[0001] This invention relates generally to turbine engines, and more specifically to environmental
coatings used with turbine engine components.
[0002] At least some known gas turbine engines include a forward fan, a core engine, and
a power turbine. The core engine includes at least one compressor that provides pressurized
air to a combustor wherein the air is mixed with fuel and ignited for generating hot
combustion gases. The combustion gases flow downstream to one or more turbines that
extract energy therefrom to power the compressor and provide useful work, such as
powering an aircraft. A turbine section may include a stationary turbine nozzle positioned
at the outlet of the combustor for channeling combustion gases into a turbine rotor
disposed downstream thereof.
[0003] The turbine nozzle may include a plurality of circumferentially spaced apart vanes.
The vanes are impinged by the hot combustion gases exiting the combustor and are at
least partially coated to facilitate protecting the vanes from the environment and
to facilitate reducing wear. Specifically, in at least same engines, a platinum aluminide
coating is be applied to turbine components, including the vanes to facilitate environmentally
protecting the components. The application of platinum aluminide coatings is generally
a three-step process that may include an electroplating process, a diffusion heat
treatment, and an aluminiding process. During electroplating, platinum is plated over
the surface of the component to be coated. Such that an electroplate coat of substantially
uniform thickness is applied across the entire surface of the component. However,
a magnetic field generated by current flow between the component to be coated and
an anode used in coating may be non-uniformly distributed across the component, and
more specifically such flux lines may be more dense adjacent sharp edges on the part,
such as adjacent the trailing edge of the nozzle vane. As a result, a thicker coating
of plating may be applied to such edges relative to the convex and concave surfaces
of the airfoil portion of the vane. Over time, the uneven distribution of coatings
may cause cracking: At least one known method of controlling the electroplate thickness
adjacent the trailing edge requires that a disposable, metallic "robber" be positioned
adjacent to the trailing edge to thieve current from the edge during the coating application.
However, within such methods the effectiveness of the robber degrades over time and
it may require frequent replacement.
[0004] In one embodiment of the invention, a method of fabricating a gas turbine engine
component are provided. The method includes positioning a non-consumable shield adjacent
to an edge of the component such that a gap is defined between the shield and the
component, wherein the shield and gap form a fluid flow restriction adjacent to the
edge, and inducing an electrical current from an anode to the component through an
electrolyte bath such that a coating is applied to the component.
[0005] In another embodiment of the invention, an electroplating apparatus is provided.
The electroplating apparatus includes an electroplating bath that includes an electrolytic
solution, a power source, an anode coupled to the power source, a component coupled
to the power source and immersed within the electrolytic solution wherein the component
includes a plating surface bordered by an edge, and a non-consumable shield positioned
adjacent to the component edge such that a gap is defined between the edge and the
shield and wherein the shield and the gap form a fluid flow restriction adjacent to
the edge.
[0006] In yet another embodiment of the invention, an electroplating apparatus is provided.
The electroplating apparatus includes an electroplating bath including an electrolytic
solution comprising platinum, a power source, an anode coupled to the power source,
a component to be electroplated coupled to the power source and immersed within the
electrolytic solution wherein the component includes a plating surface and an edge,
and a non-consumable shield positioned adjacent to the edge such that a gap is defined
between the edge and the shield and wherein the shield and the gap form a fluid flow
restriction adjacent to the edge. The shield is configured to displace an electric
field away from the edge to facilitate reducing an amount of electroplating deposited
on the edge.
[0007] The invention will now be described in greater detail, by way of example, with reference
to the drawings, in which:-
Figure 1 is a longitudinal cross-sectional view of an exemplary high bypass ratio
turbofan engine;
Figure 2 is a perspective view of an exemplary first stage, high pressure turbine
nozzle segment that may be used with the gas turbine engine (shown in Figure 1);
Figure 3 is a perspective view of an exemplary electroplating process for applying
an electroplate coating to the vanes shown in Figure 2.
Figure 4 is a cross-sectional view of high pressure turbine nozzle vane 118 that may
be used in the electroplating process shown in Figure 3; and
Figure 5 is a graph of electroplate coating thickness readings taken at each of the
plurality of test locations shown in Figure 4.
[0008] As used herein, the term "component" may include any component configured to be coupled
with a gas turbine engine that may be coated with a metallic film coating, for example
a high pressure turbine nozzle vane. A high pressure turbine nozzle vane is intended
as exemplary only, and thus is not intended to limit in any way the definition and/or
meaning of the term "component". Furthermore, although the invention is described
herein in association with a gas turbine engine, and more specifically for use with
a high pressure turbine nozzle vane for a gas turbine engine, it should be understood
that the present invention is applicable to other gas turbine engine stationary components
and rotatable components. Accordingly, practice of the present invention is not limited
to high pressure turbine nozzle vanes for a gas turbine engine. In addition, although
the invention is described herein in association with a electrolytic bath process,
it should be understood that the present invention may be applicable to any electroplating
process, for example, brush electroplating. Accordingly, practice of the present invention
is not limited to an electroplating process using an electrolytic bath.
[0009] Figure 1 is a longitudinal cross-sectional view of an exemplary high bypass ratio
turbofan engine 10. Engine 10 includes, in serial axial flow communication about a
longitudinal centerline axis 12, a fan 14, a booster 16, a high pressure compressor
18, a combustor 20, a high pressure turbine 22, and a low pressure turbine 24. High
pressure turbine 22 is drivingly connected to high pressure compressor 18 with a first
rotor shaft 26, and low pressure turbine 24 is drivingly connected to booster 16 and
fan 14 with a second rotor shaft 28.
[0010] During operation of engine 10, ambient air passes through fan 14, booster 16, and
compressor 18, the pressurized air stream enters combustor 20 where it is mixed with
fuel and burned to provide a high energy stream of hot combustion gases. The high-energy
gas stream passes through high-pressure turbine 22 to drive first rotor shaft 26.
The gas stream passes through low-pressure turbine 24 to drive second rotor shaft
28, fan 14, and booster 16. Spent combustion gases exit out of engine 10 through an
exhaust duct (not shown).
[0011] It should be noted that although the present description is given in terms of a turbofan
aircraft engine, embodiments of the present invention may be applicable to any gas
turbine engine power plant such as that used for marine and industrial applications.
The description of the engine shown in Figure 1 is only illustrative of the type of
engine to which some embodiments of the present invention is applicable.
[0012] Figure 2 is a perspective view of an exemplary first stage, high pressure turbine
nozzle segment 114 that may be used with the gas turbine engine 10 (shown in Figure
1). High pressure turbine nozzle segment 114 may be positioned axially between combustor
20 and high pressure turbine 22 such that a row of first stage turbine rotor blades
(not shown) is positioned downstream from high pressure turbine nozzle segment 114.
A plurality of high pressure turbine nozzles 114 may be circumferentially spaced about
axis 12 to form a high pressure turbine nozzle (not shown). High pressure turbine
nozzle segment 114 includes at least one nozzle vane 118 coupled at opposite radial
ends to a respective radially inner band 120 and a respective radially outer band
122. High pressure turbine nozzle segment 114 are typically formed in arcuate segments
having two or more vanes 118 per segment 114. Vanes 118 may be cooled during operation
against a flow of hot combustion gases 116 using a flow of cooling air 124 that may
be channeled from, for example, a discharge of compressor 18 to individual vanes 118
through outer band 122.
[0013] Each vane 118 includes a generally concave pressure sidewall 126, and a circumferentially
opposite generally convex, suction sidewall 128. Sidewalls 126 and 128 may extend
longitudinally in span along a radial axis of the nozzle between bands 120 and 122
wherein a root 130 couples to inner band 120 and a tip 132 couples to outer band 122.
Sidewalks 126 and 128 extend chorale or axially between a leading edge 134 and an
opposite trailing edge 136.
[0014] Figure 3 is a perspective view of an exemplary electroplating process 200 for applying
an electroplate coating to vanes 118 (shown in Figure 2). In the exemplary embodiment,
vane 118 may energized to a predetermined negative voltage with respect to a grid
202 such that when an electrolyte solution containing metal ions, for example, platinum
covers a surface of vane 118, for example, sidewall 126, the metal ions in the electrolyte
solution may be preferentially attracted to and bonded to sidewall 126 to form an
electroplate coating 204. In the exemplary embodiment, a non-conducting, non-consumable
shield 206 is positioned adjacent trailing edge 136 such that a longitudinal axis
208 of shield 206 is substantially parallel to trailing edge 136 and separated by
a gap 210 having a predetermined distance 212. In the exemplary embodiment, distance
212 is approximately thirty mils. In an alternative embodiment, distance 212 is a
distance greater than or less then thirty mils. In the exemplary embodiment, shield
206 is fabricated from a non-conducting material, for example, plastic and has an
outside diameter 218, for example, three-quarters inches, that is substantially greater
than the thickness 220 of vane 118 at trailing edge 136. The relatively larger diameter
of shield 206 with respect to the thickness of trailing edge 136 substantially blunts
the geometry of trailing edge 136 and facilitates blocking at least a portion of the
electrical current through trailing edge 136. Additionally, the close clearance of
distance 212 to trailing edge 136 facilitates reducing a flow of electrolyte solution
proximate trailing edge 136. Shield 206 may be formed to follow the contour of an
irregularly shaped or curved edge while maintaining gap distance 212. Additionally,
shield 206 may include an irregular cross-section, for example, shield 206 may be
a hollow or solid and may include a groove or slot configured to be aligned with edge
136 for optimizing the flow restrictive gap distance 212 and/or the electrical characteristics
of the electric field proximate gap distance 212.
[0015] Figure 4 is a cross-sectional view of high pressure turbine nozzle vane 118 that
may be used in electroplating process 200 (shown in Figure 3). Vane 118 includes concave
pressure sidewall 126 and convex suction sidewall 128 that each extend axially between
leading edge 134 and trailing edge 136. A plurality of thickness test locations are
located at predetermined locations about a perimeter of vane 118 and are labeled 401-410.
[0016] Figure 5 is a graph 500 of electroplate coating thickness readings taken at each
of the plurality of test locations 401-410 (shown in Figure 4). Graph 500 includes
an x-axis 502 whose units correlate with each respective test location, 401-410 (shown
in Figure 4). For example, electroplate coating thickness reading 401 is taken proximate
leading edge 134, electroplate coating thickness reading 406 is taken proximate trailing
edge 136, and electroplate coating thickness readings 404 and 409 are taken proximate
convex side 128 and proximate concave side 126 respectively. A y-axis 504 may be graduated
in units of mils indicative of a thickness of a plating coating corresponding to the
respective location, 401-410.
[0017] In the exemplary embodiment, a trace 506 joins points on graph 500 corresponding
to an exemplary electroplate process for coating nozzle vane 118 with a metallic film
coating. Trace 506 illustrates readings taken using the electroplate process wherein
shield 206 is not utilized to form a flow restrictive gap distance 212 adjacent edge
136. Trace 506 illustrates a metallic film coating thickness at location 406 that
is approximately 100% greater than the metallic film coating thickness at locations
401-405 and 407-410.
[0018] A trace 508 illustrates readings taken at locations 401-410 after using the electroplate
process wherein shield 206 is utilized to form a flow restrictive gap distance 212
adjacent edge 136 and to displace an electric field adjacent edge 136. Shield 206
facilitates plating a uniform metallic film coating thickness at locations 401-410.
Trace 506 illustrates a metallic film coating thickness at location 406 that is approximately
only 25% greater than the metallic film coating thickness at locations 401-405 and
407-410. Using shield 206 results in a more uniform metallic film coating thickness
around the perimeter of vane 118.
[0019] A thickness ration may be defined as a ratio of a maximum thickness from locations
around the perimeter of the airfoil (t
max) to a minimum thickness (t
min),
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[0020] Trace 508 exhibits a thickness ratio of approximately 1.94, using the above formula,
while trace 506 exhibits a thickness ratio of approximately 3.03, which represents
a 40% improvement in uniformity of the metallic film coating thickness about the perimeter
of vane 118.
[0021] The above-described methods and apparatus are cost-effective and highly reliable
for providing a substantially uniform metallic film coating thickness on gas turbine
engine components, such as a high pressure turbine first stage nozzle. Specifically,
the shield positioned adjacent the edge of the nozzle vane to be coated, defines an
electrolyte flow restrictive gap and displaces a portion of the electric field adjacent
the edge. Restricting the electrolyte flow adjacent the edge permits the electrolyte
to be depleted in the gap and reduces the metallic ion concentration available for
plating the edge. Displacing a portion of the electric field adjacent the edge facilitates
reducing the electroplating motive force and thus, the rate of plating on the edge.
The methods and apparatus facilitate fabrication of machines, and in particular gas
turbine engines, in a cost-effective and reliable manner.
[0022] Exemplary embodiments of electroplating methods and apparatus components are described
above in detail. The components are not limited to the specific embodiments described
herein, but rather, components of each apparatus may be utilized independently and
separately from other components described herein. Each electroplating method and
apparatus component can also be used in combination with other electroplating methods
and apparatus components.
1. A method (200) of fabricating a gas turbine engine component (118), said method comprising:
positioning a non-consumable shield (206) adjacent to an edge of the component such
that a gap (210) is defined between the shield and the component, wherein the shield
and gap form a fluid flow restriction adjacent to the edge; and
inducing an electrical current from an anode (202) to the component through an electrolyte
bath such that a coating (204) is applied to the component.
2. A method in accordance with Claim 1 further comprising electroplating the component
such that a thickness (220) of the plating coating on the edge (136) of the component
is substantially equal to a thickness of the plating coating across the surface (126,
128) of the component.
3. A method in accordance with Claim 1 or 2 wherein inducing an electrical current from
an anode to the component comprises coupling the component as a cathode in the electrical
circuit.
4. A method in accordance with Claim 1, 2 or 3 wherein positioning a non-consumable shield
adjacent to an edge of the component comprises positioning a non-conductive shield
adjacent to the edge such that at least a portion of an electric field generated is
displaced away from the edge.
5. A method in accordance with Claim 1, 2 or 3 wherein positioning a non-consumable shield
adjacent to an edge of the component comprises selecting a size of the shield to facilitate
displacing an electric field away from the edge, such that the coating deposited on
the edge is substantially uniform with respect to the coating deposited on the component.
6. A method in accordance with Claim 1, 2 or 3 wherein positioning a non-consumable shield
adjacent to an edge of the component comprises positioning a non-conductive shield
adjacent to the edge of the component.
7. A method in accordance with Claim 1, 2 or 3 wherein positioning a non-consumable shield
adjacent to an edge of the component comprises positioning a shield adjacent to the
edge of the component such that a width of the gap is equal to between approximately
0.254 mm and approximately 1.27 mm.
8. A method in accordance with Claim 1, 2 or 3 wherein positioning a non-consumable shield
adjacent to the edge of the component comprises positioning the shield adjacent to
the edge of the component such that a width of the gap is equal to approximately 0.762
mm.
9. A method in accordance with Claim 1, 2 or 3 wherein positioning a non-consumable shield
adjacent to the edge of the component comprises positioning the shield adjacent to
the edge, such that the shield has a contour that substantially matches a contour
of the edge.