TEMPERATURE RESISTANT FASTENER ARRANGEMENT

Abstract: A fastener (24) secures a thin sheet liner (16) to a supportive substrate (10) for protection against an adjacent high temperature environment (12). Cooling air (20) flows through a plurality of openings (34) and impinges (36) on the fastener (24). The fastener (24) is received within a dimple (32) in the liner (16) and includes an enlarged head portion (38).

Description: The present invention relates to a fastener for securing two members, one of which is exposed to a relatively high temperature environment. One scheme for protecting a structural member such as a substrate disposed adjacent a relatively high temperature environment such as the hot exhaust gas stream of a gas turbine engine flowing within an exhaust nozzle or conduit, is to provide a relatively thin sheet of material disposed between the hot environment and the substrate for forming a thermal shield therebetween. Such sheets may further be protected by supplying a flow of cooling air between the sheet liner and the supporting substrate. The problem of securing the liner to the substrate involves providing a fastener arrangement which is able to itself resist the high temperature environment and is preferentially uncomplicated in design. For gas turbine engine exhaust nozzles having movable flaps disposed adjacent to the high temperature exhaust gases, a protective liner disposed between, for example, the flap substrate and the hot gases must be releasable from within the gas flow path in order to provide for replacement of the liner as well as to allow access to the internal structure of the flap for servicing thereof. As such fasteners must be accessible from the hot gas side, means for protecting any exposed fastener surface or structure must be provided by any successful arrangement in order to avoid burnout or over temperature of the fastener. A protected fastener arrangement adds additional protecting structure which may be expensive and time-consuming to remove in order to release the protected fastener. A heat resistant arrangement of the type according to the precharacterizing portion of independent claim 1 is disclosed in JP-A-59 162323. The known arrangement comprises a heat insulation disposed between a casing and a heat insulating plate exposed to a hot air stream. The insulating plate is secured by a stud to the casing. The stud extends through an enlarged hole in the insulating plate and has two flanges thereon receiving the insulating plate therebetween. A pressure equalizing air passage is formed between the flanges and the insulating plate to provide fluid communication between the volume of the insulation and outer hot side of the insulating plate. Reference is also made to US-A-4 121 768 which discloses a cooling structure for the nose of the centerbody of a two-dimensional nozzle. The nose has a heat shield and a cold sheet having cooling apertures for impingement cooling of the heat shield. The cold sheet is fixed by rivets to the heat shield. Collars surround the rivets and have cooling passages to impinge cooling fluid on the heat shield adjacent the rivets to prevent localized hot spots adjacent thereto. What is needed is a heat resistant fastener arrangement which is easily releasable from the hot gas side and which does not require additional protective structure against the adjacent high temperature environment. Accordingly the object of the present invention is to provide a heat resistant arrangement having a heat resistant fastener for releasably securing a heat protective liner to an underlying substrate for providing a thermal shield between the substrate and an adjacent high temperature environment. According to the present invention, to achieve this, there is provided a heat resistant arrangement comprising a supporting substrate, disposed adjacent a flow of relatively hot gas, a protective sheet liner, disposed between the substrate and the hot gas flow, the liner being substantially uniformly spaced from the substrate and having one side thereof in contact with the hot gas, and a fastener accessible from the hot gas side of the liner, said fastener having a shank portion extending through a hole in the liner and including a first end releasably secured to the substrate and a second end contacting the hot gas flow, characterized in that the liner (16) and substrate (10) define a cooling gas flow channel therebetween and the liner includes a plurality of cooling openings, disposed adjacent the fastener for directing a flow of cooling gas from the cooling gas flow channel between the liner and substrate to impinge against the second end of the fastener and protect the fastener against overheating. The fastener of the arrangement according to the present invention is releasable from the hot gas side of the liner and substrate assembly and is thus itself at least partially exposed to the hot gas environment. Local cooling for the exposed fastener is provided by supplying a flow of impingement cooling air from a supply volume beneath the liner through the plurality of openings disposed in the liner adjacent the exposed fastener. According to one embodiment of the present invention, the individual fasteners are received within corresponding dimples or depressions in the hot gas facing surface of the sheet liner. These dimples also act as standoffs for maintaining a uniform spacing between the liner and substrate, and further include the above-mentioned cooling holes for directing the cooling air against the fastener. The fastener further can include an enlarged head portion, substantially parallel with the hot gas facing sheet surface surrounding the dimple, for defining a toroidal chamber and annular louver vent in cooperation with the surface of the dimple. Cooling air, entering the toroidal volume through the sheet liner cooling holes, impinges against the underside of the fastener head portion and exits via the annular louver, thus cooling the exposed fastener locally without additional protective structure or other cooling means. The fastener itself is of simple, one piece construction and, if threaded at the end opposite the head for cooperably engaging the substrate as in the disclosed embodiment, is easily installed and removed for releasing the protective liner for service, replacement, etc. It is further a feature of an embodiment of the arrangement according to the present invention that the fastener impingement cooling air does not traverse a complicated or tortuous path, rather passing straightforwardly through a plurality of parallel routes into the toroidal volume and venting into the hot gas environment. The simplicity and multiplicity of the gas flow routes reduce the likelihood of the occurrence of a blockage and a resultant interrruption of the fastener cooling air flow, thus resulting in a simple, effective, temperature resistant arrangement for securing the protective sheet liner to the protected substrate. Both these and other features and advantages of the fastener arrangement according to the present invention will be apparent to those skilled in the art upon review of the following specification and drawing figures, wherein: Figure 1 shows a cross section of a liner substrate, and fastener arrangement according to one embodiment of the present invention. Figure 2 shows an alternate embodiment of the arrangement according to the present invention configured for augmented fastener cooling. Figure 1 shows a cross section through the fastener arrangement. A substrate 10 is disposed adjacent a high temperature environment 12 such as the exhaust gas flow stream 14 from a gas turbine engine (not shown), or the like. The substrate 10 is protected from the harsh environment 12 by a relatively thin sheet liner 16 disposed between the hot environment 12 and the substrate 10. The liner 16 is secured in a spaced apart relationship with the supporting substrate 10 by a securing means 18 which extends through the liner 16 and releasably engages the substrate 10. The liner 16 is cooled by a flow of relatively cool gas 20 between the liner 16 and the substrate 10 which may be diverted from the compressor section of the gas turbine engine or any other suitable source. The liner cooling gas or air 20 cools the hot facing surface of the liner 16 by convective heat transfer due to impingement on the opposite underside of the liner 16, and/or by providing a transpiration film over the hot facing liner surface via transpiration openings 22 in the liner 16. The securing means 18 includes a fastener 24 having a first engagement end 26 threadedly secured at 28 to the substrate 10. The fastener 24 includes an enlarged shoulder portion 30 which contacts the liner 16 and secures it against the substrate 10. According to the preferred embodiment of the present invention, the fastener 24 is received within a dimple or depression 32 formed in the sheet liner 16. The dimple is of sufficient diameter to receive the entire fastener 24 therewithin and has a depth such that it additionally functions as a standoff for maintaining the desired spacing between the liner 16 and substrate 10. As is apparent to those skilled in the art, the fastener 24 and the surrounding portion of the liner 16 contacting the substrate 10 is subject to local overheating unless additional local cooling is provided. Such local cooling for the fastener 24 and surrounding liner 16 is achieved by a plurality of cooling openings 34 disposed in the dimple 32 of the liner 16 and oriented so as to discharge a flow of cooling air 36 from beneath the liner 16 against the portion of the fastener 24 extending into the hot environment 12. The impingement cooling air 36 provides the necessary additional local cooling capacity for protecting the fastener 24 against overheating due to contact with the hot gases 14 or due to radiation heat transfer from the hot environment 12. Further protection of the dimpled portion 32 of the liner 16 is provided by an enlarged head 38 located at the other end of the fastener 24. The enlarged head 38 is substantially coplanar with the surrounding liner 16 and forms an annular louver 40 therewith. Impingement cooling air 36 flows from a toroidal volume 42 created by the enlarged head 38, shouldered portion 30 and dimpled liner 32 in the preferred embodiment, thus preventing the entry of the hot gas 14 and maintaining a cooling film over not only the adjacent liner 16 but the coplanar head 38. It will further be appreciated by those skilled in the art that the enlarged, impingement cooled head 38 provides a radiation shield against that portion of the dimpled liner contacting the substrate 10 and hence not cooled by the air 20 flowing between the liner 16 and substrate 10. Figure 2 shows an alternative embodiment wherein the fastener 24 includes a linear, internal flow passage 44 for providing additional cooling at the hot facing surface of the head 38 and to the interior of the fastener 24. Such additional cooling capacity may be required to protect the securing means 18 under extremely severe high temperature conditions and may be added to an existing fastener 24, if required. As will be appreciated by those skilled in the art, the securing arrangement 18 is well suited for releasably securing a sheet liner 16 to an underlying, supporting substrate 10. The fastener 24 is of simple, one piece construction and easily accessed from the hot side of the liner 16. Such access is especially advantageous in an aircraft application, such as in an exhaust nozzle for a gas turbine engine, wherein removal of the sheet liner 16 may be required for replacement thereof, for access to the underlying substrate structure 10, or for other maintenance or assembly needs. The cooling air 36 directed against the fastener 24 is provided from the cool gas flow 20 present beneath the liner 16, thus avoiding any requirement for supplying additional cooling air routes to the liner fasteners. The airflow path 20, 36 is relatively uncomplicated, thus reducing the likelihood of any blockage forming in the openings 34 thereby restricting the flow of cooling air 36 into the toroidal volume 42. Likewise, the provision for a plurality of cooling openings 34 for admitting impingement air 36 into said volume 42 provides a multiplicity of parallel cooling air flow paths for insuring at least a minimal quantity of cooling air. As will further be appreciated by those skilled in the art, any one of a variety of engagement techniques for releasably attaching the fastener 24 to the substrate 10 may be used without departing from the scope of the present invention. In addition to the threaded end 26 as shown in Figures 1 and 2, such attachment may be made by a bayonet type arrangement, a stud affixed to the substrate 10 and cooperatively received within the enlarged shank 30, or by any of a variety of methods and structures well known in the art. It should further be appreciated that, although shown and discussed in terms of a circular dimple and fastener, non-circular depressions 32 and fastener heads 38 received therewithin may equivalently be used.

Claims: Heat resistant arrangement comprising a supporting substrate (10), disposed adjacent a flow of relatively hot gas; a protective sheet liner (16), disposed between the substrate (10) and the hot gas flow, the liner (16) being substantially uniformly spaced from the substrate (10) and having one side thereof in contact with the hot gas; and a fastener (24) accessible from the hot gas side of the liner (16), said fastener (24) having a shank portion extending through a hole in the liner (16) and including a first end releasably secured to the substrate (10) and a second end contacting the hot gas flow; characterized in that the liner (16) and substrate (10) define a cooling gas flow channel therebetween and the liner (16) includes a plurality of cooling openings (34), disposed adjacent the fastener (24) for directing a flow of cooling gas from the cooling gas flow channel between the liner (16) and substrate (10) to impinge against the second end of the fastener (24) and protect the fastener (24) against overheating. Heat resistant arrangement according to claim 1, characterized in that the liner (16) further includes a dimple (32) disposed therein extending toward the substrate (10) and in contact therewith and that the shank portion of the fastener (24) is located within the dimple (32) and the fastener (24) further includes an enlarged head portion (38) at the second end thereof, the head portion (38) extending laterally with respect to the shank portion and having a hot gas facing surface substantially flush with the liner surface surrounding the dimple (32). Heat resistant arrangement according to claim 2, characterized in that the enlarged head portion (38) and dimple (32) form a toroidal volume (42) therebetween disposed about the fastener shank portion, the volume (42) including an annular louver outlet (40) into the hot gas flow and defined between the lateral edge of the enlarged head portion (38) and the liner (16). Heat resistant arrangement according to claim 3, characterized in that the plurality of cooling openings (34) are located in the dimple (32) of the liner (16) and direct the flow of cooling gas into the toroidal volume (42). Heat resistant arrangement according to claim 4, characterized in that the shank portion includes an enlarged shoulder (30) disposed adjacent the fastener first end for cooperably engaging the liner (16) and releasably securing the liner (16) therewith to the substrate (10). Heat resistant arrangement according to any one of claims 1 to 5, characterized in that the fastener (24) has an internal cooling gas flow passage (44).

Inventors: BUNDT, EDGAR, ZIMMERMAN, ANTHONY M.
Applicants: UNITED TECHNOLOGIES CORPORATION
Application year: 1988
Main classification: F16B39
IPC codes: F16B5, F16B35, F23M5, F02C7, F02K1, F23R3