JP4607885B2 - Mounting mat for catalytic converter - Google Patents

Abstract

The present invention provides a mounting mat for mounting a pollution control monolith in a pollution control device. The mounting mat has a bulk density of 0.12 to 0.3 g/cm<3> and comprises (i) a layer of chopped magnesium aluminium silicate glass fibers and (ii) a layer of ceramic fibers obtainable from a sol-gel process. Preferably, the layer of chopped magnesium aluminium silicate glass fibers and the layer of ceramic fibers define opposite major surfaces of the mat. The present invention further provides a pollution control device comprising a pollution control monolith arranged in a metallic casing with the mounting mat disposed between the metallic casing and pollution control monolith. <IMAGE>

Description

  The present invention relates to a mounting mat for mounting a pollution prevention monolith on a pollution prevention apparatus. The present invention particularly relates to a mounting mat comprising a glass fiber layer and a ceramic fiber layer obtained from a sol-gel process. The invention further relates to a pollution control device.

  Pollution prevention devices are commonly used in motor vehicles to prevent air pollution. Two types of devices are currently widely used: catalytic converters and diesel particulate filters or traps. Catalytic converters contain a catalyst and are typically coated on a monolithic structure mounted within a metal housing. Metal monoliths are also used, but the monolithic structure is generally ceramic. The catalyst oxidizes carbon monoxide and hydrocarbons and reduces nitrogen oxides in automobile exhaust to prevent air pollution.

  Diesel particulate filters or traps are wall flow filters with a honeycomb monolithic structure that are typically made from porous crystalline ceramic materials. The alternating cells of the honeycomb structure are generally plugged so that the exhaust gas enters one cell and is pushed through the porous wall to the adjacent cell to exit the structure. In this way, small soot particles present in the diesel exhaust gas are collected.

  Monoliths used in pollution control devices, particularly ceramic pollution prevention monoliths, are brittle and are susceptible to damage and breakage due to vibration and impact. Its coefficient of thermal expansion is usually much smaller than the metal housing in which it is contained. That is, as the pollution control device is heated, the space between the inner peripheral wall of the housing and the outer wall of the monolith increases. Even if the temperature change of the metal casing is small due to the insulating effect of the mat, the thermal expansion coefficient of the metal casing is large, so that it expands to a large peripheral size faster than the expansion of the monolithic element. Such thermal cycling occurs hundreds of times during the life and use of the pollution control device.

  To prevent damage to the ceramic monolith due to road impact and vibration, compensate for thermal expansion differences, and prevent exhaust gas from flowing between the monolith and the metal housing (bypassing the catalyst), the mounting mat is made of ceramic monolith and metal Arranged between housings. These mats must provide enough pressure to hold the monolith in place over the desired temperature range, but not so great as to damage the ceramic monolith.

  Recently, the number of cells making a pollution control monolith per unit area has increased and the cell wall thickness has tended to decrease. Such antifouling monoliths are known as thin-walled or ultra-thin-walled monoliths and generally contain 400-1200 cells per square inch (cpsi) and a wall thickness of 5 mils, i.e. 0.005. Inch (0.127 mm) or less. As the wall thickness is reduced, these monoliths are more susceptible to damage, which makes the requirements of the mounting mat for mounting such monoliths more stringent.

  Many mounting mats have been described in the art. Known mounting mats include ceramic fiber, intumescent material, and inflatable sheet material composed of organic and / or inorganic binders. Inflatable sheet materials useful for mounting catalytic converters in a housing are described, for example, in U.S. Pat. Nos. 3,916,057 (Hatch et al.) And 4,305,992 ( Langer et al.), 5,151,253 (Merry et al.), 5,250,269 (Langer) and 5,736,109. It is described in the description (Howorth et al.). The inflatable mounting mat has the disadvantage that excessive pressure is applied to the pollution control monolith during use when it is heated. As a result, inflatable mounting mats are not well suited for mounting thin and ultra thin monoliths.

  US Pat. No. 5,290,522 describes a catalytic converter having a non-woven mounting mat comprising at least 60% by weight of shot-free high strength magnesium aluminosilicate glass fibers having a diameter greater than 5 micrometers. Yes. However, such mounting mats do not have sufficient holding strength to fully mount thin and ultra thin monoliths at high temperatures and protect them from impact and damage.

  US Pat. No. 5,380,580 discloses physically entangled shot-free oxide ceramic fibers. The mats are taught to be useful as filter media, mounting mats and sound or thermal insulation. One example discloses a nonwoven mat comprising a polycrystalline ceramic fiber layer and a glass fiber layer. This mat clearly means heat insulation, and is not suitable as a mounting mat for mounting a pollution prevention monolith on a pollution prevention device. There is no teaching on how to use such a two-layer mat as a mounting mat.

  Non-intumescent mats comprising polycrystalline ceramic fibers and binders have been proposed for mounting so-called ultra-thin monoliths. Non-inflatable mats include, for example, U.S. Pat. Nos. 4,011,651 (Bradbury et al.), 4,929,429 (Merry), 5,028. , 397 (Merry), 5,996,228 (Shoji et al.) And 5,580,532 (Robinson et al.). Are illustrated. Polycrystalline fibers are typically formed, for example, by the sol-gel process described in US Pat. No. 3,760,049, and other ceramic fibers are generally melt formed. Unfortunately, polycrystalline fibers are much more expensive than melt-formed ceramic fibers, such as ceramic glass fibers, and as a result, polycrystalline fiber mounting mats are unrealistically expensive.

  Accordingly, it is desirable to find a mounting mat suitable for mounting a pollution control monolith in a pollution control device, particularly a mounting mat that can be used to mount a thin or ultra thin monolith. Such mounting mats preferably provide good holding power of the monolith, particularly at high temperatures, without applying excessive pressure that would damage the monolith. It is preferable that the mounting mat can be manufactured at a low cost and is environmentally friendly.

The present invention provides a mounting mat for mounting a pollution control element on a pollution control device. The bulk density of the mounting mat is 0.12 to 0.3 g / cm ³ ,
(I) a layer of magnesium aluminum silicate glass fiber;
(Ii) a layer of polycrystalline ceramic fibers.
Preferably, the magnesium aluminum silicate glass fiber layer and the ceramic fiber layer define opposing major surfaces of the mat.

The present invention further provides a pollution control device that includes a pollution control element disposed within the case using a mounting mat disposed between the case and the pollution control element . Mounting mat is
(I) a layer of magnesium aluminum silicate glass fiber;
(Ii) a layer of polycrystalline ceramic fibers.

  The mounting mat is arranged so that the ceramic fiber layer faces the pollution control monolith. The term “facing” includes embodiments in which there is no layer between the monolith and the ceramic fiber layer of the mat, and embodiments in which one or more additional layers are present. Such optional layers may or may not be part of the mounting mat, but when present are preferably not part of the mounting mat and are intended to reduce skin irritation caused by the fibers, for example A coating, scrim or film may be mentioned. Also, such optional layers must be selected such that the benefits of the present invention are not substantially lost. That is, the performance of a mounting mat with such an optional layer should be at least 90% of the performance of a similar mat without any optional layer.

  It has been found that a mounting mat according to the present invention can be manufactured at a much lower cost than a mounting mat based on a single layer of polycrystalline fibers. Also, when the pollution control monolith is mounted on the pollution control device in such a way that the ceramic fiber layer resulting from the sol-gel process faces the monolith, sufficient holding power is achieved between both low and high temperatures. During a cycle, the pollution control device can be maintained for the life of the pollution control device that occurs, for example, when used in an automobile.

  It is not intended to limit the invention, but to illustrate and better understand the invention.

  Referring to FIG. 1, the pollution control device 10 has a metal case 11 with generally frustoconical inlet and outlet ends 12 and 13, respectively. A pollution prevention monolith 20 is arranged in the case 11. Surrounding the anti-contamination monolith 20 is a mounting mat 30 according to the present invention that firmly but elastically supports the monolithic element 20 within the case 11. The mounting mat 30 holds the pollution prevention monolith 20 in place on the case and seals the gap between the pollution prevention monolith 20 and the case 11 to prevent exhaust gas from bypassing the pollution prevention monolith 20, or Minimize.

  The metal case can be made from materials known in the art including stainless steel.

  Examples of the pollution prevention monolith that can be mounted by the mounting mat of the present invention include a gasoline pollution prevention monolith and a diesel pollution prevention monolith. The pollution control monolith may be a catalytic converter or a particulate filter or trap. Catalytic converters contain a catalyst and are typically coated on a monolithic structure mounted within a metal housing. The catalyst is generally applied to work and be effective at the required temperature. For example, for use with gasoline engines, catalytic converters must be effective at temperatures between 400 ° C. and 950 ° C., but diesel engines typically have lower temperatures, typically 350 ° C. or less. Metal monosys is also used, but the monolithic structure is generally ceramic. The catalyst oxidizes carbon monoxide and hydrocarbons and reduces nitrogen oxides in the exhaust gas to prevent air pollution. In gasoline engines, all three of these pollutants can be reacted simultaneously in a so-called “three-way converter”, but most diesel engines have only one diesel oxidation catalytic converter. Catalytic converters for reducing nitrogen oxides, which are limited in use today only for diesel engines, consist of separate catalytic converters. Contamination prevention monoliths used in gasoline engines include Corning Inc. (Corning, NY) or NGK Insulators, LTD. (Nagoya, Japan). Examples thereof include cordierite, which is commercially available, or metal monoliths, which are commercially available from Emitec (Lohmar, Germany).

  Diesel particulate filters or traps are wall flow filters with a honeycomb monolithic structure that are typically made from porous crystalline ceramic materials. The alternating cells of the honeycomb structure are generally plugged so that the exhaust gas enters one cell and is pushed through the porous wall to the adjacent cell to exit the structure. In this way, small soot particles present in the diesel exhaust gas are collected. Suitable diesel particulate filters made of cordierite are from Corning Inc. (Corning NY) and NGK Insulators, Inc. (Nagoya, Japan, Japan). A diesel particulate filter made of silicon carbide is commercially available from Ibiden Co. Ltd. (Japan), and is described, for example, in JP-A-2002-047070A. .

  Using the mounting mat of the present invention, a so-called thin-walled or ultra-thin wall-preventing monolith can be mounted. In particular, it is possible to mount a pollution-preventing monolith with a mounting mat of 400 to 1200 cpsi and a wall thickness of 0.005 (0.127 mm) or less. Antifouling monoliths implemented by the mounting mat include 4 mil / 400 cpsi and 4 mil / 600 cpsi thin wall monoliths and 3 mil / 600 cpsi, 2 mil / 900 cpsi and 2 mil / 1200 cpsi ultra thin wall monoliths.

  FIG. 2 is a schematic sectional view of a mounting mat according to the present invention. As shown, the mounting mat 30 includes a chopped magnesium aluminum silicate glass fiber layer 31 and a ceramic fiber layer 32 obtained from a sol-gel process. When used to mount a pollution control monolith in a pollution control device, the mounting mat 30 is such that the layer 32 is closest to the pollution control monolith, i.e. faces the pollution control monolith and the layer 31 is the metal housing of the pollution control device. It is arranged to be closest to, i.e., facing the latter. Thus, in FIG. 1, layer 31 defines a surface 33 of mounting mat 30, and layer 32 defines an opposing surface (not shown in FIG. 1) of mounting mat 30. It has been found that the advantage of the present invention cannot be obtained if the layer 32 has the opposite configuration that defines the surface 33 of the mounting mat 30.

  Although FIG. 2 shows a structure of a mounting mat composed of only two layers, a mat including layers can be considered. For example, layers with different fiber compositions may be included between layers 31 and 32 shown in FIG. Also, two or more glass fiber layers can be used, for example, the layers may differ in the chemical composition of the glass fibers that make up the layers and / or the dimensions of the glass fibers that make up the composition. Thus, instead of using a single glass fiber layer 31, two or more glass fiber layers may be used in combination with a ceramic fiber layer 32 formed from a sol-gel process. For example, the mounting mat may include a ceramic fiber layer formed from a sol-gel process, a glass fiber layer made of S2 glass, and a glass fiber layer made of R- or E-glass.

The bulk density of the mounting mat 30, that is, the density before mounting on the pollution control device is usually 0.12 to 0.3 g / cm ³ , preferably 0.12 to 0.25 g / cm ³ . When mounted, the mounting density of the mat is 0.2 to 0.6 g / cm ³ , preferably 0.3 to 0.5 g / cm ^3, that is, the mat is compressed when mounted.

  The mounting mat is generally designed so that once mounted, the ceramic fiber layer resulting from the sol-gel process has a thickness of at least 0.5 mm, preferably at least 0.7 mm. However, depending on the nature and type of the pollution control monolith, thinner ones are also conceivable. Usually, however, the thickness of the ceramic fiber layer should be sufficient to insulate the glass fiber layer.

  The average diameter of the magnesium aluminum silicate glass fiber used for the nonwoven mounting mat is generally at least 5 μm and the length is 0.5 to 15 cm, preferably 1 to 12 cm. The average diameter is preferably at least 7 μm, generally in the range of 7-14 μm. The glass fibers are preferably individualized. To make individual (ie, fibers are separated from each other) fibers, fiber tows or yarns, for example, glass roving cutters (eg, Finn & Fram, Inc., Pacoma, Calif, Calif.) )) Can be chopped using a “model 90 glass roving cutter (MODEL 90 GLASS ROVING CUTTER)” to a desired length (generally in the range of about 0.5 to about 15 cm). The fibers are generally shot free or contain very low amounts of shots, typically less than 1% by weight, based on the total weight of the fiber. Furthermore, the diameter of the fibers is substantially uniform and the amount of fibers with an average diameter within +/− 3 μm is usually at least 70% by weight, preferably at least 80% by weight of the total weight of the magnesium aluminum silicate glass fiber, Most preferably at least 90% by weight.

The magnesium aluminum silicate glass fiber preferably comprises 10-30% by weight aluminum oxide, 52-70% by weight silicon oxide and 1-12% by weight magnesium oxide. The weight percentages of the oxides described above are based on the theoretical amounts of Al ₂ O ₃ , SiO ₂ and MgO. Furthermore, it is believed that the magnesium aluminum silicate glass fiber may contain additional oxides. For example, additional oxides that may be present include sodium or potassium oxide, boron oxide and calcium oxide. Magnesium aluminum silicate glass fibers include about 55% SiO ₂ , 11% Al ₂ O ₃ , 6% B ₂ O ₃ , 18% CaO, 5% MgO and 5% other oxides. E-glass fiber, typically having a composition, S and S-2 glass fiber, typically having a composition of about 65% SiO ₂ , 25% Al ₂ O ₃ and 10% MgO, about 60% SiO Illustrative are R-glass fibers generally having a composition of ₂ , 25% Al ₂ O ₃ , 9% CaO and 6% MgO. E-glass, S-glass and S-2 are available, for example, from Advanced Glassfiber Yarns LLC, and R-glass is available from Saint-Gobain Vetrotex. It is.

  The glass fiber layer of the mat may contain up to 10% by weight of fibers other than magnesium aluminum silicate glass fibers. However, it is preferred that the glass fiber layer consist only of magnesium aluminum silicate glass fibers. If other fibers are included in the glass fiber layer, they are generally amorphous fibers and preferably have an average diameter of at least 5 μm. The glass fiber layer is preferably free or substantially free of fibers having a diameter of 3 μm or less, and more preferably free or substantially free of fibers having a diameter of less than 5 μm. Substantially free means that the amount of such small diameter fibers is 2% or less, preferably 1% or less by weight of the total weight of fibers in the glass fiber layer.

  The ceramic fiber layer includes ceramic fibers obtained by a sol-gel process. The term “sol-gel” process means that the fiber is formed by spinning or extruding a solution or dispersion or generally viscous concentrate of the fiber or its precursor components. The sol-gel process is thus in contrast to the process of melt-formed fibers that form fibers by extruding a melt of fiber components. A suitable sol-gel process is disclosed, for example, in US Pat. No. 3,760,049, in which ceramic fibers are formed by extruding a solution or dispersion of a metal compound through an orifice. Thus, it is taught to form continuous green fibers and to fire them to obtain ceramic fibers. The metal compound is generally a metal compound that can be calcined into a metal oxide. Sol-gel forming fibers are often crystalline or semi-crystalline and are known in the art as polycrystalline fibers.

  Examples of solutions or dispersions of metal compounds that form fibers by sol-gel processes include oxygen-containing compounds such as zirconium diacetate containing colloidal silica as disclosed in US Pat. No. 3,709,706. An aqueous solution of a zirconium compound is exemplified. Further exemplified are two-phase systems comprising an aqueous mixture of water-soluble or dispersible aluminum and boron compounds, such as aqueous basic aluminum acetate, and an aqueous mixture of silica and a colloidal dispersion of water-soluble or dispersible aluminum and boron compounds. Other typical refractory metal oxide fibers that can be produced by the sol-gel process include zirconia, zircon, zirconia-calcia, alumina, magnesium aluminate, aluminum silicate, and the like. Such fibers can further contain various metal oxides such as iron oxide, chromia and cobalt oxide.

  Useful ceramic fibers for the ceramic fiber layer of the mounting mat include polycrystalline oxide ceramic fibers such as mullite, alumina, high alumina aluminosilicate, aluminosilicate, zirconia, titania, chromium oxide and the like. Preferred fibers, which are generally high alumina, crystalline fibers, contain from about 67 to about 98 weight percent aluminum oxide and from about 33 to about 2 weight percent silicon oxide. These fibers are available from 3M Company under the trade designation “NEXTEL 550” and available from Dyson Group PLC (Saffield, UK), SAFFIL®, for example. ), Mitsubishi Chemical Corp. (MAFTEC, Unifrax, Niagara Falls, NY) available from Tokyo, Japan. FIBERMAX® (registered trademark) and ALTRA fibers (Rath GmbH, Germany) It is commercially available.

Suitable polycrystalline oxide ceramic fibers further preferably include oxidation in the range of about 55 to about 75 weight percent aluminum oxide, less than about 45 weight percent to more than 0 weight percent (preferably less than 44 weight percent to more than zero). silicon, and more than 25 weight to 0% by weight less than percent those (preferably of from about 1 to about 5% by weight) was calculated by the boron oxide (each Al ₂ O ₃ of, SiO ₂ and B ₂ O ₃ as a theoretical oxide basis ) Containing aluminoborosilicate. The aluminoborosilicate fiber is preferably at least 50 weight percent crystalline, more preferably at least 75 weight percent, and most preferably about 100% (ie, crystalline fiber). Aluminoborosilicate fibers are commercially available from 3M Company under the trade names “NEXTEL 312” and “NEXTEL 440”, for example.

  Ceramic fibers obtained by the sol-gel process are generally shot free or contain very low amounts, typically less than 1% by weight of shots, based on the total weight of the ceramic fibers. Similarly, the average diameter of ceramic fibers is typically 1-16 micrometers. In a preferred embodiment, the ceramic fibers have an average diameter of 5 μm or more, preferably the ceramic fibers are free or substantially free of fibers less than 3 μm in diameter, more preferably the ceramic fiber layer is free of fibers less than 5 μm in diameter. Or substantially free. Substantially free means that the amount of such small diameter fibers is no more than 2 wt%, preferably no more than 1 wt% of the total weight of fibers in the ceramic fiber layer. Thus, in a particularly preferred embodiment of the invention, the ceramic fiber layer and the glass fiber layer and any further layers are substantially free of fibers with a diameter of less than 3 μm. Ceramic fibers are usually individualized as described above for glass fibers.

  According to the method of making a non-woven mat, chopped individual fibers (preferably about 2.5 to about 5 cm in length) are made from a conventional web forming machine (Rando Machine Corp. Macedon, N., Macedon, NY). Y) from “RANDO WEBBER” and from Danish ScanWeb Co. Denmark to “DAN WEB” and the fiber is supplied to the wire screen or Stretch on a mesh belt (eg, metal or nylon belt). When using a “DAN WEB” type web forming machine, the fibers are preferably individualized using a hammer mill and blower. To facilitate handling of the mat, the mat can be formed on or placed on the scrim. Depending on the length of the fiber, the resulting mat has sufficient handleability to move to a needle punch machine without the need for a support (eg, a scrim).

  Nonwoven mats can also be made using conventional wet molding or textile carding. For wet forming processes, the fiber length is preferably about 0.5 to about 6 cm.

The mounting mat is preferably a needle punched nonwoven mat. The needle-punched non-woven mat refers to a mat in which fibers are physically entangled by, for example, full or partial (preferably complete) penetration of the mat multiple times with a barbed needle. . Nonwoven mats are conventional needle punching devices (eg, from German Foster Needle Company, Inc., Manitowoc, Wis.) With a barbed needle (eg, commercially available from Foster Needle Company, Inc., Manitowoc, Wis.). Needle punching is possible by using a needle puncher marketed under the trade name “Dilo” from Dilo (Germany) to produce a needle-punched non-woven mat. This generally includes compressing the mat and punching and pulling the mat with a barbed needle The optimum number of needle punches per area of the mat will depend on the particular application. , Non-woven When the Tsu preparative needlepunching, is about 5 to about 60 needle punches / cm ^2. Mat is needle punched preferably about 10 to about 20 needle punches / cm ^2.

  Alternatively, mats are conventional (see U.S. Pat. No. 4,181,514, the disclosure of which is incorporated herein by reference for teaching non-woven mat stitch bonding (see Lefkowitz et al.)). In general, the mat is stitchbonded with organic threads, a thin layer of organic or inorganic sheet material is used to prevent or minimize the threads from cutting the mat Can be placed on one or both sides of the mat during stitch bonding, and inorganic threads such as ceramic or metal (eg, stainless steel) can be used if it is desired that the stitch threads not be disassembled during use Yes, the stitch spacing allows the fiber to compress the entire area of the mat evenly. So that, usually, it is 3~30mm.

  The glass fiber layer and the ceramic fiber layer may be formed separately according to the process described above, and the separate needle punched or stitch bonded layers thus obtained are bonded together by needle punching or stitch bonding. May be. Alternatively, a glass fiber layer and a ceramic fiber layer web may be formed and the web may be needle punched or stitch bonded to form a nonwoven mounting mat. Thus, in the latter configuration, the glass fiber layer and the ceramic fiber layer are not separately needle punched or stitch bonded before being bonded together.

  The invention will be further described with reference to the following examples, which are not intended to limit the invention.

Material A used in Examples and Comparative Examples A ceramic fiber mat obtained from a sol-gel process (polycrystalline fiber)
A1 Maftec (registered trademark) MLS-3 needle bond blanket (72% Al ₂ O ₃ , 28% SiO ₂ , no binder, bulk density 0.16 g / cc) manufactured by Mitsubishi Chemical Company
A2 Ibiden® N4 (72% Al ₂ O ₃ , 28% SiO ₂ , no binder, bulk density 0.18 g / cc)
A3 3M1101HT (72% Al ₂ O ₃ , 28% SiO ₂ , no binder, bulk density 0.14 g / cc)
A4 3M1101HT (96% Al ₂ O ₃ , 4% SiO ₂ , no binder, bulk density 0.16 g / cc)
A5 3M Nextel® 312 needle bond mat (62% Al ₂ O ₃ , 24% SiO ₂ , 14% B ₂ O ₃ , no binder, bulk density 0.14 g / cc)

B Glass fiber mat B R glass fiber was made into a non-woven mat as follows. R glass fiber (general composition 60% SiO ₂ , 25% Al ₂ O ₃ , 9% CaO and 6% MgO), chopped to a diameter of about 10 μm and a length of 36 mm Obtained from Saint-Gobain Vetrotex Deutschland GmbH, Herzogenrat / Germany, the fiber was substantially shot-free.

  The glass fiber was opened with a two-zone Laroche opener. The feed rate for the first zone was 2 m / min and the rickerlin roll rate was 2500 rpm. The feed rate for the second zone was 4 m / min and the rickerlin roll rate was 2500 rpm. The output speed was 6.5 m / min.

  Open fiber is supplied to a conventional web forming machine (Rando Machine Corp. Macedon, NY) under the trade name “RANDO WEBBER” and the fiber is made porous. A continuous web was blown onto a metal roll, the continuous web was needle bonded with a conventional needle tacker, the needle speed was 100 cycles / min, and the output speed was 1.1 m / min. The “weight per area” could be adjusted as desired and the bulk density of the material was about 0.12 g / cc.

Test Method-Actual Condition Equipment Test (RCFT)
This test models the actual conditions during general use of a pollution control device with a catalyst-coated monolith or diesel particulate filter and measures the pressure exerted by the mounting material under these modeled conditions of use. Is. The RCFT method is described in detail in "Material Aspects in Automatic Control Devices", edited by Hans Bode, Wiley-VCH 2002, pages 206-208. ing.

  Two independently controlled 50.8 mm x 50.8 mm heated stainless steel platens were heated to different temperatures to simulate the metal housing and monolith temperatures, respectively. At the same time, the space or gap between the platens is increased by a value calculated from the temperature and coefficient of thermal expansion of a particular type of typical pollution control device. The high speed driving state of the pollution control device is simulated by raising the monolith temperature to 900 ° C. and raising the temperature of the metal housing to 530 ° C.

  Three cycles of RCFT were performed on each mounting mat sample. Table 2 summarizes the density of the mat when mounted on the test sample and the bulk density before mounting.

  The pressure generated by the mat is continuously measured by first increasing the temperature of the first and second plates, holding at the peak temperature for 15 minutes and then decreasing. The plate showing the monolith temperature is heated from room temperature to 900 ° C., held for 15 seconds, and returned to room temperature. At the same time, the plate showing the shell temperature is heated from room temperature to 530 ° C., held for 15 seconds, and returned to room temperature. Each of these heating cycles is referred to as a single RCFT cycle. After performing three RCFT cycles, the data in Table 2 was recorded.

  The pressure at the start of the test and at each peak temperature (900 ° C./500° C.) of the first and third cycles was recorded at room temperature.

Example 1
The mounting mat of Example 1 was composed of an A1 mat layer having a bulk density of 0.16 g / cc and disposed on top of a mat B layer having a bulk density of 0.12 g / cc. The bulk density of the combined mat was about 0.14 g / cc. See Table 1 below.

  The actual condition equipment test (RCFT) was performed by the method described in the above test method. The polycrystalline fiber layer side of the mat is facing the hot side of the RCFT test assembly, the R glass fiber layer side of the mat is placed on the cold side of the RCFT test assembly, and the two layer mat is mounted at a density of 0.35 g / The two-layer mat of Example 1 was tested by compressing to cc. As a result, the starting pressure at room temperature was 217 kPa.

  The RCFT results are summarized in Table 2. During the first temperature cycle, the mat exhibited a pressure of 55 kPa at the peak temperature. During the third temperature cycle, the mat exhibited a pressure of 43 kPa at the peak temperature. This pressure is such that the monolith is held in place without crushing.

Comparative Example 1
Comparative Example 1 included a mat having a single layer of needle bonded polycrystalline fibers having a composition of 72% Al ₂ O ₃ and 28% SiO ₂ . The bulk density before the test was about 0.16 g / cc. Before the start of the test, it was compressed to a packaging density of 0.35 g / cc. As a result, the starting pressure at room temperature was 257 kPa. According to the RCFT results, the pressure at the peak temperature of the first cycle was 104 kPa. The pressure at the peak temperature during the third cycle was 88 kPa.

Comparative Example 2
Comparative Example 2 included a mat having a single layer of R glass fiber with a bulk density of about 0.12 g / cc. Before the start of the test, it was compressed to a packaging density of 0.32 g / cc. As a result, the starting pressure at room temperature was 250 kPa. According to the RCFT results, the pressure at the peak temperature of the first cycle was 10 kPa. The pressure at the peak temperature during the third cycle was 0 kPa.

Comparative Example 3
Comparative Example 3 was performed using the mat described in Example 1. Contrary to the configuration of Example 1, the R glass was placed on the hot side of the RCFT and the polycrystalline fiber layer was placed on the cold side of the RCFT in a two layer mat test assembly. The mat was compressed to a mounting density of 0.35 g / cc before starting the test. As a result, the starting pressure at room temperature was 281 kPa.

  According to the RCFT results, the pressure at the peak temperature of the first cycle was 6 kPa. The pressure at the peak temperature during the third cycle was 5 kPa.

Comparative Examples 4-7
Comparative Examples 4-7 were performed using each single layer of polycrystalline fiber described in detail above in "Materials Used in Examples and Comparative Examples".

  The RCFT results are summarized in Table 2.

The perspective view of the catalytic converter of this invention shown in the decomposed | disassembled state is shown. 1 shows a schematic cross-sectional view of a mounting mat according to the present invention.

Claims (8)

The bulk density is 0.12 to 0.3 g / cm ³ ,
(I) a layer of magnesium aluminum silicate glass fiber;
(Ii) a layer of polycrystalline ceramic fibers;
A mounting mat for mounting the pollution control element on the pollution control device. The mounting mat of claim 1, wherein the layer of magnesium aluminum silicate glass fiber and the layer of ceramic fiber define opposing major surfaces of the mat. The mounting mat of claim 1, wherein the layer of magnesium aluminum silicate glass fiber comprises the glass fiber in an amount of at least 90 weight percent based on the weight of the layer. The mounting mat according to any one of claims 1 to 3, wherein the glass fiber and the ceramic fiber have a number average diameter of 5 µm or more and a length of 0.5 to 15 cm. The weight percent of aluminum oxide, silicon dioxide and magnesium oxide is Al ₂ O _Three , SiO ₂ And when calculated on the basis of theoretical criteria of MgO, the aluminum silicate glass fiber comprises aluminum oxide in an amount of 10-30% by weight and 52-70% by weight based on the total weight of the glass fiber. The mounting mat according to claim 1, comprising an amount of silicon dioxide and an amount of magnesium oxide of 1 to 12% by weight. A pollution control device including the pollution control element arranged in the case using the mounting mat according to any one of claims 1 to 5 arranged between the case and the pollution prevention element. The pollution control device according to claim 6, wherein the mounting mat is arranged so that the ceramic fiber layer faces the pollution control element. 8. A pollution control according to claim 6 or 7, wherein the pollution control element is a monolith comprising 400 to 1200 cells per square inch and a cell wall thickness of 0.005 inches (0.127 mm) or less. apparatus.

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