FR2852539A1 - Catalytic converter housing manufacture comprises use of sheet metal casing cut and/or shaped to fit over substrate and having edges joined by butt welding - Google Patents

Abstract

A catalytic converter (10), especially for IC engine exhaust gases comprises a gas-permeable substrate (12) with a catalytic coating inside a casing (18) of sheet metal measured, cut and/or shaped to fit over the substrate and having its edges joined without overlapping. The plotting of the substrate's shape is carried out by laser or video scanning or by other detection procedure that does not involve contact, and includes at least one circuit of the substrate in the direction of the gas flow through it. It takes into account the dimensions of any insulating layer (16) covering the substrate, and allows for any necessary passages between the substrate and casing. The cutting of the sheet metal is carried out by automated means, especially computer aided, and the casing edges are butt welded, preferably by laser.

Description

The present invention relates to a method for

  manufacture of a catalytic converter for the treatment of exhaust gases, in particular of motor vehicles.

  The catalysts contained in the catalytic converters 5 comprise as essential element a substrate which can be traversed by air, which is provided with a catalytic coating (called Washcoat). Such substrates generally have a cylindrical shape with an oval or circular cross section and can be traversed due to the presence of the small channels by exhaust gases in the axial direction. The substrate usually consists of a porous ceramic body (ceramic monolith) and often also of a metallic body wound with axial air channels.

  According to the present invention, the periphery of the substrate is surrounded by a casing envelope made of sheet metal, with the exception of the two front faces (surface on the inlet side and surface on the outlet side of the flow). For thermal insulation and damping, the substrate is also surrounded by an insulating material placed between the substrate and the envelope sheet: knitted elements or mats are generally used for this purpose. Fiber mats are often used which expand to (expanded mats) and thus compensate for the expansion of the casing 25 of the housing. This envelope arrangement composed of the envelope sheet and the insulating material is also called Canning. The substrates are held inside this device by a combination of pressure and friction.

  For the assembly of the substrate, the insulating material and the envelope, various processes are known (so-called Canning processes) such as the packing principle, the shell technique or the winding principle. With the winding technique, for example the envelope sheet is cut according to the predefined predefined dimensions of the substrate in addition to a certain "excess for covering" and the cut and possibly laminated envelope sheet is wound around substrate wrapped with insulating material. Then, the envelope sheet is welded in the overlap area. The disadvantage of this process is the overlapping of the envelope at the junction point of the envelope sheet, which results in an irregular passage rating between the substrate and the envelope sheet and therefore mechanical overload of the monolith in the envelope overlap area.

  In addition, the known methods are not able to take account of a precise periphery or of an individual shape of the substrate. Inevitable manufacturing tolerances of the external dimensions of the substrate therefore also lead to irregular dimensions for the flow passages and therefore non-compliance with a desired density of insulating material between the body of the substrate and the envelope sheet. All this results in a high waste of the substrates during manufacture and requires the use of expensive and precisely manufactured substrates with low tolerance. In addition, it may happen in the case of excessively large passage dimensions during subsequent operation of the catalyst, due to the extremely variable temperatures of the. exhaust gas, untimely release and displacement of the substrate in the exhaust gas path, which often results in destruction of the substrate.

  The objective of the present invention is therefore to provide a process for the manufacture of a catalytic converter which eliminates the drawbacks cited from the current state of the art.

  This objective is achieved by a process according to which a) an external shape of the area of the substrate to be enveloped by the casing of the casing is at least partially grasped, b) the casing sheet is cut and / or preformed according to the captured form of the substrate, c) the substrate is introduced into the envelope sheet cut to dimensions and / or preformed or else the envelope sheet cut to dimensions and / or preformed is applied around the substrate, and d) sheet d the envelope is closed substantially without overlapping at its juxtaposed edges.

  The method thus allows a very precise taking into account of an individual external contour, in particular of the periphery and of the shape of each individual substrate, and a precise fabrication, cut to the dimensions of the substrate, of the envelope sheet. This allows according to the invention the assembly without overlapping of the envelope sheet and compliance with a regular dimension of passages between the substrate and the envelope sheet. In conclusion, more advantageous substrates can be used with larger manufacturing tolerances. In addition, a lower scrap of the substrates is obtained due to the reduced mechanical stress both during the Canning process and during subsequent operation. It is preferably intended to detect the shape of the substrate mechanically, so that the method gains in precision and speed. This can preferably be done without contact, for example by laser beam scanning (computer assisted), video scanning and other contactless shape detection methods.

  What is important for manufacturing is that first of all the outer zone of the substrate, which must be subsequently enveloped by the envelope sheet, is gripped in the important places in order to allow the custom-made manufacture of the sheet of envelope. In the present case, it is particularly preferred that at least one periphery of the substrate or its diameter is grasped without contact. Particular preference is given to determining a path of the diameter as a function of the axial length, in the direction of flow of the exhaust gases, of the substrate, so that for example a certain linear widening is established, a twist along the axis or a narrowing (taper) of the substrate. On the other hand, provision can be made in a particularly advantageous manner for not only entering the periphery as regards its radius, but also another complex external shape of the substrate, that is to say its three-dimensional contour.

  The characteristics and advantages of the invention will become apparent from the description which follows by way of examples with reference to the appended drawings in which: FIG. 1 shows a structure of a catalytic converter in longitudinal section, FIG. 2 a structure of a catalytic converter 15 manufactured according to the current state of the art in cross section, FIG. 3 a functional diagram of a process flow for the manufacture of a catalytic converter according to a preferred design of the invention and Figure 4 a structure of a catalytic converter manufactured according to the invention in cross section.

  A characteristic structure of a catalytic converter is shown diagrammatically in FIGS. 1 and 2. FIG. 1 shows the catalytic converter generally designated by 25 10 in longitudinal section and in FIG. 2 a catalyst 10 conventionally manufactured in longitudinal section along the section shown in Figure 1.

  The essential element of the catalyst 10 is a substrate 12, for example a ceramic cordierite monolith. The substrate 12 crossed by numerous channels which can be traversed by the exhaust gases is the support for a coating with catalytic activity not shown, which consists of the Washcoat and a precious metal component. Washcoat is a porous layer based on aluminum oxide, which is used for enlarging the surface of the substrate and for adhering the precious metal. The substrate 12 has a substantially cylindrical shape with an oval cross section (see Figure 2). In FIG. 1, an inlet side of the flow of the substrate 12 is identified by the reference 14 and an outlet side of the flow by 14 '.

  The substrate 12 is surrounded by an insulating material 16.

  In the present case, it is for example a fiber mat resistant to high temperatures, which contains additives which expand at high temperatures.

  The substrate 12 and the insulating material 16 are also wrapped around their outer periphery by a housing envelope 18 made of sheet metal.

  In order to illustrate the mounting position of the catalyst in the exhaust gas path of a vehicle, the direction of flow of an exhaust gas flow 20 is also indicated in FIG. 1.

  According to conventional Canning methods, the assembly of the substrate 12 and the Canning composed of the insulating material 16 and the casing 18 is carried out by first winding the substrate 12 in a fiber mat cut to size. insulating material 16.

  Then, the substrate 12 wound in the insulating material 16 is wound in the envelope sheet cut to size with an overcut and optionally prelaminated. Finally, the envelope sheet is welded in the overlap zone 22 (see FIG. 2).

  This procedure leads to the untimely effect that, below the overlap point 22, a predefined passage dimension between the substrate 12 and the casing 18 is not respected, and in particular is below 30 (see arrow in Figure 2). The characteristic passage dimensions vary from 2.7 mm to 3.8 mm and depend on the surface weight [g / m2] and on the nature [fiber or expanded mat] of the mat. Furthermore, the method does not take into account any deviations consecutive to the production of the periphery of the substrate 12 with respect to a desired dimension. Both the overlap point 22 and the manufacturing tolerances of the substrate 12 result in irregular passage dimensions between the substrate 12 and the casing 18 as well as non-compliance with a desired material density of the material insulator 16. 5 Taking into account the mechanical load caused by this fact of the substrate 12 during the Canning process and during the mounting of the catalyst 10, one arrives at the collapse of certain cells of the substrate until finally the complete destruction of the substrate in the subsequent operation. In order to avoid this, it has been customary to use expensive substrates 12 with low manufacturing tolerances.

  In order to avoid these drawbacks, a new manufacturing process has been developed according to the invention for the catalyst 10, the progress of which is illustrated in FIG. 3. The process begins with step S1, in which an outer contour of the substrate 12 is captured by machine at least by zones. In particular, the outer periphery of the substrate 12 which must be surrounded later by the casing 18 is determined. For example, a cross section of the substrate 12 which narrows on the path of the exhaust gases can be entered. The input is preferably made by computer with a contactless system.

  In the subsequent step S2, the cut is made to the dimensions of the envelope sheet serving for the casing envelope 18 as a function of the previously entered shape of the substrate 12. In the present case, the desired passage dimension between the substrate 12 and the casing 18 18 is taken into account in the form of a certain excess of material (calculated). The dimensions of the cut part are determined by computer, the three-dimensional external shape, determined during step Si, of the substrate 12 being converted into the appropriate surface in two dimensions. Likewise, the cutting operation to dimensions is preferably carried out automatically. The calculation of the dimensions and the cut to the corresponding dimensions can be integrated into a fully automatic Canning process.

  In an optional step S3, it is possible to preform the envelope sheet. In the present case, it is possible in particular by rolling to produce a pre-curvature of the envelope sheet.

  Then, in step S4, the substrate 12, the insulating material 16 and the envelope sheet 10 are assembled. Here, the substrate 12 is wound in the insulating material 16 cut to size. Then, this unit is introduced into the envelope sheet cut to size and preformed and is enveloped by it.

  Finally, the edge-to-edge assembly of the envelope sheet 15 to form the envelope of the housing is carried out during step S5. The edges contiguous to each other of the envelope sheet are then connected without overlapping (end to end) with each other, in particular welded. The welding can be done for example by laser welding.

  The entire procedure shown in Figure 3 is performed for each individual substrate 12. In this way, each individual substrate 12 receives an envelope from the housing 18 cut almost to measure.

  The advantageous result of the process according to the invention is visible in FIG. 4, where a catalyst 10 thus produced is shown in cross section.

  Here, identical elements are designated by the same references as in FIGS. 1 and 2. The catalyst 10 30 produced in this way is characterized in particular by a regular passage rating over the entire periphery of the substrate between the substrate 12 and the housing envelope 18. In particular, the dimension of passages located below the welding point 24 does not shrink with respect to the other zones.

  List of references Catalytic converter 12 Substrate 14 Flow inlet side 16 Insulating material / mat 18 Casing casing Exhaust gas flow 22 Overlap zone 10 24 Welding point.

Claims (10)

  1. Method for manufacturing a catalytic converter (10), which comprises a substrate (12) having a catalytic coating and a housing envelope (18), enveloping at least in places the substrate (12), made of envelope sheet, a) an external shape of the area of the substrate (12), to be surrounded by the casing envelope (18) being at least partially gripped, b) the envelope sheet being cut to measurements and / or preformed according to the gripped shape of the substrate (12), c) the substrate (12) being introduced into the envelope sheet (18) cut to measurements and / or preformed or the envelope sheet (18) cut to measurements and / or preformed 15 being applied around the substrate (12), and d) the envelope sheet being closed substantially without overlapping at the juxtaposed edges.   2. Method according to claim 1, characterized in that the input of the shape of the substrate (12) is carried out by machine.   3. Method according to claim 2, characterized in that the input of the shape of the substrate (12) is carried out without contact, in particular by laser scanning, video scanning or other shape detection without contact.   4. Method according to any one of the preceding claims, characterized in that the shape entered comprises at least one periphery of the substrate (12) in the direction of flow of the exhaust gases.   5. Method according to claim 4, characterized in that a outline of the periphery is grasped over a length of the substrate (12) in the direction of flow of the exhaust gases.   6. Method according to any one of the preceding claims, characterized in that an external shape of the substrate (12) is grasped.   7. Method according to any one of the preceding claims, characterized in that the catalyst comprises an insulating material (16) arranged at least in places between the substrate (12) and the casing envelope (18) and the substrate ( 12) is wrapped with the insulating material before applying the envelope sheet cut to size and / or preformed.   8. Method according to any one of the preceding claims, characterized in that, during the cutting to the dimensions of the envelope sheet, a predefined dimension of passages between the substrate (12) and the housing envelope (18 ) is taken into account.   9. Method according to any one of the preceding claims, characterized in that the cutting to the dimensions of the envelope sheet is carried out in an automated manner, in particular computer-assisted.   10. Method according to any one of the preceding claims, characterized in that the assembly of the juxtaposed edges of the envelope sheet (18) is carried out by welding, in particular by laser welding.