METHOD FOR PREPARING A TURBOMACHINE BLADE FOOT

Abstract

The invention relates to a method for preparing (300) a blade (12) root (121) for mounting a turbomachine blade (12) made of composite material in a root support (10), characterized in that it comprises: a first step (310) of positioning on a side wall (122) of the blade (12) root (121) an anti-wear layer (220) comprising synthetic fibers coated or impregnated with an adhesive agent; a second step (320) of polymerizing the adhesive agent so that said anti-wear layer (200) adheres to the side wall (122) of the blade (121) root (12); a third step (330) of machining a free outer surface (210a) of said anti-wear layer intended to be in contact with the root support (10), so as to obtain a ground outer surface (210b). Abstract Figure: Figure 1.

Description

Title of the invention: METHOD FOR PREPARING A TURBOMACHINE BLADE FOOT TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of preparing a turbomachine blade root for mounting in a root support.

[0002] The invention relates more particularly to the preparation and assembly of a fan blade in a fan disc of a turbomachine.

[0003] The invention also relates to a turbomachine blade obtained by such a method as well as a rotor assembly of a turbomachine. TECHNICAL BACKGROUND

[0004] In the present application, the terms "upstream" and "downstream" are defined with respect to the normal flow direction of gas (from upstream to downstream) through a turbomachine.

[0005] The axis of rotation of a rotor of the turbomachine is also called "axis of the turbomachine" or "engine axis". The axial direction corresponds to the direction of the axis of the turbomachine and a radial direction is a direction perpendicular to the axis of the turbomachine and intersecting this axis. Similarly, an axial plane is a plane containing the axis of the turbomachine, and a radial plane is a plane perpendicular to this axis.

[0006] Unless otherwise specified, the adjectives “interior”, “internal”, “exterior”, “ "external" are used in the present application with reference to a radial direction such that the inner part of an element is, in a radial direction, closer to the axis of the turbomachine than the outer part of the same element.

[0007] Conventionally, a turbomachine comprises from upstream to downstream, that is to say in the direction of flow of the gas flows, a fan, one or more compressors, a combustion chamber, one or more turbines, and a nozzle for ejecting the combustion gases leaving the turbine(s).

[0008] In a rotor system (i.e. an assembly integral with the rotor), the (moving) blades are fixed to a rotor disk by attachment systems, which may be a straight or curvilinear broached attachment, hammer, or fir tree. These attachment systems can be described as being devices where the blade roots form the male parts of the system and are retained radially in the female parts of the system, arranged on the outer periphery of the disk and commonly called cells.

[0009] When the rotor is rotated, the blades are subjected mainly to centrifugal forces as well as to axial aerodynamic forces and the blade roots come into abutment against the parts of the disc bordering the external opening. cells, under the effect of centrifugal forces. The surfaces of the blade roots and the disc, in abutment against each other, are commonly called "bearings". These bearings are subjected to pressure (resulting from said forces, applied to the surface of these bearings). It can be estimated that this pressure depends as a first approximation on the square of the rotor rotation speed.

[0010] It is therefore understood that the variations in rotational speed of the rotor during the operating cycle of the turbomachine: from stopping to full throttle, passing through the particular intermediate regimes, induce pressure variations at the levels of the previously defined bearing surfaces. These pressure variations associated with the elastic deformations of the parts in contact cause relative movements between the blade root and the disk. These relative movements, called sliding or separation depending on their nature, induce wear phenomena of the bearing surfaces of the blades or of the disk when they are repeated. It is also possible to attribute to the dynamic movements of the blades at a given rotational regime (responses of the blades to alternating stresses of a harmonic or transient nature) a contribution to the wear phenomenon of said bearing surfaces.

[0011] However, these wear phenomena are detrimental to the service life of the turbomachine. So-called "anti-wear" solutions, i.e. solutions delaying the appearance of wear at the contact interfaces, can be adopted, including solutions based on the introduction of a third body, called foil, between the blade roots and the disk. This foil makes it possible, in particular, to double the contact interfaces (we go from one blade / disk interface to two blade / foil and foil / disk interfaces) and to reduce the relative movements between the parts in contact, and thereby to reduce wear during operation.

[0012] An example of known foil, of the aforementioned type, is described in document FR 2890684. This foil is made entirely of metal; it is a metal sheet folded in an appropriate manner.

[0013] An alternative to foil, described in document FR2890126, consists of introducing as a third body a non-metallic “anti-wear” film comprising resistant fibers impregnated with resin at the blade / disc contact interface.

[0014] Some of the blades are made of composite material, but their surface condition is not sufficiently flat and it is not (or very difficult) possible to machine these bearing surfaces without degrading and / or altering the fibers. The coating that protects the composite from wear is expensive, its installation range often generates non-conformities (in location) and does not completely resolve the problem of the surface condition. This leads to additional costs (repairs, in the factory, etc.).

[0015] These solutions are therefore not entirely satisfactory. Summary of the invention

[0016] An aim of the invention is to propose an alternative solution to the solutions of the state of the art, more effective than the solutions described previously, in terms of “anti-wear” performance, so as to better protect the bearing surfaces of the blades and the disc and making it possible to guarantee satisfactory flatness.

[0017] Thus, the invention seeks to propose a method for preparing a blade root for mounting a turbomachine blade made of composite material in a root support, for example a rotor disk cell in order to improve the mechanical strength of the parts under contact pressure, while allowing very easy and rapid implementation of this method.

[0018] To this end, the invention relates to a method for preparing a blade root for mounting a turbomachine blade made of composite material in a root support, characterized in that it comprises: • a first step of positioning on a side wall of the blade root an anti-wear layer comprising synthetic fibers coated or impregnated with an adhesive agent; • a second step of polymerization of the adhesive agent so that said anti-wear layer adheres to the side wall of the blade root; • a third step of machining a free external surface (of said anti-wear layer intended to be in contact with the foot support, so as to obtain a ground external surface.

[0019] Advantageously, the machining step makes it possible to reduce the thickness of the anti-wear layer so as to go from an initial thickness (e;) to a final thickness (ef), the initial thickness corresponding to the thickness of the anti-wear layer during the positioning step.

[0020] Advantageously, the initial thickness of the anti-wear layer (200) is greater than 1 millimeter. Thus, the anti-wear layer is sufficiently thick to be easily handled and has sufficient material to be ground so as to obtain a final thickness of the order of a few tenths of a millimeter.

[0021] Advantageously, the machining step is carried out by taking as the machining reference frame for the free outer surface of said anti-wear layer, the machining reference frame of the blade root.

[0022] Advantageously, the anti-wear layer comprises at least one woven ply of synthetic fibers, for example glass fibers.

[0023] Advantageously, before positioning the anti-wear layer, the synthetic fibers thereof are pre-coated with a bonding agent, on the surface or in mass.

[0024] Preferably, the adhesive agent is a thermopolymerizable glue.

[0025] Advantageously, the step of polymerizing the adhesive agent is carried out by placing the assembly comprising at least the blade root and the anti-wear layer in an autoclave brought to a temperature allowing the polymerization of the adhesive agent, for a predetermined minimum duration.

[0026] According to an alternative embodiment of the method according to the invention, the blade root may be coated with a metal foil. In this case, the anti-wear layer is positioned on a surface of the foil intended to be in contact with the root support.

[0027] The invention also relates to a method for mounting the turbomachine blade root in a root support comprising a preparation step according to the method of the invention.

[0028] The invention also relates to a method for repairing a turbomachine blade root consisting of removing, partially or totally, a damaged anti-wear member and preparing the blade root according to the method of the invention.

[0029] Thus, the preparation method according to the invention can be integrated into a method for mounting a turbomachine blade root as well as for repairing the blade root bearing surfaces.

[0030] The invention also relates to a turbomachine blade having an anti-wear member with a ground surface making it possible to be more effective than the solutions of the state of the art, in terms of “anti-wear” performance, flatness, so as to better protect the bearing surfaces of the blades and the disk.

[0031] This aim is achieved by the fact that the foot of the blade comprises at least one anti-wear layer at a bearing surface comprising synthetic fibers and having a ground outer surface. Thus, the surface condition, and in particular the flatness, of the outer surface intended to come into contact with the bearing surface of the foot support is improved and controlled.

[0032] Indeed, an improvement in the surface condition and in particular in the flatness of the bearing surfaces makes it possible to improve the mechanical strength of the interfaces with respect to the aforementioned stresses at the blade / disk interfaces.

[0033] The invention also relates to a turbomachine rotor assembly comprising a rotor disk having cells on its external periphery and a plurality of blades according to the invention fixed by their root in said cells.

[0034] The invention also relates to a turbomachine comprising a rotor assembly according to the invention.

[0035] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0036] The figures are presented for information purposes only and in no way limit the invention.

[0037] [Fig.l] represents a partial cross-sectional view of a fan blade showing the mounting of the blade root in a cell of a rotor disk, the blade being subjected to centrifugal forces.

[0038] [Fig.2] is a block diagram illustrating the main steps of the method of preparing the foot according to the invention.

[0039] [Fig.3] a schematic view in partial cross-section of the root of a fan blade according to the first step of the method according to the invention.

[0040] [Fig.4] is a schematic view in partial cross-section of the root of a fan blade according to the third step of the method according to the invention.

[0041] Unless otherwise specified, the same element appearing in different figures has a single reference. DETAILED DESCRIPTION

[0042] [Fig.l] represents a partial cross-sectional view of a fan blade 12 whose root 121 is housed in a root support, and more particularly a cell 101 of a rotor disk 10, the blade being subjected to centrifugal forces.

[0043] The invention will be described mainly by taking as an example a mounting of a fan blade in a root support formed by a fan rotor disc.

[0044] However, the present invention is not limited to fan blade assemblies in a fan rotor disc. Indeed, the invention is also applicable to other turbomachine moving blade assemblies. Thus, the invention is applicable to any composite part where flatness is important, in particular all composite parts interfacing with a metal part for which grinding is necessary.

[0045] These composite parts are formed from a woven preform which is injected with a resin. This preform can be 2D or 3D. The fan blade is manufactured from a 3D woven preform.

[0046] In a complementary manner, the present invention applies to fixed blades and associated supports, such as casings or flanges supporting fixed blades.

[0047] Conventionally, a mobile fan blade 12 is formed by two assemblies: a lower part called the root 121, an upper part formed by the blade (not shown).

[0048] The movable fan blade 12 extends along a longitudinal axis Z. It will be noted that the longitudinal axis Z of the movable fan blade 12 is perpendicular to the axis of rotation of the fan.

[0049] Each cell 101 of the rotor disk 10 has a shape substantially complementary to the shape of the root 121 of the blade 12 to form a dovetail type assembly.

[0050] The cells 101 are distributed radially equidistantly along the entire circumference of the rotor disk 10, and the opening of the cell is directed towards the outside.

[0051] As can be seen in [Fig. 1] showing an enlarged portion of the cross-section of the rotor disk 10, i.e. a section orthogonal to the axis of rotation of the fan, each root 121 of a blade 12 has a symmetrical contour with two side walls 122, forming the sides of the root 121, diverging from each other from the body of the blade 12 in the direction of the free end of the root 121 of the blade 12, up to a bottom wall 124 substantially parallel to the axis of rotation of the fan and to the periphery of the rotor disk 10, and orthogonal to the main longitudinal direction Z of the corresponding blade 12.

[0052] The cells 101 have a similar shape with side walls 102 inclined outwardly from the circumference towards the inner portion of the rotor disc 10 to a bottom wall 104.

[0053] The dimensions of the root 121 of the blade 12 and of the cell 101 are such that when the rotor disk 10 is at rest, the root 121 is retained in the cell 101, the bottom wall 124 of the root 121 then being able to touch the bottom wall 104 of the cell 101. To avoid too great a degree of freedom in the radial displacement of the blade, a shim may be present.

[0054] When the rotor disk 10 is operational during operation of the turbomachine, the rotation of the rotor disk 10 about the central axis causes the blades 12 to move radially outwards due to centrifugal forces, i.e. in the direction of the arrow 13 of [Fig. 1], substantially parallel to the longitudinal axis Z of the blade 12. At this moment, the side walls 122 of the root 121 of the blade 12 are in abutment against the side walls 102 of the cell 101, which makes it possible to ensure the retention of the blade 12 inside the cell 101, i.e. its connection with the rotor disk 10.

[0055] At each modification of the rotation speed of the rotor disk 10, the sliding movement of the root 121 of the blade 12 combined with the contact pressure of the root 121 and the coefficient of friction between the materials of the blade 12 and the disk 10, generate shear forces both on the rotor disk 10 and on the blade 12, one moving radially relative to the other by 1 to a few millimeters.

[0056] In particular, as is apparent from [Fig. 1], there exists in operation an interface zone called “span” subjected to significant forces, designated by the reference sign 14, between the lateral wall 122 of the foot 121 and the lateral wall 102 of the cell 101, as well as a non-contact region indicated under the reference sign 16, which is not subject to any mechanical contact stress during the rotation of the rotor disk 10.

[0057] According to the invention, the fatigue and wear deteriorations which occur on the contacting surfaces of the side walls 102 and 122 due to the relative movement between the root 121 of the blade 12 and the cell 101 of the rotor 10 are reduced by the use of a ground anti-wear layer 200, positioned at the bearing surfaces 14 between the side wall 122 of the root 121 and the side wall 102 of the cell 101.

[0058] More specifically, the anti-wear layer 200 is composed of synthetic fibers. For example, the anti-wear layer 200 is composed of at least one fabric of synthetic fibers.

[0059] By way of example, the anti-wear layer 200 is composed of at least one fabric made from glass fibers and / or aramid fibers.

[0060] This anti-wear layer 200 adheres to the outer surface of the foot 121 with a bonding agent coating or impregnating the synthetic fibers of the layer 200, at least on the face of the layer 200 which is to adhere.

[0061] The adhesive agent is, for example, a thermopolymerizable synthetic glue.

[0062] The adhesive agent is for example a resin and advantageously a phenolic resin. or polyurethane.

[0063] As visible in [Fig. 3], the anti-wear layer 200 has a first outer face 210a and a second inner face 220 intended to be bonded to a side wall 122 of the foot 121.

[0064] This anti-wear layer 200 has a significant initial thickness e; greater than 1 millimeter, and advantageously of the order of 2 millimeters. The thickness e;, called initial, of the anti-wear layer 200 corresponds to its thickness during manufacture and during bonding to the root 121 of the blade 12.

[0065] During a first step 310 of the preparation method 300, the main steps of which are illustrated in [Fig. 2], an anti-wear layer 200 is positioned on each side wall of the foot 121 at the level of the bearing surfaces 14, as illustrated in [Fig. 3].

[0066] This anti-wear layer 200 adheres to the outer surface of the foot 121 via the adhesive agent coating or impregnating the synthetic fibers of the layer 200.

[0067] According to an alternative embodiment, it is also possible to impregnate directly (i.e. the anti-wear layer is not pre-impregnated before its positioning), or in a complementary manner, the synthetic fibers of the anti-wear layer 200 when the latter is in position on the foot 121. In this case, the impregnation is carried out at the same time as the injection of the preform of the blade.

[0068] A second step 320 consists of polymerizing the adhesive agent. In this second step 320, the assembly formed by the root 121 of the blade 12 and the anti-wear layer 200 is pressurized with the adhesive agent until the adhesive agent polymerizes.

[0069] The pressure used is of the order of 7 to 14 MPa. This ensures good adhesion of the glue over the entire surface as well as the evacuation of solvents.

[0070] The polymerization is carried out, for example, at a temperature between 150°C and 180°C for a period of 1 hour.

[0071] This gives a thick anti-wear layer 200, of thickness e;, adhering perfectly to the side wall 122 of the foot 121.

[0072] At this stage of the preparation process, the thickness e; of the anti-wear layer 200 is greater than the operating and mounting clearance between the foot 121 and the cell 101, so that mounting as is is not possible.

[0073] It can also be noted that following this polymerization step illustrated schematically in [Fig. 3], the surface condition and in particular the flatness of the outer face 210a is substantially identical to the surface condition of the side wall 122 of the foot 121. At this stage, the surface condition of the anti-wear layer 200 has flatness defects.

[0074] After the polymerization step 320, the root 121 of the blade 12 can be cleaned to remove excess adhesive agent that has flowed, for example by sandblasting with glass beads.

[0075] In a third step 330, the outer face 210a of the anti-wear layer 200 bonded to the root 121 of the blade 12 is machined. The machining makes it possible to reduce the thickness of the anti-wear layer 200 and to grind the outer face 210a so as to obtain a flat ground outer face 210b as illustrated in [Fig.4]. This machining step makes it possible to control the final thickness ef of the anti-wear layer 200 and to improve the surface condition as well as the flatness tolerances of the outer surface 210b.

[0076] After machining, the anti-wear layer 200 has a final thickness ef of the order of a few tenths of a millimeter, advantageously of the order of 0.3 millimeters.

[0077] The machining of the outer face 210a of the anti-wear layer 200 is carried out by taking as a reference the machining reference of the lateral faces 122 of the root 121 of the blade 12, which makes it possible to control the orientation and the thickness of the anti-wear layer 200. This ensures better positioning of the root 121 of the blade 12 in the cell 101 of the rotor disk 10, as well as better distribution of the stresses.

[0078] Thus, thanks to such a method of preparing the blade roots before assembly, it is possible to significantly increase the service life of the interfaces between the roots 121 of the blade 12 and the cells 101 of the rotor disk 10, in particular by a better distribution of forces over the entire surface of the anti-wear layer 200.

[0079] The preparation method 300 described above can be integrated into a method for manufacturing a turbomachine blade.

[0080] The preparation method 300 described above can also be integrated into a more global method of mounting a blade 12 in a rotor disk 10 or even a rotor assembly.

[0081] The preparation method 300 described above can also be integrated into a more global method of repairing an anti-wear member at the junction between the blade root and the cell, whether the initial assembly was carried out in accordance with the invention or with another type of anti-wear member, whether metallic or non-metallic.

Claims

Claims

1. Method for preparing (300) a blade (12) root (121) for mounting a turbomachine blade (12) made of composite material in a root support (10) comprising: - a first step (310) of positioning on a side wall (122) of the blade (12) root (121) an anti-wear layer (220) comprising synthetic fibers coated or impregnated with an adhesive agent; - a second step (320) of polymerizing the adhesive agent so that said anti-wear layer (200) adheres to the side wall (122) of the blade (12) root (121); - characterized in that it comprises a third step (330) of machining a free external surface (210a) of said anti-wear layer intended to be in contact with the foot support (10), so as to obtain a ground external surface (210b).

2. Method for preparing (300) a blade (12) root (121) for mounting a turbomachine blade (12) made of composite material in a root support (10) according to the preceding claim, characterized in that the third machining step (330) reduces the thickness of the anti-wear layer (200) so as to go from an initial thickness (e;) to a final thickness (ef), the initial thickness (e;) of the anti-wear layer (200) corresponding to the thickness of the anti-wear layer during the positioning step (310).

3. Method for preparing (300) a blade (12) root (121) for mounting a turbomachine blade (12) made of composite material in a root support (10) according to the preceding claim, characterized in that the initial thickness (e;) of the anti-wear layer (200) is greater than 1 millimeter.

4. Method for preparing (200) a root (121) of a blade (12) for mounting a turbomachine blade (12) made of composite material in a root support (10) according to one of the preceding claims, characterized in that the third machining step (330) is carried out by taking as the machining reference frame of the free outer surface (210a) of said anti-wear layer, the machining reference frame of the root (121) of the blade (12).

5. Method for preparing (200) a blade (12) root (121) for mounting a turbomachine blade (12) made of composite material in a root support (10) according to one of the preceding claims, characterized in that the anti-wear layer (200) comprises at least one woven ply of synthetic fibers.

6. Method for preparing (300) a blade (12) root (121) for mounting a turbomachine blade (12) made of composite material in a root support (10) according to one of the preceding claims, characterized in that the anti-wear layer (200) comprises at least one woven ply of glass fibers.

7. Method for repairing a turbine engine blade (12) root (121) made of composite material, consisting of removing, partially or totally, a damaged anti-wear member and preparing the blade root according to the preparation method (300) according to one of claims 1 to 6.

8. Turbomachine blade (12) made of composite material comprising a root (121) prepared according to the preparation method (300) according to one of claims 1 to 7, characterized in that the root (121) comprises at a side wall (122) an anti-wear layer (200) comprising synthetic fibers and a polymerized adhesive agent and having a ground outer surface, obtained by machining a free outer surface of the anti-wear layer.

Images