Title of Invention	A PROCESS FOR PRODUCING A BODY FOR EXHAUST GAS TREATMENT.
Abstract	The invention relates to a method for producing a body (1) for exhaust treatment, said body comprising a plurality of metallic layers (2). According to the inventive method, the layers (2) are brought into contact with each other in an assembly region (3), and a join is made by means of a roller seam welding method in such a way that the layers (2) form channels (4) through which a gas flow can pass. The invention also relates to corresponding bodies (1) for exhaust treatment, that can especially be used as filters or catalyst carrier bodies in the car industry.

Title of Invention

A PROCESS FOR PRODUCING A BODY FOR EXHAUST GAS TREATMENT.

Abstract

The invention relates to a method for producing a body (1) for exhaust treatment, said body comprising a plurality of metallic layers (2). According to the inventive method, the layers (2) are brought into contact with each other in an assembly region (3), and a join is made by means of a roller seam welding method in such a way that the layers (2) form channels (4) through which a gas flow can pass. The invention also relates to corresponding bodies (1) for exhaust treatment, that can especially be used as filters or catalyst carrier bodies in the car industry.

Full Text	Roller seam welded body for exhaust gas treatment The present invention relates to a process for producing a body for exhaust gas treatment, which has a plurality of metallic layers forming passages through which a gas stream can flow. Bodies of this type are used in particular for purifying the exhaust gases from mobile internal combustion engines, such as spark ignition or diesel engines. Primary application areas in this context are passenger automobiles as well as trucks and motor cycles. It is also known for these bodies to be used in exhaust systems of portable hand held appliances, such as for example power saws, lawnmowers, etc. Bodies of this type have a number of different functions. For example, they are used as catalyst support bodies, as adsorbers, as filters, flow mixers or mufflers. The body is usually distinguished by a favorable ratio of surface area to volume, i.e. it has a relatively large surface area and therefore ensures intensive contact with the gas stream flowing through it. With regard to catalyst support bodies, this surface or the body is provided with a catalytically active coating, which preferably comprises washcoat. The washcoat has a particularly fissured surface, so that the ratio of surface area to volume can be improved still further. The washcoat is impregnated with various catalysts, for example platinum, rhodium or the like. Adsorbers substantially have a similar basic structure as that selected for bodies used as catalyst support bodies. However, a different objective is pursued with regard to the coating, so that consequently different coatings are used. The purpose of the adsorbers is, for example, to retain nitrogen oxides until suitable reaction partners and/or temperatures are present to allow these constituents of the exhaust gas to be converted as fully as possible. Flow mixers are distinguished by the fact that their bodies have a multiplicity of passages which are flow-connected to one another. At the same time, guide surfaces, which allow the partial gas streams to be diverted, are provided in the interior of the body or of the passages. In this way, the gas stream, is made more uniform in terms of its pollutant concentration, its flow properties, its temperature, etc. A wide range of different structural forms are known for the abovementioned bodies as catalyst support bodies, adsorbers, mufflers and flow mixers. These forms include, for example, honeycomb bodies comprising at least partially structured sheet-metal foils. Compared to known bodies made from ceramic material, the metallic honeycomb bodies have a considerably greater flexibility in terms of their intended use and also allow a greater degree of design freedom. It should also be borne in mind that particularly effective conversion processes with regard to the pollutant concentration are ensured on account of the good heat conduction and the extremely low area-specific heat capacity. A distinction is drawn in particular between two typical designs of metallic honeycomb bodies. An early design, of which DE 29 02 779 A1 shows typical examples, is the helical design, in which substantially one smooth and one corrugated sheet-metal layer are placed on top of one another and wound helically. In another design, the honeycomb body is constructed from a multiplicity of alternately arranged smooth and corrugated or differently corrugated sheet-metal layers, the sheet-metal layers initially forming one or more stacks which are then intertwined. In this case, the ends of all the sheet-metal layers come to lay on the outside and can be connected to a housing or tubular casing, producing numerous connections, which increase the durability of the honeycomb body. Typical examples of these designs are described in EP 0 245 737 B1 or WO 90/03220. It has also long been known to equip the sheet-metal layers with additional structures in order to influence the flow and/or bring about cross-mixing between the individual flow passages. Typical examples of these configurations include WO 91/01178, WO 91/01807 and WO 90/08249. Finally, there are also conical honeycomb bodies, optionally also with further additional structures for influencing the flow. A honeycomb body of this type is described, for example, in WO 97/49905. Furthermore, it is also known to leave free a cutout in a honeycomb body for a sensor, in particular for accommodating a lambda sensor. One such example is described in DE 88 16 154 U1. Of course, the designs described above are also suitable for forming filter bodies. In principle, two different principles are known for these or other filter bodies. One principle relates to what is known as the "closed particulate filter", in which the passages formed by the body are closed on alternate sides, therefore forcing the gas stream to pass through passage walls comprising filter material.. This leads to the accumulation of particulates or solids contained in the gas stream, which are burnt and/or oxidized continuously or at predeterminable intervals. An alternative known design is that of the "open particulate filter", which is not closed on alternate sides, but rather has flow diversion points in the interior of the passages, which cause the partial gas streams to be swirled up in such a way that at least 80% of the partial gas streams pass through the filter wall, preferably a number of times. The major advantage of the "open particulate filter" is that blockage of the filter material caused by an excessive accumulation of particulates is avoided. A particulate filter is described as "open" if particulates can fundamentally flow completely through it, specifically including particulates which are considerably larger than the particulates that are actually to be filtered out. As a result, a filter of this type cannot become blocked even in the event of an agglomeration of particulates during operation. A suitable method for measuring the openness of a particulate filter is, for example, to test the diameter up to which spherical particles can still trickle through a filter of this type. In present applications, a filter is open in particular if spheres with a diameter of greater than or equal to 0.1 mm can still trickle through it, preferably spheres with a diameter of over 0.2 mm. One such example is given in DE 2011783U1 to which reference is made in full for the purposes of explanation. In addition to these bodies with wound or intertwined layers, it is also known to use what are known as plate filters, which comprise a plurality of in particular sheet-like or substantially planar filter plates which are arranged spaced apart from one another. Plate filters of this type are usually also constructed in accordance with the principle of passages that are closed on alternate sides, but it is in principle also possible to realize an "open particulate filter". Whereas wound designs and plate designs of this type have the gas stream flowing through them substantially axially, bodies or filter bodies which the gas stream flows through radially are also known. Such bodies usually have an inner flow passage and an outer flow passage which is annular in form and is generally arranged coaxially with respect to the inner flow passage. The inner flow passage is generally delimited by an inner tube, which is provided with openings through which the gas stream to be purified is passed. Layers of a filter material are arranged around this inner tube. Substantially two different concepts are known in this respect. The first concept can be described on the basis of a "star shape", which is realized when the filter plates are viewed in the direction of the inner tube or a cross section perpendicular to the inner tube. This means in other words that the filter plates form folds which extend substantially parallel to the axial extent of the inner tube. Another known concept involves the formation of folds in the circumferential direction, in which case a plurality of these folds are positioned on the inner tube, spaced apart from one another in the axial direction. According to the routing of the flow, the gas stream that is to be purified is fed to the filter material from the inside (or from the outside), penetrates through this filter material and is discharged again on the opposite side. The bodies described above generally comprise a plurality or multiplicity of different components made from in some cases different materials. Considering the high thermal and dynamic stresses in the exhaust system of mobile internal combustion engines, these individual components have to be permanently connected to one another. Numerous different connection techniques are known for this purpose, for example brazing and/or welding. With regard to these connection techniques, it should be noted that they have to be suitable for at least medium-sized series production. In this respect, cost aspects also play an important role, such as cycle rates, connection quality, process reliability, etc. Known processes used to form connections by joining (in particular in the structure comprising the filter surfaces and/or the layers) require an additional material, such as, for example braze or weld filler. It is in this case particularly difficult for the filler to be applied at precisely the location at which a join is subsequently to be produced. Moreover, it should be noted that increasingly thin-walled materials need to be used, since such materials very quickly adapt to the temperature of the exhaust gas and accordingly have highly dynamic reaction properties. To ensure the long-term functionality of these bodies, however, a spatially tightly delimited introduction of heat is required to form the connections by joining. Hitherto, this has not been achievable to a satisfactory extent, and indeed brazing generally requires heating of the entire body in a high-temperature vacuum furnace, and welding has hitherto usually also been carried out through the outer housing, and consequently in this case too considerable temperature gradients have been realized across a large part of the body. Working on this basis, it is an object of the present Invention to overcome the above technical problems of the prior art. In particular, it is intended to provide an inexpensive, simple, effective and reliable process for producing metallic bodies of this type for exhaust gas purification. Moreover, the process should as far as possible be suitable for automation, producing connections by joining which are distinguished by a particularly long service life. Furthermore, it is intended to provide a corresponding body for exhaust gas treatment which can be configured variably and is versatile in use. These objects are achieved by a process having the features of patent claim 1 and a body having the features of patent claim. 18 Further advantageous configurations are described in the respective dependent patent claims, which can be combined with one another in any desired way. The process according to the invention for producing a body for exhaust gas treatment which has a plurality of metallic layers is characterized in that the layers are brought into contact with one another in a connection region, and a connection is produced by a continuous resistance welding process, in such a manner that the layers form passages through which a gas stream can at least partially flow. In other words, this means in particular that the connection between layers arranged adjacent to one another is effected by the continuous resistant welding process. In this context, it should be noted that the term "continuous" may mean that the welding takes place along one welding track, in which case the weld seam which is generated is made uninterrupted. However, this need not necessarily be the case; for example, it is also possible for a plurality of weld seams which axe spaced apart to be provided along the welding track, in which case the proportion in which the weld seams are present along the welding track is advantageously significantly greater than the proportion formed by the interruptions. It is particularly preferable for the proportion formed by the weld seam, based on the welding track, to amount to at least 80%, in particular even more than 90%. With regard to the "passages", it should also be noted that these passages need not necessarily have a tube-like structure. Rather, this term is to be understood as meaning a limited flow path which has a spatial boundary. In this case, the boundary is generally configured in such a way that it encloses the flow path over at least 60% (in particular 80%) of the circumference, with the length of the flow path advantageously being greater than the circumference. In view of the fact that the abovementioned body may also be constructed as a filter, it will be clear that the passages do not necessarily have to have a gastight passage wall, i.e. it is also eminently possible for the layers to be configured so as to be at least partially gas-permeable. In particular in this case, the gas stream does not flow completely through the passage, in which case although the passage does have a suitable cross section, the gas stream nevertheless uses a different route. Therefore, it is considered sufficient for the passage to offer the option of at least partially allowing a gas stream to flow through it, in particular with open end sides. According to an advantageous configuration of the process, the continuous resistance welding process comprises roller seam welding and/or projection seam welding. Roller seam welding and the projection seam welding process belong to the pressure-joining welding processes, in particular resistance pressure welding or conductive pressure welding. In the resistance pressure welding process, the heating at the welding location takes place as a result of Joule resistance heating when current flows and by means of an electrical conductor. The current is supplied via electrodes with a convex or planar working surface. Two roller-like (driven) electrodes are used for the roller seam welding. The metal sheets to be welded are in this case arranged predominantly overlapping. In practice, roller seam welding is a continuous spot welding, but using roller-like electrodes. Unlike when using resistance spot welding, the electrodes remain in contact after the first weld spot has been produced and are then rolled continuously onward. Further current flows at the locations where a weld spot is to be formed. Depending on the feed rate of the electrodes and the frequency of the welding current, spot seams or sealed seams with overlapping weld nuggets or weld spots are produced. Permanent direct current likewise produces a sealed seam. The use of this production process to connect the layers has proven particularly advantageous in particular with a view to series production of these bodies. The process in which the two layers adjacent or lying on top of one another are passed through the rotating electrodes is surprisingly well able to withstand the high thermal and dynamic stresses for example in the exhaust system of automobiles. It has also been established that even in the case of very thin metal foils which are connected to one another in this way, sealed weld seams can be produced in very short working cycles. As a result, it is possible to achieve in particular a cost benefit, which was unexpected in view of the additional material which is required for the overlap between the two layers. Roller seam welding is suitable in particular for connection regions which have a certain length, i.e.. extend over a predetermined portion. This should generally amount to at least 5 cm, in particular at least 15 cm, and the work can be carried out at particularly low cost beyond a length of 25 cm. The roller seam welding makes do without filler. Furthermore, it is in many cases also possible to do without a step of cleaning the layers, since the introduction of the electrode force ensures that contact between the electrodes and/or the layers which is sufficient for the flow of current and the formation of the weld spot is already ensured to a considerable extent. Moreover, only an insignificant change in the microstructure of the layer adjacent to the weld nugget can be established. Accordingly, the use of this manufacturing process offers numerous advantages and at the same time overcomes all the technical problems listed in the introduction at once. Moreover, the process can also be applied to each of the types of bodies mentioned in the introduction. According to one refinement of the process, it is proposed that at least in part a weld seam in which there are at least overlapping weld spots is formed. This applies in particular to the case in which the ends or edge regions of the layers are to be fixed to one another. These edge regions or edges for example close up flow paths, so that the exhaust gas to be purified is forced to pass through a filter material. To ensure the principle of a "closed particulate filter", a sealed seam should be at least partially present. This is to be understood as meaning that the welding current pulses take place in succession at such short time intervals that the respectively adjacent weld spots or weld nuggets merge into one another, i.e. there are no unconnected locations on the layers between adjacent weld spots. As has already been stated above, a sealed seam of this type is achieved by virtue of the frequency of the current pulses being selected to be relatively short, the feed rate being relatively low or by the presence of direct current, i.e. current flows continuously between the electrode during the feeding. According to a refinement of the process, it is also proposed that a feed rate during roller seam welding in the range from 0.5 cm/s to 30 m/s, in particular in the range from 0.5 m/min to 30 m/min, is used. This feed rate is used in particular when connecting metallic foil material which has a thickness of from 0.03 to 0.1 mm. In this case, the material to be connected preferably includes the following constituents: from 0.1 to 7.5% by weight of aluminum, and from 17 to 25% by weight of chromium. Another preferred material comprises from 12 to 32% by weight of nickel. Furthermore, it is also proposed that during the welding operation the electrodes exert a force of from 10 N to 29 kN, in particular from 200 N to 6 kN, on the layers. This ensures that, for example, any rolling oil or similar impurities adhering to the layers are forced out of the welding location. The result is both intensive contact between the components which are to be connected to one another and between the components and the electrodes. At the same time, this ensures that when the material is heated, the heated or molten materials are intimately mixed, so as to achieve a permanent connection. According to a further configuration of the process, the layers, at least in an edge region, are laid on top of one another, are welded at least over a portion in this edge region and are then deformed, so as to form the passages. In other words, this also means that the weld seam at least partially delimits the passage through which the exhaust gas can flow. With regard to the preferred magnitudes of the length of the portion, reference should be made to the statements given above. In principle, however, it should also be noted that it is customary for the complete edge regions to be connected to one another, i.e. accordingly the portion corresponds to the longest extent of the edge region. In particular, it is proposed that the layers are formed with at least one metallic foil which is made from a high-temperature-resistant and corrosion-resistant material and is preferably at least partially structured and/or allows a fluid to flow through it at least in regions. With regard to the material of the metallic foil, reference should be made at this point to the composition listed above. Furthermore, however, a person skilled in the art will be aware of a large number of further materials which are suitable for use in mobile exhaust gas systems. In this case, reference should be made to the large number of different materials which are given in the known prior art. When making a choice, it should also be borne in mind that this material must in general terms be suitable for resistance welding, i.e. in particular must also conduct current. The preferred configuration of the metallic foil with structures or apertures, pores, holes or the like is in this case predominantly located outside the edge regions which are used for connection by roller seam welding. Examples of suitable structures include corrugations, guide vanes, stamped formations or other structures. They are usually used to guide or swirl up the exhaust gas flowing along the metallic foil, in order in this way to ensure intimate contact with the surface of the body. Furthermore, these structures can also be used to make sure that the layers are at a predeterminable distance from one another. In this case, the structure represents a type of spacer. The effect of the foil being configured such that medium can flow through it at least in regions is that gas exchange can take place through the metallic foil. This usually depends on a forced flow, for example imposed by diverting vanes, sealing materials, etc. or by pressure differences in adjacent passages, which are in each case partially delimited by the metallic foil. According to an advantageous refinement of the process, it is proposed that the layers are formed with a filter fabric or a supporting structure comprising a filter material. A filter fabric comprises in particular knitted fabrics, woven fabrics or similar arrangements of chips, fibers or other particles which are bonded to one another. The are held together, for example, by sintered connections, brazed connections, welding connections or combinations thereof. The filter fabrics may be composed of metallic or ceramic material. Furthermore, it is also possible to provide a supporting structure on or in which a filter material is provided. Suitable supporting structures are once again woven fabrics, knitted fabrics, expanded metals or the like, in particular coarse-mesh formations, in the cavities of which the filter material is provided. It is this context particularly advantageous for the supporting structure to be metallic in form, in which case both ceramic and metallic materials can be used as filter material. The filter material is connected to the supporting structure by means of sintered connections, diffusion bonds, if appropriate also using filler materials, or combinations of these connection techniques. The connection according to the invention between the layers using a continuous resistance weld seam can also be carried out so as to incorporate this supporting structure, in particular by the layers being welded to one another exclusively via the supporting structures. The filter material itself forms an extremely high surface area with a multiplicity of pores, openings, flow passages and cavities. As the gas stream flows through the filter material, the undesired particulates stick to the surface and are converted into gaseous constituents when heat and/or reaction partners contained in the exhaust gas are supplied. According to a further configuration of the process, the layers are of multi-part structure, the layers being provided with a metallic foil in the connecting region, so that the metallic foils of layers arranged adjacent to one another are connected by means of roller seam welding. This means in particular that the foils are provided only in the edge region of the layers. In this case, for a filter material or a supporting structure they preferably form a construction which is suitable for roller seam welding. It is in this way possible to adapt components of the body which cannot normally be connected by such a process to the requirements of roller seam welding. It is in this context particularly advantageous if the layer comprises a filter fabric, the filter fabric, in the edge region, which subsequently forms the connecting region, being surrounded, and preferably also flanged, by in each case one metallic foil, and finally a plurality of layers produced in this way being welded to one another. In this case, the layers are configured in particular as a filter composite or filter layer as proposed by DE 101 53 284 and DE 101 53 283. With regard to the construction of filter layers or filter composites of this type, reference is made to the above-referenced publications in full, and consequently the descriptions given therein are used to explain the present situation. With regard to the above process variant for production of the body, it is particularly advantageous if the flanging and the roller seam welding are carried out simultaneously. By way of example, structured rolled electrodes are used for this purpose, which on the one hand allows the metallic foil to be hooked to the filter fabric and at the same time, on account of the flow of current, allows a connection by cohesive joining. In this case, the welding process can also be carried out in such a way that flanged connections and welded connections alternate in the welding direction. In the present context, the term flanging is to be understood in particular as meaning manual or mechanical bending-over of the edges of sheet-metal parts to remove the sharpness of the edge and/or to reinforce the workpiece. According to yet another configuration of the process, it is proposed that the layers are welded together in such a way that they are connected in the edge regions on alternate sides to in each case an adjacent layer, so as to in each case form a fold. The procedure described here for the production of a body is suitable in particular for producing filter bodies. In this case, the layers, which preferably also comprise filter fabric or a filter material, are connected to one another at their edge regions, in order to realize the principle of the "closed particulate filter". After two adjacent layers have been welded together, the layers can be folded open so that they form an angle to one another in an edge region. The intermediate space which has formed between the layers is referred to as a fold. This represents a flows passage or passage in particular in the case of the radial-flow particulate filters. Furthermore, it is proposed that the layers are designed with supporting means, which are preferably arranged in a passage and/or in a fold. The term supporting means is to be understood in particular as meaning spacers, reinforcing structures, spacer pieces or similar means which ensure that the predetermined position of the layers with respect to one another is retained even during subsequent use in the exhaust system of mobile internal combustion engines. It is in this context particularly advantageous if the supporting means are connected to the layer by the roller seam welding manufacturing process, preferably at the same time as a connection of the layers to one another is being executed. By way of example, the supporting means may be formed as a structure of the metallic foil, which therefore bear against regions of the adjacent layer and ensure the aperture angle or the spacing of the layers which are spaced apart from one another. The connection of the layers according to the invention using a continuous resistance weld seam can also be carried out incorporating these supporting means; under certain circumstances, the layers are even welded to one another exclusively via the supporting means. Moreover, it is also proposed that the welded layers are connected to at least one housing, preferably by welding or brazing. In the case of axial-flow bodies, direct connection of the layers to the housing located on the outer side is preferred. Known brazing or welding techniques can be used for this purpose. If the body realizes a radial-flow design, a connection to an outer housing is generally realized only indirectly, i.e. via additional elements. In designs of this type, a housing which is directly connected to the layers and is arranged on the outer circumference of the body is usually avoided, since this annular space is usually required for the incoming and/or outgoing flow of the gas stream. The outer housing is then fixed via any additional components, such as spacers, cover plates, collars or the like. In particular in the context of the radial-flow concept, it is proposed that the housing is an inner tube with a center axis, to the outer lateral surface of which inner tube the layers are secured. For this purpose, the inner tube is provided with holes or flow passages which allow the exhaust gas to flow through the inner tube without generating a high flow resistance. This makes is easy to connect the cavity arranged in the interior of the tubular casing toward the folds, which have been formed by the layers arranged on the outside. The connection of the layers toward the inner tube can be realized by mechanical connection means or by thermal joining. In particular with a view to securing using mechanical securing means, it is to be assumed that the inner tube is preferably of multi-part construction. To divert the gas stream toward the filter surfaces, the inner tube is usually equipped with a closed end. According to an advantageous configuration, the layers are to be arranged in such a way that the connecting regions or the folds or passages formed by the layers run in the direction of the center axis. With regard to the words "in the direction of the center axis", it should be pointed out for clarification that this does not require any particular accuracy, but rather relatively large tolerances are possible under certain circumstances. In this case, therefore, there are a plurality of folds which are arranged adjacent to one another in the circumferential direction and preferably extend over a large portion of the inner tube. The connection regions between the individual layers and between the layers and the inner tube in this case run in the axial direction parallel to the center axis. In an alternative configuration, the layers are arranged in such a way that the connecting regions and/or the folds or passages formed by the layers run perpendicular to the center axis. With regard to the words "perpendicular to the center axis", it should be pointed out for clarification that this does not require any particular accuracy, but rather relatively large tolerances are possible under certain circumstances. The feature means in particular that the fold is designed as an annular passage extending in the circumferential direction. A plurality of these annular folds are arranged spaced apart from one another (as seen in the direction of the center axis). The connection regions between the individual layers and between the layers and the inner tube run in the circumferential direction. Another aspect of the invention proposes a body for treating the exhaust gas from mobile internal combustion engines, which is produced in particular by one of the processes explained above. The body has a plurality of metallic layers, wherein the layers are in contact with one another in a connecting region, and a roller seam welded connection is provided between at least some of the layers, so that the layers form passages through which a fluid can flow. A body of this type is suitable for use as a catalyst support body, an adsorber, a filter body of a flow mixer. It is also possible for the body to be configured in such a way as to form zones with different functions, for example by having different coatings in different zones. It is also possible for the layers to be designed differently with regard to the gas permeability and/or the structuring in these zones, so that different exhaust-gas purification steps are passed through sequentially in the direction of flow. The invention and the technical background will now be explained in more detail with reference to the figures. The figures show particularly preferred exemplary embodiments, although the invention is not restricted to these embodiments. Rather, the production process of roller seam welding can be used for numerous different designs of bodies for exhaust-gas purification, with in particular the connection between the layers forming the flow passages being produced using these manufacturing processes. In the accompanying drawmg: Fig. 1 diagrammatically depicts the sequence of a configuration of the process for producing a body for exhaust-gas treatment, Fig. 2 shows a detail view of a variant embodiment of a body for exhaust-gas treatment, Fig 3 shows a further diagrammatic illustration of an exemplary embodiment of the body, Fig. 4 shows an exemplary embodiment of a body with longitudinal folds, Fig. 5 shows a further configuration of a body with coaxial folds, and Fig. 6 shows a further exemplary embodiment of a body with folds in the circumferential direction. Fig. 1 diagrammatically depicts the sequence involved in the production process of roller seam welding, which is used here to produce a body for exhaust gas treatment. Fig. 1 illustrates two metallic foils 12 which are brought into contact with one another. The foils 12 resting on top of one another are passed at a feed rate 7 through two rotating electrodes 8. In the process, the two electrodes 8 press on the surface of the foils 12 with a force 9. The two electrodes 8 are connected to one another via a current source 26, with current flowing between the electrodes 8 and therefore also locally through the foils 12 with a predetermined frequency. The current leads to heating of the foils 12, so that they become at least partially molten. The foils 12 in this case have a thickness 22 which is, for example, in the range from 0.02 to 0.1 mm. As a result of Joule resistance heating, a multiplicity of weld spots 6, which preferably merge into one another so as to form a sealed seam 5, are formed in the contact region between the two foils 12. Fig. 2 diagrammatically depicts a detailed view of a connecting region 3, which is formed between two adjacent layers 2. The layers 2 are formed with a filter fabric 13, which is provided near an edge region 10 with a foil 12 that has been flanged. The foils 12 project beyond the filter fabric 13 and form an edge region 10, which is finally pushed through the rotating electrodes 8, so that a roller seam welded connection is produced between the two foils 12. Whereas the filter fabric 13 is of gas-permeable design, as is indicated by the dashed arrows, the foil 12 itself is in this case impermeable to gases. The foil 12 in this case serves simultaneously to fix supporting means 17, ensuring a defined position of the layers 2 with respect to one another, so that the folds 16 are always of the desired shape. Fig. 3 shows a body of plate construction, with the layers 2 arranged substantially parallel to one another. The plate-like layers 2 in the embodiment illustrated comprise a supporting structure 14 in which a filter material 15 has been integrated. A connecting region 3 is in each case formed in the edge regions on alternate sides of the layers 2. The connecting region 3 again comprises roller seam welded connections. The connection region 3 bears directly against a housing 18 and is connected to it be joining. The supporting means 17 arranged between the layers 2 are, for example, structured metal foils or structures of the layers 2 themselves, which prevent the layers 2 from bearing directly flat against one another. It can also be seen that with the body 1 illustrated the principle of a "closed particulate filter" has been implemented, in which adjacent passages 4 are provided with a closure 24, so that the gas stream has to pass through the layers 2 in the direction of flow 23. Fig. 4 shows another variant embodiment of a body 1 for exhaust gas treatment, which is used in particular as a filter. This figure shows a radial-flow concept, in which the gas stream that is to be purified first of all enters an inner region in the direction of the center axis 21 through the cover plate 25. The rear-side cover plate 25 closes off the inner flow passage and therefore forces the exhaust gas to pass through the layers 2 which form the folds 16. The body 1 illustrated again has supporting means 17, which ensure the position of the layers 2 with respect to one another even in the event of pressure fluctuations occurring in the gas flow. In the exemplary embodiment illustrated, the layers 2 are arranged in such a way that the connection regions 3 and the folds 16 formed by the layers 2 run in the direction of the center axis 21. The connection regions 3 are in each case formed over a portion 11. Fig. 5 shows a further variant embodiment of a body 1, in particular a filter body. In this case, the folds 16 run substantially coaxially with respect to the center axis 21. The layers 2 are mounted on the end sides of a cover plate 25 which at least partially allows the exhaust gas to flow through it. The connection regions 3 of the layers 2 arranged adjacent to one another are arranged substantially coaxially to the center axis 21, once again realizing the principle of a "closed particulate filter". The layers 2 in this case comprise a supporting structure 14 in which the filter material 15 is additionally provided. Fig. 6 shows a body 1 in which the layers 2 are arranged in such a way that the connection regions 3 and the folds 16 formed by the layers 2 run substantially perpendicular to the center axis 21. The layers 2 are secured to an outer lateral surface 20 of an inner tube 19. The inner tube 19 has openings through which the gas stream can enter radially inward, as indicated by the arrows for the direction of flow 23. Additional supporting means 17 are arranged between the layers 2 outside the folds 16 illustrated in dotted form; these supporting means 17 are in this case connected on one side to the inner tube 19 and on the other side to the layers 2. Moreover, the entire arrangement is enclosed by a housing 18 spaced apart from the layers 2. The connection regions 3, which have been generated using the roller seam welding process, are formed on the outer circumference and the internal circumference of the layers 2. They in each case produce a connection between the layers 2 arranged adjacent to one another. List of designations 1 Body 2 Layer 3 Connection region 4 Passage 5 Sealed seam 6 Weld spot 7 Feed rate 8 Electrode 9 Force 10 Edge region 11 Portion 12 Foil 13 Filter fabric 14 Carrier structure 15 Filter material 16 Fold 17 Supporting means 18 Housing 19 Inner tube 20 Lateral surface 21 Center axis 22 Thickness 23 Direction of flow 24 Closure 25 Cover plate 26 Current source WE CLAIM 1. A procejss for producing a body (1) for exhaust gas treatment, which has a plurality of metallic layers (2) characterized in that, the layers (2) are formed with a supporting structure (14) comprising a filter material (15) and the layers (2) are designed with supporting means (17), which are preferably arranged in a passage (4) and/or in a fold (16) in which method the layers (2) are brought into contact with one another in a connection region (3), and a connection is produced by a continuous resistance welding process, in such a manner mat the layers (2) form passages (4) through which a gas stream can at least partially flow, wherein the continuous resistance welding process comprises roller seam welding, a feed rate (7) during roller seam welding in the range from 0.5 cm/s to 30 m/s, in particular in the range from 0.5m/in to 30 m/min, is used and during the welding operation the electrodes (8) exert a force (9) of from 10 N to 29 kN, in particular from 200 N to 6 kN, on the layers (2), for connecting the supporting means (17) to the layer (2) by the roller seam welding: manufacturing process, preferably at the same time as a connection of the layers (2) to one another is being executed. 2. The process as claimed in claim 1, wherein the continuous resistance welding process comprises projection seam welding. 3. The process as claimed in claim 1, in which at least in part a sealed seam (5) in which there are overlapping weld spots (6) is formed. 4. The process as claimed in one of the preceding claims, in which the layers (2), at least in an edge region (10), are laid on top of one another, are welded at least over a portion (11) in this edge region and are then deformed, so as to form the passages (4). 5. The process as claimed in one of the preceding claims, in which the layers (2) are formed with at least one metallic foil (12) which is made from a high-temperature-resistant and corrosion-resistant material and is preferably at least partially structured and/or allows a fluid to flow through it at least in regions. 6. The process as claimed in one of the preceding claims, in which the layers (2) are of multi-part structure, the layers (2) being provided with a metallic foil (12) in the connecting region (3), the metallic foils (12) of layers (2) arranged adjacent to one another being connected by means of roller seam welding. 7. The process as claimed in one of the preceding clarms, in which the layers (2) are welded together in such a way that they are connected in the edge regions (10) on alternate sides to in each case an adjacent layer (2), so as to in each case form a fold (16). 8. The process as claimed in one of me preceding claims, in which the welded layers (2) are connected to at least one housing (18), preferably by welding or brazing. 9. The process as claimed in claim 13, in which the housing (18) is an inner tube (19) with a center axis (21), to the outer lateral surface (20) of which inner tube the layers (2) are secured. 10. The process as claimed in claim 9, in which the layers (2) are arranged in such a way that the connecting regions (3) and/or the folds (16) or passages (4) formed by the layers (2) run in the direction of the center axis (21). 11. The process as claimed in claim 9, in which the layers (2) are arranged in such a way that the connecting regions (3) and/or me folds (16) or passages (4) formed by the layers (2) run substantially perpendicular to the center axis (21). 12. A body (1) for treating the exhaust gases from mobile internal combustion engines, in particular produced by the process as claimed in one of the preceding claims, which has a plurality of metallic layers (2), in which the layers (2) are formed with a supporting structure (14) comprising a filter material (15) and the layers (2) are designed with supporting means (17), which are preferably arranged in a passage (4) and/or in a fold (16) and said layers (2) are in contact with one another in a connecting region (3), wherein a roller seam welded joint is provided between at least some of the layers (2), so mat me layers (2) form passages (4) through which a fluid can flow, wherein the supporting means (17) with the layer (2) and the layers (2) with one another form a roller seam welding joint wherein the housing (18) is an inner tube (19) with a center axis (21), to the outer lateral surface (20) of which inner tube the layers (2) are secured and wherein the layers (2) are arranged in such a way that the connecting regions (3) and/or the folds (16) or passages (4) formed by the layers (2) run in the direction of the center axis (21). The invention relates to a method for producing a body (1) for exhaust treatment, said body comprising a plurality of metallic layers (2). According to the inventive method, the layers (2) are brought into contact with each other in an assembly region (3), and a join is made by means of a roller seam welding method in such a way that the layers (2) form channels (4) through which a gas flow can pass. The invention also relates to corresponding bodies (1) for exhaust treatment, that can especially be used as filters or catalyst carrier bodies in the car industry.

Full Text

Roller seam welded body for exhaust gas treatment
The present invention relates to a process for producing a body for exhaust gas
treatment, which has a plurality of metallic layers forming passages through which
a gas stream can flow. Bodies of this type are used in particular for purifying the
exhaust gases from mobile internal combustion engines, such as spark ignition or
diesel engines. Primary application areas in this context are passenger automobiles
as well as trucks and motor cycles. It is also known for these bodies to be used in
exhaust systems of portable hand held appliances, such as for example power
saws, lawnmowers, etc.
Bodies of this type have a number of different functions. For example, they are
used as catalyst support bodies, as adsorbers, as filters, flow mixers or mufflers.
The body is usually distinguished by a favorable ratio of surface area to volume,
i.e. it has a relatively large surface area and therefore ensures intensive contact
with the gas stream flowing through it.
With regard to catalyst support bodies, this surface or the body is provided with a
catalytically active coating, which preferably comprises washcoat. The washcoat
has a particularly fissured surface, so that the ratio of surface area to volume can
be improved still further. The washcoat is impregnated with various catalysts, for
example platinum, rhodium or the like.
Adsorbers substantially have a similar basic structure as that selected for bodies
used as catalyst support bodies. However, a different objective is pursued with
regard to the coating, so that consequently different coatings are used. The purpose
of the adsorbers is, for example, to retain nitrogen oxides until suitable reaction
partners and/or temperatures are present to allow these constituents of the exhaust
gas to be converted as fully as possible.
Flow mixers are distinguished by the fact that their bodies have a multiplicity of
passages which are flow-connected to one another. At the same time, guide
surfaces, which allow the partial gas streams to be diverted, are provided in the
interior of the body or of the passages. In this way, the gas stream, is made more
uniform in terms of its pollutant concentration, its flow properties, its temperature,
etc.
A wide range of different structural forms are known for the abovementioned
bodies as catalyst support bodies, adsorbers, mufflers and flow mixers. These
forms include, for example, honeycomb bodies comprising at least partially
structured sheet-metal foils. Compared to known bodies made from ceramic
material, the metallic honeycomb bodies have a considerably greater flexibility in
terms of their intended use and also allow a greater degree of design freedom. It
should also be borne in mind that particularly effective conversion processes with
regard to the pollutant concentration are ensured on account of the good heat
conduction and the extremely low area-specific heat capacity.
A distinction is drawn in particular between two typical designs of metallic
honeycomb bodies. An early design, of which DE 29 02 779 A1 shows typical
examples, is the helical design, in which substantially one smooth and one
corrugated sheet-metal layer are placed on top of one another and wound helically.
In another design, the honeycomb body is constructed from a multiplicity of
alternately arranged smooth and corrugated or differently corrugated sheet-metal
layers, the sheet-metal layers initially forming one or more stacks which are then
intertwined. In this case, the ends of all the sheet-metal layers come to lay on the
outside and can be connected to a housing or tubular casing, producing numerous
connections, which increase the durability of the honeycomb body. Typical
examples of these designs are described in EP 0 245 737 B1 or WO 90/03220. It
has also long been known to equip the sheet-metal layers with additional structures
in order to influence the flow and/or bring about cross-mixing between the
individual flow passages. Typical examples of these configurations include
WO 91/01178, WO 91/01807 and WO 90/08249. Finally, there are also conical
honeycomb bodies, optionally also with further additional structures for
influencing the flow. A honeycomb body of this type is described, for example, in
WO 97/49905. Furthermore, it is also known to leave free a cutout in a honeycomb
body for a sensor, in particular for accommodating a lambda sensor. One such
example is described in DE 88 16 154 U1.
Of course, the designs described above are also suitable for forming filter bodies.
In principle, two different principles are known for these or other filter bodies. One
principle relates to what is known as the "closed particulate filter", in which the
passages formed by the body are closed on alternate sides, therefore forcing the
gas stream to pass through passage walls comprising filter material.. This leads to
the accumulation of particulates or solids contained in the gas stream, which are
burnt and/or oxidized continuously or at predeterminable intervals. An alternative
known design is that of the "open particulate filter", which is not closed on
alternate sides, but rather has flow diversion points in the interior of the passages,
which cause the partial gas streams to be swirled up in such a way that at least 80%
of the partial gas streams pass through the filter wall, preferably a number of times.
The major advantage of the "open particulate filter" is that blockage of the filter
material caused by an excessive accumulation of particulates is avoided. A
particulate filter is described as "open" if particulates can fundamentally flow
completely through it, specifically including particulates which are considerably
larger than the particulates that are actually to be filtered out. As a result, a filter of
this type cannot become blocked even in the event of an agglomeration of
particulates during operation. A suitable method for measuring the openness of a
particulate filter is, for example, to test the diameter up to which spherical particles
can still trickle through a filter of this type. In present applications, a filter is open
in particular if spheres with a diameter of greater than or equal to 0.1 mm can still
trickle through it, preferably spheres with a diameter of over 0.2 mm. One such
example is given in DE 2011783U1 to which reference is made in full for the
purposes of explanation.
In addition to these bodies with wound or intertwined layers, it is also known to
use what are known as plate filters, which comprise a plurality of in particular
sheet-like or substantially planar filter plates which are arranged spaced apart from
one another. Plate filters of this type are usually also constructed in accordance
with the principle of passages that are closed on alternate sides, but it is in
principle also possible to realize an "open particulate filter".
Whereas wound designs and plate designs of this type have the gas stream flowing
through them substantially axially, bodies or filter bodies which the gas stream
flows through radially are also known. Such bodies usually have an inner flow
passage and an outer flow passage which is annular in form and is generally
arranged coaxially with respect to the inner flow passage. The inner flow passage
is generally delimited by an inner tube, which is provided with openings through
which the gas stream to be purified is passed. Layers of a filter material are
arranged around this inner tube. Substantially two different concepts are known in
this respect. The first concept can be described on the basis of a "star shape",
which is realized when the filter plates are viewed in the direction of the inner tube
or a cross section perpendicular to the inner tube. This means in other words that
the filter plates form folds which extend substantially parallel to the axial extent of
the inner tube. Another known concept involves the formation of folds in the
circumferential direction, in which case a plurality of these folds are positioned on
the inner tube, spaced apart from one another in the axial direction. According to
the routing of the flow, the gas stream that is to be purified is fed to the filter
material from the inside (or from the outside), penetrates through this filter
material and is discharged again on the opposite side.
The bodies described above generally comprise a plurality or multiplicity of
different components made from in some cases different materials. Considering the
high thermal and dynamic stresses in the exhaust system of mobile internal
combustion engines, these individual components have to be permanently
connected to one another. Numerous different connection techniques are known
for this purpose, for example brazing and/or welding. With regard to these
connection techniques, it should be noted that they have to be suitable for at least
medium-sized series production. In this respect, cost aspects also play an important
role, such as cycle rates, connection quality, process reliability, etc. Known
processes used to form connections by joining (in particular in the structure
comprising the filter surfaces and/or the layers) require an additional material, such
as, for example braze or weld filler. It is in this case particularly difficult for the
filler to be applied at precisely the location at which a join is subsequently to be
produced. Moreover, it should be noted that increasingly thin-walled materials
need to be used, since such materials very quickly adapt to the temperature of the
exhaust gas and accordingly have highly dynamic reaction properties. To ensure
the long-term functionality of these bodies, however, a spatially tightly delimited
introduction of heat is required to form the connections by joining. Hitherto, this
has not been achievable to a satisfactory extent, and indeed brazing generally
requires heating of the entire body in a high-temperature vacuum furnace, and
welding has hitherto usually also been carried out through the outer housing, and
consequently in this case too considerable temperature gradients have been
realized across a large part of the body.
Working on this basis, it is an object of the present Invention to overcome the
above technical problems of the prior art. In particular, it is intended to provide an
inexpensive, simple, effective and reliable process for producing metallic bodies of
this type for exhaust gas purification. Moreover, the process should as far as
possible be suitable for automation, producing connections by joining which are
distinguished by a particularly long service life. Furthermore, it is intended to
provide a corresponding body for exhaust gas treatment which can be configured
variably and is versatile in use.
These objects are achieved by a process having the features of patent claim 1 and a
body having the features of patent claim. 18 Further advantageous configurations
are described in the respective dependent patent claims, which can be combined
with one another in any desired way.
The process according to the invention for producing a body for exhaust gas
treatment which has a plurality of metallic layers is characterized in that the layers
are brought into contact with one another in a connection region, and a connection
is produced by a continuous resistance welding process, in such a manner that the
layers form passages through which a gas stream can at least partially flow. In
other words, this means in particular that the connection between layers arranged
adjacent to one another is effected by the continuous resistant welding process.
In this context, it should be noted that the term "continuous" may mean that the
welding takes place along one welding track, in which case the weld seam which is
generated is made uninterrupted. However, this need not necessarily be the case;
for example, it is also possible for a plurality of weld seams which axe spaced apart
to be provided along the welding track, in which case the proportion in which the
weld seams are present along the welding track is advantageously significantly
greater than the proportion formed by the interruptions. It is particularly preferable
for the proportion formed by the weld seam, based on the welding track, to amount
to at least 80%, in particular even more than 90%.
With regard to the "passages", it should also be noted that these passages need not
necessarily have a tube-like structure. Rather, this term is to be understood as
meaning a limited flow path which has a spatial boundary. In this case, the
boundary is generally configured in such a way that it encloses the flow path over
at least 60% (in particular 80%) of the circumference, with the length of the flow
path advantageously being greater than the circumference.
In view of the fact that the abovementioned body may also be constructed as a
filter, it will be clear that the passages do not necessarily have to have a gastight
passage wall, i.e. it is also eminently possible for the layers to be configured so as
to be at least partially gas-permeable. In particular in this case, the gas stream does
not flow completely through the passage, in which case although the passage does
have a suitable cross section, the gas stream nevertheless uses a different route.
Therefore, it is considered sufficient for the passage to offer the option of at least
partially allowing a gas stream to flow through it, in particular with open end sides.
According to an advantageous configuration of the process, the continuous
resistance welding process comprises roller seam welding and/or projection seam
welding.
Roller seam welding and the projection seam welding process belong to the
pressure-joining welding processes, in particular resistance pressure welding or
conductive pressure welding. In the resistance pressure welding process, the
heating at the welding location takes place as a result of Joule resistance heating
when current flows and by means of an electrical conductor. The current is
supplied via electrodes with a convex or planar working surface. Two roller-like
(driven) electrodes are used for the roller seam welding. The metal sheets to be
welded are in this case arranged predominantly overlapping. In practice, roller
seam welding is a continuous spot welding, but using roller-like electrodes. Unlike
when using resistance spot welding, the electrodes remain in contact after the first
weld spot has been produced and are then rolled continuously onward. Further
current flows at the locations where a weld spot is to be formed. Depending on the
feed rate of the electrodes and the frequency of the welding current, spot seams or
sealed seams with overlapping weld nuggets or weld spots are produced.
Permanent direct current likewise produces a sealed seam.
The use of this production process to connect the layers has proven particularly
advantageous in particular with a view to series production of these bodies. The
process in which the two layers adjacent or lying on top of one another are passed
through the rotating electrodes is surprisingly well able to withstand the high
thermal and dynamic stresses for example in the exhaust system of automobiles. It
has also been established that even in the case of very thin metal foils which are
connected to one another in this way, sealed weld seams can be produced in very
short working cycles. As a result, it is possible to achieve in particular a cost
benefit, which was unexpected in view of the additional material which is required
for the overlap between the two layers. Roller seam welding is suitable in
particular for connection regions which have a certain length, i.e.. extend over a
predetermined portion. This should generally amount to at least 5 cm, in particular
at least 15 cm, and the work can be carried out at particularly low cost beyond a
length of 25 cm. The roller seam welding makes do without filler. Furthermore, it
is in many cases also possible to do without a step of cleaning the layers, since the
introduction of the electrode force ensures that contact between the electrodes
and/or the layers which is sufficient for the flow of current and the formation of the
weld spot is already ensured to a considerable extent. Moreover, only an
insignificant change in the microstructure of the layer adjacent to the weld nugget
can be established. Accordingly, the use of this manufacturing process offers
numerous advantages and at the same time overcomes all the technical problems
listed in the introduction at once. Moreover, the process can also be applied to each
of the types of bodies mentioned in the introduction.
According to one refinement of the process, it is proposed that at least in part a
weld seam in which there are at least overlapping weld spots is formed. This
applies in particular to the case in which the ends or edge regions of the layers are
to be fixed to one another. These edge regions or edges for example close up flow
paths, so that the exhaust gas to be purified is forced to pass through a filter
material. To ensure the principle of a "closed particulate filter", a sealed seam
should be at least partially present. This is to be understood as meaning that the
welding current pulses take place in succession at such short time intervals that the
respectively adjacent weld spots or weld nuggets merge into one another, i.e. there
are no unconnected locations on the layers between adjacent weld spots. As has
already been stated above, a sealed seam of this type is achieved by virtue of the
frequency of the current pulses being selected to be relatively short, the feed rate
being relatively low or by the presence of direct current, i.e. current flows
continuously between the electrode during the feeding.
According to a refinement of the process, it is also proposed that a feed rate during
roller seam welding in the range from 0.5 cm/s to 30 m/s, in particular in the range
from 0.5 m/min to 30 m/min, is used.
This feed rate is used in particular when connecting metallic foil material which
has a thickness of from 0.03 to 0.1 mm. In this case, the material to be connected
preferably includes the following constituents: from 0.1 to 7.5% by weight of
aluminum, and from 17 to 25% by weight of chromium. Another preferred
material comprises from 12 to 32% by weight of nickel.
Furthermore, it is also proposed that during the welding operation the electrodes
exert a force of from 10 N to 29 kN, in particular from 200 N to 6 kN, on the
layers. This ensures that, for example, any rolling oil or similar impurities adhering
to the layers are forced out of the welding location. The result is both intensive
contact between the components which are to be connected to one another and
between the components and the electrodes. At the same time, this ensures that
when the material is heated, the heated or molten materials are intimately mixed,
so as to achieve a permanent connection.
According to a further configuration of the process, the layers, at least in an edge
region, are laid on top of one another, are welded at least over a portion in this
edge region and are then deformed, so as to form the passages. In other words, this
also means that the weld seam at least partially delimits the passage through which
the exhaust gas can flow. With regard to the preferred magnitudes of the length of
the portion, reference should be made to the statements given above. In principle,
however, it should also be noted that it is customary for the complete edge regions
to be connected to one another, i.e. accordingly the portion corresponds to the
longest extent of the edge region.
In particular, it is proposed that the layers are formed with at least one metallic foil
which is made from a high-temperature-resistant and corrosion-resistant material
and is preferably at least partially structured and/or allows a fluid to flow through
it at least in regions. With regard to the material of the metallic foil, reference
should be made at this point to the composition listed above. Furthermore,
however, a person skilled in the art will be aware of a large number of further
materials which are suitable for use in mobile exhaust gas systems. In this case,
reference should be made to the large number of different materials which are
given in the known prior art. When making a choice, it should also be borne in
mind that this material must in general terms be suitable for resistance welding, i.e.
in particular must also conduct current.
The preferred configuration of the metallic foil with structures or apertures, pores,
holes or the like is in this case predominantly located outside the edge regions
which are used for connection by roller seam welding. Examples of suitable
structures include corrugations, guide vanes, stamped formations or other
structures. They are usually used to guide or swirl up the exhaust gas flowing
along the metallic foil, in order in this way to ensure intimate contact with the
surface of the body. Furthermore, these structures can also be used to make sure
that the layers are at a predeterminable distance from one another. In this case, the
structure represents a type of spacer. The effect of the foil being configured such
that medium can flow through it at least in regions is that gas exchange can take
place through the metallic foil. This usually depends on a forced flow, for example
imposed by diverting vanes, sealing materials, etc. or by pressure differences in
adjacent passages, which are in each case partially delimited by the metallic foil.
According to an advantageous refinement of the process, it is proposed that the
layers are formed with a filter fabric or a supporting structure comprising a filter
material. A filter fabric comprises in particular knitted fabrics, woven fabrics or
similar arrangements of chips, fibers or other particles which are bonded to one
another. The are held together, for example, by sintered connections, brazed
connections, welding connections or combinations thereof. The filter fabrics may
be composed of metallic or ceramic material. Furthermore, it is also possible to
provide a supporting structure on or in which a filter material is provided. Suitable
supporting structures are once again woven fabrics, knitted fabrics, expanded
metals or the like, in particular coarse-mesh formations, in the cavities of which
the filter material is provided. It is this context particularly advantageous for the
supporting structure to be metallic in form, in which case both ceramic and
metallic materials can be used as filter material. The filter material is connected to
the supporting structure by means of sintered connections, diffusion bonds, if
appropriate also using filler materials, or combinations of these connection
techniques. The connection according to the invention between the layers using a
continuous resistance weld seam can also be carried out so as to incorporate this
supporting structure, in particular by the layers being welded to one another
exclusively via the supporting structures.
The filter material itself forms an extremely high surface area with a multiplicity of
pores, openings, flow passages and cavities. As the gas stream flows through the
filter material, the undesired particulates stick to the surface and are converted into
gaseous constituents when heat and/or reaction partners contained in the exhaust
gas are supplied.
According to a further configuration of the process, the layers are of multi-part
structure, the layers being provided with a metallic foil in the connecting region, so
that the metallic foils of layers arranged adjacent to one another are connected by
means of roller seam welding. This means in particular that the foils are provided
only in the edge region of the layers. In this case, for a filter material or a
supporting structure they preferably form a construction which is suitable for roller
seam welding. It is in this way possible to adapt components of the body which
cannot normally be connected by such a process to the requirements of roller seam
welding.
It is in this context particularly advantageous if the layer comprises a filter fabric,
the filter fabric, in the edge region, which subsequently forms the connecting
region, being surrounded, and preferably also flanged, by in each case one metallic
foil, and finally a plurality of layers produced in this way being welded to one
another. In this case, the layers are configured in particular as a filter composite or
filter layer as proposed by DE 101 53 284 and DE 101 53 283. With regard to the
construction of filter layers or filter composites of this type, reference is made to
the above-referenced publications in full, and consequently the descriptions given
therein are used to explain the present situation.
With regard to the above process variant for production of the body, it is
particularly advantageous if the flanging and the roller seam welding are carried
out simultaneously. By way of example, structured rolled electrodes are used for
this purpose, which on the one hand allows the metallic foil to be hooked to the
filter fabric and at the same time, on account of the flow of current, allows a
connection by cohesive joining. In this case, the welding process can also be
carried out in such a way that flanged connections and welded connections
alternate in the welding direction. In the present context, the term flanging is to be
understood in particular as meaning manual or mechanical bending-over of the
edges of sheet-metal parts to remove the sharpness of the edge and/or to reinforce
the workpiece.
According to yet another configuration of the process, it is proposed that the layers
are welded together in such a way that they are connected in the edge regions on
alternate sides to in each case an adjacent layer, so as to in each case form a fold.
The procedure described here for the production of a body is suitable in particular
for producing filter bodies. In this case, the layers, which preferably also comprise
filter fabric or a filter material, are connected to one another at their edge regions,
in order to realize the principle of the "closed particulate filter". After two adjacent
layers have been welded together, the layers can be folded open so that they form
an angle to one another in an edge region. The intermediate space which has
formed between the layers is referred to as a fold. This represents a flows passage
or passage in particular in the case of the radial-flow particulate filters.
Furthermore, it is proposed that the layers are designed with supporting means,
which are preferably arranged in a passage and/or in a fold. The term supporting
means is to be understood in particular as meaning spacers, reinforcing structures,
spacer pieces or similar means which ensure that the predetermined position of the
layers with respect to one another is retained even during subsequent use in the
exhaust system of mobile internal combustion engines.
It is in this context particularly advantageous if the supporting means are
connected to the layer by the roller seam welding manufacturing process,
preferably at the same time as a connection of the layers to one another is being
executed. By way of example, the supporting means may be formed as a structure
of the metallic foil, which therefore bear against regions of the adjacent layer and
ensure the aperture angle or the spacing of the layers which are spaced apart from
one another. The connection of the layers according to the invention using a
continuous resistance weld seam can also be carried out incorporating these
supporting means; under certain circumstances, the layers are even welded to one
another exclusively via the supporting means.
Moreover, it is also proposed that the welded layers are connected to at least one
housing, preferably by welding or brazing. In the case of axial-flow bodies, direct
connection of the layers to the housing located on the outer side is preferred.
Known brazing or welding techniques can be used for this purpose. If the body
realizes a radial-flow design, a connection to an outer housing is generally realized
only indirectly, i.e. via additional elements. In designs of this type, a housing
which is directly connected to the layers and is arranged on the outer
circumference of the body is usually avoided, since this annular space is usually
required for the incoming and/or outgoing flow of the gas stream. The outer
housing is then fixed via any additional components, such as spacers, cover plates,
collars or the like.
In particular in the context of the radial-flow concept, it is proposed that the
housing is an inner tube with a center axis, to the outer lateral surface of which
inner tube the layers are secured. For this purpose, the inner tube is provided with
holes or flow passages which allow the exhaust gas to flow through the inner tube
without generating a high flow resistance. This makes is easy to connect the cavity
arranged in the interior of the tubular casing toward the folds, which have been
formed by the layers arranged on the outside. The connection of the layers toward
the inner tube can be realized by mechanical connection means or by thermal
joining. In particular with a view to securing using mechanical securing means, it
is to be assumed that the inner tube is preferably of multi-part construction. To
divert the gas stream toward the filter surfaces, the inner tube is usually equipped
with a closed end.
According to an advantageous configuration, the layers are to be arranged in such
a way that the connecting regions or the folds or passages formed by the layers run
in the direction of the center axis. With regard to the words "in the direction of the
center axis", it should be pointed out for clarification that this does not require any
particular accuracy, but rather relatively large tolerances are possible under certain
circumstances. In this case, therefore, there are a plurality of folds which are
arranged adjacent to one another in the circumferential direction and preferably
extend over a large portion of the inner tube. The connection regions between the
individual layers and between the layers and the inner tube in this case run in the
axial direction parallel to the center axis.
In an alternative configuration, the layers are arranged in such a way that the
connecting regions and/or the folds or passages formed by the layers run
perpendicular to the center axis. With regard to the words "perpendicular to the
center axis", it should be pointed out for clarification that this does not require any
particular accuracy, but rather relatively large tolerances are possible under certain
circumstances. The feature means in particular that the fold is designed as an
annular passage extending in the circumferential direction. A plurality of these
annular folds are arranged spaced apart from one another (as seen in the direction
of the center axis). The connection regions between the individual layers and
between the layers and the inner tube run in the circumferential direction.
Another aspect of the invention proposes a body for treating the exhaust gas from
mobile internal combustion engines, which is produced in particular by one of the
processes explained above. The body has a plurality of metallic layers, wherein the
layers are in contact with one another in a connecting region, and a roller seam
welded connection is provided between at least some of the layers, so that the
layers form passages through which a fluid can flow. A body of this type is
suitable for use as a catalyst support body, an adsorber, a filter body of a flow
mixer. It is also possible for the body to be configured in such a way as to form
zones with different functions, for example by having different coatings in
different zones. It is also possible for the layers to be designed differently with
regard to the gas permeability and/or the structuring in these zones, so that
different exhaust-gas purification steps are passed through sequentially in the
direction of flow.
The invention and the technical background will now be explained in more detail
with reference to the figures. The figures show particularly preferred exemplary
embodiments, although the invention is not restricted to these embodiments.
Rather, the production process of roller seam welding can be used for numerous
different designs of bodies for exhaust-gas purification, with in particular the
connection between the layers forming the flow passages being produced using
these manufacturing processes. In the accompanying drawmg:
Fig. 1 diagrammatically depicts the sequence of a configuration of the
process for producing a body for exhaust-gas treatment,
Fig. 2 shows a detail view of a variant embodiment of a body for exhaust-gas
treatment,
Fig 3 shows a further diagrammatic illustration of an exemplary embodiment
of the body,
Fig. 4 shows an exemplary embodiment of a body with longitudinal folds,
Fig. 5 shows a further configuration of a body with coaxial folds, and
Fig. 6 shows a further exemplary embodiment of a body with folds in the
circumferential direction.
Fig. 1 diagrammatically depicts the sequence involved in the production process of
roller seam welding, which is used here to produce a body for exhaust gas
treatment. Fig. 1 illustrates two metallic foils 12 which are brought into contact
with one another. The foils 12 resting on top of one another are passed at a feed
rate 7 through two rotating electrodes 8. In the process, the two electrodes 8 press
on the surface of the foils 12 with a force 9. The two electrodes 8 are connected to
one another via a current source 26, with current flowing between the electrodes 8
and therefore also locally through the foils 12 with a predetermined frequency. The
current leads to heating of the foils 12, so that they become at least partially
molten. The foils 12 in this case have a thickness 22 which is, for example, in the
range from 0.02 to 0.1 mm. As a result of Joule resistance heating, a multiplicity of
weld spots 6, which preferably merge into one another so as to form a sealed seam
5, are formed in the contact region between the two foils 12.
Fig. 2 diagrammatically depicts a detailed view of a connecting region 3, which is
formed between two adjacent layers 2. The layers 2 are formed with a filter fabric
13, which is provided near an edge region 10 with a foil 12 that has been flanged.
The foils 12 project beyond the filter fabric 13 and form an edge region 10, which
is finally pushed through the rotating electrodes 8, so that a roller seam welded
connection is produced between the two foils 12. Whereas the filter fabric 13 is of
gas-permeable design, as is indicated by the dashed arrows, the foil 12 itself is in
this case impermeable to gases. The foil 12 in this case serves simultaneously to
fix supporting means 17, ensuring a defined position of the layers 2 with respect to
one another, so that the folds 16 are always of the desired shape.
Fig. 3 shows a body of plate construction, with the layers 2 arranged substantially
parallel to one another. The plate-like layers 2 in the embodiment illustrated
comprise a supporting structure 14 in which a filter material 15 has been
integrated. A connecting region 3 is in each case formed in the edge regions on
alternate sides of the layers 2. The connecting region 3 again comprises roller seam
welded connections. The connection region 3 bears directly against a housing 18
and is connected to it be joining. The supporting means 17 arranged between the
layers 2 are, for example, structured metal foils or structures of the layers 2
themselves, which prevent the layers 2 from bearing directly flat against one
another. It can also be seen that with the body 1 illustrated the principle of a
"closed particulate filter" has been implemented, in which adjacent passages 4 are
provided with a closure 24, so that the gas stream has to pass through the layers 2
in the direction of flow 23.
Fig. 4 shows another variant embodiment of a body 1 for exhaust gas treatment,
which is used in particular as a filter. This figure shows a radial-flow concept, in
which the gas stream that is to be purified first of all enters an inner region in the
direction of the center axis 21 through the cover plate 25. The rear-side cover plate
25 closes off the inner flow passage and therefore forces the exhaust gas to pass
through the layers 2 which form the folds 16. The body 1 illustrated again has
supporting means 17, which ensure the position of the layers 2 with respect to one
another even in the event of pressure fluctuations occurring in the gas flow. In the
exemplary embodiment illustrated, the layers 2 are arranged in such a way that the
connection regions 3 and the folds 16 formed by the layers 2 run in the direction of
the center axis 21. The connection regions 3 are in each case formed over a portion
11.
Fig. 5 shows a further variant embodiment of a body 1, in particular a filter body.
In this case, the folds 16 run substantially coaxially with respect to the center axis
21. The layers 2 are mounted on the end sides of a cover plate 25 which at least
partially allows the exhaust gas to flow through it. The connection regions 3 of the
layers 2 arranged adjacent to one another are arranged substantially coaxially to
the center axis 21, once again realizing the principle of a "closed particulate filter".
The layers 2 in this case comprise a supporting structure 14 in which the filter
material 15 is additionally provided.
Fig. 6 shows a body 1 in which the layers 2 are arranged in such a way that the
connection regions 3 and the folds 16 formed by the layers 2 run substantially
perpendicular to the center axis 21. The layers 2 are secured to an outer lateral
surface 20 of an inner tube 19. The inner tube 19 has openings through which the
gas stream can enter radially inward, as indicated by the arrows for the direction of
flow 23. Additional supporting means 17 are arranged between the layers 2 outside
the folds 16 illustrated in dotted form; these supporting means 17 are in this case
connected on one side to the inner tube 19 and on the other side to the layers 2.
Moreover, the entire arrangement is enclosed by a housing 18 spaced apart from
the layers 2. The connection regions 3, which have been generated using the roller
seam welding process, are formed on the outer circumference and the internal
circumference of the layers 2. They in each case produce a connection between the
layers 2 arranged adjacent to one another.
List of designations
1 Body
2 Layer
3 Connection region
4 Passage
5 Sealed seam
6 Weld spot
7 Feed rate
8 Electrode
9 Force
10 Edge region
11 Portion
12 Foil
13 Filter fabric
14 Carrier structure
15 Filter material
16 Fold
17 Supporting means
18 Housing
19 Inner tube
20 Lateral surface
21 Center axis
22 Thickness
23 Direction of flow
24 Closure
25 Cover plate
26 Current source
WE CLAIM
1. A procejss for producing a body (1) for exhaust gas treatment, which has a
plurality of metallic layers (2) characterized in that, the layers (2) are
formed with a supporting structure (14) comprising a filter material
(15) and the layers (2) are designed with supporting means (17), which
are preferably arranged in a passage (4) and/or in a fold (16) in which
method the layers (2) are brought into contact with one another in a
connection region (3), and a connection is produced by a continuous
resistance welding process, in such a manner mat the layers (2) form
passages (4) through which a gas stream can at least partially flow,
wherein the continuous resistance welding process comprises roller
seam welding, a feed rate (7) during roller seam welding in the range
from 0.5 cm/s to 30 m/s, in particular in the range from 0.5m/in to 30
m/min, is used and during the welding operation the electrodes (8) exert
a force (9) of from 10 N to 29 kN, in particular from 200 N to 6 kN, on
the layers (2), for connecting the supporting means (17) to the layer (2)
by the roller seam welding: manufacturing process, preferably at the
same time as a connection of the layers (2) to one another is being
executed.
2. The process as claimed in claim 1, wherein the continuous resistance
welding process comprises projection seam welding.
3. The process as claimed in claim 1, in which at least in part a sealed seam
(5) in which there are overlapping weld spots (6) is formed.
4. The process as claimed in one of the preceding claims, in which the layers
(2), at least in an edge region (10), are laid on top of one another, are
welded at least over a portion (11) in this edge region and are then
deformed, so as to form the passages (4).
5. The process as claimed in one of the preceding claims, in which the layers
(2) are formed with at least one metallic foil (12) which is made from a
high-temperature-resistant and corrosion-resistant material and is
preferably at least partially structured and/or allows a fluid to flow
through it at least in regions.
6. The process as claimed in one of the preceding claims, in which the layers
(2) are of multi-part structure, the layers (2) being provided with a
metallic foil (12) in the connecting region (3), the metallic foils (12) of
layers (2) arranged adjacent to one another being connected by means
of roller seam welding.
7. The process as claimed in one of the preceding clarms, in which the layers
(2) are welded together in such a way that they are connected in the
edge regions (10) on alternate sides to in each case an adjacent layer
(2), so as to in each case form a fold (16).
8. The process as claimed in one of me preceding claims, in which the welded
layers (2) are connected to at least one housing (18), preferably by
welding or brazing.
9. The process as claimed in claim 13, in which the housing (18) is an inner
tube (19) with a center axis (21), to the outer lateral surface (20) of
which inner tube the layers (2) are secured.
10. The process as claimed in claim 9, in which the layers (2) are arranged in
such a way that the connecting regions (3) and/or the folds (16) or
passages (4) formed by the layers (2) run in the direction of the center
axis (21).
11. The process as claimed in claim 9, in which the layers (2) are arranged in
such a way that the connecting regions (3) and/or me folds (16) or
passages (4) formed by the layers (2) run substantially perpendicular to
the center axis (21).
12. A body (1) for treating the exhaust gases from mobile internal combustion
engines, in particular produced by the process as claimed in one of the
preceding claims, which has a plurality of metallic layers (2), in which
the layers (2) are formed with a supporting structure (14) comprising a
filter material (15) and the layers (2) are designed with supporting
means (17), which are preferably arranged in a passage (4) and/or in a
fold (16) and said layers (2) are in contact with one another in a
connecting region (3), wherein a roller seam welded joint is provided
between at least some of the layers (2), so mat me layers (2) form
passages (4) through which a fluid can flow, wherein
the supporting means (17) with the layer (2) and the layers (2) with one
another form a roller seam welding joint wherein the housing (18) is an
inner tube (19) with a center axis (21), to the outer lateral surface (20)
of which inner tube the layers (2) are secured
and wherein the layers (2) are arranged in such a way that the
connecting regions (3) and/or the folds (16) or passages (4) formed by
the layers (2) run in the direction of the center axis (21).
The invention relates to a method for producing a body (1)
for exhaust treatment, said body comprising a plurality of
metallic layers (2). According to the inventive method,
the layers (2) are brought into contact with each other in
an assembly region (3), and a join is made by means of a
roller seam welding method in such a way that the layers
(2) form channels (4) through which a gas flow can pass.
The invention also relates to corresponding bodies (1) for
exhaust treatment, that can especially be used as filters
or catalyst carrier bodies in the car industry.

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Patent Number

224134

Indian Patent Application Number

00286/KOLNP/2006

PG Journal Number

40/2008

Publication Date

03-Oct-2008

Grant Date

01-Oct-2008

Date of Filing

07-Feb-2006

Name of Patentee

EMITEC GESELISCHAFT FUR EMISSIONS-TECHNOLOGIE MBH.

Applicant Address

HAUPTSTRASSE 150 53797 LOHMAR

Inventors:

#	Inventor's Name	Inventor's Address
1	HIRTH, PETER	FORSTSTRASSE 10 51107 KOLN
2	BRUCK, ROLF	FROBELSTRASSE 12 51429 BERGISCH GLADBACH
3	HARIG, THOMAS	RATHAUSSTRASSE 14 53819 NEUNKIRCHEN-SEELSCHEID

PCT International Classification Number

F01N 3/28

PCT International Application Number

PCT/EP2004/008560

PCT International Filing date

2004-07-30

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	103 37 285.2	2003-08-13	Germany