Stock material or miscellaneous articles – Structurally defined web or sheet – Honeycomb-like
Reexamination Certificate
1999-03-17
2001-06-05
Lorin, Francis J. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Honeycomb-like
C428S073000, C029S436000, C029S446000, C029S505000, C029S522100
Reexamination Certificate
active
06242071
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a method for producing a catalytic converter and heat exchanger used in an exhaust gas cleaning-up system for an internal combustion engine or the like, and a member to be used in the method, more particularly to the method for assembling a ceramic honeycomb structure wound with a low-friction supporting member into a metallic can while compressing the supporting member, and to the supporting member of low friction for the honeycomb structure when producing the catalytic converter and heat exchanger.
Various methods have been proposed to assemble a ceramic honeycomb structure, which is vulnerable to mechanical shocks, into a metallic protective structure. One of the common methods is the so-called clamshell method, in which a pair of symmetric half shell whose form is mutually symmetrical is welded to each other to contain a ceramic structure. Another method is rolling, in which a ceramic honeycomb structure is wound with a supporting member and further with a metallic plate forming a cylinder, and the overlapping ends of the plate are welded to each other, to form a protective structure. Still another method is intrusion, in which a honeycomb structure is intruded together with a supporting member into a cylindrical, metallic protective structure.
Each of these methods, however, has its own disadvantages. The clamshell method involves, for example, a durability-related problem. Density of the supporting member tends to decrease in the vicinity of the welding line of the clamshell, because of the limitation set by the welding. This lower-density section will be attacked more notably by the exhaust gases than are the other sections of the supporting member and hence deteriorated more, with the result that it may not be able to absorb mechanical shocks sufficiently, possibly leading to damages of the honeycomb structure while in service, including sudden destruction, and preventing it from exhibiting its inherent functions. Wind erosion originating from the welded section is another problem involved in this method.
Rolling may not be highly suitable for industrial purposes, because it needs more welding labor than the clamshell method.
Intrusion is superior to the above two methods in that it needs no welding work. A mat of ceramic fibers as the supporting member is put into a metallic can by the aid of a dedicated jig, because of large friction between the mat and can. At present, however, it is difficult for this method to put the supporting member into the can sufficiently uniformly in density to make the honeycomb structure it protects resistant to repeated attacks by the exhaust gases, when they are in service in a catalytic converter.
For example, production of a catalytic converter of an intruded honeycomb structure, disclosed by Japanese Patent Application Laid-Open No. 7-77036, needs a retainer ring to prevent misalignment of the honeycomb axes, because a mat as the supporting member alone is difficult to support the honeycomb structure uniformly at a high surface pressure, which evolves when the mat is highly compressed to increase friction resistance.
However, use of a retainer ring to prevent axial misalignment partially closes the honeycomb ends, causing partial loss of performance of the exhaust gas cleaning-up system. The adverse effect it causes is similar to that resulting from projection of the mat from a honeycomb end.
It is therefore highly demanded to develop an intrusion method which allows a honeycomb structure to be held by a mat alone at a sufficient surface pressure to support them, without needing a device, such as retainer ring, to prevent axial misalignment of the honeycombs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for assembling a ceramic honeycomb structure into a metallic can as the protective structure without causing the problems involved in the above mentioned prior art, and also to provide a supporting member to be used for the honeycomb structure. In other words, it is an object to provide a method for assembling the honeycomb structure which is supported sufficiently durably to cause no problems, e.g., gas channeling, when used in an exhaust gas system or heat exchanger for an internal combustion engine or the like.
It is considered that intrusion is a more preferable assembling method than the others in durability of the honeycomb structure. The applicants of the present invention have proposed a catalytic converter composed of ceramic honeycomb structure, supported by a mat of ceramic fibers having specific properties and assembled by intrusion (Japanese Patent Application Laid-open No. 7-77036). This intrusion method, however, is demanded to be further developed to allow commercial production of the catalytic converters to be achieved faster and more perfectly, because several practical problems are involved in this method, such as time-consuming intrusion works and mat misalignment troubles acceleratedly increasing as intrusion rate is increased. This intrusion work may be referred to as canning in this specification.
When a honeycomb structure is held by a relatively thick supporting member or assembled into a metallic can at a high surface pressure generated by compressing the supporting member in an attempt to place more importance on their durability, excessive friction may evolve between the intrusion jig and can structure, causing misalignment between the honeycomb structure and supporting member, and making it difficult to uniformly put the honeycomb structure in the can. When the misaligned assembly of the honeycomb structure and supporting member is forcefully put in the can, part of the structure may not be evenly supported, or the member may not sufficiently cover the honeycomb structure. This may cause various troubles. Gas channeling will occur at a honeycomb section which is not sufficiently supported. Moreover, such a section will be exposed to repeated mechanical shocks and no longer sustain the honeycomb structure. Uneven pressure may damage the honeycomb structure. When the supporting member extends beyond the honeycomb structure, flow of exhaust gases into the ceramic honeycomb structure will be partly prevented by the supporting member, causing pressure drop across the structures to increase. Increased pressure drop will cause various engine troubles, when the structure is used for an exhaust gas cleaning-up system, such as increased engine load, engine stalling in an extreme case, decreased fuel economy and engine drivability, and increased pollutant emissions.
The applicants of the present invention have found, by extensive studies to solve the above problems, that an assembly of ceramic honeycomb structure and supporting member can be put into a metallic can without causing the above problems, e.g., uneven coverage of the supporting member over the honeycomb structure as a result of partial misalignment of the assembly occurring while it is put in the can, and protrusion of the member beyond the honeycomb structure, when the honeycomb structure wound with the compressed supporting member is put into the can with a low-friction layer on the supporting member surface in contact with the metallic can, reaching the present invention.
This invention provides a method for intruding a ceramic honeycomb structure wound with a supporting member into a metallic can while compressing the supporting member, where the supporting member is provided with a low-friction layer on the surface in contact with the metallic can.
This invention also provides a member for a catalytic converter or heat exchanger, assembled by the above method to be used in an exhaust gas cleaning-up system for an internal combustion engine or boiler, which is produced in a manner mentioned above.
This invention also provides a member to support a ceramic honeycomb structure for the above purposes, which is provided with a low-friction layer on the surface in contact with the metallic can.
REFERENCES:
patent: 3975273 (1976
Hijikata Toshihiko
Tanaka Mikio
Yamada Toshio
Lorin Francis J.
NGK Insulators Ltd.
Parkhurst & Wendel LLP
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