CA1076754A

CA1076754A - Injectible intumescent mounting material

Info

Publication number: CA1076754A
Application number: CA236,125A
Authority: CA
Inventors: William P. Wood
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1974-10-15
Filing date: 1975-09-23
Publication date: 1980-05-06
Also published as: IT1043357B; FR2288070A1; FR2288070B1; GB1522646A; DE2546413A1; JPS5947713B2; JPS5164483A

Abstract

ABSTRACT OF THE DISCLOSURE
An intumescent injectable composition is injected into the spac? between a frangible monolithic component, such as a catalyst support, and a rigid container, such as the casing of a canister. The intumescent composition is dried in place exfoliated by careful heating to form a thermally resistant, resilient mounting for the frangible component which possesses excellent durability to repetitive mechanical shock. The composition is a pugged mixture containing intumescent material, preferably unexfoliated vermiculite, inorganic binder and liquid vehicle and may further incorporate plasticizer, fibers and fillers.

Description

10'7~754 This invention relates to compositions useful forpositioning articles in containers and particularly for positioning catalyst supports in the casings of canisters for use as components of automobile exhaust systems. Even more particularly, this inventlon relates to moldable compositions containing intumescent particles which are expanded in situ to ~ position catalyst supports in the casings of canisters.
; It has become recognized that catalytic devices are needed in the control of pollution by automobile exhaust effluents, (1) for oxidation of carbon monoxide and hydro-carbons, and (2) for reduction of the oxides of nitrogen. Due - to the relatively high temperatures required for these reactions, the catalyst substrate must withstand high temperatures and repeated thermal shock as well as mechanical vibration. Ceramic catalyst supports are the outstanding choice for such sub-strates. Because high surface areas a~e required for hetero-geneous catalysi~, ceramic substrates such as described in C United States~RE 27,747 are desirable.

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10~6'7S4 Ceramic bodies are inherently rather brittle, and have coefficients of thermal expansion differing markedly from the co-efficients of thermal expansion of metals such as are used for casings. Thus, the manner of mounting of the ceramic body used as a catalyst support in the canister is vital to the success of such catalytic devices; impact and vibration contribute mechani-cal shock and thermal cycling contributes thermal shock. Both thermal and mechanical shock may cause considerable attrition of the ceramic catalyst support, and because attrition accelerates when it has once started~ the device is quickly rendered useless.
Furthermore, because engine performance effects vari-ations in the catalytic reactions involved and the composition of the effluent from the engine affecting the life of the cata-lyst, it is desirable to be able to replace the catalyst body without necessarily replacing the metal housing or casing. A
simple and convenient method for mounting catalyst coated sub-strates or supports in casings is considered very desirable.
One object of this invention is to provide a simple method of mounting a catalyst coated substrate in a casing or other container. A further object is to provide a composition for mounting a catalyst coated substrate in a container. Other objects will become evident hereinelsewhere.
In accordance with these and other objects of the in-vention, it has been found that a very desirable method for mounting catalyst supports in containers is by injecting an in-tumescent composition into the space between the support and container and then expanding the intumescent composition in situ.
In particular, an intumescent composition of the invention which is found to be especially useful is a plastic injectable mass containing intumescent flake material~ inorganic binder, and

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liquid vehicle, and optionally also containing plasticizer and/
or fibrous materials and fillers. The intumescent flake material of choice is unexpanded vermiculite. Compositions of the inven-tion are preferably of a putty-like consistency but may be either thicker or thinner as desired.
The intumescent injectable composition of the invention is advantageously utilized as a mounting material, for example, in automobile exhaust catalytic converters. In such a use, a quantity of the putty-like composition is injected into the 10 space between the monolithic ceramic catalyst support and the inner wall of the casing. This space is preferably not too great as expansion of large masses of intumescent material may -crush relatively fragile ceramic pieces. Injection may be by flowing or under pressure as is convenient but pressure is pre-ferred as it assures filling the space. After drying to remove volatile vehicle from the mounting material, the entire canister assembly is carefully heated to expand the intumescent compo-nent of the mounting composition. Other methods of expansion, e.g., chemical methods, will be recognized as equivalents to heating. The expanded composition holds the monolithic ceramic core in place in the canister. The resilience of the composition after expansion serves to compensate for differences in thermal ~ '! "
expansion between the metal casing and the ceramic substrate and to dampen vibration transmitted to the fragile device by mechan~
ical shaking. The thermal stability assures against deterioration during operation at elevated temperatures. Additionally3 the ex-panded mounting provides a gas tight-seal to prevent by-passing of ; the catalyst and thermally insulates the ceramic catalyst carrier from the casing. A further advantage of expanded compositions of the invention is their insulative value which can maintain a 107675~

2an to 35aC. tem~erature dif~erential acro~s a 1 cm. thickness.
The ~ntume~cent mounting mater~al of the invention i~
useful and effective in that it is simple to use and effectively solves the problems assoclated with thermal and mechanical shock inherent in such devices. It is inexpensive and can be used to mount ~rregularly shaped or dimensionally varying catalyst supports. It should be noted that several catalyst ; supports can also be mounted simultaneously if desired. Further-more, it is ~ound to be superior particularly in respect to ease of application, cost and versatility of use to methods heretofore used. An illustration of one previously available method is the metallic ~ire packing of United 5tates Patent 3l6~2,477 which is not only more costly and difficult to apply but additionally is fully gas-permeable and thus is not of assistance in preventing gas leakage.
Unexpanded flakes, usually beneficlated or concentrated, of vermiculite or equivalent materials such as hydrobiotite, I or coarse water-swelling synthetic tetrasilicic fluorine-type ,. ~ pa~t ~ mica (described in United States~,001,5711, are used as the 2Q intumescent component in the injectable intumescent compositions of the invention. From about 30 to about 8Q% by weight of solids of these intumescent components are used. Vermiculite, hydro-biotite or tetrasilicic mica can be incorporated in the composi-tion individually or a combination of two or three materials can be used. Unexpanded vermiculite is generally preferred because of its low cost and ready availability.
Inorganic binders are used in amounts of about 10 to about 50% by weight of solids in preparing the intumescent compositions of the invention.~ Binders include synthetic mica p~t ; 3Q microflakes (United States~3,001,5711, pulped expanded vermiculite .

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ground to fine particle size in aqueoufi suspension, montmoril-lonite (hentonite, hectorite or saponitel, kaolinite (ball clay), or low melting glass. It will be noted that the synthetic mica may serve two purposes.
A sufficient amount of volatile liquid vehicle, pre-ferably water, is used to give a workable consistency to the mass. The exact amount varies with the characteristics of the solid materials used. In general, an amount of liquid vehicle from about 30 to about 70~ based on the weight of dry materials lQ is sufficient to give a composition which is soft enough to be worked and injected but does not contain so much water that drying is difficult. To assist in the formation of such a workable mass, a small amount, O to 10~ based on the total amount of vehicle of water-compatible plasticizer may be required such as glycerine, methylcellulose, corn syrup or molasses. However, many of the clays, which may be used as binders, also assist in plasticization of the mass.
Fibrous materials are incorporated as reinforcing agents in amount of O to about 25~ of the dry weight. These -~
; 2Q include chrysotile or amphibole asbestos, glass fibers of various ; compositions available under various trade names such as linear spun fibers, e.g., Glaswool*, and blown fibers, e.g., Kaowool*, refractory filaments (crystalline alumina whiskers), or metal filaments. Preferably both linear and blown fibers are used in combination. These fibrous materials enhance the integrity of the intumescent mounting material. It may be : .
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*Trade Mark ~' -5-,! ,, ,,j 107~;'754 deslrable to avoid the use of asbestos because of the possible health hazards associated with this material although asbestos fibers are less expensive than other fibers. Use of alass fiber materials or refractory (glassy or crystalline) filaments or whiskers provides useful reinforcement to the final composition.
Fillers, e.g., magnesia, alumina, silica or ground but not pulped, coarse exfoliated intumescent material, are also added in amounts of 0 to about 40% dry weight to modify the characteristics of the final mounting material~ for example, to decrease the expansion forces when the mounting material is intumesced.
The exact procedure of combining components is n0t critical. Generally, the intumescent material, binder, and any plasticizer are thoroughly mixed with sufficient liquid vehicle, e.g., water, to form a putty-like mass. I~hen fibrous material is incorporated into the composition, excess water is normally used to form a slurry and then this slurry is filtered to re-duce the water content to about 15-20% by weight. Under such conditions, the plasticizer is not incorporated initially because it would not be retained. Instead, the filter cake is pugged with water and plasticizer, if desired, to adjust the composition to give an injectable mass of the character of molding clay or putty. The injectable composition is forced into the space be-tween the frangible and rigid components, using for example~ a ~ 25 caulking gun or it may be forced in manually. Careful heating - of the assembly including the intumescent composition first dries : the mass and subsequently (at about 300 to 650C.) expands or intumesces the intumescent material forming a thermally resistant, resilient yet sturdy and durable mounting for the system.

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Characterist;cs, such as bond strength, mounting or expansion force, and resilience are a function of the formulation of the composition and dimensions of the mounting used. The extent and rate of expansion of the intumescent mixture are dependent upon the rate of heating, restraint applied, and the composition. The higher the concentration of intumescent material in the composition, the greater the extent of the ex-pansion in volume percent. Likewise, the higher the rate of heating, and/or the less the restraint, the greater is the volume percent expansion within, of course, certain limits normally up to about 250% by volume. It is important to realize that the force exerted during expansion of the intumescent materia1 may be so great as to crush a ceramic substrate.
Therefore, the size of the space between the ceramic substrate and the casing must be considered in selecting the composition of the intumescent material. Smaller gaps should not be filled with compositions that exhibit very high expansion in volume percent when tested against no restraint.
The durability of the mounting is tested using a "hot-shake" test. The test apparatus consists of a mechanical shaker and a source of hot gases.
IA cylindrical catalyst coated ceramic substrate 11.8 cm. outer diameter and 7.6 cm. long is mounted in a round metal casing 12.4 cm. inside diameter and 8.9 cm. long with steel end ring, 1.6 mm. thick x 9.3 wide having an O.D. slightly less than 12.38 cm. welded into the end of the canister to retain the catalyst support which is centered in the casing resting upon the end ring. The catalyst used may be any conventional catalyst such as platinum, platinum and palladium, or copper, cobalt, chromium or vanadium containing catalysts useful for ~07~ 4 oxidation, reduction or other catalytic reactions of components of off gases, exhaust gases, or reactible gases passed through the support. Intumescent composition of the invention (or to be tested) is placed in the annular space between the inner wall 5 of the casing and the outer surface of the ceramic substrate.
A second end ring is then welded to the opposite end of the canister to securely hold the ceramic substrate and the intu-mescent composition expanded. The metal end rings contact the face of the ceramic substrate, but the inner wall of the casing is not in direct contact with the outer surface of the substrate.
The mechanical shaker is a Model 1200 VMS air piston type vibrator (Cleveland Vibrator Co.) equipped with means to hold the canister in a horizontal (Test A) or vertical (Test B) mode. In Test B, the vibrator is suspended from a rigid frame by four 2.5 cm. x 15 cm. rubber straps. The unit, operated at about 4.22 kg/cm2 air pressure, provides an average acceleration of about 30 g's at 55 Hz with peak acceleration as high as 100 g's. The displacement in the vibrating mode is about three millimeters.
The source of hot gases is essentially a propane-fired blow torch. It is connected to the inlet of the canister by means of flexible metal tubing. The flame is ignited using a gas mixture at standard temperature and pressure of 793 liters per hour propane and 16,400 liters per hour air. After the catalyst substrate is warmed up (about 3 minutes operation), secondary air, 8500 liters/hr. is injected into the exhaust gas stream before entrance to the catalyst substrate to permit oxidation of residual propane in the catalyst zone. The temper-ature as the gases leave the catalyst substrate is measured by a;

10767S~

thermocouple arrangement and varies between 600 and 700 C.
As soon as the temperature is about 600C., the vibrator is started using an air pressure of about 4.22 kg/cm2. A Strobotac, a variable frequency stroboscopic light, available from General ;!
5 Radio Corp., is used to observe relative motion between the can- ~ -ister and core. Time for failure of the mounting is the elapsed ~ -; time from beginning of the vibration until the time that the core is extruded 1.5 mm. out of the exit canister end ring.
The "hot-shake" test ;s used as a convenient extremely severe accelerated test. No data are available which equate hours on the "hot-shake" test equipment to miles of normal test driving. Tests A and B do not necessarily give identical results on identical canisters and the purposes of tests are more for comparison than with the expectation that the results will cor-relate with results in actual practice. Thus, packings of wiregauze are relatively durable because of the springiness of the wire, but they may fail from other effects.
Tests on ceramic honeycombs mounted with expanded injectable intumescent compositions in canisters indicate the mounting is very much more durable than mountings usin~ only the dry intumescent material poured into place and expanded.
Dry vermiculite mountings as described by Slidell, in U.S.
Patent 1,912,544 are found to deteriorate extremely rapidly, sometimes in less than 5 minutes.
Havina described the invention in general terms, it is now more specifically illustrated by the following examples showing the best mode presently contemplated for practicing the invention.

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Exfoliated yermiculite of ayerage a . 8 to 1.2 mm.
diameter (6Q gm.l is added to 200a ml~ water in a large Waring Blendor* and agitated at high speed for a~out 10 minutes to form a smooth dispersion. Glass fibers (5 gm., available as Fiber-glas* from Johns Manville Co. as JM 106* and 15 gm. available as Kaowool*, from Babcock and Wilcox) are added and thoroughly dispersed. Vermiculite ore, that is, unexfoliated vermiculite (18Q gm., availa~le as No. 4 Zonolite* from W.R. Grace and Co.
sieved particle size from about 0.1 to Q.S mm.) bentonite C4Q gm., available as Bentolite* H. from Georgia Kaolin Co.) and 20 ml. 1% solution of Separan NP-lQ* (partially hydrolyzed polyacrylamide used as a flocculant, available from Dow Chemical Company~ are added and thoroughly mixed. The resulting mixture is filtered on a large Buchner funnel through No. 4 filter paper.
The resulting filter cake is redispersed with a sigma blade mixer, i.e., pugged, by adding a 2% aqueous methyl cellulose solution to give a plastic intumescent composition of the invention containing 50% water and 50% solids.
2a The plastic mass is loaded into a conventional caulking gun and injected into the annular space (a~out 3 mm. wide) bet~een a circular cylindrical ceramic honeycomb catalyst support and cylindrical casing having a retaining ring at one end as described a~ove. The gap volume of 89 ml. requires 55 gm.
Cdry weight~ of intumescent composition to fill the annular space.
A metal retaining ring is welded in place at the other end and the assembly is heated to 6Q0C. over a two hour period. The intumescent composition expands and fills the annular space under pressure. The entire assembly is supported in a horizontal position and connected to an exhaust gas simulator using *Trade Mark B -lo-., ~ .

~07~:;'7S4 flexible connections and with vibration directed at right ang1es to gas flow (Test A) as described above. The system fails in 45 minutes.
A similar system is provided for comparison using a dry mixture of 0.1 to 0.5 mm. vermiculite ore as above (60 gm.), 0.8 to 1.2 mm. exfoliated vermiculite (20 gm.) and bentonite (20 gm.) as a packing material in the annular space between the ceramic honeycomb and the canister. A portion of the above mix-ture (58 gm.) is carefully packed in the annular space (89 ml.) and an end ring welded to the casing. The entire assembly is heated to 600C. over a two hour period and then mounted in the exhaust gas simulator as before. Under essentially the same conditions as above, this system fails in two minutes.
Further examples are carried out using proportionsas set forth in the following table according to the above pro-cedure. "Hot-shake" test results of as little as 35 minutes and even less show utility for many purposes particularly where vibration is not excessively severe.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A pugged composition adapted to being packed around an article to be mounted in a container between said article and said container and being expanded therebetween comprising from about 30 to about 80% of intumescent material and from 10 to about 50% of inorganic binder and from 0 to about 40% filler, all on a dry weight percent basis, with liquid vehicle in amount of from about 30% to up to about 70% of the weight of dry materials.

2. The composition of claim 1 comprising on a dry weight basis from 5 to about 25% of fibrous inorganic filler.

3. The composition of claim 1 comprising from 0.5 to 10% by volume of plasticizer based on the total amount of liquid vehicle.

4. The composition according to claim 1 wherein the intumescent material is unexfoliated vermiculite of particle size from about 0.1 to about 2mm.

5. The method for mounting a ceramic catalyst substrate in a container which comprises injecting a pugged composition comprising liquid vehicle and solids comprising on a dry weight basis from about 30 to about 80% intumescent material in particle size of 0.1 to about 2 mm. and from 10 to about 50% of inorganic binder and from 0 to about 40% of filler, said composition being injected in sufficient amount substantially to fill the cavity between said substrate and said container, drying said pugged composition to remove readily volatilized components of said liquid vehicle and thereafter expanding said intumescent material in situ.

6. The method according to claim 5 wherein expansion of the intumescent material is effected by heating to a temperature in the range of about 300°C
to about 650°C.

7. The method according to claim 6 wherein the intumescent material is unexfoliated vermiculite and heating is carried out at 300° to 650°C.

8. A canister comprising catalyst for catalytic reaction of one or more components of gases comprising a casing, catalyst support within said casing and containing said catalyst and an expanded intumescent composition comprising, before expansion, from about 30 to about 80% of intumescent material in particle size of from 0.1 to about 2mm. and from 10 to about 50% of inorganic binder and from 0 to about 40% of filler, said expanded intumescent composition positioning and retaining said catalyst support in said casing and preventing movement of said catalyst support relative to said casing.