Patent Publication Number: US-2009226663-A1

Title: Adhesive bonded attachment assembly for an insulation blanket

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to improvements in and to adhesive attachments of the type designed for bonded affixation to a selected substrate, such as an adhesive stud attachment of the general type disclosed in U.S. Pat. Nos. 4,778,702 and 4,842,912. More specifically, this invention relates to an improved attachment assembly for use in a high temperature environment, particularly such as supporting and retaining an insulation blanket or the like on a substrate such as an aircraft engine nacelle to shield surrounding structures and components from heat generated during engine operation. The improved attachment assembly includes an insulated cap fastener for safeguarding a stud attachment against debonding in response to high temperature exposure. 
     Adhesive bonded attachments are generally known in the art for connecting a selected component such as a threaded stud or bolt onto a selected substrate such as a panel or other frame component in an aerospace or automotive application or the like. Such adhesive attachments typically include a base defining a bonding surface adapted to receive a selected curable bonding agent, whereupon the base is then pressed against the selected substrate for the duration of bonding agent cure time. In preferred attachment designs, a temporary attachment member or fixture is provided for temporary connection to or engagement with the substrate in a manner functioning to urge or draw the base bonding surface firmly against the substrate until the bonding agent is substantially completely cured. As a result, the adhesive bonded attachment is affixed to the substrate with a substantially optimized adhesive attachment force. Exemplary adhesive bonded stud attachments having a fastener element such as a threaded stud or bolt projecting from a radially enlarged base defining the bonding surface are disclosed in U.S. Pat. Nos. 4,778,702; 4,842,912; 4,822,565; and 4,668,546, which are incorporated by reference herein. 
     Such adhesive bonded stud attachments have been used for supporting and retaining an insulation blanket on a substrate enclosing a relatively high temperature compartment, wherein the insulation blanket is designed to heat-shield surrounding structures and components. Specifically, such insulation blankets have been mounted at the inboard side of an aircraft engine nacelle. In a typical installation, the insulation blanket comprises a suitable refractory cloth material carrying multiple grommets defining a corresponding plurality of mounting ports formed in the blanket. A plurality of adhesive bonded stud attachments are affixed onto an inboard side of the nacelle substrate at positions for stud reception into and through the grommet-defined mounting ports in the insulation blanket. Fastener nuts or the like are then secured to the ends of the studs for retaining the insulation blanket thereon at the inboard side of the nacelle substrate. 
     Use of adhesive bonded stud attachments for mounting an insulation blanket onto an aircraft engine nacelle or the like has, in the past, provided effective heat-shielding of adjacent structures and components to safeguard against heat damage during normal engine operation. In this regard, adhesive bonding agents have been available to withstand temperatures associated with thermal transmission along the fastener nuts and studs, and/or metal grommets on the insulation blanket, without significant risk or thermal-induced debonding of the stud attachment from the substrate. However, more recent aircraft engines have been designed to operate at significantly higher temperatures exceeding the thermal capacity of such bonding agents, whereby the adhesive-mounted stud attachment can debond or separate from the nacelle substrate. Such failure of the stud attachment can undesirably expose the substrate and adjoining components to thermal damage. 
     There exists, therefore, a significant need for further improvements in and to adhesive bonded attachment assemblies particularly of the type used in a high temperature environment such as mounting an insulation blanket onto a supporting aircraft engine nacelle substrate or the like, wherein such improved attachment assembly is designed to withstand significantly higher engine operating temperatures without risk of thermal debonding from the substrate. The present invention fulfills these needs and provides further related advantages. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, an improved adhesive bonded attachment assembly is provided for use in a high temperature operating environment, such as supporting and retaining an insulation blanket on a substrate such as aircraft engine nacelle or the like. The attachment assembly includes a stud attachment having an enlarged base defining a mounting surface for adhesive bonded affixation to the substrate, in combination with a fastener element such as a threaded stud extending from the base for at least partial reception into a grommet-lined mounting port formed in the insulation blanket. An insulated cap fastener is secured to the fastener element to retain the insulation blanket on the nacelle substrate in a manner shielding surrounding structures and components from heat generated during engine operation. The insulated cap fastener is sized to physically and thermally overlie the associated grommet for improved heat-shielding of the grommet and the adhesive bonded stud attachment, thereby safeguarding against debonding of the attachment base in response to high temperature exposure. 
     In one preferred form, the improved adhesive attachment assembly comprises the stud attachment such as an elongated threaded stud projecting from an enlarged, generally disk-shaped base which may be constructed in accordance with U.S. Pat. Nos. 4,778,702 and 4,842,912, which are incorporated by reference herein. The attachment base is adapted for adhesive bonded affixation onto the substrate at a selected location. 
     The insulation blanket, which may comprise a suitable refractory cloth or the like, has a plurality of mounting ports formed therein at selected locations by means of a plurality of typically metal grommets. A plurality of the stud attachments are mounted onto the substrate at respective positions for at least partial reception of the threaded studs thereof respectively into the grommet-lined mounting ports in the insulation blanket. 
     Each attachment assembly further includes the insulated cap fastener such as a threaded nut for secure thread-on assembly with the associated threaded stud. Importantly, this insulated cap fastener includes a radially enlarged insulated cap having a size sufficient to project at least slightly beyond a perimeter of the associated grommet, thereby completely overlying and insulating the underlying grommet against direct heat exposure attributable, e.g., to normal engine operation. Thus, the insulated cap fasteners associated with the respective stud attachments each overlie and insulate the associated bond-on base to safeguard against debonding from the substrate. 
     In a preferred form, the insulated cap of each cap fastener has a hollow construction for receiving and supporting a suitable insulation material, such as a refractory cloth material. In one design, the insulated cap is defined by assembled inboard and outboard cap plates each constructed from a material selected for relatively low thermal conductivity, such as a low conductivity stainless steel, or a ceramic material, or the like. In one preferred form, the outboard cap plate may incorporate a drive surface such as a hex recess for receiving a suitable tool used to thread the cap nut onto the associated threaded stud. In an alternative design, the cap fastener may comprise a press-fit sleeve in lieu of a threaded nut for press-on or press-fit connection with an unthreaded stud of the stud attachment, in which case the drive surface on the outboard cap plate may be omitted. In either configuration, the inboard cap plate may include an annular array of apertures formed therein to reduce surface-to-surface physical and thermal contact with the underlying insulation blanket and associated grommet carried thereby. 
     Other features and advantages of the present invention will become apparent from the following more detailed description, taken in connection with the accompanying drawing which illustrate, by way of example, the principals of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate the invention. In such drawings: 
         FIG. 1  is a fragmented perspective view showing multiple adhesive bonded attachment assemblies constructed in accordance with the invention for supporting and retaining an insulation blanket on a substrate such as an aircraft engine nacelle or the like; 
         FIG. 2  is an enlarged and fragmented exploded perspective view showing an exemplary adhesive bonded attachment assembly for supporting the insulation blanket relative to the substrate; 
         FIG. 3  is a further enlarged and exploded sectional view of the bonded attachment assembly including an insulated cap fastener for assembly with a bonded stud attachment; 
         FIG. 4  is an enlarged and fragmented sectional view similar to  FIG. 3 , but showing the bonded attachment assembly components in assembled relation for supporting the insulation blanket on an engine nacelle or the like; 
         FIG. 5  is an enlarged and fragmented sectional view similar to  FIG. 4 , but showing the adhesive bonded attachment assembly in accordance with one alternative preferred form of the invention; 
         FIG. 6  is an enlarged and fragmented exploded perspective view similar to  FIG. 2 , but illustrating the adhesive bonded attachment assembly in accordance with a further alternative preferred form of the invention; and 
         FIG. 7  is an enlarged and fragmented sectional view similar to  FIGS. 4 and 5 , but showing the adhesive bonded attachment assembly of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the exemplary drawings, an improved adhesive bonded attachment assembly referred to generally in  FIG. 1  by the reference numeral  10  is provided for use in a relatively high temperature operating environment, such as for use in supporting and retaining an insulation blanket  12  on a substrate  14  such as an aircraft engine nacelle or the like. Multiple attachment assemblies  10  are provided each including an attachment member such as a stud attachment  15  ( FIGS. 2 and 3 ) having a base  16  designed for secure bond-on attachment to the substrate  14 , and a fastener element  18  such as a stud to fit within as associated mounting port  20  formed in the insulation blanket  12  and lined by a cylindrical grommet  22 . Each attachment assembly  10  further includes an insulated cap fastener  24  assembled with the associated fastener element  18  to support and retain the blanket on the substrate  14 . The insulated cap fastener  24  is constructed to overlie the associated mounting port  20  and grommet  22  to heat-shield the adhesive mounted base  16  against undesired thermal debonding in response to normal and relatively high engine operating temperatures. 
     The substrate  14  comprises a wall or panel separating a relatively high temperature operating environment on one side from adjacent or adjoining equipment and components (not shown) on an opposite side. In this regard, in one typical embodiment, the substrate  14  is formed from a selected lightweight metal or a composite material defining a nacelle for an aircraft engine or the like. The insulation blanket  12  is mounted at an inboard or high temperature side of the nacelle substrate  14  to insulate and thereby safeguard adjacent structures and components against undesirable thermal damage during normal engine operation. In this regard, the insulation blanket  12  conventionally comprises refractory cloth material  26  provided typically in multiple internal layers (as shown best in  FIGS. 2-4 ) with an inboard-side facing  28  formed from a material such as a stainless steel film or the like having a relatively low thermal conductivity. An opposite or outboard-side skin  30  on the insulated blanket  12  comprises a sheet of relatively low thermal conductivity material such as a durable silicone rubber. 
     The insulation blanket  12  includes the multiple mounting ports  20  formed therein at selected spaced-apart locations for pass-through reception of fasteners used to support and retain the blanket  12  at the inboard side of the nacelle substrate  14 . These mounting ports  20  are conventionally lined by the associated or respective grommets  22  each having a generally cylindrical shape. As shown best in  FIG. 3 , each grommet  22  is normally defined by a short radially out-turned rim  32  at an outboard end thereof for locked engagement against the inner periphery of an annular washer  34  seated against the outboard-side blanket skin  30 . In addition, each grommet  22  includes, at the inboard side thereof, a radially outwardly turned flange  36  having a size and shape for locked engagement against the inboard-side blanket facing  28 . Such grommet  22  is typically constructed from a metal material, such as stainless steel or the like. 
     The improved adhesive bonded attachment assembly  10  of the present invention is designed for retaining and supporting the insulated blanket  12  at the inboard side of the nacelle substrate  14 , in a manner preventing significant heat transmission through the blanket mounting ports  20 , or along the metal grommets  22  lining such ports  20 . In addition, the improved attachment assembly  10  prevents significant thermal transmission along the stud-type fastener element  18  to the adhesive bonded base  16 . Accordingly, the improved attachment assembly effectively safeguards the adhesive bonded base  16  against thermal-caused debonding or separation from the substrate  14 , while additionally improving the overall thermal protection provided to adjacent structures and components. 
     More particularly, each stud attachment  15  comprises the base  16  which may be constructed in accordance with U.S. Pat. Nos. 4,778,702 and 4,842,912, which are incorporated by reference herein. The base  16  thus provides an underside mounting surface  38  for receiving a quantity of a selected curable bonding agent  40 . The base  16  is then seated against the substrate  14  at a selected location. In the preferred form, as shown and described in U.S. Pat. Nos. 4,778,702 and 4,842,912, a temporary attachment member or fixture (not shown herein) is provided for temporary connection to or engagement with the substrate  14  in a manner functioning to urge or draw the base bonding surface  38  firmly against the substrate until the bonding agent  40  is substantially completely cured. As a result, the adhesive bonded attachment is affixed to the substrate with a substantially optimized adhesive attachment force. 
     The fastener element  18  as shown in the exemplary drawings comprises an elongated stud having as externally threaded configuration ( FIGS. 2-4 ). This fastener element or stud  18  has a length sufficient to project at least partially into an associated grommet-lined mounting port  20  formed in the insulation blanket  12 . 
     The insulated cap fastener  24  generally comprises a fastener component such as an internally threaded sleeve or nut  42  for thread-on engagement with the stud  18 , preferably with a lock thread design to preclude inadvertent loosening of the nut  42  on the stud  18 , in combination with a radially enlarged insulated cap member  44  having a size and shape for physically and thermally overlying the associated grommet-lined mounting port  20 . In the preferred embodiment as shown ( FIGS. 2-4 ), this insulated cap fastener  24  comprises assembled inboard and outboard-side cap plates  46  and  48  each constructed from a material selected for relatively low thermal conductivity, such as a low conductivity stainless steel, or a ceramic material, or the like, and defining a hollow internal chamber  50  for receiving a quantity of insulation material  52  such as additional refractory cloth material or the like. The inboard-side cap plate  46  is shown to include a central drive surface  54  such as a hex-shaped drive socket recess or the like for receiving a matingly shaped drive tip  56  of a suitable drive tool  58  ( FIG. 2 ) used for rotatably mounting the threaded nut  42  onto the associated threaded stud  18 . In addition, the inboard-side cap plate  46  may include a peripheral rim or bead  60  ( FIG. 3 ) turned over and capturing the periphery of the outboard-side cap plate  48  for retaining the two cap plates  46 ,  48  in assembled relation. 
     The diametric size of the cap member  44  is sufficient to overlie the associated mounting port  20  and the related grommet  22  including the inboard-side grommet flange  36 . The cap member  44  projects radially outwardly at least a short distance beyond the periphery of the grommet flange  36  for physically contacting and pressing against the inboard-side facing  28  of the blanket  12  in the region surrounding or circumscribing the grommet flange  36 . In the preferred form, the outboard-side cap plate  48  of the cap member  44  includes an annular array of apertures  62  formed therein at a position radially beyond the grommet flange  36  to reduce surface-to-surface physical and thermal contact between the outboard-side cap plate  48  and the underlying insulation blanket  12 . Instead, the insulation material  52  carried within the cap chamber  50  includes an outboard-side skin  64  formed from a sheet of relatively low thermal conductivity and preferably elastomer material, such as a durable silicone rubber, for efficient gasket-type thermally sealed engagement with the underlying inboard-side facing  28  of the insulation blanket  12 . 
     With this design, the insulation blanket  12  is supported on the substrate  14  quickly and easily by means of the multiple stud attachments  15  assembled with the corresponding insulated cap fasteners  24 . Each cap fastener  24  overlies and thus heat-shields the associated mounting port  20  and grommet  22 , and also overlies and heat-shields the threaded connection between the nut  42  and the stud  18 . As a result, the mounting port  20  and structures associated therewith are effectively safeguarded against significant heat intrusion or soak-back. The associated adhesive bonded base  16  is thus safeguarded against exposure to extremely high temperatures associated with modern aircraft engines, thereby protecting the base  16  against thermal-induced debonding from the nacelle substrate  14 . Such protection of the bond-on base  16  additionally safeguards the substrate  14  as well as other adjacent or adjoining structures and components against thermal damage. 
       FIG. 5  illustrates the invention in accordance with one alternative preferred form, wherein modified components of the alternative adhesive bonded attachment assembly  110  are identified by common reference numerals increased in value by 100. In this embodiment, a modified stud attachment  115  includes an unthreaded stud  118  adapted for press-on or press-fit assembly with an unthreaded mounting sleeve  142  of a modified insulated cap fastener  124 . 
     More particularly, the stud attachment  115  ( FIG. 5 ) again includes a base  16  defining a mounting surface  38  of relatively broad surface area for bond-on attachment to the inboard side of a nacelle substrate  14  or the like as by means of a suitable bonding agent  40 . The unthreaded stud  118  protrudes from the base  16  at least a short distance into a mounting port  20  formed in an insulation blanket  12 , wherein this mounting port  20  is again lined by a grommet  22 . 
     The modified insulated cap fastener  124  includes the cap member comprising inboard and outboard-side cap plates  146  and  148  defining an internal chamber for receiving and supporting a quantity of the insulation material  152 . The outboard-side cap plate  148  includes the annular array of apertures  62  disposed radially outwardly beyond the periphery of the underlying grommet structure, and the insulation material  152  includes the outboard-side elastomer skin  64  for gasket-like sealed engagement with the inboard-side facing  28  of the blanket  12 . In addition, the outboard-side cap plate  148  defines the hollow sleeve  142  projecting with an internally unthreaded construction sized for press-fit or snap-type fit engagement with the unthreaded stud  118 . In this design, the inboard-side cap plate  146  may omit any socket-type recess but instead includes a button-shaped member  154  for facilitated manual press-on assembly with the bonded stud attachment  115 . 
     A further alternative preferred form of the invention is shown in  FIGS. 6-7 , wherein modified components of the alternative adhesive bonded attachment assembly  210  are identified by common reference numerals increased in value by 200. In this embodiment, the attachment assembly  210  includes a modified cap fastener  224  having a male-type fastener or fastener component  242  such as a threaded stud for thread-in engagement with a female-type attachment member  218  such as a threaded nut ( FIG. 7 ) carried by a nutplate unit  215  mounted onto the substrate  14 . In this regard, the nutplate unit  215  may comprise an adjustable mounting bracket designed for secure bond-on affixation to a standing rib  80  or the like on the substrate  14 . Such nutplate units  215  are shown and described in more detail in U.S. Publication 2005/0284995, which is incorporated by reference herein. 
     More particularly, the nutplate unit  215  includes nested bracket components of generally L-shaped configuration (as shown in one preferred form) defining a pair of clamp jaw plates  82  and  84  forming a base for secure bonded affixation onto the standing rib  80  at opposite sides thereof, as by means of a suitable bonding agent. The nested bracket components further define a pair of slidably overlying mounting plates  86  and  88  cooperatively forming a fastener-receiving port  90 , and supporting the threaded nut  218  in general alignment with said port  90 . 
     The modified cap fastener  224  is constructed generally as previously shown and described herein, but the associated fastener  242  comprises the male-type component such as a threaded stud for reception through one of the grommet-lined mounting ports  20  in the insulation blanket  12 , and for further thread-in coupling with the threaded nut  218  carried by the nutplate unit  215 . This cap fastener  224  again includes inboard and outboard-side cap plates  246  and  248  defining an internal chamber for receiving and supporting a disk-shaped quantity of the insulation material  252 . The outboard-side cap plate  248  includes the annular array of apertures  62  disposed radially outwardly beyond the periphery of the underlying grommet structure, and the insulation material  252  includes the outboard-side elastomer skin  64  for gasket-like sealed engagement with the inboard-side facing  28  of the blanket  12 . In addition, the outboard-side cap plate  248  defines the threaded stud fastener  242 . In this design, the inboard-side cap plate  246  includes the socket-type recess  254  for engaging with a suitable tool  58  ( FIG. 6 ) for rotatably assembling the cap fastener  210  with the nutplate unit  215 . 
     Although various embodiments and alternatives have been described in detail for purposes of illustration, various further modifications may be made without departing from the scope and spirit of the invention. Accordingly, no limitation on the invention is intended by way of the foregoing description and accompanying drawings, except as set forth in the appended claims.