Patent Publication Number: US-2004046391-A1

Title: Exhaust system flanges

Description:
REFERENCE TO RELATED APPLICATION  
     [0001] This is a continuation-in-part application based on and claiming the benefit of U.S. patent application Ser. No. 09/758,311, filed Jan. 12, 2001, which claims priority from U.S. provisional patent application No. 60/176,043, filed Jan. 14, 2000 and U.S. provisional patent application No. 60/194,765, filed Apr. 3, 2000. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] This invention relates generally to exhaust systems and more particularly mainly to an exhaust flange assembly used in exhaust systems of internal combustion engines, such as those used in automobiles and trucks.  
       BACKGROUND OF THE INVENTION  
       [0003] In the field of exhaust systems, exhaust flanges are generally used to connect the ends of exhaust pipes to each other. In such 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. However, there are various disadvantages of prior art exhaust flanges when the two flanges are mated.  
       [0004] Firstly, some prior art exhaust flanges are manufactured by a stamping process along with a machining process. However, this is quite an expensive overall process to use and maintain and requires lots of machinery and manpower to operate. Also, the use of stamping and machining does not allow for complex shapes to be manufactured at an economically feasible rate.  
       [0005] Another disadvantage of prior art flanges is that they are susceptible to leaks. When the flanges are mated, there generally exists small holes or paths whereby exhaust escapes out of the exhaust system and is released into the atmosphere. Furthermore, some of the leaks which appear in existing exhaust flanges are caused by flanges which are misaligned with each other such that when the flanges are mated, the faces of the flanges do not lie flat against each other. Another factor which causes the misalignment of exhaust flanges is that fastening means, in the form of studs or bolts, are not formed integral to the flanges. Instead, the studs are usually separate parts which may affect the alignment of the two flanges. Also, the studs may slip after being fastened causing the flanges to be further misaligned. Furthermore, in some prior art flanges, over-tightening of the fastening means causes the flanges to deflect away from each other thus causing leakage.  
       [0006] Existing exhaust flanges are also quite heavy which may affect the overall exhaust system since the heavier flanges require more support when installed. In some prior art exhaust flanges assemblies, the assemblies include gaskets which assist in the sealing process. However, some suffer from having these gaskets fall out during assembly of the system causing the system to either fail or stopped.  
       [0007] It is therefore, desirable to provide a novel exhaust flange assembly.  
       SUMMARY OF THE INVENTION  
       [0008] It is an object of the present invention to obviate or mitigate at least one disadvantage of previous exhaust system flanges.  
       [0009] In one aspect of 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. Furthermore, the powder metallurgy process also is more economically feasible than some prior art flange manufacturing processes.  
       [0010] In accordance with one aspect of an exhaust flange assembly, there are two flanges, one on the end of a first exhaust pipe and one on the end of a second exhaust pipe. The flanges have complementary shapes, such that one of the flanges, which may be seen as an “inner flange”, nests partially within the other flange, which may be seen as an “outer flange”.  
       [0011] In another aspect of the invention, one of the flanges, preferably the inner flange, has integral mounting studs on opposing sides of the exhaust pipe, configured to extend through corresponding holes in the outer flange. The studs are threaded to receive nuts which are tightened to draw the two flanges together for a secure connection when the flanges are mated. Furthermore, material may be added to the flanges in predetermined areas so as to reduce or eliminate the amount of deflection when the flanges are mated.  
       [0012] Preferably, the proximal surfaces of the flanges, i.e. the surfaces of the flanges away from their mating surfaces, comprise reinforcement ribs, which allow the overall thickness and weight of the flanges to be reduced compared to conventional flanges. As an alternative to reinforcement ribs to reduce weight, the flanges may comprises through holes formed in several locations to achieve similar weight reduction.  
       [0013] In a further aspect of the invention, the flanges have extensions for attachment by press-fitting, spinning, resistance welding, crimp rolling or other known processes to the exhaust pipes. Thus, no welding is necessary between the exhaust pipe and the extension other than as a further reinforcement of the joint.  
       [0014] Furthermore, the nesting together of the flanges provides an improved seal between the flanges, in that there is little or no escape route for exhaust gases, thus reducing the need for expensive gaskets to be placed between the flanges or perhaps eliminating the need for gaskets altogether. Also, the use of powder metallurgy allows for larger diametered studs and matching holes with close tolerances to be manufactured to form a rigid exhaust flange assembly. There may also be composite material inserted between the mating faces of the two flanges to provide further sealing properties to the exhaust flange assembly.  
       [0015] Another advantage of the invention is that since the mounting studs or bolts may be integral to the flanges, the exhaust flange assembly will tend to remain intact even if the nuts become loose or dislodged from the studs unlike prior art flanges whereby if the bolts fall out the connection between the two flanges shifts. One other advantage is that the nesting of one flange within the other reduces the lateral shifting of the exhaust flange assembly, even if the nuts are loose or missing, causing the exhaust flange assembly, or flange joint, to be mechanically secure.  
       [0016] Moreover, at least one of the flanges has an annular gasket recess located on its sealing surface. 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.  
       [0017] In another aspect, the outer flange and the inner flange have stud mounting holes arranged to receive threaded studs onto which nuts are threadable, whereby the flanges may be drawn together for a secure connection by the nuts.  
       [0018] In yet another aspect of the invention, the outer flange has a curved extension protruding in a direction opposite to the cavity defined in its sealing surface, and the inner flange has a curved extension protruding in a direction opposite to its sealing surface, the extensions arranged to be fitted into the ends of exhaust pipes. Preferably, the end of the exhaust pipe is press-fitted, spun, resistance welded, crimp rolled or roll-formed to conform to the outer surface of the extensions which has a groove surrounded by an inner ridge and an outer ridge.  
       [0019] In another aspect, the studs, and or 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 mounting holes. The studs may also include hexagonal portions which prevent the stud from spinning after the flanges have been mated.  
       [0020] Still a further embodiment of an exhaust flange assembly, according to an aspect of the invention, comprises a straight flange cooperating with a curved flange, where an outer edge of the curved flange is bent away from the surface of the curved flange which contacts the straight flange, so that, when the straight flange is mated to the curved flange by fastening means, the curved flange deflects towards the straight flange to form a flat sealing surface, thus enhancing the seal between the curved flange and the straight flange. The curved flange is substantially weakly bowl-shaped Preferably, the straight flange and the curved flange have mounting holes and the fastening means comprise mounting studs, for placement through the mounting holes, and mounting nuts to be tightened onto each mounting stud, for drawing the straight flange and the curved flange together. In another aspect of the invention, the straight and the curved flanges have gasket recesses, for accommodating gaskets.  
       [0021] In a further aspect, the exhaust flange assembly has an inner flange comprising a shaped recess for receiving one side of a gasket and an outer flange comprising a cavity for receiving another side of the gasket element. When the flanges are mated, the gasket rests in between the mating surfaces of the two flanges thereby providing improved sealing characteristics for the exhaust flange assembly.  
       [0022] An elongated substantially flat exhaust flange, according to a further aspect of the invention, comprises a sealing surface having a cavity and a pipe attachment means, seen as an extension, arranged on a surface opposite the sealing surface.  
       [0023] In another aspect of the invention, there is provided a method of producing exhaust flanges comprising the steps of press-forming metal powder to shape a first substantially flat part of an inner flange; press-forming metal powder to shape a second annular sealing part of the inner flange; fitting the first part onto the second part; and sintering the first part and the second part to thereby bond them together and form the inner flange.  
       [0024] 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.  
       [0025] Preferably a weld is applied to a joint between the first part and the second part after the first part is fitted into the second part in the embodiment where the flanges are made of composite material.  
       [0026] A further aspect of a method of producing exhaust flanges according to the invention comprises the steps of stamping metal to shape a first part of a flange; press-forming metal powder to shape a second annular sealing part of the flange; sintering the sealing part; fitting the first part onto the second part; and joining the first part and the second part to thereby bond them together and form the flange.  
       [0027] A still further aspect of a method of producing exhaust flanges according to the invention comprises the steps of press-forming metal powder to shape a first substantially flat part of a flange; press-forming metal powder to shape a second annular sealing part of the flange; sintering the first part and the second part; fitting the first part onto the second part; and joining the first part and the second part to thereby bond them together and form the flange.  
       [0028] Preferably, the materials used for making the flanges contain 0.75 to 1 weight percent of hexagonal boron nitride (BN), which enhances the corrosion resistance properties of the powder metallurgical materials used.  
       [0029] Furthermore, use of a composite flange assembly permits movement between the mating surfaces of the two flanges by virtue of the shape of the complementary shapes without affecting the leak-resistant properties of the exhaust flange assembly. Therefore, even if the mated flanges move with respect to each other, little or no exhaust is lost from the exhaust system during operation.  
       [0030] Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0031] Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:  
     [0032]FIG. 1 is a side view of an exhaust flange assembly having a first and second flange connected to ends of exhaust pipes;  
     [0033]FIG. 2 is a sectional side view of the exhaust flange assembly of FIG. 1;  
     [0034]FIG. 3 is a side view of the flanges of the exhaust flange assembly of FIG. 1 mated together;  
     [0035]FIG. 4 is a proximal end view of the first flange;  
     [0036]FIG. 5 is a side view of the first flange;  
     [0037]FIG. 6 is a distal end view of the first flange;  
     [0038]FIG. 7 is a distal end view of the second flange;  
     [0039]FIG. 8 is a side view of the second flange;  
     [0040]FIG. 9 is a proximal end view of the second flange;  
     [0041]FIG. 10 is a cross-sectional view of the second flange of FIG. 9 taken along line  10 - 10  on FIG. 9;  
     [0042]FIG. 11 is a top view of the second flange;  
     [0043]FIG. 12 is a distal end view of a second embodiment of the first flange;  
     [0044]FIG. 13 is a side view of the first flange of FIG. 12;  
     [0045]FIG. 14 is a proximal end view of the first flange of FIG. 12;  
     [0046]FIG. 15 is a proximal end view of another embodiment of a second flange;  
     [0047]FIG. 16 is a side view of the second flange of FIG. 15;  
     [0048]FIG. 17 is a distal end view of the second flange of FIG. 15;  
     [0049]FIG. 18 is a proximal end view of another embodiment of a first flange for mating with the second flange of FIG. 15;  
     [0050]FIG. 19 is a side view of the first flange of FIG. 18;  
     [0051]FIG. 20 is a distal end view of the first flange of FIG. 18;  
     [0052]FIG. 21 is a side view of an exhaust flange assembly comprising the first flange of FIG. 15 and the second flange of FIG. 18;  
     [0053]FIG. 22 is a side view of FIG. 21 with the first and second flanges mated;  
     [0054]FIG. 23 is a sectional side view of FIG. 22;  
     [0055]FIG. 23A is a side view of a further embodiment of an exhaust flange assembly;  
     [0056]FIG. 23B is a side view of yet another embodiment of an exhaust flange assembly;  
     [0057]FIG. 24 is a distal end view of another embodiment of a flange for use in an exhaust flange assembly;  
     [0058]FIG. 25 is a cross-sectional view of the flange of FIG. 24 taken along the line  25 - 25  of FIG. 24;  
     [0059]FIG. 26 is a side view of a further embodiment of an exhaust flange assembly;  
     [0060]FIG. 27 is an exploded partially sectioned side view of another embodiment of an exhaust flange assembly;  
     [0061]FIG. 28 is an exploded partially sectioned side view of yet another embodiment of an exhaust flange assembly;  
     [0062]FIG. 29 is a sectional side view of the exhaust flange assembly of FIG. 28 with the flanges mated;  
     [0063]FIG. 30A is a side view of another embodiment of first and second flanges of an exhaust flange assembly;  
     [0064]FIG. 30B is a sectional side view of the flanges of FIG. 30A;  
     [0065]FIG. 31A is a distal end view of another embodiment of a flange for use in an exhaust flange assembly;  
     [0066]FIG. 31B is a cross-sectional view of the flange of FIG. 31A taken along line  31 B- 31 B of FIG. 31A;  
     [0067]FIG. 32A is a distal end view of yet another embodiment of a flange for use in an exhaust flange assembly;  
     [0068]FIG. 32B is a cross-section view of the flange of FIG. 32A taken along line  32 B- 32 B of FIG. 32A;  
     [0069]FIG. 33 is a sectioned side view of a further embodiment of an exhaust flange assembly without the exhaust pipes;  
     [0070]FIG. 34 is a sectioned side view of another embodiment of an exhaust flange assembly without the exhaust pipes;  
     [0071]FIG. 35 is a sectional side view of another embodiment of an exhaust flange assembly without the exhaust pipes;  
     [0072]FIG. 36 is a partially sectioned side view of another embodiment of an exhaust flange assembly;  
     [0073]FIG. 37 is a sectioned side view of the gasket of FIG. 36;  
     [0074]FIG. 38 is a front view of the gasket of FIG. 36;  
     [0075]FIG. 39A is a distal view of a further embodiment of a first flange;  
     [0076]FIG. 39B is a cross-sectional view of the first flange of FIG. 39A taken along line  39 B- 39 B of FIG. 39A;  
     [0077]FIG. 40A is a distal view of a further embodiment of a second flange;  
     [0078]FIG. 40B is a cross-sectional view of the second flange of FIG. 40A taken along line  40 B- 40 B of FIG. 40A;  
     [0079]FIG. 41 is a sectioned side view of another embodiment of an exhaust flange assembly;  
     [0080]FIG. 42 is a side view of the exhaust flange assembly (with exhaust pipes) of FIG. 41;  
     [0081]FIG. 43A is a front view of yet another embodiment of a first flange;  
     [0082]FIG. 43B is a cross-sectional view of the first flange of FIG. 43A taken along line  43 B- 43 B of FIG. 43A;  
     [0083]FIG. 44A is a front view of another embodiment of a first flange;  
     [0084]FIG. 44B is a cross-sectional side view of the first flange of FIG. 44A taken along line  44 B- 44 B of FIG. 44A;  
     [0085]FIG. 45 is an exploded side view of a further embodiment of an exhaust flange assembly without exhaust pipes;  
     [0086]FIG. 46 is a sectioned side view of the second flange of FIG. 45;  
     [0087]FIG. 47 is a sectioned side view of another embodiment of an exhaust flange assembly;  
     [0088]FIG. 48A is a sectioned side view of another embodiment of a first flange;  
     [0089]FIG. 48B is a sectioned side view of the first flange of FIG. 48A;  
     [0090]FIG. 49 is a flow diagram showing a method of manufacturing a flange;  
     [0091]FIG. 50 is a flow diagram showing a second method of manufacturing a flange;  
     [0092]FIG. 51 is a flow diagram showing a third method of manufacturing a flange;  
     [0093]FIG. 52 is a flow diagram showing a fourth method of manufacturing a flange;  
     [0094]FIG. 53 is a schematic view of an angled flange assembly;  
     [0095]FIG. 54 is a schematic view of the flange assembly of FIG. 53 with the flanges mated;  
     [0096]FIG. 55 is a schematic view of a further angled flange assembly;  
     [0097]FIG. 56 is a schematic view of the flange assembly of FIG. 55 with the flange connected to an exhaust pipe;  
     [0098]FIG. 57 is a schematic view of a yet another angled flange assembly;  
     [0099]FIG. 58 is a schematic view of the flange assembly of FIG. 57 with the flange connected to an exhaust pipe;  
     [0100]FIG. 59 is a schematic view of another angled flange assembly;  
     [0101]FIG. 60 is a schematic view of the flange assembly of FIG. 59 fully assembled;  
     [0102]FIG. 61 is a schematic view of a further angled flange assembly;  
     [0103]FIG. 62 is a schematic view of the flange assembly of FIG. 61 with the flange connected to an exhaust pipe;  
     [0104]FIG. 63 is a schematic view of a further embodiment of an exhaust flange assembly;  
     [0105]FIG. 64 is a schematic view of yet another embodiment of an exhaust flange assembly;  
     [0106]FIG. 65 is a schematic view of the embodiment of FIG. 64 with spacers mounted in the first flange;  
     [0107]FIG. 66 is a schematic view of a further embodiment of an exhaust flange assembly; and  
     [0108]FIG. 67 is a schematic view of the embodiment of FIG. 66 with spacers mounted in the first flange.  
    
    
     DETAILED DESCRIPTION  
     [0109] Generally, the present invention provides an improved exhaust flange assembly for exhaust systems.  
     [0110]FIG. 1 shows an exhaust flange assembly, or flange joint, having a first flange  1 , seen as an outer flange, and a second flange  2 , seen as an inner flange, both manufactured via a powder metallurgy process and connected to ends of exhaust pipes  3 . The outer flange  1  comprises a cavity  4  with a rounded edge  7  defined in its distal, or mating, surface while the inner flange  2  comprises an abutment comprising a generally flat distal surface  5  with a rounded edge  6  complementary to the rounded edge  7  of the cavity  4  thereby providing improved sealing characteristics, seen as a sealing seat, for the exhaust flange assembly. In the present embodiment, due to the complementary shapes of the rounded edges  6  and  7 , there is little or no path for exhaust travelling in the pipes  3  to enter into the atmosphere, which reduces or eliminates the need for a gasket in between the two flanges  1  and  2 . If a gasket is required, a less expensive gasket may be used in order to lower overall costs.  
     [0111] Although in this embodiment, the edges are rounded, other edge shapes for the flanges are contemplated provided they are complementary with each other. For example, the edge shape of one flange could be a sharp edge, a radius, a chamfer or a dome while the edge shape of the other flange is complementary to the selected shape.  
     [0112] As further shown in FIGS. 1, 2 and  11 , the inner flange  2  has integral mounting studs  8  on opposing sides, configured to extend through corresponding holes  9  in the outer flange  1 . After the inner flange  2  is manufactured using powder metallurgy, the studs  8  are tapped to provide threads  10 . Preferably, the studs  8  comprise bolstered heads (not shown) which provide extra strength to the stud  8 . As shown in FIG. 3, nuts  11  are used to tighten onto the threads  10  of the studs  8  in order to draw the outer flange  1  and the inner flange  2  together for a secure and sealed connection when the flanges are mated.  
     [0113] Turning to FIG. 4, a proximal end view of the outer flange  1  is shown. As discussed above, the outer flange  1  comprises holes  9  which receive the studs  8  of the inner flange  2  when the flanges are mated. Preferably, the proximal surface of the outer flange  1 , the surface away from the mating surface, comprises a set of reinforcement ribs  12  which allow the overall thickness and weight of the outer flange  1  to be reduced compared to conventional flanges. FIG. 5 is a side view of the outer flange  1  with the cavity  4 , the rounded edge  7 , the holes  9  and the set of ribs  12  shown in dotted lines while FIG. 6 is a distal end view of the outer flange  1  showing the cavity  4 , the holes  9  and a location  15  for the exhaust to flow from the flange to the exhaust pipe  3 .  
     [0114] Turning to FIGS.  7  to  11 , more detailed schematics of the inner flange  2  are shown. FIG. 7 is a distal end view of the inner flange  2  showing the studs  8  along with the rounded edge  6  of the distal surface  5 . FIG. 8 is a side view of the inner flange  2  in which the rounded edge  6  may be more clearly seen along with the studs  8  with threads  10 . FIG. 9 is a proximal view of the inner flange  2  showing the studs  8  connected, via a set of ribs  17 , to a location  15  for the exhaust to flow. The ribs  17  of the inner flange  2  provide similar advantages to the set of ribs  12  described with respect to the outer flange  1 . FIG. 10 is a cross-sectional view taken along the line  10 - 10  of FIG. 9 showing the inner flange  2  in more detail while FIG. 11 is a top view of the inner flange  2  showing the studs  8  on opposite sides of the flange  2  along with the distal, or mating, surface  5  and rounded edge  6 .  
     [0115] Turning to FIGS.  12  to  14 , a second embodiment of an outer flange  40  is shown. In this embodiment, the outer flange  40  is almost identical to the outer flange  1  with the difference being that the outer flange  40  comprises through holes  42  formed in several locations to provide weight reduction to the outer flange  40 . The through holes  42  provide similar advantages to the set of ribs  12  shown in FIG. 4. The outer flange  40  also comprises a set of holes  44  for receiving studs  8  from a complementary inner flange. Although not shown, an exhaust pipe is connected to the flange  40  at the location  15  where the exhaust flows through the flange  40 . It will be understood that the inner flange may include a set of through holes instead of the set of ribs.  
     [0116] FIGS.  15  to  17  show a further embodiment of a second, or inner, flange  50  which is manufactured via a of powder metallurgy process which may be attached by press-fitting, spinning, resistance welding, crimp rolling to an end of an exhaust pipe while FIGS.  18  to  20  show an alternative embodiment of a first, or outer, flange  52  for mating with the inner flange  50 .  
     [0117] The inner flange  50  comprises a distal, or mating surface  56  with a rounded edge abutment  57  and an extension  54  arranged on the side opposite the distal surface  56 . The extension  54  has a co-axial hole, corresponding to a hole  51  in an exhaust pipe  3 , through which exhaust gases flow when the flanges of the exhaust flange assembly are mated, and in use. The extension  54  also comprises a substantially smooth inner surface and a grooved outer surface having a groove  58  surrounded by an inner ridge  60  and an outer ridge  62 . The outer diameter of the extension  54  is preferably smaller than the inner diameter of the exhaust pipe  3  so that when the exhaust pipe  3  is attached over the extension  58 , the exhaust pipe  3  is roll-formed or spin-welded to conform to the profile of the extension defined by the groove  58 , the inner ridge  60  and the outer ridge  62 . In this manner, the exhaust pipe  3  is held securely to the inner flange  50 . This may be more clearly seen with respect to FIGS.  21  to  23 .  
     [0118] The groove  58  may also have a variety of profile shapes, to accommodate fitting of the pipe either by induction heating or resistance welding and its shape is thus determined by the assembly process or method.  
     [0119] Furthermore, the extension  54  may be tapered, having an inner ridge  60  which is larger than the outer ridge  62  which causes the groove  58  to be optional. Pressing the exhaust pipe  3  onto the extension  54  may then be performed by using a lubricant or by inductively heating the exhaust pipe  3 .  
     [0120] The inner flange  50  further comprises a pair of holes  64  for receiving fastening means which secure the connection between the inner flange  50  and the outer flange  52  when the two flanges are mated. Through holes  66  are also formed in several locations to provide weight reduction to the inner flange  50 .  
     [0121] Turning to FIGS.  18  to  20 , schematic views of another embodiment of the outer flange  52  are shown. The outer flange  52  comprises a cavity  68 , defined in its distal surface, with a rounded edge  70 . The distal surface  56  of the inner flange  50  nests in the cavity  68  with the rounded edge abutment  57  complementing the rounded inner edge  70  of the cavity  68  to provide a sealing seat.  
     [0122] The outer flange  52  further comprises a pair of holes  72  for receiving fastening means and an extension  74  arranged on a side of the flange  52  opposite the cavity  68 . Through holes  75  are formed in several locations to provide weight reduction to the outer flange  52 .  
     [0123] As with the inner flange  50 , the extension  74  has a co-axial hole  51 , corresponding to the hole in the outer flange  52 , through which exhaust gases flow when the flange assembly is in use and a substantially smooth inner surface and a grooved outer surface having a groove  76  surrounded by an inner ridge  78  and an outer ridge  80  with the diameter of the ridges  78  and  80  of the extension being smaller than the inner diameter of the exhaust pipe  3 . As with the inner flange  50 , when the exhaust pipe  3  is attached to the extension  74  of the outer flange  52 , the exhaust pipe  3  is roll-formed or spin-welded over the extension to conform to the profile of the extension  74 .  
     [0124]FIG. 21 provides a side view of an exhaust flange assembly, or flange joint, comprising the inner flange  50  and the outer flange  52 . FIGS. 22 and 23 are side views of the exhaust flange assembly with the inner flange  50  and outer flange  52  mated.  
     [0125] When the exhaust pipe  3  is attached to the inner flange  50 , a joint  55  is formed between the pipe  3  and the inner flange  50 . A similar joint  53  is formed between the exhaust pipe  3  and the outer flange  52  when they are attached. As can be seen in FIG. 23, the exhaust pipe  3  is secured around the inner ridge  60  and the outer ridge  62  of the inner flange  50  to form the joint  55  and a second exhaust pipe is secured around the inner ridge  78  and the outer ridge  80  of the outer flange  52  to form the joint  53 .  
     [0126] When the two flanges  50  and  52  are mated, the mounting holes  64  on the inner flange  50  and the mounting holes  72  on the outer flange  52  receive fastening means, generally comprising a bolt  80  and nut  82 . A bolt  80  is inserted through each of the mounting holes  64  and  72  and a nut  82  is placed on the end of the bolt  80  and tightened onto the threads in order to draw the two flanges together and to secure the connection between the inner flange  50  and the outer flange  52 . Alternatively, one of the flanges may comprise integral mounting studs configured to extend through the mounting holes in the other flange.  
     [0127]FIG. 23A provides a further embodiment of an exhaust flange assembly comprising an inner flange  90  and an outer flange  91 .  
     [0128] In this embodiment, the outer flange  91  is almost identical to the outer flange  52  with the addition of a pair of recesses  93  formed on the mating surface of the outer flange  91  having a shape generally complementary to a pair of projections  94  located on the inner flange  90  to facilitate alignment of the two flanges for mating. Advantageously, the projections  94  and the recesses  93  are arranged concentrically to the mounting holes  64  and  72  of the inner and outer flanges  90  and  91 , respectively.  
     [0129]FIG. 23B is yet another embodiment of an exhaust flange assembly comprising further embodiments of an outer flange  95  and an inner flange  96 . In this embodiment, the outer flange  95  is identical to the outer flange  52  described above. In this embodiment, the inner flange  96  comprises recesses  97  arranged on the proximal side of the inner flange  96 . The recesses  97  have generally concave surfaces, to cooperate with bolts  80 , which preferably have heads with generally spherical lower portions to securely hold the bolt once it has been tightened into the mounting holes  64  and  72 . Thus, the bolt  80  may swivel in the holes  64  and  72 , to facilitate alignment of the flanges when mated. Advantageously, the inner flange  96  has an increased thickness, compared to the outer flange  95 , to provide strength to compensate for the recess  97 . Furthermore, the bolts  80  have a substantially cylindrical extension  98  for the bolt head so that the extension  98  has a diameter which is larger than the diameter of the threaded portion of the bolt to prevent the bolt from sliding through the recess  97  and/or mounting hole  64 .  
     [0130] In an alternative embodiment, the extension  98  may be hexagonally shaped so that when the flanges are mated and the fastening means are fastened, the bolt does not spin during the tightening process.  
     [0131]FIGS. 24 and 25 show another embodiment of a flange  100 . As will be described, the flange  100  may be used as both an inner flange and an outer flange. The flange  100  comprises raised areas  102  arranged between mounting studs  104  having mounting holes  106 . The raised areas  102  provide reinforcement for the flange  100  to reduce deflection of the flange  100  when the flange  100  is securely connected to another flange  100  using fastening means such as a bolt and nut. The flange  100  has a substantially cylindrical flange extension  108 , with an inner diameter  110 , for attachment of the flange  100  to an exhaust pipe (not shown). FIG. 25 is a cross-section of the flange  100  taken along the line  25 - 25  of FIG. 24.  
     [0132]FIG. 26 shows still a further embodiment of an exhaust flange assembly. A first flange  120 , seen as a straight flange, comprising mounting holes  122  and gasket recesses  124 , mates with a second flange  126 , seen as a curved flange, comprising mounting holes  128  and gasket recesses  130 . The curved flange  126  is substantially bowl-shaped with an outer edge  132 , bent away from the mating surface of the curved flange  126 . Thus, when fastening means in the form of mounting bolts  134  are placed through the mounting holes  122  of the straight flange  120  and the mounting holes  128  of the curved flange  126 , and a mounting nut  136  tightened onto the threads of each mounting bolt  134 , the curved flange  126  deflects towards the straight flange  120  to form a flat sealing surface which improves the sealing properties and reduces the likelihood of exhaust entering the atmosphere. This enhances the seal between the two flanges  120  and  126  and reduces further outward deflection of the curved flange  126  after the mounting nuts  136  are tightened onto the mounting bolds  134 . Although not shown, the exhaust flange assembly further comprises a gasket which is retained in the gasket recesses  124  and  130  of the flanges.  
     [0133]FIG. 27 shows yet a further embodiment of an exhaust flange assembly. The assembly comprises a gasket element  150  arranged between a second flange  154  and a first flange  152 . The second flange  154  comprises a recess  156  with sloping side walls  158 , which generally conform in shape to a curved surface  159  of the gasket element  150  having an inner diameter  160 . The second flange  154  also comprises mounting holes  162 . Similarly, the first flange  152  comprises a recess  164  with sloped side walls  166 , which generally conform in shape to the curved surface  159  of the gasket element  150  having an inner diameter  168 . The first flange  152  also comprises mounting holes  170 .  
     [0134] The gasket element  150  has an inner diameter  172 , substantially the same as inner diameters  160  and  168  and further comprises a flange gap defining protrusion  174  arranged along its circumference. When fastening means, in the form of mounting bolts  176 , are inserted into the mounting holes  162  and  170  of the second and first flanges  154  and  152 , respectively, and a mounting nut  178  is tightened onto each mounting bolt  176 , the two flanges  152  and  154  are drawn together and compress the gasket element  150 , which reduces the amount of amount of float (relative movement of the flanges) to provide an enhanced leak resistance and therefore improved sealing characteristics for the exhaust flange assembly. Also, the complementary shape of the mating surface of the flanges allows for the flanges to move with respect to each other however, retaining their sealing properties. In operation, the exhaust flows from the exhaust pipe through the inner diameters of the flange assembly to an exhaust pipe at the other end of the assembly.  
     [0135]FIGS. 28 and 29 show a further embodiment of an exhaust flange assembly comprising a composite gasket element  200  arranged between a second flange  204  and a first flange  202 . The first flange  202  is identical to the first flange  152  of FIG. 27 while the second flange  204  comprises mounting holes  206  and a substantially cylindrical flange extension  208  for attachment to an exhaust pipe (not shown). Further, the second flange  204  has a backing plate portion  210  arranged on the same side of the flange as the flange extension  208 . The backing plate portion  210  has an inner diameter  212  and an inner surface  214 , facing away from the flange extension side of the flange  204 . The inner surface  214  of the flange  204  is larger than the inner diameter  212  of the backing plate portion  210 . The composite gasket element  200  has a curved surface  218 , generally conforming in shape to the recess  164  and the sloping side walls  166  of the first flange  202  and has an inner diameter  220 , substantially the same as the inner diameters  168  and  212  of the first and second flanges  202  and  204 , respectively. The gasket element  200  further comprises an outer surface  222  and a substantially flat surface facing the second flange  204 . When mounting bolts (not shown) are inserted into the mounting holes  206  and  170 , and a mounting nut (not shown) is tightened onto each mounting bolt, the two flanges compress the gasket element  200  to provide an enhanced leak resistance for the flange assembly. The backing plate portion  210  retains the composite seal between the second flange  204  and the composite gasket element  200 . FIG. 29 shows the second flange  204  and the first flange  202  mated with the gasket  200  there between. In operation, the exhaust flows from the exhaust pipe through the inner diameters of the flange assembly to an exhaust pipe at the other end of the assembly.  
     [0136]FIGS. 30A and 30B show a further embodiment of an exhaust flange assembly similar to the embodiments shown in FIGS.  27  to  29 . A composite gasket element  220  is bonded to a second flange  222 , seen as an inner flange, by pressing and sintering the gasket element  220  and the flange  222  in one sintering step, or by sintering the inner flange  222  first then inserting the pressed gasket element  220  and sintering again. The composite gasket element  220  is arranged between a first, or outer, flange  224  (similar to the first flange  152  as described in FIG. 27) and the inner flange  222 . The inner flange  222  has mounting holes  226  and a backing plate portion  228  arranged on the side of the flange away from the gasket  220 . The backing plate portion  228  has an inner diameter  230  and an inner surface  232  facing away from the backing plate portion  228 . The inner flange  222  has a general inner diameter  234 , which is larger than the inner diameter  230  of the backing plate portion  228 .  
     [0137] The composite gasket element  220  has a curved surface  236 , generally conforming in shape to the recess  164  and sloping side walls  166  of the first flange  224 . The composite gasket element  220  further comprises an inner diameter  238 , substantially the same as the inner diameters  230  and  168  through which the exhaust flows.  
     [0138]FIGS. 31A and 31B show yet another embodiment of a unisex flange  250  which may be used as both the first and second flanges of an exhaust flange assembly. The flange  250  comprises an annular gasket recess  252 , which has an inner wall  254  and an outer wall  256 . Further, the flange  250  has mounting holes  258 , and an inner diameter  260 . The inner wall  254  and the outer wall  256  form at least one squeeze area  262 , 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 (substantially equal to the diameter of the inner wall  254 ). In this manner, the gasket is formed to fit within the groove with the four pressure points, squeeze areas, providing the pressure to retain the gasket. In other words, the generally circular gasket is stretched to fit over the substantially oval gasket recess  252  whereby the stretching of the gasket creates squeeze areas in its circumference which serve as pressure points for retaining the gasket on the gasket recess. The gasket (not shown) is also held in the gasket recess  252  after being inserted. Preferably, two such squeeze areas  262  are defined in the gasket recess  252 . FIG. 31B is a cross-sectional view taken along the line  31 B- 31 B of FIG. 31A.  
     [0139]FIGS. 32A and 32B show an alternative embodiment of a unisex flange  300  having an annular gasket recess  302  comprising an inner wall  304  and an outer wall  306  with the inner wall having an inner diameter  310 . At least one protrusion  312  is arranged along the inner wall  304  or the outer wall  306  to form at least one squeeze area  314 , where the width of the gasket recess is substantially narrower than a maximum gasket recess width so that the gasket is held in the gasket recess after insertion. Preferably, multiple squeeze areas  314  are defined in the gasket recess  302  by multiple protrusions  312  on the inner wall  304 . The flange  300  further comprises mounting holes  308 . FIG. 32B is a cross-sectional view taken along the line  32 B- 32 B of FIG. 32A.  
     [0140]FIG. 33 shows a further embodiment of an exhaust flange assembly similar to the embodiment shown in FIGS. 30A and 30B. The exhaust flange assembly comprises a first flange  320  and a second flange  322 . The first flange  320  is similar to the first flange  152  described with respect to FIG. 27 while the second flange  322  has mounting holes  326  and a backing plate portion  328  arranged on the side of the flange opposite the gasket  324 . The backing plate portion  328  has an inner diameter  330  and an inner surface  332 , facing away from the flange gasket  324 . The first flange  320  has a general inner diameter  334 , which is larger than the inner diameter  330  of the backing plate portion  328 . A composite gasket element  324  is bonded to the second flange  322 . The composite gasket element  324  is located between the first flange  320  and the second flange  322 . The composite gasket element  324  has a curved surface  336 , generally conforming in shape to the recess  164  and sloping side walls  166  of the first flange  320 . The composite gasket element has an inner diameter  338 , substantially the same as the inner diameters  330  and  168 . Additionally, the composite gasket element  324  has a gasket recess  340  arranged on the curved surface  336 , to receive an additional annular sealing gasket (not shown).  
     [0141]FIG. 34 shows still a further embodiment of an exhaust flange assembly similar to the embodiment shown in FIG. 33. The first flange  320  of FIG. 34 is the same as the first flange  320  of FIG. 33. A second flange  342  comprises an inner diameter  344 , mounting holes  346  and a protrusion  348 . The protrusion  348  has a curved surface  350  which cooperates with the first flange  320  in that it generally conforms in shape to the recess  164  of the first flange  320 . Additionally, the protrusion  348  has a gasket recess  352  arranged on the curved surface  350 , to receive an additional annular sealing gasket (not shown).  
     [0142]FIG. 35 shows yet a further embodiment of an exhaust flange assembly comprising a second flange, seen as an inner flange,  370  with an exhaust mounting extension  372 , mounting holes  374 , gasket recesses  376  and a sealing extension  378 . A first flange, seen as an outer flange,  380  has an exhaust mounting extension  382 , mounting holes  384 , gasket recesses  386  and a sealing recess  388  having an outer diameter  390  substantially corresponding to the outer diameter of the sealing extension  378 . The sealing extension  378  and the sealing recess  388  thus cooperate to provide a seal when the flanges are mated as well as enhanced alignment assistant between the two flanges. The flanges are fastened together using fastening means comprising bolts  392  and nuts  394  with a gasket located between the two flanges. The sealing extension  378  adds rigidity to the flange joint and maintains pipe alignment when the flanges are mated. Exhaust pipes are connected to the mounting extensions  372  and  382  using a roll-forming process as described above.  
     [0143]FIG. 36 shows yet a further embodiment of an exhaust flange assembly. The assembly comprises a second flange  400 , seen as an inner flange, comprising an exhaust mounting extension  402 , mounting holes  404  and an annular gasket holding ridge  406  with a base  408  and a first flange  410 , seen as an outer flange, comprises an exhaust mounting extension  412 , mounting holes  414  and an annular gasket holding recess  416  with an annular ring  418 . The gasket holding ridge  406  and the gasket holding recess  416  thus cooperate to positively hold a shaped gasket  420  to provide a positive seal and enhanced alignment between the two flanges  400  and  410 . The flanges  400  and  410  are fastened together using fastening means such as bolts  422  and nuts  424 .  
     [0144]FIGS. 37 and 38 provide detailed schematic views of the shaped gasket  420 . The gasket  420  comprises a gasket inner diameter  426 , which is substantially the same or larger than the inner diameters of the exhaust openings of the flanges. The gasket holding ridges  416  mate with a gasket ridge holder  428  while the other end of the gasket ridge holder  428  rests in the gasket holding recess. The gasket ridge holder  428  comprises an edge  430 . The gasket has five sealing surfaces on its “hat”-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.  
     [0145]FIGS. 39A to  42  show a further embodiment of a flange joint. FIGS. 39A and 39B are schematics of an outer flange  450  comprising a conical rib  452  on a sealing surface  454  of the outer flange  450  which cooperates with a conical recess  464  of an inner flange  453  (as shown in FIGS. 40A and 40B). The outer flange  450  further comprises a pipe attachment surface  456  having a pipe attachment means  458 . An exhaust through hole  460  is arranged in the outer flange  450  for passage of exhaust gas when the flange is assembled as part of the exhaust system flange joint. Mounting holes  462  are also arranged through the outer flange  450 .  
     [0146] The inner flange  453  comprises a conical recess  464  on a sealing surface  466  of the inner flange  453 . The inner flange  453  further has a pipe attachment surface  468  having a pipe attachment means  470 . An exhaust through hole  472  is arranged in the inner flange  453 , for passage of exhaust gas when the flange  453  is assembled as part of an exhaust system flange joint. Mounting holes  474  are also arranged through the outer flange. FIG. 41 shows an exhaust flange assembly comprising the mating of the outer flange  450  and the inner flange  453  while FIG. 42 shows the exhaust flange assembly of FIG. 41, with the outer flange  450  and the inner flange  453  joined to respective pipes  478  with connecting bolts  480  and nuts  482  used to draw the two flanges together. When the inner and the outer flanges  453  and  450 , respectively, are fastened together, the conical rib  452  and the conical recess  466  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.  
     [0147]FIGS. 43A and 43B show a further embodiment of a second flange, or inner flange, while FIGS. 44A and 44B show yet another embodiment of an inner flange.  
     [0148] In FIGS. 43A and 43B, the inner flange  500  mates with an outer flange  502  which is identical to the outer flange  370  of FIG. 33. The inner flange  500  is manufactured in two parts and comprises a flat part (backing plate) which has mounting holes  504 , a central through hole  506 , a recess  508  with an end wall  510  and a sealing part  512 . 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  512  has an outwardly curved surface  514  generally corresponding to the recess  516  with sloping side walls  518  of the outer flange  502 . The sealing part further has a recess  520  having an inner annular surface  522 . The sealing part  512  also has an outer annular sealing surface  524 . The sealing part  512  further has an inner diameter  526 , smaller than the inner diameters (central through hole)  506  and  528 , respectively, of the inner flange and the outer flange. The two parts of the inner flange  500  are made in separate pressing operations and assembled and bonded in a sintering 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 inner flange recess  508  contacts the sealing part recess  520 , and the inner flange recess end wall  510  contacts the outer annular sealing surface  524 , whilst the sealing part inner annular surface  522  contacts the surface of the central through hole  506 , forming mating surfaces for the two parts. Thus, the inner flange recess has a shape cooperating with and corresponding to the shape of the sealing part recess. For the two-piece inner 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 inner 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 inner 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.  
     [0149] As is shown in FIGS. 43A and 43B, the inner flange  500  may have two mounting holes  504  and a single step recess  508 , as described above.  
     [0150] An alternative embodiment of an inner flange  530  is shown in FIGS. 44A and 44B. The inner flange  530  has three mounting holes  532  and a multi-stepped recess  534  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 inner flange and a outer flange easier, and the multi-stepped recess enlarges the surface area between the two parts of the inner flange, which enhances the bonding between the two parts after final sintering. The inner flange  530  further comprises a centre through hole  536 . It will be understood that the inner flange  530  may also be used in the exhaust flange assembly of FIG. 45.  
     [0151] Turning to FIG. 47, an exhaust flange assembly, similar to the exhaust flange assembly described with respect to FIG. 42 is shown. The outer flange  453  is identical to the outer flange  453  described in FIG. 42 while the inner flange  450  includes a pair of integral stand-offs  540  which receive the fastening means  480  and provide support to the fastening means.  
     [0152] As is shown in FIGS. 48A and 48B, an outer flange  550  may be of two-piece construction (as outlined in FIGS. 43A to  46 ). The outer flange  550  comprises a flat part (backing plate) which has mounting holes  552 , a central through hole  554  and a recess  556  with an end wall  558 , and a sealing part  560 . 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  560  has an inwardly curved surface  562 . The sealing part further has a recess  564  having an inner annular surface  566  and an outer annular surface  568 . The sealing part  560  further has an inner diameter  570 , smaller than the central through hole  554 . The two parts of the outer flange  550  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 outer flange recess  556  contacts the sealing part recess  564 , and the outer flange recess end wall  558  contacts the outer annular sealing surface  568 , whilst the sealing part inner annular surface  566  contacts the surface of the central through hole  554 , forming mating surfaces for the two parts. Thus, the outer flange recess has a shape cooperating with and corresponding to the shape of the sealing part recess. For the two-piece outer 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 outer 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 outer 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.  
     [0153] Turning to FIGS.  49  to  52 , flow charts outlining methods of manufacturing the various embodiments of the flanges are shown. In the method of FIG. 49, the back plate of the flange is manufactured using a stamping process (step  600 ) while the sealing part (the recess or the rounded edge) of the flange is manufactured using a powder metallurgy process (step  602 ). After the sealing part of the flange is manufactured, the sealing part is pre-sintered (step  604 ). The sealing part and the back plate are then placed in contact and sintered together (step  606 ) and assembled as a flange (step  608 ).  
     [0154] In the method of FIG. 50, the back plate is manufactured using a stamping process (step  610 ) while the sealing part is manufactured using a powder metallurgy process (step  612 ) and then sintered (step  614 ). After the sealing part is sintered, the back plate and the sealing part are assembled (step  616 ) and then welded or bonded together to form the flange (step  618 ).  
     [0155] In the method of FIG. 51, the back plate and the sealing part are both manufactured using a powder metallurgy process (steps  620  and  622 ) and then pre-sintered (steps  624  and  626 ). After being pre-sintered, both the back plate and the sealing part are assembled together (step  628 ) and then sintered together to form the flange (step  630 ).  
     [0156] In the method of FIG. 52, both the back plate and the sealing part are manufactured via a powder metallurgy process (steps  632  and  634 ), assembled (step  636 ) and then placed in contact and sintered together to form the flange (step  637 ).  
     [0157] During the manufacture of the sealing part via a powder metallurgy process, the material of the sealing part may be selected to minimize the co-efficient of expansion to reduce the wear on a gasket if a gasket is required.  
     [0158] FIGS.  53  to  62  provide yet further embodiments of exhaust flange assemblies in which an angled flange assembly is provided whereby the angle is between a longitudinal direction of an exhaust pipe and the flange itself.  
     [0159] In the embodiment shown in FIGS. 53 and 54, the flange assembly  640  comprises a first flange  642  and a second flange  644 . Both of the flanges  642  and  644  comprise a substantially flat edge  646  (having a recess  648 ) and a spherical end  650 . Each recess  640  is shaped to receive one end  652  of an angled exhaust pipe  654 . The ends  652  of the angled exhaust pipe  654  are generally connected to the recesses  640  of the flanges  642  and  644  by welding, brazing or other known bonding processes to manufacture a flange assembly having a pre-determined angle between the mounting faces of the flanges. FIG. 54 shows a flange assembly with the flanges connected to the angled exhaust pipe.  
     [0160] Turning to FIGS. 55 and 56, another flange assembly  660  comprising a flange  662  having a flat edge  664  with a recess  666  and a spherical edge  668  is shown. The recess  666  is frusto-conical, seen as a truncated cone, allowing an exhaust pipe  670  with an angled end, i.e. the end is not perpendicular to a longitudinal direction of the pipe, to be inserted and fastened to the flange  662 . A shoulder  672  is arranged on the pipe  670  so that, after the pipe  670  has been fastened to the flange  662 , there is little or no gap between the flange  662  and the pipe  670  so that exhaust does not leak from the flange assembly during use.  
     [0161] Turning to FIGS. 57 and 58, yet a further angled flange assembly is shown. The flange assembly  672  comprises a flange  674  having a flat edge  676  with a recess  678  and a spherical edge  680  is shown. In this embodiment, the flange  672  is angled with the recess  678  adapted to receive an end  682  of the exhaust pipe  684 . The angle in the flange  674  is provided so that non-linear connections may be achieved in the exhaust system. The pipe  684  is fastened to the flange  674  by a method such as welding.  
     [0162] Turning to FIGS. 59 and 60, another angled flange assembly  686  is shown comprising a flange  688  comprising a flat edge  690  having a recess  692  and a spherical edge  694  is shown. The flange assembly  686  further comprises an angled portion  696 . Both the flange  688  and the angled portion  696  are advantageously manufactured via a powder metallurgy process and are sintered together after optional pre-sintering steps. The desired angle of the flange assembly is thus provided by the angled portion  696 . An exhaust pipe  698  is fastened to the angled portion  696  either by welding or brazing. Alternatively, the pipe  698  may be inserted in a recess in the angled portion  696  (not shown).  
     [0163] Turning to FIGS. 61 and 62, an angled flange assembly  700  comprising a flange  702  having a mating edge  704  with a recess  706  for receiving a an exhaust pipe  708  having a shoulder  710  is shown. The exhaust pipe is attached to the flange via press-fitting, spinning, resistance welding, crimp rolling or other known processes.  
     [0164] Turning to FIG. 63, a further embodiment of an exhaust flange assembly in accordance with the present invention is shown. The flange assembly  712  comprises a first flange  714  formed with a pair of integral spacers  716  using a powder metallurgical process and a second flange  718 . The first flange  714  further comprises a pair of holes  719  for receiving fastening means, in the form of bolts  720 , which assist in securing the connection between the flanges  714  and  718  when they are mated. The bolts  720  are secured by individual nuts  722 . The spacers assist in aligning the two flanges when they are to be mated.  
     [0165] The first flange  714  further comprises a recess  724  for receiving a complementary shaped abutment  726  located on the surface of the second flange  718  to assist in the mating process to align the flanges  714  and  718 .  
     [0166] Turning to FIGS. 64 and 65, another embodiment of a flange assembly is shown. In this embodiment, the flange assembly  730  includes a first flange  732  comprising a pair of spacer recesses  734  connected to mounting holes  735  for receiving fastening means, in the form of a bolt  734 , and a recess  736  for receiving a complementary shaped abutment  738  on a second flange  740 . Spacers  742 , preferably manufactured using a pressing process, are inserted into the pair of spacer recesses  734  and fastened to the first flange  732  via sintering. After the bolts  732  are inserted into the spacer recesses  734  and the spacers  742 , nuts  744  are used to secure the connection between the two flanges by tightening them on the bolts.  
     [0167] Alternatively, as shown in FIGS. 66 and 67, the spacers  746  may be aligned with the mounting holes  748  and held in place during the sintering process.  
     [0168] In the embodiments shown in FIGS.  64  to  67 , a brazing alloy may advantageously be used between the spacer and the first flange to improve the bonding between the two parts. Furthermore, the spacers and/or the flange may be pre-sintered and assembled before the final sintering process.  
     [0169] Advantageously, the present invention overcomes some of the problems in prior art exhaust flange assemblies. Firstly, by using a powder metallurgy process to manufacture the flanges, more complex flange shapes may be achieved. Also, the powder metallurgy process is also less expensive than some of the methods in the prior art.  
     [0170] Moreover, the embodiments of the present invention also reduces or eliminates the amount of exhaust which escapes into the atmosphere by providing mating surfaces on the flanges which are complementary to each other. This also assists in providing alignment to the flanges. Also, the use of spacers allows for further alignment of the flanges. Use of ribs or through holes also allows for a flange that is lighter than some prior art flanges.  
     [0171] When gaskets are required, the mating surfaces of the flanges assist in retaining the gaskets so that they do not fall out during assembly of the exhaust flange assembly. This may also be assisted by integral fastening means which are manufactured as part of the flange so that there is less opportunity for the fastening means to slip out during assembly.  
     [0172] 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 tightening 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.  
     [0173] Preferably, the outer flange is made of one material and the inner 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.  
     [0174] Preferably, the materials used for making the flanges contain between 0.75 to 1 weight percent of hexagonal boron nitride (BN), which enhances the corrosion resistance properties of the powder metallurgical materials used, as disclosed in U.S. Pat. No. 6,103,185.  
     [0175] 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.  
     [0176] The invention provides a number of advantages such as the inclusion of 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 and that the sealing configuration avoids a direct escape path for exhaust gases, thereby potentially reducing the need for gaskets and potentially reducing emissions.  
     [0177] Furthermore, 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.  
     [0178] As will be understood, although not expressly shown in each figure, it will be understood that each of the flanges comprises means for attaching to an exhaust pipe.  
     [0179] The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.