however, a remarkably lesser flow resistance between web sections  17   i ,  17   ii.    
     According to the invention, a flame trap filter  14 ,  14   a ,  14   b  having a grid structure  15 ,  15   a  is provided, wherein the grid structure  15 ,  15   a  defines grid openings  19  that are limited by web sections  17   i ,  17   ii  intersecting one another and/or wherein the grid structure  15 ,  15   a  is formed by a laid scrim. An inventive method for manufacturing a grid structure  15 ,  15   a  of a flame trap filter  14 ,  14   a ,  14   b  comprises the step of solidifying a substance  27  on a substrate  26  in order to form at least one web section  17   i ,  17   ii  of grid structure  15 ,  15   a . As an alternative or in addition, the method can, for example, comprise the step of compressing a material for the flame trap filter  14 ,  14   a ,  14   b  or a semi-finished product  28  of flame trap filter  14 ,  14   a ,  14   b  at locations  23 —for example by mechanical deformation of the material or the semi-finished product  28 , in order to form at least one web section  17   i ,  17   ii  of grid structure  15 ,  15   a . 
     
       
         
           
               
             
               
                   
               
               
                 List of Reference Signs: 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 10 
                 housing 
               
               
                   
                 11 
                 interior 
               
               
                   
                 12, 12a 
                 pressure relief opening 
               
               
                   
                 12b 
                 pressure relief opening 
               
               
                   
                 13, 13a 
                 first pressure relief body 
               
               
                   
                 13b 
                 second pressure relief body 
               
               
                   
                 14, 14a 
                 (first) flame trap filter 
               
               
                   
                 14b 
                 second flame trap filter 
               
               
                   
                 15, 15a 
                 grid structure 
               
               
                   
                 16 
                 partial opening 
               
               
                   
                 17, 17i, 17ii 
                 web section 
               
               
                   
                 18 
                 wall 
               
               
                   
                 19 
                 grid opening 
               
               
                   
                 20.1-20.8 
                 layers 
               
               
                   
                 21 
                 opening 
               
               
                   
                 22 
                 locations 
               
               
                   
                 23 
                 area 
               
               
                   
                 24 
                 side 
               
               
                   
                 25 
                 side 
               
               
                   
                 26 
                 substrate 
               
               
                   
                 27 
                 material 
               
               
                   
                 28 
                 semi-finished product 
               
               
                   
                 29 
                 warp element 
               
               
                   
                 30 
                 weft element 
               
               
                   
                 31 
                 mesh 
               
               
                   
                 D 
                 flooding direction 
               
               
                   
                 R1 
                 first direction 
               
               
                   
                 R2 
                 second direction 
               
               
                   
                 d1 
                 thickness 
               
               
                   
                 d2 
                 thickness 
               
               
                   
                 b 
                 width 
               
               
                   
                 I 
                 instrument 
               
               
                   
                 A 
                 section