Abstract:
A preformed insulation mat is provided for use between the inner and outer end cone housing of a pollution control device. The preformed insulation includes a frustum-shaped mat. The mat is formed of primarily heat moldable, silica based glass fibers containing Al 2 O 3  and is molded at a selected temperature and for a selected time duration to heat set the fibers, whereby the frustum-shaped mat is seamless and self-supporting, requiring no shape no shape retaining elements or chemical binders.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to insulating materials for high temperature applications, and, more particularly, to a preformed frustum-shaped insulation for use in a pollution control device such as a catalytic converter. 
     BACKGROUND OF THE INVENTION 
     Pollution control devices such as catalytic converters and other exhaust gas devices are well known and conventionally used to filter and/or purify the exhaust gases produced by internal combustion engines. Because these devices are subjected to relatively high temperatures during operation, it is necessary that they be sufficiently insulated to limit heat dissipation and/or damage to nearby components. 
     The most common of these devices include a filtration housing having inlet and outlet connections, with the inlet and outlet connections typically being formed as frusto-conical-shaped assemblies that are double-walled and have an insulating material, in mat form, installed between the two walls. The insulating material must be formed of a material that can withstand the anticipated high operating temperatures and repeated thermal cycles of heatup and cool down without physically or chemically degrading. 
     Heretofore, the insulating materials used in these pollution control devices have been produced in several ways: (1) they have been formed into insulating mats from slurries of inorganic materials; (2) flat sheets of high temperature resistant insulating material have been die cut to approximate shapes and crudely stuffed into double-walled inlet and outlet assemblies, or (3) flat sheets of materials have been cut and preformed into a desired freestanding shape. In the latter case, retaining elements such as tapes or films are necessary to maintain the preformed shape of the insulation prior to installation. Alternatively, chemical binders such as adhesive mixtures are added to the sheet material so that the insulation will retain a freestanding, preformed shape after an appropriate heat or curing treatment. Each of these prior techniques, however, suffer from one or more of the difficulties of handling and forming, poor fit and/or buckling of the insulation when installed, and/or high materials costs where retaining elements, binders, and the like must be employed during the manufacturing process. Also, organic binders degrade or heat up creating outgassing and concerns for health and safety. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is directed to an easily preformed, and more economically manufactured frustum-shaped insulation for use between the inner and outer end cone housing of a pollution control device, such as a catalytic converter. As such, the insulation is formed from a relatively flat mat containing, primarily heat moldable, silica based glass fibers containing a minor amount of Al 2 O 3  (0.1-20%). Surprisingly, these silica based fibers have been found suitable for direct molding, because under certain time and temperature conditions, they can be shaped and molded into freestanding insulation cones, without requiring any additional processing steps such as binding, coating, taping, sealing, seaming, etc. Rather, no additional materials, retainers, or structural features are necessary to form the high temperature resistant frustum-shaped insulation of the present invention. 
     More particularly, in one embodiment the mat is initially formed with a substantially centrally formed opening that is dimensioned to fit around the diameter of the inlet or outlet openings of the pollution control device. The mat of glass fibers is subsequently permanently molded at a selected temperature and for a selected time duration to heat set the fibers of the mat into a substantially frustum-shaped insulation mat. 
     Another aspect of the present invention is directed to an exhaust emission control device. In one embodiment, the device includes a housing having an inlet end cone assembly and an outlet end cone assembly. Each end cone assembly has an inner cone housing and an outer cone housing. A preformed insulating cone as described above is installed between the inner and outer cone housing of each end cone assembly to provide a better fitting insulation mat. 
     Yet another aspect of the present invention is directed to a method for forming the preformed insulation that is described above. According to one exemplary process, this includes a first step of forming a relatively flat fibrous mat of the silica based fibers described above, placing the mat into a substantially frustum-shaped mold, the mold comprising inner and outer cone-shaped housing sections. The mat and mold are then subjected to a selected temperature for a selected time duration, as described in greater detail below, that is sufficient to heat set the glass fibers within the non-woven mat. The sandwiched mat is thus permanently molded into a substantially frustum-shaped insulation, yet remains sufficiently flexible so that installation into the inlet and outlet cones of the exhaust emission control device can be easily accomplished. 
     These and other features and aspects of the invention will become more apparent upon review of the detailed description set forth below when taken in conjunction with the accompanying drawing figures, which are briefly described as follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a catalytic converter having inner and outer end cone housings with a preformed insulator installed between the double walls. 
         FIG. 2  is a side perspective view of one embodiment of a frusto-conically shaped preformed insulator formed according to the present invention. 
         FIG. 2A  is a plan view of the embodiment of  FIG. 2 . 
         FIG. 3  is a side perspective view of another exemplary embodiment of the shaped preformed insulator formed according to the present invention. 
         FIG. 3A  is a plan view of the embodiment of  FIG. 3 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Definitions 
     “Cone” refers to any geometric shape whose base is generally rounded and which has a side or surface that tapers upwardly and inwardly. As used herein, “cone” encompasses geometric shapes having either circular, oval, oblong, or elliptical base shapes. 
     “Frustum” refers to a part of a generally conical shape that remains after cutting off a top portion with a plane that is substantially parallel to the base of the solid. As used herein, frustum may be used interchangeably with “frusto-conical” when referring to the frustum of a cone, as defined above. 
     Referring now in more detail to the Figures, and first to  FIG. 1 , a typical (prior art) pollution control device, such as a catalytic converter, is shown generally as  100 . The pollution control device  100  comprises a generally cylindrical housing  120 , or can, having generally frusto-conical inlet  130  and outlet  140  cone assemblies affixed at opposing open ends. The housing, which is typically formed of a metal such as stainless steel, houses a catalytic element  110  for filtering the high temperature gaseous exhausts from an internal combustion engine, for example. To confine the heat of the high temperature gases, an insulating material, such as a mat  114 , is typically wrapped around the cylindrical housing. 
     The inlet  130  and outlet  140  end cone assemblies provide the interconnection between the housing of the catalytic converter and the internal combustion engine on the inlet end and the discharge manifold on the outlet end. Each of the inlet and outlet end cone assemblies  130 ,  140  respectively further comprises inner housing sections  134 ,  144  and outer housing sections  138 ,  148 . Disposed between the inner and outer housings of the cone assemblies  130 ,  140  is one embodiment of the preformed insulation  150  of the present invention. Installed in this manner, the preformed insulation protects other components proximate the catalytic converter  100  against damage or other adverse or harsh environmental effects which could be caused by the relatively high temperatures of the exhaust gases. 
     Turning now to  FIGS. 2 and 2A , one embodiment of the preformed insulation  150  is shown and will be described in detail. As shown, this embodiment of the preformed insulation is a freestanding frusto-conical insulation having a substantially circular open base  152  and a centrally formed circular open top  154 . As those skilled in the art will appreciate, the relative dimensions, including thickness, of the preformed insulation are variable, and thus not important to the invention. Unlike the prior art insulating mats attempted for the same application, the preformed insulation of the present invention has a continuous surface area; i.e., no grooves, slits, or seams. 
     The method of producing the preformed frustum-shaped insulation begins with a non-woven mat of fibrous textile material. It has been found that a non-woven mat suitable for producing the desired preformed insulation may be formed from high temperature-resistant glass fibers having textile-like properties. One such fiber is a heat stable, silica-based fiber containing a minor amount of Al 2 O 3  (0.1-20%). This fiber is described in detail in U.S. Pat. No. 6,468,932 to Richter et al., the content of which is incorporated herein in its entirety. These fibers are characterized as open, highly voluminous, and bulky, as those terms are defined in the textile arts. The inventors have found that staple fibers of material having these characteristics are thus most suitable for forming the primary constituent for a non-woven mat structure. This is due in large part to the resistance of these fibers up to temperatures of about 2000 degrees Fahrenheit, which is within the high temperature ranges (between about 1500 degrees Fahrenheit and 2000 degrees Fahrenheit) for the applications contemplated herein. The inventors have also revealed that another property of a silica-based fiber containing some small quantity of Al 2 O 3  make these fibers particularly suitable for the present applications; i.e., the fibers are sufficiently pliable and moldable when subjected to lower temperatures, making them quite suitable for molding into a preformed shape, yet are heat-stable, meaning that they will not melt at these operating temperatures. Thus, while the fibers are heat-stable and high temperature resistant on one hand, mats of these fibers can be permanently deformed and heat set into a desired shape when subjected to the heat and temperature combinations described below. 
     In one embodiment, the silica-based glass fibers containing some Al 2 O 3  used to form the non-woven mat are preferably, but not necessarily, between about 2.5 inches and 3.5 inches in length and have fibers sizes of between about 3.5 and 24 microns with 6-12 microns being preferred. The inventors have also found that forming a mat having fibers with a moisture content of between about 2 and 20% (6-15% being preferred) of water by weight (remaining at the time of the subsequent molding) facilitates the molding of the fibrous non-woven mat. 
     While other techniques, such as (1) wet-laying and (2) carding and cross-lapping, would be acceptable, in the embodiment being described herein, the fibers are formed into a non-woven mat through air-laying, which is a process whereby fibers are distributed by air currents into a random orientation within the fibrous web/batt. Subsequently, the web is needle punched to a thickness less than about one inch, and typically between about ¼ inch and ⅜ inch for catalytic converter applications. Needle punching is a process wherein hooked needles are systematically punched into the thickness of a web and retracted to entangle the fibers through the thickness of the mat into a coherent, bound structure. 
     While the examples herein are described as comprising 100% silica-based fibers containing some Al 2 O 3 , the inventors have found that a suitable preformed insulation having the necessary high-temperature resistance can be formed from mats having less than 100% percent of these fibers. Rather, mats having at least about 25% of these fibers in combination with other high heat resistant fibers should operate satisfactorily. Ceramic fibers, basalt fibers, and method fibers are just a few examples. Further possible components in low weight proportions (0-3%), such as CaO 2 , TiO 2 , MgO 2 , Fe 2 O 3 , BaO, PbO, Cr 2 O 3 , and F, may be added as described in the Richter et al. U.S. Pat. No. 6,468,932. 
     Once the needle-punched non-woven mat is formed, the mat is ready to be die-cut into a desired flat pattern. In the embodiment of  FIGS. 2 and 2A , the pattern may be substantially circular, having a centrally formed (concentric) opening that is also circular. In the embodiment shown in  FIG. 3 , the pattern may be oval or elliptical, but also has a centrally formed circular or elliptical opening. These patterns are merely examples of an unlimited number of possible shapes. 
     The cut mat pattern is next placed into a mold having sections that are dimensionally similar to the inner and outer housings of the end cone assemblies of the pollution control device  100  described above. As will be appreciated by those skilled in the art, any of a variety of mold shapes and sizes may be utilized to preform an insulation for any particular application. In this embodiment, however, the cut mat is sandwiched between inner and outer mold pieces. The mold may be pre-heated before placing the mat in the mold or heated to the desired temperature after the mat is situated within the mold. In the mold, the mat is pressed to the desired thickness. The following Table I is illustrative of various temperature and dwell time combinations for molding the fibrous mat into a completed self-supporting, preformed insulation mat. The times provided in the table include the time required to pre-heat the mold after placing the mat in the mold. Thus, the actual dwell times at these temperatures would be expected to be somewhat shortened: 
                                     TABLE I                               Result (whether self-                   supporting body is           Temperature   Dwell Time   formed)                           1292° F.     6 minutes   Acceptable           1112° F.    1 minute   Unacceptable           1112° F.     5 minutes   Acceptable           1112° F.    10 minutes   Acceptable           700° F.    3 minutes   Unacceptable           700° F.   15 minutes   Acceptable           700° F.   60 minutes   Acceptable           700° F.   120 minutes    Acceptable           600° F.   60 minutes   Acceptable           500° F.   60 minutes   Acceptable           400° F.   60 minutes   Acceptable                        
As can be seen from this limited data, there are numerous temperature/time combinations that will provide acceptable results. “Acceptable” in the above table indicates that the cone is self-supporting or retains its shape sufficiently to allow handling and insulation. For example, at temperatures as low as about 400 degrees Fahrenheit for a dwell/mold of at least about one hour, an acceptable preformed insulation will be produced. The inventors contemplate that temperatures less than 400 degrees Fahrenheit will also provide acceptable preforms if the dwell time is increased. Likewise, at higher temperatures, such as about 1100 degrees Fahrenheit or greater, the dwell times may be significantly reduced to about 10 minutes or less. Temperatures up to 2000 degrees Fahrenheit could be used to minimize the dwell time.
 
     Having already described one embodiment shown in  FIGS. 2 and 2A , a second exemplary embodiment is shown in  FIGS. 3 and 3A . As shown in these Figures, this preformed insulation is also a freestanding frusto-conical insulation, yet with a substantially elliptical open base  152  and a centrally formed circular open top  154 . Again, numerous other frusto-shapes are possible and within the scope of the present invention. 
     The invention has been described herein in terms of several embodiments and constructions that are considered by the inventors to represent the best mode of carrying out the invention. It will be understood by those skilled in the art that various modifications, variations, changes and additions can be made to the illustrated embodiments without departing from the spirit and scope of the invention. These and other modifications are possible and within the scope of the invention as set forth in the claims.