Abstract:
In order to provide for coupling between the shell and the liner, a passive mounting system is provided. The passive mounting system uses indirect metal contact between the liner or liner panel and the shell. This design serves two main objectives: to minimize heat transfer between the hot gases and ultimately the exterior of the exhaust system; and to provide flexibility and mobility between liner components for changing stress and strain conditions, whether thermally related or otherwise. A passive mounted lining system comprising an outer shell, a liner support channel having a bolt slide void, a partially threaded bolt with a predetermined length of threads, and a series of thermal expansion compatible nuts, bolts, and washers, along with a liner channel support leg is disclosed. A method of mounting a liner system is also disclosed, the method comprising providing an outer shell, mounting on the outer shell a liner support channel having a bolt slide void, providing a partially threaded bolt with a predetermined length of threads in sliding engagement with the bolt slide void, mounting successively on the bolt a series of thermal expansion compatible nuts, bolts, spacers, and washers.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/193,742, filed Mar. 31, 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to liner and shell of thermally insulated walls that are used in the lined exhaust systems used to carry or direct hot air or exhaust gases. 
     BACKGROUND OF THE INVENTION 
     Typically, hot gases are produced as a result of a reaction or thermodynamic process such as those that are produced from combustion engines. One result of a combustion process is hot gases which range from temperatures between 750° F. and 2000° F. As these gases exit the thermodynamic process, they are exhausted into the atmosphere, a duct system and/or chimney or stack depending on the application. These are considered to be types of exhaust systems. Because these systems operate from several hours a day up to 24 hours per day for 20 or more years, it is imperative that the exhaust system components have the durability to withstand the extended and severe operating conditions to which they are subjected. 
     Generally, in industrial and commercial applications, a duct system and/or chimney or stack, depending on the application is accessible to workers. For safety purposes, surface temperature of equipment that is accessible to workers should be limited 140° F. as per ASTM C1055-99, which is recognized as the national consensus standard. This means that if the gases inside the exhaust system are greater than the allowable exterior duct temperature, the duct needs to be either cooled, shielded or insulated. 
     One method of insulating exhaust systems is through the use of a liner. A liner is a barrier that protects insulation applied inside a duct shell. Typically the liner is coupled to the shell while retaining the insulation necessary to reduce the heat transmitted to the exhaust system shell exterior. The liner is directly exposed to the heat from the hot gases being directed by the exhaust system. Since the liner is exposed to extremely high temperatures, thermal expansion often creates unusual problems such as warping and buckling. 
     Typical stresses in an exhaust system include broadband exhaust noise, low-frequency noise, thermal expansion and contraction, changes in operating conditions, rupture and creep stresses, earthquakes and other various environmental, acoustical and mechanical stresses and strains. 
     In order to support or mount a liner or liner panel in the exhaust system, the primary method is active mounting. Active mounting uses direct coupling by through metal contact between the liner and the inside of the shell. However, liners with active mounting may not respond well over time to changing stresses and strains as a result of direct exposure to heat. 
     SUMMARY OF THE INVENTION 
     In order to provide for coupling between the shell and the liner, a passive mounting system is provided. The passive mounting system uses indirect metal contact between the liner or liner panel and the shell. The through-metal contact, or direct contact, is insignificant for this method of mounting. 
     This design serves two main objectives: to minimize heat transfer between the hot gases and ultimately the exterior of the exhaust system; and to provide flexibility and mobility between liner components for changing stress and strain conditions, whether thermally related or otherwise. 
     A passive mounted lining system comprising an outer shell, a liner support channel having a bolt slide void, a partially threaded bolt with a predetermined length of threads, a lock washer with a void disposed thereon, a first washer with a void disposed thereon, a spacer with a void disposed thereon, a first graphite layer with a void disposed thereon, a liner panel having a liner panel void, a second graphite layer with a void disposed thereon, a second washer with a void disposed thereon, a nut with a void disposed thereon, wherein the liner support channel is carried by the outer shell, and wherein the partially threaded bolt is slidably engagable with the bolt slide void, and the bolt carries the lock washer, the first washer, the spacer, the first graphite layer, the liner panel, the second graphite layer, the second washer, and wherein the nut is threadedly engageable with the bolt. 
     One objective of the present invention is for the disclosed method and apparatus to capably withstand seismic loads, such as those possible in seismic zones 3 and 4 as described by ANSI and ASCE design standards. 
     A method of mounting a liner system is also disclosed, the method comprising providing an outer shell, mounting on the outer shell a liner support channel having a bolt slide void, providing a partially threaded bolt with a predetermined length of threads in sliding engagement with the bolt slide void, mounting successively on the bolt a lock washer, a washer, a spacer, a graphite layer, providing a liner panel having a liner panel void, mounting the liner panel on the bolt through the liner panel void, mounting on the bolt a graphite layer, a washer, and a nut. The method further comprises tightening the nut on the partially threaded bolt, while not binding the liner panel. The method further comprises peening exposed threads that extend vertically past the nut to prevent the nut from loosening, or welding one face of the nut to the second washer to accomplish the same objective. It should be noted that the nut, the washer, the liner panel, the graphite layer, the graphite layer, the spacer, the washer and the lock washer are all provided with voids larger in diameter than the bolt. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a typical exhaust stack, showing an outer shell, a liner or liner panels, and a liner panel support leg; 
     FIG. 2 is a side cross-sectional view of a passive mounting system; 
     FIG. 2A is a perspective view of a lock washer; 
     FIG. 3 is an exploded perspective view of a passive mounting system; 
     FIG. 3A is a side perspective view of an alternate plurality of passive mounting system components; 
     FIG. 3B is a side-elevational view of a liner support channel; 
     FIG. 4 is a side view of vertically stacked inside shells showing possible passive mounting system orientations and locations; 
     FIG. 5 is a perspective view with portions broken away, of a passive mounting system. 
    
    
     DETAILED DESCRIPTION 
     Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 
     Referring now to FIG. 1 a cross sectional view of a typical exhaust system, showing an outer shell  22 , a liner panel support leg  24 , and a liner panel  20  or liner panels is shown. 
     For the purposes of describing the three dimensional aspects of the present invention, primary exhaust air flow direction will be in the y-direction, from the source to the atmosphere. In many instances, the y-direction will be vertical in an exhaust stack. The x-direction and the z-direction are each perpendicular to the y-direction, and in many instances will describe a horizontal plane in an exhaust stack. Planes are described as an xy-plane, an xz-plane, and a yz-plane. Mobility of the liner panels is desired in all three planes: the xy-plane, xz-plane, and yz-plane. 
     A passive mounting system, shown in FIG. 2, couples the mobile liner panel  20  with the fixed outer shell  22 . The passive mounting system provides axial and radial mobility, and minimizes heat transfer between the hot gas and the outer shell. 
     Referring now to FIG. 2, a side cross-sectional view of a passive mounting system  10  is shown. The passive mounting system  10  allows the outer shell  22  of an exhaust system to be coupled passively with liner covers  26  (not shown) and a liner panel  20  through the liner panel support leg  24 . Coupled to the outer shell  22  is a liner support channel  46 . A bolt  30  with threads  31 , when tightened with a nut  32 , secures in sequential order as shown: a washer  34 , a layer  36 , the liner panel  20 , a layer  38 , a spacer  40 , a washer  42 , and a lock washer  44 . 
     It is important that the components of the passive mounting system  10  react similarly to changing stress and strain conditions, such as heat. It is also important that the components of the passive mounting system minimize heat transfer along the yz-plane in the x-direction as shown in FIG. 2, or from top to bottom of the components shown in FIG.  2 . For these reasons, components with compatible materials in relation to thermal expansion coefficients are preferable. For example but not by way of limitations, it has been found that suitable materials for the washer  34  and the spacer  40  are UNS S40930, or AISI 409, or AISI 304. 12 gauge material for liner panels  20  have been found to provide sufficient thermal resistance and strength to perform suitably under the stresses and strains common in exhaust system components. More particularly a stabilized ferretic stainless steel such as Allegheny 409HP, UNS S40930, or Armco 409, UNS S40920 may perform suitably. 
     The layers  36  and  38  are preferably comprised of materials that transmit heat laterally, or disperse heat, instead of transmitting the heat. Graphite has been found to perform suitably and advantageously for this purpose for the layer  36  and the layer  38 . The washer  42  has been found to perform suitably when fabricated from ceramic paper, such as G/I-83 available from Gaskets, Inc. The ceramic paper is heat resistant, yet compressible enough to allow the components of the passive mounting system  10  to move slightly in response to changing stress and strain conditions. The lock washer  44  has been found to perform suitably when fabricated from carbon steel in 12 gauge. 
     In order to insulate the space inside the liner support channel  46 , an insulation block  60  is provided. Insulation block  60  is preferably dense enough to partially hold bolt  30  in place and remain within liner support channel  46 , yet soft enough to slightly deform underneath the head of bolt  30 . One material that performs these functions suitably is Fibrex brand FBX 1900 insulation. 
     In order to insulate between successive passive mounts, which in use will be described later, insulation  62  is provided. Insulation  62  is shown in FIG. 2 as three distinct layers, although any different number of layers may perform suitably. Stratification and different orientation of insulation  62  is preferable to accommodate expansion and contraction as the passive mounting system  10  responds to changing stresses and strains. For instance, the insulation  62  may be required to compress and expand 5-10% or more when the passive mounting system  10  responds to rising and lowering temperatures. One insulation material that has suitable heat and compression characteristics is ceramic fiber. 
     This combination of mounting system  10  component materials have been found advantageous to providing mobility, perpendicular to the main gas flow direction, as well as axial mobility. 
     Referring now to FIG. 2A, an alternative, preferred embodiment of a lock washer  44   a  is shown. In this embodiment, overhanging lips  1 ′ and  1 ″ are provided in the x-direction to prevent the bolt  30  from disengaging with the liner support channel  46 . When employed in the plurality of components in the x-direction as shown in FIG. 3, the overhanging lips  1 ′ and  1 ″ advantageously brace against rotation in the y-z plane, minimizing wear on components of the passive mounting system  10 . The lips  1 ′ and  1 ″ are oriented so that one of the lips  1 ′ or  1 ″ covers at least a portion of bolt slide void  50 . The other lip, the lip does not cover at least a portion of bolt slide void  50 , braces against movement in the y-direction by bracing itself against the liner support channel  46 . 
     Referring now to FIG. 3, an exploded perspective view of the passive mounting system  10  is shown, with a plurality of passive mounting system components shown roughly on the y-z planes. The components are preferably assembled in vertical order starting with the bolt  30 , and stacking components vertically as shown. The layers  36  and  38  are provided for lubricity in order to minimize component wear and tear for those components that contact the liner panel support leg  24 . Alternatively, in place of the layers  36  and  38 , during assembly, the washer  34  and spacer  40  may be coated with lubricant to accomplish this objective. 
     Referring now to FIG. 3A, a side perspective view of an alternate plurality of passive mounting system components is shown, with portions of components cut away. In this embodiment, select components of the previously described plurality of passive mounting system components have been omitted as can be seen by comparing FIG. 3 with FIG.  3 A. In this alternate plurality of passive mounting system components, the components are arranged in the following order on the yz-plane in increasing x-direction, about the bolt  30  with threads  31 : the liner support channel  46 , the lock washer  44 , washer  42 , the spacer  40 , the liner panel  20 , the washer  34 , and the nut  32 . This arrangement may be preferable to simplify assembly of the components. 
     As FIGS. 3 and 3A show, the bolt  30  preferably has threads  31  only partially along the length of the bolt  30 . The partial threading prevents the nut  32  from over-tightening during assembly to ensure axial mobility of liner panel  20  when exposed to heat, vibration and other noises common in the exhaust system. In order to prevent loosening of the nut  32  when exposed to the same forces, the threads  31  are preferably mechanically deformed, or peened, after the nut  32  has been tightened during assembly. Alternatively, welding of the nut to the bolt or washer, or any other means for preventing movement of the nut relative to the bolt may be performed. SAE J429, Grade 5 or ASTM A449 are materials that are suitable for construction of the bolt  30 . 
     As FIG. 3 also shows, the liner support channel  46  is provided with a bolt slide void  50  in order that the longer bolt  30  may be engaged with the liner support channel  46  which is shorter than the bolt. Also, as will be described later, the liner panel void  48  provides mobility in the yz-plane. Also as FIG. 3 shows, the surface contact between the liner support channel  46  and the outer shell  22  is preferably minimized by providing small cross-sectional contact between the outer shell  22  and the liner support channel  46 . As also shown on FIG. 3, the liner panel void  48  is shaped larger than voids provided on the washers  34  and  44  and washer  42  and spacer  40 . The larger liner panel void  48  reduces potentially destructive shear forces that could result as the liner panel  20  moves in relation to the outer shell  22  during periods of above ambient heat exposure. 
     The larger liner panel void  48  is provided such that the liner panel  20  can move relative to the liner support channel  46  without shearing the bolt  30 . This larger liner panel void  48  also eases assembly of the components by allowing fabrication in the yz-plane that an otherwise smaller sized void  48  would provide. Panels  20  are thus in free floating relationship. 
     Referring now to FIG. 3B a side-elevational view of a liner support channel  46  is shown, with portions of outer shell  22  broken away. An alternate, preferred bolt slide void  50 A is provided on liner support channel  46 , such that liner support channel  46  is continuously coupled with outer shell along two lines in the yz-plane. Comparing the bolt slide void  50 A shown in FIG. 3B with the bolt slide void  50  shown in FIG. 3, it can be seen that the preferred bolt slide void  50 A shown in FIG. 3B is continuously coupled with the outer shell  22  in the z-direction. It has been found that this design improves structural strength of the liner channel  46 . 
     Referring now to FIG. 4, an inside to outside view of vertically stacked shells  22  showing possible passive mounting system  10  orientations and locations is shown. Viewing FIG. 4, a plurality of passive mounting systems  10  are disposed on a plurality of vertically stacked shells  22 . The passive mounting systems  10  are provided in spaced-apart relationship to accommodate liner covers  26  (shown in FIG. 5) provided between adjacent liner panels  20 . The mounting systems  10  are spaced apart in relation to receive liner panels  20  and liner covers  26 . The geometry of the liner panels and liner covers may vary, thus controlling the specific geometry of the mounting system  10  deployment on the shells  22 . 
     As can be seen from the exploded portion of FIG. 4, it is preferable that the passive mounting systems  10 , and in particular the liner support channels  46  and bolt slide voids  50  be oriented differently between adjacent mounting systems  10 . One pattern of orienting adjacent mounting systems  10  is shown in FIG. 4, where orientations are alternated in a 90 relationship between each two adjacent mounting systems  10 . In one orientation, the liner channel  46 , and particularly the bolt slide void  50  (shown) or bolt slide void  50 A (not shown) is oriented to accept the bolt  30  from the direction of primary exhaust air flow direction in the y-direction. In an adjacent orientation for the mounting system  10 , the liner channel  46 , and particularly the bolt slide void  50  (shown) or bolt slide void  50 A (not shown) is oriented to accept the bolt  30  from roughly 90° of the direction of primary exhaust air flow direction in the y-direction. This is only one preferred pattern of orienting adjacent mounting systems  10 . Any pattern of orienting adjacent mounting systems  10  is acceptable, based on the preference of the fabricator. 
     This arrangement allows axial mobility, yet prevents mobility to the degree that the bolt  30  would become separated from the liner support channel  46 . The 90 relationship is preferable for welders as it allows spacing to be measured accurately from edges of shells  22 . 
     Referring now to FIG. 5, coupled with each liner panel  20  is an attachment mechanism, preferably a z-clip  28  to couple each liner panel  20  with one or more liner covers  26 . In this manner each liner cover is coupled by z-clips to adjacent liner panels  20  and mounting systems  10 . Additionally, it is preferable to couple liner covers  26  to liner panels  20 . Preferably, this coupling is a weld. Suitable welds are stitch welds or fillet welds. One stitch weld that has performed particularly well is a 2 on 10 stitch weld. As FIG. 5 shows, the welds W are preferably positioned on an upstream portion of liner covers  26 , coupled to a downstream portion of liner panels  20 . 
     A method of mounting a liner system is also shown in FIGS. 2-5. The method comprises providing an outer shell  22 , mounting on the outer shell  22  a liner support channel  46  having a bolt slide void  50 , providing a partially threaded bolt  30  with a predetermined length of threads  31  in sliding engagement with the bolt slide void  50 , mounting successively on the bolt  30  a lock washer  44 , a washer  42 , a spacer  40 , a graphite layer  38 , providing a liner panel  20  having a liner panel void  48 , mounting the liner panel  20  on the bolt  30  through the liner panel void  48 , mounting on the bolt  30  a graphite layer  36 , a washer  34 , and a nut  32 . The method further comprises tightening the nut  32  on the partially threaded bolt. The method further comprises peening exposed threads  31  that extend vertically past the nut  32  to prevent the nut  32  from loosening. It should be noted that the nut  32 , the washer  34 , the graphite layer  36 , the graphite layer  38 , the spacer  40 , the washer  42  and the lock washer  44  are all provided with voids larger in diameter than the bolt  30 . 
     The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.