U.S. patent application number 15/100606 was filed with the patent office on 2016-12-29 for high temperature use of a self lubricating coating material in a foil bearing and part coated with such a material.
This patent application is currently assigned to LIEBHERR-AEROSPACE TOULOUSE SAS. The applicant listed for this patent is LIEBHERR-AEROSPACE TOULOUSE SAS. Invention is credited to Gregory GRAU, Jerome ROCCHI.
Application Number | 20160377119 15/100606 |
Document ID | / |
Family ID | 50473422 |
Filed Date | 2016-12-29 |
United States Patent
Application |
20160377119 |
Kind Code |
A1 |
ROCCHI; Jerome ; et
al. |
December 29, 2016 |
HIGH TEMPERATURE USE OF A SELF LUBRICATING COATING MATERIAL IN A
FOIL BEARING AND PART COATED WITH SUCH A MATERIAL
Abstract
High temperature use of a self lubricating coating material in a
foil bearing and part coated with such a material. A material
according to the disclosure includes between 50 and 90 wt % of
alumina (Al2O3), as well as an oxide selected from the group
consisting of titanium oxide (TiO2), chromium oxide (Cr2O3), and a
mixture of these. Application to a rotor and/or a thrust disc at
least partially covered with such a material.
Inventors: |
ROCCHI; Jerome;
(Roqueseriere, FR) ; GRAU; Gregory; (Castelmayran,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LIEBHERR-AEROSPACE TOULOUSE SAS |
Toulouse |
|
FR |
|
|
Assignee: |
LIEBHERR-AEROSPACE TOULOUSE
SAS
Toulouse
FR
|
Family ID: |
50473422 |
Appl. No.: |
15/100606 |
Filed: |
December 5, 2014 |
PCT Filed: |
December 5, 2014 |
PCT NO: |
PCT/EP2014/076705 |
371 Date: |
September 8, 2016 |
Current U.S.
Class: |
384/105 |
Current CPC
Class: |
F16C 2206/42 20130101;
C23C 4/11 20160101; F16C 2223/42 20130101; F16C 2360/00 20130101;
F16C 33/1095 20130101; F16C 17/042 20130101; F16C 2206/44 20130101;
C23C 4/134 20160101; F16C 2202/50 20130101; F16C 17/024 20130101;
F16C 33/043 20130101 |
International
Class: |
F16C 33/10 20060101
F16C033/10; C23C 4/11 20060101 C23C004/11; C23C 4/134 20060101
C23C004/134; F16C 17/04 20060101 F16C017/04; F16C 33/04 20060101
F16C033/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2013 |
FR |
1362190 |
Claims
1. Use of a coating comprising between 50 and 90 wt % of alumina
(Al.sub.2O.sub.3) and an oxide selected from the group consisting
of: titanium oxide (TiO.sub.2), chromium oxide (Cr.sub.2O.sub.3),
and a mixture of thereof, as a self-lubricating coating for the
high-temperature use of a rotor in a foil bearing.
2. The use of a coating according to claim 1, wherein the coating
consists of a mixture of 50 to 90 wt % of alumina (Al.sub.2O.sub.3)
with an oxide selected from the group consisting of: titanium oxide
(TiO.sub.2), chromium oxide (Cr.sub.2O.sub.3), and a mixture
thereof.
3. The use of a coating according to claim 2, wherein the coating
consists of a mixture of alumina (Al.sub.2O.sub.3) and titanium
oxide (TiO.sub.2).
4. The use of a coating according to claim 1, wherein the coating
comprises between 65 and 75 wt % of alumina (Al.sub.2O.sub.3).
5. Turbomachine part comprising a circular cylindrical bearing,
wherein said bearing is at least partially coated with a
self-lubricating coating comprising between 50 and 90 wt % of
alumina (Al.sub.2O.sub.3) as well as an oxide selected from the
group consisting of: titanium oxide (TiO.sub.2), chromium oxide
(Cr.sub.2O.sub.3), and a mixture thereof.
6. The turbomachine part according to claim 5, wherein said
self-lubricating coating is deposited by an air plasma spraying
process, the coated surface then being ground.
7. The turbomachine part according to claim 5, selected from the
group of parts consisting of: rotors and thrust discs.
8. Turbomachine comprising a turbomachine part according to claim
5.
9. The turbomachine according to claim 8, comprising a foil-air
bearing having a housing which accommodates, on the one hand, a
circular cylindrical portion of a turbomachine part, said circular
cylindrical portion being at least partially coated with a
self-lubricating coating comprising between 50 and 90 wt % of
alumina (Al.sub.2O.sub.3) and an oxide selected from the group
consisting of: titanium oxide (TiO.sub.2), chromium oxide
(Cr.sub.2O.sub.3), and a mixture thereof, and on the other hand at
least one foil, called the top foil, coming to face said circular
cylindrical portion, said top foil being untreated.
10. Air conditioning device, wherein said air conditioning device
comprises a turbomachine according to claim 8.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a self-lubricating coating
material for high-temperature use and to a part coated with such a
material.
BACKGROUND
[0002] Most turbomachinery reaches very high rotational speeds, for
example from 20,000 to 120,000 revolutions per minute (rpm). To
guide a rotor rotating at such speeds, it is conventional to use
foil bearings instead of conventional ball bearings which are not
compatible with such rotational speeds. A film of ambient air is
used to support a rotor which is thus "levitated" relative to a
fixed housing. Such a bearing is therefore also called a foil-air
bearing.
[0003] When the rotor rotates at high speed, there is no contact
between the various solid components of the bearing. However,
before and after a phase of high-speed rotation, at startup or
shutdown, the film of air which serves as a bearing has not been
formed in the stationary housing, and a foil, called the top foil,
of the foil bearing is in local contact with both the rotor and the
fixed housing that receives them. Means to limit friction between
these elements should then be provided at the contact surfaces.
[0004] It is known to use PTFE (Polytetrafluoroethylene) as a
lubricant to prevent wear of the parts in a foil bearing during the
startup and shutdown phases. This material is usually covering a
foil of the bearing which faces the rotating part, also called the
top foil, and has good performance at relatively low temperatures
but cannot be used at high temperatures (above 200.degree. C. or
so).
[0005] When the rotor is part of a machine with a relatively
powerful electric motor, the motor is a source of heat. The ambient
air used for ventilation in this machine is then hot air. Due to
the heat of the motor plus the heat locally generated by friction,
insufficient heat dissipation may occur and high temperatures of
around 300 to 400.degree. C. can be reached.
[0006] U.S. Pat. No. 5,866,518 proposes a composite
self-lubricating material to reduce friction and wear which can be
used over a very wide temperature range, from cryogenic
temperatures to temperatures up to 900.degree. C. This material
comprises 60 to 80 wt % (percentage by weight) of chromium oxide
dispersed in a metal binder of an alloy containing chromium and
possibly nickel as well as 5 to 20 wt % of a fluoride from groups I
or II, or a rare earth metal and possibly a metal lubricant.
[0007] U.S. Pat. No. 7,297,367 relates to a method for applying an
inorganic lubricant coating deposited on a top foil of a foil
bearing in order to withstand higher temperatures than inorganic
coatings of the prior art. The coating is applied by spraying or by
immersion.
[0008] The present invention therefore aims to provide a new
coating to protect the foil(s) of a foil bearing from wear and to
withstand high temperatures.
SUMMARY
[0009] The invention relates to protecting the usually uncoated top
foil of the bearing from wear. It also preferably relates to
providing protection for thrust discs which may also be subjected
to friction.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0010] To this end, the invention proposes the use of a coating
comprising between 50 and 90 wt % of alumina (Al2O3) and an oxide
selected from the group consisting of titanium oxide (TiO2),
chromium oxide (Cr2O3), and a mixture of these, as a
self-lubricating coating for the high-temperature use of a rotor in
a foil bearing.
[0011] Tests have shown that such a coating, preferably purely
ceramic and without metal binder, has good lubricating properties
and is particularly well-suited for withstanding high temperatures.
A preferred embodiment provides that the coating used consists of a
mixture of 50 and 90 wt % of alumina (Al2O3) with an oxide selected
from the group consisting of titanium oxide (TiO2), chromium oxide
(Cr2O3), and a mixture of these.
[0012] In a preferred embodiment, the coating of the invention is a
mixture of alumina (Al2O3) and titanium oxide (TiO2). Tests have
shown that titanium oxide is preferred to chromium oxide which,
however, also achieves good performance in terms of lubrication and
resistance at high temperatures. According to these tests, the
coating preferably comprises between 65 and 75 wt % of alumina
(Al2O3).
[0013] The invention also relates to a turbomachine part,
comprising a circular cylindrical bearing which is at least
partially coated with a self-lubricating coating as described
above, in other words a coating comprising between 50 and 90 wt %
of alumina (Al2O3) as well as an oxide selected from the group
consisting of titanium oxide (TiO2), chromium oxide (Cr2O3), and a
mixture of these.
[0014] Such a turbomachine part can be such that its
self-lubricating coating is deposited by a thermal spraying process
followed by grinding. The thermal spraying process is preferably an
air plasma spraying process.
[0015] A turbomachine part according to the invention is, for
example, selected from the group of parts comprising rotors and
thrust discs.
[0016] The invention further relates to a turbomachine,
characterized in that it comprises a turbomachine part as described
above. Such a turbomachine then preferably comprises a foil-air
bearing having a housing which accommodates, on the one hand, a
circular cylindrical portion of a turbomachine part, said circular
cylindrical portion being at least partially coated with a
self-lubricating coating comprising between 50 and 90 wt % of
alumina (Al2O3) and an oxide selected from the group consisting of
titanium oxide (TiO2), chromium oxide (Cr2O3), and a mixture of
these, and on the other hand at least one foil, called the top
foil, coming to face said circular cylindrical portion, said top
foil being untreated.
[0017] Finally, the invention relates to an air conditioning
device, characterized in that it comprises a turbomachine as
described in the preceding paragraph.
[0018] Details and advantages of the invention will become clear
from the following description which presents a particular
embodiment of the invention.
[0019] The invention relates more particularly to the introduction
of a self-lubricating coating onto a rotor or a thrust disc of a
turbomachine in which the parts can rotate at high speeds (for
example greater than 60,000 rpm). Such a turbomachine may or may
not be powered electrically. Parts rotating at such high speeds, or
the rotor, are usually mounted on foil bearings and the invention
relates more particularly to machines comprising at least one
bearing of this type.
[0020] A foil bearing, or foil-air bearing, comprises a housing
which accommodates a circular cylindrical portion of a rotor. At
very high speeds, a film of air forms between the housing and the
cylindrical portion, which prevents contact of the cylindrical
portion with the inner wall of the corresponding housing. However,
contact may occur when a steady state is not yet established. It is
therefore arranged to have a sheet of lubricant material to prevent
wear of the housing and/or of the corresponding cylindrical
portion. This sheet provides lubrication of the bearing in the
startup and shutdown phases of the rotating part.
[0021] Documents U.S. Pat. No. 7,297,367 and WO 2007/004770 show
two different types of foil bearings to which the present invention
can be applied. Other types of bearings allowing (very) high
rotational speeds can also be concerned by the present
invention.
[0022] A thrust disc is generally associated with a bearing and is
intended to prevent longitudinal movement of the rotating part.
Here too, it is necessary to provide lubrication to prevent
premature wear of the thrust discs during the transitional phases
(turbomachine startup and shutdown).
[0023] The invention proposes coating a rotor and/or a thrust disc,
or at least the circular cylindrical portion of a rotor and/or a
face of a thrust disc accommodated by a bearing, with a
self-lubricating coating that allows withstanding high temperatures
(for example up to 400.degree. C.).
[0024] The proposed coating, in a preferred embodiment, is composed
of alumina (Al2O3) and titanium oxide (TiO2) and is applied by a
thermal spraying process. This coating then has the aim of
protecting from wear the coated parts in a foil-air bearing and the
parts coming into contact with these coated parts, in an
environment where the temperature can vary from -50.degree. C. to
+400.degree. C., particularly during transition phases (startup,
shutdown, and possibly changes in rotation speed).
[0025] While it is usual to coat a top foil of a foil-air bearing
with lubricating material, the invention proposes keeping this top
foil untreated, the top foil being the foil of the bearing that
comes to face the circular cylindrical portion of the rotating
body. The top foil therefore has no coating.
[0026] First, the invention concerns the coating itself. As
indicated, in a preferred embodiment the coating comprises alumina
and titanium oxide. The proportion of alumina (Al2O3) is between 50
and 90 wt % of the coating. In a preferred embodiment, this
proportion is around 70%, for example between 65 and 75 wt % of the
mixture forming the coating.
[0027] In the coating, titanium oxide (TiO2) is present in addition
to the alumina. A preferred embodiment proposes 70 wt % of alumina
(Al2O3) and 30 wt % of titanium oxide (TiO2).
[0028] According to an alternative embodiment of the invention, all
or part of the titanium oxide may be replaced by chromium oxide
(Cr2O3). The coating may thus consist of alumina (50 to 90 wt %),
and titanium oxide (0 to 50 wt %) and/or chromium oxide (0 to 50 wt
%).
[0029] Thus a coating according to the preferred embodiment of the
present invention contains only "hard" ceramics, and no metal
binder between these ceramics is provided.
[0030] Comparative tests were performed using a coating according
to the preferred embodiment of the invention and a reference
coating of the prior art. The selected coating of the prior art
bears the reference PS304. It corresponds to a category described
in U.S. Pat. No. 5,866,518. Its composition corresponds to a
mixture of four components: 60 wt % of NiCr as matrix, 20 wt % of
Cr2O3 to ensure wear resistance, chemical stability, and high
resistance to oxidation, 10 wt % of Ag as lubricant, and 10 wt % of
the eutectic BaF2/CaF2 as high-temperature lubricant.
[0031] Resisting torque measurements were made at a temperature of
300.degree. C. While the maximum resisting torque is between 0.30
and 0.35 Nm with a coating of the prior art, it is between 0.25 and
0.30 Nm with a coating according to the invention. As for the
residual resisting torque, this is substantially zero with a
coating of the invention while it is about 0.01 Nm with a coating
of the prior art.
[0032] The friction coefficients were also measured. At low
temperatures (20.degree. C.), the friction coefficient with a
mixture of Al2O3 and TiO2 according to the invention is higher
(0.19 versus 0.17); however, at higher temperatures the friction
coefficient decreases with the invention to about 0.13 at
300.degree. C., while this coefficient remains almost unchanged at
300.degree. C. (about 0.19) for the PS304 coating.
[0033] In terms of wear, the coating according to the invention is
of particular interest. The wear of the coating was measured in
.mu.m3 on a shaft after 10,000 cycles and after 100,000 cycles.
With a coating of the invention, in both cases the wear is limited
to a few (less than 10) .mu.m3, while it is about 150 .mu.m3 at
10,000 cycles, a wear considered too high to allow testing at
100,000 cycles.
[0034] These various tests show the excellent performance obtained
with a coating according to the invention, especially in high
temperature ranges. Such performance is unexpected and thus
illustrates the interest of the invention.
[0035] The invention also relates to a turbomachine part at least
partially coated with a ceramic self-lubricating coating as
described above.
[0036] This turbomachine part is, for example, a rotor or at least
a circular cylindrical portion of a rotor intended to be placed in
a foil-air bearing.
[0037] This turbomachine part may also be a thrust disc, in
particular a thrust disc used in combination with a foil-air
bearing. It may be arranged that at least one face of the thrust
disc intended to face the bearing with which is it associated is
coated with a self-lubricating coating.
[0038] The turbomachine containing the bearing and a rotor and/or a
thrust disc according to the invention may be any type of
turbomachine. In particular, it may be a turbomachine driven by an
electric motor or a turbomachine driven by a stream of air. The
invention also relates to such a turbomachine.
[0039] The coating described above may be applied to a rotor or to
a thrust disc (or a rotor portion or a thrust disc portion), for
example by any type of thermal spraying process. Preferably, this
coating is applied by an air plasma spraying process.
[0040] After spraying the coating on the rotor or on the thrust
disc (or at least on a portion of the rotor or disk), the coated
surface of the part is ground and/or finished by a vibratory
finishing process.
[0041] The invention thus enables an air bearing to operate at
higher temperatures than bearings of the prior art that use
fluoropolymer coatings. A coating according to the invention can be
used at temperatures up to at least 400.degree. C., which are the
temperatures encountered at very high rotational speeds and/or in
electrically driven turbomachinery.
[0042] Indeed, during operation of an air bearing when the
rotational speed increases, the shear of the aerodynamic film also
increases. When high speeds are reached, significant thermal
heating therefore occurs which causes an increase in the
temperature at the bearing (and at the thrust disc).
[0043] In addition, in electrically driven machines, the heat
generated by the motor warms the ambient air and also leads to a
temperature increase at the air bearings and thrust discs.
[0044] The invention allows working at high temperatures. Tests
have also demonstrated the high endurance of a bearing with a rotor
according to the invention, as 150,000 startup/shutdown cycles were
carried out at temperatures of up to 350.degree. C.
[0045] The invention allows effective lubrication of bearings with
parts rotating at speeds greater than 60,000 rpm (revolutions per
minute) even in turbomachinery driven by an electric motor.
[0046] The invention may find applications for example in devices
making use of turbomachinery, for example air conditioning and/or
climate control devices such as those installed on aircraft for air
management in a cabin and a cockpit.
[0047] Of course, the invention is not limited to the preferred
embodiment and to the alternative embodiments presented above by
way of non-limiting examples. It also relates to variants within
reach of the skilled person that lie within the scope of the
following claims
* * * * *