Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR THE PRODUCTION OF A SEALING SEGMENT, AND SEALING
SEGMENT TO BE USED IN COMPRESSOR AND TURBINE COMPONENTS'
[METHOD FOR PRODUCING A SEALING SEGMENT AND SEALING
SEGMENT FOR USE IN COMPRESSOR AND TURBINE COMPONENTS]
[0001] The present invention relates to a method for producing a sealing
segment for
use in compressor and turbine components, by powder injection molding, as well
as to a
sealing segment for use in compressor and turbine components composed of at
least one
first molded article as a base element and of at least one second molded
article exhibiting a
higher abrasive wear rate than the first molded article, as a grazing-contact
layer.
[0002] Sealing segments of this kind are used, in particular, when working
with what
are generally known as gap-maintaining systems in the compressor and turbine
components. Sealing segments, respectively sealing systems of this kind have
the function
of maintaining a minimal sealing gap between rotating blading [a blade
assembly, blading
system or blade row] and a housing, as well as between stationary blading and
the rotating
rotor hubs, and of thereby ensuring stable operating characteristics in the
context of a
highest possible efficiency. The rotating components of the turbine typically
have sealing
fins which run in against honeycomb seals in a manner known per se. A
honeycomb seal of
this kind is described by World Patent Application WO 2004/061340 Al. This
known
honeycomb seal is made of an individual molded article fabricated by powder-
metallurgical
injection molding.
[0003] The known running-in process can easily lead to overheating of the
sealing
fins when the contact with the honeycomb material lasts too long or the
resistance
generated by the rubbing away [abrading] of the honeycomb structures becomes
too great.
Therefore, damage to the sealing fins cannot be ruled out in the case of the
known sealing
segments, respectively corresponding run-in coatings.
[0004] It is, therefore, an object of the present invention to devise a method
for
~ Transiator's note: This is the English title provided on the published PCT
cover page of the WO
document.
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producing a sealing segment and a sealing segment produced accordingly for use
in
compressor and turbine components, which, on the one hand, make it possible to
inexpensively manufacture a broad array of sealing segment geometries and, on
the other
hand, to reduce the load that the compressor and turbine components are
subject to when
running in against the sealing segments.
[0005] These objectives are achieved by a method having the features set forth
in
claim 1, as well as by a sealing segment having the features set forth in
claim 16.
[0006] Advantageous embodiments of the present invention are described in the
respective dependent claims.
[0007] A method according to the present invention for producing a sealing
segment
for use in compressor and turbine components by powder injection molding
includes the
following method steps in accordance with the present invention: a) preparing
a first
homogeneous mixture of a metal powder or a mixture of metal powders or a
ceramic
powder or a mixture of ceramic powders and at least one binding agent; b)
producing a first
molded article by injection molding the first mixture; c) preparing a second
homogeneous
mixture of a metal powder or a mixture of metal powders or a ceramic powder or
a mixture
of ceramic powders and at least one binding agent, the second mixture being
selected to
have a higher abrasive wear rate than the first mixture following a subsequent
joint
[shared] sintering process; d) producing a second molded article as a grazing-
contact layer
by injection molding the second mixture; and e) joining the first and second
molded articles
to produce the sealing segment.
[0008] A cost-effective and also individual [targeted] production of the
requisite
sealing segments is ensured by using the powder injection molding method. In
this context,
all injection-moldable and sinterable metals, metal alloys, as well as
ceramics may be used
for the powder injection molding of the first and second molded articles.
Mixtures of the
metal powder or ceramic powder are also conceivable. The sinterable ceramics
may include
nitride ceramics, oxide ceramics and silicate ceramics, as well as carbides,
for example.
When manufacturing the sealing system according to the present invention, it
is critical that
the grazing-contact layer composed of the second molded article have a higher
abrasive
wear rate than the first molded article used as a base element and/or
fastening element for
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the sealing segment. Therefore, the present invention makes it possible to
satisfy a broad
array of material requirements for a sealing segment of this kind in
compressor and turbine
components. On the one hand, this concerns the simple production of
complicated
geometries using the powder injection molding method, and, on the other hand,
the targeted
adaptation of the material selection for producing the first and second molded
articles,
which may be carried out in conformance with the actual technical conditions.
It is thus
possible to adjust the properties of the second molded article that pertain to
the abrasion
characteristics, such as the generation of only low frictional energies and
resistances, the
effective chip formation and removability of the abraded material, or also
that relate to
preventing an ignition of the abraded material during grazing contact, in a
targeted manner,
to the turbine components making grazing contact, such as sealing fins, for
example. This
clearly lowers the loading of [stress to] the sealing fins by the grazing
contact, for example,
thereby making it possible to advantageously reduce the size of the
corresponding sealing
gap. Moreover, there is no need to use conventional geometries when producing
honeycomb seals or honeycomb-structured run-in coatings. Geometries may be
developed
that are more aerodynamically effective and more cost-effective from a
standpoint of
production engineering. In addition, the honeycomb structure may be entirely
eliminated
and, accordingly, planar layers may be produced economically. Furthermore, the
present
invention makes it possible for the first formed element, which is used as a
base element or
fastening element of the sealing segment, to be adjusted to the relevant
technical and
material engineering conditions. This relates, in particular, to temperature
resistance and
erosion resistance.
[0009] In various specific embodiments of the method according to the present
invention, the first and second molded articles may be joined immediately
following the
production thereof and prior to releasing [expelling] of the same in a joint
process.
However, it is also possible for the first and second molded articles to be
joined following a
separate release process and prior to a subsequent joint sintering process
that the molded
articles undergo. Finally, it is also possible for the first and second molded
articles to be
joined following a separate release and sintering process that they undergo.
In the latter
case, mechanical, as well as chemical joining processes are possible.
[0010] In other advantageous embodiments of the method according to the
present
invention, the higher abrasive wear rate of the second molded article is
achieved by
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reducing the metal powder or ceramic powder content in the second mixture.
Thus, in the
second mixture, for example, the metal powder or ceramic powder content is
only
approximately 15 - 30 % by volume. As a result, the sintering process yields a
porous
structure due to a reduction in intergranular contact. Advantageously, no
separation effects
ensue in the second mixture, and a homogeneous porosity distribution is
obtained. There is
also no need for any change in the process parameters.
[0011] In another advantageous embodiment of the present invention, the higher
abrasive wear rate of the second molded article is achieved by using metal
powders and
ceramic powders having reduced sintering activity. In this context, metal
powders having a
lower degree of purity, i.e., higher C- and 0-concentration may be used, for
example. The
use of air-atomized, instead of inert gas-atomized metal powder, leads to a
higher C- and
0-coverage of the surfaces and thus to a reduced sintering activity. Here, the
advantage of a
very porous structure is derived due to a reduction in the intergranular
contact, respectively
in the sintering neck formation. Moreover, inexpensive metal powders or
ceramic powders
may be used. A homogeneous porosity distribution, as well as a reduction in
separation
effects are achieved. There is again no need for any changes in the process
parameters.
[0012] In another advantageous embodiment of the method according to the
present
invention, the higher abrasive wear rate of the second molded article is
achieved by
admixing binder polymers, which do not entirely decompose during release
and/or sintering
processes, into the second mixture. In this context, the binder polymers may
be selected
from the group including the phenolic resins or novolak. Admixing binder
polymers
advantageously reduces the sintering activity. Carbon residues are produced in
the grain
interstices of the metal or ceramic powder particles in the sintered product,
making it
possible to achieve good abrasive wear properties. Advantageously in this case
as well, no
separation effects occur in the context of a homogeneous porosity
distribution.
[0013] In another advantageous embodiment of the method according to the
present
invention, the higher abrasive wear rate of the second molded article is
achieved by
admixing fillers into the second mixture. In this context, the fillers may be
formed from
easily cleavable inert materials, such as graphite, bentonite or hexagonal
boron nitride
and/or from materials which at least partially decompose during the release
and/or sintering
and contribute to pore formation in the second molded article. Evaporation
advantageously
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takes place during sintering, for example, thereby resulting in a pore
formation in the
scraping layer [grazing-contact layer],2 respectively in the second molded
article.
However, it is also possible that the fillers do not decompose, and that they
remain in the
sintered product, i.e., in the scraping layer [grazing-contact layer],3
respectively in the
second molded article, in the grain interstices of the metal or ceramic powder
particles.
Overall, therefore, the result is a quite readily cleavable, respectively
abradable grazing-
contact layer. In addition, the pore formation is optionally effected by
surface oxidation in
the later use of the sealing segment, for example when graphite is selected as
a filler.
[0014] In another advantageous embodiment of the method according to the
present
invention, a multiplicity of homogeneous mixtures of metal powder or a mixture
of metal
powders or a ceramic powder or a mixture of ceramic powders and at least one
binding
agent are prepared in accordance with method steps a) through d) to produce a
corresponding multiplicity of molded articles and a sealing segment resulting
therefrom.
Thus, even multilayer sealing segments may be produced cost-effectively in
virtually any
given geometries.
[0015] A sealing segment according to the present invention for use in
compressor
and turbine components composed of at least one first molded article as a base
element
and/or fastening element and at least one second molded article having a
higher abrasive
wear rate than the first molded article, as a grazing-contact layer, the first
and the second
molded articles each being produced by powder injection molding. The at least
two-layered
design of the sealing segment according to the present invention makes it
possible, on the
one hand, to adapt the base and/or fastening element, namely the first molded
article, as
well as the scraping layer [grazing-contact layer],4 namely the second molded
article, both
in the geometries thereof, as well as in the material compositions, in a
targeted manner to
the technical and material engineering requirements. In this context, the
sealing segment
may be a run-in coating for sealing a radial gap between a rotating rotor
blade and a
housing of a gas turbine, for example. Moreover, the sealing segment may have
a
2 Translator's note: Here, and at two other places in the Specification, the
author switches from
"Anstreifschicht" or "grazing-contact layer" to "Abstreifschicht" or
"scraping.layer." Both terms
describe the "second molded article." It seems the author made this change
inadvertently, perhaps
thinking of the layer from a different perspective. To be consistent, it would
seem to be preferable to use
"grazing-contact layer" throughout, especially as this is how it is referred
to in the claims.
3 Translator's note: See Footnote 2.
4 Translator's note: See Footnote 2.
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honeycomb design.
[0016] In this context, the sealing segment according to the present invention
is
produced in accordance with a method as described in detail in the preceding.
[0017] In another advantageous embodiment of the sealing segment according to
the
present invention, the sealing segment is made of a multiplicity of molded
articles, at least
two molded articles being produced by powder injection molding.
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