EP1771236A1

EP1771236A1 - Method for producing an area of a filter structure, especially for a particle filter in the exhaust gas system of an internal combustion engine

Info

Publication number: EP1771236A1
Application number: EP05764002A
Authority: EP
Inventors: Christoph Treutler; Uwe Glanz; Leonore Schwegler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-07-21
Filing date: 2005-06-24
Publication date: 2007-04-11
Also published as: JP2008506523A; WO2006008222A1; DE102004035311A1; US20090016923A1

Abstract

The invention relates to a method for producing at least one area of a filter structure, especially for a particle filter in the exhaust gas system of an internal combustion engine. The inventive method is characterized by the following steps: a. producing a mixture from a sintered metal powder and an organic binder; b. producing a film from said mixture; c. structuring said film; and d. sintering it.

Description

Method for producing at least one region of a filter structure, in particular for a particle filter in the exhaust gas system of an internal combustion engine

State of the art

The invention relates to a method for producing at least one region of a filter structure, in particular for a particle filter in the exhaust system of an internal combustion engine.

For the production of metallic filter mats sintered metal is suitable. In particular, the processing of powdered metal is advantageous because of the particle size and

Particle size distribution of the powder used and on the sintering conditions can set a defined density and pore size of the sintered metal.

For the production of filter mats made of sintered metal, a carrier material (for example an expanded metal or a metal fabric) is currently coated with sintered metal powder and sintered together. The carrier or framework material fulfills two tasks: it helps to fix the sintered metal powder and later stabilizes the filter bag.

Such a filter device is known from DE 101 28 936 Al. The particle filter shown there is installed in the exhaust system of a diesel internal combustion engine. The filter walls in the known filter device are made of sintered metal and arranged so that wedge-shaped filter bags are formed. The tapered wedge edges of the filter pockets show against the flow direction of the exhaust gas, the rear narrow side of a filter pocket seen in the flow direction is open. The filter bags are arranged side by side in such a way that an overall rotationally symmetrical, annular filter structure is formed. In the known particle filter, the filter walls are formed by labile sintered metal foils or sintered metal mats, which are connected to separate supporting or support structures, for example perforated plates, metal fabrics or the like.

It is also known from the market to produce a spreadable, mortar-like mass from a sintered metal and the smallest possible proportion of an organic binder. This is scribed on the cellular wheel principle in metal mesh or expanded metal. This creates a smooth and thus relatively small filter surface.

Furthermore, a flowable paste or slurry can be prepared from sintered metal powder and an organic binder and by means of solvents. The powder processed in this way can then be applied either by immersing the metal mesh or the expanded metal in the paste or the slip, or the metal mesh or the expanded metal can be cast in a casting process with the slip or overprinted with the paste (for example in screen printing technique) , In all variants of this process is a subsequent

Drying step required in which solvent is evaporated and the sintered metal powder is fixed on the metal framework.

Finally, it is still known to mix sintered metal powder with wax beads and to inflate this mixture on the expanded metal or the metal fabric. By

Heating the melted wax beads to fix the powder on the metal frame.

Depending on the coating method used, however, there remains the difficulty of precisely setting and controlling the layer thickness and layer density of the sintered metal layer. At the same time, a framework material significantly increases the weight and cost of a filter mat. It is therefore desirable to be able to dispense with a framework material and still produce defined, stable sintered metal foils. Object of the present invention is therefore to develop a method of the type mentioned so that a filter device with precisely defined properties can be produced inexpensively without the use of a support structure.

This object is achieved in a method of the type mentioned above in that the method comprises the following steps:

& Preparing a mixture of a sintered metal powder and an organic binder;

b. Producing a film from the mixture;

c. Structuring the film; and

d. Sintering.

Advantages of the invention

The use of a film has the advantage that its thickness, density and structuring of the sintered metal filling can be defined very precisely. These parameters allow the permeability of the sintered metal filter to be precisely predefined.

In addition, such a film process technology can be easily and cheaply and produced in reproducible quality. A constant quality control and storage of such a film is possible, which also facilitates the manufacturing process and lowers the production costs.

The structuring of the film allows the creation of a defined surface structure and thus the targeted enlargement of the active filter surface.

Advantageous developments of the invention will become apparent from the measures mentioned in the dependent claims. In a first development, it is proposed that in step b, the film through

Film sheeting, tape casting or film extrusion is produced. All of these methods allow an exact adjustment of the film thickness and the production of a homogeneous, smooth and bubble-free sintered metal foil.

It is also possible, after producing the films in step b (green films) and before structuring from these individual films, to produce so-called multilayer green films.

The structuring takes place in step c, preferably at a temperature in the range of 80-150 ° Celsius, preferably in the range of 80-90 ° Celsius. The structuring temperature, at which the sintered metal foil is plastically deformable, can be very well adjusted by an appropriate selection and amount of organic binder. The specified temperature range is therefore particularly advantageous since the required energy input is limited and yet a good effect is already achieved with conventional organic and thermoplastic binders. This is especially true for the range of 80 - 90 ° Celsius.

The structuring is preferably carried out by means of stamping plates, which are placed on the film and pressed. It can also be a structured one. Laminierwalze be used, or it can be arranged several rollers in a row. Also, a two-sided arrangement of the rollers is possible.

In a further advantageous development of the method according to the invention, both sides of the film are subjected to a structuring step. In this way, it is possible, for example, to obtain a bilateral wafer structure of the film, which has the advantage that not only surface is produced, but also the mechanical stability of the film is improved via suitable geometries (wafer structures, honeycomb structures, see below) becomes.

In a particularly advantageous embodiment of the method according to the invention, a plurality of differently structured films can be laminated together in order to increase the overall layer thickness or locally. This can take place before or after the embossing process, but advantageously several green sheets are first laminated together in order to achieve the desired layer thickness or even a desired gradient. Adjust powder size distribution and / or density distribution, and then embossed one or both surfaces. However, it is also conceivable to laminate pre-structured, eg perforated, films

Furthermore, films containing differently fine or coarse sintered metal powder may be combined together to influence the pore structure of the finished filter sheet. When sintered, coarse and fine powders have different tendencies to bond. An equally important factor is the so-called green density of the films, that is, how close the particles are to each other and how quickly and how well they bond to each other. It is also possible to laminate two films together, one of which can be structured particularly well due to their composition, while the other is mechanically very stable, to allow in this way a safe handling in the production process. This is determined by the organics used in film production, i.e., the polymer binder used, the softening additives, etc.

In a further embodiment of the method according to the invention, it is possible to additionally connect the film to a support structure. Advantageously, a metallic fabric, an expanded metal or a perforated plate is used as the support structure. These are inexpensive, cover only a small area and thus allow in operation a high gas flow rate.

Optimum filter properties, in particular when the filter device is used as a particle filter in the exhaust system of an internal combustion engine, are achieved if the sintered metal powder has a grain size of approximately 1-150 μm, preferably 40-70 μm, more preferably 50-60 μm.

Favorable production costs are achieved if, in step a, the sintered metal powder with approximately 8% by weight of acrylate binder and butyl acetate as solvent is processed into a sacable slip.

Brief description of the drawings Hereinafter, particularly preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. In the drawing show:

Figure 1 is a schematic representation of an internal combustion engine with a

Particulate filter with a filter structure;

Figure 2 is a perspective view of the filter structure of Figure 1;

FIG. 3 shows two filter pockets of the filter structure of FIG. 1;

FIG. 4 shows a flowchart of a method for producing a filter wall of FIG

Filter structure of Figure 1;

FIG. 5 shows a section through a sintered metal foil before the structuring step;

FIG. 6 shows a section through the sintered metal foil from FIG. 5 after structuring with a first embossing plate;

FIG. 7 shows a section through the sintered metal foil from FIG. 5 after structuring with a second embossing plate;

FIG. 8 shows an embodiment of the structuring by means of weapon-shaped embossing plates; and

Figure 9 shows various embodiments of multilayer green sheets according to the invention.

Description of the embodiments

In Figure 1, an internal combustion engine carries the reference numeral 10. It includes an exhaust system 12, in which a particulate filter 14 is arranged. By means of this, for example, soot particles can be filtered out of the exhaust gas of the internal combustion engine 10. The particulate filter 14 comprises a housing 16 and a filter structure 18 arranged in the housing 16. The filter structure 18 is shown in more detail in Figure 2: It comprises a plurality of wedge-shaped filter pockets 20, which are arranged with their tapered wedge edge opposite to the flow direction of the exhaust gas. The filter pockets 20 are arranged next to each other about an overall longitudinal axis, so that an overall rotationally symmetrical filter structure 18 is formed. The radially inner and outer narrow sides of the filter pockets 20 are closed. The downstream in the flow direction narrow sides of the filter bags 20 are open. In the area of their rear ends in the flow direction, the filter bags are interconnected.

In FIG. 3, two adjacent filter pockets 20a and 20b are shown. During operation, the exhaust gas enters an area between the two filter pockets 20a and 20b, passes through a lateral filter wall 22 and thus enters the interior of the respective filter pocket 20a and 20b. The gasbgasstrom is shown by an arrow 24. When passing through the side wall 22, the particles are separated from the exhaust gas and deposited on the upstream surface of the side wall 22.

The walls, and in particular the side walls 22 of the filter pockets 20, are made of a porous sintered metal. A method for producing, for example, the side walls 22 of the filter pockets 20 is shown in FIG. 4. First, sintered metal powder 26 having a grain size of about 50-60 μm, preferably 53 μm, with about 2-8% by weight of acrylate binder 28 and a volatile organic compound Solvent, for example. Butyl acetate or alcohol 30 processed by a device 32 to a squeegee slurry 34. This is processed with a film doctor blade 36 to a 100 - 500 .mu.m thick sintered metal foil 38 (green film). If so-called multi-layer green sheets 39 are produced from these single sheets, the thickness is preferably> 450 μm.

This metal foil or multilayer green sheets are then patterned by means of a device 40 using either embossing plates or a structured laminating roller. For this purpose, the sintered films are heated to a temperature of about 80 ⁰ C, there are various stamping plates placed and pressed. The structure of the embossing plates was clearly visible after pressing on the corresponding blank 42. In an oven 44, the blank 42 is then sintered, creating a quasi-one-piece composite 46. From the sintered metal foil 48 filter bags 22 are then produced by punching, folding and welding.

FIGS. 5, 6 and 7 show sections through a blank 42 used according to the invention. FIG. 5 shows a blank 42 having a defined layer thickness and green density, which was produced by means of a comparatively thick sintered metal foil 38. Overall, the surface 52 of the sintered metal foil 38 is smooth. The blank 42 drawn in FIG. 6 corresponds to that produced using the method described in FIG. 4: It can be seen that the surface structure of the stamping plate 40 is imaged on the surface 52 of the sintered metal foil 38. FIG. 7 shows a blank 42 which has been produced with a differently structured embossing plate 40 and whose surface 52 has a correspondingly embossed pattern 54.

As already mentioned above, the mechanical stability of the film can be improved by means of suitable geometries. Thus, for example, a sintered metal foil with a high surface area and at the same time high mechanical stability can be produced by the production of a "waffle iron structure" described below.

First, sintered metal powder 26 with a grain size of approximately 50-60 μm, preferably 53 μm, with approximately 2-8% by weight of acrylate binder and a volatile organic solvent, for example butyl acetate or alcohol 30, is processed by means 32 into a squeegee 34 , This is processed with a film doctor blade 36 to a 100-500 .mu.m, preferably> 450 .mu.m thick sintered metal green sheet 38. This foil is then structured, for example, by means of the embossing plates 56 shown in FIG. 8. For this purpose, the tool is heated to a temperature of about 8O ⁰ C, the green sheet 38 is inserted and closed the tool under pressure. After opening the tool, the green sheet 38 is removed again and has now adopted the structure of the stamping plates. In an oven 44, the blank is then sintered, whereby the geometry of the three-dimensionally structured film 38 is completely preserved. It is also possible with this tool to use the sintered metal powder in place of a defined film 38 in other geometries (tablets, roughly divided plates, flat breads, etc) in the form of a thermoplastic compound 58 (see Fig. 8). The following example shows the production of high surface area sintered metal foils by using graded green sheets or multilayer films.

First, sintered metal powder 26 having a grain size of, for example, 50 μm, with about 2-8% by weight of acrylate binder and a volatile organic solvent, for example butyl acetate or alcohol 30, is processed by means 32 into a squeegee 34. This is processed with a film doctor blade 36 to a 100-500 .mu.m, preferably <200 .mu.m thick sintered metal green sheet 38. Likewise, with powder, for example, the grain size of 30 microns and 80 microns, process.

Other green film variants are higher organics film compositions (e.g., 6-20 wt% acrylic binders), or films having pore-forming additives which completely volatilize in the sintering process. Films having different layer thicknesses are also possible variants, such as the use of defined powder mixtures (narrow monomodal, bi- or trimodal grain size distributions) or different powder types (e.g., spherical round powder types, irregular drop-shaped powder types, flaky powder types, etc.) in film production.

These film variants 38 can be combined with one another in different ways to multilayer green films 39. By means of suitable sintered profiles, the porosity and the surface properties of the sintered filter foils 46 can be adjusted or defined in a targeted manner. For example, by laminating different film variants after sintering, a filter film with a coarse-pored and a fine-pored side can be achieved, or it is obtained when using films of different green density after sintering a filter film with very strong surface roughness, since the side with the lower green density shrinks inhomogeneously during sintering, and forms porous surface structures. In both cases sintered metal filters with graded porosity and high surface area are obtained.

The above-mentioned multi-layer green sheets 39 produced by laminating single sheets 38 are processed like the green sheets 38 and can be used as needed, such as Also, the films themselves 38 are laminated to a scaffold such as an expanded metal 62 and / or additionally mechanically structured by embossing.

FIG. 9 shows various possibilities for the design of multi-seed green films 39. FIG. 9A shows a triple laminate 60 of three similar green sheets 38 with expanded metal 62 laminated on it as a support structure. Fig. 9B shows a dual laminate 64 of two different green sheets 38 each having a fine and a coarse powder (66, 68). The surface of the coarse powder film 68 is further patterned by embossing to increase the filter surface area. 9C shows a green sheet with so-called "waffle structure", produced using a multilayer green film 39 consisting of three layers (70, 72, 74) with different powder filling, and FIG. 9D finally shows a double laminate 76 of two different green sheets 78, 80, FIG. wherein one film is highly filled, and the other has a lower degree of filling of metal powder and optionally also contains pore-forming additives .Alaminated expanded metal 62 is again shown in FIG

Claims

claims

A method for producing at least one region (22) of a filter structure (18), in particular for a particle filter (14) in the exhaust gas system (12)

Internal combustion engine (10), characterized in that it comprises the following steps:

a. Producing (32) a mixture (34) from a sintered metal powder (26) and an organic binder (28);

b. Producing (36) a film (38) from the mixture (34);

c. Patterning (40) the film (38); and

d. Sintering (44).

2. The method according to claim 1, characterized by the additional step of producing multilayer green sheets (39) from the films produced in step b) (38) before the structuring step c) and structuring the multilayer green sheets (39) thus produced.

3. The method according to claim 1 or 2, characterized in that the films (38) and / or the multilayer green sheets (39) with respect. The powder size distribution and / or the density distribution of the sintered metal powder (26).

4. The method according to any one of claims 1 to 3, characterized in that in step b, the film (38) by film doctor blades (36), film casting, or film extrusion is produced.

5. The method according to any one of the preceding claims, characterized in that the structuring (40) in step c at a temperature in the range of 80 to 15O ⁰ C, preferably in the range of 80 to 9O ⁰ C, takes place.

6. The method according to any one of the preceding claims, characterized in that the structuring (40) is achieved in step c by means of embossing.

7. The method according to claim 6, characterized in that embossing plates and / or structured laminating rollers are used for embossing, whose surface structure on the film (38) or the multilayer green film (39) is imaged.

8. The method according to any one of the preceding claims, characterized in that a sintered metal powder (26) with a grain size of about 1 to 150 .mu.m, preferably 40 to

70 microns, more preferably 50 to 60 microns is used.

9. The method according to any one of the preceding claims, characterized in that processed in step a, the sintered metal powder (26) with about 2-8 wt .-% acrylate binder (28) and a volatile organic solvent (30) to a squeegee slurry (34) becomes.

10. The method according to claim 9, characterized in that the volatile organic solvent is butyl acetate or alcohol.

11. The method according to any one of the preceding claims, characterized dadaurch that a two-sided structuring (40) of the film (38) or the multilayer green sheet (39).

12. The method according to claim 11, characterized in that the film (38) or the multilayer green film (39) is a double-sided waffle structure is abandoned.

13. The method according to any one of the preceding claims, characterized in that the film (38) or the multilayer green sheet (39) is additionally connected to a support structure (62).

14. The method according to claim 13, characterized in that as a support structure (62), a metallic fabric, an expanded metal or a perforated plate is used.