Foil for a turbomachine turbine disk, rotor assembly comprising such a foil and method of mounting such an assembly

Abstract

Foil for a turbomachine turbine disk, assembly for a rotor comprising such a foil and method for mounting such an assembly The invention relates to a foil (400) for a turbomachine turbine disk (40), comprising a metal sheet forming an envelope at least partially surrounding a tooth (42) of the turbine disk (40), said tooth (42) separating a first and a second cavities (41) of the disk, each adapted to receive a root (20) of a moving blade of the turbine The invention also relates to an assembly for a turbomachine rotor, comprising: at least a first and a second moving blade (10) each comprising a blade root (20), a disk (40) comprising at least a first and a second cavities (41) each adapted to receive a blade root (20), and a tooth (42) separating the first and the second cavities (41), and a foil (400). Figure to be published with the abstract: Figure 9

Description

Title of the invention: Foil for turbine disk of a turbomachine, assembly for a rotor comprising such a foil and method of mounting such an assembly TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a foil for a turbine disk of a turbomachine. It also relates to a rotor assembly comprising such a foil mounted around a tooth of the disk. It further relates to a method of mounting this assembly.

[0002] The invention finds applications in the field of aeronautics and, in particular, in the field of turbomachine rotors to protect both the blade root and the rim of the disk and increase the service life of the rotors. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] It is known in aeronautics that a rotor blade 10, an example of which is shown in [Fig.l], comprises a blade 12 provided, in the lower part, with a platform 11 extended radially by a root 20 intended to be inserted into a cavity formed in the external periphery of a rotor disc. The root 20 of the rotor blade 10 - also called a moving blade - is retained radially in the cavity of the disc by cooperation of shapes between said root, generally in the form of a dovetail, and the cavity, generally in the form of a cell. In the upper part, the blade 12 is provided with a heel 13 intended to be arranged edge to edge with the heel of the adjacent moving blades so as to form a rotating circumferential crown delimiting a surface of revolution around the axis of rotation X of the disc.

[0004] During operation of the rotor, the contact between the roots of the moving blades (more simply called blade roots), which are for example made of titanium aluminide, and the disc, which is for example made of nickel-based alloy, causes premature wear of the blade roots and / or the cavities of the disc.

[0005] In order to limit the wear of the blade roots and the cavities of the disk, it is known to place a contact part 30, called a foil, at the contact interfaces, commonly called bearing surfaces, between the blade roots and the cavities of the disk. Conventionally, the foil is a foil for a moving blade, mounted around the root 20 of said moving blade. This foil, referenced 30, is in contact with the disk and takes up a major part of the energy dissipated by friction in the contact between the root of the moving blade and the disk, which makes it possible to limit the wear of said blade root.

[0006] [Fig.2] represents, in an enlarged form, the foot 20 of the mobile blade 10 of [Fig.l], around which is mounted a classic 30 foil. This 30 foil has a overall U-shaped section, formed by two lateral branches 32, or lateral surfaces (only one of which is visible in [Fig.2]), intended to cover the lateral flanks 22 of the root 20 of the mobile blade 10 and to hold the foil 30 on the blade root 20. The foil 30 also comprises a base 31, also called a lower surface, which connects the lateral surfaces 32 together and covers the lower face 21 of the blade root 20.

[0007] The foil 30 therefore has a function of protecting the blade root and the disk cavity by preventing wear of these parts. It thus guarantees the mechanical integrity of the parts (blade root and disk) with which it is in contact.

[0008] In order to prevent the foil 30 from disengaging from the blade root 20, the lower surface 31 of the foil generally comprises radial tabs 33 bearing against the upstream 23 and downstream 24 faces of the root 20. The radial tabs 33 (only one of which is visible in [Fig. 2]) are strips cut at the end of the lower surface 31 and folded radially along the upstream and downstream faces 23, 24 of the blade root 20. These radial tabs 33 extend over a more or less large width, between the lateral branches 32 of the foil, and form stops which make it possible to prevent relative axial movements between the blade root 20 and the foil 30.

[0009] However, despite the presence of the radial tabs 33, turbomachine maintenance operators have noticed that the foils tend to move axially, which damages the radial tabs 33 and even cuts them. Indeed, due to their radial folding during the manufacturing phase and / or their unfolding during the assembly phase, the radial tabs are weakened and the friction, generated by the repeated axial movement of the foils, has the effect of cutting or breaking them. Once the radial tabs are broken, the foils 30 can partially or even completely disengage from the blade roots 20, as shown in [Fig. 3].

[0010] The disengagement of one (or more) foils 30 can cause the foil to be released into the air stream of the turbomachine and damage the blades located downstream of the Low Pressure Turbine, and in particular the blades based on titanium aluminides (TiAl) which are particularly sensitive to impacts. The disengagement of a foil 30 can also cause greater wear between the blade root 20 and the disk 40 since the protective part is no longer present and, consequently, a degraded mechanical strength of these parts in the area.

[0011] This phenomenon of disengagement of the tinsel is initiated and maintained by two cumulative factors: • the mechanical strength of the foil which is not sufficient and which does not support the stresses generated between the blade root and the disc, during operation, and • thermal stresses generated by the sequence of thermal expansions / contractions that the blade root and the disc undergo over the operating cycles. In fact, with the succession of rises and falls in temperature of the blade root, the foil also expands and contracts, which leads to damage and its partial and then total degradation.

[0012] During maintenance, the disengagement of one or more foils leads to the rotor being removed for repair. However, removing and repairing a rotor results in significant costs in parts and labor, as well as immobilization of the turbomachine.

[0013] Furthermore, it has been observed that the rim of the disc is subject to undesirable wear on the downstream face of the disc teeth. In fact, the axial stop of the blade root 20 downstream is generally achieved by means of a retaining ring inserted into a hook of the blade. A sectional view of a blade root 20 mounted in a cavity 41 of the disc 40 is shown in [Fig.4]. This view of [Fig.4] shows the disc 40 in which the root 20 of the moving blade 10 is housed. It also shows the hook 15 of the moving blade 10, projecting from the downstream face, in which a retaining part called a retaining ring 50 is slid. The retaining ring 50 extends circularly along the downstream face of the disc 40 so as to retain all of the blade roots 20 in the cavities of the disc and prevent any axial movement of said blade roots downstream.

[0014] The retaining ring 50 is therefore in contact, not only with the downstream face of the blade roots 20, but also with the downstream rim 46 of the disc 40, at the level of the disc teeth. This contact between the retaining ring 50 and the downstream rim of the disc teeth generates contact wear zones 48, as shown in [Fig. 5]. Each contact wear zone 48 induces a risk of initiation and propagation of cracks which have a real impact on the service life of the disc. In maintenance, a crack initiated by contact wear leads to premature removal of the disc followed by repair or replacement of said disc. However, removal and repair or replacement of the disc cause significant costs in parts and labor, as well as immobilization of the turbomachine. Summary of the invention

[0015] To address the problems mentioned above of disengagement of the moving blade shims and wear by contact of the rim of the disk, the applicant proposes a shim for a turbine disk, positioned at least partly around a tooth of the disk and extending, on the one hand, along the rim of the disk and, on the other hand, between the side wall of the cavity of the disk and the root of the moving blade.

[0016] According to a first aspect, the invention relates to a foil for a turbine disk of turbomachine, comprising a casing at least partially surrounding a tooth of the turbine disk, said tooth separating a first and a second cavities of the disk, each adapted to receive a root of a moving blade of the turbine.

[0017] The foil according to the invention has the advantage of protecting not only the contact zone between the blade root and the cavity of the disc but also the contact zone between the retaining ring and the rim of the disc. It also makes it possible to avoid the risks of disengagement of the foil.

[0018] The use of a foil according to the invention, in a turbomachine, makes it possible to limit the number of engine removals, to reduce the number of parts to be changed during an engine removal and, therefore, to reduce the maintenance costs of the turbomachine. It also makes it possible to increase the service life of the turbine and to improve flight safety.

[0019] In the present application, the terms "lower", "upper", "inner" and "outer" are interpreted with reference to the position of a part or surface relative to the axis of rotation of the turbomachine, a lower or inner surface being closer to the axis of rotation than an outer or outer surface. The term "lateral" is interpreted as "which is located on the sides of a part which extends radially" along an axis substantially perpendicular to the axis of rotation X. The term "axial" is to be interpreted as "along the direction of the axis of rotation" and the term "radial" as "along a direction perpendicular to the axis of rotation" or "along the direction of a radius of the blade ring". The terms "upstream" and "downstream" will be interpreted with reference to the direction of flow of the airflow in the turbomachine.

[0020] In addition to the characteristics which have just been mentioned in the preceding paragraph, the foil for turbine disk according to one aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations: • it comprises a main surface adapted to cover an external face of the disc tooth, a first and a second lateral surface extending from the main surface to cover lateral walls of the disc tooth, and a downstream surface extending between the main surface and the lateral surfaces to at least partially cover a downstream rim of the disc tooth. • it comprises at least one tab extending radially along a rim upstream of the disc tooth. • it comprises two tabs extending radially along the upstream rim of the disc tooth and distributed along said upstream rim. • the tab(s) is formed in the extension of the main surface and folded along the upstream rim. • It has a substantially C-shaped section, with a main body of the C covering the outer face of the disc tooth and two arms of the C covering the side walls of the disc tooth. • the envelope is formed from a metal sheet.

[0021] A second aspect of the invention relates to an assembly for a turbomachine rotor, comprising: • at least one first and one second moving blade configured to be movable in rotation around an axis of rotation of the rotor and each comprising a blade root provided with a lower face and two lateral flanks extending on either side of the lower face, • a disk containing at least • a first and a second cavities each adapted to receive a blade root, and • a tooth separating the first and second cavities, and • a foil according to the first aspect of the invention.

[0022] Advantageously, the first lateral surface of the foil is housed between one of the lateral walls of the tooth of the disc and the lateral flank of the blade root of the first moving blade and the second lateral surface of the foil is housed between another of the lateral walls of the tooth of the disc and the lateral flank of the blade root of the second moving blade.

[0023] A third aspect of the invention relates to a method of mounting a rotor assembly for a turbomachine according to the second aspect. This method is characterized by the fact that it comprises the following steps: • positioning a foil according to the first aspect of the invention around a tooth of the disc so that said foil covers at least the side walls and the downstream rim of the tooth of the disc, • folding at least one tab so as to position it along the rim upstream of the disc tooth, and • installation of the first blade root in the first cavity of the disc and of the second blade root in the second cavity such that a portion of the foil is positioned between the first blade root and one of the side walls of the disc tooth and another portion of the foil is positioned between the second blade root and the other side wall of the disc tooth.

[0024] A fourth aspect of the invention relates to a turbomachine rotor, characterized in that it comprises a plurality of assemblies as defined above, juxtaposed circularly next to each other.

[0025] A fifth aspect of the invention relates to a turbomachine, characterized in that it comprises a plurality of assemblies as defined above, mounted so as to form a rotor. BRIEF DESCRIPTION OF THE FIGURES

[0026] Other advantages and characteristics of the invention will appear on reading the following description, illustrated by the figures in which:

[0027] [Fig.l], already described, represents a schematic perspective view of a moving turbomachine blade according to the state of the art;

[0028] [Fig. 2], already described, represents a schematic perspective view of a mobile blade root equipped with a foil according to the state of the art;

[0029] [Fig. 3], already described, schematically represents a perspective view of a broken foil, in the process of being disengaged from the blade root;

[0030] [Fig. 4], already described, schematically represents a radial sectional view of a blade root mounted in a disk cavity and held by a retaining ring;

[0031] [Fig. 5], already described, schematically represents a perspective view of a portion of a disc rim prematurely worn by contact with a retaining ring;

[0032] [Fig.6] schematically represents a perspective view of a disc tooth equipped with a foil according to an embodiment of the invention when a blade root is mounted in the cavity adjoining the tooth;

[0033] [Fig.7] schematically represents a perspective view of a foil for a turbine disk according to a preferred embodiment of the invention;

[0034] [Fig.8] schematically represents a perspective view, from upstream, of a foil according to an embodiment of the invention, mounted on a tooth of a turbine disk; and

[0035] [Fig.9] schematically represents a perspective view, from downstream, of a foil according to an embodiment of the invention, mounted on a tooth of a turbine disk. DETAILED DESCRIPTION

[0036] An exemplary embodiment of a foil for a turbine disk, configured both to protect the disk rim and to protect the blade root without risk of disengagement, is described in detail below, with reference to the accompanying drawings. This example illustrates the characteristics and advantages of the invention. It is however recalled that the invention is not limited to this example.

[0037] In the figures, identical elements are identified by identical references. For reasons of readability of the figures, the size scales between elements represented are not respected.

[0038] A turbomachine rotor comprises a disk and a plurality of moving blades each retained in a cavity of the disk, by their root. The root of each blade is housed in a cavity of the disk. An example of disk cavities is shown in perspective in [Fig.6]. Each cavity 41 of the disk 40, in the form of a cell, is generally formed in the external periphery of the disk 40. Each cavity 41 is separated from a neighboring cavity by a tooth 42 of the disk. A root 20 of a moving blade of the rotor, in the form of a dovetail, is engaged in each cavity 41 and is held radially in said cavity by shape cooperation between the root and the cavity.

[0039] A cavity 41 of the disc 40 comprises a bottom surface 43 and two lateral surfaces, each formed by the lateral wall 44 of an adjacent tooth 42. A tooth 42 of the disc 40 therefore comprises two lateral walls 44 as well as an external face 45, a downstream rim 46 and an upstream rim 47 (not visible in [Fig.6]).

[0040] Each blade root 20 comprises a lower face 21, facing the bottom surface 43 of the cavity 41, and two lateral flanks 22 forming the contact interfaces of the blade root 20 with the disk cavity 41.

[0041] When the rotor is rotated, the moving blades are subjected to centrifugal forces; under the effect of these centrifugal forces, the lateral flanks 22 of the blade roots 20 come into abutment against the lateral walls 44 of the teeth 42 of the disc 41 (or lateral surfaces of the cavity 41). According to the invention, a foil 400, made from a metal sheet (metal or alloy), is positioned around each tooth 42 of the disc 40 so as to envelop at least the areas to be protected. Thus, each foil 400 preferably covers at least the lateral walls 44 of the tooth 42 with which it is associated as well as the downstream rim 46 of said tooth 42.

[0042] An example of a foil 400 according to a preferred embodiment is shown in [Fig.7]. An example of this foil 400 mounted on a tooth 42 of the disc 40 is shown in [Fig.8] in a perspective view from downstream. The foil 400 according to this preferred embodiment comprises: • a main surface 450 adapted to cover the external face 45 of the tooth 42, • a first and a second lateral surface 440 for covering the lateral walls 44 of the tooth 42, and • a downstream surface 460 to at least partially cover the downstream rim 46 of tooth 42 of the disc.

[0043] The main surface 450 and the lateral surfaces 440 extend in the extension of each other, a first lateral surface 440a extending on one side of the main surface 450, a second lateral surface 440b extending on the other side of the main surface, opposite the first lateral surface. The main surface 450 and the lateral surfaces 440 have a C-shaped section, the main body of the C being formed by the main surface 450, the two arms of the C being formed by the two lateral surfaces 440a, 440b.

[0044] The downstream surface 460 extends radially along the downstream rim 46 of the tooth 42, between the two lateral surfaces 440a, 440b and the main surface 450 so that the assembly (main, lateral and upstream surfaces) generally has the shape of a hood.

[0045] Thus, with such a shape of the foil 400, each lateral flank 22 of a blade root 20 is separated from the lateral wall 44 of the adjacent tooth 42 (or lateral surface of the cavity 41) by a lateral surface 440 of the foil 400. In other words, the first lateral surface 440a of the foil 400 is positioned between the lateral flank 22 of a blade root 20 and one of the lateral walls 44 of the tooth 42 and the second lateral surface 440b of the foil 400 is positioned between the lateral flank 22 of another blade root 20 and the other lateral wall 44 of the tooth 42 of the disc 40 so that the two lateral walls of the tooth 42 and the lateral flank 22 of each of the adjacent blade roots are protected from friction by contact. against each other.

[0046] With the shape of the foil 400 described previously, the downstream rim 46 of the tooth 42 of the disc is covered by the downstream surface 460 of the foil 400. Thus, the downstream rim 46 is not in direct contact with the retaining ring 50 allowing the axial stopping of the blade root 20 downstream so that said downstream rim 46 is protected from the risks of friction by contact with said ring.

[0047] In one embodiment of the invention, the foil 400 comprises at least one tab 480 extending radially along the upstream rim 47 of the tooth 42 of the disc to lock the positioning of said foil around the tooth 42. An example of this embodiment is shown in [Fig.9] in a perspective view from upstream. The tab 480 is formed from the same metal sheet as the entire foil 400, by cutting said sheet. The tab 480 extends from the end of one of the surfaces of the foil 400, for example from the main surface 450 or from one of the lateral surfaces 440, and is folded along the rim 47 of the tooth 42. In the example of [Fig.9], the tab 480 extends in the extension of the main surface 450. The tab 480, once folded, extends along a radial plane against the upstream rim 47, ensuring axial retention of the foil 400 around the tooth 42.

[0048] According to certain embodiments, the foil 400 comprises several tabs 480, for example two as in the example of [Fig.9], all folded along the upstream rim 47. When there are several tabs 480, these are preferably distributed over the contour of the upstream rim 47 in order to optimize the retention of the foil around the tooth 42.

[0049] The foil 400 as described above is produced, for example, by folding or by stamping a metal sheet. The tab(s) are made by cutting the metal sheet. They are only folded once the foil is correctly positioned on tooth 42 of the disc.

[0050] Indeed, once the foil 400 is manufactured, it is mounted on the tooth 42 of the disc by sliding along the external face 45 and the side walls 44 of said tooth, from downstream to upstream. In other words, the foil 400 is threaded axially around a tooth 42 of the disc. It is in position when its downstream surface 460 is in contact with the downstream face 46 of the tooth 42. The foil 400 then covers the side walls 44, the external face 45 and the downstream face 46 of the tooth 42 of the disc. When they exist, the tabs 480 are then folded radially along the upstream face 47 of the tooth 42 so as to block the foil around the tooth 42. Two blade roots 20 can then each be installed in one of the cavities 41 adjacent to the tooth 42. The lateral surfaces 480a, 480b of the foil 400 are then each positioned in a cavity 41, between one of the blade roots and one of the lateral walls 44 of the tooth 42.

[0051] It is understood from the above that, unlike the foils of the state of the art, the foil 400 according to the invention is mounted on the disc, around a disc tooth, and not around the blade root. This mounting makes it possible to improve the mechanical strength of the foil without deforming it or weakening it. It also makes it possible to protect the downstream rim of the disc, in addition to the contact zone between the blade root and the wall of the cavity 41 of the disc.

[0052] The 400 foil allows, more generally, a reduction in costs by improving the durability of the rotor parts, by avoiding potential engine removals linked to premature contact wear, by reducing the number of parts changed during engine removal, by reducing maintenance costs and the number of maintenance operations. It thus allows for improved customer satisfaction and to overcome a recurring problem.

[0053] Although described through a number of examples, variations and embodiments, the turbine disk foil and rotor assembly according to the invention include various variations, modifications and improvements which will be apparent to those skilled in the art, it being understood that these variations, modifications and improvements are within the scope of the invention.

Claims

Claims

1. Foil (400) for a turbomachine turbine disk (40), comprising a casing at least partially surrounding a tooth (42) of a turbine disk (40), said tooth (42) separating a first and a second cavities (41) of the disk, each adapted to receive a root (20) of a moving blade of the turbine, characterized in that the casing is adapted to cover at least side walls (44) of the tooth (42) as well as a downstream rim (46) of said tooth (42).

2. A shim according to claim 1, characterized in that it comprises: - a main surface (450) adapted to cover an external face (45) of the tooth of the disc, - a first and a second lateral surface (440a, 440b) extending from the main surface (450) to cover lateral walls (44) of the tooth of the disc, and - a downstream surface (460) extending between the main surface (450) and the lateral surfaces (440) to at least partially cover a downstream rim (46) of the tooth of the disc.

3. A shim according to claim 1 or 2, characterized in that it comprises a tongue (480) extending radially along an upstream rim (47) of the tooth (42) of the disc.

4. A shim according to claim 2 or 3, characterized in that it comprises at least two tabs (480) extending radially along the upstream rim (47) of the tooth of the disc and distributed along said upstream rim.

5. A foil according to claim 2 and claim 3 or 4, characterized in that the tongue (480) is formed in the extension of the main surface (450) and folded along the upstream rim (47).

6. A shim according to any one of claims 1 to 5, characterized in that it comprises a substantially C-shaped section, with a main body of the C which covers the external face (45) of the tooth of the disc and two arms of the C which cover the side walls (44) of the tooth of the disc.

7. Foil according to any one of claims 1 to 6, characterized in that the envelope is formed from a metal sheet.

8. Assembly for a turbomachine rotor, comprising: - at least a first and a second moving blade (10) configured to be movable in rotation about an axis of rotation (X) of the rotor and each comprising a blade root (20) provided with a lower face (21) and two lateral flanks (22) extending on either side of the lower face, - a disc (40) comprising at least • a first and a second cavities (41) adapted to each receive a blade root (20), and • a tooth (42) separating the first and the second cavities (41), and - a foil (400) according to any one of claims 1 to 7.

9. Assembly according to claim 8, characterized in that the first lateral surface (440a) of the foil is housed between one of the lateral walls (44) of the tooth (42) of the disc and the lateral flank (22) of the blade root of the first moving blade and the second lateral surface (440b) of the foil is housed between another of the lateral walls (44) of the tooth (42) of the disc and the lateral flank (22) of the blade root of the second moving blade.

10. Method for mounting a rotor assembly for a turbomachine according to any one of claims 8 to 9, characterized in that it comprises the following steps: - positioning a foil (400) according to any one of claims 1 to 7 around a tooth (42) of the disc (40) so that said foil covers at least the side walls (44) and the downstream rim (46) of the disc tooth, - folding at least one tab (480) so as to position it along the upstream rim (47) of the disc tooth,and - installing the root (20) of the first moving blade in the first cavity (41) of the disc and the root (20) of the second moving blade in the second cavity (41) so that a portion of the foil (400) is positioned between the root of the first moving blade and one of the side walls (44) of the tooth of the disc and another portion of the foil (400) is positioned between the root of the second moving blade and the other side wall (44) of the tooth of the disc.,

11. Turbomachine rotor, characterized in that it comprises a plurality of assemblies according to any one of claims 8 and 9, juxtaposed circularly next to each other.

12. Turbomachine, characterized in that it comprises a plurality of assemblies according to any one of claims 8 and 9 mounted so as to form a rotor.

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