JPH02102744A - Metallic base body for automobile catalyst having resistance to thermal fatigue - Google Patents

Abstract

PURPOSE:To obtain a metallic base body for automobile catalyst having resistance to stream of exhaust gas at high temp. and at high velocity and having high resistance to thermal fatigue by distributing joint parts of plane foils to corrugated foils and joint parts of a honeycomb to an external cylinder, of a metallic honeycomb produced by winding superposed plane foils and corrugated foils to a specified distribution mode. CONSTITUTION:Both ends 1, 2 of a metallic honeycomb are bonded in a section in the direction of central shaft of the metallic honeycomb produced by winding superposed plane foils and corrugated foils over the whole layer of the honeycomb from the innermost periphery to the outermost periphery. Both ends 1, 2 are bonded completely but are not bonded to an external cylinder 3. Further, the outermost periphery is bonded to the external cylinder at a joint part 6 where distances L1, L2 are >=5mm apart from inside edges of the both ends 1, 2. The joint part 6 is connected to the both ends 1, 2 interposing joint parts 4, 5. The inside of the honeycomb enclosed by the joint part 6 between the honeycomb and the external cylinder 3 has an unbonded part 7. By constituting a metallic base body for automobile catalyst of a structure as described above, the resistance to thermal fatigue thereof is improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to metal substrates for automotive catalysts.

[Prior Art] More than 10 years have passed since the automobile exhaust gas regulation ItlJ was implemented, and current exhaust gas countermeasures are taken by improving engines and purifying exhaust gas using catalysts. The mainstream catalysts for exhaust gas purification have a structure in which γ-alumina powder supporting a noble metal catalyst such as PT is supported on a ceramic honeycomb such as cordierite. However, the stiff ceramic honeycomb has a rather high exhaust resistance, and the temperature at which it can be used is low due to the heat resistance of the buffer stainless steel mesh inserted between the honeycomb and the outer cylinder to prevent it from breaking. There were disadvantages such as restrictions on

In recent years, metal carriers made of stainless steel foil have attracted attention as a means of improving these drawbacks. These metal carriers are naturally required to have heat resistance to withstand high temperature and high velocity exhaust gas during the reaction and thermal fatigue resistance to withstand intense heating and cooling. Second
As shown in the cross-sectional view in the figure, metal carriers are generally made by stacking a stainless steel flat foil with a thickness of around 50 μm and a corrugated stainless steel corrugated foil, rolling it into a cylindrical or elliptical shape, and charging this into a heat-resistant stainless steel outer i43. Then, the flat foil, corrugated foil, and outer cylinder are joined together by brazing, resistance welding, or the like. FIG. 3 schematically shows this, and the diagonal line 8 and thick line 9 indicate that they 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 and increase the bonding area between the flat foil, corrugated foil, and outer cylinder. - Cannot withstand cooling. In other words, in the case of a metal carrier installed in an automobile engine, the honeycomb portion is heated before the outer cylinder when the engine is started and the vehicle starts running.
In addition, on long downhill slopes, the engine brake state continues for a long time, and in types that cut off the fuel supply during this period, the honeycomb cools down before the outer tube, creating a large temperature difference between the outer tube and the honeycomb. Moreover, since the positive and negative temperature differences change between heating and cooling, the honeycomb suffers thermal fatigue failure at a portion close to the outer cylinder, causing problems such as the honeycomb flying out in the leeward direction due to the back pressure of the exhaust gas.

As a prior art technique for preventing problems when metal carriers are firmly joined, a method for mechanically fixing honeycombs is disclosed in U.S. Pat. No. 4,186,172 and Japanese Patent Publication No. 60-2
It is disclosed in Publication No. 7807 and the like. Furthermore, methods for partially joining honeycombs are disclosed in JP-A-62-45345 and JP-A-61-19957, but the method for joining the honeycomb and the outer cylinder is not clearly described. However, the honeycomb does not exhibit sufficient properties in at least one of bonding strength to the outer cylinder and thermal fatigue resistance.

[The invention attempts to solve the problem.] Problem] The present invention has been made in view of the above-mentioned drawbacks of the prior art, and provides a metal substrate that can withstand high-temperature and high-speed exhaust gas flows and has thermal fatigue resistance that can withstand rapid heating and cooling. It is something to do.

[Means for Solving the Problems] In order to achieve this object, the present invention has devised a base structure that is less likely to cause thermal fatigue 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 provides a metal honeycomb for automobile catalysts consisting of a metal honeycomb formed by stacking and rolling together flat metal foil (hereinafter referred to as flat metal foil) and corrugated metal foil (hereinafter referred to as corrugated foil), and a metal outer cylinder surrounding them. In the base body, the flat foil and the corrugated foil are joined at least at both ends in the central axis direction of the honeycomb from the outermost circumference to the innermost circumference, and the outer tube and the honeycomb are not joined at both ends, and the remaining portion The honeycomb is such that the outermost periphery is joined to the outer cylinder at a distance of at least 5 billion meters from the middle end of the part where the ends are joined from the outermost periphery to the innermost periphery, and The part joined to the outer cylinder and the above two ends are connected via the joined honeycomb part, and the honeycomb that is roughly surrounded by the joint surface with the outer cylinder is perpendicular to the central axis. The present invention is a substrate for an automobile catalyst having heat fatigue resistance characterized in that, in a cross section, at least the unjoined portions are distributed in the radial direction.

[Detailed Description of the Invention Based on Drawings] Next, the present invention will be described in detail. FIG. 1 shows a cross section of the metal base of the present invention in the central axis direction. Generally, both end faces of the honeycomb on the exhaust gas inlet and outlet sides of the metal base are made of flat foil.
If corrugated foils are used without bonding, the foils will vibrate due to high-speed exhaust gas and cause fatigue failure. Therefore, the corrugated foil and flat foil near both ends of the honeycomb 1.2 must be bonded to each other to prevent individual vibrations. However, since the honeycomb in the joined part behaves as one rigid body, if the surface in contact with the outer cylinder of this part is joined to the outer cylinder 3, the honeycomb Thermal fatigue failure occurs near the outer periphery.

For this reason, in the present invention, a honeycomb portion (hereinafter referred to as a complete joint portion) that is joined over the entire layer from the innermost circumference to the outermost circumference of the honeycomb is not bonded to the outer cylinder 3.

However, this alone means that the honeycomb is not fixed to the outer cylinder, so the honeycomb will pop out to the leeward side of the exhaust gas during use. Therefore, it is necessary to join the honeycomb and the outer cylinder at a point other than the completely joined portion of the honeycomb.

As a result of various studies by the present inventors regarding the joint portion between the honeycomb and the outer cylinder, we found that from the viewpoint of thermal fatigue resistance, the joint portion 6 between the honeycomb and the outer cylinder is connected from the middle end of the complete joint portion 1.2 at both ends. It is necessary to separate at least 5I1m (Figure 1 (a))
11 and 1), thereby forming the complete joint 1.
In order to prevent thermal fatigue failure of the honeycomb between the joint 6 of the honeycomb and the outer cylinder, and to improve the bonding strength of the honeycomb to the outer cylinder, it is necessary to completely connect the joint 6 of the honeycomb and the outer cylinder to both ends. It has been found that the honeycomb portions (hereinafter referred to as honeycomb joints) must be connected through 4° and 5° when viewed in cross section in the central axis direction.

Furthermore, in the inside of the honeycomb, which is surrounded by the joint surface between the honeycomb and the outer cylinder, from the viewpoint of thermal fatigue resistance, at least the non-joint parts of the honeycomb are distributed in the radial direction in a cross section perpendicular to the central axis of the honeycomb. I found out that it is necessary. Depending on the cross section, the honeycomb non-bonded portion and the honeycomb bonded portion will be distributed in the radial direction, but in this case, it is desirable that the honeycomb non-bonded portion occupies 20% or more of the total cross-sectional area. Therefore, the case where the entire cross-sectional area is a honeycomb non-joined portion is also included. That is, FIG. 1(b) is (a
) shows a central axis cross section at the section 8s-A+', and there are honeycomb non-bonded parts and honeycomb joined parts on every radial line, and the thermal stress in the radial direction on this surface is relaxed. In addition, the entire cross section of the section 8, -A, j in FIG. If most of this cross section becomes a honeycomb joint, it will be difficult to alleviate the thermal stress on this surface.

In the present invention, joining refers to joining corrugated foil, flat foil, and outer cylinder to each other by brazing, resistance welding, laser welding, electron beam welding, arc welding, or the like. In addition, if a part of the brazing material, arc, etc. goes around a part that should not originally be joined and joins some of the contacts, it is not considered to be joined here. Furthermore, diffusion bonding, which occurs when stainless steels are brought into contact with each other and heated in a high vacuum or low pressure hydrogen to form pillars, is not included in the term bonding here because the bonding strength is low at honeycomb contacts. Further, in the present invention, the waveform of the corrugated foil may be any one of a sine wave, a trapezoid, a rectangle, etc.

4 to 6 show other examples of the present invention.

Here, the meanings of each part 1 to 7 are the same as in FIG. 1. The manufacturing method for products with these joint structures is brazing. Before wrapping the foil in advance, draw a developed diagram according to the pattern for each brazing joint, apply a binder of the brazing material according to the pattern, and then combine the flat foil and corrugated foil. You can apply the brazing filler metal after rolling it in. In addition, in any other joining method, joining may be performed in accordance with these developed diagrams during the process of rolling the foil.

[Example] Example-1 Figure 1 shows one embodiment of the present invention.
Diagram (a) shows inner diameter 100+n111, thickness 1.5mm,
Length 100I! This is a cross section in the central axis direction of a metal base made of a stainless steel outer cylinder of Im and a honeycomb made by 36 turns of 20Cr-5A4 stainless steel corrugated foil and flat foil with a thickness of 50μ. On both end faces 1.2 of the honeycomb part, corrugated foil and flat foil are brazed from the outermost circumference to the innermost circumference from both ends to a thickness of IOIam, or the foil contacts the stainless steel outer WJ3 in this part. The surface is not brazed to the outer cylinder. Furthermore, the joining portion 6 between the honeycomb and the outer cylinder is located in the center from a point 10IIIa inwardly away from the middle end portions 1 and 2 (Ll and L2). The joint parts 6 and 1.2 are connected via a joint part (honeycomb joint part) 4.5 between the flat foil and the corrugated foil in the honeycomb. At this time, in a cross section perpendicular to the central axis at the upper end or lower end of 6 in Fig. 1(a), the honeycomb non-joined part and the honeycomb joined part are radially aligned as shown in Fig. 1(b). The ratio of honeycomb non-bonded parts to the total cross-sectional area was about 3196.

Figure 3 shows a comparative example, which has a metal base made of the same material and the same size as the one in Figure 1, but the inside of the honeycomb 8 is entirely brazed with corrugated foil and flat foil, and the outermost periphery 9 is entirely covered. Brazed to outer cylinder 3. After baking the γ-alumina powder supporting the PT catalyst on the above two types of metal substrates,
Mounted on a 12,000cc engine and tested over 800℃ for 1 minute.

1 minute below 150℃, total! The cold test was repeated with a 15 minute cycle.

As a result, in the comparative example, after 80 cycles, any one of the first to third layer honeycombs from the outermost periphery of the honeycomb was broken over the entire circumference, and the honeycombs on the inner periphery were approximately 2
It was protruding by 0mm. On the other hand, in the case of the present invention (FIG. 1), no abnormality was observed even after 200 cycles of cooling and heating.

Example 2 FIG. 4 shows another embodiment of the present invention, showing the central axis of a metal base made of the same material and dimensions as those in FIG. 1, and a cross section perpendicular to the central axis. 1.2 is a part that is not joined to the outer cylinder and is joined by resistance welding at the stage where the contact points of all layers of the honeycomb are wrapped around the foil, and the thickness is 14 m from both end faces.
It is m. (100φ x 14f), 3 is a stainless steel outer cylinder, and 4 is a brazed portion within the honeycomb that connects the 30φ central portion of 1.2 to the joint 6 with the honeycomb, that is, the honeycomb joint. In this example, 6 is located in the center of the honeycomb from the middle edge of 1.2 614 mm (Ll, L2) away. Figure 4(b) is
), 30% of the total honeycomb cross-sectional area was a non-bonded part.

Figure 5 shows a base made of the same material and the same dimensions as the one in Figure 4, but with more finely dispersed honeycomb bonded areas and honeycomb non-bonded areas within the honeycomb to provide thermal fatigue resistance. The joint part 1.2 has a thickness of 8mm+ from both end faces (100φ
x8j2), the distance between the joint 6 with the outer cylinder and the middle end of 1.2, t,2 is 7ffIII+.

Figures 6 and 7 show the joint state of the cross section at the central axis of the metal base made of the same material and the same dimensions as in Figure 1, and 1.2 is a complete joint and is not joined to the outer cylinder. The thickness is 100101 mm (100 φ is located at the center from a distance of 10 mm from the middle end of 1.2 (Ll, L2=10I1m).

In these cases, the cross sections 4 and 5 have curved shapes. When these three types of metal substrates were subjected to a thermal test on an engine bench in the same manner as in Example 1, no structural abnormality was observed even after 1200 thermal cycles.

[Effects of the Invention] As explained above, in the present invention, the honeycomb, which is bonded over all layers from the outermost periphery to the innermost periphery, is not constrained by the outer cylinder and can freely move as the honeycomb temperature changes. It can expand and contract.

Since at least the unbonded portions of the honeycomb surrounded by the surfaces joined to the oriented cylinder are distributed in the radial direction, the bond between the outer cylinder and the honeycomb is maintained without causing thermal fatigue failure inside the honeycomb. It does not shift due to the wind pressure of engine exhaust gas, and can withstand severe temperature changes for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a state of joining 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 diagram showing a state of joining of the metal base of FIG. 2, and FIG. FIGS. 7 to 7 are diagrams showing the bonding state of the cross section of the metal base according to the present invention. 1.2--Both ends of the honeycomb, 3...Outer cylinder, 4.5
...Honeycomb joint, 6: Joint, 7: Non-joint.

Claims (1)

[Claims] 1. Flat metal foil (hereinafter referred to as flat foil) and corrugated metal foil (
In a metal base for an autocatalyst, which is composed of a metal honeycomb formed by stacking and rolling up a metal honeycomb (hereinafter referred to as "corrugated foil") and a metal outer cylinder surrounding them, at least at both ends in the central axis direction of the honeycomb, the joining of the flat foil and the corrugated foil starts from the outermost periphery. The outer tube and the honeycomb are not joined to each other at both ends, and the remaining portion of the honeycomb extends from the middle end of the joined portion from the outermost periphery to the innermost periphery at least. It is joined to the outer cylinder at a distance of 5 mm or more, and in the cross section in the central axis direction, the part joined to the outer cylinder and the both ends are connected via the joined part in the honeycomb, and A metal for an autocatalyst having thermal fatigue resistance, characterized in that in a honeycomb surrounded by a joint surface with an outer cylinder, at least unjoined portions are distributed in the radial direction in the honeycomb cross section perpendicular to the central axis. Base. 2. The metal substrate for an autocatalyst according to claim 1, wherein the radial distribution of the non-bonded portion of the honeycomb in the cross section of the honeycomb joined to the outer cylinder occupies 20% or more of the total cross-sectional area.