Abstract:
A method for manufacturing an exhaust gas converter and a tool for the method are provided. The method includes providing a cylindrical metal pipe and a cylindrical substrate surrounded in a circumferential direction by a mat mount. The substrate is deposited with the mat mount surrounding it inside the metal pipe. A compression force is exerted on the metal pipe, directed in a radial direction, for reducing the cross-section of the metal pipe to a desired size. Regions to which a compression force is applied alternate along the circumferential direction of the metal pipe with regions to which no compression force is applied. A number of regions where no compression force is applied to the metal pipe exceeds the number of tools used for applying the compression force. The tool ( 4 ), for a ring press, includes a tool body including a mounting section and a work section with recesses ( 45 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application 10 2014 218 960.8 filed Sep. 19, 2014, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for the manufacture of an exhaust gas converter and to an exhaust gas converter that can be manufactured using a ring press. The present invention further relates to a ring press and a special tool for said ring press. 
       BACKGROUND OF THE INVENTION 
       [0003]    A manufacture of exhaust gas converters often requires disposing a substrate inside a metal jacket. The substrate may be, for example, a metal support or a ceramic support. The substrate may be a monolithic substrate, for example. Between the substrate and the metal jacket a mat mount is often provided. The process of disposing the substrate inside the metal jacket is also referred to as “canning” The objective of canning is to safely dispose the substrate inside the metal jacket, whereby any damage to the substrate is to be avoided. Respective exhaust gas converters also include catalytic converters. 
         [0004]    Different canning procedures are known for this purpose: 
         [0005]    In the push canning procedure, the substrate is pushed into a metal pipe together with the mat mount surrounding the substrate. A connection geometry is then fitted to both ends of the metal pipe, which prevents the substrate and the mat mount from slipping out of the metal pipe. A detriment of the procedure is the comparatively large clearance required between an inner wall of the metal pipe and an outer side of the mat mount surrounding the substrate to allow the substrate to be placed inside the metal pipe without damaging the mat mount. There is also a risk that the clearance increases in response to the mat mount being compacted on a later stage during operation. 
         [0006]    In the wrap canning procedure, the substrate with the mat mount surrounding the substrate is wrapped with a sheet metal strip. The sheet metal strip&#39;s circumferential lines are joined together in an airtight manner. A detriment of this procedure is that it makes manufacture complex. Further, long seams remain whose leak tightness has to be ensured. 
         [0007]    In the shrink canning procedure, the substrate with the mat mount surrounding the substrate is pushed into a pipe section with the pipe section being gauged from outside afterwards. Thereafter, a connection geometry is fitted to both ends of the metal pipe, which prevents the substrate and the mat mount from slipping out of the metal pipe again. A ring press configured for being used for a manufacture of exhaust gas converters according to the shrink canning procedure is known from WO 2011/011893 A1. As an alternative to usage of a ring press it is known from U.S. Pat. No. 7,316,142 B2 to use a spin forming method and apparatus to form different diameters and shapes on a workpiece such as a metal tube. In a spin forming apparatus and method, various spin forming rollers are actuated to extend and retract radially relative to a workpiece therein. The workpiece is rotated around its axis while the spin forming rollers apply pressurize the workpiece in radial direction. The spin forming rollers may be shifted in axial direction of the workpiece during pressurizing the workpiece. It is typical for the spin-forming method and apparatus that the spin forming rollers perform a rolling movement along the circumferential surface of the workpiece. 
         [0008]    In the half-shell canning procedure, the substrate with the mat mount surrounding the substrate is placed between half-shells made from metal sheet. The half-shells are then sealed in a press. A detriment are the resulting relatively long seams whose leak tightness has to be ensured. 
         [0009]    The canning procedures described above are disadvantageous in that they are either complex, are problematic with respect to their reliability because of their long seams, or have too much clearance between the metal jacket and the substrate surrounded by the mat mount. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide a method for the manufacture of an exhaust gas converter, a ring press configured for carrying out the method, an appropriate tool for the ring press, and an exhaust gas converter manufactured using the ring press, the ring press enabling a manufacturing of the exhaust gas converter at low cost. The clearance between the metal jacket and the substrate of a thus manufactured exhaust gas converter should further be small and by avoiding long seams a reliable converter should be achieved. 
         [0011]    Embodiments of a method for a manufacture of an exhaust gas converter comprise the steps of providing a cylindrical metal pipe, providing a cylindrical substrate surrounded in a circumferential direction by a mat mount, with the cross-section of the substrate including the mat mount being less or equal than the cross-section of the metal pipe, of disposing the substrate with the mat mount surrounding the substrate inside the metal pipe, and of applying a compression force to the metal pipe, the compression force being directed in a radial direction of the metal pipe for reducing the cross-section of the metal pipe to a given size. In the step of applying a compression force to the metal pipe, regions having the compression force applied thereon alternate with regions having no compression force applied thereon in at least one of the circumferential direction and the axial direction. The number of regions where no compression force is applied to the metal pipe further exceeds the number of tools used for applying the compression. 
         [0012]    Since the cross-section of the metal pipe prior to application of compression is bigger than the substrate including the mat mount, the substrate with the mat mount surrounding the substrate may easily be disposed inside the metal pipe. Due to the reduced cross-section of the metal pipe after application of the compression, the mat mount surrounding the substrate safely mounts the substrate inside the metal pipe of the exhaust gas converter. Also a compacting of the mat mount at a later time due to temperature action may hereby be taken into account. The metal pipe thus provides an enclosure wall (a metal jacket) of the exhaust gas converter and protects the substrate from mechanical and chemical impacts from outside. The application of compression enables a true to dimension sizing of the metal pipe&#39;s cross-section. Since the number of regions where no compression is applied to the metal jacket exceeds the number of tools used for applying the compression, at least one of the tools used for applying compression has more than one region, where the tool abuts against the metal pipe to be compressed. This results in a reduction of the friction between the metal pipe and the tool, thus enabling a sliding of the metal pipe relative to the tool during application of compression resulting in a better distribution of the material of the metal pipe displaced due of the compression. 
         [0013]    According to an embodiment, the cylindrical metal pipe is stationary when the tool abuts against the pipe to be compressed. Thus, the cylindrical metal pipe is not rotated when being pressurized. According to an embodiment, even the tool does not rotate about the cylindrical metal pipe when applying pressure on the cylindrical metal pipe. 
         [0014]    According to an embodiment, the cylindrical metal pipe has a circular cross-section. According to an alternative embodiment, the cylindrical metal pipe has an oval cross-section. 
         [0015]    The metal pipe may for instance be made of stainless steel. The diameter of the metal pipe may for instance be from within 200 mm to 400 mm and the length of the metal pipe may be up to 400 mm. The wall thickness of the metal pipe may for instance be from 0.3 mm to below 1 mm and/or within 1 mm to 3 mm. According to an embodiment, the wall thickness of the metal pipe is constant along the whole of the metal pipe&#39;s circumference and length. 
         [0016]    The mat mount may for instance be a high-temperature insulation wool (e.g. alkaline earth wool, aluminium silicate wool, or polycrystalline wool comprising Al 2 O 3  in a content of more than 70% by weight), and provides a thermal insulation between the substrate and the metal pipe. The mat mount may further provide a certain damping effect and thus prevent damage to the regularly brittle substrate caused by mechanical impacts. 
         [0017]    The substrate may for instance be a metal support or a ceramic support having a catalyst applied thereon and providing fine channels for the exhaust gas to be purified. 
         [0018]    According to an embodiment, the application of compression reduces the cross-section of the metal pipe by at least 3% or at least 5%, or at least 10% with regard to the diameter of the metal pipe prior to applying compression. 
         [0019]    According to an embodiment, the cross-section of the metal pipe after application of compression is smaller than the cross-section of the substrate including the mat mount prior to application of compression. Hence, the mat mount is slightly compressed by the metal pipe after application of compression to the metal pipe. 
         [0020]    According to an embodiment, the method comprises a capping of the metal pipe&#39;s axial ends with funnels, the funnels being welded, soldered or flanged to the metal pipe. Applying compression allows the cross-section of the metal pipe to be formed into a desired shape, enabling low tolerances for fitting the funnels to the metal pipe. Low tolerances of less than 0.8 mm allow placing steady welding seams between the metal pipe and the funnels. 
         [0021]    According to an embodiment, the method further comprises a heating of the metal pipe to a temperature of between 100° C. and 600° C. prior to exposing the metal pipe to a compression force. At this temperature, the metal pipe can be formed very easily while having sufficient stability. Alternatively, an application of compression force may also be performed within a temperature range from 20° C. to 100° C. 
         [0022]    Embodiments of a tool for a ring press comprise a tool body. The tool body may be made from metal and in particular from hardened tool steel. The tool body may be solid. The tool body extends in an axial direction of the ring press, extends in a radial direction of the ring press, and extends in a circumferential direction of the ring press. The tool body comprises a mounting section and a work section, the mounting section and the work section being provided on two, with respect to a radial direction of the ring press, opposite sides of the tool body. The mounting section is configured for mounting the tool at the ring press. The mounting section may hereto be provided with appropriate protrusions, grooves or threads configured to engage in grooves, protrusions or threads of the ring press. The work section comprises a tangential surface resembling a lateral area of a right cylinder. In other words, the work section is shaped like a gutter. The curvature of the gutter, in a direction transverse to a longitudinal extension of the gutter, may hereby be constant or variable. The work section is configured to exert pressure onto a jacket of the exhaust gas converter. The working section further comprises a plurality of recesses, the maximum depth of the recesses in radial direction being at least 1/20 mm or at least 1/10 mm or at least ⅕ mm. The recesses are ignored by the tangential surface. Resulting from this, the tool comprises more than one region where the tool&#39;s work section abuts against the jacket of the exhaust gas converter. 
         [0023]    In order to match the inner diameter of the tubular metal jacket of an exhaust gas converter to the outer diameter of a substrate received in the metal jacket, the metal jacket with the substrate disposed inside the metal jacket and the mat mount positioned between the substrate and the metal jacket is put in a ring press that applies a radial pressure to it. Ring presses are also referred to as radial presses or (when the material to be processed is heated-up beforehand) as radial forging machines. For this purpose, the ring press comprises several tools that can be moved in a radial direction and allowing to exert pressure onto the work piece (the jacket of the exhaust gas converter in this case). Respective tools are also referred to as “shrinker jaws”. Allowing a radial movement of the tools requires provision of a gap between each of the tools disposed adjacently in a circumferential direction of the ring press. Due to the gap present between the tools, exerting a compression pressure to the work piece may result in material advancing between the tools. In the worst case this may result in the work piece being ruptured and becoming unusable. 
         [0024]    By providing, according to the invention, recesses in the work section of the tool, the area abutting the jacket of an exhaust gas converter to which compression is to be applied is reduced. This results in a reduction of friction caused by adhesion between the tool and the jacket of the exhaust gas converter. The recesses ventilate the jacket of the exhaust gas converter. The jacket may thus perform a sliding movement relative to the tool in the circumferential direction of the jacket. This enables a two-dimensional distribution of the pressurized material of the exhaust gas converter&#39;s jacket as far as possible. A creasing of the jacket concentrating on the circumferential line of the tool&#39;s work section may thus be prevented. The recesses also provide additional space for the material to be displaced in a controlled manner. 
         [0025]    According to an embodiment the whole area of each work section of the tools is in contact with an outer surface of the metal jacket when pressurizing the metal jacket; however, the recesses of the tools are not in contact with an outer surface of the metal jacket when pressurizing the metal jacket. According to an embodiment the tools are not suitable to perform a rolling movement along an outer surface of the metal jacket when pressurizing the metal jacket. 
         [0026]    According to an embodiment the term “a plurality of recesses” includes the case in which one single recess or more than one recess is provided in the working section of each tool. According to an alternative embodiment the term “a plurality of recesses” includes the case in which at least two recesses are provided in the working section of each tool. 
         [0027]    According to an embodiment, the shape of the work section corresponds to a desired final form of the exhaust gas converter&#39;s jacket. According to an embodiment, the curvature of the tangential surface of the work section corresponds to the desired curvature of the jacket of the exhaust gas converter. 
         [0028]    According to an embodiment, the maximum depth of the recesses in a radial direction is not more than 20 mm or not more than 10 mm or not more than 5 mm or not more than 2 mm or not more than 0.5 mm. More shallow depths of the recess guarantee that the jacket of the pressurized exhaust gas converter nevertheless abuts the working section of the tool two-dimensionally. 
         [0029]    According to an embodiment, at least one recess extends along the whole extension of the work section in an axial direction or circumferential direction. In other words, the recess runs through the entire extension of the work section. 
         [0030]    According to an embodiment, all recesses extend in the axial direction or in the circumferential direction across the whole length of the work section. 
         [0031]    According to an embodiment, the recesses do not intersect. 
         [0032]    According to an embodiment, the recesses are equally spaced in pairs. Hence, the recesses are arranged regularly at least in sections of the tool&#39;s work section. 
         [0033]    According to an embodiment, the angular distance between adjacent recesses is of from between 1° and 5°, and in particular 2° relative to the center of the tangential area of the work section forming the lateral side of the corresponding cylinder. 
         [0034]    According to an embodiment, the distance between adjacent recesses is from between 10 mm and 2 mm or from between 6 mm and 4 mm. 
         [0035]    According to an embodiment, each of the recesses extends into the longitudinal direction and into the transverse direction, with the extension in the longitudinal direction and the extension in the transverse direction being orthogonal with respect to each other and orthogonal with respect to the extension in the radial direction, and with the extension in the longitudinal direction being at least 20 times as long as the extension in the transverse direction, or the extension in the longitudinal direction being at least 80 times as long as the extension in the transverse direction. Hence, the recesses have an elongated shape. According to an embodiment, the extension of the recess in the longitudinal direction defines the orientation of each recess. 
         [0036]    According to an embodiment, an extension of the recesses in the transverse direction does not exceed 10 mm, or does not exceed 5 mm, or does not exceed 3 mm. According to an embodiment, an extension of the recesses in the transverse direction is at most 5 times or 3 times or 1 time the wall thickness of the jacket of the exhaust gas converter to be pressurized. Hence, the recesses are comparatively narrow. 
         [0037]    According to an embodiment, each of the recesses has a cross-section in the shape of a segment of a circle or in the shape of a trapezoid. 
         [0038]    According to an embodiment, the work section of the tool is polished at least in those regions where no recesses are present. Hence, the work section has a smooth surface. 
         [0039]    According to an embodiment, the work section of the tool is chamfered at its transitions to the recesses and/or its circumferential line. Hence, the work section has no sharp edges. 
         [0040]    According to an embodiment, the work section of the tool comprises in the circumferential direction at least one first and one third section having the recesses provided therein, and a second section located between the first and third sections having no recesses provided therein. Each of the first, second and third sections extend in the circumferential direction of the tool across at least 5% and at most 50% of the work section. According to an embodiment, the first and third sections are located adjacent to an outer boundary of the tools&#39;s work section. 
         [0041]    According to an embodiment, the recesses occupy at least 3% or at least 30% of the work section&#39;s surface. 
         [0042]    Embodiments of a ring press configured for implementing the above method comprise a plurality of tools as described above. The ring press hereby retains the plurality of tools at their respective mounting sections. The ring press is further configured to move each tool of the plurality of tools in either of two opposite directions of movement, the opposite directions of movement running along straight lines, and the directions of movement of all tools of the plurality of tools intersect in one point. Respective ring presses are also referred to as radial presses, since the compressive force exerted on the body to be pressurized along a circular strip is applied in radial direction. 
         [0043]    According to an embodiment, the tools are mounted in the ring press in a circular arrangement, and an air gap is provided between each two tools disposed adjacently along the circular arrangement. 
         [0044]    According to an embodiment, the tools are mounted in the ring press in an oval arrangement, and an air gap is provided between each two tools disposed adjacently along the oval arrangement. 
         [0045]    According to an embodiment the ring press is adapted to prevent rotation of the pressurized body (such as the metal jacket) during pressurizing the body. 
         [0046]    Embodiments of an exhaust gas converter that may for instance be obtained by the above method using, for example the above ring press, comprise a cylindrical encasement made from sheet material, a cylindrical substrate disposed inside the encasement, and a mat mount located between the substrate and the encasement. The encasement thereby corresponds to the metal pipe described above. The encasement comprises a plurality of at least three protrusions. In a radial direction of the encasement, the protrusions have a maximum height of at least 1/20 mm or a maximum height of at least 1/10 mm or a maximum height of at least ⅕ mm. 
         [0047]    The protrusions receive a part of the material of the originally smooth encasement of the exhaust gas converter, and thus make sure that the diameter of the encasement is reduced with respect to its original diameter. The protrusions also increase the stability of the encasement and result in a self-centering of the encasement, for instance upon connecting funnels to the end section of the encasement. 
         [0048]    According to an embodiment, the cylindrical encasement has a circular cross-section. According to an alternative embodiment, the cylindrical encasement has an oval cross-section. 
         [0049]    According to an embodiment, the protrusions have, in a radial direction of the encasement, a maximum height of not more than 20 mm, or a maximum height of not more than 5 mm, or a maximum height of not more than 2 mm, or a maximum height of not more than 0.5 mm. The residual height different can be spanned well by welding seams, when the maximum height of the protrusions is less than 0.8 mm. 
         [0050]    According to an embodiment, the at least one protrusion extends across the whole extent of the encasement in an axial direction or in a circumferential direction of the encasement. According to an embodiment, all protrusions extend across the whole extent of the encasement in an axial direction or a circumferential direction. 
         [0051]    According to an embodiment, the protrusions are equidistantly spaced in pairs. 
         [0052]    According to an embodiment, the protrusions extend in the longitudinal direction and in the transverse direction, the extension in the longitudinal direction and the extension in the transverse direction being for each protrusion orthogonal with respect to each other and orthogonal with respect to the extension in the direction of the height of each protrusion. The extension in the longitudinal direction is also either at least 20 times as long as the extension in the transverse direction, or the extension in the longitudinal direction is at least 80 times as long as the extension in the transverse direction. 
         [0053]    According to an embodiment, the extension of the protrusions in the transverse direction does not exceed 10 mm, or does not exceed 5 mm, or does not exceed 3 mm. 
         [0054]    According to an embodiment, the cross-section of each protrusion has a shape like a segment of a circle, an arc of a circle, or a trapezoid. 
         [0055]    According to an embodiment, the encasement of the exhaust gas converter comprises in the circumferential direction at least one first and one third section having the protrusions formed therein, and the encasement of the exhaust gas converter comprises in the circumferential direction further a second section located between the first and third sections and having no protrusions formed therein. Along the circumferential direction of the encasement, the first, second, and third sections thereby extend across at least 5% and at most 50% of the encasement. 
         [0056]    According to an embodiment, the protrusions occupy at least 3% or at least 30% of the encasement&#39;s surface. 
         [0057]    Further features of the invention will be apparent from the following description of exemplary embodiments together with the claims and the Figures. In the Figures, like or similar elements are indicated by like or similar reference signs. It is noted that the invention is not limited to the embodiments of the exemplary embodiments described, but is defined by the scope of the attached claims. In particular, embodiments according to the invention may implement individual features in a different number and combination than the examples provided below. In the following explanation of exemplary embodiments of the invention, reference is made to the enclosed Figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0058]    In the drawings: 
           [0059]      FIG. 1  is a schematic cross-sectional view through a ring press according to an embodiment of the invention; 
           [0060]      FIG. 2A  is a schematic cross-sectional view through an embodiment of a tool configured for being used in the ring press from  FIG. 1 , with one edge of the tool shown in an enlarged representation; 
           [0061]      FIG. 2B  is a top view of part of a work section of the tool from  FIG. 2A ; 
           [0062]      FIG. 3  is a flow diagram according to an embodiment of a method for a manufacture of an exhaust gas converter; 
           [0063]      FIG. 4A  is a schematic cross-sectional view through an embodiment of an exhaust gas converter; and 
           [0064]      FIG. 4B  is a top view of an encasement of the exhaust gas converter from  FIG. 4A . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0065]    Referring to the drawings,  FIG. 1  shows a schematic cross-sectional view through a ring press  1  according to an embodiment of the invention. 
         [0066]    The ring press  1  comprises a machine body  2  made from cast iron and supporting a plurality of hydraulic cylinders  3 . The hydraulic cylinders  3  respectively allow a shifting of tools  4  supported by the hydraulic cylinders  3  between two extreme positions in a linear translation. The double arrows in  FIG. 1  illustrate this. In the embodiment shown, eight hydraulic cylinders  3  are arranged along a ring such that the tools  4  supported by the hydraulic cylinders  3  may be moved towards a common point or may be moved away from this common point. Taking the arrangement of the hydraulic cylinders  3  along the ring into account, each of the tools moves along a radial direction of the ring press  1 . 
         [0067]    It is noted that the present invention is not limited to a machine body made from cast iron or to cylinders activated hydraulically. The cylinders may, for example, alternatively be moved pneumatically or using a screw mechanism. Also the number and/or arrangement of cylinders may vary. 
         [0068]    Having hydraulic cylinders  3  support the tools  4  allows the ring press  1  to apply a force to a work piece (the encasement of an exhaust gas converter  6 ) located in the center of the ring press  1 . The hydraulic cylinders  3  are thereby coupled electrically or mechanically such that either all tools  4  move towards the work piece or all tools  4  move away from the work piece, and each of the hydraulic cylinders  3  exerts the same force on the work piece. To prevent the tools  4  moved by the hydraulic cylinders  3  from blocking each other, an air gap  5  of sufficient size is provided between tools  4  disposed adjacently in the circumferential direction of the ring press  1 . The air gap  5  is sized to be substantially closed for the tools having reached their radial inboard target position. In the target position of the tools  4 , for example, the distance between two tools  4  and thus the air gap  5  may in the circumferential direction of the radial press  1  be smaller than 1 mm. 
         [0069]    Referencing  FIGS. 2A and 2B , the tools  4  mounted on the hydraulic cylinders  3  of ring press  1  are explained in more detail below.  FIG. 2A  thereby shows a schematic cross-sectional view and  FIG. 2B  a schematic top view of a section of a tool  4  of the plurality of tools  4 . 
         [0070]    Tool  4  comprises a solid tool body  41  made from hardened tool steel. On one side, the tool body  41  has a work section  42  and on an opposite side a mounting section  43 . As shown in the enlarged view of the edge surrounding the work section  42 , this edge of the tool has a radius R 1 . Along the longitudinal sides of the tool, the radius R 1  (shown on the right side of  FIG. 2A  in an enlarged view) is less than 0.5 mm (in the embodiment of  FIG. 2A , the radius along the longitudinal sides is 0.3 mm), and along the transverse sides (i.e. orthogonally to the edge shown in an enlarged view in  FIG. 2A ; on of theses edges is shown on the top of  FIG. 2B ) between 1 mm and 3 mm (In the embodiment of  FIG. 3A , the radius along the broadsides is 2 mm). The longitudinal sides of tools disposed adjacently in the ring press  1  are positioned in parallel and adjacently in pairs. 
         [0071]    On the mounting section  43 , an elongate mount  43   a  made from unhardened tool steel and having a trapezoidal cross-section is fixed, configured for being inserted into a correspondingly shaped recess on a hydraulic cylinder  3  of the ring press  1  so that the tool  4  is fixed to the corresponding hydraulic cylinder  3  of the ring press  1  in a torque-proof manner. 
         [0072]    The complete work section  42  of the tool body  41  is curved with its form generally resembling a shallow gutter. In the following, the tangential surface  44  corresponding to the work section  42  matches a section of a right cylinder&#39;s lateral area. For a better overall view, the tangential surface  44  is delineated from the work section  42  in  FIG. 2A  by a small distance. In fact, the tangential surface  44  clings to the work section  42  with the distance between the tangential surface  44  and the work section  42  being zero. 
         [0073]    As can well be seen from an overall view of both  FIGS. 2A and 2B , parallel recesses  45  are introduced along a longitudinal extension of the work section  42  each having a width B of 3 mm and a depth of 0.5 mm. The angular distance between adjacent recesses  45  in the embodiment shown is, with respect to the center of the cylinder defined by the tangential surface  44  2°. The absolute distance between respective adjacent recesses  45  is 3 mm. 
         [0074]    Although  FIG. 2B  does not show the tool body  41  of tool  4  in its entire longitudinal extension, some of the recesses  45  extend in the longitudinal direction of the work section  42  and thus, in the axial direction of the ring press, along the entire length of the tool body  41 . Other recesses  45  do not extend along the entire length of work section  42 , the recesses  45  thus having different lengths. Alternatively, all recesses may have the same lengths. The recesses may, for example, extend up to the beginning of radius R 1  formed at an edge of work section  42 . 
         [0075]    As can be seen from  FIG. 2B , the recesses  45  are not distributed evenly over work section  42  of tool body  41  of tool  4 . In the embodiment shown instead, two regions S 1 , S 3  having recesses are provided at each of work section&#39;s  42  end sections defining the extension of work section  42  in the circumferential direction of ring press  1 , when the tool  4  is inserted in the ring press  1 , and between the two regions a region S 2  having no recesses is provided. In the embodiment shown, the regions S 1  and S 3  each extend across 25% of the work section&#39;s  42  surface, and region S 2  across 50% of the work section&#39;s  42  surface. In the embodiment shown, the recesses  45  occupy in total about 25% of the work section&#39;s  42  area. 
         [0076]    As can be seen from  FIG. 2A , recesses  45  each have a cross-section corresponding to a segment of a circle. The transitions from the recesses  45  to the work section are thereby chamfered. 
         [0077]    By providing recesses  45 , the work section  42  of tool  4  has more than one location where the work section  42  abuts the work piece to be pressurized. This results in a reduction of the friction between the work piece and the tool  4 , allowing the work piece to slide relative to tool  4  upon compression and thus a better distribution of the work piece&#39;s material displaced due to the compression. According to this it is possible to prevent an undesired piling up of material inside the air gap  5  between two tools  4  disposed adjacently along the circumferential direction of ring press  1  that would damage the work piece processed. 
         [0078]    A method for the manufacture of an exhaust gas converter using the ring press  1  shown in  FIG. 1  with tools  4  from  FIGS. 2A and 2B  is explained below referencing  FIG. 3 . 
         [0079]    First, a cylindrical metal pipe and a cylindrical substrate surrounded by a mat mount are provided in steps S 1  and S 2 . The substrate surrounded by the mat mount thereby has a smaller cross-section than the inside cross-section of the cylindrical metal pipe. The shape of the cross-section of the substrate surrounded by the mat mount corresponds to the inside cross-section of the metal pipe. 
         [0080]    Next, the substrate with the mat mount surrounding it is placed inside the metal pipe in step S 3 . This is achieved by pushing the substrate with the mat mount into the metal pipe. 
         [0081]    Then, the metal pipe is heated in step S 4  to a temperature of between 100° C. and 300° C., prior to applying compression force on the metal pipe in step S 5 . The latter is achieved by moving the tools  4  radially towards the metal pipe  1  disposed in the interior of ring press  1 , using the hydraulic cylinders  3  of ring press  1 . 
         [0082]    Afterwards, the hydraulic cylinders  3  are retracted into their starting position, and the metal pipe with the substrate and the mat mount placed therein is removed before the axial ends of the metal pipe are capped with funnels in final step S 6 . This may for instance be accomplished by putting on the funnels and welding the remaining seam. 
         [0083]    An exhaust gas converter which may be obtained using the ring press shown in  FIG. 1  and the method illustrated in  FIG. 3  will be described below referencing  FIGS. 4A and 4B . 
         [0084]    The exhaust gas converter  6  comprises an encasement  61 , having the form of a right cylinder and being made from sheet material, in the present case from stainless steel having a wall thickness of 1.5 mm. The diameter of the encasement is 300 mm, the length 400 mm. A cylindrical ceramic substrate  63  having a diameter of 290 mm and a length of 380 mm is located inside the encasement  61 . A mat mount  62  made from aluminum silicate is placed between the substrate  63  and the encasement  61 . The encasement  61  thereby slightly pressurizes the mat mount with regard to the substrate  63 . 
         [0085]    In the embodiment shown, the encasement  61  has at its outer face twelve protrusions  64  being 0.5 mm in height. The low number of protrusions  64  shown in  FIGS. 3A and 3B  has been chosen for a clear presentation only. Since each of the tools  4  inserted into the ring press  1  from  FIG. 1  has, according to  FIGS. 2A and 2B , eight recesses, and since eight tools  4  are inserted into the ring press  1 , the actual number of protrusions would be at least 64. To this further  8  protrusions may be added that are located in the regions of the ring gaps  5  between tools  4  disposed adjacently along the circumferential direction of the ring press  1 . 
         [0086]    As can be seen well from the top view in  FIG. 3B , the protrusions  64  extend along a straight line with adjacent protrusions being spaced equidistantly. Some protrusions  64  extend across the entire longitudinal extension of the encasement  61 , other protrusions  64  do not extend across the entire longitudinal extension of the encasement  61 , resulting in the protrusions  64  having different lengths. Alternatively, it is, however, also possible to have all protrusions  64  have the same length. 
         [0087]    Corresponding to the shapes of recesses  45  in the work section  42  of tools  4 , each of the protrusions  64  has a cross-section corresponding to a segment of a circle. 
         [0088]    Using ring press  1  shown in  FIG. 1  together with the tools shown in  FIGS. 2A and 2B , the protrusions would occupy 25% of the surface of the encasement  61  of the exhaust gas converter  6 . This is not shown in  FIGS. 3A and 3B . 
         [0089]    The protrusions  64  facilitate a centering when connecting a (not shown) metal funnel to the axial ends of encasement  61 . Due to the small height of protrusions  64 , a remaining gap may easily be welded and closed. Furthermore, material displaced upon compression of encasement  61  can be received in the protrusions  64 . 
         [0090]    Also on the surface of the encasement  61  of the exhaust gas converter  6  regions A 1 , A 3  having protrusions  64  formed therein alternate in the circumferential direction of encasement  61  with regions A 2  having not protrusions formed therein. 
         [0091]    Although in the above embodiments, the recesses in the work section of the tool are oriented parallel to an axial direction of the tool inserted into the ring press, the present invention is not limited thereto. The recesses may rather also be oriented at an angle to the axial direction, and even be orthogonal to the axial direction. 
         [0092]    Although in the above embodiments, the protrusions on the encasement of the exhaust gas converter are oriented parallel to an axial direction of the encasement, the present invention is not limited thereto. The protrusions may also be oriented at an angle to the axial direction, and even be orthogonal to the axial direction. 
         [0093]    Although in the above embodiments, the recesses in the work section of the tool and the corresponding protrusions on the encasement of the exhaust gas converter extend rectilinear, the present invention is not limited thereto. The recesses and protrusions may instead also be curvilinear. Further, there is no need for the recesses and protrusions to run across the entire extension of the work section of the tool and the encasement, respectively. There is even no need to have the recesses and protrusions formed elongate. The recesses and protrusions may alternatively be circular when shown in a top view. 
         [0094]    Although the above embodiments of the present invention have been explained by way of example only, those skilled in the art will recognize that numerous modifications, additions, and replacements may be made without departing from the scope and spirit of the invention disclosed in the claims below. While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.