WO2008151947A1

WO2008151947A1 - Extrusion die orifice for producing ceramic honeycomb bodies

Info

Publication number: WO2008151947A1
Application number: PCT/EP2008/056682
Authority: WO
Inventors: Teruo Komori; Thomas Hauber
Original assignee: Robert Bosch Gmbh
Priority date: 2007-06-15
Filing date: 2008-05-30
Publication date: 2008-12-18
Also published as: DE102007027668A1

Abstract

The invention relates to an extrusion die orifice (110) which is suitable for the production of ceramic honeycomb bodies. The extrusion die orifice (110) is especially suitable for the production of ceramic honeycomb bodies (18) for ceramic exhaust gas aftertreatment devices for motor vehicles. The extrusion die orifice (110) comprises a base plate (116) having at least two openings (118) and at least one web (119) interposed between the openings (118). The base plate (116) has a metal or ceramic base material. In the zone of the openings (118), the base plate (116) is provided with at least one hard material coating (126).

Description

description

title

Extrusion mouthpiece for the production of ceramic honeycomb bodies

State of the art

The invention is based on known production methods for the production of exhaust gas purification components in automotive engineering. Examples of such exhaust gas purification components are various types of catalysts or filters, in particular diesel particulate filters (DPF).

In many cases, such exhaust gas purification components have a ceramic support as a basic structure. This carrier can be made of various ceramic materials, for example of silicon carbide, cordierite or similar ceramic materials.

In many cases, this ceramic carrier is in the form of a ceramic honeycomb body. This ceramic honeycomb body allows on the one hand a good flow through the exhaust gas purification component by the exhaust gas to be cleaned and on the other hand offers a high surface area, for example in order to increase the catalytic effect. Furthermore, the use of honeycomb bodies allows the production of stable ceramic structures with low weight. However, other types of ceramic moldings than moldings with a honeycomb structure are possible and are included in the following description of the term "honeycomb body" with.

The shaping of ceramic honeycomb bodies is in many cases on a large scale by extrusion with an extruder. Initially, an extrudable mass of a ceramic powder, water and various other auxiliaries is produced. This mass is fed to the extruder.

In the extrusion head of the extruder, the mass flow is compressed to a plug. The fin-shaped mouthpiece attached to the press head causes a build-up of pressure in the mass strand in front of the mouthpiece. From a certain pressure build-up, the mass begins to flow through the ments or openings of the mouthpiece to flow. The individual mass strands formed by the holes flow in the adjoining gate, ie a slot-shaped structure, to form a closed grid structure, which is delimited by an outer ring.

The mouthpieces used for honeycomb extrusion are costly custom-made products, usually made from a metal plate. In particular, wire or sink erosion methods are used for this purpose. The gate can also be achieved by sawing slots.

By friction of the ceramic components of the mass flow, however, it comes to a wear of the mouthpiece (removal). As a result, the slot width of the gate increases, so that as a result the wall thickness of the honeycomb body increases. This changes the properties of the finished honeycomb body, such as back pressure, weight, etc.

In practice, therefore, after a certain time, the mouthpiece must be replaced and revised. This is usually done in such a way that a metal layer (for example, nickel) is deposited galvanically on the tool, so that the original slot width is reached again.

In manufacturing, for example, the mass of the finished honeycomb body is regularly monitored. If the wall thickness increased as a result of the wear of the mouthpiece such that the finished honeycomb body exceeds a predetermined limit weight, the above-described revision can be performed.

The method described and the regular revision of the mouthpieces are complex and expensive in practice and increase the unit cost of the honeycomb body produced considerably.

Disclosure of the invention

The invention therefore provides an extrusion die and a method of manufacturing this extrusion die which substantially avoids the above described disadvantages of known extrusion dies and methods. The extrusion die can be used in particular for the production of ceramic exhaust aftertreatment devices of the type described above, for example for the production of ceramic honeycomb bodies for diesel particulate filters or catalysts. The invention provides a simple approach to increasing the service life of the extrusion dies and the entire extrusion equipment or extrusion presses. These increased service lives can reduce the cost of overhauling the extrusion nozzle and greatly reduce the production losses that occur during overhaul.

A basic idea of the present invention is to manufacture the extrusion die from two components: a base plate having at least two openings and at least one web arranged between the openings and a coating of this base plate. The base plate may for example be made of a metallic or ceramic base material, preferably tool steel. The coating, which is arranged on the base plate in the region of the openings (i.e., for example, in the vicinity of the edges of the openings, in particular on the web), has at least one hard material coating.

In contrast to pure metals such as nickel, hard materials have a variety of positive properties for the present application. Hard materials are generally not defined in the literature on common chemical properties, but the hard materials is a property profile in common, in particular, the high hardness is to be mentioned as a characteristic property of the hard materials. Hard materials usually have a Vickers hardness of at least 1000. Furthermore, hard materials generally have high melting points and high chemical resistance.

Basically, a distinction is made between metallic and non-metallic hard materials. In this case, metallic hard materials are electrical conductors, non-metallic hard materials, however, not non-conductors. Examples of non-metallic hard materials are diamond, cubic boron nitride, boron carbide, silicon carbide, corundum or silicon nitride. Examples of metallic hard materials are titanium carbide, tantalum carbide, titanium nitride or tungsten carbide. In practice, the use of tungsten carbide (WC) in particular has proven to be advantageous for the present invention, which has a melting point of about 2900 ⁰ C and a Vickers hardness of 2400. In general, metallic hard materials in particular are good for the present invention suitable.

Metallic hard materials can be referred to in particular as structurally ordered intercalated crystals, ie ordered intercalation structures with intermetallic phases. Furthermore, hard-material mixed crystals such as titanium carbide tungsten carbide, titanium carbide tantalum carbide tungsten carbide, titanium carbide titanium nitride or similar mixed crystals can be used advantageously.

However, in general, for example, nitrides, carbides, oxides, borides or phosphides or other compounds can be used.

It is advantageous if the hard material coating has a thickness of at least 0.2 mm. For practical reasons, maximum thicknesses of approximately 2.0 mm have proved to be advantageous.

Particularly preferred for the present application of the ceramic extrusion are hard coatings with a Vickers hardness of at least 1500. The hard materials described above, in particular metallic hard materials, are well suited for this purpose.

For applying the hard material coating, various methods known from the prior art can be used. In particular, chemical vapor deposition (CVD), physical vapor deposition (PVD), surface hardening, electroplating, thermal spraying, build-up welding, plating or similar processes are to be mentioned here.

Due to the hard material coating, in particular a tungsten carbide layer, the temporal removal of the tool or extrusion die through the flowing ceramic mass strand is significantly lower than without an additional "protective layer" in the exit region of the tool.

It has proved to be advantageous if the extrusion die is constructed asymmetrically. This asymmetrical design is based on the finding that a uniform coating with hard material is not required for the described purpose. Therefore, advantageously, the extrusion mouthpiece can be constructed such that this or the base plate has an inflow side and an outflow side. On the inflow side, which assigns the interior of the press head of the extruder in the installed state, the extrusion die or the base plate can remain uncoated. Abtragungen in this area, which may be made in particular of tool steel can be tolerated.

By contrast, the outflow side, which is substantially responsible for the shaping of the honeycomb body, is advantageously coated with the described hard material coating. The- se one-sided coating offers particular manufacturing technology the advantage that simple, anisotropic coating process for applying the hard coating can be used. This in turn significantly reduces the cost of manufacturing the described extrusion dies.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

Show it

Figure 1 shows a known arrangement of an exhaust aftertreatment device in one

Exhaust line of an internal combustion engine;

FIG. 2 shows a ceramic honeycomb body for use in the exhaust gas aftertreatment device in FIG. 1;

Figs. 3A and 3B are various views of a conventional extrusion die for producing ceramic honeycomb bodies; and

FIG. 4 shows an illustration of an extrusion die according to the invention with a hard material coating, corresponding to the representation in FIG. 3B.

FIGS. 1 and 2 show examples of known exhaust aftertreatment devices, which explain the need for ceramic moldings which can be produced reliably and at low cost.

FIG. 1 shows a schematic representation of an internal combustion engine with an exhaust gas aftertreatment device according to the invention. The exhaust aftertreatment device in this embodiment is a filter in which soot particles are removed from the exhaust stream, e.g. a diesel particulate filter (DPF).

An internal combustion engine 10 is connected via an exhaust pipe 12, in which a filter device 14 is arranged. With the filter device 14 soot particles are filtered out of the exhaust gas flowing in the exhaust pipe 12. This is especially necessary in diesel engines to comply with legal requirements. The filter device 14 comprises a cylindrical housing 16, in which a rotationally symmetrical in the present exemplary embodiment, also a total cylindrical filter element 18 is arranged.

The cylindrical filter element 18 is designed in the present embodiment substantially as a ceramic honeycomb body. FIG. 2 shows such a filter element 18 in longitudinal section.

The filter element 18 is produced, for example, as an extruded shaped body made of a ceramic material, for example magnesium aluminum silicate, preferably cordierite. The filter element 18 is traversed by exhaust gas in the direction of the arrows 20. The exhaust gas enters the filter element 18 via an entry surface 22 and leaves it via an exit surface 24.

Parallel to a longitudinal axis 26 of the filter element 18 extend a plurality of inlet channels 28 in alternation with outlet channels 30. The inlet channels 28 are closed at the outlet surface 24. In the embodiment shown here, sealing plugs 36 are provided for this purpose. Instead of the sealing plug 36, however, it is also possible for the inlet channels 28 to taper towards the outlet surface 24 until the walls of the inlet channel 28 touch and the inlet channel 28 is closed in this way. In this case, the inlet channel 28 has a triangular cross-section in the direction parallel to the longitudinal axis 26.

Accordingly, the outlet channels 30 are open at the outlet surface 24 and closed in the region of the entrance surface 22.

The flow path of the unpurified exhaust gas thus leads into one of the inlet channels 28 and from there through a filter wall 38 into one of the outlet channels 30. This is illustrated by the arrows 32 by way of example.

For the production of the honeycomb formed as a filter element 18 according to the embodiment shown in Figure 2, as mentioned above, usually a Strangextrusi- onsverfahren used. In this case, extrusion mouthpieces are used, which effect the subdivision into the channels 28, 30 and the filter walls 38 during the extrusion.

FIGS. 3A and 3B show an extrusion mouthpiece 110 corresponding to the prior art. FIG. 3 A shows the extrusion nozzle 110 in plan view, while FIG. 3B shows a partial section in the horizontal direction through an exemplary embodiment. The centrally located portion of the extrusion die 110 shows. The extrusion mouth piece 110 is used for producing ceramic honeycomb bodies, for example the filter element 18 shown in FIG. 2, in extruders.

The extrusion die 110 has a frame 112 (see FIG. 3A) which has a round extrusion opening 114. In the frame 112, a base plate 116 is clamped. As can be seen in FIG. 3B, this base plate 116 has a multiplicity of openings 118.

As can be seen from FIG. 3A, these openings 118 have a square cross-section in this exemplary embodiment. Thus, a round ceramic honeycomb body with square channels according to the example in FIG. 2 can be produced in total, for example, with the extrusion die 110 shown in FIG. 3A. The openings 118 can be made for example by an erosion process in a tool steel plate. The individual openings 118 are separated from one another by webs 119 arranged between the openings. The individual openings 118 define channels, each having a hydraulic diameter of about 1 mm. The thickness of the base plate 116 is typically selected as a function of the diameter of the honeycomb body, the lands 119 between the individual openings 118 have a width of between 3 and 20 mils (milli-inches), i. Widths between 3 x 1/1000 x 254 mm and 30 x 1/1000 x 254 mm. Depending on the purpose of the honeycomb body, the land width may be between 4 and 6 mils (milli-inches), for example when used as a catalyst, i. between 4 x 1/1000 x 254 mm and 6 x 1/1000 x 254 mm. If the honeycomb body is used in filters, the web width may be> 10 mils (milli-inches), i. > 10 x 1/1000 x 254 mm.

During extrusion through the extrusion die 110 according to FIG. 3A, in the illustrated frame the strand of material, after passing through the extrusion die 110, flows together to form a closed lattice structure. In this case, in FIG. 3B, the flow direction of the mass strand is designated by the reference number 120. Accordingly, the extrusion orifice 110, in particular the base plate 116, has an inflow side 122, which opposes the flow direction 120, and an outflow side 124.

The extrusion die 110 shown in FIGS. 3A and 3B has the above-described disadvantages with regard to wear. As a result of the wear, the width of the openings 118 changes, in particular on the outflow side 124, so that the width of the individual strands, which are pressed through these openings 118, increases over time. This also increases the total weight of the honeycomb body produced, and the wall thickness of ceramic walls of the honeycomb body changes. This also changes the passage behavior of the exhaust gas purification components produced, for example the filter or catalysts, since the passageway through the filter walls 38 (see arrows 32 in FIG. 2) changes.

In contrast, FIG. 4 shows a sectional illustration corresponding to FIG. 3B of an extrusion die 110 according to the invention. The extrusion die 110 may in particular be constructed, for example, as shown in FIG. 3A. Again, the extrusion die 110 has a base plate 116 with openings 118 and lands 119.

In contrast to FIG. 3B, however, the base plate 116, which in turn is made of tool steel, for example, is provided with a hard material coating 126 in this exemplary embodiment according to the invention. This hard material coating 126 is applied only on the outflow side 124 of the base plate 116 in this preferred embodiment. This reduces the wear in this area. The width of the openings 118 in the region of the downstream side 124 defines the strand width of the single strands pressed through the openings 118, so that the reduction of the wear by the hard material coating 126 leads to a reproducible and more constant strand width.

In this embodiment, the hard material coating 126 is a tungsten carbide coating. This tungsten carbide coating preferably has a thickness d of 0.2 to 2 mm. However, thinner or thicker coatings are also possible.

For applying the hard material coating 126, for example, within the framework of a revision of the mouthpiece 110 (more rarely than required in the state of the art), the base plate 116 can be removed from the frame 112 and brought into a coating device. This is generally the case even before the initial use of the sample. In this case, one of the anisotropic coating methods described above can be used, for example, to selectively apply the hard material coating 126 only on the outflow side 124 of the extrusion die 110, while the insides of the openings 118 and Webs 119 and the inflow side 122 remains uncoated. For example, spray methods or similar methods can be used for this purpose.

Claims

claims

An extrusion die (110) for making ceramic honeycomb bodies (18) comprising a base plate (116) having at least two openings (118) and at least one land (119) disposed between the openings (118), the base plate (116) being a metallic one or ceramic base material, characterized in that the base plate (116) in the region of the openings (118) has at least one hard material coating (126).

2. extrusion die (110) according to the preceding claim, wherein the base plate (116) has an inflow side (122) and an outflow side (124), wherein the hard material coating (126) is applied exclusively on the outflow side (124)

The extrusion die (110) according to one of the two preceding claims, wherein the hard coating (126) comprises at least one of the following materials: a nitride; a carbide; an oxide; a boride; a phosphide.

4. extrusion die (110) according to any one of the preceding claims, wherein the hard material coating (126) comprises tungsten carbide.

5. extrusion die (110) according to the preceding claim, wherein the hard material coating (126) comprises at least one of the following materials: titanium carbide; titanium nitride; chromium carbide; chromium nitride; boride; chromium oxide; nickel phosphide; Iron nitride; alumina; boron carbide; boron nitride; silicon nitride; silicon carbide; Diamond.

6. extrusion die (110) according to any one of the preceding claims, wherein the hard coating (126) has a Vickers hardness of at least 1500.

7. extrusion die (110) according to any one of the preceding claims, wherein the hard material coating (126) has a thickness d between 0.2 mm and 2.0 mm.

8. extrusion die (110) according to any one of the preceding claims, wherein the base plate (116) has tool steel as the base material.

9. A method for producing an extrusion die (110) according to any one of the preceding claims, wherein for applying the hard coating (126) at least one of the following methods is used: Chemical Vapor Deposition, CVD; Physical Vapor Deposition, PVD; Surface hardening; electroplating; thermal spraying; Surfacing; Plate.

10. The use of an extrusion die (110) according to any one of claims 1 to 9 for the production of a ceramic exhaust aftertreatment device (14) for a motor vehicle, in particular a catalyst or a diesel particulate filter.