U.S. patent application number 11/791189 was filed with the patent office on 2008-08-28 for process for producing a lost model, and core introduced therein.
This patent application is currently assigned to SIEMENS AKTIENGESELLSCHAFT. Invention is credited to Uwe Paul, Ursula Pickert.
Application Number | 20080202718 11/791189 |
Document ID | / |
Family ID | 34993222 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080202718 |
Kind Code |
A1 |
Paul; Uwe ; et al. |
August 28, 2008 |
Process For Producing A Lost Model, And Core Introduced Therein
Abstract
The invention relates to a method for the production of a
pattern for precision casting representation of turbine component
comprising at least one cavity, whereby the prepared pattern
comprises at least one core and an outer contour pattern, at least
partly enclosing the core and at least partly defining the outer
contour of the turbine component. The core is made from a hardening
core material, which hardens during the course of the method and
the outer contour pattern is made from a combustible or fusible
material. The outer contour model is first produced with at least
one cavity corresponding to the at least one cavity of the turbine
component and subsequently, in order to form the at least one care,
the hardening core material is introduced into the at least one
cavity and hardened.
Inventors: |
Paul; Uwe; (Ratingen,
DE) ; Pickert; Ursula; (Mulheim an der Ruhr,
DE) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Assignee: |
SIEMENS AKTIENGESELLSCHAFT
Munchen
DE
|
Family ID: |
34993222 |
Appl. No.: |
11/791189 |
Filed: |
November 4, 2005 |
PCT Filed: |
November 4, 2005 |
PCT NO: |
PCT/EP05/55769 |
371 Date: |
May 17, 2007 |
Current U.S.
Class: |
164/23 ; 164/246;
164/516; 164/521 |
Current CPC
Class: |
B33Y 70/00 20141201;
B33Y 80/00 20141201; B22C 7/02 20130101; B22C 9/10 20130101; B22C
9/04 20130101 |
Class at
Publication: |
164/23 ; 164/246;
164/516; 164/521 |
International
Class: |
B22C 9/04 20060101
B22C009/04; B22C 7/02 20060101 B22C007/02; B22C 9/10 20060101
B22C009/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 24, 2004 |
EP |
04027895.4 |
Claims
1.-12. (canceled)
13. A process for producing an investment casting model used in the
production of a turbine component having at least one cavity,
comprising: producing at least one core by introducing a hardenable
core material into the at least one cavity and hardening the
hardenable core material that hardens during the process; producing
an external contour model with at least one cavity corresponding to
the at least one cavity of the component, where the external
contour model at least partially surrounds the core and at least
partially defines the external contour of the turbine component and
where the external contour model is produced from a material that
can be burnt or melted out; and at least partially surrounding the
external contour model by a stabilizing casing.
14. The process as claimed in claim 13, wherein the external
contour model is resin model.
15. The process as claimed in claim 2, wherein the resin model is
produced by a rapid prototype process.
16. The process as claimed in claim 13, wherein the stabilizing
casing is produced by a rapid prototype process.
17. The process as claimed in claim 16, wherein the stabilizing
casing is produced from resin by a stereolithography process.
18. The process as claimed in claim 17, wherein the resin contains
a mechanically stabilizing material.
19. The process as claimed in claim 18, wherein the mechanically
stabilizing material is a metal powder.
20. The process as claimed in claim 16, wherein the stabilizing
casing is formed from metal powder by rapid laser sintering.
21. The process as claimed in claim 16, wherein the core material
is free-flowing prior to the hardening, and is poured, spread or
injected into the at least one cavity of the external contour
model.
22. The process as claimed in claim 21, wherein the core material
is a ceramic-based material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2005/055769, filed Nov. 4, 2005 and claims
the benefit thereof. The International Application claims the
benefits of European application No. 04027895.4 filed Nov. 24,
2004, both of the applications are incorporated by reference herein
in their entirety.
FIELD OF INVENTION
[0002] The present invention relates to a process for producing a
model for the production by investment casting of a component that
has a cavity, and to a process for producing a casting mold for a
component that has at least one cavity, in which a model is used
for producing the component by investment casting.
BACKGROUND OF THE INVENTION
[0003] When producing hollow cast components, such as for example
turbine components, the production of the cavity is of particular
importance. By way of example, turbine blades or vanes for gas
turbines have a main blade or vane part, which has a leading edge
and a trailing edge. Leading and trailing edges are connected to
one another via a suction-side wall and a pressure-side wall. At
least one cavity, which extends through a large part of the main
blade or vane part and is used to supply a cooling fluid, for
example air or steam, by which the main blade or vane part is
cooled when the turbine is operating, is arranged between the
suction-side wall and the pressure-side wall. The cooling action is
dependent on the configuration of the cavity and its precise
positioning within the main blade or vane part. Even relatively
minor deviations in the positioning of the cavity can lead to a
considerable variation in the cooling action.
[0004] The shape and position of the cavity within the main blade
or vane part therefore represents a particular challenge in the
design of turbine blades and vanes. It is by no means unusual for a
whole range of design changes to be required in order to optimize
the position and shape of the cavity in relation to the external
contour of the turbine blade or vane before the final design is
fixed.
[0005] Turbine blades and vanes of different designs are produced
and tested as part of the development process before the final
design is fixed.
[0006] The production of for example hollow cast turbine blades or
vanes for gas turbines is realized by means of a ceramic investment
casting technique, in which a core is injection-molded or cast from
a ceramic material in order to define the cavity. Then, this core
is placed into a mold for the injection molding or casting of a wax
model and the wax is injected or poured into the mold. After the
wax has cooled, the finished wax model, together with the ceramic
core, forms a model for producing the turbine blade or vane by
investment casting, and as the process then continues this model is
used to produce a ceramic mold for the casting of the turbine blade
or vane. To produce the ceramic mold, a ceramic sleeve is fitted
around the wax model. After the ceramic sleeve has been hardened,
the wax of the wax model is melted out, so that what remains is a
mold used to cast the hollow turbine blade or vane. This mold
comprises firstly the ceramic sleeve and secondly the ceramic core.
A process of this type is disclosed for example in U.S. Pat. No.
5,465,780.
[0007] Since, despite computer-aided technology used to simulate
flow and cooling properties, the core design none the less has to
be corrected by means of tests in the final stage of product
development, the process described is relatively complex in product
development, since new casting or injection molds for the core and
wax model have to be produced for each design.
[0008] Therefore, in DE 101 29 975 A1 it has been proposed for the
casting or injection molds for the casting of the core to be
equipped with exchangeable inserts, in order in this way to allow
the core design to be changed without a completely new casting or
injection mold having to be produced for the core. However, even
this procedure only allows local corrections but does not permit an
overall correction to the core design. Moreover, in the process
described in DE 101 29 975 A1, corrections to the design of the
external contour of the turbine blade or vane are not possible
without producing new tools, such as for example new casting
molds.
[0009] The production of tools for the manufacture of the ceramic
cores and of the wax models continues to be complex and expensive.
For example, during the production process development for hollow
cast turbine blades or vanes, a large proportion of the development
time and development costs are attributable to the production of
the tools. Moreover, the tools can only be released for series
production once the design of the hollow cast turbine component has
been released. Otherwise, changes to the design can lead to a
considerable time delay and high costs.
SUMMARY OF INVENTION
[0010] Therefore, it is an object of the present invention to
provide an improved process for producing a model for the
production by investment casting of a turbine component that has at
least one cavity, and also an improved process for producing a
casting mold for a turbine component that has at least one
cavity.
[0011] This object is achieved by the process for producing a model
for the production by investment casting of a component that has at
least one cavity as claimed in the claims and by the process for
producing a casting mold or an injection mold for a component that
has at least one cavity as claimed in the claims.
[0012] In the process according to the invention for producing a
model for the production by investment casting of a component that
has at least one cavity, the finished model comprises at least one
core and an external contour model which at least partially
surrounds the core and at least partially defines the external
contour of the component. The core is produced from a hardenable
core material that is hardened during the process. The external
contour model is produced from a material that can be burnt or
melted out. In the process according to the invention, first of all
the external contour model is produced with at least one cavity
corresponding to the at least one cavity of the component. Then, to
produce the at least one core the hardenable material is introduced
into the at least one cavity and hardened.
[0013] Therefore, in the process according to the invention, the
external contour model simultaneously serves as a casting or
injection mold for the core, and consequently there is no need for
a separate injection or casting mold to be present for the core. It
is in this way possible to dispense with the expensive production
of a dedicated casting or injection mold for the core for process
development all the way to prototype production.
[0014] The external contour model used may be a resin model. A
rapid prototype process, in particular a stereolithography process,
can be used to produce the resin model. A stereolithography process
uses a resin that hardens when irradiated with a laser. To produce
the external contour model, the previously free-flowing resin is
hardened layer by layer by means of the laser, until the external
contour model is complete in its desired contour. The laser
hardening can in this case in particular be computer-controlled, so
that designs which have already been computer-simulated can be
converted relatively quickly into a model used to produce the
component by investment casting.
[0015] When the hardenable material is being introduced and/or
hardened, the external contour model may be surrounded by a
stabilizing casing, known as a setter. The stabilizing casing can
also be produced by means of a rapid prototype process, for example
by being produced from resin by means of a stereolithography
process. It is particularly advantageous if the casing contains a
mechanically stabilizing material, for example a metal powder.
Finally, it is also possible for the casing to be produced entirely
from metal powder, in which case suitable rapid prototype
processes, for example rapid laser sintering, can be used to
consolidate the metal powder.
[0016] The stabilizing casing holds the external contour model in
shape when the hardenable material is being introduced, with the
result that the pressure on the external contour model that occurs
during this filling operation does not cause any design deviations
in the core.
[0017] A particularly suitable core material is a material that is
free-flowing prior to hardening and is poured or injected into the
at least one cavity of the external contour model. On account of
their high thermal stability, ceramic-based materials are
particularly suitable for use as the core material.
[0018] The process according to the invention for producing a model
for the production by investment casting of a component that has at
least one cavity offers greater variety and reduced cost compared
to the prior art processes, in which production tools, in
particular casting or injection molds, have to be produced for
process development and for qualification of turbine
components.
[0019] In particular if rapid prototype processes, such as
stereolithography processes or rapid laser sintering processes, are
used to produce the external contour model and/or the stabilizing
casing, the process according to the invention also results more
quickly in a model for the investment casting production of the
component compared to the prior art processes.
[0020] With the process according to the invention, the expensive
actual production tools can be dispensed with for process
development all the way to prototype production, which allows the
process development to start at a significantly earlier time,
considerably shortens development time and greatly reduces the risk
of corrections to production tools caused by design changes. The
overall tooling costs can be correspondingly reduced.
[0021] Finally, the process according to the invention allows
significantly earlier introduction of new designs to the market and
also makes it possible to react more quickly to service-related
design changes.
[0022] The process according to the invention for producing a model
for the production by investment casting of the component is used
in a process according to the invention for producing a casting
mold or an injection mold for a component that has at least one
cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Further features, properties and advantages of the present
invention will emerge from the following description of an
exemplary embodiment with reference to the accompanying figures, in
which:
[0024] FIG. 1 shows a diagrammatic illustration of an external
contour model for use in the process according to the invention, in
the form of a sectional perspective view.
[0025] FIG. 2 shows the external contour model from FIG. 1 while a
hardenable material is being introduced into openings in the
external contour model.
[0026] FIG. 3 shows an example of a partial longitudinal section
through a gas turbine.
[0027] FIG. 4 shows a perspective view of a rotor blade or guide
vane of a turbomachine.
[0028] FIG. 5 shows a combustion chamber of a gas turbine.
DETAILED DESCRIPTION OF INVENTION
[0029] FIG. 1 shows a somewhat simplified illustration of a model 1
of a turbine blade or vane as an example of a component with a
cavity, in the form of a perspective, sectional view. The model 1
has an outer surface 3, which reproduces the external contour of a
turbine blade or vane. The external contour is divided into a
pressure-side contour 4 and a suction-side contour 5. The edges at
which the pressure-side contour 4 and the suction-side contour 5
merge into one another form the leading edge (edge 6) and the
trailing edge (edge 7), respectively, in the subsequent turbine
blade or vane.
[0030] The model 1 is not solid, but rather has cavities, in the
present exemplary embodiment five cavities 8a to 8e, which
represent the subsequent cooling air passages in the turbine blade
or vane. The inner surfaces 9a to 9e, which delimit the cavities 8a
to 8e, of the model 1 correspondingly represent the internal
contour of the subsequent turbine blade or vane. In the region of
the edge 7, the fifth cavity 8e has an opening 10 which extends
parallel to the edge and represents an outlet opening for the
emergence of cooling fluid in the subsequent turbine blade or
vane.
[0031] As explained above, the model 1 already represents both the
external contour and the internal contour of the subsequent turbine
blade or vane. The model is made from synthetic resin which melts
or burns under the action of heat and is used during production of
a model for the investment casting production of the turbine blade
or vane that is to be produced.
[0032] The synthetic resin model described above, in the model for
the investment casting production of the turbine blade or vane,
merely constitutes a model for the external contour of the turbine
blade or vane, and is therefore referred to below as the external
contour model 1. The internal contour of the cavities of the
turbine blade or vane, by contrast, is formed using what is known
as a core, the outer surfaces of which represent the internal
contour of the cavities of the turbine blade or vane. The external
contour model 1 and the cores which are yet to be described
together form the model for the investment casting production of
the turbine blade or vane.
[0033] In the exemplary embodiment, the external contour model 1 is
produced by means of a stereolithography process, in which a
photoreactive liquid resin located in a container is locally
irradiated with laser radiation of a suitable wavelength. This
irradiation leads to hardening of the resin at the irradiated
location. By suitable guidance of the laser beam, it is possible to
control the hardening of the resin in such a way that structures of
any desired shape can be realized from hardened synthetic resin.
Stereolithography processes are known from the prior art and
therefore require no further explanation at this point.
[0034] The stereolithography process is used to produce the
external contour model 1 from a liquid synthetic resin by
controlled local hardening. The laser is controlled by means of a
computer, with the result that the external contour model 1 can be
produced on the basis purely of a computer model.
[0035] After the external contour model 1 has been produced, the
cores which define the cavities in the subsequent turbine blade or
vane are produced. For this purpose, a free-flowing ceramic
material, known as the core compound 11, is introduced into the
cavities 8a to 8e of the external contour model 1. This
introduction can be realized for example, as illustrated in FIG. 2,
by pouring. However, other introduction processes are also
possible. By way of example, the core compound 11 can also be
spread or injected into the cavities.
[0036] To prevent deformation of the external contour model 1 while
the core compound 11 is being introduced, on account of the
resultant pressure, the external contour model 1 is surrounded by a
stabilizing casing 12, 13 prior to the introduction of the ceramic
core compound 11. This stabilizing casing 12, 13 is of two-part
design. One part 12 of the stabilizing casing has a surface that is
the inverse of the pressure-side contour 4 of the external contour
model 1, while the other part 13 of the external contour model 1
has a surface that is the inverse of the suction-side contour 5 of
the external contour model 1. The surfaces of the stabilizing
casing that are the inverse of the external contour 4, 5 are
surrounded by abutment surfaces, at which the two parts 12, 13 abut
one another when they are surrounding the external contour model 1
in a stabilizing manner. Accordingly, the abutment surfaces are
then located in the region 15, 16 of the edges 6, 7 of the external
contour model 1.
[0037] In the region 16 of the edge 7 of the external contour model
1 there is also, for example, a widening 17 of the abutment
surfaces, so that they do not directly abut one another in the
immediate vicinity of the edge 7. The widened region 17, together
with the cavity 8e, forms the mold for the core that subsequently
defines the internal contour of the corresponding cavity of the
turbine blade or vane.
[0038] In the present exemplary embodiment, the stabilizing casing
12, 13, like the external contour model 1, is produced by means of
a stereolithography process. It is advantageous if the resin or
synthetic resin compound which is hardened in the stereolithography
process contains a stabilizing component, for example a metal
powder. A stabilizing casing 12, 13, once produced, can be reused,
provided that there are no design changes made to the external
contour of the turbine blade or vane. In a modification to the
variant embodiment described, the stabilizing casing may also
consist entirely of metal. In this case, it can be produced for
example by means of rapid laser sintering from metal powder.
[0039] After all the cavities 8a to 8e of the external contour
model 1 have been filled with the ceramic core compound 11, the
compound is hardened. After the compound has hardened, the
stabilizing casing 12, 13 is removed, so that what remains is the
external contour model 1 with ceramic cores located in its
cavities. The external contour model 1, together with the ceramic
cores, then forms a model for the investment casting production of
the turbine blade or vane.
[0040] The model produced in this way for the investment casting
production of the turbine blade or vane can then be used to produce
a casting mold for the turbine blade or vane. For this purpose, the
model is surrounded with a ceramic compound which is then hardened.
In the process, the ceramic compound is joined at selected
locations to the ceramic cores located in the external contour
model 1. After the ceramic compound surrounding the external
contour model 1 has been completely hardened, the resin forming the
external contour model 1 is melted or burnt out. What remains is a
casting mold for casting the turbine blade or vane.
[0041] On account of the destruction of the external contour model
1 when it is burnt or melted out, the external contour model 1 is
also known as a lost model. In the casting mold, the external
contours of the ceramic cores define the internal contours of the
subsequent turbine blade or vane, and the internal contour of the
ceramic mold defines the subsequent external contour of the turbine
blade or vane.
[0042] On account of the direct conversion of a computer model into
an external contour model 1 which is simultaneously used as a mold
for the ceramic cores, it is possible to dispense with the complex
and expensive production of tools, such as for example casting
molds for the manufacture of the ceramic cores and of the wax
models. The result is that a computer model can be converted much
more quickly into a model that is suitable for the investment
casting production of the turbine blade or vane. It is in this way
possible to reduce outlay on production of a casting mold for a
turbine blade or vane and the associated time.
[0043] To provide a better understanding of the invention, there
now follows a description of a typical gas turbine, a typical
turbine blade or vane and a typical combustion chamber, with
reference to FIGS. 3 to 5.
[0044] FIG. 3 shows an example of a partial longitudinal section
through a gas turbine 100. In the interior, the gas turbine 100 has
a rotor 103 which is mounted such that it can rotate about an axis
of rotation 102 and is also referred to as the turbine rotor. An
intake housing 104, a compressor 105, a, for example, toroidal
combustion chamber 110, in particular an annular combustion chamber
106, with a plurality of coaxially arranged burners 107, a turbine
108 and the exhaust-gas housing 109 follow one another along the
rotor 103.
[0045] The annular combustion chamber 106 is in communication with
a, for example, annular hot-gas passage 111, where, by way of
example, four successive turbine stages 112 form the turbine
108.
[0046] Each turbine stage 112 is formed, for example, from two
blade or vane rings. As seen in the direction of flow of a working
medium 113, in the hot-gas passage 111 a row of guide vanes 115 is
followed by a row 125 formed from rotor blades 120.
[0047] The guide vanes 130 are secured to an inner housing 138 of a
stator 143, whereas the rotor blades 120 of a row 125 are fitted to
the rotor 103 for example by means of a turbine disk 133.
[0048] A generator (not shown) is coupled to the rotor 103.
[0049] While the gas turbine 100 is operating, the compressor 105
sucks in air 135 through the intake housing 104 and compresses it.
The compressed air provided at the turbine-side end of the
compressor 105 is passed to the burners 107, where it is mixed with
a fuel. The mix is then burnt in the combustion chamber 110,
forming the working medium 113. From there, the working medium 113
flows along the hot-gas passage 111 past the guide vanes 130 and
the rotor blades 120. The working medium 113 is expanded at the
rotor blades 120, transferring its momentum, so that the rotor
blades 120 drive the rotor 103 and the latter in turn drives the
generator coupled to it.
[0050] While the gas turbine 100 is operating, the components which
are exposed to the hot working medium 113 are subject to thermal
stresses. The guide vanes 130 and rotor blades 120 of the first
turbine stage 112, as seen in the direction of flow of the working
medium 113, together with the heat shield bricks which line the
annular combustion chamber 106, are subject to the highest thermal
stresses.
[0051] To be able to withstand the temperatures which prevail
there, they may be cooled by means of a coolant.
[0052] Substrates of the components may likewise have a directional
structure, i.e. they are in single-crystal form (SX structure) or
have only longitudinally oriented grains (DS structure).
[0053] By way of example, iron-base, nickel-base or cobalt-base
superalloys are used as material for the components, in particular
for the turbine blade or vane 120, 130 and components of the
combustion chamber 110. Superalloys of this type are known, for
example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO
99/67435 or WO 00/44949; these documents form part of the
disclosure.
[0054] The blades or vanes 120, 130 may also have coatings which
protect against corrosion (MCrAlX; M is at least one element
selected from the group consisting of iron (Fe), cobalt (Co),
nickel (Ni), X is an active element and represents yttrium (Y)
and/or silicon and/or at least one rare earth element or hafnium).
Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017
B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are intended to form
part of the present disclosure.
[0055] A thermal barrier coating, consisting for example of
ZrO.sub.2, Y.sub.2O.sub.4ZrO.sub.2, i.e. unstabilized, partially
stabilized or fully stabilized by yttrium oxide and/or calcium
oxide and/or magnesium oxide, may also be present on the MCrAlX.
Columnar grains are produced in the thermal barrier coating by
suitable coating processes, such as for example electron beam
physical vapor deposition (EB-PVD).
[0056] The guide vane 130 has a guide vane root (not shown here),
which faces the inner housing 138 of the turbine 108, and a guide
vane head which is at the opposite end from the guide vane root.
The guide vane head faces the rotor 103 and is fixed to a securing
ring 140 of the stator 143.
[0057] FIG. 4 shows a perspective view of a rotor blade 120 or
guide vane 130 of a turbomachine, which extends along a
longitudinal axis 121.
[0058] The turbomachine may be a gas turbine of an aircraft or of a
power plant for generating electricity, a steam turbine or a
compressor.
[0059] The blade or vane 120, 130 has, in succession along the
longitudinal axis 121, a securing region 400, an adjoining blade or
vane platform 403 and a main blade or vane part 406.
[0060] As a guide vane 130, the vane 130 may have a further
platform (not shown) at its vane tip 415.
[0061] A blade or vane root 183, which is used to secure the rotor
blades 120, 130 to a shaft or a disk (not shown), is formed in the
securing region 400.
[0062] The blade or vane root 183 is designed, for example, in
hammerhead form. Other configurations, such as a fir-tree or
dovetail root, are possible.
[0063] The blade or vane 120, 130 has a leading edge 409 and a
trailing edge 412 for a medium which flows past the main blade or
vane part 406.
[0064] In the case of conventional blades or vanes 120, 130, by way
of example solid metallic materials, in particular superalloys, are
used in all regions 400, 403, 406 of the blade or vane 120, 130.
Superalloys of this type are known, for example, from EP 1 204 776
B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949;
these documents form part of the disclosure. The blade or vane 120,
130 may in this case be produced by a casting process, also by
means of directional solidification, by a forging process, by a
milling process or combinations thereof.
[0065] Workpieces with a single-crystal structure or structures are
used as components for machines which, in operation, are exposed to
high mechanical, thermal and/or chemical stresses. Single-crystal
workpieces of this type are produced, for example, by directional
solidification from the melt. This involves casting processes in
which the liquid metallic alloy solidifies to form the
single-crystal structure, i.e. the single-crystal workpiece, or
solidifies directionally. In this case, dendritic crystals are
oriented along the direction of heat flow and form either a
columnar crystalline grain structure (i.e. grains which run over
the entire length of the workpiece and are referred to here, in
accordance with the language customarily used, as directionally
solidified) or a single-crystal structure, i.e. the entire
workpiece consists of one single crystal. In these processes, a
transition to globular (polycrystalline) solidification needs to be
avoided, since non-directional growth inevitably forms transverse
and longitudinal grain boundaries, which negate the favorable
properties of the directionally solidified or single-crystal
component.
[0066] Where the text refers in general terms to directionally
solidified microstructures, this is to be understood as meaning
both single crystals, which do not have any grain boundaries or at
most have small-angle grain boundaries, and columnar crystal
structures, which do have grain boundaries running in the
longitudinal direction but do not have any transverse grain
boundaries. This second form of crystalline structures is also
described as directionally solidified microstructures
(directionally solidified structures). Processes of this type are
known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1; these
documents form part of the disclosure.
[0067] The blades or vanes 120, 130 may likewise have coatings
protecting against corrosion or oxidation (MCrAlX; M is at least
one element selected from the group consisting of iron (Fe), cobalt
(Co), nickel (Ni), X is an active element and represents yttrium
(Y) and/or silicon and/or at least one rare earth element, or
hafnium (Hf)). Alloys of this type are known from EP 0 486 489 B1,
EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1, which are
intended to form part of the present disclosure.
[0068] It is also possible for a thermal barrier coating,
consisting for example of ZrO.sub.2, Y.sub.2O.sub.4ZrO.sub.2, i.e.
unstabilized, partially stabilized or fully stabilized by yttrium
oxide and/or calcium oxide and/or magnesium oxide, to be present on
the MCrAlX. Columnar grains are produced in the thermal barrier
coating by means of suitable coating processes, such as for example
electron beam physical vapor deposition (EB-PVD).
[0069] Refurbishment means that after they have been used,
protective layers may have to be removed from components 120, 130
(e.g. by sand-blasting). Then, the corrosion and/or oxidation
layers and products are removed. If appropriate, cracks in the
component 120, 130 are also repaired. This is followed by recoating
of the component 120, 130, after which the component 120, 130 can
be reused.
[0070] The blade or vane 120, 130 may be hollow or solid in form.
If the blade or vane 120, 130 is to be cooled, it is hollow and may
also have film-cooling holes 418 (indicated by dashed lines).
[0071] FIG. 5 shows a combustion chamber 110 of a gas turbine. The
combustion chamber 110 is configured, for example, as what is known
as an annular combustion chamber, in which a multiplicity of
burners 107 arranged circumferentially around the axis of rotation
102 open out into a common combustion chamber space. For this
purpose, the combustion chamber 110 overall is of annular
configuration positioned around the axis of rotation 102.
[0072] To achieve a relatively high efficiency, the combustion
chamber 110 is designed for a relatively high temperature of the
working medium M of approximately 1000.degree. C. to 1600.degree.
C. To allow a relatively long service life even with these
operating parameters, which are unfavorable for the materials, the
combustion chamber wall 153 is provided, on its side which faces
the working medium M, with an inner lining formed from heat shield
elements 155.
[0073] On the working medium side, each heat shield element 155 is
equipped with a particularly heat-resistant protective layer or is
made from material that is able to withstand high temperatures.
These may be solid ceramic bricks or alloys with MCrAlX and/or
ceramic coatings. The materials of the combustion chamber wall and
their coatings may be similar to the turbine blades or vanes.
[0074] A cooling system may also be provided for the heat shield
elements 155 and/or their holding elements, on account of the high
temperatures in the interior of the combustion chamber 110.
[0075] The combustion chamber 110 is designed in particular to
detect losses of the heat shield elements 155. For this purpose, a
number of temperature sensors 158 are positioned between the
combustion chamber wall 153 and the heat shield elements 155.
* * * * *