JP3287975B2 - Metal carrier for exhaust gas purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a metal carrier for an exhaust gas purifying catalyst.

[0002]

2. Description of the Related Art A cylindrical honeycomb body obtained by winding a metal flat plate and a metal corrugated plate alternately concentrically, an intermediate cylinder covering the outer periphery of the honeycomb body, and an outer periphery of the intermediate cylinder are formed. And an outer cylinder that covers the outer peripheral surface of the intermediate cylinder at the other end of the intermediate cylinder by brazing the inner peripheral surface of the intermediate cylinder to the outer peripheral surface of the honeycomb body at one end of the intermediate cylinder. 2. Description of the Related Art A metal carrier for an exhaust gas purifying catalyst, which is brazed to a surface and carries a catalyst on a honeycomb body, is known (see Japanese Patent Application Laid-Open No. 5-57197). In this metal carrier, when the diameter of the honeycomb body changes due to thermal expansion and contraction, the intermediate cylinder deforms and absorbs the change in the diameter of the honeycomb body, thereby generating a large stress locally in the honeycomb body. To prevent cracks from occurring in the honeycomb body.

[0003]

However, cracks are generated in the honeycomb body not only because of the physical reason that a large stress is generated in the structure, but also because the honeycomb body is chemically changed by the brazing material. It is also based on the chemical reason that cracks occur as a result. That is, when the intermediate cylinder and the honeycomb body are heated to a high temperature in order to braze and join the intermediate cylinder and the honeycomb body, nickel Ni in the brazing material diffuses into the flat plate and the corrugated sheet constituting the honeycomb body. However, at this time, when a large amount of nickel Ni diffuses into the flat plate and the corrugated plate, the flat plate and the corrugated plate are embrittled, and as a result, cracks are easily generated. Further, when a large amount of nickel Ni diffuses into the flat plate and the corrugated plate, the thermal expansion coefficient of the flat plate portion and the corrugated plate portion where the nickel Ni is diffused is locally increased, and as a result, the distance between the other flat plate portion and the corrugated plate portion is increased. As a result, a large step occurs in the amount of thermal expansion. When a difference in the amount of thermal expansion occurs in the flat plate or the corrugated plate, a large stress is generated in the flat plate and the corrugated plate, and thus a crack is easily generated.

[0004] When the flat plate and the corrugated plate contain aluminum, the diffused nickel Ni and aluminum Al combine to form a Ni-Al alloy. However, this Ni
When the -Al alloy is formed, the oxidation resistance of the flat plate and the corrugated plate is reduced, and thus cracks are easily generated. When a large amount of nickel Ni diffuses into the flat plate and the corrugated sheet, a crack is easily generated. Therefore, in order to prevent the crack from being generated, it is necessary to prevent a large amount of nickel Ni from diffusing into the flat plate and the corrugated sheet. There is. However, in the above-mentioned known metal supports, no consideration is given to the occurrence of cracks based on such chemical reasons, and therefore, in the known metal supports, cracks are generated based on such chemical reasons. There is a problem that occurs.

[0005]

According to the present invention, there is provided a cylindrical honeycomb obtained by winding a metal flat plate and a metal corrugated plate alternately concentrically. Body, an intermediate cylinder covering the outer periphery of the honeycomb body, and an outer cylinder covering the outer periphery of the intermediate cylinder. At one end of the intermediate cylinder, the inner peripheral surface of the intermediate cylinder is brazed to the outer peripheral surface of the honeycomb body. At the other end of the intermediate cylinder, the outer peripheral surface of the intermediate cylinder is brazed to the inner peripheral surface of the outer cylinder, and the catalyst is carried on the honeycomb body. The amount of brazing material per unit area at the brazing joint between them is smaller than the amount of brazing material per unit area at the brazing joint between the intermediate cylinder and the outer cylinder.

[0006]

Since the amount of brazing material per unit area at the brazing joint between the intermediate cylinder and the honeycomb body is smaller than the amount of brazing material per unit area at the brazing joint between the intermediate cylinder and the outer cylinder, the intermediate cylinder and the honeycomb are joined together. The amount of nickel Ni in the brazing material that diffuses into the honeycomb body during the brazing between the bodies becomes small.

[0007]

1 and 2, reference numeral 1 denotes a cylindrical honeycomb body obtained by winding a metal flat plate 2 and a metal corrugated plate 3 alternately concentrically, and 4 denotes a honeycomb body. 1
A metal intermediate cylinder 5 coaxially disposed and covering the outer periphery of the honeycomb body 1 is a metal outer cylinder disposed coaxially with the intermediate cylinder 4 and covering the outer periphery of the intermediate cylinder 4, respectively. A catalyst is supported on the body 1. As shown in FIGS. 1 and 2, there are gaps between the honeycomb body 1 and the intermediate cylinder 4 and between the intermediate cylinder 4 and the outer cylinder 5, but these gaps are exaggerated in FIGS. 1 and 2. These gaps are actually quite small. The flat plate 2 and the corrugated plate 3 are formed from a ferrite alloy containing aluminum, and the thickness of the flat plate 2 and the corrugated plate 3 is 50 μm or less. On the other hand, the intermediate cylinder 4 has a thickness of about 0.5 mm, and the outer cylinder 5 has a thickness of about 1.5 mm.

In FIG. 1, the contact portions of the flat plate 2 and the corrugated plate 3 located outside the broken line are joined to each other by brazing. In FIG. 1, an arrow X indicates the flow direction of the exhaust gas discharged from the engine. Therefore, when viewed from the flow direction X of the exhaust gas, the flat plate 2 is formed only at the upstream end and the downstream end of the honeycomb body 1 and at the outer peripheral portion of the honeycomb body 1. And the corrugated plate 3 are joined to each other by brazing.

On the other hand, as shown in FIG. 3, a large number of slits 6 extending in the axial direction are formed at the downstream end of the intermediate cylinder 4 located on the downstream side as viewed from the flow direction X of the exhaust gas. The inner peripheral surface of the downstream end of the intermediate cylinder 4 in which the slit 6 is formed is joined to the outer peripheral surface of the downstream end of the honeycomb body 1 by brazing. On the other hand, the outer peripheral surface of the upstream end of the intermediate cylinder 4 is joined to the inner peripheral surface of the upstream end of the outer cylinder 5 by brazing. Therefore, as shown in FIG. 1, a brazing material layer extending over the length L _{1 in} the axial direction between the outer peripheral surface of the downstream end of the honeycomb body 1 and the inner peripheral surface of the downstream end of the intermediate tube 4. A brazing material layer 8 is formed between the outer peripheral surface of the upstream end of the intermediate cylinder 4 and the inner peripheral surface of the upstream end of the outer cylinder 5 so as to extend over the length L _{2 in} the axial direction. Is done.

As shown in FIG. 1, the axial length L ₁ of the brazing material layer 7 is longer than the axial length L ₂ of the brazing material layer 8, but the thickness t ₁ of the brazing material layer 7 is It is considerably thinner than the thickness t _2. Therefore, the amount of brazing material per unit area of the brazing material layer 7 is considerably smaller than the amount of brazing material per unit area of the brazing material layer 8. In the brazing operation, the regions where the respective brazing material layers 7 and 8 are to be formed are filled with the brazing material, and then the entire honeycomb body 1, the intermediate cylinder 4 and the outer cylinder 5 are vacuum-sealed for one hour.
It is performed by heating to 200 ° C. or more. When the brazing operation is performed in this manner, nickel Ni in the brazing material diffuses into the flat plate 2 and the corrugated plate 3 during the brazing operation.

As described above, when a large amount of nickel Ni diffuses into the flat plate 2 and the corrugated plate 3 at this time,
Further, the corrugated plate 3 becomes brittle, and as a result, the flat plate 2 or the corrugated plate 3 is easily cracked. When a large amount of nickel Ni diffuses into the flat plate 2 and the corrugated plate 3, the thermal expansion coefficient of the flat plate portion and the corrugated plate portion where the nickel Ni is diffused locally increases. As a result, a large step occurs in the coefficient of thermal expansion between the other flat plate portion and the corrugated plate portion, so that a large stress is generated in the flat plate 2 and the corrugated plate 3, and thus the flat plate 2 or the corrugated plate 3 Cracks are likely to occur.

When nickel Ni diffuses into flat plate 2 and corrugated plate 3 as described above, the diffused nickel Ni and aluminum Al combine to form a Ni-Al alloy. However, at this time, if a large amount of the Ni-Al alloy is generated, the oxidation resistance of the flat plate 2 and the corrugated plate 3 is reduced, and thus the flat plate 2 and the corrugated plate 3 are liable to crack. When a large amount of nickel Ni diffuses into the flat plate 2 and the corrugated plate 3, a crack is easily generated. Therefore, a large amount of nickel Ni diffuses into the flat plate 2 and the corrugated plate 3 in order to prevent the crack from being generated. Need to be stopped. Therefore, in the present invention, the amount of brazing material per unit area of the brazing material layer 7 is reduced. That is, the amount of nickel Ni diffused into the flat plate 2 and the corrugated plate 3 during the brazing operation is proportional to the amount of brazing material per unit area. Therefore, if the amount of brazing material per unit area is reduced, nickel Ni diffused into the flat plate 2 and the corrugated plate 3
Is reduced, and thus the occurrence of cracks in the flat plate 2 and the corrugated plate 3 can be prevented.

On the other hand, the joining strength between the honeycomb body 1 and the intermediate cylinder 4 is almost proportional to the total amount of the brazing material. Therefore, even when the amount of brazing material per unit area is reduced, the honeycomb body 1 and the intermediate cylinder 4 are hardened. It is necessary to increase the area of the brazing material layer 7 so that the bonding strength between them does not decrease.
In the embodiment according to the present invention is therefore the axial length L ₁ of the brazing material layer 7 as shown in FIG. 1 is longer than the axial length L ₂ of the brazing material layer 8.

When the exhaust gas starts flowing into the honeycomb body 1, the temperature of the honeycomb body 1 gradually increases, and the honeycomb body 1
Is higher than the temperature of the intermediate cylinder 4. As a result, the outer peripheral portion of the honeycomb body 1 is buckled and plastically deformed by the thermal expansion action of the honeycomb body 1. Next, when the operation of the engine is stopped, the temperature of the honeycomb body 1 gradually decreases, and thus the honeycomb body 1 contracts gradually. At this time, the honeycomb body 1
Is kept plastically deformed, so that when the temperature returns to the original temperature, the diameter of the honeycomb body 1 slightly decreases. Therefore, at this time, the downstream end of the intermediate cylinder 4 is curved inward.

When the downstream end of the intermediate cylinder 4 is bent inward as described above, a bending moment acts on the intermediate cylinder 4. In this case it is necessary to take as large as possible a gap L ₀ between the brazing material layer 7, 8 to reduce the bending moment generated. Therefore, the axial length L _{1 of the} brazing material layer 7
It is defined as to maximize the gap L ₀ while ensuring a strong bond between the honeycomb body 1 and the intermediate cylinder 4.

When the temperature of the honeycomb body 1 rises due to the exhaust gas heat, the portion of the honeycomb body 1 where the brazing material layer 7 is not formed is compared with the portion of the honeycomb body 1 where the brazing material layer 7 is formed. An attempt is made to thermally expand by a thickness t _{1 of} 7. In this case, as the thickness t ₁ of the brazing material layer 7 is larger, the difference between the deformation amount of the honeycomb body 1 portion where the brazing material layer 7 is not formed and the deformation amount of the honeycomb body 1 portion where the brazing material layer 7 is formed. When the expansion and contraction action of the honeycomb body 1 is repeated, the honeycomb body 1 where the brazing material layer 7 is not formed and the honeycomb body 1 where the brazing material layer 7 is formed
A crack will be generated at the boundary with the portion. However, in the embodiment according to the present invention, the thickness t
₁ is thin, the difference between the amount of deformation of the honeycomb body 1 portion where the brazing material layer 7 is not formed and the amount of deformation of the honeycomb body 1 portion where the brazing material layer 7 is formed is small. And the brazing material layer 7 where the honeycomb body 1 is not formed
It is possible to prevent cracks from occurring at the boundary with the honeycomb body 1 where the cracks are formed.

[0017]

According to the present invention, it is possible to prevent the occurrence of cracks in the honeycomb body, thereby improving the durability of the metal carrier provided with the honeycomb body.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a metal carrier.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is a partial cross-sectional view of a metal carrier showing an appearance of an intermediate cylinder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Honeycomb body 2 ... Flat plate 3 ... Corrugated plate 4 ... Intermediate cylinder 5 ... Outer cylinder 7, 8 ... Brazing material layer

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisashi Takei 7800 Chihama, Daito-cho, Ogasa-gun, Shizuoka Prefecture Inside Cataler Industry Co., Ltd. (56) References JP-A-3-157139 (JP, A) JP-A-5 -57197 (JP, A) JP-A-4-27443 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 B01D 53/86

Claims (1)

(57) [Claims] 1. A cylindrical honeycomb body obtained by winding a metal flat plate and a metal corrugated plate alternately concentrically, an intermediate cylinder covering the outer periphery of the honeycomb body, and an outer periphery of the intermediate cylinder. And an outer cylinder that covers the outer peripheral surface of the intermediate cylinder at the other end of the intermediate cylinder by brazing the inner peripheral surface of the intermediate cylinder to the outer peripheral surface of the honeycomb body at one end of the intermediate cylinder. In the metal carrier for exhaust gas purifying catalyst, which is brazed to the surface and carries the catalyst on the honeycomb body,
A metal carrier for an exhaust gas purification catalyst in which the amount of brazing material per unit area at the brazing joint between the intermediate cylinder and the honeycomb body is smaller than the amount of brazing material per unit area at the brazing joint between the intermediate cylinder and the outer cylinder .