TURBINE BLADE WITH A FOOT INCLUDING A FOIL LOCK

Abstract

TURBINE BLADE WITH A FOOT COMPRISING A FOIL LOCK One aspect of the invention relates to a blade (2) comprising: - a first and a second radial face (23a, 23b), - a first and a second lateral longitudinal face (24c, 24d) each joining each radial face (23a, 23b), - a lower surface (27) joining each radial face (23a, 23b) and joining each lateral longitudinal face (24c, 24d) the blade (2) comprises: - a first leg (5a) located on a first end of the lower surface (27) and on one end of the first radial face (23a); - a second leg (5b) located on a second end of the lower surface (27) and on one end of the second radial face (23b), the legs (5a, 5b) are symmetrical along a plane A passing through the middle of the foot (21) of the blade (2) and intersecting the first lateral longitudinal face (24c) and the second lateral longitudinal face (24d). Figure to be published with the abstract: Figure 2

Description

Title of the invention: TURBINE BLADE WITH A FOOT COMPRISING A FOIL LOCKING TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of turbine blades.

[0002] The present invention relates to a moving blade of a turbomachine, as well as to an assembly comprising a moving blade whose root is provided with a foil. The invention also relates to a method of manufacturing the blade. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Conventionally, an axial turbine of a turbomachine consists of a succession of axial stages (along the axis of circulation of the gas flows) arranged one behind the other. Each stage comprises a bladed moving wheel forming the rotor and a bladed distributor forming the stator. The moving wheel is rotated opposite the corresponding distributor.

[0004] The moving wheel is conventionally made up of an annular disc centered on the axis of rotation of the wheel, comprising cells and a plurality of moving blades each comprising an attachment member called hereinafter a blade root in a cell-shaped housing.

[0005] In the contact zones between the root of each moving blade and the cell of the disk housing this root, several types of constraints are exerted.

[0006] We encounter in particular "fretting", that is to say contact wear, which is the consequence of the repetitive friction of one part on another, the resulting friction forces being able to cause damage to the material by different fatigue processes. This phenomenon is particularly sensitive in the case of contact between two parts, for example metal or CMC.

[0007] These areas are therefore subject to a significant tendency towards damage to the material, as well as to wear of the blade root surfaces which are the areas in contact with the wall of the cell, or even deformation of these contact areas.

[0008] In addition, the level of local stresses is very high due to the coefficient of friction at the interface between the contacting walls of the blade root and the cell, formed by a metal / metal contact. In the following, this interface is called the blade root bearing surface and the cell bearing surface.

[0009] To solve these problems, we are seeking in particular to strengthen the wear resistance of the surfaces in contact and to reduce the coefficient of friction.

[0010] To do this, generally a protective part is used which can be a consumable, formed of one or more metal foils fitting the foot of dawn.

[0011] With this type of solution, it is possible to reduce the coefficient of friction and it is possible to change the foil instead of an entire blade.

[0012] For example, document EP2042689A1 proposes using an assembly with a metal foil between a blade root and a disc.

[0013] On turbine blades, foils are therefore placed between the blade roots and the disc cells to prevent wear of these parts. These guarantee the mechanical integrity of the parts with which they are in contact.

[0014] In the foils of the prior art, these are held in position on the blade roots by two folded tabs projecting relative to the base of the foil located at the bottom of the blade root.

[0015] During operation of the turbine, it has been observed in certain situations that there may be possible axial displacements of the foils (longitudinally relative to the blade), which may damage the sensitive tabs following the folding / unfolding of the latter during the foil assembly phase. This damage may in certain cases result in cutting and lead to possible longitudinal (axial) disengagements of the foils. Indeed, in these situations, once the tabs have been cut, the foils may then disengage from the blade roots partially or completely.

[0016] The disengagement of the foils no longer ensures the mechanical integrity of the blade root and the turbine disk. This longitudinal (axial) disengagement of the foil therefore results in at least a portion of the blade root without protection and therefore premature wear of the blade root in place of the foil produced by “fretting”.

[0017] The cut tabs can also, in certain situations, end up in an air stream and damage shock-sensitive blades located downstream of the turbine.

[0018] Also known in document EP1764480A1 is a foil whose tab is formed by two legs each extending from the ends of the branches, connected together by a connecting piece by welding or riveting or interlocking. Such a tab results in an additional production cost and furthermore even if the connecting piece makes it possible to increase the strength of the tab, it does not prevent the breaking of one of the legs of the tab at the end of one of the two branches.

[0019] Foils are also known, in particular in document EP EP2042689A1 filed by the applicant, comprising a tab folded towards the rotor rather than towards the blade, however the tab is still liable to unfold or tear and cause wear of at least a portion of the blade. Furthermore, in this document, there is a shim between the foil and the bottom of the disc cell. foil therefore comprises its base between the wedge and a surface of the blade root. A lock is mounted and retained between an upstream edge of the wedge and the blade root, so that the retaining tab is retained between the lock and the blade root, which makes it possible to prevent longitudinal (axial) movement of the foil relative to the blade root.

[0020] However, this solution is difficult to implement and is not always possible for reasons of size and mechanical strength of the blade or disc. Summary of the invention

[0021] The invention provides a solution to at least one of the problems mentioned above, by allowing the foils not to disengage from the blade roots and to ensure the mechanical integrity of the blade root and the turbine disk.

[0022] A first aspect of the invention relates to a blade of a rotor movable about an axis of rotation, comprising an internal platform, a blade extending radially from the internal platform and a blade root extending radially from this internal platform opposite the blade, the blade root comprising: • a first radial face, • a second radial face longitudinally opposite the first radial face • a first lateral longitudinal face and a second lateral longitudinal face each joining each radial face and each comprising a bearing surface intended to bear against a surface of a housing of the blade root, • a lower surface joining each radial face and joining each lateral longitudinal face dawn includes: • a first leg located on a first end of the lower surface and on one end of the first radial face; • a second leg located on a second end of the lower surface and on one end of the second radial face, the legs (5a, 5b) are symmetrical along a plane A passing through the middle of the blade root and intersecting the first lateral longitudinal face and the second lateral longitudinal face.

[0023] Thus, the invention makes it possible to longitudinally (axially) block a foil in the blade root and prevents the foil from coming out of the blade root. Thanks to the lugs, the foil cannot become dislodged from the blade root along the axis of the rotor disk, the lugs act as a stop. In addition, the lugs are stronger than a tab formed by a single fold due to the thickness of the fold. Furthermore, these lug characteristics allow a reduction in the weight of the blade compared to the prior art and therefore a reduction in fuel consumption.

[0024] In addition to the characteristics which have just been mentioned in the preceding paragraph, the blade 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:

[0025] According to one embodiment, the first and second tabs each extend from the first lateral longitudinal face to the second lateral longitudinal face. Thus the foil will come into abutment on tabs using the extension of the longitudinal faces, thus ensuring better locking of the foil.

[0026] According to one embodiment, the first leg and / or the second leg each comprises an external surface parallel to the lower surface.

[0027] According to an example of this embodiment, the first leg or the second leg comprises a length measured radially between the lower surface and the external surface respectively of the first leg or the second leg greater than 0.15 millimeters. This minimum distance is necessary in order to accommodate a foil having a thickness less than 0.15 millimeters, for example a thickness of 0.08 millimeters.

[0028] According to one embodiment, the first leg or the second leg comprises a length measured radially between the lower surface and the external surface respectively of the first leg or the second leg less than 0.30 millimeters. This maximum distance of 0.30 millimeters is necessary in order to limit air leaks.

[0029] According to one embodiment, the lugs are obtained by machining the lower surface of the blade. Thus, the lugs will be obtained during the same machining pass as when producing the underside of the blade root, thus saving time during the manufacture of the lugs.

[0030] According to one embodiment, the first leg and the second leg each comprise a stop surface opposite the stop surface of the other leg and in that this stop surface comprises machining traces. For example, the stop surface is rounded.

[0031] A second aspect of the invention relates to an assembly for a turbomachine rotor comprising: • a blade according to the first aspect of the invention described above with or without the different characteristics described above; • a foil including: • a first and a second lateral branch distant from each other, • a base joining the first and second lateral branches, the first and second lateral branches being distant from each other at the base, • a first lateral edge and a second opposite lateral edge each extending over the base and the branches, the base of the foil is in contact with the lower surface of the blade, the foil is held axially on the blade root by the lugs.

[0032] According to one embodiment, the length of the base of the foil in a longitudinal direction is less than a distance from the lower surface measured longitudinally between the two legs. Thus, the foil can be inserted into the blade root.

[0033] According to one embodiment, the foil has a thickness (measured in a plane perpendicular to the longitudinal measurement) of the base of between 0.06 and 0.10 millimeters.

[0034] A third aspect of the invention relates to a method of manufacturing the blade according to the first aspect of the invention (with or without the various features described in the preceding embodiments) comprising a step of machining the lower surface of the blade to form the lugs. Thus, the lugs will be obtained during the same machining pass as when producing the underside of the blade root, thus saving time during the manufacturing of the lugs. BRIEF DESCRIPTION OF THE FIGURES

[0035] The figures are presented for information purposes only and in no way limit the invention.

[0036] [Fig.l] is a partial view of a turbine blade according to the invention.

[0037] [Fig.2] is a partial perspective view of the turbine blade according to the invention.

[0038] [Fig.3] is a perspective view of a foil for a turbine blade.

[0039] [Fig.4] is a view of an assembly comprising the foil inserted into the blade of turbine. DETAILED DESCRIPTION

[0040] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0041] The invention relates to a moving blade of a turbomachine, in particular a root of the moving blade as well as to an assembly for a turbomachine rotor comprising the moving blade having its root inserted into a foil.

[0042] A first aspect of the invention concerns the blade 2 shown in Figures 1 and 2.

[0043] [Fig.l] shows a front view of a part of the blade 2 according to the invention.

[0044] [Fig.2] shows a perspective view of this part of the blade 2 according to the invention.

[0045] The blade 2 comprises a blade (not visible) extending radially between one end radially external and a radially internal end. At its radially external end, the blade 2 comprises a heel (not shown). At its radially internal end, the blade 2 comprises an internal platform 29 (partially shown in Figures 1, 2 and 4). The blade comprises a root 21 which makes it possible to fix the blade 2 to the rotor disk by being retained by bearing surfaces of a cell of a rotor disk.

[0046] By bearing surfaces, we mean the surfaces in contact with the blade root 21 in the absence of a foil 1. The foil 1 comprises a shape complementary to the root 21. The foil 1 mounted on the blade 2 makes it possible to protect the bearing surfaces of the blade 2.

[0047] The foot 21 of blade 2 comprises a first radial face 23a and a second radial face 23b on either side longitudinally of the foot 21.

[0048] The foot 21 radially comprises a base portion 21b comprising the bearing surfaces and a top portion 21h extending between the internal platform 29 and the base portion 21b. Dotted lines in [Fig.l] represent a boundary between the top portion 21h and the base portion 21b. The base portion 21b flares out from the top portion 21h, widening to form the bearing surfaces and then tapering down to a lower surface 27 of the foot 21 to face the bottom of the cell of the rotor disk.

[0049] The foot 21 further comprises two lateral longitudinal faces 24c, 24d of the base portion 21b and of the upper portion 21h each connecting the first radial face 23a and the second radial face 23b. Only the first lateral longitudinal face 24c is shown, the second longitudinal face 24d is referenced in [Fig.2] pointing to the hidden face of the foot 21.

[0050] Each lateral longitudinal face 24c, 24d therefore comprises in the base portion 21b at least one flank intended to form a bearing surface of the foot 21 against a bearing surface of the cell of the rotor disk.

[0051] In this example, each lateral longitudinal face 24c, 24d comprises in the upper portion 21h a flat surface 28c (only the flat surface 28c of the lateral longitudinal face 24c is shown in FIGS. 1, 2 and 4) extending from the base portion 21b and in this example a surface widening towards the internal platform.

[0052] The blade 2 comprises two tabs 5a, 5b located on the lower surface 27 and symmetrically opposite each other with respect to a plane A perpendicular to an axis of rotation of the rotor and located in the middle of the blade 2. Each of the tabs 5a, 5b extends in this example from the first lateral longitudinal face 24c to the second lateral longitudinal face 24d. The first tab 5a is located on a first end of the lower surface 27 and the second tab 5b is located on a second end of the lower surface 27. The first and second ends of the lower surface 27 are longitudinally opposite each other. The first tab 5a and the second tab 5b are symmetrical with respect to the plane A passing through the longitudinal middle of the lower surface 27 perpendicular to it. The first leg 5a comprises a surface further forming in this example one end of the first radial face 23a and the second leg 5b comprises a surface forming one end of the second radial face 23b. Thus the first leg 5a and the second leg 5b each comprise a radial surface extending respectively the first radial face 23a and the second radial face 23b.

[0053] The legs 5a, 5b may be in the shape of a rectangular parallelepiped.

[0054] In one embodiment, the width of the lugs 5a, 5b in a longitudinal direction is greater than 0.08 millimeters. Preferably, the width of the lugs 5a, 5b is greater than a thickness of the foil 1 which will be housed on the root 21 of the blade 2. In this example, the width of the lugs 5a, 5b in a longitudinal direction is 1 mm.

[0055] The legs 5a, 5b are obtained by machining the middle of the lower surface 27. The invention therefore also relates to a method of manufacturing the blade, comprising a step of machining the lower surface 27 of the blade 2 to form the legs 5a, 5b.

[0056] The machining of this surface can be carried out during the same machining pass as that carried out for the machining of the entire lower surface 27 of the root 21 of the blade 2. Thus, there is no additional machining pass but a geometric modification of a grinding wheel relative to the lower surface 27 in order to obtain the lugs 5a, 5b. For example, milling of the lower surface 27 can be carried out by a milling cutter which will start its machining stroke from one of the two lateral longitudinal faces 24c, 24d from the middle of the blade 2 and will finish its stroke by opening onto the opposite lateral longitudinal face 24c, 24d. The lower surface 27 obtained will therefore be flat. The diameter of the cutter must be less than the length of the root 21 of blade 2 between the first and second radial faces 23a, 23b so as to obtain the two legs 5a, 5b.The first leg 5a and the second leg 5b comprise an external surface 6a, 6b intended to be opposite the bottom of the cell. The external surfaces 6a, 6b are intended to be outside the foil 1 while the lower surface 27 is intended to be covered by the foil 1. The first leg 5a and the second leg 5b therefore each comprise a stop surface 7a, 7b which therefore each extend from the lower surface 27 to the external surface 6a, 6b. Each external surface 6a, 6b joins the first lateral longitudinal face 24c and the second lateral longitudinal face 24d. In this example the external surface 6a, 6b of each leg 5a, 5b is parallel to the lower surface 27.

[0057] The thickness of material removed is preferably between 0.15 and 0.30 millimeters between the external surface 6a, 6b of the first leg 5a or of the second leg 5b and the lower surface 27 in a radial direction.

[0058] Each of the abutment surfaces 7a, 7b of the legs 5a, 5b respectively is included between the lower surface 27 and the outer surface 6a, 6b of each leg 5a, 5b and in this example extends from the first 24c to the second lateral longitudinal face 24d. The abutment surface 7a, 7b is in this example fillet-shaped and can be obtained by the machining described above when machining the lower surface 27. The abutment surfaces 7a, 7b are in this case symmetrical with respect to the plane A, this is in this example due to the same milling cutter during machining.

[0059] The lower surface 27 combined with the legs 5a, 5b together form a notch for receiving the foil 1. A width of the notch is located between the lateral longitudinal faces 24c, 24d and a length of the notch is located between the legs 5a, 5b. Preferably, a depth of the notch is between 0.15 millimeters and 0.30 millimeters corresponding to the length of the first leg 5a and / or the second leg 5b, measured between the external surface 6a, 6b and the lower surface 27 of the corresponding leg 5a, 5b. The notch allows a reduction in mass compared to current blades and therefore a reduction in the fuel consumption of the turbomachine. The maximum depth of the notch of 0.30 millimeters makes it possible not to impact the mechanical strength of the blade root 2. The maximum depth of the notch also makes it possible to limit air leaks between the foil 1 and the bottom of the rotor cell.

[0060] The lower surface 27 is intended to be covered by a base 11 (referenced in FIGS. 3 and 4) of the foil 1. [Fig. 4] represents an assembly composed of the foil 1 inserted around the blade root 2. The foil 1 is for example as illustrated in perspective in [Fig. 3] according to the invention.

[0061] The base 11 of the foil 1 is surrounded on either side by the tabs 5a, 5b to block the foil 1 longitudinally or axially along the axis of rotation of the rotor.

[0062] The foil 1 further comprises, from the base 11, a first lateral branch 12c and a second lateral branch 12d. The two lateral branches 12c, 12d are connected to each other via the base 11. The foil 1 comprises, on each lateral branch 12c, 12d, a flat surface 18 located at the ends of the lateral branches 12c, 12d. The foil 1 comprises a first and a second lateral edge 15a, 15b extending over one end of the base 11 and lateral branches 12c, 12d forming the longitudinal ends of the foil 1 opposite each other longitudinally. The foil 1 also comprises at the end of each of its lateral branches 12c, 12d, a longitudinal edge 16c, 16d extending longitudinally along the flat surface 18 and connecting the two lateral edges 15a, 15b.

[0063] The thickness of the base 11 of the foil 1 is between 0.06 and 0.1 millimeter and preferably the thickness is 0.08 mm.

[0064] The length of the foil 1 between the first and second side edges 15a, 15b is less than the longitudinal length of the notch (i.e. the length of the lower surface 27 measured between the two legs 5a, 5b).

[0065] A second aspect of the invention therefore concerns the assembly composed of the foil 1 inserted into the blade root 2. As illustrated in [Fig.4], the base 11 covers the lower surface 27 of the root 21. In [Fig.4], only the first lateral branch 12c is visible. The first and second lateral branches 12c, 12d each cover one of the two corresponding longitudinal faces 24c, 24d of the root 21. The lateral branches 12c, 12d form means of protection, for example against fretting, of the longitudinal faces 24c, 24d of the root 21.

[0066] The flat surface 18 surrounds the flat surface 28c of the upper portion 21h.

[0067] The foil 1 is therefore kept locked axially along the axis of rotation of the rotor by the lugs 5a, 5b. Indeed, the foil 1 cannot come out of the root 21 of the blade 2 axially because the first lateral edge 15a at the level of the base 11 will come into abutment against the abutment surface 7a of the first lug 5a, or the second lateral edge 15b at the level of the base 11 will come into abutment against the abutment surface 7b of the second lug 5b. Thus, the foil 1 is locked longitudinally (i.e. axially) in both directions.

[0068] The foil 1 is symmetrical with respect to a plane perpendicular to the base 11 and passing through the middle of the foil. Thus, the foil 1 can be mounted in two directions on the foot 21 of the blade 2. Indeed, the first lateral branch 12c can cover either the first longitudinal face 24c or the second longitudinal face 24d of the foot 21. This helps with the assembly and prevents any assembly defects in the foil 1 on the blade foot 2.

Claims

1. Claims Turbomachine rotor assembly comprising: - a blade (2) of a rotor movable around an axis of rotation, comprising an internal platform (29), a blade extending radially from the internal platform (29) and a blade (2) root (21) extending radially from this internal platform (29) opposite the blade, the blade (2) root (21) comprising: • a first radial face (23a), • a second radial face (23b) longitudinally opposite the first radial face (23a) • a first lateral longitudinal face (24c) and a second lateral longitudinal face (24d) each joining each radial face (23a, 23b) and each comprising a bearing surface intended to bear against a surface of a housing of the root (21) of the blade (2), • a lower surface (27) joining each radial face (23a, 23b) and joining each lateral longitudinal face (24c, 24d) • a first leg (5a) located on a first end of the lower surface (27) and on one end of the first radial face (23a); • a second leg (5b) located on a second end of the lower surface (27) and on one end of the second radial face (23b), • the legs (5a, 5b) are symmetrical along a plane A passing through the middle of the foot (21) of the blade (2) and intersecting the first lateral longitudinal face (24c) and the second lateral longitudinal face (24d), - a foil (1) comprising: • a first and a second lateral branches (12c, 12d) • a base (11) joining the first and second lateral branches (12c, 12d), the first and second lateral branches (12c, 12d) being spaced apart from each other by the base (11) • a first lateral edge (15a) and a second lateral edge (15b) opposite each extending over the base (11) and the branches (12c, 12d), • the base (11) of the foil (1) is in contact with the lower surface (27) of the blade (2), the foil (1) is retained longitudinally on the blade root (2) by the lugs (5a, 5b).

2. Turbomachine rotor assembly according to the preceding claim, characterized in that the first (5a) and the second tab (5b) each extend from the first lateral longitudinal face (24c) to the second lateral longitudinal face (24d).

3. Turbomachine rotor assembly according to one of the preceding claims, characterized in that the first leg (5a) and / or the second leg (5b) each comprises an external surface (6a, 6b) parallel to the lower surface (27).

4. Turbomachine rotor assembly according to the preceding claim, in which the first lug (5a) or the second lug (5b) comprises a length measured radially between the lower surface (27) and the external surface (6a, 6b) respectively of the first lug (5a) or the second lug (5b) greater than or equal to 0.15 millimeters.

5. A turbomachine rotor assembly according to one of the preceding claims, wherein the first lug (5a) or the second lug (5b) comprises a length measured radially between the lower surface (27) and the external surface (6a, 6b) respectively of the first lug (5a) or the second lug (5b), less than or equal to 0.30 millimeters.

6. Turbomachine rotor assembly according to one of the preceding claims, characterized in that the lugs (5a, 5b) are obtained by machining the lower surface (27) of the blade (2).

7. Assembly according to one of the preceding claims, characterized in that the length of the base (11) of the foil (1) in a longitudinal direction is less than a distance from the lower surface measured longitudinally between the two legs (5a, 5b) in a longitudinal direction.

8. Assembly according to one of the preceding claims, characterized in that the foil (1) has a base thickness (11) of between 0.06 and 0.10 millimeters.

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