Variable-pitch blade for a turbine engine

Abstract

The invention relates to a variable-pitch blade (7) for a turbine engine, the blade comprising: - a tubular metal sleeve (13) comprising an opening (17) extending through the sleeve (13) along a pitch axis (Y), the opening (17) being delimited by an internal wall of the sleeve (13); - a fibrous structure (20) comprising a blade root (22), the blade root (22) comprising a tubular attachment portion (23) inserted axially into the opening (17) of the sleeve (13), this attachment portion (23) comprising a housing (20a) centered on the pitch axis (Y); - a polymerized resin for solidifying the fibrous structure (20) and securing the fibrous structure (20) to the internal wall (18) of the sleeve (13), and - a permanent insert (224) centered on the pitch axis (Y) and inserted axially into the housing (20a) of the attachment portion (23), the permanent insert (224) being separated from the attachment portion (23) by a layer of adhesive (226).

Description

[0001] DESCRIPTION

[0002] TITLE: VARIABLE TIMING TURBINE BLADE FOR A TURBOMACHINE

[0003] Technical field of the invention

[0004] The invention relates generally to the field of turbomachinery, and in particular to turbomachine blades.

[0005] The invention relates more particularly, but not exclusively, to a variable pitch blade intended for use in an unfaired aircraft engine fan rotor.

[0006] Technical background

[0007] Prior art includes documents US2010104443A1 and FR3152023A1.

[0008] The search for minimizing polluting emissions related to air transport involves, in particular, improving all the efficiencies of propulsion systems, and more specifically the propulsive efficiency which characterizes the efficiency with which the energy communicated to the air passing through the engine is converted into useful thrust effort.

[0009] The primary factors influencing propulsive efficiency are those related to the low-pressure components of the propulsion system, which contribute directly to thrust generation: the low-pressure turbine, the low-pressure transmission system, the fan, and the secondary flow guiding its operation. The known guiding principle for improving propulsive efficiency is to reduce the fan's compression ratio, thereby decreasing the flow velocity at the engine outlet and the associated kinetic energy losses.

[0010] One of the main consequences of this decrease in flow velocity at the engine outlet is that a higher mass flow rate of air must be treated in the low-pressure section (secondary flow) to ensure a given thrust level, determined by the aircraft's characteristics. This therefore leads to an increase in the engine's bypass ratio. The bypass ratio, or BPR (Bypass Ratio), is defined as the ratio between the mass flow rate in the secondary flow (cold flow) and the mass flow rate in the primary flow (hot flow), which notably feeds the combustion chamber.

[0011] This increase in secondary flow rate directly necessitates an increase in the fan diameter, and consequently, in the external dimensions of the surrounding retention casing, as well as the nacelle that forms the aerodynamic envelope of said casing. To achieve high dilution rates, the casing becomes too large and heavy (generating significant drag), so it is removed in favor of configurations with unfaired propellers.

[0012] Several unducted turbomachinery concepts could be considered, such as the Unducted Single Fan (USF) architecture: an unducted turbomachine with (at least) one upstream variable pitch propeller wheel (or "Open Fan") and a downstream stator wheel with fixed or variable pitch.

[0013] More generally, the technical field of application lies within the context of fan blades, including rotating (rotor), unshod (propeller), and variable-pitch blades, with a potential application in the aeronautical propulsion industry. Other examples of particularly relevant architectures include Contra-Rotating Open Rotors (CROR) and turboprop engines. However, the design of such blades requires consideration of conflicting constraints.

[0014] On the one hand, the design of these blades must allow for optimal aerodynamic performance, notably maximizing efficiency and providing thrust while minimizing losses. Improving the aerodynamic performance of the fan tends towards an increase in the bypass ratio, which translates into an increase in the external diameter, and therefore the span, of these blades. On the other hand, it is also necessary to guarantee resistance to the mechanical stresses that may be exerted on these blades while limiting their acoustic signature.

[0015] Furthermore, on unshod fan designs, engine start-up is generally performed with a very open valve timing. Indeed, a very open valve timing allows power to be consumed by torque, which ensures machine safety by guaranteeing low fan speeds. However, with a very open valve timing, the blades experience turbulent, completely separated aerodynamic flow, which generates broadband vibrational excitation. In particular, on large-chord, long-span blades, the bending stress is intense, even though the engine speed is not at its maximum.

[0016] In normal operation, that is, during ground and flight phases, the fan pitch is adjusted to a more closed angle. The aerodynamic flow is then perfectly controlled, particularly in relation to the airfoil. Broadband stresses disappear because the rotational speed is higher, and the bending force is controlled. However, since the engine is not enclosed in a cowling, the angle of attack experienced by the various fan blades, depending on their angular position, varies according to the aircraft's angle of attack, creating a cyclic bending moment (commonly called the 1P moment) on the blades. This cyclic bending moment then generates significant bending stresses on the blades in addition to the centrifugal forces due to their rotation.

[0017] These blades can be made of metallic material. While metallic blades have good mechanical resistance, they have the disadvantage of being relatively heavy.

[0018] Manufacturing blades from composite materials is an attractive solution for reducing blade weight. However, composite blades can be fragile due to the intense aerodynamic stresses they are subjected to. These aerodynamic stresses can damage the blades and / or the hub in the interface area between the blades and the fan rotor hub, at the blade root. To overcome these drawbacks, various solutions exist in the prior art. Most utilize reinforcing elements, particularly at the blade root, and add various structural elements to allow, for example, the blade to be attached to the pitching mechanism. Patent documents W0-A1-2022 / 018353 and W0-A1-2022 / 208002 describe the addition of reinforcing and structural elements, especially at the blade roots.However, these solutions have the drawback of requiring the manufacture of several components from potentially different materials and the assembly of these components using fastening methods. Such blades can therefore be relatively time-consuming to produce.

[0019] The present invention proposes an improvement to existing technologies, which provides a simple, efficient and economical solution to at least some of the problems of the prior art.

[0020] Summary of the invention

[0021] The invention proposes a variable-pitch blade for a turbomachine comprising:

[0022] - a tubular metal sleeve, this sleeve comprising a fixing part configured to be connected to a variable shimming mechanism, and a recess passing through the sleeve along a shimming axis, the recess being delimited by an internal wall of the sleeve;

[0023] - a fibrous structure obtained by weaving fibers, the fibrous structure comprising a blade root including a tubular attachment portion inserted axially into the sleeve recess, this attachment portion including a housing centered on the alignment axis, the fibrous structure further comprising a blade with an aerodynamic profile connected to the blade root; - a polymerized resin for solidifying the fibrous structure and for bonding the fibrous structure to at least a portion of the inner wall of the sleeve, and

[0024] - a permanent insert centered on the alignment axis and inserted axially into the housing of the attachment portion, the permanent insert being separated from the attachment portion by a layer of glue which extends around the alignment axis and over the entire axial extent of the permanent insert.

[0025] One of the problems to be solved concerns the absorption of the torsional moment around the blade's pitch axis. Indeed, the aerodynamic and centrifugal forces acting on the blade generate a resulting torsional moment that must be absorbed at the interface between the blade root and the outer metal sleeve in order to control the blade pitch via the variable pitch mechanism.

[0026] By default, this torque is absorbed by the polymerized resin (or by the resin and an adhesive joint when the latter is present), which ensures a bond between the blade root attachment and the sleeve. This bond provides a primary load path by default for torque absorption. A failure of this interface would lead to a loss of control over the blade pitch.

[0027] The invention thus proposes to integrate a secondary force path in order to take up this torque in the event of a break in the bonded interface between the attachment portion of the blade foot and the sleeve.

[0028] This is achieved by means of a permanent insert that is added to ensure a secondary torque transfer path. The distinctive feature of this insert is that it is fixed to the attachment portion by bonding. It is therefore not bonded to the attachment portion by the aforementioned resin. This means that the permanent insert is mounted and bonded to the attachment portion after it has solidified with the resin. This avoids the drawbacks associated with bonding the insert to the attachment portion with this resin. These drawbacks will be described in more detail below. The blade according to the invention may comprise one or more of the following features, taken individually or in combination:

[0029] - the layer of glue has a constant thickness;

[0030] - the permanent insert comprises a tubular wall centered on the alignment axis and defining an internal cavity, the permanent insert having at an axial end of said tubular wall a bottom wall closing said internal cavity;

[0031] -- said bottom wall forms a cap, for example hemispherical;

[0032] -- said bottom wall has a flat, pointed, beak-shaped, etc. shape;

[0033] - the layer of glue extends continuously between the tubular wall and the attachment portion, and between the bottom wall and the attachment portion;

[0034] - the tubular wall has a general frustoconical shape flared on the side opposite the bottom wall;

[0035] - the glue is made from a different material than the resin;

[0036] -- the glue is distinct from the resin;

[0037] -- the recess has surface roughness in contact with said layer of glue; in the present application, surface roughness means asperities which make the surface concerned not flat but on the contrary rough;

[0038] -- the permanent insert includes surface roughness in contact with said layer of glue;

[0039] -- the surface roughness of the permanent insert is complementary to or of the same type as that of the recess.

[0040] The present invention further relates to a method for manufacturing a blade as described above, comprising the following steps:

[0041] a) create by weaving the fibrous structure including the attachment portion, b) insert the attachment portion into the recess of the sleeve and against the inner wall, c) position a molding insert in the recess so that the attachment portion is radially interposed between the molding insert and the inner wall of the sleeve,

[0042] d) insert the fibrous structure, the sleeve and the insert into a mold and inject the resin into the mold, so as to solidify the fibrous structure and to bond the fibrous structure to the inner wall of the sleeve,

[0043] e) remove the molding insert from the recess in the attachment portion, f) machine the impression formed by the molding insert in the recess in the attachment portion, and

[0044] (g) insert and glue the permanent insert into the machined recess of the attachment portion so that the permanent insert is separated from the attachment portion by a layer of glue which extends around the shimming axis and over the entire axial extent of the permanent insert.

[0045] The method according to the invention may comprise one or more of the following features, taken individually or in combination with each other:

[0046] - the impression has a general cylindrical shape, and the machined impression has a general frustoconical shape;

[0047] - the layer of glue has a constant thickness;

[0048] - the glue is of the polymerizable type;

[0049] - the permanent insert has a maximum external diameter which is greater than the maximum external diameter of the molding insert;

[0050] - a release agent or a non-stick film is deposited on an external surface of the molding insert, between steps b) and c);

[0051] -- the release agent or non-stick film is PTFE-based;

[0052] -- the imprint is machined in step f) so as to generate surface roughness;

[0053] - the permanent insert includes surface roughnesses intended to come into contact with the surface roughnesses of the impression;

[0054] -- The surface roughness of the permanent insert is complementary to the surface roughness of the impression. Brief description of the figures

[0055] Other features and advantages will become apparent from the following description of a non-limiting embodiment of the invention with reference to the accompanying drawings in which:

[0056] [Fig.1] Figure 1 schematically represents an example of an engine including an unfaired fan;

[0057] [Fig.2] Figure 2 schematically represents a blower blade according to an embodiment of the invention assembled to a shimming mechanism;

[0058] [Fig.3] Figure 3 schematically represents a blower blade according to a first embodiment of the invention;

[0059] [Fig. 4a] Figure 4a schematically represents a sleeve according to a first embodiment of the invention in perspective view J

[0060] [Fig.4b] Figure 4b schematically represents the sleeve of figure 4a in profile view;

[0061] [Fig.4c] Figure 4c schematically represents the sleeve of figures 4a and 4b into which the attachment portion and the insert are inserted; [Fig.4d] Figure 4d schematically represents the sleeve / attachment portion / insert assembly of figure 4c inserted into the stabilizing mechanism;

[0062] [Fig.5] Figure 5 schematically represents an insert according to one embodiment of the invention;

[0063] [Fig.6] Figure 6 schematically and partially represents a blade not conforming to the invention;

[0064] [Fig.7] Figure 7 schematically and partially represents a manufacturing step of a blade according to the invention;

[0065] [Fig.8] Figure 8 schematically and partially represents another manufacturing step of the blade according to the invention; and [Fig.9] Figure 9 schematically and partially represents a blade and shows the positional differences between a molding insert and a permanent insert used within the framework of the present invention.

[0066] Detailed description of the invention

[0067] In Figure 1, the engine 1 shown is an "Open Rotor" type engine, in a configuration commonly referred to as "pusher" (i.e., the blower is placed at the rear of the power generator with an air inlet located on the side, to the right in Figure 1).

[0068] The engine comprises a nacelle 2 intended to be fixed to an aircraft fuselage, and an unfaired fan 3. The fan 3 comprises two counter-rotating fan rotors 4 and 5. In other words, when the engine 1 is running, the rotors 4 and 5 are driven in rotation relative to the nacelle 2 around the same axis of rotation X (which coincides with a principal axis of the engine), in opposite directions.

[0069] Thus, in the example illustrated in Figure 1, motor 1 is an "Open Rotor" type motor, in a "pusher" configuration, with counter-rotating fan rotors. However, the invention is not limited to this configuration. The invention also applies to "Open Rotor" type motors in a "puller" configuration (i.e., the fan is placed upstream of the power generator with an air inlet located before, between, or just behind the two fan rotors).

[0070] Furthermore, the invention also applies to motors with different architectures, such as an architecture comprising a blower rotor with moving blades and a blower stator with fixed blades, or a single blower rotor.

[0071] The invention is applicable to turboprop-type architectures (comprising a single fan rotor).

[0072] In Figure 1, each blower rotor 4, 5 comprises a hub 6 mounted rotatably relative to the nacelle 2 and a plurality of blades 7 fixed to the hub 6. The blades 7 extend substantially radially with respect to the axis of rotation X of the hub.

[0073] As illustrated in Figure 2, the fan 3 further includes an actuation mechanism 8 for collectively adjusting the pitch angle of the rotor blades to adapt engine performance to different flight phases. For this purpose, each blade 7 comprises a blade root 9 and an aerodynamically profiled blade 12. The blade root 9 is rotatably mounted relative to the hub 6 around a pitch axis Y. More precisely, the blade root 9 is rotatably mounted within a mounting device 10 formed in the hub 6, via balls 11 or other rolling elements.

[0074] The aerodynamic airfoil blade 12 has a first end connected to the blade root 9 and a second end, opposite the first end. The aerodynamic airfoil portion of the blade 12 is designed to extend into an engine air stream when the engine is running, in order to generate lift. Conversely, the blade root 9 is designed to extend out of the air stream.

[0075] With reference to figures 3, 4a and 4b, the blade 7 includes a sleeve 13 having a fixing part 14 configured to be connected to a variable pitching mechanism of a turbomachine, in particular inside the attachment device 10. The sleeve 13 has a recess 17 delimited by an internal wall 18 of the sleeve 13. The recess 17 passes through the sleeve 13 along a pitching axis Y.

[0076] With reference to Figures 3, 4c, and 4d, the blade 7 also includes a fibrous structure 20 obtained by weaving, preferably three-dimensional. The fibrous structure 20 has a blade root 22 comprising an attachment portion 23 configured to be inserted into the recess 17 formed by the attachment portion 14 of the sleeve 13. It is understood that the attachment portion 23 comprises fibers all around the alignment axis. In other words, the attachment portion 23 is continuous. The fibrous structure 20 has a tubular shape and includes a housing 20a centered on the alignment axis Y.

[0077] The fibrous structure 20 also includes a blade 21 with an aerodynamic profile connected to the blade root 22.

[0078] The blade 7 also includes an insert 24 shown in Figure 5 and which is configured to be inserted into the housing 20a of the attachment portion 23 so that the attachment portion 23 is radially intercalated between the insert 24 and the inner wall 18 of the sleeve 13.

[0079] The blade 7 further includes a polymerized resin for solidifying the fibrous structure 20 to at least part of the internal wall 18 of the sleeve 13.

[0080] The resin thus makes it possible to form a main force path, called default, when transmitting a torque recovery force around the Y alignment axis between the blade root 22 and the sleeve 13.

[0081] The blade 7 is thus formed from a few elements that fit together to form a single-piece blade. Since the blade 21 and the blade root 22 are formed from the same fibrous structure 20, there is no discontinuity between the blade 21 and the blade root 22. Furthermore, the blade root 22 is wedged between the insert 24 and the sleeve 13, and the fibrous structure 20 is thus securely joined to the blade root 9.

[0082] The blade 7 can therefore withstand significant aerodynamic stresses while maintaining a limited mass, and can thus be used with a variable pitch mechanism and in an "open rotor" type environment. Furthermore, since the components of the blade 7 are limited in number, it is quick to manufacture.

[0083] The resin typically comprises an organic material (thermosetting, thermoplastic, or elastomer) or a carbon matrix. For example, the matrix may comprise a plastic material, typically a polymer, such as epoxy, bismaleimide, or polyimide. The fibers of the fibrous structure 20 comprise at least one of the following materials: carbon, glass, aramid, polypropylene, and / or ceramic. With reference to Figures 4a, 4b, and 4c, the attachment portion 23 may have an additional thickness 23" resulting from a progressive thickening of the fibrous structure 20 forming said attachment portion 23, at its free end 23'. This additional thickness 23" is configured to fit into a recessed portion 18' of the inner wall 18. Thus, the portion 18' widens the recess 17, and the remainder of the wall portion 18 narrows the recess 17.In this way, when the insert 24 is positioned in the recess 17, any translation of the attachment portion 23 away from the free end 23' is prevented by the part of the wall 18 which narrows the recess 17 and forms a stop.

[0084] Indeed, when the fan is rotating, the blade 7 is subjected to centrifugal forces oriented in a radial direction relative to the axis of rotation of the fan, which tend to separate the aerodynamic profile blade 12 from the sleeve 13. The extra thickness 23” helps to prevent the separation of the blade 12 and the sleeve 13.

[0085] With reference to figures 3, 4a to 4d, the fixing part 14 has a rotational symmetry about the Y axis. Furthermore, the fixing part 14 has an external surface 30 with different reliefs.

[0086] The fixing part 14 has at its end through which the attachment portion 23 is inserted a first annular flange 29. This first annular flange 29 forms a stop against which the blade foot 22 is configured to bear.

[0087] The fixing part 14 also includes a second annular flange 29' at its free end opposite to the end through which the fibrous structure 20 is inserted.

[0088] The mounting portion 14 also includes a first circular groove 32 and a second circular groove 34, forming a raceway for at least one bearing, for example, a ball bearing. The mounting portion 14 thus allows the blade foot 9 to be rotatably mounted within the attachment device 10 formed in the hub 6. Alternatively, the grooves 32 and 34 could be replaced by, for example, radiating shoulders.

[0089] Sleeve 13 is preferably metallic and monolithic.

[0090] As previously described, the sleeve 13 has an inner wall 18 that defines the recess 17. The recess 17 can form a cylinder of constant diameter that widens as it approaches the free end of the sleeve 13, forming a beveled inner edge. The wall 18 thus has a recessed portion 18' that widens the recess 17 in a radial direction. The extra thickness 23" of the attachment portion 23 is then inserted into the recessed portion 18' so as to prevent any translation of the attachment portion 23 away from the free end 23' when the insert 24 is positioned in the recess 17. The portion of the wall 18 with a constant diameter then acts as a stop for the extra thickness 23".

[0091] The recessed portion can have a different shape and can be placed in a different position along wall 18.

[0092] The wall 18 could alternatively be thickened at its end opposite the free end so as to reduce the diameter of the recess 17 and form a stop allowing the insert 24 to be blocked and the attachment portion 23 to be wedged against the wall 18 in an optimized manner.

[0093] Figure 4d represents the sleeve into which the attachment portion 23 and the insert 24 are inserted, the sleeve being arranged in the attachment device 10, the rolling elements 11 being arranged in the aforementioned circular grooves 32 and 34 or radiating shoulders.

[0094] Referring to Figures 5 and 6, the insert 24 comprises a cylindrical body 40 having a free end 41 and a locking end 42 opposite the free end 41. In this embodiment, the locking end 42 is rounded. The insert 24 is preferably metallic. Solidification of the insert 24 at the attachment portion 23 by co-injection of the resin can lead to several problems:

[0095] - Residual stresses appear at the interface between the insert 24 and the attachment portion 23; these stresses can lead to: an out-of-plane tensile preload of the composite reducing its service life potential, decohesion of the insert 24 with respect to the attachment portion 23, decohesion of the sleeve 13 if it is bonded to the attachment portion 23, etc.

[0096] - geometric variabilities appear for example on the co-axiality which is controlled by the injection tooling but which may remain beyond the desired tolerance.

[0097] The problem to be solved therefore concerns in particular the integration of an insert without generating residual constraints and aiming for low geometric dispersion.

[0098] Within the framework of the present invention, two types of inserts are distinguished: the molding insert and the permanent insert.

[0099] As its name suggests, the molding insert is used during the molding of the attachment portion 23 and is not intended to remain inside the attachment portion 23. The molding insert is therefore used during part of the manufacturing process of the blade 7.

[0100] The permanent insert, on the other hand, has the function of remaining in the attachment portion 23 and replacing the molding insert after its removal.

[0101] It is therefore understood that, within the framework of the process according to the invention, the molding and permanent inserts are used one after the other, that is to say successively.

[0102] The process according to the invention comprises several steps.

[0103] The process includes a step a) consisting of producing the fibrous structure 20 comprising the attachment portion 23 by weaving, preferably three-dimensional, the attachment portion 23 being produced by forming for example unlinks in the weaving.

[0104] The process then includes step b) of inserting the attachment portion 23 into the recess 17 of the sleeve 13 and positioning said attachment portion 23 against the inner wall 18. An adhesive film not shown may be intercalated between the attachment portion 23 of the fibrous structure 20 and the inner wall 18 of the sleeve 13. In a step c), the molding insert 124 is positioned in the recess 17 so that the attachment portion 23 is intercalated radially between the molding insert 124 and the inner wall 18 of the sleeve 13 (see figure 7).

[0105] Once the fibrous structure 20, the sleeve 13 and the molding insert 124 are assembled, the blade 7 thus formed is inserted into a mold 64 in a step e), and a liquid resin is then injected into the mold 64 according to the RTM process to obtain a one-piece blade 7. The resin can be in particular an epoxy resin, a thermoplastic resin or a polybismaleimide (BMI) resin.

[0106] During the injection of the resin, the latter impregnates the entire fibrous structure 20 and thus inserts itself in particular between the molding insert 124 and the wall 18 and around the attachment portion 23. The resin thus makes it possible to maintain the different assembled elements, namely the fibrous structure 20, the sleeve 13 and the molding insert 124, in a single block.

[0107] In a subsequent step e), the molding insert 124 is removed from the recess 17 in the attachment portion 23. Removal of the molding insert 124 can be facilitated by applying a release agent or a non-stick film to the external surface of the molding insert 124 before its insertion into the attachment portion 23, and thus before the resin injection. This release agent or non-stick film is, for example, PTFE-based.

[0108] In a subsequent step f), the impression 126 formed by the molding insert 124 in the recess 17 of the attachment portion 23 is machined.

[0109] Finally, in step g), the permanent insert 124 is inserted and bonded into the machined cavity 128 of the attachment portion 23 such that the permanent insert 224 is separated from the attachment portion 23 by a layer of adhesive 226 extending around the alignment axis Y and over the entire axial extent of the permanent insert 224 (see Figure 8). In this way, the adhesive layer covers the entire internal surface of the machined cavity of the attachment portion 23. The cavity 126 may have a generally cylindrical shape as shown in Figure 8. The machined cavity 128 may have a generally truncated conical shape as illustrated in Figure 9, with the angle of inclination > of its internal surface.

[0110] It is therefore understood that the machining in step f) can consist of going from a cylindrical shape of the cavity 126 to a frustoconical shape of the machined cavity 128. This machining can also consist of going from an axisymmetric cavity to a non-axisymmetric cavity.

[0111] Machining can generate surface roughness in the recess 17, and in particular surface roughness on the surface of the attachment portion 23 intended to be covered by the adhesive layer 226. The angle of inclination > facilitates the insertion of the permanent insert 224 and also allows pressure to be generated on the adhesive layer 226 between the permanent insert 224 and the attachment portion 23.

[0112] The glue layer 226 preferably has a constant thickness.

[0113] The adhesive 226 is preferably of the heat-curing type. In this case, step g) may involve heating the adhesive 226 to induce its polymerization. Heating the adhesive may be accompanied by compressing the permanent insert 224 against the attachment portion 23. This operation may be carried out in an autoclave with a vacuum bag, or with other specific equipment that allows for the application of pressure and a temperature increase.

[0114] Before bonding, the external surface of the permanent insert 224, which is intended to be in contact with the adhesive 226, can be prepared and thus undergo surface treatment, for example by laser, plasma, or wet process. The adhesive 226 can be deposited on the insert 224, in the machined cavity 128, or both.

[0115] Glue 226 is to be based on a different material than the resin used for the RTM process.

[0116] The permanent insert 224 preferably has surface roughnesses complementary to those of the recess 17, these surface roughnesses being intended to be covered by said layer of adhesive 226. It can also be seen in Figure 8 that the permanent insert 224 has a maximum external diameter Dmax1, in particular at its open free end 41, which is greater than the maximum external diameter Dmax2 of the molding insert 124. Figure 9, for example, allows comparison of the position of the molding insert 124 with respect to the permanent insert 224. The difference in diameters at the free ends 41 of the inserts can be seen, while their opposite ends 42 may be identical.

[0117] One solution to the aforementioned problem is to apply an extra layer of resin in the foot area, then machine the internal cavity of the attachment portion 23 to the desired final geometry, and finally attach a permanent insert 224 by secondary bonding. The aforementioned surface roughness can be created by machining this extra layer.

[0118] One way to implement this invention is to use a molding insert 124 for injection which has a smaller volume than the reported permanent insert 224.

[0119] The present invention also relates to a blade 7 as partially shown in Figure 8. This blade 7 differs from the one described above essentially in that its insert is a permanent insert 224 which is separated from the attachment portion 23 by a layer of adhesive extending around the alignment axis Y and over the entire axial extent of the permanent insert. The adhesive is thus distinct from the resin in which the fibrous structure is embedded.

[0120] As mentioned above, the glue layer preferably has a constant thickness.

[0121] The permanent insert 224, visible in Figure 8, comprises a tubular wall centered on the Y-axis and defining an internal cavity 230. At one axial end of the tubular wall, the insert 224 has an end 42 closing the internal cavity 230 and forming a bottom wall. In the example shown, which is not limiting, this bottom wall has a hemispherical cap shape. Alternatively, it could have a flat, pointed, beak-like, etc., shape.

[0122] The glue layer 226 preferably extends continuously between the tubular wall and the attachment portion 23, and between the hemispherical cap and the attachment portion 23.

[0123] The attachment portion 23 preferably has a generally frustoconical shape, flared on the side opposite the end 42 and thus the hemispherical cap. Alternatively, the permanent insert 224 could be solid and not include an internal cavity 230.

[0124] The permanent insert 224 can be made of metallic or composite material. The distinctive feature of the invention compared to the prior art lies in the minimization of residual stresses in the blade root by modifying its manufacturing process. Furthermore, the invention also allows for the separation of the insert's geometric positioning from the injection molding tooling. This tends to reduce the geometric variability of the finished part.

Claims

DEMANDS 1. Variable pitch blade (7) for a turbomachine comprising: - a tubular metal sleeve (13), this sleeve comprising a fixing part (14) configured to be connected to a variable pitch mechanism, and a recess (17) passing through the sleeve (13) along a pitch axis (Y), the recess (17) being delimited by an internal wall of the sleeve (13); - a fibrous structure (20) obtained by weaving fibers, the fibrous structure (20) comprising a blade root (22) comprising a tubular attachment portion (23) inserted axially into the recess (17) of the sleeve (13), this attachment portion (23) comprising a housing (20a) centered on the alignment axis (Y), the fibrous structure (20) further comprising an aerodynamically profiled blade (12) connected to the blade root (22); - a polymerized resin for solidifying the fibrous structure (20) and for bonding the fibrous structure (20) to at least a portion of the inner wall (18) of the sleeve (13), and - a permanent insert (224) centered on the alignment axis (Y) and inserted axially in the housing (20a) of the attachment portion (23), the permanent insert (224) being separated from the attachment portion (23) by a layer of glue (226) which extends around the alignment axis (Y) and over the entire axial extent of the permanent insert (224).

2. Blade (7) according to claim 1, wherein the glue layer (226) has a constant thickness.

3. Blade (7) according to claim 1 or 2, wherein the permanent insert (224) comprises a tubular wall centered on the alignment axis (Y) and defining an internal cavity, the permanent insert (224) having at an axial end of said tubular wall a bottom wall closing said internal cavity.

4. Blade (7) according to claim 3, wherein the layer of adhesive (226) extends continuously between the tubular wall and the attachment portion (23), and between the bottom wall and the attachment portion (23).

5. Blade according to claim 3 or 4, wherein the tubular wall has a general frustoconical shape flared on the side opposite the bottom wall.

6. Blade according to any one of the preceding claims, wherein the glue is based on a material different from that of the resin.

7. Blade according to any one of the preceding claims, wherein the recess has surface roughness in contact with said glue layer.

8. Blade according to any one of the preceding claims, wherein the permanent insert comprises surface roughness in contact with said glue layer.

9. A method for manufacturing a blade (7) according to any one of the preceding claims, comprising the following steps: a) produce by weaving the fibrous structure (20) comprising the attachment portion (23), b) insert the attachment portion (23) into the recess (17) of the sleeve (13) and against the inner wall (18), c) position a molding insert (124) in the recess (17) so that the attachment portion (23) is radially interposed between the molding insert (124) and the inner wall (18) of the sleeve (13), d) insert the fibrous structure (20), the sleeve (13) and the insert (124) into a mold (64) and inject the resin into the mold (64), so as to solidify the fibrous structure (20) and to bond the fibrous structure (20) to the inner wall (18) of the sleeve (13), e) remove the molding insert (124) from the recess (17) of the attachment portion (23), f) machine the impression (126) formed by the molding insert (124) in the recess (17) of the attachment portion (23), etg) insert and glue the permanent insert (224) into the machined impression (128) of the attachment portion (23) so that the permanent insert (224) is separated from the attachment portion (23) by a layer of glue (226) which extends around the alignment axis (Y) and over the entire axial extent of the permanent insert (224).

10. Manufacturing method according to claim 9, wherein the cavity (126) has a general cylindrical shape, and the machined cavity (128) has a general frustoconical shape.

11. Manufacturing method according to claim 9 or 10, wherein the glue layer (226) has a constant thickness.

12. A manufacturing process according to any one of claims 9 to 11, wherein the glue (226) is of the polymerizable type.

13. Manufacturing method according to any one of claims 9 to 12, wherein the permanent insert (224) has a maximum external diameter (Dmaxl) which is greater than the maximum external diameter (Dmax2) of the molding insert (124).

14. A manufacturing method according to any one of claims 9 to 13, wherein a release agent or an anti-stick film is deposited on an external surface of the molding insert (124), between steps b) and c) 15. A manufacturing method according to any one of claims 9 to 14, wherein the cavity is machined in step f) so as to generate surface roughness.

Images