U.S. patent application number 11/244344 was filed with the patent office on 2006-02-09 for high temperature ceramic lubricant.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Charles J. Beall, Robert William Bruce, Jerry Donald Schell.
Application Number | 20060029494 11/244344 |
Document ID | / |
Family ID | 36636514 |
Filed Date | 2006-02-09 |
United States Patent
Application |
20060029494 |
Kind Code |
A1 |
Bruce; Robert William ; et
al. |
February 9, 2006 |
High temperature ceramic lubricant
Abstract
A gas turbine engine component having opposed surfaces in
frictional contact with each other. An antifriction coating is
disposed on one or more of the opposed surfaces. The antifriction
coating includes a binder and a friction modifier. The weight ratio
of the friction modifier to binder in the antifriction coating is
greater than or equal to about 1:1.
Inventors: |
Bruce; Robert William;
(Loveland, OH) ; Schell; Jerry Donald; (Evendale,
OH) ; Beall; Charles J.; (Peachtree City,
GA) |
Correspondence
Address: |
MCNEES WALLACE & NURICK LLC
100 PINE STREET
P.O. BOX 1166
HARRISBURG
PA
17108-1166
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
12345
|
Family ID: |
36636514 |
Appl. No.: |
11/244344 |
Filed: |
October 5, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11015936 |
Dec 17, 2004 |
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11244344 |
Oct 5, 2005 |
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10445428 |
May 27, 2003 |
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11015936 |
Dec 17, 2004 |
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60675766 |
Apr 28, 2005 |
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Current U.S.
Class: |
415/160 |
Current CPC
Class: |
Y02T 50/672 20130101;
C23C 4/11 20160101; C23C 28/341 20130101; C23C 28/3455 20130101;
F05D 2300/615 20130101; C23C 28/347 20130101; C23C 4/067 20160101;
F04D 29/023 20130101; F05D 2230/90 20130101; F05D 2300/17 20130101;
Y02T 50/60 20130101; F04D 29/563 20130101; F05D 2300/611 20130101;
F05D 2300/20 20130101; F01D 5/288 20130101; C23C 28/34 20130101;
C23C 28/321 20130101; C23C 28/322 20130101; F04D 29/057 20130101;
C23C 28/345 20130101; F01D 17/162 20130101; F04D 29/0566 20130101;
F05D 2300/509 20130101 |
Class at
Publication: |
415/160 |
International
Class: |
F04D 29/56 20060101
F04D029/56 |
Claims
1. A gas turbine engine component comprising: two or more opposed
surfaces, the opposed surfaces being in frictional contact with
each other; an antifriction coating disposed on one or more of the
opposed surfaces, the antifriction coating comprising a binder and
a friction modifier; and wherein the antifriction coating comprises
a friction modifier and a binder in a weight ratio of friction
modifier to binder greater than or equal to about 1:1.
2. The component of claim 1, wherein the weight ratio of friction
modifier to binder is at least about 1:1 to about 5:1
3. The component of claim 1, wherein the weight ratio of friction
modifier to binder is at least about 1.5:1 to about 3.5:1
4. The component of claim 1, wherein the friction modifier is
selected from the group consisting of tungsten sulfide, bismuth
telluride, bismuth oxide and combinations thereof.
5. The component of claim 1, wherein the binder is selected from
the group consisting of titanium oxide, aluminum phosphate and
combinations thereof.
6. The component of claim 1, wherein the antifriction coating
maintains a coefficient of friction between the opposed surfaces of
less than about 0.95 in atmospheres substantially devoid of water
vapor for at least 500,000 reciprocations.
7. The component of claim 1, wherein the antifriction coating
maintains a coefficient of friction between the opposed surfaces of
less than about 0.95 at temperatures greater than about 400.degree.
F. for at least 500,000 reciprocations.
8. The component of claim 1, wherein antifriction coating causes
the opposed surfaces wear less than about 0.005 inches after at
least 500,000 reciprocations.
9. A variable stator vane comprising: a bushing surface, a vane
surface, the bushing surface and vane surface being in frictional
contact with each other; an antifriction coating disposed on one or
more of the bushing surface and vane surface, the antifriction
coating comprising a binder and a friction modifier; and wherein
the antifriction coating comprises a friction modifier and a binder
in a weight ratio of friction modifier to binder greater than or
equal to about 1:1.
10. The component of claim 9, wherein the vane surface further
comprises a wear coating selected from the group consisting of
nickel-based superalloys, titanium, titanium alloys, cobalt-based
superalloys, iron-based superalloys, stainless steel, tungsten
carbide and combinations thereof disposed thereon.
11. The component of claim 9, wherein the weight ratio of friction
modifier to binder is at least about 1:1 to about 5:1
12. The component of claim 9, wherein the weight ratio of friction
modifier to binder is at least about 1.5:1 to about 3.5:1
13. The component of claim 9, wherein the friction modifier is
selected from the group consisting of tungsten sulfide, bismuth
telluride, bismuth oxide and combinations thereof.
14. The component of claim 9, wherein the binder is selected from
the group consisting of titanium oxide, aluminum phosphate and
combinations thereof.
15. The component of claim 10, wherein the antifriction coating
maintains a coefficient of friction between the bushing surface and
wear coated vane surface of less than about 0.95 in atmospheres
substantially devoid of water vapor for at least 500,000
reciprocations.
16. The component of claim 10, wherein the antifriction coating
maintains a coefficient of friction between the bushing surface and
wear coated vane surface of less than about 0.95 at temperatures
greater than about 400.degree. F. for at least 500,000
reciprocations.
17. The component of claim 10, wherein antifriction coating causes
the opposed surfaces wear less than about 0.005 inches after at
least 500,000 reciprocations.
18. A variable stator vane comprising: a bushing surface, a vane
surface having a wear coating wear coating selected from the group
consisting of nickel-based superalloys, titanium, titanium alloys,
cobalt-based superalloys, iron-based superalloys, stainless steel,
tungsten carbide and combinations thereof disposed thereon, the
bushing surface and wear coated vane surface being in frictional
contact with each other; an antifriction coating disposed on one or
more of the bushing surface and vane surface, the antifriction
coating comprising a binder selected from the group consisting of
titanium oxide, aluminum phosphate and combinations thereof and a
friction modifier selected from the group consisting of tungsten
sulfide, bismuth telluride, bismuth oxide and combinations thereof;
and wherein the antifriction coating comprises a friction modifier
and a binder in a weight ratio of friction modifier to binder
greater than or equal to about 1:1.
19. The component of claim 18, wherein the antifriction coating
maintains a coefficient of friction between the bushing surface and
wear coated vane surface of less than about 0.95 at temperatures
greater than about 400.degree. F. in atmospheres substantially
devoid of water vapor for at least 500,000 reciprocations.
20. The component of claim 18, wherein antifriction coating causes
the bushing surface and wear coated vane surface wear less than
about 0.005 inches after at least 500,000 reciprocations.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation-in-Part of U.S. patent
application Ser. No. 11/015,936 filed on Dec. 17, 2004, claims
priority to that application, which is herein incorporated by
reference in its entirety, which is a continuation-in-Part of U.S.
patent application Ser. No. 10/445,428 filed on May 27, 2003, which
is herein incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to lubricant coatings for
gas turbine engine components and, more particularly, to lubricant
coatings for use with variable stator vanes.
[0003] In a gas turbine engine, air is drawn into the front of the
engine, compressed by a shaft-mounted compressor, and mixed with
fuel. The compressor is made up of several rows or stages of
compressor stator vanes and corresponding rows or stages of
circumferentially rotating compressor rotor blades therebetween.
The stator vane rows are situated between the rotor blade rows and
direct airflow toward downstream rotor blades on the rotor blade
row. After leaving the compressor, the air/fuel mixture is
combusted, and the resulting hot combustion gases are passed
through the turbine section of the engine. The flow of hot
combustion gases turn the turbine by contacting an airfoil portion
of the turbine blade, which in turn rotates the shaft and provides
power to the compressor. The hot exhaust gases exit from the rear
of the engine, driving the engine forward. Optionally, a bypass fan
driven by a shaft extending from the turbine section, which forces
air around the center core of the engine and provides additional
thrust to the engine.
[0004] To increase the operating capacity of the compressor, at
least some of the compressor stator vane rows are designed with
vanes that can rotate in around an axis that is in its longitudinal
direction to adjust the angular orientation of the vane with
respect to the airflow traveling through the compressor. The
adjustment of the angular orientation allows control of the amount
of air flowing through the compressor. Variable stator vane designs
typically allow for about 45.degree. rotation of the stator vane to
optimize compressor performance over the operating envelope of a
gas turbine engine. The variable stator vane structures include an
outer trunnion disposed in a complementary mounting boss in the
stator casing for allowing rotation of the vane relative to the
casing. A lever arm is fixedly joined to a coaxial stem extending
outwardly from the vane trunnion. The distal end of the lever arm
is operatively joined to an actuation ring that controls the angle
of the vane. All of the vane lever arms in a single row are joined
to a common actuation ring for ensuring that all of the variable
vanes are positioned relative to the airflow in the compressor
stage at the same angular orientation.
[0005] A known variable stator vane assembly includes a bushing and
washer disposed between a trunnion attached to a variable vane and
a casing. The bushing and washer decrease the coefficient of
friction between the trunnion and the casing and facilitate
rotation of the vane through the trunnion. The bushing and washer
also help prevent wear of the trunnion and casing. A shroud may
also be placed between the trunnion and casing to prevent wear.
[0006] A number of structures in the gas turbine engine, including
the bushing and washer structures, used with variable stator vanes
are subjected to conditions of wear at temperatures ranging from
low temperatures to highly elevated temperatures. In addition, the
bushing and washers are subject to high altitude atmospheres. In
addition to low temperatures, high altitude atmospheres includes
little or no water vapor. Water vapor is required for conventional
graphite containing lubricants to maintain lubricity.
[0007] Wear occurs when contacting surfaces of two components rub
against each other. Typical results from wear include scoring of
one or both surfaces, and/or material removal from one or both
surfaces. In the bushing and washer system of the variable stator
vane assembly, scoring may occur on one or both of the surface of
the trunnion and the casing, both of which are expensive to repair
and/or replace. As the surfaces are damaged, they become even more
susceptible to the effects of wear as their effective coefficients
of friction rise and wear increases the clearance between the
wearing surfaces, so that the loads are more concentrated and
causes undue motions, so the wear damage accelerates with
increasing time in service. Wear damage may include material, such
as wear debris, removed from the wearing surfaces due to wear, or
may include foreign particles, such as dust or debris from the air
traveling through the engine. As the coefficient of friction
increases between the components of the variable stator vane, more
force is required to rotate the variable stator vane. Therefore, as
the variable stator vane system wears, increased force through the
actuator is required. The increased force requirement causes
additional strain and possible failure of the actuator and/or
results in the need for a larger actuator.
[0008] The wear conditions sometimes arise because it is not
desirable or possible to firmly affix the two components together
to prevent the rubbing action, because of the functionality of the
components. An example is a cylindrical bushing used to support a
variable stator vane in the compressor section of the gas turbine
engine where the element inserted into the bushing (e.g., the vane
trunnion) rotates or slides in contact with the surface of the
bushing.
[0009] When a bushing and washer system fails due to excessive
wear, serious problems for the gas turbine engine compressor may
occur. The failure of the bushing and washer may create an increase
in leakage of compressed air from the interior of the compressor
through the variable stator vane assembly, which results in
performance loss for the compressor. In addition, failure of the
bushing and washer can result in contact between the stator vane
and the casing, which causes wear and increases overhaul costs of
the engine.
[0010] One known material for fabrication of bushing for variable
stator vane assemblies is a specially developed composite of carbon
fiber reinforcing rods in a polyimide resin matrix manufactured by
E. I. Du Pont De Nemours and Company of Wilmington, Del. The
bushings are commonly known as VESPEL.RTM.CP.TM. bushings.
VESPEL.RTM. and CP.TM. are trademarks that are owned by E. I. Du
Pont De Nemours and Company. The polyimide resin used in the
VESPEL.RTM.CP.TM. bushings is commonly known as NR150.TM.. The
NR150.TM. trademark is owned by Cytec Technology Group of
Wilmington, Del. Although the VESPEL.RTM.CP.TM. bushings have an
extended life at temperatures 450-500.degree. F. (232-260.degree.
C.), the VESPEL.RTM.CP.TM. bushing have an upper temperature limit
of 600.degree. F. (316.degree. C.). Extended operation at
temperatures at or above 600.degree. F. (316.degree. C.) limit
their operational life. The polymer matrix bushings do not
withstand the combinations of high temperature and vibrational
loading experienced in the operation of the gas turbine engine
well, leading to a relatively short part life.
[0011] Another known method for reducing wear on the variable
stator vane assembly is placing a carbon-containing antifriction
coating on a surface in the variable stator vane assembly. This
antifriction coating is a coating fabricated from a material that
reduces the coefficient of friction between the surface of the
trunnion and the surface of the casing. One carbon-containing
component known for lubricant coating is graphite. However,
graphite has the disadvantage that water vapor is required to
maintain lubricity. Atmospheres at aircraft cruise altitudes do not
have enough water vapor present for graphite to be lubricious.
Graphite also has the disadvantage of poor tribological properties
in applications that require reciprocating motion. An additional
disadvantage of graphite is that graphite begins to oxidize rapidly
at temperatures at or greater than 500.degree. C. (932.degree. F.).
Some variable stator vane systems may experience temperatures in
excess of 500.degree. C. (932.degree. F.). Therefore, a replacement
material for graphite in antifriction coating is needed.
[0012] Attempts have also been made to coat the stator vane
trunnion with a single wear coating. The single wear coating
attempts to incorporate the low coefficient of friction materials
known in the art with hard, smooth wear resistant coating materials
into a single coating on the vane trunnion. However, the single
wear coating lacks the ability to maintain the properties of each
of the individual components (i.e., fails to maintain both low
coefficient of friction and wear resistance). In other words, the
single wear coating does not provide all of the desired
tribological properties (e.g., reduced wear and low coefficient of
friction) required for extended operation of variable stator vanes
subject to conditions of high temperature, vibration and high
altitude atmospheres.
[0013] There is accordingly a need for an improved approach to the
protection of gas turbine components, such as variable vane
trunnion surfaces, variable vane casing surface or other surfaces
in the gas turbine engine against the damage caused by wear. The
present invention fulfills this need, and further provides related
advantages.
SUMMARY OF THE INVENTION
[0014] The present invention is a gas turbine engine component
having opposed surfaces in frictional contact with each other. An
antifriction coating is disposed on one or more of the opposed
surfaces. The antifriction coating includes a binder and a friction
modifier. The weight ratio of the friction modifier to binder in
the antifriction coating is greater than or equal to about 1:1.
[0015] The present invention also includes a variable stator vane
having a bushing surface, and a vane surface in frictional contact
with each other. An antifriction coating is disposed on one or more
of the bushing surface and vane surface. The antifriction coating
includes a binder and a friction modifier having a weight ratio of
friction modifier to binder greater than or equal to about 1:1.
[0016] The present invention also includes a variable stator vane
having a bushing surface and a vane surface having a wear coating
selected from the group consisting of nickel-based superalloys,
titanium, titanium alloys, cobalt-based superalloys, iron-based
superalloys, stainless steel, tungsten carbide, and combinations
thereof disposed thereon. The bushing surface and wear coated vane
surface are in frictional contact with each other. An antifriction
coating is disposed on one or more of the bushing surface and vane
surface. The antifriction coating includes a binder selected from
the group consisting of titanium oxide, aluminum phosphate and
combinations thereof and a friction modifier selected from the
group consisting of tungsten sulfide, bismuth telluride, bismuth
oxide and combinations thereof. The antifriction coating includes a
friction modifier and a binder in a weight ratio of friction
modifier to binder greater than or equal to about 1:1.
[0017] The variable stator vane assembly having a lubricant
coating, according to the present invention, is subject to reduced
wear while having an improved resistance to vibration and improved
resistance to elevated temperatures, where the variable stator vane
assembly may be utilized at temperatures greater than about
1000.degree. F. (538.degree. C.), including operational
temperatures of greater than about 1200.degree. F. (649.degree.
C.).
[0018] Another advantage of the lubricant coating, according to the
present invention, is that the wear coating and antifriction
coating combination reduces wear and maintains desirable
tribological properties in high altitude atmospheres having little
or no water vapor.
[0019] Another advantage of the lubricant coating, according to the
present invention, is that the variable stator vane assembly
provides an efficiency improvement in the turbine engine while
reducing overhaul costs caused by wear resulting from metal on
metal contact between the stator casing surface and the stator vane
surface.
[0020] Another advantage of the lubricant coating, according to the
present invention, is that the materials used in the variable
stator vane assembly of the present invention, including the
antifriction coating, can readily withstand the higher temperatures
of operation utilized in current advanced engine designs. The
materials used in the antifriction coating of the present invention
can be utilized at temperatures greater than about 1000.degree. F.
(538.degree. C.), including operational temperatures of up to about
1200.degree. F. (649.degree. C.), without significant deterioration
due to the combined effects of temperature, vibration, and high
altitude atmosphere.
[0021] Another advantage of the lubricant coating of the present
invention is that the antifriction coating is capable of
maintaining lubricity in applications that rub in a reciprocating
motion.
[0022] Another advantage of the lubricant coating, according to the
present invention, is that the antifriction coating is resilient
and regenerates in areas where the antifriction coating is rubbed
thin or cleaned off the wear surface.
[0023] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings which illustrate, by way of example, the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic view of a portion of a prior art
high-pressure compressor for a gas turbine engine.
[0025] FIG. 2 is a cross-sectional view of a prior art variable
vane assembly used in an aircraft engine high-pressure
compressor.
[0026] FIG. 3 is a cross-section view of a variable vane bushing
assembly of the present invention used in a variable vane assembly
of the present invention.
[0027] FIGS. 4-6 are schematic views of coating arrangements
according to the present invention.
[0028] Wherever possible, the same reference numbers will be used
throughout the drawings to refer to the same or like parts.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1 is a schematic view of a section of a known
high-pressure compressor 100 for a turbine engine (not shown).
Compressor 100 includes a plurality of stages 102, and each stage
102 includes a row of rotor blades 104 and a row of variable stator
vane assemblies 106. Rotor blades 104 are typically supported by
rotor disks 108, and are connected to a rotor shaft 110. Rotor
shaft 110 is a high-pressure shaft that is also connected to a
high-pressure turbine (not shown). Rotor shaft 110 is surrounded by
a stator casing 112 that supports variable stator vane assemblies
106.
[0030] Each variable stator vane assembly 106 includes a variable
vane 114 and a vane stem 116. Vane stem 116 protrudes through an
opening 118 in casing 112. Variable vane assemblies 106 further
include a lever arm 120 extending from variable vane 114 that is
utilized to rotate variable vanes 114. The orientation of variable
vanes 114 relative to the flow path through compressor 100 control
airflow therethrough. Some variable vane assemblies 106 are secured
to shroud 124 by bolts 122.
[0031] Variable vane assemblies 106 control airflow through
compressor 100. However, variable vane assemblies 106 also provide
a potential pathway for airflow to exit compressor 100, such as
through openings 118. Airflow through openings 118 reduces the
efficiency of compressor 100.
[0032] FIG. 2 is a cross-sectional view of a known variable vane
assembly 200. Variable vane assembly 200 includes a variable vane
202. A bushing 204 is positioned on variable vane 202. A casing 206
supports variable vane 202 and includes a first recessed portion
208, an inner portion 210, and a second recessed portion 212. An
opening 214 is formed by inner portion 210.
[0033] Bushing 204 includes a first portion 216 and a second
portion 218. Bushing first portion 216 is in direct contact with
casing first recessed portion 208 and separates variable vane 202
from casing 206. Bushing second portion 218 contacts casing inner
portion 210 and separates variable vane 202 from casing 206.
Bushing first portion 216 extends substantially an entire length of
casing first recessed portion 208. In addition, bushing second
portion 218 extends substantially an entire length of casing inner
portion 210 and is substantially perpendicular to bushing first
portion 216. Bushing 204 prevents variable vane 202 from directly
contacting casing 206.
[0034] Variable vane assembly 200 further includes a washer 220.
Washer 220 is substantially flat and includes an outer diameter
surface 222 and an inner diameter surface 224. More specifically,
washer 220 includes a first wall 226, a second wall 228, and a
thickness 230 that is substantially constant from outer diameter
surface 222 to inner diameter surface 224. Washer 220 is in direct
contact with casing second recessed portion 212 and extends
substantially an entire length of casing second recessed portion
212.
[0035] Variable vane assembly 200 includes a spacer 232 in contact
with washer 220. Washer 220 prevents contact between spacer 232 and
casing second recessed portion 212. Spacer 232 includes a first
portion 234 and a second portion 236. Spacer first portion 234
contacts washer 220 and has a length substantially equal to a
radial length of washer 220. Spacer 232 is separated from bushing
204 by washer 220. Bushing 204 and washer 220 do not contact each
other. Washer 220 prevents spacer 232 from contacting casing
206.
[0036] Variable vane 202 also includes a first portion 238, a ledge
240 having an outer portion 242, and a spacer-seating portion 244.
Ledge 240 surrounds a vane stem 246. Vane stem 246 (corresponding
to FIG. 1, 116) and ledge 240 extend through opening 214
(corresponding to FIG. 1, 118) in casing 206 (corresponding to FIG.
1, 112). Bushing second portion 218 extends along inner portion 210
of casing 206. Bushing second portion 218 prevents ledge outer
portion 242 from contacting casing inner portion 210.
[0037] Variable vane assembly 200 also includes a lever arm 248
positioned around vane stem 246 and contacting spacer 232. Lever
arm 248 is utilized to adjust the angle of variable vane 202, and
thus alter the flow of air through the compressor.
[0038] In addition, variable vane assembly 200 includes a sleeve
250 contacting lever arm 248, and a lever arm nut 252 contacting
sleeve 250. Lever arm nut 252 cooperates with vane stem 246 and
maintains variable vane assembly 200 in contact with casing
206.
[0039] Variable vane assembly 200 is assembled by placing bushing
204 on variable vane 202 such that first portion 216 and second
portion 218 contact variable vane 202 and are substantially
perpendicular. Variable vane 202 and bushing 204 extend through
opening 214 of casing 206.
[0040] Washer 220 is placed on casing 206 adjacent bushing 204.
Spacer 232 is positioned on variable vane 202 and contacts washer
220. Lever arm 238 is positioned over vane stem 246 and contacts
spacer 232. Sleeve 250 is positioned over vane stem 246 and
contacts lever arm 248. Finally, lever arm nut 252 is positioned
over vane stem 246 and contacts sleeve 250.
[0041] Washer 220 and bushing 204 form a bearing assembly used in
variable vane assembly 200 and may be used, for example, in a
high-pressure compressor. Washer 220 and bushing 204 may be
utilized in other environments such as a rotor vane assembly, a
low-pressure compressor variable vane assembly, a high-pressure
turbine, an intermediate-pressure turbine or a low-pressure
turbine.
[0042] FIG. 3 is a cross-sectional view of variable vane bushing
assembly 310 according to the present invention. Variable vane
bushing assembly 310 includes casing 380 having a substantially
cylindrical opening having a center axis extending through
thickness 385 of casing 380. Vane trunnion 350 and bushing 340 are
disposed inside the cylindrical opening. Casing 380 supports and
allows rotation of trunnion 350 and bushing 340 in casing 380.
Bushing 340 provides a barrier between trunnion 350 and casing 380.
Trunnion 350 rotates about the variable vane bushing assembly
center axis and rubs against bushing 340. Bushing 340 prevents vane
trunnion 350 from directly contacting casing 380, thereby reducing
wear on each of bushing 340 and vane trunnion 350.
[0043] Variable vane bushing assembly 310 also includes a washer
330 disposed between casing 380 and vane button 320. Vane button
320 is located on the surface of the stator vane 355 nominally
perpendicular to the surface of trunnion 350 extending to the edges
of stator vane 355. The upper face of vane button 320, like the
adjacent vane trunnion 350, is coated with a wear coating 360.
Antifriction coating 370 is disposed on wear coated vane button 320
and forms a barrier between washer 330 and wear coated vane button
320. Vane button 320 having wear coating 360 and antifriction
coating 370 rub against washer 330 as vane 355 rotates. Washer 330
is preferably the same material as bushing 340 to promote even wear
of trunnion 350 and vane button 320. Washer 330 contacts casing 380
and bushing 340, and rubs against vane button 320.
[0044] Washer 330 and bushing 340 form a bearing assembly that
facilitates the motion of variable stator vane 355. The relative
motion of trunnion 350 with respect to casing 380 results in
frictional contact between trunnion 350, vane button 320, bushing
340 and casing 380. The wear on trunnion 350 and vane button 320 is
reduced by wear coating 360 and antifriction coating 370. Wear
coating 360 is disposed on trunnion 350 and wear button 320.
Antifriction coating 370 provides a barrier between the surfaces of
bushing 340 and wear coating 360. Antifriction coating 370 may be
disposed on wear coating 360, on bushing 340 or on a combination
thereof.
[0045] In addition to bushing 340, a wear coating 360 and an
antifriction coating 370 are also disposed in between vane trunnion
350 and casing 380. Wear coating 360 is disposed on surface 410
(shown in FIGS. 4-6) of vane trunnion 350 and on the upper face of
vane button 320. Surface 430 (shown in FIGS. 4-6) of the wear
coating 360 and surface 440 (shown in FIGS. 4-6) of bushing 340
form opposed surfaces that are adjacent to each other and are in
frictional contact. Antifriction coating 370 forms a lubricant
coating on the opposed surfaces and is disposed on the inside of
bushing 340, on the wear coated vane trunnion 350, on wear coated
vane button 320 or a combination thereof.
[0046] FIGS. 4-6 shows enlarged cross-sections taken from region
4-4 from FIG. 3. FIGS. 4-6 illustrate different embodiments of the
present invention. The cross sections in FIGS. 4-6 each include
casing 380, trunnion 350, wear coating 360 and antifriction coating
370. In each of FIGS. 4-6, wear coating 360 is disposed on trunnion
350. The surface of the wear coating 360 and the surface of the
trunnion 350 form opposed surfaces onto which antifriction coating
370 may be applied. Wear coating 360 may include, but are not
limited to, tungsten carbide or titanium nitride. FIGS. 4-6
illustrate alternate locations for placement of antifriction
coating 370. Antifriction coating 370 may be disposed on wear
coating 360, on bushing 340, or on a combination thereof.
Antifriction coating 370 may include, but is not limited to
tungsten sulfide, bismuth telluride or bismuth oxide in a binder of
aluminum phosphate or titanium oxide.
[0047] FIG. 4 shows an enlarged cross-section taken from region 4-4
from FIG. 3 showing an embodiment of the present invention. FIG. 4
includes casing 380, bushing 340, antifriction coating 370, wear
coating 360 and trunnion 350. Trunnion 350 rotates inside casing
380 during operation of variable stator vane 355. Bushing 340 is
disposed between trunnion 350 and casing 380 and is subject to
frictional rubbing forces on bushing 340 from rotating trunnion
350. Casing surface 382 and the bushing 340 are in contact and may
experience rubbing due to relative motion of bushing 340 against
casing surface 382. Surface 410 of trunnion 350 includes wear
coating 360 to help reduce wear of trunnion 350. Wear coating 360
may include, but is not limited to, tungsten carbide or titanium
nitride. Trunnion 350 also includes antifriction coating 370
disposed on wear coating surface 430. In the embodiment shown in
FIG. 4, an additional antifriction coating 370 is disposed on
surface 440 of bushing 340. Antifriction coating surfaces 450 are
in frictional contact and rub against each other. The embodiment
shown in FIG. 4 has the benefit that it permits antifriction
coating 370 on bushing 340 to rub against antifriction coating 370
on wear coating surface 430. Antifriction coating surfaces 450 may
contact each other and rub against each other in frictional
contact. The embodiment shown in FIG. 4 has the benefit that
antifriction coating 370 is coated onto wear coating 360 providing
desirable tribological properties. In particular, the combination
of the hard, wear resistant wear coating 360 and the soft,
lubricious antifriction coating 370 provide sliding surfaces that
simultaneously have a low coefficient of friction and increased
wear resistance. The additional antifriction coating 370 on
opposing surfaces 430 and 440 provides additional coating
protection and lubricious properties for each of the bushing
surface 440 and the wear coating surface 430. Additionally, having
antifriction surfaces 450 oppose each other allows additional
material to migrate back and forth along surfaces 450, increasing
uniformity and regeneration of the antifriction coating 370 along
the bushing surface 440 and the wear coating surface 430.
Uniformity and regeneration result from migration of the material
comprising antifriction coating 370 from location to location along
the surfaces, providing uniform distribution of antifriction
coating 370 and regeneration of antifriction coating 370 in areas
having less antifriction coating material.
[0048] FIG. 5 shows an enlarged cross-section taken from region 4-4
from FIG. 3 showing an alternate embodiment of the present
invention. FIG. 5 shows casing 380, bushing 340, wear coating 360,
and vane trunnion 350, substantially as described above with
respect to FIG. 4. As in the embodiment illustrated in FIG. 4, wear
coating 360 is disposed on surface 410 of vane trunnion 350. Casing
surface 382 and bushing 340 are in contact and may experience
rubbing due to relative motion of bushing 340 against casing
surface 382. In the embodiment illustrated by FIG. 5, the surface
440 of bushing 340 is coated with an antifriction coating 370.
Unlike the embodiment shown in FIG. 4, no antifriction coating 370
is present on the wear coating 360. The antifriction coating
surface 450 and surface 430 of the wear coating 360 may contact
each other and rub against each other in frictional contact. The
embodiment shown in FIG. 5 has the benefit that antifriction
coating 370 is coated onto bushing 340. Bushing 340 is removable
from casing 380, making replenishment of the coatings 370
relatively simple by replacing the entire coated bushing 340. This
can be done without opening the compressor case and removing the
vane 355. Therefore, the application of antifriction coating 370
requires less equipment and labor than applying antifriction
coating 370 to surface 430 of wear coating 360. Additionally,
material comprising antifriction coating 370 migrates from location
to location along surface 440 of bushing 340, providing uniform
distribution of antifriction coating 370 and regeneration of
antifriction coating 370 in areas having less antifriction coating
material. In service, bushing 340 can be readily replaced with a
replacement bushing carrying a fresh supply of antifriction coating
370.
[0049] FIG. 6 shows an enlarged cross-section taken from region 4-4
from FIG. 3 showing an alternate embodiment of the present
invention. FIG. 6 shows casing 380, bushing 340, wear coating 360
and vane trunnion 350 substantially as described above with respect
to FIG. 4. As in the embodiment illustrated in FIG. 4, wear coating
360 is disposed on surface 410 of vane trunnion 350. Casing surface
382 and bushing 340 are in contact and may experience rubbing due
to relative motion of bushing 340 against casing surface 382. In
the embodiment illustrated by FIG. 6, surface 430 of wear coating
360 is coated with antifriction coating 370. Unlike FIGS. 4 and 5,
no antifriction coating 370 is initially present on bushing 340. In
this embodiment, surface 450 of antifriction coating 370 and
surface 440 of bushing 340 may contact each other and rub against
each other in frictional contact. The embodiment shown in FIG. 6
has the benefit that antifriction coating 370 is coated onto wear
coating 360 providing desirable tribological properties. In
particular, the combination of the hard, wear resistant wear
coating 360 and the soft, lubricious antifriction coating 370
provide sliding surfaces that simultaneously have a low coefficient
of friction and increased wear resistance. Additionally, material
making up antifriction coating 370 migrates from location to
location along the surface 430 of wear coating 360, providing
uniform distribution of antifriction coating 370 and regeneration
of antifriction coating 370 in areas having less antifriction
coating material. Applying antifriction coatings 370 to the entire
vane trunnion 350 and upper face of the vane button 320 is a simple
procedure. Inspection of the coating in those areas is also simple
due to easy accessibility.
[0050] While FIG. 3 illustrates a bushing 340 and washer 330
configuration with an elongated cylindrical opening through the
casing 380, which is known as a high boss design, the coating
systems of the present invention are suitable for any variable
stator vane configurations known in the art having wear surfaces.
The alternate variable stator vane configurations include, but are
not limited to, bushing arrangements with a shortened openings
through the casing, which is known as low boss designs, bushing
arrangements having more than one bushing, bushing arrangements
having multiple bores through the casing, variable stator vane
bearing arrangements having no bushings or wear surfaces other than
bushings and combinations thereof. The present invention utilizes
the combination of the relatively hard wear coating 360 in
combination with a separate, relatively soft, lubricious
antifriction coating 370, which may be placed on wear surfaces,
including wear coatings 360 and component surfaces, within the
variable stator vane assembly.
[0051] One embodiment of the present invention includes a variable
stator vane assembly 310 having a vane structure 355 at least
partially disposed inside an opening in a casing 380, a wear
coating 360 on at least a portion of the surface of the vane
structure, an antifriction coating 370 on at least a portion of the
wear coating 360, and a bushing 340 disposed between the
antifriction coating 370 and the casing 380. During engine
operation, the antifriction coating 370 maintains a low coefficient
of friction in high altitude atmospheres. The coefficient of
friction maintained in the wear system of the variable stator vane
in operating conditions (e.g., high temperature, high vibration,
and high altitude atmosphere exposure) is equal to or less than 0.6
and preferably equal or less than 0.4. The coefficient of friction
is measured between the two surfaces rubbing against each other
within the variable stator vane assembly 310. In the embodiment of
the present invention shown in FIG. 4, the coefficient of friction
between antifriction coating 370 on bushing 340 and antifriction
coating 370 on wear coating 360, is less than or equal to about
0.6. In the embodiment of the present invention shown in FIG. 5,
the coefficient of friction between antifriction coating 370 and
wear coating 360, is less than or equal to about 0.6. In the
embodiment of the present invention shown in FIG. 6, the
coefficient of friction between antifriction coating 370 and
bushing 340, is less than or equal to about 0.6.
[0052] The vane structure includes a vane trunnion 350 that is
attached to the variable vane 355 and is at least partially
disposed inside an opening in the casing 380. The vane structure,
including the vane 355 and trunnion 350, may be fabricated from any
suitable material, including but not limited to metals and metal
alloys. Preferred materials include nickel-based superalloys,
titanium and its alloys, cobalt-based superalloys, iron-based
superalloys, stainless steel and combinations thereof. The variable
stator vane assembly 310 utilizes a bushing 340 to reduce wear
between the vane trunnion 350 and the casing 380. The bushing may
include a material selected from the group consisting of silicon
nitride (e.g., Si.sub.3N.sub.4), tungsten carbide (e.g., WC)
titanium carbide (e.g., TiC), cobalt-chromium-molybdenum alloys,
zirconium oxide (e.g., ZrO.sub.2) and combinations thereof. These
bushings 340 are strong but relatively inflexible.
[0053] Wear coatings 360 are provided on metal surfaces to provide
a surface 430 having desirable wear properties, such as high
hardness and wear resistance. Materials used in the variable stator
vane system 310 include materials that are suitable for receiving
the wear coatings 360. Suitable material for receiving wear
coatings 360 may include, but are not limited to, nickel-based
superalloys, titanium and its alloys, cobalt-based superalloys,
iron-based superalloys and stainless steel. Wear coatings 360
provide a surface 430 that has the properties of being both hard
and smooth and capable of receiving an antifriction coating 370. In
one embodiment of the present invention, the vane trunnion 350 is
coated with a cemented tungsten carbide. Cemented tungsten carbides
include those tungsten carbides that include a sufficient amount of
cobalt to impart wear resistance. Sufficient amounts of cobalt are
typically about 6-20% by weight and preferably about 12% by weight.
The wear coating 360 may be applied by a plasma spray technique or
other suitable method known in the art. A suitable plasma spray
technique is high velocity oxy-fuel (HVOF) spraying, although other
plasma spray techniques such as low-pressure plasma spray (LPPS)
and air plasma spraying (APS) may be used to successfully apply the
coating. Alternatively, the trunnion 350 may be coated with a
physical vapor deposition (PVD) deposited wear coating 360 of
titanium nitride or tungsten carbide. The preferred coating is a
relatively thin wear coating 360 of titanium nitride or tungsten
carbide applied by PVD. These wear coatings 360 may be applied to a
thickness as low as about 0.0002 inches and as high as about 0.010.
Preferably, the coating thicknesses are in the range from about
0.0005 to about 0.005 inches, most preferably coating thickness of
about 0.001 inches. The resultant wear coating 360 is a hard,
smooth surface resistant to wear.
[0054] The present invention also utilizes an antifriction coating
370 placed between the wear coated bushing 340 and the vane
trunnion 350. The antifriction coating 370 is preferably coated on
surface 430 of the wear coating 360. However, the antifriction
coating 370 may be coated on the surface of the bushing 340.
[0055] The antifriction coating 370 comprises a binder, a friction
modifying agent, and, optionally, an additive. The binder of the
antifriction coating 370 comprises a material selected from the
group consisting of sodium silicate, aluminum phosphate, titanium
oxide and combinations thereof. The friction-modifying agent is
preferably dispersed substantially uniformly through the binder.
The antifriction coating 370 reduces the coefficient of friction
between bushing 340 and wear coating 360. Of the antifriction
coating binders, aluminum phosphate and titanium oxide are
preferred. As the variable stator vane bushing assembly 310
operates, the antifriction coating 370 may eventually be consumed.
The antifriction coating 370 is resilient and regenerates in areas
where the coating is rubbed thin or cleaned off the wear surface.
The antifriction coating 370 is thin when the thickness on a
portion of the surface is insufficient to provide sufficient
lubricity to the sliding surfaces to maintain the coefficient of
friction at the desired level. During operation, the antifriction
coating 370 may migrate from location to location along the wear
surface. The migration of the antifriction coating 370 allows areas
that have less material or are rubbed completely off to receive
antifriction coating material from other locations along the wear
surface to regenerate the coating missing from the area rubbed thin
or completely off.
[0056] The binder material for use in the antifriction coating 370
is any binder material that is tribologically compatible with all
of the following materials: 1) water, 2) detergents used in the
cleaning of gas turbine engine parts, 3) deicers known in the art
used to deice aircraft in winter, 4) aircraft fuel, 5) oil and 6)
hydraulic fluid. The materials are tribologically compatible if the
binder in the antifriction coating 370 maintains tribological
properties (e.g., lubricity and wear resistance) of the
antifriction coating 370 when in contact with the surfaces
subjected to sliding friction and in contact with the materials
listed above. In order to maintain tribilogical properties, the
binder exhibits the ability to remain coated on the substrate, does
not result in separation of the friction modifier and the binder,
and does not result in substantial softening of the antifriction
coating. Suitable binder materials include, but are not limited to,
sodium silicate, aluminum phosphate, titanium oxide and
combinations thereof. Binders that provide the highest tribological
compatibility include titanium oxide and aluminum phosphate.
[0057] The friction modifier is any material that, when added to
the binder, produces a friction coefficient suitable for rotating a
stator vane in a variable stator vane assembly, capable of
maintaining desirable tribological properties at high altitude
atmospheres and and/or high temperatures. The high altitude
atmospheres include atmospheres to which aircraft are exposed
during flight. The high altitude atmosphere includes atmospheres
having reduced water vapor. High temperature exposure is a result
of the operation of the gas turbine engine. The compression of the
gas and the combustion of the fuel result in high temperatures in
gas turbine engines. Parts within the gas turbine engine are
subject to high temperatures. The coating system of the present
invention may find uses in parts within the gas turbine engine that
are exposed to temperatures up to about 1200.degree. F. Desirable
tribological properties include, but are not limited to low
coefficient of friction between sliding surfaces (i.e., high
lubricity) and low wear between sliding surfaces. Suitable friction
modifier materials include, but are not limited to, tungsten
sulfide (e.g., WS.sub.2), bismuth telluride (e.g.,
Bi.sub.2Te.sub.3), copper sulfide (e.g., Cu.sub.2S), bismuth oxide
(e.g., Bi.sub.2O.sub.3) and combinations thereof. Of the friction
modifiers, tungsten sulfide (e.g., WS.sub.2), bismuth telluride
(e.g., Bi.sub.2Te.sub.3) and bismuth oxide (e.g., Bi.sub.2O.sub.3)
are preferred.
[0058] Table 1 shows examples of antifriction coating materials
according to the present invention. The examples shown are merely
examples and do not limit the invention to the combinations of
binders and friction modifiers shown therein. Examples 1-5, shown
in Table 1, include coefficient of friction (COF) results for
particular friction modifier and binder combinations. In order to
determine the coefficient of friction, the antifriction coating
materials are subject to a sliding wear test as known in the art.
The tests were conducted with a reciprocating stroke length of
0.060 inches. Antifriction coating material (i.e., inert material,
binder and friction modifier) were loaded onto the wear surfaces
and dried to form an antifriction coating 370. The coated wear
surfaces were then subject to a load of 50 lbs. and reciprocation
motion. The coefficients of friction were measured at various
temperatures during the test and an average coefficient (i.e., Avg
COF) of friction was calculated as the coefficient of friction for
the wear system. Table 1 shows the an average coefficient of
friction for each example having the average coefficient of
friction resulting from tests run at various friction modifier to
binder loadings. The antifriction coating 370 was formed from
drying a composition on the test surface having a binder loading of
10% by weight and friction modifier loadings of from 15% by weight
to 25%, corresponding to friction modifier to binder weight ratios
of from 1.5:1 to about 2.5:1. The balance of the composition is of
essentially inert material that is removed during drying.
TABLE-US-00001 TABLE 1 COF Binder Friction COF room COF at COF at
Avg Ex. 10% Modifier Initial temp. 400.degree. F. 750.degree. F.
COF 1 titanium tungsten 0.2 0.5 0.4 0.6 0.43 oxide sulfide 2
titanium bismuth 0.3 0.7 0.7 0.6 0.58 oxide telluride 3 titanium
bismuth 0.2 0.7 0.7 0.6 0.55 oxide oxide 4 titanium copper 0.3 0.6
0.7 0.6 0.55 oxide sulfide 5 aluminum tungsten 0.3 0.4 0.5 0.5 0.43
phosphate sulfide
[0059] The friction modifier is preferably incorporated into
antifriction coating in a quantity of about 10% to about 500% by
weight of binder. More preferably, the friction modifier is
incorporated into the antifriction coating from 100% to about 350%
by weight of binder. The friction modifier is incorporated into the
binder material and is preferably encapsulated in the binder
material. Encapsulation may take place using any suitable
encapsulation method, including but not limited to powder
metallurgical encapsulation methods. The antifriction coating
including the binder and friction modifier is coated onto the
surfaces subject to wear (i.e., wear surface). Suitable methods for
coating include, but are not limited to, spraying or dipping the
surface to be coated with an antifriction coating 370 and
subsequently drying the antifriction coating 370, removing at least
some of the inert material present. The dried surface forms an
antifriction coating 370 that is tenacious and substantially
uniform across the wear surface. Optionally, the antifriction
coating 370 may be heated during the drying step. Table 2 shows the
average coefficient of friction and wear in inches for various
friction modifier loadings in the coating composition. In addition,
Table 2 shows the average number of sliding cycles (i.e.
reciprocations) used in Examples 6-11 at room temperature,
400.degree. F. (204.degree. C.), and 750.degree. F. (399.degree.
C.), which resulted in the average wear shown. TABLE-US-00002 TABLE
2 Friction Friction Modifier Average Average Binder Friction
Modifier to Binder Avg Wear Sliding Ex. (10% Loading) Modifier
Loading (%) Weight Ratio COF (inches) Cycles 6 titanium tungsten 25
2.5:1 0.47 0.001-0005 575,000 oxide sulfide 7 titanium tungsten 30
3.0:1 0.59 0.001-0.005 600,000 oxide sulfide 8 titanium tungsten 35
3.5:1 0.40 0.001-0.005 625,000 oxide sulfide 9 titanium bismuth 25
2.5:1 0.59 0.001-0.004 350,000 oxide telluride 10 titanium bismuth
30 3.0:1 0.54 0.001-0.004 362,500 oxide telluride 11 titanium
bismuth 35 3.5:1 0.55 0.001-0.004 312,500 oxide telluride
[0060] Although the average shown in Table 2 range from 350,000 to
635,000 cycles, in each of Examples 6-11, 1,000,000 sliding cycles
were made at 750.degree. F. (399.degree. C.).
[0061] The variable stator vane assembly 310 of the present
invention having the wear coating 360, antifriction coating 370 and
bushing 340 opposed surface combination preferably also is
resistant to wear over the entire operating temperature range of
the variable stator vane 355. In one embodiment of the present
invention, the opposed surfaces wear less than about 0.005 inches
after at least 500,000 reciprocations (i.e., cycles). In another
embodiment, the wear coating 360 and antifriction coating 370
combination according to the present invention results in wear to
the vane assembly of less than about 0.005 inches over 2 million
reciprocations (i.e., cycles) at temperatures up to about
800.degree. F. Where each cycle or reciprocation comprises one
movement in the reciprocating back and forth motion.
[0062] The variable stator vane assembly 310 of the present
invention having the wear coating 360 and antifriction coating 370
combination preferably maintains a friction coefficient between the
sliding surfaces at or below about 0.6 over the entire operating
range of the variable stator vane 355. More preferably, the
variable stator vane assembly 310 of the present invention
maintains a friction coefficient between the sliding surfaces of
below about 0.5 over the entire operating range of the variable
stator vane 355. In particular, the antifriction coating 370 of the
present invention preferably maintains a coefficient of friction of
less than about 0.5 when in contact with the surface 430 of the
wear coating or the surface 440 of the bushing 340 in a
reciprocating motion under a load at temperatures up to 800.degree.
F. (427.degree. C.).
[0063] In another embodiment of the present invention, additives
may be included in the antifriction coating 370 to provide
additional desirable properties for the coating. The additional
additive is an additive that provides desirable properties, such as
increased lubricity, increased adhesion, or increased coating
uniformity, to the composition. Suitable additional additives
include, but are not limited to, polytetrafluoroethylene, adhesion
promoters, dispersing agents and combinations thereof. Examples of
additional additives include graphite, molybdenum sulfide,
molybdenum diselenide and copper.
[0064] The combination of the wear coating 360 and antifriction
coating 370 of the present invention assure reduced coefficients of
friction, in the range of about 0.2 to about 0.6, over the life of
the system. This is significant, as some conventional gas turbine
engine systems have been designed to accommodate coefficients of
friction as high as about 0.95, which occur as bushing and wear
materials deteriorate during normal engine operation. Improvements
in coefficient of friction permit the reduction in size, and hence
weight of the actuation mechanism of the variable guide vanes,
including the lever arms. Although the above embodiment have been
described with respect to a variable stator vane bushing
arrangement, the coating system of the present invention may be
used with any sliding surfaces that require lubrication. The
coating system of the present invention is particularly useful for
sliding application that are exposed to higher temperatures,
including temperatures from about 400.degree. F. (204.degree. C.)
up to about 1200.degree. F. (649.degree. C.) and atmospheres of
substantially devoid of water vapor. The antifriction coating 370
preferably maintains a coefficient of friction between the opposed
surfaces of less than about 0.95 at temperatures greater than about
400.degree. F. and/or devoid of water vapor for at least 500,000
reciprocations. Alternate systems that find use with the present
invention include actuator mechanisms, dovetail surfaces of
airfoils and disks and other surfaces where a low coefficient of
friction is required or desirable.
[0065] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *