Method of repair for inlet caps of turbine engines

A method for repairing a damaged inlet cap of a turbine engine includes removing a damaged portion of a structural fiber layer positioned beneath a first erosion-resistant layer. A structural replacement layer is applied to the inlet cap to replace the removed portion of the structural fiber layer and a second erosion-resistant layer is applied to the inlet cap so that the second erosion-resistant layer is positioned over the structural fiber layer.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of turbine engine maintenance. More specifically, the present invention relates to a method for repairing an inlet cap of a turbine engine.

Turbine engines, especially those for use with airplanes, typically include an inlet cap (also referred to as an inlet cone front segment) located upstream of the air intake fan. The inlet cap is rotatably mounted to the turbine engine to affect the flow of air into the air intake fan.

Inlet caps require periodic maintenance to address wear and damage incurred by the inlet cap. Such wear or damage can be caused, for example, by birds striking the inlet cap or by particulate matter causing abrasion to exterior surfaces of the inlet cap. In addition, engine maintenance and service procedures can cause damage or wear to the inlet caps.

BRIEF SUMMARY OF THE INVENTION

The present invention includes a method for repairing an inlet cap of a turbine engine. A first erosion-resistant layer, and a portion of a structural fiber layer positioned beneath the first erosion-resistant layer, are removed from the inlet cap. A structural replacement layer is applied to the inlet cap to replace the removed portion of the structural fiber layer and a second erosion-resistant layer is applied to the inlet cap so that the second erosion-resistant layer is positioned over the structural fiber layer.

DETAILED DESCRIPTION

The present invention includes a method for repairing an inlet cap of a turbine engine.FIG. 1shows turbine engine10, which includes inlet cap12rotatably mounted to turbine engine10near rear cone segment14and fan blades16.

As shown inFIG. 2, inlet cap12includes front face20, rear face22, and a plurality of lug slots24. Lug slots24are designed to receive a fastener to secure inlet cap12relative to turbine engine10. In addition, front face20includes optional marker26, which may be included to indicate rotational movement of inlet cone12relative to turbine engine10.

FIG. 3shows a section of inlet cap12ofFIG. 2and illustrates the construction of inlet cap12. As shown inFIG. 3, inlet cap12includes structural fiber layer40, erosion-resistant layer42, intermediate layer44, and backing layer46. Front face20is formed by erosion-resistant layer42and rear face22is formed by backing layer46. Structural fiber layer40is positioned over backing layer46and beneath erosion-resistant layer42and intermediate layer44. Intermediate layer44and backing layer46protect structural fiber layer40from water intrusion and are typically formed from fiberglass.

Structural fiber layer40includes a plurality of constituent fiber layers48, which typically include high-strength fibers such as, for example, aramid fiber (also referred to as aromatic polyamide fibers). In some embodiments, fiber layers48consist of layers of fabric that are formed from aramid fibers and impregnated with epoxy resin. In one non-limiting embodiment, inlet cap12includes eleven fiber layers48.

When in service on turbine engine10ofFIG. 1, inlet cap12is subjected to conditions that frequently result in damage or wear to front face20and/or lug slots24of inlet cap12. This damage can be caused by conditions present in the operational environment of turbine engine10or service or maintenance activities performed on turbine engine10. Conventional maintenance procedures are limited to replacing erosion-resistant layer42upon showing signs of wear. Under these conventional maintenance procedures, once damage has occurred to structural fiber layer40(i.e., damage to any constituent fiber layer48), inlet cap12must be replaced with a new inlet cap12.

The method of the present invention provides a method for repairing inlet cap12even when structural fiber layer40has been damaged, which allows many inlet caps to be repaired, rather than requiring them to be replaced.FIG. 4illustrates an embodiment of a method of the present for replacing a damaged portion of structural fiber layer40.FIG. 4shows a side view of inlet cap12after a damaged area of inlet cap12has been repaired.

The method illustrated inFIG. 4includes first removing all of erosion-resistant layer42and intermediate layer44(as shown inFIG. 3), or at least those portions of erosion-resistant layer42and intermediate layer44that are positioned over the damaged portion of structural fiber layer40. The damaged portion of structural fiber layer40is then removed to create interface50. Damaged portions of constituent fiber layers48are removed so that inlet cap12does not include any damage to structural fiber layer40. Adhesive film52is applied to interface50and replacement structural layer54is applied to interface50to engage adhesive film52and replace the removed portion of structural fiber layer40. If the damage to structural fiber layer40is sufficiently deep, a plurality of constituent replacement layers56are applied to inlet cap12to form replacement structural layer54. In some embodiments, the number of replacement layers56applied to inlet cap12matches the number of removed fiber layers48.

After the application of replacement structural layer54, a replacement erosion-resistant layer42′ and a replacement intermediate layer44′ are applied to inlet cap12so that both of the layers are positioned over structural fiber layer40and replacement structural layer54. In one embodiment, erosion-resistant layer42′ and intermediate layer44′ are bonded together to form a bi-layer prior to being applied to inlet cap12.

If the damage to structural fiber layer40is deep enough so that portions of every constituent fiber layer48must be removed, some or all of backing layer56is removed and replacement backing layer46′ is applied to inlet cap12to cover all of the exposed underside of replacement structural layer54and, in some embodiments, all of the underside of structural fiber layer40.

In the embodiment ofFIG. 4, interface50is sloped or tapered to enhance the strength of the joint between structural fiber layer40and replacement structural layer54. Interface50can exhibit a continuous slope or a step-wise slope. In some embodiments the slope of interface 50 is between about 0.25 inches and about 0.50 inches in the horizontal direction (i.e., the direction parallel to fiber layers48) per each fiber layer48.

Depending upon the severity of damage to structural fiber layer40, interface50may extend through all of structural fiber layer40to backing layer46or to the uppermost or lower most undamaged constituent fiber layer48. Interface50can be formed using any method known in the art including, for example, sanding or cutting structural fiber layer40. In some embodiments, a cut is made around the damaged portion of each constituent structural layer48and the damaged portion is peeled free from structural fiber layer40.

To enhance the strength of replacement structural layer54, each replacement layer56may be applied to inlet cap12so that it is rotationally staggered with respect to an adjacent replacement layer56. This rotational staggering may be with respect to any feature of replacement layers56including, for example, a direction or orientation related to a stitching or fiber pattern of replacement layers56. In some embodiments, each replacement layer56is applied so that it is rotationally staggered by about 33 degrees relative to an adjacent layer56. In some embodiments, each layer56is applied to inlet cap12so that its orientation matches an orientation of a removed fiber layer48.

Any suitable material known in the art may be used to form replacement structural layer54. Examples of suitable materials include aramid fibers, carbon fiber, fiberglass, fabrics including any of these fibers, any other high-strength fiber or fabric known in the art, and combinations of these. Examples of commercially available aramid fibers and fabrics include the KEVLAR, NOMEX, and TWARON aramid fiber products. In some embodiments of the present invention, structural layer54includes epoxy resin.

FIGS. 5-8illustrate one non-limiting embodiment of the repair method described above for use in repairing a damaged lug slot24.FIG. 5shows a top view of lug slot24which is to be replaced with lug slot24′ ofFIG. 8. Lug slot24includes hole60, flat surface62, transition area64, vertical wall66, and transition area68. Flat surface62is recessed within front face20of inlet cap12(seeFIG. 2) and includes hole60for receiving a fastener to secure inlet cap12relative to turbine engine10. Transition area64is located on front face20between flat surface62and vertical wall66and transition area68is located between vertical wall66and main surface70of front face20. Lug slot24has a construction similar to that shown inFIG. 4, with structural fiber layer40, erosion-resistant layer42, intermediate layer44, and backing layer46extending into and forming lug slot24so that each of the layers exhibits a profile similar to the overall shape of lug slot24.

To repair a damaged lug slot24, erosion-resistant layer42and intermediate layer44are removed from inlet cap12by, for example, hand-sanding. If the damage extends deep enough into structural fiber layer40of lug slot24, then lug slot24is completely removed from inlet cap12. For example, in some embodiments, if structural fiber layer40includes eleven fiber layers48and the damage to lug slot24extends more than six layers deep into structural fiber layer40, then lug slot24is completely removed from inlet cap12(including all of backing layer46, or at least a portion of backing layer46positioned beneath the damaged portion of structural fiber layer40). Lug slot24can be removed using any method known in the art including, for example, cutting through inlet cap12from front face20to rear face22and cutting along outside edge72of transition area68until lug slot24is dislodged from inlet cap12.FIG. 6shows inlet cap12after a lug slot24has been removed by cutting along outside edge72. In some embodiments, outside edge72is spaced from vertical wall66by a distance of at least about 0.5 inches.

Interface50is then cut so that interface50tapers (or slopes) away from front face20, as shown inFIG. 7. In some embodiments, interface50is formed at the same time lug slot24is being removed. To obtain a uniformly roughened surface, interface50may be abraded with, for example, a non-metallic grit-coated cloth or paper (e.g., 180 grit or finer). Any dust caused by the abrasion process is removed from interface50and inlet cap12is dried for at least about24hours at a temperature of between about 170° F. and about 190° F.

After drying, adhesive52(e.g., an adhesive film such as the HYSOL EA 9689 product commercially available from Loctite Aerospace of Bay Point, Calif.) is applied to interface50. Replacement layers56are then applied to interface50to form portions54A and54B of structural replacement layer54, as shown inFIG. 8. In most embodiments, the number of replacement layers56applied to interface50will be the same as the number of constituent fiber layers48removed from inlet cap12. As discussed above, replacement fiber layers56may be rotationally staggered with respect to each other to enhance the strength of replacement layer54. Backing layer46′ (seeFIG. 4) is then applied beneath replacement fiber layer56to replace any portions of backing layer46that were removed. In some embodiments, backing layer46′ is formed from fiberglass such as, for example, the F161-262-120 fiberglass product commercially available from Hexcel or the CYCON 293 fiberglass product commercially available from Cytec Engineered Materials.

Inlet cap12is then sealed in a vacuum bag and positioned in a mold having a forward mold-part shaped to coincide with front face20and a bottom mold-part shaped to coincide with rear face22. In some embodiments, the forward mold-part is composed of hard tooling such as, for example, aluminum and the rear mold part is composed of soft tooling such as, for example, silicone (e.g., the ARLON precision-calendared, uncured silicone product commercially available from Arlon - Silicone Technologies Division of Bear, Del.).

The mold/vacuum-bag assembly is placed inside an autoclave and inlet cap12is held in a vacuum until a pressure of between about 15 and about 20 pounds-per-square-inch (psi) is applied to inlet cap12. The vacuum is then vented to atmosphere and a pressure of at least about 40 psi is applied to inlet cap12. The temperature of inlet cap12is ramped up from room temperature to about 355° F. ± about 15° F. at a rate of between about 2° F. per minute and about 8° F. per minute. The temperature of inlet cap12is held at about 355° F. ± about 15° F. for about 120 minutes. The pressure applied to inlet cap12is then slowly released and the vacuum is reestablished when the pressure reaches about 20 psi. Inlet cap12is cooled until it reaches a temperature of about 150° F. and is then removed from the vacuum bag and mold.

FIG. 8shows partially-repaired inlet cap12′, which results from the above autoclaving process. Inlet cap12′ includes tapered structural replacement portion54A which overlaps structural fiber layer40(seeFIG. 4) and structural replacement portion54B which includes replacement lug slot24′. Similar to lug slot24′ includes hole60′, flat surface62′, transition area64′, vertical wall66′, and transition area68′ (including outside edge72).

Hole60′ is drilled in inlet cap12′ at a location matching the location of hole60ofFIG. 5to produce the partially-repaired inlet cap12′ shown inFIG. 8. The edges of inlet cap12′ are trimmed if necessary and the interior surface of hole60′ is sealed using a sealant such as, for example, the EA9396 sealant product commercially available from Loctite Aerospace of Bay Point, Calif. The thickness and profile of inlet cap12′ is then checked to verify compliance with the specifications for inlet cap12′.

To finalize the repair of inlet cap12′, the materials for erosion-resistant layers42′ and intermediate layer44′ are prepared and applied to inlet cap12′. In one embodiment, erosion-resistant coating42′ is cut from a continuous ply of a fluoroelastomer film (e.g., the 0.02 inch thick VITON fluoroelastomer product commercially available from Eagle Elastomer of Cuyahoga Falls, Ohio) and intermediate layer44′ is cut from a continuous ply of fiberglass (e.g., the CYCON fiberglass product commercially available from Cytec Engineered Materials).

In some embodiments, erosion-resistant layer42′ and intermediate layer44′ are bonded together and applied as a bi-layer assembly to inlet cap12′. To accomplish this, the materials for erosion-resistant layer42′ and intermediate layer44′ are positioned in a bonding mold that includes a forward mold-part for engaging layer42′ and a rear mold-part for engaging layer44′. Prior to laying the materials for layer42′ or layer44′ in the bonding mold, parting agent is applied to the forward and rear mold-parts. The material for layer42′ is then positioned into the forward mold-part followed by the material for layer44′. A layer of peel ply is then positioned atop the material for layer44′ and the rear mold-part is positioned atop the peel ply. The bilayer-assembly is then sealed in the mold and a vacuum bag. The mold/vacuum bag assembly is then placed in an autoclave and autoclaved pursuant to the procedures described above in regards to the formation of inlet cap12′ ofFIG. 8, with the exception that the temperature of the bi-layer assembly is held at a temperature of about 375° F. ± about 15° F. for between about 90 and about 120 minutes at a pressure of between about 30 psi and about 50 psi (as opposed to being held at a temperature of about 355° F. ± about 15° F. for about 120 minutes at a pressure of about 40 psi).

After the bi-layer assembly including erosion-resistant layer42′ and intermediate layer44′ has been allowed to cool, the bi-layer assembly is removed from both the mold and the vacuum bag and trimmed as necessary. The exposed surface of intermediate layer44′ (i.e., the surface that will be bonded to inlet cap12′ ) is then roughened by grit blasting with 60-120 aluminum oxide grit to produce a uniform matte texture. The grit-blasted surface of intermediate layer44′ is wiped clean and the bi-layer assembly is heated to a temperature of about 150° F. for between about 15 and about 30 minutes to remove any volatiles.

Adhesive is then applied to the exposed surface of inlet cap12′ (i.e., the exposed surfaces of structural fiber layer40and replacement portions54A and54B of replacement layer54). An example of a suitable adhesive is the epoxy film adhesive HYSOL EA 9689 .080 PSF commercially available from Loctite Aerospace of Bay Point, Calif. The cured bi-layer assembly is then applied to inlet cap12′ so that intermediate layer44′ engages the adhesive. The resulting inlet cap12′ is the vacuum bagged and placed in the same mold that was used to form inlet cap12′ ofFIG. 8. The mold/vacuum bag assembly is placed in an autoclave and inlet cap12′ autoclaved pursuant to the procedures described above for forming inlet cap12′ ofFIG. 8, with the exception that the temperature of the bi-layer assembly is held at a temperature of about 250° F. ± about 15° F. for between about 90 and about 120 minutes and a pressure of between about 30 psi and about 50 psi (as opposed to being held at a temperature of about 355° F. ± about 15° F. for about120minutes at a pressure of about 40 psi).

The resulting inlet cap12′ is then trimmed and hole60′ is re-drilled if necessary. Front face20and rear face22are wiped clean and allowed to air dry for at least 15 minutes. The edges of inlet cap12′ are then sealed with a sealant (e.g., the PLV 2000 or PLV 2100 fluoroelastomer sealant products that are both commercially available from Pelseal Technologies of Newtown, Pa.) and air cured for 24 hours at room temperature or for one hour at room temperature and then for one hour at a temperature of about 175° F. ±25° F.

A modified version of the method described above in conjunction withFIGS. 5-8may be used for partial replacement of lug slot24(i.e., where portions of some, but not all, of the plurality of constituent structural layers48included in lug slot24are removed). If the damage to structural fiber layer40warrants only a partial replacement of lug slot24, then a cut is made along outside edge72(seeFIG. 5) to a desired depth within structural fiber layer40. For a partial repair, the cut is typically made so that it penetrates through the lowermost damaged constituent fiber layer48.

In some embodiments, where damage has occurred to portions of structural fiber layer40near backing layer46and erosion resistant layer42and intermediate layer44have not been damaged, the repairs to structural fiber layer40may be conducted with respect to rear face22of inlet cone12instead of front face20.

In some embodiments, a plurality of lug slots24may be replaced at the same time.

Thus, as described above, the method of the present invention provides a means for repairing an inlet cone of a turbine engine that has sustained damage to structural fiber layer located beneath an exterior erosion-resistant layer. In particular, the method of the present invention allows for a damage lug slot of an inlet cone to be either fully replaced or partially replaced, depending upon the severity of the damage to the lug slot.