WO1997002884A1

WO1997002884A1 - Structure for converter body

Info

Publication number: WO1997002884A1
Application number: PCT/US1996/011514
Authority: WO
Inventors: David Thomas Sheller; William A. Whittenberger; Joseph E. Kubsh
Original assignee: Engelhard Corporation
Priority date: 1995-07-12
Filing date: 1996-07-10
Publication date: 1997-01-30
Also published as: EP0871536A1; AU6488196A

Abstract

There is provided am improved converter body (10) formed of thin metal layers (14, 16) and a housing (12). The thin metal layers (14, 16) having two opposite ends. One end (18, 20) of the metal layers (14, 16) are secured to the housing (12), and at least some, preferably all, of the other ends of the metal layers are free of attachment to any rigid member. This structure enables the converter bodies to yield to mechanical and thermal stresses, thereby providing improved durability in severe automotive operating conditions.

Description

STRUCTURE FOR CONVERTER BODY

This invention relates to an improved structure for a metallic converter body. This structure is characterized in that the individual core elements of thin metal foil are attached at one end only to the outer jacket or housing, the other end being free to move. The principal advantage of this structure is that the durability of the device is surprisingly improved.

BACKGROUND OF THE INVENTION Converter bodies have long been formed of a plurality of thin metal strips or layers wound about a central pin or about spaced "fixation" points. Such prior converter bodies, including prior catalytic converters, have utilized a support means both at the outer end of the individual layers as well as the inner end. The support means, at a minimum, has often been the housing for the converter body in combination with a central pin or post. In certain instances, the interior support means has been, at least in part, as a result of looping the thin metal layers about a fixed point or points whereby the inner ends of the thin metal layers have been supported by another thin metal layer. Most often, the thin metal strips or layers forming the multicellular honeycomb body have been brazed together intermediate the ends thereof whereby a rigid honeycomb monolith has been formed. In all instances, however, both the inner and the outer ends of the layers have been supported.

The support has been effective by soldering, welding, brazing, riveting, clamping, reverse wrapping or folding, or the like, whereby the inner and outer ends, and usually the intermediate portion, of the layers or strips are fixedly secured to the support member. Varying degrees of success in passing tests prescribed by automobile manufacturers have been achieved. it has now been found that the structure can be improved by allowing one end, e.g., the inner end, of the thin metal core elements, also referred to herein as "thin metal layers", "thin sheet metal layers", or "thin metal foil strips", to "float" in the fluid stream. Whereas it was previously thought that rigidity was essential to prevent failure in the "Hot Tests" (described below), it has been discovered that flexure or compliance of the thin metal core elements in response to thermal and fluid flow variations as well as mechanical vibration is a desirable attribute of the converter bodies . This discovery has given rise to what we term a "cantilever" converter body, i.e., one in which the thin metal core elements forming the core are secured at one end only, preferably at the outer end, in a spirally wound device. In such a construction, the individual thin metal core elements are "compliant", that is, they yield to stresses within the elastic limit of the thin metal.

This invention will be described in connection with embodiments especially adapted for use in the exhaust lines of various types of engines, e.g., internal combustion engines of the spark ignited or compression ignited types, stationary or mobile, or gas turbines. It will be understood that the converters of the present invention may be used to effect various chemical reactions, particularly those occurring in fluid streams, especially gas streams, and which reactions are catalyzed or uncatalyzed. A particular reaction is the oxidation of pollutant materials contained in exhaust streams from internal combustion engines .

Catalytic converters containing a corrugated thin metal (stainless steel) monolith have been known since the early 1970' s. See Kitzner U.S. Patents 3,768,982 and 3,770,389 each dated 30 October 1973. More recently, corrugated thin metal monoliths have been disclosed in U.S. Patent 4,711,009 dated 8 December 1987 to Cornelison et al which discloses a process for making precoated corrugated thin metal strips in a continuous manner, and accordion folding them into predetermined shapes; U.S. Patents 4,152,302 dated 1 May 1979, 4,273,681 dated 16 June 1981, 4,282,186 dated 4 August 1981, 4,381,590 dated 3 May 1983, 4,400,860 dated 30 August 1983, 4,159,120 dated 28 May 1985,

4,521,947 dated 11 June 1985, 4,647,435 dated 3 March 1987, 4,665,051 dated 12 May 1987 all to Nonnenmann alone or with another and which disclose multicellular honeycomb monolithic converters with corrugated and flat thin metal strips having their contiguous surfaces brazed together; U.S. Patent 5,070,694 dated 10 December 1991 to Whittenberger which discloses spirally wound converters with corrugated strips and flat strips. International PCT Publication No. 90/12951 published 9 April 1990 seeks to improve axial strength by form locking layers of insulated plates. Another reference which seeks to improve axial strength is U.S. Patent 5,055,275 dated 8 October 1991 to Kannainian et al. Reference may also be had to International PCT Publication No. 92/13626 filed 29 January 1992. This application relates to a multicellular honeycomb converter body along an axis of which fluid can flow through a plurality of channels. The honeycomb has at least two discs in axially spaced relation to each other. According to the specification, there is at least one bar type support near the axis by which the discs are connected together and mutually supported. The invention is said to make possible design of the first disc for fast heating up through hot exhaust gas passing through, or applied electrical current. The honeycomb body serves as a support for catalyst in the exhaust system of an internal combustion engine. Another reference is German Patent Application 4,102,890 Al filed 31 January 1991 and published 6 August 1992. This application discloses a spirally wound corrugated and flat strip combination wherein the flat strip contains slots and perforations and is electrically heatable. The flat strips include a bridge between leading and trailing portions. Groups of strips are separated by insulating means. Another reference is U.S. Patent 5,102,743 dated 7 April 1992. This patent discloses a honeycomb catalyst carrier body of round, oval, or elliptical cross-section including a jacket tube and a stack of at least partially structured sheet metal layers intertwined in different directions in the jacket tube. The stack has a given length and a given width. At least one of the sheet metal layers has a greater thickness over at least a part of one of the dimensions than others of the layers. Such at least one layer is formed of thicker metal or of a plurality of identically structured metal sheets in contiguous relation.

European Patent Application 0,322,566 field 25 November 1988 discloses a spirally wound honeycomb core formed of corrugated and flat thin metal strips. In this structure, the head ends in the center of the strips are grasped in the middle in order to coil the strips, or they can be grasped sequentially one after the other and coiled. The strips are weakened appropriately in the middle at the head ends of the strips by a pair of inwardly directed slots.

Reference may also be had to U.S. Patent 4,832,998 dated 23 May 1989 to Cyron. This patent discloses an S-wound honeycomb converter body and a method of producing it, the body including a stack of structured metal sheets disposed in layers at least partially spaced apart from each other defining a multiplicity of channels through which gases can flow, the stack having ends looped in mutually opposite directions about at least two spaced fixation points, and a jacket tube surrounding the sheets and being formed of at least one segment, the sheets having the ends of the loops joined with the jacket tube. The devices have no central post. A method US Patent is 4,923,109 dated 9 May 1990 to Cyron, a division of the aforementioned Cyron patent, directed to the method of making the devices of the earlier U.S. patent. Reference may also be had to U.S. Patent 5,232,671 dated 3 August 1993 to Brunson. This patent discloses an improved electrically conductive metal honeycomb body having a plurality of corrugated thin metal strips, which may be heater strips, extending in electrical parallel between otherwise electrically isolated connector plates. The corrugated thin metal strips have a flat central section. A first group of strips is gathered at their flat middle portions and bent around one of a pair of rigid central posts, and a second group of strips is gathered and bent in the opposite direction about the other of the posts. Insulation in the form of flexible woven ceramic fiber strips isolate the first and second groups from each other and from the central posts . The connector plates define a segmented retainer shell about the body. A battery is connected to the connector plates whereby current flows from one connector plate through the corrugated thin metal strips to the other connector plate and back to the battery.

As indicated above, a common problem with many of the prior devices has been their inability to survive severe automotive industry tests which are known as the Hot Shake Test and the Hot Cycling Test. The Hot Shake test involves oscillating (100 to 200 Hertz and 28 to 60 G inertial loading) the device in a vertical 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 10 to 20 minutes for 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.

The Hot Shake Test and the Hot Cycling Test are hereinafter called "Hot Tests" and have proved very difficult to survive. The structures of the present invention will survive these Hot Tests . Other tests similar in nature and effect are known in the industry. In the following description, reference will be made to "ferritic" stainless steel. A suitable ferritic stainless steel is described in U.S. patent 4,414,023 dated 8 November 1983 to Aggen. A specific ferritic stainless steel alloy useful herein 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 stainless steel metal alloy especially useful herein is identified as Haynes 214 alloy which is commercially available. 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 and 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 thin metal core elements hereof, as well as the multicellular honeycomb converter bodies hereof. 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, 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", e.g, 0.04" to 0.06". Reference will also be made to ceramic fiber insulation. Details of a suitable ceramic fiber insulation will be found in U.S. Patent 3,795,524 dated 5 March 1974 to Sowman, and to U.S. Patent 3,918,057 dated 28 October 1975 to Hatch, for formulations and manufacture of fibers useful in making tapes and mats useful herein. One such woven ceramic fiber material is currently available from 3-M under the registered Trademark "NEXTEL" 312 Woven Tape and is useful for insulation between the inner and outer housings hereof. Ceramic fiber mat is commercially available under the trademark "INTERAM" also available from 3-M. Between the thin metal core elements hereof, the only insulation is provided by refractory metal oxide coating on the surfaces of the thin metal strips, or layers .

BRIEF STATEMENT OF THE INVENTION Briefly stated, the present invention is a converter body comprising a housing, and a core formed of a plurality of thin metal core elements in the form of strips, sheets, or layers, each of said core elements having a distal end and a proximal end, the distal ends being secured to said housing, and at least some, preferably all, of the proximal ends being free. The core bodies hereof may be formed of all corrugated thin metal core elements, preferably nonnesting corrugated thin metal core elements, or alternating corrugated and flat thin metal core elements .

A more specific embodiment of the invention contemplates an electrically heatable converter comprising (a) an inner housing, (b) an outer housing, (c) a multicellular core body including an electrically heatable portion formed of flat thin metal heater bands each having a distal end and a proximal end, and corrugated thin metal core elements each having a distal end and a proximal end, and a light-off portion formed of flat thin metal bands, which are not electrically heatable, and each having a distal end and a proximal end, said flat thin metal bands being in alternating relation with corrugated thin metal core elements each having a distal end and a proximal end, said corrugated thin metal core elements extending into said electrically heatable portion and overlapping the upstream portions of the flat heater bands, said core body being contained within said inner housing, (d) insulation means disposed between said inner housing and said outer housing, and (e) means for electrically heating said electrically heatable portion, the distal ends of said thin metal core elements and bands each being secured to the inner housing, as, for example, by welding or brazing, at least some, and preferably all, of the proximal ends of said bands and core elements being free and unsupported. 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 assembling a plurality of non-nesting thin metal sheets or foil leaves, each having opposite proximal and distal ends defining a leaf length, by interconnecting the proximal ends of the foil leaves to provide a continuous flexible strip of overlapping foil leaves in which the distal ends of the leaves extend freely; and subsequently forming the strip of foil leaves or thin metal sheet layers, arranging the leaves to lie in curved paths radiating inwardly from the interconnected proximal ends toward a central area. Another aspect of the present invention is directed to a catalytic converter body preferably comprising a jacket having opposite open ends, a carrier body comprising a plurality of thin sheet metal layers shaped to form fluid passage cells between the opposite open ends of the jacket; and means for supporting the thin sheet metal layers in the jacket to provide the body with a natural frequency of between 10 and 100 hertz.

According to another aspect, the present invention is directed to a catalytic carrier body preferably comprising means for supporting the thin sheet metal layers in the jacket to enable the carrier body to yield to mechanical and thermal stresses without failure. According to another aspect of the present invention, each of the thin sheet metal layers have an inner end and an outer end, the outer ends being secured to the jacket, and at least some of the inner ends being free from others of the inner ends . According to another aspect of the present invention, at least one end of at least some of the thin sheet metal layers are stronger than other portions of those layers. According to another aspect of the invention, at least one end of at least some of the thin sheet metal layers are more compliant than other portions of those layers .

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 invention will be better understood by having reference to the annexed drawings showing a preferred embodiment of the invention and wherein:

Fig. 1 is an end view of a converter body in accordance herewith showing a multicellular metallic, spiraliform converter body formed of alternating corrugated and flat thin metal core elements in the form of strips, sheets, or layers with the distal, or outer, ends thereof secured to the jacket tube or housing and the proximal, or inner ends thereof free to float.

Fig. 2 is an end view of an enlarged scale of the portion in the dotted circle in Fig. 1 and showing the free proximal ends of the corrugated and flat core elements.

Fig. 3 is a cross-sectional view of an electrically heatable catalytic converter in accordance herewith showing in diagrammatic form the free inner ends of the core elements . Fig. 4 is a perspective view of an electrically heatable converter body in accordance herewith.

Fig. 5 is a partial cross-sectional view of a subassembly prior to being formed in the arrangement shown in Fig. 1.

Fig. 5a is a partial cross-sectional view of an alternative construction of the arrangement shown in Fig. 5.

Fig. 6 is a view like Fig. 2 showing on an enlarged scale the proximal ends of the core elements in another embodiment.

Fig. 7 is an edgeview of a portion of a corrugated thin metal core element and a pair of contiguous flat thin metal core elements showing a decreasing amplitude of corrugation at the inner end as the thin metal core element approaches the center of the device.

Figs. 8-11 are cross-sectional views of a method of forming a strip of foil leaves into a catalytic converter incorporating the teachings of the present invention.

Figs. 12 and 13 respectively show a subassembly and a fixture for forming the subassembly into a catalytic converter.

Figs. 14-17 are the configurations of the flexible strip at the locations in Fig. 13 bearing their figure number.

Fig. 18 is a catalytic converter formed according to the teachings of the present invention.

Fig. 19 is an end view of a converter body structured in accordance with another embodiment of the present invention.

Fig. 19a is an enlarged scale end view of the central region of the converter shown in Fig. 19. Figs. 20 and 21 are alternative embodiments of inner end configurations for flat metal core elements in accordance with the present invention.

Fig. 22 is a perspective view of a converter body structured in accordance with a further embodiment of the invention.

Figs. 23-26 are plan views of alternate embodiments of core elements structured in accordance with the invention. Figs. 23a-26a are side views of Figs. 23-26, respectively.

Figs. 27 is a perspective view of a sheet from which the sheet metal layers are made.

Fig. 28 is a cross-secitonal view of a pair of sheet metal layers in an outer jacket constructed in accordance another embodiment of the present invention.

Fig. 28a is a fragmentary view of several pairs of sheet metal layers in enlarged scale from Fig. 28.

Figs 29-31 are partial end views of further embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION As indicated above, the present invention is a multicellular converter body formed form a housing and a plurality of core elements of thin metal. The core elements are connected to a rigid body member at one end only, hence the name "cantilever" . The multicellular converter bodies hereof are conveniently formed from precoated thin metal strips, such as may be produced by the process of Cornelison et al described in U.S. Patent 4,711,009. The converter bodies hereof may be made solely of corrugated thin metal core elements which are nonnesting, or of alternating corrugated and flat thin metal core elements. In the preferred embodiments, the thin metal strips, which will be used as core elements, are precoated or coated prior to assembly of the converter body. The distal, or outer ends are masked 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.

The corrugations generally have an amplitude of from about 0.02 inch to about 0.1 inch, and a pitch of from about 0.02 inch to about 0.25 inch. Where a nonnesting corrugated thin metal 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, albeit at an angle of from 3 degrees to about 10 degrees to the parallel marginal edges of the strips. The latter thin metal core elements may be layered without nesting. Where alternating corrugated and flat thin metal core elements are used to form the multicellular bodies hereof, 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 thin metal strips, although, as indicated above, the corrugations may be oriented along a line oblique to the longitudinal marginal edges of the thin metal strips. It should be pointed out that it has been found advantageous to lightly corrugate the "flat" thin metal core elements to reduce stress. By "lightly corrugated" we mean forming corrugations having 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". Thin metal core elements so "lightly corrugated" , will be referred to herein generically as "flat" thin metal core elements. Referring now to Figs . 1 and 2 , there is shown an end view of a "cantilever" multicellular converter body 10 formed of alternating corrugated thin metal core elements 16 and flat thin metal core elements 14. The thin metal core elements may be a ferritic stainless steel. The converter body 10 also includes a surrounding housing, or jacket tube 12, which may be formed of a 0.03" to 0.07" thick stainless steel. The distal ends of the thin metal core elements 18 and 20 are secured to the housing 12 as by brazing or welding. Brazing is preferred. The inner ends, or proximal ends of the thin metal core elements 14 and 16 are unattached. It should be noted that desirably 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. 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 as they approach the housing 12 becomes virtually constant and may be specifically constructed in such a manner.

Fig. 2 shows on an enlarged scale, the area represented by the circular dotted line 22 in Fig. 1. At the center is a gap 24 showing that the thin metal core elements 14 and 16 do not meet and are free floating in that they are not attached to another member. The gap 24 is desirably about 0.01" wide. Figs . 3 and 4 show an embodiment of the converter bodies hereof in a combined electrically heatable and light-off converter. These converters are integral in the sense that in the electrically heatable end, the flat thin metal core elements are divided into two bands. The front or upstream heater bands are electrically heatable, and the downstream bands, which are coplanar with the heater bands, are flat and located in the light-off portion of the converter body. The flat heater bands are preferably not electrically heatable and, on the upstream end, overlap the corrugated thin metal core elements, the latter extending the full axial length of the .converter body. The electrically heatable portion initiates the chemical reaction, e.g., oxidation, and the light-off portion completes the conversion to harmless by¬ products which are discharged to the atmosphere. The device shown in Figs. 3 and 4 has a special terminal bus and retainer to facilitate providing electrical power to the electrically heatable portion. While it is convenient and economical to make the thin metal core elements of a single kind of metal, it will be found advantageous to use different alloys, for example, some core elements made of ferritic stainless steel, and others made of a nickel/chromium alloy such 97/02884 P T/US96/11514

as Haynes 214 or Haynes 230. This structure provides additional durability in the Hot Tests described above. The corrugated thin metal core elements hereof are strips conveniently from about 2" to 5" wide and from about 7" to about 13" long with the ends flattened. The flat thin metal core elements hereof are strips conveniently from about 2" to about 5" wide, and from about 7" to about 13" long. The heater bands are conveniently from about 0.4" to about 0.8" wide, e.g., 0.5" wide. The flat thin metal bands are from about

1.2" to about 5.6" wide. The gap between the flat thin metal heater bands and the flat thin metal bands is from about 0.01" to about 0.15".

Referring now to Figs. 3 and 4, it will be observed that the axial extent of the sector 41 of the terminal bus and retainer 25 spans the division line 78 between the electrically heatable portion 72-74 of the converter body 11 and the light-off portion 76 downstream of the front or inlet face 70. The downstream edge 80 (Fig. 4) of the terminal bus and retainer 25 abuts the upstream edge of the inner housing 52, and may desirably be seam welded thereto. It will be seen, therefore, that there is provided in the sequence of gas passage through the converter body 11, a directly electrically heatable zone 72 having a given thermal inertia, and intermediate indirectly electrically heatable zone 74 having a larger thermal inertia, and a non-electrically heatable light-off zone 76. The three elements of a "cascade" device are present, albeit of the same diameter, in a single housing 52. This greatly simplifies the structure of a "cascade" installation while preserving the advantages thereof. Between the inner housing 52 and the outer housing 50 there may be provided insulation, such as a ceramic fiber mat, e.g., "INTERAM" as described above. Also, end cap adaptors 56 and 58 are conveniently provided to enable placement of the structure of Fig. 3 in an automobile exhaust line. There is provided in Figs. 3 and 4, a terminal bus and retainer 25 having a pair of arcuate members 51 and 53 that lie on the circular periphery of the core body 10. The arcuate members 51 and 53 each have two axially extending sectors of different axial length, the axially shorter sectors 39 and 43 of these being attached to the terminals 45 and 47 respectively, and to one end of the heater bands; and the axially longer sectors 41 and 49 of these being attached to the opposite ends of the heater bands (not shown in Figs. 3 and 4) . The axially longer sectors 41 and 49 are dimensioned axially to meet and be joined with the inner tubular housing 52 as by seam welding, for example. Narrow strips 39a and 41a join the two axially extending portions 38 and 41, and the two axially extending portions 43 and 49, respectively. The narrow strips 39a and 41a are removable after assembly, and are included only for assembly purposes. Also shown in Figs. 3 and 4 are an outer tubular housing 50 (Fig. 3) and an inner tubular housing 52 (Figs. 3 and 4) . Terminals 45 and 47 extend through the outer housing 50 through an insulated feed-through generally indicated at 60 and 62, respectively. For details of a suitable insulated feed through, reference may be had to commonly owned U.S. Patent to Sheller, 5,238,650 dated 24 August 1993. Terminal 45 is stud welded, for example, to the sector 39 of the terminal and bus retainer 25, and is, in turn, connected to one pole 64 of a voltage source generally indicated at 68 in Fig. 4. The opposite terminal 47 is stud welded, for example, to the portion 43 of the terminal bus and retainer 25, and is, in turn, connected to the other pole 66 of a voltage source 68. In an automotive vehicle, the voltage source is normally a 12 volt or 24 volt lead-acid battery. Higher voltages may be used, and may be either AC or DC, single or multiphase up to 120 volts or higher.

Fig. 6 shows making "clumps" of thin metal core elements 14 and 16 with the proximal ends of the two outer thin metal core elements joined together and clasping from 2 to 8 thin metal core elements between them. The clumps are then inserted in a form to the full number of thin metal core elements, e.g., 12 to 20 and the whole assembly encased in a jacket tube 12. Numerous other methods of making the cantilever type converter bodies hereof may be employed.

According to the present invention a method is provided for making a honeycomb structure for use as a catalytic converter structure or catalyst carrier body, comprising the steps of assembling a plurality of non- nestable thin metal layers or foil leaves, each foil leaf having opposite proximal and distal ends defining a leaf length, by interconnecting the proximal ends of the foil leaves to provide a continuous flexible strip of overlapping foil leaves to provide a continuous flexible strip of overlapping foil leaves in which the distal ends of the leaves extend freely; and subsequently forming the strip of foil leaves, arranging the leaves to lie in curved paths radiating inwardly from the interconnected proximal ends toward a central area.

Although the following preferred embodiment discloses a resulting body that can be inserted into a cylindrical jacket, bodies of other shape, such as elliptical shapes, may also be constructed according to the teachings of the invention.

As shown in Fig. 5, the plurality of foil leaves or thin metal strips or layers include and alternating series of sheets, namely corrugated foil leaves 16 and relatively flat leaves 14, that do not nest with one another and thereby define flow passages between them when they are proximate to each other. A flat core element 12 may ultimately become the outer housing of the assembled catalytic converter or may be layered with a separate outer housing 12 as shown in Fig. 1. The flat strip 12 preferably has a length equal to the inner circumference of the housing 12 and a desired thickness. Possible dimensions can be 8" for the circumferences and 0.03" for the thickness of the housing.

Therefore, it can be seen that instead of attaching the individual leaves to housing 12, which is typically 0.03" thick and relatively difficult to bend, the individual leaves preferably are first attached to a much thinner web of material such as a flattened strip of brazing foil tape, or a fabric strip, or other tape, which is easier to conform into a circular shape, and can serve as a liner for the outer housing 12. Such a web merely needs to keep the leaves together until they are formed into the final shape.

While in the flat condition shown in Fig. 5, alternating flat thin metal core elements 14 and corrugated thin metal core elements 16 are secured to a flexible strip 121 which is relatively flat at the time of assembly. Each of the leaves may be about 5" in length and have proximal ends 18 and 20, of the flat and corrugated core elements 14 and 16, respectively, which are bent at an angle or to the normal plane of the core elements, preferably about 30 to 45 degrees. If previously coated, the ends 18 and 20 are cleaned, by scraping, brushing or blasting, or otherwise rendered free of any coating on the end to enable attachment to the flat strip 12' by brazing or welding. Alternatively, the ends may be masked during the coating process . The leaves may also be attached by riveting or other connection processes .

The leaves are then preferably curled to make each leaf into a more curled shape to make it easier to form the leaves into a final structure. For example, each leaf can be curled around a pencil or narrow-diameter rod.

Strip 12 ' is bent into a circle by wrapping it on itself and formed as that the leaves lie in curved paths radiating inwardly from the interconnected proximal ends toward a central area 22, shown in Fig. 1, and in greater detail in Fig. 2. The ends of the strip 12' are butt welded to become the jacket tube or housing 12. The distal ends 17 and 19 of the thin metal core elements 14 and 16 preferably are originally unattached or may be selectively attached according to the application. In various applications, the foil leaves preferably lie in curved paths revolving through less than 360°, 270°, and 180°.

Instead of bending the strip 12' into a circle, the strip 12 ' with the thin metal strips attached may be inserted into a funnel shaped form and compressed by forcing them into the narrow opening of the desired diameter. The confronting ends of the strip 12' are then seam or butt welded to complete the core body 10.

As shown in Fig. 5A, the proximal ends 18' and 20' of the thin metal core elements 14' and 16' alternatively may be made long enough to underlie the proximal end of the next thin metal core element, and the proximal ends thus overlapped may be brazed to one another to form the interconnected proximal ends . The resulting quite flexible assembly may be inserted into a jacket tube 12 lined with brazing foil or brazing paste and this assembly inductively heated to fuse the brazing foil and secure the strips to the jacket^' tube or housing 12.

Th s, the leaves may be interconnected by attaching the individual leaves to a separate web, strip or filament through a webbing technique shown in Fig. 5 or by connecting them directly to each other through a shingling technique shown in Fig. 5a.

To perform the preferred brazing operation, the subassembly preferably is put in a chamber. The air is evacuated and preferably backfilled with argon. A vacuum can be used as well so long as the oxygen is removed. Also in that chamber is an induction coil which goes around the housing with about eighth to a quarter inch clearance between the coil and the housing. When the induction coil is energized, it heats the housing and the outermost tips of the foil with induction with a very localized heating effect, melting the braze at the outside diameter. The outside portion of the cantilever strips do not have the coating on them so they braze nicely at he outside diameter.

Fig. 5A and Figs. 8-17, show in greater detail alternative methods for assembling and forming the catalytic converter structure. In Fig. 8, the leaves

28 and 30 are shown to be interconnected at their outer ends 34 by welding overlapping end portions from which coating material has been removed or left uncoated by masking during the foil coating process. When the leaves are so assembled, they represent a subsassembly 24a in the form of a continuous interconnected strip of the alternating corrugated and flat leaves 28 and 30 as shown in Fig. 8. The inner ends of the leaves 28 and 30 extend freely in the strip.

One technique for shaping the strip subassembly 24a of leaves into the annular involute configuration shown in Fig. 1, for example, may involve use of a curved forming jig such as figure 38 in Fig. 9 having a curved end 40 which preferably approximates the involute path of the individual leaves 28 and 30 in the finished annular section 24. The fixture 38 preferably has a curved length of about one half the distance around the core so that when the subassembly is pushed into the fixture, the fixture generates a half-round body.

Thus, a leading end 39 of the flexible strip subassembly 24a is advanced longitudinally, in the direction of the leaf length, along the fixture 38 in the direction shown in Fig. 9 until the ends of the leading leaves in the subassembly 24a engage and deform as a result of contact with the arcuate end portion 40. The loose cantilevered ends move to the center, leaving the connected ends at an outer circumference. When it is no longer possible to advance the subassembly 24a toward the curve portion 40, a trailing end 41 of the flexible strip subassembly 24a is curved around the arcuate end portion of the fixture 38, as shown in Fig. 11. The trailing end of the web is brought around and may be connected to the leading end of the web to complete the core. This configuration is maintained during insertion of the subassembly 24a into a slightly convergent funnel device so that the outer periphery of the assembly 24a may be inserted directly into the outer jacket 32.

Once in the jacket 32, the interconnected outer ends 34 of the annular section 24 are secured to the jacket such as by a localized brazing technique described above and capable of imparting brazing temperatures to the outer jacket 32 without damage to the catalytic coating on the leaves 28 and 30.

In Figs. 12-17 of the drawings, an alternative method for wrapping the subassembly 24a of leaves 28 and 30 into an annular configuration is illustrated. Thus, in Fig. 12, the subassembly 24a of leaves is first placed in a tray-like structure 42 from which the subassembly is advanced into an involute funnel-shaped fixture 44 shown in Fig. 13. The funnel may be one to three feet long and have guide vanes running through to assist in the progress and closing of the subassembly. The cross-section of the fixture 44 shown in Fig. 13 varies along cutting planes represented respectively in Figs. 14, 15, 16 and 17 of the drawings.

Thus, the subassembly 24a is advanced through the fixture 44 to be formed progressively into the annular configuration shown in Fig. 17 in which the inner ends of the leaves 28 and 30 define a generally circular central opening 35. When the configuration of Fig. 17 is reached, the subassembly 24a is advanced into the cylindrical outer jacket and brazed at the outer ends of the leaves in the manner previously described.

As shown in Fig. 18, after the steps of assembling the foil leaves into a continuous flexible strip and subsequently forming the leaves into curved paths, the distal ends may be connected to other distal ends and/or a tube 23, which in turn can be connected to a core 25. In this case, core 25 includes another tube 27 and a spiral of alternating corrugated leaves 29 and flat leaves 31. Such an arrangement provides a honeycomb 33 of the foil assembly in which the leaves lie in curved paths revolving through less than about 180°, and the distal ends are 35 of corrugated foils 37 and flat foils 39 connected to a core 25 having a plurality of cells. In this arrangement, the leaves rotate through about 25° between the core 25 and the jacket 41 where proximal ends 43 are attached. The claimed catalytic converter structures and methods of making the structure can be used either as a complete catalytic converter structure or as a subcomponent or subassembly of a catalytic converter structure. For example, core 25 of the embodiment shown in Fig. 18 may be constructed according to the claimed invention so that the structure shown in Fig. 1 can be used as an alternative structure for the core 25 of the catalytic converter shown in Fig. 18.

In the embodiment illustrated in Figs. 1, 2 and 5- 7, the core elements 14 and 16 are of substantially equal lengths, such that they are arranged coextensively between the housing 12 and the core center 24. However, Figs. 19 and 19a illustrate another embodiment of the invention, wherein the inner ends of the flat foil leaf core elements 14 are terminated, e.g., generally along dashed circle 30 at the critical diameter short of the core center 24, leaving the inner portions of the corrugated foil leaf core elements 16 extending beyond the inner ends of core elements 14 free to assume progressively closer nesting relationships as they approach and terminate essentially at the core center.

Alternatively, the flat foil leaf core elements 14 may be made longer than the corrugated foil leaf core elements 16, as illustrated in Fig. 20. In accordance with this embodiment of the invention, the inner end portions of core elements 14, extending beyond the inner ends of the core elements 16, are folded around the inner ends of the core elements 16, as indicated at 15a, to envelop inner end portions of the core elements 16. The flat foil leaf core elements 14 thus present folded inner ends at the core center 24, which are inherently strengthened against fracture during converter use. The outer ends 18 and 20 of the core elements 14 and 16 may be lapped and welded (or brazed) together, as described above in connection with Fig. 5, to create an assembly for insertion into housing 12. Fig. 21 illustrates another embodiment of the reinvention, wherein the flat foil leaf core elements 14 are provided with lengths slightly in excess of twice the length of the corrugated foil leaf core elements 16. The core elements 14 are thus of sufficient length to not only be folded around the inner ends of core elements 16, but also to extend back out to the housing 12, as indicated at 15b.

It is thus seen that each double-length core element 14 serves as a pair of adjacent core elements 14 in the preceding embodiments in preventing nesting of adjacent pairs of corrugated foil leaf core elements 16. As in the embodiment of Fig. 20, the folded inner ends of core elements 14 are strengthened against fracture. Again, the outer ends 20 of the core elements 16 and the two outer ends of the core elements 14, indicated as 18a and 18b, may be lapped and welded to create a core assembly for insertion in housing 12. According to another aspect of the invention, at least one end of at least some of the metal sheet layers are stronger than other portions of the layers . It is further preferable in some applications that the inner end of each flat metal sheet layer is stronger than other portions of the flat metal sheet layer. As discussed above, strengthening may be accomplished by folding or doubling a leaf. Strengthening may also be accomplished by welding or brazing or otherwise connecting a strip of metal to the end of the leaf. As shown in Fig. 28a, the inner end of flat metal sheets 414 and corrugated metal sheets 416 are situated in the central area of a catalytic converter 410. An alloy strip 430, preferably having improved strength over metal sheets 414 and 416, are brazed or welded to the inner ends of flat metal sheets 414 prior to coating the sheets with catalytic material or with a localized brazing technique afterwards. As shown in Fig. 14, metal sheets 414 can be made from a continuous sheet 413 with alloy strips 430 brazed or welded to sheet 414 prior to coating them with a catalytic material.

The ends of the sheets may also be strengthened by slightly corrugating the sheets; creasing the sheets; hardening the sheets; working the sheets; forming ripples, ridges, or other patterns in the sheets by rolling or stamping a light corrugation, crisscross, or other pattern on the sheets; or other strengthening techniques that are appropriate to prevent failure from mechanical and thermal stresses. The sheets may be strengthened throughout their length, particularly the flat metal sheets, by such methods. Alternatively, just the end of the sheet may be so treated. Fig. 22 illustrates that the core center 24 may be occupied by a cylindrical insert 32. In accordance with one aspect of the present invention, the inner ends of the core elements 14 and 16 are not in any way attached or secured to the insert 32. 97/02884 PCT/US96/11514

In accordance with another aspect of the present invention, the ends of the core elements 514 and 516 may be attached or secured to each other and/or the insert 32, and/or jacket 12 in a compliant way or with a compliant structure such that the area 517 at or near at least one end of at least one metal sheet is more compliant than other portions of the sheet.

For example, as shown in Figs. 29-31, the end area of a flat sheet may be corrugated, such as portion 517b of Fig. 17, or attached to a corrugated segment 517a of Fig. 16, or a compliant segment of a more compliant configuration or material, such as 517c of Fig. 31. Such compliant segments or connections have more compliancy than some or all of the other portions along or throughout the length of the sheets . While according to this aspect of the invention, the compliant portions are near or at the end of the metal sheets, such compliant portions may also be positioned elsewhere in the metal sheets. Therefore, in the various arrangements of metal sheets described in this application and the applications incorporated by reference, a compliant end connection, end area, or end may be employed on one or both ends, with the preferable natural frequency of the catalytic converter being in the range of about 10 and 100 hertz. The catalytic converter structure shown, described, and claimed can be used both as the whole catalytic converter structure or a subassembly of a catalytic converter structure as well. The sheets can be precoated with catalytic material before assembly or forming steps, or can be coated after the assembly or forming steps.

It will be apparent to those skilled in the art that various modifications and variations can be made in the catalytic converter of the present invention and in construction of this converter without departing from the scope or spirit of the invention.

Numerous variations in the preferred structure above described may be used without departing from the invention. For example, although electrical connections at the outside of the core have been shown, such electrical connections may be made in the middle of the core and at the outside periphery. While straight-through cells have been shown, patterned cells, such as those formed with herringbone or chevron shaped, or angled corrugations, may also be used. Where the latter type of corrugations are used, the flat thin metal core elements may be omitted. While thin metal core elements have been shown and described without tabs on the ends of the strips, as shown for example, in US Serial No. 08/322,258 supra, the structure of the latter application may be used, if desired. While a circular core body has been shown, it will be understood that nay cross-sectional configuration, e.g., oval, elliptical, rectangular, or the like may be used. While it is desirable to make the devices hereof from a single stainless steel alloy or nickel/chromium alloy, it will be found desirable to strengthen the core body by using various reinforcing means, such as fashioning some of the thin metal strips or layers from a ferritic stainless steel, for example, and others from a nickel/chromium alloy; or by doubling or tripling the thickness of one or more of the strips or layers .

Claims

WHAT IS CLAIMED IS:

1. A converter body comprising a housing, and a core, said core comprising a plurality of thin metal, each of said metal layers having two opposite ends, one end of the metal layers being secured to said housing, and the other end of at least some of the metal layers being free.

2. A converter body as defined in Claim 1 wherein a portion of the thin metal layers are flat and in alternating relation with another portion of the thin metal layers which are corrugated.

3. A converter body as defined in Claim 1 wherein all of the thin metal layers are corrugated in a nonnesting pattern.

4. A converter body as defined in Claim 3 wherein the thin metal layers are corrugated in a herringbone pattern.

5. A converter body as defined in Claim 3 wherein the thin metal layers are corrugated in a chevron pattern.

6. A converter body as defined in Claim 1 wherein the thin metal layers are coated with a refractory metal oxide coating prior to forming the converter body.

7. A converter body as defined in Claim 6 wherein the refractory metal oxide coating comprises alumina.

8. A converter body as defined in Claim 6 wherein the refractory metal oxide coating has a noble metal catalyst supported thereon.

9. A converter body as defined in Claim 8 wherein the noble metal catalyst is selected from the group consisting of platinum, palladium, rhodium, ruthenium, indium and mixtures of two or more of such metals.

10. A converter body as defined in Claim 2 wherein the corrugations of the corrugated thin metal layers have a decreasing amplitude toward the end extending toward the center region of the converter body.

11. A converter body as defined in Claim 1 wherein all of the other ends of the core element are free.

12. The method of making a catalytic converter structure body comprising the steps of: assembling a plurality of non-nestable thin metal layers, each having two opposite ends, by interconnecting one end of the metal layers to provide a continuous flexible strip of overlapping metal layers in which the other end of the metal layers extend freely; and subsequently forming the strip of overlapping metal layer, arranging the metal layers to lie in curved paths radiating inwardly from the interconnected ends toward a central area to provide flow passages generally transverse to the length of the metal layers .

13. The method of Claim 12 wherein the metal layers are interconnected by joining one end thereof to a common web.

14. The method of Claim 12 wherein the metal layers are interconnected by joining one end thereof to each other.

15. The method recited in Claim 14 wherein the metal layers are provided with joining margins at one end thereof, the joining margins being overlapped with a longitudinal offset.

16. The method of Claim 15 wherein the metal layers covered with a coating including a catalyst material before the assembling step, the joining margins being free of the coating.

17. The method of Claim 12 wherein the forming step comprises advancing a leading end of the flexible strip longitudinally into a curved forming jig.

18. The method of Claim 17 wherein the curved forming jig has a diameter of about one-half the catalytic converter structure.

19. The method of Claim 17 including the step of subsequently wrapping a trailing end of the flexible strip around the leading end while the leading end is in the fixture.

20. The method recited in Claim 12 wherein the forming step comprises closing the interconnected ends of the metal layers into a circular configuration.

21. The method of Claim 12 wherein the forming step comprises advancing the flexible strip transversely through a funnel-shaped forming jig.

22. The method of Claim 12 wherein the forming step includes to progressively shaping the interconnected ends into a path circle and to progressively shaping the metal layers into involute paths.

23. The method of Claim 12 wherein the assembly step includes spacing the metal layers at a distance of about 0.1 to 0.5 inches along the interconnected ends.

24. The method of Claim 12 wherein the forming step includes forming the strip of overlapping metal layers into an arrangement in which the metal layers lie in curved paths revolving through less than about 360°.

25. The method of Claim 12, wherein the forming step includes forming the strip of overlapping metal layers into an arrangement in which the metal layers lie in curved paths revolving through less than about

270°.

26. The method of Claim 12 wherein the forming step includes forming the strip of foil leaves into an arrangement in which the leaves lie in curved paths revolving through less than about 180°.

27. The method of Claim 12 including subsequently inserting the formed strip of overlapping metal layers into a jacket with the ends layers proximate the jacket.

28. The method of Claim 12 including subsequently connecting the interconnected ends to the jacket.

29. The method of Claim 12 including coating the metal layers with a catalyst material before the assembly step.

30. The method of Claim 16 wherein the catalyst material coating is a refractory metal oxide layer having a catalyst supported thereon.

31. The method of Claim 30 wherein the catalyst is one or more noble metals.

32. An assembly for use in the manufacture of catalytic converter cores, comprising a plurality of non-nestable thin metal layers, each having two opposite ends defining a length thereof, one end of the metal layers extending freely, the other end of the metal layers being interconnected to provide a continuous flexible strip of overlapping metal layers lying in curved paths radiating inwardly from the interconnected ends .

33. A method of making a honeycomb carrier body comprising the steps of: providing a plurality of non-nestable metal layers, each metal layer having two opposite ends which define the length of the metal layer; joining one end of the metal layer to form a continuous, flexible strip, each metal layer of the strip having a free end; forming the strip into a body having the metal layers extending outwardly in the form of an involute from the periphery of the body to a central region within the body to provide a plurality of free ends at said central region, the metal sheets forming a plurality of passages through which a fluid can flow.

34. The method of Claim 33 including inserting the shaped body into a jacket.

35. The method of Claim 33 including joining the jacket to the periphery of the shaped body.

36. A catalyst carrier body comprising: an outer jacket having opposite open ends; a central core comprising a plurality of metal sheet layers shaped to form fluid passage cells between the opposite ends of the jacket; and means for supporting the metal sheet layers in the jacket to provide the body with a natural frequency of between 10 and 100 hertz.

37. A catalyst carrier body comprising: an outer jacket having opposite open ends; a central core comprising a plurality of structured metal sheet layers shaped to form fluid passage cells between the opposite open ends of the jacket; and means for supporting the metal sheet layers in the jacket to enable the core structure to yield to mechanical and thermal stresses without failure.

38. A catalyst carrier body comprising: a core including a plurality of metal sheet layers, and a jacket, each of said metal sheet layers having an inner end and an outer end, the outer end being secured to said jacket, and at least some of the inner ends being free from other of the inner ends.

39. The catalyst carrier body of Claim 38, wherein the metal sheet layers are alternating flat and corrugated metal sheet layers .

40. The catalyst carrier body of Claim 38, wherein all of the metal sheet layers are corrugated in a non-nesting pattern.

41. The catalyst carrier body of Claim 40, wherein the metal sheet layers are corrugated in a herringbone pattern.

42. The catalyst carrier body of Claim 40, wherein the metal sheet layers are corrugated in a chevron pattern.

43. The catalyst carrier body of Claim 38, wherein the metal sheet layers are precoated with a refractory metal oxide coating.

44. The catalyst carrier body of Claim 43, wherein the refractory metal oxide coating comprises alumina.

45. The catalyst carrier body of Claim 43 , wherein the refractory metal oxide coating has a noble metal catalyst supported thereon.

46. The catalyst carrier body of Claim 45, wherein the noble metal catalyst is selected from the group consisting of platinum, palladium, rhodium, ruthenium, indium and mixtures of two or more of such metals .

47. The catalyst carrier body of Claim 39, wherein the corrugations of the corrugated metal sheet layers have a decreasing amplitude toward the inner ends.

48. The catalyst carrier body of Claim 38, wherein the inner ends of all metal sheet layers are free from attachment to each other.

49. The catalyst carrier body of Claim 39, wherein the inner ends of the corrugated metal sheet layers extend inwardly beyond the inner ends of the flat metal sheet layers .

50. The catalyst carrier body of Claim 49, wherein the inner end portions of the corrugated metal sheet layers beyond the inner ends of the flat metal sheet layers are nested with each other.

51. The catalyst carrier body of Claim 39, wherein inner end portions of the flat metal sheet layers are folded about the inner ends of adjacent corrugated metal sheet layers .

52. The catalyst carrier body of Claim 51, wherein the folded inner end portions of the first metal sheet layers envelop inner end portions of the corrugated metal sheet layers .

53. The catalyst carrier body of Claim 39, wherein each metal sheet layer is folded double to fully envelop one of the corrugated metal foil leaves, each folded-double metal foil leaf including a pair of outer ends secured to the jacket and an inner end folded about the inner end of the enveloped corrugated metal sheet layers .

54. The catalyst carrier body of Claim 39, wherein the inner end of each flat metal sheet layer comprises a double thickness of metal.

55. The catalyst carrier body of Claim 54, wherein the double thickness of metal comprises a strip of metal welded or brazed to the inner end of each flat metal sheet layer.

56. The catalyst carrier body of Claim 38, wherein some of the metal sheet layers are flat metal sheet layers and the inner ends of each flat metal sheet layer is stronger than other portions of the flat metal sheet layer.

57. The catalyst carrier body of Claim 38, wherein the sheet metal layers are alternating lightly corrugated and more heavily corrugated sheet metal layers.

58. The catalyst carrier body of Claim 39, wherein the inner ends of each flat metal sheet layer is lightly corrugated.

59. The catalyst carrier body of Claim 38, wherein at least one end of at least some of the metal sheet layers are stronger than other portions of the said layers .

60. The catalyst carrier body of Claim 59, wherein said at least one end is the inner end.

61. The catalyst carrier body of Claim 36 wherein at least one end of at least some of the metal sheet layers are more compliant than other portions of said layers .

62. An electrically heatable converter comprising (a) an inner housing, (b) an outer housing, (c) a multicellular core body including an electrically heatable portion formed of flat thin metal heater bands each having a distal end and a proximal end, and corrugated thin metal core elements each having a distal end and a proximal end, and a light-off portion formed of flat thin metal bands which are not electrically heatable and each having a distal end and a proximal end, said flat thin metal bands being in alternating relation with corrugated thin metal core elements each having a distal end and a proximal end, said corrugated thin metal core elements extending into said electrically heatable portion and overlapping the flat thin metal heater bands, said core body being contained within said inner housing, (d) insulation means disposed between said inner housing and said outer housing, and (e) means for electrically heating said electrically heatable portion; the distal ends of said thin metal core elements and bands each being secured to the inner housing, at least some of the proximal ends of said bands and core elements being free and unsupported.

63. An electrically heatable converter as defined in Claim 62 wherein the multicellular core has a spiralform configuration.

64. An electrically heatable converter as defined in Claim 62 wherein the thin metal core elements and bands are precoated with a refractory metal oxide coating.

65. An electrically heatable converter as defined in Claim 64 wherein the coating comprises alumina.

66. An electrically heatable converter as defined in Claim 62 wherein the thin metal core elements and bands are coated with refractory metal oxide coating.

67. An electrically heatable converter as defined in Claim 64 further including a catalyst supported on said coating.

68. An electrically heatable converter as defined in Claim 67 wherein the catalyst is a noble metal catalyst.

69. An electrically heatable converter as defined in Claim 68 wherein the noble metal catalyst is selected from the group consisting of platinum, palladium, ruthenium, rhodium, indium, and mixtures of two or more of such metals.