CA2257260A1

CA2257260A1 - Hybrid mounting system for pollution control devices

Info

Publication number: CA2257260A1
Application number: CA002257260A
Authority: CA
Inventors: Paul D. Stroom; Joel H. Sabean; Richard P. Merry; Lloyd R. Hornback, Iii; Stephen M. Sanocki
Original assignee: Individual
Current assignee: 3M Co
Priority date: 1996-06-18
Filing date: 1997-04-28
Publication date: 1997-12-24
Also published as: JP5296411B2; US5882608A; ES2158560T3; JP5952216B2; JP2000513064A; JP2013137038A; EP0906495B1; CN1222219A; US20010048903A1; US7501099B2; WO1997048889A1; JP2008261339A; EP0906495A1; US20040052698A1; DE69705407T2; US6613294B2; CN1083927C; DE29709180U1; DE69705407D1

Abstract

A pollution control device has a metal housing (12), a solid pollution control device (20) disposed within the metal housing, and a mounting mat (24) disposed between the pollution control element and the housing for positioning the pollution control element and for absorbing mechanical and thermal shock. The mounting mat includes a layer of intumescent material (26) having at least one insert formed of a resilient, flexible, fibrous non-intumescent material (28). The insert is positioned along at least a portion of at least one lateral edge of the mounting mat to prevent erosion of the intumescent material and to provide a seal between the pollution control element and the housing.

Description

CA 022~7260 1998-12-02 W O 97/48889 PCTrUS97/07251 EnYB~UlD M O UNT~NG SYSllEM FO R
POLLUTION CONTROL DEVICES
s BACKGROI)ND OF THE INVENTION
The present invention relates to pollution control devices, and particularly to catalytic converters and diesel particulate filters or traps for ar automotive exhaust system. The pollution control devices typically comprise a metal housing with a monolithic element securely mounted within the casing by a resilient and ~ o flexible mounting mat. The mounting mat is comprised of an intumescent sheet material having inserts formed of a non-intumescent ceramic fiber composite.
Pollution control devices are universally employed on motor vehicles to control atmospheric pollution. Two types of devices are currently in wide spread use --catalytic converters and diesel particulate filters or traps. Catalytic converters contain a catalyst, which is typically coated on a monolithic structure mounted in the converter.
The monolithic structures are typically ceramic, although metal monoliths have been used. The catalyst oxidizes carbon monoxide and hydrocarbons, and reduces the oxides of nitrogen in automobile exhaust gases to control atmospheric pollution. Due to the relatively high temperatures encountered in these catalytic processes, ceramics have ~, been the natural choice for catalyst supports. Particularly useful catalyst supports are provided by ceramic honeycomb structures as described, for example, in U.S. Patent Re.
27,747.
More recently, catalytic converters utilizing metallic catalyst supports (metallic monoliths) have also been used for this purpose. (See, for example, in U.K.
Patent No. 1,452,982, U.S. Patent No. 4,381,590 and SAE paper 850131).
The most common diesel particulate filters or traps are monolithic wall-flow filters. These monolithic wall-~ow type diesel particulate filter elements are typically comprised of honeycombed, porous, crystalline ceramic (for example, cordierite) material. Alternate cells of the honeycombed structure are typically plugged such that exhaust gas enters in one cell and is forced through the porous wall of one cell and exits the structure through another cell. The size of the diesel particulate filter - element depends on the particular application needs. Useful diesel particulate filter elements are commercially available, for example, from Corning Inc. of Corning, New Your, and NGK Insulator Ltd. of Nagoya, Japan. Useful diesel particulate filter elements are discussed in "Cellular Ceramic Diesel Particulate Filter," Howitt et al., Paper No. 810114, SAE Technical Paper Series, 1981.

CA 022~7260 1998-12-02 W O 97/48889 PCTnUS97/07251 In the state of the art construction of these devices, each type of device has a metal housing which holds within it a monolithic structure or element that can be metal or ceramic, and is most commonly ceramic. The monolithic structure is mounted in the housing in a process referred to as c~nning There is a gap or space between the monolith and the housing which varies because there is a range of size tolerances for both the monolith and the housing. The largest gap exists when the monolith is on the small end of the range and the housing is on the large end of the range. To avoid damage to the monolith and to hold it in place a mounting material, such as an intumescent mounting mat or an intumescent paste, is typically disposed around the monolith before canning. The mounting material fills the gap. After the wrapped monolith is inserted into the housing, the can is pressed closed and ~anges along the lateral edges of the housing are welded. After installation on the vehicle, the pollution control device is heated by the hot exhaust gases which expand the intumescent materials generating additional holding pressure. The amount of pressure is determined by the mount density of the materials and the temperatures of use. If the mount density is too low, there will be insufficient pressure to hold the monolith in place. If the mount density is too high, excessive pressure can be exerted by the mounting material between the housing and the monolith causing deformation of the housing and/or damage to the monolith.
After the monolith has been secured in the housing, the intumescent mounting material serves to avoid or reduce damage from other conditions that can be problematic to the pollution control device. The device can be subjected to d~m~ging vibrations both before and after installation in a vehicle. Additionally, the entire device is subjected to elevated temperatures, for example, over 300~C, for various periods of ~s time.
A ceramic monolith has a coefficient of thermal expansion generally an order of magnitude less than the metal (usually stainless steel) housing in which it is contained, so that at elevated temperatures, the mounting materials must expand sufficiently to compensated for the di~ele-llial expansion, but not so must as to create excessive pressure which can damage the housing or the monolith. The mounting material also prevents hot exhaust gases firom passing between the monolith and the metal housing (thereby bypassing the catalyst).
Typically, the mounting materials include inorganic binders, inorganic fibers that may also serve as a binder, intumescent materials, and optionally, organic binder, fillers and other adjuvants. The-materials are used as pastes, sheets, and mats.
Ceramic mat materials, ceramic pastes, and intumescent sheet materials useful for CA 022~7260 1998-12-02 W O 97/48889 PCTrUS97/07251 mounting the monolith in the housing are described in, for t,.~l",le, U.S. Patent Nos.

3,916,057 (Hatch et al.), 4,305,992 (Langer et al.), 4,385,135 (Langer et al.), S,254,416 (Langer et al.), 5,242,871 (Hashimoto et al.), 3,001,571 (Hatch), 5,385,873 (MacNeil), 5,207,989 (MacNeil), and Great Britain Patent 1,522,646 (Wood).
U.S. Patent No. 4,999,168 to TenEyck describes a crack resistant intllme~cçnt sheet having a preformed intl~mesc~nt layer adhesively bonded to a einror.;il1g layer of a sheet material such as craft paper, plastic film, inorganic fabric.
U.S. Patent No. 4,865,818 to Merry et al. describes a method of producing a catalytic converter by wrapping a thin sheet of mat material around the monolith at least twice in a layer wise fashion.
U.S. Patent No. 4,929,429 to Merry describes a composite for catalytic converters having a ceramic fiber mat stitched-bonded to an intumescent mat material.
U.S. Patent No. 4,048,363 to Langer et al. describes a composite having at least two layers of similar sheets of intumescent materials.
As the pollution control device is cycled between high and low temperatures, the size of the gap between the monolith (metal or ceramic) and the housing continuously changes, and the mounting mat is repeatedly compressed and uncompressed. In cases where the housing reaches very high temperatures, that is, greater than about 700CC, deformation of the housing can occur. In these cases, conventional intumescent mat mounting material may lack the high temperature resiliency to provide continued support for the monolith. A need thus exists for a mounting system which is sufficiently resilient and co~,lp~es~ible to accommodate the changing gap between the monolith and the metal housing without causing derollllalion of the metal housing. Further, while the state of the art mounting materials have their own utilities and advantages, there remains an ongoing need to improve mounting materials for use in pollution control device. Additionally, it would be desirable to provide materials that function well over a broader tempel ~ure range.
SUMMARY OF THE INVENTION
The present invention provides a hybrid mounting system for pollution control devices which utilize a monolith structure within a metal housing. The mounting system comprises a mounting mat disposed between the monolith and the metal housing of the pollution control device. The mounting mat includes inserts formed of a resilient, flexible, fibrous non-intumescent material positioned along a lateral edge of the mounting mat. In a preferred embodiment, the mounting mat is an intumescent material, and the resilient, flexible, fibrous insert is formed of a non-intumescent material. The .

CA 022~7260 1998-12-02 wo 97148889 PCTtUS97/07251 hybrid mounting mat is useful for protecting fragile monolithic structures in catalytic converters, diesel particulate filters, and high temperature filters. The hybrid mounting mat offers the advantage of being able to combine the properties of the intumescent mounting mat and the non-intumescent inserts.
BRllEF DESCRIl'TION OF THE DRAWINGS
Figure 1 is a perspective exploded view of a catalytic converter showing the mounting system of the present invention.
Figure 2 is a view of the catalytic converter of Figure 1, showing the mounting system of the present invention peeled away from the monolith.
Figure 3A shows a prior art bonding system comprised of an intumescent material.
Figure 3B shows the mounting system of Figure 3A disposed about a monolith in cross-section.
Figure 4A shows a preferred embodiment of the mounting system of the present invention.
Figure 4B shows the mounting system of Figure 4A disposed about a monolith in cross-section.
Figure 4C shows a modification of the mounting system of Figure 4A.
Figure 5A shows an altemative embodiment of a mounting system of the present invention.
Figure 5B shows the mounting system of Figure 5A disposed about a monolith in cross-section.
Figure 6A shows an altemative embodiment of a mounting system of the present invention.
2s Figure 6B shows the mounting system of Figure 6A disposed about a monolith in cross-section.
Figure 7A shows an alternative embodiment of a mounting system of the present invention.
Figure 7B shows the mounting system of Figure 7A disposed about a monolith in cross-section.
Figure 8A shows an altemative embodiment of a mounting system of the present invention.
Figure 8B shows the mounting system of Figure 8A disposed about a monolith in cross-section.
Figure 9 shows an alternative embodiment of a catalytic converter having a dual monolith.

CA 022~7260 1998-12-02 W O 97/48889 PCT~US97/07251 Figure 10 shows an alternative embodiment of the mounting system of the present invention.
Figure 11 shows yet another alternative embodiment of the mounting system of the present invention.
s DETAILED DESCRIPTION OF THE INVENTION
Although the mounting system of the present invention is suitable for use in a variety of pollution control devices, such as catalytic converters and diesel particulate filters or traps, its use is described herein in connection with a catalytic converter. The description is intended to be illustrative of the use of the mounting system of the present invention and should not be construed as limiting the use of the mounting system to catalytic converters.
Referring now to Figures ~ and 2, catalytic converter 10 comprises metallic housing 12 with generally conical inlet 14 and outlet 16. The housing, which is also referred to as a can or a casing, can be made from suitable materials known in the art for such use and is typically made of metal. Preferably, the housing is made of stainless steel. Disposed within housing 12 is a monolithic catalytic element 20 formed of a honeycombed monolithic body either of ceramic or metal. Suitable catalytic converter elements, also referred to as monoliths, are known in the art and include those made of metal or ceramic. The monoliths or elements are used to support the catalyst materials for the converter. A useful catalytic converter element is disclosed, for example, in U.S. Pat. No. RE 27,747 (Johnson). Monolith 20 has a plurality of gas flow ch~nn~l~ (not shown) therethrough. The catalyst materials coated onto the catalytic converter elements include those known in the art (for example, metal such as ruthenium, osmium, rhodium, iridium, nickel, p~ m~ and platinum, and metal oxides ~s such as v~n~-lium pentoside and titanium dioxide). For further details regald~g catalytic coatings see, for example, U.S. Pat. No. 3,441,381 (Keith et al.).
Surrounding monolith 20 is hybrid mounting system 24. Mounting system 24 comprises a mat 26 of intumescent material having inserts 28 formed of a resilient, flexible, fibrous mat of essentially shot-free ceramic fiber. Inserts 28 are 30 disposed such that at least one edge of insert 28 extends along a lateral edge of intumescent mat 26.
As seen in Figures 4A-8B, there are numerous manners in which insert 28 may be positioned such that it extends along a lateral edge of intllmescçnt mat 26.
Figures 3A and 3B illustrate an intumescent mat 26 without insert 28. Figure 3B
35 provides a cross-section view of intumescent mat 26 disposed between casing 12 and monolith 20.

CA 022~7260 1998-12-02 W O 97/48889 PCTrUS97/07251 Figure 4A shows non-intllmescçnt inserts 28 alternating with in~lmescent mat 26, such that lateral edge 32 of mounting system 24 presents alternating sections of intumescent and non-intumescent. Figure 4C shows a modification of mounting system 24 where each mat 26 and insert 28 is formed with a s tab 30 at one end and a slot 31 at the other. The tab 30 of each mat 26 fits into or mates with the slot 31 of an ~ nt insert 28. Likewise, the tab 30 of each insert 28 fits into or mates with the slot 31 of an adjacent mat 26. In the illustrated embodiment, each tab 30 is sized the same and each slot 31 is sized the same. It may be desirable for the tab 30 of each mat 26 to be sized so as to only mate with the slot 31 of an insert 28 and for o the tab 30 of each insert 28 to be sized so as to only mate with the slot 31 of a mat 26.
It is understood that the mounting system 24 could be further modified in a number of ways to accommodate other types of monoliths and casings not disclosed herein, including reducing or increasing the number of each type of section and r.ll~nging the shape of one or more sections used for the mounting system 24. The use of dirrele"L
s slot and tab arrangements may also be desirable.
As illustrated in Figure 4B, when mounting system 24 is positioned around monolith 20 within casing 12, non-intumescent inserts 28 are preferably positioned along the portion of monolith 20 having the largest radius of curvature.
Inserts 28 are preferably positioned along the portion of monolith 20 having the largest radius of curvature because this area corresponds to the portion of casing 12 most likely to deform under excessive pressure caused by compression of mounting system 24. As noted above, in cases where the pollution control device reaches very high temperatures, that is, greater than about 700~C, deformation of the housing can occur. At these high temperatures, conventional intumescent mounting materials greatly expand, and the resultant pressure exerted on the interior of casing 12 is very high. In addition, at such high temperatures the metal of the casing (typically stainless steel) begins to soften and becomes more susceptible to derolma~ion. By positioning non-intl-m~cc~nt inserts 28 at the points most likely to experience deformation under high temperature conditions, mounting system 24 generates less damaging force at high temperatures, such thatdeformation of casing 12 is greatly reduced.
Figures 5A and 5B show an embodiment of mounting system 24 similar to that of Figures 4A and 4B. In the embodiment of Figures 5A and 5B, the inserts 28 do not extend throughout the width of intumescent mat 26. When positioned about monolith 20, non-int-~mescent inserts 28 are positioned in a manner like that described ~s above for Figure 4B.

CA 022~7260 1998-12-02 W O 97/48889 PCT~US97107251 Figure 6A and 6B show yet another alternative embodiment of mounting system 24 in which non-intumescent inserts 28 extend along the entire lateral edge 34 of intllmesc.ont sheet material 26 such that when mounting system 24 is disposed about monolith 20, the entire lateral edge 34 of intumescent sheet material 26 s is protected by insert 28.
Yet another embodiment of mounting system 24 is shown in Figures 7A
and 7B. In Figure 7A, mounting system 24 is shown to include inserts 28 which extend along the lateral edges 34 of the intum~cc~nt sheet material 26, but are offset from the inhlm~sct?nt sheet material to form the tab end slot configuration seen to be a l~m~ te of inhlmesc~ont material 26 and non-intllmescent material 28.
Finally, another embodiment of mounting system 24 is shown in Figures 8A and 8B. The mounting system of Figures 8A and 8B is similar to the mounting system of Figures 7A and 7B, but insert 28 extends only along one lateral edge 34 of intllm~cent sheet material 26. Insert 28 is offset from intumescent sheet material 26 to form interlocking ends.
In each of the embodiments of Figures 4A-8B, inserts 28 may be secured to intllmesc~nt mat 26 by an adhesive tape (not shown) such as p~ck~ging tape or other suitable adhesive tape. Alternatively, inserts 28 do not have to be secured with tape or they may be secured by other techniques such as stapling, stitrhing, and the like.
In some in.ct~nces, a pollution control device may use dual monoliths, rather than a single monolith. For exarnple, Figure 9 shows a prior art catalytic converter 10A which has two monoliths 20 within a metal housing 12 and which areseparated by a gap 40. In such a dua! monolith cor~guration, it is known to align a metal strip 42 with the gap 40 between the monoliths 20. (See, for example, German Patent DE 43 23 791 Al). The metal strip is typically made from high tempt;lal~lre corrosion resistant metals such as Inconel and stainless steel. The metal strip can take the form of a metal foil, corrugated metal foil, a metal fabric and the like. The metal strip 42 expands at a rate very close to that of metal housing 12. Because metal strip 42 expands at a rate similar to that of housing 12, the portion of mounting mat 44 between metal strip 42 and housing 12 tends to be co.l,~ ssed to a greater degree than the portion.of mounting mat 44 between monoliths 20 and housing 12. If the portion of mounting mat 44 between metal strip and housing 12 is con"l)lessed excessively, deformation of either housing 12 or metal strip 42 can result.
As seen in Figure 9, prior art mounting mats typically provided a continuous layer of mounting mat 44 between metal strip 42 and housing 12. As described above, this arrangement can lead to deformation of either housing 12 or metal _ .

CA 022~7260 1998-12-02 W O 97/48889 PCT~US97/07251 strip 42. It is therefore desirable to position a flexible, resilient fibrous insert 48 along metal strip 42 between metal strip 42 and housing 12. Preferably, insert 48 is a material such as SAFFIL, available from ICI Chemicals and Polymers. As ~icc~ ed above, such inserts are capable of colllpl-e~ g with less force than typically used mounting5 materials, such that deforrnation of casing 12 or metal strip 42 is avoided.
Figures 10 and 11 show alternative embodiments of the mounting system of Figure 9 which uses a flexible, resilient, fibrous non-intumescent insert positioned along metal strip 42 between metal strip 42 and housing 12. In Figure 10, metal strip 42 is inserted into routed portions 50 of mounting mat 44, and insert 48 is secured adjacent metal strip 42 with adhesive tape 52. In Figure 11, metal strip 42 is sandwiched between layers of mounting mat 44A and 44B (such that no rotating of mounting mat material is required). Flexible, resilient, fibrous insert 48 is then inserted between mounting mat portions 44B and secured in place with adhesive tape 52. Either of the embodiments of Figure 10 or Figure 11 prevent excessive con,~ ion of material between metal strip 42 and housing 12, and thereby avoid deformation of either metal strip 42 or housing 12.
In use, the mounting materials of the invention are disposed between the monolith and the housing in similar fashion for either a catalytic converter or for a diesel particulate filter. This may be done by wrapping the monolith with a sheet of the 20 mounting material, inserting the wrapped monolith into the housing, and welding the housing. Mounting system 24- holds catalytic monolith 20 in place in casing 12 and seals the gap between catalytic monolith 20 and casing 12, to thus preventing exhaust gases from bypassing catalytic monolith 20.
Intumescent sheet material 26 comprises a resilient, flexible intllmescP.nt 2. sheet comprising from about 20 to 65 percent by weight of unexpanded vermiculite flakes, such flakes being either untreated or treated by being ion exchanged with ammonium compound such as ammonium dihydrogen phosphate, ammonium carbonate, ammonium chloride or other suitable ammonium compound; from about 10 percent to 50 percent by weight of inorganic fibrous material including aluminosilicate fibers (commercially available under the tradenames FiberfraxlM from Unifrax Co., Niagara Falls, New York, and CerafiberTM from Therrnal Ceramics, Augusta, Georgia) asbestos fibers, glass fibers, zirconia-silica, and crystalline alumina whiskers; from about 3 to 25 percent by weight of binder including natural rubber lattices, styrene-butadiene lattices, butadiene acrylonitrile lattices, lattices of acrylate or methacrylate polymers and 3S copolyrners and the like; and up to about 40 percent by weight of inorganic filler including expanded vermiculite, hollow glass rnicrospheres and bentonite. Useful sheet CA 022~7260 1998-12-02 wo 97/48889 PCT/US97/07251 materials also include those described in U.S. Patent No. 5,523,059 (Langer).
Further, examples of intumesce-lt sheet materials include those described in U.S. Patent Nos. 3,916,057 (Hatch et al.), 4,305,992 (Langer et al.), 4,385,135 (Langer et al.), 5,254,410 (Langer et al.), 4,865,818 (Merry et al.), 5,151,253 (Merry et s al.), and 5,290,522 (Rogers et al.). Useful commercially available intllmPscçnt sheets and mats includes those sold under the INTERAMTM tradename by Minnesota Mining & ~mlf~r.tllring Co. of St. Paul, Minnesota. The mounting mats typically range in thickness from 0.5 to 10 mm. Additionally, useful intumescent mounting materialsinclude intumescent pastes such as those described in U.S. Patent Application No.
08/496,945 (Merry).
Organic binders include those described above such as natural rubber lattices, styrene-but~ ene lattices, butadiene acrylonitrile lattices, and Jattices of acrylate and methacrylate polymers and copolymers.
Inorganic fillers include expanded vern~iculite, hollow glass microspheres, and bentonite. Preferably, the inorganic fillers are expanded vermiculite.
F.~çnti~lly shot-free ceramic fibers useful in forming non-intumescent inserts 28 include alumina-boria-silica fibers, alumina-silica fibers, alumina-phosphorus pentoxide fibers, zirconia-silica fibers, zirconia-alumina fibers, and alumina fibers.
Useful commercially available fibers include those under the tradenames FIBERMAX, available from Unifrax, SAFFIL LD, available from ICI Chemicals & Polymers, ALCEN alumina fibers available from Denka, and MAFTECH fibers, available from Mitsubishi.
The fibers are typically formed by blowing or spinning using methods known in the industry. Preferable, the fibers are formed by spinning a sol gel solution.
The fibers are formed into a mat by various known methods including blowing the fibrous material onto a collection screen as is practiced in the nonwoven industry. A
pierell~d non-intumescent material is a polyclystalline alumina fiber, available under the tradename SAFFIL from ICI Chemicals and Polymers. The fiber is chemically resistant and may be used in selected applications up to 1600~C. It is produced in a low density mat form which consists of a predominately two-dimensional random orientation of fiber resulting in a mat of lamella form. The mat is essentially shot-free with a uniform fiber structure.
The lamella nature of the low density mat makes it necess~ry to introduce the means for preventing delall~ alion during handling and assembly in the 3s pollution control device. That is, the low density mat of alumina fiber is preferably physically restrained or compressed during handling and assembly. (As use herein, g . _, CA 022~7260 1998-12-02 "shot-free" or "e~ nti~lly shot-free" refers to a fiber mat which is at least 95 percent shot-free and preferably 99 percent shot-free). When colnl)le~sed to a mount density of about 0.10 and 0.60 grams per cubic cr.~l;".e~er cubed these materials have a unique ability to repeatedly undergo a reduction in thickness while hot and spring back to s subs~all~ially their original thickness when cooled, thus continually exerting a substantial holding force to catalytic monolith 20.
Since the fiber material preferred for the non-intumescelll inserts 28 are generally available in the density range of 0.020 to 0.060 grams per centimeter, they must be col-l~lessed by about a factor of 10 when used to mount catalytic monolith 20.
Mats of the non-intumescent insert material are generally co,--plessed and held in the compressed state to f~rilit~t~ handling of the material during assembly of catalytic converter 10. Inserts 28 may be physically compressed in a variety of manners, including the use of resin bonding, stitch bonding, or needle punching, or vacuum packing.
Resin binding is accomplished by saturating the non-intumescent material with organic binders which burn off in the presences of hot exhaust gas and allow the material of insert 28 to expand during use. Because of the low density and bulky nature of shot-free ceramic fibers and the fact that they must normally becompressed by a factor of about 10 to get the- desired mount density, it has also been 20 found useful to sew or stitchbond these materials with organic thread to form a compressed mat that is closer to its ultimate thickness in use. It is sometimes useful to add a very thin sheet material as a backing layer to both sides of the fiber mats to prevent the stitches from cutting or being pulled through the fiber mat. The spacing of the stitches is usually from 3 to 30 millimeters so that the fibers are ul~ ally25 compressed throughout the entire area ofthe mat. The organic materials burn offwhen exposed to hot exhaust gas, and allow the compressed mat to expand.
The shot-free ceramic fiber may also be compresses by needle-pllnrhing Ceramic fibers by themselves are relatively brittle and not flexible enough to be effectively needle-punched. In order to effectively needle-punch a ceramic fiber mat, the 30 mat is first overlaid with long flexible polymeric fibers, such as polypropylene fibers or polyester fibers, that are typically about 5-10 cm long. A polymeric scrim, such as a nylon fabric or nonwoven, is placed under the mat. The mat is compressed between an upper and lower platen having numerous holes in the platen. A needle bored having many small barbed needles pushes the needles through the holes. As the needles 35 penetrate the ceramic fiber mat, the barbs pull the polymeric fibers on top of the mat through the scrim, and the polymeric fibers become entangled with the scrim to CA 022~7260 1998-12-02 WO 97/48889 PCTrUS97107251 physically restrain the mat. The organic fibers and scrim will burn off when exposed to the elevated temperatures of use, and allow the ceramic fibers to expand.
The fiber mats can also be restrained by placing the fiber mat into an air-tight bag, ev~c~ting the air from the bag, and sealing the bag. Atmospheric pressure s le~Ll~ins the mat in a compressed state until the bag is punctured or burned offwhen the pollution control device is heated to the temperature of use (over 300~C).
The non-intl-mesc~nt inserts 28 provide two important functions.
Inserts 28 have superior erosion resict~n~e when compared to the in~ occPnt mat 26.
By positioning inserts 28 along lateral edges of the jntllm~.cc~nt material which are 10 otherwise exposed to hot exhaust gases, inserts 28 serve to insulate intl.n~esc~ mat 26 from the exhaust gas and thereby prevent erosion of intumescent mat 26. Although use of edge protection material is known, the prior art does not include an edge protection system which can expand and compress to accommodate the ~h~nging width of gap between monolith 20 and casing 12 under extreme t~ )e-~lure conditions or if deformation of the casing occurs. Prior edge protection merh~ni~m~ include use of a stainless steel wire screen wrapped around the edges of the intllmesc.-ont mat as described in U.S. Patent No. 5,008,086 (Merry), and braided or rope like cerarnic (that is, glass, crystalline ceramic, or glass ceramic) fiber braiding or metal wire as described in U.S. Patent No. 4,156,333 (Close et al.). Edge protection can also be formed from compositions having glass particles as described in EP 639701A1 (Howorth et al.), EP
639702A1 (Howorth et al.), and EP 639700Al (Stroom et al.).
Inserts 28 also act as a seal between monolith 20 and casing 12. The flexible and resilient nature of the plere-l~d non-intumescent materials used for inserts 28 ensure that as the pollution control device is cycled between high and low ~s temperatures, the gap between monolith 20 and casing 12 is continuously sealed, and exhaust gas is prevented from bypassing the monolith. In this manner, the efficiency of the pollution control device is ~--ai--lai--ed, and erosion of intl-mescent mat 26 by exhaust gas blow-by is also avoided.
Objects and advantages of this invention are further illustrated by the 30 following examples, but the particular materials and amounts thereof should not be construed to unduly limit this invention. All parts and percentages are by weight unless stated otherwise.
Example 1 A layer of intumescent mat material (INTERAMTM Type 100 Mat, 3100 35 gsm (grams per square meter) available-from Minnesota Mining & m~mlf~ctllring Co.) measuring 6.2 cm by 30 cm was cut as shown in Figure 5A. Strips of a resin bonded _ . .

CA 022~7260 1998-12-02 W 097/48889 PCTrUS97/07251 ceramic fiber mat (1200 gsm SA~FILTM chemically bonded mat available from ICI
Chemicals & Polymers Ltd.) were cut to dimensions of 1.27 cm by 9 cm and placed in the gaps cut in the intumescent mat. The fiber mat strips were held in place with a plastic pack~ging tape to form a hybrid mounting mat. The hybrid mounting mat was wrapped around an oval ceramic monolith measuring 170 mm by 80 mm by 76 mm long (available from Corning). A second monolith was wrapped in the same manner with a hybrid mounting mat identical to that described above. The wrapped monoliths were mounted into a dual cavity stainless steel catalytic converter housing. The mount density of the mounting mats was determined to be 0.7 glcc (grams per cubic centimetçr) for the intllmPccent mat, and 0.27 g/cc for the fiber strips. The catalytic converter containing the hybrid mounting mats was then attached to a gasoline engine (Ford Motor Co. 7.5 liter displacement V-8 powered gasoline powered internal combustion engine) at 3000 rpml220 ft Ib. The catalytic converter was subjected to an inlet gas temperature of 900~C for a duration of l O0 hours.
After testing, the catalytic converter assembly was ~1i.c~c~.o"~hled and inspected. No erosion was observed on the mounting material of the hybrid mounting mat. Additionally, there was no discoloration along the wide portion of the housing over the fiber mat strips. The presence of discoloration is indicative of hot exhaust gases passing between the mounting mat and the metal housing. The absence of any discoloration indic~tçs the assembly was sealed sufficiently to prevent exhaust gases from flowing through the hybrid mat mounting material.
Example 2 The mounting mats tested in this example were p- ~pa-ed and tested as in Example 1, except that a commercially acceptable intumescent mat material was used in 2' place of the hybrid mounting mat used in Example l. A~er testing, inspection of the mounting mat revealed that the mounting mat material had been eroded by the engine exhaust gas. The maximum erosion distance, that is, the portion of the mounting mat that had eroded away7 extended 23 mm into the edge of the mounting mat. A significant amount of discoloration was also noted on the housing.
A comparison of the performance of the mounting mats tested show significant improvements in the performance of the hybrid mounting mat of Example I
over the performance of the non-hybrid mounting mat of Example 2. The hybrid mounting mat resisted erosion when exposed to exhaust gases, and provided a better seal between the monolith and the housing (as evidenced by the absence of discoloration 3~ of the housing in Example 1). Clearly, the performance of the hybrid mounting mat (Example 1) is superior to the performance of a mounting mat which does not utilize the W 097/48889 PCTrUS97/07251 fiber mat inserts (Example 2).
Although the present invention has been described with reference to preferred embodim~nt~, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A pollution control device comprising:
a metal housing;
a solid pollution control element disposed within the metal housing; and a mounting mat disposed between the pollution control element and the metal housing for positioning the pollution control element and for absorbing mechanical and thermal shock, the mounting mat including a layer of intumescent material having at least one insert formed of a resilient, flexible, fibrous non-intumescent material.

2. The pollution control device of claim 1, wherein the insert is positioned along at least a portion of at least one lateral edge of the mounting mat.

3. The pollution control device of claim 1, wherein the intumescent material is a sheet material.

4. The pollution control device of claim 1, wherein the intumescent material is a paste.

5. The pollution control device of claim 1, wherein the non-intumescent resilient inserts are formed of essentially shot-free ceramic fibers.

6. The pollution control device of claim 1, wherein the pollution control element is a ceramic monolithic body.

7. The pollution control device of claim 1, wherein the pollution control element is a metallic monolithic body.

8. The pollution control device of claim 5, wherein the essentially shot-free ceramic fiber insert is physically compressed.

9 The pollution control device of claim 8, wherein the essentially shot-free ceramic fiber insert is resin bonded.

10. The pollution control device of claim 8, wherein the essentially shot-free ceramic fiber insert is stitch-bonded.

11. The pollution control device of claim 8, wherein the essentially shot-free ceramic fiber insert is needle-punched.

12. The pollution control device of claim 5, wherein the essentially shot-free ceramic fiber comprises alumina-boria-silica fibers, alumina-silica fibers, alumina-phosphorous pentoxide fibers, zirconia-silica fibers, alumina and, zirconia-alumina fibers.

13. The pollution control device of claim 5, wherein the essentially shot-free ceramic fiber is derived from a sol-gel process.

14. The pollution control device of claim 2, wherein the non-intumescent insert is secured to the lateral edge of the mounting mat using adhesive tape.

15. The pollution control device of claim 2, wherein the non-intumescent insert extends long the entire lateral edge of the mounting mat.

16. The pollution control device of claim 1, wherein the non-intumescent insert expands to fill a gap between the metal housing and the pollution control element.

17. The pollution control device of claim 1, wherein the resiliency of the non-intumescent insert is greater then the resiliency of the mounting mat.

18. The pollution control device of claim 2, wherein the non-intumescent insert is resin bonded in a compressed state prior to exposure to hot exhaust gases, and wherein exposure to hot exhaust gases burns off the binder to allow expansion of the resilient material.

19. A mounting mat for securing a solid pollution control element within a housing of a pollution control device, the mounting mat comprising:
a layer of intumescent sheet material; and at least one insert formed of a resilient, flexible, fibrous non-intumescent material.

20. The mounting mat of claim 19, wherein the insert is positioned along at least a portion of at least one lateral edge of the mounting mat.

21. A mounting mat for securing a first and second pollution control element within a housing of a power control device, the mounting mat comprising:a first longitudinal strip of intumescent material;
a second longitudinal strip of intumescent material;
a metal band secured along lateral edges of the first and second strips of intumescent material the metal band separating the intumescent strips; and an insert formed of a resilient, flexible, fibrous non-intumescent material, the insert positioned adjacent the metal band and at least a portion of the lateral edges of the first and second intumescent strip.