Abstract:
A method for producing an exhaust gas aftertreatment or acoustic device ( 20 ) having a maximum operating temperature T MAX . The method includes the steps of (a) providing a blanket ( 40 ) of silica fiber insulation material having a weight percentage of SiO 2  greater than 65%; (b) calcining the insulating material by heating the blanket ( 40 ) so that all of silica fiber insulation material is raised to a temperature T greater than T MAX  (where T is less than the melting temperature of the silica fibers of the blanket); and (c) securing the blanket ( 40 ) on the device ( 20 ) after the calcining step. The blanket is encapsulated in a covering ( 50 ) prior to the calcining step whereby the blanket is batting in the covering, with the covering between the blanket and the device being a selected one of wire mesh or siliconized fiber glass.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of Ser. No. 13/277,663, filed Oct. 20, 2011, the disclosure of which is hereby incorporated by reference. 
     
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       MICROFICHE/COPYRIGHT REFERENCE 
       [0003]    Not Applicable. 
       FIELD OF THE INVENTION 
       [0004]    This invention relates to exhaust gas aftertreatment and/or acoustic systems and the devices used therein that utilize external insulation blankets. 
       BACKGROUND OF THE INVENTION 
       [0005]    Heat insulating batts and blankets are utilized in exhaust gas systems in order to provide heat insulation for acoustic and aftertreatment devices of the system to control the heat exchange to and from the devices. It is known, for example, to place heat insulating blankets between adjacent wall surfaces of such devices with the material of the heat insulation blanket being compressed to provide a desired installed density for the material to help maintain the heat insulating blanket in its mounted position via frictional forces between the blanket and the adjacent wall surfaces. Such a structure is shown in U.S. Ser. No. 12/696,347, filed Jan. 29, 2010 by Keith Olivier et al., entitled “Method of Producing an Insulated Exhaust Device”, the disclosure of which is hereby incorporated by reference. 
         [0006]    It is also known to provide heat insulation blankets around the exterior of such exhaust gas system devices. However, such blankets have been found to encounter a variety of failure modes, including damage and cracking when removing and replacing insulation, damage due to exposure to vibration, damage due to loose or otherwise inappropriate fit due to thermal set, loss of insulation properties due to loose or otherwise inappropriate fit, and/or loss of insulation material. 
         [0007]    The present invention is directed to overcoming one or more of the problems set forth above. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect of the invention, a method of providing external insulation for an exhaust gas aftertreatment or acoustic device having a maximum operating temperature T MAX  is provided, where the method includes (a) providing a blanket of silica fiber insulation material having a weight percentage of SiO 2  of greater than 65%, (b) calcining the blanket by heating all of the silica fiber insulation material to a temperature T greater than T MAX , wherein T is less than a melting temperature of the silica fibers of the blanket, (c) encapsulating the blanket in a covering before the calcining step whereby the blanket is batting in the covering, and (d) securing the blanket around an outermost surface of the exhaust gas aftertreatment or acoustic device after the calcining step, wherein the covering between the blanket and the exhaust gas aftertreatment or acoustic device is a selected one of wire mesh or high temperature textile. 
         [0009]    In one form of this aspect of the invention, T is at least 1.05×T MAX . 
         [0010]    In another form of this aspect of the invention, the high temperature textile is a selected one of siliconized fiber glass or straight woven glass fiber. 
         [0011]    In yet another form of this aspect of the present invention, during the calcining step the blanket is an uncompressed state. 
         [0012]    In another form of this aspect of the present invention, T MAX  is within the range of 300° C. to 1100° C. 
         [0013]    In still another form, the securing step comprises installing the blanket so that the blanket encircles a core of the device through which the exhaust gas passes. 
         [0014]    In another aspect of the invention, a method of providing external insulation for an exhaust gas aftertreatment or acoustic device having a maximum operating temperature T MAX  is provided, where the method includes (a) providing a blanket of silica fiber insulation material having a weight percentage of SiO 2  of greater than 95%, (b) calcining the blanket by heating all of the silica fiber insulation material to a temperature T greater than T MAX , wherein T is less than a melting temperature of the silica fibers of the blanket, (c) encapsulating the blanket in a covering before the calcining step whereby the blanket is batting in the covering, and (d) securing the blanket around an outermost surface of the exhaust gas aftertreatment or acoustic device after the calcining step, wherein the covering between the blanket and the exhaust gas aftertreatment or acoustic device is a selected one of wire mesh or high temperature textile. 
         [0015]    In one form of this aspect of the invention, T is at least 1.05×T MAX . 
         [0016]    In another form of this aspect of the invention, the high temperature textile is a selected one of siliconized fiber glass or straight woven glass fiber. 
         [0017]    In yet another form of this aspect of the present invention, during the calcining step the blanket is an uncompressed state. 
         [0018]    In another form of this aspect of the present invention, T MAX  is within the range of 300° C. to 1100° C. 
         [0019]    In still another form, the securing step comprises installing the blanket so that the blanket encircles a core of the device through which the exhaust gas passes. 
         [0020]    In still another aspect of the invention, a method of providing external insulation for an exhaust gas aftertreatment or acoustic device having a maximum operating temperature T MAX  is provided, where the method includes (a) providing a blanket of silica fiber insulation material having a weight percentage of SiO 2  of greater than 65%, (b) calcining the blanket in an uncompressed state by heating all of the silica fiber insulation material to a temperature T greater than T MAX , wherein T is less than a melting temperature of the silica fibers of the blanket and is at least 1.05×T MAX  and T MAX  is within a range of 300° C. to 1100° C., (c) encapsulating the blanket in a covering before the calcining step whereby the blanket is batting in the covering, and (d) securing the blanket around an outermost surface of the exhaust gas aftertreatment or acoustic device after the encapsulating step, wherein the covering between the blanket and the exhaust gas aftertreatment or acoustic device is a selected one of wire mesh or high temperature textile. 
         [0021]    In one form of this aspect of the invention, the high temperature textile is a selected one of siliconized fiber glass or straight woven glass fiber. 
         [0022]    In another form, the securing step comprises installing the blanket so that the blanket encircles a core of the device through which the exhaust gas passes. 
         [0023]    Other objects, features, and advantages of the invention will become apparent from a review of the entire specification, including the appended claims and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a section view of an exhaust system component employing the invention; and 
           [0025]      FIG. 2  is a section view of a portion of the external blanket of the present invention encapsulated in a covering. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    The present invention may be used, for example, in an exhaust gas system such as a diesel exhaust gas aftertreatment system to treat the exhaust from a diesel combustion process (e.g., a diesel compression engine). The exhaust will typically contain oxides of nitrogen (NO x ) such as nitric oxide (NO) and nitrogen dioxide (NO 2 ) among others, particulate matter (PM), hydrocarbons, carbon monoxide (CO), and other combustion by-products. The system may include one or more exhaust gas acoustic and/or aftertreatment devices or components. Examples of such devices include catalytic converters, diesel oxidation catalysts, diesel particulate filters, gas particulate filters, lean NO x  traps, selective catalytic reduction monoliths, burners, manifolds, connecting pipes, mufflers, resonators, tail pipes, emission control system enclosure boxes, insulation rings, insulated end cones, insulated end caps, insulated inlet pipes, and insulated outlet pipes, all of any cross-sectional geometry, many of which are known. 
         [0027]    As those skilled in the art will appreciate, some of the foregoing devices may be strictly metallic components with a central core through which the exhaust flows, and other of the devices may include a core in the form of a ceramic monolithic structure and/or a woven metal structure through which the exhaust flows. These devices are conventionally used in motor vehicles (diesel or gasoline), construction equipment, locomotive engine applications (diesel or gasoline), marine engine applications (diesel or gasoline), small internal combustion engines (diesel or gasoline), and stationary power generation (diesel or gasoline). 
         [0028]      FIG. 1  shows one example of such a device for use in a system such as described above, in the form of a catalytic unit  20  such as shown in Olivier et al. U.S. Ser. No. 12/696,347, the disclosure of which was heretofore incorporated by reference. 
         [0029]    The catalytic unit  20  has a catalytic core  22 , a mount mat  24 , a cylindrical inner housing or can  26 , and heat insulating blanket or batt  28 , and a cylindrical outer housing or jacket  30 . 
         [0030]    The core  22  may typically be a ceramic substrate having a monolithic structure with a catalyst coated thereon and will typically have an oval or circular cross section. 
         [0031]    The mounting mat  24  is sandwiched between the core  22  and the can  26  to help protect the core  22  from shock and vibrational forces that can be transmitted from the can  26  to the core  22 . Typically the mounting mat  24  is made of a heat resistant and shock absorbing-type material, such as a mat of glass fibers or rock wool and is compressed between the can and the carrier in order to generate a desired holding force. 
         [0032]    The heat insulating blanket  28  located inside the catalytic unit outer housing  30  may be made of a silica fiber insulation material having a weight percentage of SiO 2  of greater than 65%, and in preferred embodiments greater than 95%, and in highly preferred embodiments greater than 98%. Such material is known and commercially available, with one suitable example being supplied by BGF Industries, Inc. under the trade name SilcoSoft®, and another suitable example being supplied by ASGLAWO technofibre GmbH under the trade name Asglasil®. Such material is typically supplied in rolls, with the individual blankets  28  being die cut to the appropriate length and width for the corresponding device  18  after the material has been taken from the roll. 
         [0033]    In accordance with the present invention, an external blanket  40  is wrapped around the unit outer housing  30  so as to substantially encapsulate the housing  30 . 
         [0034]    In one embodiment, the external blanket  40  may be advantageously made of a silica fiber insulation material having a weight percentage of SiO 2  of greater than 65%, and in preferred embodiments greater than 95%, and in highly preferred embodiments greater than 98%. Such material is known and commercially available, with one suitable example being supplied by BGF Industries, Inc. under the trade name SilcoSoft®, and another suitable example being supplied by ASGLAWO technofibre GmbH under the trade name Asglasil®. Such material is typically supplied in rolls, with the individual blankets  40  being die cut to the appropriate length and width for the corresponding device  20  after the material has been taken from the roll. In one preferred form, the blanket  40  may have an average installed density of 0.18 grams/cubic centimeter to 0.30 grams/cubic centimeter of the silica fiber insulation material of the blanket  40 . 
         [0035]    According to the invention, before the blanket  40  is installed into the device  18 , the blanket  28  is heat treated to achieve calcination of the silica fiber insulation material. In this regard, the blanket  40  is heated so that all of the silica fiber insulation material in the blanket  28  is raised to a temperature T greater than the maximum operating temperature T MAX  of the device  20 . This heat treatment improves the resiliency and erosion resistance of the silica fiber insulation material and also eliminates the potential for a “thermoset” failure mode that can result if the silica fiber material were calcinated in-situ in the device  20  during operation of the system. Preferably, this heat treatment takes place with the blanket  40  in an uncompressed or free state wherein there are no compressive forces being applied to the silica fiber insulation material of the blanket  40 . The temperature T preferably has some margin of safety above the maximum operating temperature T MAX  of the device  18 , with one preferred margin of safety being 1.05×T MAX . 
         [0036]    This heat treatment improves the resiliency and erosion resistance of the silica fiber insulation material and also eliminates the potential for a “thermoset” failure mode that could result if the silica fiber material were to be calcinated in-situ on the device during operation of the system. Preferably, such heat treatment takes place with the external blanket  40  in an uncompressed or free state wherein there are no compressive forces being applied to the silica fiber insulation material of the external blanket  40 . The temperature T preferably has some margin of safety above the maximum operating temperature T MAX  of the device  18 , with one preferred margin of safety being 1.05×T MAX . 
         [0037]    By heat treating the silica fiber heat insulation material to the temperature T greater than T MAX  before the external blanket  40  is installed on the device, the heat treated blanket can maintain suitable frictional engagement with the unit outer housing  30  over the desired life of the device because the silica fiber insulation material of the blanket  40  maintains its resiliency and does not take on a “thermoset” from the max operation temperature T MAX  of the device. 
         [0038]    The heat treatment may advantageously be accomplished using an in-line oven wherein the silica fiber heat insulation material is unrolled from a supply roll of the material and passed fiat through an oven on a conveyor so that the external blanket  40  is planar during the heat treatment to reduce or prevent differential heating of the material of the blanket  40  and variation in thickness of the material in the blanket  40 . After heat treatment, individual blankets  40  can be die cut to the desired length and width before installing on a device. Alternatively, however, a complete supply roll of the silica fiber heat insulation material can be heat treated, with or without rotation of the roll in an oven, whereby individual blankets  40  can be die cut to the desired length and width after heat treatment and before installing on the device. As yet an another alternative, the silica fiber insulation material can be die cut before heat treatment, with the blanket being slightly oversized in length and width to account for shrinkage during heat treatment, and with the die cut blankets then heat treated in an oven while laying flat on a planar surface. 
         [0039]    In accordance with a second embodiment, the external blanket  40  may also advantageously be a high alumina blanket. In one embodiment, the external blanket  40  may be advantageously made of an alumina insulation material having a weight percentage of Al 2 O 3  of greater than 65%, and in preferred embodiments greater than 95%, and in highly preferred embodiments greater than 98%. Such blankets are known and commercially available, with one suitable example being supplied by Sell Ltd. of Cheshire, U.K. under the LDM trade name, and another suitable example being supplied by Mitsubishi under the MLS-2 trade name. In accordance with the present invention, these high alumina blankets  40  are also heat treated to achieve calcination prior to placement on the device  20 . 
         [0040]    The calcined external blanket  40  of either embodiment is advantageously used as batting encapsulated in a covering  50  prior to placement on the device  20 , as illustrated in  FIG. 2 . Calcination of the blanket  40  may be accomplished before encapsulating the blanket  40  in the covering  50 . However, calcination may also be accomplished in the covering  50  where the covering  50  will not be adversely impacted by the temperatures used in the calcinations. When installed on the device  20 , the side of the covering facing the heat side (e.g., the device  20 ) may advantageously be foil, wire mesh or a high temperature textile, such as siliconized fiber glass or straight woven glass fiber. 
         [0041]    It should be appreciated that devices in exhaust gas systems having external blankets according to the present invention substantially reduce damage and cracking when removing and replacing insulation, damage due to exposure to vibration, damage due to loose or otherwise inappropriate fit due to thermal set, and/or loss of insulation properties due to loose or otherwise inappropriate fit, and/or loss of insulation material. 
         [0042]    It should also be appreciated that while the invention has been described herein in connection with a diesel combustion process in the form of, for example, a diesel compression engine, the invention may find use in devices that are utilized in exhaust gas systems for other types of combustion processes, including other types of internal combustion engines, including, for example, internal combustion engines that use gasoline or other alternative fuels.