METHOD FOR DETECTING A ROUGHNESS IN AN ABRADABLE LAYER IN A FAN CASING

Abstract

A method for detecting at least one roughness in a face of an abradable layer in a fan casing is provided. The method includes a step of depositing on the abradable layer a first coating and a second coating covering the first coating. The first and second coatings have respective thicknesses (N1, N2) and a physical appearance that differ from one another. Local appearance of the first coating is indicative of a need for a localized touch-up, and local disappearance of the first coating and the second coating is indicative of a need for a localized replacement of the abradable layer.

Claims

1. A method for detecting at least one roughness in a face of an annular layer of abradable material in a fan casing for an aircraft turbomachine, the method comprising: a deposition step of depositing on said face of the abradable layer a first coating and at least one second coating covering the first coating wherein the first coating has a first thickness and a first physical aspect, and wherein the second coating has a second thickness and a corresponding second physical aspect which differs from the first physical aspect, and an observation step of observing the abradable layer coated with the first coating and the second coating, wherein observing a local appearance of the first coating on said face is representative of a roughness requiring a local touch-up and wherein observing a local disappearance of the first and the at least one second coating on said face is representative of a roughness requiring a local replacement of the abradable layer around the roughness.

2. The method according to claim 1, further comprising a definition step performed prior to the deposition step, wherein the definition step comprises defining a first level of roughness depth and at least a second level of roughness depth affecting the abradable layer, wherein the first level of roughness depth is greater than the second level of roughness depth, wherein the first and second roughness depth levels are measured from said face, wherein the first level of roughness depth represents a need for a local replacement of the abradable layer around the roughness, wherein the second level of roughness represents a need for a local touch-up at the level of the roughness, wherein the second thickness of said at least one second coating is equal to the second level of roughness depth and wherein the first thickness of the first coating is equal to the first level of roughness depth minus the second thickness of said at least one second coating.

3. The method according to claim 1, wherein during the observation step, when a roughness is visible on said face with the first coating covered by the second coating in that roughness, it is concluded by visual recognition that the roughness does not require any local touch-up.

4. The method according to claim 1, wherein the first level of roughness depth is greater than 0.5 millimeters and wherein the second level of roughness depth is greater than 0.2 millimeters and less than 0.5 millimeters.

5. The method according to claim 1, wherein the first coating and said at least one second coating are respective paint layers, wherein depositing on said face of the abradable layer the first coating and the at least one second coating covering the first coating is carried out by lacquering or powder coating with the aid of a robot arm.

6. The method according to claim 5, wherein the first physical aspect of the first coating is a first color, and wherein the second physical aspect of the at least one second coating is a different second color.

7. The method according to claim 1, further comprising: after observing the local appearance of the first coating at a level of the roughness on said face, touching up the roughness; or after observing a local disappearance of the first coating and the at least one second coating at the level of the roughness on said face, replacing the abradable layer around the roughness.

8. A fan casing for an aircraft turbomachine comprising an annular layer of abradable material and upon which a method for detecting at least one roughness in said face of the abradable layer according to claim 1 is implemented, wherein said face of the layer of abradable material is covered by the first coating and the at least one second coating.

9. The fan casing according to claim 8, wherein the first coating and said at least one second coating are paint layers, wherein the first physical aspect and the second physical aspect are selected from the group consisting of: a color, a tone, and a texture.

10. An aircraft turbomachine, comprising the fan casing according to claim 8.

Description

BRIEF DESCRIPTION OF FIGURES

[0046] Other characteristics, purposes and advantages of the present invention will become apparent from the following detailed description and from the attached drawings, which are given as non-limiting examples and in which:

[0047] FIG. 1 is a schematic representation of a cross-sectional view of a fan of an aircraft turbomachine according to the prior art,

[0048] FIG. 2 is a schematic representation of a perspective view of a fan casing according to the prior art,

[0049] FIG. 3 is a schematic representation of a partial cross-sectional view of a fan casing according to the prior art,

[0050] FIG. 4 is a schematic representation of two schematic cross-sectional views of an abradable layer for a fan casing according to the prior art without coating of the abradable layer and according to the present invention, respectively, with, in the latter case, a face opposite at least one fan vane being coated with two coatings, advantageously in the form of a respective paint layer, with different visible characteristics for a detection and a depth classification of one or more roughnesses.

[0051] It should be kept in mind that the figures are given as examples and are not limiting of the invention. They are schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of the practical applications. In particular, the dimensions of the various elements illustrated are not representative of the reality.

DETAILED DESCRIPTION OF THE INVENTION

[0052] FIG. 1 is a partial representation of a fan of an aircraft turbomachine. In a conventional way, a turbomachine comprises from upstream to downstream, i.e. in the direction of flow of the gas flows, a fan, one or more compressors, a combustion chamber, one or more turbines, and a nozzle for the ejection of the combustion gases leaving the turbine or the turbines.

[0053] The fan 1 comprises a vane wheel 2 which is surrounded by a fan casing 3, also referred to as a retention casing because of its function of retaining the vanes in the event of their breakage, or in the event of debris entering the fan.

[0054] As can be seen from FIG. 2, the fan casing 3 has a generally cylindrical shape with an axis of revolution A.

[0055] It comprises an annular securing flange 3′ at each of its axial ends. These flanges 3′ are used to secure the casing 3 to annular walls of the nacelle of the turbomachine.

[0056] As shown in this FIG. 2, a layer of abradable material 10b is present inside the fan casing 3 by being of revolution in the fan casing 3.

[0057] The fan casing 3 therefore extends around the fan vane wheel 2. It thus comprises an inner cylindrical surface which is provided with an annular layer 10 of abradable material.

[0058] As seen in FIG. 3, the annular layer 10b of abradable material, hereinafter referred to as the abradable layer 10b, extends around and at a short radial distance from one 2a of the vanes, sequentially during the rotation of the vane wheel 2. The vanes 2a can rub against the abradable layer 10b in operation and successively and wear it down by friction. This applies to an abradable layer 10b of the prior art as well as to an abradable layer 10 according to the present invention and shown in FIG. 4.

[0059] This allows to optimize the radial clearances between the vanes 2a and the surrounding fan casing 3 and thus to limit the gas leakage at the radially outer tips or ends of the vanes, and thus to optimize the performance of the turbomachine.

[0060] In the present technique as well as in the embodiments of the present invention, the abradable layer 10b may be supported by a solid or honeycomb structure support cartridge 4. This cartridge 4 is usually riveted or screwed to the fan casing 3.

[0061] The fan casing 3 is connected to an air inlet duct 5 on the one hand and to an intermediate casing shell 6 on the other hand. It also carries an upstream acoustic shell 7 and a downstream acoustic panel 8.

[0062] Without being essential to the scope of the present invention, three types of area may be recognized on the fan casing 3.

[0063] The first type of areas, referred to as areas Z1, groups together the flange areas by comprising an upstream flange area and a downstream flange area. The upstream flange area comprises the connection between the fan casing 3 and the air inlet duct 5 and the downstream flange area comprises the connection between the fan casing 3 and the intermediate casing shell 6.

[0064] The second type of areas, referred to as the areas Z2, groups together the structural areas by comprising an upstream structural area and a downstream structural area. The upstream structural area is located at the level of the upstream acoustic shell 7 and the downstream structural area is located at the level of the downstream acoustic panel 8.

[0065] The third type of area comprises a single retention area, referred to as area Z3. This area Z3 ensures the primary function of the fan casing 3 and guarantees the static and dynamic mechanical strength of the assembly by ensuring a fast dynamics. The third area Z3 houses the median portion of the fan casing 3, the support cartridge 4 of the abradable layer 10b and the abradable layer 10b.

[0066] As mentioned above, and with reference to FIG. 4, the abradable layer 10 or 10b may be damaged, for various reasons and not only due to its cooperation with the vane wheel, by the formation of a locally recessed surface forming a local roughness 11a, 11b, 11c in the layer and this according to several levels of depth requiring respectively in the direction of an increasing depth, no repair, a local touch-up or a more important work of local replacement of the layer of abradable material.

[0067] It is difficult to differentiate between roughnesses 11a, 11b, 11c with different levels of depth with the naked eye. It is then necessary to dismount the fan casing to gain access to the abradable layer 10 or 10b, which is precisely what the present invention seeks to avoid.

[0068] Referring principally to FIG. 4 but also to FIG. 3, the present invention relates to a method for detecting at least one roughness on a face of an annular layer of abradable material 10 in a fan casing 3 for an aircraft turbomachine by identifying its depth on which the possible repair works to be undertaken on the abradable layer 10 depends.

[0069] The face 10a having this roughness or these roughnesses, advantageously a lack of material forming a more or less wide and/or more or less deep roughness 11a, 11b, 11c, of respective depths referenced I1, I2 and I3 is the face 10a opposite of sequentially one 2a of the vanes of a fan vane wheel as shown previously in FIG. 3.

[0070] The roughness or the roughnesses are caused, in particular but not only, by local crumbling on the opposite face 10a causing a creation on the face 10a, opposite a vane 2a, of a roughness 11a, 11b, 11c of a respective depth I1, I2, I3 in the abradable layer 10.

[0071] In FIG. 4, a comparison between an abradable layer 10b according to the prior art and an abradable layer 10 according to the present invention is shown, the abradable layer 10b according to the prior art being the top layer and the abradable layer 10 according to the present invention being the bottom layer in FIG. 4.

[0072] In both cases, three types of roughness are shown in the form of a respective roughness 11a, 11b, 11c. It is of course possible that there are other roughnesses with intermediate roughnesses or even deeper roughnesses.

[0073] The method according to the present invention may begin with a definition step, a step which is not necessarily necessary for its implementation.

[0074] In this step, a definition of a first N1+N2 and of at least a second level N2 of roughness depth affecting the abradable layer 10 is performed.

[0075] The first and at least second levels N1+N2, N2 of depth are measured from said face 10a and representative of a need, for the first level N1+N2, for a local replacement of the abradable layer 10 around the roughness 11c or, for the second level N2, a need for a local touch-up at the level of the roughness 11b. In FIG. 4, the roughness 11a of smallest depth, for example of a depth I1 of 0 to 0.2 millimeters, corresponds to a minor cosmetic defect requiring no treatment, the roughness 11b of average depth I2, for example of a depth of 0.2 to 0.5 millimeters corresponds to a major cosmetic defect requiring a local touch-up, and the roughness 11c of greatest thickness I3, for example of a depth greater than 0.5 millimeters, corresponds to a serious roughness requiring a local replacement of the abradable layer 10.

[0076] According to the prior art, it was not possible to differentiate these roughnesses 11a, 11b, 11c from each other, in particular an average roughness 11b from a largest roughness 11c.

[0077] For an abradable layer 10 according to the present invention, as shown in the lower part of FIG. 4, a step of depositing on the face 10a of the abradable layer 10 opposite a vane 2a a first coating 12 and at least one second coating 13, advantageously in the form of a layer of paint, covering the first coating 12 is performed, this first coating 12 being deposited directly on the abradable layer.

[0078] Each first coating 12 or second coating 13 has a precisely measured predetermined respective thickness N1, N2 and a physical aspect differentiating them from each other for recognizing which coating is visible from the opposite face 10a and, where appropriate, recognizing whether the first coating 12 has locally disappeared.

[0079] The thickness N2 of said at least one second coating 13 being the outermost to the abradable layer 10 may be equal to the second depth level N2 and the thickness N1 of the first covered coating 12 being the innermost to the abradable layer 10 may be equal to the first depth level N1+N2 minus the thickness N2 of said at least one second coating 13.

[0080] In the above-mentioned case, for the small, medium and large roughnesses 11a, 11b, 11c with a depth respectively less than 0.2 millimeters, between 0.2 and 0.5 millimeters, and greater than 0.5 millimeters, the thickness of the second coating 13 is 0.2 millimeters and the thickness N1 of the first coating 12 is 0.5-0.2 millimeters, i.e. 0.3 millimeters.

[0081] The first coating 12 and the at least one second coating 13 respectively form a wear layer of the fan casing, in particular around the abradable layer 10. Thus, according to the invention, the first coating 12 and the second coating 13 degrade respectively in their entire thickness before the abradable layer 10. Preferably, the second coating 13 firstly degrades to its entire thickness, and then the first coating 12 degrades secondly to its entire thickness. This allows to detect the roughnesses, of different depths in particular, depending, for example, on the thickness of the coatings 12, 13 and their colors.

[0082] A step of observing the abradable layer 10 thus coated is performed. A local appearance of the first coating 12 on the face 10a opposite the abradable layer 10 opposite a vane 2a is representative of a roughness 11b requiring local touch-up and a local disappearance of the first coating after disappearance of the second coating 13 on the face 10a opposite the vane 2a is representative of a roughness 11c requiring a local replacement of the abradable layer 10 around the roughness 11a, 11b, 11c.

[0083] When a roughness 11a, 11 b, 11c is visible on the face 10a opposite the vane 2a with the first coating 12 covered by the second coating 13 in this roughness 10a, it is concluded that there is a roughness 11a which does not require any local touch-up. Only the second coating 13 has been slightly damaged, which is illustrated by the smallest roughness 11a.

[0084] It is to be considered that the definition of more than two levels of roughness depth affecting the abradable layer 10 is possible.

[0085] In this case, as many coatings, preferably in the form of a respective paint layer, can be provided on the face 10a opposite a vane 2a of the abradable layer 10 as there are defined levels.

[0086] The first and at least one second coatings may be in the form of a paint layer. A surface application on the face 10a opposite a vane 2a of the abradable layer 10 with the first and second coatings 12, 13 may be carried out by a method of the lacquering or powder coating type using a robot arm.

[0087] According to the detection method in accordance with the present invention, it is possible to simultaneously detect a plurality of roughnesses of different depths on a single abradable layer 10 by observing the state of the first and second coatings 12, 13 or additional coatings.

[0088] In FIG. 4, the roughnesses 11a, 11b, 11c are not directly opposite the fan vane 2a, but this may also be possible. In any case, the repairs should be made to the roughnesses 11b, 11c corresponding to major cosmetic roughnesses.

[0089] The invention relates to a method for repairing a roughness 11b, 11c on a face of an annular layer of abradable material 10 in a fan casing 3 for an aircraft turbomachine.

[0090] After at least one roughness has been detected in accordance with a detection method as previously described, if a portion of the first coating 12 has locally appeared at the level of a roughness 11b, preferably at the level of the bottom of the roughness 11b on the face 10a of the abradable layer 10 opposite a vane 2a, a local touch-up of the roughness 11b is conducted.

[0091] Furthermore, if the first coating 12 has also disappeared as well as the second coating 13 at the level of a roughness 11c, preferably at the level of the bottom of the roughness 11c, on the face 10a of the abradable layer 10 opposite a vane 2a, a local replacement of the abradable layer 10 around the roughness 11c is conducted.

[0092] With reference to all the figures, the invention also relates to a fan casing 3 for an aircraft turbomachine comprising an annular layer of abradable material 10 having a face opposite of sequentially one 2a of the vanes of a fan vane wheel 2.

[0093] As at least one roughness on the face 10a opposite of sequentially one 2a of the vanes may be, among other possible causes of creation of roughnesses, caused by a local crumbling of the layer of abradable material on the opposite face 10a causing a creation on said face 10a of a roughness 11a, 11b, 11c of a respective depth I1, I2, I3 in the abradable layer 10, the fan casing 3 implements a method for detecting at least one roughness or a repair method as previously described.

[0094] Prior to the detection or repair methods, first and second depth levels N1+N2, N2 may have been defined.

[0095] In this fan casing 3, the face 10a opposite one 2a of the vanes of the layer of abradable material 10 is covered by at least two coatings 12, 13, advantageously of paint, the face the outermost to the abradable layer 10 of the second coating then forming the opposite face 10a. Each first 12 or second 13 coating has a precisely measured predetermined respective thickness and a physical aspect that differentiates them from each other.

[0096] The thickness N2 of the second coating 13 may be equal to the second depth level and the thickness N1 of the first coated coating 12 may be equal to the first depth level N1+N2 minus the thickness N2 of the second coating 13 or of the other coatings when their number exceeds two.

[0097] The physical aspect of the first and second coatings 12, 13 may be given by any of the following parameters taken individually or in combination: a color, a tone, a texture.

[0098] The first coating 12 and said at least one second coating 13 may, for example, have different colorimetry.

[0099] These parameters are visually recognizable parameters to help recognize the depth of a roughness.

[0100] Finally, the invention relates to an aircraft turbomachine comprising a fan casing 3 as previously described.

[0101] The invention is by no means limited to the described and illustrated embodiments which have been given only as examples.