U.S. patent application number 13/362489 was filed with the patent office on 2012-08-02 for cmc turbine engine blades and a rotor wheel for a turbine engine and a turbine engine integrating them.
This patent application is currently assigned to SNECMA. Invention is credited to Arthur COHIN, Damien CORDIER, Patrick Joseph Marie GIRARD, Son LE HONG, Jean-Luc SOUPIZON.
Application Number | 20120195766 13/362489 |
Document ID | / |
Family ID | 44534897 |
Filed Date | 2012-08-02 |
United States Patent
Application |
20120195766 |
Kind Code |
A1 |
COHIN; Arthur ; et
al. |
August 2, 2012 |
CMC TURBINE ENGINE BLADES AND A ROTOR WHEEL FOR A TURBINE ENGINE
AND A TURBINE ENGINE INTEGRATING THEM
Abstract
A rotor wheel of a turbine engine includes a plurality of CMC
blades each having a first portion constituting a blade airfoil and
root and made as a single piece with a second portion forming an
outer platform. The blades are held under twisting prestress by
mutual engagement via contact zones between the outer platforms of
adjacent blades, and the contact zones that are situated on
opposite sides of the outer platform of a blade are defined by at
least one insert that is integrated in the outer platform and that
is, for example, made of a carbon-based material.
Inventors: |
COHIN; Arthur; (La Varenne
Saint Hilaire, FR) ; CORDIER; Damien; (Les Ecrennes,
FR) ; GIRARD; Patrick Joseph Marie; (Saint Fargeau
Ponthierry, FR) ; LE HONG; Son; (Thomery, FR)
; SOUPIZON; Jean-Luc; (Vaux Le Penil, FR) |
Assignee: |
SNECMA
Paris
FR
|
Family ID: |
44534897 |
Appl. No.: |
13/362489 |
Filed: |
January 31, 2012 |
Current U.S.
Class: |
416/241A |
Current CPC
Class: |
F01D 5/288 20130101;
F05D 2260/96 20130101; F01D 5/282 20130101; Y02T 50/60 20130101;
Y02T 50/67 20130101; F05D 2300/603 20130101; Y02T 50/672 20130101;
F01D 5/225 20130101 |
Class at
Publication: |
416/241.A |
International
Class: |
F01D 5/14 20060101
F01D005/14; F01D 7/00 20060101 F01D007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 2, 2011 |
FR |
11 50821 |
Claims
1. A turbine engine rotor wheel including a plurality of blades of
composite material comprising fiber reinforcement densified with a
ceramic matrix, each blade having a first portion constituting a
blade airfoil and root and being formed as a single piece together
with at least one second portion forming an outer platform, in
which wheel the blades are prestressed in twisting about
longitudinal axes and are held under prestress by mutual engagement
via contact zones between the outer platforms of adjacent blades,
the contact zones situated on opposite sides of the outer platform
of a blade being defined by at least one insert integrated in the
outer platform of the blade.
2. A rotor wheel according to claim 1, wherein said at least one
insert is made of a carbon-based material.
3. A wheel according to claim 2, wherein said at least one insert
is made essentially of a material selected from monolithic graphite
and a carbon/carbon type composite material.
4. A wheel according to claim 1, wherein each blade outer platform
is provided with two inserts on respective sides of the outer
platform.
5. A wheel according to claim 1, wherein each blade outer platform
is provided with an insert that extends from one side of the outer
platform to the other.
6. A turbine engine including at least one rotor wheel according to
claim 1.
7. A turbine engine blade made of composite material comprising
fiber reinforcement densified with a ceramic matrix, the blade
having a first portion constituting a blade airfoil and root and
being formed as a single piece together with at least one second
portion forming an outer platform, wherein the outer platform
presents contact zones on opposite sides for coming into contact
with the outer platforms of adjacent blades when the blade is
integrated in a rotor wheel of a turbine engine, and the contact
zones are defined by at least one insert integrated in the outer
platform.
8. A blade according to claim 7, wherein said at least one insert
is made of a carbon-based material.
9. A blade according to claim 8, wherein said at least one insert
is made essentially of a carbon/carbon type material.
10. A blade according to claim 7, wherein the outer platform is
provided with two inserts arranged on opposite sides of the outer
platform.
11. A blade according to claim 7, wherein the outer platform is
provided with an insert that extends from one side of the outer
platform to the other.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to turbine engine blades made of
ceramic matrix composite (CMC) material, i.e. comprising fiber
reinforcement that is densified with a ceramic matrix.
[0002] The intended field is that of gas turbine blades for
aeroengines or for industrial turbines, and more particularly the
blades of rotor wheels of compressor or turbine stages, such as the
blades of a low pressure (LP) turbine.
[0003] Proposals have already been made to produce turbine engine
blades out of CMC. Reference may be made in particular to the
following documents: US 2011/0293828, US 2011/0311368, and US
2008/0229567.
[0004] Turbine engine blades are exposed to excitations that are
produced by their environment, in particular the wake effect from
nozzles (stationary vanes) or by unbalance. These excitations give
rise to vibratory stresses that it is desirable to damp in order to
avoid a blade breaking.
[0005] With wheels that have metal blades, it is known to damp
vibration between adjacent blades by means of parts that are
engaged freely in facing housings formed in the edges of outer
platforms of the blades, the parts being pressed against the walls
of the housings by centrifugal force in order to damp vibration.
Reference may be made to document U.S. Pat. No. 3,752,599.
[0006] Still in the context of wheels having metal blades, it is
known to provide damping by pre-twisting the blades about axes
extending substantially in the longitudinal directions of the
blades, i.e. axes that are substantially radial relative to the
axis of the wheel. The twisting prestress is maintained by mutual
engagement between the outer platforms of adjacent blades in the
wheel, via contact zones that are situated on opposite sides of the
outer platforms in the circumferential direction. A coating of
wear-resistant material is then conventionally applied to the
contact zones by welding, e.g. a coating of the material sold under
the name Stellite.RTM..
[0007] Such a solution cannot be envisaged for blades made of CMC
because of the difficulty firstly in binding a metal coating to a
CMC material, and secondly of guaranteeing that said binding is
long-lasting, given the difference between the coefficients of
thermal expansion of the metal coating and of the CMC material.
OBJECT AND SUMMARY OF THE INVENTION
[0008] An object of the invention is to provide a solution to the
problem of damping the vibratory stresses to which the blades of
rotor wheels of a turbine engine are subjected.
[0009] In a first aspect, the invention provides a turbine engine
rotor wheel including a plurality of blades of composite material
comprising fiber reinforcement densified with a ceramic matrix,
each blade having a first portion constituting a blade airfoil and
root and being formed as a single piece together with at least one
second portion forming an outer platform,
[0010] in which wheel the blades are prestressed in twisting about
longitudinal axes and are held under prestress by mutual engagement
via contact zones between the outer platforms of adjacent blades,
the contact zones situated on opposite sides of the outer platform
of a blade being defined by at least one insert integrated in the
outer platform.
[0011] The term "insert integrated in the outer platform" is used
herein to mean an insert that is made integrally with the outer
platform.
[0012] The invention is remarkable in particular by inserts being
integrated in the outer platforms of CMC blades in order to define
mutual contact zones between the outer platforms of blades that are
mounted with twisting prestress in the rotor wheel. This makes it
possible for a material to be selected for these zones in contact
that is other than a CMC material and that presents good resistance
to wear by friction, and that also advantageously presents good
behavior at high temperatures and good resistance to oxidation.
[0013] The inserts may be made of a carbon-based material, in
particular of a material selected from monolithic graphite and a
carbon/carbon (C/C) type composite material, such materials having
not only good resistance to wear but also a coefficient of thermal
expansion that is close to that of CMC type materials.
[0014] Each outer platform may be provided with two inserts
arranged on opposite sides of the outer platform, or with a single
insert extending from one side of the outer platform to the
other.
[0015] The twisting prestress angle that is applied to each of the
blades is preferably less than 7.degree., or indeed less than
5.degree., which angle may be greater when the longitudinal size of
the blade is large.
[0016] In another aspect, the invention provides a turbine engine
including at least one rotor wheel as defined above.
[0017] In yet another aspect, the invention provides a turbine
engine blade made of composite material comprising fiber
reinforcement densified with a ceramic matrix, the blade having a
first portion constituting a blade airfoil and root and being
formed as a single piece together with at least one second portion
forming an outer platform, in which blade the outer platform
presents contact zones on opposite sides for coming into contact
with the outer platforms of adjacent blades when the blade is
integrated in a rotor wheel of a turbine engine, and the contact
zones are defined by at least one insert integrated in the outer
platform.
[0018] The or each insert is made of a carbon-based material, in
particular essentially a material selected from monolithic graphite
and a C/C type composite material.
[0019] The outer platform may be provided with two inserts arranged
on either side of the outer platform or with a single insert
extending from one side of the outer platform to the other.
[0020] In yet another aspect, the invention provides a method of
fabricating a turbine engine blade as defined above, the method
comprising: [0021] making a single-piece fiber blank by
three-dimensional weaving; [0022] shaping the fiber blank to obtain
a single-piece fiber preform having a first portion forming a
preform for a blade airfoil and root and at least one second
portion forming a preform for a blade outer platform; and [0023]
densifying the fiber preform with a ceramic matrix in order to
obtain a blade of composite material that forms a single piece with
an integrated outer platform;
[0024] in which method the or each insert defining a contact zone
is inserted into the portion of the fiber blank that forms the
second preform portion.
[0025] The or each insert may for example be inserted in a zone of
non-interlinking between two layers of three-dimensional
weaving.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Other features of the invention appear on reading the
following description made by way of non-limiting indication and
with reference to the accompanying drawings, in which:
[0027] FIG. 1 is a diagrammatic perspective view of a turbine
engine blade in accordance with the invention;
[0028] FIG. 2 is a fragmentary diagrammatic view in perspective of
an LP turbine rotor wheel of a turbine engine fitted with blades
such as the blade of FIG. 1;
[0029] FIG. 3 is a view on a larger scale showing the outer
platform of the FIG. 1 blade;
[0030] FIG. 4 is a plan view of the FIG. 2 outer platform;
[0031] FIG. 5 is a section view on plane V of FIG. 4;
[0032] FIG. 6 is a highly diagrammatic illustration of an example
of how three sets of layers of yarns can be arranged in a fiber
blank that is made by three-dimensional weaving and that is
intended for use in making a fiber preform for a blade such as that
shown in FIG. 1;
[0033] FIGS. 7, 8, 9, 10, and 11 show successive steps in making a
fiber preform for a blade such as that shown in FIG. 1, starting
from a fiber blank such as that shown in FIG. 6; and
[0034] FIGS. 12 and 13 are a plan view and a section view of a
blade outer platform showing a second variant embodiment.
DETAILED DESCRIPTION OF EMBODIMENTS
[0035] The invention is applicable to various types of turbine
engine blade, in particular compressor blades or turbine blades for
various spools of a gas turbine, e.g. a blade for a rotor wheel of
an LP turbine, such as the blade 10 of FIG. 1.
[0036] In well-known manner, the blade 10 comprises an airfoil 20,
a root 30 formed by a portion of greater thickness, e.g. presenting
a bulb-shaped section, and extended by a tang 32, an inner platform
40 situated between the tang 30 and the airfoil 20 and an outer
platform 50 in the vicinity of the free end of the airfoil 20.
[0037] The airfoil 20 extends in a longitudinal direction between
the inner platform 40 and the outer platform 50, and in
cross-section it presents a curved profile of varying thickness
between its leading edge 20a and its trailing edge 20b. The root 30
is extended by the tang 32 so as to connect to the inner (or
bottom) face of the inner platform 40.
[0038] At its radially inner end, the airfoil 20 is connected to
the outer (or top) face 42 of the inner platform 40 that serves to
define the inside of the flow passage for the gas stream through
the turbine. The lower platform is terminated by overlap nibs 44
and 46. In the example shown, the face 42 of the lower platform is
sloping, so as to form generally a non-zero angle .alpha. relative
to the normal to the longitudinal direction of the blade. Depending
on the profile desired for the inside surface of the gas stream
flow passage, the angle .alpha. may be zero, or the face 42 may
have a profile that is generally non-rectilinear, e.g. that is
curved.
[0039] At its outer radial end, the airfoil 20 is connected to the
outer platform 50 via an inner (or bottom) face 52 of the outer
platform that defines the outside of the flow passage for the gas
stream. The outer platform defines a depression or bathtub 58.
Along the upstream and downstream edges of the bathtub 58, the
outer platform carries wipers 60 with ends that are suitable for
penetrating into a layer of abradable material carried by a turbine
ring (not shown) for reducing the clearance between the tip of the
blade and the turbine ring. In the example shown, the face 52 of
the outer platform extends substantially perpendicularly to the
longitudinal direction of the blade. In a variant, and depending on
the profile desired for the outer surface of the flow passage for
the gas stream, the face 52 may be sloping so as to form generally
a non-zero angle relative to the normal to the longitudinal
direction of the blade, or the face 52 may have a profile that is
generally non-rectilinear, e.g. that is curved.
[0040] In the example shown, the airfoil 20, the root 30, the inner
platform 40, and the outer platform 50 are made as a single piece
of CMC material, with the exception of inserts that are integrated
in the outer platform and that are made of a different material, as
explained below.
[0041] The rotor wheel 60 of the LP turbine is built up by
assembling blades 10 on a turbine disk 62 (FIG. 2) by engaging the
roots 30 in housings of corresponding shape formed in the periphery
of the disk 62.
[0042] The blades 10 are mounted with prestress in twisting, or
pre-twisting, along respective axes that extend substantially in
the longitudinal directions of the blades, i.e. axes that extend
radially relative within the wheel 60. The blades are held under
twisting prestress by the outer platforms 50 of adjacent blades
engaging mutually via contact zones that are situated on the
opposite sides 50a and 50b of the outer platforms, i.e. sides that
are opposite in the circumferential direction of the wheel 60.
[0043] In the example shown, the mutual engagement of the outer
platforms 50 is achieved with locking by means of complementary
shapes in relief that are formed in or on the sides 50a and 50b,
e.g. a notch 52a and a projecting portion 52b that are both
substantially V-shaped and situated substantially in the middle
portions of the sides 50a and 50b. Other complementary shapes in
relief could naturally be envisaged.
[0044] The contact zones in the notches 52a and the projecting
portions 52b are defined by respective inserts 54a and 54b that are
integrated in the outer platform 50 (see FIGS. 3 to 5). These
contact zones include at least the surfaces of the flanks 520a and
520b of the notches 52a and of the projecting portions 52b that
bear mutually against one another with contact pressure being
applied under the effect of the twisting prestress.
[0045] As shown in FIGS. 4 and 5, the insert 54a has a wedge-shaped
inner portion 540a that is engaged in the outer platform 50
substantially halfway across its thickness, and an outer portion
542a that defines the contact zone 520a, and that has top and
bottom edges substantially in continuity with the top and bottom
faces of the outer platform 50. In similar manner, the insert 54b
has a wedge-shaped inner portion 540b that is engaged in the outer
platform 50 substantially halfway across its thickness and an outer
portion 542b that defines the contact zone 520b and that has top
and bottom edges that are substantially in continuity with the top
and bottom faces of the outer platform 50.
[0046] The outer portions 542a and 542b of the inserts 54a and 54b
define the flanks 520a and 520b and possibly also adjacent portions
of the sides 50a and 50b, in particular at the bottom of the notch
52a and at the tip of the projecting portion 52b, with the
remainder of the sides 50a and 50b being defined by the CMC
material of the outer platform 50.
[0047] The CMC material of the blade 10 is formed by fiber
reinforcement that is densified with a ceramic matrix. The
reinforcement is formed of carbon fibers or of ceramic fibers, in
particular carbon fibers and/or refractory oxide fibers such as
fibers of silicon carbide (SiC) or essentially of SiC. The ceramic
matrix may be made of a refractory carbide, nitride, or oxide, e.g.
SiC. The twisting prestress needs to remain within the elastic
deformation range of the CMC material. Given the usual mechanical
properties of this type of material, a twisting angle of less than
7.degree., or indeed of less than 5.degree. is preferable for an LP
turbine blade of an airplane turbojet, in particular depending on
the longitudinal dimension of the blade, as mentioned above.
[0048] The material of the inserts 54a and 54b is selected from
materials that present better resistance to friction wear than does
the CMC material of the blade, while nevertheless being compatible
therewith, i.e. having a coefficient of thermal expansion that is
substantially equal to or close to that of the CMC material and
that is suitable for being inserted during the process of
fabricating the blade. For the inserts 54a and 54b, it is possible
to select in particular a carbon-based material such as monolithic
graphite or a composite material of the carbon-carbon (C/C) type,
i.e. comprising fiber reinforcement made of carbon fibers and
densified by a carbon matrix, possibly including ceramic particles
dispersed in the matrix and forming a minority fraction of the
matrix. Such C/C materials are well known in the friction field, in
particular for airplane brake disks.
[0049] The inserts 54a and 54b may be cut by being machined from a
block of graphite or of C/C type composite material. A block of C/C
type composite material may be obtained by superposing plies of a
fabric of carbon-precursor fibers, e.g. fibers of preoxidized
polyacrylonitrile (PAN) and by bonding them together, e.g. by
needling, and then transforming the precursor into carbon by heat
treatment in order to obtain a carbon fiber preform, and then
densifying the preform with a carbon matrix. The densification may
be performed by a liquid technique or by a gaseous technique. The
liquid technique consists in impregnating the preform with a
carbon-precursor resin and then transforming the resin into carbon
by curing and by pyrolysis. The gaseous technique consists in
depositing a matrix of pyrolytic carbon by chemical vapor
infiltration (CVI) by using a gas containing at least one
carbon-precursor gas such as methane or propane. These
densification methods are well known.
[0050] The CMC blade 10 is obtained by a process comprising making
a fiber blank by three-dimensional (or multilayer) weaving, by
shaping the fiber blank in tooling in order to obtain a fiber
preform constituting the fiber reinforcement of the CMC material,
and by densifying the fiber preform with a ceramic matrix. The
prefabricated inserts 54a and 54b are inserted in the stage of
making the fiber preform prior to the preform being densified. To
this end, zones of non-interlinking are provided, e.g. while
weaving, between two layers of yarns in the portion of the preform
that corresponds to the outer platform in order to be able to
insert the portions 540a and 540b of the inserts 54a and 54b.
[0051] A process for obtaining a blade 10 is described with
reference to FIGS. 6 to 10. With the exception of inserting inserts
into the outer platform, such a process is of the same type as
those described in the above-mentioned document US 2011/0311368 and
WO 2011/080443, the content of which is integrated herein by
reference and to which reference may be made for more details.
[0052] FIG. 6 is a very diagrammatic view of a fiber blank 100 from
which a fiber preform for the blade 10 can be shaped.
[0053] The blank 100 comprises three portions 102, 104, and 106
that are obtained by three-dimensional weaving, and only the
envelopes of those three portions are shown in FIG. 6. The portion
102 is intended, once shaped, to constitute a blade fiber preform
portion that corresponds to a preform for a blade airfoil and root.
The portion 104, once shaped, is to constitute the portions of the
blade fiber preform that correspond to preforms for blade platforms
and for blade outer platform wipers. The portion 106, once shaped,
is to constitute the portions of the blade fiber preform that
correspond to the preforms for blade platform reinforcement and for
blade outer platform overlap nibs.
[0054] The three portions 102, 104, and 106 are in the form of
strips that extend generally in a direction X that corresponds to
the longitudinal direction of the blade that is to be made. In its
portion that is to form an airfoil preform, the fiber strip 102
presents thickness that varies in determined manner as a function
of the thickness of the profile of the airfoil of the blade that is
to be made. In its portion that is to form a root preform, the
fiber strip 102 presents extra thickness 103 that is determined as
a function of the thickness of the root of the blade that is to be
made.
[0055] Various modes of three-dimensional weaving are described in
particular in document US 2010/0144227, the content of which is
integrated herein by reference. The variation in the thickness of
the strip 102 in its portion that is to form an airfoil preform may
be obtained by varying the numbers of layers of yarns, while the
extra thickness in the portion that is to form a root preform may
be obtained by inserting an insert.
[0056] The fiber strip 102 is of width l selected as a function of
the length of the (flat) developed profile of the airfoil and of
the root of the blade that is to be made, whereas each of the fiber
strips 104 and 106 presents a width L greater than l that is
selected as a function of the developed lengths of the platforms of
the blade that is to be made.
[0057] The fiber strips 104 and 106 are of substantially the same
width, and each of them is of a substantially constant thickness
that is determined as a function of the thicknesses of the
platforms of the blade that is to be made. Each of the strips 104
and 106 comprises a first portion 104b or 106b that extends along
and beside a first face 102b of the strip 102, a second portion
104a or 106a that extends along and beside the second face 102a of
the strip 102, and a third portion 105b or 107b that extends along
and beside the first face 102b of the strip 102.
[0058] The portions 104b and 104a of the strip 104 are connected
together by a connection portion 140c that extends transversely
relative to the strip 102 at a location corresponding to the
location of the inner platform of the blade that is to be made. The
connection portion 140c passes through the strip, making an angle
.alpha. relative to the normal to the longitudinal direction of the
fiber blank. Similarly, the portions 106b and 106a of the strip 106
are connected together by a connecting portion 160c that extends
transversely relative to the strip 102 and that is substantially
parallel to the connection portion 140c (and might possibly be
spaced apart therefrom).
[0059] The portions 104a and 105b of the strip 104 are connected
together by a connection portion 150c that extends transversely
relative to the strip 102 at a location corresponding to that of
the outer platform of the blade that is to be made. In the example
shown, the connection portion 150c passes through the strip 102
substantially perpendicularly to the longitudinal direction X of
the fiber blank. Similarly, the portions 106a and 107b of the strip
106 are connected together by a connection portion 155c that
extends transversely relative to the strip 102 and that is
substantially parallel and adjacent to the connection strip
150c.
[0060] Depending on the shape desired for the outer platform of the
blade, the connection portions 150c and 155c may pass through the
strip 102 while making a non-zero angle relative to the normal to
the longitudinal direction X of the blank, as for the inner
platform. In addition, the connection portions 140c, 160c, and/or
150c and 155c may be of profiles that are curvilinear instead of
being rectilinear as in the example shown.
[0061] The strips 102, 104, and 106 are woven simultaneously by
three-dimensional weaving without interlinking firstly between the
strip 102 and the portions 104b, 104a and 105b of the strip 104,
and secondly between the strip 102 and the portions 106b, 106a and
107b of the strip 106. Advantageously, a plurality of successive
blanks 100 are woven continuously in the X direction. Similarly,
there is no interlinking between the strips 104 and 106.
[0062] FIGS. 7 to 11 are highly diagrammatic and show how a fiber
preform of a shape close to that of the blade that is to be
fabricated can be obtained from a fiber blank 100.
[0063] The fiber strip 102 is cut at one end in the extra thickness
103 and at another end a little beyond the connection portions 150c
and 155c so as to provide a strip 120 of length that corresponds to
the longitudinal dimension of the blade that is to be fabricated
with an enlarged portion 130 formed by a portion of the extra
thickness 103 that is situated at a location corresponding to the
position of the root of the blade that is to be fabricated.
[0064] Furthermore, cuts are made at the ends of the portions 104b
and 105b of the strip 104, at the ends of the portions 106b and
107b of the strip 106, and in the portions 104a and 106a thereof so
as to leave segments 140a and 140b on either side of the connection
portions 140c and 160c, and also segments 150a and 150b on either
side of the connection portions 150c and 155c, as can be seen in
FIG. 7. The lengths of the segments 140a & 140b and 150a &
150b are determined as a function of the lengths of the platforms
in the blade that is to be made.
[0065] Because of the non-interlinking between the strip 102 and
the portions 104b, 104a and 105b of the strip 104, and also between
the strip 102 and the portions 106b, 106a and 107b of the strip
106, the segments 140a, 140b, 150a, and 150b can be folded out
perpendicularly relative to the strip 102 without cutting yarns so
as to form plates 140 and 150, as shown in FIG. 8.
[0066] The inserts 54a and 54b are put into place by being inserted
between the portions 151 and 152 of the strips 104 and 106 that
form the plate 150 and that are not interlinked by weaving.
Beforehand, cuts are made in the sides 150a and 150b of the plate
150 that are to form the sides 50a and 50b of the outer platform,
so as to give them the desired shapes in order to obtain the
complementary shapes in relief that are desired for these sides 50a
and 50b (FIGS. 9 and 10). The portions 151 and 152 forming the
outer and inner layers of the plate 150 may subsequently be
partially linked together, e.g. by stitching, so as to hold the
inserts 54a and 54b in place while forming the strip preform of the
blade.
[0067] A strip preform 200 of the blade that is to be fabricated is
subsequently obtained by molding, with the strip 102 being deformed
so as to reproduce the curved profile of the airfoil of the blade
(FIG. 11). The two layers of the inner plate 140 are deformed so as
to reproduce a shape similar to that of the inner platform of the
blade (in particular with its overlap nibs). The outer layer 151 of
the plate 150 is deformed so as to reproduce a shape similar to
that of the wipers of the outer platform of the blade, and the
inner layer 152 of the plate 150 is deformed to reproduce a shape
similar to that of the overlap nibs of the outer platform of the
blade. This produces a preform 200 with a portion 220 forming an
airfoil preform, a portion 230 forming a root preform (including a
tang preform), a portion 240 forming an inner platform preform (of
double thickness), a portion 250 forming an outer platform wiper
preform, and a portion 260 forming a preform of overlap nibs of the
outer platform, together with the inserts 54a and 54b between the
two layers of the plate 150 that are optionally linked together,
e.g. by stitching (153).
[0068] In a variant, instead of the strips 104 and 106, it is
possible to use a single strip, e.g. 104, by making provision while
weaving the strip 104 for zones of non-interlinking so as to make
it possible to form the portion of the preform corresponding to the
wipers of the outer platform and so as to make it possible to
insert the wedge-shaped portions of the inserts 54a and 54b.
[0069] The fiber preform may be densified with a ceramic material
in known manner. A first consolidation step with a first matrix
phase may be performed using a resin that is a precursor of the
ceramic consolidation matrix. The preform may be impregnated with
resin prior to being shaped, e.g. during the step of FIG. 7, or
after shaping and inserting the inserts 54a and 54b, with the
preform 200 being held in tooling that constitutes a mold. After
the resin has been polymerized and pyrolized, a consolidated
preform is obtained that conserves its shape without needing any
tooling to hold it. Densification may then be continued using a
liquid technique (impregnation with a resin that is a precursor of
a ceramic, followed by polymerization and pyrolysis), or by CVI. It
is possible beforehand to form a fiber/matrix interphase coating.
In particular reference may be made to documents US 2010/0015428
and US 2011/0293828. In a variant, the fiber preform may be
consolidated, not by pyrolyzing an impregnation resin, but by
partial densification by CVI, the preform being held in shape in
shaping tooling.
[0070] In the embodiment of FIGS. 4 and 5, insertion of the
wedge-shaped portions of the inserts 54a and 54b between the two
layers of the plate 150 at the fiber preform stage causes the outer
layer of the plate 150 to be deformed outwards, while the inner
layer of the plate 150 that corresponds to the face 52 of the outer
platform remains undeformed, given that the face 52 defines the
flow passage for the gas stream.
[0071] In another variant, a single insert may be provided that
extends from one side of the outer platform to the other by being
inserted between the two layers forming the plate 150. FIGS. 12 and
13 show such an arrangement with a single insert 64a extending
between the sides 50a and 50b of the outer platform 50 and having
shapes at its ends that are similar to those of the inserts 54a and
54b of FIGS. 4 and 5. The insert 64a is made of a material that is
similar to the material of the inserts 54a and 54b.
[0072] The description above relates to a blade made of CMC
material with integral platforms constituting a single piece
together with the airfoil and the root. In a variant, the blade may
be made with an outer platform that forms a single piece together
with the blade and the root, while the inner platform is fitted
separately thereto.
* * * * *