JP5014043B2 - Metal honeycomb carrier for exhaust gas purification catalyst - Google Patents

Description

  The present invention relates to a racetrack-type metal honeycomb carrier used for an exhaust gas purification catalyst or the like.

  Although regulations on exhaust gas in each country have been strengthened year by year, there is a particular demand for improvements in exhaust gas emission immediately after engine start, that is, immediately after cold start. This is because the exhaust gas purifying catalyst does not reach a temperature at which it exhibits its activity immediately after engine startup, and as a result, a larger amount of exhaust gas components, that is, chemical substances such as HC, CO, NOx, etc. than in normal engine operation. Due to being released inside.

  Conventionally, a ceramic carrier has been mainly used as a carrier for an exhaust gas purification catalyst of an internal combustion engine. However, in order to solve the problems associated with such a cold start, a metal honeycomb carrier having high thermal conductivity has recently attracted attention. .

  Generally, a metal honeycomb carrier is formed by alternately winding flat foil and corrugated foil using a heat-resistant alloy into a cylindrical honeycomb body, and after inserting the honeycomb body into a cylindrical metal outer cylinder It is manufactured by joining them by means such as brazing.

  The shape of the metal honeycomb carrier is generally cylindrical, and in this case, the cross section (transverse cross section) in the direction perpendicular to the flow of exhaust gas is circular. However, depending on the installation location, those having a cross section of racetrack type, square type, donut type, etc. are also employed. For example, a race honeycomb-shaped metal honeycomb carrier found in athletics can be mounted around an engine that cannot be installed in a cylindrical shape, so it is suitable for those with limited mounting locations such as motorcycles. It is.

  In the metal honeycomb carrier, the central part of the honeycomb body is heated by the inflow of exhaust gas, and the temperature of the central part becomes higher than the temperature of the outer periphery. Due to this temperature gradient, the central portion tends to extend from the outer peripheral portion due to thermal expansion, while the central portion extended due to thermal expansion starts to contract when cooled from the outer peripheral portion due to cooling. Therefore, when the honeycomb body and the outer cylinder portion are joined, the central portion cannot be sufficiently contracted, and as a result, thermal stress is generated, resulting in a problem that the joined portion is finally broken. In order to avoid such a problem, it is required to strengthen the joint. In JP-A-2-298620 (Patent Document 1), an intermediate cylinder that absorbs thermal strain is fitted between a honeycomb body and an outer cylinder portion, so that the honeycomb body and the outer cylinder are caused by such a temperature gradient. The technique which prevents peeling of a part is disclosed.

  Here, in the case of a racetrack-type metal honeycomb carrier, thermal stress is concentrated on the straight portion of the racetrack, while the arc portion has a smaller temperature deviation than the straight portion. As a result, the racetrack-type metal honeycomb carrier does not disperse the thermal stress as compared with the circular one, so that the straight portion is deformed and, in some cases, the honeycomb body is detached from the outer tube portion and may be damaged. is there. Japanese Patent Application Laid-Open No. 4-180838 (Patent Document 2) proposes brazing only the straight portion in order to prevent the honeycomb body from coming off from the outer cylinder portion in consideration of the properties of the racetrack metal honeycomb carrier. Yes.

  However, in the conventional brazing method or the like that is usually used for joining the honeycomb body and the outer cylinder portion, as described above, the durability of the racetrack-type metal honeycomb carrier that receives specific thermal stress is sufficiently high. It cannot be maintained. In addition, brazing materials such as nickel brazing are usually used for brazing because they have a low melting point, are self-soluble, and have good corrosion resistance. However, since nickel brazing is expensive, the amount used is reduced. Has become an important issue.

JP-A-2-298620 Japanese Patent Laid-Open No. 4-180838

  Accordingly, an object of the present invention is to provide a racetrack-shaped metal honeycomb carrier that can reduce the amount of a bonding substance such as a brazing material and can maintain or improve the structural durability.

  As a result of diligently examining the problem, the present inventors have inserted a support plate between the honeycomb body and the outer cylinder portion in which the wax foil has been conventionally inserted in the racetrack-shaped linear portion that is particularly susceptible to thermal stress, In addition, by restricting the joining between the support plate and the outer cylinder and the honeycomb body by the joining material to a part of the upstream side and the downstream side, the usage amount of the joining material is reduced, and the structure of the final metal honeycomb carrier It has become clear that maintenance or improvement of durability can be achieved.

  That is, the present invention relates to a metal honeycomb for exhaust gas purification catalyst, in which the metal honeycomb body is inserted into a metal outer cylinder, and the cross section in the exhaust gas flow direction has a racetrack shape including a straight portion and a curved portion. A support plate is disposed between the straight portion of the metal honeycomb body and the outer cylinder, and 1) between the outer cylinder and the support plate at an upstream portion in the exhaust gas flow direction, and in the exhaust gas flow direction. Only between the support plate and the metal honeycomb body in the downstream portion of the gas is bonded via the bonding substance, or 2) between the outer cylinder and the support plate in the downstream portion of the exhaust gas flow direction, and the exhaust gas flow direction There is provided a metal honeycomb carrier for an exhaust gas purification catalyst, in which only the support plate and the metal honeycomb body in the upstream portion of each are joined via a joining substance.

  With the operation cycle of 1) hot, 2) cold, and 3) hot in an internal combustion engine, the metal honeycomb carrier catalyst repeatedly expands and contracts, and as a result, between the metal honeycomb body and the outer cylinder covering it. Peeling easily occurs. In particular, when a metal honeycomb body expands due to exposure to high-temperature exhaust gas, the metal honeycomb carrier for exhaust gas purification catalyst having a racetrack-shaped cross section is affected by thermal expansion / contraction of the straight portion of the racetrack. Since it is most easily received, the peeling is remarkable in the straight portion.

  However, according to the racetrack-type metal honeycomb carrier for the exhaust gas purification catalyst of the present invention, the support plate is disposed on the straight portion of the racetrack shape between the metal honeycomb body and the outer cylinder, and one of the surfaces of the support plate is arranged. By arranging the bonding material only on the upstream side and the downstream side of the other surface and bonding the outer cylinder and the support plate, and the support and the honeycomb body to each other (for example, see FIGS. 1 and 2). A portion (play portion) where the bonding material is not disposed is formed between the outer cylinder and the metal honeycomb body. As a result, even if the metal honeycomb body repeatedly expands and contracts due to thermal fluctuations during the operation cycle, the influence is indirectly transmitted to the outer cylinder via the support plate.

  Specifically, at a high temperature, a part of the thermal expansion force of the metal honeycomb body is applied to the play portion of the support and is used as a force for pushing up toward the outside of the outer cylinder. On the other hand, when the metal honeycomb body contracts due to a decrease in temperature, the force is concentrated on the straight portion, but the carrier of the present invention has a play portion in that portion, so the force due to the shrinkage is applied to the play portion. Can be relaxed. As a result, it is possible to reduce peeling that occurs between the outer cylinder and the metal honeycomb body, which has occurred in the conventional racetrack-type metal honeycomb carrier.

  Thus, the metal carrier for an exhaust gas purifying catalyst of the present invention can improve its structural durability by interposing the support plate and limiting the location where the bonding material is disposed. In general, a brazing material is often used as the bonding material. However, since the brazing material is generally expensive, a reduction in the amount of use is desirable from the viewpoint of manufacturing cost.

  The term “metal honeycomb body” used in the present specification means a honeycomb-shaped cell formed from a metal foil. Although the metal honeycomb body is not limited, it can be formed by alternately winding or laminating a metal flat foil and a corrugated foil. Here, the properties of the “metal foil” constituting the metal honeycomb body are preferably those having a low heat capacity and excellent heat resistance, pressure resistance, and the like. Accordingly, stainless steel, heat resistant steel, and the like are preferable, but are not limited to these materials. Examples of stainless steel include steel materials such as ferritic stainless steel and austenitic stainless steel. In the present invention, these can be rolled into a foil shape and used.

  As for the thickness of the metal foil, in principle, it is preferable that the thickness of the metal foil is as thin as possible in order to improve the early activation ability of the catalyst finally produced by lowering the heat capacity. However, when determining the thickness of the metal foil, the strength aspect should also be considered. In the present specification, the metal honeycomb is inserted into a metal “outer cylinder” and joined by means of brazing or the like, and is referred to as a “metal honeycomb carrier” in the present specification. About the material of the said outer cylinder, the thing excellent in heat resistance, pressure | voltage resistance, etc. like a metal foil is preferable. Although it does not limit, the thing similar to the material of the metal foil mentioned above can be used.

  The metal honeycomb carrier of the present invention is intended for a racetrack shape whose cross section (transverse cross section) in the direction perpendicular to the exhaust gas flow is composed of a straight portion and an arc portion. For example, when winding flat foil and corrugated foil, a racetrack-shaped metal honeycomb is wound by providing a hollow portion at the center of the racetrack and then compressing the side of the metal honeycomb from two directions to push the hollow portion. It can be manufactured by crushing and flattening.

  As described above, the thermal stress tends to concentrate in the straight portion of the racetrack-shaped metal honeycomb carrier as compared with the arc portion. On the other hand, the arc portion has less temperature deviation than the straight portion. As a result, the racetrack-type metal honeycomb carrier does not disperse the thermal stress as compared with the circular one, and thus the straight portion is likely to be deformed. When brazing is used to join a metal honeycomb and an outer cylinder in the production of a racetrack-shaped metal honeycomb carrier, the brazing material is placed on the straight portion so that the metal is deformed by the straight portion. It is possible to prevent the honeycomb from being damaged and to reduce the amount of brazing material used (Japanese Patent Laid-Open No. 4-180838).

  In the present invention, a “support plate” is inserted between the metal honeycomb and the outer cylinder portion in place of the wax foil that has been arranged from the inlet gas side to the outlet gas side of the straight portion of the racetrack shape. By attaching the brazing foil only to a part of the support plate, the amount of brazing material used can be further reduced as compared with the prior art. The support plate is preferably made of a metal excellent in heat resistance, pressure resistance, etc., for example, but not limited to stainless steel, heat resistant steel and the like. In view of cost effectiveness, ferritic stainless steel is more preferable.

  Since the “support plate” used in the present invention is arranged so as to cover the entire portion from the inlet gas side end to the outlet gas side end of the straight portion, the size thereof is usually the length of the straight portion and the metal honeycomb per sheet. It is equal to the area multiplied by the length in the major axis direction of the carrier. Moreover, it is preferable that the thickness of a support plate is 0.3-1.0 mm.

  The shape of the support plate is generally a flat plate shape, but can also be a shape that is bent perpendicularly to the exhaust gas flow direction at the upstream and downstream ends. This bent portion serves as a stopper when the honeycomb is damaged and deformed, and can prevent the support plate from shifting in the axial direction.

  The bent portion may be formed to the full width of the support plate as viewed from the exhaust gas flow direction or may be formed partially. When a bent portion is partially formed, the portion can be installed at one or a plurality of locations on the support plate as viewed from the exhaust gas flow direction, and preferably can be installed only at a few locations. . In this case, each bent portion can have a width of 5 to 15 mm when a carrier substrate for a normal race track is used. Further, the height of the bent portion viewed from the exhaust gas flow direction can be set to, for example, 1 to 2 mm when a normal carrier substrate for a race track is used. These widths and heights are merely examples, and are not intended to limit the scope of the present invention. If the support plate is not displaced and does not protrude significantly from the carrier base material. Such a size may be sufficient.

  Further, the bent portion may be, for example, 1) preparing a support plate longer than the intended axial length of the carrier substrate and bending the longer portion by bending, or 2) desired for a normal support plate. It can be installed by brazing a support plate piece of the size. As for the bending method, the support plate may be bent vertically from the upstream and / or downstream end of the support plate, or may be bent so as to draw an arc from the end.

  The bent portion may be formed only in either the upstream portion or the downstream portion in the exhaust gas flow direction, or may be formed in both the upstream portion and the downstream portion. In one embodiment, when the metal honeycomb carrier is viewed from a cross section parallel to the exhaust gas flow direction, when the bent portion existing at the upstream end is bent in the outer cylinder direction (outside), the downstream end May be bent in the honeycomb body direction (inner side). As another aspect, when the bent part which exists in an upstream edge part is bent in the honeycomb body direction (inner side), the thing of a downstream edge part may be bent in the outer cylinder direction (outer side). As yet another aspect, the bent portions of the upstream end and the downstream end may be bent in the same direction.

  The metal honeycomb carrier of the present invention can be manufactured by inserting a metal honeycomb body into an outer cylinder, and further inserting a support plate between them to partially join each other. Here, the upstream side of the metal honeycomb carrier into which the exhaust gas flows is exposed to a high-temperature entering gas during the exhaust gas treatment as compared with the downstream side, and is likely to undergo thermal expansion. In addition, the straight portion of the racetrack shape has a larger expansion / contraction from the center portion of the racetrack to the straight portion. As a result, the gap between the metal honeycomb and the outer cylinder tends to increase as the position closer to the exhaust gas upstream portion of the straight portion.

  However, according to the present invention, A) between the outer cylinder and the support plate in the upstream portion in the exhaust gas flow direction, and B) between the support plate and the metal honeycomb body in the downstream portion in the exhaust gas flow direction. It is possible to achieve maintenance or improvement of the final structural durability by bonding only the portions with the bonding material. Moreover, in another aspect, a joining location is A) between the said outer cylinder and the said support plate in the downstream part of a waste gas flow direction, and B) The said support plate and the said metal honeycomb body in the upstream part of a waste gas flow direction. It can also be in two places.

  Here, such joining can be performed via a connecting substance disposed on the support plate. The “joining substance” used in the present invention means a substance capable of joining metals, for example, a substance used for brazing or welding. From the viewpoint of saving material costs, a substance used for brazing, for example, brazing material is preferable. On the other hand, also from the viewpoint of strength, the bonding material is preferably a brazing material. In this case, a nickel-based brazing material is preferable among the brazing materials. Bonding with a bonding material can be performed by adhering the bonding material together with an organic substance such as a binder to a part of a support plate as described above, and performing heat treatment under oxygen-free conditions in a vacuum furnace. it can.

  A material other than the brazing material, preferably a brazing material, is used, and the material cost can be greatly reduced by limiting the joint location to a part of the upstream portion and the downstream portion as described above. Furthermore, as a result of the play portions other than the above-mentioned joining portions relieving thermal expansion and contraction, the metal honeycomb carrier for exhaust gas purifying catalyst of the present invention has superior durability compared to the conventional one. In this respect, the invention described in JP-A-4-180838, in which the metal honeycomb body peels and breaks while the expansion and contraction are repeated during the thermal cycle, is essentially different from the present invention.

  In addition, in order to further improve the durability, a bonding substance can be arranged in addition to the above-mentioned bonding portion. For example, in order to prevent the metal honeycomb body from falling off the outer cylinder, a part of the racetrack-shaped curved portion may be joined in addition to the straight portion. However, when the area of the joined portion in the curved portion is increased, the portion that relaxes the contraction / expansion of the honeycomb body caused by thermal stress or the like is reduced, and separation between the honeycomb body and the outer cylinder is likely to occur. Therefore, it is preferable that the joining between the outer cylinder and the metal honeycomb body in the curved portion is kept to such an extent that peeling does not occur, or is not performed at all.

  Here, the term “upstream portion” used in the present specification means the periphery of a portion of the support plate used in the present invention that is exposed to a high-temperature inlet gas, and is used for the purpose of joining to an outer cylinder or a metal honeycomb. A bonding material or brazing material is disposed in part. On the other hand, the term “downstream part” means a part periphery located on the opposite side of the exhaust gas upstream part. In consideration of the amount of the joining material used and the durability of the metal honeycomb carrier, the joining material is within the range of 10 to 30% of the axial length from the inlet gas side and the axial length from the outlet gas side in the carrier. It is preferable to arrange within a range of 10 to 30%. More preferably, the ratio is 20-25%.

  The specific material, location, size, and usage conditions of the bonding material are determined by comparing the amount of bonding material used and the durability of the metal honeycomb carrier, and the metal honeycomb body inserted into the outer cylinder expands / By contracting, the optimum position can be appropriately selected within a range where the support plate and the outer cylinder and / or the metal honeycomb body do not peel. However, in any aspect, in the present invention, the total area where the bonding material used for bonding the support plate to the metal honeycomb and the outer cylinder is smaller than the area of the support plate, preferably the bonding material is disposed. The total area is less than 1/2 of the area of the support plate. The thickness of the bonding material to be arranged is 20 to 50 μm. Moreover, the said joining substance can be applied also to the joining location of the flat foil and corrugated foil inside a metal honeycomb in addition to the said joining location.

  The metal honeycomb carrier of the present invention can be coated with various catalyst components on the surface as a base material for an exhaust gas purification catalyst. In addition, there is no restriction | limiting of the use about noble metals etc. which are catalyst components, and there is no restriction | limiting also about those loading methods. In general, after forming a support layer on the surface of a metal honeycomb carrier using a slurry such as activated alumina (γ-alumina), a chemical solution containing a noble metal is immersed and supported on the surface of the support layer. A catalyst can be produced.

  The present invention will be described more specifically with reference to the following examples. The present invention is not limited to these examples.

(Example)
Ferritic stainless steel foil (thickness 50 μm, width 100 mm) is formed into a corrugated shape (300 cells / square inch). The corrugated foil thus prepared was wound together with a flat foil (50 μm or 80 mm wide) made of the same material to form a racetrack-shaped metal honeycomb body having a short diameter of 46 mm, a long diameter of 86 mm and a length of 100 mm. A ferritic stainless steel plate (thickness 0.5 mm × width 36 mm × length 100 mm) is used as a support plate, and a brazing foil (thickness) for joining the outer cylinder to the upstream portion of the surface of the support plate that contacts the outer cylinder. 25 μm × width 36 mm × length 25 mm), on the other hand, a brazing foil (thickness 25 μm × width 36 mm × length 25 mm) for joining with the metal honeycomb on the downstream side of the surface of the support plate in contact with the metal honeycomb body Attached. Subsequently, after attaching the stainless steel plate so as to be positioned on the plane portion of the metal honeycomb, the present invention is carried out by inserting them into a ferritic stainless steel outer tube (short diameter 50 mm × long diameter 90 mm × length 100 mm). A metal honeycomb carrier was prepared. FIGS. 1 and 2 show a cross section (cross section perpendicular to the exhaust gas flow) and a vertical cross section (cross section parallel to the exhaust gas flow) of the metal honeycomb carrier, respectively.

Subsequently, the carrier surface was coated with alumina, and immersed and supported using a chemical solution containing platinum and rhodium, thereby producing a metal honeycomb carrier catalyst of the present invention (Pt / Rh = 1.0 / per liter of carrier volume). 0.5 g / L). The final amount of brazing foil used was 38 cm ² .

(Comparative example)
A racetrack-shaped metal honeycomb body was formed by the same method as in the example. Of the outer periphery of the formed metal honeycomb, a nickel-based brazing foil (thickness 25 μm, width 50 mm) was wound from the inlet gas side end to the outlet gas side end of the straight part of the racetrack. After being inserted into a ferritic stainless steel outer cylinder (minor axis 50 mm x major axis 90 mm x length 100 mm), a brazing material is applied to the outer cylinder and the metal honeycomb body, and then heat-treated under oxygen-free conditions. I was in contact with wax. FIGS. 3 and 4 show a cross section and a vertical section of the metal honeycomb carrier thus manufactured, respectively.

Subsequently, a metal honeycomb carrier catalyst was produced by catalyzing the metal honeycomb carrier in the same manner as in the above example. The final amount of brazing foil used was 79.3 cm ² .

(An endurance test)
Results are not shown, the above examples and comparative examples catalyze the result of multiplying the durability test under a constant thermal cycles, the amount of catalyst used brazing material of Example was halved from 79.3Cm ² to 38cm ² Nevertheless, the structural durability was improved.

  Further, on the basis of the catalyst of the above embodiment, the bent portions are formed in the portions located at the end portions of the upstream portion and the downstream portion of the support plate and present on both sides of the support plate when viewed from the exhaust gas flow direction. The prepared catalyst was also examined (FIGS. 5 and 6). The catalyst having two bent portions at the upstream end and two bent portions at the downstream end of each support plate was found to have further improved structural durability compared to the catalyst of the above-described example (Results). Is not shown). 5 and 6 with a reduced brazing foil width (20 mm) (FIGS. 7 and 8) are also more durable than the comparative example. did.

  According to the metal honeycomb carrier of the present invention, the amount of the very expensive brazing material used can be reduced and the final structural durability can be improved. A racetrack metal honeycomb carrier can be provided.

FIG. 1 shows a cross section of the metal honeycomb carrier of the above embodiment. FIG. 2 shows a longitudinal section of the metal honeycomb carrier of the above embodiment in the AA direction in FIG. FIG. 3 shows a cross section of the metal honeycomb carrier of the comparative example. FIG. 4 shows a longitudinal section in the AA direction in FIG. 3 of the metal honeycomb carrier of the comparative example. FIG. 5 shows a shape in which two upstream end portions are bent toward the contact surface with the bonding material, and two downstream end portions are bent toward the contact surface with the bonding material per support plate. The figure which looked at the metal honeycomb carrier of this invention which looked from the exhaust gas flow direction is represented (width of brazing foil: 25 mm each). FIG. 6 shows a longitudinal section in the AA direction in FIG. FIG. 7 shows a shape in which two upstream end portions are bent toward the contact surface with the bonding material, and two downstream end portions are bent toward the contact surface with the bonding material, per support plate. The figure which looked at the metal honeycomb carrier of this invention which looked from the exhaust gas flow direction is represented (width of brazing foil: 25 mm each). FIG. 8 shows a longitudinal section in the AA direction in FIG. 7 (width of brazing foil: 20 mm each).

Explanation of symbols

1 wax foil 2 support plate 3 metal honeycomb 4 outer cylinder 5 bent part

Claims (4)

A metal honeycomb carrier for an exhaust gas purification catalyst, in which a metal honeycomb body is inserted into a metal outer cylinder, and a cross section in the exhaust gas flow direction has a racetrack shape including a straight portion and a curved portion,
A support plate is disposed between the straight portion of the metal honeycomb body and the outer cylinder,
1) Only between the outer cylinder and the support plate in the upstream portion in the exhaust gas flow direction and between the support plate and the metal honeycomb body in the downstream portion in the exhaust gas flow direction are bonded via a bonding substance, or 2) Between the outer cylinder and the support plate in the downstream portion in the exhaust gas flow direction, and only between the support plate and the metal honeycomb body in the upstream portion in the exhaust gas flow direction are bonded via the bonding material. Metal honeycomb carrier for exhaust gas purification catalyst. The bonding substance is disposed in the range of 10 to 30% of the axial length from the inlet gas side and in the range of 10 to 30% of the axial length from the outlet gas side in the upstream portion and the downstream portion , respectively. The metal honeycomb carrier for exhaust gas purification catalyst according to claim 1. The metal honeycomb for an exhaust gas purification catalyst according to claim 1 or 2, wherein at least a part of an upstream portion and / or an end portion of the downstream portion of the support plate is bent toward a contact surface with the bonding material. Carrier .   The metal honeycomb carrier for exhaust gas purification catalyst according to any one of claims 1 to 3, wherein the joining substance is a brazing material.

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