Flat gasket with calendered screen layer

Abstract

Flat gasket with at least a first metallic layer (1) and a second metallic layer (2) and a third layer (3) arranged between the first and second metallic layers, wherein the first metallic layer (1) has at least one first through-opening (7a) and the second metallic layer (2) has at least one second through-opening (7b), which are arranged adjacent to one another in a direction perpendicular to the plane of the layers, wherein the third layer (3) adjacent to the first and second through-openings (7a, 7b) has no through-opening in a direction perpendicular to the planes of the layers and spans the through-openings (7a, 7b) in its layer plane, wherein the third layer has a mesh material as a sieve layer or is made of mesh material which consists of or contains intersecting threads which form crossing points, characterized in that in the mesh material in a filter region which surrounds the first and second through-openings (7a,7b) in its layer plane, and in an area surrounding these through openings in its layer plane, at all crossing points the total height of two intersecting threads (4, 5) in the middle of a crossing point of the two threads (4, 5) is less than 1.4 times the height of a single thread (4, 5) halfway between two adjacent crossing points,

Description

[0001] The present invention relates to a flat gasket with filter elements.

[0002] To meet the increased purity requirements, there is a growing demand for the integration of filter elements into flat gaskets. These filter elements are primarily used to capture impurities created during production and other residues flowing in the operating fluids, especially during the initial operation phase of an internal combustion engine or vehicle.

[0003] Such flat gaskets are already known from the prior art, e.g., from DE 200 19 040 U1 or DE 20 2010 006 768 U1. They are primarily used as seals for water, air, and / or oil-carrying parts. These can be seals in transmissions, cylinder head gaskets, or other seals in internal combustion engines, and especially seals in the exhaust system of internal combustion engines.

[0004] DE 20 2010 006 768 U1 teaches a flat gasket with a metallic mesh material inserted between two metallic layers. The mesh material extends between the metallic layers and also spans the area of ​​the through-openings in the metallic layers. In and for these openings, the mesh material serves as a filter. According to DE 20 2010 006 768 U1, the mesh material is not compressed in these filter areas, while it is compressed in the web areas where it is covered by the material of the metallic layers. This compression creates a cross-sectional seal in the mesh material in the corresponding areas, while the uncompressed material in the filter areas has a reduced flow resistance for the fluids flowing through the flow openings in the metallic layers.

[0005] A disadvantage is that the mesh material must be compressed in a complex process in those areas covered by the metallic layers, namely the sealing areas, while the filter areas must be protected from compression. Such a structured and spatially limited compression method is complex and incurs considerable manufacturing costs.

[0006] It is therefore the object of the present invention to remedy this problem. It is therefore the object of the present invention to provide a metallic flat gasket and its use, wherein the gasket can easily be penetrated by fluids in its filter areas, has a high cross-sectional density, and can be manufactured with minimal effort.

[0007] This object is achieved by the metallic flat gasket according to claim 1. The claims dependent on claim 1 represent advantageous embodiments of the invention.

[0008] Claim 19 specifies advantageous uses of the metallic flat gasket according to the invention. These are particularly present when the gaskets are used as a transmission control plate or as a seal in the transmission, or generally as a seal for water-, air-, compressed gas-, and / or oil-carrying parts or other seals for internal combustion engines, particularly in the exhaust system of an internal combustion engine.

[0009] The invention therefore provides a flat gasket comprising at least two metallic layers, i.e., two layers comprising a sheet metal or consisting of sheet metal. These metallic layers have through-openings which, once the gasket layer has been assembled, correspond to one another and are arranged adjacent to one another in a direction perpendicular to the planes of the gasket layers. Adjacent here means that the through-openings can be arranged directly on top of one another or indirectly on top of one another, i.e., separated from one another by at least one intermediate layer. These gaskets allow the flow of fluids from one side of the through-opening to the opposite side, for example, hydraulic oil in transmissions or air in pneumatic transmission actuators, exhaust gases in seals in the exhaust gas recirculation area, or water in the supply seal of a water pump.Furthermore, the seal usually has through-holes for fastening devices, in particular for bolts and / or screws.

[0010] In both metallic layers, several through-openings are arranged adjacent to one another in the respective gasket layer plane, wherein the respective through-openings in the different layers are preferably flush with one another or at least continuous in the flow direction. These through-openings can be provided with a filter or be designed to allow unfiltered passage of the media. The present invention relates to a flat gasket with a mesh material that forms the filter for such through-openings with a filter.

[0011] According to the invention, a further, i.e., third, layer is arranged between the two metallic layers. This third layer does not have a passage opening in the area of ​​the fluid passage openings itself, but rather spans these passage openings. To still allow fluids to flow through, the third layer is designed as a sieve layer containing or consisting of a mesh material.

[0012] The mesh material contains threads that cross each other to form intersections. The mesh material is preferably a woven mesh material.

[0013] According to the invention, the height of the fabric is reduced both in the filter areas and in the adjacent areas already covered by the metallic layers such that, for all intersection points, the total height of two intersecting threads at the center of an intersection point is less than 1.4 times, preferably less than 1.2 times, the height of a single thread halfway between two adjacent intersection points. In an advantageous embodiment, the entire fabric of the screen layer is formed in this way.

[0014] This means that the fabric in the area of ​​the through-openings is compressed to 70%, advantageously to 60% or less, of its original thickness in the areas surrounding the through-opening, with the compression preferably taking place over the entire surface of the fabric. This applies to cases in which the fabric is not compressed at least in the central area between the thread crossing points, which means that the threads have their original thickness at least in this central area. If the fabric is compressed more heavily, so that the threads are also compressed in the central area between the crossing points, the total height of two threads of the fabric at one crossing point is equal to the height of one thread in the central area between two adjacent crossing points.

[0015] Advantageously, the pressed fabric has a compression ratio of more than 30%, preferably more than 35%, preferably more than 40%, and particularly preferably more than 45% compared to the unpressed starting material. For some fabrics, particularly those with larger starting mesh sizes or subdivisions, even higher compression ratios are recommended, namely more than 50% or even 55%. These values ​​apply to unpressed fabric threads with a substantially round cross-section, which are commonly used for fabrics.

[0016] In an advantageous embodiment, two intersecting stitch threads at their crossing point have, due to the pressing, a ratio of their width (extension in the layer extension direction of the fabric and substantially perpendicular to the thread extension direction) to their height (extension perpendicular to the layer extension direction of the fabric) of 1.5 to 4, preferably of 2 to 4, preferably of 2 to 3, more preferably between 2.5 and 3.

[0017] In an ordinary fabric, i.e. a non-pressed raw material, there is obviously a considerable amount of interstice in the fabric when viewed from above or from below. This interstice ensures the permeability of the fabric in a direction perpendicular to the plane of the fabric. Within the plane of intersections, each intersection point of two threads is surrounded by an alternating sequence of four free interstice spaces and four continuations of the threads that cross each other. In a plain weave fabric, each thread ascends between a first pair of threads and descends between the next pair of threads, which means that there is a lot of interstice even in a very tightly woven material.If, in a sectional view through the fabric, one follows the course of a single thread through the multitude of crossing threads exactly halfway across the width of this thread, it is obvious that the thread is only covered by crossing threads in short sections, namely at the crossing points. In particular, in the immediate vicinity of a crossing point between a longitudinal thread and a transverse thread, there are spaces between these two threads on both the right and left side of the transverse thread. In the sectional view, these spaces often have a shape that can be considered approximately triangular. These spaces allow the fluid to pass transversely through the fabric, for example along the thread.In a seal according to the invention, sufficient transverse tightness is achieved by compressing the starting fabric, i.e., by displacing thread material primarily from the upper and lower surfaces of the fabric into these interstices, which results in a reduction in the thickness of the fabric compared to the starting material. If one considers a comparable sectional view through the fabric at half the width of a single thread, the remaining free areas between this, for example, transverse thread and the longitudinal threads crossing it are much smaller compared to the interstices in the starting material. In a cross-section at half the width of the thread, a free space, i.e., a continuous free space, of ≤ 0.008 mm remains. 2 , preferably ≤ 0.006 mm 2 , preferably ≤ 0.004 mm 2 and most preferably ≤ 0.002 mm 2per intersection point. This design reduces some or all of the remaining free spaces in the mesh layer formed by the fabric to such a small size that the mesh is sufficiently impermeable in its transverse direction.

[0018] The remaining free spaces are defined as the respective contiguous space that is not intersected or covered by a fabric thread when viewed along the center of the screen layer. The remaining free spaces are present on both sides of a thread at every intersection point. This free space can also be referred to as cross-sectional free space.

[0019] The metallic flat gasket according to the invention thus provides a metallic flat gasket that allows the intended passage of fluids through the filter area. At the same time, the cross-sectional tightness of the fabric outside these filter areas is sufficient to prevent the fluid from penetrating the fabric from one passage opening to another, adjacent passage opening.

[0020] According to the invention, it is particularly advantageous if the metal layers arranged adjacent to the mesh layer contain a sealing bead that surrounds at least one of the through-openings, at least in sections. Such a sealing bead further improves the cross-sectional tightness.

[0021] It is also advantageous if the metallic layers arranged adjacent to the fabric layer are coated, at least in sections, on their surface facing the fabric layer. Elastomers such as fluoropolymers, for example FPM (vinylidene fluoride-hexafluoropropylene copolymer), are particularly suitable for such coatings. Other suitable coating materials are silicone rubber, NBR rubber (acrylic butadiene rubber), HNBR rubber (hydrogenated acrylic butadiene rubber), PUR (polyurethane), NR (natural rubber), FFKM (perfluoro rubber), SBR (styrene butadiene rubber), BR (butadiene rubber), IIR (butyl rubber), FVSQ (fluorosilicone), CSM (chlorosulfonated polyethylene), and silicone or epoxy resins, individually or in a mixture with at least one of the aforementioned substances.With this coating, the cross-sectional tightness is further improved, as the remaining free spaces are additionally sealed by the sealing material, which penetrates into the spaces between the threads.

[0022] With uncoated surfaces of the sealing layer arranged next to the screen layer, it is preferred that the screen material is compressed more strongly, for example by more than 50%, preferably by more than 55%, while with coated surfaces of the sealing layers whose coatings face the screen layer, lower degrees of compression are usually sufficient, for example between 30 and 50%, in each case including the stated limits.

[0023] The two metallic layers adjacent to the fabric layer are advantageously made of stainless steel, spring steel, spring-hardened steel, or carbon steel. As mentioned above, such layers may contain sealing beads that provide additional sealing in the direction of the sealing layer plane or parallel to it.

[0024] The threads of the fabric are advantageously made of metal, such as steel, for example, austenitic steel, ferritic steel, stainless steel, or carbon steel, or they contain these metals. If an austenitic steel is used for the starting fabric, the martensite formation that occurs during pressing causes this material to become magnetic. This fabric can then be used in the same way as ferritic steel. It is therefore possible to use a magnetic gripper for a magnetic fabric pressed in this way, which offers a significant advantage during production and handling. The wire diameter of the starting fabric material is typically between 0.04 and 0.12 mm.

[0025] Alternatively, the fabric threads can consist of or contain a thermoplastic or thermosetting material. It is advantageous to use a polyester or polyamide material.

[0026] It is advantageous to use a woven material as the fabric, in particular a fabric with a plain weave or a twill weave. The fabric can advantageously have a height of 10 to 1400 µm, preferably 60 to 400 µm, and / or a mesh size of 80 to 250 µm, preferably 100 to 225 µm, preferably 100 to 200 µm. These dimensions refer to the compressed material, which is reduced in height.

[0027] If the fabric's thickness is reduced across its entire surface, e.g., by compression, this enables particularly simplified production of the metallic flat gasket according to the invention. Such a fully compressed fabric can be produced simply and cost-effectively from a starting fabric, e.g., by calendering. Both the basis weight and the subdivision remain essentially unchanged during compression; during calendering, the division in the longitudinal direction may increase somewhat.

[0028] During calendering, the entire width of the material is compressed simultaneously along a single line, meaning that calendering requires significantly less pressing force than full-surface compression of the mesh. With an increased degree of compression, the transverse gaps in the mesh become smaller, which makes it easier to seal the remaining gaps with a coating, for example, by coating the adjacent metallic layers. The mesh layer itself remains uncoated.

[0029] Particularly high compression ratios with remaining clearances of less than 0.004 mm 2 are possible without damaging the fabric if the material is calendered, annealed, and calendered again. At the end of the process, the fabric can be hardened again.

[0030] From a manufacturing perspective, it is preferable to use a uniform piece of screen material as the screen layer. However, some special applications may require the use of fabrics with different properties.

[0031] For this purpose, it is in principle possible to use a pair of stepped calender rolls or a pair of rolls, each consisting of a sequence of calender rolls with different heights. These rolls are arranged sequentially along the axis of each composite roll, with the same sequence being used for the upper and lower composite rolls. This allows the use of screen layers with sections of different heights and thus different amounts of remaining free space. However, the zones run with a constant width, which means that this variation of different mesh properties can only be used for special applications.

[0032] Alternatively, it is possible to combine different calendered materials to form the screen layer in such a way that this layer consists of different pieces of differently calendered material that are bonded together either by a material fit or by a form fit. The bond must be in the plane of the screen layer, i.e., without overlap and without any thickening. Laser welding is particularly preferred for this purpose.

[0033] The mesh size is generally selected depending on the size of the particles to be filtered and the maximum permissible flow resistance. The starting material is selected from fabrics with a mesh size to thread diameter ratio between 2:1 and 4.5:1, preferably between 7:5 and 9:2. Increasing this ratio makes the mesh easier to compress, but at a ratio above the highest value specified above, the sealing beads commonly used in metallic flat gaskets and the typical bolt forces would be insufficient to achieve a sufficient sealing effect.

[0034] In summary, the mesh material according to the invention, especially when its entire surface has been pressed, enables simplified and cost-effective production of flat gaskets with filter areas. This flat gasket simultaneously provides good fluid flow through the through-holes and sufficient cross-sectional tightness. Along with the advantageous gasket, an advantageous method for producing such a gasket is presented.

[0035] In addition to the mesh layer and the top and bottom layers made of relatively thin metal sheets, a spacer layer can be arranged between one of the top and bottom layers and the screen layer, allowing the thickness of the seal to be adjusted. While the thickness of the top and bottom layers is typically between 0.1 and 0.25 mm, the thickness of the spacer layer is at least 0.3 mm. The spacer layer typically has the same distribution of through-holes as the top and bottom layers, although their size may be different.

[0036] Below, several examples of metallic flat gaskets according to the invention are explained in detail. Elements described for an individual example simultaneously represent elements of the invention as such. Identical or similar elements are designated by identical or similar reference numerals. All multi-layer cross-sections show the gasket layers in relation to one another in an exploded view.

[0037] It shows Fig. 1: a seal for a transmission control unit; Fig. 2: a cross-section through a gearbox seal according to the prior art; Fig. 3: Cross sections through three transmission seals as examples of flat seals according to the invention; Fig. 4: two cross-sections through mesh materials, one in the unpressed and one in the pressed state; Fig. 5: a cross section through a mesh material of a flat gasket according to the invention corresponding Fig. 4; Fig. 6: a section of a mesh material; and Fig. 7: in two sub-figures the ratio of the transverse leakage area to the compression of the material for three different starting materials.

[0038] Fig. 1 shows a seal, namely a seal 20 for a transmission control unit, in plan view. This plan view shows a first metallic layer 1 with a plurality of through-openings 6, 7, wherein only some of the through-openings are explicitly provided with a reference numeral. The through-openings are openings for passage through the transmission seal 20, in a direction perpendicular to the plane of the sheet. The through-openings 6 here are through-openings for bolts and the like; no filter is arranged in these through-openings. The through-openings 7 are through-openings for fluids, e.g., for hydraulic oil. A filter is arranged in these openings 7, which, according to the invention, is formed by a screen layer 3 made of a mesh material. The screen layer in Fig. 1 is designated by reference numeral 3. Only in the area of ​​the through openings 7 is it not covered by the sealing layer 1 and therefore is only visible in this area.

[0039] Sealing beads 11 are arranged in the first metallic layer 1 around the through-holes 7 and the bolt through-holes 6. They form sealing lines around the peripheral edge of the through-holes 6 and 7 and therefore improve the cross-sectional tightness between these through-holes 6 and 7. The cross-sectional tightness is defined as the impermeability to the passage of fluids within the plane of the layer of the gear seal 20; it refers to the ability to seal against the passage of fluids within the plane of the layer, namely the screen layer, from one through-hole 6, 7 to another through-hole 6, 7.

[0040] Fig. Figure 2 now shows, in cross-section, the composition of a prior art transmission seal 20. Such a transmission seal contains two metallic layers 1 and 2, between which a further layer 21 is arranged. In the region of the through-opening 7, the intermediate layer 21 contains an opening in which a mesh screen 22 is arranged. This mesh screen 22 is connected, for example, clamped, to the layer 21 at its outer edge. The mesh screen 22 then forms a filter for a fluid that passes through the mesh screen in a direction perpendicular to the plane of the mesh screen. However, the production of such a seal with a composite layer 21, 22 is extremely complex.

[0041] Fig. 3 therefore shows three embodiments of metallic flat gaskets according to the invention, for example gear gaskets, comparable with Fig. 1. Fig. 3 shows three cross sections, all of which correspond to line AA in Fig. 1 correspond.

[0042] Fig. Figure 3-A shows a cross-section including through-holes 6 (6a, 6b, 6c) and through-holes 7 (7a, 7b, 7c) with the filter area. In spring steel layers 1 and 2, all of these through-holes 6a, 6b, 6c, and 7a, 7b, and 7c are surrounded by elastic sealing beads 11a to 11f.

[0043] According to the invention, the middle layer 3 consists entirely of fabric with a compression ratio of more than 30%, thus a thickness less than 70% of its original thickness. The fabric screen is shown here in cross-section along the extension direction of a transverse thread 5, so that the longitudinal threads 4a, 4b, 4c, in turn, appear only as short sections in their cross-section. Only some of the longitudinal threads in Fig. 3-A are provided with their own reference symbol.

[0044] In this example, the fabric material consists of metal threads, namely stainless steel type 1.4306, and is calendered across its entire surface, i.e., across its entire width and length. This type of pressing is particularly advantageous when performed using a calender. A conventional press would require significantly greater pressing forces, making it very costly to press the entire surface with a compression ratio of more than 40%.

[0045] As already mentioned, the fabric of layer 3 spans the through-openings 7a, 7b and forms a filter area for fluid flowing through these through-openings, e.g., hydraulic oil. At the same time, with such a degree of compression, the fabric is sufficiently impermeable in its transverse direction to allow no hydraulic oil at all, or more hydraulic oil than permitted, to pass through from a through-opening 7a, 7b through the screen layer 3, i.e., within the screen layer 3 to a through-opening 6a, 6b, 6c.

[0046] No fabric is arranged in the through openings 6a, 6b, 6c, since these openings, for example as screw holes, either do not require or do not allow filter areas.

[0047] In Fig. 3-B is a similar embodiment as in Fig. 3-A. Additionally, the two sealing layers 1 and 2 are provided on their surface facing the intermediate layer 3 with an elastomeric, FPM-based coating 9, 10 with a coating thickness of approximately 40 µm. This elastomer coating seals gaps that may exist in the screen layer 3 between individual threads 4a to 4c, 5. Advantageous coating thicknesses are between 20 µm and 50 µm. It is preferred if both surfaces of the sealing layers facing the screen layer are coated. The screen layer 3 itself is uncoated.

[0048] Fig. 3-C shows a further embodiment of a metallic flat gasket according to the invention. In contrast to the embodiment of Fig. In 3-A, the direction of the sealing beads is reversed. They now point toward the screen layer, rather than away from it. This arrangement of the beads also enables good sealing in the transverse direction, i.e., in the plane of the layer and with respect to the passage of fluid from one through-opening 7a, 7b to the through-openings 6a, 6b, 6c.

[0049] Fig. 4 shows in Fig. 4-A is a sectional view through a mesh material, the section being in the middle of a thread 5 and showing its longitudinal extension. The same material is shown in Fig. 4-B, but now in the pressed state according to the invention. With this material, it is obvious that the total thickness of two intersecting threads 4a, 5 (e.g., at the intersection point 12a) at the intersection points 12a, 12b, 12c is approximately the same as the thickness of a thread 5 between the two adjacent intersection points, e.g., between the two intersection points 12a and 12b or 12b and 12c. Fig. 4-B shows the fabric with a compression ratio of approximately 50%. The compression ratio is based on the starting material from Fig. 4-A is also 50%. The distance between threads 4a and 4c in both partial figures corresponds to twice the pitch of the fabric. The mesh size, on the other hand, corresponds to the distance between the right end of thread 4a and a vertical projection of the left end of thread 4b.

[0050] Fig. 5 shows in Fig. 5-A is again a sectional view through a fabric that has already been shown in Fig. 4-B. Additionally, Fig. 5-B shows an enlarged section of the intersection point 12b. It is evident that the remaining free areas 8a, 8b are located near the longitudinal thread 4a up to the area where the transverse thread 5 reaches its full thickness. These remaining free areas are not completely covered by the threads 4a and 5 in the cross-section of the fabric. Such remaining free areas 8a, 8b allow fluid to penetrate along the thread 4a also in the transverse direction, i.e., in the direction of the plane of the fabric 3. With a sufficient reduction of these remaining free areas, the cross-sectional permeability is extremely limited and therefore the cross-sectional tightness becomes so good that the fabric is suitable not only as a filter material in the through-openings 7a, 7b, but also as a sealing material in the areas between these through-openings.Therefore, it is sufficient to compress the fabric 3 evenly over its entire surface without providing any special local structuring. While it is not possible to compress material with local structures in a calender, it is possible to produce a uniformly pressed material with a calender. This use of a calender enables cost-effective and simple production of pressed fabric with the extremely high compression ratios required for the sealing purpose described here.

[0051] Fig. Figure 6 represents a cross-section of a calendered mesh material made of steel type 1.4301. The cut was made in the middle of wire 5. Due to the position of the cut, the wires 4a, 4b, ..., which run perpendicular to the cut wire, are visible, as are the crossing points 12a, 12b, .... The section depicts the conditions in a wire mesh that has been compressed by approximately 55% and is calendered from a wire mesh with a wire thickness of 80 µm and a mesh size of 125 µm. The total thickness H of the mesh is 74.5 µm at the average of the two positions marked with arrows and therefore 46.5% of the original thickness. Accordingly, the height of the individual wires HD, with an average of 37.7 µm for the three marked positions, is less than 50% of the thickness of the original wire.The width B of the wires at the intersection points in the pressed screen material has changed considerably less; it averages 106.4 µm at the two marked positions, i.e., it is 1 / 3 larger than the original wire diameter. The ratio of width B to height HD of the pressed individual threads at the intersection points is between 2.7 and 2.8. It is evident that only very small remaining free areas F remain between the intersecting wires 4a, 4b, and 5, and the calendered fabric therefore exhibits a high cross-sectional density.

[0052] Because testing with hot oil is difficult and conducting it with standard-size samples is too dangerous, the material's suitability for practical use was tested using a few real examples on a test bench and under the conditions of an automatic transmission manufacturer. The test conditions are a trade secret of this manufacturer. The decisive factors were whether the transmission unit operated an oil pump with the expected frequency under the test conditions and whether only the desired gearshift operations occurred. Tests were conducted with the screen layer between the top and bottom layers 1 and 2, made of beaded carbon steel DC 01 C 490 with a thickness of 0.250 mm.

[0053] For example, the conditions specified by the automatic transmission manufacturer were achieved with a stainless steel screen layer with a thickness of 0.224 mm and a wire diameter of 0.08 mm at a compression ratio of 55%, even though both the top and bottom layers were uncoated. The conditions were also met with a screen layer with a mesh size of 0.125 mm and a wire thickness of 0.08 mm, a compression ratio of 30%, and an FPM coating with a thickness of 40 µm on both surfaces of layers 1 and 2. Apart from the properties of the top and bottom layers, it is primarily the remaining free surface that determines whether the screen material has the required impermeability.

[0054] Fig. Figure 7 shows two diagrams showing the size of the remaining free areas 8a, 8b of the compressed mesh material once in 10 -3 mm 2(per remaining free area) and once as a relative value related to the original leakage area for three different starting materials, all corresponding to steel type 1.4301, which is very similar to the 1.4306 type used in connection with Fig. 3. Two materials have a starting wire thickness of 0.08 mm but different mesh sizes, namely 0.224 mm – marked with diamonds – and 0.125 mm, marked with triangles. The measurement points with the circles refer to a starting material with a larger wire thickness of 0.09 mm and a mesh size of 0.200 mm.

[0055] Both Fig. 7-A and Fig. 7-B show at first glance what was expected, namely that the remaining free areas become smaller with a greater degree of compression of the fabric. Fig. As can be seen from Figure 7-A, at 30% compression, the two materials with the smaller mesh size have transverse leakage areas that are less than 40% of the corresponding values ​​of the original sieve, with the sieve material with a 0.224 mm mesh size showing a slightly larger value. At 45% compression, the transverse leakage area is reduced to less than 10% of the original value for all materials considered.

[0056] If you compare the absolute values ​​in Fig. 7-B, the screen material, which in combination with coated top and bottom layers leads to the expected result, shows a remaining transverse leakage area of ​​2.5 × 10 -3 mm 2 . Corresponding values ​​are obtained with the material, which has a mesh size of 0.200 mm and a wire diameter of 0.09 mm, at a compression ratio of 40%. At 45% compression, a remaining transverse leakage area of ​​less than 10 -3 mm 2 receive.

Claims

[1] Flat gasket with at least a first metallic layer (1) and a second metallic layer (2) and a third layer (3) arranged between the first and second metallic layers, wherein the first metallic layer (1) has at least one first through-opening (7a) and the second metallic layer (2) has at least one second through-opening (7b), which are arranged adjacent to one another in a direction perpendicular to the plane of the layers, wherein the third layer (3) adjacent to the first and second through-openings (7a, 7b) has no through-opening in a direction perpendicular to the planes of the layers and spans the through-openings (7a, 7b) in its layer plane, wherein the third layer has a mesh material as a sieve layer or consists of a mesh material which consists of or contains intersecting threads which form crossing points, characterized bythat in the mesh material in a filter area which spans the first and second through-openings (7a, 7b) in its layer plane and in a area which surrounds these through-openings in its layer plane, at all crossing points the total height of two crossing threads (4, 5) in the middle of a crossing point of the two threads (4, 5) is less than 1.4 times the height of a single thread (4, 5) halfway between two adjacent crossing points [2] Flat gasket according to the preceding claim, characterized by that in the mesh material (3) over its entire area in the plane of the layer, at all crossing points, the total height of two crossing threads (4, 5) in the middle of a crossing point of the two threads (4, 5) is equal to or less than 1.4 times the height of a single thread (4, 5) halfway between two adjacent crossing points. [3] Flat gasket according to one of the preceding claims, characterized by that the mesh material (3) in a first region or over its entire surface has a degree of compression compared to the unpressed starting material of threads (4, 5) with a substantially round diameter, which is > 30%. [4] Flat gasket according to one of the preceding claims, characterized by that in a first region or over their entire surface, two intersecting threads (4, 5) have a width to height ratio of 1.5 to 4 at their intersection point. [5] Flat gasket according to one of the preceding claims, characterized by that in a first area or over its entire area, several or all remaining free areas in the cross-section of the screen layer (3) along the center of one, several or all mesh threads (4, 5) have an area of ≤ 0.008 mm 2 per intersection point. [6] Flat gasket according to one of the preceding claims, characterized by that the mesh material has been pressed in a first area or over its entire surface by calendering. [7] Flat gasket according to one of the preceding claims, characterized by that the first layer (1), the second layer (2) and the third layer (3) each have at least one further through-opening (6), wherein the through-openings are arranged adjacent to one another in a direction perpendicular to the plane of the layers. [8] Flat gasket according to one of the preceding claims, characterized by that the first (1) and / or the second (2) layer have a sealing bead (11a to 11f) around at least one of the through openings (6, 7) at least in sections. [9] Flat gasket according to one of the preceding claims, characterized bythat the first (1) and / or the second (2) layer is coated at least on its surface facing the screen layer (3), preferably with an elastomer. [10] Flat gasket according to one of the preceding claims, characterized by that the fabric threads (4, 5) consist of metal or contain one of these substances. [11] Flat gasket according to one of claims 1 to 9, characterized by that the fabric threads (4, 5) consist of thermoplastic or duroplastic or contain at least one of these materials. [12] Flat gasket according to one of the preceding claims, characterized by that the first (1) and / or the second (2) layer are made of stainless steel, spring steel, spring-hardened steel or carbon steel or contain one of these materials. [13] Flat gasket according to one of the preceding claims, characterized by that the screen layer consists of a single section of uniformly pressed mesh material. [14] Flat gasket according to one of claims 1 to 12, characterized by that the screen layer consists of a composition of at least two sections, wherein the sections are connected to one another in the plane of the screen layer at least materially and / or positively. [15] Flat gasket according to claim 14, characterized by that the connection of at least two sections is achieved by laser welding. [16] Flat gasket according to one of the preceding claims, characterized by that the screen layer (3) has a mesh size of 80 to 250 µm, including or excluding the boundaries. [17] Flat gasket according to one of the preceding claims, characterized by that the screen layer (3) has a height of 10 to 1400 µm. [18] Flat gasket according to one of the preceding claims, characterized by that the screen layer (3) is a fabric. [19] Flat gasket according to one of the preceding claims, wherein the flat gasket is a gasket for a gearbox, a gasket for water, air, compressed gas and / or oil-carrying parts, a cylinder head gasket or another gasket for an internal combustion engine.

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