WO2011161357A1

WO2011161357A1 - Core for the manufacture of a turbine blade having impact-cooled leading edge cavity

Info

Publication number: WO2011161357A1
Application number: PCT/FR2011/051363
Authority: WO
Inventors: Huu-Thanh Tran
Original assignee: Snecma
Priority date: 2010-06-21
Filing date: 2011-06-15
Publication date: 2011-12-29
Also published as: FR2961552B1; FR2961552A1

Abstract

The invention relates to a ceramic core for producing the inner cavities of a turbine blade by means of the lost-wax foundry technique, said ceramic core comprising at least two adjacent elements (6, 7) for creating two substantially parallel cavities for circulating the air for cooling said blade, said elements being separated from each other by a spacing for forming an inter-cavity wall, wherein a first element (6) is connected to the rest of the core by means of attachment elements (10), and a second element (7) is connected to a column base (8) for forming a cooling-air supply pipe, characterized in that said attachment elements (10) are exclusively located at the ends of the first element (6).

Description

CORE FOR MANUFACTURING AN IMPACT COOLED DATTATIC CAVITY TURBINE TURBINE BLADE.

The field of the present invention is that of turbomachines and, in particular that of the manufacture of turbine blades of these turbomachines.

A turbomachine conventionally comprises, from upstream to downstream in the direction of the gas flow, a blower, one or more stages of compressors, for example a low pressure compressor and a high pressure compressor, a combustion chamber, one or more turbine stages, for example a high pressure turbine and a low pressure turbine, and a gas exhaust nozzle.

The turbine blades are subjected to high thermal stresses due to the heat of the gases in which they are immersed at the outlet of the combustion chamber, and they need to be cooled to withstand these temperatures. They are therefore hollow and traversed by cavities, in which circulates relatively cold air, taken at the output of a stage of a compressor.

To achieve these cavities, which have complex shapes and whose geometry must be respected with great precision, the blades are produced by the classical technique known as lost wax casting. This technique consists schematically in making a dawn in wax in which are drowned ceramic nuclei that reproduce cavities to come. The dawn wax is then embedded in a shell of refractory material, from which the wax is removed by heating. The metal constituting the blade is then poured into the refractory shell and the cores are then eliminated chemically, leaving in their place the desired cavities. Implementations of this method are in particular described in the patent applications of the applicant FR2875425 or FR2874186.

The cores for the modern turbine blades are constituted by elements, conventionally in the form of columns, which are positioned side by side and held together by means known to those skilled in the art. These modern turbine blades thus comprise several cavities arranged in parallel, oriented parallel to the leading edge of the blades blade. The cooling of the blade metal is made by a circulation of air within these cavities, which are fed by pipes connecting them to the feet of the blades.

In particular cases, the upstream cavity, referred to as the leading edge cavity, is not supplied with cooling air by a specific pipe but by air from the adjacent cavity. , passing through micro-holes made in the partition between these two cavities. The leading edge of the blade is thus cooled by the impact of the air passing through the inter-cavity wall.

The ceramic core used for the manufacture of such blades must therefore comprise a series of refractory rods connecting the columns forming these two cavities, to form, after casting, holes in the inter-cavity wall. These holes must be very small, the two columns are connected by a series of rods, usually silica, extremely thin and therefore extremely fragile. The necessary handling of the cores during the preparation of the wax form of the dawn inevitably causes the breakage of some of these tubes and thus the disposal of the damaged core. This waste has a significant cost that should be eliminated as much as possible.

The object of the present invention is to remedy these drawbacks by proposing a core for producing cavities of a turbine blade which does not have the drawbacks of the prior art and, in particular, which does not have any fragile part capable of to break during handling. It also proposes a method of making a blade, with the use of such a core.

To this end, the subject of the invention is a ceramic core for producing internal cavities of a turbine blade by the lost-wax foundry technique, comprising at least two adjacent elements intended to create two substantially parallel cavities for the circulation of the cooling air of said blade, said elements being separated from each other by a spacing intended to form an inter-cavity wall, a first element being connected to the remainder of the core by connecting elements and a second element being connected to a column stand intended to form a cooling air supply pipe, characterized in that said elements of attachment (10) are located exclusively at the ends of the first element.

Drilling the inter-cavity wall after the foundry avoids having to place too fine bridges between the two columns that form the corresponding cavities and thus to have a nucleus too fragile. The drilling of the inter-cavity wall is then performed by introducing a tool into one of the evacuation holes.

Advantageously, the column foot is shaped so as to direct the flow of cooling air passing through the feed pipe that it will form, exclusively to the cavity formed by said second element. In this configuration all of the cooling air which feeds the cavity coming from the first element will pass through holes made by drilling in the inter-cavity wall.

In a particular embodiment a first element is held in place by at least one bridge fixed on another element of said core, said bridge having a cylindrical or conical shape, so that the pipe that it will form can be closed by a plug having a simple geometric shape of the cylindrical, conical or spherical type.

Preferably the first element is a first column intended to form a leading edge cavity or trailing edge, the second element being a second column positioned parallel to the first column.

The invention also relates to a method for producing a turbomachine hollow turbine blade using the lost wax foundry technique using a core comprising at least two adjacent elements intended to create two substantially parallel cavities. , separated from each other by a spacing for forming an inter-cavity wall, said method comprising, after the casting and removal of the core, a first step of drilling vent holes in the wall delimiting a first cavity followed by a second step of drilling at least one feed hole in the inter-cavity wall by means of a tool penetrating into the first cavity by one of the escape holes characterized in that it further comprises a subsequent step of providing a coating on the wall delimiting the first cavity so as to reduce the section of said discharge hole. The diameter of the evacuation bore is reduced when a suitable coating is deposited on the leading edge of the vane after the drilling of the feed hole, which allows the diameter of the vane to be adjusted. this hole.

The invention will be better understood, and other objects, details, features and advantages thereof will appear more clearly in the following detailed explanatory description of an embodiment of the invention given as a purely illustrative and non-limiting example, with reference to the accompanying schematic drawings.

On these drawings:

- Figure 1 is a generic view, in section, of a high pressure turbine module of a turbomachine;

- Figure 2 is a front view of a turbine blade core, according to the prior art;

FIG. 3 is a front view of a turbine blade core, according to one embodiment of the invention;

- Figure 4 is a front view of a high pressure turbine blade, made from the core of Figure 3;

FIG. 5 is a view of a turbine blade of FIG. 4, cut substantially at mid-height of its blade, and

FIG. 6 is a sectional view of the turbine blade of FIG. 4.

Referring to FIG. 1, we can see the hot parts of an aerospace turbomachine comprising a moving blade of a high-pressure turbine 1 located downstream of a fixed vane of distributor 2 and carried by a turbine disc 3. The dawn distributor 2 and the blade 1 are positioned in a flow of gas 4 which leaves the combustion chamber, not shown, and which is at a very high temperature.

FIGS. 2 and 3 show a ceramic core 5 intended for producing a turbine blade 1, according to the prior art in the case of FIG. 2 and according to the invention in the case of FIG. ceramic 5, as shown in the figures, has five columns, without this number is imperative. The first pillar 6, which is intended to meet the arrival side of the stream 4, corresponds to the leading edge cavity that will be created after foundry, while the second pillar 7 corresponds to the cavity adjacent thereto . This the latter receives a cooling flow through a pipe resulting, after casting, the presence of a first column foot 8 on the core 5. The last three columns, which are formed in one piece making a round trip, correspond a second flow of cooling air which is brought by a pipe resulting from the presence of a second column foot 8b.

In the prior art of FIG. 2, the first and second columns 6 and 7 are connected to each other by a series of bridges 9, to which will correspond, after casting, air feed holes through the inter-cavity wall, for cooling the leading edge cavity 16. The size of these bridges 9 remains relatively large to prevent them breaking during handling of the core 5, which would make it unusable. This size constraint on the bridges 9 creates an additional constraint for the design of the blade since the passage section between the first two cavities can not be reduced below a certain value, value for which the bridges 9 become too fragile. .

In the invention shown in Figure 3, the first and second pillars 6 and 7 are separated from each other by a spacing, thus leaving room for the creation of a full intercavital wall 22 during the casting of the metal. For reasons of maintaining the first pillar 6 and rigidity of the entire core 5 a holding bridge 10 is placed between the lower end of the first pillar 6 and the first column foot 8. The presence of this holding bridge will result, after the foundry, the leading edge cavity 16 will be connected directly by a specific pipe to the supply line of the second cavity 17. A shutter must then be installed at the end of realization dawn on this specific pipe to suppress this communication and force the cooling air to enter the second cavity.

The holding bridge 10 is, here, represented in the form of a cylindrical rod coming off the first leg of the column to be attached in the lower part to the first column 6. It is not located in the axis of the circulation of the cooling air, the latter being intended to pass entirely into the second cavity 17 and the channel created by the holding bridge 10 having to be plugged for force the flow of air towards this second cavity. For reasons of aerodynamics, the column foot 8 is therefore naturally extended in the direction of the second pillar 7, leaving the holding bridge 10 to diverge frankly in this direction so as not to be in the continuity of the foot of the column .

Figure 4 shows a blade 1 through which appear the cavities created by the presence of the core 5, according to the invention, during the casting of the metal. The cavities are numbered with reference to the elements of the nucleus that created them, adding 10 to the reference of the corresponding element. The leading edge 20 of the blade 1 is conventionally pierced with a multitude of holes 23 through which the cooling air is evacuated from the first cavity 16, before flowing along the profile of the dawn to cool its metal surface.

Referring now to FIGS. 5 and 6, bores 23 are seen at the leading edge 20 of the blade. A hole 21 for feeding the leading edge cavity 16 is pierced through the inter-cavity wall 22 which separates the leading edge cavity 16 from the second cavity 17. The cooling air coming from the supply line 18 passes from the second cavity 17 into the leading edge cavity 16 from which it flows outwards through a series of evacuation holes made in the leading edge 20 and referenced from 23a to 23e. These evacuation holes are oriented substantially perpendicular to the leading edge, at the tip thereof, and are increasingly inclined towards the surface of the blade, as they move away from this tip for reasons of aerodynamic efficiency. In the case of drilling furthest away from the tip 23e, it is prolonged even by a tangential drilling which directs the flow of air along the profile of the blade.

It should be noted, as can be seen in FIG. 6, that the supply bore 21 is aligned with the exhaust bore 23c which is the one closest to the tip of the leading edge 20. Moreover, its orientation is directed to the inter-cavity wall 22. This alignment is necessary to be able to pierce the inter-cavity wall and perform the feed hole 21 by introducing a tool through the discharge bore 23c. We will now describe the process of manufacturing a turbine blade 1 with a core 5 according to the invention.

The core 5 is made according to traditional methods and embedded in a wax form reproducing the shape of the dawn to be manufactured. After the realization of a refractory shell enveloping the dawn in wax, the shell is heated to melt the wax and to evacuate it by orifices provided for this purpose. The actual dawn is then obtained by casting, casting the appropriate metal in the cavities left free by the melting of the wax, then removing the core 5 by a suitable chemical treatment.

Thus, a blade 1 is obtained in which the leading edge cavity 16 is separated from the second cavity 17 by the inter-cavity wall 22 which is solid, but which, on the other hand, is connected to the feed pipe 18 by a duct resulting from the existence of the holding bridge 10. This duct is then closed, by means, for example, of the introduction of a ball in this duct, where it is brazed.

A conventional operation of perforation of the leading edge wall 20 is then carried out, which results in the creation of the holes 23a to 23e and which vents the leading edge cavity 16 in the open. the dawn it has been provided that at least one hole 23c is oriented substantially orthogonal to the inter-cavity wall 22. The drilling operation of this hole 23c is extended so as to reach the inter-cavity wall 22 and to pierce a feed hole 21 through it. Thus, a channel for supplying the leading edge cavity 16 with cooling air is created by the second cavity 17. This air, coming from the supply pipe 18, enters the second cavity 17 which it it cools and then passes through the inter-cavity wall 22 via the feed bores 21. It thus opens into the leading edge cavity 16 from which it emerges by the evacuation holes 23 in order to envelop the profile of the blade 1 and cool its surface.

The diameter of the feed bore 21 is equal to that of the tool used to perform it while the diameter of the bore 23c through which the tool is introduced may be less than this value, its diameter then being reduced, after the drilling operation of the inter-cavity wall, by deposition treatment of various coatings on the leading edge 20. The designer of the blade is thus not limited to the choice of the size of the drilling of supply and it can freely define the diameters of the various drillings and the flows of air of cooling which they will allow.

In the end we obtain the desired result, namely a turbine blade for which we can optimize the circulation of its cooling air and which is obtained using a core 5 having sufficient strength to be handled without excessive risk. of breakage.

The invention has been described by taking as an example a leading edge cavity fed with cooling air from the adjacent cavity. It is obvious that it can be implemented on any other cavity of a hollow turbine blade and in particular on a trailing edge cavity.

Similarly, the holding bridge 10 has been described as having a cylindrical shape and the plug placed in the pipe that it generates as a ball; the bridge can also have a conical shape and the plug have any simple geometric shape that fits easily in the pipe to be plugged, such as a cylinder of the same size or a conical shape integrating into the cylindrical or conical shape of the corresponding pipeline.

Claims

Ceramic core for producing internal cavities of a turbine blade (1) by the lost wax casting technique, comprising at least two adjacent elements (6, 7) intended to create two substantially parallel cavities (16). , 17) for the circulation of the cooling air of said blade, said elements being separated from each other by a spacing intended to form an inter-cavity wall (22), a first element (6) being connected the remainder of the core by connecting elements (10) and a second element (7) being connected to a column base (8) for forming a cooling air supply duct (18),

characterized in that said connecting elements (10) are located exclusively at the ends of the first element (6).

2. Core according to claim 1 wherein said column foot (8) is shaped to direct the flow of cooling air passing through the supply pipe (18) that it will form, exclusively to the cavity (17). formed by said second element (7).

3. Core according to one of claims 1 or 2 wherein the first element (6) is held in place by at least one bridge (10) fixed on another element (7) of said core, said bridge having a cylindrical shape or conical, so that the pipe that it will form can be closed by a plug having a simple geometric shape of the cylindrical type, conical or spherical.

4. Core according to one of claims 1 to 3 wherein the first element is a first pillar (6) intended to form a leading edge cavity (16) or trailing edge, the second element being a second pillar (7) positioned parallel to the first pillar.

5. A method of producing a hollow turbine blade (1) for a turbomachine using the lost wax foundry technique using a core (5) comprising at least two adjacent elements (6, 7) intended creating two substantially parallel cavities (16, 17), separated from each other by a gap for forming an inter-cavity wall (22), said method comprising, subsequent to the foundry and removing the core, a first step of drilling outflow holes (23) in the wall defining a first cavity (16), followed by a second step of drilling at least one feed hole (21) in the inter-cavity wall (22) via a tool penetrating into the first cavity (16) through one of the discharge holes (23c), characterized in that it further comprises a subsequent step providing a coating on the wall defining the first cavity (16) so as to reduce the section of said discharge hole (23c).