Sealing ring for a turbomachine turbine

Abstract

The invention relates to a sealing ring (2) for a turbomachine turbine comprising a rotor disc rotatably mounted in a casing and surrounded by the frustoconical sealing ring comprising an annular row of ring sectors (5, 6), a first circular peripheral edge (7) of radius R1 and a second circular peripheral edge (8), opposite the first peripheral edge, of radius R2, greater than the radius R1, wherein the sealing ring comprises at least one first curved ring sector (5) having a first axial end edge (9) defining a first chord of length L1 and a second axial end edge (10) defining a second chord of chord length L2, and at least one second curved ring sector (6) having a third axial end edge (11) defining a third chord of length L3 and a fourth axial end edge (12) defining a fourth chord of length L4 strictly greater than L2, L2 being strictly less than L1.

Description

Sealing ring for a turbomachine turbine Technical Field [OOOlJThe present invention relates to a sealing ring for a turbomachine turbine, a turbine comprising such a ring and a method for dismantling the sealing ring. Previous technique

[0002] A turbomachine turbine comprises a first stage and at least one second stage positioned downstream of the first. Each stage includes a distributor consisting of an annular row of fixed blades mounted on a turbine housing, and a rotating impeller generally mounted downstream of the distributor. The impeller is surrounded by a sectored sealing ring formed by circumferentially arranged end-to-end segments mounted on the turbine housing.

[0003] An example of a turbomachine turbine is described in document W02016024060.

[0004] Each ring sector generally comprises a curved metal support with a circumferential orientation. The metal plate supports a layer of abradable material fixed to the inner surface of the support. The abradable material layer, or abradable element, is, for example, of the honeycomb type and is designed to wear away by friction against external annular grooves on the wheel blades, forming a seal and minimizing radial clearance between the wheel and the ring sectors.

[0005] The sealing ring has a frustoconical shape and comprises a circular upstream peripheral rim and a circular downstream peripheral rim, opposite the upstream peripheral rim. The radius of the downstream peripheral rim is greater than the radius of the upstream peripheral rim. The ring The sealing joint flares out along an axial direction of fluid flow in the turbine.

[0006] The turbine comprises a first stage positioned at a forward part of the turbine and at least a second stage positioned downstream of the first stage.

[0007] The terms "upstream" and "downstream" are defined in relation to the airflow in the turbomachine.

[0008] During a first stage maintenance operation, it is typically necessary to dismantle the turbine stages positioned downstream of the first stage beforehand, in order to access the first stage, which results in very long dismantling and reassembly times.

[0009] This constraint is due to the truncated conical shape of the sealing ring resulting in ring sectors which each have a curved downstream edge with a chord of greater length than the chord of the upstream edge of the ring sectors. [00 lOJTherefore, dismantling a sealing ring can only be achieved by translating the ring sectors along the axial direction of airflow (downstream), resulting in the dismantling of the entire turbine. The upstream translation of each ring sector is prevented by the blocking of the downstream edge of the ring sector, which is longer than the upstream edge, between two other circumferentially adjacent ring sectors, defining a narrower passage at the upstream peripheral edge than at the downstream peripheral edge.

[0011] To be able to translate the first stage ring sectors in a direction opposite to the axial direction of fluid flow and thus dismantle the first stage ring sectors from upstream of the turbine without having to dismantle all the stages of the turbine, it is necessary to provide a shallow flow slope, i.e. a less flared turbine, and larger clearances between the first stage ring sectors.

[0012] However, this constraint contradicts the need to increase the vein slope to values ​​greater than 30° without having to increase the clearances between the ring sectors, which would lead to air leaks and thermal leaks. Description of the invention

[0013] The invention therefore aims to resolve at least in part these drawbacks by proposing a sealing ring for a first stage of a turbomachine turbine facilitating turbine maintenance.

[0014] The invention relates to a sealing ring for a turbomachine turbine intended to be mounted around a rotating wheel mounted inside a turbine housing about an axis of rotation. The sealing ring has a frustoconical shape and comprises an annular row of circumferentially adjacent ring sectors around the axis of rotation. The sealing ring has a first circular peripheral edge of radius RI and a second circular peripheral edge, axially opposite to the first peripheral edge, of radius R2, greater than radius RI. The sealing ring comprises at least one first curved ring sector having, on the side of the first peripheral edge, a first axial end edge defining a first chord of length L1 and, on the side of the second peripheral edge,a second axial end edge defining a second chord of chord length L2, and at least a second curved ring sector having, on the side of the first peripheral edge, a third axial end edge, defining a third chord of length L3 and, on the side of the second peripheral edge, a fourth axial end edge defining a fourth chord of length L4 strictly greater than the chord length L2 of the second axial end edge of the first ring sector, L2 being strictly less than L1.,

[0015] The terms "upstream" and "downstream" are defined in relation to the airflow in the turbomachine.

[0016] The invention thus provides a sealing ring, in particular for a first stage of a turbomachine turbine, facilitating turbine maintenance.

[0017] The first ring sector of the first stage of the turbine can be extracted from the sealing ring from the upstream side of the sealing ring without its downstream edge, the second axial end edge, being blocked by two second ring sectors adjacent to the first ring sector. It is then easy to remove the other sectors from the upstream side of the turbine.

[0018] The sealing ring of the first stage of the turbine can thus be disassembled without having to first disassemble the other stages of the turbine positioned downstream of the first stage.

[0019] It is therefore possible to provide a higher vein slope (greater than 30°) without having to increase the gaps between the ring sectors, which would lead to air leaks and thermal leaks.

[0020] In some embodiments, the annular row of ring sectors is formed by an alternation of first ring sectors and second ring sectors.

[0021] The sealing ring is formed from two different sets of ring sectors.

[0022] In some embodiments, the length L1 of the first chord of the first axial end edge of the first ring sector is equal to the length L3 of the third chord of the third axial end edge of the second ring sector.

[0023] This configuration simplifies the design of the sealing ring.

[0024] In some embodiments, L3 = L1 = (2 x Pi x RI) / number of sectors, with L4 = L3 + d and L2 = L3 - d, d being a non-zero variable such that d > 2 x (R2 - RI) x sin (Pi / N).

[0025] In some embodiments, the length L4 of the fourth chord of the fourth axial end edge of the second ring sector is equal to the length L2 of the second chord of the second axial end edge of the first sector of ring with L4 = L2 = (2 x Pi x R2) / number of sectors, with L3 = L4 - d and L1 = L4 + d, d being a non-zero variable.

[0026] In some embodiments, d is between 2 mm and 25 mm.

[0027] Preferably, the first peripheral border is a first upstream peripheral border oriented towards the upstream direction, the second peripheral border being a second downstream peripheral border oriented towards a direction opposite to the upstream direction.

[0028] The invention also relates to a turbomachine turbine comprising at least one stage having an annular row of fixed blades carried by a turbine casing and a rotating movable wheel surrounded by a sealing ring as defined above.

[0029] In some embodiments, the turbine comprises several stages, including a first stage positioned upstream of at least one second stage, with the sealing ring positioned in the first stage.

[0030] The invention is particularly advantageous for facilitating the dismantling of the first stage sealing ring.

[0031] The invention also relates to a turbomachine comprising a turbine as defined above.

[0032] In some embodiments, the turbomachine includes an annular wall fixed to an upstream support, the sealing ring comprising at least one fastening element having a downstream end positioned opposite the second peripheral edge of the sealing ring and engaging in a first fastening slot of the annular wall, the first peripheral edge of the sealing ring being engaged in a second fastening slot of the upstream support.

[0033] The invention also relates to a method for dismantling a sealing ring as defined above and comprising a first step of extracting the first ring sector out of the sealing ring in an upstream direction, opposite to a direction of air flow in the turbine, followed by a second stage of extraction of the second ring sector out of the sealing ring in the upstream direction.

[0034] The invention provides a dismantling method facilitating the dismantling of the sealing ring of a first stage of the turbine and consequently facilitating the maintenance of the turbine.

[0035] The invention also relates to a disassembly method. The turbomachine includes an upstream housing fixed to the upstream support. The method comprises: - a first step of disengaging the upstream casing from the upstream support, - a second stage of disengaging the upstream support from the annular wall and the sealing ring, - a third step of axial translation of the sealing ring towards the upstream direction to disengage the sealing ring from the annular wall, and - a fourth extraction step of at least one of the first ring sectors out of the sealing ring towards the upstream direction.

[0036] The aforementioned features and advantages, as well as others, will become apparent upon reading the detailed description that follows. This detailed description refers to the attached drawings. Brief description of the drawings

[0037] The attached drawings are schematic and are primarily intended to illustrate the principles of the presentation.

[0038] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference symbols.

[0039] [Fig. 1] Figure 1 schematically represents a sealing ring for a turbomachine turbine comprising first ring sectors during their disassembly or assembly, according to an embodiment of the invention;

[0040] [Fig. 2] Figure 2 schematically represents in detail a first ring sector translating between two second ring sectors;

[0041] [Fig. 3] Figure 3 schematically represents a top view of the sealing ring in two dimensions when the sealing ring is assembled;

[0042] [Fig. 4] Figure 4 schematically represents a diagram of a turbomachine dismantling process. Description of the implementation methods

[0043] To make the explanation more concrete, an example of a sealing ring is described in detail below, with reference to the attached drawings. It should be noted that the invention is not limited to this example.

[0044] Figure 1 partially illustrates a sealing ring 2 of a low-pressure turbine in a turbomachine such as a turbojet or aircraft turboprop engine. The turbine has several stages, including a first stage and at least one second stage located downstream of the first stage. The sealing ring 2 is positioned in the first stage of the turbine.

[0045] The terms "upstream" and "downstream" are defined in relation to the airflow in the turbomachine.

[0046] Each turbine includes a distributor consisting of an annular row of fixed blades carried by a turbine casing and a movable wheel 1, called a blade wheel, mounted downstream of the distributor and rotating around an axis of rotation X in the sealing ring 2 which is attached to the casing.

[0047] The sealing ring 2 is sectored and comprises an annular row of ring sectors 5, 6 arranged so that the circumferential edges 3, 4 of two adjacent ring sectors 5, 6 are opposite each other. The ring sectors 5, 6 are circumferentially supported end to end by the turbine housing and extend around the axis of rotation X.

[0048] The sealing ring 2 has a frustoconical shape and comprises a first circular peripheral rim 7 of radius RI and a second rim circular peripheral 8, opposite the first peripheral border 7, of radius R2.

[0049] According to a preferred embodiment which is described below, the first peripheral border 7 is a first upstream peripheral border 7 oriented towards the upstream direction A, and the second peripheral border 8 is a second downstream peripheral border 8 oriented towards a direction opposite to the upstream direction A.

[0050] The radius R2 is greater than the radius RI. The perimeter of the second peripheral border 8 is greater than the perimeter of the first peripheral border 7.

[0051] Each ring sector 5, 6 is curved in the circumferential direction and includes a metal support with a circumferential orientation. The metal support carries a layer of abradable material (abradable element) fixed to the inner surface of the support by brazing and / or welding. The layer of abradable material is of the honeycomb type and is designed to wear away by friction against external annular scuffs of the rotating wheel 1 to minimize radial play between the rotating wheel 1 and the ring sectors 5, 6.

[0052] The sealing ring 2 comprises at least one first ring sector 5 having a first axial end edge 9 defining a first chord of length L1 and a second axial end edge 10 defining a second chord of length L2. The sealing ring 2 also comprises at least one second ring sector 6 having a third axial end edge 11 defining a third chord of length L3 and a fourth axial end edge 12 defining a fourth chord of length L4. The chord length L2 of the second axial end edge 10 of the first ring sector 5 is strictly less than the fourth chord of length L4. The length of the second chord L2 of the second axial end edge 10 of the first ring sector 5 is strictly less than the length of the first chord L1 of the first axial end edge 9.

[0053] Figure 1 shows the sealing ring 2 during the disassembly or assembly of the ring sectors 5 and 6, and more specifically when the first ring sectors 5 are being translated relative to the second ring sectors 6 along an upstream direction A, opposite to the direction of airflow in the turbine. The first ring sectors 5 are offset relative to the second ring sectors 6.

[0054] In the mounted position, when the first sectors of ring 5 are not translated relative to the second sectors of ring 6, the first and second peripheral borders 7, 8 are circular, as illustrated by the two circularly shaped dashed lines in Figure 1.

[0055] The first chord of length L1 is defined between two opposite upstream first ends 13 of the first axial end edge 9. The second chord of length L2 is defined between two opposite downstream second ends 14 of the second axial end edge 10. The third chord of length L3 is defined between two opposite upstream third ends 15 of the third axial end edge 11. The fourth chord of length L4 is defined between two opposite downstream fourth ends 16 of the fourth axial end edge 12.

[0056] Preferably, the annular row of sectors of rings 5, 6 is formed by an alternation of first sectors of ring 5 and second sectors of ring 6. In other words, each first sector of ring 5 is positioned between two second sectors of ring 6. And each second sector of ring 6 is positioned between two first sectors of ring 5.

[0057] Figure 3 schematically represents a two-dimensional top view of the sealing ring 2 when the sealing ring is assembled. The first and second ring sectors 5, 6 resemble two trapezoids of different dimensions but the same length on the side of the first peripheral edge 7 of the sealing ring 2. The lengths of the trapezoids are different on the side of the second peripheral edge 8 of the sealing ring 2. The trapezoids are positioned alternately.

[0058] The first ring sector 5 has two opposing first circumferential edges 3. The second ring sector 6 has two opposing second circumferential edges 4. Each first circumferential edge 3 of the first ring sectors 5 is circumferentially adjacent to one of the second circumferential edges 4 of a second ring sector 6 when the ring sectors 5, 6 are joined end to end to form the sealing ring 2.

[0059] Preferably, the length L1 of the first chord of the first axial end edge 9 of the first ring sector 5 is equal to the length L3 of the third chord of the third axial end edge 11 of the second ring sector 6.

[0060] In other words, all the first axial end edges 9 of the first ring sectors 5 and the third axial end edges 11 of the second ring sectors 6 have the same chord length. The second peripheral edge 8 of the sealing ring 2 is formed by an alternation of second axial end edges 10 having a second chord of length L2 and fourth axial end edges 12 having a fourth chord of length L4.

[0061] In other words, all the first axial end edges 9 of the first ring sectors 5 and the third axial end edges 11 of the second ring sectors 6 are arched and have the same arc length. The sum of the arc lengths defines the perimeter of the first peripheral edge 7 of the sealing ring 2.

[0062] The second peripheral edge 8 of the sealing ring 2 is formed by an alternation of a second axial end edge 10 having a first arc length and a fourth axial end edge 12 having a second arc length, the first arc length being smaller than the second arc length. The sum of the first and second arc lengths defines the perimeter of the second peripheral edge 8 of the sealing ring 2.

[0063] Let Le be the total chord length corresponding to the sum of the second chords of the second axial end edges 10 of the first ring sectors 5 and the fourth chords of the fourth axial end edges 12 of the second ring sectors 6.

[0064] Let d be a non-zero variable, each length L2 of the second chords of the second axial end edges 10 of the first sectors of ring 5 is equal to the length Le divided by the number of sectors of ring 5, 6 subtracted from the variable d (L2 = (Le / number of sectors of ring) - d).

[0065] Each length L4 of the fourth chords of the fourth axial end edges 12 of the second ring sectors 6 is equal to the length Le divided by the number of ring sectors 5, 6 incremented by the variable d (L4 = (Le / number of ring sectors) + d).

[0066] Thus, to dismantle the sealing ring 2, at least one first sector of ring 5 can be translated towards the upstream direction A. In other words, the first sector of ring 5 can be extracted from the sealing ring 2 from the upstream of the sealing ring 2.

[0067] It is then possible to translate the second ring sectors 6 out of the sealing ring 2 along the upstream direction A.

[0068] According to another variant, the string lengths are approximated to the corresponding arc lengths with L3 = L1 = circumference of the first peripheral border 7 / number of sectors 5, 6 = (2 x Pi x RI) / number of sectors 5, 6, with L4 = L3 + d and L2 = L3 - d, d being a non-zero variable such that d > 2 x (R2 - RI) x sin (Pi / N).

[0069] Preferably, d is between 2 mm and 25 mm. The gap between sectors 5, 6 is less than 15 mm, preferably equal to 10 mm.

[0070] According to another possible process, all the first sectors of ring 5 are translated towards the upstream direction A to be extracted from the sealing ring 2 from the upstream side of the turbine. The second sectors of ring 6 are then extracted from the sealing ring 2 along the upstream direction A.

[0071] According to another embodiment, several stages of the turbine include a sealing ring 2 removable from the upstream side of the turbine, as defined previously.

[0072] According to another embodiment shown in Figure 1, all stages of the turbine include a sealing ring 2 removable from the upstream side of the turbine, as defined previously.

[0073] According to another embodiment (not shown), the length L1 of the first chord of the first axial end edge 9 of the first ring sector 5 is different from the length L3 of the third chord of the third axial end edge 11 of the second ring sector 6.

[0074] The length L4 of the fourth chord of the fourth axial end edge 12 of the second ring sector 6 is equal to the length L2 of the second chord of the second axial end edge 10 of the first ring sector 5 with L4 = L2 = circumference of the first peripheral border 7 / number of sectors 5, 6 = (2 x Pi x R2) / number of sectors 5, 6, with L3 = L4 - d and L1 = L4 + d, d being a non-zero variable.

[0075] According to another variant, L3 + L1 = (2 x the circumference of the first peripheral border 7) / number of sectors 5, 6 = 2 x (2 x Pi x RI) / number of sectors 5, 6 and L4 + L2 = (2 x the circumference of the second peripheral border 8) / number of sectors 5, 6 = 2 x (2 x Pi x R2) / number of sectors 5, 6.

[0076] According to another embodiment, several stages of the turbine include a sealing ring 2 removable from the downstream side of the turbine, the first peripheral rim 7 being a first downstream peripheral rim 7 oriented towards a direction opposite to the upstream direction A, the second peripheral rim 8 being a second upstream peripheral rim 8 oriented towards the upstream direction A. This embodiment is the least preferred.

[0077] According to another embodiment illustrated in Figure 4, the turbomachine comprises an annular wall 17 fixed to an upstream support 18. The sealing ring 2 is mounted on the annular wall 17 and the upstream support 18. The turbomachine includes an upstream casing 26 fixed to the upstream support 18 by fastening elements I such as rivets.

[0078] The sealing ring 2 includes a radially internal face 28 on which is fixed an abradable element 29 which cooperates with a lick 30 fixed on the movable wheel 1 to ensure a seal.

[0079] The annular wall 17 includes at least one fixing tab 31 having a first fixing slot 19 and having a hook shape. The fixing tab 31 extends radially from a radially internal face 21 of the annular wall 17, towards the second peripheral edge 8 of the sealing ring 2 which is a downstream edge.

[0080] The sealing ring 2 includes a fixing element 23 extending radially outwards and downstream from a radially external face 24 of the sealing ring 2. A downstream end 22 of the fixing element 23 is engaged in the first fixing slot 19. The fixing element 23 is inclined relative to the radially external face 24.

[0081] The upstream support 18 is fixed to the first peripheral edge 7 of the sealing ring 2, which is an upstream edge. It includes a second fixing slot 20 into which the first peripheral edge 7 is engaged.

[0082] An example of a turbomachine dismantling procedure is illustrated in Figure 4.

[0083] The dismantling process includes a first step 100 of disengaging the upstream housing 26 from the upstream support 18. The fixing element(s) ZI are removed.

[0084] The dismantling process then includes a second step 101 of disengaging the upstream support 18 from the annular wall 17 and the sealing ring 2. The first peripheral edge 7 of the sealing ring 2 is disengaged from the second fixing slot 20.

[0085] The dismantling process then includes a third step 102 of axial translation of the sealing ring 2 towards the upstream direction A for disengage the sealing ring 2 from the annular wall 17. The downstream end 22 of the fixing element 23 is disengaged from the first fixing slot 19.

[0086] The dismantling process then includes a fourth step 103 of extracting at least one of the first ring sectors 5 out of the sealing ring 2 towards the upstream direction A. For this, an oblique translation along an oblique direction O is applied to the first ring sector 5. The second ring sectors 6 are then extracted out of the sealing ring 2 along the upstream direction A with the other first ring sectors 5.

[0087] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense. [0088JII is also evident that all the characteristics described with reference to a process are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.

Claims

Demands

1. A sealing ring (2) for a turbomachine turbine, intended to be mounted around a rotating wheel (1) mounted inside a turbine housing about an axis of rotation (X), the sealing ring (2) having a frustoconical shape and comprising an annular row of circumferentially adjacent ring sectors (5, 6) around the axis of rotation (X), the sealing ring (2) having a first circular peripheral rim (7) of radius RI and a second circular peripheral rim (8), axially opposite to the first peripheral rim (7), of radius R2, greater than radius RI, wherein the sealing ring (2) comprises at least one first curved ring sector (5) having, on the side of the first peripheral rim (7), a first axial end edge (9) defining a first chord of length L1 and, on the side of the second peripheral rim (8),a second axial end edge (10) defining a second chord of chord length L2, and at least a second curved ring sector (6) having, on the side of the first peripheral border (7), a third axial end edge (11), defining a third chord of length L3 and, on the side of the second peripheral border (8), a fourth axial end edge (12) defining a fourth chord of length L4 strictly greater than the chord length L2 of the second axial end edge (10) of the first ring sector (5), L2 being strictly less than L1.,

2. Sealing ring (2) according to claim 1, wherein the annular row of ring sectors (5, 6) is formed by an alternation of first ring sectors (5) and second ring sectors (6).

3. Sealing ring (2) according to any one of claims 1 or 2, wherein the length Ll of the first chord of the first axial end edge (9) of the first ring sector (5) is equal to the length L3 of the third chord of the third axial end edge (11) of the second ring sector (6).

4. Sealing ring (2) according to claim 3, wherein L3 = L1 = (2 x Pi x RI) / number of sectors (5, 6), L4 = L3 + d and L2 = L3 - d, d being a non-zero variable such that d > 2 x (R2 - RI) x sin (Pi / N).

5. Sealing ring (2) according to any one of claims 1 or 2, wherein the length L4 of the fourth chord of the fourth axial end edge (12) of the second ring sector (6) is equal to the length L2 of the second chord of the second axial end edge (10) of the first ring sector (5) with L4 = L2 = (2 x Pi x R2) / number of sectors (5, 6), L3 = L4 - d and L1 = L4 + d, d being a non-zero variable.

6. Sealing ring (2) according to any one of claims 4 or 5, wherein d is between 2 mm and 25 mm.

7. Sealing ring (2) according to any one of claims 1 to 6, wherein the first peripheral rim (7) is a first upstream peripheral rim (7) oriented towards the upstream direction (A), the second peripheral rim (8) being a second downstream peripheral rim (8) oriented towards a direction opposite to the upstream direction (A).

8. Turbomachine turbine comprising at least one stage having an annular row of fixed blades carried by a turbine casing and a rotating wheel (1) mounted and surrounded by a sealing ring (2) as defined according to any one of claims 1 to 7.

9. Turbomachine turbine according to claim 8, comprising several stages including a first stage positioned upstream of at least one second stage, the sealing ring (2) being positioned in the first stage.

10. Turbomachine comprising a turbomachine turbine as defined according to any one of claims 8 or 9.

11. Turbomachine according to claim 10, comprising an annular wall (17) fixed to an upstream support (18), the sealing ring (2) comprising at least one fastening element (23) comprising a downstream end (22) positioned opposite the second peripheral edge (8) of the sealing ring (2) and engaging in a first fastening slot (19) of the annular wall (17), the first peripheral edge (7) of the sealing ring (2) being engaged in a second fastening slot (20) of the upstream support (18).

12. Method of dismantling a sealing ring (2) as defined according to any one of claims 1 to 7, comprising a first step of extracting the first ring sector (5) out of the sealing ring (2) in an upstream direction (A), opposite to a direction of air flow in the turbine, followed by a second step of extracting the second ring sector (6) out of the sealing ring (2) in the upstream direction (A).

13. A method for dismantling a turbomachine according to claim 11, the turbomachine comprising an upstream housing (26) fixed to the upstream support (18), the method comprising: - a first step (100) of disengaging the upstream casing (26) from the upstream support (18), - a second step (101) of disengaging the upstream support (18) from the annular wall (17) and the sealing ring (2), - a third step (102) of axial translation of the sealing ring (2) towards the upstream direction (A) to disengage the sealing ring (2) from the annular wall (17), and - a fourth step (103) of extraction of at least one of the first ring sectors (5) out of the sealing ring (2) towards the upstream direction (A).

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