Stock material or miscellaneous articles – All metal or with adjacent metals – Honeycomb – or with grain orientation or elongated elements...
Patent
1994-10-13
1997-07-15
Zimmerman, John
Stock material or miscellaneous articles
All metal or with adjacent metals
Honeycomb, or with grain orientation or elongated elements...
428603, 428683, 228181, 228194, B01J 3504, B23K 3536, B32B 1518
Patent
active
056481764
DESCRIPTION:
BRIEF SUMMARY
This application is an application filed under 35USC371 of PCT/JP94/00688 filed Aug. 2, 1994.
1. Technical Field
The present invention relates to a metallic honeycomb body, for supporting a catalyst for purifying an exhaust gas discharged from internal combustion engines, such as automobile engines, and a process for producing the same.
2. Background Art
A metallic carrier for purifying an exhaust gas basically is comprised by a honeycomb body having a number of exhaust gas passages, in which the body is produced by alternately stacking flat or slightly corrugated metallic foils (hereinafter referred to as a "flat foils") comprising a ferritic stainless steel having a thickness of about 50 .mu.m, particularly a heat-resisting alloy steel, such as a 20% Cr-5% Al--Fe alloy containing Al and metallic foil corrugating the above flat foils (hereinafter referred to as a "corrugated foils"), or by putting the flat foil on top of the corrugated foil and winding up these foils into a spiral form. In general, it further comprises, besides this honeycomb body, an outer cylinder for housing the honeycomb body therein, the outer cylinder comprising a heat-resisting alloy having excellent corrosion resistance and heat resistance. In the above honeycomb body, the metallic foils are mutually joined, and when the honeycomb body is inserted in the outer cylinder, the honeycomb body is fixed to the outer cylinder.
After a catalyst for purifying an exhaust gas is supported on the honeycomb body, the metallic carrier is mounted and fixed within an exhaust gas passage of, for example, an automobile engine. Since the metallic carrier is used in this state, it is exposed to a rapid cooling and heating cycle (a thermal shock cycle), so that joins between metallic foils of the honeycomb body and joins or fixes between the honeycomb body and the outer cylinder should be sufficiently firm.
The inside of the honeycomb body or a particular site between the honeycomb body and the outer cylinder should be firmly joined. However, when the whole assembly is rigidly joined by full joints or the like, a large thermal stress occurs in the vicinity of the joints, so that thermal fatigue causes the joint between the outer cylinder and the honeycomb body to be broken or the inside of the honeycomb body to be broken. This in turn causes the honeycomb body to be separated from the outer cylinder, which results in problems in the engine, a lowering in exhaust gas purification activity and the like.
In order to prevent the above unfavorable phenomenon, a method for joining abutted portions between the flat foil and the corrugated foil of the honeycomb body by a method other than full joining has been proposed, and examples thereof include a method disclosed in Japanese Examined Patent Publication (Kokoku) No. 63-44466 wherein only at least one end face of the honeycomb body is brazed and a method disclosed in German Unexamined Patent Publication No. 3,312,944 wherein portions of the flat foil and the corrugated foil to be joined are intermittently brazed.
Brazing, welding and diffusion joining are already known as the method for joining the metallic carrier and the honeycomb body together. In the welding, many joining sites are joined one by one, so that the efficiency is low. For this reason, brazing or diffusion joining is generally used because many joining sites can be simultaneously joined. In particular, brazing has been most commonly used for this purpose for many years.
Brazing is a joining method which comprises: placing a metal (a brazing agent) having a melting point below the base metals to be joined around the joining interface, heating the brazing agent to melt the brazing agent, thereby enabling the melted brazing agent to permeate and fill the gaps in the joining interface without melting the base metal; and conducting cooling and solidification. In this method, a dissimilar phase having a composition different from the base metal and being formed by the brazing agent or a reaction of the brazing agent with the base metal is present
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Ishikawa Yasushi
Nakagawa Toshikazu
Ohta Hitoshi
Tsushima Sadao
Yashiro Masao
Nippon Steel Corporation
Zimmerman John
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