JPH0611405B2 - Metal base for automobile catalysts with heat fatigue resistance - Google Patents

Description

TECHNICAL FIELD The present invention relates to a metal substrate for an automobile catalyst.

[Prior Art] It has been over 10 years since the exhaust gas regulations of automobiles were enforced, but the current exhaust gas countermeasures are implemented by improving the engine and purifying the exhaust gas by a catalyst. The catalyst for purifying exhaust gas is on a ceramic honeycomb such as cordierite.
The mainstream is a structure supporting γ-alumina powder supporting a precious metal catalyst such as Pt. By the way, these ceramic honeycombs have slightly higher exhaust resistance, and due to the heat resistance of the cushioning stainless steel mesh inserted between them and the outer cylinder to prevent the honeycomb from breaking, its operating temperature should be kept low. There were drawbacks such as restrictions.

In order to improve these drawbacks, a metal carrier made of stainless steel foil has been attracting attention in recent years. Naturally, these metal carriers are required to have heat resistance to endure high temperature and high speed exhaust gas during reaction and heat fatigue resistance to endure severe heating and cooling. Second
As shown in the cross-sectional view in the figure, generally, a metal carrier is formed by stacking a stainless flat foil with a thickness of about 50 μ and a corrugated stainless corrugated foil and winding them into a cylindrical or elliptic cylinder. Then, the flat foil, the corrugated foil, and the outer cylinder are joined to each other by brazing or resistance welding. FIG. 3 schematically shows this, and shows that the shaded portion 8 and the thick portion 9 are brazed.

In order for the metal carrier to withstand high temperature and high speed exhaust gas, it is effective to use stainless steel foil with good oxidation resistance to increase the bonding area between the flat foil, corrugated foil, and outer cylinder, but that alone requires severe heating.・ Cannot stand cooling. That is, in the metal carrier mounted on the automobile engine, the honeycomb portion is heated prior to the outer cylinder from the engine start to the traveling start,
On a long downhill, the engine brake state is maintained for a long time, and during the type in which the fuel supply is cut during this period, the honeycomb is cooled prior to the outer cylinder, resulting in a large temperature difference between the outer cylinder and the honeycomb. Moreover, since the positive and negative of the temperature difference are switched between during heating and during cooling, the honeycomb undergoes thermal fatigue fracture in the portion close to the outer cylinder, and the back pressure of the exhaust gas causes the honeycomb to fly downwind.

As a prior art for preventing problems when the metal carriers are firmly bonded in this way, a method of mechanically fixing the honeycomb is disclosed in US Pat. No. 4,186,172 and JP-B-60-27807. Further, a method for partially bonding the honeycomb is disclosed in JP-A-62-45345 and JP-A-61-19957, but the method for bonding the honeycomb and the outer cylinder is not clearly described. However, at least one of the bonding strength and the thermal fatigue resistance of the honeycomb to the outer cylinder does not exhibit sufficient characteristics.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned drawbacks of the prior art, and has heat fatigue resistance that withstands high-temperature and high-speed exhaust gas flow and also withstands rapid heating and cooling. A metal substrate having the same is provided.

[Means for Solving the Problem] In order to achieve this object, the present invention has devised a structure of a base body in which thermal fatigue does not easily occur even when a temperature difference occurs between the honeycomb and the outer cylinder. The figure is an example of the present invention. That is, the present invention is a metal for an automobile catalyst comprising a metal honeycomb formed by stacking and winding a flat metal foil (hereinafter referred to as a flat foil) and a corrugated metal foil (hereinafter referred to as a corrugated foil), and a metal outer cylinder surrounding the metal honeycomb. In the substrate, the flat foil and the corrugated foil are joined from the outermost circumference to the innermost circumference at least at both ends in the central axis direction of the honeycomb, and the outer cylinder and the honeycomb are not joined at the both ends, and the remaining portion is formed. In the honeycomb of No. 2, the outermost periphery is joined to the outer cylinder at a location at least 5 mm away from the middle end of the portion where the outermost periphery to the innermost periphery of the both ends are joined together, and the outer periphery is in cross section in the central axis direction. The portion joined to the cylinder and the above-mentioned both ends are connected via the joined honeycomb portion, and in the honeycomb surrounded by the joint surface with the outer cylinder, in the honeycomb cross section perpendicular to the central axis, When Bonded portions not is an automobile catalyst substrate having a thermal fatigue resistance, characterized in that distributed in the radial direction.

[Detailed Description Based on Drawings of the Invention] Next, the present invention will be described in detail. FIG. 1 shows a cross section in the direction of the central axis of the metal substrate of the present invention. In general, both ends of the honeycomb on the exhaust side of the metal substrate on the inlet side and the outlet side of the exhaust gas are flat foils.
If used without joining the corrugated foils, the high speed exhaust gas will vibrate the foils and cause fatigue failure. Therefore, it is necessary to bond the corrugated foils 1 and 2 near both ends of the honeycomb and the flat foil to each other to prevent individual vibrations. However, since the honeycomb in the bonded part behaves as one rigid body, if the surface of this part in contact with the outer cylinder is bonded to the outer cylinder 3, the outer circumference of the honeycomb will change when the temperature difference between the outer cylinder 3 and the honeycomb repeatedly changes. Thermal fatigue failure occurs near the part.

Therefore, in the present invention, the honeycomb portion (hereinafter referred to as a completely joined portion) joined from the innermost circumference to the outermost circumference of the honeycomb is not joined to the outer cylinder 3. However, this alone means that the honeycomb is not fixed to the outer cylinder, so that the honeycomb pops out on the lee side of the exhaust gas during use. Therefore, it is necessary to bond the honeycomb and the outer cylinder at portions other than the completely bonded portion of the honeycomb.

As a result of various studies on the joining portion between the honeycomb and the outer cylinder, the inventors of the present invention have found that the joining portion 6 between the honeycomb and the outer tube is formed from the middle end portions of the complete joining portions 1 and 2 at both ends in view of heat fatigue resistance. It is necessary to separate them by at least 5 mm (L ₁ and L _{2 in} FIG. 1 (a)), which prevents the thermal fatigue failure of the honeycomb between the completely joined portions 1 and 2 and the joined portion 6 of the outer cylinder. From the viewpoint of what can be done and the bonding strength of the honeycomb to the outer cylinder, the honeycomb bonded between the bonding portion 6 of the honeycomb and the outer cylinder and the completely bonded portions 1 and 2 at both ends is bonded when viewed in a cross section in the central axis direction. It has been found that it is necessary to be connected through the portions (hereinafter referred to as honeycomb bonded portions) 4 and 5.

Further, in the inside of the honeycomb surrounded by the joining surface of the honeycomb and the outer cylinder, from the viewpoint of heat fatigue resistance, in the cross section perpendicular to the central axis of the honeycomb, at least the honeycomb non-joining portion is distributed in the radial direction. It was found necessary. Depending on the cross section, the non-bonded portions of the honeycomb and the bonded portions of the honeycomb are distributed in the radial direction. In this case, the non-bonded portions of the honeycomb preferably occupy 20% or more of the total cross-sectional area. Therefore, the case where the entire cross section is the honeycomb non-bonded portion is also included. That is, Fig. 1 (b) shows that of (a)
The cross section of the central axis in the portion A ₁ -A ₁ ′ is shown, and there is a honeycomb non-bonding portion and a honeycomb bonding portion on every radial line, and the thermal stress in the radial direction on this surface is relaxed. The A ₂ -A ₂ 'cross section of FIG. 1 (a) is the total cross-section honeycomb unbonded portion, radial thermal stresses on the surface is relaxed. If most of the cross section is a honeycomb joint,
Relaxation of thermal stress on this surface becomes difficult.

The term "joining" as used in the present invention means that the corrugated foil, the flat foil, and the outer cylinder are joined to each other by a method such as brazing, resistance welding, laser welding, electron beam welding, and arc welding. In addition, if a part of the brazing material, arc, etc. wraps around the part that should not be joined to join some of the contacts, it is not considered to be joined here. Furthermore, diffusion bonding, which often occurs when stainless steel sheets are contacted and heated in high vacuum or low pressure hydrogen, is not included in the bonding here because the contact strength of honeycomb contacts is low. In the present invention, the corrugated shape of the corrugated foil may be a sine wave, a trapezoid, a rectangle, or the like.

4 to 6 show another example of the present invention.
Here, the meanings of the respective portions 1 to 7 are the same as those in FIG. Those with these joint structures 〝The manufacturing method for brazing is to draw a development diagram according to each brazing pattern before winding the foil in advance, apply the binder of the brazing material according to them, and apply the flat foil and the corrugated foil. The brazing material may be applied after it has been rolled up. Further, in any other joining method, joining may be performed according to these development views in the process of winding the foil.

[Example] Example-1 FIG. 1 shows one embodiment of the present invention.
Figure (a) is a metal composed of a stainless steel outer cylinder with an inner diameter of 100 mm, a thickness of 1.5 mm, and a length of 100 mm, and a honeycomb made by winding 20 Cr-5Al stainless corrugated foil with a thickness of 50 μ and flat foil 36 times. It is a cross section in the direction of the central axis of the substrate. Both end faces 1 and 2 of the honeycomb part
In this part, corrugated foil and flat foil are brazed from both ends to a thickness of 10 mm from the outermost circumference to the innermost circumference, but in this part, the surface where the foil contacts the stainless steel outer cylinder 3 will be the outer cylinder. Not attached. Further, the joining portion 6 between the honeycomb and the outer cylinder is 1,
It is located 10 mm inward from the middle end of 2 (L ₁ and L ₂ ) in the center. The joining portions 6 and 1 are connected via joining portions (honeycomb joining portions) 4 and 5 of the flat foil and the corrugated foil in the honeycomb. At this time,
In the cross section perpendicular to the central axis at the upper or lower end of 6 in (a), the honeycomb non-bonding part and the honeycomb bonding part are distributed in the radial direction as shown in Fig. 1 (b), and the total cross-sectional area is The ratio of the non-bonded portion of the honeycomb was about 31%.

FIG. 3 is a comparative example, which is a metal base having the same material and size as those of FIG. 1, but the inside 8 of the honeycomb is entirely brazed with corrugated foil and flat foil, and the outermost periphery 9 is entirely covered. It was brazed to the outer cylinder 3. The γ-alumina powder carrying the Pt catalyst was baked on the above two types of metal substrates, and the displacement was 20
It was mounted on a 00cc engine and subjected to a bench test to repeat the cold heat test for 1 minute at 800 ° C or higher for 1 minute and 150 ° C or lower for 1 minute, for a total of 15 minutes.

As a result, in Comparative Example, after 80 cycles, one of the first to third layers of the honeycomb was broken from the outermost periphery of the honeycomb over the entire circumference, and the honeycomb at the inner periphery was about 20 mm on the lee side of the exhaust gas.
It was jumping out. On the other hand, the present invention (Fig. 1) is cold
No abnormalities were observed after 1200 cycles.

Example-2 FIG. 4 shows another embodiment of the present invention, and shows a central axis of a metal base having the same material and dimensions as those of FIG. 1 and a cross section perpendicular to the central axis. Numerals 1 and 2 are not joined to the outer cylinder and are joined by resistance welding at the stage where the contacts of all layers of the honeycomb are wound, and the thickness is 14 mm from both end faces. (100 φ × 14), 3 is an outer cylinder made of stainless steel, 4 is a brazed portion in the honeycomb, that is, a honeycomb joined portion, which is connected to the joined portion 6 with the honeycomb from the central portion 30φ of 1,2. In this example, 6 is 14 from the middle end of 1, 2.
It is located in the central part of the honeycomb from a distance of mm (L ₁ , L ₂ ). Fig. 4 (b) is a cross section perpendicular to the central axis of the BB 'portion in Fig. 4 (a), and 30% of the entire honeycomb cross sectional area was a non-bonded portion.

Fig. 5 shows a base material of the same material and size as shown in Fig. 4, in which the honeycomb bonded portion and the honeycomb non-bonded portion are finely dispersed in the honeycomb to have heat fatigue resistance. The joints 1 and 2 have a thickness of 8 mm from both ends (100 φ × 8
), The distance between the joint 6 with the outer cylinder and the middle end of the first and second parts
L ₁ and L ₂ are 7 mm.

FIGS. 6 and 7 show a joining state of a cross section of a metal base having the same material and dimensions as those of FIG. 1 along the central axis. Reference numerals 1 and 2 are complete joints and are not joined to the outer cylinder. The thickness is 10 mm (100 φ × 10) from both end faces, and 4 and 5 are honeycomb joining portions connecting from the portion of the outer diameter 70 φ and the inner diameter 35 φ of the central portion of 1 and 2 to the joining portion 6 between the honeycomb and the outer cylinder. _No. 6 is located at the center from 10 mm away from the middle end of ₁ , ₂ (L ₁ , L ₂ = 10 mm). In these cases, the shapes of the cross sections 4, 5 are curved. When these three types of metal substrates were subjected to a cold heat test using an engine bench in the same manner as in Example-1, no structural abnormality was found after 1200 cold heat cycles.

[Effects of the Invention] As described above, in the present invention, the honeycomb bonded to all the layers from the outermost circumference to the innermost circumference can be freely changed with the temperature change of the honeycomb without being restrained by the outer cylinder. It can expand and contract. On the other hand, in the honeycomb surrounded by the surface bonded to the outer cylinder, at least the unbonded portion is distributed in the radial direction, so that the outer cylinder and the honeycomb are maintained bonded without causing thermal fatigue failure inside the honeycomb.
Even if the wind pressure of the engine exhaust gas does not cause a deviation, it can withstand a long period of time even for a severe temperature change.

[Brief description of drawings]

FIG. 1 is a view showing a bonding state of a cross section of a metal base according to the present invention, FIG. 2 is a cross section of a conventional metal base, FIG. 3 is a schematic view showing a bonding state of the metal base of FIG. FIGS. 7 to 7 are views showing the bonding state of the cross section of the metal substrate according to the present invention. 1, 2 ... Both ends of the honeycomb, 3 ... Outer cylinder, 4, 5 ...
Honeycomb bonded part, 6 ... bonded part, 7 ... non-bonded part.

Front page continuation (72) Inventor Mikio Yamanaka 5-10-1, Fuchinobe, Sagamihara City, Kanagawa Pref., Second Research Laboratory, Nippon Steel Corporation (72) Inventor, Yasushi Ishikawa 5-10-1, Fuchinobe, Sagamihara City, Kanagawa Prefecture Nippon Steel Co., Ltd. 2nd Technical Laboratory (72) Inventor Takashi Tanaka 5-10-1 Fuchinobe, Sagamihara-shi, Kanagawa Nippon Steel Co., Ltd. 2nd Technical Laboratory (72) Inventor Yutaka Sadano Chiba 1 Kimitsu, Kimitsu-shi, Japan Inside Nippon Steel Co., Ltd. (72) Inventor Shinichi Matsumoto Shinichi Matsumoto Toyota City, Aichi Prefecture Toyota-Cho, Toyota Motor Corporation (72) Inventor Toshihiro Takada Toyota City, Aichi Prefecture Toyota Town No. 1 in Toyota Motor Corporation (72) Inventor Shinji Shibata No. 1 Toyota Town in Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Hikari Aoyagi No. 1 Toyota Town in Aichi Prefecture Toyota Motor Corporation Stock In-house (72) Inventor Yoshio Nishizawa 4-10 Funato, Itabashi-ku, Tokyo 1 Nippon Research Institute Co., Ltd. (72) Inventor Akihiko Kasahara 4-chome Funato, Itabashi-ku, Tokyo 10-1 Nippon Research Institute Co., Ltd. (56) Reference JP 63-97235 (JP, A) -194436 (JP, U)

Claims (2)

[Claims] 1. A metal base for an automobile catalyst comprising a metal honeycomb formed by stacking and winding a flat metal foil (hereinafter, flat foil) and a corrugated metal foil (hereinafter, corrugated foil), and a metal outer cylinder surrounding the metal honeycomb. At least both ends of the honeycomb in the central axis direction are joined from the outermost periphery to the innermost periphery of the flat foil and the corrugated foil, and the outer cylinder and the honeycomb are not joined at the both ends, and the remaining portion of the honeycomb is formed. Is a portion that is joined to the outer cylinder at a position at least 5 mm away from the middle end of the portion that is joined from the outermost circumference to the innermost circumference, and is joined to the outer cylinder in a cross section in the direction of the central axis. And the both end portions are connected via a bonded portion in the honeycomb, and in the honeycomb surrounded by the bonding surface with the outer cylinder, at least in the honeycomb cross section perpendicular to the central axis, at least the unbonded portion But Autocatalyst metal substrate having a thermal fatigue resistance, characterized in that distributed in the radial direction. 2. The metal base for an automobile catalyst according to claim 1, wherein the radial distribution of the non-bonded portion of the honeycomb in the honeycomb cross section bonded to the outer cylinder occupies 20% or more of the total cross-sectional area.