CERAMIC CORE FOR MULTI-CAVITY TURBINE SHAFTS

Description

Scope of the invention

[0001] The present invention relates to the general field of turbomachine turbine blades, and more particularly to turbine blades equipped with integrated cooling circuits produced by the lost-wax casting technique. Previous art

[0002] As is well known, a turbomachine consists of a combustion chamber in which air and fuel are mixed before being burned. The gases produced by this combustion flow downstream of the combustion chamber and then power a high-pressure turbine and a low-pressure turbine. Each turbine has one or more rows of fixed blades (called distributors) alternating with one or more rows of moving blades (called runners), spaced circumferentially around the turbine rotor. These turbine blades are subjected to the very high temperatures of the combustion gases, which reach values ​​far exceeding those that the blades, in direct contact with these gases, can withstand without damage, thus limiting their service life.

[0003] To solve this problem, it is known to equip these blades with internal cooling circuits having high levels of thermal efficiency and aimed at reducing the temperature of the latter by creating, inside the blade, an organized circulation of this air (simple cavities with direct supply or paper clips for example) and, in the wall of the blade, perforations intended to generate a protective film for this blade.

[0004] This technology, however, has several drawbacks. First, while trombone-shaped cavity circuits maximize the work done by the air through the circuit, they also generate significant heating of the air, resulting in a decrease in the thermal efficiency of the holes located at the ends of the trombone. Similarly, configurations with leading-edge and trailing-edge cavities with direct airflow do not provide an effective response to the high temperatures typically observed at the blade tip. Finally, the various cavities are separated from the airflow stream only by a wall of varying thickness depending on the area of ​​the blade.Given the constraints on the flow allocated to blade cooling and the current trend of increasing airflow temperatures, it is not possible to efficiently cool the blade with a circuit of this type without significantly increasing the airflow and penalizing engine performance.

[0005] There figure 5 This illustrates a high-pressure turbine blade 10 of a gas turbine engine, comprising an aerodynamic surface or blade 12 extending radially between a root 14 and a blade tip 16. The blade root is shaped to allow the blade to be mounted on a rotor disk. The blade tip has a tub-shaped portion 18 consisting of a bottom transverse to the blade and a wall forming its edge in line with the wall of the blade 12. As shown in the cross-sectional view of the figure 6In the example shown, the blade 12 comprises, for illustrative purposes only, a plurality of cavities 20, 22, 24, 26, 28, 30, 32. The first and second central cavities 20, 22 extend from the root to the tip of the blade, and two other cavities 24, 26 are arranged on either side of these central cavities, along the upper surface (extrados) between these central cavities and the upper surface (extrados) of the blade, and along the lower surface (intrados) between these central cavities and the lower surface (intrados) of the blade. Finally, a cavity 28 is located in the portion of the blade near the leading edge, and two cavities 30, 32 are arranged in a line in the portion of the blade near the trailing edge.

[0006] The shape and number of cavities, as well as the position of the external holes 34, 36 and the geometry of the trailing edge slots 38, are given for illustrative purposes only; all these elements are generally optimized to maximize thermal efficiency in the areas most sensitive to the heat of the combustion gases in which these blades are immersed. The internal cavities are also often equipped with disruptors (not shown) to increase heat exchange.

[0007] As described in application FR2961552 on behalf of the applicant, high-pressure turbine blades are classically produced by lost-wax casting, the geometry of the circuits being produced, according to its complexity, by positioning in the mold one or more ceramic cores whose outer surface forms the inner surface of the finished blade.

[0008] In particular, cooling circuits with multiple cavities, such as those of figures 5 and 6 These processes require the assembly of several separate ceramic cores (designed to create the central cold cavities isolated from hot gases and the thin external cavities with separate air supplies) to ensure the necessary metal wall thicknesses before casting. This complex operation, manually assembled by joining the base and top of the ceramic cores, prevents the casting of the blade head's tub, necessitating a costly additional finishing operation that can compromise the blade's mechanical strength in this area (for example, adding the tub or sealing it by brazing). Object and summary of the invention

[0009] The present invention therefore aims to overcome the disadvantages associated with the manual assembly of several separate cores by proposing a cooling circuit for a turbine blade which can be made in a single core in order to eliminate these bathtub assembly and finishing operations of the prior art circuits while ensuring the inter-cavity distance corresponding to the thickness of the metal partition after casting of the molten metal, in a more reliable way than in current manual assemblies.

[0010] For this purpose, a ceramic core is provided for use in the manufacture of a hollow turbine blade for a turbomachine according to claim 1.

[0011] By joining the blade body, the need for assembly devices at the blade tip is eliminated, resulting in a casting with the same mechanical properties as the blade body. Furthermore, the primary feed of the lateral cavities from their base allows for better control of airflow and overall cooling of the external walls on the finished blade. Additionally, on the core, the feeds of the various cavities can be joined during injection molding, further improving the core's mechanical strength.

[0012] According to the envisaged embodiment, the said predetermined critical zones are chosen from among the most thermo-mechanically stressed zones of the said first and second lateral cavities and the said ceramic junctions have a cross-section dimensioned to ensure the mechanical strength of the said internal partitions during the pouring of the molten metal.

[0013] The invention also relates to the method of manufacturing a hollow turbine blade of a turbomachine produced according to the lost-wax casting technique using a single-element core as explained above and any turbomachine turbine equipped with a plurality of cooled blades manufactured from such a process. Brief description of the drawings

[0014] Other features and advantages of the present invention will become apparent from the description given below, with reference to the accompanying drawings which illustrate an example of an embodiment without being limiting in any way and on which: there figure 1 is an intrados view of a turbine blade core according to the invention, the figure 2 is an extrados view of a turbine blade core according to the invention, the figure 3 is a view of the core of figures 1 and 2 cut along the height of the dawn to show its junction zones, the figures 4A, 4B and 4Care cross-sectional views at different heights of the dawn, the figure 5 is a perspective view of a turbine blade from the prior art, and the figure 6 is a cross-sectional view of the dawn of the figure 5 . Detailed description of an implementation method

[0015] THE figures 1 and 2These figures represent a ceramic core 40 intended for the production of a turbomachine turbine blade, viewed respectively from the upper and lower surfaces of this blade. In the illustrated example, the ceramic core comprises seven parts or columns forming a single element. The first column 42, which is intended to be located on the combustion gas inlet side, corresponds to the leading edge cavity 28 that will be created after casting, while the second column 44 corresponds to the adjacent central cavity 20. This latter cavity receives a flow of cooling air through a duct (not shown) resulting, after casting, from the presence of a first column foot 46 of the core 40.The three other columns 48, 50, 52, making a round trip, correspond to the following cavities 22, 30, 32, which receive a second flow of cooling air supplied by another duct originating from the presence of a second column foot 54 connected to the first column foot 46 to form the base of the core. The first and second columns 42 and 44 are connected to each other by a series of bridges 56, to which, after casting, air supply ports will correspond (see reference 80 on the . figure 4A) for cooling the leading edge cavity 28. At least two upper bridges 57, at the connection with the columns, and a head 59 of the core 40 allow the desired wall thickness to be obtained at the bottom of the casting bath during pouring and are also dimensioned to form air vents. Regarding the fourth column 50, vertically inclined bridges 58 create thinned core regions that allow for the creation of stiffened blade regions.

[0016] The size of the various bridges is determined to prevent their breakage during the handling of the core 40, which would render it unusable. In the example considered, the bridges are distributed at roughly regular intervals along the height of the core 40, particularly in the first column 42 of the core.

[0017] According to the invention, the core 40 further comprises sixth and seventh lateral columns 60 and 62, each separated from the second and third columns 44, 48 by a predetermined spacing, thus allowing space for the creation of a solid inter-cavity wall during the pouring of the molten metal. For the purpose of maintaining the stability of these columns and the overall rigidity of the core, the lower end of the sixth column 60 is connected to the first column foot 46, and the lower end of the seventh column 62 is connected to the second column foot 54 and multiple small-section ceramic junctions (see, for example, references 64, 66, 68 of the figure 3 ), dimensioned however to ensure the mechanical strength of the internal partitions formed during the pouring of the molten metal into the casting mold, are arranged on the functional part of the blade between these two lateral columns and the second and third central columns.

[0018] The presence of the two connections at the base of the column (however, only the ceramic junction 70 at the base of the seventh column 62 is illustrated) will result, after casting, in the lateral cavities 24, 26 being directly connected to the cooling air supply duct of the central cavities 20 and 22, which further improves the mechanical strength of the core and, on the finished blade, the supply through the base of the core allows for better control of the internal cooling airflow and the overall cooling of the external walls.

[0019] THE figures 4A, 4B and 4C show the openings 72, 74, 76, 78 left by the junctions between the two central cavities 20, 22 and the lateral cavities 24, 26 at different heights of the blade (or core). On the figure 4AWe can note the two orifices 72, 74 ensuring airflow between the central cavity 22 and the lateral cavities 24, 26 respectively, the orifice 80 at the level of the leading edge cavity 28 resulting from a bridge 56. On the figure 4B , the orifice 76 ensures a passage of air between the central cavity 20 and the lateral cavity 24 and on the figure 4C , the orifice 78 ensures a passage of air between the central cavity 20 and the lateral cavity 26.

[0020] The lost-wax casting process for the turbine blade, once the core is made in one piece, is a classic one. It begins by creating an injection mold into which the core is placed before the wax is injected. The resulting wax model is then dipped in slips made of ceramic suspension to create a casting mold (also called a shell mold). Finally, the wax is removed, and the shell mold is fired, into which the molten metal can then be poured.

[0021] Thanks to the ceramic junctions linking the central and lateral columns of the core, their relative spacing is controlled along the entire height of the blade. These junctions are also positioned to draw additional fresh air from the central cavities to the areas of greatest thermo-mechanical stress in the lateral cavities, thus improving local thermal efficiency and blade lifespan. These junctions are specifically sized and arranged to ensure: Their mechanical strength during casting, the relative positioning of the central and lateral cavities, i.e. the thickness of the internal partitions of the blade, sufficient additional cooling air in critical areas, particularly in relation to the proximity of the leading edge.

Claims

1. A ceramic core used for fabricating a hollow turbine blade for a turbine engine by using the lost-wax casting technique, the blade including leading edge and trailing edge cavities (28, 30, 32), at least one central cavity (20, 22), a first lateral cavity (24) arranged between said at least one central cavity and a suction side wall of the blade, and a second lateral cavity (26) arranged between said at least one central cavity and a pressure side wall of the blade, the core being shaped to constitute said cavities as a single element and, in order to feed the insides of said cavities jointly with cooling air, it includes core portions (60, 62) that are to form said first and second lateral cavities and that are connected to a core portion (44, 48) that is to form said at least one central cavity, firstly in the core root (46, 54) via at least two ceramic junctions (70), and secondly at various heights up said core via a plurality of other ceramic junctions (64, 66, 68) of positioning that defines the thickness of the internal partitions of the blade, while also ensuring additional cooling air for predetermined critical zones of said first and second lateral cavities, the ceramic core further including a core portion (59) for forming a bathtub (18) and connected to said core portion intended to form said leading edge and trailing edge cavities and at least one central cavity via ceramic junctions (57) of positioning that defines the thickness of said bathtub, while ensuring that cooling air is discharged at the blade tip.

2. A ceramic core according to claim 1, characterized in that said predetermined critical zones are selected from the zones of said first and second lateral cavities that are subjected to the greatest thermomechanical stresses.

3. A ceramic core according to claim 1, characterized in that said ceramic junctions are of section determined so as to ensure the mechanical strength of said internal partitions while casting the molten metal.

4. The use of a ceramic core according to any one of claims 1 to 3 for fabricating a hollow turbine blade for a turbine engine using the lost-wax casting technique.

5. A fabrication method for fabricating a hollow turbine blade for a turbine engine by using the lost-wax casting technique, the blade including leading edge and trailing edge cavities (28, 30, 32), at least one central cavity (20, 22), a first lateral cavity (24) arranged between said at least one central cavity and a suction side wall of the blade, and a second lateral cavity (26) arranged between said at least one central cavity and a pressure side wall of the blade, the method comprising a step of fabricating a single-element ceramic core corresponding to said leading edge and trailing edge cavities, to said at least one central cavity and to said first and second lateral cavities, core portions (60, 62) that are to form said first and second lateral cavities being connected to a core portion (42, 44, 48, 50, 52) that is to form said including leading edge and trailing edge cavities and said at least one central cavity, firstly in a core root (46, 54) via at least two ceramic junctions (70) so as to feed the insides of said cavities jointly with cooling air, and secondly, at various heights up said core via a plurality of other ceramic junctions (64, 66, 68) of positioning that defines the thickness of the internal partitions of the blade, while ensuring additional cooling air for predetermined critical zones of said first and second lateral cavities, the ceramic core a single-element further including a core portion (59) for forming a bathtub (18) and connected to said core portion intended to form said leading edge and trailing edge cavities and at least one central cavity via ceramic junctions (57) of positioning that defines the thickness of said bathtub, while ensuring that cooling air is discharged at the blade tip, the ceramic core as formed in this way being put into place in a casting mold and molten metal being cast in said mold.

6. A turbine engine including a hollow turbine blade fabricated using the fabrication method of claim 5.