The present invention relates to tooling for
fabricating a foundry core for making a cooling circuit
in a turbine engine blade.
A turbine engine blade, and in particular a blade
for a turbine wheel of a turbine engine, includes a
cooling circuit that is fed with air via or~fices formed
in the blade root, these orifices opening out into
internal cavities of the blade that communicate with a
bathtub at the tip of the airfoil of the blade. The
bathtub is formed by a recess at the tip of the blade,
being separated from internal cavities in the blade by a
bathtub bottom wall, and it is in fluid flow
communication with the internal cavities via orifices
passing through said bottom wall. In operation, air
penetrates into the orifices in the blade root, flows
along the internal cavities in the blade, and is then
expelled, in part into the bathtub via the abovementioned
orifices, and in part into the annular passage
through the turbine via air outlet orifices in the
airfoil of the blade.
The cooling circuit of a blade of this type includes
in particular the bathtub, the internal cavities in the
blade, and the orifices in the bathtub bottom wall that
provide fluid flow communication between the bathtub and
the internal cavities.
This cooling circuit is complex in shape and it is
generally obtained by means of a foundry core that is
inserted in a mold into which a molten metal is cast in
order to make the blade.
Documents EP-A1-1 661 642, EP-B1-1 754 555 and EPAl-
1 980 343 describe cores of this type.
The core is generally made from a paste comprising
ceramic fillers and a polymer-based binder, which paste
is injected into a mold of tooling and is then heated in
order to solidify the core.
In the prior art, the mold of the tooling includes
imprints for a first portion of the core that is to form
the bathtub of the blade, and for one or more other
portions imprint that are to form one or more respective
internal cavities of the blade
The mold includes a wall separating the first
portion of the imprint from the or the other portions of
the core, this wall serving to define a space in the core
between its first portion and its other portions. During
fabrication of the blade, molten metal penetrates into
this space in the core in order to form of the abovementioned
bathtub bottom wall of the blade.
As explained above, this bathtub bottom wall is
pierced by orifices. These orifices are obtained in
casting by means of ceramic rods that are positioned in
the mold, prior to fabricating the core, and that form
integral portions of the core after it has been
fabricated.
Each ceramic rod generally connects the first
portion of the core to one of the above-mentioned other
portions (EP-B1-1 754 555).
In the prior art, the mold for fabricating the core
includes means for bearing against and/or embedding end
portions of each rod. One of those means is formed on
the above-mentioned wall of the mold, and the other means
is formed on another portion of the mold, that is
opposite from the above-mentioned wall relative to the
imprint for the first portion of the core. Each rod thus
passes through the imprint of the first portion of the
mold.
In particular, the diameter of the orifices in the
bathtub bottom wall is a function of the diameter of the
ceramic rods of the core. To reduce the diameter of
these orifices, it is possible to reduce the diameter of
the rods. Nevertheless, it has been found that rods of
small diameter (e.g. of about 0.6 millimeters (rnm)) are
relatively fragile and frequently break while the paste
is being injected into the mold, thereby causing the core
to be scrapped.
5 A particular object of the present invention is to
provide a solution to this problem that is s~mple,
effective, and inexpensive.
To this end, the invention provides tooling for
fabricating a foundry core for making a cooling circuit
10 in a turbine engine blade, the core comprising a first
portion for defining a bathtub of the blade and at least
one other portion for defining an internal cavity in the
blade, and at least one rod that extends between the
first portion and the or each other port~on and that is
15 to define means for passing fluid between the bathtub and
the corresponding internal cavity in the blade, the
tooling comprising a mold for injecting a paste and
having imprints for the first portion and for the or each
other portion of the core, and means for bearing against
20 and/or embedding end portions of the or each rod, one of
these means being formed in a idall of the mold between
the imprint for the f~rst portion of the core and the
imprint for the or each other portion of the core, the
tooling being characterized in that it includes support
25 means in the imprint for the first portion of the core to
support a substantially middle portion of the or each
rod.
According to the invention, the middle portion of
the or each rod, which is the portion of the rod that is
30 most subjected to buckling while the paste is being
injected into the mold, is supported by means for holding
the or each rod in position so as to prevent them from
deforming and breaking under the effect of the forces
applied while injecting the paste. The invention makes
35 it possible to make a foundry core for a turbine engine
blade in which the rod(s) is/are of relatively small
diameter, less than 0.8 rnm, e.g. about 0.6 mm.
The support means for supporting a rod are
independent of the support means for supporting other
rods. The means for supporting the rods may be spaced
apart from one another and the means for supporting a rod
may be situated halfway from the bearing and/or
engagement means for the rod.
By way of example, the support means comprise at
least one projecting member projecting from the bottom of
the imprint for the first portion of the core, this
member being substantially semi-ovoid in shape, for
example.
The or each member may include a notch in its tip
for receiving the middle portion of a rod.
The notch may be of section that is substantially Lshaped,
preferably having trio plane intersecting faces
that are to be substantially parallel to the longitudinal
axis of the corresponding rod. The rod is to bear
against each of the faces via a bearing line that is
substantially parallel-to the axis of the rod.
The notch may also have a section that is
substantially U-shaped or C-shaped, comprising trio plane
lateral faces that are substantially parallel to each
other and to the longitudinal axis of the corresponding
rod.
When the notch is substantially L-shaped, it has
been found during injection of the paste into the tooling
that the paste can exert a lateral force on the rod,
which can then move and break. This applies in
particular when the paste exerts a force on the rod that
is directed from the side where the rod is not completely
supported by its support member.
Thus, the U-shaped or C-shaped section of the notch
in each member receives the middle portion of the rod,
which is thus supported on both sides by the member.
When the paste injected into the tooling exerts lateral
forces on the rod, the rod is held in position by the
member and cannot be moved or broken. This particular Ushaped
or C-shaped section provides better support than
the L-shaped section.
Each of the side faces of the notch is connected to
a top face of the member via a convex rounded edge, in
particular to facilitate inserting the rod into the
notch.
The rod is thus caused to bear against each of these
lateral faces via a respective bearing line that is
substantially parallel to the axis of the rod. In a
variant, in the assembled position, the rod may be at a
small distance (less than 0.1 mm) from one of the faces
or from both of them.
One of the faces of the notch may be substantially
perpendicular to the direction in which the paste is
injected into the mold, and in particular in its imprint
for the first portion of the core. During injection of
the paste into the mold, the rod bears against this face
that opposes the flow stream of the paste and that
ensures that the rod is well held in position.
When the rod has a section that is U-shaped or Cshaped,
the side faces may be substantially perpendicular
to a direction in which the paste is injected into the
mold so that during inlection of the paste into the mold,
the rod bears against these faces that oppose the flow
stream of the paste and that ensure that the rod is well
held in position.
The or each member may be formed integrally with the
mold or it may be separate and fastened to the mold.
The tooling may also include a countermold that
likewise includes support means for supporting a middle
portion of the or each rod.
Advantageously, the tooling of the invention
includes a countermold that includes means for preventing
the or each rod from moving in the notch of the
corresponding member, these means including at least one
spacer formed projecting into a imprint of the
countermold and including at its tip a finger for
engaging in the top portion of the notch and/or for
bearing against the portion of the rod received in that
notch.
When the mold and the countermold are in the
5 assembled position, the or each spacer is to occupy a
position facing the corresponding member to prevent the
rod from leaving the notch in the member, in particular
while the piste is being injected into the tooling and is
exerting a force on the rod tending to dislodge it from
10 the notch (e.g. an upwardly directed force). The rod is
then held in position by a member and by a spacer that
together prevent any movement of the rod in a plane
perpendicular to the longitudinal axis, thereby limiting
any risk of the rod breaking.
15 The or each spacer preferably includes means for
bearing against and positioning the top of the
corresponding member.
The countermold may include a number of spacers that
is smaller than the number of members of the mold, such
20 that only some of the members of the mold are associated
with spacers of the countermold.
The support means may include at least 'hree or four
projecting members. The countermold may include a single
spacer for co-operating, in the assembled position, with
25 a member of the mold situated bes'ide the trailing edge of
the core that is to be made.
The present invention also provides a method of
fabricating a foundry core by means of tooling as
described above, the method comprising steps of injecting
30 a paste including ceramic fillers into the tooling, and
of solidifying and extracting the core, the method being
characterized in that it includes an additional step,
'after extracting the core, consisting in filling in the
or each recess in the core defined by the tooping support
35 means, e.g. with a ceramic material.
The core made by means of the tooling of the
invention presents at least one small setback or rescess
in its first portion for defining the bathtub of the
blade, because of the presence of the support means in
the mold. This recess is easily filled in with a
material similar to that of the core.
The invention can be better understood and other
characteristics, details and advantages thereof appear
more clearly on reading the following description made by
way of nonlimiting example and with reference to the
accompanying drawings, in which:
Figure 1 is a diagrammatic perspective view of a
rotor blade of a turbine engine;
Figure 2 is a diagrammatic view in section on line
11-11 of Figure 1 and shows a circuit for cooling the
blade;
Figure 3 is a very diagrammatic view of a foundry
core for making a turbine engine blade;
Figures 4 and 5 are fragmentary diagrammatic views
in perspective of the tooling of the invention for
fabricating a foundry core by molding, the tooling
carrying a ceramic rod of the core;
Figure 6 is a fragmentary diagrammatic view in
perspective of other tooling of the invention for
fabricating a foundry core by molding, this tooling
carrying four ceramic rods of the core;
Figure 7 is a view similar to the view of Figure 5
and shows tooling of the invention for fabricating a
foundry core by molding;
Figure 8 is a highly diagrammatic view in
perspective of support members for supporting rods in
tooling of the invention, and also includes a
diagrammatic cross-section view of the core to be formed
in the tooling;
Figure 9 is a view on a larger scale of a portion
of Figure 8 and also shows a spacer of a countermold of
the tooling; and
Figure 10 is a section view on line X-X of
Figure 9.
Reference is made initially to Figure 1 that shows a
rotor blade 10 of a turbine-engine compressor or turbine,
the rotor blade comprising an airfoil 12 connected by a
platform 14 to a root 16.
5 The blade 10 includes an internal cooling circuit
that can be seen in part in Figure 2, the circuit being
fed with air via orifices 18 in the blade root 16. These
orifices open out into internal cavities 20 of the blade
in which the blade cooling alr flows. This air is then
10 expelled via orifices 22 in the trailing edge of the
airfoil 12 and via orifices 24 in the tip of the airfoil.
The orifices 24 in the tip of the airfoil open out
into a bathtub 26 that is formed by a set back in the tip
of the airfoil 12 and that is separated from the internal
15 cavities 20 by a bottom of bathtub rial1 28, in which the
above-mentioned orifices 24 are formed.
The cooling circuit of the blade 10 is obtained in
the casting by means of a core that is assembled in the
ceramic shell mold into which a molten metal alloy is
20 cast. After solidification and extraction of the blade,
the core is eliminated, e.g. by chemical attack.
Figure 3 shows in highly diagrammatic manner a core
30 of this type, the core 30 comprising a first portion
32 for forming the bathtub 26 of the blade, other
25 portions 34 for forming the respective internal cavities
20 of the blade, and ceramic rods 36, each connecting the
first portion 32 to one of the other portions 34.
The first portion 32 of the core 30 is of shape and
dimensions complementary to the shape and dimensions of
30 the bathtub 26 that is to be formed, and the other
portions 34 are likewise of shapes and dimensions
complementary to the shapes and dimensions of the
cavities 20 that are to be formed.
The ceramic rods 36 perform two functions:
35 mechanically interconnecting the various portions of the
core 30; and holding these portions in predetermined
positions and at predetermined spacings. As can be seen
in Figure 3, the first portion 32 of the core is
separated from the other portions 34 by a space 38 of
thickness that depends on the length of the rod portions
36 extending between the first portion and the other
5 portions of the core.
While casting the molten alloy into the ceramic
shell mold, a portion of the alloy needs to penetrate
into the space 38 of the core 30 in order to form the
bottom wall 28 of the bathtub, which is of thickness that
10 is determined by the thickness of the space 38.
The ceramic rods 36 of the core 30 are for forming
the orifices 24 in the wall 28 that provide fluid flow
communication between the bathtub 26 and the internal
cavities 20 of the blade. In particular, the diameter of
15 these orifices 24 is a function of the diameter of the
ceramic rods 36 of the core 30.
The ceramic rods 36 are assembled in the mold of the
core fabrication tooling prior to injecting the paste
into the mold. In the prior art, the mold comprises a
20 first imprint for the first portion 32 and a second
imprint for the other portions 34 of the core 30, these
imprints belng separated from each other by a rial1 that
is to form the above-mentioned space 38 of the core.
The ceramic rods 36 are assembled in the mold so
25 that they pass in full through the first imprint, an end
portion of each rod being embedded in a socket in the
mold, and the opposite end portion of the rod extending
into the second imprint of the mold and bearing against
the above-mentioned wall of the mold.
30 As explained above, it has been found that the
ceramic rods 36, in particular those of small diameter
(e. g. of the order of 0.6 mm) , tend to break while the
paste is being injected into the mold, thereby requiring
the core to be' scrapped.
35 The present invention provides a solution to that
problem by means for supporting the middle portions of
the ceramic rods assembled in the mold of the tooling.
Figures 4 and 5 show an embodiment of the tooling of
the invention, the tooling comprising a mold 40 having a
first imprint 42 for the first portion 32 of the core 30
and a second imprint 44 for the other portions 34 of the
5 core, these imprints 42, 44 being separated from each
other by a wall 46 that is to form at least a portion of
the above-mentioned space 38 of the core.
A single ceramic rod 36 is shown in Figures 4 and 5,
this rod having an end portion 48 embedded in a socket 50
10 of the mold and an opposite end portion 52 extending into
the second imprint 44 of the mold and bearing against the
wall 46 of the mold.
The wall 46 of the mold includes a notch 54 of Ushaped
C-shaped section that is substantially
15 complementary to the section of a portion of the rod 36,
which rod is substantially cylindrical in the example
shown. The socket 50 in the mold 40 is likewise
substantially complementary in shape to the shape of a
rod 36. This prevents the paste passing between the rod
20 36 and the walls of the notch 54 and of the socket 50,
whlle the paste is being injected into the mold 40.
The tooling of the invention may include a
countermold, (not shown) that likewise comprises a first
imprint for the first portion 32 of the core 30 and a
25 second imprint for the other portions 34 of the core,
these imprints being separated from each other by a wall
that is to form the above-mentioned space 38 of the core.
T his wall of the countermold has a free edge of shape
complementary to the shape of the free edge of the wall
30 46 of the mold, such that these walls are in alignment
with each other and engage one in the other when the
tooling is assembled. As can be seen in Figure 5, the
wall 46 may include projecting means 56 for co-operating
by inkerconnecting shapes with complementary means of the
35 wall of the countermold in order to ensure that the walls
are properly positioned on,assembly.
As can be seen in Figures 4 and 5, the middle
portion of the rod 36 extends through the first imprint
42 of the mold 40. According to the invention, support
means 58 are provided in this imprint 42 for supporting
5 the middle portion of the rod 36 and for holding it in
position in order to limit any deformation thereof while
the paste is being injected into the mold.
In the example shown, the support means of the rod
comprise a projecting member 58 projecting from the
10 bottom of the first imprint 42 of the mold, this member
being situated substantially halfway between the socket
50 and the notch 54 of the mold.
This member 58 may be separate and fastened to the
mold 40, as in the example shown, or else it may be
15 formed integrally with the mold. It may be. made of the
same material as the mold, i.e. of metal alloy.
In this example, the member 58 is of semi-ovoid
shape and at its top it presents a notch 60 for engaging
the rod 36. As can be seen in Figure 5, this notch is of
20 L-shaped section and has two main and intersecting faces
62 and 64 that extend substantially parallel to the
longitudinal axis of the rod 36 when the rod is assembled
in the mold. The faces' 62 and 64 form an angle of about
90".
25 The ceramic rod 36 is to come and bear against the
faces 62 and 64 via bearing lines that are substantially
parallel to the axis of the rod.
The paste is injected into the mold and is to flow
into the first imprint 42 of the mold in the direction
30 shown by the arrow 66. The face 64 of the notch 60 is
substantially perpendicular to this direction, thus
making it possible to hold the rod 36 effectively in
position while the paste is flowing around the rod,
thereby limiting any deformation thereof.
35 Figure 6 shows another embodiment of the invention
in which the mold of the tooling includes support means
58 for supportitig four ceramic rods 36, the support means
being similar to those described above and being
independent and spaced apart from one another.
After fabrication, the core 30 includes in its first
portion 32 as many recesses as there are support means
present in the mold for fabricating the core. In the
embodiment of Figures 4 and 5, the core includes one
recess, whereas in the embodiment of Figure 6, the core
includes four recesses. The recesses are complementary
in shape to the shapes of the support means. The present
invention provides a method including a step in which
these sockets are filled in with a filler ceramic
material of composition that is preferably close to the
composition of the material of the core.
As mentioned above, the paste injected into the mold
of Figure 5 can exert a force on the rod 36 in a
direction opposite to the direction of the arrow 66.
Because of the shape of the notch 60 in the member 58,
the rod is not supported by the member on the side
opposite from the face 64, and it can thus move or break
under the force exerted by the paste.
The embodiments described below remedy this
particular drawback by a support member in which the
notch for receiving the rod presents a section that is Ushaped
or C-shaped.
Figure 7 shows a first embodiment in which the
elements that are described above are designated by the
same references.
The member 58 differs from the member shown in
Figure 5 in that its notch 60' has two side faces 64 and
65 that are substantially parallel to each other and to
the longitudinal axis of the rod 36, and that have bottom
ends that are connected together via a bottom face 62 of
the notch.
In the assembly position shown in Figure 7, the rod
36 is to bear against the faces 62, 64, and 65.
Nevertheless, because of the manufacturing tolerances of
the parts, it is possible that clearance of a few tenths
or hundredths of a millimeter might exist between the rod
and the faces 62, 64, and 65.
The rod 36 is thus supported on each side by the
member 58 and is held in place even if the paste injected
5 into the tooling exerts lateral forces on the rod on both
sides of the rod (arrows 66 and 66').
Figures 8 to 10 show a variant embodiment of the
invention in which the tooling has four bars 36, with
their middle portions supported by support members
10 including notches 60' of U-shaped or C-shaped section for
receiving the rods.
In the example shown, the side faces 64 and 65 of
the notch 60' of each member 58 are connected by convex
rounded edges 70 to top faces 72 of the member (Figures 9
15 and 10). In this embodiment, the faces 64 and 65 slope a
little relative to each other, the faces being spaced
further apart from each other at their top ends than at
their bottom ends.
The countermold (not shown) of the tooling includes
20 a spacer 74 that projects into a imprint of the mold and
that, in the assembled position, is to face one of the
members 58 of the mold 40.
This spacer 74 is of elongate shape and its tip
includes a finger 76 for engaging in the top portion of
25 the notch 60' of the member 58 and for bearing against
the middle portion of the rod 36.
As can be seen in Figure 10, the tip of the spacer
74 is of a shape that is substantially complementary to
the top of the member 58 and it bears against the above-
30 mentioned top faces 72 of that member.
Figures 8 to 10 show diagrammatically a section 78
of the core that is to be formed. The spacer 74 of the
countermold co-operates with a member 58 of the mold that
is situated beside the trailing edge of the core. The
35 spacer 74 prevents the rod 36 that is supported by the
member 58 from moving and escaping from the notch in that
member, since it has been found that the paste injected
into the tooling can exert a force on the rod that is
upwardly directed and capable of dislodging the rod from
the notch in the member. The paste' injected into the
tooling does not exert such a force on the rods 36
5 supported by the other members 58, which therefore do not
need to be associated with spacers 74 of the countermold.
As can be seen in the drawings, the members 58
preferably have external profiles that are rounded so as
to perform a deflection and damping function on the force
10 to which the rods 36 are subjected by the stream of
paste.

CLAIMS
1. Tooling for fabricating a foundry core (30) for making
a cooling circuit in a turbine engine blade (lo), the
core comprising a first portion (32) for defining a
5 bathtub (26) of the blade and at least one other portion
(34) for defining an internal cavity (20) in the blade,
and at least one rod (36) that extends between the first
portion and the or each other portion and that is to
define means (24) for passing fluid between the bathtub
10 and the corresponding internal cavity in the blade, the
tooling comprising a mold (40) for injecting a paste and
having imprints (42, 44) for the first portion and for
the or each other portion of the core, and means (50, 54)
for bearing against and/or embedding end portions of the
15 or each rod of the core, one of these means being formed
in a rial1 (46) of the mold between the imprint for the
first portion of the core and the imprint for the or each
other portion of the core, the tooling being
characterized in that it includes support means (58) in
20 the imprint for the first portion of the core to support
a substantially middle portion of the or each rod.
2. Tooling according to claim 1, characterized in that
the support means (58) for supporting a rod (36) are
25 independent of the support means for supporting the or
each other rod.
3. Tooling according to claim 1 or claim 2, characterized
in that the support means comprise at least one
30 projecting member (58) projecting from the bottom of the
imprint (42) for the first portion (32) of the core (30).
4. Tooling according to claim 3, characterized in that
the member (58) includes a notch (60, 60') in its top for
35 engaging the middle portion of a rod (36).
5. Tooling according to claim 4, characterized in that
the notch (60) has a section that is substantially Lshaped.
5 6. Tooling according to claim 5, characterized in that
the notch (60) has two plane and intersecting faces (62,
64) that are to extend substantially parallel to the
longitudinal axis of the corresponding rod (36).
10 7. Tooling according to claim 4, characterized in that
the notch (60') has a section that is substantially Ushaped
or C-shaped.
8. Tooling according to claim 7, characterized in that
15 the notch (60') has two plane side faces (64, 65) that
are substantially parallel to each other and to' the
longitudinal axis of the corresponding rod (36).
9. Tooling according to claim 8, characterized in that
20 each of the side faces (64, 65) of the notch is connected
to a top face (72) of the member via a convex rounded
edge (70).
10. Tooling according to any one of claims 5 to 9,
25 characterized in that one of the faces (64, 65) of the
notch (60, 60') is substantially perpendicular to a
direction (66) for injecting paste into the mold (40).
11. Tooling according to any one of claims 3 to 6,
30 characterized in that the member (58) is formed
integrally with the mold (40) or is separate and fastened
to the mold.
12. Tooling according to any preceding claim,
35 characterized in that it includes a countermold that
likewise includes support means for supporting a middle
portion of the or each rod (36).
13. Tooling according to any preceding claim,
characterized in that it includes a countermold that
includes means for preventing the or each rod (36) from
5 moving in the notch of the corresponding member, these
means including at least one spacer (74) formed
projecting into a imprint of the countermold and
including at its tip a finger (76) for engaging in the
top portion of the notch and/or for bearing against the
10 portion of the rod received in that notch.
14. Tooling according to claim 13, characterized in that
the or each spacer (74) includes means for bearing
against and positioning the top of the corresponding
15 member (58).
15. Tooling according to claim 13 or claim 14,
characterized in that the countermold includes a number
of spacers (74) that is smaller than the number of
20 members (58) of the mold, such that only some of the
members of the mold are associated with spacers of the
countermold.
16. Tooling according to any one of claims 13 to 15,
25 characterized in that the,countermold includes only one
spacer (74) .
17. Tooling according to any preceding claim,
characterized in that the support means include at least
30 three or four projecting members (58) .
18. Tooling according to any one of claims 3 to 17 taken
together, characterized in that the or each projecting
member (58) is substantially ovoid in shape and/or as
35 rounded external profiles suitable for deflecting and
damping the force to which the rods (36) are subjected by
the stream of paste.
19. A method of fabricating a foundry core (30) by means
of the tooling according to any preceding claim, the
method comprising the steps of injecting a paste
5 including ceramic fillers into the tooling, and of
solidifying and extracting the core, the method being
characterized in that it includes an additional step,
after extracting the core, consisting in filling in the
indentation in the core defined by the tooling support
10 means, e.g. yith a ceramic material.