U.S. patent application number 09/836297 was filed with the patent office on 2001-11-22 for process for producing a thermally loaded casting.
Invention is credited to Beeck, Alexander, Ernst, Peter, Fried, Reinhard, Roesler, Hans-Joachim.
Application Number | 20010042607 09/836297 |
Document ID | / |
Family ID | 7642477 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010042607 |
Kind Code |
A1 |
Roesler, Hans-Joachim ; et
al. |
November 22, 2001 |
Process for producing a thermally loaded casting
Abstract
To produce a thermally highly loaded casting (1, 14, 16, 17) of
a thermal turbomachine which is produced using a known casting
process, the casting mold is produced from a slurry using a wax
model and a polymer foam which is fixed to the wax model or has
been introduced into a cavity. In this way, during the casting
process the liquid superalloy also penetrates into the open-cell
structure of the casting mold, so that an integral cooling
structure (7) is formed during the solidification of the casting
(1, 14, 16, 17). A single-crystal or directionally solidified
casting (1, 14, 16, 17) is advantageously produced. It is also
conceivable to vary the cell size of the polymer foam, to produce
cooling structure (7) and base material separately and to coat the
cooling structure (7) with a ceramic protective layer (thermal
barrier coating) (11).
Inventors: |
Roesler, Hans-Joachim;
(Braunschweig, DE) ; Beeck, Alexander;
(Kuessaberg, DE) ; Ernst, Peter; (Stadel, CH)
; Fried, Reinhard; (Nussbaumen, CH) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
7642477 |
Appl. No.: |
09/836297 |
Filed: |
April 18, 2001 |
Current U.S.
Class: |
164/34 ;
164/516 |
Current CPC
Class: |
F01D 5/186 20130101;
F01D 5/18 20130101; F01D 5/183 20130101; F05D 2230/211 20130101;
F05D 2300/611 20130101; B22C 9/04 20130101; F05D 2300/606 20130101;
F01D 5/187 20130101; B22C 7/023 20130101; B22C 7/02 20130101; F05D
2300/612 20130101; B22C 9/043 20130101 |
Class at
Publication: |
164/34 ;
164/516 |
International
Class: |
B22C 009/02; B22C
007/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 17, 2000 |
DE |
100 24 302.9 |
Claims
1. A process for producing a thermally loaded casting (1, 14, 16,
17) of a thermal turbomachine using a known casting process, the
thermally loaded casting (1, 14, 16, 17) having an integrated
cooling structure (7) and being produced using a casting mold,
characterized in that (a) a wax model of the part to be cooled is
prepared, (b) at least one polymer foam is prepared, which is fixed
to the wax model or is introduced into a cavity in the wax model,
(c) the at least one polymer foam and the wax model are immersed in
a ceramic material (slurry), the ceramic material accumulating
around the wax model and the polymer foam also being filled with
the ceramic material, (d) the ceramic material is dried, so that a
casting is formed, (e) the wax and the at least one polymer foam
are removed by a heat treatment, (f) the casting (1, 14, 16, 17) is
produced using the casting mold by a known casting process, and (g)
the ceramic material is removed.
2. A process for producing a thermally loaded casting (1, 14, 16,
17) of a thermal turbomachine using a known casting process, the
thermally loaded casting (1, 14, 16, 17) having an integrated
cooling structure (7) and being produced using a casting mold,
characterized in that (a) a wax model of the part to be produced is
prepared, (b) a prefabricated ceramic insert with an open-cell
structure is attached to the wax model or is introduced into a
cavity in the wax model, (c) the wax model together with the insert
is immersed in a ceramic material (slurry), (d) the ceramic
material is dried, so that a casting mold is formed, (e) the wax is
removed by a suitable heat treatment, (f) the casting (1, 14, 16,
17) is produced using the casting mold by a known casting process,
and (g) the ceramic material of the casting mold is removed.
3. The process as claimed in claim 2, characterized in that the
ceramic insert is heated before being used in step (b) of claim
2.
4. The process as claimed in claim 2, characterized in that the
open-cell structure of the prefabricated, ceramic insert is
produced by a polymer foam, the polymer foam being immersed in a
ceramic material, so that the cells in the polymer foam are filled
with the ceramic material and the ceramic material is then dried
and fired.
5. The process as claimed in claim 4, characterized in that the
polymer foam is removed by a heat treatment before use in process
step (b) of claim 2.
6. The process as claimed in claim 4, characterized in that the
open-cell structure of the prefabricated, ceramic insert is
produced by a polymer foam which is introduced into a prefabricated
mold and is then filled with the ceramic material in the mold or
separately from the mold.
7. The process as claimed in claim 6, characterized in that the
material of the prefabricated mold contains a binder.
8. A process for producing a thermally loaded casting (1, 14, 16,
17) of a thermal turbomachine using a known casting process, the
thermally loaded casting (1, 14, 16, 17) having an integrated
cooling structure (7) and being produced using a casting mold,
characterized in that (a) the casting (1, 14, 16, 17) is produced
using a casting mold by means of a known casting process, (b) the
porous cooling structure (7) is produced separately from the
casting by means of a casting mold which is formed by a porous
polymer and a ceramic material, and (c) the casting (1, 14, 16, 17)
and the cooling structure (7) are joined to one another by
soldering or welding.
9. The process as claimed in one of claims 1, 2 or 8, characterized
in that an open-cell cooling structure (7) which faces outward and
is situated on the casting (1, 14, 16, 17) is coated with a ceramic
protective layer (11).
10. The process as claimed in claim 9, characterized in that the
ceramic protective layer (11) penetrates all the way through the
cooling structure (7) or the cooling structure (7) is only coated
with the protective layer (11) close to the surface.
11. The process as claimed in claim 10, characterized in that
locations on the surface of the casting (1, 14, 16, 17) at which
cooling holes (8) are to be formed are masked prior to the coating
with a ceramic protective layer (11), and these locations are
unmasked again after the coating step.
12. The process as claimed in one of claims 1, 4, 5, 6 or 8,
characterized in that a plurality of layers of the polymer foam and
the wax are present, which serve to produce open-cell cooling
structures (7) which are separated from one another by plates
(15).
13. The process as claimed in one of claims 1, 4, 5, 6 or 8,
characterized in that the polymer foam has a variable cell
size.
14. The process as claimed in one of claims 1, 4, 5, 6 or 8,
characterized in that the polymer foam is a polyurethane foam.
15. The process as claimed in claim 1, 2 or 8, characterized in
that a casting process is used to produce single-crystal or
directionally solidified castings.
16. The process as claimed in one of claims 1, 2 or 8,
characterized in that it is a process for producing a guide vane or
a rotor blade (1), a heat-accumulation segment (14), a platform
(17) for the guide vane or rotor blade (1, 16), a
combustion-chamber wall (18) of a gas turbine or a guide vane or
rotor blade (1, 16) of a compressor.
Description
[0001] The invention relates to a process for producing a thermally
loaded casting of a thermal turbomachine according to the preamble
of claim 1.
[0002] It has long been known to provide parts of thermal
turbomachines which are exposed to hot gas, i.e. for example
turbine blades of gas turbines, with cooling-air bores or with
cooling structures, in order firstly to be able to increase the
temperature of the hot gas and secondly to extend the service life
of the parts in question. On the one hand, the inner side or a
cooling system which is of double-walled design and is used for a
turbine blade, for example, is cooled by cooling air as a result of
the heat being dissipated to the outside. On the other hand, the
outer side of the blade is cooled by a film which forms on the
surface of the turbine blade. The aim is to make the film cooling
as effective as possible and, at the same time, to reduce the
amount of cooling air.
[0003] Gas turbine blades which operate with film cooling are
known, for example, from the publications DE 43 28 401 and U.S.
Pat. No. 4,653,983.
[0004] Furthermore, it is known to use metal felts in turbine
blades. This is disclosed, for example, in document DE-C2-32 03 869
or in DE-C2-32 35 230. This use of a metal felt has the task of
providing a (internal) cooling system. At the same time, this metal
felt can serve as protection against abrasion from external
mechanical loads, in particular if it has been arranged on the
outer side of the turbine blade and has been coated with a ceramic
protective layer. A turbine blade with similar properties is also
known from European Document EP-B1-132 667.
[0005] However, a less advantageous feature of these blades is that
they do not comprise a single part, but rather the metal felt
always has to be fitted in a further process step.
[0006] The invention is based on the object of providing a process
for producing a thermally loaded casting of a thermal turbomachine
with an integrated cooling structure which increases the efficiency
of the turbomachine. The cooling structure is to consist of the
same material as the casting and as far as possible it is also to
be possible to produce it in a step which is part of the casting
process.
[0007] According to the invention, the object is achieved by a
process in accordance with the preamble of claim 1 in that a wax
model of the part to be cooled is prepared, at least one polymer
foam is prepared, which is fixed to the wax model or is introduced
into a cavity in the wax model, the at least one polymer foam and
the wax model are immersed in a ceramic material, the ceramic
material accumulating around the wax model and the polymer foam
also being filled with the ceramic material, the ceramic material
is dried, so that a casting mold is formed, the wax and the at
least one polymer foam are removed by a heat treatment, the casting
is produced using the casting mold by a known casting process, and
the ceramic material is removed.
[0008] In a second embodiment, the object is achieved in a similar
way. As a distinguishing factor, however, a ceramic insert is
prefabricated from a polymer foam with an open-cell structure. This
ceramic insert is attached to the wax model or is introduced into a
cavity in the wax model and the casting mold is produced as
described above.
[0009] To maintain the external mass of the cooling structure, it
is advantageously conceivable to use a prefabricated mold in which
the polymer foam is foamed. The slurry can be applied to the
polymer foam when it is still in the mold. In this way, it is even
possible to form complicated three-dimensional forms of the cooling
structure. For better drying of the slurry which is still liquid,
the material of this mold may also contain a binder.
[0010] A prefabricated ceramic insert of this type can be heated
considerably before being used for production of the casting mold,
in order in this way to achieve a particular strength. It is also
conceivable to burn out the polymer foam of the insert prior to
application to the wax model.
[0011] In a third embodiment, the object according to the invention
is achieved by separate production of the casting and the open-cell
cooling structure. In a further process step, the two parts are
joined to one another by soldering or welding.
[0012] Furthermore, it is possible for an open-cell cooling
structure which faces outward to be covered with a ceramic
protective layer, in order to protect the casting from additional
external abrasion and from the hot gases which surround it. Because
of the open-cell structure of the metal foam, the ceramic
protective layer adheres very well thereto and the possibility of
flaking caused by the extreme operating conditions is reduced. In
addition, cooling below the ceramic protective layer is still
ensured provided that the ceramic protective layer does not
penetrate all the way through the cooling structure.
[0013] In all the abovementioned embodiments it is advantageously
possible to use a polymer foam of variable cell size, in order in
this way to cool certain regions of the cooling system to a greater
or lesser extent than other regions. The process will
advantageously be a casting process for producing a single-crystal
or directionally solidified component. The thermally loaded casting
may, for example, be a guide vane or a rotor blade, a
heat-accumulation segment, a platform for the guide vane or the
rotor blade or a combustion-chamber wall of a gas turbine or a
rotor blade of a compressor.
[0014] In the drawing:
[0015] FIG. 1 shows part of a cooled turbine blade which has been
produced using the process according to the invention,
[0016] FIG. 2 shows a cross section through a turbine blade
according to the invention,
[0017] FIG. 3 shows a longitudinal section through a turbine blade
according to the invention,
[0018] FIG. 4 shows a section through an embodiment of a heat
shield according to the invention,
[0019] FIG. 5 shows a section through a second embodiment of a heat
shield according to the invention,
[0020] FIG. 6a shows a variation of excerpt VI in FIG. 5, FIG. 6b
shows a second variation of excerpt VI in FIG. 5,
[0021] FIG. 7 shows a guide vane according to the invention with
cooled platforms, and
[0022] FIG. 8 shows a cooled wall of a combustion chamber which has
been produced using the process according to the invention.
[0023] Only the elements which are significant to the invention are
illustrated. Identical elements are provided with the same
reference numerals in different drawings. The direction of flow is
indicated by arrows.
[0024] The invention relates to a process for producing a thermally
loaded casting for a thermal turbomachine. This casting may,
specifically, be, for example, a guide vane or rotor blade of a gas
turbine or a compressor, a heat-accumulation segment of a gas
turbine, the wall of a combustion chamber or a similar casting
which is subjected to high thermal loads. These castings and the
process according to the invention for their production are
explained in more detail below with reference to the enclosed
figures. A common feature of all these castings is that they need
to be cooled on account of the external thermal loading and for
this reason include an integrated open-cell cooling system.
[0025] The castings are produced using casting furnaces which are
generally known from the prior art. A casting furnace of this type
can be used to produce components which are of complex design and
can be exposed to high thermal and mechanical loads. Depending on
process conditions, it is possible to produce the casting in
directionally solidified form. It is possible to produce the
casting as a single crystal (SX) or in polycrystalline form as
columnar crystals which have a preferred direction (directionally
solidified, DS). It is particularly important for the directional
solidification to take place under conditions in which considerable
heat exchange takes place between a cooled part of a casting mold
which accommodates molten starting material and the starting
material which is still molten. It is then possible for a zone of
directionally solidified material to form with a solidification
front which, under the ongoing extraction of heat, migrates through
the casting mold, forming the directly solidified casting.
[0026] The document EP-A1-749 790 has disclosed, by way of example,
a process of this type and a device for producing a directionally
solidified casting. The device comprises a vacuum chamber which
includes an upper heating chamber and a lower cooling chamber. The
two chambers are separated by a baffle. The vacuum chamber
accommodates a casting mold which is filled with a molten material.
To produce thermally and mechanically loadable parts, such as in
the case of guide vanes and rotor blades of gas turbines, by way of
example a nickel-based superalloy is used. In the middle of the
baffle there is an opening, through which the casting mold is
slowly moved from the heating chamber into the cooling chamber
during the process, so that the casting is directionally solidified
from the bottom upward. The downward movement takes place by means
of a drive rod on which the casting mold is mounted. The base of
the casting mold is of water-cooled design. Means for generating
and guiding a gas flow are present beneath the baffle. By means of
the gas flow next to the lower cooling chamber, these means provide
additional cooling and therefore a greater temperature gradient at
the solidification front.
[0027] A similar process which, in addition to heating and cooling
chamber, operates with additional gas cooling, is also known, for
example, from the U.S. Pat. No. 3,690,367.
[0028] A further process for the production of a directionally
solidified casting is known from the document U.S. Pat. No.
3,763,926. In this process, a casting mold which has been filled
with a molten alloy is immersed continuously in a bath which has
been heated to approximately 260.degree. C. The result is a
particularly rapid dissipation of heat from the casting mold. This
and other similar processes are known under the term LMC (liquid
metal cooling).
[0029] It is advantageous for the invention to utilize this type of
casting furnace to produce single-crystalline or directionally
solidified castings, but the invention is not restricted
thereto.
[0030] The process according to the invention for producing a
turbine blade 1, as is shown, for example, in various embodiments
in FIGS. 1 to 3, relates to a cooling system 7 which is integrated
in the turbine blade 1 and is partially or completely filled with
an open-cell metal foam 9. The turbine blade 1 in FIG. 1 has a
cavity 6, from which, while the turbomachine is operating, cooling
air 18 is passed through inner cooling holes 8, 8b into the cooling
system 7, which is of double-walled design. The arrows indicate the
direction of flow of the cooling air 18. The cooling air 18 then
flows both upward inside the turbine blade and onto the rear edge 3
of the turbine blade 7. It is able to leave the cooling system 7
again at the rear edge 3, at outer cooling holes 8, 8a or else at
larger cooling openings 8, 8c, both of which may be present on the
front side 2, on the pressure side 4 or on the intake side 5. At
the outer cooling holes 8, 8a, film cooling is established, while
the walls in the interior of the cooling system 7 are cooled by
convection. As can be seen at the cut-away section in FIG. 1,
depending on the application it is also possible for axial ribs 10
to be present inside the cooling system 8, in which ribs there is
no metal foam 9 and in which ribs the cooling air 18 can flow
unimpeded.
[0031] FIG. 3, which shows the front edge 2 of the blade root 9
through to the blade tip 10 in the form of a longitudinal section
through a turbine blade 1 according to the invention, discloses the
direction of flow of the cooling air 18. The cooling air 18 enters
the cooling system 7 through inner cooling openings 8, 8b of the
cavity 6. The cooling air 18 then flows through the cells of the
metal foam 9 which is situated inside the cooling system 7.
[0032] It is now an object of the invention to manufacture cooling
systems 7 of this type which are filled with open-cell metal foam 9
integrally with the overall casting as early as during the casting
process, using casting furnaces as have been mentioned above. To do
this, a wax model of the part to be cooled is prepared. An
open-cell polymer foam, which may, for example, be a polyurethane
foam, is fixed to the wax model of the part which is to be cast or
is introduced into a cavity which may be present in the wax model.
It is also possible to fix together various wax/polymer models to
form an overall model. The polymer foam and the wax model are then
immersed in a liquid ceramic material, which is also known as a
slurry. In the process, not only is the subsequent casting mold for
the casting formed around the wax model, but also the ceramic
material penetrates into the cells of the polymer foam. The slurry
penetrates all the way through the polymer foam, since it is an
open-cell foam. The ceramic material is then dried, so that the
casting mold, which is used to produce the casting, is formed.
After the drying of the slurry, the wax and also the polymer foam
are removed by a suitable heat treatment, i.e. are burnt out. In
this process step, the casting mold is fired, i.e. in this way it
acquires its strength. The casting is produced using the casting
mold which has been formed in this way by a known casting furnace,
which has been described in more detail above, in a known way.
Since, during the filling step, the liquid alloy penetrates without
problems not only into the casting mold itself but also into the
cells which have been formed by the polymer foam and form the
subsequent cooling system, the abovementioned metal foam 9 is
formed, as cooling system 7, at the same time as the solidification
of the alloy. Advantageously, the casting and the metal foam then
comprise a single part and there are no further process steps
involved in the production of the cooling structure. By dint of the
casting process and the subsequent solidification, this type of
production also avoids porosity of the superalloy inside the metal
foam 9, since the liquid alloy is distributed uniformly within the
open-cell casting mold (formed by the polymer foam) as early as
during the filling step.
[0033] The ceramic casting mold can then be removed in a suitable
way, for example by using an acid or an alkali.
[0034] With the process described, it is also possible to create a
structure as can be seen in FIG. 2, which diagrammatically depicts
a section through a turbine blade 1 according to the invention. In
this case, the cooling structure 7 is only present on the front
edge 2 of the turbine blade 1. This cooling structure 7 was
created, as has already been described above, by simply attaching
the polymer foam to the wax model. All the other process steps of
the production are the same. In the exemplary embodiment shown in
FIG. 2, the cooling air 18 penetrates from the cavity 6, through
the cooling holes 8, 8b, into the cooling structure 7. The cooling
structure 7 itself is coated with a ceramic protective layer 11
(thermal barrier coating, TBC). This takes place, for example,
using a plasma spraying process which is known from the prior art
or an equivalent coating process.
[0035] Naturally, prior to the coating with the TBC from the prior
art, a known heat treatment, which is not referred to in more
detail here, of the blank casting is required. It is also
conceivable for a metallic protective layer, such as MCrAlY, to be
applied prior to the coating with TBC, using known means.
[0036] The coating of the porous cooling structure 7 with TBC can
take place in various ways (by varying the parameters such as
spraying angle, spraying distance, spraying particle size, spraying
velocity, spraying temperature, etc.). TBC can penetrate all the
way through the cooling structure 7, so that the cells of the metal
foam 9 are completely filled. Cells allow very good adhesion of the
TBC. The cooling structure 7 may also be covered with TBC only in a
layer which lies close to the surface, so that beneath the TBC
protective layer there is still a layer into which cooling air 18
can penetrate. It is also conceivable for cooling holes 8 to be
present inside the protective layer 11, through which the cooling
air 18 emerges to the outside. On account of the open-cell
structure of the metal foam 9, the ceramic protective layer 11
adheres very well thereto. The adhesion of the ceramic protective
layer 11 to the cooling structure can be improved still further by
coarsening of the cell size toward the outside (where the
protective layer 11 is applied). The flaking of the TBC while the
casting is in operation as a result of poor adhesion to the base
material is advantageously significantly reduced or prevented.
[0037] If the ceramic protective layer 11 is sufficiently porous
for it to allow cooling air to pass through to a sufficient extent,
there is no need for any external cooling holes. In this way, it is
possible to achieve a so-called sweat cooling, which has proven
highly effective in terms of its cooling action.
[0038] Possible cooling holes 8 inside the ceramic protective layer
11 may have formed as a result of suitable masking taking place
prior to the coating with TBC, and unmasking using suitable means
taking place thereafter. The masking may, for example, take place
using polymer foam which is burnt out for unmasking. A second
possibility of masking the surface consists in providing locations
which occupy this position inside the casting mold. In this case,
the ceramic casting mold at these locations is only removed after
coating with TBC.
[0039] The production of a metal foam 9, as in FIG. 2, at the outer
surface and the additional coating with TBC is appropriate in
particular at the locations at which abrasion may occur as a result
of a mechanical action, for example at the blade tip of a turbine
blade 1 or at a heat-accumulation segment, since the open-cell
structure of the metal foam 9 is highly flexible and does not
become blocked by the abrasion itself. Overall, however, the
abrasion is reduced by the flexibility of the metal foam 9.
[0040] In a second embodiment of the process according to the
invention, the polymer foam, before it is attached to the wax model
or before it is introduced into a cavity which is situated in the
wax model, is treated with a slurry, so that a separate model of
the cooling structure made from a ceramic material is formed. The
polymer foam is immersed in the slurry, so that the cells fill up.
This is followed by the obligatory drying of the slurry. When
producing this insert, it should be ensured that the size, i.e. the
external dimensions, of the polymer foam are not affected or are
affected only within narrow tolerance limits. This can also be
ensured by foaming the polymer foam in a mold, so that the external
dimensions and, under certain circumstances, also a complex
three-dimensional shape are fixedly predetermined. It is also
conceivable to introduce the slurry into the polymer foam while it
is still in this mold. This ceramic model or this insert, as has
already been described above, is fixed to the wax model or is
introduced into a cavity before the overall casting mold is
produced and the wax/polymer foam is burnt out. Optionally, the
polymer foam may be burnt out before the attachment or
introduction.
[0041] The material of the abovementioned mold in which the polymer
foam can be foamed in order to maintain the external dimensions can
contain a binder for improved drying of the slurry.
[0042] An insert of this type can additionally be heated by a heat
treatment before being attached to the wax model, which further
increases the strength. In the ceramic body, this takes place by
means of a sintering operation. Overall, the casting mold becomes
stronger and denser.
[0043] With the process according to the invention, it is also
possible to produce castings as illustrated in FIGS. 4 to 8. FIGS.
4 and 5 show a heat-accumulation segment 14 of a gas turbine. This
heat-accumulation segment 1 may have a double-walled cooling
structure 7 (FIG. 4) or an externally applied metal foam 9 (FIG.
5), which in a similar way to the turbine blade shown in FIG. 2 may
be partially or completely coated with a protective layer 11 of
TBC. In both embodiments, cooling air 18 flows through the
heat-accumulation segment. This is made possible by the open-cell
metal foam 9. The cooling air 18 penetrates through cooling holes 8
into the cooling system 7 and leaves it again through these
holes.
[0044] FIGS. 6a, 6b show two variants of the excerpt VI from FIG.
5. As can be seen from FIG. 6a, the metal foam 9 can acquire a
different cell size by varying the cell size of the polymer foam
during the production process. FIG. 6a shows the metal foam
9.sub.1, 9.sub.2 with a variable cell size. This allows greater or
lesser cooling of individual regions of the casting. As has already
been mentioned above, this is also advantageous for better
attachment of the protective layer 11 to the metal foam 9. As
described above, the protective layer 11 may also have cooling
holes 8 passing through it, through which the cooling air 18 can
flow to the outside.
[0045] While the casting is in operation, it may be necessary to
filter the cooling air, in order to prevent the fine-cell structure
from becoming blocked by contaminants which are situated in the
cooling air, thus reducing the cooling capacity.
[0046] In FIG. 6b, which shows a second variant of excerpt VI from
FIG. 5, the cooling system 7 comprises a plurality of layers of the
metal foam 9, with plates 15 between them. The number of layers of
metal foam 9/plate 15 is selected purely by way of example and is
dependent on the specific application. Even during production as
described above, a plurality of layers of wax/polymer foam are
prepared, from which the casting mold for the casting is then
produced, as described in more detail above. During production,
this leads directly to the exemplary embodiment illustrated in FIG.
6b. The cooling air 18 penetrates through the metal foam 9, can
flow within a "plane" and can cool by convection or transpiration.
Although the various planes are separated by the plates 15, there
are cooling holes 8 through which the cooling air 18 can change
plane. Generally, the specific design of this cooling system 7 is,
of course, dependent on the individual case. The cooling holes 8
within the plates 15 are likewise formed as early as during
production.
[0047] The statements which have been made also apply to the guide
vane 16 which is illustrated in FIG. 7 and has two cooled platforms
17, and the combustion-chamber wall 19 which is shown in FIG. 8 and
is likewise cooled. Further exemplary embodiments, which are not
illustrated by figures, include the cooled castings (blades etc.)
of a compressor.
[0048] The castings with an integrated, open-cell cooling system 7
which are produced using the process according to the invention are
also advantageous because the pressure difference in the cooling
medium between the external pressure and the internal pressure
(inside the cavity 6) has a considerable influence on the
efficiency of cooling. This pressure difference can be set and
controlled very accurately by suitably selecting the cells
(distribution, size, etc.) of the metal foam 9.
[0049] As a third exemplary embodiment of the process according to
the invention, the casting and the porous cooling structure 7 can
be produced by separate casting processes and can subsequently be
joined together by soldering or welding. The porous cooling
structure 7 is produced by the abovementioned polymer foam and the
slurry, if appropriate using a mold.
LIST OF REFERENCE SYMBOLS
[0050] 1 Turbine blade
[0051] 2 Front edge
[0052] 3 Rear edge
[0053] 4 Pressure side
[0054] 5 Intake side
[0055] 6 Cavity in turbine blade 1
[0056] 7 Cooling structure
[0057] 8 Cooling holes
[0058] 8a Cooling holes, outside
[0059] 8b Cooling holes, inside
[0060] 8c Cooling opening
[0061] 9 Metal foam
[0062] 9.sub.1, 9.sub.2 Metal foam of variable porosity
[0063] 10 Axial ribs
[0064] 11 Ceramic protective layer
[0065] 12 Blade root
[0066] 13 Blade tip
[0067] 14 Heat-accumulation segment
[0068] 15 Plate
[0069] 16 Guide vane
[0070] 17 Platform of guide vane 16
[0071] 18 Cooling air
[0072] 19 Combustion-chamber wall
* * * * *