Attaching an abradable material to an external turbomachine ferrule

Abstract

This document relates to a method for attaching an abradable ring (21) to a face of an outer shell (31) of a turbomachine, characterized in that it comprises the steps: a) providing an abradable ring (21) with a honeycomb structure (24); b) applying an adhesive to the face of the outer shell (31); c) shrink-fitting said abradable ring (21) inside or around said outer shell (31); d) heating the outer shell and the abradable ring (21) so as to harden the adhesive. Figure to be published with the abbreviation: Figure number 2

Description

Title of the invention: Attachment of an abradable material to an external turbomachine shell Technical field of the invention

[0001] This document relates to a method for fixing or replacing an abradable on an external shell of a turbomachine. Prior art

[0002] Conventionally, a turbomachine consists, from upstream to downstream, of a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine, and a low-pressure turbine. A turbine comprises alternating annular rows of stator blades and moving blades arranged inside a casing.

[0003] To limit air circulation between the radially external ends of the moving wheel and the turbomachine casing, it is known to arrange around the moving wheel, circumferentially end to end, a plurality of blocks or panels of abradable material forming an abradable ring which is intended to cooperate in sealing with scrapers carried by the platforms of the blade tips.

[0004] An abradable ring can be formed from a plurality of semi-hexagonal metal sheets assembled together to form a hexagonal honeycomb structure. Other types of abradable rings also exist, notably those produced by plasma spraying, but these have the disadvantage of not withstanding high temperatures despite their good sealing properties.

[0005] Conventionally, abradable rings with a honeycomb structure are brazed onto an external ferrule, which is itself fixed to the external housing. However, during brazing, the external ferrule undergoes deformation and requires further machining.

[0006] The invention aims in particular to provide a simple, effective and economical solution to the problems of the prior art described above. Presentation of the invention

[0007] To this end, the present document relates to a method for fixing an abradable ring onto a radially internal face of an external turbomachine shell, characterized in that it comprises the following steps: a) provide an abradable ring with an alveolar structure; b) apply glue to the radially inner face of the outer ferrule; c) to press-fit said abradable ring inside or around said outer ferrule; d) to heat the outer ferrule and the abradable ring so as to harden the glue.

[0008] The present solution saves time since the outer ferrule no longer undergoes deformation and therefore requires no additional machining. According to this solution, the abradable ring can be changed without having to machine the outer ferrule again.

[0009] The abradable ring may not be perfectly cylindrical, and therefore the press fit of the abradable ring onto the outer ferrule may not be perfect. The use of adhesive provides a better seal for the assembly comprising the outer ferrule and the abradable ring. Applying adhesive also eliminates radial clearances of a few tenths of a millimeter that may appear between the outer ferrule and the abradable ring due to a lack of concentricity in the abradable ring. This also prevents axial and radial displacement of the abradable ring during manual application, and thus the leaks that this can generate.

[0010] The abradable ring may include an annular sheet on one face of which is applied said annular alveolar structure.

[0011] The use of an annular sheet metal makes it possible to obtain a robust technology with regard to the mechanical stresses that the assembly comprising the external ferrule and the abradable ring can undergo.

[0012] Masking means can be applied annularily to the alveolar structure of the abradable ring, these masking means comprising an annular opening leading to the junction between the radially internal face of the external ferrule and the abradable ring.

[0013] During the shrink-fitting of the abradable ring, the adhesive is applied to the radially inner face of the outer ferrule, and excess adhesive may seep out. Under such conditions, when the adhesive is heated, it hardens and becomes difficult to remove. This can then lead to a change in the profile and surface finish. Masking devices therefore prevent such complications.

[0014] The glue can be applied in the form of a cord or a plurality of circumferentially successive cords, which can be arranged end to end.

[0015] The abradable ring may comprise an annular sheet, which may be formed in one piece over 360°, on one face of which are fixed a plurality of sectors with a honeycomb structure arranged circumferentially end to end so as to constitute a circumferentially continuous layer intended to come into contact with annular blades of an annular row of movable blades arranged in radial opposite direction.

[0016] The use of an annular sheet metal makes it possible to obtain a robust technology with regard to the mechanical stresses that the assembly comprising the external ferrule and the abradable ring can undergo.

[0017] This document relates to a method for replacing a first abradable ring with a second abradable ring, characterized in that it comprises the steps of: a) remove the first abradable ring; b) carry out the process as described above.

[0018] This document relates to an annular assembly for a turbomachine comprising an outer shell carrying on a radially internal face an abradable ring having a honeycomb structure surrounding an annular row of movable blades in which the abradable ring is shrink-fitted and bonded in the outer shell in contact with the radially internal face of the outer shell.

[0019] The abradable ring may include an annular sheet on one face of which said honeycomb structure is applied.

[0020] This document relates to a turbine comprising an annular assembly as described above. Brief description of the figures

[0021] [Fig-1] represents a low pressure turbine of a turbomachine comprising abradable rings, according to the invention.

[0022] [Fig. 2A] represents a first external ferrule fixed to a first abradable ring, according to the invention.

[0023] [Fig. 2B] represents a second external ferrule fixed to a second abradable ring, according to the invention. Detailed description of the invention

[0024] We refer first of all to [Fig.1] which represents a low pressure turbine 2 of a turbomachine which comprises a plurality of annular rows of movable blades 4 arranged axially alternating with annular rows of fixed blades 6 or statoric blades carried externally by an external annular casing 8. An annular support element 10 is fixed to the external platform 12 of the fixed blades 6 and provides the attachment to the casing 8.

[0025] Each moving blade 4 comprises an inner annular platform 14 and an outer annular platform 16 between which blades 18 extend. The outer annular platform 16 carries on its radially external annular surface, opposite the blade 18, a plurality of substantially radial annular flaps 20. These annular flaps 20 cooperate by friction with an abradable ring 21 carried by the outer housing 8 to ensure sealing at the tip of the moving blade 4, i.e., to limit parasitic air circulation between the tips of the moving blades 4 and the housing 8.

[0026] As illustrated in [Fig. 1] and 2, the abradable ring 21 comprises a honeycomb structure 24 whose honeycombs have a substantially radial axis. The structure The honeycomb structure 24 is applied to an annular sheet 26 such that the opening at one end of the honeycomb cells is sealed. More precisely, the abradable ring 21 is formed of several honeycomb structure sectors arranged circumferentially end to end to form a continuous, annular honeycomb structure 24 extending over 360°. Each honeycomb structure sector can be formed by assembling a plurality of metal sheets with a semi-hexagonal pattern. The annular sheet 26 can, for example, be brazed onto an external face 28 of said annular honeycomb structure 24. The annular sheet 26 can be formed in one piece extending over 360° or from several pieces.

[0027] The low-pressure turbine 2 also includes a first outer shell 30 fixed directly to the housing 8 by bolting and a second outer shell 32 also fixed directly to the housing 8 by bolting. The first outer shell 30 carries a first abradable ring 22 surrounding a first annular row of moving blades 4 and the second outer shell 32 carries a second abradable ring 23 surrounding a second annular row of moving blades 4, the second annular row of moving blades being arranged downstream of the first annular row.

[0028] The first outer ferrule 30 comprises a cylindrical wall 34 connected at its upstream end to a first radial annular wall 36 extending radially outwards and also connected at its upstream end to an annular portion 38 extending radially inwards. The first radial annular wall 36 serves as a passage for bolts 40 for securing the first outer ferrule 30 to the housing 8. The cylindrical wall 34 comprises an internal cylindrical surface 42, an upstream end of which is connected to a radial annular surface 44 extending radially inwards, which is connected at its radially internal end to a frustoconical wall 46 whose cross-section decreases upstream. The frustoconical wall 46 is formed on an internal face of the annular portion 38 of the first outer ferrule 30. A downstream end 48 of the internal cylindrical surface 42 opens at its downstream end.

[0029] The second outer ferrule 32 comprises a radial annular wall 50 extending radially outwards. The radial annular wall 50 of the second outer ferrule 32 includes a radial annular rim 52 extending radially inwards at its upstream end and a second radial annular wall 54 extending radially outwards from an axially median area of ​​the radial annular wall 50. The second radial annular wall 54 serves as a passage for bolts 41 for securing the second outer ferrule 32 to the housing 8.

[0030] An adhesive is applied in the form of a bead or a plurality of circumferentially successive beads to a first area comprising the internal cylindrical surface 42 of the first external ferrule 30. The adhesive is similarly applied to a second area comprising an internal radial annular surface 56 of the wall radial annular 50 of the second external ferrule 32. As illustrated in [Fig. 2A], a first abradable ring 22 is shrink-fitted at the level of the first zone and thus comes against the first external ferrule 30. As illustrated in [Fig. 2B], a second abradable ring 23 is shrink-fitted at the level of the second zone and thus comes against the second external ferrule 32.

[0031] Masking means are applied annularly, i.e. over 360°, on external faces 60 of the alveolar structure 24 not bonded and clamped to the first external ferrule 30, on the frustoconical wall 46 of the first external ferrule 30, on an internal face 62 of the annular part 38 of the first external ferrule 30 and on the downstream end 48 of the cylindrical wall 34 of the first external ferrule 30. Masking means are further applied annularly, i.e. over 360°, on external faces 64 of the alveolar structure 24 not bonded and clamped to the second external ferrule 32, on an internal face 66 and an upstream face 68 of the radial annular rim 52 of the second external ferrule 32 and on a downstream end of the radial annular wall 50 of the second external ferrule 32. These masking methods can be heat-resistant strips, preferably adhesive strips, and even more preferably aluminum adhesive strips.

[0032] The first outer ferrule 30 and the first abradable ring 22 mounted shrink-fitted on the first outer ferrule 30 as well as the second outer ferrule 32 and the second abradable ring 23 mounted shrink-fitted on the second outer ferrule 32 are heated to a temperature of at least 175°C, preferably 175°C so as to harden the glue and to be able to remove excess glue at the masking areas where the masking means are applied.

[0033] Applying glue to the first and second zones eliminates radial gaps of a few tenths of a millimeter that appear between the first outer ferrule 30 and the first abradable ring 22 and between the second outer ferrule 32 and the second abradable ring 23. This also prevents axial and radial displacement of the first abradable ring 22 or the second abradable ring 23 during manual force and therefore the leaks that this can generate.

[0034] This embodiment saves time since neither the first outer ferrule 30 nor the second outer ferrule 32 undergoes deformation and therefore no further machining is required. According to this embodiment, the first abradable ring 22 or the second abradable ring 23 can be changed without having to re-machine the first outer ferrule 30 or the second outer ferrule 32.

[0035] This embodiment also makes it easier to replace the first abradable ring 22 or the second abradable ring 23 with another abradable one.

Claims

Demands

1. A method for attaching an abradable ring (21) to a radially internal face of an external ferrule (31) of a turbomachine, characterized in that it comprises the steps: a) providing an abradable ring (21) with a honeycomb structure (24); b) applying an adhesive to the radially internal face of the external ferrule (31); c) shrink-fitting said abradable ring (21) inside said external ferrule (31); d) heating the external ferrule (31) and the abradable ring (21) so as to harden the adhesive; and wherein masking means are applied annularly to the honeycomb structure (24) of the abradable ring (21), these masking means comprising an annular opening leading to the junction between the face of the external ferrule (31) and the abradable ring (21).

2. Method according to claim 1, wherein the abradable ring (21) comprises an annular sheet (26) on one face of which is applied said annular alveolar structure (24).

3. A method according to any one of the preceding claims, wherein the glue is applied in the form of a cord or a plurality of circumferentially successive cords.

4. A method according to any one of the preceding claims, wherein the abradable ring (21) comprises an annular sheet (26), which can be formed in one piece over 360°, on one face of which are fixed a plurality of sectors with a honeycomb structure (24) arranged circumferentially end to end so as to constitute a circumferentially continuous layer intended to come into contact with annular blades (20) of an annular row of movable blades (4) arranged in radial opposite direction.

5. A method for replacing a first abradable ring (21) with a second abradable ring (21) characterized in that it comprises the steps of: a) removing the first abradable ring (21); b) carrying out the method according to any one of claims 1 to 4.

6. Annular assembly for a turbomachine comprising an outer shell (31) carrying on a radially inner face a ring abradable (21) comprising a honeycomb structure (24) surrounding an annular row of movable blades (4) in which the abradable ring (24) is shrink-fitted and bonded in the outer ferrule (31) in contact with the radially internal face of the outer ferrule (31), masking means being applied annularly on the honeycomb structure (24) of the abradable ring (21), these masking means comprising an annular opening leading to the junction between the face of the outer ferrule (31) and the abradable ring (21).

7. Annular assembly according to claim 6, wherein the abradable ring (21) comprises an annular sheet (26) on one face of which is applied said honeycomb structure (24).

8. Turbine comprising an annular assembly according to claim 6 or 7.

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