Labyrinth-type sealing device for a turbomachine comprising a retouch layer made of ceramic material

Abstract

The present invention relates to a labyrinth-type sealing device (1) for a turbomachine (10), in particular of an aircraft, comprising annular elements engaged one inside the other, one of these elements being an internal element (2) and the other of these elements being an external element, at least one of these internal and external elements being mobile in rotation about an axis of rotation (X) and comprising a plurality of rubbing strips (5) extending about the axis (X), each of the strips (5) comprising an abrasive coating (52), wherein the abrasive coating (52) comprises at least one deteriorated zone filled with at least one retouch layer (54) comprising a ceramic material.

Description

[0001]DESCRIPTION TITLE: LABYRINTH SEALING DEVICE FOR A TURBOMACHINE COMPRISING A RETOUCHING LAYER MADE OF CERAMIC MATERIAL Technical field of the invention The field of the present invention is that of turbomachines, in particular aircraft. The present invention relates more particularly to a labyrinth sealing device for a turbomachine and a method for maintaining this sealing device. Technical background The state of the art includes in particular documents CA-C-2567888, EP-A1-2143821 and FR-A1-3081498. A turbomachine, in particular an aircraft, comprises, from upstream to downstream, a fan, a low pressure (LP) compressor, a high pressure (HP) compressor, a combustion chamber, a high pressure (HP) turbine and a low pressure (LP) turbine. The LP or HP compressor and / or the LP or HP turbine comprises several stages each comprising a rotor (such as an axial wheel, impeller, centripetal wheel,etc.) provided with blades and a stator (rectifier or distributor). The rotor itself consists, in the case of an axial wheel, of a massive axisymmetric part (the disc), on which are attached (except in the case of a disc with single-piece blades or a centrifugal element) blades whose purpose is to compress or expand the flow gases. For example, and not limited to, in the case of the HP turbine, the performance and cooling of the turbine depend, among other things, on the ability to seal certain cooling air ventilation circuits. Thus, static sealing devices can be put in place to ensure proper cooling (such as gaskets, slats, tabs, etc.). In addition,it is necessary to put in place dynamic sealing devices between the rotating elements (called rotors) and static elements (called stators); these devices are commonly called "labyrinths". Such a sealing device makes it possible to control the flow of gas or air or fluid passing axially through the annular space located between the internal periphery of the stator and the external periphery of the turbine rotor. Generally speaking, the sealing device may further comprise an abradable part carried in particular by the stator, opposite a plurality of annular wipers (or in other words blades, grooves, teeth, threads or projections) perpendicular to an axis of rotation X and carried in particular by the rotor. The annular wipers are kept at a short radial distance from the abradable part,such that any flow of fluid or air from the overpressure zone on one side of the wipers to the lower pressure zone on the other side of the wipers is as small as possible. Thus, during rotation of the turbine rotor around the X axis, the annular wipers are rotated while maintaining as little clearance as possible with the abradable part. With reference to Figure 1, the wipers 5 of the rotor 2 of such a sealing device 1 are each coated with an abrasive coating 52 to promote in particular contact between the rotor and the stator. The abrasive coating is generally deposited on each wiper by thermal spraying. However, this abrasive coating may be damaged during the manufacture or handling of the rotor made up of these wipers, and / or during operation in the turbomachine. When a so-called damaged area D of the wiper 5 is damaged (Figures 1 and 2),the conventional procedure can be either the scrapping or the total reconditioning of the rotor 2. The total reconditioning of the rotor 2 consists of carrying out operations of stripping the wipers 5 by removing all of the abrasive coating 52 initially deposited and a new operation of thermal projection of a new abrasive coating 52 on these stripped wipers 5. This can therefore generate additional costs and significant delays in manufacturing and delivering the rotors of the sealing device. In this context, it is interesting to overcome at least certain drawbacks of the prior art by proposing a reliable labyrinth-type sealing device with an improved service life, while simplifying its maintenance and repair. Summary of the invention The present invention aims to overcome one or more drawbacks of the prior art by proposing a solution which is simple,efficient and economical. The invention thus proposes a labyrinth-type sealing device for a turbomachine, in particular an aircraft, comprising annular elements engaged one inside the other, one of these elements being an internal element and the other of these elements being an external element, at least one of these internal and external elements being movable in rotation about an axis of rotation X and comprising a plurality of wipers extending about the axis X, each of the wipers comprising an abrasive coating. According to the invention, the abrasive coating comprises at least one damaged area filled with at least one retouching layer comprising a ceramic material. Thus, this solution makes it possible to achieve the aforementioned objective. In particular,the abrasive coating with one or more damaged areas can be repaired quickly and efficiently by applying one or more so-called touch-up layers. Each touch-up layer completely covers the damaged area so as to protect both the abrasive coating and the lip of the sealing device. This touch-up layer is based on ceramic material to form, in particular, an adhesive that adheres easily to the abrasive coating. The ceramic material has suitable and advantageous physicochemical properties for the lips of the sealing device. Indeed, it makes it possible, on the one hand, to reinforce the resistance to corrosion and wear, and on the other hand, to obtain a uniform, smooth surface and therefore without surface defects (such as cracks, flaking, roughness, etc.) of the lips. Thus, the proposed solution makes it possible to globally optimize the service life of the sealing device. Furthermore,the proposed solution contributes significantly to limiting environmental impacts, particularly for these repair applications, by avoiding the scrapping of damaged or worn parts by allowing them to be repaired by adding the touch-up layer locally, thus helping to reduce the environmental impact. This also makes it possible to reduce the additional costs and time associated with a complete reconditioning of the sealing device having one or more damaged areas. The invention therefore has the advantage of being based on a simple design, offering very high reliability, and with little penalty in terms of costs and size. The term "damaged area" means a portion damaged by an impact originating during the manufacture, handling or operation of the part. This damaged portion may be a chip or a split (or crack, groove,etc.) of variable shape and size depending on the impact. The abrasive coating is thus absent in this damaged portion. The term "filled" means the damaged area of ​​the invention which is entirely (either totally or 100%) occupied by the retouching layer, without empty or unoccupied space or area in this damaged area. The term "ceramic" means a material having a vitreous or non-vitreous body, of crystalline or partially crystalline structure, or of glass, the body of which is formed of essentially inorganic and non-metallic substances, and which is formed by a molten mass which solidifies upon cooling, or which is formed and brought to maturity, at the same time or subsequently, by the action of heat. The sealing device according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another: - said abrasive coating is based on alumina,such as Yttria-containing zirconia; -- said abrasive coating is based on Yttria-containing zirconia; - said ceramic material comprises between 50 and 100% ceramic; - said ceramic material is in the form of a ceramic cement; - said ceramic material is in the form of a ceramic slip; - said ceramic slip comprises an alumina powder of between 60 and 70%, a dispersing agent of between 1 and 5% and water of between 25 and 39%; - the alumina powder has a particle size of between 0.1 and 0.60 µm, preferably the particle size is 0.1 and 0.45 µm; - the at least one deteriorated zone has a maximum depth of approximately 0.50 mm; - the at least one damaged area has a maximum transverse dimension of approximately 0.20 mm, for example this maximum transverse dimension is approximately 0.10 mm; -- each wiper comprises a body made of metallic material, such as titanium, or of metallic alloy,such as nickel, cobalt and / or titanium-based alloy; -- the abrasive coating is made of aluminum oxide (Al2O3), titanium dioxide (Al2O3-TiO2) or zirconium oxide (ZrO2) stabilized for example with Yttrium; - the sealing device comprises at least one sub-layer interposed between the abrasive coating and the plurality of wipers; -- the sub-layer is made of a metal alloy, such as aluminum nickel alloy (NiAl), aluminum nickel-chromium alloy (NiCrAl) or aluminum nickel-chromium-yttrium alloy (NiCrAlY); -- said ceramic slip comprises an alumina powder of between 20 and 100 g, a dispersing agent of between 1 and 10 g and water of between 10 and 50 g; -- said ceramic slip comprises an alumina powder of between 30 and 50 g,a dispersing agent of between 1 and 5 g and water of between 10 and 25 g. The invention further relates to an aircraft turbomachine comprising at least one sealing device according to one of the features of the invention, in which the internal and external elements are, respectively, a rotor and a stator of the turbomachine. For example, the internal element comprises the plurality of wipers. The turbomachine may be a turboprop, a turbojet or a turboshaft engine. The invention also provides a method for maintaining at least one labyrinth-type sealing device so as to obtain a sealing device according to one of the features of the invention. The method comprises a repair step comprising a sub-step of depositing (i) the at least one retouching layer comprising the ceramic material on said at least one damaged area of ​​the abrasive coating of the plurality of wipers,so as to fill this damaged area. The maintenance method according to the invention may comprise one or more of the following features, taken in isolation from one another or in combination with one another: - the repair step comprises a sub-step of drying (ii) said at least one retouching layer deposited on the at least one damaged area, for a minimum duration of one hour at room temperature; - the repair step comprises a sub-step of baking (iii) said at least one retouching layer deposited on the at least one damaged area at a maximum temperature of 400°C; - the deposition sub-step (i) is carried out by a tool, such as a brush or an airbrush; -- the repair step may comprise a sub-step of machining or polishing said at least one retouching layer,for example after the drying and baking sub-step(s). Brief description of the figures The invention will be better understood and other details, characteristics and advantages of the invention will appear more clearly on reading the following description given by way of non-limiting example and with reference to the appended drawings in which: Figure 1 is a partial axial sectional view schematically representing wipers of a sealing device according to the prior art, Figure 2 is an enlarged view of a damaged area of ​​the wiper of Figure 1, Figure 3 is a schematic half axial sectional view of a sealing device of the invention, Figure 4 is a partial axial sectional view schematically representing wipers of the sealing device of Figure 3 comprising a damaged area filled with a retouching layer,Figure 5 is an enlarged view showing a planar test specimen of one of the wipers of Figure 4 comprising a first example of the retouching layer, Figure 6 is an enlarged view showing a planar test specimen of one of the wipers of Figure 4 comprising a second example of the retouching layer, Figure 7 schematically represents in blocks the steps of a maintenance method so as to obtain the sealing device of Figure 4, Figure 8 is a schematic view of a repair step of the maintenance method of Figure 7. The elements having the same functions in the different implementations have the same references in the figures. Detailed description of the invention By convention, in the description below,the terms "longitudinal" and "axial" describe the orientation of structural elements extending in the direction of a longitudinal axis (such as a turbomachine). The terms "radial" or "vertical" describe an orientation of structural elements extending in a direction perpendicular to the longitudinal axis. The terms "inner" and "outer", and "internal" and "external" are used in reference to a positioning relative to the longitudinal axis. Thus, a structural element extending along the longitudinal axis has an inner face facing the longitudinal axis and an outer surface, opposite its inner surface. Similarly,the terms “upstream” and “downstream” are defined with respect to the direction of circulation of the gases in the aircraft propulsion unit. Figures 1 and 2 have been described in the technical background of the present application and illustrate a sealing device according to the prior art. The invention can be applied in a non-limiting manner to a turbomachine 10, in particular an aircraft one. The turbomachine 10 can be a turbojet, turboshaft or turboprop. As described above, one of the modules of the turbomachine 10 chosen from an LP compressor, an HP compressor, an LP turbine and an HP turbine can comprise several stages each comprising a rotor provided with blades and a stator. The turbomachine 10 can comprise at least one labyrinth-type sealing device 1. This sealing device can be placed in the HP turbine for example,to control the flow of gas or air or fluid passing axially through the annular space located between the inner periphery of a stator and the outer periphery of a rotor of the HP turbine. The sealing device 1 according to one or more embodiments of the invention is illustrated schematically and non-limitingly in Figures 3 to 6. With reference to Figure 3, the labyrinth-type sealing device 1 comprises two annular elements 2, 3 engaged one inside the other. In particular, an annular element 2 called internal is engaged, in a manner capable of moving in rotation about an axis of rotation X, inside an annular element 3 called external. This axis X may be substantially parallel and / or identical to a longitudinal axis of the turbomachine 10. In the example of Figure 3 and in a non-limiting manner, the internal annular element 2 may be a rotor (such as the rotor of the HP turbine of the turbomachine 10),and the outer annular element 3 may be a stator (such as the stator of the HP turbine of the turbomachine 10). In a variant not illustrated in the figures, the inner 2 and outer 3 annular elements may be two rotors of a rotating machine. The outer annular element 3 may comprise an abradable part 4. The inner annular element 2 may comprise a plurality of wipers 5. The wipers 5 extend around the axis X. These wipers 5 may be opposite the abradable part 4 and they may be kept at a short radial distance (relative to the axis X) from this abradable part 4, such that any flow f of fluid or air from an overpressure zone on one side of the wipers to a lower pressure zone on the other side of the wipers is as small as possible. Thus, during rotation of the inner annular element 2,the wipers 5 are driven in rotation while maintaining as little play as possible with the abradable part 4. The wipers 5 may be carried by a base body 50, in particular of the internal annular element 2. For example, the wipers 5 and in particular their bodies 50 may be made of metallic material (such as titanium) or of metallic alloy (such as an alloy based on nickel, cobalt and / or titanium). The wipers 5 may be of helical shape with various thread profiles in cross section, such as triangular, conical, trapezoidal, etc. Each of the wipers 5 comprises an abrasive coating 52. In particular, the body 50 of the wipers 5 may be covered with the abrasive coating 52. The abrasive coating 52 may be based on alumina (also referred to as aluminum oxide (Al2O3)), such as Yttria-containing zirconia, or any other metal oxide. The abrasive coating 52 may be based on Yttria-containing zirconia. For example,the abrasive coating 52 may be made of alumina (Al2O3), titanium dioxide (Al2O3-TiO2) or zirconium oxide (ZrO2) stabilized for example with Yttrium (also known as Yttrium zirconia). The abrasive coating 52 may be deposited by thermal spraying on the body 50 of the wipers 5. Advantageously, at least one sub-layer 51 may be interposed between the abrasive coating 52 and the plurality of wipers 5 (in particular of the body 50). This sub-layer 51 may be made of a metal alloy, such as an aluminum nickel alloy (NiAl), aluminum nickel-chromium alloy (NiCrAl) or aluminum nickel-chromium-yttrium alloy (NiCrAlY). This underlayer makes it possible in particular to facilitate the adhesion and the bond between the abrasive coating 52 and the wipers 5. As described above, the abrasive coating 52 may comprise at least one deteriorated zone D (FIGS. 1 and 2). The deteriorated zone D may have a first maximum depth ED of approximately 0.50 mm. The first depth ED may be measured in a radial direction relative to the X axis. The deteriorated area D may have a first maximum transverse dimension (such as a length) LD of approximately 0.20 mm. This first maximum transverse dimension LD may be measured in a direction transverse to the X axis. For example, the first maximum transverse dimension LD is approximately 0.10 mm. One of the features of the invention is that this deteriorated area D may be filled with at least one retouching layer 54, as illustrated in FIG. 4. This retouching layer 54 comprises (or consists of) a ceramic material. The retouching layer 54 may thus completely fill and cover the deteriorated area D,without empty or unoccupied space or area in this deteriorated area D. The retouching layer 54 may have a second maximum depth E54 measured in a radial direction relative to the X axis. The first and second depths ED, E54 may be identical. The second maximum depth E54 may be approximately 0.50 mm. The retouching layer 54 may have a second maximum transverse dimension (such as a length) L54 measured in a direction transverse to the X axis. The first and second transverse dimensions LD, L54 may be identical. The second maximum transverse dimension L54 may be approximately 0.20 mm, for example the second maximum transverse dimension L54 may be approximately 0,10 mm. The ceramic material of the retouching layer 54 may comprise between 50% and 100% ceramic. The advantages of the ceramic material are, for example, that it can be used at a maximum temperature of approximately 1300°C and it can have a minimum adhesive strength of approximately 15 MPa. Furthermore, the ceramic material may have physicochemical properties that are almost equivalent to those of the abrasive coating 52. The ceramic material may be in the form of a ceramic slip or a ceramic cement. The slip and / or the cement may generally form an adhesive (in particular ceramic) so as to bond the retouching layer 54 to the abrasive coating 52. According to a first exemplary embodiment of the retouching layer 54 of the invention, the ceramic material is in the form of ceramic cement. The term “cement” is understood to mean a composition essentially of powdered material (such as ceramic,in particular metal oxide (such as alumina Al2O3, Alumino-silicate or other ceramic), in particular more than 80% or 100% of this powdery material. The ceramic cement may comprise an alumina powder of between 80 and 100%. Figure 5 illustrates in a non-limiting manner a test specimen representing one of the lips 5 of the sealing device 1 comprising the touch-up layer 54 according to the first embodiment. The adhesion of this touch-up layer 54 in the form of ceramic cement was measured at approximately 30 MPa. In a non-limiting manner, this adhesion measurement can be obtained according to the ASTM C633 standard. This ASTM C633 standard makes it possible to determine the adhesion or cohesion force of a thermal projection by subjecting it to a tension perpendicular to the surface of the test specimen. According to a second exemplary embodiment of the retouching layer 54 of the invention,the ceramic material is in the form of ceramic slip. The term "slip" means a mixture of a powdered solid component (such as ceramic, in particular metal oxide (such as alumina Al2O3 or other ceramic)) in a liquid component (such as water), and possibly other components. For example, slip differs from cement in that it is fired to form cement. Indeed, the formation of slip may involve drying at room temperature (for example around 25°C) or sintering at a temperature above 750°C, whereas the formation of cement may require firing, in particular at a temperature, called moderate,less than or equal to 400°C. Figure 6 illustrates in a non-limiting manner a test specimen representing one of the lips 5 of the sealing device 1 comprising the retouching layer 54 according to the second embodiment. The adhesion of this retouching layer 54 in the form of ceramic slip was measured at approximately 16 MPa. The ceramic slip may comprise an alumina powder, water and a dispersing agent. The proportion by total weight of the alumina powder may be between 60 and 70%, of the dispersing agent may be between 1 and 5% and of the water may be between 25 and 39%. Preferably, the ceramic slip may comprise an alumina powder of between 20 and 100 g, a dispersing agent of between 1 and 10 g and water of between 10 and 50 g. Even more preferably, the ceramic slip may comprise an alumina powder of between 30 and 50 g,a dispersing agent of between 1 and 5 g and water of between 10 and 25 g. The alumina powder may have a particle size of between 0.1 and 0.60 µm. Preferably, the particle size of the alumina powder may be between 0.1 and 0.45 µm. In a non-limiting manner, this particle size may be measured according to the ISO 13320 standard. This ISO 13320 standard makes it possible to determine particles (in particular alumina powder) by analyzing their light scattering properties. In a variant, the alumina powder in the slip or cement may be replaced by another ceramic (such as zirconia ZrO2). The dispersing agent may be Darvan, ® . The Darvan ®may comprise ammonium polymethacrylate. With reference to Figures 7 and 8, the present application will now describe a method for maintaining the sealing device 1 comprising the at least one damaged area D, so as to obtain the labyrinth-type sealing device 1 of the invention (i.e. with the at least one damaged area D filled with the at least one retouching layer 54). Such a maintenance method comprises a repair step in particular of the sealing device 1 comprising the damaged area(s) D. The different sub-steps of the repair step are summarized in Figure 7. In particular, the repair step comprises a sub-step of depositing (i) the retouching layer 54 comprising the ceramic material on the damaged area D of the abrasive coating 52 of the plurality of wipers 5, so as to fill this damaged area D.The deposition sub-step (i) can be carried out by a tool O, such as a brush (figure 8), an airbrush or any other tool allowing the damaged area D to be covered uniformly and without surface defects (such as cracks). The repair step can comprise a drying sub-step (ii) of the retouching layer 54 deposited on the damaged area D, for a minimum duration of one hour at room temperature. The room temperature can be approximately 25°C. For example, the retouching layer 54 of the second embodiment (i.e. in the form of ceramic slip) can be applied to the damaged area D of the lips 5 by the brush, then this retouching layer 54 can be dried at room temperature for at least 1 hour 30 minutes. The repair step may comprise a sub-step of baking (iii) the retouching layer 54 deposited on the damaged area D at a maximum temperature of 400°C.By way of example, the retouching layer 54 of the first embodiment (i.e. in the form of ceramic cement) can be applied to the damaged area D of the lips 5, then this retouching layer 54 can be heated to 200°C, for example, in an oven. The drying sub-step (ii) can be carried out before the firing sub-step (iii). The repair step can further comprise a finalization sub-step (iv) consisting of polishing or machining the retouching layer 54 so as to obtain a smooth and uniform surface. This optional step (iv) is shown in dotted lines in FIG. 7 and can be carried out after the drying (ii) and firing (iii) sub-step(s).

Claims

CLAIMS 1. Labyrinth-type sealing device (1) for a turbomachine (10), in particular an aircraft, comprising annular elements (2, 3) engaged one inside the other, one of these elements being an internal element (2) and the other of these elements being an external element (3), at least one of these internal and external elements (2, 3) being rotatable about an axis of rotation (X) and comprising a plurality of wipers (5) extending about the axis (X), each of the wipers (5) comprising an abrasive coating (52), characterized in that the abrasive coating (52) comprises at least one damaged zone (D) filled with at least one retouching layer (54) comprising a ceramic material.

2. Sealing device according to claim 1, characterized in that said abrasive coating (52) is based on alumina, such as Yttria zirconia. 3.Sealing device according to claim 1 or 2, characterized in that said ceramic material comprises between 50 and 100% ceramic.

4. Sealing device according to any one of the preceding claims, characterized in that said ceramic material is in the form of a ceramic cement.

5. Sealing device according to any one of claims 1 to 3, characterized in that said ceramic material is in the form of a ceramic slip.

6. Sealing device according to the preceding claim, characterized in that said ceramic slip comprises an alumina powder of between 60 and 70%, a dispersing agent of between 1 and 5% and water of between 25 and 39%.

7. Sealing device according to the preceding claim, characterized in that the alumina powder has a particle size of between 0.1 and 0.60 µm, preferably the particle size is 0.1 and 0.45 µm.

8. Sealing device according to any one of the preceding claims, characterized in that the at least one deteriorated zone (D) has a maximum depth (ED) of approximately 0.50 mm.

9. Sealing device according to any one of the preceding claims, characterized in that the at least one deteriorated zone (D) has a maximum transverse dimension (LD) of approximately 0.20 mm, for example this maximum transverse dimension (LD) is approximately 0.10 mm.

10. Sealing device according to any one of the preceding claims, characterized in that the sealing device (1) comprises at least one sub-layer (51) interposed between the abrasive coating (52) and the plurality of wipers (5). 11.Aircraft turbomachine (10) comprising at least one sealing device (1) according to any one of the preceding claims, wherein the internal (2) and external (3) elements are, respectively, a rotor and a stator of the turbomachine, for example the internal element (2) comprises the plurality of wipers (5).

12. Method for maintaining at least one labyrinth-type sealing device (1) so as to obtain a sealing device (1) according to any one of claims 1 to 10, characterized in that the method comprises a repair step comprising a sub-step of depositing (i) the at least one retouching layer (54) comprising the ceramic material on said at least one damaged area (D) of the abrasive coating (52) of the plurality of wipers (5), so as to fill this damaged area (D). 13.Maintenance method according to the preceding claim, characterized in that the repair step comprises a sub-step (ii) of drying said at least one retouching layer (54) deposited on the at least one damaged area (D), for a minimum duration of one hour at room temperature.

14. Maintenance method according to claim 12 or 13, characterized in that the repair step comprises a sub-step (iii) of baking. said at least one retouching layer (54) deposited on the at least one damaged area (D) at a maximum temperature of 400°C.

15. Maintenance method according to any one of claims 12 to 14, characterized in that the deposition sub-step (i) is carried out by a tool (O), such as a brush or an airbrush.

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