Patent Application
20170239712
The invention relates to the field of cluster manufacturing of aircraft turbomachine vane elements, by the lost wax moulding technique. Each vane element is preferentially an individual vane, such as a compressor or turbine impeller moving vane. Alternatively, this can be a sector comprising a plurality of blades, such as a sector of low pressure distributor.
The invention more particularly relates to the design of the cluster-shaped pattern and that of the shell intended to be formed about this pattern partially of wax, in which shell the metal is intended to be cast for obtaining turbomachine vane elements. It relates more specifically to the problem of breaking of the wire elements equipping the shell, these wire elements being intended to be surrounded by the metal upon casting, and then removed to give way to cooling channels passing through the vane element.
The invention relates to any type of aircraft turbomachine, in particular turbojet engines and turboprop engines.
It is known from prior art to use the lost wax moulding technique to simultaneously manufacture several aircraft turbomachine vane elements, such as moving vanes. Such a technique is for example described in document FR 2 985 924.
As a reminder, the precision lost wax moulding consists in making with wax, by injecting into toolings, a pattern of each of the desired vane elements. The assembly of these patterns on a distributor of wax enables a cluster-shaped pattern to be made, which is then dipped into different substances in order to form around it a ceramic shell with a substantially uniform thickness. The cluster-shaped pattern is also known as “replica”, “cluster-assembly” or even “wax tree”, although not all its components are necessarily made of wax or in another sacrificial material.
The method is continued by melting wax, which then leaves its accurate fingerprint in the ceramic shell, in which the molten metal is poured, via a pouring bush assembled to the metal distributor. After cooling the metal, the shell is destroyed and the metal pieces are separated and completed.
This technique offers the advantage of dimensional accuracy, enabling some machinings to be reduced or even cancelled. Furthermore, it offers a very good surface aspect.
When the vane element to be manufactured has to include cooling channels, the shell is equipped with wire elements passing through the fingerprints. These wire elements are preferably made based on silica. Upon casting the metal into these fingerprints, the molten metal surrounds the wire elements, which are then removed to give way to cooling channels passing through the solidified vane element. In use, the cooling air can flow from the root to the head of the vane element, to ensure cooling thereof.
The wire elements of silica, also called glass tubes, thus travel through the fingerprints of the shell, substantially along the span direction of the vane elements. A so-called sensitive portion of these wire elements is radially facing the outlet of the metal distributor. This portion is actually said to be sensitive, because it tends out to be susceptible to breaking risks due to the impact of the metal flow exiting the distributor. If such a breaking of one or more of the wire elements occurs following the impact of the metal flow, the piece is supposed to be defective, and then discarded.
In an attempt to solve this problem, document EP 0 899 039 suggests to strengthen quartz tubes by a carbon fibre inserted inside the tube. However, this technique remains expensive, and cannot turn out to be fully satisfactory.
Thus, there is a need for optimising the current technique, to reduce the breaking risks of the glass wire elements.
The purpose of the present invention is thus to at least partially overcome the above-mentioned drawbacks, relative to embodiments of prior art.
For this, one object of the invention is first a cluster-shaped pattern, about which a shell is intended to be formed for manufacturing a plurality of vane elements of an aircraft turbomachine via lost wax moulding, said pattern comprising:
According to the invention, the cluster-shaped pattern includes at each connecting zone a protective screen aiming at protecting, during a step of casting metal into the shell, a sensitive portion of said wire elements against the direct impact of a metal flow, said sensitive portion being located in the second end part, radially outwardly with respect to the protective screen, along said centre axis.
Analogously, one object of the invention is a shell for manufacturing a plurality of vane elements of an aircraft turbomachine via lost wax moulding, said cluster-shaped shell comprising:
According to the invention, the shell includes, being associated with each second end part, a protective screen aiming at protecting a sensitive portion of said wire elements against the direct impact of a metal flow from the feeder, said sensitive portion being located in the second end part, downstream of the protective screen. Of course, the term downstream is here to be considered with regard to a primary metal flow direction, within the relevant pieces of the shell. In other words, upon casting, the metal first meets the protective screen before meeting the sensitive portion of the wire elements that this screen aims at protecting.
The invention is remarkable in that it makes it possible, in a clever and cheap way, to strongly limit the breaking risks of the wire elements during the subsequent metal casting within the shell. Indeed, the protective screens have the function to deviate the metal flow such that it does not directly impact any longer the sensitive portion of the wire elements. By virtue of this flow deviation, the metal can bypass the sensitive part before contacting the same, which dramatically reduces heat and mechanical impacts onto the wire elements.
In other words, by virtue of the invention, the wire elements are not directly impacted by the metal flow at their surface radially oriented facing the distributor outlet, but impacted at their opposite surface.
The invention has at least one of the following optional characteristics, taken alone or in combination. Furthermore, it is noted that if the below-mentioned characteristics are described in relation with the shell, it should be understood that they are analogously applicable to the cluster-shaped pattern, about which this shell is intended to be formed.
Said protective screen is arranged at said metal outlet of the distributor by axially extending through the entirety of this metal outlet, so as to force the metal flow to circulate on one side and/or on the other side of the screen.
The protective screen is arranged radially facing said sensitive portion of said wire elements.
The protective screen has a rectangular parallelepiped shape. However, many other shapes can be suitable, for example cylindrical, spherical, elliptic, ovoid, etc. The rectangular parallelepiped shape has however been retained for the high-performance results observed during tests on the shell in accordance with the invention.
The protective screen is made from a ceramic element equipping a cluster-shaped pattern about which the shell is intended to be formed, or made upon forming this shell by filling a dedicated fingerprint in said cluster-shaped pattern, partially of wax.
The shell is made of ceramics, preferably by dipping.
Said wire elements are made based on silica, preferably as tubes.
Said shell vane elements are each designed for obtaining a single moving vane, such as a compressor or turbine impeller moving vane.
Another object of the invention is a method for manufacturing such a shell, comprising making a cluster-shaped pattern about which the shell is intended to be formed, said pattern being equipped with ceramic pieces for forming said protective screens, or equipped with fingerprints in which the shell is intended to be formed to make up said protective screens. In this regard, the shell is preferentially obtained by dipping the cluster-shaped pattern into several ceramic baths.
Finally, another object of the invention is a method for manufacturing a plurality of vane elements of an aircraft turbomachine via lost wax moulding, implemented using such a shell and/or such a cluster-shaped pattern, the method comprising a step of casting metal into the shell, during which each protective screen deviates the molten metal such that this metal bypasses the sensitive part of the wire elements before contacting the same. As discussed above, by virtue of this technique unique to the invention, the wire elements are thus not directly impacted by the metal flow at their surface radially oriented facing the distributor outlet, but impacted at their opposite surface.
Preferably, the method comprises the following successive steps of:
Further advantages and characteristics of the invention will appear in the non-limiting detailed description below.
This description will be made with regard to the appended drawings in which;
In reference to
The vane 1 includes cooling airway channels 3. These cooling channels 3 fully pass through the vane, along the span direction of the vane. Thus, each channel 3 opens into the head or top of the vane, as well as at the root 4 thereof.
It is noted that in the following of the description, the terms “top”, “bottom”, “above” and “below” are intended according to the orientation of the views in the figures.
The invention aims at manufacturing the moving vane 1 from a shell intended to be made by a method specific to the invention, a preferred embodiment of which will now be described in reference to
For manufacturing the shell, a cluster-shaped pattern is first made, about which a ceramic shell is intended to be subsequently formed. The pattern 100 is essentially comprised of sacrificial elements made of wax, but not exclusively. However, in the following, it will be called “wax pattern”.
In
The pattern 100 first includes a portion for distributing metal, referenced 12a. This wax portion comprises a solid centre element 13a having a revolutionary, cylindrical or conical shape, with a centre axis 14a coincident with the centre axis of the entire wax pattern 100. The axis 14a is vertically oriented, and thus considered as representing the height direction.
The solid centre element 13a is attached to metal pouring bush 35 with a conical shape, located above this solid element 13a. The same is connected by radial arms 15a to a distribution crown 17a centred on the axis 14a. The arms 15a and the crown 17a are arranged just below the pouring bush 35.
To enhance holding of the crown 17a of the distribution portion 12a, several wax/ceramic holding reinforcements 23a connecting the crown 17a to the bush 35 are provided. These reinforcements 23a are substantially vertically oriented in the position of the pattern 100 depicted in
Furthermore, at the periphery of the distribution crown 17a, wax replicas 1a of the turbine vane represented in
Each replica 1a thus comprises a blade 2a, arranged between a first end 4a and a second end 6a to which the blade is connected. The first end 4a forms a vane root, and comprises a platform 8a. The second end 6a is in turn arranged above the blade head, at the distribution crown 17a along the height direction. The second end 6a has an enlarged shape with respect to the blade 2a, as has been schematically represented in
The direction along which the blade 2a and the ends 4a, 6a follow each other corresponds to the radial direction or span direction of the wax vane element 1a, this direction being preferably substantially parallel to the direction of the axis 14a, that is parallel to the height direction of the replica 100.
Wire elements 19 of glass, intended to form subsequently the above-mentioned cooling channels 3, represented in
The wax vanes 1a thus extend upwardly, by being provided about the axis 14a, and also about a wax centre support 24a extending along the same axis, downwardly from the centre element 13a of the distribution portion 12a. The support 24a has preferentially the shape of a cylinder with the axis 14a, which extends up to the vicinity of the end 4a of the wax vane 1a.
Intermediate wax radial arms 26a connect the support 24a to the blades 2a, at mid-height of the same.
Finally, the low end of the support 24a is connected to the ends 4a of the wax vanes 1a, via a secondary distribution crown 27a, similar to the above-mentioned crown 17a.
The wax vanes 1a form the peripheral wall of the wax replica 100, with the axis 14a. They are circumferentially spaced from each other, and define an internal space centred on this axis 14a, in which space the above-mentioned support 24a is thus located.
It is noted that if the replicas 1a have been represented with the vane root 4a arranged in the bottom with respect to the blade 2a in the position of
In reference now more specifically to
Each protective screen 28 has a substantially rectangular parallelepiped shape, or that of an angular sector of a revolutionary piece, with an axis 14a. Its major axis is preferably substantially oriented in parallel to the axis 14a. The screen 28 is housed in a depression of the periphery of the crown 17a, such that its radially outwardly oriented surface is substantially in the geometric continuity of the peripheral rim of this crown, as visible in
In
Furthermore, the protective screen 28 extends vertically beyond the distribution crown 17a, on either side of the same, as is best visible in
As will be described hereinafter, the shell is intended to be formed about the wire pattern 100, and thus about the screens 28 which will remain integrated to this shell upon casting metal, and which thus will not be removed with the rest of the pattern 100 before this cast. However, in the alternative embodiment represented in
After obtaining the wax pattern 100 described in
After being dried, the shell 200 which is obtained is schematically represented in
The shell 200 first includes a metal distributor, referenced 12b. The distributor comprises a solid centre element 13b with a revolutionary, cylindrical or conical shape, with a centre axis 14b coincident with the centre axis of the shell 200, which is vertically oriented.
The solid centre element 13b is attached to the metal pouring bush 35, which can be entirely or partially covered with the shell. Radial arms 15b connect the solid centre element 13b to a distribution crown 17b centred on the axis 14b. The arms 15b and the crown 17b are arranged just below the pouring bush 35.
To enhance holding the crown 17b, several wax/ceramic holding reinforcements 23b connecting the crown 17b to the bush 35 are provided. These reinforcements 23b are substantially vertically oriented in the position of the shell 200 depicted in
Moreover, in the periphery of the distribution crown 17b, shell vane elements 1b are attached. These elements 1b are so-called vane elements because after removing the wax replica 1a, they each form internally a cavity corresponding to one of the vanes 1.
As is visible in the schematic
The direction along which the blade part 2b and the ends 4b, 6b follow each other corresponds to the radial direction or span direction of the shell vane element 1b, this direction being preferably substantially parallel to the direction of the axis 14b, that is parallel to the height direction of the shell 200.
The glass wire elements 19, for subsequently forming the channels for cooling the vanes, pass through the cavities defined by the shell vanes 1b. They entirely pass through each element 1b, by successively passing through the first end part 4b, the blade part 2b, and the second end part 6b connected to the distribution crown 17b. As is visible in
The shell vane elements 1b thus extend upwardly, by being provided about the axis 14b, and also about a centre support 24b extending along the same axis, downwardly from the centre element 13b. The support 24b has preferentially the shape of a hollow cylinder with an axis 14b, which extends up to the vicinity of the end 4b of the vane elements 1b.
Intermediate radial arms 26b connect the support 24b to the blade parts 2b, at mid-height of the same.
Further, the low end of the support 24b is connected to the ends 4b of the vane elements 1b, via a secondary metal distribution crown 27b, similar to the afore-mentioned crown 17b.
The vane elements 1b form the peripheral wall of the shell 200, with the axis 14b. They are circumferentially spaced from each other, and define an internal space centred on this axis 14b, in which space the support 24b is thus located.
In reference now more specifically to
The metal outlet 30 is equipped with the protective screen 28, sealing a circumferential end part of this outlet. The screen 28, arranged at the junction with the second end part 6b, is thus located upstream of the sensitive portion of the wire elements 19 housed in the cavity of this second end part 6b, the term upstream to be considered with regard to a primary metal flow direction within the relevant pieces.
It is also contemplated to be surrounded by the shell at its high and low ends, as is visible in
Furthermore, the protective screen 28 is arranged radially facing the sensitive portion of the glass wire elements 19. The circumferential extent of the screen is not necessarily identical to that of the network of wire elements, but can be lower. This circumferential extent, as well as other parameters such as the position of the screen 28 within the metal outlet 30, can be adjusted such that during the subsequent cast, the metal flow is properly deviated and that it does not directly impact the sensitive portion of the wire elements 19. Consequently, depending on the shell geometry and the position of the wire elements 19, the screen 28 could be placed in a different location from that at one of the ends of the metal outlet 30, so as to force the metal to flow on either side of the same, in order to properly protect the sensitive part of these wire elements.
After obtaining the shell 200 and removing most of the pattern 100 enclosed in the same, the shell is preheated at a high temperature in a dedicated oven, for example at 1150° C., in order to promote metal fluidity in the shell during casting.
Following preheating the shell, metal exiting a melting oven is cast into the fingerprints via the bush 35, with the shell in the position as shown in
The molten metal thus successively travels the bush 35, the distributor 12b, and then the shell vane elements 1b, by simply flowing by gravity. The metal also flows downwardly inside the support 24b, to supply thereafter the intermediate radial arms 26b and the secondary distribution crown 27b. On the other hand, even if it is a less sensitive region, the second end parts 4b located in the bottom of the shell could be equipped with substantially identical screens for protecting the portion of the glass tubes 19 which is located radially facing the metal outlets of the secondary distributor 27b, without departing from the scope of the invention.
It is noted that the reinforcements 23b are preferentially solid, of ceramic, thus the molten metal upon casting in the shell 300 does not pass therethrough.
Upon initiating this cast, the metal flows through the solid centre element 13b, the radial arms 15b, and then circumferentially travels through the crown 17b up to arrive in the proximity of the metal outlet 30. As has been schematically represented in
By virtue of this deviation and the velocity of the metal flow, the latter can bypass the sensitive part of the glass wire elements 19, before contacting these elements, which reduces heat and mechanical impacts on the glass wire elements. As has been depicted in
After cooling the metal following the cast, the shell is destroyed, and then the moving vanes 1 are extracted from the cluster for possible machinings and finishing and check operations. Among these steps, there is that of removing the glass tubes 19 that are still present within the obtained vanes. This removing step is conventionally made, for example by chemical destruction.
Of course, various modifications can be made by those skilled in the art to the invention just described, only by way of non-limiting examples.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14 59834 | Oct 2014 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2015/052735 | 10/12/2015 | WO | 00 |
