EP0336002B1 - Knit wire mesh and its production process, and device for carrying out the process - Google Patents

Abstract

The knitted wire mesh (21) is used as a sleeve for a catalytically coated, preferably cylindrical, ceramic monolith (20), which is used for detoxifying the exhaust gas of internal-combustion engines, and which has, on its two end faces, an inlet and outlet side for the exhaust gas and a jacket. The knitted wire mesh (21) is characterised by its stable-shaped, sleeve-like design with a circumferential bead (24) arranged on each of its two sides for overlapping the edge region of the inlet and outlet side of the monolith (20). <IMAGE>

Description

The invention relates to a sleeve made of wire, a method for its production and a device for carrying out the method.

Catalytic coated, preferably cylindrical, ceramic monoliths are used for exhaust gas detoxification from internal combustion engines. These monoliths are permanently stored in a housing, with the interposition of a cover, usually made of wire mesh.

In the known methods, the monolith is first provided with the shell, then these two parts are inserted loosely into the two-part housing and this is pressed when it is closed. Attempts were first made to stop the axial movement of the monolith resulting from the pulsating exhaust gas flow via radial forces in the form of pressed-in beads, but this has not proven successful. Excessively high pressures applied during manufacture involve the risk of damaging the ceramic monolith. If the pressures are too low, there is a risk of insufficient holding force.

It has therefore already been proposed to use special components encompassing the edges of the end face in the form of a ring (DE-OS 24 12 863). It has also been proposed to use a multiply folded and thus reinforced sheath in the area of the end face to absorb the axial forces of the monolith (DE-OS 35 19 965).

A disadvantage of the known casings is that due to the forces acting on the monolith - both when pressing in Monolith and casing in the housing as well as in operation due to the pulsating gas flow, as occurs in exhaust gases from internal combustion engines - the monolith is brought into contact with the housing and is thereby damaged. In addition, the multiple wrapping of the monolith has the disadvantage that a high surface pressure occurs at the edge of the monolith due to the many layers and this can therefore be damaged.

A generic cover according to the preamble of the main claim is also known (EP-A1 0 250 384). This sheath consists of pre-tensioned, flat rolled wire from a high-alloy steel and is placed over the surface of the monolith. Two beads surround the edge areas of the entry and exit sides of the monoliths used.

However, even this known casing is not suitable for ruling out damage to the monolith during assembly or during operation that is sufficiently permissible.

The invention is based on the object of proposing a casing, a method for its production and an apparatus for carrying out the method, with which a maximum degree of safety can be achieved for the monolith in the production of the catalyst and in its operation.

This object is achieved by the subject matter, method and main claim.

According to the invention, the flat wire mesh, preferably in the form of a tube, which is provided with oblique embossments, is wound onto a surface adapted to the jacket of the monolith, preferably a mandrel which corresponds in shape and dimension to the monolith. The preload between the monolith and the metal housing can be adjusted with the depth or the height of the impressions. When the protrusion of the knitted wire protruding from the mandrel in the axial direction is pressed, each of the two Overhangs each produced a bead which protrudes both in the axial direction and radially inwards with respect to the size of the monolith to be accommodated. This thus shaped sleeve is then pushed over the monolith by means of a conical sleeve and then the conical sleeve is removed again, so that the monolith surrounded by the sleeve can now be inserted into the two-part housing and permanently held in this position, with a defined one Axial dimension between the monolith and the housing can be achieved and not only the elastic bearing in the radial direction between the housing and the monolith can be generated, but also the axial forces can be absorbed. Both the density and the elastic properties in the axial direction can be influenced by the bead. As a result, the length tolerances between the housing and the monolith can be absorbed by the bead and a different elasticity than the otherwise formed knitted fabric. Finally, sealing against an undesired bypass flow of the exhaust gas is achieved. At the same time, there is a uniform surface pressure in the areas without a bulge of the molded shell on the monoliths.

In an alternative embodiment of the method according to the invention, the wire mesh can also be wound directly onto the monolith and pressed there in the longitudinal direction, if an abutment that can be removed afterwards is only placed on the edges of the end faces when pressing, in order to absorb the pressing forces, so that damage to the monolith is not is to be feared. Because of the knitted wire knitting before winding with an acute angle to the circumferential winding direction cause a certain axial deflection after pressing, so that despite the abutment the compressed bead comes to rest against the end faces of the monolith. As an alternative or in addition, it is also possible to pull the wire mesh slightly apart in the axial direction before pressing the bead in order to achieve a firm fit of the bead by deflecting the shaped casing after the pressing process of the bead. If, in a preferred embodiment, the surface is longitudinal the edges of its end face has a circumferential projection, which is correspondingly formed as an indentation on the bead to be pressed, so there is the additional advantage that the particularly sensitive edges of the ceramic monolith do not lie directly on the shell, but in the through the projection generated indentation.

Further expedient refinements and developments of the invention are characterized in the subclaims.

Figur 1

die Vorrichtung zur Durchführung des Verfahrens, im schematischen teilweise abgebrochenen Querschnitt und der Anfangsstellung;

Figur 2

die Vorrichtung gemäß Fig. 1 in gleicher Darstellung und Preßendstellung;

Figur 3

die über einen Monolithen gestreifte geformte Hülle;

Figur 4

die Bauteile gemäß Fig. 3, im in das Gehäuse eingesetzten Zustand, im schematischen Halbschnitt; und

Figur 5

die Einzelheit 5 gemäß Fig. 2.

A preferred embodiment of the device for performing the method and a schematic process sequence are shown in the drawing. In this shows:

Figure 1

the device for performing the method, in schematic, partially broken cross-section and the starting position;

Figure 2

the device of Figure 1 in the same representation and press end position.

Figure 3

the molded envelope streaked over a monolith;

Figure 4

3, in the state inserted into the housing, in a schematic half-section; and

Figure 5

detail 5 according to FIG. 2.

In Fig. 1 the device is shown. It has a mandrel 10, the shell 11 of which forms the surface 11 in shape and extent corresponds to the monolith 20 (FIGS. 3 and 4). The wire mesh 21 is preferably wound twice around the surface 11 of the mandrel 10 in the circumferential direction. The width of the wire mesh is dimensioned such that there is an overhang 18 for the wire mesh 21.

The mandrel is located in two axially open mold jaws 12, 13 that are movable towards one another and radially surround the mandrel with play. Through the two axial openings of the mold jaws 12, 13, sliding sleeves 14 penetrate as actual pressing tools, which are axially displaceable.

The mandrel 10 has two terminal fixed first shoulders 15 of smaller diameter in the region of the protrusion 18 of the wire mesh over the surface 11 of the mandrel 10. The first paragraphs 15 have further second paragraphs 16 with a smaller diameter than the guide for the sliding sleeves 14. The actual projecting pressed parts of the sliding sleeve 14 rest on the surfaces of the shoulders 15 and have projecting shoulders 14a on their front side, which in the end position are at a distance from the annular end face.

The shaped jaws 12, 13 also have a ring 25 of larger diameter located in the area of the surface 11 of the mandrel 10, so that the knitted wire 21 is not compressed too much in this area when the shaped jaws 12, 13 are closed in the direction of arrow A (FIG. 2). This annular space 25 is followed by a circumferential circumferential clamping projection 26 for holding the wire mesh 21 while the overhang 18 is pressed together when the sliding sleeves 14 move together in the direction of arrow B. The circumferential clamping projection 26 has an undercut 27 in the region of the - circumferential - edges 28 of the surface 11 with the annular end face 19. The undercut 27 goes into an area 29 of the pressing tools 12, 13 with a smaller diameter than the area of the annular space 25 about. This device produces a inherently dimensionally shaped and provided with a bead 24 shaped sleeve 22 as shown in FIG. 3, which can jump over the circumferential edge of each end face of the monolith 20 somewhat radially inward when it is pushed over the monolith, as that is shown in Fig. 3. The components prefabricated in this way (shaped casing with monolith) are then inserted into the two-part housing 23 (FIG. 4) and, when they are connected, are permanently and reliably secured against damage as a result of axial displacements of the monolith 20 in the pulsating gas stream.

Claims (25)

1. A sheath (22) of wire for a preferably cylindrical monolith (20) of ceramic material which serves for internal combustion engine exhaust gas decontamination and which is catalytically coated and which at its two ends has an inlet and an outlet end for the exhaust gas and a peripheral portion, wherein the sheath (22) is of such a length in the direction of the longitudinal axis of the monolith (20) that, when the monolith is inserted, it embraces its edge regions at the inlet and outlet ends, forming a respective lip (24) thereat,
      characterised in that

   - the sheath (22) is in the form of preshaped wire mesh (21), and

   - the lips (24) are pressed in such a way that they are of greater density than the remainder of the wire mesh (21), forming a firm and stable shape for the sheath (22).
2. A sheath according to claim 1 characterised in that the wire mesh (21) comprises a tubular mesh portion.
3. A sheath (22) according to claim 1 or claim 2 characterised in that in the region of the transition to each lip (24) its inside surface has impressed portions such that the peripherally extending edge of the monolith (20) at its ends is not touched.
4. A sheath (22) according to one of claims 1 to 3 characterised in that the inside surface of one or both lips (24) extends at an angle which is not equal to 90° relative to the inside surface of the sheath, corresponding to the peripheral portion of the monolith (20).
5. A procecess for the production of a sheath (22) according to one of claims 1 to 4
      wherein the shaped mesh serves as a sheath for a preferably cylindrical monolith (20) of ceramic material, which is catalytically coated and which can be used for internal combustion engine exhaust gas decontamination,
      wherein the shaped mesh comprises wire mesh, preferably a tubular mesh portion,
      wherein the wire mesh is longer in the axial direction than the length determined by the distance between the two ends of the monolith (20) and projects in the axial direction at both ends beyond the surface as projecting portions (18) and forms respective lips (24),
      wherein at its two ends the monolith (20) has an inlet and an outlet end for the exhaust gas and a peripheral portion, and
      wherein the monolith is intended for subsequent insertion in a housing and serves as a catalyst,
      characterised in that
      the wire mesh is wound in the peripheral direction on to a surface (11) which is adapted to the peripheral portion of the monolith (20),
      the wire mesh (21) is secured on the surface (11) at least in the region directly adjoining the region of the projecting portion (18),
      with the wire mesh (21) being otherwise held fast the projecting portion (18) is compressed in the axial direction to a predeterminable axial dimension to provide a lip (24), and
      the wire mesh is shaped to provide the sheath (22) in the compression operation.
6. A process according to claim 5 characterised in that the wire mesh (21) is wound at least twice around the surface (11).
7. A process according to one of claims 5 and 6 characterised in that prior to the winding operation the wire mesh (21) is provided with impression portions which extend at an acute angle relative to the winding direction which is in the peripheral direction.
8. A process according to claim 7 characterised in that the impression portions extend at an angle of from 50 to 70° relative to the winding direction.
9. A process according to claim 7 or claim 8 characterised in that the impression portions extend parallel to each other.
10. A process according to one of claims 5 to 9 characterised in that the surface of a mandrel (10) is used as the surface (11).
11. A process according to one of claims 5 to 10 characterised in that the wire mesh (21) is fixed in the region immediately adjoining the beginning of the projecting portion (18).
12. A process according to one of claims 5 to 11 characterised in that the projecting portions (18) are of the same size.
13. A process according to one of claims 5 to 12 characterised in that the respective periphery of the surface (11) is at a maximum as large as the relevant periphery of the monolith (20).
14. A process according to one of claims 5 to 13 characterised in that the surface (11) is at a maximum as large as the length of the monolith (20).
15. A process according to one of claims 5 to 14 characterised in that the surface (11) has a peripherally extending projection along the edges of its ends (19).
16. A process according to one of claims 5 to 15 characterised in that deflection of the wire mesh (21) radially outwardly and in the axial direction in the region of the surface (11) is prevented in the compression operation in the axial direction by means of an abutment.
17. A process according to one of claims 5 to 16 characterised in that in the operation of compressing the wire mesh to provide the sheath (22) in the axial direction the wire mesh is at the same time bent somewhat radially inwardly.
18. A process according to one of claims 5 to 17 characterised in that the pressed wire mesh (21) is drawn over a monolith (20).
19. A process according to claim 18 characterised in that the monolith (20) provided with a sheath (22) is laid into a portion of a housing and a second portion is then laid thereover and finally both portions are connected together to provide the housing (23).
20. Apparatus for carrying out the process according to one of claims 5 to 19 characterised by
       a mandrel (10) for receiving the wire mesh (21) on its peripheral portion which forms the surface (11), two axially open shaping jaws (12, 13) which are movable towards each other and which radially surround the mandrel with clearance for the mesh (21) and two thrust sleeves which engage through the axial openings, as actual, axially displaceable pressing tools.
21. Apparatus according to claim 20 characterised in that the mandrel (10) is of a cylindrical configuration with two first end portions (15) of smaller diameter for the projecting portions (18) of the wire mesh (21).
22. Apparatus according to claim 21 characterised in that each portion (15) has a further portion (16) of smaller diameter as a guide for the thrust sleeve (14).
23. Apparatus according to one of claims 20 to 22 characterised in that the surface (11) of the mandrel (10) has a projection along its edges which are formed by the first portion (15).
24. Apparatus according to one of claims 20 to 23 characterised in that the annular end face (19) extends at an angle which is different from 90° relative to the first portion (15).
25. Apparatus according to one of claims 20 to 24 characterised in that the thrust sleeve (14) has a projecting portion (14a).

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