SHELL MOULD FOR MANUFACTURING AIRCRAFT TURBOMACHINE
BLADED ELEMENTS USING THE LOST-WAX MOULDING TECHNIQUE
AND COMPRISING SCREENS THAT FORM HEAT ACCUMULATORS
Technical field
The invention relates to the field of the cluster
manufacturing of aircraft turbomachine bladed elements,
using the lost-wax moulding technique. Each bladed
element can be a sector comprising a plurality of
5 blades, such as a low-pressure feeder sector, or be an
individual blade, such as a blade of a turbine or
compressor mobile wheel.
The invention relates more particularly to the
design of the shell mould in the shape of a cluster,
10 wherein the metal is intended to be cast in order to
obtain turbomachine bladed elements.
The invention relates to all types of aircraft
turbomachines, in particular turbojets and turboprop
engines.
15
Prior art
In prior art, it is effectively known to use the
lost-wax moulding technique to simultaneously
manufacture several aircraft turbomachine bladed
elements, such as feeder sectors, or individual blades.
2 0 Recall that the lost-wax precision moulding
technique consists in creating in wax, via injection
into tooling, a model for each of the bladed elements
desired. Assembling these models on casting arms also
made of wax, which are in turn connected to a metal
25 feeder made of wax, makes it possible to constitute a
cluster which is then plunged into various substances
in order to form around the latter a ceramic shell
mould with a substantially uniform thickness.
The method is continued by melting the wax, which
then leaves its exact impression in the ceramic,
5 wherein the molten metal is poured, generally via a
casting cup assembled on the metal feeder. After
cooling of the metal, the shell mould is destroyed and
the metal parts are separated and finished.
This technique offers the advantage of dimensional
10 precision, which makes it possible to reduce and even
suppress certain machine tooling. In addition, it
offers a very good surface aspect.
More precisely, the shell mould bladed elements
are arranged at the periphery of the shell mould, and
15 each has a blade portion of which the trailing edge
zone is outwardly-directed from the shell mould. This
trailing edge zone is used of course to delimit the
impression of the trailing edge of each blade intended
to be obtained by the intermediary of the bladed
20 element concerned.
This solution is satisfactory for the obtaining of
trailing edges with a standard thickness, for example
of a magnitude of 0.7mm. It is however interesting to
reduce the thickness of the trailing edges of the
25 blades in order to improve the performance of aircraft
turbomachines. By way of example, increased performance
is obtained by providing a thickness of about 0.5 rnm on
the trailing edges of the feeder sector blades,
likewise with a thickness of about 0.45 mm on . the
30 trailing edges of individual mobile blades.
However, the current technology can still be
perfected in the framework of obtaining such
thicknesses, referred to a thin or very thin. Indeed,
with such low thicknesses, problems concerning the
5 material not arriving in the impressions defining these
trailing edges can arise.
Disclosure of the invention
The invention therefore has for purpose to
overcome at least partially the disadvantages mentioned
10 hereinabove, concerning the embodiments of prior art.
To do this, the invention has for object a shell
mould for manufacturing a plurality of aircraft
turbomachine bladed elements using the lost-wax
moulding technique, said shell mould in the shape of a
15 cluster comprising:
- a plurality of shell mould bladed elements each
intended for the obtaining of one of said turbomachine
bladed elements, with each bladed element comprising a
blade portion located between a first end part
20 delimiting the impression of a platform as well as a
second end part delimiting the impression of another
platform, said blade portion comprising a trailing edge
zone as well as a leading edge zone that is opposite to
it;
25 - a metal feeder having a central axis around
which said shell mould bladed elements are distributed;
and
- a shell mould interior space centred on said
central axis, and delimited by said shell mould bladed
30 elements.
According to the invention, said shell mould is
provided with one or a plurality of screens that form
heat accumulators arranged in the shell mould interior
space, across from inwardly-directed trailing edge
5 zones of said shell mould interior space.
The invention is remarkable in that it is entirely
suitable for the obtaining of thin or very thin
trailing edges, in the terms mentioned hereinabove.
Indeed, during the casting in the shell mould
10 which in general has been preheated, the screen / the
screens form a reservoir of heat making it possible to
maintain at a high temperature the trailing edge zones
located across from them, and of which the position has
been voluntarily reversed in relation to prior art so
15 that they are directed inwards of the shell mould. The
heat loss is therefore largely reduced, which makes it
possible to obtain a better fluidity of the cast metal,
and which results in a greater faculty to penetrate
into these zones of low thicknesses of the impressions.
20 From this stems an improved moulding precision, and a
better metallurgical health of the cast metal, with in
particular a decrease in shrinkage.
In addition, by housing therein the screen / the
screens, the interior space of the shell mould becomes
25 advantageously functionalised, although it usually
remained largely recessed in solutions of prior art. In
this regard, it is noted that the presence of the
screens does not affect the total encumbrance of the
shell mould.
30 Preferably, each screen extends across from the
blade portion, between the first and second end parts
delimiting the platform impressions. In other words, it
is arranged in such a way that each screen is located
only across from the blade portion, i.e. it does not
extend sufficiently according to the direction of the
5 central axis of the feeder to be across from the first
and second end parts.
Each screen that forms a heat accumulator is
preferentially made from a single piece with said shell
mould. Each screen is then obtained in a way identical
10 to that of the other members of the shell mould, i.e.
using a screen made of wax which is then eliminated or
not eliminated, then filled or not filled with metal.
Preferably, these screens obtained in a single piece
with the shell mould are not filled with metal during
15 the casting.
According to a first possibility, a screen
associated with each shell mould bladed element is
provided, with each screen being more preferably of a
substantially planar form.
2 0 According to a possibility, a single screen is
provided associated to all said shell mould bladed
elements, with said single screen being more preferably
of revolutionary shape, centred on said central axis of
the metal feeder.
25 Whether there are one or several screens, their
shape can be adapted to be as close as possible to the
trailing edge zones of the shell mould bladed elements,
in such a way as to procure the greatest effectiveness
possible.
3 0 In this regard, more preferably, each trailing
edge zone is separated from its screen associated with
a distance between 1 and 40 mm, with this distance
being preferentially substantially constant along each
trailing edge of the zone.
Preferably, the shell mould comprises a central
5 support extending from the metal feeder according to
the direction of the central axis of the latter, with
each screen being arranged around said central support
whereon it is added. This central support can also be
used in order to porter support reinforcements for the
10 shell mould bladed elements.
Preferably, said shell mould is made of ceramic,
in a way known to those skilled in the art.
Preferably, the blade portion of each shell mould
bladed element delimits one or several blades. As
15 already mentioned, this can be a bladed element
dedicated to obtaining a plurality of blades, such as a
low-pressure feeder sector, or a bladed element
dedicated to obtaining an individual blade, such as a
blade of a turbine or compressor mobile wheel.
2 0 The number of these bladed elements distributed
clrcumferent~ally around the central axis of the feeder
can vary, for example from 3 to 10 for sectors each
comprising several blades, and for example from 10 to
50 for individual blades.
2 5 The invention also has for object a shell mould
for manufacturing a plurality of aircraft turbomachine
bladed elements using the lost-wax moulding technique,
said shell mould in the shape of a cluster comprising:
- a plurality of shell mould bladed elements each
30 intended to the obtaining of one of said turbomachine
bladed elements;
- a metal feeder having a central axis; and
- a plurality of metal casting arms distributed
around the central axis of the metal feeder, with each
of the casting arms having a first end connected to
5 said feeder.
According to the invention, said shell mould is
provided with a thermal insulation coating made using a
plurality of thermal insulation strips that cover at
least a portion of the outside surface of the shell
10 mould.
The invention is remarkable in that it is entirely
suitable for obtaining thin or very thin trailing edges,
in the sense mentioned hereinabove. Indeed, during and
after the casting of the metal in the shell mould, the
15 thermal insulation coating makes it possible to reduce
the heat loss and as such maintain the shell mould and
the cast metal at a high temperature for an extended
period of time. From this stems a better fluidity of
the cast metal, which results in a greater faculty to
20 penetrate into the zones of low thicknesses of the
impressions, and in particular the trailing edges.
The moulding precision is improved, likewise as
the metallurgical health of the cast metal, with in
particular a decrease in shrinkage.
25 In addition, by using a plurality of strips to
form the thermal insulation coating, the invention
constitutes an advantageous and simple solution making
it possible to vary the heat resistance according to
the zones of the shell mould, and this in such a way as
30 to obtain a satisfactory filling as well as a good
metallurgical health of the cast metal.
Preferably, said coating is carried out using
thermal insulation strips each surrounding a shell
mould bladed element on at least one radial portion of
the latter, and using at least one thermal insulation
5 strip surrounding said shell mould.
Preferably, said coating is carried out in such a
way that for each shell mould bladed element, it has a
thermal resistance gradient according to the radial
direction of said shell mould bladed element. This
10 radial gradient can moreover vary along the contour of
the bladed element. In particular, the radial gradient
differs between the surface of the outwardly-directed
bladed element of the shell mould and its other
inwardly-directed surface, across from the central axis
15 of the feeder.
Preferably, said strips are made of rock wool, and
for example all have the same thermal resistance. The
thicknesses are therefore preferably identical, only
the widths can therefore vary. By way of an example for
20 the purposes of information, the thicknesses retained
for the various layers can be identical, but with
simple or double densities, according to the needs.
Preferably, each shell mould bladed element
comprises a blade portion located between a first end
25 part delimiting the impression of a platform as well as
a second end part delimiting the impression of another
platform, and the second end of each casting arm is
connected to said first end part of one of the shell
mould bladed elements, of which the second end part is
30 offset from the first end part according to the
direction of the central axis of the metal feeder,
preferably in the same direction of offsetting as that
of the second end of the casting arm in relation to its
first end. In addition, each blade portion comprises a
trailing edge zone as well as a leading edge zone that
5 is opposite to it.
In the first case where each shell mould bladed
element is dedicated to the obtaining of a feeder
sector, said thermal insulation coating is particularly
effective when it comprises the following thermal
10 insulation strips:
- a first strip associated with each shell mould
bladed element, with each first strip surrounding its
element associated over the entire length of the latter,
according to the radial direction of this element;
15 - a second strip associated with each shell mould
bladed element, partially recovering the first strip,
with each second strip surrounding its element
associated over a radial portion of the latter,
comprising the first end part and the blade portion,
20 but excluding the second end part;
- a third strip surrounding the periphery of the
shell mould in such a way as to cover the casting arms,
the first end parts of the shell mould bladed elements,
as well as an upper radial portion of their blade
25 portions;
- a fourth strip partially covering the third
strip and surrounding the periphery of the shell mould
in such a way as to cover only the casting arms; and
- a fifth strip surrounding the periphery of the
30 shell mould in such a way as to cover the shell mould
bladed elements, but not the casting arms.
In the second case where each shell mould bladed
element is dedicated to obtaining an individual blade,
and comprises a reservoir of metal connected to the
second end part in such a way as to extend across from
5 and at a distance from the leading edge zone of the
bladed element, the thermal insulation coating is
particularly effective when it comprises the following
thermal insulation strips:
- a first strip associated with each shell mould
10 bladed element, each first strip surrounding its
element associated on a radial portion of the latter,
comprising only a portion of the blade portion (2b)
extending from the second end part;
- a second strip placed in an annular space
15 centred on the axis of the feeder and defined between
the reservoirs and the trailing edge zones, said second
strip centred on the central axis of the feeder being
arranged in such a way as to cover the first strips and
surround exteriorly a radial portion of each bladed
20 element, comprising only a portion of the blade portion
extending from the second end part;
- a third strip surrounding the periphery of the
shell mould in such a way as to cover a radial portion
of each shell mould bladed element, comprising the
25 first end part and a portion of the blade portion, but
excluding the second end part, with the second and the
third strips having ends across from them defining
between them an annular window whereon the shell mould
is devoid of a strip;
- a fourth and a fifth superimposed layers, each
surrounding the periphery of the shell mould in such a
way as to cover only the casting arms;
- a sixth strip surrounding the periphery of the
5 shell mould as well as the third layer in such a way as
to cover a radial portion of each shell mould bladed
element, comprising the first end part and a portion of
the blade portion, but excluding the second end part,
with said sixth strip extending to said annular window;
10 - a seventh strip surrounding the periphery of the
shell mould in such a way as to cover the surfaces of
radially outwardly-directed reservoirs as well as the
radial ends of the second end parts;
- an eighth strip surrounding the periphery of the
15 shell mould and partially covers said seventh strip in
such a way as to cover the surfaces of radially
outwardly-directed reservoirs; and
- a ninth strip arranged substantially
orthogonally to the central axis whereon it is centred,
20 and starting from which it radially extends until it
covers the circumferential end of said eighth strip.
Of course, the two aspects of the invention
mentioned hereinabove, namely the heat-accumulating
screens on the one hand and the thermal insulation
25 coating on the other hand, can be combined.
The invention also has for object a method for
manufacturing a plurality of aircraft turbomachine
bladed elements using the lost-wax moulding technique,
implemented using a shell mould such as described
30 hereinabove.
Preferably, the metal is cast in the shell mould
with the central axis of the vertically-directed metal
feeder .
When the method is implemented with the screen /
5 the screens made from a single piece with the shell
mould, the accumulation of heat is carried out of
course at the time where the rest of the shell mould is
preheated, before the casting of the metal.
Other advantages and characteristics of the
10 invention shall appear in the detailed and nonrestricted
description hereinbelow.
Brief description of the drawings
This description shall be given with regards to
the annexed drawings among which;
15 - figure 1 shows a perspective view of a
turbomachine bladed element intended to be obtained by
the implementation of the method according to this
invention, with said bladed element having the shape of
a low-pressure feeder sector;
20 - figures 2 to 4 show perspective views of a model
made of wax used to create a shell mould for the
implementation of the method for manufacturing using
the lost-wax moulding technique according to the
invention, for the purposes of obtaining the element of
25 figurel;
- figure 4a shows a view that diagrammatically
shows the distance of separation between the screens
made of wax and the trailing edges of the blades of the
replica made of wax;
- figure 5 shows a perspective view of the shell
mould obtained using the model made of wax shown in
figures 2 to 4;
- figure 5a shows a view that diagrammatically
5 shows the distance of separation between the heataccumulating
screens and the trailing edge zones of the
shell mould bladed elements;
- figure 6 shows a view that diagrammatically
shows the shell mould provided with a plurality of
10 thermal insulation strips, forming a coating on at
least a portion of the outside surface of the shell
mould;
- figure 7 shows a perspective view of another
turbomachine bladed element intended to be obtained by
15 the implementation of the method according to this
invention, with said bladed element having the shape of
an individual mobile blade;
- figures 8 and 9 show perspective views of a
model made of wax used to create a shell mould for the
20 implementation of the method of manufacturing using the
lost-wax moulding technique according to the invention,
for the purposes of obtaining the element of figure 7;
- figure 10 shows a view that diagrammatically
shows the distance of separation between the screen
25 made of wax and the trailing edges of the blades of the
replica made of wax;
- figure 11 shows a perspective view of the shell
mould obtained using the model made of wax shown in
figures 8 and 9;
3 0 - figure lla shows a view that diagrammatically
shows the distance of separation between the heataccumulating
screen and the trailing edge zones of the
shell mould bladed elements; and
- figure 12 shows a view that diagrammatically
shows the shell mould provided with a plurality of
5 thermal insulation strips, that form a coating on at
least a portion of the outside surface of this shell
mould.
Detailed description of preferred embodiments
In reference to figure 1, a turbine low-pressure
10 feeder sector 1 for an aircraft turbomachine is shown.
This sector comprises a plurality of blades 2 arranged
between a first end 4 and a second end 6 . The two ends
4, 6 respectively form an outside crown angular sector
and an inside crown angular sector, and each comprise a
15 platform 8 that delimits a main stream 10 of gas flow.
In addition to the platform 8 to which is attached an
aerodynamic function, each end further comprises a
conventional structure that allows for the mounting of
this bladed element on the turbomachine model.
2 0 The invention ails to manufacture the feeder
sector 1 via a method of lost-wax moulding, of which a
preferred embodiment shall now be described in
reference to figures 2 to 6.
First of all, a model made of wax is carried out,
25 also called a replica, around which a ceramic shell
mould is intended to be formed later.
In figures 2 to 4, the model 100 is shown in a
reversed position in relation to the position wherein
the shell mould is then filled with metal. This
30 reversed position facilitates the operation of
assembling various elements that comprise the model
made of wax, which shall now be described.
The model 100 first of all comprises a portion for
the distribution of metal, referenced as 12a. It takes
5 a solid revolutionary, cylindrical or tapered shape,
with a central axis 14a that coincides with the central
axis of the whole of the model made of wax 100. This
axis 14a is vertically oriented, and therefore
considered as representative of the direction of the
10 height. This portion of distribution 12a is fixed
directly to a specific tooling 16, above which it is
located.
The portion 12a finishes towards the top by an end
18a of a larger diameter, from which radially extends a
15 plurality of portions 20a for the forming of several
casting arms. The portions 20a are here in the number
of three, distributed at 120' around the axis 14a. Each
portion 20a therefore comprises a first end 21a
connected to the widened end 18a of the distribution
20 portion 12a, and extends in a straight or slightly
curved manner to a second end 22a. The first and second
ends 21a, 22a are offset from each other according to
the direction of the axis 14a, with the first being
located lower than the second. The average angle of
25 inclination between each portion forming arms 20a and
the horizontal is between 5 and 45".
For each portion forming arms 20a, a reinforcement
for maintaining made of wax/ceramic 23a can be provided
between the distribution portion 12a and the second end
30 22a of the portion 20a.
In addition, starting from each second end 22a, a
replica is fastened made of wax la of the turbomachine
feeder sector shown in figure 1. This replica la
therefore comprises a plurality of adjacent blades 2a,
5 arranged between a first end 4a and a second end 6a to
which the blades are connected. The two ends 4a, 6a
respectively form outside crown angular sector and an
inside crown angular sector, and each comprises a
platform 8a. In addition to the platform 8a, each end
10 further comprises a conventional structure
corresponding to the structure shown in figure 1,
dedicated to the mounting of the feeder sector 1 on the
turbomachine module.
The direction according to which the blades 2a and
15 the ends 4a, 6a succeed corresponds to the radial
direction of the bladed sector made of wax la, with
this radial direction being more preferably
substantially parallel to the direction of the axis 14a,
i.e. parallel to the direction of the height of the
20 replica 100.
The bladed sectors made of wax la extend therefore
upwards, by being arranged around the axis 14a, and
also around a central support made of wax 24a extending
according to this same axis starting from the end 18a
25 of the distribution portion 12a. The support 24a
preferentially takes the form of an axis rod 14a, that
extends to the vicinity of the ends 6a of the bladed
sectors made of wax la.
Moreover, as can be seen in figure 2, for each
30 bladed sector made of wax la, a reinforcement for
maintaining made of r.rax/ceramic 25a can be provided
between the top end of the central support rod 24a, and
the second end 6a of the sector la. In the same way,
reinforcements for maintaining made of wax/ceramic 27a
connect between them the adjacent ends 6a of the
5 various sectors la.
The sectors made of tiax la form the peripheral
wall of the replica made of wax 100. They are spaced
circumferentially from one another, and inwardly define
an interior space 28a centred on the axis 14a, wherein
10 is therefore located the central support rod 24a.
In this interior space 28a, a plurality of screens
made of wax are provided, of which the future shell
mould elements intended to be obtained around these
screens 29a are provided in order to form heat-
15 accumulating screens.
Each screen 29a is associated with a single bladed
sector made of wax la, across from which it is located.
More precisely, each screen has a substantially planar,
square or rectangular shape, of low thickness, for
20 example of a few millimetres only. The screen 29a,
substantially parallel to the vertical direction, is
located across from trailing edges of the blades made
of wax 2a. These trailing edges 30a are therefore
inwardly-directed from the shell mould in the direction
25 of the axis 14a, in opposition to the radially
outwardly-directed leading edges 31a, in order to
constitute the periphery of the replica 100.
Each screen 29a is added to the central support
rod 24a using reinforcements 32a also in the shape of
30 rods of a smaller diameter. As can be seen in figure 4,
each screen 29a extends across from blades 2a, between
the first and second ends 4a, 6a. In other terms, it is
arranged in such a way that according to the radial
direction of the replica 100, each screen 29a is
located only across from blades 2a, i.e. it does not
5 extend sufficiently according to the direction of the
central axis 14a in order to be across from first and
second ends 4a, 6a.
In figure 4a, the fact that each screen 29a is
located very close to the trailing edges 30a is
10 diagrammatically shown, since the distance of
separation A between the two elements is between 2 and
50 mm, and even more preferentially of a magnitude of
10 to 35 mm, with this distance being substantially
constant along the trailing edges 30a.
15 Once the replica made of wax 100 is created, a
shell mould of ceramic 200 is manufactured around the
latter in a manner known to those skilled in the art,
by soaking in successive substances and baths.
The shell mould 200 that is obtained is shown in
20 figure 5. It also has the general shape of a cluster,
and of course comprises elements that are similar to
those of the replica made of wax 100. These shell mould
elements shall now be described, with the shell mould
shown in a reversed position in relation to the
25 position wherein it is then filled with metal.
This first entails the metal feeder, referenced as
12b, and therefore having a hollow revolutionary,
cylindrical or tapered shape, with a central axis 14a
that coincides with the central axis of the shell mould
30 200. This axis 14b is vertically directed, and
therefore is considered as representing the direction
of the height. This feeder 12b is fastened directly to
a tapered-shape casting cup 35 above which it is
located.
The feeder 12b finishes towards the top with a
5 hollow end 18b of a greater diameter, from which
radially extend a plurality of metal casting arms 20b.
The arms 20b here are of a number of three, distributed
at 120' around the axis 14a. Each arm 20b therefore
comprises a first end 21b connected to the widened end
10 28a of the feeder 12b, and extends in a straight or
slightly curved manner to a second end 22b. The first
and second ends 21b, 22b are offset from one another
according to the direction of the axis 14b, with the
first being located lower than the second. The average
15 angle of inclination between each arm 20b and the
horizontal is between 5 and 45".
Each arm 20a is therefore provided to be hollow
and former a duct for conveying metal after elimination
of the wax 20a. Here also, a reinforcement for
20 maintaining 23b can be provided between the
distribution portion 12b and the second end 22b of each
arm 20b.
Starting with each second end 22b, is a shell
mould bladed element lb. These elements lb are referred
25 to as bladed because after the elimination of the
replica made of wax la, they each interiorly form an
impression corresponding to one of the feeder sectors 1.
The bladed element lb, also referred to as shell
mould feeder sector, as such comprises a blade portion
30 2b delimiting the impressions of adjacent blades, with
this portion 2b being arranged between a first end part
4b and a second end part 6b. The two end parts 4b, 6b
respectively, delimit an outside crown angular sector
impression and an inside crown angular sector
impression, each comprising a platform impression 8b.
5 In addition to the platform 8b, each end part further
comprises an impression of conventional structure
dedicated to the mounting of the feeder sector l'on the
turbomachine module.
The direction according to which succeed the blade
10 portion 2b and the end parts 4b, 6b corresponds to the
radial direction of the shell mould bladed element lb,
with this radial direction being preferably
substantially parallel to the direction of the axis 14b,
i.e. parallel to the direction of the height of the
15 shell mould 200. In order to be able to benefit later
from a high-performance casting via simple gravity, in
the direction of the axis 14b, the direction of
offsetting of the first end of the arm 21b in relation
to the second end of the arm 22b is identical to the
20 direction of offsetting of the first end part 4b in
relation to the second end part 6b of the bladed
element lb.
The bladed elements lb therefore extend upwards,
by being arranged around the axis 14b, and also around
25 a central support 24b extending according to this same
axis starting from the end 18b of the feeder 12b. The
support 24b preferably takes the shape of a hollow
cylinder of axis 14b, that extends to the vicinity of
the ends 6b of the bladed elements lb.
30 In addition, as can be seen in figure 5, for each
bladed element lb, a reinforcement for maintaining 25b
is provided between the top end of the central support
cylinder 24b, and the second end 6b of the element lb.
In the same way, reinforcements for maintaining 27b
connecting together the adjacent end parts 6b of the
5 various elements lb.
The shell mould bladed elements lb form the
peripheral wall of the shell mould 200. They are spaced
circumferentially from one another, and define towards
the interior an interior space 28b centred on the axis
10 14b, wherein is therefore located the central support
cylinder 24b.
In this interior space 28b, a plurality of screens
that form heat accumulators is provided.
Each screen 29b is associated with a single shell
15 mould bladed element lb, across from which it is
located. More precisely, each screen has a
substantially hollow and planar, square or rectangular
shape, of low thickness, for example of only a few
millimetres. The screen 29b, substantially parallel to
20 the vertical direction, is located across from a
trailing edge zone of the blade portion 2b. These
trailing edge zones 30b are therefore inwardly-directed
from the shell mould in the direction of the axis 14b,
by opposition to the radially outwardly-directed
25 leading edge zones 31b, in order to constitute the
periphery of the shell mould 200.
Each screen 29b is added onto the central support
cylinder 24b using reinforcements 32b also in the shape
of hollow rods of a smaller diameter. As can be seen in
30 figure 5b, each screen 29b extends across from the
blade portion 2b, between the first and second end
parts 4b, 6b. In other terms, this is done in such a
way that according to the radial direction of the shell
mould 200, each screen 29b is located only across from
the blade portion 2b, i.e. it does not extend
5 sufficiently according to the direction of the central
axis 14b to be across from the first and second end
parts 4b, 6b.
In figure 5a, the fact that each screen 29b is
located very close to the trailing edge zones 30b is
10 diagrammatically shown, since the distance of
separation B between the two elements is also between 1
and 40 mm, and even more preferentially of a magnitude
from 10 to 20 mm, with this distance being
substantially identical and constant along each
15 trailing edge of the zone 30b. The number of trailing
edges defined by the zone 30b is of course identical to
the number of blades that the bladed element lb defines,
for example between 6 and 10.
All of the shell mould elements mentioned
20 hereinabove are made from a single pike of ceramic,
during the same step. The thickness of the ceramic
shell mould is low, for example of a magnitude of only
a few millimetres. It is noted that as for the replica
made of wax 100, in the shell mould 200, the numbers of
25 arms 20b, of bladed elements lb and of screens 29b are
identical. However, the same screen may be associated
with several shell mould bladed elements, without
leaving the scope of the invention.
After the obtaining of the shell mould and the
30 elimination of the replica made of wax 100 enclosed in
the latter, the shell mould is preheated to a high
temperature in a dedicated oven, for example to 1150°C,
in order to favour the fluidity of the metal in the
shell mould during the casting. Note that the casting
cup 35 is preferentially made integral with the replica
5 made of wax 100 before the forming of the shell mould
200, in such a way that a portion of the latter comes,
during its formation, to hug the cup 35.
A step of applying a thermal insulation coating 48,
which shall now be described, is more preferably
10 carried out before the preheating.
It consists in coating the outside surface of the
shell mould with a plurality of thermal insulation
strips, which are here made of rock wool and which can
all have the same thickness as well as the same thermal
15 resistance, with then only the arrangement and the
width of the strips being specific to each strip.
Alternatively, the same thickness can be retained for
these strips, with different densities, for example
simple or double.
20 This is first of all a plurality of first strips
50a, each associated with a shell mould bladed element
lb. Each first strip 50a surrounds its associated
element lb over the entire length of the latter,
according to the radial direction of this element, i.e.
25 this strip surrounds over 360' the blade portion 2b as
well as the two end parts 4b, 6b of the element lb
concerned. The arms 20b are not covered by this first
strip, likewise the portion of the end part 6b directed
downwards according to the direction of the axis 14b
30 remains uncovered. This portion is however covered by
none of the strips that constitute the thermal
insulation coating 48. These strips 50a are made of
rock wool, more preferably of simple density.
Second strips 50b, also made of rock rvool more
preferably of simple density, and also each one
5 associated to a shell mould bladed element lb,
partially cover the first strips 50a. Indeed, each
second strip 50b surrounds its associated element lb
over a radial portion of the latter, comprising the
first end part 4b and the blade portion 2b, but
10 excluding the second end part 6b. This second strip 50b
stops as such at the level of the junction between the
blade portion 2b and the second end part 6b concerned.
Here also, each second strip extends over 360" around
the radial direction of the shell mould bladed element
15 lb, but therefore only over a radial portion of the
latter.
A third strip 50c is then provided that surrounds
the periphery of the shell mould 200 in such a way as
to cover the casting arms 20b, the first end parts 4b
20 of the shell mould bladed elements lb, as well as an
upper radial portion of their blade portions 2b. This
here can be a portion extending over substantially half
of the total radial length of the blade portion 2b,
even over 40 to 50% of this length.
25 This third strip 50c, preferably of simple density
and extending over 360° around the axis 14b, is as such
arranged at the periphery of the shell mould 200. Among
the elements mentioned hereinabove that it covers, only
the portions located radially towards the exterior of
30 this shell mould are directly covered by the third
strip 50c, in particular the leading edge zones 31b of
the blade portions 2b.
A fourth strip 50d, preferably of double density,
partially covers the third strip 50c by surrounding the
5 periphery of the shell mould 200, in such a way as to
cover only the casting arms 20b. This fourth strip 50d,
which extends over 360" around the axis 14b, therefore
does not cover the lower portion of the shell mould. In
particular, the elements lb are not covered by this
10 fourth strip.
A fifth and last strip 50e, preferably of double
density, is then applied over 360' around the axis 14b
in order to cover a portion of the other strips 50a-50c
and surround the periphery of the shell mould 200, in
15 such a way as to cover only the shell mould bladed
elements lb over their entire radial length, but
without covering the casting arms 20b.
Note that for the strips 50c, 50d intended to
cover the arms 20b, when reinforcements 23b are
20 provided between these arms and the feeder 12b, these
same strips are preferably directly pressing all along
these arms, having slots that allow for the passage of
supper reinforcements 23b.
In the same way, the first and second strips 50a,
25 50b can be pressing against the surface of the screen
29b located radially towards the inside of the shell
mould, and not directly in contact with the trailing
edge zones 30b of the bladed elements lb. This results
in a greater facility of setting up these strips.
Note that the fastening of the strips can be
carried out in any manner considered as suitable by
those skilled in the art, such as using iron wires.
The particular disposition of strips 50a-50e which
5 has just been described makes it possible to obtain a
good metallurgical health of the cast metal in the
shell mould, in particular thanks to the presence of a
thermal resistance gradient of the coating 4 8 along
each bladed element lb, according to the radial
10 direction of the latter. This gradient extends moreover
over the entire shell mould, according to the direction
of the axis 14b.
More precisely, the arrangement of these strips
allows the metal, after casting in the shell mould, to
15 solidify in the following way. Firstly, the metal
solidifies in the first place in the second end part 6b,
under the lower end of the strip 50b. The fact that the
strips 50b and 50c are offset upwards in relation to
the strip 50a then makes it possible for the metal to
20 solidify in the zone of the blade portion 2b located
between the iower end of the strip 50c, and the second
end part 6b. The arrangement of the strips 50d and 50e
finally enable the metal to solidify in the first end
part 4b.
25 The metal of the feeder therefore solidifies
progressively from the bottom to the top, by procuring
a healthy metallurgical health.
At the exit of the preheating of the shell mould
provided with such a coating 48, metal exiting a
30 melting furnace is therefore cast in the impressions
via the cup 35 shown in figure 5, with the shell mould
in reversed position in relation to that shown in this
figure, i.e. with the cup 35 open upwards and the axis
14b still vertically directed. In this position, the
first end 21b of the arms 20b is then located above the
5 second end 22b.
The molten metal therefore successively follows
the cup 35, the feeder 12b, the casting arms 20b, then
the shell mould bladed elements lb, by flowing simply
via gravity. Note that prior to the casting, the
10 central support 24b has its end closed off in order to
not be filled with metal, and in such a way that the
cast metal necessarily passes through the arms 20b
before entering into the bladed elements lb. Because of
this, the screens 29b are also devoid of metal, and may
15 or may not retain the wax 29a located interiorly. The
reinforcements 23b, the reinforcements 32b and the
reinforcements for maintaining 27b are preferentially
solid, made of ceramic.
The screens have for role to store heat during the
20 preheating of the shell mould 200, and to restore this
heat to the trailing edge zones 30b across from them
during the casting, in such a way as to ensure a proper
filling thanks to a good fluidity of the metal
propitious to the penetration of this metal into the
25 impressions of low thicknesses.
After the cooling of the metal, the shell mould is
destroyed, then the feeder sectors 1 are separated from
the cluster for possible machining and finishing and
control operations.
30 In reference to figure 7, a turbine individual
mobile blade 1 for an aircraft turbomachine is shown.
Unlike the sector 1 shown in figure 1, this blade has
only a single blade 2, here arranged between a first
end 4 and a second end 6.
The invention also aims to manufacture the blade 1
5 by a method of lost-wax moulding, of which a preferred
embodiment is shown in figures 8 to 12.
In these figures, the elements bearing the same
numerical references as the elements of figures 1 to 6
correspond to identical or similar elements.
10 Consequently, a great similarity is observed
between the two methods, with only a few minor
differences being notable, resulting primarily from the
difference in shape between and individual blade and a
feeder sector.
15 As such, on the replica made of wax 100 shown in
figure 8 and partially in figure 9, it is possible to
see that if the number of portions of arms 20a remains
identical to the number of individual blades made of
wax la, the number of reinforcements for maintaining
20 made of wax/ceramic 23a is however lower. For example,
only four reinforcements 23a are provided, with these
reinforcements able moreover to be directly added on
the cup when the latter is already assembled to the
replica made of wax 100.
25 Likewise, the number of reinforcements for
maintaining made of wax/ceramic 25a can be reduced, for
example to four. These reinforcements 25a are connected
on the top end of the central support rod 24a, and on
the reinforcements for maintaining made of wax/ceramic
30 27a connected between them the blades la. In this
regard, each individual blade made of wax la has a
flyweights made of wax 7a on its heel, i.e. connected
to its end 6a. Each flyweight 7a extends downwards,
across from and at a distance from the leading edge 31a
of the blade la, preferably over a short distance. It
5 is then these flyweights 7a that are connected by the
reinforcements for maintaining 27a, at the periphery of
the replica made of wax 100.
During the casting, the metal penetrates into the
reservoirs 7b of the shell mould formed around these
10 flyweights 7a. These reservoirs make it possible to
prevent shrinkage on the heel of the mobile blade.
Another function of these reservoirs consists in that
during this casting and the cooling, the undesired
metallurgical deposits are concentrated in these
15 reservoirs, and therefore do not affect the
metallurgical health of the turbomachine blades
obtained.
In this configuration, a single screen made of wax
29a is provided associated with all of the blades la.
20 This screen 29a is of revolutionary shape centred on
the axis 14a, for example cylindrical or tapered,
always with the same characteristics of spacing with
regards to the blades, as has been diagrammed in figure
10.
25 The screen 29a also has an arrangement and
dimensions according to the direction of the axis 14b
that are identical or similar to those of the screens
29a of the preceding embodiment. It is added on the
central support rod 24a using reinforcements 32a in the
30 form of ribs of low thickness.
Furthermore, these slight structural modifications
necessarily have an impact on the constitution of the
shell mould 200 shown in figure 11. As such, all of the
elements of the replica 100 mentioned hereinabove give
5 rise to shell mould elements identified with the same
numerical radical, followed by the letter "b". In this
respect, note that the single heat-accumulating screen
29b has the same characteristics of spacing with
regards to the trailing edge zones 30b, as has been
10 diagrammed in figure lla.
The later operations of preheating, casting and
cooling of the metal are carried out in a manner that
is identical or similar to that described for the
preceding embodiment, with only the application of the
15 thermal insulation coating 48 being distinct from that
described in reference to figure 6.
Indeed, in reference to figure 12, the thermal
insulation coating 48 first of all comprises first
strips 52a each associated to a shell mould bladed
20 element lb, with each first strip surrounding its
associated element lb over a radial portion of the
latter, comprising only a lower portion of the blade
portion 2b that extends starting from the second end
part 6b. This here can be a portion extending over 10
25 to 30% of the total radial length of the blade portion
2b.
A second strip 52b is then provided placed in an
annular space 54 centred on the axis 14b, and defined
between the reservoirs 7b and the leading edge zones
30 31b. The second strip 52b is centred on the axis 14b
and arranged in such a way as to cover the first strips
52a and exteriorly surround a radial portion of each
bladed element lb, comprising a lower portion of the
blade portion 2b extending from the second end part 6b.
This is more preferably a portion of identical or
5 similar length to that covered by the first strips 52a,
and even extending slightly beyond the strips 52a,
upwards. The strips 52a and 52b are more preferably of
simple density.
A third strip 52c, preferably of simple density,
10 surrounds the periphery of the shell mould 200, in such
a way as to cover a radial portion of each shell mould
bladed element lb, comprising the first end part 4b and
a portion of the blade portion 2b, but excluding the
second end part 6b. In this regard, note that the
15 second and the third strips 52b, 52c having ends across
from them defining between them an annular window 56
centred on the axis 14b, on which the shell mould 200
is devoid of a strip. This window 56, which subsists
once all of the strips have been installed, can have a
20 height of a magnitude of 20 to 60mm.
Then, a fourth and a fifth strips 52d, 52e, each
of double density, are superimposed in order to each
surround the periphery of the shell mould 200, in such
a way as to cover only the casting arms 20b. These two
25 strips also extend over 360" around the axis 14b.
On the other hand, a sixth strip 52f of double
density is provided surrounding the periphery of the
shell mould 200 as well as the third strip 52c, in such
a way as to cover a radial portion of each shell mould
30 bladed element lb, comprising the first end part 4b and
a portion of the blade portion 2b, but excluding the
second end part 6b. This sixth strip 52f extends to the
annular window 56, without obstructing it.
A seventh strip 52g of simple density extending
over 360" around the axis 14b surrounds the periphery
5 of the shell mould 200 in such a way as to cover the
surfaces of the radially outwardly-directed reservoirs
7b, as well as the radial ends of the second end parts
6b.
In a similar manner, an eighth strip 52h of double
10 density surrounds over 360" the periphery of the shell
mould 200 and partially covers this seventh strip 52g,
in such a way as to cover the surfaces of the radially
outwardly-directed reservoirs 7b, but without covering
the radial ends of the second end parts 6b.
15 Finally, a ninth strip 52i is arranged
substantially orthogonally to the central axis 14b
whereon it is centred, and starting from which it
extends radially until it covers the circumferential
end of said eighth strip 52h. This last strip 52i
20 therefore allows the coating 48 to close the lower end
of the shell mould 200.
Note that for the strips 52d and 52e intended to
cover the arms 20b, when reinforcements 23b are
provided between these arms and the feeder 12b, these
25 same strips are preferably directly pressing all along
these arms, having slots allowing for the passage of
upper reinforcements 23b.
Here also, the fastening of the strips can be
carried out in any manner considered as suitable by
30 those skilled in the art, such as using iron wires.
The particular arrangement of the strips 52a-52i
that has just been described makes it possible to
obtain good metallurgical health of the metal cast in
the shell mould, in particular thanks to the presence
5 of a thermal resistance gradient of the coating 48
along each bladed element lb, according to the radial
direction of the latter. This gradient extends moreover
over the entire shell mould, according to the direction
of the axis 14b.
10 More precisely, the arrangement of these strips
allows the metal, after casting in the shell mould, to
solidify in the following way. Firstly, the metal
begins to solidify in the zone located on the window 56,
devoid of rock wool. The arrangement of the'layers 52a,
15 52b and 52c, 52f allows the metal to solidify
symmetrically in the blade portion 2b on either side of
the window, then still symmetrically, in the second end
part 6b and the upper portion of the blade portion 2b.
Finally, the solidification of the metal is completed
20 in the first end part 4b.
Of course, various modifications can be made by
those skilled in the art to the invention that has just
been described, only in terms of non-restricted
examples.
2 5
CLAIMS
1. Shell mould (200) for manufacturing a plurality
aircraft turbomachine bladed elements (1) using the
lost-wax moulding technique, said shell mould in the
shape of a cluster comprising:
5 - a plurality of shell mould bladed elements (lb)
each intended for the obtaining of one of said
turbomachine bladed elements (I), each shell mould
bladed element (lb) comprising a blade portion (2b)
located between a first end part (4b) delimiting the
10 impression of a platform (8b) as well as a second end
part (6b) delimiting the impression of another platform
(8b), said blade portion comprising a trailing edge
zone (30b) as well as a leading edge zone (31b) that is
opposite to it;
15 - a metal feeder (12b) having a central axis (14b)
around which said shell mould bladed elements (lb) are
distributed; and
- a shell mould interior space (28b) centred on
said central axis (14b), and delimited by said shell
20 mould bladed elements (lb),
characterised in that said shell mould is provided
with one or a plurality of screens (29b) that form heat
accumulators arranged in the shell mould interior space
(28b), across from inwardly-directed trailing edge
25 zones (30b) of said shell mould interior space (28b).
2. Shell mould according to claim 1, characterised
in that each screen (29b) that forms a heat accumulator
is made from a single piece with said shell mould (200).
30
3. Shell mould according to claim 1 or claim 2,
characterised in that a screen (29b) is provided
associated to each shell mould bladed elements (lb),
with each screen being more preferably of a
5 substantially planar shape.
4. Shell mould according to claim 1 or claim 2,
characterised in that a single screen (29b) is provided
associated to all said shell mould bladed elements (lb),
10 with said single screen being more preferably of
revolutionary shape, centred on said central axis (14b)
of the metal feeder (12b).
5. Shell mould as claimed in any preceding claim,
15 characterised in that each trailing edge zone (3Ob) is
separated from its associated screen (29b) by a
distance (B) between 1 and 40 mrn.
6. Shell mould as claimed in any preceding claim,
20 characterised in that it comprises a central support
(24b) extending from the metal feeder (12b) according
to the direction of the central axis (14b) of the
latter, with each screen (29b) being arranged around
said central support (24b) whereon it is added.
25
7. Shell mould as claimed in any preceding claim,
characterised in that it is made of ceramic.
8. Shell mould as claimed in any preceding claim,
30 characterised in that the blade portion (2b) of each
shell mould bladed element (lb) delimits one or several
blades.
9. Shell mould (200) for manufacturing a plurality
5 of aircraft turbomachine bladed elements (1) using the
lost-wax moulding technique, said shell mould in the
shape of a cluster comprising:
- a plurality of shell mould bladed elements (lb)
each intended for the obtaining of one of said
10 turbomachine bladed elements (1);
- a metal feeder (12b) having a central axis (14b);
and
- a plurality of metal casting arms (20b)
distributed around the central axis (14b) of the metal
15 feeder, with each of the casting arms having a first
end (21a) connected to said feeder,
characterised in that said shell mould (200) is
provided with a thermal insulation coating (48) carried
out using a plurality of thermal insulation strips
20 (50a-50e; 52a-52i) covering at least a portion of the
outside surface of the sheii mould.
10. Shell mould according to claim 9,
characterised in that said.coating is carried out using
25 thermal insulation strips each surrounding a shell
mould bladed element (lb) over at least one radial
portion of the latter, and using at least one thermal
insulation strip surrounding said shell mould (200).
11. Method for manufacturing a plurality of
aircraft turbomachine bladed elements (1) using the
lost-wax moulding technique, characterised in that it
is implemented using a shell mould (200) as claimed in
any preceding claim.
5 12. Method according to claim 11, characterised in
that the metal is cast in the shell mould (200) with
the central axis (14b) of the vertically-directed metal
feeder (12b).
Dated this 14/07/2014
W J N A MEHTA-DUTT]
OF REMFRY & SAGAR
ATTORNEY FOR THE APPLICANT[S]
ABSTRACT
The invention relates to a shell mould (200) for
manufacturing aircraft turbomachine bladed elements
using the lost-wax moulding technique, comprising:
- shell mould bladed elements (lb) comprising a
5 blade portion (2b) located between a first end part (4b)
delimiting the impression of a platform (8b) as well as
a second end part (6b) delimiting the impression of
another platform (8b), with the blade portion
comprising a trailing edge zone (30b);
10 - a metal feeder (12b) having a central axis (14b)
around which the bladed elements (lb) are distributed;
and
According to the invention, the shell mould is
provided with one or a plurality of screens (29b) that
15 form heat accumulators arranged in a shell mould
interior space (28b), across from inwardly-directed
trailing edge zones (30b).
Figure 5.