Patent Description:
Gas turbine engines (broadly inclusive of industrial gas turbines, turbofans, turbojets, turboshafts, turboprops, and the like) are subject to periodic or other servicing requiring the removal, cleaning, inspection, and repair or restoration of individual components. Of particular note are the airfoil elements (blades and vanes) of the turbine section(s) of such engines. Turbine blades and vanes are typically formed of high temperature alloys, generally nickel-based superalloys. The elements have internal cooling passage systems (e.g., with inlets typically along the roots of blades and along either an inner diameter platform or outer diameter shroud of vanes).

At least along the exterior of the airfoil, the turbine elements typically also bear a thermal barrier coating system. Exemplary thermal barrier coating systems comprise one or more bondcoat layers (often metallic) and one or more barrier layers (typically ceramic). Additionally, abradable and/or abrasive coatings may be located such as at the blade tip for engaging the inner diameter surface of a blade outer airseal (BOAS).

So-called cantilevered vanes only have outer diameter shrouds and may have inner diameter ends similar to outer diameter ends of blades. Typical blade outer diameter ends are formed by a tip of the blade airfoil bearing an abrasive coating. Other blades include shrouds at the outer diameter end of the airfoil. Such shrouds may bear sealing teeth or the like.

The cooling passageway systems include outlets. Typically, the outlets include outlets along the airfoil itself such as outlets adjacent the leading edge, outlets adjacent the trailing edge (e.g., a discharge slot), outlets along the respective suction side and/or pressure side, and outlets at blade tips. Additional outlets may be along gaspath-facing surfaces of platforms or shrouds. For vanes, in particular, there may be one or more large outlets along the non-gaspath-facing surface of whichever of the platform and shroud does not bear the inlet(s).

In service, numerous wear, damage, fouling, and the like may occur. Coatings may become worn or delaminated. Wear may extend down to substrate material. There may be chipping or other foreign object damage. Fine cooling passageway outlets may become plugged and larger accumulations of material may foul even feed passageway portions of the cooling passageway system. Tip wear and cracking is also a relevant consideration for blades.

Thus, an exemplary servicing process for blades involves cleaning, optional coating removal, inspection, machining at wear or damage locations, subsequent repair/restoration (e.g., build-up weld repairs, tip cap replacement, and the like), and recoating).

In a service operation, the airfoil elements are typically processed in their respective stages of the engine. For example, all the blades of a given stage may be removed from the associated disk and processed as a batch. Many alternatives exist including aggregating like blades from multiple engines. These blades are sent to repair shops to restore to the original condition. The blades are initially sent for grit blasting to remove the top ceramic coat. Once blasted, the parts are checked if they are salvageable (e.g., based on visual inspection). If the parts are salvageable, they are sent for internal cavity cleaning.

A typical internal cleaning process is an iterative process including radiographic imaging inspection. An exemplary baseline initial cleaning process <NUM> (<FIG>) comprises an autoclave chemical cleaning or leaching <NUM>. This may be performed on individual blades or groups as discussed above. The leaching is performed using an alkaline solution (e.g., KOH). The exemplary autoclaving involves an autoclave operating temperature of <NUM>°F to <NUM>°F (<NUM> to <NUM>), an operating pressure of about <NUM> psi (<NUM>. 4MPa), and a hold time at operating temperature and pressure of <NUM> hours to <NUM> hours.

After the autoclave cleaning, a flushing <NUM> may be performed. An exemplary flushing is a high pressure water jet cleaning. An exemplary flushing comprises inserting one or more nozzles into the blade platform inlet(s) and blasting with deionized water at high pressure (e.g., <NUM> psi to <NUM> psi) (<NUM>. 4MPa to <NUM>. This flushing tends to remove material left by the autoclaving. For example, the autoclaving may tend to loosen internal layers of sand and dust, leaving these relatively fragile.

After the flushing, a boiling step <NUM> and a conductivity check step <NUM> may be performed. In exemplary boiling, a body of water is heated to a boil. One or more of the elements may be placed in a tray and fully immersed in the boiling water and soaked for a period of time. The elements are removed and then rinsed in deionized water. During the rinse, the deionized water may accumulate material from moisture left after the boiling or from contaminants otherwise still inside the element. For the conductivity check <NUM>, a sample of the rinse water is collected and its conductivity tested. A high conductivity will indicate the presence of dissolved solids and ions left over from the autoclave alkaline solution. An exemplary threshold is <NUM> micro-Siemens per centimeter. Excess conductivity mandates a re-flushing.

Thereafter, there may be an oven dry <NUM> to remove residual water. Exemplary operating temperatures are <NUM>°F to <NUM>°F (<NUM> to <NUM>) in a drying oven or atmospheric furnace.

Radiographic inspection <NUM> may involve installing one or more blades in a fixture. Exemplary fixtures are serialized to provide visible indication of the particular blade being tested in the radiographic image. Exemplary radiographic imaging is a digital x-ray.

<FIG> shows an exemplary radiographic image with areas of residual fouling <NUM> (dark spots) highlighted in light boxes. Upon detection of such areas of fouling, the process repeats. The process may repeat for many cycles. Thus, it may take many days to process a given stage of elements. The costs of this are substantial. It is not merely the time required for processing but labor and downtime. Also, there is a cost to unpredictability. A great variation in the amount of time needed for blade stages also imposes a predictability cost. Going in, one does not know whether a given stage of blades may require many days of cycles or only one or two days.

<CIT> discloses a prior art ultrasonic cleaning system and method.

<CIT> discloses a prior art method for removing undesired material from internal spaces of parts.

<CIT> discloses a prior art high pressure internal cleaning method and apparatus.

<CIT> discloses prior art turbine engine cleaning systems and methods.

One aspect of the disclosure involves a method for processing a turbomachine airfoil element as recited in claim <NUM>.

<FIG> shows a turbine blade <NUM>. The blade comprises a metallic substrate <NUM> (<FIG>). The blade may further comprise one or more coatings. As is discussed below, the exemplary coatings may include a thermal barrier coating (TBC) system and/or an abrasive coating system (not shown). Each of these coating systems may, in turn, include one or more layers. For example, the exemplary thermal barrier coating system includes a metallic bondcoat atop the substrate and a ceramic thermal barrier coating (TBC) layer atop the bondcoat. Similarly, the abrasive coating system may include a metallic underlayer (base layer) and an abrasive layer. The abrasive layer comprises a matrix and abrasive particles at least partially embedded in the matrix. In the illustrated <FIG> example, the ceramic layer(s) have been removed but at least a portion of the bondcoat <NUM> may remain.

An exemplary substrate comprises a unitary metallic casting (e.g., of a nickel-based superalloy) and defines the overall gross features of the blade. The substrate and blade thus include an airfoil <NUM> and an attachment feature <NUM> (e.g., a firtree root). The blade and substrate may further include a platform <NUM> between the airfoil and the firtree root.

The firtree root <NUM> extends from an inboard end <NUM> forming an inboard end of the blade to an outboard end at an underside of the platform. The airfoil <NUM> extends from an inboard end at an outer surface (gaspath-facing surface) of the platform to a tip <NUM>. The airfoil extends from a leading edge <NUM> to a trailing edge <NUM> and has a pressure side surface <NUM> and a suction side surface <NUM>.

The tip <NUM> has a primary radially-outward facing surface <NUM>. The surface <NUM> may at least partially surround a tip squealer pocket (not shown) extending radially inward from the tip surface <NUM>. As noted above, an abrasive coating may be applied along the surface <NUM> and the TBC system may be applied along the pressure and suction side surfaces and the gaspath-facing surface of the platform.

<FIG> shows the cooling passageway system <NUM> as including multiple trunks 102A, 102B, 102C extending from respective outlets 104A, 104B, 104C along the inner diameter face of the root. Depending upon blade configuration, the trunks may branch in multiple spanwise cavities optionally with turns such that a cavity with tipward flow is termed an up-pass and a cavity leg with rootward flow is termed a down-pass. Additionally, there may be one or more impingement cavities such as a leading edge impingement cavity <NUM> fed by impingement holes from one of the up-pass or down-pass cavities and discharging via associated outlets to the airfoil exterior surface. Various of the cavity legs may discharge to the tip/tip pocket. Additionally, there may be a tip flag leg <NUM> passing in a rearward to the trailing edge from one of the more forward trunks. The exemplary trailing edge slot <NUM> is fed by the most rearward trunk.

In an improved process <NUM> (<FIG>), a vibrating step <NUM> is added to the baseline steps. The exemplary vibrating step is a targeted local vibrating via contacting a vibrator with the exterior of the turbine element. In particular, this is likely to be along a suction side or pressure side of the airfoil. As is discussed below, in at least some of the iterations, the particular location(s) for vibrating may be determined in response to the radiographic inspection <NUM>.

In terms of modifying the exemplary baseline process <NUM>, there may be multiple simple implementations or more complex implementations. For example, in one simple implementation, the vibrating <NUM> is performed only after the first iteration of the baseline process <NUM> and repeats through further iterations. In another implementation, an initial vibrating step <NUM> is performed at one or more locations which, via experience, are believed to be adjacent likely locations of fouling. In subsequent iterations, the targeting may be responsive to the inspection <NUM>.

An exemplary vibrator is a pneumatic pen-type vibrator/air hammer such as used for engraving. CP <NUM> air hammer, Chicago Pneumatic Tool Company LLC, Rock Hill, South Carolina. A buffer element or member <NUM> (<FIG>) may be introduced between the vibrator and the turbine element. An exemplary buffer may serve one or more of at least two purposes. First, it may distribute force to avoid damaging the surface of the turbine element. Second, it may provide means for positioning the vibrator and retaining it in position. The positioning may comprise registering in a predetermined position. For example, an exemplary buffer may be sheet-like (e.g., comprising a metallic strip <NUM>). An exemplary strip is SAE <NUM> high-carbon steel strip. The strip has a first face <NUM> (<FIG>) for engaging the turbine element and a second face <NUM> for engaging the vibrator. An exemplary strip thickness is <NUM> inch (<NUM>), more broadly <NUM> to <NUM>. Along the first face, to further distribute and attenuate force, there may be a non-metallic layer <NUM> intervening between the strip and the element to serve as a cushion to prevent metal-to-metal contact to protect the part surface. For example, a tape layer may be applied to the first face. Exemplary tape is a high temperature glass fiber masking tape (e.g., Scotch® Performance Green Masking Tape <NUM>+ glass-reinforced adhesive paper masking tape of <NUM>, St. Paul, Minnesota). Exemplary tape thickness is <NUM> inch (<NUM>), more broadly <NUM> to <NUM>. Exemplary tape width is about <NUM> and length is about <NUM>.

The positioning features may comprise recesses <NUM> along the second face for capturing the tip <NUM> of the vibrator. Exemplary recesses may be in elevated areas <NUM> so as to not actually be below the remainder of the second face <NUM>. For example, one or more circular pieces may be tack welded to the first face <NUM> of a rectangular plate/strip <NUM> of steel. The circular pieces may be of a similar steel to the strip <NUM>. An exemplary piece thickness is <NUM> inch (<NUM>), more broadly <NUM> to <NUM>. The tack welding creates a recess in the exposed face of the circular pieces, leaving a perimeter as the associated elevated area <NUM>. Exemplary recess depth is <NUM> to <NUM> (thus potentially below the ambient surface level of the strip), but leaving a thickness of at least <NUM> of strip thickness. Exemplary circular piece diameter is about <NUM> inch (<NUM>) and exemplary recess diameter is about <NUM> inch (<NUM>). Alternatively, the piece(s) may have a washer-like circular (annular) shape and be secured to the strip such as by welding so that their hole(s) define the recess(es).

In one example, the technician manually aligns one of the positioning features with the observed fouling location and then vibrates. More complex implementations may make use of the multiple positioning features. For example, the strip may be dimensioned to fit along one side (pressure side or suction side) of the airfoil. Particular locations may be known as likely candidates for fouling. Each of these locations may have an associated positioning feature (e.g., typically likely only two or three such features being appropriate). Based upon the radiographic inspection, a technician may place the buffer on the element and then sequentially engage the vibrator to one or more of the features to vibrate the airfoil at the associated target location. Alternatively, the multiple positioning features may provide redundancy. For example, the symmetric illustrated buffer element allows a technician to use either feature to address a given location on the blade (such as by a <NUM>° rotation). This may approximately double the life of the buffer element as the positioning features wear or break off (e.g., due to vibration fatiguing the tack weld.

By targeting locations of fouling and vibrating proximate those locations, the number of cycles may be greatly reduced. This can, for example, reduce the required number of cycles from something in the vicinity of ten to four or less. This may reduce overall time required for the multiple cycles.

Where a measure is given in English units followed by a parenthetical containing SI or other units, the parenthetical's units are a conversion and should not imply a degree of precision not found in the English units.

Claim 1:
A method for processing a turbomachine airfoil element (<NUM>), the airfoil element (<NUM>) comprising a metallic substrate (<NUM>) having:
an airfoil (<NUM>) extending from a first end to a second end; and
a cooling passageway system (<NUM>) extending through the airfoil (<NUM>),
the method comprising:
applying an external vibration to an area of the airfoil (<NUM>) element targeting internal fouling (<NUM>) of the cooling passageway system (<NUM>) via a pneumatic vibrator, wherein the applying comprises placing a buffer (<NUM>) between the substrate and the pneumatic vibrator, wherein the buffer (<NUM>) comprises: a metallic strip (<NUM>) having a first face (<NUM>) and a second face (<NUM>) opposite the first face (<NUM>); means along the second face (<NUM>) for registering the pneumatic vibrator; and
a cushion (<NUM>) along the first face (<NUM>);
flushing the cooling passageway system (<NUM>); and imaging the cooling passageway system (<NUM>).