Note: Descriptions are shown in the official language in which they were submitted.
CA 02740094 2011-04-08
METHOD FOR CONNECTING AT LEAST ONE TURBINE BLADE TO A TURBINE
DISK OR A TURBINE RING
DESCRIPTION
[001] The invention relates to a method for connecting at least one turbine
blade to
a turbine disk or a turbine ring for a turbine stage of a turbomachine, in
particular a
thermal gas turbine. The invention further relates to a turbine stage of the
type
indicated in the preamble of patent claim 4 for a turbine of a turbomachine as
well as
a turbomachine of the type indicated in the preamble of patent claim 6.
[002] This type of method for connecting at least one turbine blade to a
turbine disk
or a turbine ring as well as this type of turbine stage, which comprises a
turbine disk
or a turbine ring that is connected to one or more turbine blades at least
indirectly,
are known from the prior art. For its part, the turbine stage is arranged in a
single-
stage or multi-stage turbine of a turbomachine, particularly constructed as a
thermal
gas turbine. Advances in gas turbine construction, however, set continually
higher
requirements for the materials used. The turbine blades serving as rotating
blades or
vanes are thus essentially produced as polycrystalline, monocrystalline or
directionally solidified cast parts made of high-temperature-resistant base
alloys.
Turbine blades that are produced from composite materials that perform well at
high
temperatures are also known.
[003] This configuration, however, leads to the fact that the turbine blades
cannot
be fusion welded or can be fusion welded only with great difficulty. A
connection to
a turbine disk or a corresponding turbine ring that can be fusion welded and
that
can be produced from a nickel base alloy is thus not possible via conventional
fusion welding methods and leads to considerable increased cost.
Alternatively,
friction welding or diffusion welding methods are known for at least an
indirect
connection between turbine blade and turbine disk or turbine ring, but these
methods require a high equipment expense. In addition, temperatures that are
incompatible for the usual base alloys may occur with these welding methods.
[004] The problem of the present invention is thus to create a method of the
type
named initially, which can be conducted in a cost-effective and flexible
manner.
Another problem of the invention is to provide a corresponding turbine stage
having
a turbine disk or a turbine ring and at least one turbine blade, which can be
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produced in a cost-effective and flexible manner.
[005] The problem is solved according to the invention by a method according
to
patent claim 1, a turbine stage with the features of patent claim 4 as well as
by a
turbomachine with the features of patent claim 6. Advantageous embodiments
with
appropriate and non-trivial enhancements of the invention are indicated in the
respective dependent claims, wherein advantageous configurations of the method
are also to be viewed-insofar as they are applicable-as advantageous
configurations of the turbine stage, and vice versa.
[006] n a method according to the invention for connecting at least one
turbine
blade to a turbine disk or a turbine ring for a turbine stage of a
turbomachine, in
particular a thermal gas turbine, first a connecting body is formed on at
least one
turbine blade by means of a cold gas spraying method, and the connecting body
is
subsequently connected to the turbine disk or the turbine ring by means of a
fusion
welding method. A coating method in which the material in powder form for the
later connecting body is introduced onto the turbine blade at a high speed is
called
a cold gas spraying method. It may be provided for this purpose that a gas
heated
to a comparatively low temperature is accelerated to supersonic speed by
expansion in a nozzle (so-called Laval nozzle). Subsequently, the powder
particles are introduced into this gas and in this way are accelerated to such
high
velocities that they form a solidly adhering layer with a high density and
compactness without fusing upon impact on the turbine blade. The cold gas
spraying method is preferably conducted in such a way that the kinetic energy
of
the powder particles is insufficient for a complete fusion at the time point
of the
impact. In this way, a minimum input of heat into the turbine blade serving as
the
substrate is simultaneously assured. The impact velocity of the powder
particles
can be adjusted in a targeted manner as a function of the material used, for
example, by means of an optimized nozzle design, changes in gas temperature,
higher gas pressure or changes in particle size. Since the material of the
connecting body formed in this way is not fused, an oxidation of the involved
materials is reliably prevented. Subsequently, the turbine blade is connected
indirectly to the turbine disk or the turbine ring via the connecting body by
means of
the fusion welding method. Basically, as the material of the connecting body,
all
materials can thus be used that can be plastically deformed, can be fusion
welded
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and can withstand the later loads during operation in an assigned
turbomachine.
The method according to the invention can thus be conducted in a considerably
cost-effective manner without high equipment expense. Since the connection
between the turbine blade and the turbine disk or the turbine ring is effected
by
means of the connecting body, the material and the geometry of the turbine
blade
are of secondary importance, for which reason the method can be carried out in
a
particularly flexible manner. It may thus be basically provided that the
connecting
body can be formed of multiple parts.
[007] In an advantageous embodiment of the invention, it is provided that the
connecting body is machined, particularly precision-machined, prior to the
fusion
welding method. Precision-machined is to be understood here preferably as a
machining by cutting, whereupon both a desired surface quality as well as a
required dimensional stability of the connecting body can be assured in a
simple
and cost-effective manner.
[008] Further advantages result if the connecting body is formed in the region
of a
blade foot of the turbine blade and/or as a blade foot of the turbine blade.
In this
way, a simple and mechanically stable connection of the turbine blade to the
turbine disk or the turbine ring is made possible via the connecting body.
[009] In another advantageous embodiment of the invention, it is provided that
the
connecting body is formed as a function of the geometry of the turbine blade
and/or of the turbine disk or of the turbine ring. The method can be used here
in a
particularly flexible manner for producing different turbine stages.
[0010] In another embodiment, it has been shown to be advantageous, if an
electron-beam welding method and/or a laser welding method and/or an inductive
high-frequency pressure welding method and/or an inductive low-frequency
pressure welding method is used as the fusion welding method. In this way,
high
welding speeds with extremely deep and narrow welds are possible with short
thermal delay.
[0011]Since several turbine blades are connected to the turbine disk or the
turbine
ring via respective connecting bodies, a complete turbine stage for a
turbomachine
can be produced with the advantages according to the invention and
particularly
with reduced costs and an increased flexibility.
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[0012]Another aspect of the invention relates to a turbine stage for a turbine
of a
turbomachine, wherein the turbine stage can be produced in a cost-effective
and
flexible manner by connecting at least one turbine blade to the turbine disk
or the
turbine ring via a connecting body which has been formed on the turbine blade
by
means of a cold gas spraying method. Additional advantages that result can be
taken from the preceding descriptions.
[0013] Since the connecting body is connected to the turbine disk or the
turbine
ring by means of a fusion welding method, the manufacturing costs of the
turbine
stage can be additionally reduced.
[0014] In another advantageous embodiment of the invention, it is provided
that the
turbine disk or the turbine ring and/or the turbine blade is manufactured from
a
nickel base alloy and/or a cobalt base alloy and/or a titanium aluminide
and/or a
metal-matrix composite material and/or a ceramic-matrix composite material. In
this way, the turbine stage reliably possesses the required mechanical and
thermal
properties for later use in an assigned turbomachine and also can be adapted
in a
particularly flexible manner to the specific requirement profile.
[0015]Another aspect of the invention relates to a turbomachine, in particular
a
thermal gas turbine, with a turbine that comprises a turbine stage having a
turbine
disk or a turbine ring that is connected to at least one turbine blade, at
least
indirectly, wherein it is provided according to the invention that the turbine
disk or
the turbine ring and the at least one turbine blade of the turbine stage are
connected to one another by means of a method according to one of the
preceding
examples of embodiment, or that the turbine stage is formed according to one
of
the preceding embodiment examples. The combinations of features resulting from
this and their advantages can be taken from the corresponding descriptions.
[0016] Further advantages, features and particulars of the invention result
based
on the following description of an example of embodiment and based on the
drawings. Here:
[0017] Fig. 1 shows a perspective frontal view of a turbine blade;
[0018] Fig. 2 shows a perspective oblique view of a connecting body formed on
a
blade foot of the turbine blade shown in Fig. 1; and
[0019] Fig. 3 shows a cut-away and perspective frontal view of a turbine disk,
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which is connected to the turbine blade via the connecting body.
[0020] Fig. 1 shows a perspective frontal view of a turbine blade 10, the
general
construction of which is known from the prior art. Turbine blade 10, which is
manufactured as a cast part from a high-temperature-resistant nickel base
alloy,
comprises a radial outer shroud 12 and a radial inner blade foot 14. Since the
material from which turbine blade 10 is manufactured cannot be fusion welded
or can
be fusion welded only with great difficulty, a connecting body 16 shown in
perspective oblique view in Fig. 2 is formed by means of a cold gas spraying
method
in the region of blade foot 14 of turbine blade 10. The connecting body 16,
which is
formed from a plastically deformable material that can be fusion welded, makes
it
possible in a subsequent step to connect turbine blade 10 to a turbine disk 18
via a
cost-effective fusion-welding method. Basically, instead of turbine disk 18, a
turbine
ring (not shown) may be provided, wherein both turbine disk 18 as well as the
turbine
ring can be formed of one part or of several parts. In addition, it may be
provided that
connecting body 16 forms blade foot 14. Likewise, it can be basically provided
that
connecting body 16 is or will be formed of several parts or several pieces, so
that the
connection between turbine blade 10 and turbine disk 18 is produced indirectly
via
several connecting body parts (not shown).
[0021] Fig. 3 shows a cut-away and perspective frontal view of turbine disk
18, which
is connected in the region labeled with arrow III to turbine blade 10 via
connecting
body 16 presently formed in one piece. For example, an electron-beam welding
method, a laser welding method, an inductive high-frequency pressure welding
method and/or an inductive low-frequency pressure welding method can be used
as
the fusion-welding method. Basically, however, other welding methods familiar
to the
person skilled in the art also can be provided. In addition, it can be
provided that
connecting body 16 is precision-machined prior to fusion welding, whereby a
simple
geometric fitting between turbine blade 10 and turbine disk 18 is made
possible. A
complete turbine stage for a turbine of a thermal gas turbine can be produced
by
connecting several turbine blades 10 in an analogous way to turbine disk 18.
In this
way, it can be basically provided that the method is also used for the
production of
compressor stages for a compressor of a turbomachine or for connecting
compressor blades to a compressor disk.
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