WO1997023325A1

WO1997023325A1 - Assembly and method for making catalytic converter structures

Info

Publication number: WO1997023325A1
Application number: PCT/US1996/019881
Authority: WO
Inventors: David T. Sheller
Original assignee: W.R. Grace & Co.
Priority date: 1995-12-22
Filing date: 1996-12-17
Publication date: 1997-07-03
Also published as: AU1685397A

Abstract

A method for making a catalytic converter by providing a form (50) for holding metal strips (28, 30) in place, individually placing metal strips or groups of metal strips (28, 30) within the form (50) until it is filled, sliding the assembled metal strips (24a) from the form (50) into a jacket tube (13), and connecting distal ends of the metal strips (28, 30) to the jacket tube (13). The form (50) may have a shaped vane (52), preferably of S-shaped configuration, therein to separate the groups of metal strips (28, 30) within the form (50). Alternatively, the form (50) may be shaped to define one of complementary sections of the converter body, such as a cross section of a yin-shape (60) or a yang-shape (60').

Description

Description Assembly and Method for Making Catalytic Converter Structures CROSS REFERENCE TO RELATED APPLICATION This application claims the benefit of U.S. Provisional application Ser. No. 60/009,186 filed on December 22, 1995, entitled ASSEMBLY AND METHOD FOR MAKING CATALYTIC CONVERTER STRUCTURES the disclosure of which is incorporated by reference . The present application is also related to co-pending applications Ser. No. 08/501,755, filed July 12, 1995 by David T. Sheller and William A. Whittenberger, and U.S. applications, entitled Assembly and Method for Making Catalytic Converter Structures, as follows: Ser. No. (Atty Dkt. 04605.0078) by William A. Whittenberger, John J. Chlebus, Joseph E. Kubsh, and Boris Y. Brodsky; Ser. No. (Atty Dkt. 04605.0079) by David T. Sheller and William A. Whittenberger; Ser. No. (Atty Dkt. 04605.0080) by William A. Whittenberger and Boris Y. Brodsky; Ser. No. (Atty Dkt. 04605.0081) by David T. Sheller, Steven Edson and William A. Whittenberger; Ser. No. (Atty Dkt. 04605.0082) by William A. Whittenberger, David T. Sheller, and Gordon W. Brunson; Ser. No. (Atty Dkt. 04605.0084) by William A. Whittenberger, Gordon W. Brunson, and Boris Y. Brodsky; and Ser. No. (Atty Dkt. 04605.0087) by William A. Whittenberger and Gordon W. Brunson. The complete disclosure of all of these applications are incorporated herein by reference. Background Art

The present invention relates to methods for the manufacture of metallic catalytic converters, and, more particularly, to such converters especially adapted for use in vehicular engines to control exhaust emissions, and to foil subassemblies useful in the practice of such methods.

Des rip ion

Catalytic converters containing a corrugated thin metal (stainless steel) monolith typically have been formed of a plurality of thin metal strips or foil leaves wound about a central pin or about spaced "fixation" points. Such prior catalytic converters bodies, have supported both the outer and inner end of the individual layers by fixing them to the housing for the converter body and a central pin or post. In certain instances, the interior support has been provided by looping the foil leaves about a fixed point or portions whereby the inner ends of the leaves have been supported by other foil leaves. The thin metal strips or leaves forming the multicellular honeycomb body also have been brazed together at points intermediate the ends to form a rigid honeycomb monolith. Various techniques such as soldering, welding, brazing, riveting, clamping, reverse wrapping or folding, or the like, have been used to secure the inner and outer ends, and usually the intermediate portion, of the leaves or strips to the support member. While many techniques have been used to assemble the leaves into the housing and many leaf arrangements have been constructed, many arrangements have been unable to survive severe automotive industry tests known as the Hot Shake Test, the Hot Cycling Test, combinations of these tests, cold vibration testing, water quench testing, and impact testing.

The Hot Shake test involves oscillating (50 to 200 Hertz and 28 to 80 G inertial loading) the device in a vertical, radial or angular attitude at a high temperature (between 800 and 1050 degrees C; 1472 to 1922 degrees F., respectively) with exhaust gas from a gas burner or a running internal combustion engine simultaneously passing through the device. If the device telescopes, or displays separation or folding over of the leading or upstream edges of the foil leaves, or shows other mechanical deformation or breakage up to a predetermined time, e.g., 5 to 200 hours, the device is said to fail the test.

The Hot Cycling Test is run with exhaust flowing at 800 to 1050 degrees C; (1472 to 1922 degrees F.) and cycled to 120 to 200 degrees C. once every 5 to 20 minutes for up to 300 hours. Telescoping or separation of the leading edges of the thin metal foil strips, or mechanical deformation, cracking or breakage is considered a failure.

Also, the Hot Shake Test and the Hot Cycling Test are sometimes combined, that is, the two tests are conducted simultaneously or superimposed one on the other. The Hot Shake Test and the Hot Cycling Test are hereinafter called "Hot Tests." While they have proved very difficult to survive, the structures of the present invention are designed to survive these Hot Tests and other tests similar in nature and effect that are known in the industry.

From the foregoing, it will be appreciated that catalytic converter bodies and their method of manufacture have received considerable attention, particularly by the automotive industry, are complex in design and manufacture, and are in need of improvement. Disclosure of the Invention

The advantages and purpose of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purpose of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

To attain the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein a method of making a catalytic converter is provided, comprising the steps of providing a form for holding metal strips in place; individually placing metal strips within the form until it is filled; sliding the assembled metal strips from the form into a jacket tube; and connecting distal ends of the metal strips to the jacket tube. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

Brief Description of the Drawings

The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings,

Fig. IA is a partial cross-sectional view of a catalytic converter incorporating the teachings of the present invention;

Fig. IB is an enlarged cross-sectional view of the center portion of Fig. IA;

Fig. 2 is an end view like Fig. IA showing in enlarged scale a small cluster of converter core elements structured in accordance with another embodiment of the invention;

Fig. 3 is a fragmentary edge view of inner end portions of several adjacent core elements seen in Fig. 2; Fig. 4 is a perspective view illustrating the assembly of a catalytic converter body using a method of the present invention; Fig. 5 is a perspective view of illustrating a more advanced phase of forming the catalytic converter body using the method of Fig. 4;

Fig. 6 is an end view illustrating a cluster of joined metal foil leaves used in the catalytic converter body;

Fig. 7 illustrates the insertion of a plurality of the clusters of Fig. 6 into a form or jig;

Fig. 8 illustrates alternative forms of forms or jigs usable in another method of the present invention;

Fig. 9 is an end view illustrating the assembly of metal strips in the form;

Fig. 10 is an exploded perspective view further illustrating a method of the present invention;

Figs. 11-14 are plan views of alternate embodiments of core elements structured in accordance with the invention; and

Figs. 11A - 14A are side views of Figs. 11-14, respectively.

Best Mode for Carrying Out the Invention

Reference will now be made in detail to the present preferred embodiments of the invention, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

One aspect of the present invention is based on a finding by the inventors that the structure of a metallic catalytic converter body can be improved by allowing the metal sheets referred to as foil leaf core elements or foil leaves to be compliant, move, flex, or float in the fluid stream. Whereas it was previously thought that rigidity was essential to prevent failure in the "Hot Tests," it has been discovered that flexure or compliance of the foil heat core elements in response to thermal and fluid flow variations as well as mechanical vibration were desirable attributes in converter bodies used in various applications.

This discovery has given rise to what is termed a "cantilever" converter body, namely, one in which the foil leaf elements forming the core are secured at one end only or are secured at their second end in a manner, so the individual foil leaf core elements are "compliant", that is, they move or yield to stresses within the elastic limit of the thin metal.

The foil leaf arrangement may be constructed from "ferritic" stainless steel such as that described in U.S. Patent 4,414,023 to Aggen. One usable ferritic stainless steel alloy contains 20% chromium, 5% aluminum, and from 0.002% to 0.05% of at least one rare earth metal selected from cerium, lanthanum, neodymium, yttrium, and praseodymium, or a mixture of two or more of such rare earth metals, balance iron and trace steel making impurities. A ferritic stainless steel is commercially available from Allegheny Ludlum Steel Co. under the trademark "Alfa IV.

Another usable commercially available stainless steel metal alloy is identified as Haynes 214 alloy. This alloy and other useful nickeliferous alloys are described in U.S. Patent 4,671,931 dated 9 June 1987 to Herchenroeder et al. These alloys are characterized by high resistance to oxidation at high temperatures. A specific example contains 75% nickel, 16% chromium, 4.5% aluminum, 3% iron, optionally trace amounts of one or more rare earth metals except yttrium, 0.05% carbon, and steel making impurities. Haynes 230 alloy, also useful herein has a composition containing 22% chromium, 14% tungsten, 2% molybdenum, 0.10% carbon, a trace amount of lanthanum, balance nickel.

The ferritic stainless steels, and the Haynes alloys 214 and 230, all of which are considered to be stainless steels, are examples of high temperature resistive, oxidation resistant (or corrosion resistant) metal alloys that are useful for use in making the foil leaf core elements or leaves of the present invention, as well as the multicellular honeycomb converter bodies thereof. Suitable metal alloys must be able to withstand "high" temperature, e.g., from 900 degrees C. to 1200 degrees C. (1652 degrees F. to 2012 degrees F.) over prolonged periods.

Other high temperature resistive, oxidation resistant metal alloys are known and may be used herein. For most applications, and particularly automotive applications, these alloys are used as "thin" metal or foil, that is, having a thickness of from about 0.001" to about 0.005", and preferably from 0.0015" to about 0.0037". The housings, or jacket tubes, hereof are of stainless steel and have a thickness of from about 0.03" to about 0.08", preferably, 0.04" to 0.06".

The multicellular converter bodies of the present invention preferably are formed from foil leaves precoated before assembly, such as described in U.S. Patent 4,711,009 Cornelison et al. The converter bodies of the invention may be made solely of corrugated foil core elements which are non-nesting, or of alternating corrugated and flat foil core elements, or of other non¬ nesting arrangements or of other arrangements providing cells, flow passages, or a honeycomb structure when assembled. In the preferred embodiments, the foil leaves, which will be used as core elements, are precoated before assembly. The ends are masked or cleansed to maintain them free of any coating so as to facilitate brazing or welding to the housing or to an intermediate sleeve.

As indicated in U.S. Patent 4,911,007, supra, the coating is desirably a refractory metal oxide, e.g., alumina, alumina/ceria, titania, titania/alumina, silica, zirconia, etc., and if desired, a catalyst may be supported on the refractory metal oxide coating. For use in catalytic converters, the catalyst is normally a noble metal, e.g., platinum, palladium, rhodium, ruthenium, indium, or a mixture of two or more of such metals, e.g., platinum/rhodium. The refractory metal oxide coating is generally applied in an amount ranging from about 10 mgs/square inch to about 80 mgs/ square inch. In some applications, corrugations preferably have an amplitude of from about 0.01 inch to about 0.15 inch, and a pitch of from about 0.02 inch to about 0.25 inch. The amplitude and pitch of the corrugations determine cell density, that is, the number of cells per unit of cross-sectional area in the converter body. Typically, the cell density is expressed in cells per square inch (cpsi) and may vary from about 50 cpsi to 2000 cpsi.

Where a non-nesting corrugated foil leaf core element is used, the corrugations are generally patterned, e.g., a herringbone pattern or a chevron pattern, or skewed pattern. in a "skewed pattern", the corrugations are straight, but at an angle of from 3 degrees to about 15 degrees to the parallel marginal edges of the strips. The latter foil leaf core elements may be layered without nesting.

Where alternating corrugated and flat foil leaf core elements are used in a non-nesting arrangement to form the multicellular bodies, straight-through corrugations may be conveniently used, these exhibiting the lowest pressure drop at high flow in fluid flowing through the converter body. The straight-through corrugations are usually oriented along a line normal to the longitudinal marginal edges of the foil leaves, although, as indicated above, the corrugations may be oriented along a line oblique to the longitudinal marginal edges of the leaves.

To reduce stress, the "flat" foil leaf core elements preferably are lightly corrugated to have corrugations with an amplitude of from about 0.002" to about 0.01", e.g., 0.005" and a pitch of from about 0.02" to about 0.2", e.g., 0.1".

The coated corrugated and flat foil leaves that form the working gas flow passageways in the converter body of the invention constitute the major metal foil content thereof and are preferably formed of the lower cost ferritic stainless steel alloys. Because of its greater strength, albeit higher cost, he nickeliferous stainless steel alloys may be used in the converter of the invention particularly in the center area and other areas where the requirement for foil strength justifies the higher cost of these alloys.

Referring now to Figs. IA and IB, there is shown an end view of a "cantilever" multicellular converter body 10 formed of alternating corrugated foil leaf core elements 16 and flat foil leaf core elements 14. The foil leaf core elements may be a ferritic stainless steel. The converter body 10 also includes a surrounding housing or jacket tube 13, which may be formed of a 0.03" to 0.07" thick stainless steel. The outer ends of the foil leaf core elements 18 and 20 are secured to the housing 13, such as by brazing or welding. Brazing is preferred. The inner ends of the foil leaf core elements 14 and 16 are unattached to each other. It should be noted that desirably, in one embodiment, the corrugated core elements 16 decrease in amplitude, although the pitch remains the same, as they approach the center 24 of the core body 10, illustrated in Figs. 2 and 3. Because of the involute shape of the core elements 14 and 16, the farther away from the center 24, the more nearly constant becomes the amplitude and the pitch of the corrugations. Thus, from a practical point of view, the amplitude of the corrugations is constant outside the critical diameter 22. Alternatively, the area inside the critical diameter 22 may be filled with another structure, such as a core or plug such as those described in the patent applications incorporated by reference.

Fig. IB shows on an enlarged scale, the area represented by the circular dotted line 22 in Fig. IA. At the center is a gap 24 showing that the foil leaf core elements 14 and 16 do not meet and are free floating in that they are not attached at their inner ends to each other or to another member. The gap 24 is desirably about 0.01" wide.

Figs. 4 - 10 show in greater detail alternative methods for assembling and forming the catalytic converter structure. In Fig. 4, the illustrated form or jig 50 has an "S" or involute shaped vane 52 extending across a cylindrical form. Individual leaves or sheets alternatingly corrugated and flat, 28 and 30, respectively, are placed in form 50 individually, or a few at a time, until it is filled. Once it is filled, vane 52 may be removed by axially sliding it from form 50, or alternatively, it may itself attach to a metal sheet which becomes part of the subassembly in the catalytic converter. The formed assembly of non- nestable sheets 24a may be then passed through a funnel- like form (not shown) and into a jacket tube 13 to which the outer ends of the leaves are brazed.

Figs. 6 and 7 show a similar type of form or jig for forming subassemblies 24a, however, in this embodiment the individual leaves or sheets are arranged first in clumps or clusters 54 (Fig. 6) before they are placed into form 50 having vane 52 extending across it. Clumps or clusters 54 may be formed by joining the individual leaves or sheets 28, 30 at their centers, one or both outer ends, or any combination of these. It is possible that the ends may be directly connected to each other by means such as gluing or welding 56 or the ends may be indirectly connected by means of a strip of material 58 such as foil or fabric, laid along the ends of the leaves. Once clumps or clusters 54 are formed, they are inserted into form 50 having vane 52 as shown in Fig. 7 until form 50 is filled. Once form 50 is filled, central "S" shaped vane 52 is removed axially, the assembled leaves are compressed, placed in a jacket tube and brazed at the outer ends of the leaves to the jacket tube.

Figs. 8 - 10 show yet another alternative embodiment of a form to be used to form the subassemblies 24a. As seen in Fig. 8, form 60 resembling one half of a "ying-yang" pair may be used as a mold or form to receive individual alternating leaves 28, 30 as seen in Fig. 4 or clusters of leaves 54 of the type shown in Fig. 6. Once form 60 is filled as seen in Fig. 9 such that the subassembly 24a is formed, the assembled leaves may be extended axially from form 60 into a jacket tube 13, as will be described below, and brazed in place. The form 62 is a mirror image of the form and thus differs only with respect to the direction of the involute cavity it defines.

As shown in Fig. 10, two complementary forms 60 and 60' may be used to form complementary ying and yang foil clusters. The forms 60 and 60' are filled with metal strips 28, 30 or clumps of strips 54 as desired. Alternating flat and corrugated strips or all corrugated strips may be used. The corrugations on the corrugated thin metal strips may be variable, being of lesser amplitude at the center, but essentially the same pitch, e.g., they are tapered. The loaded forms are inserted partially into the jacket tube 13 and the cluster metal strips are then pushed from each form into engagement as a complementing pair of involute halves of metal strips filling the circular cross section of the jacket tube. The forms are withdrawn as the involute halves of metal strips are pushed fully into the jacket tube. The distal ends of the metal strips filling the jacket tube are then brazed.

From the foregoing description of the method depicted in Fig. 10, it will be seen that as the forms 60 and 60' are removed from the jacket tube 13 the ying and yang shaped clusters of metal strips suport each other and may be advanced axially relative to each other after the forms are removed from the jacket tube. This principle may be used to preassemble a large number of the metal strip clusters in an enlongated assembly tube from which the clusters are advanced in pairs into the jacket tube. In particular, a single ying-shaped form of a length shorter than the length of each metal strip cluster is used to shape a yang-shaped cluster at one end of the assembly tube. The yang-shaped cluster is then used to form a ying-shaped cluster. This procedure is repeated and the form, with the formed clusters, are advanced in the assembly tube. When the form reaches the other end of the assembly tube, it is removed. The pairs of ying and yang-shaped clusters, while offset axially, are advanced from the other end of the assembly tube into individual jacket tubes. The axial offset is eliminated by pushing the following one of the two clusters fully into the jacket tube while the leading one of the two clusters is retained against movement in the jacket tube to complete the insertion of the clusters.

Figs. 11-14 show alternative arrangements of sheet metal layers to form fluid passage cells. Figs. 11 and 11A show a flat sheet 114 and a corrugated sheet 116. Figs. 12 and 12A show a chevron patterned corrugated sheet 118 folded or cut and flipped back on itself at fold 120 to form two sheet metal layers 122 and 124. Figs. 13 and 13A show the same folded or cut and flipped arrangement as Figs. 12 and 12A, but with a herringbone pattern. Figs. 14 and 14A show a single sheet with sheet 318 with skewed corrugations, and it is folded or cut and flipped at 320 to form two sheet metal layers 322 and 324.

Alternatively, a jig may be provided having a desired geometric periphery, e.g., a circle. A metal involute form is then placed within the jig with a free end thereof at the center, and the opposite end at the periphery of the outer shell. Thin metal strips, or clumps thereof, are cut to length and each inserted into the jig and bent to conform to the convolute form. When the jig is filled, the involute form is withdrawn and the assembled strips are compressed and inserted into a jacket tube and induction heated to secure the outer ends to the tube. The involute form may be made from one of the foil leaves. Thus, no removal of the form would be required. The involute formed leaf will stick out of the main core body and is retained there by an involute slot. After the jig is filled, the subassembly is removed from the slotted jig and the involute formed leaf is pushed into the main core body. The contents of the jig are then compressed and inserted into the jacket tube and induction heated to secure the outer ends to the jacket tube.

It will be apparent to those skilled in the art that various modifications and variations can be made in the methods of forming a catalytic converter core according to the present invention and in the construction of this catalytic converter core without departing from the scope or spirit of the invention. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

1. A method of making a catalytic converter body comprising: providing a form of a predetermined shape for holding metal strips in place; placing metal strips within the form to provide shaped metal strips; removing the shaped metal strips from the form and inserting the shaped metal strips into a jacket tube; and connecting ends of the shaped metal strips to the jacket tube.

2. The method of claim 1 wherein the placing step includes alternatingly placing flat and corrugated metal strips within the form.

3. The method of claim 1 wherein the shaped metal strips are compressed before being placed into the jacket tube.

4. The method of claim 1 wherein the shaped metal strips are advanced through a funnel-shaped device before being placed in the jacket tube.

5. The method of claim 3 wherein the form is a cylindrical form having a diametrically oriented S- shaped vane and the vane is removed before the assembled metal strips are compressed.

6. The method of claim 1, wherein the metal strips are non-nestable corrugated metal strips.

7. The method of claim 1, wherein the outer ends of metal strips are secured the the jacket tube.

8. A method of making a catalytic converter body comprising the steps of: assembling a plurality of non-nestable metal strips by connecting ends of the metal strips to one another to provide groups of metal strips; inserting the groups of metal strips into a form having a shaped vane therein to separate the groups of metal strips within the form; placing the groups of metal strips into a jacket tube; and securing ends of the metal strips to the jacket tube.

9. The method of claim 8, wherein the groups of metal strips are compressed into the jacket tube.

10. The method of claim 8, wherein the outer ends of the metal strips are secured to the jacket tube

11. The method of claim 10 wherein the securing step includes brazing the outer ends of the metal strips to the jacket tube.

12. The method of claim 8, wherein the spaped vane is of S-shaped configuration.

13. The method of claim 12 wherein the S-shaped vane is removed axially when the form is full.

14. The method of claim 13 wherein the S-shaped vane is removed from the form with the assembled metal strips and is secured to the jacket tube.

15. A method of forming a catalytic converter structure body comprising the steps of: providing at least one form defining one of complementary sections of the converter body; placing non-nestable metal strips into the form to shape the metal strips and to provide two or more complementary sections of shaped metal strips; placing the complementary sections of shaped metal strips within a jacket tube; and securing the complementary sections to the jacket tube.

16. The method of claim 15 wherein the placing step includes individually placing alternating flat and corrugated metal strips within the form.

17. The method of claim 15 wherein the placing step includes individually placing only non-nestable corrugated metal strips within the form.

18. The method of claim 15 further including the step of: assembling a plurality of non-nestable metal strips into groups before placing the metal strips into the form.

19. The method of claim 15 wherein the form has a cross-section of one of a ying-shape and a yang-shape.

20. The method of claim 19 wherein the form is of a length shorter than the length of the shaped metal strips, thereby to provide a portion of the shaped metal strips axially offset from the form, and including the step of using the axially offset portion of the shaped metal stips to form a successive complementing section of shaped metal strips.

21. The method of claim 20 wherein the form is an elongated assembly tube in which shaped metal strips are progressively formed.

22. The method of claim 21 wherein the shaped metal strips are advanced in the assembly tube and discharged from the assembly tube in pairs into the jacket tube.

23. The method of claim 15 wherein the outer ends of the metal strips are secured to the jacket tube.

24. An assembly for use in the manufacture of catalytic converter cores, comprising: clusters of non-nestable corrugated metal strips, each strip being connected to every other strip.