Method for assembling a ring sector of a turbine distributor onto a fixed turbine structure, and associated ring sector

Abstract

Method for assembling a distributor ring sector onto a fixed turbine structure, and associated ring sector. The invention relates to a method for assembling a ring sector (10) of a turbine distributor, the ring sector comprising a fixed blade (11) and a mast (26) to be inserted into an internal housing (20) of the fixed blade, the mast having a plate to be fixed to a fixed structure (24) of the turbine, the method comprising: a measurement step, during which a positioning of the ring sector relative to the fixed structure is determined; a step of determining a rectification to be applied to an interface between the mast plate and the fixed structure to obtain a nominal positioning of the ring sector; and a step of rectifying the interface between the mast plate and the fixed structure, in accordance with the rectification to be applied determined previously. Figure for the abstract: Figure 1

Description

Description Title of the invention: Method for assembling a ring sector of a turbine distributor on a fixed structure of the turbine, and associated ring sector Technical field

[0001] = The invention relates generally to turbomachines, in particular tur- aeronautical engines. More specifically, it concerns an assembly process of a ring sector of a turbine distributor on a fixed structure of a turbine of turbomachine, the ring sector being able in particular to comprise a blading fixed in ceramic matrix composite material. STATE OF THE PRIOR ART

[0002] = An improvement in the performance of turbomachines and a reduction in their polluting emissions lead to considering operating temperatures of higher and higher.

[0003] — For elements of hot parts of turbomachines, it has therefore been proposed to use ceramic matrix composite materials, also called CMC materials.

[0004] — CMC materials are typically formed from a fibrous reinforcement made of re- fractories, such as carbon or ceramic fibers, densified by a matrix in ceramic or at least partially ceramic.

[0005] = Such CMC materials have remarkable thermo-structural properties, that is to say mechanical properties making them suitable for constituting in particular structural elements and an ability to retain such properties at temperatures high.

[0006] — In addition, CMC materials have a density much lower than that of metallic materials, traditionally used for hot parts elements of turbomachines.

[0007] = A metal turbine distributor has a crown shape composed of several sectors assembled, each sector comprising a blade which has a inner platform, an outer platform and a blade extending between the inner platform and the outer platform and fixed to them. A sector of dis- metal turbine impeller may sometimes include several blades extending each between an interior platform and an exterior platform of the dis- tributor, instead of a single blade.

[0008] The juxtaposed interior platforms form an interior shell and the pla- juxtaposed outer forms form an outer ferrule. The inner ferrule and the outer shell delimits a gas flow vein in the turbine distributor. Introducing a turbine distributor made of CMC materials, for example a high pressure turbine distributor, allows the maximum tolerated temperature to be increased compared to a metal turbine distributor. Thus, a turbine distributor made of CMC materials requires less cooling, which also reduces the amount of cooling air used. This in turn increases the performance of the turbomachine. It is also known that the turbine distributor further comprises metal reinforcing masts, each mast extending radially inside an inner housing passing through the blade. Such an arrangement allows the turbine distributor to be fixed to a fixed structure of the turbine. The positioning and mounting of the blade and the mast are carried out in particular by bringing the blade and the mast into contact at respective facing portions. In particular, the mast may comprise portions projecting relative to a main wall of the mast, the projecting portions extending perpendicular to a main axis of the mast, each projecting portion bearing at a point on an internal surface of the blade which delimits the internal housing. To obtain a good positioning of the blade in relation to the fixed structure of the turbine, it is known to make adjustments by machining the portions of the mast which come into contact with the blade, for example the projecting portions. However, such machining of the protruding portions may not be sufficient to compensate for potentially significant dimensional differences. It is then necessary to machine the internal surface of the blade in addition. However, the CMC material is very hard and the internal surface of the blade is difficult to access. In addition, the thickness of the blade that can be machined is relatively small. In practice, the possibilities for adjustment are therefore limited. The aim of the invention is to propose a method for obtaining correct positioning of the blade relative to the fixed structure of the turbine. Description of the invention The invention proposes: a method of assembling a ring sector of a nozzle of a turbine on a fixed structure of the turbine, the ring sector comprising a fixed blade and a mast, the turbine defining an axial direction and a radial direction, the fixed vane comprising an inner platform, an outer platform and a blade extending radially between the inner platform and the outer platform and having a hollow profile defining an inner housing which extends radially and which opens radially at least on one external side of the fixed blade, the mast being shaped to fit into the internal housing of the fixed blades and comprising a plate at an external end of the mast, the plate being intended to be fixed to the fixed structure, the process comprising: a step of positioning the ring sector, during which the mast is inserted into the inner housing of the fixed vane and the mast plate is fixed on the fixed structure: a measurement step, during which a positioning of the sector ring relative to the fixed structure is determined; a step of determining a rectification to be applied to an interface between the mast plate and the fixed structure; a step of rectification of the interface between the mast plate and the structure fixed, in accordance with the rectification to be applied determined previously; and a step of assembling the ring sector on the fixed structure of the turbine. At the interface between the mast plate and the fixed structure, grinding is relatively easy since this interface is easily accessible, and the mast and fixed structure are generally made of metal, which makes them easier to machine. In addition, the extent of grinding can be relatively large since the thickness of the mast plate is less subject to aerodynamic constraints than the fixed blades. By interface between the plate and the fixed structure we mean an assembly comprising: the plate, an optional intermediate piece which can be located between the plate and the fixed structure, as well as a part of the fixed structure in contact with the plate, or in contact with the intermediate piece in question if the intermediate piece is present. Grinding may include machining, for example by abrasion or milling. It is also possible to peel off a peelable part of the mast, fixed structure or intermediate piece. The assembly process which has just been presented may have one or more of the following characteristics, considered alone or in all technically conceivable combinations: the measuring step includes a measurement of positions of different points of the fixed blade in a reference frame linked to the fixed structure. This measurement can in particular be carried out using a three-dimensional measuring machine or a stereovision device; the rectification to be applied is a rectification of the mast plate or a rectification of a part of the fixed structure in contact with the plate when the plate is fixed to the fixed structure. It is also possible to provide a rec- ification of an intermediate piece located between the plate and the fixed structure; the rectification of the plate is: a rectification of a bearing surface of the plate, bearing surface intended to come into contact with the fixed structure, or drilling or grinding of fixing holes allowing fix the plate to the fixed structure; the rectification to be applied is determined: depending on the positioning of the ring sector relative to the fixed structure determined during the measurement step, and depending on a nominal positioning of the ring sector by report to the fixed structure to be obtained at the end of the assembly process. The rectification to be applied is determined in such a way as to obtain, after rectification, a corrected positioning of the ring sector compared to the fixed structure which is closer to the positioning nominal target than the initially measured positioning, when the measurement step; the mast is metallic; the fixed structure is metallic; the fixed blade is made of ceramic matrix composite material; an initial dimension presented by the plate before the grinding step, for example an initial thickness or an initial length of the plate or still an initial width of the plate, is greater by at least one tenth of a millimeter, or even greater by at least five tenths of a millimeter than a corresponding nominal dimension of the plate. The nominal dimension, which is in some way a theoretical dimension of the plate, is for example specified in a drawing representing the ring sector assembled on the fixed structure. In the drawing in question, the ring sector is assumed to be without manufacturing defects, that is to say without any deviation in execution from the target dimensions, even if the drawing may include indications of mechanical tolerances. The plate thus has an excess thickness, or excess length, equal to the difference between the initial dimension and the corresponding nominal dimension. This excess thickness makes it possible to rectify the plate by machining by removing material, to correct the positioning of the blades in relation to the fixed structure. The excess thickness or excess length value mentioned above is greater than 0.1 mm, or even greater than 0.5 mm, or between 0.1 mm and 2 mm. It generally allows the plate to be rectified sufficiently to correct the positioning deviations observed, deviations which are rarely greater than 0.5 mm in practice. The excess thickness or excess length in question could nevertheless be greater than 1 mm or even 2 mm, depending on the manufacturing precision of the fixed blades and the mast.The present invention also relates to a ring sector of a distributor of a turbine, intended to be assembled on a fixed structure of the turbine, the turbine defining an axial direction and a radial direction, the ring sector comprising a fixed blading and a mast, the fixed blading comprising an inner platform, an outer platform and a blade extending radially between the inner platform and the outer platform and having a hollow profile defining an inner housing which extends radially and which opens radially at least on one external side of the fixed blading, the mast being arranged to be housed in the inner housing of the fixed blading and comprising a plate at an external end of the mast, the plate being intended to be fixed to the fixed structure, the ring sector being capable of being assembled on the fixed structure of the turbine in accordance with the assembly method described above. The mast plate may in particular have a certain excess thickness or excess length compared to a theoretical, nominal dimension of the plate, as explained above. Thus, an initial dimension presented by the plate before the rectification step, for example an initial thickness or an initial length of the plate, is at least one tenth of a millimeter greater, or even at least five tenths of a millimeter greater, than a corresponding nominal dimension of the plate. It may also be provided that the mast comprises a main wall comprising support means against which an internal wall of the blade is in contact. The support means may comprise a plurality of lugs projecting relative to a main wall of the mast. The fixed blading of the ring sector may comprise a flange at an outer end of the fixed blading, the flange bearing on the mast plate, the plate comprising orifices and the flange comprising corresponding orifices located opposite the orifices of the plate. Brief description of the drawings Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which: [Fig. 1] is a schematic sectional view of a ring sector of a dis- turbine generator according to one embodiment of the invention; [Fig.2] is an exploded perspective representation of the ring sector represented in [Fig.1] showing a blade and a mast of the ring sector; [Fig.3] is a perspective representation of the dawn and mast re- presented in [Fig.2], assembled on an external shell supporting the tur- machine according to an assembly method of the invention; [Fig.4] is a detail view of one outer end of the assembly comprising the blade and mast shown in Figures 2 and 3, assembled, showing an example of rectification of an outer end of the mast; and [Fig.5] is a detail view of the outer end of the assembly comprising the blade and mast shown in Figures 2 and 3, assembled, showing mast mounting holes on the external support ferrule. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS [Fig. 1] is a schematic sectional view of a ring sector 10 of a turbine distributor, in particular for a high-pressure turbine of a turbomachine, for example an aeronautical turboshaft engine. The ring sector 10 comprises a blade 11, also called a “fixed blade”, extending in a radial direction. The blade 11 comprises an inner platform 12, an outer platform 14 and a blade 16. The blade 16 is the part of the blade 11 extending in the radial direction between the inner platform 12 and the outer platform 14, from an inner end 16i of the blade to an outer end 16e of the blade. Furthermore, the blade 16 is fixed to the inner platform 12 and to the outer platform 14. Relative to an axis of rotation of the turbine, the inner platform 12 extends axially and circumferentially from the inner end 16i of the blade 16, and the outer platform 14 extends axially and circumferentially from the outer end 16e of the blade 16. It will be noted that, in the present document, the radial and axial directions are defined relative to the axis of rotation of the turbine. The blade is formed from CMC material. The turbine distributor is made up of an assembly of a plurality of such ring sectors 10 to form a single turbine distributor crown having an inner shroud formed by the juxtaposition of the inner platforms 12 and an outer shroud formed by the juxtaposition of the outer platforms 14. The inner shell and the outer shell delimit between them a vein 18, allowing a flow of fluid, inside which a gas flow F flows during operation of the turbine. In the description of the invention, the terms “upstream” and “downstream” are used with reference to the direction of flow of the gas flow F in the vein 18 indicated by an arrow. The inner platform 12 has an outer surface 12e intended to be in contact with the gas flow F. The outer surface 12e is therefore arranged radially opposite the outer platform 14 forming the outer shell. The inner platform 12 further has an inner surface 12i arranged opposite the axis of rotation of the turbine. Furthermore, the outer platform 14 has an inner surface 14i intended to be in contact with the gas flow F. The inner surface 14i is therefore arranged radially opposite the inner platform 12 forming the inner shell and opposite the axis of rotation of the turbine. . The blade 11 extends radially from an inner end 111 of the blade 11 to an outer end 11e of the blade 11. The blade 11 extends radially, outwardly, beyond the outer platform 14. The outer end 11c of the blade thus projects outwardly, relative to the outer platform 14. Furthermore, the blade 11 may extend radially, inwardly, beyond the inner platform 12. It will be understood that the invention is not limited to such a blade 11 and that the blade may extend radially only between the inner platform 12 and the outer platform 14. According to the invention, the blade 11 has a hollow profile forming an inner housing 20, visible in [Fig. 2]. The inner housing 20 extends between the inner end 11i and the outer end 11e of the blade 11. The inner housing 20 opens radially outwards. It thus comprises an opening 42 located at the outer end 11e of the blade 11. In the example shown, the inner housing 20 also opens inwards, at the inner end 11i of the blade. The inner housing 20 thus passes radially through the blade 11 from one side to the other. The ring sector 10 further comprises a mast 26 extending in a radial direction relative to the axis of rotation of the turbine. The mast 26 is intended to be inserted into the internal housing 20 of the blade 11. The mast 26 is preferably metallic. The mast 26 is hollow in order to allow in particular air to be brought into a cavity arranged radially inside the inner shell delimited by the inner platform 12. Such a configuration makes it possible to pressurize the inner shell and to prevent the gas flow circulating in the vein 18 from escaping towards the cavity arranged radially inside the inner shell. Indeed, such a leak would reduce the performance of the turbomachine and increase the risk of overheating of the parts. For this purpose, the mast 26 comprises an internal cavity 28 extending, in the radial direction, between an inner end 26i of the mast 26 and an outer end 26e of the mast 26. As shown in [Fig.2], the mast 26 comprises a main wall 30 extending radially between the inner end 26i and the outer end 26e of the mast 26. The main wall 30 delimits the internal cavity 28 of the mast 26. When the mast 26 is inserted into the inner housing 20 of the blade 11, the main wall 30 extends radially over the entire radial length of the inner housing 20 of the blade 11. According to a particular embodiment, as shown in Figures 1 and 3, the inner end 26i of the mast 26 can project radially relative to the inner end 11i of the blade 11. Furthermore, the outer end 26e of the mast 26 projects radially relative to the outer end 11e of the blade 11. The outer end 26e of the mast 26 is fixed to a fixed structure of the turbine, in this case to an external support shell 24 secured to a casing of the turbine. In the example of [Fig.2], the outer end 26e is formed of a plate 26p extending along a plane perpendicular to a main axis of the mast 26. The mast 26 comprises lugs 32 distributed on the main wall 30, projecting relative to the latter. When the mast 26 is inserted into the blade 11, an internal wall of the inner housing 20 of the blade 11 is in contact against the lugs 32, thus positioning the blade 11 with respect to the mast 26. Preferably, the lugs 32 are distributed over the main wall 30 of the mast 26, so as to obtain isostatic positioning of the blade 11 relative to the mast 26. For example, the main wall 30 of the mast 26 comprises six lugs 32 distributed to form a contact plane, a contact line and a contact point between the blade 11 and the mast 26. Alternatively, the blade 11 could be positioned relative to the mast 26 by positioning members other than lugs, for example by ribs or veins projecting relative to the main wall 30 of the mast, or by an assembly comprising both ribs and lugs. As can be seen in Figures 2 and 5, the outer end 11e of the blade 11 comprises a flange 36. In particular, the flange 36 extends in a plane perpendicular to a main axis of the blade 11. In the embodiment shown in the figures, the flange 36 bears on the plate 26p of the mast, when the mast 26 is inserted, in the usage position, into the blade 11. Centering or alignment pins (not shrunk), connecting the outer end 26e of the mast and the outer end 11e of the blade, can participate in the positioning of the blade 11 relative to the mast 26. In this case, the plate 26p comprises 38° orifices (see [Fig.5]) and the flange 36 of the blade comprises corresponding 38°” orifices (see [Fig.2]), located opposite the orifices 38' when the mast 26 is inserted, in the use position, in the blade 11. Each centering or alignment pin is then mounted in one of the orifices 38' and in the corresponding orifice 38”. The centering or alignment pins are mounted with a slight clearance when cold, to allow differential expansion of the blade 11 relative to the mast 26. Furthermore, the outer end 26e of the mast 26 comprises fixing orifices 38, capable of ensuring fixing of the mast 26 to the external support shell 24, being crossed by threaded rods for fixing by bolting or by shrink-fit pins for fixing the mast 26 to the external support shell 24 of the turbine 10. The manufacture of the blade 11 and the mast 26 involves dimensional deviations of these components which do not allow for, with certainty, a correct relative positioning of the blade 11 and the mast 26 with respect to the external support shroud 24. In particular, an inclination of the blade 11 with respect to the external support shroud 24, and therefore an orientation of the blade 11 in the vein 18 may be different from a desired nominal orientation, to be obtained at the end of the assembly. To correct such positioning deviations, the blade 11 and the mast 26 are assembled, i.e. mounted or fixed, together and on the fixed structure of the turbine according to an assembly method described below. The assembly method comprises at least one positioning step, during which the blade 11 and the mast 26 are positioned relative to each other, in particular mounted with each other. More particularly, the blade 11 is positioned around the mast 26. For this purpose, during the positioning step, the mast 26 is introduced into the internal housing 20 of the blade 11. For example, the introduction of the mast 26 into the internal housing 20 of the blade 11 is carried out by a fitting along the main axis of the blade 11 from the external end 16e, open, of the blade 11. When the mast 26 is received in the blade, the lugs 32 of the main wall 30 of the mast 26 come to bear against the internal wall of the internal housing 20 of the blade, thus positioning the blade relative to the mast 26. Furthermore, during the positioning step, the mast plate 26p is fixed to the external support ferrule 24. The assembly method then comprises a measuring step, during which a positioning of the ring sector 10, more precisely a positioning of the blade 11, relative to the external support shroud 24 is determined. The positioning in question can be defined for example by: three angles identifying an orientation of the blade 11 relative to the shell external support 24, and by three coordinates, for example Cartesian, identifying a position of the dawn 11 relative to the outer support shell 24 along three axes. The measuring step comprises a measurement of positions of different points of the blade 11 in a reference frame linked to the external support shroud 24. This measurement can in particular be carried out using a three-dimensional measuring machine or a stereovision device. The method then comprises a step of determining a rectification to be applied to an interface between the plate 26p of the mast and the external support ferrule 24. The rectification to be applied includes for example: a rectification of a bearing surface 26s of the plate 26p, bearing surface intended to come into contact with the external support ferrule 24 or with a spacer piece inserted between the 26p patina and the external support ferrule 24 and / or a rectification or drilling of the fixing holes 38 which pass through the 26p plate and which are intended to fix the plate to the external support ferrule 24. The correction to be applied is determined: depending on the positioning of the blade 11 relative to the external shell of support 24, determined during the measurement step, and depending on a nominal positioning of the blade 11 relative to the external support ferrule 24, so as to obtain, after rectification, a corrected positioning of the blade relative to the external support shell which is closer to the nominal positioning targeted than the positioning initially measured, during the measurement step. For example, the blade 11 may have a tangential balancing error, i.e. be inclined, about an axis parallel to the axis of rotation of the turbine, by a measured inclination angle different from a nominal inclination angle. The measured inclination angle is determined on the basis of the measurements carried out during the measurement step. To correct the tangential balancing error, the bearing surface 26s of the plate 26p can be ground so as to obtain an interface surface 40 ([Fig. 4]) which has a compensating inclination, around an axis parallel to the axis of rotation of the turbine, relative to the bearing surface 26s presented by the plate before grinding. The compensating inclination can be equal to the opposite of the difference between the measured inclination angle and the nominal inclination angle of the blade, to compensate for the tangential balancing error. In [Fig. 4], which is a detail view of the outer end 11e of the blade and the mast inserted in the blade, the dotted line P designates the limit of the grinding to be applied, to obtain the interface surface 40 in question. The blade 11 may also have an axial balancing error, i.e. be inclined, around an ortho-radial axis, by an angle different from that corresponding to a nominal assembly. The axial balancing error can also be corrected by grinding the bearing surface 26s of the plate 26p, so as to obtain an interface surface inclined relative to the bearing surface initially presented by the plate, before grinding. The blade 11 may also have a timing error, i.e. be inclined around the radial axis by an angle different from that corresponding to a nominal assembly. It may also have a position error, in terms of Cartesian position. The timing error may be corrected by rectifying the positions of the fixing holes 38. The position error may also be corrected by rectifying the positions of the fixing holes 38, or by uniformly rectifying the thickness of the plate, with regard to the position along the radial axis. The method then comprises a step of rectification of the interface between the plate 26p of the mast and the external support ferrule 24, in accordance with the rectification to be applied determined previously. In the example described here, the rectification to be applied is a rectification of the plate. To enable this rectification, the 26p plate has, before the rectification step, an initial thickness at least one tenth of a millimeter greater, or even at least five tenths of a millimeter greater than a corresponding nominal thickness of the plate. This excess thickness makes it possible to machine the plate by removing material, so as to correct the positioning deviations previously identified. The 26p plate may also have a length or width, before rectification, at least one tenth of a millimeter greater, or even at least five tenths of a millimeter greater than a nominal length or width of the plate. The rectification step may also include drilling in the plate 26p, holes 38' presented above, and counter-drilling the flange 36, through the holes 38', to produce the corresponding holes 38”, located opposite the holes 38°. Finally, after having rectified the interface between the plate and the external support shell 24, the ring sector 10 is mounted and assembled on the external support shell 24. Thanks to such a method, the contact between the blade 11 and the mast 26 takes place at the level of two raw parts of these two components. There is therefore no added fragility on the blade, nor on the mast 26. Alternatively, the rectification step could however also include a rectification of the support means, in this case the lugs present on the mast, or even a rectification of the internal wall of the blade.

Claims

Claims

1. Method of assembling an annular sector (10) of a distributor of a turbine on a fixed structure (24) of the turbine, the ring sector comprising a fixed blade (11) and a mast (26), the turbine defining an axial direction and a radial direction, the fixed vane (11) comprising an inner platform (12), a outer platform (14) and a blade (16) extending radially between the inner platform (12) and the outer platform (14) and having a hollow profile defining an interior housing (20) which extends radially and which opens radially at least on one side external of the fixed blade (11), the mast (26) being shaped to fit into the interior housing (20) of the fixed blading (11) and comprising a plate (26p) with a external end (26e) of the mast, the plate (26p) being intended to be fixed to the fixed structure (24), the process comprising: a step of positioning the ring sector (10), at during which the mast (26) is inserted into the housing interior (20) of the fixed vane (11) and the plate (26p) of the mast is fixed to the fixed structure (24); a measurement step, during which a positioning of the ring sector (10) relative to the fixed structure (24) is determined ; a step of determining a rectification to be applied to an interface between the mast plate (26p) and the fixed structure (24); a step of rectification of the interface between the mast plate and the fixed structure, in accordance with the rectification to be applied previously determined; and a step of assembling the ring sector (10) on the fixed structure (24) of the turbine.

2. The assembly method of claim 1, wherein the step of measurement includes a measurement of positions of different points of the fixed blade (11) in a reference frame linked to the fixed structure (24).

3. Assembly method according to claim 1 or 2, in which the rectifi- The modification to be applied is a rectification of the plate (26p) of the mast or a rectification of a part of the fixed structure (24) which is in contact with the mast plate when the plate is fixed to the fixed structure.

4. Assembly method according to claim 3, wherein the rectifi- fication of the turntable (26p) is: a rectification of a support surface (26s) of the plate, support surface intended to come into contact with the structure fixed (24), or drilling or grinding of fixing holes (38) allowing the plate (26p) to be fixed to the fixed structure (24).

5. Assembly method according to one of claims 1 to 4, in which the rectification to be applied is determined: depending on the positioning of the ring sector (10) by relation to the fixed structure (24) determined during the step of measure, and depending on a nominal positioning of the sector ring (10) relative to the fixed structure (24), to be obtained at the outcome of the assembly process.

6. Assembly method according to one of claims 1 to 5, in which the mast (26) is metallic and the fixed vane (11) is made of material ceramic matrix composite.

7. Assembly method according to one of claims 1 to 6, in which an initial dimension presented by the plate (26p) before the step of rectification, for example an initial thickness or an initial length of the plate, is at least a tenth of a millimeter higher, or even greater than one dimension by at least five tenths of a millimeter corresponding nominal value of the turntable.

8. Ring sector (10) of a distributor of a turbine, intended to be assembled on a fixed structure (24) of the turbine, the turbine defining an axial direction and a radial direction, the ring sector comprising a fixed vane (11) and a mast (26), the fixed vane (11) comprising an inner platform (12), a outer platform (14) and a blade (16) extending radially between the inner platform (12) and the outer platform (14) and having a hollow profile defining an interior housing (20) which extends radially and which opens radially at least on one side external of the fixed blade (11), the mast (26) being shaped to fit into the interior housing (20) of the fixed blading (11) and comprising a plate (26p) with a external end (26e) of the mast, the plate (26p) being intended to be fixed to the fixed structure (24), the ring sector (10) being able to be assembled on the fixed structure (24) of the turbine in accordance with the assembly method according to one of of the preceding claims.

9. Ring sector (10) according to the preceding claim, in which the mast (26) comprises a main wall (30) comprising means support (32) against which an internal wall of the blade (16) is in contact.

10. Ring sector (10) according to one of claims 8 or 9, wherein the fixed vane (11) has a flange (36) at an outer end (11e) of the fixed vane, the flange (36) resting on the plate (26p) of the mast, the plate (26p) comprising orifices (38°) and the flange comprising corresponding holes (38”) located opposite the holes (38”) of the platinum.