Rotor assembly with independent platforms and method for mounting such a rotor

Abstract

Independent platform rotor assembly and method for mounting such a rotor. The invention relates to a turbomachine turbine rotor assembly comprising: a rotor disk centered on an X-axis and having recesses, movable blades each comprising a foot mounted in a recess, a plurality of platforms for retaining the movable blades in the disk recesses, and a flange for retaining the movable blades in the recesses, each platform comprising: a flow wall delimiting a gas flow channel, an L-shaped downstream hook with a vertical portion extending radially from the flow wall and a horizontal portion housed in a retaining hook positioned at the apex of a disk tooth; and an upstream hook extending substantially radially from an upstream area of ​​the flow wall and held axially between the flange and the disk. Figure to be published with the abstract: Figure 3

Description

Description Title of the invention: Rotor assembly with independent platforms- pendants and method of mounting such a rotor TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a turbine rotor assembly whose platforms moving blades are independent of the blades of said moving blades. It concerns also a method of mounting these moving blades in the rotor disk.

[0002] — The invention finds applications in the field of aeronautics and, in par- particular, in the field of low pressure turbines for aircraft turbomachines. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] As is known, a low pressure (LP) turbine comprises several bladed wheels successive, separated by distributor stages. A paddle wheel, also called a wheel, consists of so-called "moving" blades and a rotor disc. Each moving blade generally comprises a blade extended by a blade root. The external periphery The rotor disc has mounting grooves, called dimples, that extend in substantially axial directions (i.e. with an angle of up to a few degrees from the axial direction). Each cell is designed so that to receive the foot of a moving blade mounted by fitting into said cell.

[0004] — Conventionally, the moving blades each comprise a platform extending circum- conferentially around the blade of the dawn, in a plane substantially perpen- dicular to the plane containing the blade. The platforms are designed to form, with the platforms of the other moving blades, an internal vein in which the gases circulate hot air passing through the turbine. On conventional blades, generally from foundries, the platform is integrated into the mobile blade, that is to say it is made from a single part with the blade and the foot of the blade,

[0005] — Usually, a first axial retention ring, or flange, is provided, arranged on the upstream face of the turbine disc and a second axial retention ring, arranged on the downstream face of the turbine disc. These rings form axial stops for the blade roots housed in the cells. An example of a portion of a turbine BP comprising three paddle wheels | a, 1 b, lc according to the state of the art is re- shown in [Fig.1]. The paddle wheels 1a, 1b, 1c are separated from each other by distributors 7, 8 each equipped with a ferrule 9, 10 forming the internal wall of the vein of the flow F. Each paddle wheel 1 a, 1 b, lc, comprises a rotating disc around the central axis of the turbine, represented by the X axis, and comprising a rim outer peripheral 2a, 2b, 2c, to which the blades are fixed by their foot 3a, 3b, 3c. In particular, a first wheel 1a comprises a moving blade 4a mounted axially, by its root 3a, in a cell 6a of the rim 2a of the disc. The root 3a of the blade 4a is blocked axially, upstream, by an annular flange 13 and, downstream, by an annular flange 14, the flanges 13 and 14 being of different types. Nowadays, turbine blades, particularly LP (low pressure) turbine blades, are often made of a ceramic matrix composite (CMC) material, which has the advantage of being lightweight. CMC blades are therefore lighter than conventional metal blades. However, the manufacture of CMC blades with a retaining hook is complex because it involves weaving and requires forming two texture layers on the blade, at the platform Sa, Sb, Sc located between the blade and the root 3a, 3b, 3c of the blade, one of which constitutes the surface delimiting the air stream and the hook and the other serves as the anti-tilt of the blade and the downstream overlap. To address this issue, it has been proposed to separate the platform from the blade and the blade root. However, the fact that the platforms are independent of the blade and blade root assembly creates a problem of absorbing the centrifugal force. Indeed, each platform is carried by the two adjacent blade and blade root assemblies (hereinafter called blades), for example, by means of a retaining shoulder resting on each of the two circumferentially adjacent blades. The centrifugal force of each platform is then absorbed by the two circumferentially adjacent blades: the centrifugal force passes through the blade root and the blade-disc attachment of each of the two adjacent blades to be absorbed by the disc. The blade-disc attachment is therefore loaded, in addition to the centrifugal force of the blade itself, by the centrifugal force of the platform.As the centrifugal force of the platform is not negligible compared to that of the blade, the load of the blade-disc attachment therefore increases significantly. One solution to lighten this blade-disc load could be to use blade-disc attachments in the shape of fir tree roots (i.e. with several bearing stages). However, the current state of the art on CMC blades does not allow the manufacture of blade-disc attachments in the shape of a fir tree root. Current knowledge limits the attachment to the simpler form known as a "dovetail". It is therefore not possible to increase the capacity of the blade-disc attachment by adding a bearing stage. To produce a LP turbine with CMC blades and independent platforms, it is therefore necessary to respect the limit of the admissible centrifugal force of a blade-disc attachment, this limit being determined according to the installation radius, the number of blades and the chord at the root of the blade. There is therefore a real need for a technology to limit the mechanical loading of the blade-disc attachment for CMC blades with independent platforms (as opposed to integrated platforms). Summary of the invention To address the problems mentioned above of absorbing the centrifugal forces of the platform by the blade-disc attachment, the applicant proposes a platform equipped with a downstream hook anchored to the top of a tooth of the disc and an upstream hook held axially by a flange. In the following description, the terms "upstream" and "downstream" are defined in relation to the direction of air flow from the air inlet into the LP turbine to the air outlet from the LP turbine. In other words, upstream and downstream are understood to be along a central axis X relative to the general direction of the gases in operation. In the description, the term "exterior" designates the surfaces or parts of parts furthest from the central axis X of the air stream of the turbomachine (i.e. the axis of rotation of the fan blades), as opposed to the term "interior" which designates the surfaces and parts of parts closest to said central axis X. According to a first aspect, the invention relates to an X-axis turbomachine turbine rotor assembly comprising: a rotor disc centered on the X axis and having cells which de- close at the external periphery of the disc, two circumferential alveoli- adjacent teeth delimiting a tooth of the disc, and moving blades each comprising a foot mounted in one of the cells of the disc and a blade which extends the foot, a plurality of platforms for holding the moving blades in the cells of the disc, each platform being mounted circumferentially between two circumferentially adjacent moving blades, and a flange for holding the moving blades in the cells. This rotor assembly is characterized by the fact that each platform includes: a vein wall configured to delimit a gas flow vein of the turbomachine, an L-shaped downstream hook with the vertical portion of the L extending ra- dially from the vein wall and the horizontal portion of the L housed in a corresponding retaining hook positioned at the top of a tooth of the disc > êt an upstream hook extending substantially radially from an upstream zone of the vein wall and held axially between the flange and the disc. The platforms of this rotor assembly are designed to allow the centrifugal forces of the platforms to be absorbed onto the disc (unlike the state of the art where the centrifugal forces are absorbed by the blade-disc attachment), which makes it possible to limit the mechanical loading of the blade-disc attachment. In addition to the characteristics which have just been mentioned in the preceding paragraph, the rotor assembly according to one aspect of the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations: the upstream hook of each platform extends at least partially along of an upstream face of the disc, between said upstream face of the disc and the flange. the upstream hook of each platform is in the shape of an inverted L with a vertical portion of the inverted L extending substantially radially from the vein wall and a horizontal portion of the inverted L extending substantially perpendicularly from the vertical portion of the inverted L and housed in a flange groove. The upstream hook of each platform is L-shaped with a portion vertical of the L extending substantially radially from the vein wall and a horizontal portion of the L extending substantially perpendicularly from the vertical portion of the L and housed in a rib of the upstream face of the disk. The upstream hook of each platform is L-shaped with a portion vertical of the L extending substantially radially from the vein wall and a horizontal portion of the L extending substantially perpendicularly from the vertical portion of the L and housed in a retaining tab at the top of the disc tooth. the downstream hook of each platform extends from a downstream area of ​​the wall vein, radially to the right of the hook holding the disc tooth. the downstream hook of each platform extends from a central area of ​​the vein wall, radially to the right of the tooth holding hook of the disk. it includes an axial blade retaining ring positioned downstream of the disc. the platform has a radial wall extending downstream from the wall of vein to the top of a tooth of the disc. each platform has a circumferential end edge of shape complementary to the shape of a blade of the moving vane, a sealing ring being housed in a recess in each circumferential end edge. it has a retaining ring housed in a groove in the rotor disc, at a radially inner end of the flange, the snap ring being configured to secure the flange to the disc after mounting the said flange on the disc. A second aspect of the invention relates to a turbomachine, characterized in that it comprises a rotor assembly according to the first aspect. A third aspect of the invention relates to a method of mounting moving blades in cells of a rotor disk, characterized in that it comprises the following steps: choice of a first and second blade holding platforms mobile, installation of a sealing bead in a recess of an end edge circumferential of a vein wall of each of the first and second platforms, assembly of the first and second circumferential platforms partly on either side of a moving blade, assembly of successive platforms, one after the other, circumfer- entially on either side of moving blades so as to form a crown of moving blades, assembly of the crown of moving blades in the disc by translation of the blade roots in cells of the disc from an upstream face of the disc, positioning a retaining ring in a groove of the disc, and positioning of the flange in the groove of the disc, along the upstream face of the disk. BRIEF DESCRIPTION OF THE FIGURES Other advantages and characteristics of the invention will appear on reading the following description, illustrated by the figures in which: [Fig. 1], already described, represents a schematic view in longitudinal section- Tudinal view of part of a LP turbine with several blade wheels according to the condition of the technique; [Fig.2A] schematically represents a partial sectional view of a disc and a moving blade of an LP turbine rotor assembly according to a embodiment of the invention, the section being along the section line AA” of [Fig.2C]; [Fig.2B] schematically represents a partial sectional view of a disc and a moving blade of a LP turbine rotor assembly according to the same embodiment as [Fig.2A], with a section along the line of section BB' of [Fig.2C]; [Fig.3] schematically represents a partial perspective view of a disc and a blade wheel of a LP turbine rotor assembly according to a embodiment of the invention; Figures 4A, 4B, 4C and 4D schematically represent views in partial perspective of a disc and a moving blade of a rotor assembly LP turbine according to embodiments different from figures ZA and 2B; Figures 5A and 5B schematically represent a perspective view and a sectional view of a sealing ring housed in each platform of the LP turbine rotor assembly; and [Fig.6] schematically represents different perspective views of a disc and blade wheel of a LP turbine rotor assembly during of the process of mounting the blade wheel in the disc. In the figures, identical elements are identified by identical references. For reasons of readability of the figures, the size scales between elements represented are not respected. DETAILED DESCRIPTION An exemplary embodiment of an LP turbine rotor assembly is described in detail below, with reference to the accompanying drawings. This example illustrates the characteristics and advantages of the invention. It is however recalled that the invention is not limited to this example. An example of a portion of an LP turbine rotor assembly is shown in Figures ZA and 2B as well as in [Fig. 3]. In particular, [Fig. 2A] shows the LP turbine rotor assembly in a sectional view along the section line AA' (shown in [Fig. 2C]) passing through the top of a tooth 111 of the disc 110. [Fig. 2B] shows this same LP turbine rotor assembly in a sectional view along the section line BB° (shown in [Fig. 2C]) passing through the cell 112 of the disc 110. [Fig. 3] shows a perspective view of a portion of the disc 110 in which two blades 120 are mounted. Figures ZA and 2B show a portion of a moving blade 120 whose blade 122 extends radially along a radial axis R, perpendicular to the axis of rotation X of the rotor, and whose root 121, here in the form of a dovetail, is housed in a cell 112 of the disk 110. As a reminder, a LP turbine rotor disk comprises a plurality of cells 112 which open at the outer periphery of said disk and extend axially between an upstream face 113 and a downstream face 114 of said disk, two successive cells 112 being separated by a tooth 111. A platform 130, independent of the blade 120, is mounted between the two blades 122 of two circumferentially consecutive blades 120, as shown in FIGS. 2A and 3. The platform 130 comprises a main wall 131 extending substantially axially (along the axis of rotation X) between the two blades 122 to form a gas circulation vein. The main wall 131, or vein wall, is preferably inclined from upstream to downstream, for example from the inside of the rotor to the outside or from the outside to the inside; to form a more or less steep vein slope; the main wall 131 may alternatively not be inclined. The main wall 131 comprises two circumferential end edges 131a, 131b, respectively, convex and concave, each having a curvature adapted to the curvature of the blades 122. In particular, when a platform 130 is arranged between two circumferentially consecutive blades 122, the convex edge 131a matches the shape of the intrados of one of the blades and the concave edge 131b matches the shape of the extrados of the other of these two blades so as to ensure the continuity of the gas circulation vein. As shown in [Fig.Z2A], the platform 130 comprises a downstream hook 132 and an upstream hook 133. The downstream hook 132 is a fastener, integral with the main wall 131, the cross-section of which is L-shaped. The L-shape of the downstream hook 132 comprises a leg 132a, or vertical portion, extending substantially radially from the main wall 131 towards the disc 110 and an arm 132b, or horizontal portion, extending substantially perpendicularly from the leg 132a downstream, into a first holding tab 115 positioned at the top of a tooth 111 of the disc 110. Whatever the inclination of the main wall 131 of the platform 130, the downstream hook 132a extends from the main wall 131 of the platform 130, in line with the holding hook 115 of the disc. The upstream hook 133 is a tab, integral with the main wall 131, which extends radially from the main wall 131 along or in continuity with the upstream face 113 of the disc 110. In certain embodiments described later, the tab forming the upstream hook 133 is a flat and rectilinear tab. In other embodiments, such as that of [Fig.2A], the tab forming the upstream hook 133 is curved at its free end (or inner end) and has a cross-section in the shape of an inverted L. In these embodiments, the upstream hook 133 comprises a leg 133a extending substantially radially from the main wall 131 towards the disc 110 and an arm 133b extending substantially perpendicularly from the leg 133a towards the upstream to be housed in a groove 141 of the flange 140, itself secured to the disc 110.Indeed, the rotor assembly 100 comprises a flange 140, or retaining ring, mounted radially along the upstream face 113 of the disc 110. This flange 140, of annular shape, extends parallel to the cells 112 and to the inter-cell teeth 111 of the disc 110 over the entire circumferential length of the disc. This flange 140, the shape of which is conventional for an LP turbine flange, comprises a spoiler 142 at least partially housed in a groove 116 of the disc 110. This spoiler 142 ensures the attachment of the flange 140 to the disc 110, making the flange integral with the disc 110. Thus mounted along the disc 110, the flange 140 extends upstream of the upstream face 113 of the disc to axially hold (from downstream to upstream) the blades 120 in the disc 110. It is thus understood that, in the embodiment of figures 2A, 2B and 3, the platform 130 is secured to the disc 110, on the one hand, directly by means of the downstream hook 132 and, on the other hand, indirectly (via the flange 140) by means of the upstream hook 133. Such an architecture of the platform 130 makes it possible to take up the centrifugal forces of the platform directly on the disc 110, avoiding excessive mechanical loading of the blade-disc attachment. This take-up of the centrifugal forces of the platform also has the advantage of not requiring any additional part to the parts usually used in a LP turbine rotor assembly since the flange is a part usually used for holding the blades; only the means of attachment of the platform is modified so that it is attached to the disc and not to the moving blade. Figures 4A, 4B, 4C and 4D represent embodiments different from that described previously in connection with Figures 2 and 3. In the embodiment of [Fig.4A], the downstream hook 132 is identical to that described previously for [Fig.2A] but the upstream hook 133 differs somewhat. Indeed, in this embodiment, the tab forming the upstream hook 133 is curved at its free end so that the upstream hook has an L-shaped section with a leg 133a extending substantially radially from the main wall 131 towards the disc 110 and an arm 133c extending substantially perpendicularly from the leg 133a in the downstream direction. The arm 133c of the upstream hook 133 is designed to be housed in a rib 117 of the upstream face 113 of the disc 110.The rib 117 of the disc 110 is positioned at a radial height covered upstream by the flange 140 so that, when the arm 133c of the upstream hook 133 is in place in the rib 117, the upstream hook 133 is held integral with the disc 110. Thus, in this embodiment of [Fig.4A], the platform 130 is secured directly to the disc 110 upstream by the upstream hook 133 and downstream by the downstream hook 132. As previously, the architecture of the platform 130 makes it possible to take up the centrifugal forces of said platform directly on the disc 110, without requiring any additional part to the parts usually used in a LP turbine rotor assembly. In the embodiment of [Fig.4B], the downstream hook 132 is identical to that described previously for [Fig.2A] but the upstream hook 133 differs somewhat. In this embodiment, the tab forming the upstream hook 133 is curved at its free end so that the upstream hook has an L-shaped section with a leg 133a extending substantially radially from the main wall 131 towards the disc 110 and an arm 133d extending substantially perpendicularly from the leg 133a in the downstream direction. The arm 133d of the upstream hook 133 is designed to be housed in a holding tab 118 at the top of the tooth of the disc 111. The holding tab 118 of the tooth 111 of the disc 110, which has for example an inverted C-shaped section, is positioned at the top of the tooth 111 in an area close to the upstream face 113 of the disc 110, the holding hook 115 (whose shape may be similar to that of the holding tab 118) being positioned in an area close to the downstream face 114 of the disc 110. In this embodiment, the surface of the flange 140 may be radially larger than the surface of a usual flange so as to cover the upstream face 113 of the disc up to the top of the tooth 111 and at least up to the holding tab in order, when the arm 133d of the upstream hook 133 is in place in the holding tab 118, to keep the upstream hook 133 secured to the disc 110. As for the embodiment of [Fig.4A], the platform 130 is secured directly to the disc 110 upstream by the upstream hook 133 and downstream by the downstream hook 132. As previously, the architecture of the platform 130 makes it possible to take up the centrifugal forces of said platform directly on the disc 110, without requiring any additional parts to the parts usually used in an LP turbine rotor assembly. In the embodiment of [Fig.4C], the downstream hook 132 is substantially identical to that described previously for [Fig.2A] except that it extends from a substantially central zone of the main wall 131 (i.e., a zone which is neither close to the upstream end of the main wall nor close to the downstream end of said main wall) to the retaining hook 115. This retaining hook 115 is then positioned in a substantially central zone of the top of the tooth 111 (more or less halfway between the upstream face 113 and the downstream face 114 of the disc 110). In this embodiment, the upstream hook 133 comprises a flat and rectilinear tab which extends substantially radially from the main wall 131 towards the disc 110, along the upstream face 113 of the disc 110. When the rotor assembly is mounted, the flat tab forming the upstream hook 133 is then inserted between the upstream face 113 of the disc and the flange 140.In this embodiment, the surface of the flange 140 is radially larger than the surface of a conventional flange so as to cover the upstream face 113 of the disc up to the top of the tooth 111 and contain the upstream hook 133 against the upstream face 113 of the disc. As for the embodiment of [Fig.2A], the platform 130 is secured to the disc 110, on the one hand, directly by means of the downstream hook 132 and, on the other hand, indirectly (via the flange 140) by means of the upstream hook 133. To improve its radial retention, the platform 130 may comprise a radial wall 123 extending in a downstream zone of the platform, from the main wall 131 to the top of the tooth 111 of the disc. This radial wall extends in the continuity of the downstream end 114 of the disc, in line with the downstream end 111a of the tooth 111.As previously, the architecture of the platform 130 of this embodiment makes it possible to take up the centrifugal forces of said platform directly on the disk 110, without requiring any additional part to the parts usually used in a LP turbine rotor assembly. In the embodiment of [Fig.4D], the downstream hook 132 and the upstream hook 133 are identical to those described previously for [Fig.4C]. In this embodiment, an axial retaining element 150 is mounted along the downstream face 114 of the disk and the downstream zone of the blade root 121 in order to improve the radial retention of the platform 130. This axial retaining element 150 may extend, for example, between a bottom zone 119 of the disk 110 and a shoulder 135 in the main wall 131 of the platform 130. This axial retaining element 150 may provide not only the function of radial retention of the platform 130 but also of axial retention of the moving blade 120 in the disk 110. As previously, the architecture of the platform 130 of this embodiment makes it possible to take up the centrifugal forces of said platform directly on the disk 110. Regardless of the embodiment of the platform 130, the rotor assembly 100 may advantageously comprise a plurality of sealing rings 160, as shown in [Fig.SA] and [Fig.5B]. It preferably comprises two sealing rings per moving blade 120. Indeed, a sealing ring 160 may be housed in a recess 131c made in each of the circumferential end edges 131a and 131b of the main wall 131 of the platform 130. Each of the sealing rings 160 is designed to provide a seal around the blade 122 of the moving blade 120 when the platforms 130 are mounted between the moving blades. In other words, a sealing ring 160 is housed in each recess 131c of the main wall 131 so as to seal the junction between each of the platforms 130 and the intrados and the extrados of each of the blades 122 and, thus, ensure the sealing of the gas circulation vein. The rotor assembly 100 as described above is mounted by successively assembling its various parts. Whatever the embodiment of the platform 130, the method of mounting the rotor assembly 100 may comprise, for example, the following steps, shown in drawings A to F of [Fig. 6]. A first step consists of choosing a first and a second platform 130 suitable for holding the moving blades 120, as shown in drawing A of [Fig. 6]. A second step (drawings B of [Fig. 6]) consists of installing a sealing ring 160 in a recess 131c, or rib, of a circumferential end edge 131a or 131b of the main wall 131 of each of the platforms 130. The third step (drawing C of [Fig.6]) then consists of assembling the first and second platforms 130 on either side of a blade 122 of a moving vane, the sealing ring 160 then being compressed between the recess 131c and the intrados or the extrados of the blade 122. All the platforms 130 are assembled circumferentially one after the other, circumferentially on either side of the blades 122 of the moving vanes so as to form a wheel, or crown, of moving vanes 120n. The wheel of moving vanes is thus assembled. A fourth step (drawings D of . [Fig. 6]) consists of assembling the mobile blade wheel 120n in the disc 110 by translating the blade roots 121 in the cells 112 of the disc 110. This translation is carried out by sliding each blade root 121 of the mobile blade wheel 120n in a cell 112 of the disc, from the upstream face 113 of the disc towards the downstream face 114 of the disc. Once all the blade roots 121 are installed in the cells 112, it is checked that the downstream hooks 132 are correctly installed in the first holding tabs 115 and / or that the upstream hooks 133 are correctly installed in the locations provided depending on the chosen embodiment. A retaining ring 170 is then positioned in the groove 116 of the disc (drawing E of [Fig. 6]). The groove 116 is a cavity made in the upstream face 113 of the disc over the entire circumference of the disc.The retaining ring 170 is a substantially annular part, made of a flexible, substantially elastic material (for example in one of the superalloys conventionally used in turbines) and comprising a radial slot allowing a lowering of said retaining ring into the groove 116 for the insertion of the flange 140. A sixth step (drawing F of [Fig.6]) finally consists of positioning the flange 140 at least partially in the groove 116 of the disc by pushing the retaining ring 170 into the bottom of the groove so as to ensure the securing of the flange on the disc. Although described through a number of examples, variations and embodiments, the rotor assembly according to the invention includes various variations, modifications and improvements which will be obvious to those skilled in the art, it being understood that these variations, modifications and improvements are part of the scope of the invention.

Claims

Claims

1. Rotor assembly (100) of DC turbine turbomachine of axis (X) comprising: a rotor disc (110) centered on the axis (X) and having alveoli (112) which open at the external periphery of the disc (110), two circumferentially adjacent alveoli delimiting a tooth (111) of the disc (110), moving blades (120) each comprising a mounted foot in one of the cells (112) of the disc (110) and a blade which extends the foot, a plurality of blade holding platforms (130) mobile in the alveoli of the disc (110), each platform (130) being mounted circumferentially between two blades circumferentially adjacent movable (120), and a flange (140) for holding the moving blades (120) in the alveoli, characterized in that each platform (130) comprises: a vein wall (131) configured to define a vein flow of gases from the turbomachine, an L-shaped downstream hook (132) with the vertical portion of the L (132a) extending radially from the vein wall (131) and the horizontal portion of the L (132b) housed in a corresponding holding hook (115) positioned at top of a tooth (11) of the disc (110); and an upstream hook (133) extending substantially radially from an upstream area of ​​the vein wall (131) and maintained axially between the flange (140) and the disc (110).

2. Rotor assembly according to claim 1, characterized in that the upstream hook (133) of each platform (130) extends at least par- initially along an upstream face of the disc (113), between said face upstream of the disc (113) and the flange (140).

3. A rotor assembly according to claim 1 or 2, characterized in that the upstream hook (133) of each platform (130) is L-shaped inverted with the vertical portion of the inverted L (133a) extending sen- possibly radially from the vein wall (131) and the portion ho- rhizomatous inverted L (133b) extending approximately perpendicular- clearly from the vertical portion of the inverted L and housed in a groove (141) of the flange (140).

4. A rotor assembly according to claim 1 or 2, characterized in that the upstream hook (133) of each platform (130) is L-shaped with the vertical portion of the L (133a) extending substantially radially from the vein wall and the horizontal portion of the L (133b) extending substantially perpendicularly from the vertical portion of the L and housed in a rib (117) of the upstream face (113) of the disc.

5. Rotor assembly according to claim 1 or 2, characterized in that the upstream hook (133) of each platform (130) is L-shaped with the vertical portion of the L (133a) extending substantially radially from the vein wall and the horizontal portion of the L (133b) extending substantially perpendicularly from the vertical portion of the L and housed in a second holding tab (118) at the top of the tooth (111) of the disc.

6. A rotor assembly according to any one of claims 1 to 5, ca- characterized in that the downstream hook (132) of each platform (130) extends from a downstream zone and / or a central zone of the vein wall (131), radially to the right of the retaining hook (115) of the tooth of the disk.

7. Rotor assembly according to claim 6, characterized in that it comprises an axial retaining ring (150) of blades positioned downstream of the disk (110).

8. A rotor assembly according to claim 6, characterized in that the platform (130) comprises a radial wall (123) extending downstream, from the vein wall (131) to the top of a tooth (111) of the disc (110).

9. A rotor assembly according to any one of the preceding claims- preceding, in which each platform (130) has an edge circumferential end (131a, 131b) of complementary shape to the shape of a blade (122) of the moving vane, and a sealing ring being housed in a recess (131c) of the circumferential end edge.

10. | A rotor assembly according to any one of the preceding claims preceding, characterized in that it comprises a stop ring (150) housed in a groove (116) of the rotor disc, at one end radially internal of the flange (140), the retaining ring being configured to secure the flange (140) to the disc (110) after mounting said flange (140) on the disc (110).

11. Turbomachine, characterized in that it comprises a rotor assembly according to any one of the preceding claims.

12. Method of mounting mobile blades (120) in cells (112) of a rotor disc (110) of a rotor assembly (100) according to one of the res- indications 1 to 10, characterized in that it comprises the following steps: choice of a first and a second platform (130) of maintenance of the moving blades, installation of a sealing bead (160) in a recess (131c) of a circumferential end edge (131a, 131b) of a vein wall (131) of each of the first and second platforms, assembly of the first and second platforms (130) circumferentially on either side of a moving blade (120), assembly of successive platforms, one after the other others, circumferentially on either side of blades movable so as to form a crown (120n) of blades mobile, assembly of the crown (120n) of mobile blades (120) in the disc (110) by translation of the blade roots (121) in alveoli (112) of the disc from an upstream face (113) of the disk, positioning of a stop ring (150) in a groove (116) of the disk, and positioning of the flange (140) in the groove of the disc, the along the upstream face (113) of the disc.