EXHAUST SYSTEM FLANGES

Abstract: Flanges (1, 2) formed by powder metallurgical methods are used for joining, for example, exhaust pipes (3), instead of manufacturing flanges by stamping, forging and/or machining. This offers a number of advantages, including the ability to produce a large variety of flange shapes which cannot be obtained by stamping, forging and/or machining.

Description: EXHAUST SYSTEM FLANGES TECHNICAL FIELD This invention relates mainly to flanges used in exhaust systems of internal combustion engines, for example those commonly used in automobiles and trucks. BACKGROUND ART In exhaust systems it is common to have stamped or forged and/or machined flanges which are welded to the ends of exhaust pipes which are to be joined to each other, with the flanges having flat mating surfaces which are bolted together with a gasket in between. The flanges are commonly produced by casting and/or machining. DISCLOSURE OF INVENTION It is an object of the invention to improve on the existing flanges used in exhaust systems and other welded or assembled flange joints. In the invention, instead of manufacturing flanges by stamping, forging and/or machining, the flanges are formed by powder metallurgy, which offers a number of advantages, including the ability to achieve flange shapes which cannot be obtained by stamping. There are two flanges in the invention, one for the end of one pipe and one for the end of the other pipe. The flanges have complementary shapes, such that in most embodiments one flange, hereinafter referred to as the "male flange", nests partially within the other flange, hereinafter referred to as the "female flange". For simplicity of description, the terminology "male flange" and "female flange" will be maintained herein, regardless of whether or not one nests within the other. In one embodiment of the invention, one flange, preferably but not necessarily the male one, has integral mounting studs on opposing sides of the pipe, configured to extend through corresponding holes in the other flange. The studs are threaded to receive nuts which are tightened to pull the two flanges together for a secure connection. Preferably, the proximal surfaces of the flanges, i.e. the surfaces of the flanges away from their distal or mating surfaces, have reinforcement ribs, which permits the overall thickness and therefore the weight of the flanges to be reduced compared to conventional flanges. As an alternative to reinforcement ribs and thin sections to reduce weight, the flanges could be of uniform thickness, with through holes formed in several locations to achieve the same weight reduction. In a further embodiment of the invention, the flanges have extensions for attachment by press-fitting, spinning, resistance welding, crimp rolling etc. to the exhaust pipes. Thus, no welding is necessary, other than as a further reinforcement of the joint. The complementary shapes of the flanges provide a better seal than in the prior art, in that there is no direct escape route for exhaust gases, thus reducing the need for expensive gaskets or perhaps eliminating the need for gaskets altogether. Also, larger diameter stud posts and matching holes with close tolerances become possible with powder metallurgy. This helps ensure a rigid joint. Another advantage of the invention is that since the mounting studs may be integral to the flanges, the assembly joint will tend to remain intact even if the nuts become loose or dislodged, whereas in typical prior art flanges, the separate bolts will fall out, permitting the joint to shift. In the invention, the nesting eliminates lateral shifting of the joint, even if the nuts are loose or missing, making the joint much more mechanically secure. Of course, if both nuts are missing, the joint may come apart longitudinally, but at least it will not separate laterally. Thus, in the invention, an exhaust flange assembly for joining ends of exhaust pipes comprises a female flange or flange assembly securable to one pipe end and having a sealing surface, and a male flange or flange assembly securable to the other pipe end and having a sealing surface of a complementary shape to female flange's sealing surface. The flanges are made of powder metallurgically produced material. In one embodiment of the invention, the female flange has a cavity defined in the sealing surface and the sealing surface of the male flange is shaped to be closely received by the cavity. Further, one of the flanges advantageously has integral mounting studs extending from the sealing surface of the flange, the studs configured to extend through corresponding holes in the other the flange, the studs being threaded to receive nuts whereby the flanges may be pulled together for a secure connection by tightening the nuts. Preferably, at least one of the flanges has an annular gasket recess arranged on the sealing surface of the flange. The annular gasket recess preferably has gasket retaining means, either gasket recess protrusions or the gasket recess being generally oval for retaining the gasket by bending the substantially circular gasket to an oval shape inside the gasket recess. The flanges preferably have a plurality of reinforcement ribs. The flanges may further have at least one hole therethrough for weight reduction. Preferably, the female flange and the male flange have bolt mounting holes arranged to receive threaded bolts onto which nuts are threadable, whereby the flanges may be pulled together for a secure connection by tightening the nuts. Alternatively, the female flange has a curved extension protruding in a direction opposite to the cavity, and the male flange has a curved extension protruding in a direction opposite to the sealing surface of the male flange, the extensions arranged to be fitted into the ends of exhaust pipes, thereby deforming the exhaust pipes to form a joint. Preferably, the extensions have a groove surrounded by an inner ridge and an outer ridge, arranged on an outer surface of the extension. Advantageously, at least one of the flanges has an annular gasket recess arranged on the sealing surface of the flange. Optionally, the flanges have a plurality of reinforcement ribs. The flanges may further have at least one hole therethrough for weight reduction. Advantageously, the bolts have generally spherical portions facing the bolt thread, the spherical portions of the bolts arranged to cooperate with generally concave recesses arranged in the flanges around the mounting holes. The male flange advantageously comprises a first substantially flat part and a second annular sealing part. The first part has a first recess and the second part has a second recess, the recesses having complimentary shapes so that the first recess fits in the second recess. Preferably, the first recess and the second recess have multiple steps. Still a further embodiment of an exhaust flange assembly according to the invention comprises a straight flange cooperating with a slightly-curved flange, where an outer edge of the curved flange is bent away from a surface of the curved flange which contacts the straight flange, so that, when the straight flange is mounted to the curved flange by fasteners, the curved flange deflects toward the flat flange to form a flat sealing surface, thus enhancing the seal between the curved flange and the straight flange, the flanges being made of powder metallurgically produced material. Preferably, the straight flange and the curved flange have mounting holes and the fasteners comprise mounting bolts, for placing through the mounting holes, and mounting nuts to be tightened onto each the mounting bolt, for fastening the straight flange to the curved flange. Advantageously, the straight flange and the curved flange have gasket recesses, for accommodating gaskets. Preferably, the curved flange is substantially weakly bowl- shaped. Preferably, the female flange is made of one material and the male flange is made of another material. A preferred exhaust flange assembly has a male flange comprising a recess having a gasket element shaped to be closely received in the recess on one side of the gasket element and to be closely received by the cavity of the female flange on another side of the gasket element. An elongated substantially flat exhaust flange, according to a further embodiment of the invention, comprises a sealing surface having a cavity. At least a part of the flange is made of powder metallurgically produced material. The flange advantageously comprises a first substantially flat part and a second annular sealing part, the first part having a first recess and the second part having a second recess and where the first recess and the second recess have complimentary shapes so that the first recess fits in the second recess. The second part is made of powder metallurgically produced material. Alternatively, the first part is made of powder metallurgically produced material. Still a further alternative is that both the first part and the second part are made of powder metallurgically produced material. The flange preferably has an annular gasket recess arranged on the sealing surface of the flange. The annular gasket recess advantageously has gasket retaining means. The gasket retaining means comprise either gasket recess protrusions or the gasket recess being generally oval will hold the generally circular gasket by deforming it into an oval shape. Advantageously, at least one of the flanges has one or more reinforcement ribs, and may alternatively or additionally have at least one hole therethrough for weight reduction. The flange further has bolt mounting holes arranged to receive threaded bolts onto which nuts are threadable. The bolts preferably have generally spherical portions facing the bolt thread, the spherical portions of the bolts arranged to cooperate with generally concave recesses arranged in the flange around the mounting holes. The flange preferably has a curved extension protruding in a direction opposite to the cavity, the extension arranged to be fitted into the end of the exhaust pipe, thereby deforming the exhaust pipe to form a joint. The extension advantageously has a groove surrounded by an inner ridge and an outer ridge, arranged on an outer surface of the extension. An elongated substantially flat exhaust flange, according to still a further embodiment of the invention, comprises a sealing surface having a protrusion, and where at least a part of the flange is made of powder metallurgically produced material. The flange preferably comprises a first substantially flat part and a second annular sealing part, the first part having a first recess and the second part having a second recess and where the first recess and the second recess have complimentary shapes so that the first recess fits in the second recess. The second part is preferably made of powder metallurgically produced material. Alternatively, the first part is made of powder metallurgically produced material. A further alternative is that both the first part and the second part are made of powder metallurgically produced material. Advantageously, the flange has an annular gasket recess arranged on the sealing surface of the flange. The annular gasket recess preferably has gasket retaining means. The gasket retaining means comprise either gasket recess protrusions or the gasket recess being generally oval will deform the generally circular gasket to an oval shape to retain it in the gasket recess. The flange preferably has one or more reinforcement ribs. The flange advantageously has at least one hole therethrough for weight reduction. The flange further preferably has bolt mounting holes arranged to receive threaded bolts onto which nuts are threadable. The bolts advantageously have generally spherical portions facing the bolt thread, the spherical portions of the bolts arranged to cooperate with generally concave recesses arranged in the flange around the mounting holes. The flange preferably has a curved extension protruding in a direction opposite to the cavity, the extension arranged to be fitted into the end of the exhaust pipe, thereby deforming the exhaust pipe to form a joint. The extension advantageously has a groove surrounded by an inner ridge and an outer ridge, arranged on an outer surface of the extension. A preferred method of producing two-part exhaust flanges, comprises the steps of: a) press-forming metal powder to shape a first substantially flat part of a male flange; b) press-forming metal powder to shape a second annular sealing part of the male flange; c) fitting the first part onto the second part; and d) sintering the first part and the second part to thereby bond them together and form the male flange. Advantageously, the method further comprises the step of pre-sintering the first part and the second part after press-forming but before fitting the first part onto the second part. Preferably but not necessarily, a weld is applied to a joint between the first part and the second part after joining. A further embodiment of a method of producing exhaust flanges according to the invention comprises the steps of: a) stamping metal to shape a first part of a flange; b) press-forming metal powder to shape a second annular sealing part of the flange; c) sintering the sealing part; d) fitting the first part onto the second part; and e) joining the first part and the second part to thereby bond them together and form the flange. Advantageously, the joining step comprises either welding, brazing or glueing the first part to the second part. A still further embodiment of a method of producing exhaust flanges according to the invention comprises the steps of: a) press-forming metal powder to shape a first substantially flat part of a flange; b) press-forming metal powder to shape a second annular sealing part of the flange; c) sintering the first part and the second part; d) fitting the first part onto the second part; and e) joining the first part and the second part to thereby bond them together and form the flange. Advantageously, the joining step comprises either welding, brazing or glueing the first part to the second part. A further preferred embodiment of the invention provides a multiple part powder metallurgically produced flange. By making smaller parts, which are later joined to form the finished flange, tool wear is reduced during the powder compaction process, and a smaller press can be used, i.e. a press with a lower rating. This is due to the fact that the total surface area of the piece to be compacted is reduced compared to a flange compacted as one integral part. The multiple parts are compacted separately, assembled and then sinter-bonded or, alternatively, compacted separately, pre-sintered, assembled and sinter-bonded. The sinter-bonded joint is advantageously enhanced by using a sintering activator, for example hexagonal boron nitride (h-BN), either dispersed throughout the material or only in the area around the joint. Other preferred sinter- bonding enhancement processes are copper infiltration, either throughout the material or only in the area around the joint. Thus, a preferred method of making a flange using powder metallurgical processes includes the steps: a) compacting multiple parts of a flange separately, preferably at a pressure of 30 to 65 tsi (the unit tsi is converted to MPa by multiplying with 13.793, i.e. 2000/145, equalling a pressure range of 413.8 to 896.6 MPa), to form green bodies; b) assembling the green bodies; c) sintering the assembled green bodies, preferably in a vacuum, hydrogen or hydrogen/nitrogen mixture atmosphere and preferably at a temperature range of 2050 °F to 2600 °F (1121 °C to 1426.7 °C). An alternative preferred method of making a flange using powder metallurgical processes includes the steps: a) compacting multiple parts of a flange separately, preferably at a pressure of 30 to 65 tsi (413.8 to 896.6 MPa), to form green bodies; b) pre-sintering the multiple parts, preferably in a vacuum, hydrogen or hydrogen/nitrogen mixture atmosphere and preferably at a temperature of 1800 °F to 2200 °F(982 °C to 1204 °C); d) assembling the pre-sintered bodies; e) sintering the assembled pre-sintered bodies, preferably in a vacuum, hydrogen or hydrogen/nitrogen mixture atmosphere and preferably at a temperature range of 2050 °F to 2600 °F (1121 °C to 1427 °C). Preferably, the powder metal materials used for making the flanges contain 0.1 % to 1 % by weight of hexagonal boron nitride (BN), which enhances the corrosion resistance properties of the powder metallurgical materials used. Further features will be described or will become apparent in the course of the detailed description which follows. BRIEF DESCRIPTION OF DRAWINGS The invention will now be described in greater detail, with reference to the accompanying drawings of the preferred embodiment, in which: Fig. 1 is an exploded side view showing the male and female flanges welded on ends of exhaust pipes to be joined; Fig. 2 is a sectional side view corresponding to Fig. 1 ; Fig. 3 is a side view showing the assembled exhaust pipes; Fig. 4 is a proximal end view of the female flange; Fig. 5 is a side view of the female flange; Fig. 6 is a distal end view of the female flange; Fig. 7 is a distal end view of the male flange; Fig. 8 is a side view of the male flange; Fig. 9 is a proximal end view of the male flange; Fig. 10 is a sectional view of the male flange at A-A on Fig. 9; Fig. 11 is a top view of the male flange; Fig. 12 is a distal end view of an alternative embodiment of the female flange; Fig. 13 is a side view of the alternative embodiment of the female flange; Fig. 14 is a proximal end view of the alternative embodiment of the female flange; Fig. 15 is a proximal end view of the female flange according to yet another embodiment; Fig. 16 is a side view of the female flange according to Fig. 15; Fig. 17 is a distal end view of the female flange of Fig. 15; Fig. 18 is a proximal end view of the male flange corresponding to and cooperating with the female flange according to Fig. 15; Fig. 19 is a side view of the male flange according to Fig. 18; Fig. 20 is a distal end view of the male flange according to Fig. 18; Fig. 21 is an exploded side view showing the male and female flanges, according to Figs. 15 and 18, pushed on ends of exhaust pipes to be joined; Fig. 22 is a sectional side view corresponding to Fig. 21 ; showing the assembled flange joint; Fig. 23 is a side view showing the assembled exhaust pipes, for flanges according to Fig. 15 and 18; Fig. 23A is an exploded side view of still a further embodiment of a flange joint according to the invention; Fig. 23B is an exploded side view of yet a further embodiment of a flange joint according to the invention; Fig. 24 is an end view of a flange joint according to a further embodiment of the invention; showing a flange having reinforced areas; Fig. 25 is a sectional side view of the flange of Fig. 24 along line C-C; Fig. 26 is a side view of a flange joint according to a yet further embodiment of the invention; showing a flange having a curved half; Fig. 27 is an exploded partially sectioned side view of a flange joint according to a further embodiment of the invention; showing a flange having a gasket; Fig. 28 is an exploded partially sectioned side view of a flange joint according to still a further embodiment of the invention; showing a flange having a further embodiment of a gasket; Fig. 29 is an assembled partially sectioned side view of the flange joint of Fig. 28; Fig. 30A is an exploded side view of a flange joint according to a further embodiment of the invention, similar to the embodiment of Fig. 28; having the composite gasket bonded onto the male flange; Fig. 30B is an assembled sectioned side view of the flange joint of Fig. 30A; Fig. 31 A is an end view of a flange joint according to a further embodiment of the invention, showing a gasket recess; Fig. 31 B is a sectioned side view of the flange joint of Fig. 31 A; Fig. 32A is an end view of a flange joint according to still a further embodiment of the invention, showing a further variation of a gasket recess; Fig. 32B is a sectioned side view of the flange joint of Fig. 32A; Fig. 33 is a sectioned side view of a further embodiment of a flange joint of the invention, similar to the flange of Fig. 30B with the addition of a gasket recess on the composite gasket; Fig. 34 is a sectioned side view of a still further embodiment of a flange joint of the invention, similar to the flange of Fig. 30B with the addition of a gasket recess on the composite gasket, which is an integral part of the male flange; Fig. 35 is a sectional side view of yet a further embodiment of a flange joint of the invention, showing a pair of flanges where the male flange has a sealing extension for cooperation with a sealing recess arranged in the female flange; Fig. 36 is a partially sectioned side view of another embodiment of a flange joint of the invention, showing a pair of flanges where the male flange has a gasket holding ridge for cooperation with a gasket holding recess arranged in the female flange and a gasket; Fig. 37 is a sectioned side view of the gasket of Fig. 36; Fig. 38 is a front view of the gasket of Fig. 37; Fig. 39A is a front view of a further embodiment of a male flange according to the invention, having a conical rib on its sealing side; Fig. 39B is a sectioned side view of the male flange as seen from line F-F of Fig. 39A; Fig. 40A is a front view of a further embodiment of a female flange according to the invention, having a conical recess on its sealing side; Fig. 40B is a sectioned side view of the female flange as seen from line G-G of Fig. 40A; Fig. 41 is a sectioned side view of another embodiment of a flange joint of the invention, showing the male flange of Figs. 39A and 39B and the female flange of Figs. 40A and 40B; Fig.42 is a side view of the embodiment of a flange joint of Fig.41 , showing the male flange of Figs. 39A and 39B and the female flange of Figs. 40A and 40B joined to respective pipes and the connecting bolts used to clamp the flange joint together; Fig.43A is a front view of yet a further embodiment of a female flange according to the invention, having a recess for cooperating with a further part of the flange and two bolt mounting holes; Fig. 43B is a sectioned side view of the female flange according to Fig. 43A; Fig.44A is a front view of still a further embodiment of a female flange according to the invention, having a stepped recess for cooperating with a further part of the flange and three bolt mounting holes; Fig. 44B is a sectioned side view of the female flange according to Fig. 44A; Fig. 45 is a sectioned side view of a further embodiment of a female and a male flange according to the invention, where the male flange is manufactured in two parts; Fig. 46 is a sectioned side view of the male flange according to Fig. 45, after assembly; Fig. 47 is a sectioned side view of another embodiment of a flange joint of the invention, similar to the embodiment shown in Figs.41 and 42, but having an integral stand-off on the male flange; Fig.48A is a sectioned side view of a female flange according to a further embodiment of the invention, where the flange is manufactured in two parts; Fig. 48B is a sectioned side view of the female flange according to Fig. 48A after assembly; Fig.49A is a partially sectioned side view of a female flange according to yet a further embodiment of the invention, where the flange is manufactured in several parts (three parts in the example); Fig.49B is an exploded partially sectioned side view of the female flange according to Fig. 49A; Fig. 50 is an exploded view of a further flange assembly; Fig. 51 is a corresponding view of the components of Fig. 50; Fig. 52 is a side view of the partially assembled flange of Fig. 50; Fig. 53 is a corresponding front view; Fig. 54 is an exploded view of a further flange, with an offset sealing portion; and Fig. 55 is a corresponding view, partially assembled. BEST MODE FOR CARRYING OUT THE INVENTION Fig. 1 shows an exhaust flange assembly, having two flanges 1 and 2 made of powdered metal welded to ends of exhaust pipes 3 to be joined. One flange, namely the female flange 1, has a cavity 4 defined in its distal surface. The other flange, i.e. the male flange 2, has a distal surface 5 with a shape complementing the shape of the cavity. Preferably, that shape involves a generally flat surface 5, with a rounded edge 6 to match a rounded inner edge 7 of the cavity 4 and thereby provide a sealing seat. In view of this rounding, there is no direct escape path for exhaust, which reduces or eliminates the need for a gasket. If a gasket is still needed, it may be that it could be a less expensive gasket in view of the reduced sealing needs. Other edge shapes are certainly possible. For example, there could be a sharp edge, a radius, chamfer or domed seal, or combinations thereof. One of the flanges, for example the male flange 2, has integral mounting studs 8 on opposing sides, configured to extend through corresponding holes 9 in the other flange, i.e. the female flange 1. After production of the flange by a typical powder metallurgy process, the studs are tapped to provide threads 10. Preferably, the studs are also provided with bolstered heads, to provide extra strength. Nuts 11 are installed to pull the flanges together for a secure connection by tightening the nuts. Preferably, the proximal surfaces of the flanges, i.e. the surfaces of the flanges away from their distal mating surfaces, have reinforcement ribs 12, which permits the overall thickness and thus weight of the flanges to be reduced compared to conventional flanges. Figs. 12 to 14 show an example of the above-mentioned alternative to reinforcement ribs and thin sections to reduce weight, in which the flanges are of uniform thickness, with through holes 13 formed in several locations to achieve the same weight reduction. Only the female flange is shown, but preferably the male flange would have corresponding aligned holes as well. The invention provides a number of advantages, which include that the integral mounting studs avoid the need for separate studs, that the use of powdered metal permits reduced thickness and weight by permitting the use of reinforcing ribs, that the sealing configuration avoids a direct escape path for exhaust gases, thereby potentially reducing the need for gaskets and potentially reducing emissions. Figs. 15 to 17 show a further embodiment of a male flange 2', made of powdered metal and attached by press-fitting, spinning, resistance welding, crimp rolling etc. to ends of exhaust pipes 3" to be joined. In Figs. 18 to 20, a female flange 1 * is shown, which is cooperating with the male flange of the embodiment according to Figs. 15 to 17. The female flange has a cavity 4", defined in its distal surface. The male flange 2' has a distal surface 5' with a shape complementing the shape of the cavity 4". Preferably, the distal shape 5' involves a generally flat surface, with a rounded edge 6", to match a rounded inner edge T of the cavity 4' and thereby provide a sealing seat. In view of this rounding, there is no direct escape path for exhaust, which reduces or eliminates the need for a gasket. If a gasket is still needed, it may be that it could be a less expensive gasket in view of the reduced sealing needs. Other edge shapes are certainly possible. For example, there could be a sharp edge, a radius, chamfer or domed seal, or combinations thereof. The male flange 2" further has an extension 17 arranged on the side of the flange opposite the distal shape 5". The extension has a coaxial hole, corresponding to the hole in the flange, through which exhaust gases are flowing when the flange combination is in use. The extension has a substantially smooth inner surface and a grooved outer surface, preferably having a groove 18 surrounded by an inner ridge 20 and an outer ridge 19. The outer diameter of the extension is larger than the inner diameter of the exhaust pipe 3'. When the exhaust pipe is attached by press-fitting, spinning, resistance welding, crimp rolling etc. onto the flange 2', the exhaust pipe expands and generally forms itself corresponding to the extensions outer profile, i.e. the groove 18, inner ridge 20 and outer ridge 19 (see Figs. 21 to 23). In this way, the exhaust pipe is held securely to the flange. The extension may be tapered, having a larger outer diameter at a distal end of the extension as seen from the flange. In this case, the groove 18 is optional. Pressing the exhaust pipe onto the extension may be performed using a lubricant or inductively heating the pipe prior to installation. The grooves 18 may have a variety of profile shapes, to accommodate fitting of the pipes either by induction heating or resistance welding. The groove shape is thus determined by the assembly process or method. The female flange 1" further has an extension 13 arranged on the side of the flange opposite the cavity 4'. The extension has a coaxial hole, corresponding to the hole in the flange, through which exhaust gases are flowing when the flange combination is in use. The extension has a substantially smooth inner surface and a grooved outer surface, preferably having a groove 14 surrounded by an inner ridge 15 and an outer ridge 16. The outer diameter of the extension is larger than the inner diameter of the exhaust pipe 3'. When the exhaust pipe is attached by press-fitting, spinning, resistance welding, crimp rolling etc. onto the flange 1", the exhaust pipe expands and generally forms itself corresponding to the extensions outer profile, i.e. the groove 14, inner ridge 15 and outer ridge 16 (see Figs. 21 to 23). In this way, the exhaust pipe is held securely to the flange. The extension may be tapered, having a larger outer diameter at a distal end of the extension as seen from the flange. In this case, the groove 14 is optional. Pressing the exhaust pipe onto the extension may be performed using a lubricant or inductively heating the pipe prior to installation. The grooves 14 may have a variety of profile shapes, to accommodate fitting of the pipes either by induction heating or resistance welding. The groove shape is thus determined by the assembly process or method. The male flange 2" is preferably made of powdered metal and attached by press-fitting, spinning, resistance welding, crimp rolling etc. to ends of the exhaust pipes 3' to be joined, forming a joint 22". The female flange 1" is also preferably made of powdered metal and attached by press-fitting, spinning, resistance welding, crimp rolling etc. to ends of the exhaust pipes 3" to be joined, forming a joint 21". The flanges have mounting holes 8", 9', respectively, for mounting a bolt 10' and nut 11'. Alternatively, one flange has integral mounting studs on opposing sides, configured to extend through corresponding holes in the other flange, as described in conjunction with the previous embodiment. The nuts 11" are installed to pull the flanges together for a secure connection by tightening the nuts. Preferably, the proximal surfaces of the flanges, i.e. the surfaces of the flanges away from their distal mating surfaces, have reinforcement ribs 12', which permits the overall thickness and thus weight of the flanges to be reduced compared to conventional flanges. Fig. 21 shows the female flange 1' and the male flange 2' attached by press-fitting, spinning, resistance welding, crimp rolling etc. onto exhaust pipes 3" and ready for having bolts 10' inserted into holes 8' and 9' and nuts 11" threaded onto the bolts, to tighten the flange joint. A tightened flange joint is shown in Figs. 22 and 23. Fig. 23A shows a female flange 1" and a male flange 2" pressed onto exhaust pipes 3" and ready for having bolts 10" inserted into holes 8" and 9", respectively, and nuts 11 " threaded onto the bolts, to tighten the flange joint. The male flange 2" is preferably made of powdered metal and press-fitted to ends of the exhaust pipes 3' to be joined, forming a joint 22". The female flange 1" is also preferably made of powdered metal and attached by press-fitting, spinning, resistance welding, crimp rolling etc. to ends of the exhaust pipes 3' to be joined, forming a joint 21 ". The female flange 1 " cooperates with the male flange. The female flange has a cavity 4", defined in its distal surface. The male flange 2" has a distal surface 5" with a shape complementing the shape of the cavity 4". Preferably, the distal shape 5" involves a generally flat surface, with a rounded edge 6", to match a rounded inner edge 7" of the cavity 4" and thereby provide a sealing seat. In view of this rounding, there is no direct escape path for exhaust, which reduces or eliminates the need for a gasket. If a gasket is still needed, it may be that it could be a less expensive gasket in view of the reduced sealing needs. Other edge shapes are certainly possible. For example, there could be a sharp edge, a radius, chamfer or domed seal, or combinations thereof. The male flange 2" has a projection 24 arranged on its surface, which faces the female flange 1". A recess 23, formed on a surface of the female flange 1 ", which faces the male flange 2", has a shape generally complementary to the projection 24, to facilitate the alignment of the two flanges with each other. Advantageously, the projections 24 and the recesses 23 are arranged concentrically to the holes 8" and 9", respectively. Fig. 23B shows an alternative embodiment to the embodiment shown in Fig, 23A. The female flange 1'" is essentially the same as shown in Fig. 23B, except it does not have any recesses, the holes 9"' are thus of one diameter. Instead, the male flange 2'" has holes 8"' which have recesses 25 arranged on the side of the male flange which faces away from the female flange 1"". The recesses 25 have generally concave surfaces, to cooperate with bolts 10'", which have heads with generally spherical lower portions. Thus, the bolt is allowed to swivel in the holes 8"" and 9'", respectively, to facilitate alignment of the flanges. Advantageously, the male flange 2"' has an increased thickness, compared to the female flange 1 "', to provide strength to compensate for the enlarged hole 8'". Further, the bolts 10"' advantageously have a substantially cylindrical extension 40 of the bolt head. The extension has a diameter which is larger than the diameter of the threaded portion of the bolt. A bolt recess 40' arranged in the hole 8'" of the male flange 2'" has a shape corresponding to the extension 40 of the bolt head, to securely hold the bolt once it has been tightened into the hole. Figs. 24 and 25 show another embodiment of a flange 300 according to the invention. The flange has raised areas 301 arranged between mounting studs 320 having mounting holes 321. The raised areas provide reinforcement of the flange, to prevent deflection of the flange when tightening the flange to another flange using fastening means (not shown). The flange further has a substantially cylindrical flange extension 310, for attachment of the flange to an exhaust pipe (not shown). The flange extension has an inner diameter 311. Fig. 26 shows still a further flange pair combination. A straight flange 400, having mounting holes 404 and gasket recesses 402, cooperates with a slightly-curved flange 401, having mounting holes 405 and gasket recesses 403. The curved flange is substantially weakly bowl-shaped, the outer edge of the flange bent away from the surface of the curved flange which contacts the straight flange. Thus, when mounting bolts 407 are placed through the mounting holes 404 and 405, respectively, and a mounting nut 406 tightened onto each mounting bolt, the curved flange will deflect toward the flat flange to form a flat sealing surface. This enhances the seal between the two flanges and prevents the further outward deflection of the flange after tightening of the mounting bolts. Fig. 27 shows yet a further embodiment of a flange joint, having a gasket element 504 arranged between a fifth flange 500 and a sixth flange 501. The fifth flange has a recess 502, with sloping side walls 513, which generally conforms in shape to a curved surface 505 of the gasket element. The fifth flange further has an inner diameter 508 and mounting holes 510. Similarly, the sixth flange 501 has a recess 503, with curved side walls 512, which generally conforms in shape to the curved surface 505 of the gasket element. The sixth flange further has an inner diameter 509 and mounting holes 511. The gasket element 504 has an inner diameter 507, substantially the same as the inner diameters 508 and 509, respectively, of the flanges. The gasket element further has a flange gap defining protrusion 506 arranged along its circumference. When mounting bolts 515 are inserted into the mounting holes 510 and 511 , respectively, and a mounting nut 514 is tightened onto each mounting bolt, the two flanges compress the gasket element 504, which will allow only a limited amount of float (relative movement of the flanges) to provide an enhanced leak resistance for the flange joint. Figs.28 and 29 show a further embodiment of a flange joint, having a composite gasket element 504' arranged between a sixth flange 501 (as described in conjunction with Fig. 27) and a male flange 500'. The male flange has mounting holes 510' and a substantially cylindrical flange extension 517, for attachment of the flange to an exhaust pipe (not shown). Further, the male flange 500' has a backing plate portion 516 arranged on the same side of the flange as the flange extension. The backing plate portion has an inner diameter 508" and an inner surface 519, facing away from the flange extension side of the flange. The male flange has a general inner diameter 508', which is larger than the inner diameter 508" of the backing plate portion 516. The composite gasket element 504' has a curved surface 505", generally conforming in shape to the recess 503, with sloping side walls 512 of the sixth flange. The composite gasket element further has an inner diameter 508", substantially the same as the inner diameters 508' and 509, respectively, of the flanges. The gasket element further has an outer surface 517 and a substantially flat surface facing the male flange 500". When mounting bolts (not shown) are inserted into the mounting holes 510' and 511, respectively, and a mounting nut (not shown) is tightened onto each mounting bolt, the two flanges compress the gasket element 504', which will allow only a limited amount of float (relative movement of the flanges) to provide an enhanced leak resistance for the flange joint. The backing plate portion 516 retains the composite seal between the male flange 500' and the composite gasket element 504'. Figs. 30A and 30B show a further embodiment of a flange joint similar to the embodiment shown in Figs. 27 to 29, except that a composite gasket element 504" is bonded to a male flange 500", for example by pressing and sintering the two in one sintering step, or sintering the male flange first then inserting the pressed gasket element and sintering again. The composite gasket element 504" is thus arranged between a sixth flange 501 (as described in conjunction with Fig. 27) and the male flange 500". The male flange has mounting holes 510" and a backing plate portion 516' arranged on the same side of the flange as the flange extension. The backing plate portion has an inner diameter 508 ιv and an inner surface 519', facing away from the flange extension side of the flange. The male flange has a general inner diameter 508 v , which is larger than the inner diameter 508 ιv of the backing plate portion 516". The composite gasket element 504" has a curved surface 505", generally conforming in shape to the recess 503, with sloping side walls 512 of the sixth flange. The composite gasket element further has an inner diameter 508 vι , substantially the same as the inner diameters 508 1V and 509, respectively, of the flanges. Figs. 31 A and 31 B show a preferred embodiment of a flange 400' having an annular gasket recess 402', which has an inner wall 411 and an outer wall 410. Further, the flange has mounting holes 414, and an inner diameter 415. The inner wall 411 and the outer wall 410 form at least one squeeze area 412, where the width of the gasket recess, the distance between the outer wall and the inner wall, is substantially narrower than a maximum gasket recess width 411. In this way, the gasket (not shown) will be held in the gasket recess after insertion of the gasket. Preferably, two such squeeze areas 412 are defined in the gasket recess 402'. Figs. 32A and 32B show an alternative preferred embodiment of a flange 400" having an annular gasket recess 402", which has an inner wall 411' and an outer wall 410'. Further, the flange has mounting holes 414", and an inner diameter 415'. At least one protrusion 416 is arranged along the inner wall 411' and/or (not shown) the outer wall 410 to form at least one squeeze area 412", where the width of the gasket recess, the distance between the outer wall and the protrusion, is substantially narrower than a maximum gasket recess width 411". In this way, the gasket (not shown) will be held in the gasket recess after insertion of the gasket. Preferably, two, three or four such squeeze areas 412' are defined in the gasket recess 402", by arranging two, three or four protrusions 416, respectively, on the inner wall 411". Fig. 33 shows a further embodiment of a flange joint similar to the embodiment shown in Figs. 30A to 30B. A composite gasket element 504"" is bonded to a male flange 500", for example by pressing and sintering the two in one sintering step, or sintering the male flange first then inserting the pressed gasket element and sintering again. The composite gasket element 504'" is thus arranged between a sixth flange 501 (as described in conjunction with Fig. 27) and the male flange 500". The male flange has mounting holes 510" and a backing plate portion 516" arranged on the same side of the flange as the flange extension. The backing plate portion has an inner diameter 508 ιv and an inner surface 519', facing away from the flange extension side of the flange. The male flange has a general inner diameter 508 v , which is larger than the inner diameter 508 ιv of the backing plate portion 516". The composite gasket element 504'" has a curved surface 505", generally conforming in shape to the recess 503, with sloping side walls 512 of the sixth flange. The composite gasket element further has an inner diameter 508 vι , substantially the same as the inner diameters 508 ιv and 509, respectively, of the flanges. Additionally, the composite gasket element 504'" has a gasket recess 402' arranged on the curved surface 505", to receive an additional annular sealing gasket (not shown). Fig. 34 shows still a further embodiment of a flange joint similar to the embodiment shown in Fig. 33. A male flange 500"' has an inner diameter 508 v ", mounting holes 510'" and a protrusion 504 ιv . The protrusion has a curved surface 505'", which cooperates with a sixth flange 501 (as described in conjunction with Fig. 27) in that it generally conforms in shape to the recess 503, with sloping side walls 512 of the sixth flange. Additionally, the protrusion 504 ιv has a gasket recess 402" arranged on the curved surface 505'", to receive an additional annular sealing gasket (not shown). Fig. 35 shows a further embodiment of a flange joint according to the invention, where a male flange 602 has an exhaust mounting extension 22"', mounting holes 604, gasket recesses 607 and a sealing extension 603. A female flange 601 has an exhaust mounting extension 21'", mounting holes 605, gasket recesses 606 and a sealing recess 608 having an outer diameter substantially corresponding to the outer diameter of the sealing extension 603. The sealing extension and the sealing recess thus cooperate to provide a positive seal and enhanced alignment between the two flanges. The flanges are fastened together using bolts 10" and nuts 11". Figs. 36 to 38 show yet a further embodiment of a flange joint according to the invention, where a male flange 702 has an exhaust mounting extension 706, mounting holes 703 and an annular gasket holding ridge 713 with a base 714. A female flange 701 has an exhaust mounting extension 705, mounting holes 704 and an annular gasket holding recess 712 with an annular ring 711. The gasket holding ridge and the gasket holding recess thus cooperate to positively hold a shaped gasket 710 to provide a positive seal and enhanced alignment between the two flanges. The flanges are fastened together using bolts 10" and nuts 11". The gasket is shown in detail in Figs. 37 and 38, showing the gasket inner diameter 717, which is substantially the same or larger as the inner diameters of the exhaust openings of the flanges. The gasket has five sealing surfaces on its "haf-like cross-section (brim, side, top, other side and other brim), and this shape gives no direct escape for gases. The gasket is made of a resilient material, and preferably laminated and/or spirally wound. Figs. 39A to 42 show a further advantageous embodiment of a flange joint according to the invention. Figs. 39A and 39B show a female flange 800, having a conical rib 810 on a sealing surface 801 of the female flange, which cooperates with a male flange 850 (Fig. 40A). The female flange further has a pipe attachment surface 802 having a pipe attachment means 830. An exhaust through hole 840 is arranged in the female flange, for passage of exhaust gas when the flange is assembled as part of an exhaust system flange joint. Mounting holes 820 are also arranged through the female flange. Figs.40A and 40B show the male flange 850, having a conical recess 860 on a sealing surface 851 of the male flange. The male flange further has a pipe attachment surface 852 having a pipe attachment means 880. An exhaust through hole 890 is arranged in the male flange, for passage of exhaust gas when the flange is assembled as part of an exhaust system flange joint. Mounting holes 870 are also arranged through the female flange. Fig. 41 shows a flange joint made of the female flange 800 and the male flange 850. Fig. 42 shows the flange joint of Fig. 41 , with the female flange 800 and the male flange 850 joined to respective pipes 3 and connecting bolts 10' with nuts 11', used to clamp the flange joint together. When a male and a female flange are fastened together, the conical rib 810 and the conical recess 860 form a compression fitting to eliminate leaks in the flange joint. The rigidity of the joint is also enhanced by the compression fitting of the invention. Figs. 43A to 46 show a further embodiment of a flange joint of the invention. The male flange 850', cooperating with a female flange 501 as described in Figs. 30A and 30B or a female flange as described in Figs.48A and 48B below, is manufactured in two parts, a flat part (backing plate) which has mounting holes 870", a central through hole 890' and a recess 855 with an end wall 855", and a sealing part 504'". The flange material is preferably sintered material, possibly different material in the two different parts, for instance using material with enhanced sealing properties for the sealing part and material with enhanced strength for the backing plate. The sealing part has an outwardly curved surface 505'" generally corresponding to the recess 503, with sloping side walls 512 of the female flange 501. The sealing part further has a recess 519" having an inner annular surface 520. The sealing part also has an outer annular sealing surface 518. The sealing part 504"' further has an inner diameter 508 v ", smaller than the inner diameters (central through hole) 890' and 509, respectively, of the male flange and the female flange. The two parts of the male flange 850' are made in separate pressing operations of a sintering manufacturing process. The required press force is lower, making it possible to use smaller and cheaper presses. Both parts are optionally pre- sintered at relatively low temperatures and then pressed together and subjected to a final sintering step, during which the two parts bond together. When the two parts are pressed together, the male flange recess 855 contacts the sealing part recess 519", and the male flange recess end wall 855" contacts the outer annular sealing surface 518, whilst the sealing part inner annular surface 520 contacts the surface of the central through hole 890", forming mating surfaces for the two parts. Thus, the male flange recess has a shape cooperating with and corresponding to the shape of the sealing part recess. For the two-piece male flange described above, a bonding agent/welding flux may be applied to the mating surfaces after an optional pre-sintering step but before final sintering, to enhance the bond between the two parts after sintering. Further, an optional weld may be applied to the male flange after sintering, to additionally strengthen the joint between the sealing part and the backing plate. The weld would be applied on the side of the male flange where the sealing part extends from the backing plate, and either be in the form of a tack weld or a continuous weld along the full joint between the sealing part and the backing plate. As is shown in Figs. 43A and 43B, the male flange 850' may have two mounting holes 870' and a single step recess 855, as described above. An alternative embodiment of a male flange 850" is shown in Figs.44A and 44B. The male flange has three mounting holes 870" and a multi-stepped recess 855' corresponding in shape to a multi-stepped recess of the sealing part (not shown). The larger number of mounting holes makes a secure attachment of the male flange and a female flange easier, and the multi-stepped recess enlarges the surface area between the two parts of the male flange, which enhances the bonding between the two parts after final sintering. As is shown in Figs. 48A and 48B, also the female flange 501' may be of two-piece construction (as male flange of Figs. 43A to 46). The female flange is thus manufactured in two parts, a flat part (backing plate) which has mounting holes 511', a central through hole 890" and a recess 855"" with an end wall 855 ιv , and a sealing part 504 ,v . The flange material is preferably sintered material, possibly different material in the two different parts, for instance using material with enhanced sealing properties for the sealing part and material with enhanced strength for the backing plate. The sealing part has an inwardly curved surface 505 ιv . The sealing part further has a recess 519"" having an inner annular surface 520' and an outer annular surface 518". The sealing part 504 ιv further has an inner diameter 508 vι ", smaller than the central through hole 890". The two parts of the female flange 501' are made in separate pressing operations of a sintering manufacturing process. The required press force is lower, making it possible to use smaller and cheaper presses. Both parts are optionally pre- sintered at relatively low temperatures and then pressed together and subjected to a final sintering step, during which the two parts bond together. When the two parts are pressed together, the female flange recess 855'" contacts the sealing part recess 519"", and the female flange recess end wall 855 ιv contacts the outer annular sealing surface 518", whilst the sealing part inner annular surface 520' contacts the surface of the central through hole 890", forming mating surfaces for the two parts. Thus, the female flange recess has a shape cooperating with and corresponding to the shape of the sealing part recess. For the two-piece female flange described above, a bonding agent/welding flux may be applied to the mating surfaces after an optional pre-sintering step but before final sintering, to enhance the bond between the two parts after sintering. Further, an optional weld may be applied to the female flange after sintering, to additionally strengthen the joint between the sealing part and the backing plate. The weld would be applied on the side of the female flange where the sealing part extends from the backing plate, and either be in the form of a tack weld or a continuous weld along the full joint between the sealing part and the backing plate. Figs. 49A and 49B show a further embodiment of a flange according to the invention. The flange has multiple parts 550, 560, 570, which are made separately, preferably using powder metallurgical processes and assembled to form a flange. A first ring 550 having through holes 551 for accommodating screws 10' is adapted to receive a second ring 560. The second ring has a first outer diameter part 561 , which has a diameter corresponding to an inner diameter 552 of the first ring 550, so that the second ring fits snugly in the first ring. The second ring further has a protruding portion 564 which has a curved outer surface 565 which slopes from a larger diameter to a smaller diameter in a spherical section. An inner diameter 563 of the second ring is chosen to be smaller than an inner diameter of the exhaust pipes to e fastened to the flange. At the larger diameter of the protruding portion, a stop surface 562 is formed, which abuts a surface of the first ring 550 when the second ring is assembled with the first ring. An exhaust pipe 3, having a flared end 3", is placed with the flared end contacting and generally conforming in shape with the curved outer surface 565 of the second ring 560. A third ring 570, having screw mounting holes 571 and a flange contacting portion 572, is placed over the flared end so that a bevelled surface 573 of the flange contacting portion is making contact with the flared end and pressing the flared end towards the curved outer surface, when the screws 10' are tightened using nuts, for example (not shown). The third ring has an inner diameter 574 chosen to make the bevelled surface contact the flared end 3" of the exhaust pipe 3 and press the exhaust pipe against the curved outer surface 565 of the second ring 560. The exhaust pipe flared end is either formed during the fastening of the exhaust pipe onto the flange, or preformed before assembly. A preferred method of making a flange as shown in Figs. 49A and 49B, using powder metallurgical processes, includes the steps: a) compacting multiple parts of a flange separately (first ring 550, second ring 560 and third ring 570), preferably at a pressure of 30 to 65 tsi (413.8 to 896.6 MPa), more preferably 50 tsi (689.7 Mpa), to form green bodies; b) assembling the green bodies; c) sintering the assembled green bodies, preferably in a vacuum, hydrogen or hydrogen/nitrogen mixture atmosphere, and preferably at a temperature range of 2050 °F to 2600 °F (1121 °C to 1426.7 °C), more preferably at 2400 °F (1316 °C). Alternatively, a method of making a flange as shown in Figs. 49A and 49B, using powder metallurgical processes, includes the steps: a) compacting multiple parts of a flange separately (first ring 550, second ring 560 and third ring 570), preferably at a pressure of 30 to 65 tsi (413.8 to 896.6 MPa), more preferably 50 tsi (689.7 Mpa), to form green bodies; b) pre-sintering the multiple parts, preferably in a vacuum, hydrogen or hydrogen/nitrogen mixture atmosphere and preferably at a temperature of 1800 °F to 2200 °F(982 °C to 1204 °C), more preferably at 2050 °F (1121 °C); d) assembling the pre-sintered bodies; e) sintering the assembled pre-sintered bodies, preferably in a vacuum, hydrogen or hydrogen/nitrogen mixture atmosphere and preferably at a temperature range of 2050 °F to 2600 °F (1121 °C to 1427 °C), more preferably at 2400 °F (1316 °C). Figs.50-53 show a "floating sealing portion" that includes a sealing dome, a gasket, and a backing plate with a recess. The sealing dome has enlarged mounting holes, is slightly smaller than the recess in the backing plate, and sits inside the recess over the gasket. A smaller sealing dome permits movement of the dome in relation to the female flange and facilitates alignment (in the event of pipe misalignment). Figs. 54 and 55 show the dome attached (by any suitable means) to the backing plate with an offset. This feature will facilitate alignment of non-aligned mating parts. The invention provides a number of advantages, which include that the use of powdered metal permits reduced thickness and weight by permitting the use of reinforcing ribs or the formed lightening holes, that the sealing configuration avoids a direct escape path for exhaust gases, thereby potentially reducing the need for gaskets and potentially reducing emissions and to facilitate the alignment of the different parts of the exhaust system. Preferably, the female flange is made of one material and the male flange is made of another material. In this way, the heat expansion of the flange can be regulated to compensate for differences in heating of the flanges (the flange closest to the engine will theoretically be heated more than the flange further away). By choosing a material having a lower heat expansion for the flange closest to the engine, and a material having a higher heat expansion for the other flange, both flanges can be made to expand equally much during use, thus enhancing the fit and seal of the flange assembly. Preferably, the materials used for making the flanges contain between 0.1 % to 1 % by weight of hexagonal boron nitride (h-BN), which enhances the corrosion resistance properties of the powder metallurgical materials used, as disclosed in US 6,103,185. The use of h-BN in either part also allows the multiple parts to strongly sinter-bond during the sintering step, by strongly activating diffusion bonding of the two pieces. Using flanges as described in the different embodiments of the invention will enhance the sealing and rigidity properties of the flange joint, compared to known flange assemblies. It will be appreciated that the above description relates to the preferred embodiment by way of example only. Many variations on the invention will be obvious to those knowledgeable in the field, and such obvious variations are within the scope of the invention as described and claimed, whether or not expressly described. For example, when assembling exhaust pipes it might be economical to use standard length bolts, which might be too long for the application and possibly interfere with the pipe if it has a sharp bend adjacent the flange. To accommodate longer bolts, it is foreseen to produce the sintered flanges having a stand-off sleeve integrally formed on the surface of the flange which faces away from the sealing surface of the flange, as shown in Fig. 47. When using a two-piece flange, having a separate sealing part, the two parts may be fixed to each-other by low-strength glue, or similar, to secure the sealing part in place until the flange is used with another flange to form a flange assembly. After the flanges are joined, the sealing part will be held in place by the joining forces. INDUSTRIAL APPLICABILITY The invention provides an improved flange connection, for instance for use with exhaust system flanges.

Claims: CLAIMS: 1. An exhaust flange assembly for connecting two exhaust pipes to each other, said assembly comprising: a female flange securable to the end of one pipe, having a distal sealing surface; and a male flange securable to the end of the other pipe, having a distal sealing surface; where said sealing surface of said female flange has a cavity and said sealing surface of said male flange is shaped to be closely received by said cavity when said female flange and said male flange are assembled, and at least a portion of said female flange and at least a portion of said male flange are made of powder metallurgically produced material. 2. The exhaust flange assembly as recited in claim 1 , wherein said female flange is made of one material and said male flange is made of a different material. 3. The exhaust flange assembly as recited in any of claims 1 to 2, wherein said female flange has a curved extension protruding in a direction opposite to said cavity, and said male flange has a curved extension protruding in a direction opposite to said sealing surface of said male flange, said extensions arranged to be fitted into said ends of exhaust pipes, thereby deforming said exhaust pipes to form a joint. 4. The exhaust flange assembly as recited in claim 3, wherein said extensions have a groove surrounded by an inner ridge and an outer ridge, arranged on an outer surface of said extension. 5. The exhaust flange assembly as recited in any of claims 1 to 4, wherein said male flange comprises a first substantially flat part and a second annular sealing part, said first part having a first recess and said second part having a second recess and where said first recess and said second recess have complimentary shapes so that said first recess fits in said second recess. 6. The exhaust flange assembly as recited in claim 5, wherein said first recess and said second recess have multiple steps. 7. The exhaust flange assembly as recited in any of claims 1 to 6, wherein one of said flanges has integral mounting studs extending from said sealing surface of said flange, said studs configured to extend through corresponding holes in the other said flange, said studs being threaded to receive nuts whereby said flanges may be pulled together for a secure connection by tightening said nuts. 8. The exhaust flange assembly as recited in any of claims 1 to 7, wherein one of said female flange and said male flange is generally straight and the other flange is slightly curved, where an outer edge of said slightly curved flange is bent away from a surface of said slightly curved flange which contacts said straight flange, so that, when said straight flange is mounted to said slightly curved flange by fasteners, said slightly curved flange deflects towards said flat flange to form a flat sealing surface, thus enhancing the seal between said slightly curved flange and said straight flange. 9. The exhaust flange assembly as recited in claim 8, wherein said slightly curved flange is substantially weakly bowl-shaped. 10. The exhaust flange assembly as recited in any of claims 1 to 9, wherein said male flange comprises a recess having a gasket element shaped to be closely received in said recess on one side of said gasket element and to be closely received by said cavity of said female flange on another side of said gasket element. 11. The exhaust flange assembly as recited in any of claims 1 to 10, wherein at least one of said flanges has an annular gasket recess arranged on said sealing surface of said flange. 12. The exhaust flange assembly as recited in claim 11 , wherein said annular gasket recess has gasket retaining means. 13. The exhaust flange assembly as recited in claim 12, wherein said gasket retaining means comprise gasket recess protrusions. 14. The exhaust flange assembly as recited in claim 12, wherein said gasket retaining means comprise said gasket recess being generally oval. 15. The exhaust flange assembly as recited in any of claims 1 to 14, wherein at least one of said flanges has one or more reinforcement ribs. 16. The exhaust flange assembly as recited in any of claims 1 to 15, wherein said flanges have at least one hole therethrough for weight reduction. 17. The exhaust flange assembly as recited in any of claims 1 to 16, wherein said female flange and said male flange have bolt mounting holes arranged to receive threaded bolts onto which nuts are threadable, whereby said flanges may be pulled together for a secure connection by tightening said nuts. 18. The exhaust flange assembly as recited in claim 17, wherein said bolts have generally spherical portions facing said bolt thread, said spherical portions of said bolts arranged to cooperate with generally concave recesses arranged in said flanges around said mounting holes. 19. An elongated substantially flat exhaust flange comprising a sealing surface and a pipe attachment means arranged on a pipe attachment surface opposite to said sealing surface, said sealing surface having a cavity, and where at least a part of said flange is made of powder metallurgically produced material. 20. The exhaust flange as recited in claim 19, wherein said flange comprises a first substantially flat part and a second annular sealing part, said first part having a first recess and said second part having a second recess and where said first recess and said second recess have complimentary shapes so that said first recess fits in said second recess. 21. The exhaust flange as recited in claim 20, wherein said second part is made of powder metallurgically produced material. 22. The exhaust flange as recited in claim 20, wherein said first part is made of powder metallurgically produced material. 23. The exhaust flange as recited in claim 20, wherein said first part and said second part are made of powder metallurgically produced material. 24. The exhaust flange as recited in any of claims 19 to 23, wherein said flange has an annular gasket recess arranged on said sealing surface of said flange. 25. The exhaust flange as recited in claim 24, wherein said annular gasket recess has gasket retaining means. 26. The exhaust flange as recited in claim 25, wherein said gasket retaining means comprise gasket recess protrusions. 27. The exhaust flange as recited in claim 25, wherein said gasket retaining means comprise said gasket recess being generally oval. 28. The exhaust flange as recited in any of claims 19 to 27, wherein at least one of said flanges has one or more reinforcement ribs. 29. The exhaust flange as recited in any of claims 19 to 28, wherein said flange has at least one hole therethrough for weight reduction. 30. The exhaust flange as recited in any of claims 19 to 29, wherein said flange has bolt mounting holes arranged to receive threaded bolts onto which nuts are threadable. 31. The exhaust flange as recited in claim 30, wherein said bolts have generally spherical portions facing the bolt thread, said spherical portions of said bolts arranged to cooperate with generally concave recesses arranged in said flange around said mounting holes. 32. The exhaust flange as recited in any of claims 19 to 31 , wherein said flange has a curved extension protruding in a direction opposite to said cavity, said extension arranged to be fitted into said end of said exhaust pipe, thereby deforming said exhaust pipe to form a joint. 33. The exhaust flange as recited in claim 32, wherein said extension has a groove surrounded by an inner ridge and an outer ridge, arranged on an outer surface of said extension. 35. An elongated substantially flat exhaust flange comprising a sealing surface and a pipe attachment means arranged on a pipe attachment surface opposite to said sealing surface, said sealing surface having a protrusion, and where at least a part of said flange is made of powder metallurgically produced material. 36. The exhaust flange as recited in claim 35, wherein said flange comprises a first substantially flat part and a second annular sealing part, said first part having a first recess and said second part having a second recess and where said first recess and said second recess have complimentary shapes so that said first recess fits in said second recess. 37. The exhaust flange as recited in claim 36, wherein said second part is made of powder metallurgically produced material. 38. The exhaust flange as recited in claim 36, wherein said first part is made of powder metallurgically produced material. 39. The exhaust flange as recited in claim 36, wherein said first part and said second part are made of powder metallurgically produced material. 40. The exhaust flange as recited in any of claims 35 to 39, wherein said flange has an annular gasket recess arranged on said sealing surface of said flange. 41. The exhaust flange as recited in claim 40, wherein said annular gasket recess has gasket retaining means. 42. The exhaust flange as recited in claim 41 , wherein said gasket retaining means comprise gasket recess protrusions. 43. The exhaust flange as recited in claim 41 , wherein said gasket retaining means comprise said gasket recess being generally oval. 44. The exhaust flange as recited in any of claims 35 to 43, wherein at least one of said flanges has one or more reinforcement ribs. 45. The exhaust flange as recited in any of claims 35 to 44, wherein said flange has at least one hole therethrough for weight reduction. 46. The exhaust flange as recited in any of claims 35 to 45, wherein said flange has bolt mounting holes arranged to receive threaded bolts onto which nuts are threadable. 47. The exhaust flange as recited in claim 46, wherein said bolts have generally spherical portions facing the bolt thread, said spherical portions of said bolts arranged to cooperate with generally concave recesses arranged in said flange around said mounting holes. 48. The exhaust flange as recited in any of claims 35 to 47, wherein said flange has a curved extension protruding in a direction opposite to said cavity, said extension arranged to be fitted into said end of said exhaust pipe, thereby deforming said exhaust pipe to form a joint. 49. The exhaust flange as recited in claim 48, wherein said extension has a groove surrounded by an inner ridge and an outer ridge, arranged on an outer surface of said extension. 50. The exhaust flange assembly as recited in any of claims 1 to 18, wherein the sintered materials used for making the flanges contain between 0.1 percent and 1 percent by weight of hexagonal boron nitride for enhanced corrosion resistance. 51. The exhaust flange assembly as recited in any of claims 19 to 33, wherein the sintered materials used for making the flanges contain between 0.1 percent and 1 percent by weight of hexagonal boron nitride for enhanced corrosion resistance. 52. The exhaust flange assembly as recited in any of claims 34 to 49, wherein the sintered materials used for making the flanges contain between 0.1 percent and 1 percent by weight of hexagonal boron nitride for enhanced corrosion resistance. 53. A method of producing exhaust flanges, comprising the steps of: a) press-forming metal powder to shape a first substantially flat part of a flange; b) press-forming metal powder to shape a second annular sealing part of said flange; c) fitting said first part onto said second part; and d) sintering said first part and said second part to thereby bond them together and form said flange. 54. The method of producing exhaust flanges as recited in claim 53, wherein said method comprises the step of pre-sintering said first part and said second part after press-forming but before fitting said first part onto said second part. 55. The method of producing exhaust flanges as recited in claim 54, wherein a weld is applied to a joint between said first part and said second part. 56. A method of producing exhaust flanges, comprising the steps of: a) stamping metal to shape a first part of a flange; b) press-forming metal powder to shape a second annular sealing part of said flange; c) sintering said sealing part; d) fitting said first part onto said second part; and e) joining said first part and said second part to thereby bond them together and form said flange. 57. The method of producing exhaust flanges as recited in claim 56, wherein said joining step comprises welding said first part to said second part. 58. The method of producing exhaust flanges as recited in claim 56, wherein said joining step comprises brazing said first part to said second part. 59. The method of producing exhaust flanges as recited in claim 56, wherein said joining step comprises glueing said first part to said second part. 60. A method of producing exhaust flanges, comprising the steps of: a) press-forming metal powder to shape a first substantially flat part of a flange; b) press-forming metal powder to shape a second annular sealing part of said flange; c) sintering said first part and said second part; d) fitting said first part onto said second part; and e) joining said first part and said second part to thereby bond them together and form said flange. 61. The method of producing exhaust flanges as recited in claim 60, wherein said joining step comprises welding said first and second parts to each other. 62. The method of producing exhaust flanges as recited in claim 60, wherein said joining step comprises brazing said first and second parts to each other. 63. The method of producing exhaust flanges as recited in claim 60, wherein said joining step comprises glueing said first and second parts to each other. 64. The method of producing exhaust flanges as recited in claim 60, wherein said joining step comprises soldering said first and second parts to each other. 65. A method of producing flanges using powder metallurgical processes, said method comprising the steps of: a) compacting multiple parts of a flange separately to form green bodies; b) assembling the green bodies; c) sintering the assembled green bodies, to sinter-bond said multiple parts to form an integral flange. 66. The method of producing flanges as recited in claim 65, wherein said compacting is performed at a pressure of 30 to 65 tsi (413.8 to 896.6 Mpa). 67. The method of producing flanges as recited in claim 66, wherein said compacting is performed at a pressure of 50 tsi (689.7 Mpa). 68. The method of producing flanges as recited in any of claims 65 to 67, wherein said sintering is performed in an atmosphere chosen from the group consisting of vacuum, hydrogen and a mixture of hydrogen and nitrogen. 69. The method of producing flanges as recited in any of claims 65 to 68, wherein said sintering is performed at a temperature range of 2050 °F to 2600 °F (1121 °C to 1426.7 °C). 70. The method of producing flanges as recited in claim 69, wherein said sintering is performed at 2400 °F (1316 °C). 71. The method of producing flanges as recited in any of claims 65 to 70, wherein a pre-sintering step is performed between said compacting step and said assembly step. 72. The method of producing flanges as recited in claim 71 , wherein said pre- sintering step is performed in an atmosphere chosen from the group consisting of vacuum, hydrogen and a mixture of hydrogen and nitrogen. 73. The method of producing flanges as recited in any of claims 71 to 72, wherein said pre-sintering step is performed at a temperature of 1800 of to 2200 of (982 °C to 1204 °C). 74. The method of producing flanges as recited in claim 73, wherein said pre- sintering step is performed at a temperature of 2050 of (1121 °C).

Inventors: VASUDEVA KAILASH C, VASUDEVA, KAILASH, C.
Applicants: MAXTECH MFG INC, VASUDEVA KAILASH C, MAXTECH MANUFACTURING INC., VASUDEVA, KAILASH, C.
Application year: 2001
Main classification: F16L23
IPC codes: F01N7, F16L23