U.S. patent application number 09/907462 was filed with the patent office on 2003-10-30 for enhanced capacity bearing.
Invention is credited to Telakowski, Robert.
Application Number | 20030201033 09/907462 |
Document ID | / |
Family ID | 25424133 |
Filed Date | 2003-10-30 |
United States Patent
Application |
20030201033 |
Kind Code |
A1 |
Telakowski, Robert |
October 30, 2003 |
Enhanced capacity bearing
Abstract
A bearing is provided particularly suitable for a turbine and
turbine related components used in the aerospace industry. More
particularly, the bearing is suitable for such applications as
pneumatic starters for turbines. The bearing is preferably
constructed from a M50 steel, which typically has a pre-treated
hardness in the range of approximately 60 to 64 Rc. With the
present invention, the bearing is nitrided to obtain a case
hardness of approximately 74 Rc. To achieve such a case hardness,
the bearing may require nitriding over several days. In one
preferred embodiment of the present invention, a pneumatic starter
includes a shaft, preferably constructed from M50, that has a
portion of its outer surface nitrided. The nitrided surface
functions as an inner race of a bearing assembly. Nitriding the
portion of the shaft extends the bearing life of the bearing due to
its increased hardness.
Inventors: |
Telakowski, Robert;
(Windsor, CT) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
25424133 |
Appl. No.: |
09/907462 |
Filed: |
July 17, 2001 |
Current U.S.
Class: |
148/230 ;
148/318 |
Current CPC
Class: |
F16C 33/62 20130101;
C23C 8/26 20130101; F02C 7/06 20130101; F16C 33/64 20130101 |
Class at
Publication: |
148/230 ;
148/318 |
International
Class: |
C23C 008/26 |
Claims
What is claimed is:
1. A bearing component constructed from an M50 alloy with a
nitrided case having a case hardness of approximately 74 Rc.
2. The bearing component according to claim 1, wherein said thru
hardened M50 alloy has a pre-treated hardness in a range of
approximately 60 to 64 Rc.
3. The bearing component according to claim 1, wherein said bearing
component is an inner race.
4. The bearing component according to claim 3, wherein said inner
race is a shaft of a pneumatic starter for a turbine engine.
5. A method of manufacturing a bearing comprising the steps of: a)
providing a bearing component constructed from a an M50 alloy; b)
nitriding the bearing component to increase the nitrogen content of
an exterior portion of the bearing component; and c) achieving a
case hardness of approximately 74 Rc.
6. The method according to claim 5, wherein said bearing component
is an inner race.
7. The method according to claim 6, wherein said inner race is a
shaft of a pneumatic starter for a turbine.
8. A starter comprising: a housing; planetary gear assembly
supported within said housing; a bearing assembly arranged within
said planetary gear assembly wherein a portion of said bearing
assembly is constructed from a nitrided high speed steel.
9. The starter according to claim 8, wherein said high speed steel
is an M50 alloy.
10. The starter according to claim 8, wherein said bearing
component is an inner race.
11. The starter according to claim 9, wherein planetary gear
assembly includes a shaft with a portion of said shaft providing
said inner.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to an improved bearing, and more
specifically, the invention relates to an improved bearing
particularly suitable for turbines used in the aerospace
industry.
[0002] It is desirable to increase the life of bearings to decrease
the amount of service necessary for the bearing and the components
associated with the bearing. One way of increasing the bearing life
is to increase the hardness of the bearing to reduce bearing wear.
One way to increase bearing hardness is to utilize a premium grade
steel which provides increased hardness. For example, bearing life
standards are based upon an SAE 52100 steel, which typically has a
hardness in the range of 60 to 62 Rc. By utilizing a premium grade
steel such as M50, a hardness in the range of 64 Rc may be obtained
thereby increasing the bearing fatigue life. M50 materials are
frequently used in the aerospace industry for such components as
turbine bearings, for which extended bearing life is particularly
desirable. In spite of the increased bearing life that M50
provides, further improvements are desirable to increase bearing
durability.
[0003] Increased bearing life may also be achieved by utilizing
alternative materials such as ceramics. However, ceramics are an
exotic material which may cost significantly more than a premium
grade steel such as M50. The size of the bearing may also be
increased to increase the bearing life. However, by increasing the
size of the bearing weight is added and it may be more difficult to
package the bearing. Alternatively, coatings may be added to the
bearing surfaces to reduce wear and increase the life of the
bearing. However, once the coatings wear from the bearing, the
bearing life may rapidly decrease. The coating must be carefully
selected to provide sufficient adhesion between the coating and the
base material.
[0004] Nitriding is a known process used to increase the case
hardness, or surface hardness, of a component. However, nitriding
has not been applied to turbine applications, and particularly
nitriding has not been applied to premium grade thru hardened steel
such as M50. Prior art bearing materials does not provide adequate
hardness in the event that the case hardened portion wears through.
Therefore, what is needed is a hardened premium grade steel
particularly suitable for aerospace applications such as
turbines.
SUMMARY OF THE INVENTION AND ADVANTAGES
[0005] The present invention provides a bearing particularly
suitable for a turbine and turbine related components used in the
aerospace industry. More particularly, the bearing is suitable for
such applications as pneumatic starters for turbines. The bearing
is preferably constructed from a thru hardened M50 steel, which
typically has a pre-treated hardness in the range of approximately
60 to 64 Rc. With the present invention, the bearing is nitrided to
obtain a case hardness of approximately 74 Rc. To achieve such a
case hardness, the bearing may require nitriding over several
days.
[0006] In one preferred embodiment of the present invention, a
pneumatic starter includes a planetary gear assembly having a
shaft, which is the life limiting component for particular
applications. The shaft is preferably constructed from M50 alloy
steel that has a portion of its outer surface nitrided. The
nitrided surface functions as an inner race of a bearing assembly.
Nitriding the portion of the shaft extends the bearing life of the
bearing due to its increased hardness.
[0007] Accordingly, a bearing is provided having an increased
bearing life without utilizing alternative materials or increasing
the size of the bearing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Other advantages of the present invention can be understood
by reference to the following detailed description when considered
in connection with the accompanying drawings wherein:
[0009] FIG. 1 is a cross-sectional view of a turbine having a
pneumatic starter; and
[0010] FIG. 2 is a schematic view of a nitriding process for
bearings of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0011] Achieving increased bearing life and improved performance of
bearings is critical for many applications. For example, increasing
bearing life for bearings used in aerospace applications such as
turbine starters is desirable to increase durability and
reliability. In the bearing industry, bearing life standards are
based upon an SAE 52100 steel, which has a hardness of typically in
the range of 60 to 62 Rc. Increasing the hardness of a life
limiting bearing component may have the effect of extending the
overall bearing life and lengthening the service interval of the
components associated with the bearing.
[0012] A turbine starter 10 commonly used in the aerospace industry
is shown in FIG. 1. The starter 10 includes a portion of a
planetary gear assembly 12 supported within a housing by a bearing
assembly 14. Bearing assemblies typically includes an inner race,
an outer race, and a plurality of rolling elements arranged between
the inner and outer races to reduce the friction there between. In
the embodiments shown, the inner race may be defined by an exterior
surface of a gear shaft 16, and the outer race may be defined by an
inner diameter of a planetary gear 18. The gear shaft 16 is
supported by the planetary gear 18 and a plurality of rolling
elements 20, such as needle or tapered rollers, arranged between
the gear shaft 16 and planetary gear 18.
[0013] Premium grade, high speed steels are commonly used in the
aerospace industries due to their increased hardness and extended
life as compared to standard bearing materials such as SAE 52100
steels. M50 alloys typically have a maximum hardness of
approximately 64 Rc. Despite the increased hardness and improved
bearing life provided by M50 alloys, it is desirable to further
extend bearing life.
[0014] Depending on the particular application, a different part of
the bearing assembly may be more highly stressed than another
bearing component and therefore have a shorter fatigue life. For
example, the inner race of the gear shaft 16 may fatigue earlier
than the other bearing components. Accordingly, it is desirable to
increase the hardness of the inner race.
[0015] In one preferred embodiment, the gear shaft 16 of the
pneumatic starter 10 may be nitrided. The gear shaft 16 is
preferably constructed from a M50 alloy. Referring to FIG. 2, the
untreated gear shaft 32 would be loaded into a chamber 34 for
nitriding.
[0016] Ammonia gas or another suitable nitrogen rich mixture 36 is
provided to the chamber 34. The gear shaft 32 remains in the
nitrogen rich atmosphere within the chamber 34 to increase the
nitrogen content of the exterior portion of the gear shaft 16 and
thereby increase the case hardness. The case hardness, or depth of
the hardness, is dependent upon the temperature within the chamber
34 and the time the gear shaft 16 spends within the chamber 34,
among other factors. By nitriding the gear shaft 16 for several
days in the chamber 34 a case hardness of approximately 74 Rc may
be achieved. If the case hardened portion of the bearing wears
through, the underlying unhardened M50 material provides
considerable wear resistance. In this manner, the bearing life may
be increased by at least three-fold.
[0017] The invention has been described in an illustrative manner,
and it is to be understood that the terminology that has been used
is intended to be in the nature of words of description rather than
of limitation. Obviously, many modifications and variations of the
present invention are possible in light of the above teachings. It
is, therefore, to be understood that within the scope of the
appended claims the invention may be practiced otherwise than as
specifically described.
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