Method for maintaining a bladed wheel of a high-pressure turbine of a turbomachine

Abstract

The invention relates to a method for maintaining a bladed wheel of a high-pressure turbine of a turbomachine, extending along an axis, comprising a disc (11) comprising cavities (15), and blades (12) extending radially and each comprising an airfoil and a radially inner root (14), the root (14) of each blade (12) being mounted in a cavity (15) of the disc (11), the root (14) bearing on the disc (11) via surfaces of the root (14) and of the disc (11) which form bearing surfaces (19), characterized in that at least one foil (21) is mounted removably between the root (14) of at least one blade (12) and the disc (11), at the corresponding bearing surfaces (19), the method comprising the following steps: measuring a radial clearance between the tip of at least one blade (12), that is to say the radially outer end of the blade (12), and a casing of the turbomachine situated facing the bladed wheel, and, if the radial clearance is greater than a predetermined value, removing the foil (21).

Description

[0001] DESCRIPTION

[0002] TITLE: Maintenance process for a high-pressure turbine bladed wheel of a turbomachine

[0003] Technical field of the invention

[0004] The invention relates to a method for maintaining a high-pressure turbine bladed wheel of a turbomachine, such as an aircraft turbojet or turboprop.

[0005] State of the prior art

[0006] Figure 1 shows a double-flow, double-spool turbomachine 1. The axis of the turbomachine is referenced X. In the following, the terms axial and radial are defined relative to the X axis.

[0007] The turbomachine 1 comprises, from upstream to downstream in the direction of flow of the gases within the turbomachine 1, a fan 2, a low pressure compressor 3, a high pressure compressor 4, a combustion chamber 5, a high pressure turbine 6 and a low pressure turbine 7.

[0008] The air from the blower 2 is divided into a primary flow A flowing in a primary vein 8, and a secondary flow B flowing in a secondary vein 9.

[0009] The low pressure compressor 3, the high pressure compressor 4, the combustion chamber 5, the high pressure turbine 6 and the low pressure turbine 7 are arranged in the primary vein 8.

[0010] The high-pressure turbine 6 and the high-pressure compressor 4 are rotationally coupled via a first shaft 10 so as to form a high-pressure body.

[0011] The low pressure turbine 7, the low pressure compressor 3 and the blower 2 are rotationally coupled via a second shaft (not shown) so as to form a low pressure body.

[0012] As shown in Figure 2, the high-pressure turbine 6 conventionally comprises a disc 11 on which blades 12 are mounted. Each blade 12 comprises a blade 13 extending radially outwards from a blade root 14 mounted in a cell 15 of the disc 11.

[0013] The top 16 of the blade 12 is formed by the radially external end of the blade 12. The root 14 and the blade 13 are here separated by a radially internal platform 17. The root 14 has a general fir tree shape, here with four branches or lobes 18. The shape of the cell 15 is complementary to the shape of the root 14. Each branch or lobe 18 bears on a complementary opposite surface of the disc 11. The surfaces of the root 14 and the disc 11 bearing on each other are called bearing surfaces 19. In the embodiment illustrated in FIG. 4, the root 14 has four bearing surfaces 19, arranged symmetrically with respect to a median radial plane P.

[0014] The blades 12 are surrounded by an annular casing 20. A clearance j is formed between the tips 16 of the blades 12 and the casing 20 surrounding the blades 12.

[0015] In order to maximize the efficiency of the turbomachine, it is necessary to limit the gas flow rate flowing in the clearances located between the tips of the blades and the casing.

[0016] In operation, this clearance tends to increase over time due to two phenomena.

[0017] The first phenomenon is wear of the blade tip generated by friction between the blade tip and the casing facing it.

[0018] The second phenomenon is thermal erosion, i.e. oxidation, of the tip of the blade, due to the high temperatures to which the blade is subjected during operation, particularly in the case of a high-pressure turbine.

[0019] The increase in this clearance leads to a deterioration in the performance of the turbomachine and, consequently, to an increase in the consumption and operating temperatures of the turbomachine, further aggravating the oxidation phenomenon.

[0020] Currently, when a blade is too worn or too oxidized at its tip, it is replaced and scrapped. Such a maintenance operation is therefore very costly and / or results in unplanned removals of the turbomachine due to performance limits being reached.

[0021] Presentation of the invention

[0022] The invention aims to remedy the aforementioned problems in a simple, reliable and inexpensive manner.

[0023] To this end, the invention proposes a method for maintaining a high-pressure turbine bladed wheel of a turbomachine, extending along an axis, comprising a disc comprising cells, and blades extending radially and each comprising a blade and a radially internal root, the root of each blade being mounted in a cell of the disc, said root bearing on the disc via surfaces of the root and of the disc forming bearing surfaces, characterized in that at least one foil is removably mounted between the root of at least one blade and the disc, at the corresponding bearing surfaces, said method comprising the following steps: measuring a radial clearance between the tip of at least one blade, i.e. the radially external end of the blade, and a casing of the turbomachine located opposite the bladed wheel, if the radial clearance is greater than a determined value, removing said foil.The method according to the invention thus aims to determine the state of wear or deformation of the high-pressure turbine by measuring the radial clearance between the tip of the blade and the casing and, if the aforementioned radial clearance is too large, removing the shim. Removing the shim then makes it possible to reduce the radial clearance between the tip of the blade and the casing, so as to regain acceptable performance, at lower cost, without replacing or repairing the blades or the casing.

[0024] At least one shim may be mounted between the root of each blade and the disc, at the level of the corresponding bearing surfaces, all of the shims being removed if the radial clearance is greater than the said determined value.

[0025] In this way, the creation of disparities or steps formed by differences in the positioning of the blade tips on the circumference of the turbomachine is avoided. Such steps can generate aerodynamic disturbances affecting the proper operation of the turbomachine.

[0026] The foil can be removably mounted on the blade foot.

[0027] The foil can be removably mounted on the disc, for example in the socket or on a tooth of the disc delimited between two adjacent sockets.

[0028] The foil may include a radial stop surface, bearing on a complementary stop surface of the blade root or disc.

[0029] Such a feature facilitates the correct axial positioning of the shim and also makes it possible to axially retain the shim in position during operation of the turbomachine.

[0030] The foil can have a thickness between 0.1 and 0.9 mm.

[0031] The foil can be made from a cobalt-based alloy.

[0032] The foil is for example made from an alloy known under the reference MP 159.

[0033] The foot of the dawn can be a foot in the general shape of a fir tree.

[0034] Each foot can have a symmetrical shape with respect to a median radial plane.

[0035] A single foil can be mounted between the blade root and the disc. This single foil can be inserted between several blade and disc bearing surfaces.

[0036] Several foils can be removably mounted between the root of at least one blade and the disc.

[0037] In such a case, the foils can be arranged symmetrically with respect to the aforementioned median radial plane.

[0038] It is also possible to place a stack of several foils between the blade root bearing surfaces and the disc bearing surfaces. In this case, one or more foils can be removed at each maintenance operation.

[0039] Each foot may have two pairs of bearing surfaces, cooperating with two pairs of bearing surfaces of the disc cavity. The foot may thus have a four-branched or four-lobed fir tree shape, such a shape being frequently used in the case of a high-pressure turbine bladed wheel. The cavity of course has a shape complementary to that of the foot.

[0040] The foil can be produced by stamping sheet metal or by sintering a metal powder. The invention also relates to a high-pressure turbine bladed wheel comprising a disc comprising cells, and blades each comprising a blade and a root, the root of each blade being mounted in a cell of the disc, said root bearing on the disc via surfaces of the root and the disc forming bearing surfaces, characterized in that at least one foil is removably mounted between the root of at least one blade and the disc, at the level of the corresponding bearing surfaces.

[0041] The bladed wheel is preferably a rotor bladed wheel.

[0042] The foil is formed by a thin metal sheet.

[0043] The invention also relates to a turbomachine, characterized in that it comprises a bladed wheel of the aforementioned type.

[0044] The turbomachine can be a turbojet or an aircraft turboprop. The aircraft can be an airplane.

[0045] Brief description of the figures

[0046] [Fig. 1] is a schematic sectional view of a prior art turbomachine;

[0047] [Fig. 2] is a schematic view of a portion of a prior art high pressure turbine;

[0048] [Fig. 3] is a view illustrating the mounting of a blade root in a cell of a disc of a bladed wheel according to an embodiment of the present document;

[0049] [Fig. 4] is a perspective view of a cell equipped with a foil, according to the embodiment of Figure 3;

[0050] [Fig. 5] is a perspective view of a blade root equipped with two lateral foils, according to another embodiment;

[0051] [Fig. 6] is a perspective view of a blade root equipped with a single foil, according to another embodiment;

[0052] [Fig. 7] is a view corresponding to Figure 3, in which the foil has been removed following a maintenance operation.

[0053] Detailed description of the invention

[0054] Figures 3 and 4 illustrate a high pressure turbine rotor bladed wheel 6 according to one embodiment. This embodiment differs from that illustrated in Figure 2 in that a foil 21 is removably mounted in each cell 15 and completely or almost completely covers the internal surface of each of the cells 15 of the bladed wheel. The foil

[0055] 21 thus has a general II shape and includes recesses capable of housing the lobes 18 of the root 14 of the corresponding blade 12. The foil 21 thus includes surfaces

[0056] 22 intended to come into contact with the bearing surfaces of the foot 14 of the blade 12. These surfaces are called bearing surfaces 22 of the foil 21.

[0057] The foil 21 is formed by a sheet of thickness between 0.1 and 0.9 mm, and made from a cobalt-based alloy.

[0058] The foot 14 of the blade 12 rests on the bearing surfaces 22 of the foil 21 after mounting in the cell 15.

[0059] It will be noted that the radial position of the tip 16 of the blade 12 takes into account the thickness of the foil 21 in its specifications so as to obtain the desired clearance j.

[0060] It is also possible to use two foils 21, located on either side of the median plane P and arranged symmetrically, said foils 21 covering the bearing surfaces 19 of the cell 15. Each foil 21 covers only half, or less, of the cell 15.

[0061] Figures 4 and 5 illustrate two embodiments in which the foils 21 are removably mounted, not in the cells 15, but on the roots 14 of the blades 12. The assembly formed by the blade root 14 and the foil(s) 21 is then mounted in the corresponding cell 15 of the disc 11.

[0062] Figure 5 illustrates in particular an embodiment in which two lateral foils 21 are mounted on either side of the root 14, symmetrically with respect to the median radial plane P. Each foil 21 has a shape complementary to the lateral flank of the root 14, each foil 21 thus covers the two lateral bearing surfaces 19 concerned of the root 14 of the blade 12.

[0063] Figure 6 illustrates an embodiment in which a single foil 21 covers the two lateral flanks of the root 14 of the blade 12, that is to say covers all of the bearing surfaces 19 of the root 14.

[0064] The foil 21 has a shape complementary to that of the foot 14 and comprises a radial wall 23 capable of forming an axial stop bearing against a radial end surface 24 of the foot 14, which may be an upstream surface or a downstream surface of the foot 14.

[0065] Note that the foil 21 does not cover the radially inner end surface 25 of the root 14. Indeed, cooling air circulation channels of the blade 12 open at this end surface 25 and it is necessary not to block said channels. Alternatively, the foil 21 may cover said radially inner end surface 25 of the root 14 but then comprises orifices or slots opposite the outlets of said channels, so as to allow the passage of cooling air. As indicated previously, the present document proposes a method for maintaining such a high-pressure turbine bladed wheel 6, said method comprising a step during which the radial clearance j between the tip 16 of the blade 12 and the casing 20 is measured and, if this radial clearance j is greater than a determined value, the foil(s) 21 are removed, as illustrated in FIG. 7.This has the effect of bringing the tip of the blade 16 closer to the casing 20, and therefore of reducing the clearance j by the value of the thickness of the foil 21.

[0066] It is thus possible to reduce the clearance j in a simple, rapid and inexpensive manner, so as to improve the performance of the turbomachine and compensate for the aforementioned wear or corrosion phenomena.

Claims

DEMANDS 1. A method for maintaining a high-pressure turbine bladed wheel (6) of a turbomachine, extending along an axis, comprising a disk (11) having recesses (15), and blades (12) extending radially and each having a blade (13) and a radially internal foot (14), the foot (14) of each blade (12) being mounted in a recess (15) of the disk (11), said foot (14) bearing on the disk (11) via surfaces of the foot (14) and the disk (11) forming bearing surfaces (19), characterized in that at least one shim (21) is removably mounted between the foot (14) of at least one blade (12) and the disk (11), at the level of the corresponding bearing surfaces (19), said method comprising the following steps: measuring a radial clearance (j) between the apex (16) of at least one blade (12), that is to say the radially external end of the blade (12), and a housing (20) of the turbomachine located opposite the bladed wheel,If the radial clearance (j) is greater than a specified value, remove the said shim (21).

2. Method according to the preceding claim, wherein at least one shim (21) is mounted between the foot (14) of each blade (12) and the disc (11), at the level of the corresponding bearing surfaces (19), the entire set of shims (21) being removed if the radial clearance (j) is greater than said determined value.

3. Method according to any one of the preceding claims, wherein the shim (21) is mounted removably on the paddle foot (14).

4. A method according to any one of claims 1 or 2, wherein the shim (21) is mounted removably on the disc (11), for example in the cavity (15) or on a tooth of the disc (11) delimited between two adjacent cavities (15).

5. Method according to any one of the preceding claims, wherein the shim (21) comprises a radial stop surface (23), bearing against a complementary stop surface (24) of the foot (14) of the blade (12) or of the disc (11).

6. A method according to any one of the preceding claims, wherein the shim (21) has a thickness of between 0.1 and 0.9 mm.

7. A method according to any one of the preceding claims, wherein the shim (21) is made from a cobalt-based alloy.

8. A method according to any one of the preceding claims, wherein several shims are removably mounted between the foot (14) of at least one blade (12) and the disc

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