EP3717749B1 - Assembly for axial turbomachine, associated assembly method and seals - Google Patents

Description

Technical area

The invention relates to an assembly for an axial turbomachine, to a method of assembling an assembly for a turbomachine and to a seal for a mounting platform for the stator blade of an axial turbomachine.

Prior art

The document EP 2 930 308 A1 describes a turbomachine compressor in which the wall of the casing is made of a composite material and has, on its internal surface, flat facets for securing the stator vanes. To this end, the blades are provided with platforms arranged at the outer radial end of each blade, each of the platforms coming into contact with a facet. This makes it possible to reduce the stress concentrations between the wall of the casing and the blades. A layer of abradable material is provided on the internal face of the wall of the housing. This abradable layer is placed at the junction of the platforms and ensures the continuity of the guiding surface of the air flow. However, it appears that this arrangement is insufficient to ensure the tightness of the flow, and in particular air leaks may appear under certain pressure and temperature conditions, between the platforms and the wall of the casing. This mainly impacts the efficiency of the turbomachine and can affect the durability of the mechanical strength of the blade attachment.

Summary of the invention Technical problem

The object of the invention is to solve at least one of the problems posed by the prior art. More precisely, the object of the invention is to increase the efficiency of the turbomachine and to ensure the reliability of the attachment of the blades to the casing.

Technical solution

The invention relates to an assembly for an axial turbomachine, in particular an aircraft turbojet, the assembly comprising: an annular casing with an internal surface; an annular row of stator vanes with at least one stator vane comprising a blade extending radially from a fixing platform, said fixing platform being fixed to the housing and having a polygonal outline; remarkable in that it further comprises a seal formed by an element distinct from the casing and distinct from the fixing platform, and comprising a frame the outline of which follows the polygonal outline of the fixing platform, said frame being in radial contact of the fixing platform and the casing in order to ensure a seal.

According to an advantageous embodiment of the invention, the frame sealingly delimits a pocket radially between the fixing platform and the casing, said pocket extending in particular over the majority of the fixing platform.

According to an advantageous embodiment of the invention, the frame is formed of bars running along the sides of the platform.

According to an advantageous embodiment of the invention, the frame of the seal has a general exterior shape in parallelogram and preferably rectangular.

According to an advantageous embodiment of the invention, the platform has a fixing pin which passes through an orifice in the casing, and in that the fixing pin passes through the seal.

According to an advantageous embodiment of the invention, a portion of the seal is O-ring or cylindrical, and surrounds the fixing axis.

According to an advantageous embodiment of the invention, segments connect the toric or cylindrical portion to the frame.

According to an advantageous embodiment of the invention, the segments comprise two circumferential segments oriented in the circumferential direction of the turbomachine and at least one axial segment oriented in the axial direction of the turbomachine.

According to an advantageous embodiment of the invention, the toric or cylindrical portion is enclosed in the upstream half of the seal.

According to an advantageous embodiment of the invention, the seal comprises a downstream reinforcing tongue, preferably extending mainly in the circumferential direction of the turbomachine.

According to an advantageous embodiment of the invention, the seal is interposed between the casing and several adjacent blade platforms, said seal following the polygonal contours of each of said several platforms. adjacent vanes. For example, several adjacent pairs of platforms and facets can share the same joint.

According to an advantageous embodiment of the invention, the internal surface of the casing comprises an annular row of facets receiving the stator vanes, an external radial surface of the platform being inclined with respect to the associated facet and / or the radial thickness of the seal is more important downstream than upstream. Due to the non-direct contact between the two respective surfaces of the platform and of the facet, they may not be parallel because they are not resting on one another. Thus, it is possible, but not essential, for the seal to have a greater thickness downstream than upstream, that is to say at the place where the pressure of the air flow is greatest.

According to an advantageous embodiment of the invention, a layer of abradable material is provided on the internal face of the casing, in particular upstream and / or downstream of the facets, and at a distance axially from the platforms and / or from the seal.

The subject of the invention is also a method of assembling an assembly for a turbomachine, remarkable in that the assembly is one of the embodiments described above and in that the method comprises a step (a) of placing the seal between the casing and the blade platform, and a step (b) of fixing the blade to the casing during which the seal is compressed radially between the platform of the blade and the casing.

According to an advantageous embodiment of the invention, the seal is more compressed downstream than upstream.

According to an advantageous embodiment of the invention, the fixing step (b) comprises the tightening of a nut on the fixing axis so as to compress the seal.

Thus, the invention also relates to a seal for a fixing platform for the stator blade of an axial turbomachine, in particular of an aircraft turbojet, said fixing platform having a polygonal outline, the seal comprising: a frame of which the outline is able to match the polygonal outline of the fixing platform, and of the thermoformed studs.

According to an advantageous embodiment of the invention, the studs are inserts for molding the seal.

According to an advantageous embodiment of the invention, the studs comprise holes, preferably opening, able to cooperate with pins provided on the platform.

The invention also relates to a seal for an axial turbomachine stator blade fixing platform, in particular for an aircraft turbojet, said fixing platform having a polygonal outline, the seal comprising: a frame whose outline is able to follow the polygonal contour of the fixing platform, and an adhesive element at least on part of the frame.

According to an advantageous embodiment of the invention, the adhesive element is an adhesive layer provided on the part of the frame capable of coming into contact with the platform.

According to an advantageous embodiment of the invention, the adhesive element is covered with a cover.

According to an advantageous embodiment of the invention, the assembly method is remarkable in that the seal is according to one of the embodiments described above, step (a) of fitting the seal between the casing and the blade platform comprising a sub-step of pre-assembly of the seal to the platform.

According to an advantageous embodiment of the invention, the pre-assembly sub-step comprises fixing the studs to pins provided on the platform.

According to an advantageous embodiment of the invention, the pre-assembly sub-step comprises the removal of the cover and the attachment by adhesion of the seal to the platform via the adhesive element.

According to an advantageous embodiment of the invention, the platforms of the blades comprise sides of polygons in contact with one another.

According to an advantageous embodiment of the invention, the frame forms a continuous loop, and / or the outline is closed.

According to an advantageous embodiment of the invention, the seal, in particular the frame, forms a closed and sealed loop which is inscribed in the polygonal outline of the fixing platform.

Benefits provided

The presence of the seal allows a simpler and more flexible design: the abradable layer which must be contiguous to the platform in known systems can be positioned at a distance because it is no longer essential for the sealing function. Also, the precision of machining and positioning of the surfaces of the facets and of the platforms of the blades is no longer as important because the manufacturing tolerances can be widened thanks to the presence of the seal.

Brief description of the drawings

• The figure 1 represents an axial turbomachine according to the invention;
• The figure 2 is a diagram of a turbomachine compressor;
• The figure 3 sketch an axial view of the casing of the turbomachine compressor according to the invention;
• The figure 4 illustrates a stator vane with a platform in contact with a facet of the housing;
• The figure 5 represents a top view of the dawn;
• The figure 6 represents a portion of the casing wall to which a blade is fixed;
• The figure 7 shows a top view of an embodiment of a seal;
• The figure 8 shows an isometric view of a gasket according to a second embodiment;
• The figure 9 shows a third embodiment of the seal;
• The figure 10 represents an isometric view of the joint of the figure 9 ;
• The figure 11 shows a fourth embodiment of the seal;
• The figure 12 shows a fifth embodiment of the seal;
• The figure 13 shows a sixth embodiment of the seal.

Description of the embodiments

In the description which follows, the terms interior and exterior refer to a positioning relative to the axis of rotation of an axial turbomachine. The axial direction is along the axis of rotation, and the radial direction is perpendicular to the axial direction. The lateral direction is understood according to the circumference, and may be perpendicular to the axis.

The figure 1 shows a double-flow turbojet 2. The turbojet 2 comprises a low-pressure compressor 4, a high-pressure compressor 6, a combustion chamber 8 and a turbine 10. In operation, the mechanical power of the turbine 10 transmitted via the central shaft up to rotor 12 sets in motion the two compressors 4 and 6.

Compressors have several rows of rotor blades associated with rows of stator vanes. The rotation of the rotor around its axis of rotation 14 thus makes it possible to generate a flow of progressively compressed air to the combustion chamber 8.

A fan 16 is coupled to the rotor 12 and generates an air flow which is divided into a primary flow 18 and a secondary flow 20. The primary 18 and secondary 20 flows are annular flows, they are channeled using partitions. cylindrical, or ferrules, which can be internal and / or external.

The figure 2 is a sectional view of a compressor of an axial turbomachine such as that of the figure 1 . The compressor can be a low-pressure compressor 4. Part of the fan 16 can be seen there as well as the spout 22 for separating the primary flow 18 and the secondary flow 20. The rotor 12 can include several rows of rotor blades 24.

The low-pressure compressor 4 comprises at least one rectifier which contains an annular row of stator vanes 26. Each rectifier is associated with the fan 16 or with a row of rotor vanes 24 in order to straighten the air flow, so as to converting flow velocity into pressure.

The compressor comprises at least one casing 28. The casing 28 may have a generally circular or tubular shape. It can be an external compressor casing and can be made of composite materials, which makes it possible to reduce its mass while optimizing its rigidity. The casing 28 may comprise fixing flanges 30, for example annular fixing flanges 30 for fixing the separating nozzle 22 and / or for fixing to an intermediate fan casing of the turbomachine. The housing then acts as a mechanical link between the separating spout 22 and the intermediate housing 32. The housing also performs a function of centering the separating spout 22 with respect to the intermediate housing, for example using its annular flanges. . The annular flanges 30 can be made of composite and include fixing holes (not shown) to allow fixing by bolts, or by lockbolts. The flanges 30 may include centering surfaces, such as centering holes.

The casing 28 may comprise a wall 32 which is generally circular or in the form of an arc of a circle, the axial edges of which may be delimited by the flanges 30. The wall 32 may have a profile of revolution around the axis of rotation 14. The wall 32 may be in composite material, with a matrix and a reinforcement. The wall 32 may have the shape of an ogive, with a variation in radius along the axis 14.

The housing can be formed of half-shells or half-housings, which are separated by an axial plane. The housing half-shells are connected using axial flanges.

The stator vanes 26 extend essentially radially from the wall 32, at the level of annular zones for receiving the vanes. These zones can comprise fixing means such as annular grooves, or fixing holes. The blades 26 can be fixed therein individually, or form blade segments fixed to the wall 32. The wall forms a mechanical link between several blades of different rows and / or of the same row of blades.

The stator vanes 26 each comprise a fixing platform 34, optionally provided with fixing pins 36 such as threaded rods or any other equivalent means. The wall may comprise annular layers of abradable material 38 between the platforms 34 of the blades, so as to form a barrier between the primary flow 18 and the wall 32.

The casing 28, or at least its wall 32, can be made of a composite material. The composite material can be produced using a fiber reinforcement pre-impregnated and cured by autoclave, or by injection. The injection may consist in impregnating a fibrous reinforcement with a resin, possibly organic, such as epoxy. The impregnation can be according to a process of the RTM type (acronym for Resin Transfer Molding).

The fibrous reinforcement may be a woven preform, optionally three-dimensionally, or comprise a stack or a winding of different fibrous sheets or fibrous plies, which may extend over the wall, and over at least one or more flanges. The plies can comprise carbon fibers, and / or graphite fibers, and / or glass fibers to prevent galvanic corrosion, and / or kevlar fibers, and / or carbotitanium fibers. Thanks to the materials mentioned, a turbomachine casing can measure between 3 and 5 mm thick for a diameter greater than 1 meter.

The figure 3 represents a half-shell of the axial turbine housing, for example an external compressor casing, possibly low-pressure. The casing is seen axially, from upstream. The present teaching can be applied to any casing of the turbomachine, such as a fan casing or a turbine casing.

The wall 32 has a curved internal surface 40. The internal surface 40 may include a continuous curvature along the circumference of the circular wall and / or along the axial direction. The internal surface 40 may be circular around the axis of rotation 14 of the turbomachine, and possibly facing said axis. The wall 32, or at least the internal surface 40 can be annular, possibly generally tubular. Depending on the circumference, the curvature of the internal surface 40 can be monotonic, and possibly constant. The curvature can vary axially, for example be more curved downstream. The internal surface 40 may be a conical surface portion, a spheroidal surface portion, optionally spherical, or a combination of each of these surfaces.

The wall 32 may comprise facets 42, optionally arranged in at least one annular row along the circumference of the wall 32. Each facet 42 defines a flat surface. The facets 42 of a row can be regularly distributed angularly. The wall 32 may include several annular rows of facets 42 spaced axially along the axially of the wall 32. At least one or each facet 42 is flush with the internal surface 40 of the wall. By flush it can be understood that a facet is level, and / or extends, and / or touches the internal surface.

The facets 42 can have different shapes, possibly the facets of the same row have the same shape. Each row can have different shapes of facets. The facets 42 may have disk shapes, oval shapes. The average diameters of the facets 42 can vary gradually, they can increase towards the end of the wall 32 having a minimum diameter, which in the example illustrated in figure 2 is the direction from upstream to downstream.

The facets 42 of the same row can be distant from each other. They can then be separated by portions of internal surface 40 which have continuous curvatures. Each facet 42 of the same row can be surrounded by the internal surface 40. The facets 42 of the same row can be tangent to each other, they can be in contact at the level of contact points. Or, the facets of the same row can be truncated laterally. These facets can be contiguous along junction lines 44.

One or each facet 42 can comprise a fixing means, such as a fixing hole 46, which can cooperate with a blade fixing pin. Preferably, each fixing orifice 46 is disposed at the center of the associated facet. The fixing holes 46 can be arranged in one or more annular row (s). These can be distributed axially along the wall 32.

At least one or each axial flange 48 can be integral with the wall 32, as can at least one or each annular flange 30. Alternatively, at least one type of flange, or each flange can be attached to the wall. For example, the wall can be made of composite and the flanges can be metallic and fixed to the wall.

The figure 4 represents a turbomachine blade, for example a stator blade 26 of a low pressure compressor rectifier. The vane can also be a turbine vane.

The blade 26 comprises a body 50, or blade, forming a profiled surface intended to extend into the primary flow. Its shape makes it possible to modify the flow of the flow. The blade extends axially from a leading edge 60 to a trailing edge 62. The “lower surface” and “upper surface” faces connect the leading edge 60 to the trailing edge 62 and a medium camber (noted 64 on the figure 5 ) is defined equidistant from these two faces.

The platform 34 for fixing the blade 26 to the wall of the casing may have the general shape of a plate. It can comprise at least one or two zones of lesser thickness 52, and optionally a zone with increased thickness 54. The zone with increased thickness 54 can be surrounded by a zone of lesser thickness 52, or be placed between two zones of lesser thickness 52. The fixing axis 36 may extend opposite the blade 50 of the blade. The or each platform 34 comprises an external radial bearing surface 56 intended to come opposite a facet.

The figure 5 represents a model of a blade platform seen from the outside radially (or seen from above compared to the view of the figure 4 ). The blade 50 of the vane which is on the other side of the platform 34 is shown in dotted lines. Platform models can change from one row of blades to another.

The platform 34 may have the general shape of a quadrilateral such as a parallelogram, a trapezoid or a rectangle. The contour of the platform 34 comprises opposite lateral edges 58, which may optionally come into contact with the adjacent lateral edges 58 of the other blades in the same row, and with the upstream and downstream edges 59. The lateral edges 58 can be bent or arched for limit their rotation when tightening their fasteners.

The platform 34 is made of metal, preferably of titanium. It can also be made of a composite with an organic matrix. It may be integral with the body of the vane 26. To comply with a precise shape, its outline is machined, possibly rectified in order to comply with strict tolerances.

The extra thick zone 54 may have the shape of a disc, the fixing axis 36 possibly being placed in the center of the disc and / or of the rectangle. Alternatively, the axis can be arranged eccentrically and not in the center of the platform. For example, the center of axis 36 may be at a distance of 20 to 50% of the axial dimension of the platform on the upstream side. The axis 36 can be circumscribed in the first half or the first upstream third of the platform.

The figure 6 shows a stator vane 26 fixed to the wall 32.

The wall 32 may have a generally constant thickness, for example at the level of at least one or of each facet 42. Its outer surface 70 may be curved at the level of each facet 42, preferably with a continuous and / or monotonic curvature axially and / or circumferentially at the level of each facet 42. Alternatively, the external surface 70 of the wall 32 can comprise a flat 72 at the level of at least one facet 42, preferably at the level of every facet. One or each flat 72 may be parallel to the associated facet 42. A flat 72 forms a flat surface, possibly smooth. It can form a discontinuity in the curvature of the outer surface 70. The flat provides a flat surface for a clamping means 74 of the fixing pin 36, preferably a nut 74 on a threaded pin 36.

The outer radial surface 56 of the or each platform 34 faces the facet 42. This facing surface 56 and this facing facet 42 may be parallel and of substantially similar dimensions. Alternatively the surfaces 42, 56 can be inclined with respect to one another. The surface 56 of the platform may not be flat.

The extra thick zone 54 comes into contact with the facet 42 and the axis 36 penetrates into the orifice (noted 46 on the figure 3 ) of facet 42.

The abradable 38 can be inserted between the surfaces 42 and 56. The abradable 38 can stop at the edges of the platform or be at an axial distance therefrom.

The or each facet 42 forms a discontinuity in the internal surface 40. The contour of at least one or each facet 42 may form a line of rupture of the curvature of the internal surface. All around each facet 42, the tangents of the inner surface may be inclined relative to the facet 42. The facets 42 may form flattens in the inner surface 40, the flattens being inward. The wall has a continuity of material between the facets and the internal surface, and possibly a geometric discontinuity.

Between the facet 42 and the surface 56 is provided a seal 80 of elastic material to prevent air leaks between the platform and the housing. This seal contains a pocket 68 delimited by the seal 80, the outer radial surface 56 of the platform 34 and the wall 32 of the housing.

Although the example illustrated shows a casing with facets, the casing may not be provided with facets and the surface 56 therefore faces the tubular or cylindrical wall 32.

The joint can be made of bars. Its outer contour may at least partially correspond to the contour of the surface 56 and therefore be in the form of a polygon, in particular a trapezoid, parallelogram or rectangle. Three of the segments of the seal 82, 84, 86 forming the polygon are visible on the figure 6 . Alternatively, the seal can include flat portions.

One or both surfaces 42 and 56 may have housings, for example grooves to receive one or more segments of the seal 80.

The figure 7 details the seal 80 in this same embodiment. The seal 80 has a frame 81 composed of upstream 82 and downstream 84 outer segments and axial outer segments 86, 88 forming a rectangle.

The seal may further comprise an O-ring portion 90 preferably connected to the frame 81 by segments at 90 °, in particular in this example two axial segments 92, 94 and two circumferential segments 96, 98, that is to say which s' mainly extend along the circumference. The toric portion 90 can be connected to the frame 81 by means of a cross, in particular formed by the segments.

In this example, the O-ring portion 90 is at the center of the seal 80. The latter can alternatively be offset upstream or downstream, that is to say in the direction of the segment 82 or 84 respectively. The toric portion 90 can also be offset circumferentially, that is to say towards the segment 86 or the segment 88.

Preferably, the section of the circumferential segments 96, 98 is greater than the section of the segments 92, 94. If the segments are all of the same thickness - the thickness being their dimension in the radial direction which is perpendicular to the plane of the figure 7 -, the section of the circumferential segments 96, 98 is larger because of their dimension in the axial direction which is greater than the circumferential dimension of the segments 92, 94.

The thickness of the downstream segment 84 of the frame 81 can be greater than the thickness of the upstream segment 82 of the frame 81.

The figure 8 shows an isometric view of a gasket 180 according to a second embodiment. The segments of the seal 180 are incremented by 100 relative to that of the figure 7 .

In this example, the toric portion 190 is only connected to the frame 181 formed by the segments 182, 184, 186, 188 by three segments 192, 196 and 198. This example shows in particular the variation in thickness along the seal. 180. The downstream segment 184 in particular has a greater thickness than the upstream segment 182. This allows a greater compression ratio of the seal 180 downstream when the surfaces 42 and 56 are parallel. This also allows the mounting of a seal between two surfaces 42 and 56 which are not parallel, the variable thickness of the seal “catching up” the variable gap between the two surfaces 42 and 56.

The figures 9 and 10 describe a seal 280 according to a third embodiment. The segments of the seal 280 are incremented by 100 relative to that of the figure 8 . The O-ring portion 290 has an oval shape and the latter is not disposed in the middle of the seal but in the upstream half. The toric portion 290 is connected to the frame 281 by the circumferential segments 296, 298 and the axial segment 292. To replace the downstream segment, a reinforcing strip 284 is provided. figure 10 illustrates this strip 284 and highlights the significant variation in thickness between upstream and downstream. The strip 284 can also come in addition to a downstream segment (like the segment 184 of the previous embodiment), the strip extending upstream or downstream of such a segment, possibly at a distance from it. The frame 281 is formed by the segments 282, 286, 288 and the strip 284.

The joints of two adjacent platforms can come into contact with each other. The axial outer segments 86, 88, 186, 188, 286, 288 of two joints of adjacent platforms may be parallel and come into contact with one another.

A platform may have one side of the outline parallel to one side of an adjacent platform and contact that side.

Alternatively, as shown in the figure 11 , two or more adjacent joints may form a single joint 380 common to several platforms.

This seal 380 comprises an upstream segment 382 and a downstream segment 384 common to several platforms. O-ring portions 390 are each provided to circumcise the fixing axis of the respective platforms and inner segments are provided to connect the O-ring portions 390 to the upstream 382 and downstream 384 segments. The arrangement of the O-ring portions 390 and the respective inner segments correspond the layout of the platforms. Thus, certain O-ring portions can be positioned at different places axially, and the dimension of the gasket portions facing a platform can be greater or lesser. The fact that the seal 380 is not symmetrical can serve as a polarizing device during the assembly of the turbomachine.

The seal can follow the polygonal contours of each of the adjacent vane platforms. The joint is therefore formed of several frames 381 and two adjacent frames can share a segment in common.

Such a seal 380 can cooperate with several blades of the annular row of blades, such as for example two or four adjacent blades, or all the blades facing a half-casing. Alternatively, a seal can cooperate with a plurality of adjacent vanes, at least one of which is fixed to a half-casing and at least one other is fixed to the other half-casing. The seal can also be common to all the blades of a row of blades and be in the form of a crown.

The figures 12 and 13 illustrate a seal 480, 580 according to the invention. This can have the various elements already described in the other embodiments (O-ring portion, tongue, a single joint common to several platforms, etc.).

In addition, the seal 480 has thermoformed pads 483, produced in the form of molding inserts. These pads 483 are preferably arranged at the level of the frame 481 of the seal. Alternatively, one or more studs can be arranged at other locations of the seal 480. These studs can include a hole which can cooperate with pins provided on the platform. The pins can be such that a tight assembly in the studs is obtained. This allows the seal to be pre-assembled on the platform. The studs can alternatively be provided with an internal thread to receive a threaded rod of the platforms. The studs are 2, 4 or 6 in number. The studs can be of identical or different dimensions, in particular when the seal is thicker downstream as shown in the figure. figure 12 . Alternatively, a single stud can also be provided on the seal.

The figure 13 shows a pad 580 provided with an adhesive element 583 on its frame 581. The elements are shown schematically and the scale of sizes is not respected. The adhesive element may be a dot of glue or an adhesive layer 583, which may be covered with a seal 585. During assembly, the seal 585 is removed from the seal 580, then the seal is positioned on the platform. To this end, the cover has a part 587 that does not adhere to the adhesive means in order to facilitate its removal.

Thus, the seal adheres to the platform and facilitates the assembly of the platform and its seal in the housing.

The joint of the various embodiments illustrated above can be made completely of elastomer, polymer or foam. One or more of the segments may comprise a rigid wire (metallic or other) in its core coated with elastomer, polymer or foam.

The different details of the different embodiments set out in the present application can be combined unless it is explicitly described as alternatives and such a combination is made mechanically impossible.

Claims (15)

1. An assembly for an axial turbomachine (2), in particular an aircraft turbojet engine, the assembly comprising:

   - an annular casing (28) with an internal surface (40);

   - an annular row of stator vanes (26) with at least one stator vane (26) comprising an airfoil (50) extending radially from a fixing platform (34), said fixing platform (34) being fixed to the casing (28) and having a polygonal contour (58, 59);

   characterized in that it further comprises
   a gasket (80, 180, 280, 380, 480, 580) formed by an element distinct from the casing (28) and distinct from the fixing platform (34), and comprising a frame (81, 181, 281, 381, 481, 581), contour of which matches the polygonal contour (58, 59) of the fixing platform (34), said frame (81, 181, 281, 381, 481, 581) being in radial contact with the fixing platform (34) and the casing (28) in order to ensure a seal.
2. Assembly according to claim 1, characterized in that the frame (81, 181, 281, 381, 481, 581) sealingly delimits a pocket (68) radially between the fixing platform (34) and the casing (28), said pocket (68) extending in particular over the majority of the fixing platform (34).
3. Assembly according to any of claims 1 and 2, characterized in that the platform comprises polygon sides in contact with each other and the frame (81, 181, 281, 381, 481, 581) is formed of bars (82, 84, 86, 88, 182, 184, 186, 188, 282, 284, 286, 288, 382, 384, 386, 388) running along the sides of the platform.
4. Assembly according to any of claims 1 to 3, characterized in that the frame (81, 181, 281, 381, 481, 581) of the gasket (80, 180, 280, 380, 480, 580) has a general exterior shape as a parallelogram and preferably rectangular, or in that the platform (34) has a fixing axis (36) which passes through an orifice (46) of the casing (28), and in that the fixing axis (36) passes through the gasket (80, 180, 280, 380, 480, 580), a portion (90, 190, 290, 390) of the gasket (80, 180, 280, 380) being optionally toric or cylindrical and surrounding the fixing axis (36), and segments (92, 94, 96, 98, 192, 196, 198, 292, 296, 298) preferably connecting the toric or cylindrical portion (90, 190, 290, 390) to the frame (81, 181, 281, 381) optionally comprising two circumferential segments (96, 98, 196, 198, 296, 298) oriented in the circumferential direction of the turbomachine and at least one axial segment (92, 94, 192, 292) oriented in the axial direction of the turbomachine, and/or the toric or cylindrical portion (290), 390) being optionally enclosed in the upstream half of the gasket (180, 280, 380).
5. Assembly according to any of claims 1 to 4, characterized in that the gasket (80, 180, 280, 380, 480, 580), in particular the frame (81, 181, 281, 381, 481, 581), forms a closed and sealed loop which is inscribed in the polygonal contour (58, 59) of the fixing platform (34).
6. Assembly according to any of claims 1 to 5, characterized in that the gasket (280) comprises a downstream reinforcement tab (284), preferably extending mainly in the circumferential direction of the turbomachine.
7. Assembly according to any of claims 1 to 6, characterized in that the gasket (380) is interposed between the casing (28) and several platforms (34) of adjacent vanes, said gasket (380) matching the polygonal contours (58, 59) of each of said several platforms (34) of adjacent vanes.
8. Assembly according to any of claims 1 to 7, characterized in that the internal surface (40) of the casing (28) comprises an annular row of facets (42) receiving the stator vanes (26), an external radial surface (56) of the platform (34) being inclined relative to the associated facet (42) and/or the radial thickness of the gasket (80, 180, 280, 380, 480, 580) is greater downstream than upstream.
9. Assembly according to any of claims 1 to 8, characterized in that a layer of abradable material (38) is provided on the internal surface (40) of the casing (28), in particular upstream and/or downstream of the facets (42), and axially spaced from the platforms (34) and/or the gasket (80, 180, 280, 380, 480, 580).
10. Method for assembling an assembly for a turbomachine, characterized in that the assembly is according to any of claims 1 to 9 and in that the method comprises a step (a) of placing the gasket (80 , 180, 280, 380, 480, 580) between the casing (28) and the vane (26) platform (34), and a step (b) of fixing the vane (26) to the casing (28) during which the gasket (80, 180, 280, 380, 480, 580) is compressed radially between the vane (26) platform (34) and the casing (28), the gasket (80, 180, 280, 380, 480, 580) being preferably more compressed downstream than upstream.
11. Method according to claim 10 and the assembly according to claim 4, characterized in that the step (b) of fixing comprises the tightening of a nut (74) on the fixing axis (36) so as to compress the gasket (80, 180, 280, 380, 480, 580).
12. Gasket (480) for a platform for fixing a stator vane of an axial turbomachine (2), in particular of an aircraft turbojet, said fixing platform (34) having a polygonal contour (58, 59), the gasket (480) comprising: a frame (481) the outline of which is adapted to match the polygonal contour (58, 59) of the fixing platform (34), and thermoformed studs (483), the studs (483) being molding inserts (480) of the gasket (480), the studs optionally comprising holes, preferably through-holes, capable of cooperating with pins provided on the platform (34).
13. Gasket (580) for a platform for fixing a stator vane of an axial turbomachine (2), in particular of an aircraft turbojet, said fixing platform (34) having a polygonal contour (58, 59), the gasket (580) comprising: a frame (581), contour of which is adapted to match the polygonal contour (58, 59) of the fixing platform (34), and an adhesive element (583) at least on a part of the frame (581), the adhesive element (583) being covered with a lid (585), the adhesive element (583) being optionally an adhesive layer provided on the part of the frame (581) capable of coming into contact with the platform (34).
14. Method according to any of claims 10 and 11, characterized in that the gasket (480, 580) is according to any of claims 12 and 13, the step (a) of placing the gasket (480, 580) between the casing (28) and the vane (26) platform (34) comprising a sub-step of pre-assembly of the gasket (480, 580) with the platform (34).
15. Method according to claim 14 in combination with a gasket (480) according to claim 12, characterized in that the pre-assembly sub-step comprises the fixing of the studs (483) to pins provided on the platform (34), or method according to claim 14 in combination with a gasket (580) according to claim 13, characterized in that the pre-assembly sub-step comprises the removal of the lid (585) and the fixing by adhesion of the gasket (580) to the platform (34).

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